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Sample records for avalanche detector based

  1. Avalanche photodiode based detector for beam emission spectroscopy

    SciTech Connect

    Dunai, D.; Zoletnik, S.; Sarkoezi, J.; Field, A. R.

    2010-10-15

    An avalanche photodiode based (APD) detector for the visible wavelength range was developed for low light level, high frequency beam emission spectroscopy (BES) experiments in fusion plasmas. This solid state detector has higher quantum efficiency than photomultiplier tubes, and unlike normal photodiodes, it has internal gain. This paper describes the developed detector as well as the noise model of the electronic circuit. By understanding the noise sources and the amplification process, the optimal amplifier and APD reverse voltage setting can be determined, where the signal-to-noise ratio is the highest for a given photon flux. The calculations are compared to the absolute calibration results of the implemented circuit. It was found that for a certain photon flux range, relevant for BES measurements ({approx_equal}10{sup 8}-10{sup 10} photons/s), the new detector is superior to both photomultipliers and photodiodes, although it does not require cryogenic cooling of any component. The position of this photon flux window sensitively depends on the parameters of the actual experimental implementation (desired bandwidth, detector size, etc.) Several detector units based on these developments have been built and installed in various tokamaks. Some illustrative results are presented from the 8-channel trial BES system installed at Mega-Ampere Spherical Tokamak (MAST) and the 16-channel BES system installed at the Torus Experiment for Technology Oriented Research (TEXTOR).

  2. A new type of thermal-neutron detector based on ZnS(Ag)/LiF scintillator and avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Marin, V. N.; Sadykov, R. A.; Trunov, D. N.; Litvin, V. S.; Aksenov, S. N.; Stolyarov, A. A.

    2015-09-01

    A high-efficiency thermal-neutron detector based on ZnS(Ag)/LiF scintillator is described, which employs a new technique of signal pick-up with the aid of a light guide and avalanche photodiodes instead of optical fibers and photomultipliers. Results of tests on the RADEX pulsed neutron source are presented, in which neutron diffraction patterns of test objects have been obtained.

  3. Gallium-based avalanche photodiode optical crosstalk

    NASA Astrophysics Data System (ADS)

    Blazej, Josef; Prochazka, Ivan; Hamal, Karel; Sopko, Bruno; Chren, Dominik

    2006-11-01

    Solid-state single photon detectors based on avalanche photodiode are getting more attention in various areas of applied physics: optical sensors, quantum key distribution, optical ranging and Lidar, time-resolved spectroscopy, X-ray laser diagnostics, and turbid media imaging. Avalanche photodiodes specifically designed for single photon counting semiconductor avalanche structures have been developed on the basis of various materials: Si, Ge, GaP, GaAsP, and InGaP/InGaAs at the Czech Technical University in Prague during the last 20 years. They have been tailored for numerous applications. Trends in demand are focused on detection array construction recently. Even extremely small arrays containing a few cells are of great importance for users. Electrical crosstalk between individual gating and quenching circuits and optical crosstalk between individual detecting cells are serious limitation for array design and performance. Optical crosstalk is caused by the parasitic light emission of the avalanche which accompanies the photon detection process. We have studied in detail the optical emission of the avalanche photon counting structure in the silicon- and gallium-based photodiodes. The timing properties and spectral distribution of the emitted light have been measured for different operating conditions to quantify optical crosstalk. We conclude that optical crosstalk is an inherent property of avalanche photodiode operated in Geiger mode. The only way to minimize optical crosstalk in avalanche photodiode array is to build active quenching circuit with minimum response time.

  4. Athermal avalanche in bilayer superconducting nanowire single-photon detectors

    NASA Astrophysics Data System (ADS)

    Verma, V. B.; Lita, A. E.; Stevens, M. J.; Mirin, R. P.; Nam, S. W.

    2016-03-01

    We demonstrate that two superconducting nanowires separated by a thin insulating barrier can undergo an avalanche process. In this process, Joule heating caused by a photodetection event in one nanowire and the associated production of athermal phonons which are transmitted through the barrier cause the transition of the adjacent nanowire from the superconducting to the normal state. We show that this process can be utilized in the fabrication of superconducting nanowire single photon detectors to improve the signal-to-noise ratio, reduce system jitter, maximize device area, and increase the external efficiency over a very broad range of wavelengths. Furthermore, the avalanche mechanism may provide a path towards a superconducting logic element based on athermal gating.

  5. Negative Avalanche Feedback Detectors for Photon-Counting Optical Communications

    NASA Technical Reports Server (NTRS)

    Farr, William H.

    2009-01-01

    Negative Avalanche Feedback photon counting detectors with near-infrared spectral sensitivity offer an alternative to conventional Geiger mode avalanche photodiode or phototube detectors for free space communications links at 1 and 1.55 microns. These devices demonstrate linear mode photon counting without requiring any external reset circuitry and may even be operated at room temperature. We have now characterized the detection efficiency, dark count rate, after-pulsing, and single photon jitter for three variants of this new detector class, as well as operated these uniquely simple to use devices in actual photon starved free space optical communications links.

  6. Miniaturized time-resolved Raman spectrometer for planetary science based on a fast single photon avalanche diode detector array.

    PubMed

    Blacksberg, Jordana; Alerstam, Erik; Maruyama, Yuki; Cochrane, Corey J; Rossman, George R

    2016-02-01

    We present recent developments in time-resolved Raman spectroscopy instrumentation and measurement techniques for in situ planetary surface exploration, leading to improved performance and identification of minerals and organics. The time-resolved Raman spectrometer uses a 532 nm pulsed microchip laser source synchronized with a single photon avalanche diode array to achieve sub-nanosecond time resolution. This instrument can detect Raman spectral signatures from a wide variety of minerals and organics relevant to planetary science while eliminating pervasive background interference caused by fluorescence. We present an overview of the instrument design and operation and demonstrate high signal-to-noise ratio Raman spectra for several relevant samples of sulfates, clays, and polycyclic aromatic hydrocarbons. Finally, we present an instrument design suitable for operation on a rover or lander and discuss future directions that promise great advancement in capability. PMID:26836075

  7. Transient and steady-state dark current mechanisms in amorphous selenium avalanche radiation detectors

    SciTech Connect

    Kabir, M. Z.; Imam, Safayat-Al

    2013-04-15

    A theoretical model for describing bias-dependent transient and steady-state behaviors of dark current in amorphous selenium (a-Se) avalanche detector structures has been developed. The analytical model considers bulk thermal generation current from mid-gap sates, transient carrier depletion, and carrier injection from the electrodes incorporating avalanche multiplication. The proposed physics-based dark current model is compared with the published experimental results on three potential a-Se avalanche detector structures. The steady-state dark current is the minimum for the structures that have effective blocking layers for both holes and electrons. The transient decay time to reach a plateau decreases considerably with increasing electric field.

  8. Signal-to-noise ratio of Geiger-mode avalanche photodiode single-photon counting detectors

    NASA Astrophysics Data System (ADS)

    Kolb, Kimberly

    2014-08-01

    Geiger-mode avalanche photodiodes (GM-APDs) use the avalanche mechanism of semiconductors to amplify signals in individual pixels. With proper thresholding, a pixel will be either "on" (avalanching) or "off." This discrete detection scheme eliminates read noise, which makes these devices capable of counting single photons. Using these detectors for imaging applications requires a well-developed and comprehensive expression for the expected signal-to-noise ratio (SNR). This paper derives the expected SNR of a GM-APD detector in gated operation based on gate length, number of samples, signal flux, dark count rate, photon detection efficiency, and afterpulsing probability. To verify the theoretical results, carrier-level Monte Carlo simulation results are compared to the derived equations and found to be in good agreement.

  9. Design and feasibility of active matrix flat panel detector using avalanche amorphous selenium for protein crystallography.

    PubMed

    Sultana, Afrin; Reznik, Alla; Karim, Karim S; Rowlands, J A

    2008-10-01

    Protein crystallography is the most important technique for resolving the three-dimensional atomic structure of protein by measuring the intensity of its x-ray diffraction pattern. This work proposes a large area flat panel detector for protein crystallography based on direct conversion x-ray detection technique using avalanche amorphous selenium (a-Se) as the high gain photoconductor, and active matrix readout using amorphous silicon (a-Si:H) thin film transistors. The detector employs avalanche multiplication phenomenon of a-Se to make the detector sensitive to each incident x ray. The advantages of the proposed detector over the existing imaging plate and charge coupled device detectors are large area, high dynamic range coupled to single x-ray detection capability, fast readout, high spatial resolution, and inexpensive manufacturing process. The optimal detector design parameters (such as detector size, pixel size, and thickness of a-Se layer), and operating parameters (such as electric field across the a-Se layer) are determined based on the requirements for protein crystallography application. The performance of the detector is evaluated in terms of readout time (<1 s), dynamic range (approximately 10(5)), and sensitivity (approximately 1 x-ray photon), thus validating the detector's efficacy for protein crystallography. PMID:18975678

  10. High resolution, low energy avalanche photodiode X-ray detectors

    NASA Technical Reports Server (NTRS)

    Farrell, R.; Vanderpuye, K.; Entine, G.; Squillante, M. R.

    1991-01-01

    Silicon avalanche photodiodes have been fabricated, and their performance as X-ray detectors has been measured. Photon sensitivity and energy resolution were measured as a function of size and operating parameters. Noise thresholds as low as 212 eV were obtained at room temperature, and backscatter X-ray fluorescence data were obtained for aluminum and other light elements. It is concluded that the results with the X-ray detector are extremely encouraging, and the performance is challenging the best available proportional counters. While not at the performance level of either cryogenic silicon or HgI2, these device operate at room temperature and can be reproduced in large numbers and with much larger areas than typically achieved with HgI2. In addition, they are rugged and appear to be indefinitely stable.

  11. Avalanche Effect in Si Heavily Irradiated Detectors: Physical Model and Perspectives for Application

    SciTech Connect

    Eremin V.; Li Z.; Verbitskaya, E.; Zabrodskii, A.; Harkonen, J.

    2011-05-07

    The model explaining an enhanced collected charge in detectors irradiated to 10{sup 15}-10{sup 16} n{sub eq}/cm{sup 2} is developed. This effect was first revealed in heavily irradiated n-on-p detectors operated at high bias voltage ranging from 900 to 1700 V. The model is based on the fundamental effect of carrier avalanche multiplication in the space charge region and in our case is extended with a consideration of p-n junctions with a high concentration of the deep levels. It is shown that the efficient trapping of free carriers from the bulk generation current to the deep levels of radiation induced defects leads to the stabilization of the irradiated detector operation in avalanche multiplication mode due to the reduction of the electric field at the junction. The charge collection efficiency and the detector reverse current dependences on the applied bias have been numerically simulated in this study and they well correlate to the recent experimental results of CERN RD50 collaboration. The developed model of enhanced collected charge predicts a controllable operation of heavily irradiated detectors that is promising for the detector application in the upcoming experiments in a high luminosity collider.

  12. Single-Photon-Sensitive HgCdTe Avalanche Photodiode Detector

    NASA Technical Reports Server (NTRS)

    Huntington, Andrew

    2013-01-01

    The purpose of this program was to develop single-photon-sensitive short-wavelength infrared (SWIR) and mid-wavelength infrared (MWIR) avalanche photodiode (APD) receivers based on linear-mode HgCdTe APDs, for application by NASA in light detection and ranging (lidar) sensors. Linear-mode photon-counting APDs are desired for lidar because they have a shorter pixel dead time than Geiger APDs, and can detect sequential pulse returns from multiple objects that are closely spaced in range. Linear-mode APDs can also measure photon number, which Geiger APDs cannot, adding an extra dimension to lidar scene data for multi-photon returns. High-gain APDs with low multiplication noise are required for efficient linear-mode detection of single photons because of APD gain statistics -- a low-excess-noise APD will generate detectible current pulses from single photon input at a much higher rate of occurrence than will a noisy APD operated at the same average gain. MWIR and LWIR electron-avalanche HgCdTe APDs have been shown to operate in linear mode at high average avalanche gain (M > 1000) without excess multiplication noise (F = 1), and are therefore very good candidates for linear-mode photon counting. However, detectors fashioned from these narrow-bandgap alloys require aggressive cooling to control thermal dark current. Wider-bandgap SWIR HgCdTe APDs were investigated in this program as a strategy to reduce detector cooling requirements.

  13. A field-shaping multi-well avalanche detector for direct conversion amorphous selenium

    SciTech Connect

    Goldan, A. H.; Zhao, W.

    2013-01-15

    Purpose: A practical detector structure is proposed to achieve stable avalanche multiplication gain in direct-conversion amorphous selenium radiation detectors. Methods: The detector structure is referred to as a field-shaping multi-well avalanche detector. Stable avalanche multiplication gain is achieved by eliminating field hot spots using high-density avalanche wells with insulated walls and field-shaping inside each well. Results: The authors demonstrate the impact of high-density insulated wells and field-shaping to eliminate the formation of both field hot spots in the avalanche region and high fields at the metal-semiconductor interface. Results show a semi-Gaussian field distribution inside each well using the field-shaping electrodes, and the electric field at the metal-semiconductor interface can be one order-of-magnitude lower than the peak value where avalanche occurs. Conclusions: This is the first attempt to design a practical direct-conversion amorphous selenium detector with avalanche gain.

  14. A theoretical study of improved front-illuminated avalanche drift detectors

    NASA Astrophysics Data System (ADS)

    Liang, K.; Yuan, J.; Li, H. R.; Yang, R.; Han, D. J.

    2013-06-01

    In this study, two avalanche drift detector (ADD) concepts were theoretically examined. One was an improved detector with an avalanche photodiode (APD) collecting and double pn-junction drift configuration, and the other was a combination of an APD collecting and metal oxide semiconductor (MOS) drift structure. The feasibility of the devices was theoretically investigated by the ISE-TCAD program. ADD can be operated in either Geiger mode or linear mode. In the former case, the detector was found to be appropriate for a single photon avalanche detector with a large collection area. In the latter case, the detector was observed to be well suited to be coupled to a scintillator for gamma-ray detection. The improved ADDs are considered to have good performances in the short wavelength optical detection and in matching common scintillation crystals with more flexibility.

  15. Characterization of avalanche photodiodes for lidar atmospheric return signal detectors

    NASA Technical Reports Server (NTRS)

    Antill, C. W., Jr.; Holloway, R. M.

    1988-01-01

    Results are presented from tests to characterize noise, dark current, overload, and gain versus bias, relationships of ten avalanche photodiodes. The advantages of avalanche photodiodes over photomultiplier tubes for given laser wavelengths and return signal amplitudes are outlined. The relationship between responsivity and temperature and dark current and temperature are examined. Also, measurements of the noise equivalent power, the excess noise factor, and linearity are given. The advantages of using avalanche photodiodes in the Lidar Atmospheric Sensing Experiment and the Lidar In-Space Technology Experiment are discussed.

  16. Radiation hardness of semiconductor avalanche detectors for calorimeters in future HEP experiments

    NASA Astrophysics Data System (ADS)

    Kushpil, V.; Mikhaylov, V.; Kugler, A.; Kushpil, S.; Ladygin, V. P.; Svoboda, O.; Tlustý, P.

    2016-02-01

    During the last years, semiconductor avalanche detectors are being widely used as the replacement of classical PMTs in calorimeters for many HEP experiments. In this report, basic selection criteria for replacement of PMTs by solid state devices and specific problems in the investigation of detectors radiation hardness are discussed. The design and performance of the hadron calorimeters developed for the future high energy nuclear physics experiments at FAIR, NICA, and CERN are discussed. The Projectile Spectator Detector (PSD) for the CBM experiment at the future FAIR facility, the Forward Calorimeter for the NA61 experiment at CERN and the Multi Purpose Detector at the future NICA facility are reviewed. Moreover, new methods of data analysis and results interpretation for radiation experiments are described. Specific problems of development of detectors control systems and possibilities of reliability improvement of multi-channel detectors systems are shortly overviewed. All experimental material is based on the investigation of SiPM and MPPC at the neutron source in NPI Rez.

  17. High-Gain Avalanche Rushing amorphous Photoconductor (HARP) detector

    NASA Astrophysics Data System (ADS)

    Tanioka, K.

    2009-09-01

    We have been studying a very sensitive image sensor since the early 1980s. In 1985, the author found for the first time that an experimental pickup tube with an amorphous selenium photoconductive target exhibits high sensitivity with excellent picture quality because of a continuous and stable avalanche multiplication phenomenon. We named the pickup tube with an amorphous photoconductive layer operating in the avalanche-mode "HARP": High-gain Avalanche Rushing amorphous Photoconductor. A color camera equipped with the HARP pickup tubes has a maximum sensitivity of 11 lx at F8. This means that the HARP camera is about 100 times as sensitive as that of CCD camera for broadcasting. This ultrahigh-sensitivity HARP pickup tube is a powerful tool for reporting breaking news at night and other low-light conditions, the production of scientific programs, and numerous other applications, including medical diagnoses, biotech research, and nighttime surveillance. In addition, since the HARP target can convert X-rays into electrons directly, it should be possible to exploit this capability to produce X-ray imaging devices with unparalleled levels of resolution and sensitivity.

  18. Modeling of high-precision wavefront sensing with new generation of CMT avalanche photodiode infrared detectors.

    PubMed

    Gousset, Silvère; Petit, Cyril; Michau, Vincent; Fusco, Thierry; Robert, Clelia

    2015-12-01

    Near-infrared wavefront sensing allows for the enhancement of sky coverage with adaptive optics. The recently developed HgCdTe avalanche photodiode arrays are promising due to their very low detector noise, but still present an imperfect cosmetic that may directly impact real-time wavefront measurements for adaptive optics and thus degrade performance in astronomical applications. We propose here a model of a Shack-Hartmann wavefront measurement in the presence of residual fixed pattern noise and defective pixels. To adjust our models, a fine characterization of such an HgCdTe array, the RAPID sensor, is proposed. The impact of the cosmetic defects on the Shack-Hartmann measurement is assessed through numerical simulations. This study provides both a new insight on the applicability of cadmium mercury telluride (CMT) avalanche photodiodes detectors for astronomical applications and criteria to specify the cosmetic qualities of future arrays. PMID:26836674

  19. Assessing risk based on uncertain avalanche activity patterns

    NASA Astrophysics Data System (ADS)

    Zeidler, Antonia; Fromm, Reinhard

    2015-04-01

    Avalanches may affect critical infrastructure and may cause great economic losses. The planning horizon of infrastructures, e.g. hydropower generation facilities, reaches well into the future. Based on the results of previous studies on the effect of changing meteorological parameters (precipitation, temperature) and the effect on avalanche activity we assume that there will be a change of the risk pattern in future. The decision makers need to understand what the future might bring to best formulate their mitigation strategies. Therefore, we explore a commercial risk software to calculate risk for the coming years that might help in decision processes. The software @risk, is known to many larger companies, and therefore we explore its capabilities to include avalanche risk simulations in order to guarantee a comparability of different risks. In a first step, we develop a model for a hydropower generation facility that reflects the problem of changing avalanche activity patterns in future by selecting relevant input parameters and assigning likely probability distributions. The uncertain input variables include the probability of avalanches affecting an object, the vulnerability of an object, the expected costs for repairing the object and the expected cost due to interruption. The crux is to find the distribution that best represents the input variables under changing meteorological conditions. Our focus is on including the uncertain probability of avalanches based on the analysis of past avalanche data and expert knowledge. In order to explore different likely outcomes we base the analysis on three different climate scenarios (likely, worst case, baseline). For some variables, it is possible to fit a distribution to historical data, whereas in cases where the past dataset is insufficient or not available the software allows to select from over 30 different distribution types. The Monte Carlo simulation uses the probability distribution of uncertain variables

  20. Single photon avalanche detectors: prospects of new quenching and gain mechanisms

    NASA Astrophysics Data System (ADS)

    Hall, David; Liu, Yu-Hsin; Lo, Yu-Hwa

    2015-11-01

    While silicon single-photon avalanche diodes (SPAD) have reached very high detection efficiency and timing resolution, their use in fibre-optic communications, optical free space communications, and infrared sensing and imaging remains limited. III-V compounds including InGaAs and InP are the prevalent materials for 1550 nm light detection. However, even the most sensitive 1550 nm photoreceivers in optical communication have a sensitivity limit of a few hundred photons. Today, the only viable approach to achieve single-photon sensitivity at 1550 nm wavelength from semiconductor devices is to operate the avalanche detectors in Geiger mode, essentially trading dynamic range and speed for sensitivity. As material properties limit the performance of Ge and III-V detectors, new conceptual insight with regard to novel quenching and gain mechanisms could potentially address the performance limitations of III-V SPADs. Novel designs that utilise internal self-quenching and negative feedback can be used to harness the sensitivity of single-photon detectors,while drastically reducing the device complexity and increasing the level of integration. Incorporation of multiple gain mechanisms, together with self-quenching and built-in negative feedback, into a single device also hold promise for a new type of detector with single-photon sensitivity and large dynamic range.

  1. Predictions of silicon avalanche photodiode detector performance in water vapor differential absorption lidar

    NASA Technical Reports Server (NTRS)

    Kenimer, R. L.

    1988-01-01

    Performance analyses are presented which establish that over most of the range of signals expected for a down-looking differential absorption lidar (DIAL) operated at 16 km the silicon avalanche photodiode (APD) is the preferred detector for DIAL measurements of atmospheric water vapor in the 730 nm spectral region. The higher quantum efficiency of the APD's, (0.8-0.9) compared to a photomultiplier's (0.04-0.18) more than offsets the higher noise of an APD receiver. In addition to offering lower noise and hence lower random error the APD's excellent linearity and impulse recovery minimize DIAL systematic errors attributable to the detector. Estimates of the effect of detector system parameters on overall random and systematic DIAL errors are presented, and performance predictions are supported by laboratory characterization data for an APD receiver system.

  2. Design and fabrication of an optimum peripheral region for low gain avalanche detectors

    NASA Astrophysics Data System (ADS)

    Fernández-Martínez, Pablo; Flores, D.; Hidalgo, S.; Greco, V.; Merlos, A.; Pellegrini, G.; Quirion, D.

    2016-06-01

    Low Gain Avalanche Detectors (LGAD) represent a remarkable advance in high energy particle detection, since they provide a moderate increase (gain ~10) of the collected charge, thus leading to a notable improvement of the signal-to-noise ratio, which largely extends the possible application of Silicon detectors beyond their present working field. The optimum detection performance requires a careful implementation of the multiplication junction, in order to obtain the desired gain on the read out signal, but also a proper design of the edge termination and the peripheral region, which prevents the LGAD detectors from premature breakdown and large leakage current. This work deals with the critical technological aspects required to optimize the LGAD structure. The impact of several design strategies for the device periphery is evaluated with the aid of TCAD simulations, and compared with the experimental results obtained from the first LGAD prototypes fabricated at the IMB-CNM clean room. Solutions for the peripheral region improvement are also provided.

  3. A prototype avalanche photodiode array for scintillating-fiber tracking detectors

    NASA Astrophysics Data System (ADS)

    Yoshida, tracking detectors T.; Sora, T.

    2004-12-01

    We have evaluated the performance of a prototype 16-channel avalanche photodiode (APD) array developed primarily for scintillating-fiber (SCIFI) tracking detectors. The APD array was coupled to a 2.5 m long SCIFI array, and the detection efficiency was measured for minimum ionizing particles passing through the SCIFI array. The APD array was cooled to -50 °C to improve the S/N ratio. We have found that the APD array can read out each individual SCIFI with sufficiently high efficiency.

  4. Modeling of InGaAsSb-Based Avalanche Photodetectors for 2-Micron Wavelengths

    NASA Technical Reports Server (NTRS)

    Joshi, Ravindra P.; Abedin, M. Nurul (Technical Monitor)

    2002-01-01

    The main focus of this research is to study and evaluate the potential of InGaAsSb-AlGaAsSb based 2 micron avalanche photo-detectors. The photodetector contains a separate absorption and multiplication region (SAM) structure. The analysis has mainly been done to understand the electrical response characteristics of the devices existing at NASA, and to evaluate alternate structures proposed. Calculating the current flow for the existing detector structure, on the basis of its energy band diagram, is important. This analysis also helps to find shortcomings in the existing detector structure. It is shown that, unfortunately, the existing structure cannot lead to strong multiplication or voltage dependent gain. Two alternate structures are suggested, that could overcome the inherent flaws, and help achieve improved performance. These devices are obtained through modifications of the original structure, which include varying the doping levels, and changing the thicknesses of detector sub-regions. The results of our study are presented and discussed.

  5. Avalanche photodiode based time-of-flight mass spectrometry

    SciTech Connect

    Ogasawara, Keiichi Livi, Stefano A.; Desai, Mihir I.; Ebert, Robert W.; McComas, David J.; Walther, Brandon C.

    2015-08-15

    This study reports on the performance of Avalanche Photodiodes (APDs) as a timing detector for ion Time-of-Flight (TOF) mass spectroscopy. We found that the fast signal carrier speed in a reach-through type APD enables an extremely short timescale response with a mass or energy independent <2 ns rise time for <200 keV ions (1−40 AMU) under proper bias voltage operations. When combined with a microchannel plate to detect start electron signals from an ultra-thin carbon foil, the APD comprises a novel TOF system that successfully operates with a <0.8 ns intrinsic timing resolution even using commercial off-the-shelf constant-fraction discriminators. By replacing conventional total-energy detectors in the TOF-Energy system, APDs offer significant power and mass savings or an anti-coincidence background rejection capability in future space instrumentation.

  6. Preliminary results for the design, fabrication, and performance of a backside-illuminated avalanche drift detector

    NASA Astrophysics Data System (ADS)

    Qiao, Yun; Liang, Kun; Chen, Wen-Fei; Han, De-Jun

    2013-10-01

    The detection of low-level light is a key technology in various experimental scientific studies. As a photon detector, the silicon photomultiplier (SiPM) has gradually become an alternative to the photomultiplier tube (PMT) in many applications in high-energy physics, astroparticle physics, and medical imaging because of its high photon detection efficiency (PDE), good resolution for single-photon detection, insensitivity to magnetic field, low operating voltage, compactness, and low cost. However, primarily because of the geometric fill factor, the PDE of most SiPMs is not very high; in particular, for those SiPMs with a high density of micro cells, the effective area is small, and the bandwidth of the light response is narrow. As a building block of the SiPM, the concept of the backside-illuminated avalanche drift detector (ADD) was first proposed by the Max Planck Institute of Germany eight years ago; the ADD is promising to have high PDE over the full energy range of optical photons, even ultraviolet light and X-ray light, and because the avalanche multiplication region is very small, the ADD is beneficial for the fabrication of large-area SiPMs. However, because of difficulties in design and fabrication, no significant progress had been made, and the concept had not yet been verified. In this paper, preliminary results in the design, fabrication, and performance of a backside-illuminated ADD are reported; the difficulties in and limitations to the backside-illuminated ADD are analyzed.

  7. High-speed bridge circuit for InGaAs avalanche photodiode single-photon detector

    NASA Astrophysics Data System (ADS)

    Hashimoto, Hirofumi; Tomita, Akihisa; Okamoto, Atsushi

    2014-02-01

    Because of low power consumption and small footprint, avalanche photodiodes (APD) have been commonly applied to photon detection. Recently, high speed quantum communication has been demonstrated for high bit-rate quantum key distribution. For the high speed quantum communication, photon detectors should operate at GHz-clock frequencies. We propose balanced detection circuits for GHz-clock operation of InGaAs-APD photon detectors. The balanced single photon detector operates with sinusoidal wave gating. The sinusoidal wave appearing in the output is removed by the subtraction from APD signal without sharp band-elimination filters. Omission of the sharp filters removes the constraint on the operating frequency of the single photon detector. We present two designs, one works with two identical APDs, the other with one APD and a low-pass filter. The sinusoidal gating enables to eliminate the gating noise even with the simple configuration of the latter design. We demonstrated the balanced single photon detector operating with 1.020GHz clock at 233 K, 193 K, and 186.5 K. The dark count probability was 4.0 x 10-4 counts/pulse with the quantum efficiency of 10% at 233K, and 1.6 x 10-4 counts/pulse at 186.5 K. These results were obtained with easily available APDs (NR8300FP-C.C, RENESASS) originally developed for optical time-domain reflectmeters.

  8. Negative feedback avalanche diode

    NASA Technical Reports Server (NTRS)

    Itzler, Mark Allen (Inventor)

    2010-01-01

    A single-photon avalanche detector is disclosed that is operable at wavelengths greater than 1000 nm and at operating speeds greater than 10 MHz. The single-photon avalanche detector comprises a thin-film resistor and avalanche photodiode that are monolithically integrated such that little or no additional capacitance is associated with the addition of the resistor.

  9. Comparative Performance of the Photomultiplier Tube and the Silicon Avalanche Photodiode When Used as Detectors in Angular Scattering Measurements

    NASA Astrophysics Data System (ADS)

    Kroner, D. O.; Nelson, R. M.; Boryta, M. D.; Hapke, B. W.; Manatt, K.; Smythe, W. D.

    2014-12-01

    We report the results of a comparative study of two types of photometric detectors that are commonly used for, spacecraft, ground-based telescope, and laboratory observations in support of precise angular scattering investigations of the type described in a companion paper (Nelson et al., this meeting). The performance of the state of the art Hamamatsu C12703-01 Silicon Avalanche photodiode (SAD) was compared to that of the Hamamatsu R928 Photomultiplier tube (PMT). The Hamamatsu R928 evolved from a sequence of photometric detectors with a long history of use in support of laboratory and remote sensing studies, tracing backwards to include the RCA 1P21 and the RCA 931A. Two newly acquired SADs were bench tested along with a new R928 photomultiplier tube that was thermoelectrically cooled to -10 deg C. The SAD's employed electronic thermal compensation supplied by the manufacturer. The SADs and PMT measured electromagnetic radiation from solid-state lasers of wavelength 635 nm after the radiation was reflected from diffusely-scattering surfaces of varying albedos. The SADs were housed on tripods that were co-aligned with the PMT and laser. The photometric detectors were placed 4.3 meters from a reflecting disk. The disk was rotated to reduce the effect of laser speckle. All detectors in the experiment were equipped with notch filters that transmit light only of the wavelength emitted by the laser. Three SR830 DSP Lock-in Amplifiers were connected to the detectors and various setting configurations were compared in order to optimize signal to noise. Neutral Density filters (ND 0,3 and ND 0,9) were placed in the light path to determine the linearity in the response function of the detectors. We conclude that in this application SADs and PMTs produce comparable photometric precision and fidelity. SADs offer greater convenience because thermal compensation circuitry is integrated with the detector. This work was partially supported by NASA's Cassini Science

  10. SWAD: inherent photon counting performance of amorphous selenium multi-well avalanche detector

    NASA Astrophysics Data System (ADS)

    Stavro, Jann; Goldan, Amir H.; Zhao, Wei

    2016-03-01

    Photon counting detectors (PCDs) have the potential to improve x-ray imaging, however they are still hindered by several performance limitations and high production cost. By using amorphous Selenium (a-Se) the cost of PCDs can be significantly reduced compared to crystalline materials and enable large area detector fabrication. To overcome the problem of low carrier mobility and low charge conversion gain in a-Se, we are developing a novel direct conversion a- Se field-Shaping multi-Well Avalanche Detector (SWAD). SWAD circumvents the charge transport limitation by using a Frisch grid built within the readout circuit, reducing charge collection time to ~200 ns. Field shaping permits depth independent avalanche gain in wells, resulting in total conversion gain that is comparable to Si and CdTe. In the present work we investigate the effects of charge sharing and energy loss to understand the inherent photon counting performance for SWAD at x-ray energies used in breast imaging applications (20-50keV). The energy deposition profile for each interacting x-ray was determined with Monte Carlo simulation. For the energy ranges we are interested in, photoelectric interaction dominates, with a k-fluorescence yield of approximately 60%. Using a monoenergetic 45 keV beam incident on a target pixel in 400um of a-Se, our results show that only 20.42 % and 22.4 % of primary interacting photons have kfluorescence emissions which escape the target pixel for 100um and 85um pixel sizes respectively, demonstrating SWAD's potential for high spatial resolution applications.

  11. MPPC versus MRS APD in two-phase Cryogenic Avalanche Detectors

    NASA Astrophysics Data System (ADS)

    Bondar, A.; Buzulutskov, A.; Dolgov, A.; Shemyakina, E.; Sokolov, A.; Bondar, A.; Buzulutskov, A.; Dolgov, A.; Shemyakina, E.; Sokolov, A.

    2015-04-01

    Two-phase Cryogenic Avalanche Detectors (CRADs) with combined THGEM/GAPD multiplier have become an emerging potential technique for dark matter search and coherent neu\\-tri\\-no-nucleus scattering experiments. In such a multiplier the THGEM hole avalanches are optically recorded in the Near Infrared (NIR) using a matrix of Geiger-mode APDs (GAPDs). To select the proper sensor, the performances of six GAPD types manufactured by different companies, namely by Hamamatsu (MPPCs), CPTA (MRS APDs) and SensL (SiPMs), have been comparatively studied at cryogenic temperatures when operated in two-phase CRADs in Ar at 87 K. While the GAPDs with ceramic packages failed to operate properly at cryogenic temperatures, those with plastic packages, namely MPPC S10931-100P and MRS APD 149-35, showed satisfactory performances at 87 K. In addition, MPPC S10931-100P turned out to be superior in terms of the higher detection efficiency, lower noise rate, lower pixel quenching resistor and better characteristics reproducibility.

  12. Avalanche Debris Detection Using Satellite- and Drone Based Radar and Optical Remote Sensing

    NASA Astrophysics Data System (ADS)

    Eckerstorfer, M.; Malnes, E.; Vickers, H.; Solbø, S. A.; Tøllefsen, A.

    2014-12-01

    The mountainous fjord landscape in the county of Troms, around its capital Tromsø in Northern Norway is prone to high avalanche activity during the snow season. Large avalanches pose a hazard to infrastructure, such as buildings and roads, located between the steep mountainsides and the fjords. A prolonged cold spell during January and February 2014 was followed by rapid new-snow loading during March 2014, inducing a significant avalanche cycle with many spontaneous, size D4 avalanches that affected major transport veins. During and shortly after the avalanche cycle of March 2014, we obtained 11 Radarsat-2 Ultrafine mode scenes, chosen according to reported avalanche activity. We further collected four Radarsat-2 ScanSAR mode scenes and two Landsat-8 scenes covering the entire county of Troms. For one particular avalanche, we obtained a drone-based orthophoto, from which a DEM of the avalanche debris surface was derived, using structure-from-motion photogrammetry. This enabled us to calculate the debris volume accurately. We detected avalanche debris in the radar images visually, by applying two detection algorithms that make use of the increased backscatter in avalanche debris. This backscatter increase is a product of increased snow water equivalent and surface roughness, roughly of the order of 3 dB. In addition, we applied a multi-temporal approach by repeatedly detecting avalanche debris at different acquisition times, as well as a multi-sensor approach, covering similar areas with different sensors. This multi-temporal and multi-sensor approach enabled us to map the spatial extent and magnitude of the March 2014 avalanche cycle in the county Troms. With ESA's Sentinel-1 satellite, providing high-resolution, large swath radar images with a short repeat cycle, a complete avalanche record for a forecasting region could become feasible. In this first test season, we detected more than 550 avalanches that were released during a one-month period over an area of

  13. A comparison of avalanche photodiode and photomultiplier tube detectors for flow cytometry

    NASA Astrophysics Data System (ADS)

    Lawrence, William G.; Varadi, Gyula; Entine, Gerald; Podniesinski, Edward; Wallace, Paul K.

    2008-02-01

    Commercial flow cytometers use photomultiplier tubes (PMTs) for fluorescence detection. These detectors have high linear gain and broad dynamic range, but have limited sensitivity in the red and near infrared spectral regions. We present a comparison of avalanche photodiodes (APDs) and PMTs as detectors in flow cytometry instruments, and demonstrate improved sensitivity and resolution in the red and near infrared spectral regions using the APD. The relative performance of the PMT and APD were evaluated by simultaneously measuring the mean fluorescence intensity and coefficient of variation for emission from light emitting diode pulses, flow cytometry test beads, and fluorescently labeled cells. The relative signal to noise performance of the APD and PMT was evaluated over the 500 nm to 1050 nm wavelength range using pulsed light emitting diode light sources. While APDs have higher quantum efficiency but lower internal gain than PMTs, with appropriate external amplification the APD has signal to noise response that is comparable to PMTs in the 500 nm to 650 nm range and improved response in the 650 nm to 850 nm range The data demonstrates that the APD had performance comparable to the PMT in the spectral region between 500 to 650 nm and improved performance in the range of 650 to 1000 nm, where the PMT performance is quite poor. CD4 positive lymphocyte populations were easily identified in normal human blood both by APD and PMT using phycoerythrin labeled antibodies. In contrast, only the APD detector could resolve CD4 positive populations using 800 nm Quantum dot labeled antibodies.

  14. A new web-based system to improve the monitoring of snow avalanche hazard in France

    NASA Astrophysics Data System (ADS)

    Bourova, Ekaterina; Maldonado, Eric; Leroy, Jean-Baptiste; Alouani, Rachid; Eckert, Nicolas; Bonnefoy-Demongeot, Mylene; Deschatres, Michael

    2016-05-01

    Snow avalanche data in the French Alps and Pyrenees have been recorded for more than 100 years in several databases. The increasing amount of observed data required a more integrative and automated service. Here we report the comprehensive web-based Snow Avalanche Information System newly developed to this end for three important data sets: an avalanche chronicle (Enquête Permanente sur les Avalanches, EPA), an avalanche map (Carte de Localisation des Phénomènes d'Avalanche, CLPA) and a compilation of hazard and vulnerability data recorded on selected paths endangering human settlements (Sites Habités Sensibles aux Avalanches, SSA). These data sets are now integrated into a common database, enabling full interoperability between all different types of snow avalanche records: digitized geographic data, avalanche descriptive parameters, eyewitness reports, photographs, hazard and risk levels, etc. The new information system is implemented through modular components using Java-based web technologies with Spring and Hibernate frameworks. It automates the manual data entry and improves the process of information collection and sharing, enhancing user experience and data quality, and offering new outlooks to explore and exploit the huge amount of snow avalanche data available for fundamental research and more applied risk assessment.

  15. Investigation of a clinical PET detector module design that employs large-area avalanche photodetectors

    NASA Astrophysics Data System (ADS)

    Peng, Hao; Olcott, Peter D.; Spanoudaki, Virginia; Levin, Craig S.

    2011-06-01

    We investigated the feasibility of designing an Anger-logic PET detector module using large-area high-gain avalanche photodiodes (APDs) for a brain-dedicated PET/MRI system. Using Monte Carlo simulations, we systematically optimized the detector design with regard to the scintillation crystal, optical diffuser, surface treatment, layout of large-area APDs, and signal-to-noise ratio (SNR, defined as the 511 keV photopeak position divided by the standard deviation of noise floor in an energy spectrum) of the APD devices. A detector prototype was built comprising an 8 × 8 array of 2.75 × 3.00 × 20.0 mm3 LYSO (lutetium-yttrium-oxyorthosilicate) crystals and a 22.0 × 24.0 × 9.0 mm3 optical diffuser. From the four designs of the optical diffuser tested, two designs employing a slotted diffuser are able to resolve all 64 crystals within the block with good uniformity and peak-to-valley ratio. Good agreement was found between the simulation and experimental results. For the detector employing a slotted optical diffuser, the energy resolution of the global energy spectrum after normalization is 13.4 ± 0.4%. The energy resolution of individual crystals varies between 11.3 ± 0.3% and 17.3 ± 0.4%. The time resolution varies between 4.85 ± 0.04 (center crystal), 5.17 ± 0.06 (edge crystal), and 5.18 ± 0.07 ns (corner crystal). The generalized framework proposed in this work helps to guide the design of detector modules for selected PET system configurations, including scaling the design down to a preclinical PET system, scaling up to a whole-body clinical scanner, as well as replacing APDs with other novel photodetectors that have higher gain or SNR such as silicon photomultipliers.

  16. Non-Geiger-Mode Single-Photon Avalanche Detector with Low Excess Noise

    NASA Technical Reports Server (NTRS)

    Zhao, Kai; Lo, YuHwa; Farr, William

    2010-01-01

    This design constitutes a self-resetting (gain quenching), room-temperature operational semiconductor single-photon-sensitive detector that is sensitive to telecommunications optical wavelengths and is scalable to large areas (millimeter diameter) with high bandwidth and efficiencies. The device can detect single photons at a 1,550-nm wavelength at a gain of 1 x 10(exp 6). Unlike conventional single photon avalanche detectors (SPADs), where gain is an extremely sensitive function to the bias voltage, the multiplication gain of this device is stable at 1 x 10(exp 6) over a wide range of bias from 30.2 to 30.9 V. Here, the multiplication gain is defined as the total number of charge carriers contained in one output pulse that is triggered by the absorption of a single photon. The statistics of magnitude of output signals also shows that the device has a very narrow pulse height distribution, which demonstrates a greatly suppressed gain fluctuation. From the histograms of both pulse height and pulse charge, the equivalent gain variance (excess noise) is between 1.001 and 1.007 at a gain of 1 x 10(exp 6). With these advantages, the device holds promise to function as a PMT-like photon counter at a 1,550- nm wavelength. The epitaxial layer structure of the device allows photons to be absorbed in the InGaAs layer, generating electron/hole (e-h) pairs. Driven by an electrical field in InGaAs, electrons are collected at the anode while holes reach the multiplication region (InAlAs p-i-n structure) and trigger the avalanche process. As a result, a large number of e-h pairs are created, and the holes move toward the cathode. Holes created by the avalanche process gain large kinetic energy through the electric field, and are considered hot. These hot holes are cooled as they travel across a p -InAlAs low field region, and are eventually blocked by energy barriers formed by the InGaAsP/ InAlAs heterojunctions. The composition of the InGaAsP alloy was chosen to have an 80 me

  17. Lutetium oxyorthosilicate block detector readout by avalanche photodiode arrays for high resolution animal PET

    NASA Astrophysics Data System (ADS)

    Pichler, B. J.; Swann, B. K.; Rochelle, J.; Nutt, R. E.; Cherry, S. R.; Siegel, S. B.

    2004-09-01

    Avalanche photodiodes (APDs) have proven to be useful as light detectors for high resolution positron emission tomography (PET). Their compactness makes these devices excellent candidates for replacing bulky photomultiplier tubes (PMTs) in PET systems where space limitations are an issue. The readout of densely packed, 10 × 10 lutetium oxyorthosilicate (LSO) block detectors (crystal size 2.0 × 2.0 × 12 mm3) with custom-built monolithic 3 × 3 APD arrays was investigated. The APDs had a 5 × 5 mm2 active surface and were arranged on a 6.25 mm pitch. The dead space on the edges of the array was 1.25 mm. The APDs were operated at a bias voltage of approximately 380 V for a gain of 100 and a dark current of 10 nA per APD. The standard deviation in gain between the APDs in the array ranged from 1.8 to 6.5% as the gain was varied from 50 to 108. A fast, low-noise, multi-channel charge sensitive preamplifier application-specific integrated circuit (ASIC) was developed for the APD readout. The amplifier had a rise time of 8 ns, a noise floor of 515 e- rms and a 9 e- pF-1 noise slope. An acquired flood image showed that all 100 crystals from the block detector could be resolved. Timing measurements with single-channel LSO-APD detectors, as well as with the array, against a plastic scintillator and PMT assembly showed a time resolution of 1.2 ns and 2.5 ns, respectively. The energy resolution measured with a single 4.0 × 4.0 × 10 mm3 LSO crystal, wrapped in four-layer polytetrafluoroethylene (PTFE) tape and coupled with optical grease on a single APD of the array, yielded 15% (full width at half maximum, FWHM) at 511 keV. Stability tests over 9 months of operation showed that the APD arrays do not degrade appreciably. These results demonstrate the ability to decode densely packed LSO scintillation blocks with compact APD arrays. The good timing and energy resolution makes these detectors suitable for high resolution PET.

  18. Investigation of the possibility of creating a multichannel photodetector based on the avalanche MRS-structure

    NASA Astrophysics Data System (ADS)

    Sadyigov, Z. Y.; Gasanov, A. G.; Yusipov, N. Y.; Golovin, V. M.; Gulanian, Emin H.; Vinokurov, Y. S.; Simonov, A. V.

    1991-11-01

    Investigation results of the avalanche process in MRS-structure are given and the possibility of creating the multichannel avalanche photodetector based on such a structure for the one- dimensional hologram disk memory system is considered. The experimental sample of the photodetector has sensitivity approximately 104 A/W with wavelength (lambda) approximately equals 0.63 micrometers and response speed approximately 5 nsec.

  19. Assessing wet snow avalanche activity using detailed physics based snowpack simulations

    NASA Astrophysics Data System (ADS)

    Wever, N.; Vera Valero, C.; Fierz, C.

    2016-06-01

    Water accumulating on microstructural transitions inside a snowpack is often considered a prerequisite for wet snow avalanches. Recent advances in numerical snowpack modeling allow for an explicit simulation of this process. We analyze detailed snowpack simulations driven by meteorological stations in three different climate regimes (Alps, Central Andes, and Pyrenees), with accompanying wet snow avalanche activity observations. Predicting wet snow avalanche activity based on whether modeled water accumulations inside the snowpack locally exceed 5-6% volumetric liquid water content is providing a higher prediction skill than using thresholds for daily mean air temperature, or the daily sum of the positive snow energy balance. Additionally, the depth of the maximum water accumulation in the simulations showed a significant correlation with observed avalanche size. Direct output from detailed snow cover models thereby is able to provide a better regional assessment of dangerous slope aspects and potential avalanche size than traditional methods.

  20. A study of Gd-based parallel plate avalanche counter for thermal neutrons by MC simulation

    NASA Astrophysics Data System (ADS)

    Rhee, J. T.; Kim, H. G.; Ahmad, Farzana; Jeon, Y. J.; Jamil, M.

    2013-12-01

    In this work, we demonstrate the feasibility and characteristics of a single-gap parallel plate avalanche counter (PPAC) as a low energy neutron detector, based on Gd-converter coating. Upon falling on the Gd-converter surface, the incident low energy neutrons produce internal conversion electrons which are evaluated and detected. For estimating the performance of the Gd-based PPAC, a simulation study has been performed using GEANT4 Monte Carlo (MC) code. The detector response as a function of incident neutron energies in the range of 25-100 meV has been evaluated with two different physics lists. Using the QGSP_BIC_HP physics list and assuming 5 μm converter thickness, 11.8%, 18.48%, and 30.28% detection efficiencies have been achieved for the forward-, the backward-, and the total response of the converter-based PPAC. On the other hand, considering the same converter thickness and detector configuration, with the QGSP_BERT_HP physics list efficiencies of 12.19%, 18.62%, and 30.81%, respectively, were obtained. These simulation results are briefly discussed.

  1. A new modeling and simulation method for important statistical performance prediction of single photon avalanche diode detectors

    NASA Astrophysics Data System (ADS)

    Xu, Yue; Xiang, Ping; Xie, Xiaopeng; Huang, Yang

    2016-06-01

    This paper presents a new modeling and simulation method to predict the important statistical performance of single photon avalanche diode (SPAD) detectors, including photon detection efficiency (PDE), dark count rate (DCR) and afterpulsing probability (AP). Three local electric field models are derived for the PDE, DCR and AP calculations, which show analytical dependence of key parameters such as avalanche triggering probability, impact ionization rate and electric field distributions that can be directly obtained from Geiger mode Technology Computer Aided Design (TCAD) simulation. The model calculation results are proven to be in good agreement with the reported experimental data in the open literature, suggesting that the proposed modeling and simulation method is very suitable for the prediction of SPAD statistical performance.

  2. Characterization of photo-multiplier tubes for the Cryogenic Avalanche Detector

    NASA Astrophysics Data System (ADS)

    Bondar, A.; Buzulutskov, A.; Dolgov, A.; Nosov, V.; Shekhtman, L.; Sokolov, A.

    2015-10-01

    New Cryogenic Avalanche Detector (CRAD) with ultimate sensitivity, that will be able to detect one primary electron released in the cryogenic liquid, is under development in the Laboratory of Cosmology and Particle Physics of the Novosibirsk State University jointly with the Budker Institute of Nuclear Physics. The CRAD will use two sets of cryogenic PMTs in order to get trigger signal either from primary scintillations in liquid Ar or from secondary scintillations in high field gap above the liquid. Two types of cryogenic PMTs produced by Hamamatsu Photonics were tested and the results are presented in this paper. Low background 3 inch PMT R11065-10 demonstrated excellent performance according to its specifications provided by the producer. The gain measured with single electron response (SER) in liquid Ar reached 107, dark count rate rate did not exceed 300 Hz and pulse height resolution of single electron signals was close to 50%(FWHM). However, two R11065-10 PMTs out of 7 tested stopped functioning after several tens minutes of operation immersed completely into liquid Ar. The remaining 5 devices and one R11065-MOD were operated successfully for several hours each with all the parameters according to the producer specifications. Compact 2 inch PMT R6041-506-MOD with metal-channel dynode structure is a candidate for side wall PMT system that will look at electroluminescence in high field region above liquid. Four of these PMTs were tested in liquid Ar and demonstrated gain up to 2× 107, dark count rate rate below 100 Hz and pulse height resolution of single electron signals of about 110% (FWHM).

  3. Avalanches in One-Dimensional Piles with Different Types of Bases

    SciTech Connect

    Altshuler, E.; Ramos, O.; Martinez, C.; Flores, L. E.; Noda, C.

    2001-06-11

    We perform a systematic experimental study of the influence of the type of base on the avalanche dynamics of slowly driven 1D ball piles. The control of base details allows us to explore a wide spectrum of pile structures and dynamics. The scaling properties of the observed avalanche distributions suggest that self-organized critical behavior is approached as the {open_quotes}base-induced{close_quotes} disorder at the pile profile increases.

  4. Development of a 144-channel Hybrid Avalanche Photo-Detector for Belle II ring-imaging Cherenkov counter with an aerogel radiator

    NASA Astrophysics Data System (ADS)

    Nishida, S.; Adachi, I.; Hamada, N.; Hara, K.; Iijima, T.; Iwata, S.; Kakuno, H.; Kawai, H.; Korpar, S.; Kriz^an, P.; Ogawa, S.; Pestotnik, R.; Ŝantelj, L.; Seljak, A.; Sumiyoshi, T.; Tabata, M.; Tahirovic, E.; Yoshida, K.; Yusa, Y.

    2015-07-01

    The Belle II detector, a follow up of the very successful Belle experiment, is under construction at the SuperKEKB electron-positron collider at KEK in Japan. For the PID system in the forward region of the spectrometer, a proximity-focusing ring-imaging Cherenkov counter with an aerogel radiator is being developed. For the position sensitive photon sensor, a 144-channel Hybrid Avalanche Photo-Detector has been developed with Hamamatsu Photonics K.K. In this report, we describe the specification of the Hybrid Avalanche Photo-Detector and the status of the mass production.

  5. Avalanches in compressed porous SiO(2)-based materials.

    PubMed

    Nataf, Guillaume F; Castillo-Villa, Pedro O; Baró, Jordi; Illa, Xavier; Vives, Eduard; Planes, Antoni; Salje, Ekhard K H

    2014-08-01

    The failure dynamics in SiO(2)-based porous materials under compression, namely the synthetic glass Gelsil and three natural sandstones, has been studied for slowly increasing compressive uniaxial stress with rates between 0.2 and 2.8 kPa/s. The measured collapsed dynamics is similar to Vycor, which is another synthetic porous SiO(2) glass similar to Gelsil but with a different porous mesostructure. Compression occurs by jerks of strain release and a major collapse at the failure point. The acoustic emission and shrinking of the samples during jerks are measured and analyzed. The energy of acoustic emission events, its duration, and waiting times between events show that the failure process follows avalanche criticality with power law statistics over ca. 4 decades with a power law exponent ɛ≃ 1.4 for the energy distribution. This exponent is consistent with the mean-field value for the collapse of granular media. Besides the absence of length, energy, and time scales, we demonstrate the existence of aftershock correlations during the failure process. PMID:25215740

  6. Design and testing of an active quenching circuit for an avalanche photodiode photon detector

    NASA Technical Reports Server (NTRS)

    Arbel, D.; Schwartz, J. A.

    1991-01-01

    The photon-detection capabilities of avalanche photodiodes (APDs) operating above their theoretical breakdown voltages are described, with particular attention given to the needs and methods of quenching an avalanche once breakdown has occurred. A brief background on the motives of and previous work with this mode of operation is presented. Finally, a description of the design and testing of an active quenching circuit is given. Although the active quenching circuit did not perform as expected, knowledge was gained as to the signal amplitudes necessary for quenching and the need for a better model for the above-breakdown circuit characteristics of the Geiger-mode APD.

  7. Fast single photon avalanche photodiode-based time-resolved diffuse optical tomography scanner

    PubMed Central

    Mu, Ying; Niedre, Mark

    2015-01-01

    Resolution in diffuse optical tomography (DOT) is a persistent problem and is primarily limited by high degree of light scatter in biological tissue. We showed previously that the reduction in photon scatter between a source and detector pair at early time points following a laser pulse in time-resolved DOT is highly dependent on the temporal response of the instrument. To this end, we developed a new single-photon avalanche photodiode (SPAD) based time-resolved DOT scanner. This instrument uses an array of fast SPADs, a femto-second Titanium Sapphire laser and single photon counting electronics. In combination, the overall instrument temporal impulse response function width was 59 ps. In this paper, we report the design of this instrument and validate its operation in symmetrical and irregularly shaped optical phantoms of approximately small animal size. We were able to accurately reconstruct the size and position of up to 4 absorbing inclusions, with increasing image quality at earlier time windows. We attribute these results primarily to the rapid response time of our instrument. These data illustrate the potential utility of fast SPAD detectors in time-resolved DOT. PMID:26417526

  8. Indirect flat-panel detector with avalanche gain: Fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager)

    SciTech Connect

    Zhao Wei; Li Dan; Reznik, Alla; Lui, B.J.M.; Hunt, D.C.; Rowlands, J.A.; Ohkawa, Yuji; Tanioka, Kenkichi

    2005-09-15

    An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed detector SHARP-AMFPI (scintillator HARP active matrix flat panel imager). The advantage of the SHARP-AMFPI is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. The purpose of this paper is to investigate the important design considerations for SHARP-AMFPI such as avalanche gain, which depends on both the thickness d{sub Se} and the applied electric field E{sub Se} of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E{sub Se} dependence of both avalanche gain and optical quantum efficiency of an 8 {mu}m HARP layer. The results were used in a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and nonavalanche modes as a function of E{sub Se}: (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; (4) gain nonuniformity resulting from thickness nonuniformity; and (5) effects of direct x-ray interaction in HARP. Our results showed that a HARP layer thickness of 8 {mu}m can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy.

  9. Indirect flat-panel detector with avalanche gain: fundamental feasibility investigation for SHARP-AMFPI (scintillator HARP active matrix flat panel imager).

    PubMed

    Zhao, Wei; Li, Dan; Reznik, Alla; Lui, B J M; Hunt, D C; Rowlands, J A; Ohkawa, Yuji; Tanioka, Kenkichi

    2005-09-01

    An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP (high-gain avalanche rushing photoconductor). The final electronic image is read out using an active matrix array of thin film transistors (TFT). We call the proposed detector SHARP-AMFPI (scintillator HARP active matrix flat panel imager). The advantage of the SHARP-AMFPI is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. The purpose of this paper is to investigate the important design considerations for SHARP-AMFPI such as avalanche gain, which depends on both the thickness d(Se) and the applied electric field E(Se) of the HARP layer. To determine the optimal design parameter and operational conditions for HARP, we measured the E(Se) dependence of both avalanche gain and optical quantum efficiency of an 8 microm HARP layer. The results were used in a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and nonavalanche modes as a function of E(Se): (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; (4) gain nonuniformity resulting from thickness nonuniformity; and (5) effects of direct x-ray interaction in HARP. Our results showed that a HARP layer thickness of 8 microm can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy. PMID:16266110

  10. Avalanche proton-boron fusion based on elastic nuclear collisions

    NASA Astrophysics Data System (ADS)

    Eliezer, Shalom; Hora, Heinrich; Korn, Georg; Nissim, Noaz; Martinez Val, Josè Maria

    2016-05-01

    Recent experiments done at Prague with the 600 J/0.2 ns PALS laser interacting with a layer of boron dopants in a hydrogen enriched target have produced around 109 alphas. We suggest that these unexpected very high fusion reactions of proton with 11B indicate an avalanche multiplication for the measured anomalously high nuclear reaction yields. This can be explained by elastic nuclear collisions in the broad 600 keV energy band, which is coincident with the high nuclear p-11B fusion cross section, by the way of multiplication through generation of three secondary alpha particles from a single primarily produced alpha particle.

  11. Electron-avalanche amplifier based on the electronic Venturi effect

    NASA Astrophysics Data System (ADS)

    Taubert, D.; Schinner, G. J.; Tranitz, H. P.; Wegscheider, W.; Tomaras, C.; Kehrein, S.; Ludwig, S.

    2010-10-01

    Scattering of otherwise ballistic electrons far from equilibrium is investigated in a cold two-dimensional electron system. The interaction between excited electrons and the degenerate Fermi liquid induces a positive charge in a nanoscale region which would be negatively charged for diffusive transport at local thermal equilibrium. In a three-terminal device we observe avalanche amplification of electrical current, resulting in a situation comparable to the Venturi effect in hydrodynamics. Numerical calculations using a random-phase approximation are in agreement with our data and suggest Coulomb interaction as the dominant scattering mechanism.

  12. Research and development on a sub 100 PICO second time-of-flight system based on silicon avalanche diodes

    SciTech Connect

    Choi, Y.; Hirsch, A.; Hauger, A.; Scharenberg, R.; Tincknell, M.; Rai, G.

    1991-12-31

    Particle identification requires a momentum measurement and a second independent determination either energy loss (dE/dx) or time of flight (TOF). To cover a momentum range from 0.1 GeV/c to 1.5 GeV/c in the STAR detector requires both the dE/dx and TOF techniques. This research is designed to develop the avalanche diode (AVD) detectors for TOF systems and evaluate their performance. The test of a small prototype system would be carried out at Purdue and at accelerator test beam sites. The Purdue group has developed a complete test setup for evaluating the time resolution of the AVD`s which includes fast-slow electronic channels, CAMAC based electronic modules and a temperature controlled environment. The AVDs also need to be tested in a 0.5 tesla magnetic field. The Purdue group would augment this test set up to include a magnetic field.

  13. Fill-factor improvement of Si CMOS single-photon avalanche diode detector arrays by integration of diffractive microlens arrays.

    PubMed

    Intermite, Giuseppe; McCarthy, Aongus; Warburton, Ryan E; Ren, Ximing; Villa, Federica; Lussana, Rudi; Waddie, Andrew J; Taghizadeh, Mohammad R; Tosi, Alberto; Zappa, Franco; Buller, Gerald S

    2015-12-28

    Single-photon avalanche diode (SPAD) detector arrays generally suffer from having a low fill-factor, in which the photo-sensitive area of each pixel is small compared to the overall area of the pixel. This paper describes the integration of different configurations of high efficiency diffractive optical microlens arrays onto a 32 × 32 SPAD array, fabricated using a 0.35 µm CMOS technology process. The characterization of SPAD arrays with integrated microlens arrays is reported over the spectral range of 500-900 nm, and a range of f-numbers from f/2 to f/22. We report an average concentration factor of 15 measured for the entire SPAD array with integrated microlens array. The integrated SPAD and microlens array demonstrated a very high uniformity in overall efficiency. PMID:26832039

  14. The 1.06 micrometer avalanche photodiode detectors with integrated circuit preamplifiers

    NASA Technical Reports Server (NTRS)

    Eden, R. C.

    1975-01-01

    The development of a complete solid state 1.06 micron optical receiver which can be used in optical communications at data rates approaching 1.5 Gb/s, or in other applications requiring sensitive, short-pulse detection, is reported. This work entailed both the development of a new type of heterojunction 3-5 semiconductor alloy avalanche photodiode and an extremely charge-sensitive wideband low-noise preamp design making use of GaAs Schottky barrier-gate field effect transistors.

  15. High resolution tree-ring based spatial reconstructions of snow avalanche activity in Glacier National Park, Montana, USA

    USGS Publications Warehouse

    Pederson, Gregory T.; Reardon, Blase; Caruso, C.J.; Fagre, Daniel B.

    2006-01-01

    Effective design of avalanche hazard mitigation measures requires long-term records of natural avalanche frequency and extent. Such records are also vital for determining whether natural avalanche frequency and extent vary over time due to climatic or biophysical changes. Where historic records are lacking, an accepted substitute is a chronology developed from tree-ring responses to avalanche-induced damage. This study evaluates a method for using tree-ring chronologies to provide spatially explicit differentiations of avalanche frequency and temporally explicit records of avalanche extent that are often lacking. The study area - part of John F. Stevens Canyon on the southern border of Glacier National Park – is within a heavily used railroad and highway corridor with two dozen active avalanche paths. Using a spatially geo-referenced network of avalanche-damaged trees (n=109) from a single path, we reconstructed a 96-year tree-ring based chronology of avalanche extent and frequency. Comparison of the chronology with historic records revealed that trees recorded all known events as well as the same number of previously unidentified events. Kriging methods provided spatially explicit estimates of avalanche return periods. Estimated return periods for the entire avalanche path averaged 3.2 years. Within this path, return intervals ranged from ~2.3 yrs in the lower track, to ~9-11 yrs and ~12 to >25 yrs in the runout zone, where the railroad and highway are located. For avalanche professionals, engineers, and transportation managers this technique proves a powerful tool in landscape risk assessment and decision making.

  16. Large-area NbN superconducting nanowire avalanche photon detectors with saturated detection efficiency

    NASA Astrophysics Data System (ADS)

    Murphy, Ryan P.; Grein, Matthew E.; Gudmundsen, Theodore J.; McCaughan, Adam; Najafi, Faraz; Berggren, Karl K.; Marsili, Francesco; Dauler, Eric A.

    2015-05-01

    Superconducting circuits comprising SNSPDs placed in parallel—superconducting nanowire avalanche photodetectors, or SNAPs—have previously been demonstrated to improve the output signal-to-noise ratio (SNR) by increasing the critical current. In this work, we employ a 2-SNAP superconducting circuit with narrow (40 nm) niobium nitride (NbN) nanowires to improve the system detection efficiency to near-IR photons while maintaining high SNR. Additionally, while previous 2-SNAP demonstrations have added external choke inductance to stabilize the avalanching photocurrent, we show that the external inductance can be entirely folded into the active area by cascading 2-SNAP devices in series to produce a greatly increased active area. We fabricated series-2-SNAP (s2-SNAP) circuits with a nanowire length of 20 μm with cascades of 2-SNAPs providing the choke inductance necessary for SNAP operation. We observed that (1) the detection efficiency saturated at high bias currents, and (2) the 40 nm 2-SNAP circuit critical current was approximately twice that for a 40 nm non-SNAP configuration.

  17. Avalanche properties in a transport model based on critical-gradient fluctuation dynamics

    SciTech Connect

    Garcia, L.; Carreras, B.A.

    2005-09-15

    A simple one-dimensional transport model based on critical-gradient fluctuation dynamics is applied to describe some of the properties of plasma-turbulence-induced transport. This model combines avalanche-like transport with diffusion. The particle flux is self-regulated by the stability properties of the fluctuations. A high-gradient edge region emerges where transport dynamics is close to marginal stability. In steady state, the core remains at the subcritical gradient. The avalanches change from quasiperiodic events triggered mostly near the edge region to intermittent transport events depending on the noise level of the particle source.

  18. Sensitivity Analysis of a Spatio-Temporal Avalanche Forecasting Model Based on Support Vector Machines

    NASA Astrophysics Data System (ADS)

    Matasci, G.; Pozdnoukhov, A.; Kanevski, M.

    2009-04-01

    The recent progress in environmental monitoring technologies allows capturing extensive amount of data that can be used to assist in avalanche forecasting. While it is not straightforward to directly obtain the stability factors with the available technologies, the snow-pack profiles and especially meteorological parameters are becoming more and more available at finer spatial and temporal scales. Being very useful for improving physical modelling, these data are also of particular interest regarding their use involving the contemporary data-driven techniques of machine learning. Such, the use of support vector machine classifier opens ways to discriminate the ``safe'' and ``dangerous'' conditions in the feature space of factors related to avalanche activity based on historical observations. The input space of factors is constructed from the number of direct and indirect snowpack and weather observations pre-processed with heuristic and physical models into a high-dimensional spatially varying vector of input parameters. The particular system presented in this work is implemented for the avalanche-prone site of Ben Nevis, Lochaber region in Scotland. A data-driven model for spatio-temporal avalanche danger forecasting provides an avalanche danger map for this local (5x5 km) region at the resolution of 10m based on weather and avalanche observations made by forecasters on a daily basis at the site. We present the further work aimed at overcoming the ``black-box'' type modelling, a disadvantage the machine learning methods are often criticized for. It explores what the data-driven method of support vector machine has to offer to improve the interpretability of the forecast, uncovers the properties of the developed system with respect to highlighting which are the important features that led to the particular prediction (both in time and space), and presents the analysis of sensitivity of the prediction with respect to the varying input parameters. The purpose of the

  19. Avalanche for shape and feature-based virtual screening with 3D alignment.

    PubMed

    Diller, David J; Connell, Nancy D; Welsh, William J

    2015-11-01

    This report introduces a new ligand-based virtual screening tool called Avalanche that incorporates both shape- and feature-based comparison with three-dimensional (3D) alignment between the query molecule and test compounds residing in a chemical database. Avalanche proceeds in two steps. The first step is an extremely rapid shape/feature based comparison which is used to narrow the focus from potentially millions or billions of candidate molecules and conformations to a more manageable number that are then passed to the second step. The second step is a detailed yet still rapid 3D alignment of the remaining candidate conformations to the query conformation. Using the 3D alignment, these remaining candidate conformations are scored, re-ranked and presented to the user as the top hits for further visualization and evaluation. To provide further insight into the method, the results from two prospective virtual screens are presented which show the ability of Avalanche to identify hits from chemical databases that would likely be missed by common substructure-based or fingerprint-based search methods. The Avalanche method is extended to enable patent landscaping, i.e., structural refinements to improve the patentability of hits for deployment in drug discovery campaigns. PMID:26458937

  20. Analysis of avalanche risk factors in backcountry terrain based on usage frequency and accident data in Switzerland

    NASA Astrophysics Data System (ADS)

    Techel, F.; Zweifel, B.; Winkler, K.

    2015-09-01

    Recreational activities in snow-covered mountainous terrain in the backcountry account for the vast majority of avalanche accidents. Studies analyzing avalanche risk mostly rely on accident statistics without considering exposure (or the elements at risk), i.e., how many, when and where people are recreating, as data on recreational activity in the winter mountains are scarce. To fill this gap, we explored volunteered geographic information on two social media mountaineering websites - bergportal.ch and camptocamp.org. Based on these data, we present a spatiotemporal pattern of winter backcountry touring activity in the Swiss Alps and compare this with accident statistics. Geographically, activity was concentrated in Alpine regions relatively close to the main Swiss population centers in the west and north. In contrast, accidents occurred equally often in the less-frequented inner-alpine regions. Weekends, weather and avalanche conditions influenced the number of recreationists, while the odds to be involved in a severe avalanche accident did not depend on weekends or weather conditions. However, the likelihood of being involved in an accident increased with increasing avalanche danger level, but also with a more unfavorable snowpack containing persistent weak layers (also referred to as an old snow problem). In fact, the most critical situation for backcountry recreationists and professionals occurred on days and in regions when both the avalanche danger was critical and when the snowpack contained persistent weak layers. The frequently occurring geographical pattern of a more unfavorable snowpack structure also explains the relatively high proportion of accidents in the less-frequented inner-alpine regions. These results have practical implications: avalanche forecasters should clearly communicate the avalanche danger and the avalanche problem to the backcountry user, particularly if persistent weak layers are of concern. Professionals and recreationists, on the

  1. Impact of a New Highly Sensitive HgCdTe Avalanche Photodiode Detector on Receiver Performance for the CO2 Sounder Lidar for the ASCENDS Mission

    NASA Astrophysics Data System (ADS)

    Sun, X.; Abshire, J. B.

