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1

A Liquid-Cryogen-Free Cryostat for Ultrahigh Resolution Gamma-Ray Spectrometers  

SciTech Connect

We are developing ultra-high energy resolution gamma-ray detectors based on superconducting transition edge sensors (TESs) for nuclear non-proliferation and fundamental science applications. They use bulk tin absorbers attached to molybdenum-copper multilayer TESs, and have achieved an energy resolution between 50 and 90 eV FWHM for gamma-ray energies below 122 keV. For increased user-friendliness, we have built a cryostat that attains the required detector operating temperature of 0.1 K at the push of a button without the use of cryogenic liquids. It uses a two-stage mechanical pulse tube refrigerator for precooling to {approx}3 K, and a two-stage adiabatic demagnetization refrigerator for cooling to the base temperature. The cryostat is fully automated, attains a base temperature below 30 mK without the use of cryogenic liquids, and has a hold time of {approx}2 days at 0.1 K between 1-hour demagnetization cycles. Here we discuss the performance of the cryostat for operation in a Gamma-spectrometer with 112-pixel arrays of superconducting TES detectors.

Dreyer, J G; Hertrich, T; Drury, O B; Hohne, J; Friedrich, S

2008-06-30

2

Ultra-high energy gamma rays  

NASA Technical Reports Server (NTRS)

The production of ultrahigh energy gamma rays by proton interactions with relicit radiation, propagation of gamma rays through the universe, and proton cascading in the presence and absence of galactic magnetic fields is discussed. Detailed data are given on proton spectrum link, gamma ray intensity, and energy spectra of gamma rays on production.

Strong, A. W.; Wdowczyk, J.; Wolfendale, A. W.

1973-01-01

3

A high resolution scintillating fiber gamma-ray telescope  

Microsoft Academic Search

Scintillating fibers coupled to position sensitive photomultipliers have good angular precision and good energy resolution in detecting gamma-rays. Scintillating fibers stacked up into scintillating fiber planes U, V and W that are rotated by 60° angle relative to each other and coupled to position sensitive photomultipliers can be used as high resolution imaging gamma-ray detectors. With this arrangement the Compton

M. Atac; D. B. Cline; E. J. Fenyves; R. C. Chaney; H. Hammack

1989-01-01

4

Detecting Gamma-Ray Bursts with Ultra-High Energy Neutrinos  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are candidate sources of ultra-high energy cosmic rays and neutrinos. While cosmic rays are scattered in the intervening magnetic field, neutrinos point back to their sources being charge neutral and make neutrino astronomy possible. Detection of ultrahigh energy neutrinos by future experiments such as ANITA, ANTARES, Ice-Cube and RICE can provide useful information such as particle acceleration, radiation mechanism and magnetic field about the sources and their progenitors. Detection of ultrahigh energy neutrinos which point back to their sources may establish gamma-ray bursts as the sources of GZK cosmic rays.

Razzaque, Soebur; Mészáros, Peter; Waxman, Eli

5

The Transient Gamma-Ray Spectrometer: A New High Resolution Detector for Gamma-Ray Burst Spectroscopy  

Microsoft Academic Search

The Transient Gamma-Ray Spectrometer (TGRS) to be flown aboard the WIND spacecraft is primarily designed to perform high resolution spectroscopy of transient gamma-ray events, such as cosmic [gamma]-ray bursts and solar flares, over the energy range 20 keV to 10 MeV with an expected spectroscopic resolution of E\\/[delta]E = 500. The detector itself consists of a 215 cm[sup 3] high

H. Seifert; R. Baker; T. L. Cline; N. Gehrels; J. Jermakian; T. Nolan; R. Ramaty; D. A. Sheppard; G. Smith; D. E. Stilwell; B. J. Teegarden; J. Trombka; A. Owens; C. P. Cork; D. A. Landis; P. N. Luke; N. W. Madden; D. Malone; R. H. Pehl; H. Yaver; K. Hurley; S. Mathias; A. H. Post Jr.

1992-01-01

6

High Resolution Scintillating Fiber Gamma Ray Detectors For Medical Imaging  

Microsoft Academic Search

High spatial and time resolution gamma ray detectors have been developed using plastic 'scintillating fibers coupled to position sensitive vacuum photomultipliers under development. These detectors can significantly improve the spatial resolution, time resolution, and efficiency of both SPECT and PET, extend the application of these technologies into new fields of medical research, and improve currently existing methods of medical diagnosis.

M. Atac; D. B. Cline; R. C. Chancy; E. J. Fenyves; G. Hademenos; P. P. Antich; M. D. Petroff

1990-01-01

7

PANGU: A high resolution gamma-ray space telescope  

NASA Astrophysics Data System (ADS)

We describe the instrument concept of a high angular resolution telescope dedicated to the sub-GeV (from >=10 MeV to >=1 GeV) gamma-ray photon detection. This mission, named PANGU (PAir-productioN Gamma-ray Unit), has been suggested as a candidate for the joint small mission between the European Space Agency (ESA) and the Chinese Academy of Science (CAS). A wide range of topics of both astronomy and fundamental physics can be attacked with PANGU, covering Galactic and extragalactic cosmic-ray physics, extreme physics of a variety of extended (e.g. supernova remnants, galaxies, galaxy clusters) and compact (e.g. black holes, pulsars, gamma-ray bursts) objects, solar and terrestrial gamma-ray phenomena, and searching for dark matter decay and/or annihilation signature etc. The unprecedented point spread function can be achieved with a pair-production telescope with a large number of thin active tracking layers to precisely reconstruct the pair-produced electron and positron tracks. Scintillating fibers or thin silicon micro-strip detectors are suitable technology for such a tracker. The energy measurement is achieved by measuring the momentum of the electrons and positrons through a magnetic field. The innovated spectrometer approach provides superior photon pointing resolution, and is particular suitable in the sub-GeV range. The level of tracking precision makes it possible to measure the polarization of gamma rays, which would open up a new frontier in gamma-ray astronomy. The frequent full-sky survey at sub-GeV with PANGU's large field of view and significantly improved point spread function would provide crucial information to GeV-TeV astrophysics for current/future missions including Fermi, DAMPE, HERD, and CTA, and other multi-wavelength telescopes.

Wu, Xin; Su, Meng; Bravar, Alessandro; Chang, Jin; Fan, Yizhong; Pohl, Martin; Walter, Roland

2014-07-01

8

Ultra-high brilliance multi-MeV $\\gamma$-ray beam from non-linear Thomson scattering  

E-print Network

We report on the generation of a narrow divergence ($\\theta\\approx 2.5$ mrad), multi-MeV ($E_\\text{MAX} = 18$ MeV) and ultra-high brilliance ($\\approx 2\\times10^{19}$ photons s$^{-1}$ mm$^{-2}$ mrad $^{-2}$ 0.1\\% BW) $\\gamma$-ray beam from the scattering of an ultra-relativistic laser-wakefield accelerated electron beam in the field of a relativistically intense laser (dimensionless amplitude $a_0\\approx2$). The spectrum of the generated $\\gamma$-ray beam is measured, with MeV resolution, seamlessly from 6 MeV to 18 MeV, giving clear evidence of the onset of non-linear Thomson scattering. The photon source has the highest brilliance in the multi-MeV regime ever reported in the literature.

Sarri, G; Schumaker, W; Cole, J; Di Piazza, A; Ahmed, H; Harvey, C; Keitel, C H; Krushelnick, K; Mangles, S P D; Najmudin, Z; Symes, D; Thomas, A G R; Yeung, M; Zhao, Z; Zepf, M

2014-01-01

9

Development of a high resolution scintillating fiber gamma ray telescope  

Microsoft Academic Search

The authors report on further development and testing of a Compton telescope composed of scintillating fibers and position-sensitive photomultipliers. Initial tests of the telescope showed a better than 1-mm (RMS) position resolution and a 17.5-mrad (RMS) angular resolution for 1.2-MeV photons from a collimated 60Co gamma source. This type of device can be used for constructing large-area telescopes for gamma-ray

M. Atac; R. Chaney; D. Chrisman; E. Fenyves; P. Antich

1991-01-01

10

Development of a high resolution scintillating fiber gamma ray telescope  

Microsoft Academic Search

We report on the initia development and testing of a Compton telescope that is composed of scintillating fibers and position sensitive photomultiphers. Initial tests of the telescope result in a 17.5 mrad (rms) angular resolution for 1.2 MeV photons from a collimated 60Co gamma source. This type of device can be used for constructing large area telescopes for gamma ray

P. Antich; M. Atac; R. Chaney; D. Chrisman; D. Cline; E. Fenyves

1990-01-01

11

A high resolution scintillating fiber gamma-ray-telescope  

Microsoft Academic Search

The design of a large-area gamma-ray detector with high angular and energy resolution for space-based experiments, using scintillating fibers and recently developed position-sensitive photomultiplier tubes, is presented. The structural and functional characteristics of the telescope instruments, a Compton-pair production converter, gas drift time projection chamber (TPC), and calorimeter, are given. It is concluded that with this design the Compton electron

M. Atac; D. B. Cline; E. J. Fenyves; R. C. Chaney

1989-01-01

12

WINKLER - An imaging high resolution gamma-ray spectrometer  

NASA Astrophysics Data System (ADS)

The WINKLER high-resolution gamma-ray spectrometer was originally developed to fly on a high-altitude aircraft. Following the discovery of Supernova 1987A in the Large Magellanic Cloud, arrangements were made to perform balloon-borne observations of this event. The instrument was quickly adapted to fit on a gondola furnished by NASA/MSFC in a collaborative effort and was flown in a series of three successful flights from Alice Springs, Australia. The second flight on October 29-31, 1987 resulted in the first high-resolution detection of the 847-keV line emission from the decay of 56Co and provided definitive confirmation of the explosive nucleosynthesis process. WINKLER comprises an array of nine coaxial n-type germanium detectors which are housed in a common vaccuum cryostat and surrounded by an NaI(Tl) scintillator shield that suppresses Compton interactions and gamma-ray background. Gamma-ray images are obtained with a rotational modulation collimator system attached to the spectrometer. Collimator holes in the upper section of the shield define the angular field of view of the instrument to 22 deg FWHM. The energy range of the spectrometer is 20 eV to 8 MeV, and the composite energy resolution from all detectors is 1.5 keV at 100 keV and about 2.5 keV at 1.33 MeV. The total frontal area of the sensor array is 214 cm2 with a volume of 1177 cm3, providing sufficient detection sensitivity for gamma-ray astronomy as well as for land-based applications such as treaty verification monitoring.

Nakano, G. H.; Sandie, W. G.; Kilner, J. R.; Pang, F.; Imai, B. B.

1991-04-01

13

Are gamma-ray bursts the sources of ultra-high energy cosmic rays?  

E-print Network

We reconsider the possibility that gamma-ray bursts (GRBs) are the sources of the ultra-high energy cosmic rays (UHECRs) within the internal shock model, assuming a pure proton composition of the UHECRs. For the first time, we combine the information from gamma-rays, cosmic rays, prompt neutrinos, and cosmogenic neutrinos quantitatively in a joint cosmic ray production and propagation model, and we show that the information on the cosmic energy budget can be obtained as a consequence. In addition to the neutron model, we consider alternative scenarios for the cosmic ray escape from the GRBs, i.e., that cosmic rays can leak from the sources. We find that the dip model, which describes the ankle in UHECR observations by the pair production dip, is strongly disfavored in combination with the internal shock model because a) unrealistically high baryonic loadings (energy in protons versus energy in electrons/gamma-rays) are needed for the individual GRBs and b) the prompt neutrino flux easily overshoots the corresponding neutrino bound. On the other hand, GRBs may account for the UHECRs in the ankle transition model if cosmic rays leak out from the source at the highest energies. In that case, we demonstrate that future neutrino observations can efficiently test most of the parameter space -- unless the baryonic loading is much larger than previously anticipated.

Philipp Baerwald; Mauricio Bustamante; Walter Winter

2014-07-07

14

Generation of ultrahigh-energy gamma rays in accreting x ray pulsars  

NASA Technical Reports Server (NTRS)

Relativistic protons producing ultrahigh energy gamma rays as a result of nuclear collisions ought to be generated in close proximity to the surface of a neutron star due to accretion. The main features of the mechanism in question are a high efficiency of conversion of the gravitational energy of the accreting matter into acceleration energy and a high efficiency of the acceleration itself. It is shown that in accretion to a neutron star with a strong magnetic field, a loss cone type distribution of accreting protons is formed, which due to instability effectively generates small scale Alfven and proton cyclotron waves, as well as nonlinear waves (magneto-acoustic and Alfven solitons). The electric field of the moving solitons may accelerate the protons to energies of greater than 10(exp 15) eV. The region of acceleration is not locally isolated, but extends from its surface. New possible sources of ultrahigh energy gamma rays are predicted. They may be binary x ray systems containing neutron stars with magnetic fields of about 10(exp 9) gauss.

Gnedin, Yu. N.; Ikhsanov, N. R.

1991-01-01

15

The Universe Viewed in Gamma-Rays 1 High-Resolution Cherenkov Telescopes for the Observation  

E-print Network

The Universe Viewed in Gamma-Rays 1 High-Resolution Cherenkov Telescopes for the Observation optics and camera used for recent Cherenkov telescopes is usually limited to be only about 0.1 degree with very fine pixels to detect the images of the Cherenkov photons generated by high energy gamma rays

Enomoto, Ryoji

16

A search for correlations of TeV gamma-rays with ultra-high energy cosmic rays  

E-print Network

A search was conducted for TeV gamma-rays emitted from the direction of the ultra-high energy cosmic ray detected by the Fly's Eye Experiment with E ~ 3 x 10**20 eV. No enhancement was found at a level of 10**-10 gamma/cm**2-sec for E>350 GeV. This upper limit is consistent with theoretical estimates based on topological defects as sources of UHE cosmic rays. An upper limit was also set for the flux of TeV gamma rays from 3C147, the most prominent AGN in the error box.

C. W. Akerlof; S. Biller; P. Boyle; J. Buckley; D. A. Carter-Lewis; M. Catanese; M. F. Cawley; V. Connaughton; D. J. Fegan; J. Finley; J. Gaidos; A. M. Hillas; F. Krennrich; R. C. Lamb; R. Lessard; J. McEnery; G. Mohanty; N. A. Porter; J. Quinn; A. Rodgers; H. J. Rose; F. Samuelson; M. S. Schubnell; G. Sembroski; R. Srinivasan; T. C. Weekes; J. Zweerink; .

1997-06-12

17

High resolution gamma-ray spectroscopy at GANIL  

NASA Astrophysics Data System (ADS)

Gamma-ray spectroscopy is intensively used at GANIL to measure low lying states in exotic nuclei on the neutron-rich as well as on the neutron-deficient side of the nuclear chart. On the neutron deficient border, gamma-rays have been observed for the first time in 92Pd . The level scheme which could be established points to the role of isoscalar pairing. On the neutron rich side, the lifetime of excited states in nuclei around 68Ni have been been measured using the plunger technique. This allows us to study the evolution of collectivity in a broad range of nuclei. In 2014 GANIL will host the AGATA array for a campaign of at least 2 years. This array is based on the gamma-ray tracking technique, which allows an impressive gain in resolving power.

de France, G.

2014-11-01

18

Gamma-Ray Spectroscopy with Microsecond Time Resolution Using Global Fit Analysis  

Microsoft Academic Search

Even modern large area detectors for gamma-ray spectroscopy often do not provide sensitivity, sufficient for high time resolution spectroscopy of variable and transient astrophysical phenomena-especially those involving beaming, instabilities and relativistic motion. We propose a general method for analysis of time resolved gamma-ray spectra of astrophysical transients-the Global Fit Analysis (GFA), which allows one to increase time resolution by an

A. Chernenko

2008-01-01

19

Ultra-high resolution computed tomography imaging  

DOEpatents

A method for ultra-high resolution computed tomography imaging, comprising the steps of: focusing a high energy particle beam, for example x-rays or gamma-rays, onto a target object; acquiring a 2-dimensional projection data set representative of the target object; generating a corrected projection data set by applying a deconvolution algorithm, having an experimentally determined a transfer function, to the 2-dimensional data set; storing the corrected projection data set; incrementally rotating the target object through an angle of approximately 180.degree., and after each the incremental rotation, repeating the radiating, acquiring, generating and storing steps; and, after the rotating step, applying a cone-beam algorithm, for example a modified tomographic reconstruction algorithm, to the corrected projection data sets to generate a 3-dimensional image. The size of the spot focus of the beam is reduced to not greater than approximately 1 micron, and even to not greater than approximately 0.5 microns.

Paulus, Michael J. (Knoxville, TN); Sari-Sarraf, Hamed (Knoxville, TN); Tobin, Jr., Kenneth William (Harriman, TN); Gleason, Shaun S. (Knoxville, TN); Thomas, Jr., Clarence E. (Knoxville, TN)

2002-01-01

20

Development of a high-resolution liquid xenon detector for gamma-ray astrophysics  

Microsoft Academic Search

It has been shown here that liquid xenon is one of the most promising detector media for future gamma-ray detectors, owing to an excellent combination of physical properties. The feasibility of the construction of a high resolution liquid xenon detector as a gamma-ray detector for astrophysics has been demonstrated. Up to 3.5 liters of liquid xenon has been successfully purified

Reshmi Mukherjee

1993-01-01

21

Search for very high energy gamma rays from possible ultra-high energy cosmic ray sources by the MAGIC Telescope  

E-print Network

The origin of ultra-high energy (UHE) cosmic rays is still an open question. In the present work, we searched the possible UHE cosmic ray sources using the MAGIC telescope for the associated very high energy (VHE) gamma ray emission. Due to constrained propagation distance of such cosmic rays, we selected nearby galaxies in vicinity of the direction of the AGASA triplet and a HiRes UHE cosmic ray event: NGC 3610 and NGC 3613 (quasar remnants); Arp 299 (a system of colliding galaxies). No significant excess in the VHE region was found found from these objects or their surrounding region. At multi-100 GeV regime, the upper limits on fluxes were given against gamma ray sources in surrounding region. The presented limits constrain the flux of a new hypothetical source in the region, provided the cosmic rays are emitted from a single point-like origin.

K. Shinozaki; M. Teshima; for the MAGIC Collaboration

2007-09-17

22

Development of a high resolution liquid xenon imaging chamber for gamma-ray astronomy  

NASA Technical Reports Server (NTRS)

The objective was to develop the technology of liquid xenon (LXe) detectors for spectroscopy and imaging of gamma rays from astrophysical sources emitting in the low to medium energy regime. In particular, the technical challenges and the physical processes relevant to the realization of the LXe detector operated as a Time Projection Chamber (TPC) were addressed and studied. Experimental results were obtained on the following topics: (1) long distance drift of free electrons in LXe (purity); (2) scintillation light yield for electrons and alphas in LXe (triggering); and (3) ionization yield for electrons and gamma rays in LXe (energy resolution). The major results from the investigations are summarized.

Aprile, Elena

1991-01-01

23

Ultrahigh resolution AMOLED  

Microsoft Academic Search

AMOLED microdisplays continue to show improvement in resolution and optical performance, enhancing their appeal for a broad range of near-eye applications such as night vision, simulation and training, situational awareness, augmented reality, medical imaging, and mobile video entertainment and gaming. eMagin's latest development of an HDTV+ resolution technology integrates an OLED pixel of 3.2 × 9.6 microns in size on

Ihor Wacyk; Olivier Prache; Amal Ghosh

2011-01-01

24

Gamma-ray generation in ultrahigh-intensity laser-foil interactions  

NASA Astrophysics Data System (ADS)

Incoherent photon emission by ultrarelativistic electrons in the normal incidence of a laser pulse on a foil is investigated by means of three-dimensional numerical simulations in the range of intensities 2 × 1021-2 × 1025 W cm-2 and electron densities 2 × 1022-1 × 1024 cm-3. We focus on properties of the resulting synchrotron radiation, such as its overall energy, directivity of the radiation pattern, and slope of the energy spectrum. Regimes of laser-foil interactions are studied in the framework of a simple analytical model. The laser-plasma parameters for efficient gamma-ray generation are found and revealed to be close to the parameters for relativistic foil motion. It is shown that in the case of oblique incidence of a 3 PW, 10 fs laser pulse on a thin foil about 108 photons/0.1% bandwidth are produced at the energy level of 1 MeV that significantly exceeds performance of the modern Compton gamma-ray sources. Various applications of the gamma-ray bunches are discussed.

Nerush, E. N.; Kostyukov, I. Yu.; Ji, L.; Pukhov, A.

2014-01-01

25

Low-resolution gamma-ray measurements of uranium enrichment.  

PubMed

We have developed smaller, lighter hardware (MCA and shielded detectors) that has been successfully transferred to the commercial sector. We have developed software that has received limited testing, the next release should be sufficiently robust for wide release to the general public. We have had initial success with more sophisticated analysis methods. We are pursuing medium-resolution tors and response function fitting in the expectation that both will cause significant improvements in this measurement technique. PMID:9463875

Sprinkle, J K; Christiansen, A; Cole, R; Collins, M L; Hsue, S T; Knepper, P L; McKown, T O; Siebelist, R

1997-01-01

26

Development of a high-resolution liquid xenon detector for gamma-ray astrophysics  

NASA Astrophysics Data System (ADS)

It has been shown here that liquid xenon is one of the most promising detector media for future gamma-ray detectors, owing to an excellent combination of physical properties. The feasibility of the construction of a high resolution liquid xenon detector as a gamma-ray detector for astrophysics has been demonstrated. Up to 3.5 liters of liquid xenon has been successfully purified and using both small and large volume prototypes, the charge and the energy resolution response of such detectors to gamma-rays, internal conversion electrons and alpha particles have been measured. The best energy resolution measured was 4.5 percent FWHM at 1 MeV. Cosmic ray tracks have been imaged using a 2-dimensional liquid xenon multiwire imaging chamber. The spatial resolution along the direction of the drifting electrons was 180 microns rms. Experiments have been performed to study the scintillation light in liquid xenon, as the prompt scintillation signal in the liquid is an electron-ion pair in liquid krypton was measured for the first time with a pulsed ionization chamber to be 18.4 plus or minus 0.3 eV.

Mukherjee, Reshmi

27

Compact high-resolution gamma-ray computed tomography system for multiphase flow studies  

SciTech Connect

In this paper, a compact high-resolution gamma-ray Computed Tomography (CompaCT) measurement system for multiphase flow studies and tomographic imaging of technical objects is presented. Its compact and robust design makes it particularly suitable for studies on industrial facilities and outdoor applications. Special care has been given to thermal ruggedness, shock resistance, and radiation protection. Main components of the system are a collimated {sup 137}Cs isotopic source, a thermally stabilised modular high-resolution gamma-ray detector arc with 112 scintillation detector elements, and a transportable rotary unit. The CompaCT allows full CT scans of objects with a diameter of up to 130 mm and can be operated with any tilting angle from 0 Degree-Sign (horizontal) to 90 Degree-Sign (vertical).

Bieberle, A.; Nehring, H.; Berger, R.; Arlit, M.; Haerting, H.-U.; Schubert, M. [Helmholtz-Zentrum Dresden-Rossendorf, Institute of Fluid Dynamics, Bautzner Landstrasse 400, 01328 Dresden (Germany); Hampel, U. [Helmholtz-Zentrum Dresden-Rossendorf, Institute of Fluid Dynamics, Bautzner Landstrasse 400, 01328 Dresden (Germany); Technische Universitaet Dresden, AREVA Endowed Chair of Imaging Techniques in Energy and Process Engineering, 01062 Dresden (Germany)

2013-03-15

28

Multi-stage shifter for subsecond time resolution of emulsion gamma-ray telescopes  

NASA Astrophysics Data System (ADS)

To observe gamma-ray sources precisely, a balloon-borne experiment with a new type of detector, the emulsion gamma-ray telescope, is planned. A multi-stage shifter mechanism based on the concept of an analog clock serves as a time stamper with subsecond time resolution and uses multiple moving stages mounted on the emulsion chambers. This new technique was employed in a test experiment using a small-scale model in a short-duration balloon flight. Tracks recorded in nuclear emulsion were read by a fully automated scanning system, were reconstructed, and time information were assigned by analysis of their position displacements in the shifter layers. The estimated time resolution was 0.06-0.15 s. The number of tracks passing through the detector was counted every second, and hadron jets were detected as significant excesses observed in the counting rate. In future, the multi-stage shifter is greatly contributing to ongoing efforts to increase the effective area of emulsion gamma-ray telescopes.

Rokujo, H.; Aoki, S.; Takahashi, S.; Kamada, K.; Mizutani, S.; Nakagawa, R.; Ozaki, K.

2013-02-01

29

SONGS - A high resolution imaging gamma-ray spectrometer for the Space Station  

NASA Technical Reports Server (NTRS)

The overall design and the instrumental features of the Space-Station Observer for Nuclear Gamma-ray Spectroscopy (SONGS) instrument are described. SONGS comprises an array of 19 two-segment n-type Ge detectors, which have the capability of determining the interaction site in either the upper or the lower segment or in both segments. The detectors provide high energy resolution of 1 keV at 100 keV and of 2 keV at 1 MeV. The close-packed Ge sensor array provides a natural sensitivity for the measurement of gamma ray polarization in the 100 keV to 1 MeV energy range, making it possible to obtain information on the structure of the magnetosphere of neutron stars and of the accretion disk of black holes.

Nakano, G. H.; Chase, L. F.; Kilner, J. R.; Sandie, W. G.; Fishman, G. J.; Paciesas, W. S.

1989-01-01

30

On the categorization of uranium materials using low resolution gamma ray spectrometry.  

PubMed

In order to characterize uranium materials during e.g. nuclear safeguards inspections and in initial stages of nuclear forensic investigations, hand-held low resolution gamma ray detection instruments with automatic uranium categorization capabilities may be used. In this paper, simulated response curves for a number of matrices applied on NaI(Tl) scintillation detector spectra show that the result of the categorization is strongly dependent on the physical properties of the uranium material. Recommendations on how to minimize the possibility of misclassification are discussed. PMID:23208231

Vesterlund, A; Ulvsand, T; Lidström, K; Skarnemark, G; Ekberg, C; Ramebäck, H

2013-02-01

31

High-resolution imaging gamma-ray spectroscopy with externally segmented germanium detectors  

NASA Technical Reports Server (NTRS)

Externally segmented germanium detectors promise a breakthrough in gamma-ray imaging capabilities while retaining the superb energy resolution of germanium spectrometers. An angular resolution of 0.2 deg becomes practical by combining position-sensitive germanium detectors having a segment thickness of a few millimeters with a one-dimensional coded aperture located about a meter from the detectors. Correspondingly higher angular resolutions are possible with larger separations between the detectors and the coded aperture. Two-dimensional images can be obtained by rotating the instrument. Although the basic concept is similar to optical or X-ray coded-aperture imaging techniques, several complicating effects arise because of the penetrating nature of gamma rays. The complications include partial transmission through the coded aperture elements, Compton scattering in the germanium detectors, and high background count rates. Extensive electron-photon Monte Carlo modeling of a realistic detector/coded-aperture/collimator system has been performed. Results show that these complicating effects can be characterized and accounted for with no significant loss in instrument sensitivity.

Callas, J. L.; Mahoney, W. A.; Varnell, L. S.; Wheaton, W. A.

1993-01-01

32

Energy resolution tests of 125 mm diameter cylindrical NE213 detector using monoenergetic gamma rays  

NASA Astrophysics Data System (ADS)

Pulse height tests have been carried out for cylindrical NE213 liquid scintillation detectors of diameters 50 and 125 mm, using monoenergetic gamma rays. The 125 and 50 mm NE213 scintillator cells, each having a thickness of 50 mm, were directly coupled to 130 mm and 52 mm diameter photomultipliers respectively. Gamma-gamma coincidence technique was used to determine the detector's energy resolution and pulse height corresponding to the maximum energy of Compton electrons over the gamma rays energy range of 0.5-1.2 MeV. For the 125 mm detector, the energy corresponding to half height of Compton maxima is 14.4-6.6% higher than the maximum energy of Compton electrons while its energy resolution varies from 24.0 to 18.0%. For the 50 mm detector the energy corresponding to half height of Compton maxima is 9.8-4.0% higher than the maximum energy of Compton electrons while its energy resolution varies from 18.8 to 12.2%. For the 125 mm diameter detector results are presented for the first time.

Naqvi, A. A.; Al-Juwair, H.; Gul, K.

1991-08-01

33

Gamma ray spectroscopy at high energy and high time resolution at JET.  

PubMed

In fusion plasmas gamma ray emission is caused by reactions of fast particles, such as fusion alpha particles, with impurities. Gamma ray spectroscopy at JET has provided valuable diagnostic information on fast fuel as well as fusion product ions. Improvements of these measurements are needed to fully exploit the flux increase provided by future high power experiments at JET and ITER. Limiting aspects are, for instance, the count rate capability due to a high neutron/gamma background combined with slow detector response and a modest energy resolution due to the low light yield of the scintillators. This paper describes the solutions developed for achieving higher energy resolution, signal to background, and time resolution. The detector design is described based on the new BrLa3 scintillator crystal. The paper will focus on hardware development, including a photomultiplier tube capable of stable operation at counting rate as high as 1 MHz, the magnetic shielding, and the fast digital data acquisition system. PMID:19068513

Tardocchi, M; Proverbio, L I; Gorini, G; Grosso, G; Locatelli, M; Chugonov, I N; Gin, D B; Shevelev, A E; Murari, A; Kiptily, V G; Syme, B; Fernandes, A M; Pereira, R C; Sousa, J

2008-10-01

34

Limits on the transient ultra-high energy neutrino flux from gamma-ray bursts (GRB) derived from RICE data  

NASA Astrophysics Data System (ADS)

We present limits on ultra-high energy (UHE; E? > 1015 eV) neutrino fluxes from gamma-ray bursts (GRBs), based on recently presented data, limits, and simulations from the RICE experiment. We use data from five recorded transients with sufficient photon spectral shape and redshift information to derive an expected neutrino flux, assuming that the observed photons are linked to neutrino production through pion decay via the well-known “Waxman Bahcall” prescription. Knowing the declination of the observed burst, as well as the RICE sensitivity as a function of polar angle and the previously published non-observation of any neutrino events allows an estimate of the sensitivity to a given neutrino flux. Although several orders of magnitude weaker than the expected fluxes, our GRB neutrino flux limits are nevertheless the first in the PeV EeV energy regime. For completeness, we also provide a listing of other bursts, recorded at times when the RICE experiment was active, but requiring some assumptions regarding luminosity and redshift to permit estimates of the neutrino flux.

Besson, D.; Razzaque, S.; Adams, J.; Harris, P.

2007-01-01

35

Topics in gamma ray astronomy  

NASA Technical Reports Server (NTRS)

Observations of gamma rays from solar flares, gamma ray bursts, the Galactic center, galactic nucleosynthesis, SS433, and Cygnus X-3, and their effects on astrophysical problems are discussed. It is observed that gamma ray spectra from solar flares are applicable to the study of particle acceleration and confinement and the determination of chemical abundances in the solar atmosphere. The gamma ray lines from the compact galactic object SS433 are utilized to examine the acceleration of jets, and analysis of the gamma ray lines of Cygnus X-3 reveal that particles can be accelerated in compact sources to ultrahigh energies.

Ramaty, R.; Lingenfelter, R. E.

1986-01-01

36

Development of a High Resolution Liquid Xenon Imaging Telescope for Medium Energy Gamma Ray Astrophysics  

NASA Technical Reports Server (NTRS)

In the third year of the research project, we have (1) tested a 3.5 liter prototype of the Liquid Xenon Time Projection Chamber, (2) used a prototype having a 4.4 cm drift gap to study the charge and energy resolution response of the 3.5 liter chamber, (3) obtained an energy resolution as good as that previously measured by us using chambers with drift gaps of the order of millimeters, (4) observed the induction signals produced by MeV gamma rays, (4) used the 20 hybrid charge sensitive preamplifiers for a nondestructive readout of the electron image on the induction wires, (5) performed extensive Monte Carlo simulations to obtain results on efficiency, background rejection capability, and source flux sensitivity, and (6) developed a reconstruction algorithm for events with multiple interaction points.

Aprile, Elena

1992-01-01

37

High resolution phoswich gamma-ray imager utilizing monolithic MPPC arrays with submillimeter pixelized crystals  

NASA Astrophysics Data System (ADS)

We report the development of a high spatial resolution tweezers-type coincidence gamma-ray camera for medical imaging. This application consists of large-area monolithic Multi-Pixel Photon Counters (MPPCs) and submillimeter pixelized scintillator matrices. The MPPC array has 4 × 4 channels with a three-side buttable, very compact package. For typical operational gain of 7.5 × 105 at + 20 °C, gain fluctuation over the entire MPPC device is only ± 5.6%, and dark count rates (as measured at the 1 p.e. level) amount to <= 400 kcps per channel. We selected Ce-doped (Lu,Y)2(SiO4)O (Ce:LYSO) and a brand-new scintillator, Ce-doped Gd3Al2Ga3O12 (Ce:GAGG) due to their high light yield and density. To improve the spatial resolution, these scintillators were fabricated into 15 × 15 matrices of 0.5 × 0.5 mm2 pixels. The Ce:LYSO and Ce:GAGG scintillator matrices were assembled into phosphor sandwich (phoswich) detectors, and then coupled to the MPPC array along with an acrylic light guide measuring 1 mm thick, and with summing operational amplifiers that compile the signals into four position-encoded analog outputs being used for signal readout. Spatial resolution of 1.1 mm was achieved with the coincidence imaging system using a 22Na point source. These results suggest that the gamma-ray imagers offer excellent potential for applications in high spatial medical imaging.

Kato, T.; Kataoka, J.; Nakamori, T.; Kishimoto, A.; Yamamoto, S.; Sato, K.; Ishikawa, Y.; Yamamura, K.; Kawabata, N.; Ikeda, H.; Kamada, K.

2013-05-01

38

CAN ULTRAHIGH-ENERGY COSMIC RAYS COME FROM GAMMA-RAY BURSTS? COSMIC RAYS BELOW THE ANKLE AND GALACTIC GAMMA-RAY BURSTS  

SciTech Connect

The maximum cosmic-ray energy achievable by acceleration by a relativistic blast wave is derived. It is shown that forward shocks from long gamma-ray bursts (GRBs) in the interstellar medium accelerate protons to large enough energies, and have a sufficient energy budget, to produce the Galactic cosmic-ray component just below the ankle at 4 x 10{sup 18} eV, as per an earlier suggestion. It is further argued that, were extragalactic long GRBs responsible for the component above the ankle as well, the occasional Galactic GRB within the solar circle would contribute more than the observational limits on the outward flux from the solar circle, unless an avoidance scenario, such as intermittency and/or beaming, allows the present-day local flux to be less than 10{sup -3} of the average. Difficulties with these avoidance scenarios are noted.

Eichler, David [Physics Department, Ben-Gurion University, Be'er-Sheva 84105 (Israel); Pohl, Martin [Institut fuer Physik und Astronomie, Universitaet Potsdam, 14476 Potsdam-Golm (Germany)

2011-09-10

39

High-Resolution Gamma-Ray Imaging Measurements Using Externally Segmented Germanium Detectors  

NASA Technical Reports Server (NTRS)

Fully two-dimensional gamma-ray imaging with simultaneous high-resolution spectroscopy has been demonstrated using an externally segmented germanium sensor. The system employs a single high-purity coaxial detector with its outer electrode segmented into 5 distinct charge collection regions and a lead coded aperture with a uniformly redundant array (URA) pattern. A series of one-dimensional responses was collected around 511 keV while the system was rotated in steps through 180 degrees. A non-negative, linear least-squares algorithm was then employed to reconstruct a 2-dimensional image. Corrections for multiple scattering in the detector, and the finite distance of source and detector are made in the reconstruction process.

Callas, J.; Mahoney, W.; Skelton, R.; Varnell, L.; Wheaton, W.

1994-01-01

40

Studies on sensitivity, resolution, and Doppler broadening in gamma-ray imaging with pixellated semiconductor detectors  

NASA Astrophysics Data System (ADS)

We studied the Doppler broadening effect which is one of the major issues pertaining to overall imaging quality in Compton cameras. For the study of Doppler broadening due to the pre-collision electron momentum, we used a collimated beam of 662-keV gamma rays and selected events corresponding to the 90° Compton scattering using a Compton spectrometer, consisting of a 25-fold segmented germanium detector and a coaxial germanium detector shielded with a bismuth germanate (BGO) scintillator. Comparison of the energy spread due to Doppler broadening between a silicon and a germanium detector was made with the Monte Carlo simulation. To see the effect of Doppler broadening on the image resolution, we performed the Monte Carlo simulation in a simple backprojection method.

Lee, J. H.; Lee, C. S.

2004-12-01

41

High resolution, high speed ultrahigh vacuum microscopy  

Microsoft Academic Search

The history and future of transmission electron microscopy (TEM) is discussed as it refers to the eventual development of instruments and techniques applicable to the real time in situ investigation of surface processes with high resolution. To reach this objective, it was necessary to transform conventional high resolution instruments so that an ultrahigh vacuum (UHV) environment at the sample site

Helmut Poppa

2004-01-01

42

The Gamma-ray Large Area Space Telescope (GLAST): a Wide Field, High Angular Resolution Observatory for High Energy Astrophysics  

NASA Astrophysics Data System (ADS)

The Gamma-ray Large Area Space Telescope (GLAST) is a proposed next-generation high-energy gamma-ray telescope for studying emission from astrophysical sources in the 10 MeV to 300 GeV energy range. It has been se;ected by NASA for a Mission Concept Study. The primary scientific targets include active galactic nuclei, gamma-ray bursts, neutron stars, and diffuse galactic and extragalactic high-energy radiation. GLAST relies on the unambigious identification of incident gamma-rays by detection of the electron and positron that result from pair creation in a thin converter material. Measurement of the energy and direction of the electron-positron shower provides information about the energy and direction of the incident gamma-ray. The GLAST design utilizes modern solid-state particle detector technology and recently developed advanced space-qualified computers. In particular, position-sensitive silicon strip detectors, interleaved between thin converters, are used to track particles. Because of this technical approach, the telescope design can be easily optimized to a range of sizes. For example, accomodation of GLAST within a Delta II size launch system results in an instrument with capabilities well beyond those of the highly successful EGRET currently operating on the Compton Observatory; namely, a broader energy range, larger effective area, wider field of view, and single-photon angular resolution 2 to 5 times more precise than EGRET's resolution. GLAST will have a maximum effective area of 8000 cm(2) above 300 MeV, a field of view of 2.6 sr, and a single photon angular resolution (rms projected) of 0.3deg at 1 GeV, approaching 0.03deg above 20 GeV.

Wood, K.; Michelson, P.; GLAST Collaboration

1995-12-01

43

High Resolution Gamma Ray Tomography and its Application to the Measurement of Phase Fractions in Chemical Reactors  

NASA Astrophysics Data System (ADS)

We applied gamma ray tomography to the problem of phase fraction measurement in chemical reactors. Therefore, we used a new tomography device that is operated with a Cs-137 source and a high resolution gamma ray detector. One application example is the reconstruction of the fluid distribution and the measurement of radial gas fraction profiles in a laboratory scale stirred vessel. The tomograph was used to obtain radiographic projections of the averaged gamma ray attenuation for different stirrer speeds along the height of the vessel. With tomographic reconstruction techniques we calculated the angularly averaged radial distribution of the attenuation coefficient for as many as 150 single cross-sectional planes and synthesised from this data set the axial and radial fluid distribution pattern. Further, we exemplarily reconstructed the radial gas fraction distributions induced by the stirrer in the area of the stirrer blades. In a second application the gamma ray measurement system was used to visualise gas inclusions in a water cleaning column that is used to remove hazardous heavy metal species from water.

Hampel, Uwe; Bieberle, Andre; Schleicher, Eckhard; Hessel, Günther; Zippe, Cornelius; Friedrich, Hans-Jürgen

2007-06-01

44

Ultrahigh resolution absolute Cartesian electronic autocollimator  

Microsoft Academic Search

The development of a compact, ultra-high resolution, electronic autocollimator with excellent readout stability, linearity, and coordinate orthogonality is presented. This optical metrology tool relies on new advances in Cartesian optical encoders based on pattern recognition technology. Readout instabilities characteristic of conventional electronic autocollimators whose lateral effect photodetectors and operational amplifiers exhibit temporal and thermal drifts, are absent in this new

Douglas B. Leviton

2003-01-01

45

Hot-Electron Tunneling sensors for high-resolution x-ray and gamma-ray spectroscopy  

SciTech Connect

Over the past 2 years, we have been studying the use of Hot Electron Tunneling sensors for use in high-energy-resolution x-ray and gamma-ray spectrometers. These sensors promise several advantages over existing cryogenic sensors, including simultaneous high count rate and high resolution capability, and relative ease of use. Using simple shadow mask lithography, we verified the basic principles of operation of these devices and discovered new physics in their thermal behavior as a function applied voltage bias. We also began to develop ways to use this new sensor in practical x-ray and gamma-ray detectors based on superconducting absorbers. This requires the use of quasiparticle trapping to concentrate the signal in the sensing elements.

Mears, C.A.; Labov, S.E.; Frank, M.; Netel, H.

1997-02-07

46

Development of a high resolution liquid xenon imaging chamber for gamma-ray astronomy  

Microsoft Academic Search

The objective was to develop the technology of liquid xenon (LXe) detectors for spectroscopy and imaging of gamma rays from astrophysical sources emitting in the low to medium energy regime. In particular, the technical challenges and the physical processes relevant to the realization of the LXe detector operated as a Time Projection Chamber (TPC) were addressed and studied. Experimental results

Elena Aprile

1991-01-01

47

Coupled multi-group neutron photon transport for the simulation of high-resolution gamma-ray spectroscopy applications  

NASA Astrophysics Data System (ADS)

The accurate and efficient simulation of coupled neutron-photon problems is necessary for several important radiation detection applications. Examples include the detection of nuclear threats concealed in cargo containers and prompt gamma neutron activation analysis for nondestructive determination of elemental composition of unknown samples. In these applications, high-resolution gamma-ray spectrometers are used to preserve as much information as possible about the emitted photon flux, which consists of both continuum and characteristic gamma rays with discrete energies. Monte Carlo transport is the most commonly used modeling tool for this type of problem, but computational times for many problems can be prohibitive. This work explores the use of coupled Monte Carlo-deterministic methods for the simulation of neutron-induced photons for high-resolution gamma-ray spectroscopy applications. RAdiation Detection Scenario Analysis Toolbox (RADSAT), a code which couples deterministic and Monte Carlo transport to perform radiation detection scenario analysis in three dimensions [1], was used as the building block for the methods derived in this work. RADSAT was capable of performing coupled deterministic-Monte Carlo simulations for gamma-only and neutron-only problems. The purpose of this work was to develop the methodology necessary to perform coupled neutron-photon calculations and add this capability to RADSAT. Performing coupled neutron-photon calculations requires four main steps: the deterministic neutron transport calculation, the neutron-induced photon spectrum calculation, the deterministic photon transport calculation, and the Monte Carlo detector response calculation. The necessary requirements for each of these steps were determined. A major challenge in utilizing multigroup deterministic transport methods for neutron-photon problems was maintaining the discrete neutron-induced photon signatures throughout the simulation. Existing coupled neutron-photon cross-section libraries and the methods used to produce neutron-induced photons were unsuitable for high-resolution gamma-ray spectroscopy applications. Central to this work was the development of a method for generating multigroup neutron-photon cross-sections in a way that separates the discrete and continuum photon emissions so the neutron-induced photon signatures were preserved. The RADSAT-NG cross-section library was developed as a specialized multigroup neutron-photon cross-section set for the simulation of high-resolution gamma-ray spectroscopy applications. The methodology and cross sections were tested using code-to-code comparison with MCNP5 [2] and NJOY [3]. A simple benchmark geometry was used for all cases compared with MCNP. The geometry consists of a cubical sample with a 252Cf neutron source on one side and a HPGe gamma-ray spectrometer on the opposing side. Different materials were examined in the cubical sample: polyethylene (C2H4), P, N, O, and Fe. The cross sections for each of the materials were compared to cross sections collapsed using NJOY. Comparisons of the volume-averaged neutron flux within the sample, volume-averaged photon flux within the detector, and high-purity gamma-ray spectrometer response (only for polyethylene) were completed using RADSAT and MCNP. The code-to-code comparisons show promising results for the coupled Monte Carlo-deterministic method. The RADSAT-NG cross-section production method showed good agreement with NJOY for all materials considered although some additional work is needed in the resonance region and in the first and last energy bin. Some cross section discrepancies existed in the lowest and highest energy bin, but the overall shape and magnitude of the two methods agreed. For the volume-averaged photon flux within the detector, typically the five most intense lines agree to within approximately 5% of the MCNP calculated flux for all of materials considered. The agreement in the code-to-code comparisons cases demonstrates a proof-of-concept of the method for use in RADSAT for coupled neutron-photon problems

Burns, Kimberly Ann

48

Ultra-high resolution AMOLED  

NASA Astrophysics Data System (ADS)

AMOLED microdisplays continue to show improvement in resolution and optical performance, enhancing their appeal for a broad range of near-eye applications such as night vision, simulation and training, situational awareness, augmented reality, medical imaging, and mobile video entertainment and gaming. eMagin's latest development of an HDTV+ resolution technology integrates an OLED pixel of 3.2 × 9.6 microns in size on a 0.18 micron CMOS backplane to deliver significant new functionality as well as the capability to implement a 1920×1200 microdisplay in a 0.86" diagonal area. In addition to the conventional matrix addressing circuitry, the HDTV+ display includes a very lowpower, low-voltage-differential-signaling (LVDS) serialized interface to minimize cable and connector size as well as electromagnetic emissions (EMI), an on-chip set of look-up-tables for digital gamma correction, and a novel pulsewidth- modulation (PWM) scheme that together with the standard analog control provides a total dimming range of 0.05cd/m2 to 2000cd/m2 in the monochrome version. The PWM function also enables an impulse drive mode of operation that significantly reduces motion artifacts in high speed scene changes. An internal 10-bit DAC ensures that a full 256 gamma-corrected gray levels are available across the entire dimming range, resulting in a measured dynamic range exceeding 20-bits. This device has been successfully tested for operation at frame rates ranging from 30Hz up to 85Hz. This paper describes the operational features and detailed optical and electrical test results for the new AMOLED WUXGA resolution microdisplay.

Wacyk, Ihor; Prache, Olivier; Ghosh, Amal

2011-06-01

49

Gamma Ray Bursts and CETI  

Microsoft Academic Search

Gamma ray burst sources are isotropically distributed. They could be located at distances 1000 AU. (Katz (4)) GRB signals have many narrow peaks that are unresolved at the millisecond time resolution of existing observations. (1) CETI could use stars as gravitational lenses for interstellar gamma ray laser beam communication. Much better time resolution of GRB signals could rule out (or

50

A balloon-borne high-resolution spectrometer for observations of gamma-ray emission from solar flares  

NASA Technical Reports Server (NTRS)

The design, development, and balloon-flight verification of a payload for observations of gamma-ray emission from solar flares are reported. The payload incorporates a high-purity germanium semiconductor detector, standard NIM and CAMAC electronics modules, a thermally stabilized pressure housing, and regulated battery power supplies. The flight system is supported on the ground with interactive data-handling equipment comprised of similar electronics hardware. The modularity and flexibility of the payload, together with the resolution and stability obtained throughout a 30-hour flight, make it readily adaptable for high-sensitivity, long-duration balloon fight applications.

Crannell, C. J.; Starr, R.; Stottlemyre, A. R.; Trombka, J. I.

1984-01-01

51

High resolution spectroscopy of two gamma-ray bursts in November 1978  

NASA Technical Reports Server (NTRS)

The first results from the ISSEE-3 radiatively colled germanium gamma ray burst spectrometer are presented. Spectra and time histories from two events on the 1978 November 4 and 1978 November 19 are given. A significant difference in the continuum spectra for the two events was observed. Evidence is presented for two spectral features in the features in the November 19 events, a broad one at approximately 420 key KeV and a narrower one at 740 KeV with a suggestion of an accompanying high energy tail.

Teegarden, B. J.; Cline, T. L.

1979-01-01

52

Ultrahigh resolution photoacoustic microscopy via transient absorption.  

PubMed

We have developed a novel, hybrid imaging modality, Transient Absorption Ultrasonic Microscopy (TAUM), which takes advantage of the optical nonlinearities afforded by transient absorption to achieve ultrahigh-resolution photoacoustic microscopy. The theoretical point spread function for TAUM is functionally equivalent to confocal and two-photon fluorescence microscopy, potentially enabling cellular/subcellular photoacoustic imaging. A prototype TAUM system was designed, built, and used to image a cross-section through several capillaries in the excised cheek pouch of a Syrian Hamster. The well-resolved capillaries in the TAUM image provided experimental evidence of the spatial resolution. These results suggest that TAUM has excellent potential for producing volumetric images with cellular/subcellular resolution in three dimensions deep inside living tissue. PMID:21258499

Shelton, Ryan L; Applegate, Brian E

2010-01-01

53

Ultrahigh resolution absolute Cartesian electronic autocollimator  

NASA Astrophysics Data System (ADS)

The development of a compact, ultra-high resolution, electronic autocollimator with excellent readout stability, linearity, and coordinate orthogonality is presented. This optical metrology tool relies on new advances in Cartesian optical encoders based on pattern recognition technology. Readout instabilities characteristic of conventional electronic autocollimators whose lateral effect photodetectors and operational amplifiers exhibit temporal and thermal drifts, are absent in this new technology. An autocollimator with a form factor similar to conventional alignment telescopes has been demonstrated with an angular resolution of 0.02 arcseconds peak-to-peak and less than 0.01 arcseconds rms. Various optical metrology applications for the laboratory and for space flight, including cryostatic ones, are described.

Leviton, Douglas B.

2003-11-01

54

The Application of High-Resolution Gamma-Ray Spectrometry (HRGS) to Nuclear Safeguards, Nonproliferation, and Arms Control Activities  

SciTech Connect

While well-developed methodologies exist for the employment of high- resolution gamma ray spectrometry (HRGS) in determining the isotopic composition of plutonium samples, the potential capabilities of such measurements in determining the properties of nuclear materials otherwise remain largely unexploited. These measurements contain information sufficiently detailed such that not only can the isotopic composition of uranium and plutonium materials be determined, but the details of the spectrum obtained will depend reproducibly upon other factors including the total mass, density, chemical composition, and geometrical configuration of the material, and for certain materials, the elapsed time since chemical processing. The potential thus exists to obtain a `gamma-ray fingerprint` for typical containers or assemblies of nuclear material which will then serve to identify that class of item in a later confirmatory measurement. These measurements have the additional advantage that, by comparison with active interrogation techniques which usually require the introduction of some extraneous form of radiation or other intrusive activity, they are totally passive, and thus impose only minimal additional safety or regulatory burdens on the operators. In the application of these measurements to the verification of treaty-limited items, where the information acquired may be sensitive in nature, the use of the CIVET (Controlled Intrusiveness Verification Technique) approach, where a computer-based interface is employed to limit access to the information obtained, may be followed.