    2013-12-01

    NASA Goddard Space Flight Center (GSFC) is currently developing a CO2 lidar as a candidate for the NASA's planned ASCENDS mission under the support of Earth Science Technology Office (ESTO) Instrument Incubator Program (IIP). As part of this work we have demonstrated new type of lower noise HgCdTe avalanche photodiode (APD) multi-element detector for the lidar receiver. This significantly improves the receiver sensitivity, lower the laser power, and reduce the receiver telescope size compared to InGaAs photomultiplier tubes (PMT) and APDs currently used. The HgCdTe APD arrays were designed and manufactured by DRS Technologies, Reconnaissance, Surveillance and Target Acquisition (RSTA) Division, which combines their mature HgCdTe APD detector in a hybrid package with a new custom cryogenic silicon preamplifier. The new detectors were specially designed for our airborne CO2 lidar and operate at ~ 77K inside a turn-key closed-cycle cooler. The detector has 80 μm square pixels in a 4x4 array, and >70% fill factor and was custom designed to match the optics of our airborne and eventually space-based CO2 lidar. The initial results of evaluating the detector at NASA GSFC showed the HgCdTe APD assembly has a quantum efficiency of ~90% near 1550-nm, >500 APD gain, 8-10 MHz electrical bandwidth, and an average noise equivalent power of <1fW/Hz1/2. The detector also has a much wider linear dynamic range than PMTs, since it operates in a linear analog mode and has variable gain. Given the wide range of surface reflectivities this is important for ASCENDS. The new detector also greatly improves our CO2 lidar's receiver sensitivity. Calculations show it enables us to reduce the laser transmitter power by half for the space borne instrument while staying with a conventional reasonably sized (~1.2 m) diameter receiver telescope. We will show analysis and laboratory test results of the CO2 lidar performance using a receiver with this new detector. We are also funded by NASA ESTO

  2. Near infrared single photon avalanche detector with negative feedback and self quenching

    NASA Astrophysics Data System (ADS)

    Linga, Krishna; Yevtukhov, Yuriy; Liang, Bing

    2009-08-01

    We present the design and development of a negative feedback devices using the internal discrete amplifier approach used for the development of a single photon avalanche photodetector in the near infrared wavelength region. This new family of photodetectors with negative feedback, requiring no quenching mechanism using Internal Discrete Amplification (IDA) mechanism for the realization of very high gain and low excess noise factor in the visible and near infrared spectral regions, operates in the non-gated mode under a constant bias voltage. The demonstrated device performance far exceeds any available solid state Photodetectors in the near infrared wavelength range. The measured devices have Gain > 2×105, Excess noise factor < 1.05, Rise time < 350ps, Fall time < 500ps, Dark current < 2×106 cps at room temperature, and Operating Voltage < 60V. These devices are ideal for researchers in the field of Ladar/Lidar, free space optical communication, 3D imaging, industrial and scientific instrumentation, night vision, quantum cryptography, and other military, defence and aerospace applications.

  3. Nanowire-based detector

    DOEpatents

    Berggren, Karl K; Hu, Xiaolong; Masciarelli, Daniele

    2014-06-24

    Systems, articles, and methods are provided related to nanowire-based detectors, which can be used for light detection in, for example, single-photon detectors. In one aspect, a variety of detectors are provided, for example one including an electrically superconductive nanowire or nanowires constructed and arranged to interact with photons to produce a detectable signal. In another aspect, fabrication methods are provided, including techniques to precisely reproduce patterns in subsequently formed layers of material using a relatively small number of fabrication steps. By precisely reproducing patterns in multiple material layers, one can form electrically insulating materials and electrically conductive materials in shapes such that incoming photons are redirected toward a nearby electrically superconductive materials (e.g., electrically superconductive nanowire(s)). For example, one or more resonance structures (e.g., comprising an electrically insulating material), which can trap electromagnetic radiation within its boundaries, can be positioned proximate the nanowire(s). The resonance structure can include, at its boundaries, electrically conductive material positioned proximate the electrically superconductive nanowire such that light that would otherwise be transmitted through the sensor is redirected toward the nanowire(s) and detected. In addition, electrically conductive material can be positioned proximate the electrically superconductive nanowire (e.g. at the aperture of the resonant structure), such that light is directed by scattering from this structure into the nanowire.

  4. High-gain and low-excess noise near-infrared single-photon avalanche detector arrays

    NASA Astrophysics Data System (ADS)

    Linga, Krishna; Yevtukhov, Yuriy; Liang, Bing

    2010-04-01

    We have designed and developed a new family of photodetectors and arrays with Internal Discrete Amplification (IDA) mechanism for the realization of very high gain and low excess noise factor in the visible and near infrared spectral regions. These devices surpass many limitations of the Single Photon Avalanche Photodetectors such as ultra low excess noise factor, very high gain, lower reset time (< 200 ns). These devices are very simple to operate in the non-gated mode under a constant dc bias voltage. Because of its unique characteristics of self-quenching and self-recovery, no external quenching circuit is needed. This unique feature of self quenching and self-recovery makes it simple to less complex readout integrated circuit to realize large format detector arrays. In this paper, we present the discrete amplification design approach used for the development of self reset, high gain photodetector arrays in the near infrared wavelength region. The demonstrated device performance far exceeds any available solid state Photodetectors in the near infrared wavelength range. These devices are ideal for researchers in the field of spectroscopy, industrial and scientific instrumentation, Ladar, quantum cryptography, night vision and other military, defense and aerospace applications.

  5. Fluorescence-suppressed time-resolved Raman spectroscopy of pharmaceuticals using complementary metal-oxide semiconductor (CMOS) single-photon avalanche diode (SPAD) detector.

    PubMed

    Rojalin, Tatu; Kurki, Lauri; Laaksonen, Timo; Viitala, Tapani; Kostamovaara, Juha; Gordon, Keith C; Galvis, Leonardo; Wachsmann-Hogiu, Sebastian; Strachan, Clare J; Yliperttula, Marjo

    2016-01-01

    In this work, we utilize a short-wavelength, 532-nm picosecond pulsed laser coupled with a time-gated complementary metal-oxide semiconductor (CMOS) single-photon avalanche diode (SPAD) detector to acquire Raman spectra of several drugs of interest. With this approach, we are able to reveal previously unseen Raman features and suppress the fluorescence background of these drugs. Compared to traditional Raman setups, the present time-resolved technique has two major improvements. First, it is possible to overcome the strong fluorescence background that usually interferes with the much weaker Raman spectra. Second, using the high photon energy excitation light source, we are able to generate a stronger Raman signal compared to traditional instruments. In addition, observations in the time domain can be performed, thus enabling new capabilities in the field of Raman and fluorescence spectroscopy. With this system, we demonstrate for the first time the possibility of recording fluorescence-suppressed Raman spectra of solid, amorphous and crystalline, and non-photoluminescent and photoluminescent drugs such as caffeine, ranitidine hydrochloride, and indomethacin (amorphous and crystalline forms). The raw data acquired by utilizing only the picosecond pulsed laser and a CMOS SPAD detector could be used for identifying the compounds directly without any data processing. Moreover, to validate the accuracy of this time-resolved technique, we present density functional theory (DFT) calculations for a widely used gastric acid inhibitor, ranitidine hydrochloride. The obtained time-resolved Raman peaks were identified based on the calculations and existing literature. Raman spectra using non-time-resolved setups with continuous-wave 785- and 532-nm excitation lasers were used as reference data. Overall, this demonstration of time-resolved Raman and fluorescence measurements with a CMOS SPAD detector shows promise in diverse areas, including fundamental chemical research, the

  6. Development of the HgCdTe Avalanche Photodiode Detectors and the Improvement in the CO2 Lidar Performance for the ASCENDS Mission

    NASA Astrophysics Data System (ADS)

    Sun, X.; Abshire, J. B.; Chen, J. R.; Ramanathan, A. K.; Mao, J.

    2015-12-01

    NASA Goddard Space Flight Center (GSFC) is developing the CO2 lidar as a candidate for the NASA's planned ASCENDS mission under the support of Earth Science Technology Office (ESTO) IIP and ATI-QRS programs. A new type of HgCdTe avalanche photodiode (APD) detector has been developed by the DRS Technologies under the IIP program. The new detectors achieved >70% quantum efficiency, including the effect of the fill factor, over the spectral range from 0.4 to 4.3 μm, which significantly improves the receiver performance of our CO2 lidar and enabled other remote sending measurements. The HgCdTe APD arrays have 80 μm square pixels in a 4x4 array along with a bank of 16 preamplifiers on the same chip carrier. Test results at both DRS and GSFC showed the HgCdTe APD array has achieved, an APD gain of 500-1000, 8-10 MHz electrical bandwidth, and an average noise equivalent power (NEP) of <0.5 fW/Hz1/2. It has demonstrated at least a 3 orders of magnitude dynamic range at a fixed APD gain setting. The gains of the APD and the preamplifier can also be adjusted to further extend the receiver dynamic range. During summer 2014 we successfully demonstrated airborne lidar measurements of column CO2 using one of these detectors. The Aerospace Corporation is currently building a 3U CubeSat with one of these detectors in a small closed-cycle cryocooler as the primary payload under the ESTO In-space Validation of Earth Science Technology (InVEST) program. The CubeSat is scheduled to be launched in late 2016 and will fly in a low Earth orbit and monitor the performance for at least a year. We have also updated the performance analysis of a space-based version of our CO2 lidar with the new HgCdTe APD detector. For the retrievals, a least-square-error method is used to fit the measured transmittances to a predetermined line shape function using 8 to 16 sampling wavelengths. The error in the derived total optical depth and the CO2 mixing ratio are estimated via the standard error

  7. Graphene based GHz detectors

    NASA Astrophysics Data System (ADS)

    Boyd, Anthony K.; El Fatimy, Abdel; Barbara, Paola; Nath, Anindya; Campbell, Paul M.; Myers-Ward, Rachael; Daniels, Kevin; Gaskill, D. Kurt

    Graphene demonstrates great promise as a detector over a wide spectral range especially in the GHz range. This is because absorption is enhanced due to the Drude contribution. In the GHz range there are viable detection mechanisms for graphene devices. With this in mind, two types of GHz detectors are fabricated on epitaxial graphene using a lift off resist-based clean lithography process to produce low contact resistance. Both device types use asymmetry for detection, consistent with recent thoughts of the photothermoelectric effect (PTE) mechanism. The first is an antenna coupled device. It utilizes two dissimilar contact metals and the work function difference produces the asymmetry. The other device is a field effect transistor constructed with an asymmetric top gate that creates a PN junction and facilitates tuning the photovoltaic response. The response of both device types, tested from 100GHz to 170GHz, are reported. This work was sponsored by the U.S. Office of Naval Research (Award Number N000141310865).

  8. Low dose digital X-ray imaging with avalanche amorphous selenium

    NASA Astrophysics Data System (ADS)

    Scheuermann, James R.; Goldan, Amir H.; Tousignant, Olivier; Léveillé, Sébastien; Zhao, Wei

    2015-03-01

    Active Matrix Flat Panel Imagers (AMFPI) based on an array of thin film transistors (TFT) have become the dominant technology for digital x-ray imaging. In low dose applications, the performance of both direct and indirect conversion detectors are limited by the electronic noise associated with the TFT array. New concepts of direct and indirect detectors have been proposed using avalanche amorphous selenium (a-Se), referred to as high gain avalanche rushing photoconductor (HARP). The indirect detector utilizes a planar layer of HARP to detect light from an x-ray scintillator and amplify the photogenerated charge. The direct detector utilizes separate interaction (non-avalanche) and amplification (avalanche) regions within the a-Se to achieve depth-independent signal gain. Both detectors require the development of large area, solid state HARP. We have previously reported the first avalanche gain in a-Se with deposition techniques scalable to large area detectors. The goal of the present work is to demonstrate the feasibility of large area HARP fabrication in an a-Se deposition facility established for commercial large area AMFPI. We also examine the effect of alternative pixel electrode materials on avalanche gain. The results show that avalanche gain > 50 is achievable in the HARP layers developed in large area coaters, which is sufficient to achieve x-ray quantum noise limited performance down to a single x-ray photon per pixel. Both chromium (Cr) and indium tin oxide (ITO) have been successfully tested as pixel electrodes.

  9. Space-based detectors

    NASA Astrophysics Data System (ADS)

    Sesana, A.; Weber, W. J.; Killow, C. J.; Perreur-Lloyd, M.; Robertson, D. I.; Ward, H.; Fitzsimons, E. D.; Bryant, J.; Cruise, A. M.; Dixon, G.; Hoyland, D.; Smith, D.; Bogenstahl, J.; McNamara, P. W.; Gerndt, R.; Flatscher, R.; Hechenblaikner, G.; Hewitson, M.; Gerberding, O.; Barke, S.; Brause, N.; Bykov, I.; Danzmann, K.; Enggaard, A.; Gianolio, A.; Vendt Hansen, T.; Heinzel, G.; Hornstrup, A.; Jennrich, O.; Kullmann, J.; Møller-Pedersen, S.; Rasmussen, T.; Reiche, J.; Sodnik, Z.; Suess, M.; Armano, M.; Sumner, T.; Bender, P. L.; Akutsu, T.; Sathyaprakash, B. S.

    2014-12-01

    The parallel session C5 on Space-Based Detectors gave a broad overview over the planned space missions related to gravitational wave detection. Overviews of the revolutionary science to be expected from LISA was given by Alberto Sesana and Sasha Buchman. The launch of LISA Pathfinder (LPF) is planned for 2015. This mission and its payload "LISA Technology Package" will demonstrate key technologies for LISA. In this context, reference masses in free fall for LISA, and gravitational physics in general, was described by William Weber, laser interferometry at the pico-metre level and the optical bench of LPF was presented by Christian Killow and the performance of the LPF optical metrology system by Paul McNamara. While LPF will not yet be sensitive to gravitational waves, it may nevertheless be used to explore fundamental physics questions, which was discussed by Michele Armano. Some parts of the LISA technology that are not going to be demonstrated by LPF, but under intensive development at the moment, were presented by Oliver Jennrich and Oliver Gerberding. Looking into the future, Japan is studying the design of a mid-frequency detector called DECIGO, which was discussed by Tomotada Akutsu. Using atom interferometry for gravitational wave detection has also been recently proposed, and it was critically reviewed by Peter Bender. In the nearer future, the launch of GRACE Follow-On (for Earth gravity observation) is scheduled for 2017, and it will include a Laser Ranging Interferometer as technology demonstrator. This will be the first inter-spacecraft laser interferometer and has many aspects in common with the LISA long arm, as discussed by Andrew Sutton.

  10. Betabox: a beta particle imaging system based on a position sensitive avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Dooraghi, A. A.; Vu, N. T.; Silverman, R. W.; Farrell, R.; Shah, K. S.; Wang, J.; Heath, J. R.; Chatziioannou, A. F.

    2013-06-01

    A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm2 position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as 18F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for 18F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm-2 at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of 18F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm-2 for 1 min acquisitions and a 62 × 62 µm2 pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm2. We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ˜180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ˜200 µm of additional LDPE film. Lastly

  11. Betabox: a beta particle imaging system based on a position sensitive avalanche photodiode

    PubMed Central

    Dooraghi, AA; Vu, NT; Silverman, RW; Farrell, R; Shah, KS; Wang, J; Heath, JR; Chatziioannou, AF

    2013-01-01

    A beta camera has been developed that allows planar imaging of the spatial and temporal distribution of beta particles using a 14 × 14 mm2 position sensitive avalanche photodiode (PSAPD). This camera system, which we call Betabox, can be directly coupled to microfluidic chips designed for cell incubation or other biological applications. Betabox allows for imaging the cellular uptake of molecular imaging probes labeled with charged particle emitters such as 18F inside these chips. In this work, we investigate the quantitative imaging capabilities of Betabox for 18F beta particles, in terms of background rate, efficiency, spatial resolution, and count rate. Measurements of background and spatial resolution are considered both at room temperature (21 °C ± 1 °C) and at an elevated operating temperature (37 °C ± 1 °C), as is often required for biological assays. The background rate measured with a 4 keV energy cutoff is below 2 cph mm−2 at both 21 and 37 °C. The absolute efficiency of Betabox for the detection of 18F positron sources in contact with a PSAPD with the surface passivated from ambient light and damage is 46% ± 1%. The lower detection limit is estimated using the Rose Criterion to be 0.2 cps mm−2 for 1 min acquisitions and a 62 × 62 µm2 pixel size. The upper detection limit is approximately 21 000 cps. The spatial resolution at both 21 and 37 °C ranges from 0.4 mm FWHM at the center of the field of view (FOV), and degrades to 1 mm at a distance of 5 mm away from center yielding a useful FOV of approximately 10 × 10 mm2. We also investigate the effects on spatial resolution and sensitivity that result from the use of a polymer based microfluidic chip. For these studies we place varying layers of low-density polyethylene (LDPE) between the detector and the source and find that the spatial resolution degrades by ~180 µm for every 100 µm of LDPE film. Sensitivity is reduced by half with the inclusion of ~200 µm of additional LDPE film

  12. Photoelectron multipliers based on avalanche pn — i — pn structures

    NASA Astrophysics Data System (ADS)

    Lukin, K. A.; Maksymov, P. P.; Cerdeira, H. A.

    2014-12-01

    We present a new physical principle to design an optoelectronic device, which consists of a multilayered semiconductor structure, where the necessary conditions for generation of photoelectrons are met, such that it will enable sequential avalanche multiplication of electrons and holes inside two depletion slabs created around the p - n junctions of a reverse biased pn - i - pn structure. The mathematical model and computer simulations of this Semiconductor Photo-electron Multiplier (SPEM) for different semiconductor materials are presented. Its performance is evaluated and compared with that of conventional devices. The Geiger operational mode is briefly discussed which may be used in Silicon Photomultiplier (SiPM) as an elementary photo detector to enhance its performance.

  13. Four-layer depth-of-interaction PET detector for high resolution PET using a multi-pixel S8550 avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Nishikido, Fumihiko; Inadama, Naoko; Oda, Ichiro; Shibuya, Kengo; Yoshida, Eiji; Yamaya, Taiga; Kitamura, Keishi; Murayama, Hideo

    2010-09-01

    Avalanche photodiodes (APDs) are being used as photodetectors in positron emission tomography (PET) because they have many advantages over photomultipliers (PMTs) typically used in PET detectors. We have developed a PET detector that consists of a multi-pixel APD and a 6×6×4 array of 1.46×1.46 mm 2×4.5 m LYSO crystals for a small animal PET scanner. The detector can identify four-layer depth of interaction (DOI) with a position-sensitive APD coupled to the backside of a crystal array by just an optimized reflector arrangement. Since scintillation lights are shared among many pixels by the method, weaker signals in APD pixels far from the interacting crystals are affected by noise. To evaluate the performance of the four-layer DOI detector with the APD and the influence of electrical noise on our method, we constructed a prototype DOI detector and tested its performance. We found, except for crystal elements on the edge of the crystal array, all crystal elements could be identified from the 2D position histogram. An energy resolution of 16.9% was obtained for the whole crystal array of the APD detector. The results of noise dependence of detector performances indicated that the DOI detector using the APD could achieve sufficient performance even when using application-specific integrated circuits.

  14. Pulse-resolved multi-photon X-ray detection at 31 MHz based on a quadrant avalanche photodiode.

    PubMed

    Reusch, Tobias; Osterhoff, Markus; Agricola, Johannes; Salditt, Tim

    2014-07-01

    The technical realisation and the commissioning experiments of a high-speed X-ray detector based on a quadrant avalanche silicon photodiode and high-speed digitizers are described. The development is driven by the need for X-ray detectors dedicated to time-resolved diffraction and imaging experiments, ideally requiring pulse-resolved data processing at the synchrotron bunch repetition rate. By a novel multi-photon detection scheme, the exact number of X-ray photons within each X-ray pulse can be recorded. Commissioning experiments at beamlines P08 and P10 of the storage ring PETRA III, at DESY, Hamburg, Germany, have been used to validate the pulse-wise multi-photon counting scheme at bunch frequencies ≥ 31 MHz, enabling pulse-by-pulse readout during the PETRA III 240-bunch mode with single-photon detection capability. An X-ray flux of ≥ 3.7 × 10(9) photons s(-1) can be detected while still resolving individual photons at low count rates. PMID:24971964

  15. Effective amplifier noise for an optical receiver based on linear mode avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Chen, C.-C.

    1989-01-01

    The rms noise charge induced by the amplifier for an optical receiver based on the linear-mode avalanche photodiode (APD) was analyzed. It is shown that for an amplifier with a 1-pF capacitor and a noise temperature of 100 K, the rms noise charge due to the amplifier is about 300. Since the noise charge must be small compared to the signal gain, APD gains on the order of 1000 will be required to operate the receiver in the linear mode.

  16. III-V strain layer superlattice based band engineered avalanche photodiodes (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Ghosh, Sid

    2015-08-01

    Laser detection and ranging (LADAR)-based systems operating in the Near Infrared (NIR) and Short Wave Infrared (SWIR) have become popular optical sensors for remote sensing, medical, and environmental applications. Sophisticated laser-based radar and weapon systems used for long-range military and astronomical applications need to detect, recognize, and track a variety of targets under a wide spectrum of atmospheric conditions. Infrared APDs play an important role in LADAR systems by integrating the detection and gain stages in a single device. Robust silicon-APDs are limited to visible and very near infrared region (< 1 um), while InGaAs works well up to wavelengths of about 1.5um. Si APDs have low multiplication or excess noise but are limited to below 1um due very poor quantum efficiency above 0.8um. InGaAs and Ge APDs operate up to wavelengths of 1.5um but have poor multiplication or excess noise due to a low impact ionization coefficient ratio between electrons and holes. For the past several decades HgCdTe has been traditionally used in longer wavelength (> 3um) infrared photon detection applications. Recently, various research groups (including Ghosh et. al.) have reported SWIR and MWIR HgCdTe APDs on CdZnTe and Si substrates. However, HgCdTe APDs suffer from low breakdown fields due to material defects, and excess noise increases significantly at high electric fields. During the past decade, InAs/GaSb Strain Layer Superlattice (SLS) material system has emerged as a potential material for the entire infrared spectrum because of relatively easier growth, comparable absorption coefficients, lower tunneling currents and longer Auger lifetimes resulting in enhanced detectivities (D*). Band engineering in type II SLS allows us to engineer avalanche properties of electrons and holes. This is a great advantage over bulk InGaAs and HgCdTe APDs where engineering avalanche properties is not possible. The talk will discuss the evolution of superlattice based avalanche

  17. Nuclear resonant scattering measurements on {sup 57}Fe by multichannel scaling with a 64-pixel silicon avalanche photodiode linear-array detector

    SciTech Connect

    Kishimoto, S. Haruki, R.; Mitsui, T.; Yoda, Y.; Taniguchi, T.; Shimazaki, S.; Ikeno, M.; Saito, M.; Tanaka, M.

    2014-11-15

    We developed a silicon avalanche photodiode (Si-APD) linear-array detector for use in nuclear resonant scattering experiments using synchrotron X-rays. The Si-APD linear array consists of 64 pixels (pixel size: 100 × 200 μm{sup 2}) with a pixel pitch of 150 μm and depletion depth of 10 μm. An ultrafast frontend circuit allows the X-ray detector to obtain a high output rate of >10{sup 7} cps per pixel. High-performance integrated circuits achieve multichannel scaling over 1024 continuous time bins with a 1 ns resolution for each pixel without dead time. The multichannel scaling method enabled us to record a time spectrum of the 14.4 keV nuclear radiation at each pixel with a time resolution of 1.4 ns (FWHM). This method was successfully applied to nuclear forward scattering and nuclear small-angle scattering on {sup 57}Fe.

  18. Solar-Blind Avalanche Photodetector Based On Single ZnO-Ga₂O₃ Core-Shell Microwire.

    PubMed

    Zhao, Bin; Wang, Fei; Chen, Hongyu; Wang, Yunpeng; Jiang, Mingming; Fang, Xiaosheng; Zhao, Dongxu

    2015-06-10

    High-performance solar-blind (200-280 nm) avalanche photodetectors (APDs) were fabricated based on highly crystallized ZnO-Ga2O3 core-shell microwires. The responsivity can reach up to 1.3 × 10(3) A/W under -6 V bias. Moreover, the corresponding detectivity was as high as 9.91 × 10(14) cm·Hz(1/2)/W. The device also showed a fast response, with a rise time shorter than 20 μs and a decay time of 42 μs. The quality of the detectors in solar-blind waveband is comparable to or even higher than that of commercial Si APD (APD120A2 from Thorlabs Inc.), with a responsivity ∼8 A/W, detectivity ∼10(12) cm·Hz(1/2)/W, and response time ∼20 ns. The high performance of this APD make it highly suitable for practical applications as solar-blind photodetectors, and this core-shell microstructure heterojunction design method would provide a new approach for realizing an APD device. PMID:25946467

  19. Integrated avalanche photodiode arrays

    DOEpatents

    Harmon, Eric S.

    2015-07-07

    The present disclosure includes devices for detecting photons, including avalanche photon detectors, arrays of such detectors, and circuits including such arrays. In some aspects, the detectors and arrays include a virtual beveled edge mesa structure surrounded by resistive material damaged by ion implantation and having side wall profiles that taper inwardly towards the top of the mesa structures, or towards the direction from which the ion implantation occurred. Other aspects are directed to masking and multiple implantation and/or annealing steps. Furthermore, methods for fabricating and using such devices, circuits and arrays are disclosed.

  20. Monte Carlo simulations of compact gamma cameras based on avalanche photodiodes.

    PubMed

    Després, Philippe; Funk, Tobias; Shah, Kanai S; Hasegawa, Bruce H

    2007-06-01

    Avalanche photodiodes (APDs), and in particular position-sensitive avalanche photodiodes (PSAPDs), are an attractive alternative to photomultiplier tubes (PMTs) for reading out scintillators for PET and SPECT. These solid-state devices offer high gain and quantum efficiency, and can potentially lead to more compact and robust imaging systems with improved spatial and energy resolution. In order to evaluate this performance improvement, we have conducted Monte Carlo simulations of gamma cameras based on avalanche photodiodes. Specifically, we investigated the relative merit of discrete and PSAPDs in a simple continuous crystal gamma camera. The simulated camera was composed of either a 4 x 4 array of four channels 8 x 8 mm2 PSAPDs or an 8 x 8 array of 4 x 4 mm2 discrete APDs. These configurations, requiring 64 channels readout each, were used to read the scintillation light from a 6 mm thick continuous CsI:Tl crystal covering the entire 3.6 x 3.6 cm2 photodiode array. The simulations, conducted with GEANT4, accounted for the optical properties of the materials, the noise characteristics of the photodiodes and the nonlinear charge division in PSAPDs. The performance of the simulated camera was evaluated in terms of spatial resolution, energy resolution and spatial uniformity at 99mTc (140 keV) and 125I ( approximately 30 keV) energies. Intrinsic spatial resolutions of 1.0 and 0.9 mm were obtained for the APD- and PSAPD-based cameras respectively for 99mTc, and corresponding values of 1.2 and 1.3 mm FWHM for 125I. The simulations yielded maximal energy resolutions of 7% and 23% for 99mTc and 125I, respectively. PSAPDs also provided better spatial uniformity than APDs in the simple system studied. These results suggest that APDs constitute an attractive technology especially suitable to build compact, small field of view gamma cameras dedicated, for example, to small animal or organ imaging. PMID:17505089

  1. Avalanche risk in backcountry terrain based on usage frequency and accident data

    NASA Astrophysics Data System (ADS)

    Techel, F.; Zweifel, B.; Winkler, K.

    2014-08-01

    In Switzerland, the vast majority of avalanche accidents occurs during recreational activities. Risk analysis studies mostly rely on accident statistics without considering exposure (or the elements at risk), i.e. how many and where people are recreating. We compared the accident data (backcountry touring) with reports from two social media mountaineering networks - bergportal.ch and camptocamp.org. On these websites, users reported more than 15 000 backcountry tours during the five winters 2009/2010 to 2013/2014. We noted similar patterns in avalanche accident data and user data like demographics of recreationists, distribution of the day of the week (weekday vs. weekend) or weather conditions (fine vs. poor weather). However, we also found differences such as the avalanche danger conditions on days with activities and accidents, but also the geographic distribution. While backcountry activities are concentrated in proximity to the main population centres in the West and North of the Swiss Alps, a large proportion of the severe avalanche accidents occurred in the inner-alpine, more continental regions with frequently unfavorably snowpack structure. This suggests that even greater emphasis should be put on the type of avalanche problem in avalanche education and avalanche forecasting to increase the safety of backcountry recreationists.

  2. Critical avalanches and subsampling in map-based neural networks coupled with noisy synapses.

    PubMed

    Girardi-Schappo, M; Kinouchi, O; Tragtenberg, M H R

    2013-08-01

    Many different kinds of noise are experimentally observed in the brain. Among them, we study a model of noisy chemical synapse and obtain critical avalanches for the spatiotemporal activity of the neural network. Neurons and synapses are modeled by dynamical maps. We discuss the relevant neuronal and synaptic properties to achieve the critical state. We verify that networks of functionally excitable neurons with fast synapses present power-law avalanches, due to rebound spiking dynamics. We also discuss the measuring of neuronal avalanches by subsampling our data, shedding light on the experimental search for self-organized criticality in neural networks. PMID:24032969

  3. Fast scintillation timing detector using proportional-mode avalanche photodiode for nuclear resonant scattering experiments in high-energy synchrotron X-ray region

    NASA Astrophysics Data System (ADS)

    Inoue, Keisuke; Kishimoto, Shunji

    2016-01-01

    To obtain both a high count rate of >107 s-1 and a detection efficiency sufficient for high-energy X-rays of >30 keV, we propose a scintillation timing detector using a proportional-mode silicon avalanche photodiode (Si-APD) for synchrotron radiation nuclear resonant scattering. We here present results obtained with a prototype detector using a lead-loaded plastic scintillator (EJ-256) mounted on a proportional-mode Si-APD (active area size: 3 mm in diameter). The detector was operated at ‒35 °C for a better signal-to-noise ratio. Using synchrotron X-rays of 67.41 keV, which is the same energy as the first excited level of 61Ni, we successfully measured pulse-height and time spectra of the scintillation light. A good time resolution of 0.50±0.06 ns (full width at half-maximum) was obtained for 67.41 keV X-rays with a scintillator 3 mm in diameter and 2 mm thick.

  4. Terahertz Detectors based on graphene

    NASA Astrophysics Data System (ADS)

    Gouider, Fathi; Salman, Majdi; Göthlich, Markus; Schmidt, Hennrik; Ahlers, Franz-J.; Haug, Rolf; Nachtwei, Georg

    2013-08-01

    In this study we present magnetotransport an magnetooptical data obtained in the magnetic field range 0T < B < 7T at detectors patterned in Corbino geometry on epitaxial graphene wafer using a Ge detector. We observed the cyclotron resonance of charge carriers in these wafers by measurement of the transmission of THz wafes through the unpatterned squares (about 4 × 4mm2) of the wafers as a function of the magnetic field B applied perpendicular to the wafer. Further, we performed measurements of the photocunductivity of graphene-based devices shaped in Corbino geometry, induced by terahertz (THz) radiation generated by a p-Ge laser (emitting in the energy range 7.5meV <= Eph <= 11meV). Our photoconductivity measurement imply that graphene devices are suitable for the detection of terahertz radiation.

  5. Low-voltage-operation avalanche photodiode based on n-gallium oxide/p-crystalline selenium heterojunction

    SciTech Connect

    Imura, S. Kikuchi, K.; Miyakawa, K.; Ohtake, H.; Kubota, M.

    2014-06-16

    In this study, we demonstrate the avalanche multiplication phenomenon in a crystalline-selenium (c-Se)-based heterojunction photodiode. The carrier injection from an external electrode, which is considered to be the major factor contributing to dark current at a high electric field, was significantly decreased by employing a thin n-type Ga{sub 2}O{sub 3} layer with a high hole-injection barrier. The fabricated Ga{sub 2}O{sub 3}/c-Se diode exhibited extremely high external quantum efficiency of over 100% in the short-wavelength region at a relatively low reverse-bias voltage of ∼20 V. Furthermore, Sn-doping of the Ga{sub 2}O{sub 3} layer increases the carrier concentration; hence, the resulting device has a lower threshold voltage for avalanche multiplication.

  6. A branching process model for sand avalanches

    SciTech Connect

    Garcia-Pelayo, R.; Salazar, I.; Schieve, W.C. )

    1993-07-01

    An analytically solvable model for sand avalanches of noninteracting grains of sand, based on the Chapman-Kolmogorov equations, is presented. For a single avalanche, distributions of lifetimes, sizes of overflows and avalanches, and correlation functions are calculated. Some of these are exponentials, some are power laws. Spatially homogeneous distributions of avalanches are also studied. Computer simulations of avalanches of interacting grains of sand are compared to the solutions to the Chapman-Kolmogorov equations. It is found that within the range of parameters explored in the simulation, the approximation of noninteracting grains of sand is a good one. 20 refs., 4 figs.

  7. Avalanche Photodiode Arrays for Optical Communications Receivers

    NASA Technical Reports Server (NTRS)

    Srinivasan, M.; Vilnrotter, V.

    2001-01-01

    An avalanche photodiode (APD) array for ground-based optical communications receivers is investigated for the reception of optical signals through the turbulent atmosphere. Kolmogorov phase screen simulations are used to generate realistic spatial distributions of the received optical field. It is shown that use of an APD array for pulse-position modulation detection can improve performance by up to 4 dB over single APD detection in the presence of turbulence, but that photon-counting detector arrays yield even greater gains.

  8. [Avalanche accidents and treatment of avalanche victims].

    PubMed

    Skaiaa, Sven Christjar; Thomassen, Øyvind

    2016-03-15

    Avalanches may be provoked spontaneously or as a result of human activity, and they trigger the need for considerable rescue resources. Avalanche search and rescue operations are complex and characterised by physical and mental stress. The guidelines for resuscitation of avalanche victims may be perceived as complex and abstruse, which can lead to suboptimal treatment and an increased strain on rescue teams. The purpose of this article is to summarise the principles for medical treatment of avalanche victims. PMID:26983147

  9. Pulse-resolved multi-photon X-ray detection at 31 MHz based on a quadrant avalanche photodiode

    PubMed Central

    Reusch, Tobias; Osterhoff, Markus; Agricola, Johannes; Salditt, Tim

    2014-01-01

    The technical realisation and the commissioning experiments of a high-speed X-ray detector based on a quadrant avalanche silicon photodiode and high-speed digitizers are described. The development is driven by the need for X-ray detectors dedicated to time-resolved diffraction and imaging experiments, ideally requiring pulse-resolved data processing at the synchrotron bunch repetition rate. By a novel multi-photon detection scheme, the exact number of X-ray photons within each X-ray pulse can be recorded. Commissioning experiments at beamlines P08 and P10 of the storage ring PETRA III, at DESY, Hamburg, Germany, have been used to validate the pulse-wise multi-photon counting scheme at bunch frequencies ≥31 MHz, enabling pulse-by-pulse readout during the PETRA III 240-bunch mode with single-photon detection capability. An X-ray flux of ≥3.7 × 109 photons s−1 can be detected while still resolving individual photons at low count rates. PMID:24971964

  10. Long-distance entanglement-based quantum key distribution experiment using practical detectors.

    PubMed

    Takesue, Hiroki; Harada, Ken-Ichi; Tamaki, Kiyoshi; Fukuda, Hiroshi; Tsuchizawa, Tai; Watanabe, Toshifumi; Yamada, Koji; Itabashi, Sei-Ichi

    2010-08-01

    We report an entanglement-based quantum key distribution experiment that we performed over 100 km of optical fiber using a practical source and detectors. We used a silicon-based photon-pair source that generated high-purity time-bin entangled photons, and high-speed single photon detectors based on InGaAs/InP avalanche photodiodes with the sinusoidal gating technique. To calculate the secure key rate, we employed a security proof that validated the use of practical detectors. As a result, we confirmed the successful generation of sifted keys over 100 km of optical fiber with a key rate of 4.8 bit/s and an error rate of 9.1%, with which we can distill secure keys with a key rate of 0.15 bit/s. PMID:20721069

  11. Reuyl Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2002-01-01

    (Released 13 May 2002) The Science The rugged, arcuate rim of the 90 km crater Reuyl dominates this THEMIS image. Reuyl crater is at the southern edge of a region known to be blanketed in thick dust based on its high albedo (brightness) and low thermal inertia values. This thick mantle of dust creates the appearance of snow covered mountains in the image. Like snow accumulation on Earth, Martian dust can become so thick that it eventually slides down the face of steep slopes, creating runaway avalanches of dust. In the center of this image about 1/3 of the way down is evidence of this phenomenon. A few dozen dark streaks can be seen on the bright, sunlit slopes of the crater rim. The narrow streaks extend downslope following the local topography in a manner very similar to snow avalanches on Earth. But unlike their terrestrial counterparts, no accumulation occurs at the bottom. The dust particles are so small that they are easily launched into the thin atmosphere where they remain suspended and ultimately blow away. The apparent darkness of the avalanche scars is due to the presence of relatively dark underlying material that becomes exposed following the passage of the avalanche. Over time, new dust deposition occurs, brightening the scars until they fade into the background. Although dark slope streaks had been observed in Viking mission images, a clear understanding of this dynamic phenomenon wasn't possible until the much higher resolution images from the Mars Global Surveyor MOC camera revealed the details. MOC images also showed that new avalanches have occurred during the time MGS has been in orbit. THEMIS images will allow additional mapping of their distribution and frequency, contributing new insights about Martian dust avalanches. The Story The stiff peaks in this image might remind you of the Alps here on Earth, but they really outline the choppy edge of a large Martian crater over 50 miles wide (seen in the context image at right). While these aren

  12. Amorphous Silicon Based Neutron Detector

    SciTech Connect

    Xu, Liwei

    2004-12-12

    Various large-scale neutron sources already build or to be constructed, are important for materials research and life science research. For all these neutron sources, neutron detectors are very important aspect. However, there is a lack of a high-performance and low-cost neutron beam monitor that provides time and temporal resolution. The objective of this SBIR Phase I research, collaboratively performed by Midwest Optoelectronics, LLC (MWOE), the University of Toledo (UT) and Oak Ridge National Laboratory (ORNL), is to demonstrate the feasibility for amorphous silicon based neutron beam monitors that are pixilated, reliable, durable, fully packaged, and fabricated with high yield using low-cost method. During the Phase I effort, work as been focused in the following areas: 1) Deposition of high quality, low-defect-density, low-stress a-Si films using very high frequency plasma enhanced chemical vapor deposition (VHF PECVD) at high deposition rate and with low device shunting; 2) Fabrication of Si/SiO2/metal/p/i/n/metal/n/i/p/metal/SiO2/ device for the detection of alpha particles which are daughter particles of neutrons through appropriate nuclear reactions; and 3) Testing of various devices fabricated for alpha and neutron detection; As the main results: · High quality, low-defect-density, low-stress a-Si films have been successfully deposited using VHF PECVD on various low-cost substrates; · Various single-junction and double junction detector devices have been fabricated; · The detector devices fabricated have been systematically tested and analyzed. · Some of the fabricated devices are found to successfully detect alpha particles. Further research is required to bring this Phase I work beyond the feasibility demonstration toward the final prototype devices. The success of this project will lead to a high-performance, low-cost, X-Y pixilated neutron beam monitor that could be used in all of the neutron facilities worldwide. In addition, the technologies

  13. LiDAR-based characterization of the Mt Shasta debris avalanche deposit

    NASA Astrophysics Data System (ADS)

    Tortini, R.; Carn, S. A.; van Wyk de Vries, B.

    2013-12-01

    The failure of destabilized volcano flanks, due either to tectonic activity on basement structures underlying the volcanic edifice, magmatic intrusion or external forcing (e.g. weather events), is a likely occurrence during the lifetime of a stratovolcano. Flank failure can generate large debris avalanches, and the significant hazards associated with volcanic debris avalanches in the Cascade range were demonstrated by the collapse of Mt St Helens (WA, USA), which triggered its devastating explosive eruption in May 1980. Mt Shasta is a 4,317 m high, snow-capped, steep-sloped stratovolcano located in Northern California. The most voluminous of the Cascade volcanoes, the current edifice began forming on the remnants of an ancestral Mt Shasta that collapsed approximately 300,000 to 380,000 years ago producing one of the largest debris avalanches known on Earth. The debris avalanche deposit (DAD) covers a surface of 450 km2 across the Shasta valley, for a total volume of approximately 26 km3. A LiDAR point cloud and orthophoto of the Shasta DAD surveyed by the NCALM consortium provides a new topographic dataset of the area with unprecedented resolution. This will permit the identification of subtle topographic features of the Shasta DAD not apparent in the field or in coarser resolution datasets. Statistical measures of the LiDAR-derived digital elevation model, such as surface texture, will be used to detect and characterize the hummock topography, differentiate between various DAD facies and geomorphic units, and extract the morphological parameters for subsequent analogue and numerical modeling of the debris avalanche. This work aims to improve our understanding of the Mt Shasta DAD morphology and its dynamics, and provide insight into the cause, timing of events and mode of emplacement of the DAD. The Cascade range includes numerous large extinct, dormant or active stratovolcanoes, and knowledge of the link between basement structures and the Mt Shasta DAD will

  14. Model of turn-on characteristics of InP-based Geiger-mode avalanche photodiodes suitable for circuit simulations

    NASA Astrophysics Data System (ADS)

    Jordy, George; Donnelly, Joseph

    2015-05-01

    A model for the turn-on characteristics of separate-absorber-multiplier InP-based Geiger-mode Avalanche Photodiodes (APDs) has been developed. Verilog-A was used to implement the model in a manner that can be incorporated into circuit simulations. Rather than using SPICE elements to mimic the voltage and current characteristics of the APD, Verilog-A can represent the first order nonlinear differential equations that govern the avalanche current of the APD. This continuous time representation is fundamentally different than the piecewise linear characteristics of other models. The model is based on a driving term for the differential current, which is given by the voltage overbias minus the voltage drop across the device's space-charge resistance RSC. This drop is primarily due to electrons transiting the separate absorber. RSC starts off high and decreases with time as the initial breakdown filament spreads laterally to fill the APD. With constant bias voltage, the initial current grows exponentially until space charge effects reduce the driving function. With increasing current the driving term eventually goes to zero and the APD current saturates. On the other hand, if the APD is biased with a capacitor, the driving term becomes negative as the capacitor discharges, reducing the current and driving the voltage below breakdown. The model parameters depend on device design and are obtained from fitting the model to Monte-Carlo turn-on simulations that include lateral spreading of the carriers of the relevant structure. The Monte-Carlo simulations also provide information on the probability of avalanche, and jitter due to where the photon is absorbed in the APD.

  15. Investigations On The Change of Avalanche Risk In Settlements Based On Insurance Data For The Canton of GraubÜnden, Switzerland

    NASA Astrophysics Data System (ADS)

    Fuchs, S.; Bründl, M.

    Since 1950 more than 1 billion Swiss Francs have been invested in avalanche pro- tection measures in Switzerland. Despite these efforts, avalanches caused direct and indirect damages around 620 million Swiss Francs during the winter 1998/99. In an ongoing project we investigate how the avalanche risk in settlements has changed since 1950. In the field of natural hazards, risk can be expressed as a function of reoccurrence interval and potential damage. As shown in numerous investigations, the long-term natural avalanche hazard potential is regarded as constant. It can therefore be assumed that the avalanche risk is primarily affected by the potential damage. Variations in the amount of damage paid by the insurance companies must have been caused by changes in the land-use pattern and the accumulation of item values in the affected areas. In this paper, the development of land-use is compared with insured values and dam- age payments in the Canton of Graubünden, Switzerland, 1950-2000. The investiga- tion is based on data of the building insurance. The statistical analysis shows that, when taking into account the inflation rate, the absolute amount of damage in extreme avalanche winters is declining although the insured value of buildings has risen by a factor of six. Regarding the increasing number of buildings at altitudes above 1000 meters a.s.l., the relative amount of damage declined rapidly during the last fifty years, even in tourist areas. These first results indicate the effects of active and passive avalanche protection mea- sures. Further investigations are still needed to evaluate these results and to compare them with other mountain areas as well as with damages caused by other natural haz- ards.

  16. Cosmic Ray Measurements by Scintillators with Metal Resistor Semiconductor Avalanche Photo Diodes

    ERIC Educational Resources Information Center

    Blanco, Francesco; La Rocca, Paola; Riggi, Francesco; Akindinov, Alexandre; Mal'kevich, Dmitry

    2008-01-01

    An educational set-up for cosmic ray physics experiments is described. The detector is based on scintillator tiles with a readout through metal resistor semiconductor (MRS) avalanche photo diode (APD) arrays. Typical measurements of the cosmic angular distribution at sea level and a study of the East-West asymmetry obtained by such a device are…

  17. Geiger-Mode Avalanche Photodiode Arrays Integrated to All-Digital CMOS Circuits

    PubMed Central

    Aull, Brian

    2016-01-01

    This article reviews MIT Lincoln Laboratory's work over the past 20 years to develop photon-sensitive image sensors based on arrays of silicon Geiger-mode avalanche photodiodes. Integration of these detectors to all-digital CMOS readout circuits enable exquisitely sensitive solid-state imagers for lidar, wavefront sensing, and passive imaging. PMID:27070609

  18. Geiger-Mode Avalanche Photodiode Arrays Integrated to All-Digital CMOS Circuits.

    PubMed

    Aull, Brian

    2016-01-01

    This article reviews MIT Lincoln Laboratory's work over the past 20 years to develop photon-sensitive image sensors based on arrays of silicon Geiger-mode avalanche photodiodes. Integration of these detectors to all-digital CMOS readout circuits enable exquisitely sensitive solid-state imagers for lidar, wavefront sensing, and passive imaging. PMID:27070609

  19. Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Crater wall dust avalanches in southern Arabia Terra.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

    Image information: VIS instrument. Latitude 10.3, Longitude 24.5 East (335.5 West). 19 meter/pixel resolution.

  20. Photon counting modules using RCA silicon avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Lightstone, Alexander W.; Macgregor, Andrew D.; Macsween, Darlene E.; Mcintyre, Robert J.; Trottier, Claude; Webb, Paul P.

    1989-01-01

    Avalanche photodiodes (APD) are excellent small area, solid state detectors for photon counting. Performance possibilities include: photon detection efficiency in excess of 50 percent; wavelength response from 400 to 1000 nm; count rate to 10 (exp 7) counts per sec; afterpulsing at negligible levels; timing resolution better than 1 ns. Unfortunately, these performance levels are not simultaneously available in a single detector amplifier configuration. By considering theoretical performance predictions and previous and new measurements of APD performance, the anticipated performance of a range of proposed APD-based photon counting modules is derived.

  1. Seismic signal of avalanches

    NASA Astrophysics Data System (ADS)

    Pesaresi, Damiano; Ravanat, Xavier; Thibert, Emmanuel

    2010-05-01

    The characterization of avalanches with seismic signals is an important task. For risk mitigation, estimating remotely avalanche activity by means of seismic signals is a good alternative to direct observations that are often limited by visual conditions and observer's availability. In seismology, the main challenge is to discriminate avalanche signals within the natural earth seismic activity and background noise. Some anthropogenic low frequency (infra-sound) sources like helicopters also generate seismic signals. In order to characterize an avalanche seismic signal, a 3-axis broad band seismometer (Guralp 3T) has been set-up on a real scale avalanche test site in Lautaret (France). The sensor is located in proximity of 2 avalanche paths where avalanches can be artificially released. Preliminary results of seismic records are presented, correlated with avalanche physical parameters (volume released, velocity, energy).

  2. Plasma Panel Based Radiation Detectors

    SciTech Connect

    Friedman, Dr. Peter S.; Varner Jr, Robert L; Ball, Robert; Beene, James R; Ben Moshe, M.; Benhammou, Yan; Chapman, J. Wehrley; Etzion, E; Ferretti, Claudio; Bentefour, E; Levin, Daniel S.; Moshe, M.; Silver, Yiftah; Weaverdyck, Curtis; Zhou, Bing

    2013-01-01

    The plasma panel sensor (PPS) is a gaseous micropattern radiation detector under current development. It has many operational and fabrication principles common to plasma display panels (PDPs). It comprises a dense matrix of small, gas plasma discharge cells within a hermetically sealed panel. As in PDPs, it uses non-reactive, intrinsically radiation-hard materials such as glass substrates, refractory metal electrodes, and mostly inert gas mixtures. We are developing these devices primarily as thin, low-mass detectors with gas gaps from a few hundred microns to a few millimeters. The PPS is a high gain, inherently digital device with the potential for fast response times, fine position resolution (< 50 m RMS) and low cost. In this paper we report here on prototype PPS experimental results in detecting betas, protons and cosmic muons, and we extrapolate on the PPS potential for applications including detection of alphas, heavy-ions at low to medium energy, thermal neutrons and X-rays.

  3. Analysis and modeling of optical crosstalk in InP-based Geiger-mode avalanche photodiode FPAs

    NASA Astrophysics Data System (ADS)

    Chau, Quan; Jiang, Xudong; Itzler, Mark A.; Entwistle, Mark; Piccione, Brian; Owens, Mark; Slomkowski, Krystyna

    2015-05-01

    Optical crosstalk is a major factor limiting the performance of Geiger-mode avalanche photodiode (GmAPD) focal plane arrays (FPAs). This is especially true for arrays with increased pixel density and broader spectral operation. We have performed extensive experimental and theoretical investigations on the crosstalk effects in InP-based GmAPD FPAs for both 1.06-μm and 1.55-μm applications. Mechanisms responsible for intrinsic dark counts are Poisson processes, and their inter-arrival time distribution is an exponential function. In FPAs, intrinsic dark counts and cross talk events coexist, and the inter-arrival time distribution deviates from purely exponential behavior. From both experimental data and computer simulations, we show the dependence of this deviation on the crosstalk probability. The spatial characteristics of crosstalk are also demonstrated. From the temporal and spatial distribution of crosstalk, an efficient algorithm to identify and quantify crosstalk is introduced.

  4. Determination of snow avalanche return periods using a tree-ring based reconstruction in the French Alps: cross validation with the predictions of a statistical-dynamical model

    NASA Astrophysics Data System (ADS)

    Schläppy, Romain; Eckert, Nicolas; Jomelli, Vincent; Grancher, Delphine; Brunstein, Daniel; Stoffel, Markus; Naaim, Mohamed

    2013-04-01

    Documenting past avalanche activity represents an indispensable step in avalanche hazard assessment. Nevertheless, (i) archival records of past avalanche events do not normally yield data with satisfying spatial and temporal resolution and (ii) precision concerning runout distance is generally poorly defined. In addition, historic documentation is most often (iii) biased toward events that caused damage to structure or loss of life on the one hand and (iv) undersampled in unpopulated areas on the other hand. On forested paths dendrogeomorphology has been demonstrated to represent a powerful tool to reconstruct past activity of avalanches with annual resolution and for periods covering the past decades to centuries. This method is based on the fact that living trees may be affected by snow avalanches during their flow and deposition phases. Affected trees will react upon these disturbances with a certain growth response. An analysis of the responses recorded in tree rings coupled with an evaluation of the position of reacting trees within the path allows the dendrogeomorphic expert to identify past snow avalanche events and deduced their minimum runout distance. The objective of the work presented here is firstly to dendrochronogically -reconstruct snow avalanche activity in the Château Jouan path located near Montgenèvre in the French Alps. Minimal runout distances are then determined for each reconstructed event by considering the point of further reach along the topographic profile. Related empirical return intervals are evaluated, combining the extent of each event with the average local frequency of the dendrological record. In a second step, the runout distance distribution derived from dendrochronological reconstruction is compared to the one derived from historical archives and to high return period avalanches predicted by an up-to-date locally calibrated statistical-numerical model. It appears that dendrochronological reconstructions correspond mostly to

  5. A cooled avalanche photodiode with high photon detection probability

    NASA Technical Reports Server (NTRS)

    Robinson, D. L.; Metscher, B. D.

    1986-01-01

    An avalanche photodiode has been operated as a photon-counting detector with 2 to 3 times the sensitivity of currently-available photomultiplier tubes. APD (avalanche photodiodes) detection probabilities that exceed 27% and approach 50% have been measured at an optimum operating temperature which minimizes noise. The sources of noise and their dependence on operating temperature and bias voltage are discussed.

  6. An Efficient Ant-Based Edge Detector

    NASA Astrophysics Data System (ADS)

    Aydın, Doğan

    An efficient ant-based edge detector is presented. It is based on the distribution of ants on an image, ants try to find possible edges by using a state transition function based on 5x5 edge structures. Visual comparisons show that the proposed method gives finer details and thinner edges at lesser computational times when compared to earlier ant-based approaches. When compared to standard edge detectors, it shows robustness to Gaussian and Salt & Pepper noise and provides finer details than others with same parameter set in both clear and noisy images.

  7. Ion chamber based neutron detectors

    DOEpatents

    Derzon, Mark S; Galambos, Paul C; Renzi, Ronald F

    2014-12-16

    A neutron detector with monolithically integrated readout circuitry, including: a bonded semiconductor die; an ion chamber formed in the bonded semiconductor die; a first electrode and a second electrode formed in the ion chamber; a neutron absorbing material filling the ion chamber; and the readout circuitry which is electrically coupled to the first and second electrodes. The bonded semiconductor die includes an etched semiconductor substrate bonded to an active semiconductor substrate. The readout circuitry is formed in a portion of the active semiconductor substrate. The ion chamber has a substantially planar first surface on which the first electrode is formed and a substantially planar second surface, parallel to the first surface, on which the second electrode is formed. The distance between the first electrode and the second electrode may be equal to or less than the 50% attenuation length for neutrons in the neutron absorbing material filling the ion chamber.

  8. Ground-based LiDAR integration with avalanche control operations: target planning and assessment of control effectiveness

    NASA Astrophysics Data System (ADS)

    Deems, J. S.; LeWinter, A.; Gadomski, P. J.; Finnegan, D. C.

    2015-12-01

    The varying distribution of snow depth in avalanche starting zones exerts a strong influence on avalanche potential and character. Extreme depth changes over short distances are common, especially in wind-affected, above-treeline environments. Snow depth also affects the ease of avalanche triggering. Experience shows that avalanche reduction efforts are often more successful when targeting shallow trigger point areas near deeper slabs with explosives or ski cutting. We are exploring the use of high resolution snow depth and depth change maps from differential LiDAR scans to quantify loading patterns for use in both pre-control planning and in post-control assessment. We present results from our ongoing work at the Arapahoe Basin and Aspen Highlands ski areas in Colorado, USA, and from a new collaboration with the Colorado Department of Transportation. At Arapahoe Basin we have tested rapid snow depth product generation for use in planning placement of explosives for artificial avalanche triggering. At Aspen Highlands we have explored measurement of minimum disturbance depth from bootpacking. In a new application, we are assessing avalanche hazard reduction with new Gazex exploder arrays on Loveland and Berthoud Passes.

  9. Assessing the importance of terrain parameters on glide avalanche release

    USGS Publications Warehouse

    Peitzsch, Erich H.; Hendrikx, Jordy; Fagre, Daniel B.

    2014-01-01

    avalanches failed as cohesive slabs on this bedrock surface. Consequently, surface roughness proved to be a useful descriptive variable to discriminate between slopes that avalanched and those that did not. Annual 'repeat offender' glide avalanche paths were characterized by smooth outcropping rock plates with stratification planes parallel to the slope. Combined with aspect these repeat offenders were also members of the highest glide category. Using this understanding of the role of topographic parameters on glide avalanche activity, a spatial terrain based model was developed to identify other areas with high glide avalanche potential outside of our immediate observation area.

  10. Modeling and measurement of a whole-cell bioluminescent biosensor based on a single photon avalanche diode.

    PubMed

    Daniel, Ramiz; Almog, Ronen; Ron, Amit; Belkin, Shimshon; Diamand, Yosi Shacahm

    2008-12-01

    Whole-cell biosensors are potential candidates for on-line and in situ environmental monitoring. In this work we present a new design of a whole-cell bioluminescence biosensor for water toxicity detection, based on genetically engineered Escherichia coli bacteria, carrying a recA::luxCDABE promoter-reporter fusion. Sensitive optical detection is achieved using a single photon avalanche photodiode (SPAD) working in the Geiger mode. The present work describes a simple mathematical model for the kinetic process of the bioluminescence based SOS toxin response of E. coli bacteria. We find that initially the bioluminescence signal depends on the time square and we show that the spectral intensity of the bioluminescence signal is inverse proportional to the frequency. We get excellent agreement between the theoretical model and the measured light signal. Furthermore, we present experimental results of the bioluminescent signal measurement using a SPAD and a photomultiplier, and demonstrate improvement of the measurement by applying a matched digital filter. Low intensity bioluminescence signals were measured after the whole-cell sensors were exposed to various toxicant concentrations (5, 15 and 20ppm). PMID:18774705

  11. Mapping starting zone snow depth with a ground-based LiDAR to improve avalanche control and forecasting

    NASA Astrophysics Data System (ADS)

    Deems, J. S.; Gadomski, P. J.; Vellone, D.; Evanczyk, R.; LeWinter, A. L.; Birkeland, K.; Finnegan, D. C.

    2014-12-01

    The varying distribution of snow depth in avalanche starting zones exerts a strong influence on avalanche potential and character. Extreme depth changes over short distances are common, especially in wind-affected, above-treeline environments. Snow depth also affects the ease of avalanche triggering. Experience shows that avalanche reduction efforts are often more successful when targeting shallow trigger point areas near deeper slabs with explosives or ski cutting. Our pilot study explores the use of high resolution snow depth and depth change maps from differential LiDAR scans to quantify loading patterns for use in both pre-control planning and in post-control assessment. We present results from our initial work at the Arapahoe Basin Ski Area in Colorado, USA. A-Basin has a large number avalanche starting zones above treeline at elevations up to 4,000 m. The three study areas represent a range of institutional avalanche management history - the East Wall has been operated since 1970, Montezuma Bowl since 2008, and the Steep Gullies are under study for area expansion. Summer mapping produced a zero depth surface. Mapping multiple times during the snow season allowed us to produce time series maps of snow depth and snow depth change at high resolution to explore depth and slab thickness variations due to wind redistribution. We conducted surveys before and after loading events and control work, allowing the exploration of loading patterns, slab thickness, shot and ski cut locations, bed surfaces, entrainment, and avalanche characteristics. We also evaluate the state of terrestrial laser scanning for use in operational settings.

  12. X-ray imaging using avalanche multiplication in amorphous selenium: Investigation of intrinsic avalanche noise

    SciTech Connect

    Hunt, D. C.; Tanioka, Kenkichi; Rowlands, J. A.

    2007-12-15

    The flat-panel detector (FPD) is the state-of-the-art detector for digital radiography. The FPD can acquire images in real-time, has superior spatial resolution, and is free of the problems of x-ray image intensifiers--veiling glare, pin-cushion and magnetic distortion. However, FPDs suffer from poor signal to noise ratio performance at typical fluoroscopic exposure rates where the quantum noise is reduced to the point that it becomes comparable to the fixed electronic noise. It has been shown previously that avalanche multiplication gain in amorphous selenium (a-Se) can provide the necessary amplification to overcome the electronic noise of the FPD. Avalanche multiplication, however, comes with its own intrinsic contribution to the noise in the form of gain fluctuation noise. In this article a cascaded systems analysis is used to present a modified metric related to the detective quantum efficiency. The modified metric is used to study a diagnostic x-ray imaging system in the presence of intrinsic avalanche multiplication noise independently from other noise sources, such as electronic noise. An indirect conversion imaging system is considered to make the study independent of other avalanche multiplication related noise sources, such as the fluctuations arising from the depth of x-ray absorption. In this case all the avalanche events are initiated at the surface of the avalanche layer, and there are no fluctuations in the depth of absorption. Experiments on an indirect conversion x-ray imaging system using avalanche multiplication in a layer of a-Se are also presented. The cascaded systems analysis shows that intrinsic noise of avalanche multiplication will not have any deleterious influence on detector performance at zero spatial frequency in x-ray imaging provided the product of conversion gain, coupling efficiency, and optical quantum efficiency are much greater than a factor of 2. The experimental results show that avalanche multiplication in a-Se behaves as

  13. Traceable calibration of Si avalanche photodiodes using synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Müller, I.; Klein, R. M.; Hollandt, J.; Ulm, G.; Werner, L.

    2012-04-01

    In this paper, we present a new substitution method based on the unique properties of synchrotron radiation and of the Metrology Light Source (MLS), the dedicated electron storage ring of the PTB. The MLS is used as a light source with a dynamic range of its photon flux of 11 orders of magnitude to bridge the gap in optical power measurement between a cryogenic electrical substitution radiometer and a single photon detector. Two single photon avalanche diodes were calibrated at 651 nm with combined relative uncertainties of 0.17% and 0.16% traceable to a primary standard, a cryogenic electrical substitution radiometer.

  14. Initial results from the Sherbrooke avalanche photodiode positron tomograph

    SciTech Connect

    Lecomte, R.; Cadorette, J.; Rodrigue, S.; Lapointe, D.; Rouleau, D.; Bentourkia, M.; Yao, R.; Msaki, P.

    1996-06-01

    The design features and engineering constraints of a PET system based on avalanche photodiode (APD) detectors have been described in a previous report. In this paper, the authors present the initial results obtained with the Sherbrooke APD-PET scanner, a very high spatial resolution device designed for dynamic imaging of small and medium-sized laboratory animals such as rats, cats, rabbits and small monkeys. Its physical performance has been evaluated in terms of resolution, sensitivity, count rate, random and scatter fractions, contrast and relative activity recovery as a function of object size. The capabilities of the scanner for biomedical research applications have been demonstrated using phantom and animal studies.

  15. Cooled avalanche photodiode used for photon detection

    NASA Technical Reports Server (NTRS)

    Robinson, Deborah L.; Metscher, Brian D.

    1987-01-01

    Commercial avalanche photodiodes have been operated as single-photon detectors at an optimum operating temperature and bias voltage. These detectors were found to be 1.5 to 3 times more sensitive than presently-available photomultiplier tubes (PPMTs). Both single-photon detection probability and detector noise increase with bias voltage; detection probabilities greater than 25 percent were obtained with detector noise levels comparable to the noise of a PMT; higher probabilities were measured at higher noise levels. The sources of noise and their dependence on temperature and bias voltage are discussed.

  16. Photon detection with cooled avalanche photodiodes

    NASA Technical Reports Server (NTRS)

    Robinson, D. L.; Metscher, B. D.

    1987-01-01

    Commercial avalanche photodiodes have been operated as single-photon detectors at an optimum operating temperature and bias voltage. These detectors were found to be 1.5-3 times more sensitive than presently available photomultiplier tubes (PMTs). Both single-photon detection probability and detector noise increase with bias voltage; detection probabilities greater than twice that of a PMT were obtained with detector noise levels below 100 counts per second. Higher probabilities were measured at higher noise levels. The sources of noise and their dependence on temperature and bias voltage are discussed.

  17. Continuum description of avalanches in granular media.

    SciTech Connect

    Aranson, I. S.; Tsimring, L. S.

    2000-12-05

    A continuum theory of partially fluidized granular flows is proposed. The theory is based on a combination of the mass and momentum conservation equations with the order parameter equation which describes the transition between flowing and static components of the granular system. We apply this model to the dynamics of avalanches in chutes. The theory provides a quantitative description of recent observations of granular flows on rough inclined planes (Daerr and Douady 1999): layer bistability, and the transition from triangular avalanches propagating downhill at small inclination angles to balloon-shaped avalanches also propagating uphill for larger angles.

  18. Very high-gain and low-excess noise near-infrared single-photon avalanche detector: an NIR solid state photomultiplier

    NASA Astrophysics Data System (ADS)

    Linga, Krishna; Yevtukhov, Yuriy; Liang, Bing

    2009-05-01

    A new family of photodetectors with a Discrete Amplification (DA) mechanism allows the realization of very high gain and low excess noise factor in the visible and near infrared spectral regions and offers an alternative to conventional photomultiplier tubes and Geiger mode avalanche photodetectors. These photodetectors can operate in linear detection mode with gain-bandwidth product in excess of 4X1014 and in photon counting mode with count rates up to 108 counts/sec. Potential benefits of this technology over conventional avalanche photodetectors include ultra low excess noise factor, very high gain, and lower reset time (<< 1 μs). In the photon counting mode, the devices can be operated in the non-gated mode under a constant dc bias. Because of its unique characteristics of self-quenching and self-recovery, no external quenching circuit is needed. We present the discrete amplification design approach used for the development of a solid state photomultiplier in the near infrared wavelength region. The demonstrated device performance far exceeds any available solid state photodetectors in the near infrared wavelength range. The measured devices have the following performance characteristics: gain > 2X105, excess noise factor < 1.05, rise time < 350ps, fall time < 500ps, dark current < 2X106 cps, operating voltage < 60V. These devices are ideal for researchers in the field of deep space optical communication, spectroscopy, industrial and scientific instrumentation, Ladar/Lidar, quantum cryptography, night vision and other military, defence and aerospace applications.

  19. The performance of 2D array detectors for light sheet based fluorescence correlation spectroscopy.

    PubMed

    Singh, Anand Pratap; Krieger, Jan Wolfgang; Buchholz, Jan; Charbon, Edoardo; Langowski, Jörg; Wohland, Thorsten

    2013-04-01

    Single plane illumination microscopy based fluorescence correlation spectroscopy (SPIM-FCS) is a new method for imaging FCS in 3D samples, providing diffusion coefficients, transport, flow velocities and concentrations in an imaging mode. SPIM-FCS records correlation functions over a whole plane in a sample, which requires array detectors for recording the fluorescence signal. Several types of image sensors are suitable for FCS. They differ in properties such as effective area per pixel, quantum efficiency, noise level and read-out speed. Here we compare the performance of several low light array detectors based on three different technologies: (1) Single-photon avalanche diode (SPAD) arrays, (2) passive-pixel electron multiplying charge coupled device (EMCCD) and (3) active-pixel scientific-grade complementary metal oxide semiconductor cameras (sCMOS). We discuss the influence of the detector characteristics on the effective FCS observation volume, and demonstrate that light sheet based SPIM-FCS provides absolute diffusion coefficients. This is verified by parallel measurements with confocal FCS, single particle tracking (SPT), and the determination of concentration gradients in space and time. While EMCCD cameras have a temporal resolution in the millisecond range, sCMOS cameras and SPAD arrays can extend the time resolution of SPIM-FCS down to 10 μs or lower. PMID:23571955

  20. Electron avalanches in liquid argon mixtures

    SciTech Connect

    Kim, J.G.; Dardin, S.M.; Kadel, R.W.; Kadyk, J.A.; Wenzel, W.B.; Peskov, V.

    2004-03-19

    We have observed stable avalanche gain in liquid argon when mixed with small amounts of xenon in the high electric field (>7 MV/cm) near the point of a chemically etched needle in a point-plane geometry. We identify two gain mechanisms, one pressure dependent, and the other independent of the applied pressure. We conclude that the pressure dependent signals are from avalanche gain in gas bubbles at the tip of the needle, while the pressure independent pulses are from avalanche gain in liquid. We measure the decay time spectra of photons from both types of avalanches. The decay times from the pressure dependent pulses decrease (increase) with the applied pressure (high voltage), while the decay times from the pressure independent pulses are approximately independent of pressure or high voltage. For our operating conditions, the collected charge distribution from avalanches is similar for 60 keV or 122 keV photon sources. With krypton additives, instead of Xe, we measure behavior consistent with only the pressure dependent pulses. Neon and TMS were also investigated as additives, and designs for practical detectors were tested.

  1. Electron avalanches in liquid argon mixtures

    NASA Astrophysics Data System (ADS)

    Kim, J. G.; Dardin, S. M.; Kadel, R. W.; Kadyk, J. A.; Peskov, V.; Wenzel, W. A.

    2004-12-01

    We have observed stable avalanche gain in liquid argon when mixed with small amounts of xenon (xe) in the high electric field ( >7 MV/cm) near the point of a chemically etched needle in a point-plane geometry. We identify two gain mechanisms, one pressure dependent, and the other independent of the applied pressure. We conclude that the pressure-dependent signals are from avalanche gain in gas bubbles at the tip of the needle, while the pressure-independent pulses are from avalanche gain in liquid. We measure the decay time spectra of photons from both types of avalanches. The decay times from the pressure-dependent pulses decrease (increase) with the applied pressure (high voltage), while the decay times from the pressure-independent pulses are approximately independent of pressure or high voltage. For our operating conditions, the collected charge distribution from avalanches is similar for 60 or 122 keV photon sources. With krypton additives, instead of Xe, we measure behavior consistent with only the pressure-dependent pulses. Neon and TMS were also investigated as additives, and designs for practical detectors were tested.

  2. Avalanche Sedimentation in Seas and Oceans, Paper 3: The Second Global Level of Avalanche Sedimentation: The Base of the Continental Slope

    SciTech Connect

    Lisilsyn, A.P.

    1986-03-01

    The paper discusses the sedimentation pattern at the second global hypsometric level - at the base of continental slope, where the bulk of the planet's sedimentary matter is concentrated. Typifying examples are given, and the patterns of quantitative distribution of sedimentary matter at that level are described.

  3. Photon detector system

    DOEpatents

    Ekstrom, Philip A.

    1981-01-01

    A photon detector includes a semiconductor device, such as a Schottky barrier diode, which has an avalanche breakdown characteristic. The diode is cooled to cryogenic temperatures to eliminate thermally generated charge carriers from the device. The diode is then biased to a voltage level exceeding the avalanche breakdown threshold level such that, upon receipt of a photon, avalanche breakdown occurs. This breakdown is detected by appropriate circuitry which thereafter reduces the diode bias potential to a level below the avalanche breakdown threshold level to terminate the avalanche condition. Subsequently, the bias potential is reapplied to the diode in preparation for detection of a subsequently received photon.

  4. Compact ion chamber based neutron detector

    SciTech Connect

    Derzon, Mark S.; Galambos, Paul C.; Renzi, Ronald F.