Kane, Walter R.; Lemley, James R.; Forman, Leon

1997-12-31

55

Imaging of gamma rays with the WINKLER high-resolution germanium spectrometer  

SciTech Connect

The WINKLER spectrometer is a matrix of nine high-purity {ital n}-type germanium detectors developed for astrophysical observations and terrestrial radiation monitoring. The spectrometer has been fitted with a set of modulation collimator grids designed for imaging hard x-ray and gamma-ray sources by the Mertz, Nakano, and Kilner method. This technique employs a pair of gridded collimators in front of each detector with the number of grid bars varying from one to {ital N}, where {ital N} is the number of detectors. When the collimator pairs are rotated through a full 360-degree angular range, the detector signals provide the information for a two-dimensional band-limited Fourier reconstruction of order {ital N}. Tests of the spectrometer with single and multiple point sources as well as continuous source distributions are reported.

Fisher, T.R.; Hamilton, T.W.; Hawley, J.D.; Kilner, J.R.; Murphy, M.J.; Nakano, G.H. (Luckheed Palo Alto Research Lab., Palo Alto, CA (US))

1990-06-01

56

Monte Carlo Simulations of Ultra-High Energy Resolution Gamma Detectors for Nuclear Safeguards  

SciTech Connect

Ultra-high energy resolution superconducting gamma-ray detectors can improve the accuracy of non-destructive analysis for unknown radioactive materials. These detectors offer an order of magnitude improvement in resolution over conventional high purity germanium detectors. The increase in resolution reduces errors from line overlap and allows for the identification of weaker gamma-rays by increasing the magnitude of the peaks above the background. In order to optimize the detector geometry and to understand the spectral response function Geant4, a Monte Carlo simulation package coded in C++, was used to model the detectors. Using a 1 mm{sup 3} Sn absorber and a monochromatic gamma source, different absorber geometries were tested. The simulation was expanded to include the Cu block behind the absorber and four layers of shielding required for detector operation at 0.1 K. The energy spectrum was modeled for an Am-241 and a Cs-137 source, including scattering events in the shielding, and the results were compared to experimental data. For both sources the main spectral features such as the photopeak, the Compton continuum, the escape x-rays and the backscatter peak were identified. Finally, the low energy response of a Pu-239 source was modeled to assess the feasibility of Pu-239 detection in spent fuel. This modeling of superconducting detectors can serve as a guide to optimize the configuration in future spectrometer designs.

Robles, A; Drury, O B; Friedrich, S

2009-08-19

57

Assay for uranium and determination of disequilibrium by means of in situ high resolution gamma-ray spectrometry  

USGS Publications Warehouse

Two sealed sondes, using germanium gamma-ray detectors cooled by melting propane, have been field tested to depths of 79 m in water-filled boreholes at the Pawnee Uranium Mine in Bee Co., Texas. When, used as total-count devices, the sondes are comparable in logging speed and counting rate with conventional scintillation detectors for locating zones of high radioactivity. When used with a multichannel analyzer, the sondes are detectors with such high resolution that individual lines from the complex spectra of the uranium and thorium series can be distinguished. Gamma rays from each group of the uranium series can be measured in ore zones permitting determination of the state of equilibrium at each measurement point. Series of 10-minute spectra taken at 0.3- to 0.5-m intervals in several holes showed zones where maxima from the uranium group and from the 222Rn group were displaced relative to each other. Apparent excesses of 230Th at some locations suggest that uranium-group concentrations at those locations were severalfold greater some tens of kiloyears, ago. At the current state of development a 10-minute count yields a sensitivity of about 80 ppm U308. Data reduction could in practice be accomplished in about 5 minutes. The result is practically unaffected by disequilibrium or radon contamination. In comparison with core assay, high-resolution spectrometry samples a larger volume; avoids problems due to incomplete core recovery, loss of friable material to drilling fluids, and errors in depth and marking; and permits use of less expensive drilling methods. Because gamma rays from the radionuclides are accumulated simultaneously, it also avoids the problems inherent in trying to correlate logs made in separate runs with different equipment. Continuous-motion delayed-gamma activation by a 163-?g 252Cf neutron source attached to the sonde yielded poor sensitivity. A better neutron-activation method, in which the sonde is moved in steps so as to place the detector at the previous activation point, could not be evaluated because of equipment failure.

Tanner, Allan B.; Moxham, Robert M.; Senftle, F.E.

1977-01-01

58

Development of a high resolution liquid xenon imaging chamber for gamma-ray astronomy. Final Technical Report, 1 May 1988 - 30 Apr. 1990  

SciTech Connect

The objective was to develop the technology of liquid xenon (LXe) detectors for spectroscopy and imaging of gamma rays from astrophysical sources emitting in the low to medium energy regime. In particular, the technical challenges and the physical processes relevant to the realization of the LXe detector operated as a Time Projection Chamber (TPC) were addressed and studied. Experimental results were obtained on the following topics: (1) long distance drift of free electrons in LXe (purity); (2) scintillation light yield for electrons and alphas in LXe (triggering); and (3) ionization yield for electrons and gamma rays in LXe (energy resolution). The major results from the investigations are summarized.

Aprile, E.

1991-10-01

59

High resolution, high speed ultrahigh vacuum microscopy  

NASA Astrophysics Data System (ADS)

The history and future of transmission electron microscopy (TEM) is discussed as it refers to the eventual development of instruments and techniques applicable to the real time in situ investigation of surface processes with high resolution. To reach this objective, it was necessary to transform conventional high resolution instruments so that an ultrahigh vacuum (UHV) environment at the sample site was created, that access to the sample by various in situ sample modification procedures was provided, and that in situ sample exchanges with other integrated surface analytical systems became possible. Furthermore, high resolution image acquisition systems had to be developed to take advantage of the high speed imaging capabilities of projection imaging microscopes. These changes to conventional electron microscopy and its uses were slowly realized in a few international laboratories over a period of almost 40 years by a relatively small number of researchers crucially interested in advancing the state of the art of electron microscopy and its applications to diverse areas of interest; often concentrating on the nucleation, growth, and properties of thin films on well defined material surfaces. A part of this review is dedicated to the recognition of the major contributions to surface and thin film science by these pioneers. Finally, some of the important current developments in aberration corrected electron optics and eventual adaptations to in situ UHV microscopy are discussed. As a result of all the path breaking developments that have led to today's highly sophisticated UHV-TEM systems, integrated fundamental studies are now possible that combine many traditional surface science approaches. Combined investigations to date have involved in situ and ex situ surface microscopies such as scanning tunneling microscopy/atomic force microscopy, scanning Auger microscopy, and photoemission electron microscopy, and area-integrating techniques such as x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, temperature programmed desorption, high-resolution electron energy-loss and Fourier-transform infrared spectroscopies, and others. Material systems ranging from atomic layers of metals and semiconductors to biology related depositions are being investigated. In the case of biological materials, however, strict limitations to high-resolution applications are imposed by electron radiation damage considerations.

Poppa, Helmut

2004-09-01

60

Ultrahigh-resolution Cartesian absolute optical encoder  

NASA Astrophysics Data System (ADS)

A new optical encoder which measures absolute, true-Cartesian displacement with ultra-high sensitivity and linearity has been developed at NASA"s Goddard Space Flight Center. The device is the two-dimensional analog of recently developed linear and rotary encoders based on optical pattern recognition. In this encoder, a glass scale carrying absolute Cartesian position information travels with the payload in an X-Y motion system. Because the scale comprises the entire measurement coordinate system in a monolithic form, motion control axes can be skew to one another to an arbitrary degree and can exhibit substantial lateral drift with no effect on the correctness of X-Y readout, thus eliminating challenges of orthogonal mounting for motion axes and challenges of mounting independent encoders parallel to the directions of travel for each constituent X and Y axis. Prototype devices with ranges of 30 x 30 mm and 150 x 150 mm with 5 nm and 50 nm resolutions, respectively, have been built in the laboratory. Performance data from the Cartesian encoder in the Point Target Assembly for the optical calibration stimulus for Hubble Space Telescope"s Wide Field Camera 3 are presented.

Leviton, Douglas B.; Kirk, Jeff; Lobsinger, Luke

2003-11-01

61

Prospects for High Energy Resolution Gamma Ray Spectroscopy with Europium-Doped Strontium  

SciTech Connect

Europium-doped strontium iodide scintillators offer a light yield exceeding 100,000 photons/MeV and excellent light yield proportionality, while at the same time, SrI2 is readily grown in single crystal form. Thus far, our collaboration has demonstrated an energy resolution with strontium iodide of 2.6% at 662 keV and 7.6% at 60 keV, and we have grown single crystals surpassing 30 cm3 in size (with lower resolution). Our analysis indicates that SrI2(Eu) has the potential to offer 2% energy resolution at 662 keV with optimized material, optics, and read-out. In particular, improvements in feedstock purity may result in crystal structural and chemical homogeneity, leading to improved light yield uniformity throughout the crystal volume, and consequently, better energy resolution. Uniform, efficient light collection and detection, is also required to achieve the best energy resolution with a SrI2(Eu) scintillator device.

Cherepy, Nerine [Lawrence Livermore National Laboratory (LLNL); Payne, Stephen A. [Lawrence Livermore National Laboratory (LLNL); Hawrami, Rastgo [Fisk University, Nashville, TN; Burger, Arnold [Fisk University, Nashville, TN; Boatner, Lynn A [ORNL; Van Loef, Edgar [Radiation Monitoring Devices, Watertown, MA; Shah, Kanai [Radiation Monitoring Devices, Watertown, MA

2009-01-01

62

Inter-pulse high-resolution gamma-ray spectra using a 14 MeV pulsed neutron generator  

USGS Publications Warehouse

A neutron generator pulsed at 100 s-1 was suspended in an artificial borehole containing a 7.7 metric ton mixture of sand, aragonite, magnetite, sulfur, and salt. Two Ge(HP) gamma-ray detectors were used: one in a borehole sonde, and one at the outside wall of the sample tank opposite the neutron generator target. Gamma-ray spectra were collected by the outside detector during each of 10 discrete time windows during the 10 ms period following the onset of gamma-ray build-up after each neutron burst. The sample was measured first when dry and then when saturated with water. In the dry sample, gamma rays due to inelastic neutron scattering, neutron capture, and decay were counted during the first (150 ??s) time window. Subsequently only capture and decay gamma rays were observed. In the wet sample, only neutron capture and decay gamma rays were observed. Neutron capture gamma rays dominated the spectrum during the period from 150 to 400 ??s after the neutron burst in both samples, but decreased with time much more rapidly in the wet sample. A signal-to-noise-ratio (S/N) analysis indicates that optimum conditions for neutron capture analysis occurred in the 350-800 ??s window. A poor S/N in the first 100-150 ??s is due to a large background continuum during the first time interval. Time gating can be used to enhance gamma-ray spectra, depending on the nuclides in the target material and the reactions needed to produce them, and should improve the sensitivity of in situ well logging. ?? 1984.

Evans, L.G.; Trombka, J.I.; Jensen, D.H.; Stephenson, W.A.; Hoover, R.A.; Mikesell, J.L.; Tanner, A.B.; Senftle, F.E.

1984-01-01

63

Background radiation reduction for a high-resolution gamma-ray spectrometer used for environmental radioactivity measurements  

NASA Astrophysics Data System (ADS)

A detailed analysis is presented of background radiation spectra for a high-resolution gamma-ray spectrometer used to measure environmental radioactivity, for various shielding configurations. The main goal is to improve the detection limits of low-level activity measurements by reducing the background as much as possible. Passive shielding configurations are used to decrease the total background counting rate by adding new layers. Subsequently, for the maximum shielding configuration, the Minimum Detectable Activity (MDA) is improved by at least 13-fold for 137Cs, 8-fold for 214Bi (609.31 keV), 7-fold for 40K and 5.5-fold for 208Tl (2614.53 keV). A reduction factor of 240 for the 137Cs peak (counting rate) at maximum shielding and an insignificant peak for this radionuclide was determined. For other radionuclides, peaks below the detection limit of the detector system were also found. These results show that the shielding was successful in reducing and removing peaks from the background spectrum.

Radulescu, I.; Blebea-Apostu, A. M.; Margineanu, R. M.; Mocanu, N.

2013-07-01

64

A 3D CZT high resolution detector for x- and gamma-ray astronomy  

NASA Astrophysics Data System (ADS)

At DTU Space we have developed a high resolution three dimensional (3D) position sensitive CZT detector for high energy astronomy. The design of the 3D CZT detector is based on the CZT Drift Strip detector principle. The position determination perpendicular to the anode strips is performed using a novel interpolating technique based on the drift strip signals. The position determination in the detector depth direction, is made using the DOI technique based the detector cathode and anode signals. The position determination along the anode strips is made with the help of 10 cathode strips orthogonal to the anode strips. The position resolutions are at low energies dominated by the electronic noise and improve therefore with increased signal to noise ratio as the energy increases. The achievable position resolution at higher energies will however be dominated by the extended spatial distribution of the photon produced ionization charge. The main sources of noise contribution of the drift signals are the leakage current between the strips and the strip capacitance. For the leakage current, we used a metallization process that reduces the leakage current by means of a high resistive thin layer between the drift strip electrodes and CZT detector material. This method was applied to all the proto type detectors and was a very effective method to reduce the surface leakage current between the strips. The proto type detector was recently investigated at the European Synchrotron Radiation Facility, Grenoble which provided a fine 50 × 50 ?m2 collimated X-ray beam covering an energy band up to 600 keV. The Beam positions are resolved very well with a ~ 0.2 mm position resolution (FWHM ) at 400 keV in all directions.

Kuvvetli, I.; Budtz-Jørgensen, C.; Zappettini, A.; Zambelli, N.; Benassi, G.; Kalemci, E.; Caroli, E.; Stephen, J. B.; Auricchio, N.

2014-07-01

65

Gamma ray generator  

DOEpatents

An embodiment of a gamma ray generator includes a neutron generator and a moderator. The moderator is coupled to the neutron generator. The moderator includes a neutron capture material. In operation, the neutron generator produces neutrons and the neutron capture material captures at least some of the neutrons to produces gamma rays. An application of the gamma ray generator is as a source of gamma rays for calibration of gamma ray detectors.

Firestone, Richard B; Reijonen, Jani

2014-05-27

66

An achromatized endoscope for ultrahigh-resolution optical coherence tomography  

Microsoft Academic Search

Mouse models are increasingly important for studying human GI pathology. OCT provides minimally invasive, cross-sectional images that indicate the thickness and scattering density of underlying tissue. We have developed endoscopic ultrahigh resolution OCT (UHR-OCT) to imaging mouse colon in vivo. The reduced scale of the mouse colon makes tissue light penetration much less problematic, and high resolution acutely necessary. Higher

Alexandre R. Tumlinson; Jennifer K. Barton; James McNally; Angelika Unterhuber; Boris Hermann; Harald Sattmann; Wolfgang Drexler

2005-01-01

67

Preliminary results from the high resolution gamma-ray and hard x-ray spectrometer (HIREGS) '92-'93 long duration balloon flight in Antarctica  

SciTech Connect

HIREGS consists of an array of twelve 6.7 cm diameter x 6.1 cm long liquid nitrogen-cooled segmented germanium detectors enclosed in a bismuth germanate (BGO) active anticoincidence shield. A CsI front collimator defines a 24 degree FWHM field-of-view. The energy resolution is one to several keV FWHM over the instrument energy range of 20 keV to 16 MeV. HIREGS was flown on a 10-day (31 Dec 92--10 Jan 93) circumpolar balloon flight from McMurdo Station, Antarctica. 30.5 hours of observation were obtained between 31 Dec 0400-2130 UT and 1 Jan 0600-1900 UT. Because the Sun was inactive during the flight, only one small flare was detected on 31 Dec 1933 UT. Excellent high resolution [open quotes]quiet[close quotes] Sun hard X-ray and gamma-ray spectra were obtained. These provide stringent upper limits for solar gamma-ray line and hard X-ray and gamma-ray continuum emission, which in turn can constrain the storage and/or continuous acceleration of ions and electrons by the Sun.

Lin, R.P.; Feffer, P.T.; Slassi, S.; Whiteside, W.; Smith, D.M.; Hurley, K.C.; Kane, S.R.; McBride, S.; Primbsch, J.H.; Youssefi, K.; Zimmer, G. (Univ. of California, Berkeley, CA (United States)); Pelling, R.M. (Univ. of California, San Diego, CA (United States)); Cotin, F.; Lavigne, J.M.; Rouaix, G.; Vedrenne, G.; Pehl, R.; Cork, C.; Luke, P.; Madden, N.; Malone, D.

1993-01-01

68

Imaging brain morphology with ultrahigh-resolution optical coherence tomography  

Microsoft Academic Search

The morphology of healthy and pathological human brain tissue, as well as the brain structural organization of various animal models has been imaged in-vitro using ultrahigh resolution optical coherence tomography (UHR OCT). Micrometer-scale OCT resolution (< 2 mum axial resolution) was achieved at different central wavelengths by interfacing three state-of-the-art broad bandwidth light sources (Ti:Al2O3, lambdac = 790 nm, Deltalambda

Kostadinka K. Bizheva; Angelika Unterhuber; Boris Hermann; Boris Povazay; Harald Sattmann; Michael Mei; Ronald Holzwarth; Matthias Preusser; Herbert Reitsamer; Michael Seefeldt; Ralf Menzel; Herbert Budka; Adolf F. Fercher; Wolfgang Drexler

2003-01-01

69

High-Resolution Timing Observations of Spin-Powered Pulsars with the AGILE Gamma-Ray Telescope  

E-print Network

AGILE is a small gamma-ray astronomy satellite mission of the Italian Space Agency dedicated to high-energy astrophysics launched in 2007 April. Its 1 microsecond absolute time tagging capability coupled with a good sensitivity in the 30 MeV-30 GeV range, with simultaneous X-ray monitoring in the 18-60 keV band, makes it perfectly suited for the study of gamma-ray pulsars following up on the CGRO/EGRET heritage. In this paper we present the first AGILE timing results on the known gamma-ray pulsars Vela, Crab, Geminga and B 1706-44. The data were collected from 2007 July to 2008 April, exploiting the mission Science Verification Phase, the Instrument Timing Calibration and the early Observing Pointing Program. Thanks to its large field of view, AGILE collected a large number of gamma-ray photons from these pulsars (about 10,000 pulsed counts for Vela) in only few months of observations. The coupling of AGILE timing capabilities, simultaneous radio/X-ray monitoring and new tools aimed at precise photon phasing, exploiting also timing noise correction, unveiled new interesting features at sub-millisecond level in the pulsars' high-energy light-curves.

A. Pellizzoni; M. Pilia; A. Possenti; F. Fornari; P. Caraveo; E. Del Monte; S. Mereghetti; M. Tavani; A. Argan; A. Trois; M. Burgay; A. Chen; I. Cognard; E. Costa; N. D'Amico; P. Esposito; Y. Evangelista; M. Feroci; F. Fuschino; A. Giuliani; J. Halpern; G. Hobbs; A. Hotan; S. Johnston; M. Kramer; F. Longo; R. N. Manchester; M. Marisaldi; J. Palfreyman; P. Weltevrede; G. Barbiellini; F. Boffelli; A. Bulgarelli; P. W. Cattaneo; V. Cocco; F. D'Ammando; G. De Paris; G. Di Cocco; I. Donnarumma; M. Fiorini; T. Froysland; M. Galli; F. Gianotti; A. Harding; C. Labanti; I. Lapshov; F. Lazzarotto; P. Lipari; F. Mauri; A. Morselli; L. Pacciani; F. Perotti; P. Picozza; M. Prest; G. Pucella; M. Rapisarda; A. Rappoldi; P. Soffitta; M. Trifoglio; E. Vallazza; S. Vercellone; V. Vittorini; A. Zambra; D. Zanello; C. Pittori; F. Verrecchia; B. Preger; P. Santolamazza; P. Giommi; L. Salotti

2008-10-10

70

The BATSE Gamma-Ray Burst Spectral Catalog. 1; High Time Resolution Spectroscopy of Bright Bursts Using High Energy Resolution Data  

NASA Technical Reports Server (NTRS)

This is the first in a series of gamma-ray burst spectroscopy catalogs from the Burst And Transient Source Experiment (BATSE) on the Compton Gamma Ray Abstract: Observatory, each covering a different aspect of burst phenomenology. In this paper, we present time-sequences of spectral fit parameters for 156 bursts selected either for their high peak flux or fluence.

Preece, Robert D.; Briggs, Michael S.; Mallozzi, Robert S.; Pendleton, Geoffrey N.; Paciesas, W. S.; Band, David L.

1999-01-01

71

Investigation of gamma-ray families originating from nucleus-nucleus interactions at ultrahigh energies E 0 in excess of 1016 eV  

NASA Astrophysics Data System (ADS)

Various spatial and energy features of gamma-ray families originating from the interactions of primary nuclei of galactic cosmic rays with nuclei of atmospheric atoms ( AA interactions) are studied. The mass composition of galactic cosmic rays is analyzed on the basis of data from x-ray emulsion chambers of the Pamir experiment with the aid of a criterion for selecting gamma-ray families originating from AA interactions ( A families) at energies E 0 of primary galactic cosmic rays in excess of 1016 eV. According to the results obtained in this way only the experimental spatial parameters R 1 E and ? differ from their counterparts in the MC0 model.

Yuldashbaev, T. S.; Nuritdinov, Kh.

2013-12-01

72

X-ray Interferometry with Transmissive Beam Combiners for Ultra-High Angular Resolution Astronomy  

NASA Technical Reports Server (NTRS)

Abstract Interferometry provides one of the possible routes to ultra-high angular resolution for X-ray and gamma-ray astronomy. Sub-micro-arc-second angular resolution, necessary to achieve objectives such as imaging the regions around the event horizon of a super-massive black hole at the center of an active galaxy, can be achieved if beams from parts of the incoming wavefront separated by 100s of meters can be stably and accurately brought together at small angles. One way of achieving this is by using grazing incidence mirrors. We here investigate an alternative approach in which the beams are recombined by optical elements working in transmission. It is shown that the use of diffractive elements is a particularly attractive option. We report experimental results from a simple 2-beam interferometer using a low-cost commercially available profiled film as the diffractive elements. A rotationally symmetric filled (or mostly filled) aperture variant of such an interferometer, equivalent to an X-ray axicon, is shown to offer a much wider bandpass than either a Phase Fresnel Lens (PFL) or a PFL with a refractive lens in an achromatic pair. Simulations of an example system are presented.

Skinner, G. K.; Krismanic, John F.

2009-01-01

73

High-Resolution Timing Observations of Spin-Powered Pulsars with the AGILE Gamma-Ray Telescope  

Microsoft Academic Search

Astro-rivelatore Gamma ad Immagini LEggero (AGILE) is a small gamma-ray astronomy satellite mission of the Italian Space Agency dedicated to high-energy astrophysics launched in 2007 April. Its ~ 1 mus absolute time tagging capability coupled with a good sensitivity in the 30 MeV-30 GeV range, with simultaneous X-ray monitoring in the 18-60 keV band, makes it perfectly suited for the

A. Pellizzoni; M. Pilia; A. Possenti; F. Fornari; P. Caraveo; E. del Monte; S. Mereghetti; M. Tavani; A. Argan; A. Trois; M. Burgay; A. Chen; I. Cognard; E. Costa; N. D'Amico; P. Esposito; Y. Evangelista; M. Feroci; F. Fuschino; A. Giuliani; J. Halpern; G. Hobbs; A. Hotan; S. Johnston; M. Kramer; F. Longo; R. N. Manchester; M. Marisaldi; J. Palfreyman; P. Weltevrede; G. Barbiellini; F. Boffelli; A. Bulgarelli; P. W. Cattaneo; V. Cocco; F. D'Ammando; G. DeParis; G. Di Cocco; I. Donnarumma; M. Fiorini; T. Froysland; M. Galli; F. Gianotti; A. Harding; C. Labanti; I. Lapshov; F. Lazzarotto; P. Lipari; F. Mauri; A. Morselli; L. Pacciani; F. Perotti; P. Picozza; M. Prest; G. Pucella; M. Rapisarda; A. Rappoldi; P. Soffitta; M. Trifoglio; E. Vallazza; S. Vercellone; V. Vittorini; A. Zambra; D. Zanello; C. Pittori; F. Verrecchia; B. Preger; P. Santolamazza; P. Giommi; L. Salotti

2009-01-01

74

Towards Ultra-High Resolution Models of Climate and Weather  

SciTech Connect

We present a speculative extrapolation of the performance aspects of an atmospheric general circulation model to ultra-high resolution and describe alternative technological paths to realize integration of such a model in the relatively near future. Due to a superlinear scaling of the computational burden dictated by stability criterion, the solution of the equations of motion dominate the calculation at ultra-high resolutions. From this extrapolation, it is estimated that a credible kilometer scale atmospheric model would require at least a sustained ten petaflop computer to provide scientifically useful climate simulations. Our design study portends an alternate strategy for practical power-efficient implementations of petaflop scale systems. Embedded processor technology could be exploited to tailor a custom machine designed to ultra-high climate model specifications at relatively affordable cost and power considerations. The major conceptual changes required by a kilometer scale climate model are certain to be difficult to implement. Although the hardware, software, and algorithms are all equally critical in conducting ultra-high climate resolution studies, it is likely that the necessary petaflop computing technology will be available in advance of a credible kilometer scale climate model.

Wehner, Michael; Oliker, Leonid; Shalf, John

2007-01-01

75

Cloaked Gamma Ray Bursts  

E-print Network

It is suggested that many $\\gamma$-ray bursts (GRBs) are cloaked by an ultra-relativistic baryonic shell that has high optical depth when the photons are manufactured. Such a shell would not fully block photons reflected or emitted from its inner surface, because the radial velocity of the photons can be less than that of the shell. This avoids the standard problem associated with GRBs that the thermal component should be produced where the flow is still obscured by high optical depth. The radiation that escapes high optical depth obeys the Amati relation. Observational implications may include a) anomalously high ratios of afterglow to prompt emission, such as may have been the case in the recently discovered PTF 11agg, and b) ultrahigh-energy neutrino pulses that are non-coincident with detectable GRB. It is suggested that GRB 090510, a short, very hard GRB with very little afterglow, was an {\\it exposed} GRB, in contrast to those cloaked by baryonic shells. \\end{abstract}

Eichler, David

2014-01-01

76

Determination of the natural radioactivity levels in north west of Dukhan, Qatar using high-resolution gamma-ray spectrometry.  

PubMed

This study is aimed at the determination of the activity concentrations of naturally occuring and technologically enhanced levels of radiation in 34 representative soil samples that have been collected from an inshore oil field area which was found to have, in a previous study, the highest observed value of 226Ra concentration among 129 soil samples. The activity concentrations of 238U and 226Ra have been inferred from gamma-ray transitions associated with their decay progenies and measured using a hyper-pure germanium detector. Details of the sample preparation and the gamma-ray spectroscopic analysis techniques are presented, together with the values of the activity concentrations associated with the naturally occuring radionuclide chains for all the samples collected from NW Dukhan. Discrete-line, gamma-ray energy transitions from spectral lines ranging in energy from ?100 keV up to 2.6 MeV have been associated with characteristic decays of the various decay products within the 235.8U and 232Th radioactive decay chains. These data have been analyzed, under the assumption of secular equilibrium for the U and Th decay chains. Details of the sample preparation and the gamma-ray spectroscopic analysis techniques are presented. The weighted mean value of the activity concentrations of 226Ra in one of the samples was found to be around a factor of 2 higher than the values obtained in the previous study and approximately a factor of 10 higher than the accepted worldwide average value of 35 Bq/kg. The weighted mean values of the activity concentrations of 232Th and 40K were also deduced and found to be within the worldwide average values of 30 and 400 Bq/kg, respectively. Our previous study reported a value of 201.9±1.5Stat.±13Syst.Bq/kg for 226Ra in one sample and further investigation in the current work determined a measured value for 226Ra of 342.00±1.9Stat.±25Syst.Bq/kg in a sample taken from the same locality. This is significantly higher than all the other investigated soil samples in the current and previous works. Notably, the Th levels in the same sample are within the worldwide average expectations, implying that the increased 226Ra concentration arises from TENORM processes. PMID:22244196

Al-Sulaiti, Huda; Nasir, Tabassum; Al Mugren, K S; Alkhomashi, N; Al-Dahan, N; Al-Dosari, M; Bradley, D A; Bukhari, S; Matthews, M; Regan, P H; Santawamaitre, T; Malain, D; Habib, A

2012-07-01

77

Energy resolution and throughput of a new real time digital pulse processing system for x-ray and gamma ray semiconductor detectors  

NASA Astrophysics Data System (ADS)

New generation spectroscopy systems have advanced towards digital pulse processing (DPP) approaches. DPP systems, based on direct digitizing and processing of detector signals, have recently been favoured over analog pulse processing electronics, ensuring higher flexibility, stability, lower dead time, higher throughput and better spectroscopic performance. In this work, we present the performance of a new real time DPP system for X-ray and gamma ray semiconductor detectors. The system is based on a commercial digitizer equipped with a custom DPP firmware, developed by our group, for on-line pulse shape and height analysis. X-ray and gamma ray spectra measurements with cadmium telluride (CdTe) and germanium (Ge) detectors, coupled to resistive-feedback preamplifiers, highlight the excellent performance of the system both at low and high rate environments (up to 800 kcps). A comparison with a conventional analog electronics showed the better high-rate capabilities of the digital approach, in terms of energy resolution and throughput. These results make the proposed DPP system a very attractive tool for both laboratory research and for the development of advanced detection systems for high-rate-resolution spectroscopic imaging, recently proposed in diagnostic medicine, industrial imaging and security screening.

Abbene, L.; Gerardi, G.; Raso, G.; Basile, S.; Brai, M.; Principato, F.

2013-07-01

78

Gamma ray transients  

NASA Technical Reports Server (NTRS)

The discovery of cosmic gamma ray bursts was made with systems designed at Los Alamos Laboratory for the detection of nuclear explosions beyond the atmosphere. HELIOS-2 was the first gamma ray burst instrument launched; its initial results in 1976, seemed to deepen the mystery around gamma ray transients. Interplanetary spacecraft data were reviewed in terms of explaining the behavior and source of the transients.

Cline, Thomas L.

1987-01-01

79

Nucleosynthesis in gamma-ray bursts outflows  

E-print Network

It is shown that fusion of neutrons and protons to He-4 nuclei occurs in gamma-ray burst outflows in a process similar to big-bang nucleosynthesis in the early Universe. Only the surviving free neutrons can then decouple kinematically from the charged fluid so that the multi-GeV neutrino signal predicted from inelastic nuclear n-p collisions is significantly reduced. It is also argued that a sizeable fraction of ultra-high energy cosmic rays accelerated in gamma-ray bursts should be He-4 nuclei.

M. Lemoine

2002-05-07

80

Gamma-ray astrophysics  

NASA Technical Reports Server (NTRS)

Conference papers on gamma ray astrophysics are summarized. Data cover the energy region from about 0.3 MeV to a few hundred GeV and theoretical models of production mechanisms that give rise to both galactic and extragalactic gamma rays.

Stecker, F. W. (editor); Trombka, J. I. (editor)

1973-01-01

81

Gamma-ray Bursts  

NASA Astrophysics Data System (ADS)

Prologue C. Kouveliotou, R. A . M. J. Wijers and S. E. Woosley; 1. The discovery of the gamma-ray burst phenomenon R. W. Klebesadel; 2. Instrumental principles E. E. Fenimore; 3. The BATSE era G. J. Fishman and C. A. Meegan; 4. The cosmological era L. Piro and K. Hurley; 5. The Swift era N. Gehrels and D. N. Burrows; 6. Discoveries enabled by multi-wavelength afterglow observations of gamma-ray bursts J. Greiner; 7. Prompt emission from gamma-ray bursts T. Piran, R. Sari and R. Mochkovitch; 8. Basic gamma-ray burst afterglows P. Mészáros and R. A. M. J. Wijers; 9. The GRB-supernova connection J. Hjorth and J. S. Bloom; 10. Models for gamma-ray burst progenitors and central engines S. E. Woosley; 11. Jets and gamma-ray burst unification schemes J. Granot and E. Ramirez-Ruiz; 12. High-energy cosmic rays and neutrinos E. Waxman; 13. Long gamma-ray burst host galaxies and their environments J. P. U. Fynbo, D. Malesani and P. Jakobsson; 14. Gamma-ray burst cosmology V. Bromm and A. Loeb; 15. Epilogue R. D. Blandford; Index.

Kouveliotou, Chryssa; Wijers, Ralph A. M. J.; Woosley, Stan

2012-11-01

82

A High Resolution Liquid Xenon Imaging Telescope for 0.3-10 MeV Gamma Ray Astrophysics: Construction and Initial Balloon Flights  

NASA Technical Reports Server (NTRS)

The results achieved with a 3.5 liter liquid xenon time projection chamber (LXe-TPC) prototype during the first year include: the efficiency of detecting the primary scintillation light for event triggering has been measured to be higher than 85%; the charge response has been measured to be stable to within 0.1% for a period of time of about 30 hours; the electron lifetime has been measured to be in excess of 1.3 ms; the energy resolution has been measured to be consistent with previous results obtained with small volume chambers; X-Y gamma ray imaging has been demonstrated with a nondestructive orthogonal wires readout; Monte Carlo simulation results on detection efficiency, expected background count rate at balloon altitude, background reduction algorithms, telescope response to point-like and diffuse sources, and polarization sensitivity calculations; and work on a 10 liter LXe-TPC prototype and gas purification/recovery system.

Aprile, Elena

1993-01-01

83

Ultrahigh-resolution optical coherence tomography with a fiber laser source at 1 m  

E-print Network

, high-power, fiber-based source for ultrahigh-resolution optical coherence tomography (OCT) near 1 m-brightness, and broad-bandwidth light sources are essential in high-speed, high-resolution OCT imaging. For artifactUltrahigh-resolution optical coherence tomography with a fiber laser source at 1 m Hyungsik Lim, Yi

Chen, Zhongping

84

Gamma-ray Astronomy and GLAST  

NASA Technical Reports Server (NTRS)

The high energy gamma-ray (30 MeV to 100 GeV) sky has been relatively poorly studied. Most of our current knowledge comes from observations made by the Energetic Gamma Ray Experiment Telescope (EGRET) detector on the Compton Gamma Ray Observatory (CGRO), which revealed that the GeV gamma-ray sky is rich and vibrant. Studies of astrophysical objects at GeV energies are interesting for several reasons: The high energy gamma-rays are often produced by a different physical process than the better studied X-ray and optical emission, thus providing a unique information for understanding these sources. Production of such high-energy photons requires that charged particles are accelerated to equally high energies, or much greater. Thus gamma-ray astronomy is the study of extreme environments, with natural and fundamental connections to cosmic-ray and neutrino astrophysics. The launch of GLAST in 2008 will herald a watershed in our understanding of the high energy gamma-ray sky, providing dramatic improvements in sensitivity, angular resolution and energy range. GLAST will open a new avenue to study our Universe as well as to answer scientific questions EGRET observations have raised. In this talk, I will describe the GLAST instruments and capabilities and highlight some of the science we expect to address.

McEnery, Julie

2007-01-01

85

Gamma-ray Astronomy  

E-print Network

The relevance of gamma-ray astronomy to the search for the origin of the galactic and, to a lesser extent, the ultra-high-energy cosmic rays has long been recognised. The current renaissance in the TeV gamma-ray field has resulted in a wealth of new data on galactic and extragalactic particle accelerators, and almost all the new results in this field were presented at the recent International Cosmic Ray Conference (ICRC). Here I summarise the 175 papers submitted on the topic of gamma-ray astronomy to the 30th ICRC in Merida, Mexico in July 2007.

Jim Hinton

2007-12-20

86

Gamma ray astrophysics to the year 2000. Report of the NASA Gamma Ray Program Working Group  

NASA Technical Reports Server (NTRS)

Important developments in gamma-ray astrophysics up to energies of 100 GeV during the last decade are reviewed. Also, the report seeks to define the major current scientific goals of the field and proposes a vigorous program to pursue them, extending to the year 2000. The goals of gamma-ray astronomy include the study of gamma rays which provide the most direct means of studying many important problems in high energy astrophysics including explosive nucleosynthesis, accelerated particle interactions and sources, and high-energy processes around compact objects. The current research program in gamma-ray astronomy in the U.S. including the space program, balloon program and foreign programs in gamma-ray astronomy is described. The high priority recommendations for future study include an Explorer-class high resolution gamma-ray spectroscopy mission and a Get Away Special cannister (GAS-can) or Scout class multiwavelength experiment for the study of gamma-ray bursts. Continuing programs include an extended Gamma Ray Observatory mission, continuation of the vigorous program of balloon observations of the nearby Supernova 1987A, augmentation of the balloon program to provide for new instruments and rapid scientific results, and continuation of support for theoretical research. Long term recommendations include new space missions using advanced detectors to better study gamma-ray sources, the development of these detectors, continued study for the assembly of large detectors in space, collaboration with the gamma-ray astronomy missions initiated by other countries, and consideration of the Space Station attached payloads for gamma-ray experiments.

1988-01-01

87

Gamma ray astrophysics to the year 2000. Report of the NASA Gamma Ray Program Working Group  

NASA Astrophysics Data System (ADS)

Important developments in gamma-ray astrophysics up to energies of 100 GeV during the last decade are reviewed. Also, the report seeks to define the major current scientific goals of the field and proposes a vigorous program to pursue them, extending to the year 2000. The goals of gamma-ray astronomy include the study of gamma rays which provide the most direct means of studying many important problems in high energy astrophysics including explosive nucleosynthesis, accelerated particle interactions and sources, and high-energy processes around compact objects. The current research program in gamma-ray astronomy in the U.S. including the space program, balloon program and foreign programs in gamma-ray astronomy is described. The high priority recommendations for future study include an Explorer-class high resolution gamma-ray spectroscopy mission and a Get Away Special cannister (GAS-can) or Scout class multiwavelength experiment for the study of gamma-ray bursts. Continuing programs include an extended Gamma Ray Observatory mission, continuation of the vigorous program of balloon observations of the nearby Supernova 1987A, augmentation of the balloon program to provide for new instruments and rapid scientific results, and continuation of support for theoretical research. Long term recommendations include new space missions using advanced detectors to better study gamma-ray sources, the development of these detectors, continued study for the assembly of large detectors in space, collaboration with the gamma-ray astronomy missions initiated by other countries, and consideration of the Space Station attached payloads for gamma-ray experiments.

1988-10-01

88

Ultra-high resolution mass spectroscopy of boron cluster ions  

NASA Astrophysics Data System (ADS)

Boron clusters have recently received considerable attention as a possible solution to the throughput dilemma associated with ultra-low energy (sub keV) p-type source drain extension implants required by cutting edge complimentary metal-oxide semiconductor (CMOS) technology. Boron cluster ion beams contain many masses due to the binomial distribution of the two naturally occurring isotopes (masses 10 and 11) of boron. The broadness of the mass distribution peak in the dispersive plane is further complicated by a plurality of ion states, due to the varying number of hydrogen atoms remaining attached to the borohydride molecule when it is ionized. The B18Hx+ cluster ion mass spectrum from an electron impact ionization source will be analyzed in detail. An ultra-high resolution mass spectrum, exhibiting 1 AMU resolution of a mass 220 cluster ion will be shown. It will be compared to high-resolution spectra of decaborane (B 10H 14) cluster ions obtained from natural abundance decaborane and from isotopically enriched material. The deconvolution of the binominal distribution from ion states present in the cluster ion beam reveals the hydrogen distribution function. The hydrogen distribution functions as well as the binomial distributions will be presented and discussed. Physical models will be presented that explain the origin of hydrogen distribution function for these high mass borohydride cluster ions. This ultra-high mass resolution is usually unavailable to the ion implant community, however our 120° mass analyzing magnet and the extremely low emittance of the ion beam extracted from the ClusterIon ® source coupled with a variable width beam defining aperture and variable width mass defining slits allow for superior mass resolution.

Jacobson, Dale; Horsky, Thomas; Krull, Wade; Milgate, Bob

2005-08-01

89

High Energy Gamma Rays  

E-print Network

This article reviews the present status of high energy gamma-ray astronomy at energies above 30 MeV. Observations in the past decade using both space- and ground-based experiments have been primarily responsible for giving a tremendous boost to our knowledge of the high energy Universe. High energy gamma-rays have been detected from a wide range of Galactic and extragalactic astrophysical sources, such as gamma-ray bursters, pulsars, and active galaxies. These observations have established high energy gamma-ray astronomy as a vital and exciting field, that has a bright future. This review summarizes the experimental techniques, observations and results obtained with recent experiments, and concludes with a short description of future prospects.

R. Mukherjee

2000-09-22

90

Ultrahigh resolution multicolor colocalization of single fluorescent nanocrystals  

SciTech Connect

A new method for in vitro and possibly in vivo ultrahigh-resolution colocalization and distance measurement between biomolecules is described, based on semiconductor nanocrystal probes. This ruler bridges the gap between FRET and far-field (or near-field scanning optical microscope) imaging and has a dynamic range from few nanometers to tens of micrometers. The ruler is based on a stage-scanning confocal microscope that allows the simultaneous excitation and localization of the excitation point-spread-function (PSF) of various colors nanocrystals while maintaining perfect registry between the channels. Fit of the observed diffraction and photophysics-limited images of the PSFs with a two-dimensional Gaussian allows one to determine their position with nanometer accuracy. This new high-resolution tool opens new windows in various molecular, cell biology and biotechnology applications.

Michalet, X.; Lacoste, T.D.; Pinaud, F.; Chemla, D.S.; Alivisatos, A.P.; Weiss, S.

2000-12-20

91

Position and energy resolution of a new gamma-ray detector based on a single CsI(Tl) scintillator coupled to a silicon drift chamber array  

SciTech Connect

The authors have developed a first prototype of gamma-ray detector for imaging and spectroscopy which is based on a single CsI(Tl) scintillator coupled to a linear array of Silicon Drift Chambers (SDCs). The detector performs the measurement of the position of interaction in one coordinate, by the centroid method, and the measurement of the {gamma} photon energy, by summing the signals of all the single units. The small size and the compactness of the CsI(Tl)-SDC assembly make this detector scheme an interesting solution for the realization of small scintillation cameras for nuclear medicine. Moreover, the low electronics noise offered by the SDC allows good performance in both position and energy resolution. The first experimental results obtained on the prototype are reported in this work. A position resolution better than 1 mm FWHM and an energy resolution of about 16% FWHM at 122 keV have been measured. A comparison of the experimental results with the results of Monte Carlo simulations is also reported.

Fiorini, C.; Longoni, A. [Politecnico di Milano (Italy). Dipt. di Elettronica e Informazione] [Politecnico di Milano (Italy). Dipt. di Elettronica e Informazione; Perotti, F. [C.N.R., Milano (Italy). Ist. di Fisica Cosmica e Technologies Relative] [C.N.R., Milano (Italy). Ist. di Fisica Cosmica e Technologies Relative; Labanti, C.; Rossi, E. [C.N.R., Bologna (Italy). Ist. di Tecnologie e Studio delle Radiazioni Extraterrestri] [C.N.R., Bologna (Italy). Ist. di Tecnologie e Studio delle Radiazioni Extraterrestri

1999-08-01

92

Gamma-ray spectroscopy: An historical perspective  

SciTech Connect

The possibility of MeV-range gamma-rays from extraterrestrial sources had been speculated on by cosmic-ray physicists since the late 1940's. The first definitive detection occurred with balloon-borne cosmic-ray instrumentation during a class 2 solar flare in March 1958, apparently associated with the acceleration of a nonthermal particle population. Following this detection, physicists were motivated to develop instrumentation specific for observation of astronomical gamma-ray sources. Gamma-ray lines were also first observed during the flares of August 1972, apparently associated with accelerated particles undergoing nuclear interactions in the solar atmosphere. The development of low background, high resolution Ge counters has permitted construction of gamma-ray telescopes with unprecedented resolution and sensitivity. Even modest versions of these devices have measured discrete gamma-ray lines from sources as diverse as cosmic gamma-ray bursts, the galactic center and the galactic plane. Many other predictions are within the range of modern detectors.

Peterson, L.E.

1988-09-25

93

Precision X-Band Linac Technologies for Nuclear Photonics Gamma-Ray Sources  

SciTech Connect

Nuclear photonics is an emerging field of research requiring new tools, including high spectral brightness, tunable gamma-ray sources; high photon energy, ultrahigh-resolution crystal spectrometers; and novel detectors. This presentation focuses on the precision linac technology required for Compton scattering gamma-ray light sources, and on the optimization of the laser and electron beam pulse format to achieve unprecedented spectral brightness. Within this context, high-gradient X-band technology will be shown to offer optimal performance in a compact package, when used in conjunction with the appropriate pulse format, and photocathode illumination and interaction laser technologies. The nascent field of nuclear photonics is enabled by the recent maturation of new technologies, including high-gradient X-band electron acceleration, robust fiber laser systems, and hyper-dispersion CPA. Recent work has been performed at LLNL to demonstrate isotope-specific detection of shielded materials via NRF using a tunable, quasi-monochromatic Compton scattering gamma-ray source operating between 0.2 MeV and 0.9 MeV photon energy. This technique is called Fluorescence Imaging in the Nuclear Domain with Energetic Radiation (or FINDER). This work has, among other things, demonstrated the detection of {sup 7}Li shielded by Pb, utilizing gamma rays generated by a linac-driven, laser-based Compton scattering gamma-ray source developed at LLNL. Within this context, a new facility is currently under construction at LLNL, with the goal of generating tunable {gamma}-rays in the 0.5-2.5 MeV photon energy range, at a repetition rate of 120 Hz, and with a peak brightness in the 10{sup 20} photons/(s x mm{sup 2} x mrad{sup 2} x 0.1% bw).

Hartemann, F V; Albert, F; Anderson, S G; Bayramian, A J; Cross, R R; Ebbers, C A; Gibson, D J; Houck, T L; Marsh, R A; Messerly, M J; Siders, C W; McNabb, D P; Barty, C J; Adolphsen, C E; Chu, T S; Jongewaard, E N; Tantawi, S G; Vlieks, A E; Wang, F; Wang, J W; Raubenheimer, T O; Ighigeanu, D; Toma, M; Cutoiu, D

2011-08-31

94

EFFECTIVENESS OF QUIKSCAT'S ULTRA-HIGH RESOLUTION IMAGES IN DETERMINING TROPICAL CYCLONE EYE LOCATION  

E-print Network

EFFECTIVENESS OF QUIKSCAT'S ULTRA-HIGH RESOLUTION IMAGES IN DETERMINING TROPICAL CYCLONE EYE be enhanced to yield a 2.5km ultra-high resolution (UHR) product that can be used to identify hurricane eye centers more accurately. A comparison is made between the ana- lyst's choice of eye location based on UHR

Long, David G.

95

Imaging of the lens capsule with an ultrahigh-resolution spectral optical coherence tomography prototype based on a femtosecond laser  

Microsoft Academic Search

AimTo demonstrate the applicability of ultrahigh-speed, ultrahigh-resolution spectral optical coherence tomography (SOCT) to cross-sectional imaging of the capsular bag in vivo.MethodsThe ultrahigh-speed and ultrahigh-resolution SOCT prototype was designed and constructed at Nicolaus Copernicus University (Torun, Poland). To obtain an ultrahigh speed up to 100 000 lines\\/s a new spectrometer with fast CMOS line-scan camera was built. A femtosecond laser with

Bartlomiej J Kaluzny; Michalina Gora; Karol Karnowski; Ireneusz Grulkowski; Andrzej Kowalczyk; Maciej Wojtkowski

2010-01-01

96

Three-dimensional retinal imaging with ultrahigh resolution Fourier\\/spectral domain optical coherence tomography  

Microsoft Academic Search

Ultrahigh resolution OCT using broadband light sources achieves improved axial image resolutions of ~2-3 um compared to standard 10 um resolution OCT used in current commercial instruments. High-speed OCT using Fourier\\/spectral domain detection enables dramatic increases in imaging speeds. 3D OCT retinal imaging is performed in human subjects using high-speed, ultrahigh resolution OCT, and the concept of an OCT fundus

Vivek J. Srinivasan; Maciej Wojtkowski; Tony Ko; Mariana Carvalho; James Fujimoto; Jay Duker; Joel Schumann; Andrzej Kowalczyk

2005-01-01

97

Gamma ray camera  

DOEpatents

A gamma ray camera for detecting rays emanating from a radiation source such as an isotope. The gamma ray camera includes a sensor array formed of a visible light crystal for converting incident gamma rays to a plurality of corresponding visible light photons, and a photosensor array responsive to the visible light photons in order to form an electronic image of the radiation therefrom. The photosensor array is adapted to record an integrated amount of charge proportional to the incident gamma rays closest to it, and includes a transparent metallic layer, photodiode consisting of a p-i-n structure formed on one side of the transparent metallic layer, and comprising an upper p-type layer, an intermediate layer and a lower n-type layer. In the preferred mode, the scintillator crystal is composed essentially of a cesium iodide (CsI) crystal preferably doped with a predetermined amount impurity, and the p-type upper intermediate layers and said n-type layer are essentially composed of hydrogenated amorphous silicon (a-Si:H). The gamma ray camera further includes a collimator interposed between the radiation source and the sensor array, and a readout circuit formed on one side of the photosensor array.

Perez-Mendez, Victor (Berkeley, CA)

1997-01-01

98

Ultra-high resolution optical trap with single fluorophore sensitivity”  

PubMed Central

We present a single-molecule instrument that combines a timeshared ultra-high resolution dual optical trap interlaced with a confocal fluorescence microscope. In a demonstration experiment, individual single-fluorophore labeled DNA oligonucleotides were observed to bind and unbind to complementary DNA suspended between two trapped beads. Simultaneous with the single-fluorophore detection, coincident angstrom-scale changes in tether extension could be clearly observed. Fluorescence readout allowed us to determine the duplex melting rate as a function of force. The new instrument will enable the simultaneous measurement of angstrom-scale mechanical motion of individual DNA-binding proteins (e.g., single base pair stepping of DNA translocases) along with the detection of fluorescently labeled protein properties (e.g., internal configuration). PMID:21336286

Comstock, Matthew J; Ha, Taekjip; Chemla, Yann R

2013-01-01

99

Characteristics of the Telescope for High Energy Gamma-ray Astronomy Selected for Definition Studies on the Gamma Ray Observatory  

NASA Technical Reports Server (NTRS)

The high energy gamma-ray selected for definition studies on the Gamma Ray Observatory provides a substantial improvement in observational capability over earlier instruments. It will have about 20 times more sensitivity, cover a much broader energy range, have considerably better energy resolution and provide a significantly improved angular resolution. The design and performance are described.

Hughes, E. B.; Hofstadter, R.; Johansson, A.; Rolfe, J.; Bertsch, D. L.; Cruickshank, W. J.; Ehrmann, C. H.; Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.

1979-01-01

100

GAMMA RAY IMAGING FOR ENVIRONMENTAL REMEDIATION  

EPA Science Inventory

The research is a three year development program to apply high resolution gamma-ray imaging technologies to environmental remediation of radioactive hazards. High resolution, position-sensitive germanium detectors are being developed at the Naval Research Laboratory for space app...