    2015-10-27

    A directional neutron detector has an ion chamber formed in a dielectric material; a signal electrode and a ground electrode formed in the ion chamber; a neutron absorbing material filling the ion chamber; readout circuitry which is electrically coupled to the signal and ground electrodes; and a signal processor electrically coupled to the readout circuitry. The ion chamber has a pair of substantially planar electrode surfaces. The chamber pressure of the neutron absorbing material is selected such that the reaction particle ion trail length for neutrons absorbed by the neutron absorbing material is equal to or less than the distance between the electrode surfaces. The signal processor is adapted to determine a path angle for each absorbed neutron based on the rise time of the corresponding pulse in a time-varying detector signal.

  5. A Stream Encryption Scheme with Both Key and Plaintext Avalanche Effects for Designing Chaos-Based Pseudorandom Number Generator with Application to Image Encryption

    NASA Astrophysics Data System (ADS)

    Han, Dandan; Min, Lequan; Chen, Guanrong

    Based on a stream encryption scheme with avalanche effect (SESAE), a stream encryption scheme with both key avalanche effect and plaintext avalanche effect (SESKPAE) is introduced. Using this scheme and an ideal 2d-word (d-segment) pseudorandom number generator (PRNG), a plaintext can be encrypted such that each bit of the ciphertext block has a change with the probable probability of (2d ‑ 1)/2d when any word of the key is changed or any bit of the plaintext is changed. To that end, a novel four-dimensional discrete chaotic system (4DDCS) is proposed. Combining the 4DDCS with a generalized synchronization (GS) theorem, a novel eight-dimensional discrete GS chaotic system (8DDGSCS) is constructed. Using the 8DDGSCS, a 216-word chaotic pseudorandom number generator (CPRNG) is designed. The keyspace of the 216-word CPRNG is larger than 21195. Then, the FIPS 140-2 test suit/generalized FIPS 140-2 test suit is used to test the randomness of the 1000-key streams consisting of 20000 bits generated by the 216-word CPRNG, the RC4 algorithm PRNG and the ZUC algorithm PRNG, respectively. The test results show that for the three PRNGs, there are 100%/98.9%, 99.9%/98.8%, 100%/97.9% key streams passing the tests, respectively. Furthermore, the SP800-22 test suite is used to test the randomness of four 100-key streams consisting of 1000000 bits generated by four PRNGs, respectively. The numerical results show that the randomness performances of the 216-word CPRNG is promising, showing that there are no significant correlations between the key streams and the perturbed key streams generated via the 216-word CPRNG. Finally, using the 216-word CPRNG and the SESKPAE to encrypt two gray-scale images, test results demonstrate that the 216-word CPRNG is able to generate both key avalanche effect and plaintext avalanche effect, which are similar to those generated via an ideal CPRNG, and performs better than other comparable schemes.

  6. X-ray imaging using avalanche multiplication in amorphous selenium: Investigation of depth dependent avalanche noise

    SciTech Connect

    Hunt, D. C.; Tanioka, Kenkichi; Rowlands, J. A.

    2007-03-15

    The past decade has seen the swift development of the flat-panel detector (FPD), also known as the active matrix flat-panel imager, for digital radiography. This new technology is applicable to other modalities, such as fluoroscopy, which require the acquisition of multiple images, but could benefit from some improvements. In such applications where more than one image is acquired less radiation is available to form each image and amplifier noise becomes a serious problem. Avalanche multiplication in amorphous selenium (a-Se) can provide the necessary amplification prior to read out so as to reduce the effect of electronic noise of the FPD. However, in direct conversion detectors avalanche multiplication can lead to a new source of gain fluctuation noise called depth dependent avalanche noise. A theoretical model was developed to understand depth dependent avalanche noise. Experiments were performed on a direct imaging system implementing avalanche multiplication in a layer of a-Se to validate the theory. For parameters appropriate for a diagnostic imaging FPD for fluoroscopy the detective quantum efficiency (DQE) was found to drop by as much as 50% with increasing electric field, as predicted by the theoretical model. This drop in DQE can be eliminated by separating the collection and avalanche regions. For example by having a region of low electric field where x rays are absorbed and converted into charge that then drifts into a region of high electric field where the x-ray generated charge undergoes avalanche multiplication. This means quantum noise limited direct conversion FPD for low exposure imaging techniques are a possibility.

  7. ALS-based hummock size-distance relationship assessment of Mt Shasta debris avalanche deposit, Northern California, USA

    NASA Astrophysics Data System (ADS)

    Tortini, Riccardo; Carn, Simon; van Wyk de Vries, Benjamin

    2015-04-01

    The failure of destabilized volcano flanks is a likely occurrence during the lifetime of a stratovolcano, generating large debris avalanches and drastically changing landforms around volcanoes. The significant hazards associated with these events in the Cascade range were demonstrated, for example, by the collapse of Mt St Helens (WA), which triggered its devastating explosive eruption in 1980. The rapid modification of the landforms due to these events makes it difficult to estimate the magnitude of prehistoric avalanches. However, the widespread preservation of hummocks along the course of rockslide-debris avalanches is highly significant for understanding the physical characteristics of these landslides. Mt Shasta is a 4,317 m high, snow-capped, steep-sloped stratovolcano located in Northern California. The current edifice began forming on the remnants of an ancestral Mt Shasta that collapsed ~300-380k years ago producing one of the largest debris avalanches known on Earth. The debris avalanche deposit (DAD) covers a surface of ~450 km2 across the Shasta valley, with an estimated volume of ~26 km3. We analyze ALS data on hummocks from the prehistoric Shasta valley DAD in northern California (USA) to derive the relationship between hummock size and distance from landslide source, and interpret the geomorphic significance of the intercept and slope coefficients of the observed functional relationships. Given the limited extent of the ALS survey (i.e. 40 km2), the high-resolution dataset is used for validation of the morphological parameters extracted from freely available, broader coverage DTMs such as the National Elevation Dataset (NED). The ALS dataset also permits the identification of subtle topographic features not apparent in the field or in coarser resolution datasets, including a previously unmapped fault, of crucial importance for both seismic and volcanic hazard assessment in volcanic areas. We present evidence from the Shasta DAD of neotectonic

  8. Neuronal avalanches and brain plasticity

    NASA Astrophysics Data System (ADS)

    de Arcangelis, L.; Herrmann, H. J.; Perrone-Capano, C.

    2007-12-01

    Networks of living neurons exhibit an avalanche mode of activity, experimentally found in organotypic cultures. Moreover, experimental studies of morphology indicate that neurons develop a network of small-world-like connections, with the possibility of a very high connectivity degree. Here we discuss a recent model based on self-organized criticality, which consists of an electrical network with threshold firing and activity-dependent synapse strengths. The model is implemented on regular and small world lattices and on a scale-free network, the Apollonian network. The system exhibits an avalanche activity with a power law distribution of sizes and durations. The analysis of the power spectra of the electrical signal reproduces very robustly the power law behaviour with the exponent 0.8, experimentally measured in electroencephalogram (EEG) spectra. The exponents are found to be quite stable with respect to initial configurations and strength of plastic remodelling, indicating that universality holds for a wide class of neural network models.

  9. Advanced active quenching circuits for single-photon avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Stipčević, M.; Christensen, B. G.; Kwiat, P. G.; Gauthier, D. J.

    2016-05-01

    Commercial photon-counting modules, often based on actively quenched solid-state avalanche photodiode sensors, are used in wide variety of applications. Manufacturers characterize their detectors by specifying a small set of parameters, such as detection efficiency, dead time, dark counts rate, afterpulsing probability and single photon arrival time resolution (jitter), however they usually do not specify the conditions under which these parameters are constant or present a sufficient description. In this work, we present an in-depth analysis of the active quenching process and identify intrinsic limitations and engineering challenges. Based on that, we investigate the range of validity of the typical parameters used by two commercial detectors. We identify an additional set of imperfections that must be specified in order to sufficiently characterize the behavior of single-photon counting detectors in realistic applications. The additional imperfections include rate-dependence of the dead time, jitter, detection delay shift, and "twilighting." Also, the temporal distribution of afterpulsing and various artifacts of the electronics are important. We find that these additional non-ideal behaviors can lead to unexpected effects or strong deterioration of the system's performance. Specifically, we discuss implications of these new findings in a few applications in which single-photon detectors play a major role: the security of a quantum cryptographic protocol, the quality of single-photon-based random number generators and a few other applications. Finally, we describe an example of an optimized avalanche quenching circuit for a high-rate quantum key distribution system based on time-bin entangled photons.

  10. Lightning initiation mechanism based on the development of relativistic runaway electron avalanches triggered by background cosmic radiation: Numerical simulation

    SciTech Connect

    Babich, L. P. Bochkov, E. I.; Kutsyk, I. M.

    2011-05-15

    The mechanism of lightning initiation due to electric field enhancement by the polarization of a conducting channel produced by relativistic runaway electron avalanches triggered by background cosmic radiation has been simulated numerically. It is shown that the fields at which the start of a lightning leader is possible even in the absence of precipitations are locally realized for realistic thundercloud configurations and charges. The computational results agree with the in-situ observations of penetrating radiation enhancement in thunderclouds.

  11. Ionization-based detectors for gas chromatography.

    PubMed

    Poole, Colin F

    2015-11-20

    The gas phase ionization detectors are the most widely used detectors for gas chromatography. The column and makeup gases commonly used in gas chromatography are near perfect insulators. This facilitates the detection of a minute number of charge carriers facilitating the use of ionization mechanisms of low efficiency while providing high sensitivity. The main ionization mechanism discussed in this report are combustion in a hydrogen diffusion flame (flame ionization detector), surface ionization in a plasma (thermionic ionization detector), photon ionization (photoionization detector and pulsed discharge helium ionization detector), attachment of thermal electrons (electron-capture detector), and ionization by collision with metastable helium species (helium ionization detector). The design, response characteristics, response mechanism, and suitability for fast gas chromatography are the main features summarized in this report. Mass spectrometric detection and atomic emission detection, which could be considered as ionization detectors of a more sophisticated and complex design, are not discussed in this report. PMID:25757823

  12. Mechanisms of evolution of avalanches in regular graphs

    NASA Astrophysics Data System (ADS)

    Handford, Thomas P.; Pérez-Reche, Francisco J.; Taraskin, Sergei N.

    2013-06-01

    A mapping of avalanches occurring in the zero-temperature random-field Ising model to life periods of a population experiencing immigration is established. Such a mapping allows the microscopic criteria for the occurrence of an infinite avalanche in a q-regular graph to be determined. A key factor for an avalanche of spin flips to become infinite is that it interacts in an optimal way with previously flipped spins. Based on these criteria, we explain why an infinite avalanche can occur in q-regular graphs only for q>3 and suggest that this criterion might be relevant for other systems. The generating function techniques developed for branching processes are applied to obtain analytical expressions for the durations, pulse shapes, and power spectra of the avalanches. The results show that only very long avalanches exhibit a significant degree of universality.

  13. Multi-step avalanche chambers for final experiment E605

    NASA Astrophysics Data System (ADS)

    Hubbard, J. R.; Coutrakon, G.; Cribier, M.; Mangeot, Ph.; Martin, H.; Mullié, J.; Palanque, S.; Pelle, J.

    1980-10-01

    Physical processein multi-step avalanche chambers, detector properties, and difficulties in operation are discussed. Advantages of multi-step chambers over classical MWPCs for specific experimental problems encountered in experiment E605 (high-flux environment and Cherenkov imaging) are described. Some details of detector design are presented.

  14. Unambiguous reconstruction of network structure using avalanche dynamics.

    PubMed

    Leleu, Timothée; Aihara, Kazuyuki

    2015-02-01

    A robust method for inferring the structure of networks is presented based on the one-to-one correspondence between the expected composition of cascades of bursts of activity, called crackling noise or avalanches, and the weight matrix. Using a model of neuronal avalanches as a paradigmatic example, we derive this correspondence exactly by calculating the closed-form expression of the joint probability distribution of avalanche sizes obtained by counting separately the number of elements active in each subnetwork during avalanches. PMID:25768549

  15. Analysis of Cadmium Based Neutron Detector Configurations

    NASA Astrophysics Data System (ADS)

    James, Brian; Rees, Lawrence; Czirr, J. Bart

    2012-10-01

    Due to national security concerns pertaining to the smuggling of special nuclear materials and a small supply of He-3 for use in neutron detectors, there is currently a need for a new kind of neutron detector. Using Monte Carlo techniques I have studied the neutron capture efficiency of an array of cadmium wedge detectors in the presence of a californium source. By using varying numbers of wedges and comparing their capture ratios we will be better able to design future detectors.

  16. Advantages of gated silicon single photon detectors

    NASA Astrophysics Data System (ADS)

    Legré, Matthieu; Lunghi, Tommaso; Stucki, Damien; Zbinden, Hugo

    2013-05-01

    We present gated silicon single photon detectors based on two commercially available avalanche photodiodes (APDs) and one customised APD from ID Quantique SA. This customised APD is used in a commercially available device called id110. A brief comparison of the two commercial APDs is presented. Then, the charge persistence effect of all of those detectors that occurs just after a strong illumination is shown and discussed.

  17. Ultraviolet avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    McClintock, Ryan; Razeghi, Manijeh

    2015-08-01

    The III-Nitride material system is rapidly maturing; having proved itself as a material for LEDs and laser, and now finding use in the area of UV photodetectors. However, many UV applications are still dominated by the use of photomultiplier tubes (PMT). PMTs are capable of obtaining very high sensitivity using internal electron multiplication gain (typically ~106). It is highly desirable to develop a compact semiconductor-based photodetector capable of realizing this level of sensitivity. In principle, this can be obtained in III-Nitrides by taking advantage of avalanche multiplication under high electric fields - typically 2.7 MV/cm, which with proper design can correspond to an external reverse bias of less than 100 volts. In this talk, we review the current state-of-the-art in III-Nitride solar- and visible-blind APDs, and present our latest results on GaN APDs grown on both conventional sapphire and low dislocation density free-standing c- and m-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. The spectral response and Geiger-mode photon counting performance of UV APDs are studied under low photon fluxes, with single photon detection capabilities as much as 30% being demonstrated in smaller devices. Geiger-mode operation conditions are optimized for enhanced SPDE.

  18. Effect of atmospheric turbulence on the bit error probability of a space to ground near infrared laser communications link using binary pulse position modulation and an avalanche photodiode detector

    NASA Technical Reports Server (NTRS)

    Safren, H. G.

    1987-01-01

    The effect of atmospheric turbulence on the bit error rate of a space-to-ground near infrared laser communications link is investigated, for a link using binary pulse position modulation and an avalanche photodiode detector. Formulas are presented for the mean and variance of the bit error rate as a function of signal strength. Because these formulas require numerical integration, they are of limited practical use. Approximate formulas are derived which are easy to compute and sufficiently accurate for system feasibility studies, as shown by numerical comparison with the exact formulas. A very simple formula is derived for the bit error rate as a function of signal strength, which requires only the evaluation of an error function. It is shown by numerical calculations that, for realistic values of the system parameters, the increase in the bit error rate due to turbulence does not exceed about thirty percent for signal strengths of four hundred photons per bit or less. The increase in signal strength required to maintain an error rate of one in 10 million is about one or two tenths of a db.

  19. Performance comparisons of contour-based corner detectors.

    PubMed

    Awrangjeb, Mohammad; Lu, Guojun; Fraser, Clive S

    2012-09-01

    Corner detectors have many applications in computer vision and image identification and retrieval. Contour-based corner detectors directly or indirectly estimate a significance measure (e.g., curvature) on the points of a planar curve, and select the curvature extrema points as corners. While an extensive number of contour-based corner detectors have been proposed over the last four decades, there is no comparative study of recently proposed detectors. This paper is an attempt to fill this gap. The general framework of contour-based corner detection is presented, and two major issues-curve smoothing and curvature estimation, which have major impacts on the corner detection performance, are discussed. A number of promising detectors are compared using both automatic and manual evaluation systems on two large datasets. It is observed that while the detectors using indirect curvature estimation techniques are more robust, the detectors using direct curvature estimation techniques are faster. PMID:22645267

  20. Dune Avalanche Scars

    NASA Technical Reports Server (NTRS)

    2004-01-01

    05 August 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows large, low albedo (dark) sand dunes in Kaiser Crater near 47.2oS, 340.4oW. The dunes are--ever so slowly--moving east to west (right to left) as sand avalanches down the steeper, slip face slopes of each. Avalanching sand in the Kaiser dune field has left deep scars on these slopes, suggesting that the sand is not loose but is instead weakly cemented. The image covers an area approximately 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  1. Avalanches in Wood Compression.

    PubMed

    Mäkinen, T; Miksic, A; Ovaska, M; Alava, Mikko J

    2015-07-31

    Wood is a multiscale material exhibiting a complex viscoplastic response. We study avalanches in small wood samples in compression. "Woodquakes" measured by acoustic emission are surprisingly similar to earthquakes and crackling noise in rocks and laboratory tests on brittle materials. Both the distributions of event energies and of waiting (silent) times follow power laws. The stress-strain response exhibits clear signatures of localization of deformation to "weak spots" or softwood layers, as identified using digital image correlation. Even though material structure-dependent localization takes place, the avalanche behavior remains scale-free. PMID:26274428

  2. Inverse avalanches on Abelian sandpiles

    SciTech Connect

    Chau, H.F. Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080 )

    1994-11-01

    A simple and computationally efficient way of finding inverse avalanches for Abelian sandpiles, called the inverse particle addition operator, is presented. In addition, the method is shown to be optimal in the sense that it requires the minimum amount of computation among methods of the same kind. The method is also conceptually succinct because avalanche and inverse avalanche are placed in the same footing.

  3. Room temperature single-photon detectors for high bit rate quantum key distribution

    SciTech Connect

    Comandar, L. C.; Patel, K. A.; Fröhlich, B. Lucamarini, M.; Sharpe, A. W.; Dynes, J. F.; Yuan, Z. L.; Shields, A. J.; Penty, R. V.

    2014-01-13

    We report room temperature operation of telecom wavelength single-photon detectors for high bit rate quantum key distribution (QKD). Room temperature operation is achieved using InGaAs avalanche photodiodes integrated with electronics based on the self-differencing technique that increases avalanche discrimination sensitivity. Despite using room temperature detectors, we demonstrate QKD with record secure bit rates over a range of fiber lengths (e.g., 1.26 Mbit/s over 50 km). Furthermore, our results indicate that operating the detectors at room temperature increases the secure bit rate for short distances.

  4. Performance evaluation of a dual-crystal APD-based detector modules for positron emission tomography

    NASA Astrophysics Data System (ADS)

    Pepin, Catherine M.; Bérard, Philippe; Cadorette, Jules; Tétrault, Marc-André; Leroux, Jean-Daniel; Michaud, Jean-Baptiste; Robert, Stéfan; Dautet, Henri; Davies, Murray; Fontaine, Réjean; Lecomte, Roger

    2006-03-01

    Positron Emission Tomography (PET) scanners dedicated to small animal studies have seen a swift development in recent years. Higher spatial resolution, greater sensitivity and faster scanning procedures are the leading factors driving further improvements. The new LabPET TM system is a second-generation APD-based animal PET scanner that combines avalanche photodiode (APD) technology with a highly integrated, fully digital, parallel electronic architecture. This work reports on the performance characteristics of the LabPET quad detector module, which consists of LYSO/LGSO phoswich assemblies individually coupled to reach-through APDs. Individual crystals 2×2×~10 mm 3 in size are optically coupled in pair along one long side to form the phoswich detectors. Although the LYSO and LGSO photopeaks partially overlap, the good energy resolution and decay time difference allow for efficient crystal identification by pulse-shape discrimination. Conventional analog discrimination techniques result in significant misidentification, but advanced digital signal processing methods make it possible to circumvent this limitation, achieving virtually error-free decoding. Timing resolution results of 3.4 ns and 4.5 ns FWHM have been obtained for LYSO and LGSO, respectively, using analog CFD techniques. However, test bench measurements with digital techniques have shown that resolutions in the range of 2 to 4 ns FWHM can be achieved.

  5. Superlinear threshold detectors in quantum cryptography

    SciTech Connect

    Lydersen, Lars; Maroey, Oystein; Skaar, Johannes; Makarov, Vadim; Jain, Nitin; Wittmann, Christoffer; Marquardt, Christoph; Leuchs, Gerd

    2011-09-15

    We introduce the concept of a superlinear threshold detector, a detector that has a higher probability to detect multiple photons if it receives them simultaneously rather than at separate times. Highly superlinear threshold detectors in quantum key distribution systems allow eavesdropping the full secret key without being revealed. Here, we generalize the detector control attack, and analyze how it performs against quantum key distribution systems with moderately superlinear detectors. We quantify the superlinearity in superconducting single-photon detectors based on earlier published data, and gated avalanche photodiode detectors based on our own measurements. The analysis shows that quantum key distribution systems using detector(s) of either type can be vulnerable to eavesdropping. The avalanche photodiode detector becomes superlinear toward the end of the gate. For systems expecting substantial loss, or for systems not monitoring loss, this would allow eavesdropping using trigger pulses containing less than 120 photons per pulse. Such an attack would be virtually impossible to catch with an optical power meter at the receiver entrance.

  6. Modelisation de photodetecteurs a base de matrices de diodes avalanche monophotoniques pour tomographie d'emission par positrons

    NASA Astrophysics Data System (ADS)

    Corbeil Therrien, Audrey

    La tomographie d'emission par positrons (TEP) est un outil precieux en recherche preclinique et pour le diagnostic medical. Cette technique permet d'obtenir une image quantitative de fonctions metaboliques specifiques par la detection de photons d'annihilation. La detection des ces photons se fait a l'aide de deux composantes. D'abord, un scintillateur convertit l'energie du photon 511 keV en photons du spectre visible. Ensuite, un photodetecteur convertit l'energie lumineuse en signal electrique. Recemment, les photodiodes avalanche monophotoniques (PAMP) disposees en matrice suscitent beaucoup d'interet pour la TEP. Ces matrices forment des detecteurs sensibles, robustes, compacts et avec une resolution en temps hors pair. Ces qualites en font un photodetecteur prometteur pour la TEP, mais il faut optimiser les parametres de la matrice et de l'electronique de lecture afin d'atteindre les performances optimales pour la TEP. L'optimisation de la matrice devient rapidement une operation difficile, car les differents parametres interagissent de maniere complexe avec les processus d'avalanche et de generation de bruit. Enfin, l'electronique de lecture pour les matrices de PAMP demeure encore rudimentaire et il serait profitable d'analyser differentes strategies de lecture. Pour repondre a cette question, la solution la plus economique est d'utiliser un simulateur pour converger vers la configuration donnant les meilleures performances. Les travaux de ce memoire presentent le developpement d'un tel simulateur. Celui-ci modelise le comportement d'une matrice de PAMP en se basant sur les equations de physique des semiconducteurs et des modeles probabilistes. Il inclut les trois principales sources de bruit, soit le bruit thermique, les declenchements intempestifs correles et la diaphonie optique. Le simulateur permet aussi de tester et de comparer de nouvelles approches pour l'electronique de lecture plus adaptees a ce type de detecteur. Au final, le simulateur vise a

  7. The performance of photon counting imaging with a Geiger mode silicon avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Qu, Hui-Ming; Zhang, Yi-Fan; Ji, Zhong-Jie; Chen, Qian

    2013-10-01

    In principle, photon counting imaging can detect a photon. With the development of low-level-light image intensifier techniques and low-level-light detection devices, photon counting imaging can now detect photon images under extremely low illumination. Based on a Geiger mode silicon avalanche photodiode single photon counter, an experimental system for photon counting imaging was built through two-dimensional scanning of a SPAD (single photon avalanche diode) detector. The feasibility of the imaging platform was validated experimentally. Two images with different characteristics, namely, the USAF 1951 resolution test panel and the image of Lena, were chosen to evaluate the imaging performance of the experimental system. The results were compared and analysed. The imaging properties under various illumination and scanning steps were studied. The lowest illumination limit of the SPAD photon counting imaging was determined.

  8. Future of Semiconductor Based Thermal Neutron Detectors

    SciTech Connect

    Nikolic, R J; Cheung, C L; Reinhardt, C E; Wang, T F

    2006-02-22

    Thermal neutron detectors have seen only incremental improvements over the last decades. In this paper we overview the current technology of choice for thermal neutron detection--{sup 3}He tubes, which suffer from, moderate to poor fieldability, and low absolute efficiency. The need for improved neutron detection is evident due to this technology gap and the fact that neutrons are a highly specific indicator of fissile material. Recognizing this need, we propose to exploit recent advances in microfabrication technology for building the next generation of semiconductor thermal neutron detectors for national security requirements, for applications requiring excellent fieldability of small devices. We have developed an innovative pathway taking advantage of advanced processing and fabrication technology to produce the proposed device. The crucial advantage of our Pillar Detector is that it can simultaneously meet the requirements of high efficiency and fieldability in the optimized configuration, the detector efficiency could be higher than 70%.

  9. Breakdown of avalanche critical behaviour in polycrystalline plasticity.

    PubMed

    Richeton, Thiebaud; Weiss, Jérôme; Louchet, François

    2005-06-01

    Acoustic emission experiments on creeping ice as well as numerical simulations argue for a self-organization of collective dislocation dynamics during plastic deformation of single crystals into a scale-free pattern of dislocation avalanches characterized by intermittency, power-law distributions of avalanche sizes, complex space-time correlations and aftershock triggering. Here, we address the question of whether such scale-free, close-to-critical dislocation dynamics will still apply to polycrystals. We show that polycrystalline plasticity is also characterized by intermittency and dislocation avalanches. However, grain boundaries hinder the propagation of avalanches, as revealed by a finite (grain)-size effect on avalanche size distributions. We propose that the restraint of large avalanches builds up internal stresses that push temporally the dynamical system into a supercritical state, off the scale-invariant critical regime, and trigger secondary avalanches in neighbouring grains. This modifies the statistical properties of the avalanche population. The results might also bring into question the classical ways of modelling plasticity in polycrystalline materials, based on homogenization procedures. PMID:15880114

  10. Neutron Detection with Water Cerenkov Based Detectors

    SciTech Connect

    Dazeley, S; Bernstein, A; Bowden, N; Carr, D; Ouedraogo, S; Svoboda, R; Sweany, M; Tripathi, M

    2009-05-13

    Legitimate cross border trade involves the transport of an enormous number of cargo containers. Especially following the September 11 attacks, it has become an international priority to verify that these containers are not transporting Special Nuclear Material (SNM) without impeding legitimate trade. Fission events from SNM produce a number of neutrons and MeV-scale gammas correlated in time. The observation of consistent time correlations between neutrons and gammas emitted from a cargo container could, therefore, constitute a robust signature for SNM, since this time coincident signature stands out strongly against the higher rate of uncorrelated gamma-ray backgrounds from the local environment. We are developing a cost effective way to build very large neutron detectors for this purpose. We have recently completed the construction of two new water Cherenkov detectors, a 250 liter prototype and a new 4 ton detector. We present both the results from our prototype detector and an update on the newly commissioned large detector. We will also present pictures from the construction and outline our future detector development plans.

  11. Avalanche Photodiode Statistics in Triggered-avalanche Detection Mode

    NASA Technical Reports Server (NTRS)

    Tan, H. H.

    1984-01-01

    The output of a triggered avalanche mode avalanche photodiode is modeled as Poisson distributed primary avalanche events plus conditionally Poisson distributed trapped carrier induced secondary events. The moment generating function as well as the mean and variance of the diode output statistics are derived. The dispersion of the output statistics is shown to always exceed that of the Poisson distribution. Several examples are considered in detail.

  12. Modeling and monitoring avalanches caused by rain-on-snow events

    NASA Astrophysics Data System (ADS)

    Havens, S.; Marshall, H. P.; Trisca, G. O.; Johnson, J. B.; Nicholson, B.

    2014-12-01

    Direct-action avalanches occur during large storm cycles in mountainous regions, when stresses on the snowpack increase rapidly due to the load of new snow and outpace snow strengthening due to compaction. If temperatures rise above freezing during the storm and snowfall turns to rain, the near-surface snow undergoes rapid densification caused by the introduction of liquid water. This shock to the snowpack, if stability is near critical, can cause widespread immediate avalanching due to the large induced strain rates in the slab, followed by secondary delayed avalanches due to both the increased load as well as water percolation to the depth of a weak layer. We use the semi-empirical SNOow Slope Stability model (SNOSS) to estimate the evolution of stability prior to large avalanches during rain-on-snow events on Highway 21 north of Boise, Idaho. We have continuously monitored avalanche activity using arrays of infrasound sensors in the avalanche-prone section of HW21 near Stanley, in collaboration with the Idaho Transportation Department's avalanche forecasting program. The autonomous infrasound avalanche monitoring system provides accurate timing of avalanche events, in addition to capturing avalanche dynamics during some major releases adjacent to the array. Due to the remote location and low winter traffic volume, the highway is typically closed for multiple days during major avalanche cycles. Many major avalanches typically release naturally and reach the road, but due the complex terrain and poor visibility, manual observations are often not possible until several days later. Since most avalanche programs typically use explosives on a regular basis to control slope stability, the infrasound record of avalanche activity we have recorded on HW21 provides a unique opportunity to study large naturally triggered avalanches. We use a first-order physically based stability model to estimate the importance of precipitation phase, amount, and rate during major rain

  13. Hebes Chasma Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located in Hebes Chasma.

    Image information: VIS instrument. Latitude -1.4, Longitude 286.6 East (73.4 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  14. Radiation detector system having heat pipe based cooling

    DOEpatents

    Iwanczyk, Jan S.; Saveliev, Valeri D.; Barkan, Shaul

    2006-10-31

    A radiation detector system having a heat pipe based cooling. The radiation detector system includes a radiation detector thermally coupled to a thermo electric cooler (TEC). The TEC cools down the radiation detector, whereby heat is generated by the TEC. A heat removal device dissipates the heat generated by the TEC to surrounding environment. A heat pipe has a first end thermally coupled to the TEC to receive the heat generated by the TEC, and a second end thermally coupled to the heat removal device. The heat pipe transfers the heat generated by the TEC from the first end to the second end to be removed by the heat removal device.

  15. Novel infrared detector based on a tunneling displacement transducer

    NASA Technical Reports Server (NTRS)

    Kenny, T. W.; Kaiser, W. J.; Waltman, S. B.; Reynolds, J. K.

    1991-01-01

    The paper describes the design, fabrication, and characteristics of a novel infrared detector based on the principle of Golay's (1947) pneumatic infrared detector, which uses the expansion of a gas to detect infrared radiation. The present detector is constructed entirely from micromachined silicon and uses an electron tunneling displacement transducer for the detection of gas expansion. The sensitivity of the new detector is competitive with the best commercial pyroelectric sensors and can be readily improved by an order of magnitude through the use of an optimized transducer.

  16. Interplanetary space weather effects on Lunar Reconnaissance Orbiter avalanche photodiode performance

    NASA Astrophysics Data System (ADS)

    Clements, E. B.; Carlton, A. K.; Joyce, C. J.; Schwadron, N. A.; Spence, H. E.; Sun, X.; Cahoy, K.

    2016-05-01

    Space weather is a major concern for radiation-sensitive space systems, particularly for interplanetary missions, which operate outside of the protection of Earth's magnetic field. We examine and quantify the effects of space weather on silicon avalanche photodiodes (SiAPDs), which are used for interplanetary laser altimeters and communications systems and can be sensitive to even low levels of radiation (less than 50 cGy). While ground-based radiation testing has been performed on avalanche photodiode (APDs) for space missions, in-space measurements of SiAPD response to interplanetary space weather have not been previously reported. We compare noise data from the Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA) SiAPDs with radiation measurements from the onboard Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument. We did not find any evidence to support radiation as the cause of changes in detector threshold voltage during radiation storms, both for transient detector noise and long-term average detector noise, suggesting that the approximately 1.3 cm thick shielding (a combination of titanium and beryllium) of the LOLA detectors is sufficient for SiAPDs on interplanetary missions with radiation environments similar to what the LRO experienced (559 cGy of radiation over 4 years).

  17. Cyclotene diaphragm for MEMS based IR detectors

    NASA Astrophysics Data System (ADS)

    Guo, Shuwen

    2003-01-01

    A novel structure employing Dow Chemical (Midland, MI) benzocyclobutene (BCB) Cyclotene as a diaphragm material is presented in this report. The main advantages of this BCB diaphragm are its low thermal conductivity, robustness, chemical inertness, low curing temperature and high structure yield. Moreover, a BCB film can be either photo-defined or plasma etched and is a suitable micromachining material for post IC processing. Micromachined IR thermopile single detectors and lineal detector arrays (1×16), using BiSeTeSb/BiSbTe sensing elements on BCB diaphragms, have been constructed and tested. Up to 100% structure yield has been obtained. The process used to realize this detector structure is compatible with the eventual inclusion of on-chip circuitry for signal amplification and conditioning.

  18. Metamaterials for Cherenkov Radiation Based Particle Detectors

    SciTech Connect

    Tyukhtin, A. V.; Schoessow, P.; Kanareykin, A.; Antipov, S.

    2009-01-22

    Measurement of Cherenkov radiation (CR) has long been a useful technique for charged particle detection and beam diagnostics. We are investigating metamaterials engineered to have refractive indices tailored to enhance properties of CR that are useful for particle detectors and that cannot be obtained using conventional media. Cherenkov radiation in dispersive media with a large refractive index differs significantly from the same effect in conventional detector media, like gases or aerogel. The radiation pattern of CR in dispersive metamaterials presents lobes at very large angles with respect to particle motion. Moreover, the frequency and particle velocity dependence of the radiated energy can differ significantly from CR in a conventional dielectric medium.

  19. Performance Dependences of Multiplication Layer Thickness for InP/InGaAs Avalanche Photodiodes Based on Time Domain Modeling

    NASA Technical Reports Server (NTRS)

    Xiao, Yegao; Bhat, Ishwara; Abedin, M. Nurul

    2005-01-01

    InP/InGaAs avalanche photodiodes (APDs) are being widely utilized in optical receivers for modern long haul and high bit-rate optical fiber communication systems. The separate absorption, grading, charge, and multiplication (SAGCM) structure is an important design consideration for APDs with high performance characteristics. Time domain modeling techniques have been previously developed to provide better understanding and optimize design issues by saving time and cost for the APD research and development. In this work, performance dependences on multiplication layer thickness have been investigated by time domain modeling. These performance characteristics include breakdown field and breakdown voltage, multiplication gain, excess noise factor, frequency response and bandwidth etc. The simulations are performed versus various multiplication layer thicknesses with certain fixed values for the areal charge sheet density whereas the values for the other structure and material parameters are kept unchanged. The frequency response is obtained from the impulse response by fast Fourier transformation. The modeling results are presented and discussed, and design considerations, especially for high speed operation at 10 Gbit/s, are further analyzed.

  20. A four-layer attenuation compensated PET detector based on APD arrays without discrete crystal elements.

    PubMed

    McCallum, Stephen; Clowes, Peter; Welch, Andrew

    2005-09-01

    Scintillation detectors developed for PET traditionally use relatively thick crystals coupled to photomultiplier tubes. To ensure good efficiency the crystals typically measure between 10 and 30 mm thick. Detectors also require good spatial resolution so the scintillator is normally made up of a densely packed array of long thin crystals. In this paper, we present a novel design in which the detection crystal is divided into a number of layers along its length with an avalanche photo diode (APD) inserted between each layer. With thin layers of crystal, it is possible to use a continuous rather than a pixelated crystal. The potential advantages of this design over a conventional PMT-based detector are: (i) improved light collection efficiency, (ii) reduced dependency on dense crystal to achieve good stopping power, (iii) ease of crystal manufacture, (iv) reduced detector dead-time and increased count rate, and (v) inherent depth of interaction. We have built a four-layer detector to test this design concept using Hamamatsu S8550 APD arrays and LYSO crystals. We used the centre 16 pixels of each of the arrays to give an active area of 9.5 mm x 9.5 mm. Four crystals 9.5 mm x 9.5 mm were used with thickness increasing from 2 mm at the front to 2.5 mm, 3.1 mm and 4.3 mm at the back, to ensure a similar count rate in each layer. Calculations for the thickness of the four layers were initially made using the linear attenuation coefficient for photons at 511 keV of LYSO. Experimental results and further simulation demonstrated that a correction to the thickness of each layer should be considered to take into account the scattered events. The energy resolution for each of the layers at 511 keV was around 15%, coincidence-timing resolution was 2.2 ns and the special resolution was less than 2 mm using a statistical-based positioning algorithm. PMID:16177539

  1. Infrared imaging using carbon nanotube-based detector

    NASA Astrophysics Data System (ADS)

    Chen, Hongzhi; Xi, Ning; Song, Bo; Chen, Liangliang; Lai, King W. C.; Lou, Jianyong

    2011-06-01

    Using carbon nanotubes (CNT), high performance infrared detectors have been developed. Since the CNTs have extraordinary optoelectronics properties due to its unique one dimensional geometry and structure, the CNT based infrared detectors have extremely low dark current, low noise equivalent temperature difference (NETD), short response time, and high dynamic range. Most importantly, it can detect 3-5 um middle-wave infrared (MWIR) at room temperature. This unique feature can significantly reduce the size and weight of a MWIR imaging system by eliminating a cryogenic cooling system. However, there are two major difficulties that impede the application of CNT based IR detectors for imaging systems. First, the small diameter of the CNTs results in low fill factor. Secondly, it is difficult to fabricate large scale of detector array for high resolution focal plane due to the limitations on the efficiency and cost of the manufacturing. In this paper, a new CNT based IR imaging system will be presented. Integrating the CNT detectors with photonic crystal resonant cavity, the fill factor of the CNT based IR sensor can reach as high as 0.91. Furthermore, using the compressive sensing technology, a high resolution imaging can be achieved by CNT based IR detectors. The experimental testing results show that the new imaging system can achieve the superb performance enabled by CNT based IR detectors, and, at the same time, overcame its difficulties to achieve high resolution and efficient imaging.

  2. EUV mirror based absolute incident flux detector

    DOEpatents

    Berger, Kurt W.

    2004-03-23

    A device for the in-situ monitoring of EUV radiation flux includes an integrated reflective multilayer stack. This device operates on the principle that a finite amount of in-band EUV radiation is transmitted through the entire multilayer stack. This device offers improvements over existing vacuum photo-detector devices since its calibration does not change with surface contamination.

  3. Solid-state flat panel imager with avalanche amorphous selenium

    NASA Astrophysics Data System (ADS)

    Scheuermann, James R.; Howansky, Adrian; Goldan, Amir H.; Tousignant, Olivier; Levéille, Sébastien; Tanioka, K.; Zhao, Wei

    2016-03-01

    Active matrix flat panel imagers (AMFPI) have become the dominant detector technology for digital radiography and fluoroscopy. For low dose imaging, electronic noise from the amorphous silicon thin film transistor (TFT) array degrades imaging performance. We have fabricated the first prototype solid-state AMFPI using a uniform layer of avalanche amorphous selenium (a-Se) photoconductor to amplify the signal to eliminate the effect of electronic noise. We have previously developed a large area solid-state avalanche a-Se sensor structure referred to as High Gain Avalanche Rushing Photoconductor (HARP) capable of achieving gains of 75. In this work we successfully deposited this HARP structure onto a 24 x 30 cm2 TFT array with a pixel pitch of 85 μm. An electric field (ESe) up to 105 Vμm-1 was applied across the a-Se layer without breakdown. Using the HARP layer as a direct detector, an X-ray avalanche gain of 15 +/- 3 was achieved at ESe = 105 Vμm-1. In indirect mode with a 150 μm thick structured CsI scintillator, an optical gain of 76 +/- 5 was measured at ESe = 105 Vμm-1. Image quality at low dose increases with the avalanche gain until the electronic noise is overcome at a constant exposure level of 0.76 mR. We demonstrate the success of a solid-state HARP X-ray imager as well as the largest active area HARP sensor to date.

  4. Detectors

    DOEpatents

    Orr, Christopher Henry; Luff, Craig Janson; Dockray, Thomas; Macarthur, Duncan Whittemore; Bounds, John Alan; Allander, Krag

    2002-01-01

    The apparatus and method provide techniques through which both alpha and beta emission determinations can be made simultaneously using a simple detector structure. The technique uses a beta detector covered in an electrically conducting material, the electrically conducting material discharging ions generated by alpha emissions, and as a consequence providing a measure of those alpha emissions. The technique also offers improved mountings for alpha detectors and other forms of detectors against vibration and the consequential effects vibration has on measurement accuracy.

  5. Radioiodine detector based on laser induced fluorescence

    DOEpatents

    McDonald, Jimmie R.; Baronavski, Andrew P.

    1980-01-01

    The invention involves the measurement of the concentration of the radioisotope .sup.129 I.sub.2 in the presence of a gas. The invention uses a laser to excite a sample of the .sup.129 I.sub.2 in a sample gas chamber and a reference sample of a known concentration of .sup.129 I.sub.2 in a reference gas chamber. The .sup.129 I.sub.2 in the sample and reference gas chamber each gives off fluorescence emissions which are received by photomultipliers which provide signals to a detector. The detector uses a ratioing technique to determine the concentration of .sup.129 I.sub.2 in the sample gas chamber.

  6. Tikhonravov Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located within a small crater inside Tikhonravov Crater.

    Image information: VIS instrument. Latitude 12.6, Longitude 37.1 East (322.9 West). 36 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  7. Lycus Sulci Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches occur on the slopes of Lycus Sulci near Olympus Mons.

    Image information: VIS instrument. Latitude 28.1, Longitude 220.4 East (139.6 West). 18 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  8. Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    These dust avalanches are located in a small canyon within a crater rim northeast of Naktong Vallis.

    Image information: VIS instrument. Latitude 7.1, Longitude 34.7 East (325.3 West). 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  9. Crater Dust Avalanches

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    Dust avalanches, also called slope streaks, occur on many Martian terrains. The deposition of airborne dust on surfaces causes a bright tone in the THEMIS VIS images. Any movement of the dust downhill, a dust avalanche, will leave behind a streak where the darker, dust-free surface is exposed.

    This region of dust avalanches is located in and around a crater to the west of yesterday's image.

    Image information: VIS instrument. Latitude 14.7, Longitude 32.7 East (327.3 West). 18 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  10. Polyaniline-based optical ammonia detector

    DOEpatents

    Duan, Yixiang; Jin, Zhe; Su, Yongxuan

    2002-01-01

    Electronic absorption spectroscopy of a polyaniline film deposited on a polyethylene surface by chemical oxidation of aniline monomer at room temperature was used to quantitatively detect ammonia gas. The present optical ammonia gas detector was found to have a response time of less than 15 s, a regeneration time of less than 2 min. at room temperature, and a detection limit of 1 ppm (v/v) for ammonia, with a linear dynamic range from 180 ppm to 18,000 ppm.

  11. Analysis of laser jamming to satellite-based detector

    NASA Astrophysics Data System (ADS)

    Wang, Si-wen; Guo, Li-hong; Guo, Ru-hai

    2009-07-01

    The reconnaissance satellite, communication satellite and navigation satellite used in the military applications have played more and more important role in the advanced technique wars and already become the significant support and aid system for military actions. With the development of all kinds of satellites, anti-satellite laser weapons emerge as the times require. The experiments and analyses of laser disturbing CCD (charge coupled detector) in near ground have been studied by many research groups, but their results are not suitable to the case that using laser disturbs the satellite-based detector. Because the distance between the satellite-based detector and the ground is very large, it is difficult to damage it directly. However the optical receive system of satellite detector has large optical gain, so laser disturbing satellite detector is possible. In order to determine its feasibility, the theoretical analyses and experimental study are carried out in the paper. Firstly, the influence factors of laser disturbing satellite detector are analyzed in detail, which including laser power density on the surface of the detector after long distance transmission, and laser power density threshold for disturbing etc. These factors are not only induced by the satellite orbit, but dependence on the following parameters: laser average power in the ground, laser beam quality, tracing and aiming precision and atmospheric transmission. A calculation model is developed by considering all factors which then the power density entering into the detector can be calculated. Secondly, the laser disturbing experiment is performed by using LD (laser diode) with the wavelength 808 nm disturbing CCD 5 kilometer away, which the disturbing threshold value is obtained as 3.55×10-4mW/cm2 that coincides with other researcher's results. Finally, using the theoretical model, the energy density of laser on the photosensitive surface of MSTI-3 satellite detector is estimated as about 100m

  12. A Passive FPAA-Based RF Scatter Meteor Detector

    NASA Astrophysics Data System (ADS)

    Popowicz, A.; Malcher, A.; Bernacki, K.; Fietkiewicz, K.

    2015-02-01

    In the article, we present a hardware meteor detector. The detection principle is based on the electromagnetic wave reflection from the ionized meteor trail in the atmosphere. The detector uses the ANADIGM field programmable analog array (FPAA), which is an attractive alternative for typically used detecting equipment—a PC computer with dedicated software. We implement an analog signal path using most of available FPAA resources to obtain precise audio signal detection. Our new detector was verified in collaboration with the Polish Fireball Network, the organization which monitors meteor activity in Poland. When compared with currently used signal processing PC software employing real radio meteor scatter signals, our low-cost detector proved to be more precise and reliable. Due to its cost and efficiency superiority over the current solution, the presented module is going to be implemented in the planned distributed detectors system.

  13. Room temperature particle detectors based on indium phosphide

    NASA Astrophysics Data System (ADS)

    Yatskiv, R.; Grym, J.; Zdansky, K.; Pekarek, L.

    2010-01-01

    A study of electrical properties and detection performance of particle detectors based on bulk InP and semiconducting LPE layers operated at room temperature is presented. Bulk detectors were fabricated on semi-insulating InP crystals grown by liquid-encapsulated Czochralski (LEC) technique. High purity InP layers of both n- and p-type conductivity were used to fabricate detector structures with p-n junction. The detection performance of particle detectors was measured by pulse-height spectra with alpha particles emitted from 241Am source at room temperature. Better noise properties were achieved for detectors with p-n junctions due to better quality contacts on p-type layers.

  14. A detector insert based on continuous scintillators for hybrid MR-PET imaging of the human brain

    NASA Astrophysics Data System (ADS)

    Rato Mendes, P.; Cuerdo, R.; Sarasola, I.; García de Acilu, P.; Navarrete, J.; Vela, O.; Oller, J. C.; Cela, J. M.; Núñez, L.; Pastrana, M.; Romero, L.; Willmott, C.

    2013-02-01

    We are developing a positron emission tomography (PET) insert for existing magnetic resonance (MR) equipment, aiming at hybrid MR-PET imaging. Our detector block design is based on trapezoid-shaped LYSO:Ce monolithic scintillators coupled to magnetically compatible Hamamatsu S8550-02 silicon avalanche photodiode (APD) matrices with a dedicated ASIC front-end readout from GammaMedica-Ideas (Fornebu, Norway). The detectors are position sensitive, capable of determining the incidence point of 511 keV gammas with an intrinsic spatial resolution on the order of 2 mm by means of supervised learning neural-network (NN) algorithms. These algorithms, apart from providing continuous coordinates, are also intrinsically corrected for depth of interaction effects and thus parallax-free. Recently we have implemented an advanced prototype featuring two heads with four detector blocks each and final front-end and readout electronics, improving the spatial resolution of reconstructed point source images down to 1.7 mm full width at half maximum (FWHM). Presently we are carrying out operational tests of components and systems under magnetic fields using a 3 T MR scanner. In this paper we present a description of our project, a summary of the results obtained with laboratory prototypes, and the strategy to build and install the complete system at the nuclear medicine department of a collaborating hospital.

  15. Special Nuclear Material Detection with a Water Cherenkov based Detector

    SciTech Connect

    Sweany, M; Bernstein, A; Bowden, N; Dazeley, S; Svoboda, R

    2008-11-10

    Fission events from Special Nuclear Material (SNM), such as highly enriched uranium or plutonium, produce a number of neutrons and high energy gamma-rays. Assuming the neutron multiplicity is approximately Poissonian with an average of 2 to 3, the observation of time correlations between these particles from a cargo container would constitute a robust signature of the presence of SNM inside. However, in order to be sensitive to the multiplicity, one would require a high total efficiency. There are two approaches to maximize the total efficiency; maximizing the detector efficiency or maximizing the detector solid angle coverage. The advanced detector group at LLNL is investigating one way to maximize the detector size. We are designing and building a water Cerenkov based gamma and neutron detector for the purpose of developing an efficient and cost effective way to deploy a large solid angle car wash style detector. We report on our progress in constructing a larger detector and also present preliminary results from our prototype detector that indicates detection of neutrons.

  16. Diffraction measurements with a boron-based GEM neutron detector

    NASA Astrophysics Data System (ADS)

    Croci, Gabriele; Albani, Giorgia; Cazzaniga, Carlo; Perelli Cippo, Enrico; Schooneveld, Erik; Claps, Gerardo; Cremona, Anna; Grosso, Giovanni; Muraro, Andrea; Murtas, Fabrizio; Rebai, Marica; Scherillo, Antonella; Tardocchi, Marco; Gorini, Giuseppe

    2014-07-01

    The research of reliable substitutes of 3He detectors is an important task for the affordability of new neutron scattering instrumentation for future spallation sources like the European Spallation Source. GEM (Gas Electron Multiplier)-based detectors represent a valid alternative since they can combine high-rate capability, coverage of up to 1\\ \\text{m}^{2} area and good intrinsic spatial resolution (for this detector class it can be better than 0.5 mm). The first neutron diffraction measurements performed using a borated GEM detector are reported. The detector has an active area of 10 \\times 5\\ \\text{cm}^{2} and is equipped with a borated cathode. The GEM detector was read out using the standard ISIS Data Acquisition System. The comparison with measurements performed with standard 3He detectors shows that the broadening of the peaks measured on the diffractogram obtained with the GEM is 20-30% wider than the one obtained by 3He tubes but the active area of the GEM is twice that of 3He tubes. The GEM resolution is improved if half of its active area is considered. The signal-to-background ratio of the GEM is about 1.5 to 2 times lower than that of 3He. This measurement proves that GEM detectors can be used for neutron diffraction measurements and paves the way for their use at future neutron spallation sources.

  17. Snow avalanche detection and identification for near real-time application

    NASA Astrophysics Data System (ADS)

    Havens, S.; Johnson, J. B.; Marshall, H.; Nicholson, B.; Trisca, G. O.

    2013-12-01

    A near real-time avalanche detection system will provide highway avalanche forecasters with a tool to remotely monitor major avalanche paths and provide information about regional avalanche activity and timing. For the last three winters, a network of infrasound arrays has been remotely monitoring both avalanche and non-avalanche events along a 10 mile section of Highway 21 in Idaho. To provide the best results to avalanche forecasters, the system must be robust and detect all major avalanche events of interest that affect the highway. Over the last three winters, the infrasound arrays recorded multiple avalanche cycles and we explore different methods of event detection for both large dry avalanches (strong infrasound signal) and small wet avalanches (weak infrasound signal). We compare the F-statistic and cross-correlation techniques (i.e. PMCC) to determine the most robust method and develop computationally efficient algorithms to implement in near-real time using parallel processing and GPU computing. Once an event has been detected, we use the artificial intelligence method of recursive neural networks to classify based on similar characteristics to past known signals.

  18. Forensic Analysis of the May 2014 West Salt Creek Rock Avalanche in Western Colorado

    NASA Astrophysics Data System (ADS)

    Coe, J. A.; Baum, R. L.; Allstadt, K.; Kochevar, B. F.; Schmitt, R. G.; Morgan, M. L.; White, J. L.; Stratton, B. T.; Hayashi, T. A.; Kean, J. W.

    2015-12-01

    The rain-on-snow induced West Salt Creek rock avalanche occurred on May 25, 2014 on the northern flank of Grand Mesa. The avalanche was rare for the contiguous U.S. because of its large size (59 M m3) and high mobility (Length/Height=7.2). To understand the avalanche failure sequence, mechanisms, and mobility, we conducted a forensic analysis using large-scale (1:1000) structural mapping and seismic data. We used high-resolution, Unmanned Aircraft System (UAS) imagery as a base for our field mapping and analyzed seismic data from 22 broadband stations (distances <656 km) and one short-period network. We inverted broadband data to derive a time series of forces that the avalanche exerted on the earth and tracked these forces using curves in the avalanche path. Our results revealed that the rock avalanche was a cascade of landslide events, rather than a single massive failure. The sequence began with a landslide/debris flow that started about 10 hours before the main avalanche. The main avalanche lasted just over 3 minutes and traveled at average velocities ranging from 15 to 36 m/s. For at least two hours after the avalanche ceased movement, a central, hummock-rich, strike-slip bound core continued to move slowly. Following movement of the core, numerous shallow landslides, rock slides, and rock falls created new structures and modified topography. Mobility of the main avalanche and central core were likely enhanced by valley floor material that liquefied from undrained loading by the overriding avalanche. Although the base was likely at least partially liquefied, our mapping indicates that the overriding avalanche internally deformed predominantly by sliding along discrete shear surfaces in material that was nearly dry and had substantial frictional strength. These results indicate that the West Salt Creek avalanche, and probably other long-traveled avalanches, could be modeled as two layers: a liquefied basal layer; and a thicker and stronger overriding layer.

  19. Development of Numerical Models for Performance Predictions of Single-Photon Avalanche Photodetectors (SPAP) for the 2-Micron Regime

    NASA Technical Reports Server (NTRS)

    Joshi, Ravindra P.; Abedin, M. Nurul (Technical Monitor)

    2001-01-01

    Field dependent drift velocity results are presented for electron transport in bulk Indium Arsenide (InAs) material based on a Monte Carlo model, which includes an analytical treatment of band-to-band impact ionization. Avalanche multiplication and related excess noise factor (F) are computed as a function of device length and applied voltage. A decrease in F with increases in device length is obtained. The results suggest an inherent utility for InAs-based single-photon avalanche detectors, particularly around the 2 microns region of interest for atmospheric remote sensing applications. The dark current response was also evaluated. The role of the various components has been analyzed. For shorter devices, the tunneling component is shown to dominate at low temperatures. Finally, possible structures for enhanced photodetection are proposed for future research.

  20. Development of a large area InGaAs APD receiver based on an impact ionization engineered detector for free-space lasercomm applications

    NASA Astrophysics Data System (ADS)

    Burris, H. R.; Ferraro, M. S.; Freeman, W. T.; Moore, C. I.; Murphy, J. L.; Rabinovich, W. S.; Smith, W. R.; Summers, L. L.; Thomas, L. M.; Vilcheck, M. J.; Clark, W. R.; Waters, W. D.

    2012-06-01

    The U.S. Naval Research Laboratory (NRL) is developing a small size, weight and power (SWaP) free space lasercomm terminal for small unmanned airborne platforms. The terminal is based on a small gimbal developed by CloudCap Technology. A receiver with a large field of view and with sensitivity sufficient to meet the program range goals is required for this terminal. An InGaAs Avalanche Photodiode (APD) with internal structures engineered to reduce excess noise and keff in high gain applications was selected as the detector. The detector is a 350 micron diameter impact ionization engineered (I2E) APD developed by Optogration, Inc. Results of development and characterization of the receiver will be presented.

  1. Selective detector of cosmic particles based on diamond sensitive elements

    NASA Astrophysics Data System (ADS)

    Altukhov, A. A.; Zaharchenko, K. V.; Kolyubin, V. A.; Lvov, S. A.; Nedosekin, P. G.; Tyurin, E. M.; Ibragimov, R. F.; Kadilin, V. V.; Nikolaev, I. V.

    2016-02-01

    The article describes the device for selective registration of electrons, protons and heavy ions fluxes from the solar and galactic cosmic rays in the twelve energy ranges, built on a base of diamond detector. The use of the diamond detectors allowed for the creation a device for registration of cosmic particles fluxes at the external spacecraft surface with the resource not less than 20 years. Selective detector is aimed for continuous monitoring of radiation situation on board the spacecrafts, in order to predict the residual life of their work and prompt measures to actively protect the spacecraft when the flow of cosmic particles is sharply increased.

  2. Development of video processing based on coal flame detector system

    SciTech Connect

    He Wanqing; Yu Yuefeng; Xu Weiyong; Ma Liqun

    1999-07-01

    The principle and development of a set of pulverized coal combustion flame detection system, which is called intelligent image flame detector device based on digital video processing, is addressed in this paper. The system realizes multi-burner flame detection and processing using a distributive structure of engineering workstation and flame detectors via multi-serial-port communication. The software can deal with multi-tasks in a parallel way based on multi-thread mechanism. Streaming video capture and storage is provided to safe and playback the accidental Audio and Visual Interfaces (AVI) clips. The layer flame detectors can give the flame on/off signal through image processing. Pseudo-color visualization of flame temperature calculated from chromatic CCD signal is integrated into the system. The image flame detector system has been successfully used in thermal power generation units in China.

  3. Mosaic-Detector-Based Fluorescence Spectral Imager

    NASA Technical Reports Server (NTRS)

    Son, Kyung-Ah; Moon, Jeong

    2007-01-01

    A battery-powered, pen-sized, portable instrument for measuring molecular fluorescence spectra of chemical and biological samples in the field has been proposed. Molecular fluorescence spectroscopy is among the techniques used most frequently in laboratories to analyze compositions of chemical and biological samples. Heretofore, it has been possible to measure fluorescence spectra of molecular species at relative concentrations as low as parts per billion (ppb), with a few nm spectral resolution. The proposed instrument would include a planar array (mosaic) of detectors, onto which a fluorescence spectrum would be spatially mapped. Unlike in the larger laboratory-type molecular fluorescence spectrometers, mapping of wavelengths to spatial positions would be accomplished without use of relatively bulky optical parts. The proposed instrument is expected to be sensitive enough to enable measurement of spectra of chemical species at relative concentrations <1 ppb, with spectral resolution that could be tailored by design to be comparable to a laboratory molecular fluorescence spectrometer. The proposed instrument (see figure) would include a button-cell battery and a laser diode, which would generate the monochromatic ultraviolet light needed to excite fluorescence in a sample. The sample would be held in a cell bounded by far-ultraviolet-transparent quartz or optical glass. The detector array would be, more specifically, a complementary metal oxide/ semiconductor or charge-coupled- device imaging photodetector array, the photodetectors of which would be tailored to respond to light in the wavelength range of the fluorescence spectrum to be measured. The light-input face of the photodetector array would be covered with a matching checkerboard array of multilayer thin film interference filters, such that each pixel in the array would be sensitive only to light in a spectral band narrow enough so as not to overlap significantly with the band of an adjacent pixel. The

  4. Initiation of immersed granular avalanches

    NASA Astrophysics Data System (ADS)

    Mutabaruka, Patrick; Delenne, Jean-Yves; Soga, Kenichi; Radjai, Farhang

    2014-05-01

    By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the

  5. Initiation of immersed granular avalanches.

    PubMed

    Mutabaruka, Patrick; Delenne, Jean-Yves; Soga, Kenichi; Radjai, Farhang

    2014-05-01

    By means of coupled molecular dynamics-computational fluid dynamics simulations, we analyze the initiation of avalanches in a granular bed of spherical particles immersed in a viscous fluid and inclined above its angle of repose. In quantitative agreement with experiments, we find that the bed is unstable for a packing fraction below 0.59 but is stabilized above this packing fraction by negative excess pore pressure induced by the effect of dilatancy. From detailed numerical data, we explore the time evolution of shear strain, packing fraction, excess pore pressures, and granular microstructure in this creeplike pressure redistribution regime, and we show that they scale excellently with a characteristic time extracted from a model based on the balance of granular stresses in the presence of a negative excess pressure and its interplay with dilatancy. The cumulative shear strain at failure is found to be ≃ 0.2, in close agreement with the experiments, irrespective of the initial packing fraction and inclination angle. Remarkably, the avalanche is triggered when dilatancy vanishes instantly as a result of fluctuations while the average dilatancy is still positive (expanding bed) with a packing fraction that declines with the initial packing fraction. Another nontrivial feature of this creeplike regime is that, in contrast to dry granular materials, the internal friction angle of the bed at failure is independent of dilatancy but depends on the inclination angle, leading therefore to a nonlinear dependence of the excess pore pressure on the inclination angle. We show that this behavior may be described in terms of the contact network anisotropy, which increases with a nearly constant connectivity and levels off at a value (critical state) that increases with the inclination angle. These features suggest that the behavior of immersed granular materials is controlled not only directly by hydrodynamic forces acting on the particles but also by the influence of the

  6. Optical detectors based on thermoelastic effect in crystalline quartz

    NASA Astrophysics Data System (ADS)

    Chelibanov, V. P.; Ishanin, G. G.

    2015-06-01

    Optical detectors developed on base of thermo elastic effect In quartz crystalline (PTEK) attributed to the thermal detectors group. Such detectors occurred very effective for the registration of pulsed light energy or power of harmonically modulated laser radiation flux in a wide spectral (from UV to far IR) and dynamic ranges (from 10-6 to 300 W / cm2 with cooling) with a time constant up to10-6 seconds. When exposed to electromagnetic radiation occurs at the receiver thermal field which causes mechanical stress in the transient crystalline quartz, which in turn leads to a change in the polarization of crystalline quartz and, as a consequence, to an electric potential difference at the electrodes (the front surface with a conductive coating and damper). The capacitive characteristic of the detector, based on a thermo elastic effect in crystalline quartz, eliminates the possibility of working with constant flow of radiation, which also affects at the frequency response of the detector, since the potential difference appearance in the piezoelectric plate depends on the direction of the forces relative to the axes X, Y, Z of the crystal. Therefore, a certain choice of orientation of the receiving element is necessary in accordance with the physical properties of crystalline quartz. In this paper, a calculation of the sensitivity and frequency characteristics of optical detectors based on the thermo elastic effect in crystalline quartz at the harmonic effects of electromagnetic radiation flux are reported.

  7. Radiation hard avalanche photodiodes for CMS ECAL

    NASA Astrophysics Data System (ADS)

    Grahl, J.; Kronquist, I.; Rusack, R.; Singovski, A.; Kuznetsov, A.; Musienko, Y.; Reucroft, S.; Swain, J.; Deiters, K.; Ingram, Q.; Renker, D.; Sakhelashvili, T.

    2003-05-01

    The photo detectors of the CMS electromagnetic calorimeter have to operate in a rather hostile environment, in a strong magnetic field of 4 T and under unprecedented radiation levels. Avalanche Photo Diodes (APDs) have been chosen to detect the scintillation light of the 62,000 lead tungstate crystals in the barrel part of the calorimeter. After a 6 year long R&D work Hamamatsu Photonics produces APDs with a structure that is basically radiation hard. Only a few percent of the delivered APDs are weak due to defects at the surface caused by dust particles in the production process. Since a reliability of 99.9% is required, a method to detect weak APDs before they are built into the detector had to be developed. The described screening method is a combination of 60Co irradiations and annealing under bias of all APDs and irradiations with hadrons on a sampling basis.

  8. A multi path, weather independent avalanche monitoring tool using distributed acoustic fiber optic sensing

    NASA Astrophysics Data System (ADS)

    Prokop, Alexander; Wirbel, Anna

    2013-04-01

    Information on avalanche activity is a paramount parameter in avalanche forecasting. When avalanches are released spontaneously, the risk of avalanches is very high. Triggering avalanches by artificial means, such as explosives launched from helicopter or avalanche towers, can also give information on the stability of the snow pack. Hence, monitoring of avalanches released naturally or artificially, is an important quantity in avalanche forecasting. This information is also needed when deciding whether to close or not endangered ski runs, roads or railway lines. So far monitoring systems lack certain benefits. Either they monitor only large avalanches, can only be used for single avalanche tracks or are weather/sight dependant. Therefore a new tool for avalanche- monitoring, a distributed fiber optic system, is for the first time installed and adapted for the purpose of monitoring snow avalanche activity. The method is based on an optical time domain reflectometer (OTDR) system, which dates back to the 1970`s and detects seismic vibrations and acoustic signals on a fiber optic cable that can have a length of up to 30 km. An appropriate test slope for this configuration has been found in the ski area of "Lech am Arlberg". In this work a detailed description of the theoretical background, the system implementation, the field installation, realization of tests and an investigation of the recorded data is presented. We conducted 100 tests and triggered 41 avalanches so far with a runout distances ranging from a few meters to approximately 250 meters, all of which were detected by the system, as well as the 59 not successful attempts of artificial triggering. Moreover we measured properly if critical infrastructure (in our case a ski run) was reached by the avalanches or not. The spatial distributed sensing approach allowed us to relate the amplitude and spectral content of the signals to avalanche size, avalanche speed and snow properties of the avalanches. In

  9. Al0.52In0.48P avalanche photodiodes for soft X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Auckloo, A.; Cheong, J. S.; Meng, X.; Tan, C. H.; Ng, J. S.; Krysa, A.; Tozer, R. C.; David, J. P. R.

    2016-03-01

    The performance of Al0.52In0.48P avalanche photodiodes was assessed as soft X-ray detectors at room temperature. The effect of the avalanche gain improved the energy resolution and an energy resolution (FWHM) of 682 eV is reported for 5.9 keV X-rays.

  10. Neuronal avalanches and learning

    NASA Astrophysics Data System (ADS)

    de Arcangelis, Lucilla

    2011-05-01

    Networks of living neurons represent one of the most fascinating systems of biology. If the physical and chemical mechanisms at the basis of the functioning of a single neuron are quite well understood, the collective behaviour of a system of many neurons is an extremely intriguing subject. Crucial ingredient of this complex behaviour is the plasticity property of the network, namely the capacity to adapt and evolve depending on the level of activity. This plastic ability is believed, nowadays, to be at the basis of learning and memory in real brains. Spontaneous neuronal activity has recently shown features in common to other complex systems. Experimental data have, in fact, shown that electrical information propagates in a cortex slice via an avalanche mode. These avalanches are characterized by a power law distribution for the size and duration, features found in other problems in the context of the physics of complex systems and successful models have been developed to describe their behaviour. In this contribution we discuss a statistical mechanical model for the complex activity in a neuronal network. The model implements the main physiological properties of living neurons and is able to reproduce recent experimental results. Then, we discuss the learning abilities of this neuronal network. Learning occurs via plastic adaptation of synaptic strengths by a non-uniform negative feedback mechanism. The system is able to learn all the tested rules, in particular the exclusive OR (XOR) and a random rule with three inputs. The learning dynamics exhibits universal features as function of the strength of plastic adaptation. Any rule could be learned provided that the plastic adaptation is sufficiently slow.

  11. Particle detectors based on semiconducting InP epitaxial layers

    NASA Astrophysics Data System (ADS)

    Yatskiv, R.; Grym, J.; Zdansky, K.

    2011-01-01

    A study of electrical properties and detection performance of two types of Indium Phosphide detector structures was performed: (i) with p-n-junction and (ii) with Schottky contact prepared on high purity p-type InP. The p-n junction detectors were based on a high purity InP:Pr layers of both n- and p- type conductivity with carrier concentration on the order of 1014 cm-3 grown on Sn doped n-type substrate. Schottky barrier detectors were prepared by vacuum evaporation of Pd on high purity p-type epitaxial layer grown on Mn doped p-type substrate. The detection performance of particle detectors was measured by pulse-height spectra with alpha particles emitted from 241Am source at room temperature.

  12. Integrated atom detector based on field ionization near carbon nanotubes

    SciTech Connect

    Gruener, B.; Jag, M.; Stibor, A.; Visanescu, G.; Haeffner, M.; Kern, D.; Guenther, A.; Fortagh, J.

    2009-12-15

    We demonstrate an atom detector based on field ionization and subsequent ion counting. We make use of field enhancement near tips of carbon nanotubes to reach extreme electrostatic field values of up to 9x10{sup 9} V/m, which ionize ground-state rubidium atoms. The detector is based on a carpet of multiwall carbon nanotubes grown on a substrate and used for field ionization, and a channel electron multiplier used for ion counting. We measure the field enhancement at the tips of carbon nanotubes by field emission of electrons. We demonstrate the operation of the field ionization detector by counting atoms from a thermal beam of a rubidium dispenser source. By measuring the ionization rate of rubidium as a function of the applied detector voltage we identify the field ionization distance, which is below a few tens of nanometers in front of nanotube tips. We deduce from the experimental data that field ionization of rubidium near nanotube tips takes place on a time scale faster than 10{sup -10} s. This property is particularly interesting for the development of fast atom detectors suitable for measuring correlations in ultracold quantum gases. We also describe an application of the detector as partial pressure gauge.

  13. Evaluation and operationalization of a novel forest detrainment modeling approach for computational snow avalanche simulation

    NASA Astrophysics Data System (ADS)

    Teich, M.; Feistl, T.; Fischer, J.; Bartelt, P.; Bebi, P.; Christen, M.; Grêt-Regamey, A.