101

Hypernuclear gamma rays  

SciTech Connect

The observation of hypernuclear ..gamma.. rays pprovides a method of determining the spin dependence of the ..lambda..-nucleon interaction with a sensitivity not approachable by other means in the forseeable future. The transitions of primary interest are those between states that differ only in the orientation of the spin of the ..lambda.. particle with respect to the angular momentum of the nuclear core. The effective ..lambda..-nucleon interaction can be specified by a small number of ..gamma..-ray measurements. A program of experiments directed at this goal is in progress at Brookhaven National Laboratory. This paper reviews the status of the subject with emphasis on the recent experiment to measure ground state doublet splittings using germanium ..gamma..-ray detectors.

May, M.

1985-01-01

102

A high resolution liquid xenon imaging telescope for 0.3-10 MeV gamma-ray astrophysics: Construction and initial balloon flights  

Microsoft Academic Search

The results achieved during the third year grant period are summarized. These achievements include the time stability of the charge gain of the demonstration of the 10 liter LXe-TPC gamma-ray detector prototype; the efficiency of the Xe scintillation light signal to trigger gamma-ray events with a minimum energy deposition of about 300 keV was measured to be higher than 90%;

Elena Aprile

1995-01-01

103

Response of a high-resolution high-energy photon spectrometer (HHS) to monochromatic high-energy gamma rays  

Microsoft Academic Search

The response function of a high-resolution high-energy photon spectrometer (HHS), consisting of a twin Ge detector and BGO (Bi3Ge4O12) anti-coincidence shields, has been measured for 10.763MeV monochromatic ?-rays generated in a resonant reaction 27Al(p,?)28Si. The experimental response functions measured with and without the anti-coincidence were compared with results by Monte Carlo simulations, in which a pulse-height degradation effect associated with

H. Harada; K. Furutaka; S. Nakamura; K. Osaka; H. Akimune; H. Utsunomiya; T. Ohsaki; M. Igashira

2005-01-01

104

Gamma Ray Astronomy  

NASA Technical Reports Server (NTRS)

The project has progressed successfully during this period of performance. The highlights of the Gamma Ray Astronomy teams efforts are: (1) Support daily BATSE data operations, including receipt, archival and dissemination of data, quick-look science analysis, rapid gamma-ray burst and transient monitoring and response efforts, instrument state-of-health monitoring, and instrument commanding and configuration; (2) On-going scientific analysis, including production and maintenance of gamma-ray burst, pulsed source and occultation source catalogs, gamma-ray burst spectroscopy, studies of the properties of pulsars and black holes, and long-term monitoring of hard x-ray sources; (3) Maintenance and continuous improvement of BATSE instrument response and calibration data bases; (4) Investigation of the use of solid state detectors for eventual application and instrument to perform all sky monitoring of X-Ray and Gamma sources with high sensitivity; and (5) Support of BATSE outreach activities, including seminars, colloquia and World Wide Web pages. The highlights of this efforts can be summarized in the publications and presentation list.

Wu, S. T.

2000-01-01

105

Celestial gamma ray study  

NASA Technical Reports Server (NTRS)

This report documents the research activities performed by Stanford University investigators as part of the data reduction effort and overall support of the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. This report is arranged chronologically, with each subsection detailing activities during roughly a one year period of time, beginning in June 1991.

Michelson, Peter F.

1995-01-01

106

Ultrahigh-speed ultrahigh-resolution adaptive optics: optical coherence tomography system for in-vivo small animal retinal imaging  

NASA Astrophysics Data System (ADS)

Small animal models of human retinal diseases are a critical component of vision research. In this report, we present an ultrahigh-resolution ultrahigh-speed adaptive optics optical coherence tomography (AO-OCT) system for small animal retinal imaging (mouse, fish, etc.). We adapted our imaging system to different types of small animals in accordance with the optical properties of their eyes. Results of AO-OCT images of small animal retinas acquired with AO correction are presented. Cellular structures including nerve fiber bundles, capillary networks and detailed double-cone photoreceptors are visualized.

Jian, Yifan; Xu, Jing; Zawadzki, Robert J.; Sarunic, Marinko V.

2013-03-01

107

Gamma rays from Galactic pulsars  

E-print Network

Gamma rays from young pulsars and milli-second pulsars are expected to contribute to the diffuse gamma-ray emission measured by the {\\it Fermi} Large Area Telescope (LAT) at high latitudes. We derive the contribution of the pulsars undetected counterpart by using information from radio to gamma rays and we show that they explain only a small fraction of the isotropic diffuse gamma-ray background.

Calore, Francesca; Donato, Fiorenza

2014-01-01

108

High-Resolution Spectroscopy of Gamma-Ray Lines from the X-Class Solar Flare of 23 July, 2002  

E-print Network

The Reuven Ramaty High Energy Solar Spectroscopy Imager (RHESSI) has obtained the first high-resolution measurements of nuclear de-excitation lines produced by energetic ions accelerated in a solar flare, a GOES X4.8 event occurring on 23 July, 2002 at a heliocentric angle of 73 degrees. Lines of neon, magnesium, silicon, iron, carbon, and oxygen were resolved for the first time. They exhibit Doppler redshifts of 0.1--0.8% and broadening of 0.1--2.1% (FWHM), generally decreasing with mass. The measured redshifts are larger than expected for a model of an interacting ion distribution isotropic in the downward hemisphere in a radial magnetic field. Possible interpretations of the large redshifts include 1) an inclination of the loop magnetic field to the solar surface so that the ion distribution is oriented more directly away from the observer, and 2) extreme beaming of the ions downward along a magnetic field normal to the solar surface. Bulk downward motion of the plasma in which the accelerated ions interact can be ruled out.

David M. Smith; Gerald H. Share; Ronald J. Murphy; Richard A. Schwartz; Albert Y. Shih; Robert P. Lin

2003-06-14

109

New shield for gamma-ray spectrometry  

NASA Technical Reports Server (NTRS)

Gamma-ray shield that can be evacuated, refilled with a clean gas, and pressurized for exclusion of airborne radioactive contaminants effectively lowers background noise. Under working conditions, repeated evacuation and filling procedures have not adversely affected the sensitivity and resolution of the crystal detector.

Brar, S. S.; Gustafson, P. F.; Nelson, D. M.

1969-01-01

110

Technology Needs for Gamma Ray Astronomy  

NASA Technical Reports Server (NTRS)

Gamma ray astronomy is currently in an exciting period of multiple missions and a wealth of data. Results from INTEGRAL, Fermi, AGILE, Suzaku and Swift are making large contributions to our knowledge of high energy processes in the universe. The advances are due to new detector and imaging technologies. The steps to date have been from scintillators to solid state detectors for sensors and from light buckets to coded aperture masks and pair telescopes for imagers. A key direction for the future is toward focusing telescopes pushing into the hard X-ray regime and Compton telescopes and pair telescopes with fine spatial resolution for medium and high energy gamma rays. These technologies will provide finer imaging of gamma-ray sources. Importantly, they will also enable large steps forward in sensitivity by reducing background.

Gehrels, Neil

2011-01-01

111

Gamma-Ray Imaging for Explosives Detection  

NASA Technical Reports Server (NTRS)

We describe a gamma-ray imaging camera (GIC) for active interrogation of explosives being developed by NASA/GSFC and NSWCICarderock. The GIC is based on the Three-dimensional Track Imager (3-DTI) technology developed at GSFC for gamma-ray astrophysics. The 3-DTI, a large volume time-projection chamber, provides accurate, approx.0.4 mm resolution, 3-D tracking of charged particles. The incident direction of gamma rays, E, > 6 MeV, are reconstructed from the momenta and energies of the electron-positron pair resulting from interactions in the 3-DTI volume. The optimization of the 3-DTI technology for this specific application and the performance of the GIC from laboratory tests is presented.

deNolfo, G. A.; Hunter, S. D.; Barbier, L. M.; Link, J. T.; Son, S.; Floyd, S. R.; Guardala, N.; Skopec, M.; Stark, B.

2008-01-01

112

Cosmic gamma-ray bursts  

NASA Technical Reports Server (NTRS)

A review of the cosmic gamma-ray burst phenomenon is presented. Both the light curves and the energy spectra of these short transient events display a great diversity. However, rapid rise times and periodicities sometimes observed in the light curves suggest a compact object origin. Similarly, absorption and emission features in the energy spectra argue strongly in favor of this interpretation. Counterparts to gamma-bursters in other energy ranges, such as optical and sort x-ray, have still not been identified, however, leading to a large uncertainty in the distances to bursters. Although gamma-ray burst sources have not yet been observed to repeat, numerous bursts from three objects which may be related to the gamma-bursters, called Soft Gamma Repeaters, have been recorded; there is weak evidence that they may be relatively distant on a galactic scale. Future missions, particularly those emphasizing high energy, time, and/or spatial resolution, as well as a multiwavelength approach, are likely to advance our understanding of this enigmatic phenomenon.

Hurley, K.

1991-01-01

113

Development of a high resolution liquid xenon imaging chamber for gamma-ray astronomy. Final Technical Report, 1 May 1988 - 30 Apr. 1990  

Microsoft Academic Search

The objective was to develop the technology of liquid xenon (LXe) detectors for spectroscopy and imaging of gamma rays from astrophysical sources emitting in the low to medium energy regime. In particular, the technical challenges and the physical processes relevant to the realization of the LXe detector operated as a Time Projection Chamber (TPC) were addressed and studied. Experimental results

Aprile

1991-01-01

114

A high resolution liquid xenon imaging telescope for 0.3-10 MeV gamma-ray astrophysics: Construction and initial balloon flights  

NASA Technical Reports Server (NTRS)

An instrument is described which will provide a direct image of gamma-ray line or continuum sources in the energy range 300 keV to 10 MeV. The use of this instrument to study the celestial distribution of the (exp 26)Al isotope by observing the 1.809 MeV deexcitation gamma-ray line is illustrated. The source location accuracy is 2' or better. The imaging telescope is a liquid xenon time projection chamber coupled with a coded aperture mask (LXe-CAT). This instrument will confirm and extend the COMPTEL observations from the Compton Gamma-Ray Observatory (CGRO) with an improved capability for identifying the actual Galactic source or sources of (exp 26)Al, which are currently not known with certainty. sources currently under consideration include red giants on the asymptotic giant branch (AGB), novae, Type 1b or Type 2 supernovae, Wolf-Rayet stars and cosmic-rays interacting in molecular clouds. The instrument could also identify a local source of the celestial 1.809 MeV gamma-ray line, such as a recent nearby supernova.

Aprile, Elena

1994-01-01

115

Gamma-Ray Localization of Terrestrial Gamma-Ray Flashes  

SciTech Connect

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by the AGILE Mini-Calorimeter. We detect 8 TGFs with gamma-ray photons of energies above 20 MeV localized by the AGILE gamma-ray imager with an accuracy of {approx}5-10 deg. at 50 MeV. Remarkably, all TGF-associated gamma rays are compatible with a terrestrial production site closer to the subsatellite point than 400 km. Considering that our gamma rays reach the AGILE satellite at 540 km altitude with limited scattering or attenuation, our measurements provide the first precise direct localization of TGFs from space.

Marisaldi, M.; Labanti, C.; Fuschino, F.; Bulgarelli, A.; Trifoglio, M.; Di Cocco, G.; Gianotti, F. [INAF-IASF Bologna, Via Gobetti 101, I-40129 Bologna (Italy); Argan, A.; De Paris, G. [INAF, Viale del Parco Mellini 84, Roma (Italy); Trois, A.; Del Monte, E.; Costa, E.; Di Persio, G.; Donnarumma, I.; Evangelista, Y.; Feroci, M.; Lazzarotto, F.; Pacciani, L.; Rubini, A.; Sabatini, S. [INAF-IASF Roma, via del Fosso del Cavaliere 100, I-00133 Roma (Italy)

2010-09-17

116

Ultra-high resolution and high-brightness AMOLED  

NASA Astrophysics Data System (ADS)

As part of its continuing effort to improve both the resolution and optical performance of AMOLED microdisplays, eMagin has recently developed an SXGA (1280×3×1024) microdisplay under a US Army RDECOM CERDEC NVESD contract that combines the world's smallest OLED pixel pitch with an ultra-high brightness green OLED emitter. This development is aimed at next-generation HMD systems with "see-through" and daylight imaging requirements. The OLED pixel array is built on a 0.18-micron CMOS backplane and contains over 4 million individually addressable pixels with a pixel pitch of 2.7 × 8.1 microns, resulting in an active area of 0.52 inches diagonal. Using both spatial and temporal enhancement, the display can provide over 10-bits of gray-level control for high dynamic range applications. The new pixel design also enables the future implementation of a full-color QSXGA (2560 × RGB × 2048) microdisplay in an active area of only 1.05 inch diagonal. A low-power serialized low-voltage-differential-signaling (LVDS) interface is integrated into the display for use as a remote video link for tethered systems. The new SXGA backplane has been combined with the high-brightness green OLED device developed by eMagin under an NVESD contract. This OLED device has produced an output brightness of more than 8000fL with all pixels on; lifetime measurements are currently underway and will presented at the meeting. This paper will describe the operational features and first optical and electrical test results of the new SXGA demonstrator microdisplay.

Wacyk, Ihor; Ghosh, Amal; Prache, Olivier; Draper, Russ; Fellowes, Dave

2012-06-01

117

The LXeCAT instrument for gamma-ray astrophysics  

NASA Technical Reports Server (NTRS)

The Liquid Xenon Coded Aperture Telescope (LXeCAT) and its capability to image astrophysical gamma-ray sources in the MeV region is described. The gamma-ray detector is a Liquid Xenon Time Projection Chamber (LXeTPC) triggered by the primary scintillation light. Effective background rejection is a direct consequence of the intrinsic three-dimensional imaging capability of the LXeTPC. Initial results with a 10 liter prototype confirm an energy resolution of 6% FWHM, a position resolution of 1 mm RMS and a light triggering efficiency higher than 90% for 1 MeV gamma-rays.

Aprile, E.; Xu, F.; Zhou, M.; Doke, T.; Kikuchi, J.; Masuda, K.; Chupp, E. L.; Dunphy, P. P.; Fishman, G.; Pendelton, G.

1995-01-01

118

Observing terrestrial gamma ray flashes  

NASA Astrophysics Data System (ADS)

Terrestrial Gamma Ray Flash Workshop; Huntsville, Alabama, 13-14 July 2011 Terrestrial gamma ray flashes (TGFs) were the focus of a workshop held at the University of Alabama in Huntsville (UAH), with observation and theory well represented by the 38 attendees. Discovered in 1991 as brief (submillisecond), bright flashes of gamma rays detected over regions of thunderstorm activity by the spaceborne Burst And Transient Source Experiment, TGFs may be entering an observational golden era. Three space-based gamma ray telescopes currently make TGFs a scientific priority.

Connaughton, Valerie; Briggs, Michael S.

2011-12-01

119

Gamma-ray imaging with germanium detectors  

NASA Technical Reports Server (NTRS)

Externally segmented germanium detectors promise a breakthrough in gamma-ray imaging capabilities while retaining the superb energy resolution of germanium spectrometers. By combining existing position-sensitive detectors with an appropriate code aperture, two-dimensional imaging with 0.2-deg angular resolution becomes practical for a typical balloon experiment. Much finer resolutions are possible with larger separations between detectors and the coded aperture as would be applicable for space-based or lunar-based observatories. Two coaxial germanium detectors divided into five external segments have been fabricated and have undergone extensive performance evaluation and imaging testing in our laboratory. These tests together with detailed Monte Carlo modeling calculations have demonstrated the great promise of this sensor technology for future gamma-ray missions.

Mahoney, W. A.; Callas, J. L.; Ling, J. C.; Radocinski, R. G.; Skelton, R. T.; Varnell, L. S.; Wheaton, W. A.

1993-01-01

120

Ultrahigh-Resolution Optical Coherence Tomography with LED-Phosphor-Based Broadband Light Source  

NASA Astrophysics Data System (ADS)

This study proposed and demonstrated the potential use of LED phosphors as a simple light source for ultrahigh-resolution spectral-domain optical coherence tomography (SD-OCT) in the visible regime. Excited by a 405 nm diode laser, broadband spontaneous emission from three different LED phosphors was generated. The best axial resolution was 1.7 µm in air, and finally, corresponding three-dimensional (3D) ultrahigh-resolution SD-OCT imaging was performed with the proposed broadband light source.

Tsai, Meng-Tsan; Hung, Jeng-Jie; Chan, Ming-Che

2013-12-01

121

Spectral interference corrections for the measurement of (238)U in materials rich in thorium by a high resolution gamma-ray spectrometry.  

PubMed

In this study, the spectral interferences are investigated for the analytical peaks at 63.3 keV of (234)Th and 1001.0 keV of (234m)Pa, which are often used in the measurement of (238)U activity by the gamma-ray spectrometry. The correction methods are suggested to estimate the net peak areas of the gamma-rays overlapping the analytical peaks, due to the contribution of (232)Th that may not be negligible in materials rich in natural thorium. The activity results for the certified reference materials (CRMs) containing U and Th were measured with a well type Ge detector. The self-absorption and true coincidence-summing (TCS) effects were also taken into account in the measurements. It is found that ignoring the contributions of the interference gamma-rays of (232)Th and (235)U to the mixed peak at 63.3 keV of (234)Th ((238)U) leads to the remarkably large systematic influence of 0.8-122% in the measured (238)U activity, but in case of ignoring the contribution of (232)Th via the interference gamma-ray at 1000.7 keV of (228)Ac to the mixed peak at 1001 keV of (234m)Pa ((238)U) results in relatively smaller systematic influence of 0.05-3%, depending on thorium contents in the samples. The present results showed that the necessary correction for the spectral interferences besides self-absorption and TCS effects is also very important to obtain more accurate (238)U activity results. Additionally, if one ignores the contribution of (232)Th to both (238)U and (40)K activities in materials, the maximum systematic influence on the effective radiation dose is estimated to be ~6% and ~1% via the analytical peaks at 63.3 and 1001 keV for measurement of the (238)U activity, respectively. PMID:19683454

Yücel, H; Solmaz, A N; Köse, E; Bor, D

2009-11-01

122

Digital Pulse Processing and Gamma Ray Tracking  

NSDL National Science Digital Library

Two of the big changes in new generations of Nuclear Physics instrumentation will be the incorporation of digital processing and the use of gamma ray tracking. The Nuclear Physics Group at Daresbury has set up a project to investigate digital pulse processing for gamma ray detectors and how best to implement gamma ray tracking in large Germanium gamma ray detectors. Topics on this site include but are not limited to: gamma ray tracking, overview of the Gamma Ray Tracking Project, pictures of one of the tracking gamma ray detectors (TIGRE), pictures of test experiment, gamma ray tracking project publications, and links to other gamma ray tracking pages.

2010-09-21

123

Dual SLO/T-scan based en face ultrahigh resolution OCT for ophthalmic imaging  

NASA Astrophysics Data System (ADS)

We report a versatile imaging system combining scanning laser ophthalmoscopy (SLO) and T-scan based en face ultrahigh resolution optical coherence tomography (OCT). The image carrier is generated using the optical path difference modulation introduced by the X-Y galvo-scanner mirrors specific to en face OCT (without optical modulators in the reference arm). The light source is a compact superluminescent diode based source with 150 nm FWHM spectrum, centered at 890 nm. We demonstrate en face B-scan and C-scan ultrahigh resolution OCT imaging of the human retina in vivo, with an axial resolution of 3.2 ?m in tissue. The system is capable of acquiring large lateral size ultrahigh resolution OCT scans of a maximum field size of 20°. The acquisition speed is up to 2 frames/s for both OCT B-scans and C-scans. The measured system sensitivity is more than 98 dB, for a power level to the target of 1 mW and maximum lateral scan size. The C-scans are, to the best of our knowledge, the first and the largest size reported ultrahigh resolution C-scans of the human retina in vivo. The instrument is assembled on a chin rest and ready to be used for clinical imaging. SLO and ultrahigh resolution OCT C-scans are acquired simultaneously and displayed side by side. This allows users in a clinical environment to correlate details of the same feature in the area of interest in both images and also choose precisely in the SLO image the location where to perform the ultrahigh resolution en face B-scan.

Cucu, Radu G.; Podoleanu, Adrian Gh.; Pedro, Justin; Rogers, John A.; Rosen, Richard B.; van Velthoven, Mirjam; Garcia, Patricia; Shidlovski, Vladimir

2006-02-01

124

The solar gamma ray and neutron capabilities of COMPTEL on the Gamma Ray Observatory  

NASA Technical Reports Server (NTRS)

The imaging Compton telescope COMPTEL on the Gamma Ray Observatory (GRO) has unusual spectroscopic capabilities for measuring solar gamma-ray and neutron emission. The launch of the GRO is scheduled for June 1990 near the peak of the sunspot cycle. With a 30 to 40 percent probability for the Sun being in the COMPTEL field-of-view during the sunlit part of an orbit, a large number of flares will be observed above the 800 keV gamma-ray threshold of the telescope. The telescope energy range extends to 30 MeV with high time resolution burst spectra available from 0.1 to 10 MeV. Strong Compton tail suppression of instrumental gamma-ray interactions will facilitate improved spectral analysis of solar flare emissions. In addition, the high signal to noise ratio for neutron detection and measurement will provide new neutron spectroscopic capabilities. Specifically, a flare similar to that of 3 June 1982 will provide spectroscopic data on greater than 1500 individual neutrons, enough to construct an unambiguous spectrum in the energy range of 20 to 200 MeV. Details of the instrument and its response to solar gamma-rays and neutrons will be presented.

Ryan, James M.; Lockwood, John A.

1989-01-01

125

Mirrors for gamma ray astronomy  

Microsoft Academic Search

The atmosperic Cherenkov technique is widely used for the detection of high energy gamma rays (Egamma > 1011 eV) from space [L.K. Resvanis et al., Astrophys. J. Lett. 328 (1988) L9]. Most current detectors use large arrays of optical mirrors to collect and focus the Cherenkov light from gamma ray induced showers onto photomultipliers. We describe herein a simple and

F. J. Loeffler

1993-01-01

126

The Compton Gamma Ray Observatory  

Microsoft Academic Search

The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments,

N. Gehrels; E. Chipman; D. Kniffen

1994-01-01

127

The Compton Gamma Ray Observatory  

NASA Technical Reports Server (NTRS)

The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

Gehrels, N.; Chipman, E.; Kniffen, D.

1994-01-01

128

The Compton Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

Gehrels, N.; Chipman, E.; Kniffen, D.

1994-06-01

129

Gamma Ray Bursts - Observations  

NASA Technical Reports Server (NTRS)

We are in an exciting period of discovery for gamma-ray bursts. The Swift observatory is detecting 100 bursts per year, providing arcsecond localizations and sensitive observations of the prompt and afterglow emission. The Fermi observatory is observing 250 bursts per year with its medium-energy GRB instrument and about 10 bursts per year with its high-energy LAT instrument. In addition, rapid-response telescopes on the ground are providing new capabilities to study optical emission during the prompt phase and spectral signatures of the host galaxies. The combined data set is enabling great advances in our understanding of GRBs including afterglow physics, short burst origin, and high energy emission.

Gehrels, N.; Cannizzo, J. K.

2010-01-01

130

Gamma-Ray Pulsar Revolution  

NASA Astrophysics Data System (ADS)

Isolated neutron stars (INSs) were the first sources identified in the field of high-energy gamma-ray astronomy. In the 1970s, only two sources had been identified, the Crab and Vela pulsars. However, although few in number, these objects were crucial in establishing the very concept of a gamma-ray source. Moreover, they opened up significant discovery space in both the theoretical and phenomenological fronts. The need to explain the copious gamma-ray emission of these pulsars led to breakthrough developments in understanding the structure and physics of neutron star (NS) magnetospheres. In parallel, the 20-year-long chase to understand the nature of Geminga unveiled the existence of a radio-quiet, gamma-ray-emitting INS, adding a new dimension to the INS family. We are living through an extraordinary time of discovery. The current generation of gamma-ray detectors has vastly increased the population of known gamma-ray-emitting NSs. The 100 mark was crossed in 2011, and we are now over 150. The gamma-ray-emitting NS population exhibits roughly equal numbers of radio-loud and radio-quiet young INSs, plus an astonishing, and unexpected, group of isolated and binary millisecond pulsars (MSPs). The number of MSPs is growing so rapidly that they are on their way to becoming the most numerous members of the family of gamma-ray-emitting NSs. Even as these findings have set the stage for a revolution in our understanding of gamma-ray-emitting NSs, long-term monitoring of the gamma-ray sky has revealed evidence of flux variability in the Crab Nebula as well as in the pulsed emission from PSR J2021+4026, challenging a four-decades-old, constant-emission paradigm. Now we know that both pulsars and their nebulae can, indeed, display variable emission.

Caraveo, Patrizia A.

2014-08-01

131

A directional low energy gamma-ray detector  

NASA Technical Reports Server (NTRS)

The sensitivity of a directional gamma ray detector, which relies on blocking a source to determine its direction and energy spectrum, is calculated and compared to the more conventional well-shaped shielded detectors. It is shown that such an anticollimator detection system provides a basis for measuring the celestial diffuse gamma ray background, gamma ray sources and bursts with good energy, angular, and time resolution, and that additionally the system is 20 to 50 times as sensitive as conventional detectors when compared on a per unit mass basis.

Morfill, G.; Pieper, G. F.

1973-01-01

132

Simulation of Gamma Rays from Proton Interaction in Local Galaxies  

SciTech Connect

The GLAST Large Area Telescope will provide unprecedented opportunities to detect cosmic GeV gamma rays, thanks to its large effective area, field of view and angular resolution compared with earlier telescopes. We present here the possibility of detecting GeV gamma rays produced by interactions of accelerated protons (or hadrons) with surrounding ambient material. Sources where such detection could be made include local galaxies, such as the Large Magellanic Cloud (LMC), molecular clouds and other extended sources. We have calculated the expected gamma-ray spectrum for an isotropic distribution of protons in the LMC and simulated a one-year GLAST-LAT observation.