    2013-12-01

    Two-dimensional avalanche simulation software operating in three-dimensional terrain are widely used for hazard zoning and engineering to predict runout distances and impact pressures of snow avalanche events. Mountain forests are an effective biological protection measure; however, the protective capacity of forests to decelerate or even to stop avalanches that start within forested areas or directly above the treeline is seldom considered in this context. In particular, runout distances of small- to medium-scale avalanches are strongly influenced by the structural conditions of forests in the avalanche path. This varying decelerating effect has rarely been addressed or implemented in avalanche simulation. We present an evaluation and operationalization of a novel forest detrainment modeling approach implemented in the avalanche simulation software RAMMS. The new approach accounts for the effect of forests in the avalanche path by detraining mass, which leads to a deceleration and runout shortening of avalanches. The extracted avalanche mass caught behind trees stops immediately and, therefore, is instantly subtracted from the flow and the momentum of the stopped mass is removed from the total momentum of the avalanche flow. This relationship is parameterized by the empirical detrainment coefficient K [Pa] which accounts for the braking power of different forest types per unit area. To define K dependent on specific forest characteristics, we simulated 40 well-documented small- to medium-scale avalanches which released in and ran through forests with varying K-values. Comparing two-dimensional simulation results with one-dimensional field observations for a high number of avalanche events and simulations manually is however time consuming and rather subjective. In order to process simulation results in a comprehensive and standardized way, we used a recently developed automatic evaluation and comparison method defining runout distances based on a pressure-based

  14. Monte Carlo simulations within avalanche rescue

    NASA Astrophysics Data System (ADS)

    Reiweger, Ingrid; Genswein, Manuel; Schweizer, Jürg

    2016-04-01

    Refining concepts for avalanche rescue involves calculating suitable settings for rescue strategies such as an adequate probing depth for probe line searches or an optimal time for performing resuscitation for a recovered avalanche victim in case of additional burials. In the latter case, treatment decisions have to be made in the context of triage. However, given the low number of incidents it is rarely possible to derive quantitative criteria based on historical statistics in the context of evidence-based medicine. For these rare, but complex rescue scenarios, most of the associated concepts, theories, and processes involve a number of unknown "random" parameters which have to be estimated in order to calculate anything quantitatively. An obvious approach for incorporating a number of random variables and their distributions into a calculation is to perform a Monte Carlo (MC) simulation. We here present Monte Carlo simulations for calculating the most suitable probing depth for probe line searches depending on search area and an optimal resuscitation time in case of multiple avalanche burials. The MC approach reveals, e.g., new optimized values for the duration of resuscitation that differ from previous, mainly case-based assumptions.

  15. Instrumentation for Kinetic-Inductance-Detector-Based Submillimeter Radio Astronomy

    NASA Astrophysics Data System (ADS)

    Duan, Ran

    A substantial amount of important scientific information is contained within astronomical data at the submillimeter and far-infrared (FIR) wavelengths, including information regarding dusty galaxies, galaxy clusters, and star-forming regions; however, these wavelengths are among the least-explored fields in astronomy because of the technological difficulties involved in such research. Over the past 20 years, considerable efforts have been devoted to developing submillimeter- and millimeter-wavelength astronomical instruments and telescopes. The number of detectors is an important property of such instruments and is the subject of the current study. Future telescopes will require as many as hundreds of thousands of detectors to meet the necessary requirements in terms of the field of view, scan speed, and resolution. A large pixel count is one benefit of the development of multiplexable detectors that use kinetic inductance detector (KID) technology. This dissertation presents the development of a KID-based instrument including a portion of the millimeter-wave bandpass filters and all aspects of the readout electronics, which together enabled one of the largest detector counts achieved to date in submillimeter-/millimeter-wavelength imaging arrays: a total of 2304 detectors. The work presented in this dissertation has been implemented in the MUltiwavelength Submillimeter Inductance Camera (MUSIC), a new instrument for the Caltech Submillimeter Observatory (CSO).

  16. Neuronal avalanches and coherence potentials

    NASA Astrophysics Data System (ADS)

    Plenz, D.

    2012-05-01

    The mammalian cortex consists of a vast network of weakly interacting excitable cells called neurons. Neurons must synchronize their activities in order to trigger activity in neighboring neurons. Moreover, interactions must be carefully regulated to remain weak (but not too weak) such that cascades of active neuronal groups avoid explosive growth yet allow for activity propagation over long-distances. Such a balance is robustly realized for neuronal avalanches, which are defined as cortical activity cascades that follow precise power laws. In experiments, scale-invariant neuronal avalanche dynamics have been observed during spontaneous cortical activity in isolated preparations in vitro as well as in the ongoing cortical activity of awake animals and in humans. Theory, models, and experiments suggest that neuronal avalanches are the signature of brain function near criticality at which the cortex optimally responds to inputs and maximizes its information capacity. Importantly, avalanche dynamics allow for the emergence of a subset of avalanches, the coherence potentials. They emerge when the synchronization of a local neuronal group exceeds a local threshold, at which the system spawns replicas of the local group activity at distant network sites. The functional importance of coherence potentials will be discussed in the context of propagating structures, such as gliders in balanced cellular automata. Gliders constitute local population dynamics that replicate in space after a finite number of generations and are thought to provide cellular automata with universal computation. Avalanches and coherence potentials are proposed to constitute a modern framework of cortical synchronization dynamics that underlies brain function.

  17. Hybrid AlGaN-SiC Avalanche Photodiode for Deep-UV Photon Detection

    NASA Technical Reports Server (NTRS)

    Aslam, Shahid; Herrero, Federico A.; Sigwarth, John; Goldsman, Neil; Akturk, Akin

    2010-01-01

    The proposed device is capable of counting ultraviolet (UV) photons, is compatible for inclusion into space instruments, and has applications as deep- UV detectors for calibration systems, curing systems, and crack detection. The device is based on a Separate Absorption and Charge Multiplication (SACM) structure. It is based on aluminum gallium nitride (AlGaN) absorber on a silicon carbide APD (avalanche photodiode). The AlGaN layer absorbs incident UV photons and injects photogenerated carriers into an underlying SiC APD that is operated in Geiger mode and provides current multiplication via avalanche breakdown. The solid-state detector is capable of sensing 100-to-365-nanometer wavelength radiation at a flux level as low as 6 photons/pixel/s. Advantages include, visible-light blindness, operation in harsh environments (e.g., high temperatures), deep-UV detection response, high gain, and Geiger mode operation at low voltage. Furthermore, the device can also be designed in array formats, e.g., linear arrays or 2D arrays (micropixels inside a superpixel).

  18. A mass spectrometer based explosives trace detector

    NASA Astrophysics Data System (ADS)

    Vilkov, Andrey; Jorabchi, Kaveh; Hanold, Karl; Syage, Jack A.

    2011-05-01

    In this paper we describe the application of mass spectrometry (MS) to the detection of trace explosives. We begin by reviewing the issue of explosives trace detection (ETD) and describe the method of mass spectrometry (MS) as an alternative to existing technologies. Effective security screening devices must be accurate (high detection and low false positive rate), fast and cost effective (upfront and operating costs). Ion mobility spectrometry (IMS) is the most commonly deployed method for ETD devices. Its advantages are compact size and relatively low price. For applications requiring a handheld detector, IMS is an excellent choice. For applications that are more stationary (e.g., checkpoint and alternatives to IMS are available. MS is recognized for its superior performance with regard to sensitivity and specificity, which translate to lower false negative and false positive rates. In almost all applications outside of security where accurate chemical analysis is needed, MS is usually the method of choice and is often referred to as the gold standard for chemical analysis. There are many review articles and proceedings that describe detection technologies for explosives. 1,2,3,4 Here we compare MS and IMS and identify the strengths and weaknesses of each method. - Mass spectrometry (MS): MS offers high levels of sensitivity and specificity compared to other technologies for chemical detection. Its traditional disadvantages have been high cost and complexity. Over the last few years, however, the economics have greatly improved and MS is now capable of routine and automated operation. Here we compare MS and IMS and identify the strengths and weaknesses of each method. - Ion mobility spectrometry (IMS): 5 MS-ETD Screening System IMS is similar in concept to MS except that the ions are dispersed by gas-phase viscosity and not by molecular weight. The main advantage of IMS is that it does not use a vacuum system, which greatly reduces the size, cost, and complexity

  19. Infrared Detector Activities at NASA Langley Research Center

    NASA Technical Reports Server (NTRS)

    Abedin, M. N.; Refaat, T. F.; Sulima, O. V.; Amzajerdian, F.

    2008-01-01

    Infrared detector development and characterization at NASA Langley Research Center will be reviewed. These detectors were intended for ground, airborne, and space borne remote sensing applications. Discussion will be focused on recently developed single-element infrared detector and future development of near-infrared focal plane arrays (FPA). The FPA will be applied to next generation space-based instruments. These activities are based on phototransistor and avalanche photodiode technologies, which offer high internal gain and relatively low noise-equivalent-power. These novel devices will improve the sensitivity of active remote sensing instruments while eliminating the need for a high power laser transmitter.

  20. Development of a NDVI detector based on optics and spectroscopy

    NASA Astrophysics Data System (ADS)

    Yang, Wei; Li, Minzan; Sun, Hong; Zhao, Ruijiao

    2012-01-01

    A NDVI detector is developed based on ground-based remote sensing, which uses proper wavebands and embeds a new optimization algorithm of nitrogen fertilization. The detector has two main units, optical unit and electronic unit. In optical unit there are four special different photoelectrical sensors used for detecting sunlight incidence and reflect light of plant canopy in red and NIR wavebands, respectively. Analog signals measured by sensors are amplified and then converted to digital in electronic unit. After processing the digital signal, NDVI of the plant can be calculated. Performance and stability experiments are conducted to cucumber plants in greenhouse. The results show that the detector has a good stability. In order to eliminate the error from sunlight a new artificial light source is suggested.

  1. Characterization of Advanced Avalanche Photodiodes for Water Vapor Lidar Receivers

    NASA Technical Reports Server (NTRS)

    Refaat, Tamer F.; Halama, Gary E.; DeYoung, Russell J.

    2000-01-01

    Development of advanced differential absorption lidar (DIAL) receivers is very important to increase the accuracy of atmospheric water vapor measurements. A major component of such receivers is the optical detector. In the near-infrared wavelength range avalanche photodiodes (APD's) are the best choice for higher signal-to-noise ratio, where there are many water vapor absorption lines. In this study, characterization experiments were performed to evaluate a group of silicon-based APD's. The APD's have different structures representative of different manufacturers. The experiments include setups to calibrate these devices, as well as characterization of the effects of voltage bias and temperature on the responsivity, surface scans, noise measurements, and frequency response measurements. For each experiment, the setup, procedure, data analysis, and results are given and discussed. This research was done to choose a suitable APD detector for the development of an advanced atmospheric water vapor differential absorption lidar detection system operating either at 720, 820, or 940 nm. The results point out the benefits of using the super low ionization ratio (SLIK) structure APD for its lower noise-equivalent power, which was found to be on the order of 2 to 4 fW/Hz(sup (1/2)), with an appropriate optical system and electronics. The water vapor detection systems signal-to-noise ratio will increase by a factor of 10.

  2. Nucleation and development of dendritic flux avalanches in superconducting films

    NASA Astrophysics Data System (ADS)

    Vestgården, Jørn Inge; Shantsev, Daniil; Galperin, Yuri; Henning Johansen, Tom

    2012-02-01

    The stability of superconducting films is threatened by thermomagnetic runaways commonly observed as abrupt dendritic flux avalanches. We report numerical simulations of the electrodynamics and thermal behavior of superconducting films, where the gradual flux penetration is interrupted by such avalanches. The simulation formalism is based on an efficient method for treating the nonlinear and nonlocal electrodynamics, and it handles both the slow flux creep dynamics prior to the avalanches and the transition to the many orders of magnitude faster instability regime. Then the temperature rises quickly above the critical temperature, and the avalanche develops fully in less than 100 nanoseconds, with an initial velocity of approximately 100 km/s. Both the morphology and speed of the avalanches are in excellent agreement with results from magneto-optical imaging experiments. The sample is seeded with randomly distributed disorder, which results in a significantly reduced threshold for onset of avalanches. Interaction with the material disorder also contributes to branching and irreprodusibility of the flux structures. However, disorder is not the main mechanism behind branching and dendritic structures are also found to develop in completely uniform samples.

  3. GEM-based detectors for thermal and fast neutrons

    NASA Astrophysics Data System (ADS)

    Croci, G.; Claps, G.; Cazzaniga, C.; Foggetta, L.; Muraro, A.; Valente, P.

    2015-06-01

    Lately the problem of 3He replacement for neutron detection stimulated an intense activity research on alternative technologies based on alternative neutron converters. This paper presents briefly the results obtained with new GEM detectors optimized for fast and thermal neutrons. For thermal neutrons, we realized a side-on GEM detector based on a series of boron-coated alumina sheets placed perpendicularly to the incident neutron beam direction. This prototype has been tested at n@BTF photo-production neutron facilty in order to test its effectiveness under a very high flux gamma background. For fast neutrons, we developed new GEM detectors (called nGEM) for the CNESM diagnostic system of the SPIDER NBI prototype for ITER (RFX-Consortium, Italy) and as beam monitor for fast neutrons lines at spallation sources. The nGEM is a Triple GEM gaseous detector equipped with a polyethylene layer used to convert fast neutrons into recoil protons through the elastic scattering process. This paper describes the results obtained by testing a medium size (30 × 25 cm2 active area) nGEM detector at the ISIS spallation source on the VESUVIO beam line.

  4. Avalanche effects near nanojunctions

    NASA Astrophysics Data System (ADS)

    Nandigana, Vishal V. R.; Aluru, N. R.

    2016-07-01

    In this article, we perform a computational investigation of a nanopore connected to external fluidic reservoirs of asymmetric geometries. The asymmetry between the reservoirs is achieved by changing the cross-sectional areas, and the reservoirs are designated as the micropore reservoir and macropore reservoir. When an electric field is applied, which is directed from the macropore towards the micropore reservoir, we observe local nonequilibrium chaotic current oscillations. The current oscillations originate at the micropore-nanopore interface owing to the local cascade of ions; we refer to this phenomenon as the "avalanche effects." We mathematically quantify chaos in terms of the maximum Lyapunov exponent. The maximum Lyapunov exponent exhibits a monotonic increase with the applied voltage and the macropore reservoir diameter. The temporal power spectra maps of the chaotic currents depict a low-frequency "1 /f "-type dynamics for the voltage chaos and "1 /f2 "-type dynamics for the macropore reservoir chaos. The results presented here offer avenues to manipulate ionic diodes and fluidic pumps.

  5. Avalanche effects near nanojunctions.

    PubMed

    Nandigana, Vishal V R; Aluru, N R

    2016-07-01

    In this article, we perform a computational investigation of a nanopore connected to external fluidic reservoirs of asymmetric geometries. The asymmetry between the reservoirs is achieved by changing the cross-sectional areas, and the reservoirs are designated as the micropore reservoir and macropore reservoir. When an electric field is applied, which is directed from the macropore towards the micropore reservoir, we observe local nonequilibrium chaotic current oscillations. The current oscillations originate at the micropore-nanopore interface owing to the local cascade of ions; we refer to this phenomenon as the "avalanche effects." We mathematically quantify chaos in terms of the maximum Lyapunov exponent. The maximum Lyapunov exponent exhibits a monotonic increase with the applied voltage and the macropore reservoir diameter. The temporal power spectra maps of the chaotic currents depict a low-frequency "1/f"-type dynamics for the voltage chaos and "1/f^{2}"-type dynamics for the macropore reservoir chaos. The results presented here offer avenues to manipulate ionic diodes and fluidic pumps. PMID:27575159

  6. Note: All solid-state high repetitive sub-nanosecond risetime pulse generator based on bulk gallium arsenide avalanche semiconductor switches

    NASA Astrophysics Data System (ADS)

    Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Fan, Yajun; Liu, Chunliang

    2016-08-01

    An all solid-state high repetitive sub-nanosecond risetime pulse generator featuring low-energy-triggered bulk gallium arsenide (GaAs) avalanche semiconductor switches and a step-type transmission line is presented. The step-type transmission line with two stages is charged to a potential of 5.0 kV also biasing at the switches. The bulk GaAs avalanche semiconductor switch closes within sub-nanosecond range when illuminated with approximately 87 nJ of laser energy at 905 nm in a single pulse. An asymmetric dipolar pulse with peak-to-peak amplitude of 9.6 kV and risetime of 0.65 ns is produced on a resistive load of 50 Ω. A technique that allows for repetition-rate multiplication of pulse trains experimentally demonstrated that the parallel-connected bulk GaAs avalanche semiconductor switches are triggered in sequence. The highest repetition rate is decided by recovery time of the bulk GaAs avalanche semiconductor switch, and the operating result of 100 kHz of the generator is discussed.

  7. Note: All solid-state high repetitive sub-nanosecond risetime pulse generator based on bulk gallium arsenide avalanche semiconductor switches.

    PubMed

    Hu, Long; Su, Jiancang; Ding, Zhenjie; Hao, Qingsong; Fan, Yajun; Liu, Chunliang

    2016-08-01

    An all solid-state high repetitive sub-nanosecond risetime pulse generator featuring low-energy-triggered bulk gallium arsenide (GaAs) avalanche semiconductor switches and a step-type transmission line is presented. The step-type transmission line with two stages is charged to a potential of 5.0 kV also biasing at the switches. The bulk GaAs avalanche semiconductor switch closes within sub-nanosecond range when illuminated with approximately 87 nJ of laser energy at 905 nm in a single pulse. An asymmetric dipolar pulse with peak-to-peak amplitude of 9.6 kV and risetime of 0.65 ns is produced on a resistive load of 50 Ω. A technique that allows for repetition-rate multiplication of pulse trains experimentally demonstrated that the parallel-connected bulk GaAs avalanche semiconductor switches are triggered in sequence. The highest repetition rate is decided by recovery time of the bulk GaAs avalanche semiconductor switch, and the operating result of 100 kHz of the generator is discussed. PMID:27587178

  8. Hydrazine Detectors Based On Raman Scattering

    NASA Technical Reports Server (NTRS)

    Rupich, Martin W.; Carrabba, Michael M.

    1992-01-01

    Goal of sensor-development program to measure concentrations as low as few parts per billion in continuous monitoring as well as peak concentrations up to hundreds of parts per million, such as encountered near leaks. Sensors based on Raman scattering from hydrazine or monomethyl hydrazine adsorbed on roughened metal or metal oxide substrates. Similar systems developed to detect nitrogen oxides and other gases.

  9. Application of PN and avalanche silicon photodiodes to low-level optical

    NASA Technical Reports Server (NTRS)

    Eppeldauer, G.; Schaefer, A. R.

    1988-01-01

    New approaches to the discovery of other planetary systems require very sensitive and stable detection techniques in order to succeed. Two methods in particular, the astrometric and the photometric methods, require this. To begin understanding the problems and limitations of solid state detectors regarding this application, preliminary experiments were performed at the National Bureau of Standards and a low light level detector characterization facility was built. This facility is briefly described, and the results of tests conducted in it are outlined. A breadboard photometer that was used to obtain stellar brightness ratio precision data is described. The design principles of PN and avalanche silicon photodiodes based on low light level measuring circuits are discussed.

  10. Ultra-low noise charge sensitive preamplifier for scintillation detection with avalanche photodiodes in PET applications

    SciTech Connect

    Schmitt, D.; Lecomte, R.; Lapointe, M.; Martel, G.; Carrier, C.; Karuta, B.; Duval, F.

    1987-02-01

    The need for compact, fast, low-noise front-end electronics in high resolution positron emission tomography (PET) has prompted this effort to design a preamplifier suitable for avalanche photodiode-based scintillation detectors. Due to the small signals from the detectors (< .03 rhoC/meV), a preamplifier with ultra-low noise performance in the 5 to 20 MHz range is essential to achieve the timing resolution required by the PET application. Out of many available technologies, a new third generation MOSFET was selected and implemented as input transistor in an original charge sensitive (CSP) design. Performance among the best reported to date are obtained. The new design was implemented as a dual-channel preamplifier in high density hybrid (thick film) technology.

  11. Zinc Oxide Nanorod Based Ultraviolet Detectors with Wheatstone Bridge Design

    NASA Astrophysics Data System (ADS)

    Vasudevan, Arun

    This research work, for the first time, investigated metal semiconductor-metal (MSM) zine oxide (ZnO) nanorod based ultra-violet (UV) detectors having a Wheatstone bridge design with a high responsivity at room temperature and above, as well as a responsivity that was largely independent of the change in ambient conditions. The ZnO nanorods which acted as the sensing element of the detector were grown by a chemical growth technique. Studies were conducted to determine the effects on ZnO nanorod properties by varying the concentration of the chemicals used for the rod growth. These studies showed how the rod diameter and the deposition of ZnO nanorods from the solution was controlled by varying the concentration of the chemicals used for the rod growth. Conventional MSM UV detectors were fabricated with ZnO nanorods grown under optimized conditions to determine the dependence of UV response on electrode dimension and rod dimension. These studies gave insights into the dependence of UV response on the width of the electrode, spacing between the electrodes, density of the rod growth, and length and diameter of the rods. The UV responsivity was affected by varying the number of times the seed layer was spin coated, by varying the spin speed of seed layer coating and by varying the annealing temperature of the seed and rod. Based on these studies, optimum conditions for the fabrication of Wheatstone bridge UV ZnO nanorod detectors were determined. The Wheatstone bridge ZnO nanorod UV detectors were fabricated in three different configurations, namely, symmetric, asymmetric, and quasi-symmetric. The transient responses of the symmetric, asymmetric and quasi-symmetric configurations at room temperature and above showed how the response stability differed. At high temperature the responsivity of quasi-symmetric Wheatstone bridge detector configuration did not drop after saturation and the responsivity drifted by 17% to 25% from the room temperature response

  12. Reversible Avalanches and Criticality in Amorphous Solids

    NASA Astrophysics Data System (ADS)

    Reichhardt, Charles

    2015-03-01

    Despite its importance for basic science and industry, the physical process that causes a solid to change its shape permanently under external deformation is still not well understood. In this paper we use molecular dynamics simulations of amorphous solids under oscillatory shear to study this phenomenon, and show that at a critical strain amplitude, the size of the cooperative atomic motion that allows for a permanent deformation diverges. We compare this non-equilibrium critical behavior to that of a ``front depinning'' transition. This viewpoint, based on fluctuations and statistics, is complementary to the dynamical ``transition to chaos'' which was previously identified at the same strain amplitude. Below this irreversibile-depinning transition, we observe large avalanches which are completely repetitive with each shear strain cycle. This suggests that while avalanches on their own do not cause irreversible deformation, it is likely that the irreversibility transition and the ``depinning-like'' transition are two aspects of the same phenomena. One implication is that the transition could be detected before the onset of irreversible flow by an analysis of the power spectra of avalanches. Work done in collaboration with Ido Regev, Karin Dahmen, John Weber, and Turab Lookman.

  13. Polycrystalline diamond based detector for Z-pinch plasma diagnosis

    SciTech Connect

    Liu Linyue; Zhao Jizhen; Chen Liang; Ouyang Xiaoping; Wang Lan

    2010-08-15

    A detector setup based on polycrystalline chemical-vapor-deposition diamond film is developed with great characteristics: low dark current (lower than 60 pA within 3 V/{mu}m), fast pulsed response time (rise time: 2-3 ns), flat spectral response (3-5 keV), easy acquisition, low cost, and relative large sensitive area. The characterizing data on Qiangguang-I accelerator show that this detector can satisfy the practical requirements in Z-pinch plasma diagnosis very well, which offers a promising prototype for the x-ray detection in Z-pinch diagnosis.

  14. A Weak Value Based QKD Protocol Robust Against Detector Attacks

    NASA Astrophysics Data System (ADS)

    Troupe, James

    2015-03-01

    We propose a variation of the BB84 quantum key distribution protocol that utilizes the properties of weak values to insure the validity of the quantum bit error rate estimates used to detect an eavesdropper. The protocol is shown theoretically to be secure against recently demonstrated attacks utilizing detector blinding and control and should also be robust against all detector based hacking. Importantly, the new protocol promises to achieve this additional security without negatively impacting the secure key generation rate as compared to that originally promised by the standard BB84 scheme. Implementation of the weak measurements needed by the protocol should be very feasible using standard quantum optical techniques.

  15. Universal ultrafast detector for short optical pulses based on graphene.

    PubMed

    Mittendorff, Martin; Kamann, Josef; Eroms, Jonathan; Weiss, Dieter; Drexler, Christoph; Ganichev, Sergey D; Kerbusch, Jochen; Erbe, Artur; Suess, Ryan J; Murphy, Thomas E; Chatterjee, Sangam; Kolata, Kolja; Ohser, Joachim; König-Otto, Jacob C; Schneider, Harald; Helm, Manfred; Winnerl, Stephan

    2015-11-01

    Graphene has unique optical and electronic properties that make it attractive as an active material for broadband ultrafast detection. We present here a graphene-based detector that shows 40-picosecond electrical rise time over a spectral range that spans nearly three orders of magnitude, from the visible to the far-infrared. The detector employs a large area graphene active region with interdigitated electrodes that are connected to a log-periodic antenna to improve the long-wavelength collection efficiency, and a silicon carbide substrate that is transparent throughout the visible regime. The detector exhibits a noise-equivalent power of approximately 100 µW·Hz(-½) and is characterized at wavelengths from 780 nm to 500 µm. PMID:26561141

  16. Experimental characterization of semiconductor-based thermal neutron detectors

    NASA Astrophysics Data System (ADS)

    Bedogni, R.; Bortot, D.; Pola, A.; Introini, M. V.; Lorenzoli, M.; Gómez-Ros, J. M.; Sacco, D.; Esposito, A.; Gentile, A.; Buonomo, B.; Palomba, M.; Grossi, A.

    2015-04-01

    In the framework of NESCOFI@BTF and NEURAPID projects, active thermal neutron detectors were manufactured by depositing appropriate thickness of 6LiF on commercially available windowless p-i-n diodes. Detectors with different radiator thickness, ranging from 5 to 62 μm, were manufactured by evaporation-based deposition technique and exposed to known values of thermal neutron fluence in two thermal neutron facilities exhibiting different irradiation geometries. The following properties of the detector response were investigated and presented in this work: thickness dependence, impact of parasitic effects (photons and epithermal neutrons), linearity, isotropy, and radiation damage following exposure to large fluence (in the order of 1012 cm-2).

  17. Characterization and Monte Carlo simulation of single ion Geiger mode avalanche diodes integrated with a quantum dot nanostructure

    NASA Astrophysics Data System (ADS)

    Sharma, Peter; Abraham, J. B. S.; Ten Eyck, G.; Childs, K. D.; Bielejec, E.; Carroll, M. S.

    Detection of single ion implantation within a nanostructure is necessary for the high yield fabrication of implanted donor-based quantum computing architectures. Single ion Geiger mode avalanche (SIGMA) diodes with a laterally integrated nanostructure capable of forming a quantum dot were fabricated and characterized using photon pulses. The detection efficiency of this design was measured as a function of wavelength, lateral position, and for varying delay times between the photon pulse and the overbias detection window. Monte Carlo simulations based only on the random diffusion of photo-generated carriers and the geometrical placement of the avalanche region agrees qualitatively with device characterization. Based on these results, SIGMA detection efficiency appears to be determined solely by the diffusion of photo-generated electron-hole pairs into a buried avalanche region. Device performance is then highly dependent on the uniformity of the underlying silicon substrate and the proximity of photo-generated carriers to the silicon-silicon dioxide interface, which are the most important limiting factors for reaching the single ion detection limit with SIGMA detectors. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  18. Beta ray spectroscopy based on a plastic scintillation detector/silicon surface barrier detector coincidence telescope

    NASA Astrophysics Data System (ADS)

    Horowitz, Y. S.; Hirning, C. R.; Yuen, P.; Aikens, M.

    1994-01-01

    Beta radiation is now recognized as a significant radiation safety problem and several international conferences have recently been devoted to the problems of mixed field beta/photon dosimetry. Conventional dosimetry applies algorithms to thermoluminescence dosimetry (TLD) multi-element badges which attempt to extract dose information based on the comparison of TL signals from ``thick/thin'' and/or ``bare/filtered'' elements. These may be grossly innacurate due to inadequate or non-existant knowledge of the energy spectrum of both the beta radiation and the accompanying photon field, as well as other factors. In this paper, we discuss the operation of a beta-ray energy spectrometer based on a two element, E × dE detector telescope intended to support dose algorithms with beta spectral information. Beta energies are measured via a 5 cm diameter × 2 cm thick BC-404 plastic scintillator preceded by a single, 100 μm thick, totally depleted, silicon dE detector. Photon events in the E detector are rejected by requiring a coincidence between the E and dE detectors. Photon rejection ratios vary from 225:1 at 1.25 MeV (60Co) to 360:1 at 0.36 MeV (133Ba). The spectrometer is capable of measuring electron energies from a lower energy coincidence threshold of approximately 125 keV to an upper limit of 3.5 MeV. This energy range spans the great majority of beta-emitting radionuclides in nuclear facilities.

  19. Performance of OOK and low-order PPM modulations in optical communications when using APD-based receivers. [Off-On Keying and Pulse Position Modulation using Avalanche PhotoDiodes

    NASA Technical Reports Server (NTRS)

    Abshire, J. B.

    1984-01-01

    The paper computes direct detection laser communications receiver performance when using avalanche photodiode (APD) detectors. The performances are compared in terms of bit error probability vs average signal required per bit when the transmitter uses either on-off keying (OOK) or low-order PPM formats. It is shown that QPPM requires 3 dB less signal than OOK, while BPPM requires the same or slightly more than OOK for the same performance. Optimum APD gain values range from 200 to 400. When using QPPM, k(eff) = 0.006, and optimum gain, 60 signal counts/bit are required at 500 Mbits/s for a 0.000001 bit error probability. It is concluded that QPPM may be an attractive signaling format for some fiber or free space laser communication applications.

  20. Skyrmion based microwave detectors and harvesting

    SciTech Connect

    Finocchio, G.; Giordano, A.; Ricci, M.; Burrascano, P.; Tomasello, R.; Lanuzza, M.; Puliafito, V.; Azzerboni, B.; Carpentieri, M.

    2015-12-28

    Magnetic skyrmions are topologically protected states that are very promising for the design of the next generation of ultra-low-power electronic devices. In this letter, we propose a magnetic tunnel junction based spin-transfer torque diode with a magnetic skyrmion as ground state and a perpendicular polarizer patterned as nano-contact for a local injection of the current. The key result is the possibility to achieve sensitivities (i.e., detection voltage over input microwave power) larger than 2000 V/W for optimized contact diameters. We also pointed out that large enough voltage controlled magnetocrystalline anisotropy could significantly improve the sensitivity. Our results can be very useful for the identification of a class of spin-torque diodes with a non-uniform ground state and to understand the fundamental physics of the skyrmion dynamical properties.

  1. Electro-thermal simulation of superconducting nanowire avalanche photodetectors

    SciTech Connect

    Marsili, F.; Najafi, F.; Herder, C.; Berggren, K. K.

    2011-01-01

    We developed an electrothermal model of NbN superconducting nanowire avalanche photodetectors (SNAPs) on sapphire substrates. SNAPs are single-photon detectors consisting of the parallel connection of N superconducting nanowires. We extrapolated the physical constants of the model from experimental data and we simulated the time evolution of the device resistance, temperature and current by solving two coupled electrical and thermal differential equations describing the nanowires. The predictions of the model were in good quantitative agreement with the experimental results.

  2. Photoacoustic-based detector for infrared laser spectroscopy

    NASA Astrophysics Data System (ADS)

    Scholz, L.; Palzer, S.

    2016-07-01

    In this contribution, we present an alternative detector technology for use in direct absorption spectroscopy setups. Instead of a semiconductor based detector, we use the photoacoustic effect to gauge the light intensity. To this end, the target gas species is hermetically sealed under excess pressure inside a miniature cell along with a MEMS microphone. Optical access to the cell is provided by a quartz window. The approach is particularly suitable for tunable diode laser spectroscopy in the mid-infrared range, where numerous molecules exhibit large absorption cross sections. Moreover, a frequency standard is integrated into the method since the number density and pressure inside the cell are constant. We demonstrate that the information extracted by our method is at least equivalent to that achieved using a semiconductor-based photon detector. As exemplary and highly relevant target gas, we have performed direct spectroscopy of methane at the R3-line of the 2v3 band at 6046.95 cm-1 using both detector technologies in parallel. The results may be transferred to other infrared-active transitions without loss of generality.

  3. Characterization of a GEM-based fast neutron detector

    NASA Astrophysics Data System (ADS)

    Esposito, B.; Marocco, D.; Villari, R.; Murtas, F.; Rodionov, R.

    2014-03-01

    The neutron efficiency of a Gas Electron Multiplier (GEM)-based detector designed for fast neutron measurements in fusion devices was determined through the combined use of Monte Carlo (MCNPX) calculations and analysis of deuterium-deuterium and deuterium-tritium neutron irradiation experiments. The detector, characterized by a triple GEM structure flushed with a Ar/CO2/CF4 - 45/15/40 gas mixture, features a digital read-out system and has two sub-units for the detection of 2.5+14 MeV neutrons and 14 MeV neutrons (UDD and UDT, respectively). The pulse height spectra (PHS) determined from the curves of experimental efficiency as a function of the detector's high voltage (HV) and the MCNPX-simulated PHS were compared using a fitting routine that finds the best match between the experimental and simulated PHS by assuming a parametric model for the relation between HV (that determines the detector's gain) and the energy deposited in the gas. This led to express the experimental neutron efficiency as a function of the discrimination level set on the deposited energy (energy threshold). The detector sensitivity to γ-rays was also analyzed and the operational range in which the γ-ray contribution to the signal is not negligible was determined. It is found that this detector can reach a maximum neutron efficiency of ~1×10-3 counts/n at 2.5 MeV (UDD sub-unit) and of ~4×10-3 counts/n at 14 MeV (UDT and UDD sub-units).

  4. Statistical Evaluation of Waveform Collapse Reveals Scale-Free Properties of Neuronal Avalanches

    PubMed Central

    Shaukat, Aleena; Thivierge, Jean-Philippe

    2016-01-01

    Neural avalanches are a prominent form of brain activity characterized by network-wide bursts whose statistics follow a power-law distribution with a slope near 3/2. Recent work suggests that avalanches of different durations can be rescaled and thus collapsed together. This collapse mirrors work in statistical physics where it is proposed to form a signature of systems evolving in a critical state. However, no rigorous statistical test has been proposed to examine the degree to which neuronal avalanches collapse together. Here, we describe a statistical test based on functional data analysis, where raw avalanches are first smoothed with a Fourier basis, then rescaled using a time-warping function. Finally, an F ratio test combined with a bootstrap permutation is employed to determine if avalanches collapse together in a statistically reliable fashion. To illustrate this approach, we recorded avalanches from cortical cultures on multielectrode arrays as in previous work. Analyses show that avalanches of various durations can be collapsed together in a statistically robust fashion. However, a principal components analysis revealed that the offset of avalanches resulted in marked variance in the time-warping function, thus arguing for limitations to the strict fractal nature of avalanche dynamics. We compared these results with those obtained from cultures treated with an AMPA/NMDA receptor antagonist (APV/DNQX), which yield a power-law of avalanche durations with a slope greater than 3/2. When collapsed together, these avalanches showed marked misalignments both at onset and offset time-points. In sum, the proposed statistical evaluation suggests the presence of scale-free avalanche waveforms and constitutes an avenue for examining critical dynamics in neuronal systems. PMID:27092071

  5. Statistical Evaluation of Waveform Collapse Reveals Scale-Free Properties of Neuronal Avalanches.

    PubMed

    Shaukat, Aleena; Thivierge, Jean-Philippe

    2016-01-01

    Neural avalanches are a prominent form of brain activity characterized by network-wide bursts whose statistics follow a power-law distribution with a slope near 3/2. Recent work suggests that avalanches of different durations can be rescaled and thus collapsed together. This collapse mirrors work in statistical physics where it is proposed to form a signature of systems evolving in a critical state. However, no rigorous statistical test has been proposed to examine the degree to which neuronal avalanches collapse together. Here, we describe a statistical test based on functional data analysis, where raw avalanches are first smoothed with a Fourier basis, then rescaled using a time-warping function. Finally, an F ratio test combined with a bootstrap permutation is employed to determine if avalanches collapse together in a statistically reliable fashion. To illustrate this approach, we recorded avalanches from cortical cultures on multielectrode arrays as in previous work. Analyses show that avalanches of various durations can be collapsed together in a statistically robust fashion. However, a principal components analysis revealed that the offset of avalanches resulted in marked variance in the time-warping function, thus arguing for limitations to the strict fractal nature of avalanche dynamics. We compared these results with those obtained from cultures treated with an AMPA/NMDA receptor antagonist (APV/DNQX), which yield a power-law of avalanche durations with a slope greater than 3/2. When collapsed together, these avalanches showed marked misalignments both at onset and offset time-points. In sum, the proposed statistical evaluation suggests the presence of scale-free avalanche waveforms and constitutes an avenue for examining critical dynamics in neuronal systems. PMID:27092071

  6. A MAPS based vertex detector for the STAR experiment at RHIC

    SciTech Connect

    Anderssen, E; Ritter, H G; Schambach, J; Sun, X; Szelezniak, M; Thomas, J; Vu, C; Wieman, H

    2011-09-11

    The STAR experiment at RHIC is in the process of upgrading the inner detector region of the experiment to improve the vertex resolution. We describe the current design of a MAPS based vertex detector, which is the innermost and highest resolution detector of the set of three planned upgrade detectors. This detector will enable the identification of decay vertices displaced from the interaction vertex by 100-150 {micro}m and extend the capabilities of the STAR detector in the heavy flavor domain. We present selected detector design characteristics and prototyping results, which help to validate the design in preparation for the construction of the detector.

  7. Correlations in avalanche critical points.

    PubMed

    Cerruti, Benedetta; Vives, Eduard

    2009-07-01

    Avalanche dynamics and related power-law statistics are ubiquitous in nature, arising in phenomena such as earthquakes, forest fires, and solar flares. Very interestingly, an analogous behavior is associated with many condensed-matter systems, such as ferromagnets and martensites. Bearing it in mind, we study the prototypical random-field Ising model at T=0. We find a finite correlation between waiting intervals and the previous avalanche size. This correlation is not found in other models for avalanches but it is experimentally found in earthquakes and in forest fires. Our study suggests that this effect occurs in critical points that are at the end of a first-order discontinuity separating two regimes: one with high activity from another with low activity. PMID:19658651

  8. Non-Geiger mode single photon detector with multiple amplification and gain control mechanisms

    SciTech Connect

    Nawar Rahman, Samia Hall, David; Lo, Yu-Hwa

    2014-05-07

    A new type of single photon detector, Multiple Amplification Gain with Internal Control (MAGIC), is proposed and analyzed using Monte Carlo simulations based on a physical model of the device. The MAGIC detector has two coupled amplification mechanisms, avalanche multiplication and bipolar gain, and the net gain is regulated by a built-in feedback mechanism. Compared to conventional Geiger mode single photon avalanche detectors (SPADs), the MAGIC detector produces a much greater single photon detection efficiency of nearly 100%, low bit-error-ratio for single photon signals, and a large dynamic range. All these properties are highly desirable for applications that require single photon sensitivity and are absent for conventional Geiger-mode SPADs.

  9. Characterization of an advanced harmonic subtraction single-photon detection system based on an InGaAs/InP avalanche diode

    NASA Astrophysics Data System (ADS)

    Bienfang, Joshua C.; Restelli, Alessandro

    2016-05-01

    We discuss the performance of a 1.25 GHz gated single-photon avalanche diode (SPAD) with bias gates of 150 ps FWHM and AC amplitude up to 25 V, a high-efficiency, high-speed SPAD system. This system uses an interferometric readout technique known as harmonic subtraction, and recent development efforts have enabled the use of up to the 4th harmonic of the gate to discriminate avalanche signals from the gate transient. With an improved design of the RF control system we have been able to demonstrate an ultra-low minimum detectable charge. We discuss the performance of this system, particularly its afterpulsing performance when counting at rates > 108 s-1. Systems of this type require unique characterization techniques, and we will discuss the methods we have developed for this purpose.

  10. Avalanche Collapse of Interdependent Networks

    NASA Astrophysics Data System (ADS)

    Baxter, G. J.; Dorogovtsev, S. N.; Goltsev, A. V.; Mendes, J. F. F.

    2012-12-01

    We reveal the nature of the avalanche collapse of the giant viable component in multiplex networks under perturbations such as random damage. Specifically, we identify latent critical clusters associated with the avalanches of random damage. Divergence of their mean size signals the approach to the hybrid phase transition from one side, while there are no critical precursors on the other side. We find that this discontinuous transition occurs in scale-free multiplex networks whenever the mean degree of at least one of the interdependent networks does not diverge.

  11. Avalanche-like behavior in ciliary import

    PubMed Central

    Ludington, William B.; Wemmer, Kimberly A.; Lechtreck, Karl F.; Witman, George B.; Marshall, Wallace F.

    2013-01-01

    Cilia and flagella are microtubule-based organelles that protrude from the cell body. Ciliary assembly requires intraflagellar transport (IFT), a motile system that delivers cargo from the cell body to the flagellar tip for assembly. The process controlling injections of IFT proteins into the flagellar compartment is, therefore, crucial to ciliogenesis. Extensive biochemical and genetic analyses have determined the molecular machinery of IFT, but these studies do not explain what regulates IFT injection rate. Here, we provide evidence that IFT injections result from avalanche-like releases of accumulated IFT material at the flagellar base and that the key regulated feature of length control is the recruitment of IFT material to the flagellar base. We used total internal reflection fluorescence microscopy of IFT proteins in live cells to quantify the size and frequency of injections over time. The injection dynamics reveal a power-law tailed distribution of injection event sizes and a negative correlation between injection size and frequency, as well as rich behaviors such as quasiperiodicity, bursting, and long-memory effects tied to the size of the localized load of IFT material awaiting injection at the flagellar base, collectively indicating that IFT injection dynamics result from avalanche-like behavior. Computational models based on avalanching recapitulate observed IFT dynamics, and we further show that the flagellar Ras-related nuclear protein (Ran) guanosine 5'-triphosphate (GTP) gradient can in theory act as a flagellar length sensor to regulate this localized accumulation of IFT. These results demonstrate that a self-organizing, physical mechanism can control a biochemically complex intracellular transport pathway. PMID:23431147

  12. Dose Imaging Detectors for Radiotherapy Based on Gas Electron Multipliers

    PubMed Central

    Klyachko, A.V.; Friesel, D.L.; Kline, C.; Liechty, J.; Nichiporov, D.F.; Solberg, K.A.

    2010-01-01

    New techniques in charged particle therapy and widespread use of modern dynamic beam delivery systems demand new beam monitoring devices as well as accurate 2D dosimetry systems to verify the delivered dose distribution. We are developing dose imaging detectors based on gas electron multipliers (GEM) with the goal of improving dose measurement linearity, position and timing resolution, and to ultimately allow pre-treatment verification of dose distributions and dose delivery monitoring employing scanning beam technology. A prototype 10×10 cm2 double-GEM detector has been tested in the 205 MeV proton beam using electronic and optical readout modes. Preliminary results with electronic cross-strip readout demonstrate fast response and single-pixel (4 mm) position resolution. In optical readout mode, the line spread function of the detector was found to have σ=0.7 mm. In both readout modes, the detector response was linear up to dose rates of 50 Gy/min, with adequate representation of the Bragg peak in depth-dose profile measurements. PMID:21528010

  13. Monitoring of a debris-covered and avalanche-fed glacier in the Eastern Italian Alps using ground-based SfM-MVS

    NASA Astrophysics Data System (ADS)

    Piermattei, Livia; Carturan, Luca; Cazorzi, Federico; Colucci, Renato R.; Dalla Fontana, Giancarlo; Forte, Emanuele

    2015-04-01

    The Montasio Occidentale glacier is a 0.07 km2 wide, avalanche-fed glacier located at very low-altitude (1860-2050 m a.s.l.) in the Eastern Italian Alps. The glacier is still active and shows a detectable mass transfer from the accumulation area to the lower ablation area, which is covered by a thick debris mantle. Geometric changes and mass balance have been monitored starting in 2010, combining glaciological methods and high-resolution geodetic surveying with a terrestrial laser scanner (TLS). The TLS technique has proved to be very effective in determining the volume change of this glacier, but presents several limitations as high costs, high level of specialized training and low portability. On the other hand, the recent improvements in close-range photogrammetric techniques like the Structure from Motion (SfM), combined with dense image matching algorithms as Multi View Stereo (MVS), make them competitive for high quality 3D models production. The purpose of this work was to apply ground-based photogrammetric surveys for the monitoring of the annual mass balance and surface processes of Montasio Occidentale glacier. A consumer-grade SLR camera and the SfM-MVS software PhotoScan were used to detect the changes in the surface topography of the glacier from 2012 to 2014. Different data acquisition settings were tested, in order to optimize the quality and the spatial coverage of the 3D glacier model. The accuracy of the image-based 3D models was estimated in stable areas outside the glacier, using the TLS 3D model as reference. A ground penetrating radar (GPR) survey was carried out in 2014, simultaneously to the photogrammetric survey, that was used to compare the snow height estimations obtained by photogrammetry with those obtained by geophysics. The achieved results indicate that the resolution and accuracy of the 3D models generated by the SfM-MVS technique are comparable with those obtained from TLS surveys. Consequently, almost identical volumetric changes

  14. Performances of a HGCDTE APD Based Detector with Electric Cooling for 2-μm DIAL/IPDA Applications

    NASA Astrophysics Data System (ADS)

    Dumas, A.; Rothman, J.; Gibert, F.; Lasfargues, G.; Zanatta, J.-P.; Edouart, D.

    2016-06-01

    In this work we report on design and testing of an HgCdTe Avalanche Photodiode (APD) detector assembly for lidar applications in the Short Wavelength Infrared Region (SWIR : 1,5 - 2 μm). This detector consists in a set of diodes set in parallel -making a 200 μm large sensitive area- and connected to a custom high gain TransImpedance Amplifier (TIA). A commercial four stages Peltier cooler is used to reach an operating temperature of 185K. Crucial performances for lidar use are investigated : linearity, dynamic range, spatial homogeneity, noise and resistance to intense illumination.

  15. A VXIbus based trigger for the CLAS detector at CEBAF

    SciTech Connect

    Doughty, D.C. Jr.; Englert, J.; Hale, R.; Lemon, S. ); Leung, P. ); Cuevas, C.; Joyce, D. )

    1992-04-01

    This paper discusses a VXIbus based first level triggering system for the CLAS detector at CEBAF which has been designed and prototyped. It uses pipelining and a triple memory lookup to produce a dead-timeless trigger decision with an average latency of 110 ns and a jitter of 20 ns. The VXIbus Extended Start/Stop triggering protocols allow sub-nanosecond time synchronization.

  16. A VXIbus based trigger for the CLAS detector at CEBAF

    SciTech Connect

    D.C. Doughty, Jr.; J. Englert; R. Hale; S. Lemon; P. Leung; C. Cuevas; D. Joyce

    1992-04-01

    A VXIbus based first level triggering system for the CLAS detector at CEBAF has been designed and prototyped. It uses pipelining and a triple memory lookup to produce a dead-timeless trigger decision with an average latency of 110 nS and a jitter of 20 nS. The VXIbus Extended Start/Stop triggering protocols allow sub-nanosecond time synchronization.

  17. A risk-based approach to flammable gas detector spacing.

    PubMed

    Defriend, Stephen; Dejmek, Mark; Porter, Leisa; Deshotels, Bob; Natvig, Bernt

    2008-11-15

    Flammable gas detectors allow an operating company to address leaks before they become serious, by automatically alarming and by initiating isolation and safe venting. Without effective gas detection, there is very limited defense against a flammable gas leak developing into a fire or explosion that could cause loss of life or escalate to cascading failures of nearby vessels, piping, and equipment. While it is commonly recognized that some gas detectors are needed in a process plant containing flammable gas or volatile liquids, there is usually a question of how many are needed. The areas that need protection can be determined by dispersion modeling from potential leak sites. Within the areas that must be protected, the spacing of detectors (or alternatively, number of detectors) should be based on risk. Detector design can be characterized by spacing criteria, which is convenient for design - or alternatively by number of detectors, which is convenient for cost reporting. The factors that influence the risk are site-specific, including process conditions, chemical composition, number of potential leak sites, piping design standards, arrangement of plant equipment and structures, design of isolation and depressurization systems, and frequency of detector testing. Site-specific factors such as those just mentioned affect the size of flammable gas cloud that must be detected (within a specified probability) by the gas detection system. A probability of detection must be specified that gives a design with a tolerable risk of fires and explosions. To determine the optimum spacing of detectors, it is important to consider the probability that a detector will fail at some time and be inoperative until replaced or repaired. A cost-effective approach is based on the combined risk from a representative selection of leakage scenarios, rather than a worst-case evaluation. This means that probability and severity of leak consequences must be evaluated together. In marine and

  18. Multi-element double ring infrared detector based on InSb

    NASA Astrophysics Data System (ADS)

    Li, Mo; Lv, Hui; Guo, Li; Liu, Zhu

    2015-10-01

    A multi-element double ring infrared detector based on InSb p-n photodiodes is presented. The presented detector includes an outer ring detector and an inner ring detector. Each ring consist 10 detector elements, five mid-wave infrared detector elements and five short wave infrared detector elements. Two wavebands of 3.5-5 μm and 1.5-3 μm in mid-wave infrared and short wave infrared are adopted. The mid-wave infrared and short wave infrared detector elements are arranged alternately and close to each other to form detection pair. Between the adjacent detector elements, there is an interval to avoid cross talk. Dual band filter thin films are directly coated on the photodiode surface to form a dual band infrared detector. The double ring detector which can perform dual band IR counter-countermeasures can track target effectively under infrared countermeasure conditions.

  19. A Methodology To Allow Avalanche Forecasting on an Information Retrieval System.

    ERIC Educational Resources Information Center

    Purves, R. S.; Sanderson, M.

    1998-01-01

    Presents adaptations and tests undertaken to allow an information retrieval system to forecast the likelihood of avalanches on a particular day; the forecasting process uses historical data of the weather and avalanche conditions for a large number of days. Describes a method for adapting these data into a form usable by a text-based IR system and…

  20. Lumped transmission line avalanche pulser

    DOEpatents

    Booth, R.

    1995-07-18

    A lumped linear avalanche transistor pulse generator utilizes stacked transistors in parallel within a stage and couples a plurality of said stages, in series with increasing zener diode limited voltages per stage and decreasing balanced capacitance load per stage to yield a high voltage, high and constant current, very short pulse. 8 figs.

  1. Lumped transmission line avalanche pulser

    DOEpatents

    Booth, Rex

    1995-01-01

    A lumped linear avalanche transistor pulse generator utilizes stacked transistors in parallel within a stage and couples a plurality of said stages, in series with increasing zener diode limited voltages per stage and decreasing balanced capacitance load per stage to yield a high voltage, high and constant current, very short pulse.

  2. Statistics of electron avalanches and bursts in low pressure gases below the breakdown voltage

    SciTech Connect

    Donko, Z.

    1995-12-31

    Avalanches in different types of dynamical systems have been subject of recent interest. Avalanches building up in gases play an important role in radiation detectors and in the breakdown process of gas discharges. We have used computer simulation to study statistical properties of electron avalanches and bursts (sequences of avalanches) in a gas subjected to a homogeneous electric field. Helium was used as buffer gas, but we believe that our results are more general. The bursts were initiated by injecting low energy electrons into the gas. We applied Monte Carlo procedure to trace the trajectories of electrons. The elementary processes considered in the model were anisotropic elastic scattering of electrons from He atoms, electron impact excitation and ionization of He atoms. The electrons were traced until the are reached the perfectly absorbing anode.

  3. Single photon avalanche diode radiation tests

    NASA Astrophysics Data System (ADS)

    Kodet, Jan; Prochazka, Ivan; Blazej, Josef; Sun, Xiaoli; Cavanaugh, John

    2012-12-01

    The single photon counting diodes are recently planned for applications in deep space missions. That is why the proton radiation and gamma ray radiation tests of silicon based single photon avalanche diodes were measured and compared. The main characteristic that changed after the irradiation was effective dark count rate, which was measured using actively quenching and gating circuit. The radiation reached 6.5 krad at 53 MeV protons energy and 34 krad using gamma ray radiation source 60Co. The annealing rates were monitored at room temperature and at 60 °C.

  4. Smartphone-based fluorescence detector for mHealth.

    PubMed

    Balsam, Joshua; Bruck, Hugh Alan; Rasooly, Avraham

    2015-01-01

    We describe here a compact smartphone-based fluorescence detector for mHealth. A key element to achieving high sensitivity using low sensitivity phone cameras is a capillary array, which increases sensitivity by 100×. The capillary array was combined with a white LED illumination system to enable wide spectra fluorescent excitation in the range of 450-740 nm. The detector utilizes an orthographic projection system to form parallel light projection images from the capillaries at a close distance via an object-space telecentric lens configuration that reduces the total lens-to-object distance while maintaining uniformity in measurement between capillaries. To further increase the limit of detection (LOD), a computational image processing approach was employed to decrease the level of noise. This enables an additional 5-10× decrease in LOD. This smartphone-based detector was used to measure serial dilutions of fluorescein with a LOD of 1 nM with image stacking and 10 nM without image stacking, similar to the LOD obtained with a commercial plate reader. Moreover, the capillary array required a sample volume of less than 10 μl, which is an order of magnitude less than the 100 μl required for the plate reader.As fluorescence detection is widely used in sensitive biomedical assays, the approach described here has the potential to increase mHealth clinical utility, especially for telemedicine and for resource-poor settings in global health applications. PMID:25626543

  5. Studying inflation with future space-based gravitational wave detectors

    SciTech Connect

    Jinno, Ryusuke; Moroi, Takeo; Takahashi, Tomo E-mail: moroi@phys.s.u-tokyo.ac.jp

    2014-12-01

    Motivated by recent progress in our understanding of the B-mode polarization of cosmic microwave background (CMB), which provides important information about the inflationary gravitational waves (IGWs), we study the possibility to acquire information about the early universe using future space-based gravitational wave (GW) detectors. We perform a detailed statistical analysis to estimate how well we can determine the reheating temperature after inflation as well as the amplitude, the tensor spectral index, and the running of the inflationary gravitational waves. We discuss how the accuracies depend on noise parameters of the detector and the minimum frequency available in the analysis. Implication of such a study on the test of inflation models is also discussed.

  6. Reconstruction algorithms for optoacoustic imaging based on fiber optic detectors

    NASA Astrophysics Data System (ADS)

    Lamela, Horacio; Díaz-Tendero, Gonzalo; Gutiérrez, Rebeca; Gallego, Daniel

    2011-06-01

    Optoacoustic Imaging (OAI), a novel hybrid imaging technology, offers high contrast, molecular specificity and excellent resolution to overcome limitations of the current clinical modalities for detection of solid tumors. The exact time-domain reconstruction formula produces images with excellent resolution but poor contrast. Some approximate time-domain filtered back-projection reconstruction algorithms have also been reported to solve this problem. A wavelet transform implementation filtering can be used to sharpen object boundaries while simultaneously preserving high contrast of the reconstructed objects. In this paper, several algorithms, based on Back Projection (BP) techniques, have been suggested to process OA images in conjunction with signal filtering for ultrasonic point detectors and integral detectors. We apply these techniques first directly to a numerical generated sample image and then to the laserdigitalized image of a tissue phantom, obtaining in both cases the best results in resolution and contrast for a waveletbased filter.

  7. Microfabricated cantilever-based detector for molecular beam experiments

    NASA Astrophysics Data System (ADS)

    Bachels, T.; Schäfer, R.

    1998-11-01

    A low cost detector for particles in molecular beam experiments is presented which can easily be mounted in a molecular beam apparatus. The detector is based on microfabricated cantilevers, which can be employed either as single sensors or as sensor arrays. The single cantilever technique has been used to measure the absolute number of atoms coming out of a pulsed laser vaporization cluster source. The particles are detected by the shift of the thermally excited resonance frequency of the cantilever due to the cluster deposition. We have determined with the single cantilever the ratio of neutral to ionized clusters and we have investigated the cluster generation at different source conditions. In addition to this, a microfabricated cantilever array has been used to measure molecular beam profiles, which opens new possibilities for molecular beam deflection experiments.

  8. Heterodyne detection with mismatch correction based on array detector

    NASA Astrophysics Data System (ADS)

    Dong, Hongzhou; Li, Guoqiang; Yang, Ruofu; Yang, Chunping; Ao, Mingwu

    2016-07-01

    Based on an array detector, a new heterodyne detection system, which can correct the mismatches of amplitude and phase between signal and local oscillation (LO) beams, is presented in this paper. In the light of the fact that, for a heterodyne signal, there is a certain phase difference between the adjacent two samples of analog-to-digital converter (ADC), we propose to correct the spatial phase mismatch by use of the time-domain phase difference. The corrections can be realized by shifting the output sequences acquired from the detector elements in the array, and the steps of the shifting depend on the quantity of spatial phase mismatch. Numerical calculations of heterodyne efficiency are conducted to confirm the excellent performance of our system. Being different from previous works, our system needs not extra optical devices, so it provides probably an effective means to ease the problem resulted from the mismatches.

  9. Heterodyne detection with mismatch correction base on array detector

    NASA Astrophysics Data System (ADS)

    Hongzhou, Dong; Guoqiang, Li; Ruofu, Yang; Chunping, Yang; Mingwu, Ao

    2016-07-01

    Based on an array detector, a new heterodyne detection system, which can correct the mismatches of amplitude and phase between signal and local oscillation (LO) beams, is presented in this paper. In the light of the fact that, for a heterodyne signal, there is a certain phase difference between the adjacent two samples of analog-to-digital converter (ADC), we propose to correct the spatial phase mismatch by use of the time-domain phase difference. The corrections can be realized by shifting the output sequences acquired from the detector elements in the array, and the steps of the shifting depend on the quantity of spatial phase mismatch. Numerical calculations of heterodyne efficiency are conducted to confirm the excellent performance of our system. Being different from previous works, our system needs not extra optical devices, so it provides probably an effective means to ease the problem resulted from the mismatches.

  10. Undersampling Correction for Array Detector-Based Satellite Spectrometers

    NASA Technical Reports Server (NTRS)

    Chance, Kelly; Kurosu, Thomas P.; Sioris, Christopher E.

    2004-01-01

    Array detector-based instruments are now fundamental to measurements of ozone and other atmospheric trace gases from space in the ultraviolet, visible, and infrared. The present generation of such instruments suffers, to a greater or lesser degree, from undersampling of the spectra, leading to difficulties in the analysis of atmospheric radiances. We provide extended analysis of the undersampling suffered by modem satellite spectrometers, which include Global Ozone Monitoring Experiment (GOME), Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), Ozone Monitoring Instrument (OMI), and Ozone Mapping and Profiler Suite (OMPS). The analysis includes basic undersampling, the effects of binning into separate detector pixels, and the application of high-resolution Fraunhofer spectral data to correct for undersampling in many useful cases.

  11. Prototype of a large neutron detector based on MWPC

    NASA Astrophysics Data System (ADS)

    Tian, LiChao; Qi, HuiRong; Sun, ZhiJia; Wang, YanFeng; Zhang, Jian; Liu, RongGuang; Zhao, YuBin; Zhang, HongYu; Zhao, DongXu; Dong, Jing; Xie, Wan; Yang, GuiAn; Ouyang, Qun; Chen, YuanBo

    2014-11-01

    A prototype of large-area position sensitive neutron detector was designed and constructed according to the requirements of the Small-Angle Scattering spectrometer of China Spallation Neutron Source (CSNS). The detector was based on the 3He neutron convertor and MWPC with an effective area of 650 mm×650 mm. A prototype was completed and tested with 55Fe X-ray.The high-pressure vessel was designed and constructed with high-strength aluminum alloy. A position resolution of about 4.6 mm×2.3 mm (FWHM) and efficiency > 65% for neutrons with wavelength of 1.8 Å was determined after the operational gas filled.

  12. Improved x-ray detection and particle identification with avalanche photodiodes

    SciTech Connect

    Diepold, Marc Franke, Beatrice; Götzfried, Johannes; Hänsch, Theodor W.; Krauth, Julian J.; Mulhauser, Françoise; Nebel, Tobias; Pohl, Randolf; Fernandes, Luis M. P.; Amaro, Fernando D.; Gouvea, Andrea L.; Monteiro, Cristina M. B.; Santos, Joaquim M. F. dos; Machado, Jorge; Amaro, Pedro; Santos, José Paulo; and others

    2015-05-15

    Avalanche photodiodes are commonly used as detectors for low energy x-rays. In this work, we report on a fitting technique used to account for different detector responses resulting from photoabsorption in the various avalanche photodiode layers. The use of this technique results in an improvement of the energy resolution at 8.2 keV by up to a factor of 2 and corrects the timing information by up to 25 ns to account for space dependent electron drift time. In addition, this waveform analysis is used for particle identification, e.g., to distinguish between x-rays and MeV electrons in our experiment.

  13. Sediment Transport by Spring Avalanches in the Southern Swiss Alps

    NASA Astrophysics Data System (ADS)

    Egloff, J. M.; Hunziker, M.; Moore, J. R.; Christen, M.

    2010-12-01

    Dense wet-snow avalanches breaking through to the base of the snow pack or overriding snow-free surfaces can entrain basal material and act as important agents of sediment transport in steep Alpine catchments. As part of an ongoing study, we investigated two debris fans in the Matter Valley of southern Switzerland during spring 2009 and 2010, with emphasis on quantifying avalanche sediment transport. Deposited debris ranged from soil parcels and plant material to cobbles and boulders greater than 1 m3. Large boulders were generally angular and fresh with clear signs of recent impacts. The seasonal sediment load transported by avalanches was estimated at one fan by sampling the debris content within a number of representative areas, and then extrapolating the cumulative volume. Results reveal a total transported sediment volume of ~150 m3 in 2009 and ~15 m3 in 2010, which likely reflects varying snowfall and avalanche frequency between years. When distributed over the deposition area on the fan, these results imply an average accumulated sediment thickness of 12 mm in 2009 and 3 mm in 2010. Calculated catchment-wide erosion rates are ~0.1 mm/yr for 2009 and ~0.01 mm/yr for 2010. Cross-sections through avalanche debris revealed that transported sediment generally resides on top of the snow surface. As the avalanches melt, entrained sediment is set down gently, often resulting in precariously balanced boulders and rows of blocks perched on the walls of the fan’s channels. In flat lying areas, snowmelt resulted in sparse sediment deposits with no clear structure or sorting. Observations show that the fan surface is usually protected from erosion by snow and older avalanche deposits, which provide a smooth gliding plane for new events. Within the bedrock gulley adjacent to the fan, and in the avalanche source region above, signs of abrasive wear were evident on exposed bedrock surfaces. These include rounded and scoured bedrock, fresh signs of boulder impacts, and

  14. Optical sensors based on the molecular condensation nuclei detector

    NASA Astrophysics Data System (ADS)

    Kuptsov, Vladimir D.; Katelevsky, Vadim Y.; Valyukhov, Vladimir P.

    2015-05-01

    Molecular condensation nuclei (MCN) detector is a specialized optical sensor which provides for monitoring of various chemicals impurity in the environment and diagnosis of diseases in human exhaled air ("electronic nose" biosensor). Structurally MCN detector is included in the highly sensitive gas analyzers based on MCN method. The article describes the fundamental principles, specific features and application fields of the advanced highly sensitive MCN method. The MCN method is based on the application of various physico-chemical processes to the flow of a gas containing impurities. As a result of these processes aerosol particle that are about 106 times larger than the original molecule of the impurity are produced. The ability of the aerosol particle to scatter incident light also increases ~1014÷1016 times compared with the original molecule and the aerosol particle with the molecule of the impurity in the center is easily detected by light scattering inside a photometer. By measuring of the light scattering intensity is determined concentration of chemical impurities in the air. Aerosol particles in the MCN detector are formed in the condensing devices through overgrowth of the molecule detectable impurity by molecules so-called «developer» substance. At the final stage of the analysis in the MCN detector is measured light scattering by aerosol particles which is proportional to the concentration of determined impurities in the environment. For calculations of the scattered radiation is applicable Mie's theory considering the scattering of light by spherical particles whose size is comparable to the wavelength of light. We have determined that the light scattering by aerosol particles is interferometric and is comparable within an order of magnitude with light scattering by the air inside a photometer. The detection threshold for the target component of the gas analyzer is attained at the spontaneous ionization background level and not at the limiting

  15. Experimental Avalanches in a Rotating Drum

    NASA Astrophysics Data System (ADS)

    Hubard, Aline; O'Hern, Corey; Shattuck, Mark

    We address the question of universality in granular avalanches and the system size effects on it. We set up an experiment made from a quasi-two-dimensional rotating drum half-filled with a monolayer of stainless-steel spheres. We measure the size of the avalanches created by the increased gravitational stress on the pile as we quasi-statically rotate the drum. We find two kinds of avalanches determined by the drum size. The size and duration distributions of the avalanches that do not span the whole system follow a power law and the avalanche shapes are self-similar and nearly parabolic. The distributions of the avalanches that span the whole system are limited by the maximal amount of potential energy stored in the system at the moment of the avalanche. NSF CMMI-1462439, CMMI-1463455.

  16. SENTIRAD—An innovative personal radiation detector based on a scintillation detector and a silicon photomultiplier

    NASA Astrophysics Data System (ADS)

    Osovizky, A.; Ginzburg, D.; Manor, A.; Seif, R.; Ghelman, M.; Cohen-Zada, I.; Ellenbogen, M.; Bronfenmakher, V.; Pushkarsky, V.; Gonen, E.; Mazor, T.; Cohen, Y.

    2011-10-01

    The alarming personal radiation detector (PRD) is a device intended for Homeland Security (HLS) applications. This portable device is designed to be worn or carried by security personnel to detect photon-emitting radioactive materials for the purpose of crime prevention. PRD is required to meet the scope of specifications defined by various HLS standards for radiation detection. It is mandatory that the device be sensitive and simultaneously small, pocket-sized, of robust mechanical design and carriable on the user's body. To serve these specialized purposes and requirements, we developed the SENTIRAD, a new radiation detector designed to meet the performance criteria established for counterterrorist applications. SENTIRAD is the first commercially available PRD based on a CsI(Tl) scintillation crystal that is optically coupled with a silicon photomultiplier (SiPM) serving as a light sensor. The rapidly developing technology of SiPM, a multipixel semiconductor photodiode that operates in Geiger mode, has been thoroughly investigated in previous studies. This paper presents the design considerations, constraints and radiological performance relating to the SENTIRAD radiation sensor.

  17. Enhanced Red and Near Infrared Detection in Flow Cytometry Using Avalanche Photodiodes

    PubMed Central

    Lawrence, William G.; Varadi, Gyula; Entine, Gerald; Podniesinski, Edward; Wallace, Paul K.

    2008-01-01

    Background Polychromatic flow cytometry enables detailed identification of cell phenotype using multiple fluorescent parameters. The photomultiplier tubes used to detect fluorescence in current instruments limit the sensitivity in the long wavelength spectral range. We demonstrate the flow cytometric applications of silicon avalanche photodiodes, which have improved red sensitivity and a working fluorescence detection range beyond 1000 nm. Methods A comparison of the wavelength dependent performance of the avalanche photodiode and photomultiplier tube was carried out using pulsed light emitting diode sources, calibrated test beads and biological samples. A breadboard flow cytometer test bench was constructed to compare the performance of photomultiplier tubes and avalanche photodiode detectors. The avalanche photodiode used an additional amplifier stage to match the internal gain of the photomultiplier tube. Results The resolution of the avalanche photodiode and photomultiplier tube was compared for flow cytometry applications using a pulsed light emitting diode source over the 500 nm to 1060 nm spectral range. These measurements showed the relative changes in the signal to noise performance of the APD and PMT over a broad spectral range. Both the avalanche photodiode and photomultiplier tubes were used to measure the signal to noise response for a set of 6 peak calibration beads over the 530 to 800 nm wavelength range. CD4 positive cells labeled with antibody conjugated phycoerythrin or 800 nm quantum dots were identified by simultaneous detection using the avalanche photodiode and the photomultiplier tube. The ratios of the intensities of the CD4− and CD4+ populations were found to be similar for both detectors in the visible wavelengths, but only the avalanche photodiode was able to separate these populations at wavelengths above 800 nm. Conclusions These measurements illustrate the differences in APD and PMT performance at different wavelengths and signal

  18. Retrieving avalanche basal friction law parameters from high rate positioning of avalanches

    NASA Astrophysics Data System (ADS)

    Pulfer, Gaëtan; Naaim, Mohamed; Thibert, Emmanuel; Soruco, Alvaro

    2015-04-01

    The Voellmy avalanche basal friction parameters are retrieved from high rate positioning of artificially released avalanches. Avalanche fronts were tracked thanks to an accurate photogrammetric system set up at the Lautaret full-scale avalanche test-site (French Alps). Couples of images were acquired at 1 frame per second with 2 APS-C DSLR synchronized cameras set at 800 meters from the avalanche track. The avalanche height and velocity are also measured at a fixed location in the avalanche track. Rheological parameters of the avalanche flow are reconstructed by an inverse optimization method using these in situ data. The direct model is a Saint-Venant type model were basal friction is parameterized according to the Voellmy's friction law. A Sensitivity analysis of the friction parameters is conducted and theirs uncertainty are determined. Finally the results obtained from different avalanches are compared and discussed.

  19. Correcting for accidental correlations in saturated avalanche photodiodes.

    PubMed

    Grieve, J A; Chandrasekara, R; Tang, Z; Cheng, C; Ling, A

    2016-02-22

    In this paper we present a general method for estimating rates of accidental coincidence between a pair of single photon detectors operated within their saturation regimes. By folding the effects of recovery time of both detectors and the detection circuit into an "effective duty cycle" we are able to accomodate complex recovery behaviour at high event rates. As an example, we provide a detailed high-level model for the behaviour of passively quenched avalanche photodiodes, and demonstrate effective background subtraction at rates commonly associated with detector saturation. We show that by post-processing using the updated model, we observe an improvement in polarization correlation visibility from 88.7% to 96.9% in our experimental dataset. This technique will be useful in improving the signal-to-noise ratio in applications which depend on coincidence measurements, especially in situations where rapid changes in flux may cause detector saturation. PMID:26907016

  20. The dynamic time-over-threshold method for multi-channel APD based gamma-ray detectors

    NASA Astrophysics Data System (ADS)

    Orita, T.; Shimazoe, K.; Takahashi, H.

    2015-03-01

    t- Recent advances in manufacturing technology have enabled the use of multi-channel pixelated detectors in gamma-ray imaging applications. When obtaining gamma-ray measurements, it is important to obtain pulse height information in order to avoid unnecessary events such as scattering. However, as the number of channels increases, more electronics are needed to process each channel's signal, and the corresponding increases in circuit size and power consumption can result in practical problems. The time-over-threshold (ToT) method, which has recently become popular in the medical field, is a signal processing technique that can effectively avoid such problems. However, ToT suffers from poor linearity and its dynamic range is limited. We therefore propose a new ToT technique called the dynamic time-over-threshold (dToT) method [4]. A new signal processing system using dToT and CR-RC shaping demonstrated much better linearity than that of a conventional ToT. Using a test circuit with a new Gd3Al2Ga3O12 (GAGG) scintillator and an avalanche photodiode, the pulse height spectra of 137Cs and 22Na sources were measured with high linearity. Based on these results, we designed a new application-specific integrated circuit (ASIC) for this multi-channel dToT system, measured the spectra of a 22Na source, and investigated the linearity of the system.

  1. Large area radiation detectors based on II VI thin films

    NASA Astrophysics Data System (ADS)

    Quevedo-Lopez, Manuel

    2015-03-01

    The development of low temperature device technologies that have enabled flexible displays also present opportunities for flexible electronics and flexible integrated systems. Of particular interest are possible applications in flexible, low metal content, sensor systems for unattended ground sensors, smart medical bandages, electronic ID tags for geo-location, conformal antennas, neutron/gamma-ray/x-ray detectors, etc. In this talk, our efforts to develop novel CMOS integration schemes, circuits, memory, sensors as well as novel contacts, dielectrics and semiconductors for flexible electronics are presented. In particular, in this presentation we discuss fundamental materials properties including crystalline structure, interfacial reactions, doping, etc. defining performance and reliability of II-VI-based radiation sensors. We investigate the optimal thickness of a semiconductor diode for thin-film solid state thermal neutron detectors. Besides II-VI materials, we also evaluated several diode materials, Si, CdTe,GaAs, C (diamond), and ZnO, and two neutron converter materials,10B and 6LiF. We determine the minimum semiconductor thickness needed to achieve maximum neutron detection efficiency. By keeping the semiconductor thickness to a minimum, gamma rejection is kept as high as possible. In this way, we optimize detector performance for different thin-film semiconductor materials.

  2. The Effect of Personalization on Smartphone-Based Fall Detectors.

    PubMed

    Medrano, Carlos; Plaza, Inmaculada; Igual, Raúl; Sánchez, Ángel; Castro, Manuel

    2016-01-01

    The risk of falling is high among different groups of people, such as older people, individuals with Parkinson's disease or patients in neuro-rehabilitation units. Developing robust fall detectors is important for acting promptly in case of a fall. Therefore, in this study we propose to personalize smartphone-based detectors to boost their performance as compared to a non-personalized system. Four algorithms were investigated using a public dataset: three novelty detection algorithms--Nearest Neighbor (NN), Local Outlier Factor (LOF) and One-Class Support Vector Machine (OneClass-SVM)--and a traditional supervised algorithm, Support Vector Machine (SVM). The effect of personalization was studied for each subject by considering two different training conditions: data coming only from that subject or data coming from the remaining subjects. The area under the receiver operating characteristic curve (AUC) was selected as the primary figure of merit. The results show that there is a general trend towards the increase in performance by personalizing the detector, but the effect depends on the individual being considered. A personalized NN can reach the performance of a non-personalized SVM (average AUC of 0.9861 and 0.9795, respectively), which is remarkable since NN only uses activities of daily living for training. PMID:26797614

  3. The Effect of Personalization on Smartphone-Based Fall Detectors

    PubMed Central

    Medrano, Carlos; Plaza, Inmaculada; Igual, Raúl; Sánchez, Ángel; Castro, Manuel

    2016-01-01

    The risk of falling is high among different groups of people, such as older people, individuals with Parkinson's disease or patients in neuro-rehabilitation units. Developing robust fall detectors is important for acting promptly in case of a fall. Therefore, in this study we propose to personalize smartphone-based detectors to boost their performance as compared to a non-personalized system. Four algorithms were investigated using a public dataset: three novelty detection algorithms—Nearest Neighbor (NN), Local Outlier Factor (LOF) and One-Class Support Vector Machine (OneClass-SVM)—and a traditional supervised algorithm, Support Vector Machine (SVM). The effect of personalization was studied for each subject by considering two different training conditions: data coming only from that subject or data coming from the remaining subjects. The area under the receiver operating characteristic curve (AUC) was selected as the primary figure of merit. The results show that there is a general trend towards the increase in performance by personalizing the detector, but the effect depends on the individual being considered. A personalized NN can reach the performance of a non-personalized SVM (average AUC of 0.9861 and 0.9795, respectively), which is remarkable since NN only uses activities of daily living for training. PMID:26797614

  4. A compact gas-filled avalanche counter for DANCE

    SciTech Connect

    Wu, C. Y.; Chyzh, A.; Kwan, E.; Henderson, R. A.; Gostic, J. M.; Carter, D.; Bredeweg, T. A.; Couture, A.; Jandel, M.; Ullmann, J. L.

    2012-08-04

    A compact gas-filled avalanche counter for the detection of fission fragments was developed for a highly segmented 4π γ-ray calorimeter, namely the Detector for Advanced Neutron Capture Experiments located at the Lujan Center of the Los Alamos Neutron Science Center. It has been used successfully for experiments with 235U, 238Pu,239Pu, and 241Pu isotopes to provide a unique signature to differentiate the fission from the competing neutron-capture reaction channel. We also used it to study the spontaneous fission in 252Cf. The design and performance of this avalanche counter for targets with extreme α-decay rate up to ~2.4×108/s are described.

  5. A compact gas-filled avalanche counter for DANCE

    DOE PAGESBeta

    Wu, C. Y.; Chyzh, A.; Kwan, E.; Henderson, R. A.; Gostic, J. M.; Carter, D.; Bredeweg, T. A.; Couture, A.; Jandel, M.; Ullmann, J. L.

    2012-08-04

    A compact gas-filled avalanche counter for the detection of fission fragments was developed for a highly segmented 4π γ-ray calorimeter, namely the Detector for Advanced Neutron Capture Experiments located at the Lujan Center of the Los Alamos Neutron Science Center. It has been used successfully for experiments with 235U, 238Pu,239Pu, and 241Pu isotopes to provide a unique signature to differentiate the fission from the competing neutron-capture reaction channel. We also used it to study the spontaneous fission in 252Cf. The design and performance of this avalanche counter for targets with extreme α-decay rate up to ~2.4×108/s are described.

  6. Type-II Superlattice Avalanche Photodiodes

    NASA Astrophysics Data System (ADS)

    Huang, Jun

    Type-II superlattice avalanche photodiodes have shown advantages compared to conventional mercury cadmium telluride photodiodes for infrared wavelength detection. However, surface or interface leakage current has been a major issue for superlattice avalanche photodiodes, especially in infrared wavelength region. First, passivation of the superlattice device with ammonium sulfide and thioacetamide was carried out, and its surface quality was studied by X-ray Photoelectron Spectroscopy. The study showed that both ammonium sulfide and thiacetamide passivation can actively remove the native oxide at the surface. Thiacetamide passivation combine more sulfur bonds with III-V elements than that of ammonium sulfide. Another X-ray photoelectron spectra of thiacetamide-treated atomic layer deposited zinc sulfide capped InAs/GaSb superlattice was performed to investigate the interface sulfur bond conditions. Sb--S and As--S bonds disappear while In-S bond gets enhanced, indicating that Indium Sulfide should be the major components at the interface after ZnS deposition. Second, the simulation of electrical characteristics for zinc sulfide, silicon nitride and silicon dioxide passivated superlattice devices was performed by SILVACO software to fit the experimental results and to discover the surface current mechanism. Different surface current mechanism strengths were found. Third, several novel dual-carrier avalanche photodiode structures were designed and simulated. The structures had alternate carrier multiplication regions, placed next to a wider electron multiplication region, creating dual-carrier multiplication feedback systems. Gain and excess noise factor of these structures were simulated and compared based on the dead space multiplication theory under uniform electric field. From the simulation, the applied bias can be greatly lowered or the thickness can be shrunk to achieve the same gain from the conventional device. The width of the thin region was the most

  7. The MAPS based PXL vertex detector for the STAR experiment

    NASA Astrophysics Data System (ADS)

    Contin, G.; Anderssen, E.; Greiner, L.; Schambach, J.; Silber, J.; Stezelberger, T.; Sun, X.; Szelezniak, M.; Vu, C.; Wieman, H.; Woodmansee, S.

    2015-03-01

    The Heavy Flavor Tracker (HFT) was installed in the STAR experiment for the 2014 heavy ion run of RHIC. Designed to improve the vertex resolution and extend the measurement capabilities in the heavy flavor domain, the HFT is composed of three different silicon detectors based on CMOS monolithic active pixels (MAPS), pads and strips respectively, arranged in four concentric cylinders close to the STAR interaction point. The two innermost HFT layers are placed at a radius of 2.7 and 8 cm from the beam line, respectively, and accommodate 400 ultra-thin (50 μ m) high resolution MAPS sensors arranged in 10-sensor ladders to cover a total silicon area of 0.16 m2. Each sensor includes a pixel array of 928 rows and 960 columns with a 20.7 μ m pixel pitch, providing a sensitive area of ~ 3.8 cm2. The architecture is based on a column parallel readout with amplification and correlated double sampling inside each pixel. Each column is terminated with a high precision discriminator, is read out in a rolling shutter mode and the output is processed through an integrated zero suppression logic. The results are stored in two SRAM with ping-pong arrangement for a continuous readout. The sensor features 185.6 μ s readout time and 170 mW/cm2 power dissipation. The detector is air-cooled, allowing a global material budget as low as 0.39% on the inner layer. A novel mechanical approach to detector insertion enables effective installation and integration of the pixel layers within an 8 hour shift during the on-going STAR run.In addition to a detailed description of the detector characteristics, the experience of the first months of data taking will be presented in this paper, with a particular focus on sensor threshold calibration, latch-up protection procedures and general system operations aimed at stabilizing the running conditions. Issues faced during the 2014 run will be discussed together with the implemented solutions. A preliminary analysis of the detector performance

  8. Data analysis for space-based gravitational wave detectors

    NASA Astrophysics Data System (ADS)

    Crowder, Jefferson Osborn

    With the launch of the Laser Interferometer Space Antenna (LISA) expected for the next decade, the nascent field of gravitational wave astronomy will be taking a giant leap forward. The data that will be gathered from space-borne gravitational wave detectors such as LISA will provide an expansive look through a new window on the Universe. This dissertation is presented to help open that window by exploring some of the techniques and methods that will be needed to understand the data from these detectors. The first original work presented here investigates the resolution of LISA and follow-on space-based gravitational wave missions. This work presents the methods of measuring the precision of these detectors and gives results for their resolving power for a large class of expected gravitational wave sources. The second original investigation involves the effect that multiple gravitational wave sources will have on the resolution of LISA. Previous results concerning detector resolution were limited to isolated sources of gravitational waves. As LISA is an all-sky detector, it is necessary to understand the role played by concurrent detection of numerous sources. This work derives an extension of the Fisher Information Matrix approach for determining parameter resolution, and applies it to multiple sources for LISA. The next original work is an exploration of the method of genetic algorithms on the problem of extracting the binary parameters of gravitational wave sources from the LISA data stream. These are global algorithms providing a means to cover the entire search space of parameter values. This work describes the basics of and provides the results for such genetic algorithm-based searches, with a focus on improving algorithm efficiency. The last original work included is a study of Markov Chain Monte Carlo (MCMC) methods applied to parameter extraction of gravitational wave sources in the LISA data stream. This work shows how an MCMC approach provides a global

  9. Photon-Noise Limited Direct Detector Based on Disorder-Controlled Electron Heating

    NASA Technical Reports Server (NTRS)

    Karasik, B.; McGrath, W.; Gershenson, M.; Sergeev, A.

    1999-01-01

    We present a new concept for a hot-electron direct detector (HEDD) capable of counting single millimeter-wave photons. The detector is based on a transition edge sensor (1-meu size bridge) made form a disordered superconducting film.

  10. High-speed, high-voltage pulse generation using avalanche transistor.

    PubMed

    Yong-Sheng, Gou; Bai-Yu, Liu; Yong-Lin, Bai; Jun-Jun, Qin; Xiao-Hong, Bai; Bo, Wang; Bing-Li, Zhu; Chuan-Dong, Sun

    2016-05-01

    In this work, the conduction mechanism of avalanche transistors was demonstrated and the operation condition for generating high-speed pulse using avalanche transistors was illustrated. Based on the above analysis, a high-speed and high-voltage pulse (HHP) generating circuit using avalanche transistors was designed, and its working principle and process were studied. To improve the speed of the output pulse, an approach of reducing the rise time of the leading edge is proposed. Methods for selecting avalanche transistor and reducing the parasitic inductance and capacitance of printed circuit board (PCB) were demonstrated. With these instructions, a PCB with a tapered transmission line was carefully designed and manufactured. Output pulse with amplitude of 2 kV and rise time of about 200 ps was realized with this PCB mounted with avalanche transistors FMMT417, indicating the effectiveness of the HHP generating circuit design. PMID:27250452

  11. NASA's Potential Contributions to Avalanche Forecasting Using Active and Passive Microwave Measurements

    NASA Technical Reports Server (NTRS)

    Blonski, Slawomir

    2007-01-01

    This Candidate Solution is based on using active and passive microwave measurements acquired from NASA satellites to improve USDA (U.S. Department of Agriculture) Forest Service forecasting of avalanche danger. Regional Avalanche Centers prepare avalanche forecasts using ground measurements of snowpack and mountain weather conditions. In this Solution, range of the in situ observations is extended by adding remote sensing measurements of snow depth, snow water equivalent, and snowfall rate acquired by satellite missions that include Aqua, CloudSat, future GPM (Global Precipitation Measurement), and the proposed SCLP (Snow and Cold Land Processes). Measurements of snowpack conditions and time evolution are improved by combining the in situ and satellite observations with a snow model. Recurring snow observations from NASA satellites increase accuracy of avalanche forecasting, which helps the public and the managers of public facilities make better avalanche safety decisions.

  12. Geometrical properties of avalanches in self-organized critical models of solar flares.

    PubMed

    McIntosh, Scott W; Charbonneau, Paul; Bogdan, Thomas J; Liu, Han-Li; Norman, James P

    2002-04-01

    We investigate the geometrical properties of avalanches in self-organized critical models of solar flares. Traditionally, such models differ from the classical sandpile model in their formulation of stability criteria in terms of the curvature of the nodal field, and belong to a distinct universality class. With a view toward comparing these properties to those inferred from spatially and temporally resolved flare observations, we consider the properties of avalanche peak snapshots, time-integrated avalanches in two and three dimensions, and the two-dimensional projections of the latter. The nature of the relationship between the avalanching volume and its projected area is an issue of particular interest in the solar flare context. Using our simulation results we investigate this relationship, and demonstrate that proper accounting of the fractal nature of avalanches can bring into agreement hitherto discrepant results of observational analyses based on simple, nonfractal geometries for the flaring volume. PMID:12005944

  13. High-speed, high-voltage pulse generation using avalanche transistor

    NASA Astrophysics Data System (ADS)

    Yong-sheng, Gou; Bai-yu, Liu; Yong-lin, Bai; Jun-jun, Qin; Xiao-hong, Bai; Bo, Wang; Bing-li, Zhu; Chuan-dong, Sun

    2016-05-01

    In this work, the conduction mechanism of avalanche transistors was demonstrated and the operation condition for generating high-speed pulse using avalanche transistors was illustrated. Based on the above analysis, a high-speed and high-voltage pulse (HHP) generating circuit using avalanche transistors was designed, and its working principle and process were studied. To improve the speed of the output pulse, an approach of reducing the rise time of the leading edge is proposed. Methods for selecting avalanche transistor and reducing the parasitic inductance and capacitance of printed circuit board (PCB) were demonstrated. With these instructions, a PCB with a tapered transmission line was carefully designed and manufactured. Output pulse with amplitude of 2 kV and rise time of about 200 ps was realized with this PCB mounted with avalanche transistors FMMT417, indicating the effectiveness of the HHP generating circuit design.

  14. The interpretation of gamma-ray enhancements in thunderstorms with and without avalanche multiplication

    NASA Astrophysics Data System (ADS)

    Kelley, N. A.

    2015-12-01

    Relativistic Runaway Electron Avalanches (RREAs) are the acceleration and subsequent multiplication of relativistic electrons inside by electric field. Inside thunderstorms, RREA are thought to be involved in the creation of extraordinarily bright bursts of gamma rays, called Terrestrial Gamma-ray Flashes (TGFs), and long duration production of gamma rays (called gamma-ray glows or thunderstorm ground enhancements (TGEs)). However, Chilingarian has proposed that some electric fields inside thunderstorms may not be strong enough or have large enough spatial extent to result in significant avalanche multiplication by RREA to make a glow. High-energy electrons and gamma rays would still be present by a modification of the spectra (MOS) of cosmic-ray air showers. MOS and RREA glows have both been detected many times from the ground but distinguishing between the two is difficult since differing count rates can be the result of either these two distinct production models or attenuation due to various source distances. We will present GEANT4 models showing how these spectra differ as a function of source distance as well as discuss the differences in their gamma ray/electron signature in ground-based, gamma-ray detectors. These models will be compared to measurements made with instruments already in place in Mexico and Japan.

  15. Geophysical investigation of the Sandalp rock avalanche deposits

    NASA Astrophysics Data System (ADS)

    Socco, Laura Valentina; Jongmans, Denis; Boiero, Daniele; Stocco, Stefano; Maraschini, Margherita; Tokeshi, Ken; Hantz, Didier

    2010-04-01

    In the study of rock avalanche phenomena, numerical modelling makes use of back analyses of the rock avalanche propagation for calibration of the modelling assumptions and parameters. The back analyses require knowledge of the run-out area boundaries and the thickness distribution of the deposit. Geophysical methods can be applied to retrieve the thickness distribution, but, due to strong heterogeneities and logistic problems they are seldom applied. The aim of this work is to assess the potential of integrated geophysical methods to recognise and characterise a deposit created by two rock avalanches which occurred in the Sandalp valley (Switzerland) in 1996. The topography of the site before and after the rock avalanche is known and can be used as a benchmark. Resistivity tomography, seismic P-wave tomography, and active and passive surface wave analysis have been applied on several profiles deployed both on the rock avalanche deposit and in the surrounding area. Innovative approaches for surface wave analysis based on laterally constrained inversion and multimodal inversion have been applied to the data. A comparison of the results of the geophysical investigations with the topographic benchmark has shown the capability of the geophysical methods to locate the bottom of the deposit in the areas where the contrast with the host sediments properties is significant. In these areas, the deposit has higher resistivities and lower seismic velocities than the underlying materials. In the areas where the deposit is thicker and richer in fine-grained materials the geophysical parameters are not able to discriminate between the rock avalanche deposit and the underlying sediments. As a secondary task, the geophysical methods also allowed the bedrock pattern to be outlined.

  16. Quantitative Scaling of Magnetic Avalanches.

    PubMed

    Durin, G; Bohn, F; Corrêa, M A; Sommer, R L; Le Doussal, P; Wiese, K J

    2016-08-19

    We provide the first quantitative comparison between Barkhausen noise experiments and recent predictions from the theory of avalanches for pinned interfaces, both in and beyond mean field. We study different classes of soft magnetic materials, including polycrystals and amorphous samples-which are characterized by long-range and short-range elasticity, respectively-both for thick and thin samples, i.e., with and without eddy currents. The temporal avalanche shape at fixed size as well as observables related to the joint distribution of sizes and durations are analyzed in detail. Both long-range and short-range samples with no eddy currents are fitted extremely well by the theoretical predictions. In particular, the short-range samples provide the first reliable test of the theory beyond mean field. The thick samples show systematic deviations from the scaling theory, providing unambiguous signatures for the presence of eddy currents. PMID:27588876

  17. Quantitative Scaling of Magnetic Avalanches

    NASA Astrophysics Data System (ADS)

    Durin, G.; Bohn, F.; Corrêa, M. A.; Sommer, R. L.; Le Doussal, P.; Wiese, K. J.

    2016-08-01

    We provide the first quantitative comparison between Barkhausen noise experiments and recent predictions from the theory of avalanches for pinned interfaces, both in and beyond mean field. We study different classes of soft magnetic materials, including polycrystals and amorphous samples—which are characterized by long-range and short-range elasticity, respectively—both for thick and thin samples, i.e., with and without eddy currents. The temporal avalanche shape at fixed size as well as observables related to the joint distribution of sizes and durations are analyzed in detail. Both long-range and short-range samples with no eddy currents are fitted extremely well by the theoretical predictions. In particular, the short-range samples provide the first reliable test of the theory beyond mean field. The thick samples show systematic deviations from the scaling theory, providing unambiguous signatures for the presence of eddy currents.

  18. Imaging performance of amorphous selenium based flat-panel detectors for digital mammography: characterization of a small area prototype detector.

    PubMed

    Zhao, Wei; Ji, W G; Debrie, Anne; Rowlands, J A

    2003-02-01

    Our work is to investigate and understand the factors affecting the imaging performance of amorphous selenium (a-Se) flat-panel detectors for digital mammography. Both theoretical and experimental methods were developed to investigate the spatial frequency dependent detective quantum efficiency [DQE(f)] of a-Se flat-panel detectors for digital mammography. Since the K edge of a-Se is 12.66 keV and within the energy range of a mammographic spectrum, a theoretical model was developed based on cascaded linear system analysis with parallel processes to take into account the effect of K fluorescence on the modulation transfer function (MTF), noise power spectrum (NPS), and DQE(f) of the detector. This model was used to understand the performance of a small-area prototype detector with 85 microm pixel size. The presampling MTF, NPS, and DQE(f) of the prototype were measured, and compared to the theoretical calculation of the model. The calculation showed that K fluorescence accounted for a 15% reduction in the MTF at the Nyquist frequency (fNy) of the prototype detector, and the NPS at fNy was reduced to 89% of that at zero spatial frequency. The measurement of presampling MTF of the prototype detector revealed an additional source of blurring, which was attributed to charge trapping in the blocking layer at the interface between a-Se and the active matrix. This introduced a drop in both presampling MTF and NPS at high spatial frequency, and reduced aliasing in the NPS. As a result, the DQE(f) of the prototype detector at fNy approached 40% of that at zero spatial frequency. The measured and calculated DQE(f) using the linear system model have reasonable agreement, indicating that the factors controlling image quality in a-Se based mammographic detectors are fully understood, and the model can be used to further optimize detector imaging performance. PMID:12607843

  19. Micro flame-based detector suite for universal gas sensing.

    SciTech Connect

    Hamilton, Thomas Warren; Washburn, Cody M.; Moorman, Matthew Wallace; Manley, Robert George; Lewis, Patrick Raymond; Miller, James Edward; Clem, Paul Gilbert; Shelmidine, Gregory J.; Manginell, Ronald Paul; Okandan, Murat

    2005-11-01

    A microflame-based detector suit has been developed for sensing of a broad range of chemical analytes. This detector combines calorimetry, flame ionization detection (FID), nitrogen-phosphorous detection (NPD) and flame photometric detection (FPD) modes into one convenient platform based on a microcombustor. The microcombustor consists in a micromachined microhotplate with a catalyst or low-work function material added to its surface. For the NPD mode a low work function material selectively ionizes chemical analytes; for all other modes a supported catalyst such as platinum/alumina is used. The microcombustor design permits rapid, efficient heating of the deposited film at low power. To perform calorimetric detection of analytes, the change in power required to maintain the resistive microhotplate heater at a constant temperature is measured. For FID and NPD modes, electrodes are placed around the microcombustor flame zone and an electrometer circuit measures the production of ions. For FPD, the flame zone is optically interrogated to search for light emission indicative of deexcitation of flame-produced analyte compounds. The calorimetric and FID modes respond generally to all hydrocarbons, while sulfur compounds only alarm in the calorimetric mode, providing speciation. The NPD mode provides 10,000:1 selectivity of nitrogen and phosphorous compounds over hydrocarbons. The FPD can distinguish between sulfur and phosphorous compounds. Importantly all detection modes can be established on one convenient microcombustor platform, in fact the calorimetric, FID and FPD modes can be achieved simultaneously on only one microcombustor. Therefore, it is possible to make a very universal chemical detector array with as little as two microcombustor elements. A demonstration of the performance of the microcombustor in each of the detection modes is provided herein.

  20. Optimizing timing performance of silicon photomultiplier-based scintillation detectors

    PubMed Central

    Yeom, Jung Yeol; Vinke, Ruud

    2013-01-01

    Precise timing resolution is crucial for applications requiring photon time-of-flight (ToF) information such as ToF positron emission tomography (PET). Silicon photomultipliers (SiPM) for PET, with their high output capacitance, are known to require custom preamplifiers to optimize timing performance. In this paper, we describe simple alternative front-end electronics based on a commercial low-noise RF preamplifier and methods that have been implemented to achieve excellent timing resolution. Two radiation detectors with L(Y)SO scintillators coupled to Hamamatsu SiPMs (MPPC S10362–33-050C) and front-end electronics based on an RF amplifier (MAR-3SM+), typically used for wireless applications that require minimal additional circuitry, have been fabricated. These detectors were used to detect annihilation photons from a Ge-68 source and the output signals were subsequently digitized by a high speed oscilloscope for offline processing. A coincident resolving time (CRT) of 147 ± 3 ps FWHM and 186 ± 3 ps FWHM with 3 × 3 × 5 mm3 and with 3 × 3 × 20 mm3 LYSO crystal elements were measured, respectively. With smaller 2 × 2 × 3 mm3 LSO crystals, a CRT of 125 ± 2 ps FWHM was achieved with slight improvement to 121 ± 3 ps at a lower temperature (15°C). Finally, with the 20 mm length crystals, a degradation of timing resolution was observed for annihilation photon interactions that occur close to the photosensor compared to shallow depth-of-interaction (DOI). We conclude that commercial RF amplifiers optimized for noise, besides their ease of use, can produce excellent timing resolution comparable to best reported values acquired with custom readout electronics. On the other hand, as timing performance degrades with increasing photon DOI, a head-on detector configuration will produce better CRT than a side-irradiated setup for longer crystals. PMID:23369872

  1. Compressive spectral imaging systems based on linear detector

    NASA Astrophysics Data System (ADS)

    Liu, Yanli; Zhong, Xiaoming; Zhao, Haibo; Li, Huan

    2015-08-01

    The spectrometers capture large amount of raw and 3-dimensional (3D) spatial-spectral scene information with 2- dimensional (2D) focal plane arrays(FPA). In many applications, including imaging system and video cameras, the Nyquist rate is so high that too many samples result, making compression a precondition to storage or transmission. Compressive sensing theory employs non-adaptive linear projections that preserve the structure of the signal, the signal is then reconstructed from these projections using an optimization process. This article overview the fundamental spectral imagers based on compressive sensing, the coded aperture snapshot spectral imagers (CASSI) and high-resolution imagers via moving random exposure. Besides that, the article propose a new method to implement spectral imagers with linear detector imager systems based on spectrum compressed. The article describes the system introduction and code process, and it illustrates results with real data and imagery. Simulations are shown to illustrate the performance improvement attained by the new model and complexity of the imaging system greatly reduced by using linear detector.

  2. Development of a soil detector based on an optical sensor

    NASA Astrophysics Data System (ADS)

    Zheng, Lihua; Pan, Luan; Li, Minzan; An, Xiaofei

    2008-12-01

    An estimation model of the soil organic matter content has been built based on NIR spectroscopy and a portable soil organic matter detector based on optical sensor is developed. The detector uses a micro processor 89S52 as the Micro Controller Unit (MCU) and consists of an optical system and a control system. The optical system includes a 850nm near-infrared lamp-house, a lamp-house driving-circuit, a Y type optical fiber, a probe, and a photoelectric sensor. The control system includes an amplified circuit, an A/D circuit, a display circuit with LCD, and a storage circuit with USB interface. Firstly the single waveband optical signal from the near-infrared lamp-house is transferred to the surface of the target soil via the incidence fibers. Then the reflected optical signal is collected and transferred to photoelectric sensor, where the optical signal is conveyed to the electrical signal. Subsequently, the obtained electrical signal is processed by 89S52 MCU. Finally, the calculated soil organic matter content is displayed on the LCD and stored in the USB disk. The calibration experiment using the estimation model of the soil organic matter is conducted. The decision coefficient (R2) reaches 0.9839 between the measured data by the soil organic matter sensor and by the laboratory chemistry method.

  3. Atmospheric Neutron Measurements using a Small Scintillator Based Detector

    NASA Astrophysics Data System (ADS)

    Kole, Merlin; Pearce, Mark; Fukazawa, Yasushi; Fukuda, Kentaro; Ishizu, Sumito; Jackson, Miranda; Kamae, Tune; Kawaguchi, Noriaki; Kawano, Takafumi; Kiss, Mozsi; Moretti, Elena; Yanagida, Takayuki; Chauvin, Maxime; Mikhalev, Victor; Rydstrom, Stefan; Takahashi, Hiromitsu

    PoGOLino is a standalone scintillator-based neutron detector designed for balloon-borne missions. Its main purpose is to provide data of the neutron flux in 2 different energy ranges in the high altitude / high latitude region where the highest neutron flux in the atmosphere is found. Furthermore the influence of the Solar activity upon the neutron environment in this region is relatively strong. As a result both short and long term time fluctuations are strongest in this region. At high altitudes neutrons can form a source of background for balloon-borne scientific measurements. They can furthermore form a major source for single event upsets in electronics. A good understanding of the high altitude / high latitude neutron environment is therefore important. Measurements of the neutron environment in this region are however lacking. PoGOLino contains two 5 mm thick Lithium Calcium Aluminium Fluoride (LiCAF) scintillators used for neutron detection. The LiCAF crystals are sandwiched between 2 Bismuth Germanium Oxide (BGO) scintillating crystals, which serve to veto signals produced by gamma-rays and charged particles. The veto system makes measurements of the neutron flux possible even in high radiation environments. One LiCAF detector is shielded with polyethylene while the second remains unshielded, making the detectors sensitive in different energy ranges. The choice of a scintillator crystals as the detection material ensures a high detection efficiency while keeping the instrument small, robust and light weight. The full standalone cylindrical instrument has a radius of 120 mm, a height of 670 mm and a total mass of 13 kg, making it suitable as a piggy back mission. PoGOLino was successfully launched on March 20th 2013 from the Esrange Space Center in Northern Sweden to an altitude of 30.9 km. A detailed description of the detector design is presented, along with results of of the flight. The neutron flux measured during flight is compared to predictions based

  4. Angle sensitive single photon avalanche diode

    SciTech Connect

    Lee, Changhyuk Johnson, Ben Molnar, Alyosha

    2015-06-08

    An ideal light sensor would provide exact information on intensity, timing, location, and angle of incoming photons. Single photon avalanche diodes (SPADs) provide such desired high (single photon) sensitivity with precise time information and can be implemented at a pixel-scale to form an array to extract spatial information. Furthermore, recent work has demonstrated photodiode-based structures (combined with micro-lenses or diffraction gratings) that are capable of encoding both spatial and angular information of incident light. In this letter, we describe the implementation of such a grating structure on SPADs to realize a pixel-scale angle-sensitive single photon avalanche diode (A-SPAD) built in a standard CMOS process. While the underlying SPAD structure provides high sensitivity, the time information of the two layers of diffraction gratings above offers angle-sensitivity. Such a unique combination of SPAD and diffraction gratings expands the sensing dimensions to pave a path towards lens-less 3-D imaging and light-field time-of-flight imaging.

  5. A method to precisely identify the afterpulses when using the S9717 avalanche photodiode

    NASA Astrophysics Data System (ADS)

    Rusu, Alexandru; Rusu, Lucian

    2015-12-01

    The detection ratio of an avalanche photodiode (APD) biased in Geiger-mode increases versus the excess voltage; the afterpulsing rate increases too. The last one can be reduced by inserting an artificial dead time and accepting a lower measuring top rate. So, in order to tune a single-photon detector system, it is necessary to exactly identify afterpulses and measure their rate; the experimental results are presented. When using the S9717 APD in Geiger-mode, the cathode to ground voltage waveform reveals the existence of a particular sequence of pulses: a usual one followed, within 1μs, by a least one appearing to have been generated for negative excess voltage values. All these characteristics are the signature of the afterpulsing generation. Based on this observation, we were able to precisely measure the afterpulsing rate.

  6. A method to precisely identify the afterpulses when using the S9717 avalanche photodiode

    SciTech Connect

    Rusu, Alexandru Rusu, Lucian

    2015-12-07

    The detection ratio of an avalanche photodiode (APD) biased in Geiger-mode increases versus the excess voltage; the afterpulsing rate increases too. The last one can be reduced by inserting an artificial dead time and accepting a lower measuring top rate. So, in order to tune a single-photon detector system, it is necessary to exactly identify afterpulses and measure their rate; the experimental results are presented. When using the S9717 APD in Geiger-mode, the cathode to ground voltage waveform reveals the existence of a particular sequence of pulses: a usual one followed, within 1μs, by a least one appearing to have been generated for negative excess voltage values. All these characteristics are the signature of the afterpulsing generation. Based on this observation, we were able to precisely measure the afterpulsing rate.

  7. Avoiding sensor blindness in Geiger mode avalanche photodiode arrays fabricated in a conventional CMOS process

    NASA Astrophysics Data System (ADS)

    Vilella, E.; Diéguez, A.

    2011-12-01

    The need to move forward in the knowledge of the subatomic world has stimulated the development of new particle colliders. However, the objectives of the next generation of colliders sets unprecedented challenges to the detector performance. The purpose of this contribution is to present a bidimensional array based on avalanche photodiodes operated in the Geiger mode to track high energy particles in future linear colliders. The bidimensional array can function in a gated mode to reduce the probability to detect noise counts interfering with real events. Low reverse overvoltages are used to lessen the dark count rate. Experimental results demonstrate that the prototype fabricated with a standard HV-CMOS process presents an increased efficiency and avoids sensor blindness by applying the proposed techniques.

  8. Avalanche dynamics of elastic interfaces.

    PubMed

    Le Doussal, Pierre; Wiese, Kay Jörg

    2013-08-01

    Slowly driven elastic interfaces, such as domain walls in dirty magnets, contact lines wetting a nonhomogeneous substrate, or cracks in brittle disordered material proceed via intermittent motion, called avalanches. Here we develop a field-theoretic treatment to calculate, from first principles, the space-time statistics of instantaneous velocities within an avalanche. For elastic interfaces at (or above) their (internal) upper critical dimension d≥d(uc) (d(uc)=2,4 respectively for long-ranged and short-ranged elasticity) we show that the field theory for the center of mass reduces to the motion of a point particle in a random-force landscape, which is itself a random walk [Alessandro, Beatrice, Bertotti, and Montorsi (ABBM) model]. Furthermore, the full spatial dependence of the velocity correlations is described by the Brownian-force model (BFM) where each point of the interface sees an independent Brownian-force landscape. Both ABBM and BFM can be solved exactly in any dimension d (for monotonous driving) by summing tree graphs, equivalent to solving a (nonlinear) instanton equation. We focus on the limit of slow uniform driving. This tree approximation is the mean-field theory (MFT) for realistic interfaces in short-ranged disorder, up to the renormalization of two parameters at d=d(uc). We calculate a number of observables of direct experimental interest: Both for the center of mass, and for a given Fourier mode q, we obtain various correlations and probability distribution functions (PDF's) of the velocity inside an avalanche, as well as the avalanche shape and its fluctuations (second shape). Within MFT we find that velocity correlations at nonzero q are asymmetric under time reversal. Next we calculate, beyond MFT, i.e., including loop corrections, the one-time PDF of the center-of-mass velocity u[over ·] for dimension d

  9. Avalanche ecology and large magnitude avalanche events: Glacier National Park, Montana, USA

    USGS Publications Warehouse

    Fagre, Daniel B.; Peitzsch, Erich H.

    2010-01-01

    Large magnitude snow avalanches play an important role ecologically in terms of wildlife habitat, vegetation diversity, and sediment transport within a watershed. Ecological effects from these infrequent avalanches can last for decades. Understanding the frequency of such large magnitude avalanches is also critical to avalanche forecasting for the Going-to-the-Sun Road (GTSR). In January 2009, a large magnitude avalanche cycle occurred in and around Glacier National Park, Montana. The study site is the Little Granite avalanche path located along the GTSR. The study is designed to quantify change in vegetative cover immediately after a large magnitude event and document ecological response over a multi-year period. GPS field mapping was completed to determine the redefined perimeter of the avalanche path. Vegetation was inventoried using modified U.S. Forest Service Forest Inventory and Analysis plots, cross sections were taken from over 100 dead trees throughout the avalanche path, and an avalanche chronology was developed. Initial results indicate that the perimeter of this path was expanded by 30%. The avalanche travelled approximately 1200 vertical meters and 3 linear kilometers. Stands of large conifers as old as 150 years were decimated by the avalanche, causing a shift in dominant vegetation types in many parts of the avalanche path. Woody debris is a major ground cover up to 3 m in depth on lower portions of the avalanche path and will likely affect tree regrowth. Monitoring and measuring the post-avalanche vegetation recovery of this particular avalanche path provides a unique dataset for determining the ecological role of avalanches in mountain landscapes.

  10. Highly enhanced avalanche probability using sinusoidally-gated silicon avalanche photodiode

    SciTech Connect

    Suzuki, Shingo; Namekata, Naoto Inoue, Shuichiro; Tsujino, Kenji

    2014-01-27

    We report on visible light single photon detection using a sinusoidally-gated silicon avalanche photodiode. Detection efficiency of 70.6% was achieved at a wavelength of 520 nm when an electrically cooled silicon avalanche photodiode with a quantum efficiency of 72.4% was used, which implies that a photo-excited single charge carrier in a silicon avalanche photodiode can trigger a detectable avalanche (charge) signal with a probability of 97.6%.

  11. Snowfall and avalanche synchronization: beyond observational statistics

    NASA Astrophysics Data System (ADS)

    Crouzy, Benoît; Forclaz, Romain; Sovilla, Betty; Corripio, Javier; Perona, Paolo

    2015-04-01

    We present a methodology for quantifying the synchronization between snowfall and avalanches in relation to slope and terrain properties at the detachment zone. Focusing on a particular field situation (SLF study site, Vallée de la Sionne, Valais, Switzerland), we present a dataset consisting of 549 avalanche events and use a stochastic framework (Perona et al., Proceedings of the Royal Society A, 2012) for capturing the avalanche statistics with a minimal number of ingredients. Over the observation period (7 years), meteorological data was collected and pictures of the slope were taken every 30 minutes. For the avalanche events, slope, aspect, coordinates and altitude of the detachment zone are available from georeferenced images, and the timing of the events can be obtained from selecting the images before and after avalanche events. All model parameters can directly be computed from meteorological data (snow depth evolution), except for one parameter: the state-dependent avalanche release rate, which aggregates the influence of slope and terrain properties. From the timing distribution of the precipitation events and of the avalanche events, we calibrate the model and fix the value of the missing parameter by maximizing the likelihood of the field observations, conditional to the value of the model parameter. We carefully discuss confidence intervals for our parameter estimation. The calibrated model allows us to obtain statistical properties of the avalanches in our study site, beyond observational statistics. We compute the synchronization between snowfall and avalanches for low and high slopes, which in turn allows us to derive the return period of avalanche events (dependent and independent on the release depth). We obtain the critical event magnitude above which the return period of avalanche events with release depth h* is shorter than the return period of snowfall with equal deposited snow depth h*. Finally, using the concept of information entropy, we

  12. Comparison of seismic and infrasound wave fields generated by snow avalanches

    NASA Astrophysics Data System (ADS)

    Suriñach, Emma; Tapia, Mar; Pérez-Guillén, Cristina; Khazaradze, Giorgi; Roig, Pere

    2016-04-01

    Snow avalanches are a source of waves that are transmitted through the ground and the air. These wave fields are detected by seismic and infrasound sensors. During the winter seasons 2008 -2016, a good quality database of avalanches was obtained at the VdlS test site with an accurate instrumentation. These avalanches were both natural and artificially triggered and were of varying types and sizes. Distances involved were 0.5 -3 km. Seismic signals were acquired using three seismometers (3-components, 1Hz) spaced 600 m apart along the avalanche track. One infrasound sensor (0.1Hz) and one seismometer (3-components, 1Hz) were placed one next to the other with a common base of time on the slope opposite the path. The database obtained enables us to compare the different signals generated. Differences in the frequency content and shape of the signals depending on the type and size of the avalanche are detected. A clear evolution of the recorded seismic signals along the path is observed. The cross correlation of the infrasound and seismic signals generated by the avalanches allows us to determine different characteristics for powder, transitional and wet avalanches concerning their wave fields. The joint analysis of infrasound and seismic waves enables us to obtain valuable information about the internal parts of the avalanche as a source of each wave field. This study has repercussions on avalanche dynamics and on the selection of the appropriate avalanche detection system. This study is supported by the Spanish Ministry of Science and Innovation project CHARMA: CHAracterization and ContRol of MAss Movements. A Challenge for Geohazard Mitigation (CGL2013-40828-R), and RISKNAT group (2014GR/1243).

  13. Topographic Avalanche Risk: DEM Sensitivity Analysis

    NASA Astrophysics Data System (ADS)

    Nazarkulova, Ainura; Strobl, Josef

    2015-04-01

    GIS-based models are frequently used to assess the risk and trigger probabilities of (snow) avalanche releases, based on parameters and geomorphometric derivatives like elevation, exposure, slope, proximity to ridges and local relief energy. Numerous models, and model-based specific applications and project results have been published based on a variety of approaches and parametrizations as well as calibrations. Digital Elevation Models (DEM) come with many different resolution (scale) and quality (accuracy) properties, some of these resulting from sensor characteristics and DEM generation algorithms, others from different DEM processing workflows and analysis strategies. This paper explores the impact of using different types and characteristics of DEMs for avalanche risk modeling approaches, and aims at establishing a framework for assessing the uncertainty of results. The research question is derived from simply demonstrating the differences in release risk areas and intensities by applying identical models to DEMs with different properties, and then extending this into a broader sensitivity analysis. For the quantification and calibration of uncertainty parameters different metrics are established, based on simple value ranges, probabilities, as well as fuzzy expressions and fractal metrics. As a specific approach the work on DEM resolution-dependent 'slope spectra' is being considered and linked with the specific application of geomorphometry-base risk assessment. For the purpose of this study focusing on DEM characteristics, factors like land cover, meteorological recordings and snowpack structure and transformation are kept constant, i.e. not considered explicitly. Key aims of the research presented here are the development of a multi-resolution and multi-scale framework supporting the consistent combination of large area basic risk assessment with local mitigation-oriented studies, and the transferability of the latter into areas without availability of

  14. Accelerometer-Based Event Detector for Low-Power Applications

    PubMed Central

    Smidla, József; Simon, Gyula

    2013-01-01

    In this paper, an adaptive, autocovariance-based event detection algorithm is proposed, which can be used with micro-electro-mechanical systems (MEMS) accelerometer sensors to build inexpensive and power efficient event detectors. The algorithm works well with low signal-to-noise ratio input signals, and its computational complexity is very low, allowing its utilization on inexpensive low-end embedded sensor devices. The proposed algorithm decreases its energy consumption by lowering its duty cycle, as much as the event to be detected allows it. The performance of the algorithm is tested and compared to the conventional filter-based approach. The comparison was performed in an application where illegal entering of vehicles into restricted areas was detected. PMID:24135991

  15. Modulator based high bandwidth optical readout for HEP detectors

    NASA Astrophysics Data System (ADS)

    Drake, G.; Fernando, W. S.; Stanek, R. W.; Underwood, D. G.

    2013-02-01

    Optical links will be an integral part of future LHC experiments at various scales from coupled sensors to off-detector communication. We are investigating CW lasers and light modulators as an alternative to VCSELs. Light modulators are small, use less power, have high bandwidth, are reliable, have low bit error rates and are very rad-hard. We present the quality of the links at 10Gbps and the results of radiation hardness measurements for the modulators built based on LiNbO3, InP, and Si. Also we present results on modulator-based free space data links, steered by MEMS mirrors and optical feedback paths for the control loop.

  16. Time Directed Avalanches in Invasion Models

    SciTech Connect

    Maslov, S. Department of Physics, SUNY at Stony Brook, Stony Brook, New York 11794 )

    1995-01-23

    We define forward and backward time-directed avalanches for a broad class of self-organized critical models including invasion percolation, interface depinning, and a simple model of evolution. Although the geometrical properties of the avalanches do not change under time reversal, their stationary state statistical distribution does. The overall distribution of forward avalanches [ital P]([ital s])[similar to][ital s][sup [minus]2] is superuniversal in this class of models. The power-law exponent [pi] for the distribution of distances between subsequent active sites is derived from the properties of backward avalanches.

  17. A probabilistic model for snow avalanche occurrence

    NASA Astrophysics Data System (ADS)

    Perona, P.; Miescher, A.; Porporato, A.

    2009-04-01

    Avalanche hazard forecasting is an important issue in relation to the protection of urbanized environments, ski resorts and of ski-touring alpinists. A critical point is to predict the conditions that trigger the snow mass instability determining the onset and the size of avalanches. On steep terrains the risk of avalanches is known to be related to preceding consistent snowfall events and to subsequent changes in the local climatic conditions. Regression analysis has shown that avalanche occurrence indeed correlates to the amount of snow fallen in consecutive three snowing days and to the state of the settled snow at the ground. Moreover, since different type of avalanches may occur as a result of the interactions of different factors, the process of snow avalanche formation is inherently complex and with some degree of unpredictability. For this reason, although several models assess the risk of avalanche by accounting for all the involved processes with a great detail, a high margin of uncertainty invariably remains. In this work, we explicitly describe such an unpredictable behaviour with an intrinsic noise affecting the processes leading snow instability. Eventually, this sets the basis for a minimalist stochastic model, which allows us to investigate the avalanche dynamics and its statistical properties. We employ a continuous time process with stochastic jumps (snowfalls), deterministic decay (snowmelt and compaction) and state dependent avalanche occurrence (renewals) as a minimalist model for the determination of avalanche size and related intertime occurrence. The physics leading to avalanches is simplified to the extent where only meteorological data and terrain data are necessary to estimate avalanche danger. We explore the analytical formulation of the process and the properties of the probability density function of the avalanche process variables. We also discuss what is the probabilistic link between avalanche size and preceding snowfall event and

  18. Forest damage and snow avalanche flow regime

    NASA Astrophysics Data System (ADS)

    Feistl, T.; Bebi, P.; Christen, M.; Margreth, S.; Diefenbach, L.; Bartelt, P.

    2015-01-01

    Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. In the powder regime, the blast of the cloud can produce large bending moments in the tree stem because of the impact area extending over the entire tree crown. We demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. In the wet snow case, avalanche pressure is calculated using a quasi-static model accounting for the motion of plug-like wet snow flows. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. We find (1) powder clouds with velocities over 20 m s-1 can break tree stems, (2) the intermittent regime seldom controls tree breakage and (3) quasi-static pressures of wet snow avalanches can be much higher than pressures calculated using dynamic pressure formulas.

  19. The blocking probability of Geiger-mode avalanche photo-diodes

    NASA Technical Reports Server (NTRS)

    Moision, Bruce; Srinivasan, Meera; Hamkins, Jon

    2005-01-01

    When a photo is detected by a Geiger-mode avalanche photo-diode (GMAPD), the detector is rendered inactive, or blocked, for a certain period of time. In this paper we derive the blocking probability for a GMAPD whose input is either an unmodulated, Benoulli modulated or pulse-position-modulated Poisson process.

  20. Photon Detection with Cooled Avalanche Photodiodes: Theory and Preliminary Experimental Results

    NASA Technical Reports Server (NTRS)

    Robinson, D. L.; Hays, D. A.

    1985-01-01

    Avalanche photodiodes (APDs) can be operated in a geiger-tube mode so that they can respond to single electron events and thus be used as photon counting detectors. Operational characteristics and theory of APDs while used in this mode are analyzed and assessed. Preliminary experimental investigation of several commercially available APDs has commenced, and initial results for dark count statistics are presented.

  1. Time-based position estimation in monolithic scintillator detectors.

    PubMed

    Tabacchini, Valerio; Borghi, Giacomo; Schaart, Dennis R

    2015-07-21

    Gamma-ray detectors based on bright monolithic scintillation crystals coupled to pixelated photodetectors are currently being considered for several applications in the medical imaging field. In a typical monolithic detector, both the light intensity and the time of arrival of the earliest scintillation photons can be recorded by each of the photosensor pixels every time a gamma interaction occurs. Generally, the time stamps are used to determine the gamma interaction time while the light intensities are used to estimate the 3D position of the interaction point. In this work we show that the spatio-temporal distribution of the time stamps also carries information on the location of the gamma interaction point and thus the time stamps can be used as explanatory variables for position estimation. We present a model for the spatial resolution obtainable when the interaction position is estimated using exclusively the time stamp of the first photon detected on each of the photosensor pixels. The model is shown to be in agreement with experimental measurements on a 16 mm  ×  16 mm  ×  10 mm LSO : Ce,0.2%Ca crystal coupled to a digital photon counter (DPC) array where a spatial resolution of 3 mm (root mean squared error) is obtained. Finally we discuss the effects of the main parameters such as scintillator rise and decay time, light output and photosensor single photon time resolution and pixel size. PMID:26133784

  2. Time-based position estimation in monolithic scintillator detectors

    NASA Astrophysics Data System (ADS)

    Tabacchini, Valerio; Borghi, Giacomo; Schaart, Dennis R.

    2015-07-01

    Gamma-ray detectors based on bright monolithic scintillation crystals coupled to pixelated photodetectors are currently being considered for several applications in the medical imaging field. In a typical monolithic detector, both the light intensity and the time of arrival of the earliest scintillation photons can be recorded by each of the photosensor pixels every time a gamma interaction occurs. Generally, the time stamps are used to determine the gamma interaction time while the light intensities are used to estimate the 3D position of the interaction point. In this work we show that the spatio-temporal distribution of the time stamps also carries information on the location of the gamma interaction point and thus the time stamps can be used as explanatory variables for position estimation. We present a model for the spatial resolution obtainable when the interaction position is estimated using exclusively the time stamp of the first photon detected on each of the photosensor pixels. The model is shown to be in agreement with experimental measurements on a 16 mm  ×  16 mm  ×  10 mm LSO : Ce,0.2%Ca crystal coupled to a digital photon counter (DPC) array where a spatial resolution of 3 mm (root mean squared error) is obtained. Finally we discuss the effects of the main parameters such as scintillator rise and decay time, light output and photosensor single photon time resolution and pixel size.

  3. Illicit material detector based on gas sensors and neural networks

    NASA Astrophysics Data System (ADS)

    Grimaldi, Vincent; Politano, Jean-Luc

    1997-02-01

    In accordance with its missions, le Centre de Recherches et d'Etudes de la Logistique de la Police Nationale francaise (CREL) has been conducting research for the past few years targeted at detecting drugs and explosives. We have focused our approach of the underlying physical and chemical detection principles on solid state gas sensors, in the hope of developing a hand-held drugs and explosives detector. The CREL and Laboratory and Scientific Services Directorate are research partners for this project. Using generic hydrocarbon, industrially available, metal oxide sensors as illicit material detectors, requires usage precautions. Indeed, neither the product's concentrations, nor even the products themselves, belong to the intended usage specifications. Therefore, the CREL is currently investigating two major research topics: controlling the sensor's environment: with environmental control we improve the detection of small product concentration; determining detection thresholds: both drugs and explosives disseminate low gas concentration. We are attempting to quantify the minimal concentration which triggers detection. In the long run, we foresee a computer-based tool likely to detect a target gas in a noisy atmosphere. A neural network is the suitable tool for interpreting the response of heterogeneous sensor matrix. This information processing structure, alongside with proper sensor environment control, will lessen the repercussions of common MOS sensor sensitivity characteristic dispersion.

  4. New Fast Shower Max Detector Based on MCP as an Active Element

    NASA Astrophysics Data System (ADS)

    Ronzhin, A.; Los, S.; Ramberg, E.; Spiropulu, M.; Apresyan, A.; Xie, S.; Kim, H.; Zatserklyaniy, A.

    2015-02-01

    One possibility to make a fast and radiation resistant shower maximum (SM) detector is to use a secondary emitter as an active element. We present below test beam results, obtained with different types of photo detectors based on micro channel plates (MCP) as secondary emitter. The SM time resolution - we obtained for this new type of detector is at the level of 20-30 ps. We estimate that a significant contribution to the detector response originates from secondary emission of the MCP.

  5. Gamma detectors based on high-pressure xenon: their development and application

    NASA Astrophysics Data System (ADS)

    Ulin, Sergey E.; Dmitrenko, Valery V.; Grachev, V. M.; Uteshev, Z. M.; Vlasik, K. F.; Chernysheva, I. V.; Dukhvalov, A. G.; Kotler, F. G.; Pushkin, K. N.

    2004-10-01

    Various modifications of xenon detectors and their parameters in comparison with gamma-detectors of other types are considered. Prospects of xenon detectors' applicatins in gamma-spectroscopy based on experimental results are discussed including detection and control of radioactive and fissile materials displacement, definition of uranium enrichment rate, and measurements of nuclear reactor radioactive gas waste concentration. Possibilities for xenon detector use for environmental control and measurement of cosmic gamma radiation on orbital stations are considered.

  6. Gamma detectors based on high pressure xenon: their development and application

    NASA Astrophysics Data System (ADS)

    Ulin, Sergey E.; Dmitrenko, Valery V.; Grachev, V. M.; Uteshev, Z. M.; Vlasic, K. F.; Chernysheva, I. V.; Duhvalov, A. G.; Kotler, F. G.; Pushkin, K. N.

    2004-01-01

    Various modifications of xenon detectors and their parameters in comparison with gamma-detectors of other types are considered. Prospects of xenon detectors' applications in gamma-spectroscopy based on experimental results are discussed including detection and control of radioactive and fissile materials displacement, definition of uranium enrichment rate, and measurements of nuclear reactor radioactive gas waste concentration. Possibilities for xenon detector use for environmental control and measurement of cosmic gamma radiation on orbital stations are considered.

  7. Study of avalanche mode operation of resistive plate chambers with different gas gap structures

    NASA Astrophysics Data System (ADS)

    Ammosov, V. V.; Gapienko, V. A.; Konstantinov, V. F.; Sviridov, Yu. M.; Zaets, V. G.

    2000-03-01

    The operation of narrow gap, wide gap and multigap resistive plate chambers in an avalanche mode was studied. No advantage in avalanche-streamer separation was found for the wide gap and multigap chambers operating with Ar-based mixture as compared with the narrow gap chamber. For dense tetrafluoroethane-based mixture, proportionality was observed between streamer-free plateau width and total gas thickness, in rough agreement with corresponding shift of the maximum of avalanche charge distributions from zero. The best result was obtained for double-gap chamber with the read-out electrode located between two subgaps.

  8. Practical photon number detection with electric field-modulated silicon avalanche photodiodes.

    PubMed

    Thomas, O; Yuan, Z L; Shields, A J

    2012-01-01

    Low-noise single-photon detection is a prerequisite for quantum information processing using photonic qubits. In particular, detectors that are able to accurately resolve the number of photons in an incident light pulse will find application in functions such as quantum teleportation and linear optics quantum computing. More generally, such a detector will allow the advantages of quantum light detection to be extended to stronger optical signals, permitting optical measurements limited only by fluctuations in the photon number of the source. Here we demonstrate a practical high-speed device, which allows the signals arising from multiple photon-induced avalanches to be precisely discriminated. We use a type of silicon avalanche photodiode in which the lateral electric field profile is strongly modulated in order to realize a spatially multiplexed detector. Clearly discerned multiphoton signals are obtained by applying sub-nanosecond voltage gates in order to restrict the detector current. PMID:22273682

  9. Position sensitive and energy dispersive x-ray detector based on silicon strip detector technology

    NASA Astrophysics Data System (ADS)

    Wiącek, P.; Dąbrowski, W.; Fink, J.; Fiutowski, T.; Krane, H.-G.; Loyer, F.; Schwamberger, A.; Świentek, K.; Venanzi, C.

    2015-04-01

    A new position sensitive detector with a global energy resolution for the entire detector of about 380 eV FWHM for 8.04 keV line at ambient temperature is presented. The measured global energy resolution is defined by the energy spectra summed over all strips of the detector, and thus it includes electronic noise of the front-end electronics, charge sharing effects, matching of parameters across the channels and other system noise sources. The target energy resolution has been achieved by segmentation of the strips to reduce their capacitance and by careful optimization of the front-end electronics. The key design aspects and parameters of the detector are discussed briefly in the paper. Excellent noise and matching performance of the readout ASIC and negligible system noise allow us to operate the detector with a discrimination threshold as low as 1 keV and to measure fluorescence radiation lines of light elements, down to Al Kα of 1.49 keV, simultaneously with measurements of the diffraction patterns. The measurement results that demonstrate the spectrometric and count rate performance of the developed detector are presented and discussed in the paper.

  10. On the temporal organization of neuronal avalanches

    PubMed Central

    Lombardi, Fabrizio; Herrmann, Hans J.; Plenz, Dietmar; De Arcangelis, Lucilla

    2014-01-01

    Spontaneous activity of cortex in vitro and in vivo has been shown to organize as neuronal avalanches. Avalanches are cascades of neuronal activity that exhibit a power law in their size and duration distribution, typical features of balanced systems in a critical state. Recently it has been shown that the distribution of quiet times between consecutive avalanches in rat cortex slice cultures displays a non-monotonic behavior with a power law decay at short time scales. This behavior has been attributed to the slow alternation between up and down-states. Here we further characterize the avalanche process and investigate how the functional behavior of the quiet time distribution depends on the fine structure of avalanche sequences. By systematically removing smaller avalanches from the experimental time series we show that size and quiet times are correlated and highlight that avalanche occurrence exhibits the characteristic periodicity of θ and β/γ oscillations, which jointly emerge in most of the analyzed samples. Furthermore, our analysis indicates that smaller avalanches tend to be associated with faster β/γ oscillations, whereas larger ones are associated with slower θ and 1–2 Hz oscillations. In particular, large avalanches corresponding to θ cycles trigger cascades of smaller ones, which occur at β/γ frequency. This temporal structure follows closely the one of nested θ − β/γ oscillations. Finally we demonstrate that, because of the multiple time scales characterizing avalanche dynamics, the distributions of quiet times between avalanches larger than a certain size do not collapse onto a unique function when rescaled by the average occurrence rate. However, when considered separately in the up-state and in the down-state, these distributions are solely controlled by the respective average rate and two different unique function can be identified. PMID:25389393

  11. Using GIS and Google Earth for the creation of the Going-to-the-Sun Road Avalanche Atlas, Glacier National Park, Montana, USA

    USGS Publications Warehouse

    Peitzsch, Erich H.; Fagre, Daniel B.; Dundas, Mark

    2010-01-01

    Snow avalanche paths are key geomorphologic features in Glacier National Park, Montana, and an important component of mountain ecosystems: they are isolated within a larger ecosystem, they are continuously disturbed, and they contain unique physical characteristics (Malanson and Butler, 1984). Avalanches impact subalpine forest structure and function, as well as overall biodiversity (Bebi et al., 2009). Because avalanches are dynamic phenomena, avalanche path geometry and spatial extent depend upon climatic regimes. The USGS/GNP Avalanche Program formally began in 2003 as an avalanche forecasting program for the spring opening of the ever-popular Going-to-the-Sun Road (GTSR), which crosses through 37 identified avalanche paths. Avalanche safety and forecasting is a necessary part of the GTSR spring opening procedures. An avalanche atlas detailing topographic parameters and oblique photographs was completed for the GTSR corridor in response to a request from GNP personnel for planning and resource management. Using ArcMap 9.2 GIS software, polygons were created for every avalanche path affecting the GTSR using aerial imagery, field-based observations, and GPS measurements of sub-meter accuracy. Spatial attributes for each path were derived within the GIS. Resulting products include an avalanche atlas book for operational use, a geoPDF of the atlas, and a Google Earth flyover illustrating each path and associated photographs. The avalanche atlas aids park management in worker safety, infrastructure planning, and natural resource protection by identifying avalanche path patterns and location. The atlas was created for operational and planning purposes and is also used as a foundation for research such as avalanche ecology projects and avalanche path runout modeling.

  12. LAMBDA — Large Area Medipix3-Based Detector Array

    NASA Astrophysics Data System (ADS)

    Pennicard, D.; Lange, S.; Smoljanin, S.; Hirsemann, H.; Graafsma, H.

    2012-11-01

    Medipix3 is a photon-counting readout chip for X-ray detection. It has a small pixel size (55 μm) and a high frame rate with zero dead time, which makes it attractive for experiments at synchrotrons. Using Medipix3, DESY are developing the LAMBDA (Large Area Medipix3-Based Detector Array) system. A single LAMBDA module carries either a single large silicon sensor of 1536 by 512 pixels, or two smaller high-Z sensors. The sensor is bonded to 12 Medipix3 chips, and mounted on a ceramic carrier board. The readout system for the module then provides a fast FPGA, a large RAM and four 10 Gigabit Ethernet links to allow operation at high frame rates. Multiple modules may then be tiled together a larger area. Currently, the first large silicon modules have been constructed and tested at low speed, and the firmware for fast readout is being developed.

  13. Optimizing timing performance of silicon photomultiplier-based scintillation detectors.

    PubMed

    Yeom, Jung Yeol; Vinke, Ruud; Levin, Craig S

    2013-02-21

    Precise timing resolution is crucial for applications requiring photon time-of-flight (ToF) information such as ToF positron emission tomography (PET). Silicon photomultipliers (SiPM) for PET, with their high output capacitance, are known to require custom preamplifiers to optimize timing performance. In this paper, we describe simple alternative front-end electronics based on a commercial low-noise RF preamplifier and methods that have been implemented to achieve excellent timing resolution. Two radiation detectors with L(Y)SO scintillators coupled to Hamamatsu SiPMs (MPPC S10362-33-050C) and front-end electronics based on an RF amplifier (MAR-3SM+), typically used for wireless applications that require minimal additional circuitry, have been fabricated. These detectors were used to detect annihilation photons from a Ge-68 source and the output signals were subsequently digitized by a high speed oscilloscope for offline processing. A coincident resolving time (CRT) of 147 ± 3 ps FWHM and 186 ± 3 ps FWHM with 3 × 3 × 5 mm(3) and with 3 × 3 × 20 mm(3) LYSO crystal elements were measured, respectively. With smaller 2 × 2 × 3 mm(3) LSO crystals, a CRT of 125 ± 2 ps FWHM was achieved with slight improvement to 121 ± 3 ps at a lower temperature (15° C). Finally, with the 20 mm length crystals, a degradation of timing resolution was observed for annihilation photon interactions that occur close to the photosensor compared to shallow depth-of-interaction (DOI). We conclude that commercial RF amplifiers optimized for noise, besides their ease of use, can produce excellent timing resolution comparable to best reported values acquired with custom readout electronics. On the other hand, as timing performance degrades with increasing photon DOI, a head-on detector configuration will produce better CRT than a side-irradiated setup for longer crystals. PMID:23369872

  14. Transport and emplacement mechanisms of channelised long-runout debris avalanches, Ruapehu volcano, New Zealand

    NASA Astrophysics Data System (ADS)

    Tost, M.; Cronin, S. J.; Procter, J. N.

    2014-12-01

    The steep flanks of composite volcanoes are prone to collapse, producing debris avalanches that completely reshape the landscape. This study describes new insights into the runout of large debris avalanches enhanced by topography, using the example of six debris avalanche deposits from Mount Ruapehu, New Zealand. Individual large flank collapses (>1 km3) produced all of these units, with four not previously recognised. Five major valleys within the highly dissected landscape surrounding Mount Ruapehu channelled the debris avalanches into deep gorges (≥15 m) and resulted in extremely long debris avalanche runouts of up to 80 km from source. Classical sedimentary features of debris avalanche deposits preserved in these units include the following: very poor sorting with a clay-sand matrix hosting large subrounded boulders up to 5 m in diameter, jigsaw-fractured clasts, deformed clasts and numerous rip-up clasts of late-Pliocene marine sediments. The unusually long runouts led to unique features in distal deposits, including a pervasive and consolidated interclast matrix, and common rip-up clasts of Tertiary mudstone, as well as fluvial gravels and boulders. The great travel distances can be explained by the debris avalanches entering deep confined channels (≥15 m), where friction was minimised by a reduced basal contact area along with loading of water-saturated substrates which formed a basal lubrication zone for the overlying flowing mass. Extremely long-runout debris avalanches are most likely to occur in settings where initially partly saturated collapsing masses move down deep valleys and become thoroughly liquified at their base. This happens when pore water is available within the base of the flowing mass or in the sediments immediately below it. Based on their H/L ratio, confined volcanic debris avalanches are two to three times longer than unconfined, spreading flows of similar volume. The hybrid qualities of the deposits, which have some similarities to

  15. Gaussian Velocity Distributions in Avalanches

    NASA Astrophysics Data System (ADS)

    Shattuck, Mark

    2004-03-01

    Imagine a world where gravity is so strong that if an ice cube is tilted the shear forces melt the surface and water avalanches down. Further imagine that the ambient temperature is so low that the water re-freezes almost immediately. This is the world of granular flows. As a granular solid is tilted the surface undergoes a sublimation phase transition and a granular gas avalanches down the surface, but the inelastic collisions rapidly remove energy from the flow lowering the granular temperature (kinetic energy per particle) until the gas solidifies again. It is under these extreme conditions that we attempt to uncover continuum granular flow properties. Typical continuum theories like Navier-Stokes equation for fluids follow the space-time evolution of the first few moments of the velocity distribution. We study continuously avalanching flow in a rotating two-dimensional granular drum using high-speed video imaging and extract the position and velocities of the particles. We find a universal near Gaussian velocity distribution throughout the flowing regions, which are characterized by a liquid-like radial distribution function. In the remaining regions, in which the radial distribution function develops sharp crystalline peaks, the velocity distribution has a Gaussian peak but is much broader in the tails. In a companion experiment on a vibrated two-dimensional granular fluid under constant pressure, we find a clear gas-solid phase transition in which both the temperature and density change discontinuously. This suggests that a low temperature crystal and a high temperature gas can coexist in steady state. This coexistence could result in a narrower, cooler, Gaussian peak and a broader, warmer, Gaussian tail like the non-Gaussian behavior seen in the crystalline portions of the rotating drum.

  16. Avalanches in dry and saturated disordered media at fracture.

    PubMed

    Milanese, Enrico; Yılmaz, Okan; Molinari, Jean-François; Schrefler, Bernhard

    2016-04-01

    This paper analyzes fracturing in inhomogeneous media under dry and fully saturated conditions. We adopt a central force model with continuous damage to study avalanche behavior in a two-dimensional truss lattice undergoing dilation. Multiple fractures can develop at once and a power-law distribution of the avalanche size is observed. The values for the power-law exponent are compared with the ones found in the literature and scale-free behavior is suggested. The fracture evolves intermittently in time because only some avalanches correspond to fracture advancement. A fully saturated model with continuous damage based on the extended Biot's theory is developed and avalanche behavior is studied in the presence of fluid, varying the fluid boundary conditions. We show that power-law behavior is destroyed when the fluid flux governs the problem. Fluid pressure behavior during intermittent crack tip advancement is studied for the continuous-damage fully saturated model. It is found that when mechanical loading prevails, the pressure rises when the crack advances, while when fluid loading prevails, the pressure drops when the crack advances. PMID:27176380

  17. Electron avalanche structure determined by random walk theory

    NASA Technical Reports Server (NTRS)

    Englert, G. W.

    1973-01-01

    A self-consistent avalanche solution which accounts for collective long range Coulomb interactions as well as short range elastic and inelastic collisions between electrons and background atoms is made possible by a random walk technique. Results show that the electric field patterns in the early formation stages of avalanches in helium are close to those obtained from theory based on constant transport coefficients. Regions of maximum and minimum induced electrostatic potential phi are located on the axis of symmetry and within the volume covered by the electron swarm. As formation time continues, however, the region of minimum phi moves to slightly higher radii and the electric field between the extrema becomes somewhat erratic. In the intermediate formation periods the avalanche growth is slightly retarded by the high concentration of ions in the tail which oppose the external electric field. Eventually the formation of ions and electrons in the localized regions of high field strength more than offset this effect causing a very abrupt increase in avalanche growth.