Karlsson, Niklas; /SLAC /Stockholm U.; Cohen-Tanugi, Johann; Kamae, Tuneyoshi; Tajima, Hiroyasu; /SLAC /KIPAC, Menlo Park

2007-06-06

133

Sub-aperture coherence method to realize ultra-high resolution laser beam deflection  

NASA Astrophysics Data System (ADS)

A new phase controlled method is proposed to realize ultra-high resolution laser beam deflection on the physics of coherence between sub-apertures on one device of liquid crystal optical phased array (LC-OPA). Sub-apertures are electronically switchable and divided from a uniform device of LC-OPA. In the approach of sub-aperture coherence (SAC), numerical simulation results show the characteristics of far field including SAC steering step and angular width. Meanwhile, the method of SAC has also been verified by experiments showing a good agreement with the simulation results of ultra-high resolution beam deflection.

Tang, Zhenhui; Wang, Xiangru; Huang, Ziqiang; Tan, Qinggui; Duan, Yingying; Suo, Guoguo; Du, Jing; Qiu, Qi

2015-01-01

134

Development of a gamma-ray detector with iridium transition edge sensor coupled to a Pb absorber  

E-print Network

We have recently started to develop a high-resolution gamma-ray spectrometer for material defect analysis. Our gamma-ray detector is a microcalorimeter consisting of an iridium/gold bilayer transition edge sensor (TES) ...

Leman, Steven W.

135

High energy gamma ray astronomy  

NASA Technical Reports Server (NTRS)

High energy gamma ray astronomy has evolved with the space age. Nonexistent twenty-five years ago, there is now a general sketch of the gamma ray sky which should develop into a detailed picture with the results expected to be forthcoming over the next decade. The galactic plane is the dominant feature of the gamma ray sky, the longitude and latitude distribution being generally correlated with galactic structural features including the spiral arms. Two molecular clouds were already seen. Two of the three strongest gamma ray sources are pulsars. The highly variable X-ray source Cygnus X-3 was seen at one time, but not another in the 100 MeV region, and it was also observed at very high energies. Beyond the Milky Way Galaxy, there is seen a diffuse radiation, whose origin remains uncertain, as well as at least one quasar, 3C 273. Looking to the future, the satellite opportunities for high energy gamma ray astronomy in the near term are the GAMMA-I planned to be launched in late 1987 and the Gamma Ray Observatory, scheduled for launch in 1990. The Gamma Ray Observatory will carry a total of four instruments covering the entire energy range from 30,000 eV to 3 x 10 to the 10th eV with over an order of magnitude increase in sensitivity relative to previous satellite instruments.

Fichtel, Carl E.

1987-01-01

136

Studies of Cosmic Rays with GeV Gamma Rays  

E-print Network

We describe the role of GeV gamma-ray observations with GLAST-LAT (Gamma-ray Large Area Space Telescope - Large Area Telescope) in identifying interaction sites of cosmic-ray proton (or hadrons) with interstellar medium (ISM). We expect to detect gamma rays from neutral pion decays in high-density ISM regions in the Galaxy, Large Magellanic Cloud, and other satellite galaxies. These gamma-ray sources have been detected already with EGRET (Energetic Gamma Ray Experiment Telescope) as extended sources (eg. LMC and Orion clouds) and GLAST-LAT will detect many more with a higher spatial resolution and in a wider spectral range. We have developed a novel image restoration technique based on the Richardson-Lucy algorithm optimized for GLAST-LAT observation of extended sources. Our algorithm calculates PSF (point spread function) for each event. This step is very important for GLAST-LAT and EGRET image analysis since PSF varies more than one order of magnitude from one gamma ray to another depending on its energy as well as its impact point and angle in the instrument. The GLAST-LAT and EGRET image analysis has to cope with Poisson fluctuation due to low number of detected photons for most sources. Our technique incorporates wavelet filtering to minimize effects due to the fluctuation. Preliminary studies on some EGRET sources are presented, which shows potential of this novel image restoration technique for the identification and characterisation of extended gamma-ray sources.

Hiroyasu Tajima; Tuneyoshi Kamae; Stefano Finazzi; Johann Cohen-Tanugi; James Chiang

2007-05-10

137

X-ray and gamma ray astronomy detectors  

NASA Technical Reports Server (NTRS)

X-ray and gamma ray astronomy was made possible by the advent of space flight. Discovery and early observations of celestial x-rays and gamma rays, dating back almost 40 years, were first done with high altitude rockets, followed by Earth-orbiting satellites> once it became possible to carry detectors above the Earth's atmosphere, a new view of the universe in the high-energy part of the electromagnetic spectrum evolved. Many of the detector concepts used for x-ray and gamma ray astronomy were derived from radiation measuring instruments used in atomic physics, nuclear physics, and other fields. However, these instruments, when used in x-ray and gamma ray astronomy, have to meet unique and demanding requirements related to their operation in space and the need to detect and measure extremely weak radiation fluxes from celestial x-ray and gamma ray sources. Their design for x-ray and gamma ray astronomy has, therefore, become a rather specialized and rapidly advancing field in which improved sensitivity, higher energy and spatial resolution, wider spectral coverage, and enhanced imaging capabilities are all sought. This text is intended as an introduction to x-ray and gamma ray astronomy instruments. It provides an overview of detector design and technology and is aimed at scientists, engineers, and technical personnel and managers associated with this field. The discussion is limited to basic principles and design concepts and provides examples of applications in past, present, and future space flight missions.

Decher, Rudolf; Ramsey, Brian D.; Austin, Robert

1994-01-01

138

Ultrahigh-speed imaging of the rat retina using ultrahigh-resolution spectral/Fourier domain OCT  

NASA Astrophysics Data System (ADS)

We performed OCT imaging of the rat retina at 70,000 axial scans per second with ~3 ?m axial resolution. Three-dimensional OCT (3D-OCT) data sets of the rat retina were acquired. The high speed and high density data sets enable improved en face visualization by reducing eye motion artifacts and improve Doppler OCT measurements. Minimal motion artifacts were visible and the OCT fundus images offer more precise registration of individual OCT images to retinal fundus features. Projection OCT fundus images show features such as the nerve fiber layer, retinal capillary networks and choroidal vasculature. Doppler OCT images and quantitative measurements show pulsatility in retinal blood vessels. Doppler OCT provides noninvasive in vivo quantitative measurements of retinal blood flow properties and may benefit studies of diseases such as glaucoma and diabetic retinopathy. Ultrahigh speed imaging using ultrahigh resolution spectral / Fourier domain OCT promises to enable novel protocols for measuring small animal retinal structure and retinal blood flow. This non-invasive imaging technology is a promising tool for monitoring disease progression in rat and mouse models to assess ocular disease pathogenesis and response to treatment.

Liu, Jonathan J.; Potsaid, Benjamin; Chen, Yueli; Gorczynska, Iwona; Srinivasan, Vivek J.; Duker, Jay S.; Fujimoto, James G.

2010-02-01

139

Gamma-Ray Localization of Terrestrial Gamma-Ray Flashes  

Microsoft Academic Search

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by

M. Marisaldi; A. Argan; A. Trois; A. Giuliani; M. Tavani; C. Labanti; F. Fuschino; A. Bulgarelli; F. Longo; G. Barbiellini; E. Del Monte; E. Moretti; M. Trifoglio; E. Costa; P. Caraveo; P. W. Cattaneo; A. Chen; F. D'Ammando; G. de Paris; G. Di Cocco; G. di Persio; I. Donnarumma; Y. Evangelista; M. Feroci; A. Ferrari; M. Fiorini; T. Froysland; M. Galli; F. Gianotti; I. Lapshov; F. Lazzarotto; P. Lipari; S. Mereghetti; A. Morselli; L. Pacciani; A. Pellizzoni; F. Perotti; P. Picozza; G. Piano; M. Pilia; M. Prest; G. Pucella; M. Rapisarda; A. Rappoldi; A. Rubini; S. Sabatini; P. Soffitta; E. Striani; E. Vallazza; S. Vercellone; V. Vittorini; A. Zambra; D. Zanello; L. A. Antonelli; S. Colafrancesco; S. Cutini; P. Giommi; F. Lucarelli; C. Pittori; P. Santolamazza; F. Verrecchia; L. Salotti

2010-01-01

140

The diffuse galactic gamma ray emission  

NASA Technical Reports Server (NTRS)

The EGRET (Energetic Gamma-Ray Experiment Telescope) detector will provide a much more detailed view of the diffuse galactic gamma ray intensity in terms of higher resolution, greater statistical significance, and broader energy range than earlier missions. These observations will furnish insight into a number of very important questions related to the dynamics and structure of the Galaxy. A diffuse emission model is being developed that incorporates the latest information on matter distribution and source functions. In addition, it is tailored to the EGRET instrument response functions. The analysis code of the model maintains flexibility to accommodate the quality of the data that is anticipated. The discussion here focuses on the issues of the distributions of matter, cosmic rays, and radiation fields, and on the important source functions that enter into the model calculation of diffuse emission.

Bertsch, David L.

1990-01-01

141

Gamma ray bursts: a 1983 overview  

SciTech Connect

Gamma ray burst observations are reviewed with mention of new gamma-ray and optical transient measurements and with discussions of the controversial, contradictory and unresolved issues that have recently emerged: burst spectra appear to fluctuate in time as rapidly as they are measured, implying that any one spectrum may be incorrect. Energy spectra can be obligingly fitted to practically any desired shape, implying, in effect, that no objective spectral resolution exists at all. Burst fluxes and temporal quantities, including the total event energy, are characterized very differently with differing instruments, implying that even elementary knowledge of their properties is instrumentally subjective. Finally, the log N-log S determinations are deficient in the weak bursts, while there is no detection of a source direction anisotropy, implying that Ptolemy was right or that burst source distance estimates are basically guesswork. These issues may remain unsolved until vastly improved instruments are flown.

Cline, T.L.

1983-10-01

142

Gamma Ray Bursts: a 1983 Overview  

NASA Technical Reports Server (NTRS)

Gamma ray burst observations are reviewed with mention of new gamma-ray and optical transient measurements and with discussions of the controversial, contradictory and unresolved issues that have recently emerged: burst spectra appear to fluctuate in time as rapidly as they are measured, implying that any one spectrum may be incorrect; energy spectra can be obligingly fitted to practically any desired shape, implying, in effect, that no objective spectral resolution exists at all; burst fluxes and temporal quantities, including the total event energy, are characterized very differently with differing instruments, implying that even elementary knowledge of their properties is instrumentally subjective; finally, the log N-log S determinations are deficient in the weak bursts, while there is no detection of a source direction anisotropy, implying that Ptolemy was right or that burst source distance estimates are basically guesswork. These issues may remain unsolved until vastly improved instruments are flown.

Cline, T. L.

1983-01-01

143

Nucleosynthesis and astrophysical gamma ray spectroscopy  

NASA Technical Reports Server (NTRS)

The HEAO-3 gamma ray spectrometer has provided evidence in the quest for the understanding of complex element formation in the universe with the discovery of Al-26 in the interstellar medium. It has demonstrated that the synthesis of intermediate mass nuclei is currently going on in the galaxy. This discovery was confirmed by the Solar Maximum Mission. The flux is peaked near the galactic center and indicates about 3 solar masses of Al-26 in the interstellar medium, with an implied ratio of Al-26/Al-27 = .00001. Several possible distributions were studied but the data gathered thus far do not allow discrimination between them. It is felt that only the spaceflight of a high resolution gamma ray spectrometer with adequate sensitivity will ultimately resolve the issue of the source of this material.

Jacobson, Allan S.

1987-01-01

144

SuperAGILE and Gamma Ray Bursts  

SciTech Connect

The solid-state hard X-ray imager of AGILE gamma-ray mission -- SuperAGILE -- has a six arcmin on-axis angular resolution in the 15-45 keV range, a field of view in excess of 1 steradian. The instrument is very light: 5 kg only. It is equipped with an on-board self triggering logic, image deconvolution, and it is able to transmit the coordinates of a GRB to the ground in real-time through the ORBCOMM constellation of satellites. Photon by photon Scientific Data are sent to the Malindi ground station at every contact. In this paper we review the performance of the SuperAGILE experiment (scheduled for a launch in the middle of 2006), after its first onground calibrations, and show the perspectives for Gamma Ray Bursts.

Pacciani, Luigi; Costa, Enrico; Del Monte, Ettore; Donnarumma, Immacolata; Evangelista, Yuri; Feroci, Marco; Frutti, Massimo; Lazzarotto, Francesco; Lapshov, Igor; Rubini, Alda; Soffitta, Paolo; Tavani, Marco [IASF-INAF Rome (Italy); Barbiellini, Guido [INFN Trieste (Italy); Mastropietro, Marcello [CNR Montelibretti (Italy); Morelli, Ennio [IASF-INAF-Bologna (Italy); Rapisarda, Massimo [ENEA Frascati (Italy)

2006-05-19

145

Spatial transform in non-conventional ultra-high resolution image-carrying fiber bundle  

Microsoft Academic Search

Restricted by the device fabrication technology, traditional scanning imaging system can not get high spatial resolution, and it's difficult to get a line array whose sensor number is over 6000. A kind of non-conventional fiber bundle is designed to couple information. Using existing small scale plane arrays to receive the signals of the fiber bundle's output can acquire ultra-high spatial

Bowen An; Junbo Gao; Guozhong Wang

2008-01-01

146

Efficient packing Fourier-transform approach for ultrahigh resolution isotopic distribution calculations.  

PubMed

Fine isotopic structure patterns resolvable by ultrahigh-resolution mass spectrometers are diagnostic of the elemental composition of moderately large compounds. Despite the proven performance of Fourier transforms algorithms to calculate accurate high resolution isotopic distribution, its application to finer ultrahigh resolving power exhibits limited performance. Fast Fourier transforms algorithm requires sampling the relevant range at equally spaced mass values, but ultrahigh resolution mass spectrum displays highly localized complex patterns (peaks) separated in between by relatively large unstructured intervals. Computational efforts consumed on those uninformative intervals are a waste of resources. A fast and memory efficient procedure is introduced in this paper to calculate the isotopic distribution of a single relatively high-mass molecule at ultrahigh resolution by Fourier transforms approaches. The whole isotopic distribution is packed closer to the monoisotopic peak without distorting the actual scale of the peak fine structure. This packing procedure reduced 8 to 32 times the computation resources in comparison to the same calculation performed without packing. The procedure can be readily implemented in existing software. PMID:20112948

Fernandez-de-Cossio, Jorge

2010-03-01

147

Chemical analysis by ultrahigh-resolution nuclear magnetic resonance in the Earth's  

E-print Network

LETTERS Chemical analysis by ultrahigh-resolution nuclear magnetic resonance in the Earth spectroscopy2 in the Earth's magnetic field. We show that in the Earth's field the transverse relaxation time T electronics Data acquisition d.c. transmission coil Earth's field N S B0 B0 = 1 T Figure 1 Setup of mobile

Loss, Daniel

148

Endoscopic ultrahigh-resolution OCT for in vivo imaging colon disease model mice  

Microsoft Academic Search

Mouse models are increasingly important for studying human GI pathology. OCT provides minimally invasive, cross-sectional images that indicate the thickness and scattering density of underlying tissue. We have developed endoscopic ultrahigh resolution OCT (UHR-OCT) for the purpose of in vivo imaging in mouse colon. The reduced scale of the mouse colon makes tissue light penetration much less problematic, and high

Alexandre R. Tumlinson; James McNally; Angelika Unterhuber; Boris Hermann; Harald Sattmann; Lida Hariri; Wolfgang Drexler; Jennifer K. Barton

2005-01-01

149

A Comparison of Hurricane Eye Determination Using Standard and Ultra-High Resolution  

E-print Network

A Comparison of Hurricane Eye Determination Using Standard and Ultra-High Resolution QuikSCAT Winds of hurricanes. I. INTRODUCTION Space-borne scatterometers such as SeaWinds on QuikSCAT are instruments designed these is the observation and tracking of tropical cyclones including hurricanes. Several fea- tures of interest

Long, David G.

150

Atomically thin hexagonal boron nitride probed by ultrahigh-resolution transmission electron microscopy  

E-print Network

Atomically thin hexagonal boron nitride probed by ultrahigh-resolution transmission electron to prepare monolayer and multilayer suspended sheets of hexagonal boron nitride h-BN , using a combinationRevB.80.155425 PACS number s : 68.37.Og I. INTRODUCTION Boron nitride BN is a synthetic material

Zettl, Alex

151

Gamma-Ray Burst Lines  

E-print Network

The evidence for spectral features in gamma-ray bursts is summarized. As a guide for evaluating the evidence, the properties of gamma-ray detectors and the methods of analyzing gamma-ray spectra are reviewed. In the 1980's, observations indicated that absorption features below 100 keV were present in a large fraction of bright gamma-ray bursts. There were also reports of emission features around 400 keV. During the 1990's the situation has become much less clear. A small fraction of bursts observed with BATSE have statistically significant low-energy features, but the reality of the features is suspect because in several cases the data of the BATSE detectors appear to be inconsistent. Furthermore, most of the possible features appear in emission rather than the expected absorption. Analysis of data from other instruments has either not been finalized or has not detected lines.

Michael S. Briggs

1999-10-20

152

Improvement of {gamma}-ray energy resolution of LaBr{sub 3}:Ce{sup 3+} scintillation detectors by Sr{sup 2+} and Ca{sup 2+} co-doping  

SciTech Connect

Commercially available LaBr{sub 3}:5% Ce{sup 3+} scintillators show with photomultiplier tube readout about 2.7% energy resolution for the detection of 662 keV {gamma}-rays. Here we will show that by co-doping LaBr{sub 3}:Ce{sup 3+} with Sr{sup 2+} or Ca{sup 2+} the resolution is improved to 2.0%. Such an improvement is attributed to a strong reduction of the scintillation light losses that are due to radiationless recombination of free electrons and holes during the earliest stages (1-10 ps) inside the high free charge carrier density parts of the ionization track.

Alekhin, M. S.; Haas, J. T. M. de; Khodyuk, I. V.; Dorenbos, P. [Department of Radiation Science and Technology, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands)] [Department of Radiation Science and Technology, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Kraemer, K. W. [Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern (Switzerland)] [Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern (Switzerland); Menge, P. R. [Saint-Gobain Crystals, 17900 Great Lakes Parkway, Hiram, Ohio 44234 (United States)] [Saint-Gobain Crystals, 17900 Great Lakes Parkway, Hiram, Ohio 44234 (United States); Ouspenski, V. [Saint Gobain Recherche, 39, Quai Lucien Lefranc, 93303 Aubervilliers (France)] [Saint Gobain Recherche, 39, Quai Lucien Lefranc, 93303 Aubervilliers (France)

2013-04-22

153

Multiwavelength Astronomy: Gamma Ray Science  

NSDL National Science Digital Library

Dieter Hartmann, a high-energy physicist, presents a story-based lesson on the science of Gamma-Ray astronomy. The lesson focuses on gamma-ray bursts; examining their sources, types, and links to the origin and evolution of the Universe. The story-based format of the lesson also provides insights into the nature of science. Students answer questions based on the reading guide. A list of supplemental websites is also included.

154

Compton Gamma-Ray Observatory  

SciTech Connect

The symposium represents the topics on varied aspects ofgamma-ray astronomy. The Compton Gamma-Ray Observatory representsa dramatic increase in capability over previous gamma-ray missions.A large number of reports were presented on the topic of gamma-raybursts. A total of two hundred and ten papers were presented at thesymposium, out of which twenty four have been abstracted for thedatabase. (AIP)

Friedlander, M. (ed.) (Washington University, St. Louis,Missouri (United States)); Gehrels, N.; Macomb, D.J. (eds.) (Laboratory forHigh Energy Astrophysics, NASA/Goddard Space Flight Center,Greenbelt, Maryland (United States))

1993-01-01

155

Gamma-ray Pulsar Revolution  

E-print Network

Isolated Neutron Stars (INSs) were the first sources identified in the field of high-energy gamma-ray astronomy. At first, in the 70s, there were only two identified sources, the Crab and Vela pulsars. However, although few in number, these objects were crucial in establishing the very concept of a gamma-ray source. Moreover, they opened up significant discovery space both in the theoretical and phenomenological fronts. The need to explain the copious gamma-ray emission of these pulsars led to breakthrough developments in understanding the structure and physics of neutron star magnetospheres. In parallel, the 20-year-long chase to understand the nature of Geminga unveiled the existence of a radio-quiet, gamma-ray-emitting, INS, adding a new dimension to the INS family. Today we are living through an extraordinary time of discovery. The current generation of gamma-ray detectors has vastly increased the population of known of gamma-ray-emitting neutron stars. The 100 mark was crossed in 2011 and we are now appr...

Caraveo, Patrizia A

2013-01-01

156

The Animated Gamma-ray Sky Revealed by the Fermi Gamma-ray Space Telescope  

ScienceCinema

The Fermi Gamma-ray Space Telescope has been observing the sky in gamma-rays since August 2008.  In addition to breakthrough capabilities in energy coverage (20 MeV-300 GeV) and angular resolution, the wide field of view of the Large Area Telescope enables observations of 20% of the sky at any instant, and of the whole sky every three hours. It has revealed a very animated sky with bright gamma-ray bursts flashing and vanishing in minutes, powerful active galactic nuclei flaring over hours and days, many pulsars twinkling in the Milky Way, and X-ray binaries shimmering along their orbit. Most of these variable sources had not been seen by the Fermi predecessor, EGRET, and the wealth of new data already brings important clues to the origin of the high-energy emission and particles powered by the compact objects. The telescope also brings crisp images of the bright gamma-ray emission produced by cosmic-ray interactions in the interstellar medium, thus allowing to measure the cosmic nuclei and electron spectra across the Galaxy, to weigh interstellar clouds, in particular in the dark-gas phase. The telescope sensitivity at high energy will soon provide useful constraints on dark-matter annihilations in a variety of environments. I will review the current results and future prospects of the Fermi mission.

Isabelle Grenier

2010-01-08

157

Three-dimensional ultrahigh resolution optical coherence tomography imaging of age-related macular degeneration?  

PubMed Central

Ultrahigh resolution optical coherence tomography (OCT) enhances the ability to visualize different intra retinal layers. In age-related macular degeneration (AMD), pathological changes in individual retinal layers, including photoreceptor inner and outer segments and retinal pigment epithelium, can be detected. OCT using spectral / Fourier domain detection enables high speed, volumetric imaging of the macula, which provides comprehensive three-dimensional tomographic and morphologic information. We present a case series of AMD patients, from mild drusen to more advanced geographic atrophy and exudative AMD. Patients were imaged with a research prototype, ultrahigh resolution spectral / Fourier domain OCT instrument with 3.5 ?m axial image resolution operating at 25,000 axial scans per second. These cases provide representative volumetric datasets of well-documented AMD pathologies which could be used for the development of visualization and imaging processing methods and algorithms. PMID:19259245

Chen, Yueli; Vuong, Laurel N.; Liu, Jonathan; Ho, Joseph; Srinivasan, Vivek J.; Gorczynska, Iwona; Witkin, Andre J.; Duker, Jay S.; Schuman, Joel; Fujimoto, James G.

2009-01-01

158

Compton Gamma-Ray Observatory  

NASA Technical Reports Server (NTRS)

This photograph shows the Compton Gamma-Ray Observatory being released from the Remote Manipulator System (RMS) arm aboard the Space Shuttle Atlantis during the STS-35 mission in April 1991. The GRO reentered the Earth's atmosphere and ended its successful mission in June 2000. For nearly 9 years, GRO's Burst and Transient Source Experiment (BATSE), designed and built by the Marshall Space Flight Center, kept an unblinking watch on the universe to alert scientist to the invisible, mysterious gamma-ray bursts that had puzzled them for decades. By studying gamma-rays from objects like black holes, pulsars, quasars, neutron stars, and other exotic objects, scientists could discover clues to the birth, evolution, and death of star, galaxies, and the universe. The gamma-ray instrument was one of four major science instruments aboard the Compton. It consisted of eight detectors, or modules, located at each corner of the rectangular satellite to simultaneously scan the entire universe for bursts of gamma-rays ranging in duration from fractions of a second to minutes. In January 1999, the instrument, via the Internet, cued a computer-controlled telescope at Las Alamos National Laboratory in Los Alamos, New Mexico, within 20 seconds of registering a burst. With this capability, the gamma-ray experiment came to serve as a gamma-ray burst alert for the Hubble Space Telescope, the Chandra X-Ray Observatory, and major gound-based observatories around the world. Thirty-seven universities, observatories, and NASA centers in 19 states, and 11 more institutions in Europe and Russia, participated in BATSE's science program.

1991-01-01

159

Compton Gamma-Ray Observatory  

NASA Technical Reports Server (NTRS)

This photograph shows the Compton Gamma-Ray Observatory (GRO) being deployed by the Remote Manipulator System (RMS) arm aboard the Space Shuttle Atlantis during the STS-37 mission in April 1991. The GRO reentered Earth atmosphere and ended its successful mission in June 2000. For nearly 9 years, the GRO Burst and Transient Source Experiment (BATSE), designed and built by the Marshall Space Flight Center (MSFC), kept an unblinking watch on the universe to alert scientists to the invisible, mysterious gamma-ray bursts that had puzzled them for decades. By studying gamma-rays from objects like black holes, pulsars, quasars, neutron stars, and other exotic objects, scientists could discover clues to the birth, evolution, and death of stars, galaxies, and the universe. The gamma-ray instrument was one of four major science instruments aboard the Compton. It consisted of eight detectors, or modules, located at each corner of the rectangular satellite to simultaneously scan the entire universe for bursts of gamma-rays ranging in duration from fractions of a second to minutes. In January 1999, the instrument, via the Internet, cued a computer-controlled telescope at Las Alamos National Laboratory in Los Alamos, New Mexico, within 20 seconds of registering a burst. With this capability, the gamma-ray experiment came to serve as a gamma-ray burst alert for the Hubble Space Telescope, the Chandra X-Ray Observatory, and major gound-based observatories around the world. Thirty-seven universities, observatories, and NASA centers in 19 states, and 11 more institutions in Europe and Russia, participated in the BATSE science program.