  18. Avalanches in dry and saturated disordered media at fracture

    NASA Astrophysics Data System (ADS)

    Milanese, Enrico; Yılmaz, Okan; Molinari, Jean-François; Schrefler, Bernhard

    2016-04-01

    This paper analyzes fracturing in inhomogeneous media under dry and fully saturated conditions. We adopt a central force model with continuous damage to study avalanche behavior in a two-dimensional truss lattice undergoing dilation. Multiple fractures can develop at once and a power-law distribution of the avalanche size is observed. The values for the power-law exponent are compared with the ones found in the literature and scale-free behavior is suggested. The fracture evolves intermittently in time because only some avalanches correspond to fracture advancement. A fully saturated model with continuous damage based on the extended Biot's theory is developed and avalanche behavior is studied in the presence of fluid, varying the fluid boundary conditions. We show that power-law behavior is destroyed when the fluid flux governs the problem. Fluid pressure behavior during intermittent crack tip advancement is studied for the continuous-damage fully saturated model. It is found that when mechanical loading prevails, the pressure rises when the crack advances, while when fluid loading prevails, the pressure drops when the crack advances.

  19. VME-based data acquisition system for the India-based Neutrino Observatory prototype detector

    NASA Astrophysics Data System (ADS)

    Bhuyan, M.; Chandratre, V. B.; Dasgupta, S.; Datar, V. M.; Kalmani, S. D.; Lahamge, S. M.; Mondal, N. K.; Nagaraj, P.; Pal, S.; Rao, S. K.; Redij, A.; Samuel, D.; Saraf, M. N.; Satyanarayana, B.; Shinde, R. R.; Upadhya, S. S.

    2012-01-01

    The India-based Neutrino Observatory (INO) collaboration has proposed to build a 50 kton Iron-Calorimeter (ICAL) to study neutrino oscillations. About 28,800 Resistive Plate Chambers will be used as active detector elements in this experiment. Preliminary studies are currently underway and as a part of it, a prototype detector was developed which now serves as a cosmic-ray telescope and as a test-bench to study the indigenously built RPCs. A VME-based data acquisition system was designed for this prototype system. Modern software tools were used in the designing of the DAQ software. The design and development of this DAQ system are discussed.

  20. Avalanche!--Teachable Moments in Outdoor Education

    ERIC Educational Resources Information Center

    Galloway, Shayne

    2005-01-01

    Rarely do outdoor educators get the opportunity to safely incorporate an avalanche while the topic of the day is actually avalanche awareness and forecasting. Many similar possibilities exist in the expeditionary context, but even brief excursions may result in incredible learning experiences. These "teachable moments" occur regularly in the…

  1. Forest damage and snow avalanche flow regime

    NASA Astrophysics Data System (ADS)

    Feistl, T.; Bebi, P.; Christen, M.; Margreth, S.; Diefenbach, L.; Bartelt, P.

    2015-06-01

    Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. First we show that in the powder regime, although the applied impact pressures can be small, large bending moments in the tree stem can be produced due to the torque action of the blast. The impact area of the blast extends over the entire tree crown. We find that, powder clouds with velocities over 20 m s-1 can break tree stems. Second we demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. The intermittent regime seldom controls tree breakage. Third we calculate quasi-static pressures of wet snow avalanches and show that they can be much higher than pressures calculated using dynamic pressure formulas. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree.

  2. Integrated electronics for time-resolved array of single-photon avalanche diodes

    NASA Astrophysics Data System (ADS)

    Acconcia, G.; Crotti, M.; Rech, I.; Ghioni, M.

    2013-12-01

    The Time Correlated Single Photon Counting (TCSPC) technique has reached a prominent position among analytical methods employed in a great variety of fields, from medicine and biology (fluorescence spectroscopy) to telemetry (laser ranging) and communication (quantum cryptography). Nevertheless the development of TCSPC acquisition systems featuring both a high number of parallel channels and very high performance is still an open challenge: to satisfy the tight requirements set by the applications, a fully parallel acquisition system requires not only high efficiency single photon detectors but also a read-out electronics specifically designed to obtain the highest performance in conjunction with these sensors. To this aim three main blocks have been designed: a gigahertz bandwidth front-end stage to directly read the custom technology SPAD array avalanche current, a reconfigurable logic to route the detectors output signals to the acquisition chain and an array of time measurement circuits capable of recording the photon arrival times with picoseconds time resolution and a very high linearity. An innovative architecture based on these three circuits will feature a very high number of detectors to perform a truly parallel spatial or spectral analysis and a smaller number of high performance time-to-amplitude converter offering very high performance and a very high conversion frequency while limiting the area occupation and power dissipation. The routing logic will make the dynamic connection between the two arrays possible in order to guarantee that no information gets lost.

  3. Avalanche Survival After Rescue With the RECCO Rescue System: A Case Report.

    PubMed

    Grasegger, Katharina; Strapazzon, Giacomo; Procter, Emily; Brugger, Hermann; Soteras, Inigo

    2016-06-01

    We report a case of survival of a completely buried avalanche victim after being located with the radar-based RECCO Rescue System. In the winter of 2015, 2 off-piste skiers were completely buried in an avalanche near the secured ski area in Baqueira Beret, Spain. The first victim was located with the RECCO Rescue System in less than 35 minutes and was alive and conscious at extrication. This system emits radio waves and requires a specific reflector. It is a portable device that is used by more than 600 rescue organizations worldwide, especially in secured ski areas. The device should be brought to the avalanche site together with electronic avalanche transceivers, a probing team, and avalanche dogs. In the hands of experienced professionals, the device may allow rapid location of victims not carrying an electronic avalanche transceiver. Although it is not the first successful extrication of a victim with the RECCO Rescue System, it is the first case published in the medical literature and is intended to encourage data collection and to increase our understanding of the effectiveness of this device in avalanche rescue. PMID:27116920

  4. New Analysis Techniques for Avalanches in a Conical Bead Pile with Cohesion

    NASA Astrophysics Data System (ADS)

    Tieman, Catherine; Lehman, Susan

    2015-03-01

    Avalanche statistics and pile geometry for 3 mm steel spheres dropped on a conical bead pile were studied at different drop heights and different cohesion strengths. The pile is initially built on a circular base and is subsequently slowly driven by adding one bead at a time to the apex of the pile. We investigate the dynamic response of the pile by recording avalanches off the pile over the course of tens of thousands of bead drops. The level of cohesion is tuned through use of an applied uniform magnetic field. Changes in the pile mass and geometry were investigated to determine the effect of cohesion and drop height on the angle of repose. The angle of repose increased with cohesion strength, and decreased somewhat for higher drop heights. The packing density of beads is expected to decrease as magnetic cohesion increases, but for our 20 000-bead pile, this effect has not been observed. The proportion of beads removed from the pile by different avalanche sizes was also calculated. Although larger avalanches are much rarer occurrences, they carry away a larger fraction of the total avalanched mass than small avalanches. As the pile cohesion increases, the number of small and medium avalanches decreases so that this mass loss distribution shifts more strongly to large sizes.

  5. Avalanche in Adhesion at Metal Interfaces

    NASA Technical Reports Server (NTRS)

    Banerjea, Amitava; Good, Brian S.

    1994-01-01

    Simulations have shown that as two metal surfaces approach each other, the surface layers can avalanche together when the rigid interfacial spacing falls below a critical distance. This is accompanied by a discontinuous decrease in the adhesive energy. Here we present an examination of this phenomenon for the body centered cubic (BCC) metals Fe and W using the Equivalent Crystal Theory. In order to identify the circumstances under which avalanche might be inhibited, the effect of loss of registry between the two surfaces is investigated in detail. The avalanche is inhibited when the two surfaces are sufficiently far out of registry and when only a few layers near the surface are allowed to relax. As the relaxing slabs get thicker a sharp avalanche reappears. However, as the loss of registry increases the energy released in the avalanche decreases.

  6. Fission-fragment detector for DANCE based on thin scintillating films

    NASA Astrophysics Data System (ADS)

    Rusev, G.; Roman, A. R.; Daum, J. K.; Springs, R. K.; Bond, E. M.; Jandel, M.; Baramsai, B.; Bredeweg, T. A.; Couture, A.; Favalli, A.; Ianakiev, K. D.; Iliev, M. L.; Mosby, S.; Ullmann, J. L.; Walker, C. L.

    2015-12-01

    A fission-fragment detector based on thin scintillating films has been built to serve as a trigger/veto detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing 4 π detection of the fission fragments. The scintillation photons were registered with silicon photomultipliers. A measurement of the 235U (n , f) reaction with this detector at DANCE revealed a correct time-of-flight spectrum and provided an estimate for the efficiency of the prototype detector of 11.6(7)%. Design and test measurements with the detector are described.

  7. Overspill avalanching in a dense reservoir network

    PubMed Central

    Mamede, George L.; Araújo, Nuno A. M.; Schneider, Christian M.; de Araújo, José Carlos; Herrmann, Hans J.

    2012-01-01

    Sustainability of communities, agriculture, and industry is strongly dependent on an effective storage and supply of water resources. In some regions the economic growth has led to a level of water demand that can only be accomplished through efficient reservoir networks. Such infrastructures are not always planned at larger scale but rather made by farmers according to their local needs of irrigation during droughts. Based on extensive data from the upper Jaguaribe basin, one of the world’s largest system of reservoirs, located in the Brazilian semiarid northeast, we reveal that surprisingly it self-organizes into a scale-free network exhibiting also a power-law in the distribution of the lakes and avalanches of discharges. With a new self-organized-criticality-type model we manage to explain the novel critical exponents. Implementing a flow model we are able to reproduce the measured overspill evolution providing a tool for catastrophe mitigation and future planning. PMID:22529343

  8. Thermal energy in dry snow avalanches

    NASA Astrophysics Data System (ADS)

    Steinkogler, W.; Sovilla, B.; Lehning, M.

    2015-09-01

    Avalanches can exhibit many different flow regimes from powder clouds to slush flows. Flow regimes are largely controlled by the properties of the snow released and entrained along the path. Recent investigations showed the temperature of the moving snow to be one of the most important factors controlling the mobility of the flow. The temperature of an avalanche is determined by the temperature of the released and entrained snow but also increases by frictional processes with time. For three artificially released avalanches, we conducted snow profiles along the avalanche track and in the deposition area, which allowed quantifying the temperature of the eroded snow layers. This data set allowed to calculate the thermal balance, from release to deposition, and to discuss the magnitudes of different sources of thermal energy of the avalanches. For the investigated dry avalanches, the thermal energy increase due to friction was mainly depending on the effective elevation drop of the mass of the avalanche with a warming of approximately 0.3 °C per 100 vertical metres. Contrarily, the temperature change due to entrainment varied for the individual avalanches, from -0.08 to 0.3 °C, and depended on the temperature of the snow along the path and the erosion depth. Infrared radiation thermography (IRT) was used to assess the surface temperature before, during and just after the avalanche with high spatial resolution. This data set allowed to identify the warmest temperatures to be located in the deposits of the dense core. Future research directions, especially for the application of IRT, in the field of thermal investigations in avalanche dynamics are discussed.

  9. Monitoring and modeling ice-rock avalanches from ice-capped volcanoes: A case study of frequent large avalanches on Iliamna Volcano, Alaska

    USGS Publications Warehouse

    Huggel, C.; Caplan-Auerbach, J.; Waythomas, C.F.; Wessels, R.L.

    2007-01-01

    Iliamna is an andesitic stratovolcano of the Aleutian arc with regular gas and steam emissions and mantled by several large glaciers. Iliamna Volcano exhibits an unusual combination of frequent and large ice-rock avalanches in the order of 1 ?? 106??m3 to 3 ?? 107??m3 with recent return periods of 2-4??years. We have reconstructed an avalanche event record for the past 45??years that indicates Iliamna avalanches occur at higher frequency at a given magnitude than other mass failures in volcanic and alpine environments. Iliamna Volcano is thus an ideal site to study such mass failures and its relation to volcanic activity. In this study, we present different methods that fit into a concept of (1) long-term monitoring, (2) early warning, and (3) event documentation and analysis of ice-rock avalanches on ice-capped active volcanoes. Long-term monitoring methods include seismic signal analysis, and space-and airborne observations. Landsat and ASTER satellite data was used to study the extent of hydrothermally altered rocks and surface thermal anomalies at the summit region of Iliamna. Subpixel heat source calculation for the summit regions where avalanches initiate yielded temperatures of 307 to 613??K assuming heat source areas of 1000 to 25??m2, respectively, indicating strong convective heat flux processes. Such heat flow causes ice melting conditions and is thus likely to reduce the strength at the base of the glacier. We furthermore demonstrate typical seismic records of Iliamna avalanches with rarely observed precursory signals up to two hours prior to failure, and show how such signals could be used for a multi-stage avalanche warning system in the future. For event analysis and documentation, space- and airborne observations and seismic records in combination with SRTM and ASTER derived terrain data allowed us to reconstruct avalanche dynamics and to identify remarkably similar failure and propagation mechanisms of Iliamna avalanches for the past 45??years

  10. Optical position detectors based on thin film amorphous silicon

    NASA Astrophysics Data System (ADS)

    Henry, Jasmine; Livingstone, John

    2001-10-01

    Thin film optical position sensitive detectors (PSDs) based on novel hydrogenated amorphous silicon Schottky barrier (SB) structures are compared in this work. The three structures reported here have been tested under different light sources to measure their linear properties and wavelength response characteristics. The sputtered a-Si sensors were configured as layered structures of platinum, a-Si and indium tin oxide, forming SB-i-n devices and exhibited linear properties similar to multi-layer a-Si p-i- n devices produced by complex chemical vapor deposition procedures, which involve flammable and toxic gases. All structures were test4ed as possible configurations for 2D sensors. The devices were tested under white light, filtered white light and also a red diode laser. Each of the three structures responded quite differently to each of the sources. Results, based on the correlation coefficient, which measures the linearity of output and which has a maximum value of 1, produced r values ranging between 0.992 to 0.999, in the best performances.

  11. 3D avalanche multiplication in Si-Ge lateral avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Jamil, Erum; Hayat, Majeed M.; Davids, Paul S.; Camacho, Ryan M.

    2016-05-01

    Si-Ge lateral avalanche photodiodes (Si-Ge LAPDs) are promising devices for single photon detection, but they also have technology challenges. Si-Ge LAPDs are CMOS compatible and capable of detecting photons near the 1550 nm telecommunications bands. However, the Si-Ge LAPD exhibits a unique avalanche multiplication process in silicon, where the electrons and holes follow curved paths in three-dimensional space. Traditional models for the analysis of the avalanche multiplication process assume one-dimensional paths for the carriers that undergo the chains of impact ionizations; therefore, they are not suitable for analyzing the avalanche properties of Si-Ge LAPDs. In this paper, the statistics of the avalanche process in the Si-Ge LAPD are modeled analytically using a method that was recently developed by our group for understanding the avalanche multiplication in nanopillar, core-shell GaAs avalanche photodiodes, for which the electric field is non-uniform in magnitude and direction. Specifically, the calculated mean avalanche gain and the excess noise are presented for the Si-Ge LAPD device. It is also shown that the avalanche characteristics depend upon the specific avalanche path taken by the carrier, which depends, in turn, on the lateral location where each photon is absorbed in the Ge absorber. This property can be exploited to achieve reduced excess noise as well as wavelength-sensitive single-photon detection.

  12. Blind multiuser detector for chaos-based CDMA using support vector machine.

    PubMed

    Kao, Johnny Wei-Hsun; Berber, Stevan Mirko; Kecman, Vojislav

    2010-08-01

    The algorithm and the results of a blind multiuser detector using a machine learning technique called support vector machine (SVM) on a chaos-based code division multiple access system is presented in this paper. Simulation results showed that the performance achieved by using SVM is comparable to existing minimum mean square error (MMSE) detector under both additive white Gaussian noise (AWGN) and Rayleigh fading conditions. However, unlike the MMSE detector, the SVM detector does not require the knowledge of spreading codes of other users in the system or the estimate of the channel noise variance. The optimization of this algorithm is considered in this paper and its complexity is compared with the MMSE detector. This detector is much more suitable to work in the forward link than MMSE. In addition, original theoretical bit-error rate expressions for the SVM detector under both AWGN and Rayleigh fading are derived to verify the simulation results. PMID:20570769

  13. Development of stable nuclear radiation detectors based on n-silicon/cobalt-phthalocyanine heterojunctions

    NASA Astrophysics Data System (ADS)

    Ray, A.; Prasad, R.; Betty, C. A.; Chandrasekhar Rao, T. V.

    2016-03-01

    n-silicon/cobalt-phthalocyanine (CoPc) heterojunction based nuclear detectors have been fabricated using thermally evaporated CoPc films. Two different thicknesses of CoPc film (viz. 100 nm and 200 nm) were tried out to make detectors by depositing on chemically polished n-Si wafers. Gold film on CoPc was used as electrical contact. The detectors were characterized by measuring their current-voltage (I-V) and leakage current-time (I-t) characteristics, followed by alpha energy spectra obtained on exposure to α-particles. Variation of alpha energy resolution with applied reverse bias voltage for each of the detectors was also studied. The detectors showed very low leakage current and high breakdown voltage as compared to conventional Au/n-Si surface barrier detectors. Finally, the durability of the detectors was established by measuring their I-V characteristics and energy resolution for nearly 15 months.

  14. Analytical Solutions Involving Shock Waves for Testing Debris Avalanche Numerical Models

    NASA Astrophysics Data System (ADS)

    Mungkasi, Sudi; Roberts, Stephen Gwyn

    2012-10-01

    Analytical solutions to debris avalanche problems involving shock waves are derived. The debris avalanche problems are described in two different coordinate systems, namely, the standard Cartesian and topography-linked coordinate systems. The analytical solutions can then be used to test debris avalanche numerical models. In this article, finite volume methods are applied as the numerical models. We compare the performance of the finite volume method with reconstruction of the conserved quantities based on stage, height, and velocity to that of the conserved quantities based on stage, height, and momentum for solving the debris avalanche problems involving shock waves. The numerical solutions agree with the analytical solution. In addition, both reconstructions lead to similar numerical results. This article is an extension of the work of Mangeney et al. (Pure Appl Geophys 157(6-8):1081-1096, 2000).

  15. Ethernet-Based DAQ System for QUIET-II Detectors

    NASA Astrophysics Data System (ADS)

    Nagai, M.; Ishidoshiro, K.; Higuchi, T.; Ikeno, M.; Hasegawa, M.; Hazumi, M.; Tajima, O.; Tanaka, M.; Uchida, T.

    2012-06-01

    The B-modes in cosmic microwave background polarization are a smoking gun for the inflationary universe. For the detection of the B-modes, having a large detector array is a generic approach since the B-modes is so faint pattern ( T b≲0.1 μK). The Q/U Imaging ExperimenT Phase-II (QUIET-II) is proposed to search the B-modes, using an array with 500 HEMT-based polarimeters. Each polarimeter element has 4-outputs, therefore we have to manage 2000 channels in total. We developed a scalable DAQ system based on TCP/Ethernet for QUIET-II. The DAQ system is composed of the polarimeters, ADC boards, a Master Clock and a control computer (PC). The analog signals from the polarimeters are digitized on the ADC boards. On-board demodulation, which synchronizes the phase flip modulations on the polarimeter, extracts the polarized components in the digitized signal. The Master Clock distributes all necessary clocks to the ADC boards as well as the polarimeters. This scheme guarantees the synchronization of the modulations and demodulations. We employed Ethernet-based communication scheme between the data collection program (Collector) on the PC and the ADC boards as well as the Master Clock. Such an Ethernet-based communication scheme allows us to construct a simple structure of the upper level software, which results in the high scalability to increase the number of channels. All basic functions and requirements are confirmed by the laboratory tests; demonstration with test signals as well as the signals from the polarimeters, measurements of the data transfer rate, and the synchronous operation with two ADC boards. Therefore, the DAQ system is confirmed to be suitable for QUIET-II.

  16. Plasmonic field confinement for separate absorption-multiplication in InGaAs nanopillar avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Farrell, Alan C.; Senanayake, Pradeep; Hung, Chung-Hong; El-Howayek, Georges; Rajagopal, Abhejit; Currie, Marc; Hayat, Majeed M.; Huffaker, Diana L.

    2015-12-01

    Avalanche photodiodes (APDs) are essential components in quantum key distribution systems and active imaging systems requiring both ultrafast response time to measure photon time of flight and high gain to detect low photon flux. The internal gain of an APD can improve system signal-to-noise ratio (SNR). Excess noise is typically kept low through the selection of material with intrinsically low excess noise, using separate-absorption-multiplication (SAM) heterostructures, or taking advantage of the dead-space effect using thin multiplication regions. In this work we demonstrate the first measurement of excess noise and gain-bandwidth product in III-V nanopillars exhibiting substantially lower excess noise factors compared to bulk and gain-bandwidth products greater than 200 GHz. The nanopillar optical antenna avalanche detector (NOAAD) architecture is utilized for spatially separating the absorption region from the avalanche region via the NOA resulting in single carrier injection without the use of a traditional SAM heterostructure.

  17. Characterization of the KID-Based Light Detectors of CALDER

    NASA Astrophysics Data System (ADS)

    Casali, N.; Bellini, F.; Cardani, L.; Castellano, M. G.; Colantoni, I.; Coppolecchia, A.; Cosmelli, C.; Cruciani, A.; D'Addabbo, A.; Di Domizio, S.; Martinez, M.; Tomei, C.; Vignati, M.

    2016-07-01

    The aim of the Cryogenic wide-Area Light Detectors with Excellent Resolution (CALDER) project is the development of light detectors with active area of 5 × 5 cm2 and noise energy resolution smaller than 20 eV RMS, implementing phonon-mediated kinetic inductance detectors. The detectors are developed to improve the background suppression in large-mass bolometric experiments such as CUORE, via the double read-out of the light and the heat released by particles interacting in the bolometers. In this work, we present the characterization of the first light detectors developed by CALDER. We describe the analysis tools to evaluate the resonator parameters (resonant frequency and quality factors) taking into account simultaneously all the resonance distortions introduced by the read-out chain (as the feed-line impedance and its mismatch) and by the power stored in the resonator itself. We detail the method for the selection of the optimal point for the detector operation (maximizing the signal-to-noise ratio). Finally, we present the response of the detector to optical pulses in the energy range of 0{-}30 keV.

  18. Characterization of the KID-Based Light Detectors of CALDER

    NASA Astrophysics Data System (ADS)

    Casali, N.; Bellini, F.; Cardani, L.; Castellano, M. G.; Colantoni, I.; Coppolecchia, A.; Cosmelli, C.; Cruciani, A.; D'Addabbo, A.; Di Domizio, S.; Martinez, M.; Tomei, C.; Vignati, M.

    2015-11-01

    The aim of the Cryogenic wide-Area Light Detectors with Excellent Resolution (CALDER) project is the development of light detectors with active area of 5 × 5 cm2 and noise energy resolution smaller than 20 eV RMS, implementing phonon-mediated kinetic inductance detectors. The detectors are developed to improve the background suppression in large-mass bolometric experiments such as CUORE, via the double read-out of the light and the heat released by particles interacting in the bolometers. In this work, we present the characterization of the first light detectors developed by CALDER. We describe the analysis tools to evaluate the resonator parameters (resonant frequency and quality factors) taking into account simultaneously all the resonance distortions introduced by the read-out chain (as the feed-line impedance and its mismatch) and by the power stored in the resonator itself. We detail the method for the selection of the optimal point for the detector operation (maximizing the signal-to-noise ratio). Finally, we present the response of the detector to optical pulses in the energy range of 0{-}30 keV.

  19. Study of a nTHGEM-based thermal neutron detector

    NASA Astrophysics Data System (ADS)

    Li, Ke; Zhou, Jian-Rong; Wang, Xiao-Dong; Xiong, Tao; Zhang, Ying; Xie, Yu-Guang; Zhou, Liang; Xu, Hong; Yang, Gui-An; Wang, Yan-Feng; Wang, Yan; Wu, Jin-Jie; Sun, Zhi-Jia; Hu, Bi-Tao

    2016-07-01

    With new generation neutron sources, traditional neutron detectors cannot satisfy the demands of the applications, especially under high flux. Furthermore, facing the global crisis in 3He gas supply, research on new types of neutron detector as an alternative to 3He is a research hotspot in the field of particle detection. GEM (Gaseous Electron Multiplier) neutron detectors have high counting rate, good spatial and time resolution, and could be one future direction of the development of neutron detectors. In this paper, the physical process of neutron detection is simulated with Geant4 code, studying the relations between thermal conversion efficiency, boron thickness and number of boron layers. Due to the special characteristics of neutron detection, we have developed a novel type of special ceramic nTHGEM (neutron THick GEM) for neutron detection. The performance of the nTHGEM working in different Ar/CO2 mixtures is presented, including measurements of the gain and the count rate plateau using a copper target X-ray source. A detector with a single nTHGEM has been tested for 2-D imaging using a 252Cf neutron source. The key parameters of the performance of the nTHGEM detector have been obtained, providing necessary experimental data as a reference for further research on this detector. Supported by National Natural Science Foundation of China (11127508, 11175199, 11205253, 11405191), Key Laboratory of Neutron Physics, CAEP (2013DB06, 2013BB04) and CAS (YZ201512)

  20. A beta-ray spectrometer based on a two-or three silicon detector coincidence telescope

    NASA Astrophysics Data System (ADS)

    Horowitz, Y. S.; Weizman, Y.; Hirning, C. R.

    1996-02-01

    This report describes the operation of a beta-ray energy spectrometer based on a silicon detector telescope using two or three elements. The front detector is a planar, totally-depleted, silicon surface barrier detector that is 97 μm thick, the back detector is a room-temperature, lithium compensated, silicon detector that is 5000 μm thick, and the intermediate detector is similar to the front detector but 72 μm thick and intended to be used only in intense photon fields. The three detectors are mounted in a light-tight aluminum housing. The capability of the spectrometer to reject photons is based upon the fact that the incident photon will have a small probability of simultaneously losing detectable energy in two detectors, and an even smaller probability of losing detectable energy in all three detectors. Electrons will, however, almost always record measurable events in either the front two or all three detectors. A coincidence requirement between the detectors thus rejects photon induced events. With a 97 μm thick detector the lower energy coincidence threshold is approximately 110 keV. With an ultra-thin 40 μm thick front detector, and operated at 15°C, the spectrometer is capable of detecting even 60-70 keV electrons with a coincidence efficiency of 60%. The spectrometer has been used to measure beta radiation fields in CANDU reactor working environments, and the spectral information is intended to support dose algorithms for the LiF TLD chips used in the Ontario Hydro dosimetry program.

  1. Photon-number-resolving superconducting nanowire detectors

    NASA Astrophysics Data System (ADS)

    Mattioli, Francesco; Zhou, Zili; Gaggero, Alessandro; Gaudio, Rosalinda; Jahanmirinejad, Saeedeh; Sahin, Döndü; Marsili, Francesco; Leoni, Roberto; Fiore, Andrea

    2015-10-01

    In recent years, photon-number-resolving (PNR) detectors have attracted great interest, mainly because they can play a key role in diverse application fields. A PNR detector with a large dynamic range would represent an ideal photon detector, bringing the linear response of conventional analogue detectors down to the single-photon level. Several technologies, such as InGaAs single photon avalanche detectors (SPADs), arrays of silicon photomultipliers, InGaAs SPADs with self-differencing circuits and transition edge sensors have shown photon number resolving capability. Superconducting nanowires provide free-running single-photon sensitivity from visible to mid-infrared frequencies, low dark counts, excellent timing resolution (<60 ps) and short dead time (˜10 ns), at an easily accessible temperature (2-3 K), but they do not inherently resolve the photon number. In this framework, PNR detectors based on arrays of superconducting nanowires have been proposed. In this article we describe a number of methods and device configurations that have been pursued to obtain PNR capability using superconducting nanowire detectors.

  2. Development of solid-state avalanche amorphous selenium for medical imaging

    SciTech Connect

    Scheuermann, James R. Goldan, Amir H.; Zhao, Wei; Tousignant, Olivier; Léveillé, Sébastien

    2015-03-15

    Purpose: Active matrix flat panel imagers (AMFPI) have limited performance in low dose applications due to the electronic noise of the thin film transistor (TFT) array. A uniform layer of avalanche amorphous selenium (a-Se) called high gain avalanche rushing photoconductor (HARP) allows for signal amplification prior to readout from the TFT array, largely eliminating the effects of the electronic noise. The authors report preliminary avalanche gain measurements from the first HARP structure developed for direct deposition onto a TFT array. Methods: The HARP structure is fabricated on a glass substrate in the form of p-i-n, i.e., the electron blocking layer (p) followed by an intrinsic (i) a-Se layer and finally the hole blocking layer (n). All deposition procedures are scalable to large area detectors. Integrated charge is measured from pulsed optical excitation incident on the top electrode (as would in an indirect AMFPI) under continuous high voltage bias. Avalanche gain measurements were obtained from samples fabricated simultaneously at different locations in the evaporator to evaluate performance uniformity across large area. Results: An avalanche gain of up to 80 was obtained, which showed field dependence consistent with previous measurements from n-i-p HARP structures established for vacuum tubes. Measurements from multiple samples demonstrate the spatial uniformity of performance using large area deposition methods. Finally, the results were highly reproducible during the time course of the entire study. Conclusions: We present promising avalanche gain measurement results from a novel HARP structure that can be deposited onto a TFT array. This is a crucial step toward the practical feasibility of AMFPI with avalanche gain, enabling quantum noise limited performance down to a single x-ray photon per pixel.

  3. Development of solid-state avalanche amorphous selenium for medical imaging

    PubMed Central

    Scheuermann, James R.; Goldan, Amir H.; Tousignant, Olivier; Léveillé, Sébastien; Zhao, Wei

    2015-01-01

    Purpose: Active matrix flat panel imagers (AMFPI) have limited performance in low dose applications due to the electronic noise of the thin film transistor (TFT) array. A uniform layer of avalanche amorphous selenium (a-Se) called high gain avalanche rushing photoconductor (HARP) allows for signal amplification prior to readout from the TFT array, largely eliminating the effects of the electronic noise. The authors report preliminary avalanche gain measurements from the first HARP structure developed for direct deposition onto a TFT array. Methods: The HARP structure is fabricated on a glass substrate in the form of p-i-n, i.e., the electron blocking layer (p) followed by an intrinsic (i) a-Se layer and finally the hole blocking layer (n). All deposition procedures are scalable to large area detectors. Integrated charge is measured from pulsed optical excitation incident on the top electrode (as would in an indirect AMFPI) under continuous high voltage bias. Avalanche gain measurements were obtained from samples fabricated simultaneously at different locations in the evaporator to evaluate performance uniformity across large area. Results: An avalanche gain of up to 80 was obtained, which showed field dependence consistent with previous measurements from n-i-p HARP structures established for vacuum tubes. Measurements from multiple samples demonstrate the spatial uniformity of performance using large area deposition methods. Finally, the results were highly reproducible during the time course of the entire study. Conclusions: We present promising avalanche gain measurement results from a novel HARP structure that can be deposited onto a TFT array. This is a crucial step toward the practical feasibility of AMFPI with avalanche gain, enabling quantum noise limited performance down to a single x-ray photon per pixel. PMID:25735277

  4. Temporal correlations in neuronal avalanche occurrence

    PubMed Central

    Lombardi, F.; Herrmann, H. J.; Plenz, D.; de Arcangelis, L.

    2016-01-01

    Ongoing cortical activity consists of sequences of synchronized bursts, named neuronal avalanches, whose size and duration are power law distributed. These features have been observed in a variety of systems and conditions, at all spatial scales, supporting scale invariance, universality and therefore criticality. However, the mechanisms leading to burst triggering, as well as the relationship between bursts and quiescence, are still unclear. The analysis of temporal correlations constitutes a major step towards a deeper understanding of burst dynamics. Here, we investigate the relation between avalanche sizes and quiet times, as well as between sizes of consecutive avalanches recorded in cortex slice cultures. We show that quiet times depend on the size of preceding avalanches and, at the same time, influence the size of the following one. Moreover we evidence that sizes of consecutive avalanches are correlated. In particular, we show that an avalanche tends to be larger or smaller than the following one for short or long time separation, respectively. Our analysis represents the first attempt to provide a quantitative estimate of correlations between activity and quiescence in the framework of neuronal avalanches and will help to enlighten the mechanisms underlying spontaneous activity. PMID:27094323

  5. Temporal correlations in neuronal avalanche occurrence.

    PubMed

    Lombardi, F; Herrmann, H J; Plenz, D; de Arcangelis, L

    2016-01-01

    Ongoing cortical activity consists of sequences of synchronized bursts, named neuronal avalanches, whose size and duration are power law distributed. These features have been observed in a variety of systems and conditions, at all spatial scales, supporting scale invariance, universality and therefore criticality. However, the mechanisms leading to burst triggering, as well as the relationship between bursts and quiescence, are still unclear. The analysis of temporal correlations constitutes a major step towards a deeper understanding of burst dynamics. Here, we investigate the relation between avalanche sizes and quiet times, as well as between sizes of consecutive avalanches recorded in cortex slice cultures. We show that quiet times depend on the size of preceding avalanches and, at the same time, influence the size of the following one. Moreover we evidence that sizes of consecutive avalanches are correlated. In particular, we show that an avalanche tends to be larger or smaller than the following one for short or long time separation, respectively. Our analysis represents the first attempt to provide a quantitative estimate of correlations between activity and quiescence in the framework of neuronal avalanches and will help to enlighten the mechanisms underlying spontaneous activity. PMID:27094323

  6. Temporal correlations in neuronal avalanche occurrence

    NASA Astrophysics Data System (ADS)

    Lombardi, F.; Herrmann, H. J.; Plenz, D.; de Arcangelis, L.

    2016-04-01

    Ongoing cortical activity consists of sequences of synchronized bursts, named neuronal avalanches, whose size and duration are power law distributed. These features have been observed in a variety of systems and conditions, at all spatial scales, supporting scale invariance, universality and therefore criticality. However, the mechanisms leading to burst triggering, as well as the relationship between bursts and quiescence, are still unclear. The analysis of temporal correlations constitutes a major step towards a deeper understanding of burst dynamics. Here, we investigate the relation between avalanche sizes and quiet times, as well as between sizes of consecutive avalanches recorded in cortex slice cultures. We show that quiet times depend on the size of preceding avalanches and, at the same time, influence the size of the following one. Moreover we evidence that sizes of consecutive avalanches are correlated. In particular, we show that an avalanche tends to be larger or smaller than the following one for short or long time separation, respectively. Our analysis represents the first attempt to provide a quantitative estimate of correlations between activity and quiescence in the framework of neuronal avalanches and will help to enlighten the mechanisms underlying spontaneous activity.

  7. Screening of Avalanche Photodiodes for the Cms Ecal

    NASA Astrophysics Data System (ADS)

    Antunovic, Z.; Britvitch, I.; Kuznetsov, A.; Musienko, Y.; Reucroft, S.; Swain, J.; Deiters, K.; Ingram, Q.; Renker, D.; Sakhelashvili, T.; Godinovic, N.; Puljak, I.; Soric, I.; Rusack, R.; Singovski, A.

    2004-07-01

    The Compact Muon Solenoid is one of two general purpose detectors currently being constructed for the Large Hadron Collider at CERN foreseen to begin data taking in 2007. Avalanche Photo Diodes (APDs) have been chosen to detect the scintillation light of the 61 200 lead tungstate crystals in the barrel part of the electromagnetic calorimeter of CMS. After a 8 years long R&D work Hamamatsu Photonics produces now APDs with a structure that is basically radiation resistant. Since a reliability of 99.9% is required, a method to detect weak APDs before they are built into the detector had to be developed. The described screening method is a combination of an irradiation with 60Co and annealing under bias of all APDs and on a sampling basis only an irradiation with hadrons.

  8. Physics-based generation of gamma-ray response functions for CDZNTE detectors

    SciTech Connect

    Prettyman, T.H.; Mercer, D.J.; Cooper, C.; Russo, P.A.; Rawool-Sullivan, M.; Close, D.A.; Luke, P.N.; Amman, M.; Soldner, S.

    1997-09-01

    A physics-based approach to gamma-ray response-function generation is presented in which the response of CdZnTe detectors is modeled from first principles. Computer modeling is used to generate response functions needed for spectrum analysis for general detector configurations (e.g., electrode design, detector materials and geometry, and operating conditions). With computer modeling, requirements for calibration and characterization are significantly reduced. Elements of the physics-based model, including gamma-ray transport, charge drift-diffusion, and circuit response, are presented. Calculated and experimental gamma-ray spectra are compared for a coplanar-grid CdZnTe detector.

  9. Electronics and data acquisition system for the ICAL prototype detector of India-based neutrino observatory

    NASA Astrophysics Data System (ADS)

    Behere, A.; Bhuyan, M.; Chandratre, V. B.; Dasgupta, S.; Datar, V. M.; Kalmani, S. D.; Lahamge, S. M.; Mondal, N. K.; Mukhopadhyay, P. K.; Nagaraj, P.; Nagesh, B. K.; Pal, S.; Rao, Shobha K.; Samuel, D.; Saraf, M. N.; Satyanarayana, B.; Shastrakar, R. S.; Shinde, R. R.; Sudheer, K. M.; Upadhya, S. S.; Verma, P.

    2013-02-01

    The India-based Neutrino Observatory (INO) collaboration has proposed to build a 50 kton magnetized Iron Calorimeter (ICAL) detector with the primary goal to study neutrino oscillations, employing Resistive Plate Chambers (RPCs) as active detector elements. A prototype of the ICAL detector has been built in order to develop and characterize the intrinsic sub-systems, like RPCs, gas system, electronics and data acquisition system, etc. This paper describes in detail the readout electronics as well as the VME-based data acquisition system for the prototype detector.

  10. Radiation Response of Emerging High Gain, Low Noise Detectors

    NASA Technical Reports Server (NTRS)

    Becker, Heidi N.; Farr, William H; Zhu, David Q.

    2007-01-01

    Data illustrating the radiation response of emerging high gain, low noise detectors are presented. Ionizing dose testing of silicon internal discrete avalanche photodiodes, and 51-MeV proton testing of InGaAs/InAlAs avalanche photodiodes operated in Geiger mode are discussed.

  11. Minimal Conductance-Based Model of Auditory Coincidence Detector Neurons

    PubMed Central

    Ashida, Go; Funabiki, Kazuo; Kretzberg, Jutta

    2015-01-01

    Sound localization is a fundamental sensory function of a wide variety of animals. The interaural time difference (ITD), an important cue for sound localization, is computed in the auditory brainstem. In our previous modeling study, we introduced a two-compartment Hodgkin-Huxley type model to investigate how cellular and synaptic specializations may contribute to precise ITD computation of the barn owl's auditory coincidence detector neuron. Although our model successfully reproduced fundamental physiological properties observed in vivo, it was unsuitable for mathematical analyses and large scale simulations because of a number of nonlinear variables. In the present study, we reduce our former model into three types of conductance-based integrate-and-fire (IF) models. We test their electrophysiological properties using data from published in vivo and in vitro studies. Their robustness to parameter changes and computational efficiencies are also examined. Our numerical results suggest that the single-compartment active IF model is superior to other reduced models in terms of physiological reproducibility and computational performance. This model will allow future theoretical studies that use more rigorous mathematical analysis and network simulations. PMID:25844803

  12. MEMS-based infrared detector for body thermometer

    NASA Astrophysics Data System (ADS)

    Yoo, Kum-Pyo; Kim, Yun-Ho; Min, Nam-Ki

    2005-12-01

    Infrared detectors have many application fields. One of those, MEMS based thermopile is attractive for many low-cost commercial and industrial applications, mainly because it does not require cooling for operation and the process technologies are relatively simple. The MEMS thermopile fabricated on a silicon nitride microbridge structure was proposed. Using microbridge rather conventional membrane makes it possible to fabricate much smaller micro thermopile and to reduce heat loss because of small contact area at silicon rim. The bridge material is only composed of Si3N4. The thermocouple was used a poly-Si and an aluminum. The characteristic of electromotive force (EMF) generation was evaluated for various patterns at hot junction. Aluminum thermocouple shape on bridge structure was designed two patterns. One was a square shape and the other shape was a hollow square. The output voltage of hollow square-type electrode was increased in compared with square-type electrode from 3.03uV/°C to 4.609uV/°C at body temperature (37°C). With the same membrane dimensions and the same overall thickness of the chip a thermopile on microbridge is almost 53% smaller a conventional thermopile chip.

  13. Low power adder based digital filter for QRS detector.

    PubMed

    Murali, L; Chitra, D; Manigandan, T

    2014-01-01

    Most of the Biomedical applications use dedicated processors for the implementation of complex signal processing. Among them, sensor network is also a type, which has the constraint of low power consumption. Since the processing elements are the most copiously used operations in the signal processors, the power consumption of this has the major impact on the system level application. In this paper, we introduce low power concept of transistor stacking to reduce leakage power; and new architectures based on stacking to implement the full adder and its significance at the digital filter level for QRS detector are implemented. The proposed concept has lesser leakage power at the adder as well as filter level with trade-off in other quality metrics of the design. This enabled the design to be dealt with as the low-power corner and can be made adaptable to any level of hierarchical abstractions as per the requirement of the application. The proposed architectures are designed, modeled at RTL level using the Verilog-HDL, and synthesized in Synopsys Design Compiler by mapping the design to 65 nm technology library standard cells. PMID:24895649

  14. Characterization of the artificially triggered avalanches in the MonterosaSki resort (North-western Italian Alps)

    NASA Astrophysics Data System (ADS)

    Maggioni, Margherita; Brulport, A.; Freppaz, M.; Welf, A.; Purves, R.

    2010-05-01

    Artificially triggering methods are nowadays commonly used for avalanche prevention within ski-resorts. The knowledge of possible relations between the characteristics of the avalanche events and the snowpack and weather conditions might help to foresee the avalanche release probability after a favorable weather cycle. The forecast might be helped by models, like for example snowpack evolution models or nearest neighbor models. The latters are based on statistics performed on large databases where the avalanche events, together with the related snow and weather conditions, are well recorded. Within the Operational programme 'Italy - France (Alps - ALCOTRA)', Project "Gestion en sécurité des territories de montagne transfrontalière - Risk-Nat", from winter 2009-2010, in the MonterosaSki resort all the artificially triggered avalanches are registered with their characteristics (e.g. outline, type of avalanches, elevation, aspect), the triggering method (e.g. explosive, Daisy-Bell) and the snow and weather conditions. The aim of this project is to create a well documented database in order to perform some simple statistical analysis to find possible relation between the characteristics of the avalanches (e.g. type, size, run-out distance), the topography of the site (e.g. slope angle, aspect), snowpack condition (e.g. snow crystal type, snow temperature, density) and meteorological parameters (e.g. new snow, air temperature, wind). Moreover, the avalanche release method and the result of the triggering are recorded, in order to understand which are the most favorable conditions for avalanche release. This project is at its first operational winter, therefore in this work we present preliminary data concerning the study area, the methodology and the results from the first winter season, which might be useful to improve our knowledge about artificially triggered avalanches and to help the ski-piste security personnel to take decisions about the avalanche situation

  15. Airplane Ice Detector Based on a Microwave Transmission Line

    NASA Technical Reports Server (NTRS)

    Ngo, Phong; Arndt, G. Dickey; Carl, James R.

    2004-01-01

    An electronic instrument that could detect the potentially dangerous buildup of ice on an airplane wing is undergoing development. The instrument is based on a microwave transmission line configured as a capacitance probe: at selected spots, the transmission-line conductors are partly exposed to allow any ice and/or liquid water present at those spots to act as predominantly capacitive electrical loads on the transmission line. These loads change the input impedance of the transmission line, as measured at a suitable excitation frequency. Thus, it should be possible to infer the presence of ice and/or liquid water from measurements of the input impedance and/or electrical parameters related to the input impedance. The sensory transmission line is of the microstrip type and thus thin enough to be placed on an airplane wing without unduly disturbing airflow in flight. The sensory spots are small areas from which the upper layer of the microstrip has been removed to allow any liquid water or ice on the surface to reach the transmission line. The sensory spots are spaced at nominal open-circuit points, which are at intervals of a half wavelength (in the transmission line, not in air) at the excitation frequency. The excitation frequency used in the experiments has been 1 GHz, for which a half wavelength in the transmission line is .4 in. (.10 cm). The figure depicts a laboratory prototype of the instrument. The impedance-related quantities chosen for use in this version of the instrument are the magnitude and phase of the scattering parameter S11 as manifested in the in-phase (I ) and quadrature (Q) outputs of the phase detector. By careful layout of the transmission line (including the half-wavelength sensor spacing), one can ensure that the amplitude and phase of the input to the phase detector keep shifting in the same direction as ice forms on one or more of the sensor areas. Although only one transmission-line sensor strip is used in the laboratory version, in a

  16. Performance of a PSPMT based detector for scintimammography.

    PubMed

    Williams, M B; Williams, M B; Goode, A R; Galbis-Reig, V; Majewski, S; Weisenberger, A G; Wojcik, R

    2000-03-01

    In breast scintigraphy, compact detectors with high intrinsic spatial resolution and small inactive peripheries can provide improvements in extrinsic spatial resolution, efficiency and contrast for small lesions relative to larger conventional cameras. We are developing a pixelated small field-of-view gamma camera for scintimammography. Extensive measurements of the imaging properties of a prototype system have been made, including spatial resolution, sensitivity, uniformity of response, geometric linearity and energy resolution. An anthropomorphic torso phantom providing a realistic breast exit gamma spectrum has been used in a qualitative study of lesion detectability. A new type of breast imaging system that combines scintimammography and digital mammography in a single upright unit has also been developed. The system provides automatic co-registration between the scintigram and the digital mammogram, obtained with the breast in a single configuration. Intrinsic spatial resolution was evaluated via calculation of the phase-dependent modulation transfer function (MTF). Measurements of extrinsic spatial resolution, sensitivity and uniformity of response were made for two types of parallel hole collimator using NEMA (National Electrical Manufacturers Association) protocols. Geometric linearity was quantified using a line input and least squares analysis of the measured line shape. Energy resolution was measured for seven different crystal types, and the effectiveness of optical grease coupling was assessed. Exit gamma spectra were obtained using a cadmium zinc telluride based spectrometer. These were used to identify appropriate radioisotope concentrations for the various regions of an anthropomorphic torso phantom, such that realistic scatter conditions could be obtained during phantom measurements. For prone scintimammography, a special imaging table was constructed that permits simultaneous imaging of both breasts, as well as craniocaudal views. A dedicated

  17. Performance of 6cmx6cm MCP-based picosecond photo-detectors

    NASA Astrophysics Data System (ADS)

    Wang, Jingbo; Xie, Junqi; Wagner, Robert; Walters, Dean; Byrum, Karen; Xia, Lei; Zhao, Allen; May, Edward; Demarteau, Marcel; Anlpd Team

    2015-04-01

    Microchannel plate (MCP)-based photo-detectors are capable of micron-level spatial imaging and picosecond-level timing resolution, making them a promising candidate for the next generation high-precision photo-detectors. Argonne National Laboratory (ANL) is currently producing 6x6 cm2, cost-effective, thin planar, glass-body, MCP-based photo-detectors at a newly constructed production system. An indium sealing technique was successfully developed for a permanent detector seal and a several photo-detectors have been produced. The performance of the photo-detectors were characterized with a pulsed laser facility, showing a 60 ps Transit Time Spread (TTS) resolution and <500 μm spatial resolution. The test setup, data acquisition, data analysis and the experimental results will be presented and discussed.

  18. Simulation for Iron Calorimeter prototype detector of India-based Neutrino Observatory

    SciTech Connect

    Ghosh, Tapasi; Chattopadhyay, Subhasis

    2010-03-30

    The India-based Neutrino Observatory (INO) collaboration is proposing to build a 50 kton magnetized iron calorimeter (ICAL) detector in an underground laboratory to be located in South India. As a first step towards building the ICAL detector, a 35 ton prototype of the same design has been set up on the surface to track cosmic ray muons. This paper discusses the prototype detector geometry simulation by GEANT4, and the detector response to the cosmic muons. We have developed a track fitting procedure based on the Kalman Filter technique for the prototype detector when the detector is exposed to single muon tracks. The relevant track parameters i.e., momentum, direction and charge are reconstructed and analyzed. Finally we show the resolution of reconstructed momenta.

  19. Dynamics of Avalanche Activities in Financial Markets

    NASA Astrophysics Data System (ADS)

    Kim, Cheol-Hyun; Park, C. H.; Kim, Soo Yong; Kim, Kyungsik; Scalas, Enrico

    We study the dynamical properties of avalanche activities in the Korean Treasury Bond (KTB) futures price and the S&P 500 stock index. We apply the detrended fluctuation analysis, multiscale sample entropy and wavelet coefficient correlation to them, which revealed the scale-free dynamics of the bursting time series, avalanche size, and laminar time. We found that the laminar time and the avalanche size are anti-correlated in a short scale but in a large scale strongly correlated in KTB503, and are strongly correlated over all scales in S&P 500.

  20. Theoretical performance analysis for CMOS based high resolution detectors.

    PubMed

    Jain, Amit; Bednarek, Daniel R; Rudin, Stephen

    2013-03-01

    High resolution imaging capabilities are essential for accurately guiding successful endovascular interventional procedures. Present x-ray imaging detectors are not always adequate due to their inherent limitations. The newly-developed high-resolution micro-angiographic fluoroscope (MAF-CCD) detector has demonstrated excellent clinical image quality; however, further improvement in performance and physical design may be possible using CMOS sensors. We have thus calculated the theoretical performance of two proposed CMOS detectors which may be used as a successor to the MAF. The proposed detectors have a 300 μm thick HL-type CsI phosphor, a 50 μm-pixel CMOS sensor with and without a variable gain light image intensifier (LII), and are designated MAF-CMOS-LII and MAF-CMOS, respectively. For the performance evaluation, linear cascade modeling was used. The detector imaging chains were divided into individual stages characterized by one of the basic processes (quantum gain, binomial selection, stochastic and deterministic blurring, additive noise). Ranges of readout noise and exposure were used to calculate the detectors' MTF and DQE. The MAF-CMOS showed slightly better MTF than the MAF-CMOS-LII, but the MAF-CMOS-LII showed far better DQE, especially for lower exposures. The proposed detectors can have improved MTF and DQE compared with the present high resolution MAF detector. The performance of the MAF-CMOS is excellent for the angiography exposure range; however it is limited at fluoroscopic levels due to additive instrumentation noise. The MAF-CMOS-LII, having the advantage of the variable LII gain, can overcome the noise limitation and hence may perform exceptionally for the full range of required exposures; however, it is more complex and hence more expensive. PMID:24353390

  1. Characterization of Silicon Photomultiplier based detectors with digital electronics

    NASA Astrophysics Data System (ADS)

    Daugherty, Hadyn; Taylor, Steven; Hasse, Adam; Grzywacz, Robert

    2014-09-01

    Due to their compact design and good timing performance Silicon Photomultipliers (SiPMT) were chosen to be used to readout the light from the plastic scintillator detector used as a trigger for the Versatile Array of Neutron Detectors at Low Energy (VANDLE). Prior to development of the new system, we have performed proof of principle studies, to demonstrate that the SiPMT, provided by Sensl is a viable replacement for the conventional photomultiplier. We have build a prototype detector, develop electronics readout chain and characterized its performance using the Digital Data Acquisition system at the University of Tennessee. This experience led to construction of segmented trigger detector which will be used in future VANDLE experiments. *This research was sponsored in part by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Cooperative Agreement No. DE-FG52-08NA28552 and the DOE Office of Nuclear Physics. Due to their compact design and good timing performance Silicon Photomultipliers (SiPMT) were chosen to be used to readout the light from the plastic scintillator detector used as a trigger for the Versatile Array of Neutron Detectors at Low Energy (VANDLE). Prior to development of the new system, we have performed proof of principle studies, to demonstrate that the SiPMT, provided by Sensl is a viable replacement for the conventional photomultiplier. We have build a prototype detector, develop electronics readout chain and characterized its performance using the Digital Data Acquisition system at the University of Tennessee. This experience led to construction of segmented trigger detector which will be used in future VANDLE experiments. *This research was sponsored in part by the National Nuclear Security Administration under the Stewardship Science Academic Alliances program through DOE Cooperative Agreement No. DE-FG52-08NA28552 and the DOE Office of Nuclear Physics. University of Tennessee

  2. Infrasound array criteria for automatic detection and front velocity estimation of snow avalanches: towards a real-time early-warning system

    NASA Astrophysics Data System (ADS)

    Marchetti, E.; Ripepe, M.; Ulivieri, G.; Kogelnig, A.

    2015-11-01

    Avalanche risk management is strongly related to the ability to identify and timely report the occurrence of snow avalanches. Infrasound has been applied to avalanche research and monitoring for the last 20 years but it never turned into an operational tool to identify clear signals related to avalanches. We present here a method based on the analysis of infrasound signals recorded by a small aperture array in Ischgl (Austria), which provides a significant improvement to overcome this limit. The method is based on array-derived wave parameters, such as back azimuth and apparent velocity. The method defines threshold criteria for automatic avalanche identification by considering avalanches as a moving source of infrasound. We validate the efficiency of the automatic infrasound detection with continuous observations with Doppler radar and we show how the velocity of a snow avalanche in any given path around the array can be efficiently derived. Our results indicate that a proper infrasound array analysis allows a robust, real-time, remote detection of snow avalanches that is able to provide the number and the time of occurrence of snow avalanches occurring all around the array, which represent key information for a proper validation of avalanche forecast models and risk management in a given area.

  3. Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials.

    PubMed

    Nikzad, Shouleh; Hoenk, Michael; Jewell, April D; Hennessy, John J; Carver, Alexander G; Jones, Todd J; Goodsall, Timothy M; Hamden, Erika T; Suvarna, Puneet; Bulmer, J; Shahedipour-Sandvik, F; Charbon, Edoardo; Padmanabhan, Preethi; Hancock, Bruce; Bell, L Douglas

    2016-01-01

    Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100-300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness. PMID:27338399

  4. Single Photon Counting UV Solar-Blind Detectors Using Silicon and III-Nitride Materials

    PubMed Central

    Nikzad, Shouleh; Hoenk, Michael; Jewell, April D.; Hennessy, John J.; Carver, Alexander G.; Jones, Todd J.; Goodsall, Timothy M.; Hamden, Erika T.; Suvarna, Puneet; Bulmer, J.; Shahedipour-Sandvik, F.; Charbon, Edoardo; Padmanabhan, Preethi; Hancock, Bruce; Bell, L. Douglas

    2016-01-01

    Ultraviolet (UV) studies in astronomy, cosmology, planetary studies, biological and medical applications often require precision detection of faint objects and in many cases require photon-counting detection. We present an overview of two approaches for achieving photon counting in the UV. The first approach involves UV enhancement of photon-counting silicon detectors, including electron multiplying charge-coupled devices and avalanche photodiodes. The approach used here employs molecular beam epitaxy for delta doping and superlattice doping for surface passivation and high UV quantum efficiency. Additional UV enhancements include antireflection (AR) and solar-blind UV bandpass coatings prepared by atomic layer deposition. Quantum efficiency (QE) measurements show QE > 50% in the 100–300 nm range for detectors with simple AR coatings, and QE ≅ 80% at ~206 nm has been shown when more complex AR coatings are used. The second approach is based on avalanche photodiodes in III-nitride materials with high QE and intrinsic solar blindness. PMID:27338399

  5. SiC-based Photo-detectors for UV, VUV, EUV and Soft X-ray Detection

    NASA Technical Reports Server (NTRS)

    Yan, Feng

    2006-01-01

    A viewgraph presentation describing an ideal Silicon Carbide detector for ultraviolet, vacuum ultraviolet, extreme ultraviolet and soft x-ray detection is shown. The topics include: 1) An ideal photo-detector; 2) Dark current density of SiC photodiodes at room temperature; 3) Dark current in SiC detectors; 4) Resistive and capacitive feedback trans-impedance amplifier; 5) Avalanche gain; 6) Excess noise; 7) SNR in single photon counting mode; 8) Structure of SiC single photon counting APD and testing structure; 9) Single photon counting waveform and testing circuit; 10) Amplitude of SiC single photon counter; 11) Dark count of SiC APD photon counters; 12) Temperature-dependence of dark count rate; 13) Reduce the dark count rate by reducing the breakdown electric field; 14) Spectrum range for SiC detectors; 15) QE curves of Pt/4H-SiC photodiodes; 16) QE curve of SiC; 17) QE curves of SiC photodiode vs. penetration depth; 18) Visible rejection of SiC photodiodes; 19) Advantages of SiC photodiodes; 20) Competitors of SiC detectors; 21) Extraterrestrial solar spectra; 22) Visible-blind EUV detection; 23) Terrestrial solar spectra; and 24) Less than 1KeV soft x-ray detection.

  6. Evaluation of a compact, high-resolution SPECT detector based on digital silicon photomultipliers.

    PubMed

    Bouckaert, Carmen; Vandenberghe, Stefaan; Van Holen, Roel

    2014-12-01

    MicroSPECT is one of the main functional imaging techniques used in the preclinical setting. Even though high-resolution images can be obtained with currently available systems, their sensitivity is often quite low due to the use of multi-pinhole collimation. This results in long acquisition times and hampers dynamic imaging. However, it has already been shown that this limited sensitivity can be overcome using high-resolution detectors. In this article, we therefore investigated the use of a digital photon counter (DPC) in combination with a 2 mm thick monolithic LYSO crystal for SPECT imaging. These light sensors contain arrays of avalanche photodiodes whose signals are directly digitised. The DPCs have the advantage that they are very compact, have a high intrinsic resolution, are MR compatible and allow disabling cells with a high dark count rate. In order to investigate the influence of the temperature dependent dark count rate on the detector performance, we compared it at 3 °C and 18 °C. At 3 °C, we observed an energy resolution of 28.8% and an intrinsic spatial resolution of 0.48 mm. Furthermore, the count rate at 10% loss is 60 kcps. Next, we looked at the event loss at 18 °C caused by the higher dark count rate and found a 5% loss compared to the 3 °C measurements. At this higher temperature the energy resolution becomes 29.2% and the intrinsic spatial resolution decreases to 0.52 mm. Due to the 5% count loss, the count rate at 10% loss increases to 63 kcps. A small degradation of the detector performance is thus observed at 18 °C.These results show the usefulness of this detector for SPECT imaging together with its excellent intrinsic spatial resolution. A drawback of the detector is its low, spatially varying energy resolution. Even though the detection efficiency and intrinsic spatial resolution are better at 3 °C, results are still acceptable at 18 °C. PMID:25401505

  7. Evaluation of a compact, high-resolution SPECT detector based on digital silicon photomultipliers

    NASA Astrophysics Data System (ADS)

    Bouckaert, Carmen; Vandenberghe, Stefaan; Van Holen, Roel

    2014-12-01

    MicroSPECT is one of the main functional imaging techniques used in the preclinical setting. Even though high-resolution images can be obtained with currently available systems, their sensitivity is often quite low due to the use of multi-pinhole collimation. This results in long acquisition times and hampers dynamic imaging. However, it has already been shown that this limited sensitivity can be overcome using high-resolution detectors. In this article, we therefore investigated the use of a digital photon counter (DPC) in combination with a 2 mm thick monolithic LYSO crystal for SPECT imaging. These light sensors contain arrays of avalanche photodiodes whose signals are directly digitised. The DPCs have the advantage that they are very compact, have a high intrinsic resolution, are MR compatible and allow disabling cells with a high dark count rate. In order to investigate the influence of the temperature dependent dark count rate on the detector performance, we compared it at 3 °C and 18 °C. At 3 °C, we observed an energy resolution of 28.8% and an intrinsic spatial resolution of 0.48 mm. Furthermore, the count rate at 10% loss is 60 kcps. Next, we looked at the event loss at 18 °C caused by the higher dark count rate and found a 5% loss compared to the 3 °C measurements. At this higher temperature the energy resolution becomes 29.2% and the intrinsic spatial resolution decreases to 0.52 mm. Due to the 5% count loss, the count rate at 10% loss increases to 63 kcps. A small degradation of the detector performance is thus observed at 18 °C. These results show the usefulness of this detector for SPECT imaging together with its excellent intrinsic spatial resolution. A drawback of the detector is its low, spatially varying energy resolution. Even though the detection efficiency and intrinsic spatial resolution are better at 3 °C, results are still acceptable at 18 °C.

  8. Precursory seismicity associated with frequent, large ice avalanches on Iliamna Volcano, Alaska, USA

    USGS Publications Warehouse

    Caplan-Auerbach, Jacqueline; Huggel, C.

    2007-01-01

    Since 1994, at least six major (volume>106 m3) ice and rock avalanches have occurred on Iliamna volcano, Alaska, USA. Each of the avalanches was preceded by up to 2 hours of seismicity believed to represent the initial stages of failure. Each seismic sequence begins with a series of repeating earthquakes thought to represent slip on an ice-rock interface, or between layers of ice. This stage is followed by a prolonged period of continuous ground-shaking that reflects constant slip accommodated by deformation at the glacier base. Finally the glacier fails in a large avalanche. Some of the events appear to have entrained large amounts of rock, while others comprise mostly snow and ice. Several avalanches initiated from the same source region, suggesting that this part of the volcano is particularly susceptible to failure, possibly due to the presence of nearby fumaroles. Although thermal conditions at the time of failure are not well constrained, it is likely that geothermal energy causes melting at the glacier base, promoting slip and culminating in failure. The frequent nature and predictable failure sequence of Iliamna avalanches makes the volcano an excellent laboratory for the study of ice avalanches. The prolonged nature of the seismic signal suggests that warning may one day be given for similar events occurring in populated regions.

  9. Avalanche control: Conservation Guide Series No. 5

    SciTech Connect

    Not Available

    1985-01-01

    This book examines different methods for determining the characteristics of snow cover and for localizing avalanche risk. It describes various techniques for temporary defense; for snow stabilization in the starting zone; and for wind deflection.

  10. Shocks generate crossover behavior in lattice avalanches.

    PubMed

    Burridge, James

    2013-11-22

    A spatial avalanche model is introduced, in which avalanches increase stability in the regions where they occur. Instability is driven globally by a driving process that contains shocks. The system is typically subcritical, but the shocks occasionally lift it into a near- or supercritical state from which it rapidly retreats due to large avalanches. These shocks leave behind a signature-a distinct power-law crossover in the avalanche size distribution. The model is inspired by landslide field data, but the principles may be applied to any system that experiences stabilizing failures, possesses a critical point, and is subject to an ongoing process of destabilization that includes occasional dramatic destabilizing events. PMID:24313528

  11. Robust snow avalanche detection using machine learning on infrasonic array data

    NASA Astrophysics Data System (ADS)

    Thüring, Thomas; Schoch, Marcel; van Herwijnen, Alec; Schweizer, Jürg

    2014-05-01

    Snow avalanches may threaten people and infrastructure in mountain areas. Automated detection of avalanche activity would be highly desirable, in particular during times of poor visibility, to improve hazard assessment, but also to monitor the effectiveness of avalanche control by explosives. In the past, a variety of remote sensing techniques and instruments for the automated detection of avalanche activity have been reported, which are based on radio waves (radar), seismic signals (geophone), optical signals (imaging sensor) or infrasonic signals (microphone). Optical imagery enables to assess avalanche activity with very high spatial resolution, however it is strongly weather dependent. Radar and geophone-based detection typically provide robust avalanche detection for all weather conditions, but are very limited in the size of the monitoring area. On the other hand, due to the long propagation distance of infrasound through air, the monitoring area of infrasonic sensors can cover a large territory using a single sensor (or an array). In addition, they are by far more cost effective than radars or optical imaging systems. Unfortunately, the reliability of infrasonic sensor systems has so far been rather low due to the strong variation of ambient noise (e.g. wind) causing a high false alarm rate. We analyzed the data collected by a low-cost infrasonic array system consisting of four sensors for the automated detection of avalanche activity at Lavin in the eastern Swiss Alps. A comparably large array aperture (~350m) allows highly accurate time delay estimations of signals which arrive at different times at the sensors, enabling precise source localization. An array of four sensors is sufficient for the time resolved source localization of signals in full 3D space, which is an excellent method to anticipate true avalanche activity. Robust avalanche detection is then achieved by using machine learning methods such as support vector machines. The system is initially

  12. [Calorimeter based detectors for high energy hadron colliders]. [Progress report

    SciTech Connect

    Not Available

    1992-08-04

    This document provides a progress report on research that has been conducted under DOE Grant DEFG0292ER40697 for the past year, and describes proposed work for the second year of this 8 year grant starting November 15, 1992. Personnel supported by the contract include 4 faculty, 1 research faculty, 4 postdocs, and 9 graduate students. The work under this grant has in the past been directed in two complementary directions -- DO at Fermilab, and the second SSC detector GEM. A major effort has been towards the construction and commissioning of the new Fermilab Collider detector DO, including design, construction, testing, the commissioning of the central tracking and the central calorimeters. The first DO run is now underway, with data taking and analysis of the first events. Trigger algorithms, data acquisition, calibration of tracking and calorimetry, data scanning and analysis, and planning for future upgrades of the DO detector with the advent of the FNAL Main Injector are all involved. The other effort supported by this grant has been towards the design of GEM, a large and general-purpose SSC detector with special emphasis on accurate muon measurement over a large solid angle. This effort will culminate this year in the presentation to the SSC laboratory of the GEM Technical Design Report. Contributions are being made to the detector design, coordination, and physics simulation studies with special emphasis on muon final states. Collaboration with the RD5 group at CERN to study muon punch through and to test cathode strip chamber prototypes was begun.

  13. The Next Generation of Ground-based Gravitational Wave Detectors

    NASA Astrophysics Data System (ADS)

    Losurdo, Giovanni; LIGO Scientific Collaboration; Virgo Collaboration

    2007-12-01

    LIGO, Virgo and GEO600, the first generation long-baseline interferometric detectors of gravitational waves, were taking data up until last fall. The analysis of the data collected is in progress and the first detection might be possible with these instruments. But, more sensitive detectors will be needed to start the field of gravitational wave astronomy. Advanced interferometers will improve the sensitivity by a factor of ten, thus enabling the exploration of a universe volume that is 1000 times larger than the present. The technology is almost ready and the construction of Advanced LIGO and Advanced Virgo is planned to start at the beginning of the next decade. With an expected event rate of 1/week-1/day these detectors will be powerful instruments that will provide a new way of observing the universe. As an intermediate step, in 2008 LIGO and Virgo will start the upgrade of the current detectors, working towards Enhanced LIGO and Virgo+. GEO600 has also planned a set of incremental upgrades (GEO HF) in order to enhance sensitivity in the high frequency range. In this talk the path towards the advanced detectors will be reviewed and the perspectives of the so-called 2nd generation long-baseline interferometers will be outlined.

  14. A Selenium-Based Detector System For Digital Slot-Radiography

    NASA Astrophysics Data System (ADS)

    Hillen, W.; Schiebel, U.; Zaengel, T.

    1988-06-01

    A research system for digital radiography is described, which is based on a selenium detector with capacitive probe readout. The detector, in which a selenium drum is used as the primary image receptor, is exposed by a scanning fan beam. Scatter reduction and primary transmission by slot-radiography as well as the imaging properties of the selenium detector are discussed. The spatial resolution and the noise behaviour of the detector are analysed. The signal-to-noise ratios expressed in terms of noise equivalent quanta and detective quantum efficiency are calculated and compared with competitive systems.

  15. Study of aging of nuclear detector based on n-silicon/copper phthalocyanine heterojunction

    SciTech Connect

    Ray, A.; Gupta, S. K.

    2013-02-05

    Nuclear detectors based on n-silicon/copper-phthalocyanine (CuPc) heterojunction were fabricated using thermally evaporated CuPc thin film. These detectors exhibited stable electrical and {alpha}-particle characteristics for prolonged periods of time under ordinary laboratory conditions and also exposing to {alpha}- particles (during {alpha}- spectroscopic measurements). The electrical and alpha particle characteristics of these detectors were studied after a long gap of 3 - 5 years and the best result obtained from one detector (five year old) is reported here. Degradation in electrical and alpha particle characteristics were not found to be very significant over the period.

  16. Development of wide-ranged diamond-based detector unit for gamma radiation measurement

    NASA Astrophysics Data System (ADS)

    Baranova, M. A.; Boyko, A. V.; Chebyshev, S. B.; Cherkashin, I. I.; Kireev, V. P.; Petrov, V. I.

    2016-02-01

    In the article the description of wide-ranged diamond-based detector unit is given. Characteristics of the diamond detector were studied in current and in impulse mode. As well it was studied how detector's sensitivity depends on power doze within the limits from 10-3 to 0,4Gy/h (impulse mode) and from 10-1to 2 104Gy/h (current mode). On the basis of the obtained data it is possible to estimate about the possibility of using the detector to prevent emergency accident on a nuclear power plant and for everyday control at a nuclear power plant.