1991-01-01

160

The Compton Gamma Ray Observatory  

NASA Technical Reports Server (NTRS)

The Arthur Holly Compton Gamma Ray Observatory (Compton) was launched by the Space Shuttle Atlantis on 5 April 1991. The spacecraft and instruments are in good health and returning exciting results. The mission provides nearly six orders of magnitude in spectral coverage, from 30 keV to 30 GeV, with sensitivity over the entire range an order of magnitude better than that of previous observations. The 16,000 kilogram observatory contains four instruments on a stabilized platform. The mission began normal operations on 16 May 1991 and is now over half-way through a full-sky survey. The mission duration is expected to be from six to ten years. A Science Support Center has been established at Goddard Space Flight Center for the purpose of supporting a vigorous Guest Investigator Program. New scientific results to date include: (1) the establishment of the isotropy, combined with spatial inhomogeneity, of the distribution of gamma-ray bursts in the sky; (2) the discovery of intense high energy (100 MeV) gamma-ray emission from 3C 279 and other quasars and BL Lac objects, making these the most distant and luminous gamma-ray sources ever detected; (3) one of the first images of a gamma-ray burst; (4) the observation of intense nuclear and position-annihilation gamma-ray lines and neutrons from several large solar flares; and (5) the detection of a third gamma-ray pulsar, plus several other transient and pulsing hard X-ray sources.

Gehrels, N.; Chipman, E.; Kniffen, D. A.

1993-01-01

161

LOW-RESOLUTION SPECTROSCOPY OF GAMMA-RAY BURST OPTICAL AFTERGLOWS: BIASES IN THE SWIFT SAMPLE AND CHARACTERIZATION OF THE ABSORBERS  

SciTech Connect

We present a sample of 77 optical afterglows (OAs) of Swift detected gamma-ray bursts (GRBs) for which spectroscopic follow-up observations have been secured. Our first objective is to measure the redshifts of the bursts. For the majority (90%) of the afterglows, the redshifts have been determined from the spectra. We provide line lists and equivalent widths (EWs) for all detected lines redward of Ly{alpha} covered by the spectra. In addition to the GRB absorption systems, these lists include line strengths for a total of 33 intervening absorption systems. We discuss to what extent the current sample of Swift bursts with OA spectroscopy is a biased subsample of all Swift detected GRBs. For that purpose we define an X-ray-selected statistical sample of Swift bursts with optimal conditions for ground-based follow-up from the period 2005 March to 2008 September; 146 bursts fulfill our sample criteria. We derive the redshift distribution for the statistical (X-ray selected) sample and conclude that less than 18% of Swift bursts can be at z > 7. We compare the high-energy properties (e.g., {gamma}-ray (15-350 keV) fluence and duration, X-ray flux, and excess absorption) for three subsamples of bursts in the statistical sample: (1) bursts with redshifts measured from OA spectroscopy; (2) bursts with detected optical and/or near-IR afterglow, but no afterglow-based redshift; and (3) bursts with no detection of the OA. The bursts in group (1) have slightly higher {gamma}-ray fluences and higher X-ray fluxes and significantly less excess X-ray absorption than bursts in the other two groups. In addition, the fractions of dark bursts, defined as bursts with an optical to X-ray slope {beta}{sub OX} < 0.5, is 14% in group (1), 38% in group (2), and >39% in group (3). For the full sample, the dark burst fraction is constrained to be in the range 25%-42%. From this we conclude that the sample of GRBs with OA spectroscopy is not representative for all Swift bursts, most likely due to a bias against the most dusty sight lines. This should be taken into account when determining, e.g., the redshift or metallicity distribution of GRBs and when using GRBs as a probe of star formation. Finally, we characterize GRB absorption systems as a class and compare them to QSO absorption systems, in particular the damped Ly{alpha} absorbers (DLAs). On average GRB absorbers are characterized by significantly stronger EWs for H I as well as for both low and high ionization metal lines than what is seen in intervening QSO absorbers. However, the distribution of line strengths is very broad and several GRB absorbers have lines with EWs well within the range spanned by QSO-DLAs. Based on the 33 z > 2 bursts in the sample, we place a 95% confidence upper limit of 7.5% on the mean escape fraction of ionizing photons from star-forming galaxies.

Fynbo, J. P. U.; Malesani, D.; Vreeswijk, P. M.; Hjorth, J.; Sollerman, J.; Thoene, C. C. [Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen Oe (Denmark); Jakobsson, P.; Bjoernsson, G.; De Cia, A. [Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, IS-107 ReykjavIk (Iceland); Prochaska, J. X. [Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Ledoux, C.; De Ugarte Postigo, A. [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago 19 (Chile); Nardini, M. [SISSA, Via Beirut 2/4, I-34014 Trieste (Italy); Wiersema, K. [Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH (United Kingdom); Chen, H.-W. [Department of Astronomy and Astrophysics and Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637 (United States); Bloom, J. S. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Castro-Tirado, A. J.; Gorosabel, J. [IAA-CSIC, P.O. Box 03004, E-18080 Granada (Spain); Christensen, L. [European Southern Observatory, Karl-Schwarzschildstrasse 2, D-85748 Garching (Germany); Fruchter, A. S. [Space Telescope Science Institute, Department of Physics and Astronomy, Johns Hopkins University, 3700 San Martin Drive, Baltimore, MD 21218 (United States)] (and others)

2009-12-01

162

Time correlations between low and high energy gamma rays from discrete sources  

NASA Technical Reports Server (NTRS)

Activities covered the following areas: (1) continuing analysis of the Cygnus Experiment data on the shadowing of cosmic rays by the moon and sun, which led to a direct confirmation of the angular resolution of the CYGNUS EAS array; and (2) development of analysis methods for the daily search overlapping with EGRET targets. To date, no steady emission of ultrahigh energy (UHE) gamma rays from any source has been detected by the Cygnus Experiment, but some evidence for sporadic emission had been found. Upper limits on steady fluxes from 49 sources in the northern hemisphere have been published. In addition, a daily search of 51 possible sources over the interval April 1986 to June 1992 found no evidence for emission. From these source lists, four candidates were selected for comparison with EGRET data.

Ellsworth, R. W.

1995-01-01

163

Elemental mapping of the moon using gamma rays : past, present, and future /  

SciTech Connect

The energies and intensities of gamma rays From a planetary surface can be used to infer the elemental composition of an object with no or a thin atmosphere. The Apollo gamma-ray spectrometers in 1972 and 1973 produced many of the results for the distribution of elements in the Moon that are now generally well accepted. Lunar Prospector in 1998 and 1999 globally mapped the Moon with gamma rays and neutrons. Both missions used spectrometers with poor energy resolution ({approx}8-10%). The Japanese plan to send a high-resolution germanium gamma-ray spectrometer to the Moon in about 2004 on their SELENE mission. However, little has been done since the 1970s on the models used to unfold planetary gamma-ray spectra. More work needs to be done on understanding what to expect in future gamma-ray spectra and how to unfold such data.

Reedy, R. C. (Robert C.)

2001-01-01

164

Development of liquid xenon detectors for gamma ray astronomy  

NASA Technical Reports Server (NTRS)

The application of liquid xenon in high-resolution detectors for gamma-ray astronomy is being investigated. Initial results from a pulse-shape analysis of ionization signals in a liquid-xenon gridded chamber indicate that it is possible to achieve the necessary liquid purity for the transport of free electrons with simple techniques. The energy resolution has been measured as a function of applied electric field, using electrons and gamma-rays from a 207Bi source. At a field of 12 kV/cm the noise-substracted energy resolution of the dominant 569-keV gamma-ray line is 34 keV FWHM (full width at half maximum). This value is mostly determined by recombination of electron-ion pairs on delta-electron tracks.

Aprile, Elena; Suzuki, Masayo

1989-01-01

165

Ultra-high resolution optical CT dosimetry for the visualisation of synchrotron microbeam therapy doses  

NASA Astrophysics Data System (ADS)

Optical CT is a method that can potentially provide both accurate dosimetry at high spatial resolution and 3-D visualisation over a large field-of-view in a single dataset. The major factors limiting spatial resolution in previous studies are analysed here and it is shown that improvements in equipment specification can overcome many of these. The need for ultra-high spatial resolution in the verification of microbeam radiation therapy verification is demonstrated and example images of a PRESAGE® sample are presented.

Doran, S. J.; Rahman, A. T. Abdul; Bräuer-Krisch, E.; Brochard, T.; Adamovics, J.

2013-06-01

166

The Gamma-ray Sky with Fermi  

NASA Technical Reports Server (NTRS)

Gamma rays reveal extreme, nonthermal conditions in the Universe. The Fermi Gamma-ray Space Telescope has been exploring the gamma-ray sky for more than four years, enabling a search for powerful transients like gamma-ray bursts, novae, solar flares, and flaring active galactic nuclei, as well as long-term studies including pulsars, binary systems, supernova remnants, and searches for predicted sources of gamma rays such as dark matter annihilation. Some results include a stringent limit on Lorentz invariance derived from a gamma-ray burst, unexpected gamma-ray variability from the Crab Nebula, a huge gamma-ray structure associated with the center of our galaxy, surprising behavior from some gamma-ray binary systems, and a possible constraint on some WIMP models for dark matter.

Thompson, David

2012-01-01

167

A model of unpulsed very high energy gamma rays from the Crab Nebula and pulsar  

NASA Technical Reports Server (NTRS)

The angular resolution of gamma-ray detectors does not allow one to separate the nebula from the pulsar in the Crab. It is generally assumed that the steady emission of gamma rays comes from the nebula. Using the 'outer magnetospheric gap' model, an alternative mechanism in which the steady emission of gamma rays could come from a compact region, a couple of light cylinder radii beyond the pulsar.

Kwok, P. W.; Cheng, K. S.; Lau, M. M.

1991-01-01

168

Gamma rays from molecular clouds  

E-print Network

It is believed that the observed diffuse gamma ray emission from the galactic plane is the result of interactions between cosmic rays and the interstellar gas. Such emission can be amplified if cosmic rays penetrate into dense molecular clouds. The propagation of cosmic rays inside a molecular cloud has been studied assuming an arbitrary energy and space dependent diffusion coefficient. If the diffusion coefficient inside the cloud is significantly smaller compared to the average one derived for the galactic disk, the observed gamma ray spectrum appears harder than the cosmic ray spectrum, mainly due to the slower penetration of the low energy particles towards the core of the cloud. This may produce a great variety of gamma ray spectra.

Stefano Gabici; Felix Aharonian; Pasquale Blasi

2006-10-02

169

Terrestrial gamma-ray flashes  

NASA Astrophysics Data System (ADS)

Lightning and thunderstorm systems in general have been recently recognized as powerful particle accelerators, capable of producing electrons, positrons, gamma-rays and neutrons with energies as high as several tens of MeV. In fact, these natural systems turn out to be the highest energy and most efficient natural particle accelerators on Earth. Terrestrial Gamma-ray Flashes (TGFs) are millisecond long, very intense bursts of gamma-rays and are one of the most intriguing manifestation of these natural accelerators. Only three currently operative missions are capable of detecting TGFs from space: the RHESSI, Fermi and AGILE satellites. In this paper we review the characteristics of TGFs, including energy spectrum, timing structure, beam geometry and correlation with lightning, and the basic principles of the associated production models. Then we focus on the recent AGILE discoveries concerning the high energy extension of the TGF spectrum up to 100 MeV, which is difficult to reconcile with current theoretical models.

Marisaldi, Martino; Fuschino, Fabio; Labanti, Claudio; Tavani, Marco; Argan, Andrea; Del Monte, Ettore; Longo, Francesco; Barbiellini, Guido; Giuliani, Andrea; Trois, Alessio; Bulgarelli, Andrea; Gianotti, Fulvio; Trifoglio, Massimo

2013-08-01

170

Towed seabed gamma ray spectrometer  

SciTech Connect

For more than 50 years, the measurement of radioactivity has been used for onshore geological surveys and in laboratories. The British Geological Survey (BGS) has extended the use of this type of equipment to the marine environment with the development of seabed gamma ray spectrometer systems. The present seabed gamma ray spectrometer, known as the Eel, has been successfully used for sediment and solid rock mapping, mineral exploration, and radioactive pollution studies. The range of applications for the system continues to expand. This paper examines the technological aspects of the Eel and some of the applications for which it has been used.

Jones, D.G. (British Geological Survey, Nottingham (United Kingdom))

1994-08-01

171

Cosmography by gamma ray bursts  

NASA Astrophysics Data System (ADS)

Aims: Relations connecting gamma ray burst quantities can be used to constrain cosmographic parameters of the Hubble law at medium-high redshifts. Methods: We consider a sample of 27 gamma ray bursts to construct the luminosity distance to redshift relation and derive the values of the parameters q_0, j_0, and s_0. The analysis is compared with other methods in the literature. Results: Gamma gay bursts, if calibrated by SNeIa, seem reliable as distance indicators and give cosmographic parameters in agreement with the ?CDM model.

Capozziello, S.; Izzo, L.

2008-10-01

172

Stroboscopic ultrahigh-resolution full-field optical coherence tomography  

Microsoft Academic Search

We present a new technique that produces en face tomographic images with a 10-mus acquisition time per image. The setup consists of an interference microscope with stroboscopic illumination provided by a xenon arc flash lamp (10-mus flashes at 15 Hz). The tomographic images are obtained from two phase-opposed interferometric images recorded simultaneously by two synchronized CCD cameras. Transverse resolution better

G. Moneron; A. C. Boccara; A. Dubois

2005-01-01

173

UltraHigh Resolution Imaging by Fluorescence Photoactivation Localization Microscopy  

Microsoft Academic Search

Biological structures span many orders of magnitude in size, but far-field visible light microscopy suffers from limited resolution. A new method for fluorescence imaging has been developed that can obtain spatial distributions of large numbers of fluorescent molecules on length scales shorter than the classical diffraction limit. Fluorescence photoactivation localization microscopy (FPALM) analyzes thousands of single fluorophores per acquisition, localizing

Samuel T. Hess; Thanu P. K. Girirajan; Michael D. Mason

2006-01-01

174

Cosmogenic gamma rays and the composition of cosmic rays  

SciTech Connect

We discuss the prospects of detecting the sources of ultrahigh energy (UHE) cosmic ray (CR) nuclei via their emission of cosmogenic {gamma} rays in the GeV to TeV energy range. These {gamma} rays result from electromagnetic cascades initiated by high energy photons, electrons, and positrons that are emitted by CRs during their propagation in the cosmic radiation background and are independent of the simultaneous emission of {gamma} rays in the vicinity of the source. The corresponding production power by UHE CR nuclei (with mass number A and charge Z) is dominated by pion photo production ({proportional_to}A) and Bethe-Heitler pair production ({proportional_to}Z{sup 2}). We show that the cosmogenic {gamma}-ray signal from a single steady UHE CR source is typically more robust with respect to variations of the source composition and injection spectrum than the accompanying signal of cosmogenic neutrinos. We study the diffuse emission from the sum of extragalactic CR sources as well as the point-source emission of the closest sources.

Ahlers, Markus [C. N. Yang Institute for Theoretical Physics, SUNY at Stony Brook, Stony Brook, New York 11794-3840 (United States); Salvado, Jordi [Departament d'Estructura i Constituents de la Materia and Institut de Ciencies del Cosmos, Universitat de Barcelona, 647 Diagonal, E-08028 Barcelona (Spain)

2011-10-15

175

Feasibility study of gamma-ray medical radiography.  

PubMed

This research explores the feasibility of using gamma-ray radiography in medical imaging. We will show that gamma-ray medical radiography has the potential to provide alternative diagnostic medical information to X-ray radiography. Approximately one Ci Am-241 radioactive source which emits mono-energetic 59.5 keV gamma rays was used. Several factors that influence the feasibility of this study were tested. They were the radiation source uniformity, image uniformity, and image quality parameters such as contrast, noise, and spatial resolution. In addition, several gamma-ray and X-ray images were acquired using humanoid phantoms. These images were recorded on computed radiography image receptors and displayed on a standard monitor. Visual assessments of these images were then conducted. The Am-241 radioactive source provided relatively uniform radiation exposure and images. Image noise and image contrast were mainly dependent on the exposure time and source size, whereas spatial resolution was dependent on source size and magnification factor. The gamma-ray humanoid phantom images were of lower quality than the X-ray images mainly due to the low radioactivity used and not enough exposure time. Nevertheless, the gamma-ray images displayed most of the main structures contained in the humanoid phantoms. Higher exposure rates and thus lower exposure times were estimated for different pure Am-241 source sizes that are hypothesized to provide high quality images similar to X-ray images. For instance, a 10mm source size of pure Am-241 with 7s exposure time should produce images similar in contrast and noise to X-ray images. This research paves the way for the production and usage of a highly radioactive Am-241 source with the potential to lead to the feasibility of acceptable quality medical gamma-ray radiography. PMID:23208227

Alyassin, Abdalmajeid M; Maqsoud, Hamza A; Mashat, Ahmad M; Al-Mohr, Al-Sayed; Abdulwajid, Subhan

2013-02-01

176

Ultra-high resolution, absolute position sensors for cryostatic applications  

NASA Astrophysics Data System (ADS)

Recent advances in new technology, optical pattern recognition encoders at NASA have resulted in high speed, reliable, compact position sensors for use in cryostatic space flight mechanisms. New encoder scale patterns and image processing algorithms combine with digital signal processors (DSP) and field programmable gate array (FPGA) logic elements to enable encoders with conversion rates in excess of 1.5 kHz (suitable for high speed servo motion control for mechanisms), linear resolutions of less than 10 nm, and angular resolutions in the single digit milli-arcseconds in relatively compact packages. Fiber optic light guides allow encoders to function in cryostats with extremely low power dissipation. Ambient test data for fiber optic configurations suitable for cryogenic environments are presented. Cryostatic test capabilities under development are discussed. Potential applications exist for NGST and other infrared and sub-millimeter missions, such as fine guidance sensing, attitude control, mirror segment position sensing, and mirror scanning.

Leviton, Douglas B.; Frey, Brad

2003-03-01

177

Gamma Ray Spectroscopy with Scintillation Light in Liquid Xenon  

E-print Network

Scintillation light from gamma ray irradiation in liquid xenon is detected by two Hamamatsu R9288 photomultiplier tubes (PMTs) immersed in the liquid. UV light reflector material, PTFE, is used to optimize the light collection efficiency. The detector gives a high light yield of 6 photoelectron per keV (pe/keV), which allows efficient detection of the 122 keV gamma-ray line from Co-57, with a measured energy resolution of (8.8+/-0.6)% (sigma). The best achievable energy resolution, by removing the instrumental fluctuations, from liquid xenon scintillation light is estimated to be around 6-8% (sigma) for gamma-ray with energy between 662 keV and 122 keV.

K. Ni; E. Aprile; K. L. Giboni; P. Majewski; M. Yamashita

2006-08-04

178

Cosmological gamma-ray bursts  

NASA Technical Reports Server (NTRS)

The distribution in angle and flux of gamma-ray bursts indicates that the majority of gamma-ray bursters are at cosmological distances, i.e., at z of about 1. The rate is then about 10 exp -8/yr in a galaxy like the Milky Way, i.e., orders of magnitude lower than the estimated rate for collisions between neutron stars in close binary systems. The energy per burst is about 10 exp 51 ergs, assuming isotropic emission. The events appear to be less energetic and more frequent if their emission is strongly beamed. Some tests for the distance scale are discussed: a correlation between the burst's strength and its spectrum; the absorption by the Galactic gas below about 2 keV; the X-ray tails caused by forward scattering by the Galactic dust; about 1 month recurrence of some bursts caused by gravitational lensing by foreground galaxies; and a search for gamma-ray bursts in M31. The bursts appear to be a manifestation of something exotic, but conventional compact objects can provide an explanation. The best possibility is offered by a decay of a bindary composed of a spinning-stellar-mass black-hole primary and a neutron or a strange-quark star secondary. In the final phase the secondary is tidally disrupted, forms an accretion disk, and up to 10 exp 54 ergs are released. A very small fraction of this energy powers the gamma-ray burst.

Paczynski, Bohdan

1991-01-01

179

Cosmological gamma-ray bursts  

SciTech Connect

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Gamma-ray bursts are brief events that dominate the emission from all other gamma-ray objects in the sky, flicker for tens of seconds, and then turn off. Their nature remains uncertain despite years of efforts to understand them. One hypothesis is that the bursts arise within our galaxy albeit in an extended halo of neutron stars. Another hypothesis uses the isotropic distribution of gamma-ray bursts to argue that they come from nearly the edge of the universe. If gamma-ray bursts originate from cosmological distances, then the expansion of the universe should cause the dimmer (and presumably further) bursts to last longer. The authors have developed methods for measuring this time stretching, related the time stretching to the distance to the bursts, determined how the detailed physics causes temporal variations, and found the amount of total energy and peak luminosity that the events must be producing.

Fenimore, E.; Epstein, R.; Ho, C.; Intzand, J.

1996-04-01

180

Gamma-ray camera flyby  

SciTech Connect

Animation based on an actual classroom demonstration of the prototype CCI-2 gamma-ray camera's ability to image a hidden radioactive source, a cesium-137 line source, in three dimensions. For more information see http://newscenter.lbl.gov/feature-stories/2010/06/02/applied-nuclear-physics/.

None

2010-01-01

181

Swift: Gamma-Ray Bursts  

NSDL National Science Digital Library

In this video segment adapted from Penn State Public Broadcasting's Swift: Eyes Through Time, learn about the Swift satellite — a NASA mission with international participation — and how it is collecting data about gamma-ray bursts that may yield important discoveries about the Universe.

2005-12-17

182

The Compton Gamma Ray Observatory  

Microsoft Academic Search

The Arthur Holly Compton Gamma Ray Observatory (Compton) was launched by the Space Shuttle Atlantis on 5 April 1991. The spacecraft and instruments are in good health and returning exciting results. The mission provides nearly six orders of magnitude in spectral coverage, from 30 keV to 30 GeV, with sensitivity over the entire range an order of magnitude better than

N. Gehrels; E. Chipman; D. A. Kniffen

1993-01-01

183

Recommended Priorities for NASA's Gamma Ray Astronomy Program 1999-2013  

NASA Technical Reports Server (NTRS)

The Gamma-Ray Astronomy Program Working Group (GRAPWG) recommends priorities for the NASA Gamma-Ray Astronomy Program. The highest priority science topic is nuclear astrophysics and sites of gamma ray line emission. Other high priority topics are gamma ray bursts, hard x-ray emission from accreting black holes and neutron stars, the Advanced Compton Telescope (ACT), the High-resolution Spectroscopic Imager (HSI), and the Energetic X-ray Imaging Survey Telescope (EXIST). The recommendations include special consideration for technology development, TeV astronomy, the ultra-long duration balloon (ULDB) program, the International Space Station, optical telescope support, and data analysis and theory.

Carol, Ladd

1999-01-01

184

The structure and content of the galaxy and galactic gamma rays. [conferences  

NASA Technical Reports Server (NTRS)

Papers are presented dealing with galactic structure drawing on all branches of galactic astronomy with emphasis on the implications of the new gamma ray observations. Topics discussed include: (1) results from the COS-B gamma ray satellite; (2) results from SAS-2 on gamma ray pulsar, Cygnus X-3, and maps of the galactic diffuse flux; (3) recent data from CO surveys of the galaxy; (4) high resolution radio surveys of external galaxies; (5) results on the galactic distribution of pulsars; and (6) theoretical work on galactic gamma ray emission.

Fichtel, C. E.; Stecker, F. W.

1976-01-01

185

The gamma-ray spectrometer experiment on the solar maximum mission satellite  

NASA Technical Reports Server (NTRS)

The major activities summarized include: Gamma-Ray Spectrometer (GRS) instrument response and flight operation; solar flare studies; cosmic gamma-ray studies; summary of computer operations; search for flare-precursor protons; diffuse galactic annihilation radiation; cosmic ray bursts; atmospheric gamma ray spectrum; gamma ray line emission from supernovae and novae; improved angular resolutions using Earth occultation; and production processing of NASA IPD data. In addition, an updated list of published papers and invited papers or contributed papers presented at scientific meetings is provided.

Chupp, E. L.

1987-01-01

186

Ultrahigh-resolution, high-speed spectral domain optical coherence phase microscopy.  