  17. Flexible infrared detectors based on p-n junctions of multi-walled carbon nanotubes.

    PubMed

    Huang, Zhenlong; Gao, Min; Yan, Zhuocheng; Pan, Taisong; Liao, Feiyi; Lin, Yuan

    2016-05-14

    Different types of multi-walled carbon nanotubes (CNTs), synthesized by chemical vapor deposition, are used to fabricate infrared (IR) detectors on flexible substrates based on CNT p-n junctions. It is found that this kind of detector is sensitive to infrared signals with a power density as low as 90 μW mm(-2) even at room temperature. Besides, unlike other devices, the detector with this unique structure can be bent for 100 cycles without any damage and its functionality does not degenerate once it recovers to the initial state. The results give a good reference for developing efficient, low-cost, and flexible IR detectors. PMID:27101973

  18. Hummocks: how they form and evolve in debris avalanches (Invited)

    NASA Astrophysics Data System (ADS)

    Paguican, E. R.; van Wyk de Vries, B.; Lagmay, A.

    2013-12-01

    rubbly carapace. The central parts of many hummocks are dissected by high angle normal faults that descend and merge into low angle detachments of listric shear zones and merge at the base. In the upper parts of the hummocks, second-order smaller ones can form when the layers parallel to the thinning boudinage and generate blocks. The type of stretch structure depends on the lithology and layer interface. The study shows that hummock distribution is independent of distance and transport disintegration but could be related to lithology, initial position, and avalanche kinematics. In conclusion, hummocks as intact survivors do not provide clear evidence of fragmentation during transport, but do provide information on the transport conditions, kinematics, and initial composition of the landslide.

  19. An Omnidirectional Polarization Detector Based on a Metamaterial Absorber.

    PubMed

    Zhang, Binzhen; Zhang, Yong; Duan, Junping; Zhang, Wendong; Wang, Wanjun

    2016-01-01

    The theory, design, simulation, fabrication, and performance of an omnidirectional polarization detector (PD) with two resonances located in the X and Ka ranges based on a metamaterial absorber (MMA) are presented in this paper. The sandwich structure of PD is composed of 0.1 μm periodic "I" shaped patches on the metasurface, a dielectric of 200 μm FR-4 on the interlayer, and a 0.3 μm copper film on the substrate. PD absorptivity is first used to reflect and describe the polarization of the incident wave. The numerical results, derived from the standard full wave finite integration technology (FIT) of CST 2015, indicates that the designed PD shows polarization sensitivity at all incidence angles. The effects on absorptivity produced by the incidence angles, polarization angles, and materials are investigated. The amplitude of absorptivity change caused by polarization reaches 99.802%. A laser ablation process is adopted to prepare the designed PD on a FR-4 board coated with copper on the double plane with a thickness that was 1/93 and 1/48 of wavelength at a resonance frequency of 16.055 GHz and 30.9 GHz, respectively. The sample test results verify the designed PD excellent detectability on the polarization of the incident waves. The proposed PD, which greatly enriches the applications of metamaterials in bolometers, thermal images, stealth materials, microstructure measurements, and electromagnetic devices, is easy to mass produce and market because of its strong detectability, ultrathin thickness, effective cost, and convenient process. PMID:27455280

  20. Design and construct of a new detector for gas chromatography based on continuous negative corona discharge.

    PubMed

    Ghahfarokhi, M Sharifian; Khayamian, T

    2011-05-01

    In this work, a new detector was designed and constructed based on negative corona discharge. This detector can be used separately or as a detector in gas chromatography. The detector and chromatographic variables including cell temperature, gas flow rates, voltage between the two electrodes, and column temperature were optimized. Chloroform was used as a test compound to evaluate the performance of the detector. The detection limit of chloroform was obtained 0.78 ng∕ml and its dynamic range was over the range of 2-840 ng∕ml. The relative standard detection was about 6% for the limit of quantification. This detector is able to be used as an alternative for analysis of compounds containing electronegative elements. PMID:21639545

  1. A measurement method of a detector response function for monochromatic electrons based on the Compton scattering

    NASA Astrophysics Data System (ADS)

    Bakhlanov, S. V.; Bazlov, N. V.; Derbin, A. V.; Drachnev, I. S.; Kayunov, A. S.; Muratova, V. N.; Semenov, D. A.; Unzhakov, E. V.

    2016-06-01

    In this paper we present a method of scintillation detector energy calibration using the gamma-rays. The technique is based on the Compton scattering of gamma-rays in a scintillation detector and subsequent photoelectric absorption of the scattered photon in the Ge-detector. The novelty of this method is that the source of gamma rays, the germanium and scintillation detectors are immediately arranged adjacent to each other. The method presents an effective solution for the detectors consisting of a low atomic number materials, when the ratio between Compton effect and photoelectric absorption is large and the mean path of gamma-rays is comparable to the size of the detector. The technique can be used for the precision measurements of the scintillator light yield dependence on the electron energy.

  2. Defective pixel map creation based on wavelet analysis in digital radiography detectors

    NASA Astrophysics Data System (ADS)

    Park, Chun Joo; Lee, Hyoung Koo; Song, William Y.; Achterkirchen, Thorsten Graeve; Kim, Ho Kyung

    2011-04-01

    The application of digital radiography detectors has attracted increasing attention in both medicine and industry. Since the imaging detectors are fabricated by semiconductor manufacturing process over large areas, defective pixels in the detectors are unavoidable. Moreover, the radiation damage due to the routine use of the detectors progressively increases the density of defective pixels. In this study, we present a method of identifying defective pixels in digital radiography detectors based on wavelet analysis. Artifacts generated due to wavelet transformations have been prevented by an additional local threshold method. The proposed method was applied to a sample digital radiography and the result was promising. The proposed method uses a single pair of dark and white images and does not require them to be corrected in gain-and-offset properties. This method will be helpful for the reliable use of digital radiography detectors through the working lifetime.

  3. Quantum structure based infrared detector research and development within Acreo’s centre of excellence IMAGIC

    NASA Astrophysics Data System (ADS)

    Andersson, J. Y.; Höglund, L.; Noharet, B.; Wang, Q.; Ericsson, P.; Wissmar, S.; Asplund, C.; Malm, H.; Martijn, H.; Hammar, M.; Gustafsson, O.; Hellström, S.; Radamson, H.; Holtz, P. O.

    2010-07-01

    Acreo has a long tradition of working with quantum structure based infrared (IR) detectors and arrays. This includes QWIP (quantum well infrared photodetector), QDIP (quantum dot infrared photodetector), and InAs/GaInSb based photon detectors of different structure and composition. It also covers R&D on uncooled microbolometers. The integrated thermistor material of such detectors is advantageously based on quantum structures that are optimised for high temperature coefficient and low noise. Especially the SiGe material system is preferred due to the compatibility with silicon technology. The R&D work on IR detectors is a prominent part of Acreo's centre of excellence "IMAGIC" on imaging detectors and systems for non-visible wavelengths. IMAGIC is a collaboration between Acreo, several industry partners and universities like the Royal Institute of Technology (KTH) and Linköping University.

  4. A resonance ionization imaging detector based on cesium atomic vapor

    NASA Astrophysics Data System (ADS)

    Temirov, J. P.; Chigarev, N. V.; Matveev, O. I.; Omenetto, N.; Smith, B. W.; Winefordner, J. D.

    2004-05-01

    A novel Cs resonance ionization imaging detector (RIID) has been developed and evaluated. The detector is capable of two-dimensional imaging with high spectral resolution, which is determined by the Doppler broadened atomic linewidth of Cs at given temperature. Ionization schemes of Cs have been investigated using dye and color center tunable lasers pumped by an excimer laser and by a Nd:YAG laser. It has been experimentally shown that the most efficient ionization scheme for Cs RIID should include a three-step excitation/ionization ladder, for example, with transitions at λ1=852.11 (852.113) nm, λ2=917.22 (917.2197) nm, and λ3=1064 nm. The imaging capabilities of the detector have been evaluated using a simpler two-step ionization scheme with wavelengths λ1=852.11 nm and λ2=508 nm.

  5. InAs/AlAsSb based quantum cascade detector

    SciTech Connect

    Reininger, Peter Zederbauer, Tobias; Schwarz, Benedikt; MacFarland, Donald; Andrews, Aaron Maxwell; Schrenk, Werner; Strasser, Gottfried; Detz, Hermann

    2015-08-24

    In this letter, we introduce the InAs/AlAsSb material system for quantum cascade detectors (QCDs). InAs/AlAsSb can be grown lattice matched to InAs and exhibits a conduction band offset of approximately 2.1 eV, enabling the design of very short wavelength quantum cascade detectors. Another benefit using this material system is the low effective mass of the well material that improves the total absorption of the detector and decreases the intersubband scattering rates, which increases the device resistance and thus enhances the noise behavior. We have designed, grown, and measured a QCD that detects at a wavelength of λ = 4.84 μm and shows a peak specific detectivity of approximately 2.7 × 10{sup 7 }Jones at T = 300 K.

  6. Hybridization of a sigma-delta-based CMOS hybrid detector

    NASA Astrophysics Data System (ADS)

    Kolb, K. E.; Stoffel, N. C.; Douglas, B.; Maloney, C. W.; Raisanen, A. D.; Ashe, B.; Figer, D. F.; Tamagawa, T.; Halpern, B.; Ignjatovic, Zeljko

    2010-07-01

    The Rochester Imaging Detector Laboratory, University of Rochester, Infotonics Technology Center, and Jet Process Corporation developed a hybrid silicon detector with an on-chip sigma-delta (ΣΔ) ADC. This paper describes the process and reports the results of developing a fabrication process to robustly produce high-quality bump bonds to hybridize a back-illuminated detector with its ΣΔ ADC. The design utilizes aluminum pads on both the readout circuit and the photodiode array with interconnecting indium bumps between them. The development of the bump bonding process is discussed, including specific material choices, interim process structures, and final functionality. Results include measurements of bond integrity, cross-wafer uniformity of indium bumps, and effects of process parameters on the final product. Future plans for improving the bump bonding process are summarized.

  7. Particle tracking with a Timepix based triple GEM detector

    NASA Astrophysics Data System (ADS)

    George, S. P.; Murtas, F.; Alozy, J.; Curioni, A.; Rosenfeld, A. B.; Silari, M.

    2015-11-01

    This paper details the response of a triple GEM detector with a 55 μmetre pitch pixelated ASIC for readout. The detector is operated as a micro TPC with 9.5 cm3 sensitive volume and characterized with a mixed beam of 120 GeV protons and positive pions. A process for reconstruction of incident particle tracks from individual ionization clusters is described and scans of the gain and drift fields are performed. The angular resolution of the measured tracks is characterized. Also, the readout was operated in a mixed mode where some pixels measure drift time and others charge. This was used to measure the energy deposition in the detector and the charge cloud size as a function of interaction depth. The future uses of the device, including in microdosimetry are discussed.

  8. Origin of the Avalanche-Like Photoluminescence from Metallic Nanowires

    PubMed Central

    Ma, Zongwei; Yu, Ying; Shen, Shaoxin; Dai, Hongwei; Yao, Linhua; Han, Yibo; Wang, Xia; Han, Jun-Bo; Li, Liang

    2016-01-01

    Surface plasmonic systems provide extremely efficient ways to modulate light-matter interaction in photon emission, light harvesting, energy conversion and transferring, etc. Various surface plasmon enhanced luminescent behaviors have been observed and investigated in these systems. But the origin of an avalanche-like photoluminescence, which was firstly reported in 2007 from Au and subsequently from Ag nanowire arrays/monomers, is still not clear. Here we show, based on systematic investigations including the excitation power/time related photoluminescent measurements as well as calculations, that this avalanche-like photoluminescence is in fact a result of surface plasmon assisted thermal radiation. Nearly all of the related observations could be perfectly interpreted with this concept. Our finding is crucial for understanding the surface plasmon mediated thermal and photoemission behaviors in plasmonic structures, which is of great importance in designing functional plasmonic devices. PMID:26728439

  9. Photon avalanche up-conversion in holmium doped fluoride glasses

    SciTech Connect

    Chen, Y.H.; Liu, G.K.; Beitz, J.V.; Jie Wang

    1996-08-01

    Photon avalanche green up-conversion emission centered at 545 nm has been observed in Ho{sup 3+} doped and Ho{sup 3+}, Tm{sup 3+} co-doped ZrF{sub 4}-based fluoride glasses when excited near 585 nm which is off resonance with any ground state absorption bands of either Ho{sup 3+} or Tm{sup 3+} ions. Detailed spectral measurements and analysis suggest that the 545 nm emission occurs from the {sup 5}S{sub 2},{sup 5}F{sub 4} states of Ho{sup 3+} that are populated by excited state absorption from the {sup 5}I{sub 7} state of Ho{sup 3+}. Strong cross-relaxation that efficiently populates the {sup 5}I{sub 7} state makes the photon avalanche process possible in this system.

  10. Origin of the Avalanche-Like Photoluminescence from Metallic Nanowires

    NASA Astrophysics Data System (ADS)

    Ma, Zongwei; Yu, Ying; Shen, Shaoxin; Dai, Hongwei; Yao, Linhua; Han, Yibo; Wang, Xia; Han, Jun-Bo; Li, Liang

    2016-01-01

    Surface plasmonic systems provide extremely efficient ways to modulate light-matter interaction in photon emission, light harvesting, energy conversion and transferring, etc. Various surface plasmon enhanced luminescent behaviors have been observed and investigated in these systems. But the origin of an avalanche-like photoluminescence, which was firstly reported in 2007 from Au and subsequently from Ag nanowire arrays/monomers, is still not clear. Here we show, based on systematic investigations including the excitation power/time related photoluminescent measurements as well as calculations, that this avalanche-like photoluminescence is in fact a result of surface plasmon assisted thermal radiation. Nearly all of the related observations could be perfectly interpreted with this concept. Our finding is crucial for understanding the surface plasmon mediated thermal and photoemission behaviors in plasmonic structures, which is of great importance in designing functional plasmonic devices.

  11. A robot-based detector manipulator system for a hard x-ray nanoprobe instrument.

    SciTech Connect

    Shu, D., Maser, J., Holt, M. , Winarski, R., Preissner, C.,Lai, B., Vogt, S., Stephenson, G.B.

    2007-11-11

    This paper presents the design of a robot-based detector manipulator for microdiffraction applications with a hard X-ray nanoprobe instrument system being constructed at the Advanced Photon Source (APS) for the Center for Nanoscale Materials (CNM) being constructed at Argonne National Laboratory (ANL). Applications for detectors weighing from 1.5 to 100 kg were discussed in three configurations.

  12. Monte Carlo simulation of a quantum noise limited Čerenkov detector based on air-spaced light guiding taper for megavoltage x-ray imaging

    SciTech Connect

    Teymurazyan, A.; Rowlands, J. A.; Pang, G.

    2014-04-15

    Purpose: Electronic Portal Imaging Devices (EPIDs) have been widely used in radiation therapy and are still needed on linear accelerators (Linacs) equipped with kilovoltage cone beam CT (kV-CBCT) or MRI systems. Our aim is to develop a new high quantum efficiency (QE) Čerenkov Portal Imaging Device (CPID) that is quantum noise limited at dose levels corresponding to a single Linac pulse. Methods: Recently a new concept of CPID for MV x-ray imaging in radiation therapy was introduced. It relies on Čerenkov effect for x-ray detection. The proposed design consisted of a matrix of optical fibers aligned with the incident x-rays and coupled to an active matrix flat panel imager (AMFPI) for image readout. A weakness of such design is that too few Čerenkov light photons reach the AMFPI for each incident x-ray and an AMFPI with an avalanche gain is required in order to overcome the readout noise for portal imaging application. In this work the authors propose to replace the optical fibers in the CPID with light guides without a cladding layer that are suspended in air. The air between the light guides takes on the role of the cladding layer found in a regular optical fiber. Since air has a significantly lower refractive index (∼1 versus 1.38 in a typical cladding layer), a much superior light collection efficiency is achieved. Results: A Monte Carlo simulation of the new design has been conducted to investigate its feasibility. Detector quantities such as quantum efficiency (QE), spatial resolution (MTF), and frequency dependent detective quantum efficiency (DQE) have been evaluated. The detector signal and the quantum noise have been compared to the readout noise. Conclusions: Our studies show that the modified new CPID has a QE and DQE more than an order of magnitude greater than that of current clinical systems and yet a spatial resolution similar to that of current low-QE flat-panel based EPIDs. Furthermore it was demonstrated that the new CPID does not require an

  13. Avalanche grainflow on a simulated aeolian dune

    NASA Astrophysics Data System (ADS)

    Sutton, S. L. F.; McKenna Neuman, C.; Nickling, W.

    2013-09-01

    Avalanches maintain the slipface of aeolian dunes, which alters their airflow characteristics and sediment dynamics, and results in the development of grainflow cross-bedding. We report on a series of experiments in which avalanches were observed on a 1:1 replica of a small (1.2 m brink height) transverse dune in the Dune Simulation Wind Tunnel under wind velocities of 8-11 m s-1. Changes in slipface topography were observed photographically and measured utilizing a 3-D laser scanner with 1 mm2 spatial resolution. Avalanches in noncohesive sands were observed to progress through scarp recession from the point of initiation and continue until the slope angle is reduced. Changes in local slope confirm that the steep, pre-avalanche mean slope relaxes to a uniform value equal to the angle of repose of the test sand (32°) over all involved portions of the slipface. Avalanche volumes are measured, and demonstrate that avalanche magnitude is independent of wind speed over the range of velocities observed. This independence provides the potential to significantly simplify the modeling of grainflow as a function of only the total cross brink sediment transport.

  14. Resonant metamaterial detectors based on THz quantum-cascade structures

    PubMed Central

    Benz, A.; Krall, M.; Schwarz, S.; Dietze, D.; Detz, H.; Andrews, A. M.; Schrenk, W.; Strasser, G.; Unterrainer, K.

    2014-01-01

    We present the design, fabrication and characterisation of an intersubband detector employing a resonant metamaterial coupling structure. The semiconductor heterostructure relies on a conventional THz quantum-cascade laser design and is operated at zero bias for the detector operation. The same active region can be used to generate or detect light depending on the bias conditions and the vertical confinement. The metamaterial is processed directly into the top metal contact and is used to couple normal incidence radiation resonantly to the intersubband transitions. The device is capable of detecting light below and above the reststrahlenband of gallium-arsenide corresponding to the mid-infrared and THz spectral region. PMID:24608677

  15. Arrest of Avalanche Propagation by Discontinuities on Snow Cover

    NASA Astrophysics Data System (ADS)

    Frigo, B.; Chiaia, B.

    2009-04-01

    Considering the spatial variability of the snow cover, the paper analyses, in the framework of Fracture Mechanics, the Mode II fracture propagation on snow cover that leads to large dry slab avalanches. Under the hypothesis of a perfectly brittle phenomenon, avalanche triggering is usually investigated numerically by means of Linear Elastic Fracture Mechanics (McClung, 1979; Chiaia et al., 2008). Since, however, the real phenomenon is intrinsically dynamical, another aspect to investigate is represented by dynamic fracture propagation. In this paper, we model dynamic crack propagation into a dry snow slab, to assess the possibility of crack arrest due to the presence of weak zones distributed along the snow slope. As a consequence of the first triggering mechanism (the Mode II fracture propagation on the weak plane), the secondary Mode I crack propagation in the crown is studied by means of numerical simulations based on Dynamic Elastic Fracture Mechanics and on the theory of crack arresters. By taking into account kinetic energy and using the FEM software FRANC 2D (Wawrzynek and Ingraffea, 1993), several paths of crown fracture propagation and their stability have been investigated. The snowpack is considered as a linear-elastic plate (2D problem), whose physical and mechanical parameters are chosen according to classical literature values. To investigate the possible arrest of crown fracture, we apply the theory of crack arresters, usually adopted for pipelines and perforated steel sheets fracture problems. To study crack arrest, different crack paths are simulated, in discontinuous (equipped with different shapes and geometries of artificial voids) snowpacks. The simulations show the effectiveness of these weak zones, to reduce substantially the crack driving force of the propagating fracture. This means that, increasing spatial variability tends to stabilize the snow slope, eventually splitting a major avalanche event into smaller, independent avalanches. Our

  16. Single-Photon Avalanche Diodes (SPAD) in CMOS 0.35 μm technology

    NASA Astrophysics Data System (ADS)

    Pellion, D.; Jradi, K.; Brochard, N.; Prêle, D.; Ginhac, D.

    2015-07-01

    Some decades ago single photon detection used to be the terrain of photomultiplier tube (PMT), thanks to its characteristics of sensitivity and speed. However, PMT has several disadvantages such as low quantum efficiency, overall dimensions, and cost, making them unsuitable for compact design of integrated systems. So, the past decade has seen a dramatic increase in interest in new integrated single-photon detectors called Single-Photon Avalanche Diodes (SPAD) or Geiger-mode APD. SPAD are working in avalanche mode above the breakdown level. When an incident photon is captured, a very fast avalanche is triggered, generating an easily detectable current pulse. This paper discusses SPAD detectors fabricated in a standard CMOS technology featuring both single-photon sensitivity, and excellent timing resolution, while guaranteeing a high integration. In this work, we investigate the design of SPAD detectors using the AMS 0.35 μm CMOS Opto technology. Indeed, such standard CMOS technology allows producing large surface (few mm2) of single photon sensitive detectors. Moreover, SPAD in CMOS technologies could be associated to electronic readout such as active quenching, digital to analog converter, memories and any specific processing required to build efficient calorimeters1

  17. Smaller, Lower-Power Fast-Neutron Scintillation Detectors

    NASA Technical Reports Server (NTRS)

    Patel, Jagdish; Blaes, Brent

    2008-01-01

    Scintillation-based fast-neutron detectors that are smaller and less power-hungry than mainstream scintillation-based fast-neutron detectors are undergoing development. There are numerous applications for such detectors in monitoring fast-neutron fluxes from nuclear reactors, nuclear materials, and natural sources, both on Earth and in outer space. A particularly important terrestrial application for small, low-power, portable fast-neutron detectors lies in the requirement to scan for nuclear materials in cargo and baggage arriving at international transportation facilities. The present development of miniature, low-power scintillation-based fast-neutron detectors exploits recent advances in the fabrication of avalanche photodiodes (APDs). Basically, such a detector includes a plastic scintillator, typically between 300 and 400 m thick with very thin silver mirror coating on all its faces except the one bonded to an APD. All photons generated from scintillation are thus internally reflected and eventually directed to the APD. This design affords not only compactness but also tight optical coupling for utilization of a relatively large proportion of the scintillation light. The combination of this tight coupling and the avalanche-multiplication gain (typically between 750 and 1,000) of the APD is expected to have enough sensitivity to enable monitoring of a fast-neutron flux as small as 1,000 cm(exp -2)s(exp -1). Moreover, pulse-height analysis can be expected to provide information on the kinetic energies of incident neutrons. It has been estimated that a complete, fully developed fast-neutron detector of this type, would be characterized by linear dimensions of the order of 10 cm or less, a mass of no more than about 0.5 kg, and a power demand of no more than a few watts.

  18. Snow-avalanche modeling and hazard level assessment using statistical and physical modeling, DSS and WebGIS: case study from Czechia

    NASA Astrophysics Data System (ADS)

    Blahut, J.; Balek, J.; Juras, R.; Klimes, J.; Klose, Z.; Roubinek, J.; Pavlasek, J.

    2014-12-01

    Snow-avalanche modeling and hazard level assessment are important issues to be solved within mountain regions worldwide. In Czechia, there are two mountain ranges (Krkonoše and Jeseníky Mountains), which suffer from regular avalanche activity every year. Mountain Rescue Service is responsible for issuing avalanche bulletins. However, its approaches are still lacking objective assessments and procedures for hazard level estimations. This lack is mainly caused by missing expert avalanche information system. This paper presents preliminary results from a project funded by the Ministry of Interior of the Czech Republic. This project is focused on development of an information system for snow-avalanche hazard level forecasting. It is composed of three main modules, which should act as a Decision Support System (DSS) for the Mountain Rescue Service. Firstly, snow-avalanche susceptibility model is used for delimiting areas where avalanches can occur based on accurate statistical analyses. For that purpose a waste database is used, containing more than 1100 avalanche events from 1961/62 till present. Secondly, a physical modeling of the avalanches is being performed on avalanche paths using RAMMS modeling code. Regular paths, where avalanches occur every year, and irregular paths are being assessed. Their footprint is being updated using return period information for each path. Thirdly, snow distribution and stability models (distributed HBV-ETH, Snowtran 3D, Snowpack and Alpine 3D) are used to assess the critical conditions for avalanche release. For calibration of the models data about meteo/snow cover data and snowpits is used. Those three parts are being coupled in a WebGIS platform used as the principal component of the DSS in snow-avalanche hazard level assessment.

  19. Some influences of rock strength and strain rate on propagation of rock avalanches

    NASA Astrophysics Data System (ADS)

    Bowman, Elisabeth; Rait, Kim

    2016-04-01

    Rock avalanches are extreme and destructive mass movements in which large volumes of rock (typically >1 million cubic metres) travel at high speeds, covering large distances, and the occurrence of which is highly unpredictable. The "size effect" in rock avalanches, whereby those with larger volumes produce greater spreading efficiency (as defined by an increase in normalised runout) or lower farboschung angle (defined as the tangent of the ratio of fall height to runout length), is well known. Studies have shown that rock strength is a controlling factor in the mobility of rock avalanches - that is, mass movements involving lower strength rock are generally found to produce greater mobility as evidenced by the spread of deposits or low farboschung angle. However, there are conflicting ideas as to how and why this influence is manifested. This paper discusses different theories of rock comminution in light of numerical simulations of rock clasts undergoing normal and shear induced loading, experimental work on rock avalanche behaviour, and dynamic fracture mechanics. In doing so, we introduce the idea of thresholds of strain rate for the production of dynamic fragmentation (as opposed to pseudo-static clast crushing) that are based, inter alia, on static rock strength. To do this, we refer to data from physical models using rock analogue materials, field data on chalk cliff collapses, and field statistics from documented rock avalanches. The roles of normal and shear loading and loading rate within a rock avalanche are examined numerically using 3D Discrete Element Method models of rock clasts loaded to failure. Results may help to reconcile the observations that large rock avalanches in stronger materials tend not to fragment as much as those in weaker materials and also possess lower mobility, while small cliff collapses (typically > 1000 cubic metres) in weak chalk can exhibit rock avalanche-like behaviour at much smaller volumes.

  20. Silicon photon-counting avalanche diodes for single-molecule fluorescence spectroscopy

    PubMed Central

    Michalet, Xavier; Ingargiola, Antonino; Colyer, Ryan A.; Scalia, Giuseppe; Weiss, Shimon; Maccagnani, Piera; Gulinatti, Angelo; Rech, Ivan; Ghioni, Massimo

    2014-01-01

    Solution-based single-molecule fluorescence spectroscopy is a powerful experimental tool with applications in cell biology, biochemistry and biophysics. The basic feature of this technique is to excite and collect light from a very small volume and work in a low concentration regime resulting in rare burst-like events corresponding to the transit of a single molecule. Detecting photon bursts is a challenging task: the small number of emitted photons in each burst calls for high detector sensitivity. Bursts are very brief, requiring detectors with fast response time and capable of sustaining high count rates. Finally, many bursts need to be accumulated to achieve proper statistical accuracy, resulting in long measurement time unless parallelization strategies are implemented to speed up data acquisition. In this paper we will show that silicon single-photon avalanche diodes (SPADs) best meet the needs of single-molecule detection. We will review the key SPAD parameters and highlight the issues to be addressed in their design, fabrication and operation. After surveying the state-of-the-art SPAD technologies, we will describe our recent progress towards increasing the throughput of single-molecule fluorescence spectroscopy in solution using parallel arrays of SPADs. The potential of this approach is illustrated with single-molecule Förster resonance energy transfer measurements. PMID:25309114

  1. Silicon photon-counting avalanche diodes for single-molecule fluorescence spectroscopy.

    PubMed

    Michalet, Xavier; Ingargiola, Antonino; Colyer, Ryan A; Scalia, Giuseppe; Weiss, Shimon; Maccagnani, Piera; Gulinatti, Angelo; Rech, Ivan; Ghioni, Massimo

    2014-11-01

    Solution-based single-molecule fluorescence spectroscopy is a powerful experimental tool with applications in cell biology, biochemistry and biophysics. The basic feature of this technique is to excite and collect light from a very small volume and work in a low concentration regime resulting in rare burst-like events corresponding to the transit of a single molecule. Detecting photon bursts is a challenging task: the small number of emitted photons in each burst calls for high detector sensitivity. Bursts are very brief, requiring detectors with fast response time and capable of sustaining high count rates. Finally, many bursts need to be accumulated to achieve proper statistical accuracy, resulting in long measurement time unless parallelization strategies are implemented to speed up data acquisition. In this paper we will show that silicon single-photon avalanche diodes (SPADs) best meet the needs of single-molecule detection. We will review the key SPAD parameters and highlight the issues to be addressed in their design, fabrication and operation. After surveying the state-of-the-art SPAD technologies, we will describe our recent progress towards increasing the throughput of single-molecule fluorescence spectroscopy in solution using parallel arrays of SPADs. The potential of this approach is illustrated with single-molecule Förster resonance energy transfer measurements. PMID:25309114

  2. A solid-state amorphous selenium avalanche technology for low photon flux imaging applications

    PubMed Central

    Wronski, M. M.; Zhao, W.; Reznik, A.; Tanioka, K.; DeCrescenzo, G.; Rowlands, J. A.

    2010-01-01

    Purpose: The feasibility of a practical solid-state technology for low photon flux imaging applications was investigated. The technology is based on an amorphous selenium photoreceptor with a voltage-controlled avalanche multiplication gain. If this photoreceptor can provide sufficient internal gain, it will be useful for an extensive range of diagnostic imaging systems. Methods: The avalanche photoreceptor under investigation is referred to as HARP-DRL. This is a novel concept in which a high-gain avalanche rushing photoconductor (HARP) is integrated with a distributed resistance layer (DRL) and sandwiched between two electrodes. The avalanche gain and leakage current characteristics of this photoreceptor were measured. Results: HARP-DRL has been found to sustain very high electric field strengths without electrical breakdown. It has shown avalanche multiplication gains as high as 104 and a very low leakage current (≤20 pA∕mm2). Conclusions: This is the first experimental demonstration of a solid-state amorphous photoreceptor which provides sufficient internal avalanche gain for photon counting and photon starved imaging applications. PMID:20964217

  3. Channelized free-surface flow of cohesionless granular avalanches in a chute with shallow lateral curvature

    NASA Astrophysics Data System (ADS)

    Wieland, M.; Gray, J. M. N. T.; Hutter, K.

    1999-08-01

    A series of laboratory experiments and numerical simulations have been performed to investigate the rapid fluid-like flow of a finite mass of granular material down a chute with partial lateral confinement. The chute consists of a section inclined at 40° to the horizontal, which is connected to a plane run-out zone by a smooth transition. The flow is confined on the inclined section by a shallow parabolic cross-slope profile. Photogrammetric techniques have been used to determine the position of the evolving boundary during the flow, and the free-surface height of the stationary granular deposit in the run-out zone. The results of three experiments with different granular materials are presented and shown to be in very good agreement with numerical simulations based on the Savage Hutter theory for granular avalanches. The basal topography over which the avalanche flows has a strong channelizing effect on the inclined section of the chute. As the avalanche reaches the run-out zone, where the lateral confinement ceases, the head spreads out to give the avalanche a characteristic ‘tadpole’ shape. Sharp gradients in the avalanche thickness and velocity began to develop at the interface between the nose and tail of the avalanche as it came to rest, indicating that a shock wave develops close to the end of the experiments.

  4. On the vulnerability of basic quantum key distribution protocols and three protocols stable to attack with 'blinding' of avalanche photodetectors

    SciTech Connect

    Molotkov, S. N.

    2012-05-15

    The fundamental quantum mechanics prohibitions on the measurability of quantum states allow secure key distribution between spatially remote users to be performed. Experimental and commercial implementations of quantum cryptography systems, however, use components that exist at the current technology level, in particular, one-photon avalanche photodetectors. These detectors are subject to the blinding effect. It was shown that all the known basic quantum key distribution protocols and systems based on them are vulnerable to attacks with blinding of photodetectors. In such attacks, an eavesdropper knows all the key transferred, does not produce errors at the reception side, and remains undetected. Three protocols of quantum key distribution stable toward such attacks are suggested. The security of keys and detection of eavesdropping attempts are guaranteed by the internal structure of protocols themselves rather than additional technical improvements.

  5. Flexible infrared detectors based on p-n junctions of multi-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Huang, Zhenlong; Gao, Min; Yan, Zhuocheng; Pan, Taisong; Liao, Feiyi; Lin, Yuan

    2016-05-01

    Different types of multi-walled carbon nanotubes (CNTs), synthesized by chemical vapor deposition, are used to fabricate infrared (IR) detectors on flexible substrates based on CNT p-n junctions. It is found that this kind of detector is sensitive to infrared signals with a power density as low as 90 μW mm-2 even at room temperature. Besides, unlike other devices, the detector with this unique structure can be bent for 100 cycles without any damage and its functionality does not degenerate once it recovers to the initial state. The results give a good reference for developing efficient, low-cost, and flexible IR detectors.Different types of multi-walled carbon nanotubes (CNTs), synthesized by chemical vapor deposition, are used to fabricate infrared (IR) detectors on flexible substrates based on CNT p-n junctions. It is found that this kind of detector is sensitive to infrared signals with a power density as low as 90 μW mm-2 even at room temperature. Besides, unlike other devices, the detector with this unique structure can be bent for 100 cycles without any damage and its functionality does not degenerate once it recovers to the initial state. The results give a good reference for developing efficient, low-cost, and flexible IR detectors. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08791k

  6. Relativistic electron avalanches as a thunderstorm discharge competing with lightning.

    PubMed

    Kelley, Nicole A; Smith, David M; Dwyer, Joseph R; Splitt, Michael; Lazarus, Steven; Martinez-McKinney, Forest; Hazelton, Bryna; Grefenstette, Brian; Lowell, Alexander; Rassoul, Hamid K

    2015-01-01

    Gamma-ray 'glows' are long duration (seconds to tens of minutes) X-ray and gamma-ray emission coming from thunderclouds. Measurements suggest the presence of relativistic runaway electron avalanches (RREA), the same process underlying terrestrial gamma-ray flashes. Here we demonstrate that glows are relatively a common phenomena near the tops of thunderstorms, when compared with events such as terrestrial gamma-ray flashes. Examining the strongest glow measured by the airborne detector for energetic emissions, we show that this glow is measured near the end of a downward RREA, consistent with occurring between the upper positive charge layer and the negative screening layer above it. The glow discharges the upper positive layer by ≥9.6 mA, strong enough to be an important charging mechanism of the storm. For this glow, the gamma-ray flux observed is close to the value at which relativistic feedback processes become important, with an avalanche multiplication factor of 4,500. PMID:26263880

  7. Relativistic electron avalanches as a thunderstorm discharge competing with lightning

    NASA Astrophysics Data System (ADS)

    Kelley, Nicole A.; Smith, David M.; Dwyer, Joseph R.; Splitt, Michael; Lazarus, Steven; Martinez-McKinney, Forest; Hazelton, Bryna; Grefenstette, Brian; Lowell, Alexander; Rassoul, Hamid K.

    2015-08-01

    Gamma-ray `glows' are long duration (seconds to tens of minutes) X-ray and gamma-ray emission coming from thunderclouds. Measurements suggest the presence of relativistic runaway electron avalanches (RREA), the same process underlying terrestrial gamma-ray flashes. Here we demonstrate that glows are relatively a common phenomena near the tops of thunderstorms, when compared with events such as terrestrial gamma-ray flashes. Examining the strongest glow measured by the airborne detector for energetic emissions, we show that this glow is measured near the end of a downward RREA, consistent with occurring between the upper positive charge layer and the negative screening layer above it. The glow discharges the upper positive layer by >=9.6 mA, strong enough to be an important charging mechanism of the storm. For this glow, the gamma-ray flux observed is close to the value at which relativistic feedback processes become important, with an avalanche multiplication factor of 4,500.

  8. Prehistoric rock avalanches in the Olympic Mountains, Washington

    USGS Publications Warehouse

    Schuster, R.L.; Logan, R.L.; Pringle, P.T.

    1992-01-01

    Rock avalanches blocked streams in the Olympic Mountains southwest of Puget Sound during the past few thousand years. Limiting radiocarbon ages indicated that three or four of six avalanches occurred from 1000 to 1300 years ago or shortly thereafter. Most of the dates were from the outer preserved rings of trees drowned behind avalanche dams. These three or four avalanches may be coeval not only with one another but also with abrupt tectonic deformation in western Washington. No rock avalanches in the Olympic Mountains are known to have resulted from storms or earthquakes during the past century. The avalanches strengthen the case that a large prehistoric earthquake occurred in the Puget Sound region.

  9. Porous Silicon-Based Quantum Dot Broad Spectrum Radiation Detector

    PubMed Central

    Urdaneta, M.; Stepanov, P.; Weinberg, I. N.; Pala, I. R.; Brock, S.

    2013-01-01

    Silicon is a convenient and inexpensive platform for radiation detection, but has low stopping power for x-rays and gamma-rays with high energy (e.g., 100 keV, as used in computed tomography and digital radiography, or 1 MeV, as desired for detection of nuclear materials). We have effectively increased the stopping power of silicon detectors by producing a layer of porous or micro-machined silicon, and infusing this layer with semiconductor quantum dots made of electron-dense materials. Results of prototype detectors show sensitivity to infrared, visible light, and x-rays, with dark current of less than 1 nA/mm2. PMID:24432047

  10. Performance characteristics of a silicon photomultiplier based compact radiation detector for Homeland Security applications

    NASA Astrophysics Data System (ADS)

    Park, Hye Min; Joo, Koan Sik

    2015-05-01

    A next-generation compact radiation detector was studied for more accurate measurement of radiation and for improvement of detector reliability for the purpose of developing radiation protection technology and military applications. The previously used radiation detector had some limitations due to its bulky size, limited range and its environment for radiation measurement. On the other hand, the compact radiation detector examined in this study utilizes a silicon photomultiplier which appears to be more suitable for this application because of its physical superiority characterized by its small size, high sensitivity, and durability. Accordingly, a SiPM based scintillation detector has been developed as part of this basic study of military radiation detectors. The detector has been tested for its ability to obtain the operating characteristics of a sensor and analyzed with variations of parameter values and for efficiency of detection in accordance with its ability to measure radiation in the environment. Two SiPM based Scintillation detectors with LYSO, BGO and CsI:Tl scintillators were developed and the detectors were analyzed by a number of operating characteristics such as reverse bias, operating temperature and high magnetic field, that depend on environmental changes in radiation measurement. The Photon count rate and spectra were compared for these three scintillators. We found that there were variations in the radiation detection which were characterized by reverse bias, temperature and high magnetic field. It was also found that there was an 11.9% energy resolution for the LYSO, 15.5% for BGO and 13.5% for CsI:Tl using Array SiPM, and 18% for CsI:Tl energy resolution using single SiPM when we measured energy resolution of 511 keV for 22Na. These results demonstrate the potential widespread use of SiPM based compact radiation detectors for Homeland Security applications.

  11. HgZnTe-based detectors for LWIR NASA applications

    NASA Technical Reports Server (NTRS)

    Patten, Elizabeth A.; Kalisher, Murray H.

    1990-01-01

    The initial goal was to grow and characterize HgZnTe and determine if it indeed had the advantageous properties that were predicted. Researchers grew both bulk and liquid phase epitaxial HgZnTe. It was determined that HgZnTe had the following properties: (1) microhardness at least 50 percent greater than HgCdTe of equivalent bandgap; (2) Hg annealing rates of at least 2 to 4 times longer than HgCdTe; and (3) higher Hg vacancy formation energies. This early work did not focus on one specific composition (x-value) of HgZnTe since NASA was interested in HgZnTe's potential for a variety of applications. Since the beginning of 1989, researchers have been concentrating, however, on the liquid phase growth of very long wavelength infrared (VLWIR) HgZnTe (cutoff approx. equals 17 microns at 65K) to address the requirements of the Earth Observing System (EOS). Since there are no device models to predict the advantages in reliability one can gain with increased microhardness, surface stability, etc., one must fabricate HgZnTe detectors and assess their relative bake stability (accelerated life test behavior) compared with HgCdTe devices fabricated in the same manner. Researchers chose to fabricate HIT detectors as a development vehicle for this program because high performance in the VLWIR has been demonstrated with HgCdTe HIT detectors and the HgCdTe HIT process should be applicable to HgZnTe. HIT detectors have a significant advantage for satellite applications since these devices dissipate much less power than conventional photoconductors to achieve the same responsivity.

  12. Development of a Microcantilever-Based Pathogen Detector

    SciTech Connect

    Weeks, B L; Camarero, J; Noy, A; Miller, A E; De Yoreo, J J

    2002-11-18

    The ability to detect small amounts of materials, especially whole organisms, is important for medical diagnostics and national security issues. Engineered micro-mechanical systems can serve as multifunctional, highly sensitive, real time, immunospecific biological detectors under certain circumstances. We present qualitative detection of specific Salmonella strains using a functionalized silicon nitride microcantilever. Detection is achieved due to differential surface stress on the cantilever surface in-situ. Scanning electron micrographs indicate that less than 25 adsorbed bacteria are required for detection.

  13. Novel semiconductor radiation detector based on mercurous halides

    NASA Astrophysics Data System (ADS)

    Chen, Henry; Kim, Joo-Soo; Amarasinghe, Proyanthi; Palosz, Withold; Jin, Feng; Trivedi, Sudhir; Burger, Arnold; Marsh, Jarrod C.; Litz, Marc S.; Wiejewarnasuriya, Priyalal S.; Gupta, Neelam; Jensen, Janet; Jensen, James

    2015-08-01

    The three most important desirable features in the search for room temperature semiconductor detector (RTSD) candidate as an alternative material to current commercially off-the-shelf (COTS) material for gamma and/or thermal neutron detection are: low cost, high performance and long term stability. This is especially important for pager form application in homeland security. Despite years of research, no RTSD candidate so far can satisfy the above 3 features simultaneously. In this work, we show that mercurous halide materials Hg2X2 (X= I, Cl, Br) is a new class of innovative compound semiconductors that is capable of delivering breakthrough advances to COTS radiation detector materials. These materials are much easier to grow thicker and larger volume crystals. They can detect gamma and potentially neutron radiation making it possible to detect two types of radiation with just one crystal material. The materials have wider bandgaps (compared to COTS) meaning higher resistivity and lower leakage current, making this new technology more compatible with available microelectronics. The materials also have higher atomic number and density leading to higher stopping power and better detector sensitivity/efficiency. They are not hazardous so there are no environmental and health concerns during manufacturing and are more stable making them more practical for commercial deployment. Focus will be on Hg2I2. Material characterization and detector performance will be presented and discussed. Initial results show that an energy resolution better than 2% @ 59.6 keV gamma from Am-241 and near 1% @ 662 keV from Cs-137 source can be achieved at room temperature.

  14. Development of LAMBDA: Large Area Medipix-Based Detector Array

    NASA Astrophysics Data System (ADS)

    Pennicard, David; Lange, Sabine; Smoljanin, Sergej; Becker, Julian; Hirsemann, Helmut; Epple, Michael; Graafsma, Heinz

    2011-11-01

    The Medipix3 photon counting readout chip has a range of features — small pixel size, high readout rate and inter-pixel communication — which make it attractive for X-ray scattering and imaging at synchrotrons. DESY have produced a prototype large-area detector module that can carry a 6 by 2 array of Medipix3 chips (1536 by 512 pixels), which can be used with a single large silicon sensor (85mm by 28mm) or two ``hexa'' high-Z sensors. The detector head is designed to be tilable and compatible with low temperatures, and will allow high speed parallel readout of the Medipix3 chips. It consists of a ceramic board, on which the sensor assembly is mounted, and a secondary board for signal routing and voltage regulators. A prototype DAQ board using USB2 readout has also been produced. A ``quad'' Medipix3 sensor assembly has been mounted on the detector head, and successfully configured and read out by the DAQ board. Development has begun on a high-speed readout board, and large-area silicon assemblies are in production.

  15. Miniature Trace Gas Detector Based on Microfabricated Optical Resonators

    NASA Technical Reports Server (NTRS)

    Aveline, David C.; Yu, Nan; Thompson, Robert J.; Strekalov, Dmitry V.

    2013-01-01

    While a variety of techniques exist to monitor trace gases, methods relying on absorption of laser light are the most commonly used in terrestrial applications. Cavity-enhanced absorption techniques typically use high-reflectivity mirrors to form a resonant cavity, inside of which a sample gas can be analyzed. The effective absorption length is augmented by the cavity's high quality factor, or Q, because the light reflects many times between the mirrors. The sensitivity of such mirror-based sensors scales with size, generally making them somewhat bulky in volume. Also, specialized coatings for the high-reflectivity mirrors have limited bandwidth (typically just a few nanometers), and the delicate mirror surfaces can easily be degraded by dust or chemical films. As a highly sensitive and compact alternative, JPL is developing a novel trace gas sensor based on a monolithic optical resonator structure that has been modified such that a gas sample can be directly injected into the cavity. This device concept combines ultra-high Q optical whispering gallery mode resonators (WGMR) with microfabrication technology used in the semiconductor industry. For direct access to the optical mode inside a resonator, material can be precisely milled from its perimeter, creating an open gap within the WGMR. Within this open notch, the full optical mode of the resonator can be accessed. While this modification may limit the obtainable Q, calculations show that the reduction is not significant enough to outweigh its utility for trace gas detection. The notch can be milled from the high- Q crystalline WGMR with a focused ion beam (FIB) instrument with resolution much finer than an optical wavelength, thereby minimizing scattering losses and preserving the optical quality. Initial experimental demonstrations have shown that these opened cavities still support high-Q whispering gallery modes. This technology could provide ultrasensitive detection of a variety of molecular species in an

  16. Monitoring of full-depth avalanches contaminated by soil and rocks - their origin and consequences, (Krkonose/Karkonosze Mts.- High Sudetes)

    NASA Astrophysics Data System (ADS)

    Kocianova, M.

    2009-04-01

    Monitoring of full-depth avalanches contaminated by soil and rocks - their origin and consequences, (Krkonose/Karkonosze Mts.- High Sudetes) Milena Kocianova Valerian Spusta, Irena Spatenkova, Alena Tondrova, Igor Jan Dvorak, Vlastimil Pilous Krkonoše National Park Administration, Dobrovskeho 3, 543 01 Vrchlabi, Czech republic Monitoring of snow avalanches is provided in Czech part of the Krkonose/Karkonosze Mountains since the winter season 1961/62. The full-depth avalanches contaminated by soil and rocks represent about 4% of the monitored number. There are six bigger avalanches of this type recorded during last 10 years. The areas of snutched weathering mantles reached at about 3000 - 23 000 m2 per individual avalanche track. In deposit zones the areas from 2600 to 18700 m2 were covered by soil, sods and small rock fragments whose volume ranged from about 130 to 880 m3 per individual avalanche track. The volume of large rock fragments in one concrete track was counted up to 144 m3. The great influence of full depth avalanches on relief and slope development is evident. Based on monitoring the speed of snutched areas overgrowing by vegetation and on comparison of space design of plant communities out off and on the avalanche tracks respectively, it would be possible to estimate the period of such bigger events. Very important thing is that four avalanche events were triggered by water, which infiltrated the base of snowpack within upper or central parts of avalanche slopes. Water origin was probably either a) in mires on adjacent summit plateau (ground water flown on inclined bedrock layers to the avalanche slopes) and b) in thawing water of snow patches situated on the cryoplanation terraces above the avalanche slopes. More detailed study of these phenomena is needed in the future.

  17. A new 3He-free thermal neutrons detector concept based on the GEM technology

    NASA Astrophysics Data System (ADS)

    Pietropaolo, A.; Murtas, F.; Claps, G.; Quintieri, L.; Raspino, D.; Celentano, G.; Vannozzi, A.; Frasciello, O.

    2013-11-01

    A thermal neutron detector based on the Gas Electron Multiplier technology is presented. It is configured to let a neutron beam interact with a series of borated glass layers placed in sequence along the neutron path inside the device. The detector has been tested on beam both at the ISIS (UK) spallation neutron source and at the TRIGA reactor of ENEA, at the Casaccia Research Center, near Rome in Italy. For a complete characterization and description of the physical mechanism underlying the detector operation, several Monte Carlo simulations were performed using both Fluka and Geant4 code. These simulations are intended to help in seeking the optimal geometrical set-up and material thickness (converter layer, gas gap, sheet substrate) to improve the final detector design in terms of achieving the best detector efficiency possible.

  18. Terahertz detectors arrays based on orderly aligned InN nanowires

    PubMed Central

    Chen, Xuechen; Liu, Huiqiang; Li, Qiuguo; Chen, Hao; Peng, Rufang; Chu, Sheng; Cheng, Binbin

    2015-01-01

    Nanostructured terahertz detectors employing a single semiconducting nanowire or graphene sheet have recently generated considerable interest as an alternative to existing THz technologies, for their merit on the ease of fabrication and above-room-temperature operation. However, the lack of alignment in nanostructure device hindered their potential toward practical applications. The present work reports ordered terahertz detectors arrays based on neatly aligned InN nanowires. The InN nanostructures (nanowires and nano-necklaces) were achieved by chemical vapor deposition growth, and then InN nanowires were successfully transferred and aligned into micrometer-sized groups by a “transfer-printing” method. Field effect transistors on aligned nanowires were fabricated and tested for terahertz detection purpose. The detector showed good photoresponse as well as low noise level. Besides, dense arrays of such detectors were also fabricated, which rendered a peak responsivity of 1.1 V/W from 7 detectors connected in series. PMID:26289498

  19. Antenna-integrated 0.6 THz FET direct detectors based on CVD graphene.

    PubMed

    Zak, Audrey; Andersson, Michael A; Bauer, Maris; Matukas, Jonas; Lisauskas, Alvydas; Roskos, Hartmut G; Stake, Jan

    2014-10-01

    We present terahertz (THz) detectors based on top-gated graphene field effect transistors (GFETs) with integrated split bow-tie antennas. The GFETs were fabricated using graphene grown by chemical vapor deposition (CVD). The THz detectors are capable of room-temperature rectification of a 0.6 THz signal and achieve a maximum optical responsivity better than 14 V/W and minimum optical noise-equivalent power (NEP) of 515 pW/Hz(0.5). Our results are a significant improvement over previous work on graphene direct detectors and are comparable to other established direct detector technologies. This is the first time room-temperature direct detection has been demonstrated using CVD graphene, which introduces the potential for scalable, wafer-level production of graphene detectors. PMID:25203787

  20. Instruments, Detectors and the Future of Astronomy with Large Ground Based Telescopes

    NASA Astrophysics Data System (ADS)

    Simons, Douglas A.; Amico, Paola; Baade, Dietrich; Barden, Sam; Campbell, Randall; Finger, Gert; Gilmore, Kirk; Gredel, Roland; Hickson, Paul; Howell, Steve; Hubin, Norbert; Kaufer, Andreas; Kohley, Ralf; MacQueen, Philip; Markelov, Sergej; Merrill, Mike; Miyazaki, Satoshi; Nakaya, Hidehiko; O'Donoghue, Darragh; Oliva, Tino; Richichi, Andrea; Salmon, Derrick; Schmidt, Ricardo; Su, Hongjun; Tulloch, Simon; García Vargas, Maria Luisa; Wagner, R. Mark; Wiecha, Olivier; Ye, Binxun

    2005-01-01

    Results of a survey of instrumentation and detector systems, either currently deployed or planned for use at telescopes larger than 3.5 m, in ground based observatories world-wide, are presented. This survey revealed a number of instrumentation design trends at optical, near, and mid-infrared wavelengths. Some of the most prominent trends include the development of vastly larger optical detector systems (> 109 pixels) than anything built to date, and the frequent use of mosaics of near-infrared detectors - something that was quite rare only a decade ago in astronomy. Some future science applications for detectors are then explored, in an attempt to build a bridge between current detectors and what will be needed to support the research ambitions of astronomers in the future.

  1. GRAVITY detector systems

    NASA Astrophysics Data System (ADS)

    Mehrgan, Leander H.; Finger, Gert; Accardo, Matteo; Lizon, Jean-Louis; Stegmeier, Joerg; Eisenhauer, Frank

    2014-07-01

    GRAVITY is a second generation instrument for the VLT Interferometer, designed to enhance the near-infrared astrometric and spectro-imaging capabilities of VLTI. It will combine the AO corrected beams of the four VLT telescopes. The GRAVITY instrument uses a total of five eAPD detectors, four of which are for wavefront sensing and one for the Fringe tracker. In addition two Hawaii2RG are used, one for the acquisition camera and one for the spectrometer. A compact bath cryostat is used for each WFS unit, one for each of the VLT Unit Telescopes. Both Hawaii2RG detectors have a cutoff wavelength of 2.5 microns. A new and unique element of GRAVITY is the use of infrared wavefront sensors. For this reason SELEX-Galileo has developed a new high speed avalanche photo diode detector for ESO. The SAPHIRA detector, which stands for Selex Avalanche Photodiodes for Highspeed Infra Red Applications, has been already evaluated by ESO. At a frame rate of 1 KHz, a read noise of less than one electron can be demonstrated. A more detailed presentation about the performance of the SPAHIRA detector will be given at this conference 1. Each SAPHIRA detector is installed in an LN2 bath cryostat. The detector stage, filter wheel and optics are mounted on the cold plate of the LN2 vessel and enclosed by a radiation shield. All seven detector systems are controlled and read out by the standard ESO NGC controller. The NGC is a controller platform which can be adapted and customized for all infrared and optical detectors. This paper will discuss specific controller modifications implemented to meet the special requirements of the GRAVITY detector systems and give an overview of the GRAVITY detector systems and their performance.

  2. Rock avalanches: significance and progress (Invited)

    NASA Astrophysics Data System (ADS)

    Davies, T. R.

    2013-12-01

    1. The probability distribution of landslide volumes follows a power-law indicating that large rock avalanches dominate the terrestrial sediment supply from mountains, and that their source area morphologies dominate mountain topography. 2. Large rock slope failures (~ 106 m3 or greater) often mobilise into rock avalanches, which can travel extraordinarily long distances with devastating effect. This hypermobility has been the subject of many investigations; we have demonstrated that it can be explained quantitatively and accurately by considering the energetics of the intense rock fragmentation that always occurs during motion of a large rock mass. 3. Study of rock avalanche debris psd shows that the energy used in creating new rock surface area during fragmentation is not lost to surface energy, but is recycled generating a high-frequency elastic energy field that reduces the frictional resistance to motion during runout. 4. Rock avalanches that deposit on glaciers can eventually form large terminal moraines that have no connection with any climatic event; unless these are identified as rock-avalanche-influenced they can confuse palaeoclimatic inferences drawn from moraine ages. Rock-avalanche-derived fines, however, can be identified in moraine debris up to ten thousand years old by the characteristic micron-scale agglomerates that form during intense fragmentation, and which are absent from purely climatically-induced moraines; there is thus a strong case for re-examining existing palaeoclimatic databases to eliminate potentially rock-avalanche-influenced moraine ages. 5. Rock avalanches (especially coseismic ones) are a serious hazard, being very destructive in their own right; they also block river valleys, forming landslide dams and potentially devastating dambreak floods, and subsequent severe decade-scale aggradation of downstream fans and floodplains. Rock avalanches falling into lakes or fiords can cause catastrophic tsunami that pose a serious risk to

  3. Trend towards low cost, low power, ultra-violet (UV) based biological agent detectors

    NASA Astrophysics Data System (ADS)

    Sickenberger, David

    2005-11-01

    Ultra-violet fluorescence remains a corner stone technique for the detection of biological agent aerosols. Historically, these UV based detectors have employed relatively costly and power demanding lasers that have influenced the exploitation of the technology to wider use. Recent advancements from the Defense Advanced Research Project Agency's (DARPA) Solid-state Ultra Violet Optical Sources (SUVOS) program has changed this. The UV light emitting diode (LED) devices based on Gallium Nitride offer a unique opportunity to produce small, low power, and inexpensive detectors. It may, in fact, be possible to extend the SUVOS technology into detectors that are potentially disposable. This report will present ongoing efforts to explore this possibility. It will present candidate UV fluorescence based detector designs along with the biological aerosol responses obtained from these designs.

  4. Temperature Control of Avalanche Photodiode Using Thermoelectric Cooler

    NASA Technical Reports Server (NTRS)

    Refaat, Tamer F.; Luck, William S., Jr.; DeYoung, Russell J.

    1999-01-01

    Avalanche photodiodes (APDS) are quantum optical detectors that are used for visible and near infrared optical detection applications. Although APDs are compact, rugged, and have an internal gain mechanism that is suitable for low light intensity; their responsivity, and therefore their output, is strongly dependent on the device temperature. Thermoelectric coolers (TEC) offers a suitable solution to this problem. A TEC is a solid state cooling device, which can be controlled by changing its current. TECs are compact and rugged, and they can precisely control the temperature to within 0.1 C with more than a 150 C temperature gradient between its surfaces. In this Memorandum, a proportional integral (PI) temperature controller for APDs using a TEC is discussed. The controller is compact and can successfully cool the APD to almost 0 C in an ambient temperature environment of up to 27 C.

  5. Silicon technologies for arrays of Single Photon Avalanche Diodes

    NASA Astrophysics Data System (ADS)

    Gulinatti, Angelo; Ceccarelli, Francesco; Rech, Ivan; Ghioni, Massimo

    2016-05-01

    In order to fulfill the requirements of many applications, we recently developed a new technology aimed at combining the advantages of traditional thin and thick silicon Single Photon Avalanche Diodes (SPAD). In particular we demonstrated single-pixel detectors with a remarkable improvement in the Photon Detection Efficiency in the red/nearinfrared spectrum (e.g. 40% at 800nm) while maintaining a timing jitter better than 100ps. In this paper we discuss the limitations of such Red-Enhanced (RE) technology from the point of view of the fabrication of small arrays of SPAD and we propose modifications to the structure aimed at overcoming these issues. We also report the first preliminary experimental results attained on devices fabricated adopting the improved structure.

  6. The September 1988 intracaldera avalanche and eruption at Fernandina volcano, Galapagos Islands

    USGS Publications Warehouse

    Chadwick, W.W., Jr.; De Roy, T.; Carrasco, A.

    1991-01-01

    During 14-16 September 1988, a large intracaldera avalanche and an eruption of basaltic tephra and lava at Fernandina volcano, Galapagos, produced the most profound changes within the caldera since its collapse in 1968. A swarm of eight earthquakes (mb 4.7-5.5) occurred in a 14 h period on 24 February 1988 at Fernandina, and two more earthquakes of this size followed on 15 April and 20 May, respectively. On 14 September 1988, another earthquake (mb 4.6) preceded a complex series of events. A debris avalanche was generated by the failure of a fault-bounded segment of the east caldera wall, approximately 2 km long and 300 m wide. The avalanche deposit is up to 250 m thick and has an approximate volume of 0.9 km3. The avalanche rapidly displaced a preexisting lake from the southeast end of the caldera floor to the northwest end, where the water washed up against the lower part of the caldera wall, then gradually seeped into the avalanche deposit and was completely gone by mid-January 1989. An eruption began in the caldera within about 1-2 h of the earthquake, producing a vigorous tephra plume for about 12 h, then lava flows during the next two days. The eruption ended late on 16 September. Most of the eruptive activity was from vents on the caldera floor near the base of the new avalanche scar. Unequivocal relative timing of events is difficult to determine, but seismic records suggest that the avalanche may have occurred 1.6 h after the earthquake, and field relations show that lava was clearly erupted after the avalanche was emplaced. The most likely sequence of events seems to be that the 1988 feeder dike intruded upward into the east caldera wall, dislocated the unstable wall block, and triggered the avalanche. The avalanche immediately exposed the newly emplaced dike and initiated the eruption. The exact cause of the earthquakes is unknown. ?? 1991 Springer-Verlag.

  7. The Electromagnetic Calorimeter of the future PANDA Detector

    SciTech Connect

    Novotny, Rainer

    2006-10-27

    Experiments with a cooled antiproton beam at the future accelerator facility FAIR at GSI, Darmstadt, will be performed with the 4{pi} detector PANDA comprising a high resolution, compact and fast homogeneous electromagnetic calorimeter to detect photons between 10MeV and 10GeV energy inside a superconducting solenoid (2T). The target calorimeter comprises more than 20,000 PbWO4 crystals of significantly enhanced quality read-out with large area avalanche photodiodes at an operating temperature of -25 degree sign C. The paper describes the quality of PWO-II and illustrates the future performance based on response measurements with high-energy photons.

  8. Smartphone based point-of-care detector of urine albumin

    NASA Astrophysics Data System (ADS)

    Cmiel, Vratislav; Svoboda, Ondrej; Koscova, Pavlina; Provaznik, Ivo

    2016-03-01

    Albumin plays an important role in human body. Its changed level in urine may indicate serious kidney disorders. We present a new point-of-care solution for sensitive detection of urine albumin - the miniature optical adapter for iPhone with in-built optical filters and a sample slot. The adapter exploits smart-phone flash to generate excitation light and camera to measure the level of emitted light. Albumin Blue 580 is used as albumin reagent. The proposed light-weight adapter can be produced at low cost using a 3D printer. Thus, the miniaturized detector is easy to use out of lab.

  9. Tests of a multichannel photometer based on silicon diode detectors

    NASA Technical Reports Server (NTRS)

    Borucki, William J.; Allen, L. E.; Taylor, S. W.; Torbet, E. B.; Schaefer, A. R.; Fowler, J.

    1988-01-01

    A breadboard photometer was constructed that demonstrates a precision of 2 times 10 to the 4th power in the laboratory and scintillation-limited performance when used with an 0.5 m aperture telescope. Because the detectors and preamps are not cooled, only stars with m sub v approx. less than 4 are bright enough to allow the photometer to attain a precision of 1 times 10 to the 3rd power for three minute observations with an 0.5 m aperature telescope. Cooling the telescope should allow much fainter stars to be observed. Increasing the aperture of the telescope will allow higher precision and the observation of fainter stars.

  10. The application of Landsat data to mapping avalanche hazards

    NASA Technical Reports Server (NTRS)

    Waterman, S.

    1979-01-01

    Two test areas, representing a variety of avalanche hazards, were selected in the San Juan Mountains of Colorado. Midwinter Landsat digital data were analyzed using a clustering technique, and the results compared to 1:24,000 scale maps of avalanche hazards derived from air photo interpretation and field surveys. Confined avalanches were readily identified because of the high contrast between the snow covered avalanche track and the adjacent forested slopes. Unconfined avalanches could not be identified without supplementary topographic data. Spatial characteristics were of primary importance in delineating avalanche tracks. Spatial resolution was the limiting factor in avalanche detection. Landsat data should prove useful for rapid reconnaissance mapping of avalanche hazards, particularly in the absence of other data sources.

  11. Image quality in two phosphor-based flat panel digital radiographic detectors.

    PubMed

    Samei, Ehsan

    2003-07-01

    Two general types of phosphor screens are currently used in indirect digital radiographic systems: structured phosphor screens and turbid phosphor screens. The purpose of the study was to experimentally compare the image quality characteristics of two flat-panel digital radiography detectors with similar electronics and pixel sizes (0.127 mm), but otherwise equipped with the two types of screens (0.6-mm-thick structured CsI and Lanex Regular). The presampled modulation transfer functions (MTFs) of the detectors were assessed using an edge method. The noise power spectra (NPS) were measured by two-dimensional Fourier analysis of uniformly-exposed radiographs at 50-100 kVp with 19 mm added Al filtration. The detective quantum efficiencies (DQEs) were assessed from the MTF, the NPS, and estimates of the ideal signal-to-noise ratio. The MTF measures of the two detectors were generally similar above a spatial frequency of 2 mm(-1), with approximately 2.5 and approximately 3.8 mm(-1) spatial frequencies corresponding to 0.2 MTF and 0.1 MTF, respectively. Below 2 mm(-1), the MTF for the CsI-based detector was slightly higher by an average of 0.07. At 70 kVp, the measured DQE values in the diagonal (and axial) direction(s) at spatial frequencies of 0.15 mm(-1) and 2.5 mm(-1) were 78% (78%) and 26% (20%) for the CsI-based detector, and 20% (20%) and 7% (6%) for the Lanex-based detector, respectively. The comparative findings experimentally confirm that in indirect flat-panel detectors, structured phosphor screens provide a more favorable tradeoff between resolution and noise compared to turbid-phosphor screens, effectively increasing the detection efficiency of the detector without a negative impact on the detector's spatial resolution response. PMID:12906192

  12. AQUARIUS, the next generation mid-IR detector for ground-based astronomy

    NASA Astrophysics Data System (ADS)

    Ives, Derek; Finger, Gert; Jakob, Gerd; Eschbaumer, Siegfried; Mehrgan, Leander; Meyer, Manfred; Steigmeier, Joerg

    2012-07-01

    ESO has recently funded the development of the AQUARIUS detector at Raytheon Vision Systems, a new mega-pixel Si:As Impurity Band Conduction array for use in ground based astronomical applications at wavelengths between 3 - 28 μm. The array has been designed to have low noise, low dark current, switchable gain and be read out at very high frame rates. It has 64 individual outputs capable of pixel read rates of 3MHz, implying continuous data-rates in excess of 300 Mbytes/second. It is scheduled for deployment into the VISIR instrument at the VLT in 2012, for next generation VLTI instruments and base-lined for METIS, the mid-IR candidate instrument for the E-ELT. A new mid-IR test facility has been developed for AQUARIUS detector development which includes a low thermal background cryostat, high speed cryogenic pre-amplification and high speed data acquisition and detector operation at 5K. We report on all the major performance aspects of this new detector including conversion gain, read noise, dark generation rate, linearity, well capacity, pixel operability, low frequency noise, persistence and electrical cross-talk. We describe the many possible readout modes of this detector and their application. We also report on external issues with the operation of these detectors at such low temperatures. Finally we report on the electronic developments required to operate such a detector at the required high data rates and in a typical mid-IR instrument.

  13. Spatial aspects of vulnerability and risk resulting from snow avalanches

    NASA Astrophysics Data System (ADS)

    Fuchs, S.; Koltermann, P.; Sokratov, S.; Seliverstov, Y.; Shnyparkov, A.

    2012-04-01

    Mountain regions provide a significant proportion of areas used for human settlements, economic purpose, and recreation. Simultaneously, due to steep vertical gradients mountain areas are prone to mass movement processes. The intersection of such processes with areas used by human action turns them into hazards. In particular in arctic regions, which show a greater susceptibility to disturbances than many landscapes, considerable efforts have been undertaken in recent decades to reduce the adverse effects of mountain hazards. The concept of risk supplemented the traditional engineering approaches of technical mitigation since the 1990s to comprehensively manage these threats, and to develop strategies for a sustainable use of these areas. The concept of risk is based on a mathematical combination of hazards and consequences, but is static over time. However, three major dynamic systems interact in the field of mountain hazard risk management: the physical environment, which includes hazardous events; the social and demographic characteristics of the communities that experience them; and the values at risk such as buildings, roads, and other components of the built environment. These dynamics have not sufficiently been taken into account so far in natural hazard risk management, in particular with respect to industrialised artic regions. Within the city of Kirovsk, Kola Peninsula, Russian Federation, these dynamics were assessed by taking snow avalanche risk as an example. The test site is exposed to multiple avalanche tracks with repeated releases during individual winter seasons, endangering the built environment and any kind of infrastructure lines. The aim was to contribute to the development of a spatial risk model for mountain regions on different temporal scales. The spatial characteristics of the long-term avalanche risk, as a result of the evolution of the built environment, was analysed on an annual as well as inter-annual level. This long-term development

  14. Dynamic scaling for avalanches in disordered systems

    SciTech Connect

    Zheng, Guang-Ping; Li, Mo

    2001-03-01

    Dynamic scaling for fracture or breakdown process in disordered systems is investigated in a two-dimensional random field Ising model (RFIM). We find two evolving stages in the avalanche process in the RFIM. At the short-time regime, a power-law growth of the avalanche size {Delta}s is observed; and at late times, the conventional nucleation and growth process is found. At the critical point of the RFIM, the avalanche size is found to obey the dynamic scaling law {Delta}s{approx}t{sup (d-{beta}/{nu})/z}. From this dynamic scaling relation, the critical strength of the random field D{sub c} and the critical exponents, {beta}, {nu}, and z, are determined. The observed dynamics is explained by a simple nucleation theory of first-order phase transformations.

  15. Identifying single electron avalanches in streamer discharges

    NASA Astrophysics Data System (ADS)

    Wormeester, Gideon; Nijdam, Sander; Ebert, Ute

    2011-10-01

    Although some properties of positive streamers in nitrogen-oxygen mixtures, such as velocity and diameter, are remarkably insensitive to the N 2 :O 2 -ratio of the background gas, the visible structure can be quite different. In particular, experiments in high purity nitrogen have demonstrated that streamers can exhibit a feather-like structure, with small hairs connecting to the main streamer channel. Such structures were not observed in mixtures with higher oxygen density, such as air. We hypothesize that these hairs are avalanches started by single electrons that move towards the positively charged streamer head. Using results from numerical simulations, the presence or absence of these hairs can be explained: In air, the electron density outside the streamer channel is high and avalanches overlap, while in high purity nitrogen, the electron density is sufficiently low that avalanches are distinct and visible individually.

  16. Microgap ultra-violet detector

    DOEpatents

    Wuest, Craig R.; Bionta, Richard M.

    1994-01-01

    A microgap ultra-violet detector of photons with wavelengths less than 400 run (4000 Angstroms) which comprises an anode and a cathode separated by a gas-filled gap and having an electric field placed across the gap. Either the anode or the cathode is semi-transparent to UV light. Upon a UV photon striking the cathode an electron is expelled and accelerated across the gap by the electric field causing interactions with other electrons to create an electron avalanche which contacts the anode. The electron avalanche is detected and converted to an output pulse.

  17. Microgap ultra-violet detector

    DOEpatents

    Wuest, C.R.; Bionta, R.M.

    1994-09-20

    A microgap ultra-violet detector of photons with wavelengths less than 400 run (4,000 Angstroms) which comprises an anode and a cathode separated by a gas-filled gap and having an electric field placed across the gap is disclosed. Either the anode or the cathode is semi-transparent to UV light. Upon a UV photon striking the cathode an electron is expelled and accelerated across the gap by the electric field causing interactions with other electrons to create an electron avalanche which contacts the anode. The electron avalanche is detected and converted to an output pulse. 2 figs.

  18. Experimental and theoretical performance analysis for a CMOS-based high resolution image detector

    NASA Astrophysics Data System (ADS)

    Jain, Amit; Bednarek, Daniel R.; Rudin, Stephen

    2014-03-01

    Increasing complexity of endovascular interventional procedures requires superior x-ray imaging quality. Present stateof- the-art x-ray imaging detectors may not be adequate due to their inherent noise and resolution limitations. With recent developments, CMOS based detectors are presenting an option to fulfill the need for better image quality. For this work, a new CMOS detector has been analyzed experimentally and theoretically in terms of sensitivity, MTF and DQE. The detector (Dexela Model 1207, Perkin-Elmer Co., London, UK) features 14-bit image acquisition, a CsI phosphor, 75 μm pixels and an active area of 12 cm x 7 cm with over 30 fps frame rate. This detector has two modes of operations with two different full-well capacities: high and low sensitivity. The sensitivity and instrumentation noise equivalent exposure (INEE) were calculated for both modes. The detector modulation-transfer function (MTF), noise-power spectra (NPS) and detective quantum efficiency (DQE) were measured using an RQA5 spectrum. For the theoretical performance evaluation, a linear cascade model with an added aliasing stage was used. The detector showed excellent linearity in both modes. The sensitivity and the INEE of the detector were found to be 31.55 DN/μR and 0.55 μR in high sensitivity mode, while they were 9.87 DN/μR and 2.77 μR in low sensitivity mode. The theoretical and experimental values for the MTF and DQE showed close agreement with good DQE even at fluoroscopic exposure levels. In summary, the Dexela detector's imaging performance in terms of sensitivity, linear system metrics, and INEE demonstrates that it can overcome the noise and resolution limitations of present state-of-the-art x-ray detectors.

  19. Rockfalls and Avalanches from Little Tahoma Peak on Mount Rainier, Washington

    USGS Publications Warehouse

    Crandell, Dwight Raymond; Fahnestock, Robert K.

    1965-01-01

    In December 1963 rockfalls from Little Tahoma Peak on the east side of Mount Rainier volcano fell onto Emmons Glacier and formed avalanches of rock debris that traveled about 4 miles down the glacier and the White River valley. In this distance, the rock debris descended as much as 6,200 feet in altitude. Minor lithologic differences and crosscutting relations indicate that the rockfalls caused at least seven separate avalanches, having an estimated total volume of 14 million cubic yards. The initial rockfall may have been caused by a small steam explosion near the base of Little Tahoma Peak. During movement, some of the avalanches were deflected from one side of the valley to the other. Calculations based on the height to which the avalanches rose on the valley walls suggest that their velocity reached at least 80 or 90 miles per hour. The unusually long distance some of the avalanches were transported is attributed to a cushion of trapped and compressed air at their base, which buoyed them up amid reduced friction.

  20. Reproducibility and calibration of MMC-based high-resolution gamma detectors

    DOE PAGESBeta

    Bates, C. R.; Pies, C.; Kempf, S.; Hengstler, D.; Fleischmann, A.; Gastaldo, L.; Enss, C.; Friedrich, S.

    2016-07-15

    Here, we describe a prototype γ-ray detector based on a metallic magnetic calorimeter with an energy resolution of 46 eV at 60 keV and a reproducible response function that follows a simple second-order polynomial. The simple detector calibration allows adding high-resolution spectra from different pixels and different cool-downs without loss in energy resolution to determine γ-ray centroids with high accuracy. As an example of an application in nuclear safeguards enabled by such a γ-ray detector, we discuss the non-destructive assay of 242Pu in a mixed-isotope Pu sample.

  1. Reproducibility and calibration of MMC-based high-resolution gamma detectors

    NASA Astrophysics Data System (ADS)

    Bates, C. R.; Pies, C.; Kempf, S.; Hengstler, D.; Fleischmann, A.; Gastaldo, L.; Enss, C.; Friedrich, S.

    2016-07-01

    We describe a prototype γ-ray detector based on a metallic magnetic calorimeter with an energy resolution of 46 eV at 60 keV and a reproducible response function that follows a simple second-order polynomial. The simple detector calibration allows adding high-resolution spectra from different pixels and different cool-downs without loss in energy resolution to determine γ-ray centroids with high accuracy. As an example of an application in nuclear safeguards enabled by such a γ-ray detector, we discuss the non-destructive assay of 242Pu in a mixed-isotope Pu sample.

  2. A V-BLAST Detector Based on Modified Householder QRD over the Spatially Correlated Fading Channel

    NASA Astrophysics Data System (ADS)

    Jing, Xiaorong; Zhou, Zhengzhong; Zhang, Tianqi

    We propose a feasible V-BLAST detector based on modified Householder QRD (M-H-QRD) over spatially correlated fading channel, which can almost match the performance of the V-BLAST algorithm with much lower complexity and better numerical stability. Compared to the sorted QRD (S-QRD) detector, the proposed detector requires a smaller minimum word-length to reach the same value of error floor for fixed-point (FP) numerical precision despite no significant performance difference for floating-point machine precision. All these advantages make it attractive when implemented using FP arithmetic.

  3. Microwave detectors based on the spin-torque diode effect

    NASA Astrophysics Data System (ADS)

    Prokopenko, O. V.; Slavin, A. N.

    2015-05-01

    The spin-transfer torque (STT) effect provides a new method of manipulation of magnetization in nanoscale objects. The STT effect manifests itself as a transfer of spin angular momentum between the parallel magnetic layers separated by a nonmagnetic spacer and traversed by a dc electric current. The transfer of the spin angular momentum from one layer to another could result in the excitation of the microwave-frequency magnetization dynamics in one of the magnetic layers. On the other hand, when a magnetization dynamics is excited in a magnetic layered structure by an external microwave signal both the structure electrical resistance and current through the structure will acquire microwave components resulting in the appearance of a rectified dc voltage on the magnetic structure. This "spin-torque diode effect" can be used for the development of ultra-sensitive spin-torque microwave detectors (STMD). Below we present a brief review of our recent work on the general properties of STMDs, analyze the performance of the "resonance-type" and "threshold-type STMD" and consider the possible applications for such microwave detectors.

  4. Laboratory study of avalanches in magnetized plasmas.

    PubMed

    Van Compernolle, B; Morales, G J; Maggs, J E; Sydora, R D

    2015-03-01

    It is demonstrated that a novel heating configuration applied to a large and cold magnetized plasma allows the study of avalanche phenomena under controlled conditions. Intermittent collapses of the plasma pressure profile, associated with unstable drift-Alfvén waves, exhibit a two-slope power-law spectrum with exponents near -1 at lower frequencies and in the range of -2 to -4 at higher frequencies. A detailed mapping of the spatiotemporal evolution of a single avalanche event is presented. PMID:25871044

  5. Phase avalanches in near-adiabatic evolutions

    SciTech Connect

    Vertesi, T.; Englman, R.

    2006-02-15

    In the course of slow, nearly adiabatic motion of a system, relative changes in the slowness can cause abrupt and high magnitude phase changes, ''phase avalanches,'' superimposed on the ordinary geometric phases. The generality of this effect is examined for arbitrary Hamiltonians and multicomponent (>2) wave packets and is found to be connected (through the Blaschke term in the theory of analytic signals) to amplitude zeros in the lower half of the complex time plane. Motion on a nonmaximal circle on the Poincare-sphere suppresses the effect. A spectroscopic transition experiment can independently verify the phase-avalanche magnitudes.

  6. Why small avalanche photodiodes are beautiful

    NASA Astrophysics Data System (ADS)

    Rees, Graham J.; David, John P. R.

    2003-07-01

    Conventional wisdom suggests that, for low avalanche noise, avalanche photodiodes should operate at low electric fields, where electron and hole ionisation coefficients can differ widely. However, the associated weak ionization requires long multiplication regions, which in turn demand high bias voltages and result in long carrier transit times, reducing device speed. Moreover, multiplication is particularly sensitive to temperature in this region. In this paper we discuss the effects of dead space on reducing noise in short devices and on the associated benefits in predicted response time and reduced temperature sensitivity. The paper is illustrated with work from the Sheffield group.

  7. Relating rock avalanche morphology to emplacement processes

    NASA Astrophysics Data System (ADS)

    Dufresne, Anja; Prager, Christoph; Bösmeier, Annette

    2015-04-01

    The morphology, structure and sedimentological characteristics of rock avalanche deposits reflect both internal emplacement processes and external influences, such as runout path characteristics. The latter is mainly predisposed by topography, substrate types, and hydrogeological conditions. Additionally, the geological setting at the source slope controls, e.g. the spatial distribution of accumulated lithologies and hence material property-related changes in morphology, or the maximum clast size and amount of fines of different lithological units. The Holocene Tschirgant rock avalanche (Tyrol, Austria) resulted from failure of an intensely deformed carbonate rock mass on the southeast face of a 2,370-m-high mountain ridge. The initially sliding rock mass rapidly fragmented as it moved towards the floor of the Inn River valley. Part of the 200-250 x 106 m3 (Patzelt 2012) rock avalanche debris collided with and moved around an opposing bedrock ridge and flowed into the Ötz valley, reaching up to 6.3 km from source. Where the Tschirgant rock avalanche spread freely it formed longitudinal ridges aligned along motion direction as well as smaller hummocks. Encountering high topography, it left runup ridges, fallback patterns (i.e. secondary collapse), and compressional morphology (successively elevated, transverse ridges). Further evidence for the mechanical landslide behaviour is given by large volumes of mobilized valley-fill sediments (polymict gravels and sands). These sediments indicate both shearing and compressional faulting within the rock avalanche mass (forming their own morphological units through, e.g. in situ bulldozing or as distinctly different hummocky terrain), but also indicate extension of the spreading landslide mass (i.e. intercalated/injected gravels encountered mainly in morphological depressions between hummocks). Further influences on its morphology are given by the different lithological units. E.g. the transition from massive dolomite

  8. Low noise InGaAs/InP single-photon detector for singlet oxygen detection

    NASA Astrophysics Data System (ADS)

    Boso, Gianluca; Korzh, Boris; Lunghi, Tommaso; Sanguinetti, Bruno; Zbinden, Hugo

    2015-01-01

    Single-photon detectors are the best option for applications where low noise measurements and/or high timing resolution are required. At wavelengths between 900 nm and 1700 nm, however, low noise detectors have typically been based on cryogenic superconducting technology, precluding their extended use in industrial or clinical applications. Here we present a practical (i.e. compact, reliable and affordable) detector, based on a negative feedback InGaAs/InP avalanche photodiode and exhibiting dark counts < 1 count-per-second at 10% efficiency, and with efficiencies of up to 27%. We show how this detector enables novel applications such as singlet-oxygen luminescence detection for Photo Dynamic Therapy (PDT) but can be an enabling technology also for a diverse set of applications in both quantum communication (e.g. long-distance quantum key distribution) and biomedical imaging.

  9. High dynamic range CMOS-based mammography detector for FFDM and DBT

    NASA Astrophysics Data System (ADS)

    Peters, Inge M.; Smit, Chiel; Miller, James J.; Lomako, Andrey

    2016-03-01

    Digital Breast Tomosynthesis (DBT) requires excellent image quality in a dynamic mode at very low dose levels while Full Field Digital Mammography (FFDM) is a static imaging modality that requires high saturation dose levels. These opposing requirements can only be met by a dynamic detector with a high dynamic range. This paper will discuss a wafer-scale CMOS-based mammography detector with 49.5 μm pixels and a CsI scintillator. Excellent image quality is obtained for FFDM as well as DBT applications, comparing favorably with a-Se detectors that dominate the X-ray mammography market today. The typical dynamic range of a mammography detector is not high enough to accommodate both the low noise and the high saturation dose requirements for DBT and FFDM applications, respectively. An approach based on gain switching does not provide the signal-to-noise benefits in the low-dose DBT conditions. The solution to this is to add frame summing functionality to the detector. In one X-ray pulse several image frames will be acquired and summed. The requirements to implement this into a detector are low noise levels, high frame rates and low lag performance, all of which are unique characteristics of CMOS detectors. Results are presented to prove that excellent image quality is achieved, using a single detector for both DBT as well as FFDM dose conditions. This method of frame summing gave the opportunity to optimize the detector noise and saturation level for DBT applications, to achieve high DQE level at low dose, without compromising the FFDM performance.

  10. Avalanche mode of motion: Implications from lunar examples

    USGS Publications Warehouse

    Howard, K.A.

    1973-01-01

    A large avalanche (21 square kilometers) at the Apollo 17 landing site moved out several kilometers over flat ground beyond its source slope. If not triggered by impacts, then it was as "efficient" as terrestrial avalanches attributed to air-cushion sliding. Evidently lunar avalanches are able to flow despite the lack of lubricating or cushioning fluid.

  11. Avalanche mode of motion - Implications from lunar examples.

    NASA Technical Reports Server (NTRS)

    Howard, K. A.

    1973-01-01

    A large avalanche (21 square kilometers) at the Apollo 17 landing site moved out several kilometers over flat ground beyond its source slope. If not triggered by impacts, then it was as 'efficient' as terrestrial avalanches attributed to air-cushion sliding. Evidently lunar avalanches are able to flow despite the lack of lubricating or cushioning fluid.

  12. Ultrahigh-sensitivity single-photon detection with linear-mode silicon avalanche photodiode.

    PubMed

    Akiba, Makoto; Tsujino, Kenji; Sasaki, Masahide

    2010-08-01

    We developed an ultrahigh-sensitivity single-photon detector using a linear-mode avalanche photodiode (APD) with a cryogenic low-noise readout circuit; the APD is operated at 78K. The noise-equivalent power of the detector is as low as 2.2x10(-20)W/Hz(1/2) at a wavelength of 450nm. The photon-detection efficiency and dark-count rate (DCR) are 0.72 and 0.0008counts/s, respectively. A low DCR is achieved by thermal treatment for reducing the trapped carriers when the thermal treatment temperature is above 100K. PMID:20680078

  13. Active quenching circuit for single-photon detection with Geiger mode avalanche photodiodes.

    PubMed

    Stipcević, Mario

    2009-03-20

    In this paper a novel construction of an active quenching circuit intended for single-photon detection is presented, along with a few original methods for its evaluation. The circuit has been combined with a standard avalanche photodiode C30902S to form a single-photon detector. This detector has a dead time of 39 ns, maximum random counting frequency of 14 MHz, small afterpulsing probability, an estimated peak detection efficiency of over 20%, and a dark count rate of less than 100 Hz. This simple and robust active quenching circuit can be built from off-the-shelf electronic components and is presented with the detailed schematic diagram. PMID:19305468

  14. Gamma-Free Neutron Detector Based upon Lithium Phosphate Nanoparticles

    SciTech Connect

    Steven Wallace

    2007-08-28

    A gamma-free neutron-sensitive scintillator is needed to enhance radiaition sensing and detection for nonproliferation applications. Such a scintillator would allow very large detectors to be placed at the perimeter of spent-fuel storage facilities at commercial nuclear power plants, so that any movement of spontaneously emitted neutrons from spent nuclear fuel or weapons grade plutonium would be noted in real-time. This task is to demonstrate that the technology for manufacturing large panels of fluor-doped plastic containing lithium-6 phosphate nanoparticles can be achieved. In order to detect neutrons, the nanoparticles must be sufficiently small so that the plastic remains transparent. In this way, the triton and alpha particles generated by the capture of the neutron will result in a photon burst that can be coupled to a wavelength shifting fiber (WLS) producing an optical signal of about ten nanoseconds duration signaling the presence of a neutron emitting source.

  15. A large area, silicon photomultiplier-based PET detector module

    PubMed Central

    Raylman, RR; Stolin, A; Majewski, S; Proffitt, J

    2013-01-01

    The introduction of silicon photomultipliers (SiPM) has facilitated construction of compact, efficient and magnetic field-hardened positron emission tomography (PET) scanners. To take full advantage of these devices, methods for using them to produce large field-of-view PET scanners are needed. In this investigation, we explored techniques to combine two SiPM arrays to form the building block for a small animal PET scanner. The module consists of a 26 × 58 array of 1.5 × 1.5mm2 LYSO elements (spanning 41 × 91mm2) coupled to two SensL SiPM arrays. The SiPMs were read out with new multiplexing electronics developed for this project. To facilitate calculation of event position with multiple SiPM arrays it was necessary to spread scintillation light amongst a number of elements with a small light guide. This method was successful in permitting identification of all detector elements, even at the seam between two SiPM arrays. Since the performance of SiPMs is enhanced by cooling, the detector module was fitted with a cooling jacket, which allowed the temperature of the device and electronics to be controlled. Testing demonstrated that the peak-to-valley contrast ratio of the light detected from the scintillation array was increased by ∼45% when the temperature was reduced from 28 °C to 16 °C. Energy resolution for 511 keV photons improved slightly from 18.8% at 28 °C to 17.8% at 16 °C. Finally, the coincidence timing resolution of the module was found to be insufficient for time-of-flight applications (∼2100 ps at 14 °C). The first use of these new modules will be in the construction of a small animal PET scanner to be integrated with a 3T clinical magnetic resonance imaging scanner. PMID:24319305

  16. A large area, silicon photomultiplier-based PET detector module

    NASA Astrophysics Data System (ADS)

    Raylman, R. R.; Stolin, A.; Majewski, S.; Proffitt, J.

    2014-01-01

    The introduction of silicon photomultipliers (SiPM) has facilitated construction of compact, efficient and magnetic field-hardened positron emission tomography (PET) scanners. To take full advantage of these devices, methods for using them to produce large field-of-view PET scanners are needed. In this investigation, we explored techniques to combine two SiPM arrays to form the building block for a small animal PET scanner. The module consists of a 26×58 array of 1.5×1.5 mm2 LYSO elements (spanning 41×91 mm2) coupled to two SensL SiPM arrays. The SiPMs were read out with new multiplexing electronics developed for this project. To facilitate calculation of event position with multiple SiPM arrays it was necessary to spread scintillation light amongst a number of elements with a small light guide. This method was successful in permitting identification of all detector elements, even at the seam between two SiPM arrays. Since the performance of SiPMs is enhanced by cooling, the detector module was fitted with a cooling jacket, which allowed the temperature of the device and electronics to be controlled. Testing demonstrated that the peak-to-valley contrast ratio of the light detected from the scintillation array was increased by ~45% when the temperature was reduced from 28 °C to 16 °C. Energy resolution for 511 keV photons improved slightly from 18.8% at 28 °C to 17.8% at 16 °C. Finally, the coincidence timing resolution of the module was found to be insufficient for time-of-flight applications (~2100 ps at 14 °C). The first use of these new modules will be in the construction of a small animal PET scanner to be integrated with a 3 T clinical magnetic resonance imaging scanner.

  17. Hard X-ray and gamma-ray detector for ASTRO-H based on Si and CdTe imaging sensors

    NASA Astrophysics Data System (ADS)

    Hxi/Sgd Team; Kokubun, M.; Watanabe, S.; Nakazawa, K.; Tajima, H.; Fukazawa, Y.; Takahashi, T.; Kataoka, J.; Kamae, T.; Katagiri, H.; Madejski, G. M.; Makishima, K.; Mizuno, T.; Ohno, M.; Sato, R.; Takahashi, H.; Tanaka, T.; Tashiro, M.; Terada, Y.; Yamaoka, K.; HXI/SGD Team

    2010-11-01

    We have been developing a hard X-ray imager and soft gamma-ray detector as on board instruments of the ASTRO-H mission. The Hard X-ray Imager (HXI) is one of the three focal plane detectors of ASTRO-H, which is aimed to realize the focusing imaging of hard X-ray photons in combination with hard X-ray telescopes. By use of the hybrid structure composed of double-sided silicon strip detectors and a cadmium telluride strip detector, it fully covers the energy range up to 80 keV with a high quantum efficiency. High spatial resolutions of 250μm pitch and energy resolutions of 1-2 keV (FWMH) are at the same time achieved with low noise front-end ASICs. The Soft Gamma-ray Detector (SGD) is a novel and unique detector which is characterized by semiconductor Compton cameras surrounded by narrow field-of-view active shields, and covers a higher energy range (30-600 keV) than that of HXI. It consists of four Compton Cameras constructed with many layers of Silicon and CdTe pad detectors. With its multi-layer structure and Compton reconstruction capability, in addition to the BGO active shields read by Avalanche photo-diodes, this detector will achieve an extremely high background rejection efficiency in the orbit. We report the current status of hardware development including the design requirement, expected performance, and technical readinesses of key technologies.

  18. The solid state detector technology for picosecond laser ranging

    NASA Technical Reports Server (NTRS)

    Prochazka, Ivan

    1993-01-01

    We developed an all solid state laser ranging detector technology, which makes the goal of millimeter accuracy achievable. Our design and construction philosophy is to combine the techniques of single photon ranging, ultrashort laser pulses, and fast fixed threshold discrimination while avoiding any analog signal processing within the laser ranging chain. The all solid state laser ranging detector package consists of the START detector and the STOP solid state photon counting module. Both the detectors are working in an optically triggered avalanche switching regime. The optical signal is triggering an avalanche current buildup which results in the generation of a uniform, fast risetime output pulse.

  19. Monte Carlo based performance assessment of different animal PET architectures using pixellated CZT detectors

    NASA Astrophysics Data System (ADS)

    Visvikis, D.; Lefevre, T.; Lamare, F.; Kontaxakis, G.; Santos, A.; Darambara, D.

    2006-12-01

    The majority of present position emission tomography (PET) animal systems are based on the coupling of high-density scintillators and light detectors. A disadvantage of these detector configurations is the compromise between image resolution, sensitivity and energy resolution. In addition, current combined imaging devices are based on simply placing back-to-back and in axial alignment different apparatus without any significant level of software or hardware integration. The use of semiconductor CdZnTe (CZT) detectors is a promising alternative to scintillators for gamma-ray imaging systems. At the same time CZT detectors have the potential properties necessary for the construction of a truly integrated imaging device (PET/SPECT/CT). The aims of this study was to assess the performance of different small animal PET scanner architectures based on CZT pixellated detectors and compare their performance with that of state of the art existing PET animal scanners. Different scanner architectures were modelled using GATE (Geant4 Application for Tomographic Emission). Particular scanner design characteristics included an overall cylindrical scanner format of 8 and 24 cm in axial and transaxial field of view, respectively, and a temporal coincidence window of 8 ns. Different individual detector modules were investigated, considering pixel pitch down to 0.625 mm and detector thickness from 1 to 5 mm. Modified NEMA NU2-2001 protocols were used in order to simulate performance based on mouse, rat and monkey imaging conditions. These protocols allowed us to directly compare the performance of the proposed geometries with the latest generation of current small animal systems. Results attained demonstrate the potential for higher NECR with CZT based scanners in comparison to scintillator based animal systems.

  20. Gated STED microscopy with time-gated single-photon avalanche diode

    PubMed Central

    Hernández, Iván Coto; Buttafava, Mauro; Boso, Gianluca; Diaspro, Alberto; Tosi, Alberto; Vicidomini, Giuseppe

    2015-01-01

    Stimulated emission depletion (STED) microscopy provides fluorescence imaging with sub-diffraction resolution. Experimentally demonstrated at the end of the 90s, STED microscopy has gained substantial momentum and impact only in the last few years. Indeed, advances in many fields improved its compatibility with everyday biological research. Among them, a fundamental step was represented by the introduction in a STED architecture of the time-gated detection, which greatly reduced the complexity of the implementation and the illumination intensity needed. However, the benefits of the time-gated detection came along with a reduction of the fluorescence signal forming the STED microscopy images. The maximization of the useful (within the time gate) photon flux is then an important aspect to obtain super-resolved images. Here we show that by using a fast-gated single-photon avalanche diode (SPAD), i.e. a detector able to rapidly (hundreds picoseconds) switch-on and -off can improve significantly the signal-to-noise ratio (SNR) of the gated STED image. In addition to an enhancement of the image SNR, the use of the fast-gated SPAD reduces also the system complexity. We demonstrate these abilities both on calibration and biological sample. The experiments were carried on a gated STED microscope based on a STED beam operating in continuous-wave (CW), although the fast-gated SPAD is fully compatible with gated STED implementations based on pulsed STED beams. PMID:26114044

  1. Gated STED microscopy with time-gated single-photon avalanche diode.

    PubMed

    Hernández, Iván Coto; Buttafava, Mauro; Boso, Gianluca; Diaspro, Alberto; Tosi, Alberto; Vicidomini, Giuseppe

    2015-06-01

    Stimulated emission depletion (STED) microscopy provides fluorescence imaging with sub-diffraction resolution. Experimentally demonstrated at the end of the 90s, STED microscopy has gained substantial momentum and impact only in the last few years. Indeed, advances in many fields improved its compatibility with everyday biological research. Among them, a fundamental step was represented by the introduction in a STED architecture of the time-gated detection, which greatly reduced the complexity of the implementation and the illumination intensity needed. However, the benefits of the time-gated detection came along with a reduction of the fluorescence signal forming the STED microscopy images. The maximization of the useful (within the time gate) photon flux is then an important aspect to obtain super-resolved images. Here we show that by using a fast-gated single-photon avalanche diode (SPAD), i.e. a detector able to rapidly (hundreds picoseconds) switch-on and -off can improve significantly the signal-to-noise ratio (SNR) of the gated STED image. In addition to an enhancement of the image SNR, the use of the fast-gated SPAD reduces also the system complexity. We demonstrate these abilities both on calibration and biological sample. The experiments were carried on a gated STED microscope based on a STED beam operating in continuous-wave (CW), although the fast-gated SPAD is fully compatible with gated STED implementations based on pulsed STED beams. PMID:26114044

  2. High temperature and wavelength dependence of avalanche gain of AlAsSb avalanche photodiodes.

    PubMed

    Sandall, Ian C; Xie, Shiyu; Xie, Jingjing; Tan, Chee Hing

    2011-11-01

    The evolution of the dark currents and breakdown at elevated temperatures of up to 450  K are studied using thin AlAsSb avalanche regions. While the dark currents increase rapidly as the temperature is increased, the avalanche gain is shown to only have a weak temperature dependence. Temperature coefficients of breakdown voltage of 0.93 and 1.93  mV/K were obtained from the diodes of 80 and 230  nm avalanche regions (i-regions), respectively. These values are significantly lower than for other available avalanche materials at these temperatures. The wavelength dependence of multiplication characteristics of AlAsSb p-i-n diodes has also been investigated, and it was found that the ionization coefficients for electrons and holes are comparable within the electric field and wavelength ranges measured. PMID:22048393

  3. Prototyping of MWIR MEMS-based optical filter combined with HgCdTe detector

    NASA Astrophysics Data System (ADS)

    Kozak, Dmitry A.; Fernandez, Bautista; Velicu, Silviu; Kubby, Joel

    2010-02-01

    In the past decades, there have been several attempts to create a tunable optical detector with operation in the infrared. The drive for creating such a filter is its wide range of applications, from passive night vision to biological and chemical sensors. Such a device would combine a tunable optical filter with a wide-range detector. In this work, we propose using a Fabry-Perot interferometer centered in the mid-wave infrared (MWIR) spectrum with an HgCdTe detector. Using a MEMS-based interferometer with an integrated Bragg stack will allow in-plane operation over a wide range. Because such devices have a tendency to warp, creating less-than-perfect optical surfaces, the Fabry-Perot interferometer is prototyped using the SOI-MUMPS process to ensure desirable operation. The mechanical design is aimed at optimal optical flatness of the moving membranes and a low operating voltage. The prototype is tested for these requirements. An HgCdTe detector provides greater performance than a pyroelectic detector used in some previous work, allowing for lower noise, greater detection speed and higher sensitivity. Both a custom HgCdTe detector and commercially available pyroelectric detector are tested with commercial optical filter. In previous work, monolithic integration of HgCdTe detectors with optical filters proved to be problematic. Part of this work investigates the best approach to combining these two components, either monolithically in HgCdTe or using a hybrid packaging approach where a silicon MEMS Fabry-Perot filter is bonded at low temperature to a HgCdTe detector.

  4. GaN-Based Detector Enabling Technology for Next Generation Ultraviolet Planetary Missions

    NASA Technical Reports Server (NTRS)

    Aslam, S.; Gronoff, G.; Hewagama, T.; Janz, S.; Kotecki, C.

    2012-01-01

    The ternary alloy AlN-GaN-InN system provides several distinct advantages for the development of UV detectors for future planetary missions. First, (InN), (GaN) and (AlN) have direct bandgaps 0.8, 3.4 and 6.2 eV, respectively, with corresponding wavelength cutoffs of 1550 nm, 365 nm and 200 nm. Since they are miscible with each other, these nitrides form complete series of indium gallium nitride (In(sub l-x)Ga(sub x)N) and aluminum gallium nitride (Al(sub l-x)Ga(sub x)N) alloys thus allowing the development of detectors with a wavelength cut-off anywhere in this range. For the 2S0-365 nm spectral wavelength range AlGaN detectors can be designed to give a 1000x solar radiation rejection at cut-off wavelength of 325 nm, than can be achieved with Si based detectors. For tailored wavelength cut-offs in the 365-4S0 nm range, InGaN based detectors can be fabricated, which still give 20-40x better solar radiation rejection than Si based detectors. This reduced need for blocking filters greatly increases the Detective Quantum efficiency (DQE) and simplifies the instrument's optical systems. Second, the wide direct bandgap reduces the thermally generated dark current to levels allowing many observations to be performed at room temperature. Third, compared to narrow bandgap materials, wide bandgap semiconductors are significantly more radiation tolerant. Finally, with the use of an (AI, In)GaN array, the overall system cost is reduced by eliminating stringent Si CCD cooling systems. Compared to silicon, GaN based detectors have superior QE based on a direct bandgap and longer absorption lengths in the UV.

  5. Nanosecond X-ray detector based on high resistivity ZnO single crystal semiconductor

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaolong; Chen, Liang; He, Yongning; Liu, Jinliang; Peng, Wenbo; Huang, Zhiyong; Qi, Xiaomeng; Pan, Zijian; Zhang, Wenting; Zhang, Zhongbing; Ouyang, Xiaoping

    2016-04-01

    The pulse radiation detectors are sorely needed in the fields of nuclear reaction monitoring, material analysis, astronomy study, spacecraft navigation, and space communication. In this work, we demonstrate a nanosecond X-ray detector based on ZnO single crystal semiconductor, which emerges as a promising compound-semiconductor radiation detection material for its high radiation tolerance and advanced large-size bulk crystal growth technique. The resistivity of the ZnO single crystal is as high as 1013 Ω cm due to the compensation of the donor defects (VO) and acceptor defects (VZn and Oi) after high temperature annealing in oxygen. The photoconductive X-ray detector was fabricated using the high resistivity ZnO single crystal. The rise time and fall time of the detector to a 10 ps pulse electron beam are 0.8 ns and 3.3 ns, respectively, indicating great potential for ultrafast X-ray detection applications.

  6. Near midplane scintillator-based fast ion loss detector on DIII-D

    SciTech Connect

    Chen, X.; Heidbrink, W. W.; Fisher, R. K.; Pace, D. C.; Chavez, J. A.; Van Zeeland, M. A.; Garcia-Munoz, M.

    2012-10-15

    A new scintillator-based fast-ion loss detector (FILD) installed near the outer midplane of the plasma has been commissioned on DIII-D. This detector successfully measures coherent fast ion losses produced by fast-ion driven instabilities ({<=}500 kHz). Combined with the first FILD at {approx}45 Degree-Sign below the outer midplane [R. K. Fisher, et al., Rev. Sci. Instrum. 81, 10D307 (2010)], the two-detector system measures poloidal variation of losses. The phase space sensitivity of the new detector (gyroradius r{sub L}{approx}[1.5-8] cm and pitch angle {alpha}{approx}[35 Degree-Sign -85 Degree-Sign ]) is calibrated using neutral beam first orbit loss measurements. Since fast ion losses are localized poloidally, having two FILDs at different poloidal locations allows for the study of losses over a wider range of plasma shapes and types of loss orbits.

  7. Calibration method for spectral responsivity of infrared detector based on blackbody at multiple temperature

    NASA Astrophysics Data System (ADS)

    Zhang, Y. F.; Shao, Z. F.; Wu, Y. Q.

    2015-08-01

    The spectral responsivity is one of the most important technical indicators of infrared detector which has an important significance for radiation thermometry and emissivity measurement. Using a blackbody radiation at multiple temperatures, the calibration for spectral responsivity of the infrared detector is proposed. With the Planck's law, the spectral radiance of blackbody at the different temperature is calculated. The detector captures the radiation and generates output values each of those is the function of spectral responsivity, spectral radiance and environmental radiation. Calibration equation is established by means of the calculated radiance and output values. By solving the equations based on principle of least squares, the calibration of spectral responsivity is implemented. From the comparison experiment of measuring the radiance of blackbody at 850K, radiance value measured by the MCT detector has a good consistency with the theoretical data.

  8. Optimization of a bolometer detector for ITER based on Pt absorber on SiN membrane.

    PubMed

    Meister, H; Eich, T; Endstrasser, N; Giannone, L; Kannamüller, M; Kling, A; Koll, J; Trautmann, T; Detemple, P; Schmitt, S

    2010-10-01

    Any plasma diagnostic in ITER must be able to operate at temperatures in excess of 200 °C and neutron loads corresponding to 0.1 dpa over its lifetime. To achieve this aim for the bolometer diagnostic, a miniaturized metal resistor bolometer detector based on Pt absorbers galvanically deposited on SiN membranes is being developed. The first two generations of detectors featured up to 4.5 μm thick absorbers. Results from laboratory tests are presented characterizing the dependence of their calibration constants under thermal loads up to 450 °C. Several detectors have been tested in ASDEX Upgrade providing reliable data but also pointing out the need for further optimization. A laser trimming procedure has been implemented to reduce the mismatch in meander resistances below 1% for one detector and the thermal drifts from this mismatch. PMID:21061487

  9. A Hybrid Multiuser Detector Based on MMSE and AFSA for TDRS System Forward Link

    PubMed Central

    Yin, Zhendong; Liu, Xiaohui

    2014-01-01

    This study mainly focuses on multiuser detection in tracking and data relay satellite (TDRS) system forward link. Minimum mean square error (MMSE) is a low complexity multiuser detection method, but MMSE detector cannot achieve satisfactory bit error ratio and near-far resistance, whereas artificial fish swarm algorithm (AFSA) is expert in optimization and it can realize the global convergence efficiently. Therefore, a hybrid multiuser detector based on MMSE and AFSA (MMSE-AFSA) is proposed in this paper. The result of MMSE and its modified formations are used as the initial values of artificial fishes to accelerate the speed of global convergence and reduce the iteration times for AFSA. The simulation results show that the bit error ratio and near-far resistance performances of the proposed detector are much better, compared with MF, DEC, and MMSE, and are quite close to OMD. Furthermore, the proposed MMSE-AFSA detector also has a large system capacity. PMID:24883418

  10. Multi-class geospatial object detection and geographic image classification based on collection of part detectors

    NASA Astrophysics Data System (ADS)

    Cheng, Gong; Han, Junwei; Zhou, Peicheng; Guo, Lei

    2014-12-01

    The rapid development of remote sensing technology has facilitated us the acquisition of remote sensing images with higher and higher spatial resolution, but how to automatically understand the image contents is still a big challenge. In this paper, we develop a practical and rotation-invariant framework for multi-class geospatial object detection and geographic image classification based on collection of part detectors (COPD). The COPD is composed of a set of representative and discriminative part detectors, where each part detector is a linear support vector machine (SVM) classifier used for the detection of objects or recurring spatial patterns within a certain range of orientation. Specifically, when performing multi-class geospatial object detection, we learn a set of seed-based part detectors where each part detector corresponds to a particular viewpoint of an object class, so the collection of them provides a solution for rotation-invariant detection of multi-class objects. When performing geographic image classification, we utilize a large number of pre-trained part detectors to discovery distinctive visual parts from images and use them as attributes to represent the images. Comprehensive evaluations on two remote sensing image databases and comparisons with some state-of-the-art approaches demonstrate the effectiveness and superiority of the developed framework.

  11. Vortex avalanches in a type II superconductor

    SciTech Connect

    Behnia, K.; Capan, C.; Mailly, D.; Etienne, B.

    1999-12-01

    The authors report on a study of the spatiotemporal variation of magnetic induction in a superconducting niobium sample during a slow sweep of external magnetic field. A sizable fraction of the increase in the local vortex population occurs in abrupt jumps. They compare the size distribution of these avalanches with the predictions of self-organized-criticality models for vortex dynamics.

  12. Rock avalanches caused by earthquakes: Source characteristics

    USGS Publications Warehouse

    Keefer, D.K.

    1984-01-01

    Study of a worldwide sample of historical earthquakes showed that slopes most susceptible to catastrophic rock avalanches were higher than 150 meters and steeper than 25 degrees. The slopes were undercut by fluvial or glacial erosion, were composed ofintensely fractured rock, and exhibited at least one other indicator of low strength or potential instability.

  13. Fractal avalanche ruptures in biological membranes

    NASA Astrophysics Data System (ADS)

    Gözen, Irep; Dommersnes, Paul; Czolkos, Ilja; Jesorka, Aldo; Lobovkina, Tatsiana; Orwar, Owe

    2010-11-01

    Bilayer membranes envelope cells as well as organelles, and constitute the most ubiquitous biological material found in all branches of the phylogenetic tree. Cell membrane rupture is an important biological process, and substantial rupture rates are found in skeletal and cardiac muscle cells under a mechanical load. Rupture can also be induced by processes such as cell death, and active cell membrane repair mechanisms are essential to preserve cell integrity. Pore formation in cell membranes is also at the heart of many biomedical applications such as in drug, gene and short interfering RNA delivery. Membrane rupture dynamics has been studied in bilayer vesicles under tensile stress, which consistently produce circular pores. We observed very different rupture mechanics in bilayer membranes spreading on solid supports: in one instance fingering instabilities were seen resulting in floral-like pores and in another, the rupture proceeded in a series of rapid avalanches causing fractal membrane fragmentation. The intermittent character of rupture evolution and the broad distribution in avalanche sizes is consistent with crackling-noise dynamics. Such noisy dynamics appear in fracture of solid disordered materials, in dislocation avalanches in plastic deformations and domain wall magnetization avalanches. We also observed similar fractal rupture mechanics in spreading cell membranes.

  14. Rock avalanches caused by earthquakes: source characteristics.

    PubMed

    Keefer, D K

    1984-03-23

    Study of a worldwide sample of historical earthquakes showed that slopes most susceptible to catastrophic rock avalanches were higher than 150 meters and steeper than 25 degrees. The slopes were undercut by fluvial or glacial erosion, were composed of intensely fractured rock, and exhibited at least one other indicator of low strength or potential instability. PMID:17759365

  15. Nano-multiplication region avalanche photodiodes and arrays

    NASA Technical Reports Server (NTRS)

    Zheng, Xinyu (Inventor); Pain, Bedabrata (Inventor); Cunningham, Thomas J. (Inventor)

    2011-01-01

    An avalanche photodiode with a nano-scale reach-through structure comprising n-doped and p-doped regions, formed on a silicon island on an insulator, so that the avalanche photodiode may be electrically isolated from other circuitry on other silicon islands on the same silicon chip as the avalanche photodiode. For some embodiments, multiplied holes generated by an avalanche reduces the electric field in the depletion region of the n-doped and p-doped regions to bring about self-quenching of the avalanche photodiode. Other embodiments are described and claimed.

  16. 3-D-numerical approach to simulate an avalanche impact into a reservoir

    NASA Astrophysics Data System (ADS)

    Gabl, R.; Seibl, J.; Gems, B.; Aufleger, M.

    2015-06-01

    The impact of an avalanche into a reservoir induces an impulse wave, which poses a threat to population and infrastructure. For a good approximation of the generated wave height and length as well as the resulting outflow volume over structures and dams, formulas, which base on different simplifying assumptions, can be used. Further project-specific investigations by means of a scale model test or numerical simulations are advisable for complex reservoirs as well as the inclusion of hydraulic structures such as spillways. The paper presents a new approach for a 3-D-numerical simulation of an avalanche impact into a reservoir. In this model concept the energy and mass of the avalanche are represented by accelerated water on the real hill slope. Instead of snow, only water and air are used to simulate the moving avalanche with the software FLOW-3D. A significant advantage of this assumption is the self-adaptation of the model avalanche onto the terrain. In order to reach good comparability of the results with existing research at the ETH Zürich, a simplified reservoir geometry is investigated. Thus, a reference case has been analysed including a variation of three geometry parameters (still water depth in the reservoir, freeboard of the dam and reservoir width).

  17. Classification of circulation type sequences applied to snow avalanches over the eastern Pyrenees (Andorra and Catalonia)

    NASA Astrophysics Data System (ADS)

    Esteban, Pere; Beck, Christoph; Philipp, Andreas

    2010-05-01

    Using data associated with accidents or damages caused by snow avalanches over the eastern Pyrenees (Andorra and Catalonia) several atmospheric circulation type catalogues have been obtained. For this purpose, different circulation type classification methods based on Principal Component Analysis (T-mode and S-mode using the extreme scores) and on optimization procedures (Improved K-means and SANDRA) were applied . Considering the characteristics of the phenomena studied, not only single day circulation patterns were taken into account but also sequences of circulation types of varying length. Thus different classifications with different numbers of types and for different sequence lengths were obtained using the different classification methods. Simple between type variability, within type variability, and outlier detection procedures have been applied for selecting the best result concerning snow avalanches type classifications. Furthermore, days without occurrence of the hazards were also related to the avalanche centroids using pattern-correlations, facilitating the calculation of the anomalies between hazardous and no hazardous days, and also frequencies of occurrence of hazardous events for each circulation type. Finally, the catalogues statistically considered the best results are evaluated using the avalanche forecaster expert knowledge. Consistent explanation of snow avalanches occurrence by means of circulation sequences is obtained, but always considering results from classifications with different sequence length. This work has been developed in the framework of the COST Action 733 (Harmonisation and Applications of Weather Type Classifications for European regions).

  18. Silicon avalanche photodiode operation and lifetime analysis for small satellites.

    PubMed

    Tan, Yue Chuan; Chandrasekara, Rakhitha; Cheng, Cliff; Ling, Alexander

    2013-07-15

    Silicon avalanche photodiodes (APDs) are sensitive to operating temperature fluctuations and are also susceptible to radiation flux expected in satellite-based quantum experiments. We introduce a low power voltage adjusting mechanism to overcome the effects of in-orbit temperature fluctuations. We also present data on the performance of Si APDs after irradiation (γ-ray and proton beam). Combined with an analysis of expected orbital irradiation, we propose that a Si APD in a 400 km equatorial orbit may operate beyond the lifetime of the satellite. PMID:23938543

  19. Study on avalanche photodiode influence on heterodyne laser interferometer linearity

    NASA Astrophysics Data System (ADS)

    Budzyn, Grzegorz; Podzorny, Tomasz

    2016-06-01

    In the paper we analyze factors reducing the possible accuracy of the heterodyne laser interferometers. The analysis is performed for the avalanche-photodiode input stages but is in main points valid also for stages with other type of photodetectors. Instrumental error originating from optical, electronic and digital signal processing factors is taken into consideration. We stress factors which are critical and those which can be neglected at certain accuracy requirements. In the work we prove that it is possible to reduce errors of the laser instrument below 1 nm point for multiaxial APD based interferometers by precise control of incident optical power and the temperature of the photodiode.

  20. X-ray detectors based on GaN

    NASA Astrophysics Data System (ADS)

    Duboz, J. Y.; Frayssinet, E.; Chenot, Sebastien; Reverchon, J. L.; Idir, M.

    2013-03-01

    The potential of GaN for X-ray detection in the range from 5 to 40 keV has been assessed. The absorption coefficient has been measured as a fonction of photon energy. Various detectors have been fabricated including MSM and Schottky diodes. They were tested under polychromatic X-ray illumination and under monochromatic irradiation from 6 to 22 keV in the Soleil synchrotron facility. The vertical Schottky diodes perform better as their geometry is better suited to the thick layers required by the low absorption coefficient. The operation mode is discussed in terms of photoconductive and photovoltaic behaviors. Some parasitic effects related to the electrical activation of defects by high energy photons and to the tunnel effect in lightly doped Schottky diodes have been evidenced. These effects disappear in diodes where the doping profile has been optimized. The spectral response is found to be very consistent with the spectral absorption coefficient. The sensitivity of GaN Schottky diodes is evaluated and found to be on the order of 40 photons per second. The response is fast nd linear.

  1. Fabrication and characterization of cubic SrI2(Eu) scintillators for use in array detectors

    NASA Astrophysics Data System (ADS)

    Shimazoe, K.; Koyama, A.; Takahashi, H.; Sakuragi, S.; Yamasaki, Y.

    2016-02-01

    Strontium iodide (SrI2(Eu)) is a promising spectroscopic detector for use in both nuclear security and medical imaging owing to its excellent energy resolution and low internal background radiation. A cubic form is preferable when coupling with a silicon-based photosensor in order to build an array detector for use in applications such as Compton cameras. Here, cubic SrI2(Eu) crystals with 10 mm sides were fabricated and evaluated. The cubic SrI2(Eu) samples coupled to an avalanche photodiode exhibited an energy resolution of approximately 3.6% at 662 keV when using a shaping time of 3 μs. An increase in light output and an improvement of energy resolution were also observed at lower temperatures. The excellent energy resolution of these devices indicates that these crystals are promising potential detectors for use in Compton cameras and other imaging detectors.

  2. Effect of temperature on avalanche region width and DC to RF conversion efficiency of the p+nn-n+ 4H-SiC impact avalanche transit time diodes

    NASA Astrophysics Data System (ADS)

    Chen, Qing; Yang, Lin'an; Wang, Shulong; Hao, Yue

    2016-06-01

    The effect of temperature on avalanche region width and DC to RF conversion efficiency of the p+nn-n+ impact ionization avalanche transit time diodes based on 4H-SiC material for 140 GHz design frequency has been investigated by means of the MEDICI simulation platform. It is shown that the avalanche region width of the IMPATT diodes working at the same operating current densities first decreases and then increases with the increasing temperature. The DC to RF conversion efficiency of the IMPATT diodes first increases and then decreases with the increasing temperature. The increase in ionization rate of impurities with increasing temperature and the decrease in the carrier impact ionization rate with increasing temperature are responsible for the results. In addition, the expansion of avalanche region and the degradation of DC to RF conversion efficiency at lower temperature are more pronounced in lower p+ region doping concentration diode than that in higher p+ region doping concentration.

  3. Adaptive non-uniformity correction method based on temperature for infrared detector array

    NASA Astrophysics Data System (ADS)

    Zhang, Zhijie; Yue, Song; Hong, Pu; Jia, Guowei; Lei, Bo

    2013-09-01

    The existence of non-uniformities in the responsitivity of the element array is a severe problem typical to common infrared detector. These non-uniformities result in a "curtain'' like fixed pattern noises (FPN) that appear in the image. Some random noise can be restrained by the method kind of equalization method. But the fixed pattern noise can only be removed by .non uniformity correction method. The produce of non uniformities of detector array is the combined action of infrared detector array, readout circuit, semiconductor device performance, the amplifier circuit and optical system. Conventional linear correction techniques require costly recalibration due to the drift of the detector or changes in temperature. Therefore, an adaptive non-uniformity method is needed to solve this problem. A lot factors including detectors and environment conditions variety are considered to analyze and conduct the cause of detector drift. Several experiments are designed to verify the guess. Based on the experiments, an adaptive non-uniformity correction method is put forward in this paper. The strength of this method lies in its simplicity and low computational complexity. Extensive experimental results demonstrate the disadvantage of traditional non-uniformity correct method is conquered by the proposed scheme.

  4. A MAPS Based Micro-Vertex Detector for the STAR Experiment

    NASA Astrophysics Data System (ADS)

    Schambach, Joachim; Anderssen, Eric; Contin, Giacomo; Greiner, Leo; Silber, Joe; Stezelberger, Thorsten; Sun, Xiangming; Szelezniak, Michal; Videbaek, Flemming; Vu, Chinh; Wieman, Howard; Woodmansee, Sam

    For the 2014 heavy ion run of RHIC a new micro-vertex detector called the Heavy Flavor Tracker (HFT) was installed in the STAR experiment. The HFT consists of three detector subsystems with various silicon technologies arranged in 4 approximately concentric cylinders close to the STAR interaction point designed to improve the STAR detector's vertex resolution and extend its measurement capabilities in the heavy flavor domain. The two innermost HFT layers are placed at radii of 2.8 cm and 8 cm from the beam line. These layers are constructed with 400 high resolution sensors based on CMOS Monolithic Active Pixel Sensor (MAPS) technology arranged in 10-sensor ladders mounted on 10 thin carbon fiber sectors to cover a total silicon area of 0.16 m2. Each sensor of this PiXeL ("PXL") sub-detector combines a pixel array of 928 rows and 960 columns with a 20.7 μm pixel pitch together with front-end electronics and zero-suppression circuitry in one silicon die providing a sensitive area of ˜3.8 cm2. This sensor architecture features 185.6 μs readout time and 170 mW/cm2 power dissipation. This low power dissipation allows the PXL detector to be air-cooled, and with the sensors thinned down to 50 μm results in a global material budget of only 0.4% radiation length per layer. A novel mechanical approach to detector insertion allows us to effectively install and integrate the PXL sub-detector within a 12 hour period during an on-going multi-month data taking period. The detector requirements, architecture and design, as well as the performance after installation, are presented in this paper.

  5. Metal frame as local protection of superconducting films from thermomagnetic avalanches

    NASA Astrophysics Data System (ADS)

    Mikheenko, P.; Vestgârden, J. I.; Chaudhuri, S.; Maasilta, I. J.; Galperin, Y. M.; Johansen, T. H.

    2016-03-01

    Thermomagnetic avalanches in superconducting films propagating extremely fast while forming unpredictable patterns, represent a serious threat for the performance of devices based on such materials. It is shown here that a normal-metal frame surrounding a selected region inside the film area can provide efficient protection from the avalanches during their propagation stage. Protective behavior is confirmed by magneto-optical imaging experiments on NbN films equipped with Cu and Al frames, and also by performing numerical simulations. Experimentally, it is found that while conventional flux creep is not affected by the frames, the dendritic avalanches are partially or fully screened by them. The level of screening depends on the ratio of the sheet conductance of the metal and the superconductor in the resistive state, and for ratios much larger than unity the screening is very efficient.

  6. Fast-gated single-photon avalanche diode for extremely wide dynamic-range applications

    NASA Astrophysics Data System (ADS)

    Tosi, A.; Dalla Mora, A.; Zappa, F.; Cova, S.; Contini, D.; Pifferi, A.; Spinelli, L.; Torricelli, A.; Cubeddu, R.

    2009-02-01

    Near-Infrared (NIR) picosecond pulsed light shined in biological tissues (e.g. brain, breast, muscle) offers the opportunity for non-invasive quantitative spectroscopy and imaging. Tissue optical properties determine high attenuation levels of optical signals and nanosecond scale dynamics. Therefore high-performance set-ups are needed. We aimed at developing a winning photodetector-electronics pairing for a broad field of multiple-wavelengths faint-signal optical investigations, like brain functional imaging, optical mammography, in-vivo spectroscopy, drugs characterization, molecular imaging. We present an electronic instrumentation based on silicon Single-Photon Avalanche Diode (SPAD) and fast-gating frontend electronics, in a Time-Correlated Single-Photon Counting (TCSPC) set-up. Detection efficiency is very high (50% at 550 nm and 15% at 800 nm), allowing acquisition of very faint optical signals on a wide spectral range. Furthermore, the fast-gating circuitry enables the detector very quickly (500 ps) and for user-selectable (200 ps - 510 ns) durations, thus allowing the rejection of very intense optical signals (e.g. scattered light from more superficial layers of the tissue under investigation) preceding useful faint signals (e.g. scattered light from sub-cellular components or coming from "deep" tissue layers), which would be otherwise overwhelmed and made undetectable. We attain photon-counting dynamic ranges up to 107 with photon-timing resolutions of 95 ps.

  7. DDG4 A Simulation Framework based on the DD4hep Detector Description Toolkit

    NASA Astrophysics Data System (ADS)

    Frank, M.; Gaede, F.; Nikiforou, N.; Petric, M.; Sailer, A.

    2015-12-01

    The detector description is an essential component that has to be used to analyse and simulate data resulting from particle collisions in high energy physics experiments. Based on the DD4hep detector description toolkit a flexible and data driven simulation framework was designed using the Geant4 tool-kit. We present this framework and describe the guiding requirements and the architectural design, which was strongly driven by ease of use. The goal was, given an existing detector description, to simulate the detector response to particle collisions in high energy physics experiments with minimal effort, but not impose restrictions to support enhanced or improved behaviour. Starting from the ROOT based geometry implementation used by DD4hep an automatic conversion mechanism to Geant4 was developed. The physics response and the mechanism to input particle data from generators was highly formalized and can be instantiated on demand using known factory patterns. A palette of components to model the detector response is provided by default, but improved or more sophisticated components may easily be added using the factory pattern. Only the final configuration of the instantiated components has to be provided by end-users using either C++ or python scripting or an XML based description.

  8. Direct-conversion flat-panel imager with avalanche gain: Feasibility investigation for HARP-AMFPI

    SciTech Connect

    Wronski, M. M.; Rowlands, J. A.

    2008-12-15

    The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmable avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10{sup -7}-10{sup -2} R/frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct

  9. Direct-conversion flat-panel imager with avalanche gain: feasibility investigation for HARP-AMFPI.

    PubMed

    Wronski, M M; Rowlands, J A

    2008-12-01

    The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmable avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10(-7)-10(-2) R/frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct interaction

  10. Direct-conversion flat-panel imager with avalanche gain: Feasibility investigation for HARP-AMFPI

    PubMed Central

    Wronski, M. M.; Rowlands, J. A.

    2008-01-01

    The authors are investigating the concept of a direct-conversion flat-panel imager with avalanche gain for low-dose x-ray imaging. It consists of an amorphous selenium (a-Se) photoconductor partitioned into a thick drift region for x-ray-to-charge conversion and a relatively thin region called high-gain avalanche rushing photoconductor (HARP) in which the charge undergoes avalanche multiplication. An active matrix of thin film transistors is used to read out the electronic image. The authors call the proposed imager HARP active matrix flat panel imager (HARP-AMFPI). The key advantages of HARP-AMFPI are its high spatial resolution, owing to the direct-conversion a-Se layer, and its programmable avalanche gain, which can be enabled during low dose fluoroscopy to overcome electronic noise and disabled during high dose radiography to prevent saturation of the detector elements. This article investigates key design considerations for HARP-AMFPI. The effects of electronic noise on the imaging performance of HARP-AMFPI were modeled theoretically and system parameters were optimized for radiography and fluoroscopy. The following imager properties were determined as a function of avalanche gain: (1) the spatial frequency dependent detective quantum efficiency; (2) fill factor; (3) dynamic range and linearity; and (4) gain nonuniformities resulting from electric field strength nonuniformities. The authors results showed that avalanche gains of 5 and 20 enable x-ray quantum noise limited performance throughout the entire exposure range in radiography and fluoroscopy, respectively. It was shown that HARP-AMFPI can provide the required gain while maintaining a 100% effective fill factor and a piecewise dynamic range over five orders of magnitude (10−7–10−2 R∕frame). The authors have also shown that imaging performance is not significantly affected by the following: electric field strength nonuniformities, avalanche noise for x-ray energies above 1 keV and direct

  11. AQUARIUS: the next generation mid-IR detector for ground-based astronomy, an update.

    NASA Astrophysics Data System (ADS)

    Ives, Derek; Finger, Gert; Jakob, Gerd; Beckmann, Udo

    2014-07-01

    ESO has already published data from a preliminary laboratory analysis on the new mid-IR detector, AQUARIUS, at the previous SPIE conference of 2012, held in Amsterdam2. This data analysis indicated that this new mid-IR Si:As IBC detector, from Raytheon Vision Systems, was an excellent astronomical detector when compared to previous generations of this detector type, specifically in terms of stability, read noise and cosmetic quality. Since that time, the detector has been deployed into the VISIR1 instrument at the VLT, with very mixed performance results, especially when used with the telescope secondary mirror, to chop between two areas of sky to do background subtraction and at the same time when many frames are co-added to improve the signal to noise performance. This is the typical mode of operation for a mid-IR instrument on a ground based telescope. Preliminary astronomical data analysis indicated that the new detector was a factor of two to three times less sensitive in terms of its signal to noise per unit time performance when directly compared to the old DRS detector that AQUARIUS was designed to replace. To determine the reason for this loss of sensitivity, the instrument was removed from the telescope and not offered to the ESO user community. A detector testing campaign was then initiated in our laboratory to determine the reasons for this loss of sensitivity, assuming that it was an issue with the new detector itself. This paper reports on our latest laboratory measurements to determine the reasons for this loss of sensitivity. We specifically report on indirect measurements made to measure the quantum efficiency of the detector, which can be difficult to measure directly. We also report on a little known source of noise, called Excess Low Frequency Noise (ELFN). Detailed analysis and testing has confirmed that this ELFN is the reason for the loss of instrument sensitivity. This has been proven by a re-commissioning phase at the telescope with the

  12. Comparative analysis of high-performance infrared avalanche InxGa1-xAsyP1-y and Hg1-xCdxTe heterophotodiodes

    NASA Astrophysics Data System (ADS)

    Kholodnov, Viacheslav; Drugova, Albina; Nikitin, Mikhail; Chekanova, Galina

    2012-10-01

    Technology of infrared (IR) avalanche photodiodes (APDs) gradually moves from simple single element APD to 2D focal plane arrays (FPA). Spectral covering of APDs is expanded continuously from classic 1.3 μm to longer wavelengths due to using of narrow-gap semiconductor materials like Hg1-xCdxTe. APDs are of great interest to developers and manufacturers of different optical communication, measuring and 3D reconstruction thermal imaging systems. Major IR detector materials for manufacturing of high-performance APDs became heteroepitaxial structures InxGa1-xAsyP1-y and Hg1-xCdxTe. Progress in IR APD technology was achieved through serious improvement in material growing techniques enabling forming of multilayer heterostuctures with separate absorption and multiplication regions (SAM). Today SAM-APD design can be implemented both on InxGa1-xAsyP1-y and Hg1-xCdxTe multilayer heteroepitaxial structures. To create the best performance optimal design avalanche heterophotodiode (AHPD) it is necessary to carry out a detailed theoretical analysis of basic features of generation, avalanche breakdown and multiplication of charge carriers in proper heterostructure. Optimization of AHPD properties requires comprehensive estimation of AHPD's pixel performance depending on pixel's multi-layer structure design, layers doping, distribution of electric field in the structure and operating temperature. Objective of the present article is to compare some features of 1.55 μm SAM-AHPDs based on InxGa1-xAsyP1-y and Hg1-xCdxTe.

  13. Performance evaluation of new large-area avalanche photodiodes for scintillation spectroscopy

    NASA Astrophysics Data System (ADS)

    James, K. M.; Masterson, M. J.; Farrell, R.

    Avalanche photodiodes (APD's) appear promising for certain applications as a solid state replacement for the photomultiplier tube. The increase in leakage current and capacitance noise with device active area has in the past kept the size of commercially available devices to less than 1 mm (exp 2). Recent advances in fabrication technology have, however, resulted in relatively low noise devices of up to 1 inch in diameter. We have recently evaluated the performance as scintillation spectroscopy detectors of two commercial large area avalanche photodiodes. These APD's exhibit exceptional performance: at 662 KeV a 1 inch diameter device coupled to a CsI(Tl) scintillator and operating at room temperature yielded 6.9 pct. resolution and a 1 cm device coupled to CsI(Tl) and cooled to 260 K gave 4.4 pct. resolution, which is believed to be the best resolution ever recorded for a scintillation spectrometer.

  14. Large-area avalanche photodiodes for the detection of soft x rays

    SciTech Connect

    Gullikson, E.M.; Gramsch, E. |; Szawlowski, M.

    1995-08-01

    The charge-collection efficiency of beveled-edge-type silicon avalanche photodiodes has been determined for soft x rays in the 50--300-eV range. An efficiency of greater than 80% is measured for energies below the Si {ital L} absorption edge. The measured efficiency is well described by a model that accounts for absorption in an oxide overlayer and recombination at the front surface of the diode. The avalanche photodiodes are shown to be significantly more sensitive compared with other detectors for pulsed sources such as a laser-produced plasma source. These results are also very encouraging for soft-x-ray/extreme-UV applications involving synchrotron radiation.{ital PACS} {ital numbers}: 29.40.Wk, 07.85.+n, 85.60.Dw.

  15. Software-Based Real-Time Acquisition and Processing of PET Detector Raw Data.

    PubMed

    Goldschmidt, Benjamin; Schug, David; Lerche, Christoph W; Salomon, André; Gebhardt, Pierre; Weissler, Bjoern; Wehner, Jakob; Dueppenbecker, Peter M; Kiessling, Fabian; Schulz, Volkmar

    2016-02-01

    In modern positron emission tomography (PET) readout architectures, the position and energy estimation of scintillation events (singles) and the detection of coincident events (coincidences) are typically carried out on highly integrated, programmable printed circuit boards. The implementation of advanced singles and coincidence processing (SCP) algorithms for these architectures is often limited by the strict constraints of hardware-based data processing. In this paper, we present a software-based data acquisition and processing architecture (DAPA) that offers a high degree of flexibility for advanced SCP algorithms through relaxed real-time constraints and an easily extendible data processing framework. The DAPA is designed to acquire detector raw data from independent (but synchronized) detector modules and process the data for singles and coincidences in real-time using a center-of-gravity (COG)-based, a least-squares (LS)-based, or a maximum-likelihood (ML)-based crystal position and energy estimation approach (CPEEA). To test the DAPA, we adapted it to a preclinical PET detector that outputs detector raw data from 60 independent digital silicon photomultiplier (dSiPM)-based detector stacks and evaluated it with a [(18)F]-fluorodeoxyglucose-filled hot-rod phantom. The DAPA is highly reliable with less than 0.1% of all detector raw data lost or corrupted. For high validation thresholds (37.1 ± 12.8 photons per pixel) of the dSiPM detector tiles, the DAPA is real time capable up to 55 MBq for the COG-based CPEEA, up to 31 MBq for the LS-based CPEEA, and up to 28 MBq for the ML-based CPEEA. Compared to the COG-based CPEEA, the rods in the image reconstruction of the hot-rod phantom are only slightly better separable and less blurred for the LS- and ML-based CPEEA. While the coincidence time resolution (∼ 500 ps) and energy resolution (∼12.3%) are comparable for all three CPEEA, the system sensitivity is up to 2.5 × higher for the LS- and ML-based CPEEA

  16. Martian Dust Devil Electron Avalanche Process and Associated Electrochemistry

    NASA Technical Reports Server (NTRS)

    Jackson, Telana L.; Farrell, William M.; Delory, Gregory T.; Nithianandam, Jeyasingh

    2010-01-01

    Mars' dynamic atmosphere displays localized dust devils and larger, global dust storms. Based on terrestrial analog studies, electrostatic modeling, and laboratory work these features will contain large electrostatic fields formed via triboelectric processes. In the low-pressure Martian atmosphere, these fields may create an electron avalanche and collisional plasma due to an increase in electron density driven by the internal electrical forces. To test the hypothesis that an electron avalanche is sustained under these conditions, a self-consistent atmospheric process model is created including electron impact ionization sources and electron losses via dust absorption, electron dissociation attachment, and electron/ion recombination. This new model is called the Dust Devil Electron Avalanche Model (DDEAM). This model solves simultaneously nine continuity equations describing the evolution of the primary gaseous chemical species involved in the electrochemistry. DDEAM monitors the evolution of the electrons and primary gas constituents, including electron/water interactions. We especially focus on electron dynamics and follow the electrons as they evolve in the E field driven collisional gas. When sources and losses are self-consistently included in the electron continuity equation, the electron density grows exponentially with increasing electric field, reaching an equilibrium that forms a sustained time-stable collisional plasma. However, the character of this plasma differs depending upon the assumed growth rate saturation process (chemical saturation versus space charge). DDEAM also shows the possibility of the loss of atmospheric methane as a function of electric field due to electron dissociative attachment of the hydrocarbon. The methane destruction rates are presented and can be included in other larger atmospheric models.

  17. Development of a detector based on Silicon Drift Detectors for gamma-ray spectroscopy and imaging applications

    NASA Astrophysics Data System (ADS)

    Busca, P.; Butt, A. D.; Fiorini, C.; Marone, A.; Occhipinti, M.; Peloso, R.; Quaglia, R.; Bombelli, L.; Giacomini, G.; Piemonte, C.; Camera, F.; Giaz, A.; Million, B.; Nelms, N.; Shortt, B.

    2014-05-01

    This work deals with the development of a new gamma detector based on Silicon Drift Detectors (SDDs) to readout large LaBr3:Ce scintillators for gamma-ray spectroscopy and imaging applications. The research is supported by the European Space Agency through the Technology Research Programme (TRP) and by Istituto Nazionale di Fisica Nucleare (INFN) within the Gamma project. The SDDs, produced at Fondazione Bruno Kessler (FBK) semiconductor laboratories, are designed as monolithic arrays of 3 × 3 units, each one of an active area of 8 mm × 8 mm (overall area of 26 mm × 26 mm). The readout electronics and the architecture of the camera are briefly described and then first experimental results coupling the SDD array with a 1'' × 1'' LaBr3:Ce scintillator are reported. An energy resolution of 3% FWHM at 662 keV has been measured at -20°C, better than coupling the same scintillator with a photomultiplier tube. The same scintillator is also used to evaluate position sensitivity with a 1 mm collimated Cs-137 source. The main difficulty in determining the position of the gamma-ray interaction in the crystal is associated to the high thickness/diameter ratio of the crystal (1:1) and the use of reflectors on all lateral and top sides the crystal. This last choice enhances energy resolution but makes imaging capability more challenging because light is spread over all photodetectors. Preliminary results show that the camera is able to detect shifts in the measured signals, when the source is moved with steps of 5 mm. A modified version of the centroid method is finally implemented to evaluate the imaging capability of the system.

  18. Driving Rate Dependence of Avalanche Statistics and Shapes at the Yielding Transition.

    PubMed

    Liu, Chen; Ferrero, Ezequiel E; Puosi, Francesco; Barrat, Jean-Louis; Martens, Kirsten

    2016-02-12

    We study stress time series caused by plastic avalanches in athermally sheared disordered materials. Using particle-based simulations and a mesoscopic elastoplastic model, we analyze system size and shear-rate dependence of the stress-drop duration and size distributions together with their average temporal shape. We find critical exponents different from mean-field predictions, and a clear asymmetry for individual avalanches. We probe scaling relations for the rate dependency of the dynamics and we report a crossover towards mean-field results for strong driving. PMID:26918998

  19. Development of Fuses for Protection of Geiger-Mode Avalanche Photodiode Arrays

    NASA Astrophysics Data System (ADS)

    Grzesik, Michael; Bailey, Robert; Mahan, Joe; Ampe, Jim

    2015-11-01

    Current-limiting fuses composed of Ti/Al/Ni were developed for use in Geiger-mode avalanche photodiode arrays for each individual pixel in the array. The fuses were designed to burn out at ˜4.5 × 10-3 A and maintain post-burnout leakage currents less than 10-7 A at 70 V sustained for several minutes. Experimental fuse data are presented and successful incorporation of the fuses into a 256 × 64 pixel InP-based Geiger-mode avalanche photodiode array is reported.

  20. Cheaper by the dozen: The avalanche of rideshares in the 21st century

    NASA Astrophysics Data System (ADS)

    Swartwout, M.

    In the previous two conferences, we presented a statistics-based history of rideshares, first with the 300 rideshares launched from 1990-2010, then with the 600 rideshares launched in the first 54 years of spaceflight. We showed that there have been several waves of rideshares, each with their own particular characteristics: the avalanche of US military rideshares of the 60s (acting as calibration targets, environmental sensors and performing other space-qualification tasks); the slow-build of commercial rideshares starting with the Ariane ASAP in the early 80s, and now a bifurcation into 100-kg ESPA-class spacecraft and a second, larger avalanche of CubeSats.