PubMed

We present an ultrahigh-resolution, high-speed spectral domain optical coherence phase microscopy (SD-OCPM) system that combines submicrometer transverse spatial resolution and subnanometer optical path length sensitivity, with an acquisition speed of over 217,000 voxels/s. The proposed SD-OCPM system overcomes two significant drawbacks of traditional common-path interferometers-limited transverse spatial resolution and suboptimal detection sensitivity-while maintaining phase stability that is comparable with common-path interferometer setups. The transverse and axial spatial resolution of the setup is measured to be 0.6 and 1.9 ?m, respectively, with a phase sensitivity of 0.0027 rad (corresponds to optical path length sensitivity of 110 pm). High-speed acquisition allows for phase-sensitive 4D imaging of biological samples with subcellular resolution. PMID:24365818

Ansari, Rehman; Myrtus, Christian; Aherrahrou, Redouane; Erdmann, Jeanette; Schweikard, Achim; Hüttmann, Gereon

2014-01-01

187

Brain Activity Movie Functional MRI with UltraHigh Temporal Resolution at 7 Tesla  

Microsoft Academic Search

\\u000a Increased signal changes in blood oxygen dependant (BOLD) weighted functional magnetic resonance imaging (fMRI) data sets\\u000a at ultra-high field strengths enable an increase in spatial and temporal resolution. Here we examine activation patterns in\\u000a the human motor cortex on a 7 Tesla scanner employing temporal resolutions of 100ms, 200ms and 300ms, respectively. Based\\u000a on Finite-impulse response (FIR) analysis we generate

C. Windischberger; F. Gerstl; F. Ph. S. Fischmeister; V. Schöpf; C. Kaseß; E. Moser

188

Cosmic Rays: What Gamma Rays Can Say  

E-print Network

We will review the main channels of gamma ray emission due to the acceleration and propagation of cosmic rays, discussing the cases of both galactic and extra-galactic cosmic rays and their connection with gamma rays observations.

Aloisio, Roberto

2014-01-01

189

Cosmic Gamma-ray Background Radiation  

E-print Network

The cosmic gamma-ray background radiation is one of the most fundamental observables in the gamma-ray band. Although the origin of the cosmic gamma-ray background radiation has been a mystery for a long time, the Fermi gamma-ray space telescope has recently measured it at 0.1-820 GeV and revealed that the cosmic GeV gamma-ray background is composed of blazars, radio galaxies, and star-forming galaxies. However, Fermi still leaves the following questions. Those are dark matter contribution, origins of the cosmic MeV gamma-ray background, and the connection to the IceCube TeV-PeV neutrino events. In this proceeding, I will review the current understandings of the cosmic gamma-ray background and discuss future prospects of cosmic gamma-ray background radiation studies. I also briefly review the current status of cosmic infrared/optical background radiation studies.

Inoue, Yoshiyuki

2014-01-01

190

[gamma]-ray signatures from ordinary cosmic strings  

SciTech Connect

We calculate the flux of ultrahigh-energy photons from individual ordinary (i.e., nonsuperconducting) cosmic strings and compare the results with the sensitivity of current and proposed TeV and EeV telescopes. Our calculations give only upper limits for the [gamma]-ray flux, since the source of the photons, jets from particle production at cusps, may be weakened by back-reaction effects. For the usual cosmic distribution of strings, the predicted bursts from strings with the value of mass per unit length associated with galaxy formation or light strings may just be detectable. A diffuse [gamma]-ray background from light strings may also be seen by the Fly's Eye detector at above 7[times]10[sup 10] GeV.

MacGibbon, J.H. (Code 665, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States)); Brandenberger, R.H. (Department of Physics, Brown University, Providence, Rhode Island 02912 (United States))

1993-03-15

191

POSITION SENSITIVE GERMANIUM DETECTORS FOR GAMMA-RAY IMAGING AND SPECTROSCOPY  

EPA Science Inventory

Gamma-ray imaging with position-sensitive germanium detectors offers the advantages of excellent energy resolution, high detection efficiency, and potentially good sptial resolution. The development of the amorphous-semiconductor electrical contact technology for germanium detec...

192

Portable compton gamma-ray detection system  

DOEpatents

A Compton scattered gamma-ray detector system. The system comprises a gamma-ray spectrometer and an annular array of individual scintillators. The scintillators are positioned so that they are arrayed around the gamma-ray spectrometer. The annular array of individual scintillators includes a first scintillator. A radiation shield is positioned around the first scintillator. A multi-channel analyzer is operatively connected to the gamma-ray spectrometer and the annular array of individual scintillators.

Rowland, Mark S. (Alamo, CA); Oldaker, Mark E. (Pleasanton, CA)

2008-03-04

193

Multifrequency Observations of Gamma-Ray Burst  

E-print Network

Neither a flaring nor a quiescent counterpart to a gamma-ray burst has yet been convincingly identified at any wavelength region. The present status of the search for counterparts of classical gamma-ray bursts is given. Particular emphasis is put on the search for flaring counterparts, i.e. emission during or shortly after the gamma-ray emission.

J. Greiner

1995-10-04

194

Gamma ray spectroscopy in astrophysics. [conferences  

NASA Technical Reports Server (NTRS)

Experimental and theoretical aspects of gamma ray spectroscopy in high energy astrophysics are discussed. Line spectra from solar, stellar, planetary, and cosmic gamma rays are examined as well as HEAO investigations, the prospects of a gamma ray observatory, and follow-on X-ray experiments in space.

Cline, T. L. (editor); Ramaty, R. (editor)

1978-01-01

195

Gamma ray astrophysics. [emphasizing processes and absorption  

NASA Technical Reports Server (NTRS)

Gamma ray production processes are reviewed, including Compton scattering, synchrotron radiation, bremsstrahlung interactions, meson decay, nucleon-antinucleon annihilations, and pion production. Gamma ray absorption mechanisms through interactions with radiation and with matter are discussed, along with redshifts and gamma ray fluxes.

Stecker, F. W.

1974-01-01

196

Nuclear gamma rays from energetic particle interactions  

NASA Technical Reports Server (NTRS)

Gamma ray line emission from nuclear deexcitation following energetic particle reactions is evaluated. The compiled nuclear data and the calculated gamma ray spectra and intensities can be used for the study of astrophysical sites which contain large fluxes of energetic protons and nuclei. A detailed evaluation of gamma ray line production in the interstellar medium is made.

Ramaty, R.; Kozlovsky, B.; Lingenfelter, R. E.

1978-01-01

197

The Universe Viewed in Gamma-Rays 1 Concept of new gamma ray detector  

E-print Network

The Universe Viewed in Gamma-Rays 1 Concept of new gamma ray detector Satoko Osone Institute for Cosmic Ray Research, University of Tokyo, 5-1-5 Kashiwa-no-Ha, Kashiwa City,Chiba 277-8582, Japan Abstract We present a concept of a new gamma ray detector in order to observe undetected TeV gamma ray

Enomoto, Ryoji

198

PROGRESS ON MARGIE, A GAMMA-RAY BURST ULTRA-LONG DURATION BALLOON MISSION  

SciTech Connect

We are designing the Minute of Arc Resolution Gamma-ray Imaging Experiment (MARGIE) as a 100 day Ultra Long Duration Balloon (ULDB) mission to: (1) detect and localize gamma-ray bursts; and (2) survey the hard X-ray sky. Major advances in designing the CZT detectors increase the sensitivity to higher energy. Design of the gondola has also progressed.

D. BAND; ET AL

2001-02-01

199

Ultrahigh-resolution and non-contact diameter measurement of metallic wire using eddy current sensor.  

PubMed

This paper proposes a new method using eddy current sensor (ECS) for online non-contact diameter measurement of metallic wires with ultrahigh resolution. A prototype sensor was designed, fabricated, and tested for copper wires with diameters ranging from 1.12 mm to 1.30 mm. A solenoid coil with dimensions of 16 mm long and 2.1 mm in diameter is used as sensing element with a working frequency of 1.3 MHz. With a well-designed bridge, the sensing coil's inductance variation can be detected and the wire's diameter can be calculated. The ECS system demonstrated a dynamic resolution better than 2.2 ?m and a static resolution better than 0.42 nm for a wire with a diameter of 1.3 mm. This non-contact method has competitive advantages over other methods in many aspects, especially in terms of measurement resolution. PMID:25173300

Li, Wei; Wang, Hongbo; Feng, Zhihua

2014-08-01

200

Ultra-high aspect ratio high-resolution nanofabrication for hard X-ray diffractive optics.  

PubMed

Although diffractive optics have played a major role in nanoscale soft X-ray imaging, high-resolution and high-efficiency diffractive optics have largely been unavailable for hard X-rays where many scientific, technological and biomedical applications exist. This is owing to the long-standing challenge of fabricating ultra-high aspect ratio high-resolution dense nanostructures. Here we report significant progress in ultra-high aspect ratio nanofabrication of high-resolution, dense silicon nanostructures using vertical directionality controlled metal-assisted chemical etching. The resulting structures have very smooth sidewalls and can be used to pattern arbitrary features, not limited to linear or circular. We focus on the application of X-ray zone plate fabrication for high-efficiency, high-resolution diffractive optics, and demonstrate the process with linear, circular, and spiral zone plates. X-ray measurements demonstrate high efficiency in the critical outer layers. This method has broad applications including patterning for thermoelectric materials, battery anodes and sensors among others. PMID:24970569

Chang, Chieh; Sakdinawat, Anne

2014-01-01

201

High-energy gamma rays from the intense 1993 January 31 gamma-ray burst  

Microsoft Academic Search

The intense gamma-ray burst of 1993 January 31 was detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. Sixteen gamma rays above 30 MeV were imaged in the telescope when only 0.04 gamma rays were expected by chance. Two of these gamma rays have energies of approximately 1 GeV, and the five bin spectrum of the

M. Sommer; D. L. Bertsch; B. L. Dingus; C. E. Fichtel; G. J. Fishman; A. K. Harding; R. C. Hartman; S. D. Hunter; K. Hurley; G. Kanbach; D. A. Kniffen; C. Kouveliotou; Y. C. Lin; J. R. Mattox; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; P. L. Nolan; E. Schneid; P. Sreekumar; D. J. Thompson

1994-01-01

202

Terrestrial Gamma-Ray Flashes (TGFs)  

NASA Technical Reports Server (NTRS)

This slide presentation reviews the observation of Terrestrial Gamma Ray Flashes (TGFs) by Gamma-Ray Telescopes. These were: (1) BATSE /Compton Observatory, (2) Solar Spectroscopic Imager, (3) AGILE Gamma-ray Telescope, and (4) Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope. It contains charts which display the counts over time, a map or the TGFs observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). and a map showing the latitude and longitude of 85 of the TGFs observed by the Fermi GBM.

Fishman, Gerald J.

2010-01-01

203

GeV AND HIGHER ENERGY PHOTON INTERACTIONS IN GAMMA-RAY BURST FIREBALLS AND SURROUNDINGS  

E-print Network

GeV AND HIGHER ENERGY PHOTON INTERACTIONS IN GAMMA-RAY BURST FIREBALLS AND SURROUNDINGS Soebur in the prompt phase. Photons above this range are subject to electron-positron pair production with fireball, the fireball becomes optically thin again at ultrahigh energies (kPeV). On the other hand, for sufficiently

Zhang, Bing

204

Gamma-ray imaging with coaxial HPGe detector  

SciTech Connect

We report on the first experimental demonstration of Compton imaging of gamma rays with a single coaxial high-purity germanium (HPGe) detector. This imaging capability is realized by two-dimensional segmentation of the outside contact in combination with digital pulse-shape analysis, which enables to image gamma rays in 4{pi} without employing a collimator. We are able to demonstrate the ability to image the 662keV gamma ray from a {sup 137}Cs source with preliminary event selection with an angular accuracy of 5 degree with an relative efficiency of 0.2%. In addition to the 4{pi} imaging capability, such a system is characterized by its excellent energy resolution and can be implemented in any size possible for Ge detectors to achieve high efficiency.

Niedermayr, T; Vetter, K; Mihailescu, L; Schmid, G J; Beckedahl, D; Kammeraad, J; Blair, J

2005-04-12

205

The Fermi Gamma-ray Burst Monitor Instrument  

SciTech Connect

The Fermi Gamma-ray Space Telescope launched on June 11, 2008 carries two experiments onboard--the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The primary mission of the GBM instrument is to support the LAT in observing {gamma}-ray bursts (GRBs) by providing low-energy measurements with high temporal and spectral resolution as well as rapid burst locations over a large field-of-view ({>=}8 sr). The GBM will complement the LAT measurements by observing GRBs in the energy range 8 keV to 40 MeV, the region of the spectral turnover in most GRBs. The GBM detector signals are processed by the onboard digital processing unit (DPU). We describe some of the hardware features of the DPU and its expected limitations during intense triggers.

Bhat, P. N.; Briggs, M. S.; Connaughton, V.; Paciesas, W. S.; Preece, R. D. [University of Alabama in Huntsville, Huntsville AL (United States); Meegan, C. A. [Universities Space Research Association, Huntsville AL (United States); Lichti, G. G.; Diehl, R.; Greiner, J.; Kienlin, A. von [Max-Planck-Institut fuer extraterrestrische Physik, Garching (Germany); Fishman, G. J.; Kouveliotou, C. [NASA Marshall Space Flight Center, Huntsville AL (United States); Kippen, R. M. [Los Alamos National Laboratory, Los Alamos NM (United States)

2009-05-25

206

Pulsed Photofission Delayed Gamma Ray Detection for Nuclear Material Identification  

SciTech Connect

Innovative systems with increased sensitivity and resolution are in great demand to detect diversion and to prevent misuse in support of nuclear materials management for the U.S. fuel cycle. Nuclear fission is the most important multiplicative process involved in non-destructive active interrogation. This process produces the most easily recognizable signature for nuclear materials. High-energy gamma rays can also excite a nucleus and cause fission through a process known as photofission. After photofission reactions, delayed signals are easily distinguishable from the interrogating radiation. Linac-based, advanced inspection techniques utilizing the fission signals after photofission have been extensively studied for homeland security applications. Previous research also showed that a unique delayed gamma ray energy spectrum exists for each fissionable isotope. Isotopic composition measurement methods based on delayed gamma ray spectroscopy will be the primary focus of this work.

John Kavouras; Xianfei Wen; Daren R. Norman; Dante R. Nakazawa; Haori Yang

2012-11-01

207

Solar gamma-ray lines  

NASA Technical Reports Server (NTRS)

The gamma-ray spectrometer on the Solar Maximum Mission satellite has observed emissions produced by nuclear reactions in over 20 separate solar flares. The observed intensity from different flares ranges over a factor of 100, and the time scale for their production ranges from 10-s pulses to complete events lasting over 1000 s. The emissions include narrow and broadened prompt gamma-ray lines from numerous isotopes from Li-7 to Fe-56 and cover the energy range from 0.431 MeV (Be-7) to 7.12 MeV (O-16). The instrument has also observed emissions at energies greater than 10 MeV from the decay of pi0 mesons, from electron bremsstrahlung, and from the direct observation of greater-than-100-MeV solar neutrons. The intensity, temporal and spectral properties of these emissions are reviewed from the point of view that solar flares represent an astrophysical particle-acceleration site.

Forrest, D. J.

1983-01-01

208

Micrometer scale contact lens movements imaged by ultra-high resolution optical coherence tomography  

PubMed Central

PURPOSE To dynamically evaluate contact lens movement and ocular surface shape using ultra-high resolution and ultra-long scan depth optical coherence tomography (OCT). DESIGN Clinical research study of a laboratory technique. METHODS Four different types of soft contact lenses were tested on the left eye of 10 subjects (6 males and 4 females). Lenses edges at primary gaze and temporal and nasal gazes were imaged by ultra-high resolution OCT. Excursion lag was obtained as the distance between the lens edge at primary gaze and immediately after the eye was quickly turned either nasally or temporally. The inferior lens edges were imaged continuously to track vertical movements during blinking. Ultra-long scan depth OCT provided quantifiable images of the ocular surface, and the contour was acquired using custom software. RESULTS Excursion lag at the horizontal meridian was 366 ± 134 ?m at temporal gaze and 320 ± 137 ?m at nasal gaze (P > .05). The lens uplift at the vertical meridian was 342 ± 155 ?m after blinking. There were significant differences in horizontal lags and vertical movements among different lenses (P < .05). Horizontal lags were correlated with radii of curvatures and sagittal heights at 6- and 14- mm horizontal meridian radii (P < .05). The blink-induced lens uplift first lowered by 104 ± 8 ?m, and then lifted 342 ± 155 ?m after the blink. CONCLUSIONS Ultra-high resolution and ultra-long scan depth OCT can assess micrometer scale lens movements and ocular surface contours. Both lens design and ocular surface shape affected lens movements. PMID:21920493

Cui, Lele; Shen, Meixiao; Wang, Michael R.; Wang, Jianhua

2011-01-01

209

In vivo volumetric imaging of chicken retina with ultrahigh-resolution spectral domain optical coherence tomography  

PubMed Central

The chicken retina is an established animal model for myopia and light-associated growth studies. It has a unique morphology: it is afoveate and avascular; oxygen and nutrition to the inner retina is delivered by a vascular tissue (pecten) that protrudes into the vitreous. Here we present, to the best of our knowledge, the first in vivo, volumetric high-resolution images of the chicken retina. Images were acquired with an ultrahigh-resolution optical coherence tomography (UHROCT) system with 3.5 µm axial resolution in the retina, at the rate of 47,000 A-scans/s. Spatial variations in the thickness of the nerve fiber and ganglion cell layers were mapped by segmenting and measuring the layer thickness with a semi-automatic segmentation algorithm. Volumetric visualization of the morphology and morphometric analysis of the chicken retina could aid significantly studies with chicken retinal models of ophthalmic diseases. PMID:21559138

Moayed, Alireza Akhlagh; Hariri, Sepideh; Song, Eun Sun; Choh, Vivian; Bizheva, Kostadinka

2011-01-01

210

Gamma-ray and Cosmic-ray Tests of Lorentz Invariance Violation and Quantum Gravity Models and Their Implications  

E-print Network

The topic of Lorentz invariance violation is a fundamental question in physics that has taken on particular interest in theoretical explorations of quantum gravity scenarios. I discuss various gamma-ray observations that give limits on predicted potential effects of Lorentz invariance violation. Among these are spectral data from ground based observations of the multi-TeV gamma-rays from nearby AGN, INTEGRAL detections of polarized soft gamma-rays from the vicinity of the Crab pulsar, Fermi Gamma Ray Space Telescope studies of photon propagation timing from gamma-ray bursts, and Auger data on the spectrum of ultrahigh energy cosmic rays. These results can be used to seriously constrain or rule out some models involving Planck scale physics. Possible implications of these limits for quantum gravity and Planck scale physics will be discussed.

Floyd W. Stecker

2009-12-14

211

Gamma-ray and Cosmic-ray Tests of Lorentz Invariance Violation and Quantum Gravity Models and Their Implications  

E-print Network

The topic of Lorentz invariance violation is a fundamental question in physics that has taken on particular interest in theoretical explorations of quantum gravity scenarios. I discuss various gamma-ray observations that give limits on predicted potential effects of Lorentz invariance violation. Among these are spectral data from ground based observations of the multi-TeV gamma-rays from nearby AGN, INTEGRAL detections of polarized soft gamma-rays from the vicinity of the Crab pulsar, Fermi Gamma Ray Space Telescope studies of photon propagation timing from gamma-ray bursts, and Auger data on the spectrum of ultrahigh energy cosmic rays. These results can be used to seriously constrain or rule out some models involving Planck scale physics. Possible implications of these limits for quantum gravity and Planck scale physics will be discussed.

Stecker, Floyd W

2009-01-01

212

Anomalous Thermal Behavior in Microcalorimeter Gamma-Ray Detectors  

SciTech Connect

Improving the resolution of gamma-ray detectors is important for many fields, including determinations of the Lamb shift in atoms with high atomic numbers, nuclear treaty verification, and environmental monitoring. High-purity germanium detectors are currently the tool of choice for precision gamma-ray spectroscopy. The resolution of these detectors is limited to about 500 eV full-width-at-half-maximum at 100 keV by Fano statistics. In comparison, low-temperature microcalorimeters can provide over an order of magnitude improvement in photon resolution. For instance, a gamma-ray microcalorimeter has achieved 25 eV FWHM resolution at 103 keV. These calorimeters consist of two components, a bulk absorber to stop incident gamma rays and a thermometer made from a thin film electrically biased in the superconducting-to-normal phase transition, called a Transition Edge Sensor, or TES. The standard absorber is bulk, superconducting tin. While tin has historically been the best performing absorber, pulse decays in Sn devices are much slower than predicted. We have begun a systematic study of absorber behavior in order to assess and improve response times. This study leverages two capabilities: the ability to microfabricate highly uniform arrays of gamma-ray detectors and the ability to read out many detectors in a single cool-down using SQUID multiplexer circuits. Here, we present two experiments to identify the source of thermal time constants. The first involves varying properties of the Sn absorber including purity, vendor, and crystal grain size. The second examines the role of the other elements in the microcalorimeter assembly.

Horansky, Robert D.; Beall, James A.; Irwin, Kent D.; Ullom, Joel N. [National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305 (United States)

2009-12-16

213

Ultrahigh resolution mass spectrometry and accurate mass measurements for high-throughput food lipids profiling.  

PubMed

In the present study, accurate mass measurements by ultrahigh resolution mass spectrometry with Orbitrap-Exactive working at resolving power R: 100,000 (m/z 200, full width at half maximum) with an accuracy better than 2?ppm in all the mass range (m/z 200 to 2000) were used to show a detailed molecular composition of diverse edible oils and fats. Flow injection was used to introduce samples into the mass spectrometer, obtaining a complete analysis of each sample in less than 10 min, including blanks. Meticulous choice of organic solvents and optimization of the ion source and Orbitrap mass analyzer parameters were carried out, in order to achieve reproducible mass spectra giving reliable elemental compositions of the lipid samples and to prevent carry over. More than 200 elemental compositions attributable to diacylglycerols, triacylglycerols (TAGs), and their oxidation products have been found in the spectra of food lipids from different origin. Several compounds with very close molecular mass could only be resolved through ultrahigh resolution, allowing detailed and robust TAG profiling with a high characterization potential. PMID:22972786

Vichi, Stefania; Cortés-Francisco, Nuria; Caixach, Josep

2012-09-01

214

Extracting and compensating dispersion mismatch in ultrahigh-resolution Fourier domain OCT imaging of the retina.  

PubMed

We present a numerical approach to extract the dispersion mismatch in ultrahigh-resolution Fourier domain optical coherence tomography (OCT) imaging of the retina. The method draws upon an analogy with a Shack-Hartmann wavefront sensor. By exploiting mathematical similarities between the expressions for aberration in optical imaging and dispersion mismatch in spectral / Fourier domain OCT, Shack-Hartmann principles can be extended from the two-dimensional paraxial wavevector space (or the x-y plane in the spatial domain) to the one-dimensional wavenumber space (or the z-axis in the spatial domain). For OCT imaging of the retina, different retinal layers, such as the retinal nerve fiber layer (RNFL), the photoreceptor inner and outer segment junction (IS/OS), or all the retinal layers near the retinal pigment epithelium (RPE) can be used as point source beacons in the axial direction, analogous to point source beacons used in conventional two-dimensional Shack-Hartman wavefront sensors for aberration characterization. Subtleties regarding speckle phenomena in optical imaging, which affect the Shack-Hartmann wavefront sensor used in adaptive optics, also occur analogously in this application. Using this approach and carefully suppressing speckle, the dispersion mismatch in spectral / Fourier domain OCT retinal imaging can be successfully extracted numerically and used for numerical dispersion compensation to generate sharper, ultrahigh-resolution OCT images. PMID:23187353

Choi, WooJhon; Baumann, Bernhard; Swanson, Eric A; Fujimoto, James G

2012-11-01

215

Extracting and compensating dispersion mismatch in ultrahigh-resolution Fourier domain OCT imaging of the retina  

PubMed Central

We present a numerical approach to extract the dispersion mismatch in ultrahigh-resolution Fourier domain optical coherence tomography (OCT) imaging of the retina. The method draws upon an analogy with a Shack-Hartmann wavefront sensor. By exploiting mathematical similarities between the expressions for aberration in optical imaging and dispersion mismatch in spectral / Fourier domain OCT, Shack-Hartmann principles can be extended from the two-dimensional paraxial wavevector space (or the x-y plane in the spatial domain) to the one-dimensional wavenumber space (or the z-axis in the spatial domain). For OCT imaging of the retina, different retinal layers, such as the retinal nerve fiber layer (RNFL), the photoreceptor inner and outer segment junction (IS/OS), or all the retinal layers near the retinal pigment epithelium (RPE) can be used as point source beacons in the axial direction, analogous to point source beacons used in conventional two-dimensional Shack-Hartman wavefront sensors for aberration characterization. Subtleties regarding speckle phenomena in optical imaging, which affect the Shack-Hartmann wavefront sensor used in adaptive optics, also occur analogously in this application. Using this approach and carefully suppressing speckle, the dispersion mismatch in spectral / Fourier domain OCT retinal imaging can be successfully extracted numerically and used for numerical dispersion compensation to generate sharper, ultrahigh-resolution OCT images. PMID:23187353

Choi, WooJhon; Baumann, Bernhard; Swanson, Eric A.; Fujimoto, James G.

2012-01-01

216

Quantification of photoreceptor layer thickness in different macular pathologies using ultrahigh-resolution optical coherence tomography  

NASA Astrophysics Data System (ADS)

In vivo ultrahigh resolution ophthalmic OCT has been performed in more than 300 eyes of 200 patients with several retinal pathologies, demonstrating unprecedented visualization of all major intraretinal layers, in particular the photoreceptor layer. Visualization as well as quantification of the inner and outer segment of the photoreceptor layer especially in the foveal region has been acvhieved. In normal subjects the photoreceptor layer thickness in the center of the fovea is about of 90 ?m, approximately equally distributed to the inner and the outer photoreceptor segment. In the parafoveal region this thickness is reduced to ~50 ?m (~30 ?m for the inner and ~20 ?m for the outer segment). This is in good agreement with well known increase of cone outer segments in the central foveal region. Photoreceptor layer impairment in different macular pathologies like macular hole, central serous chorioretinopathy, age related macular degeneration, foveomacular dystrophies, Stargardt dystrophy as well as retinitis pigmentosa has been investigated. Photoreceptor layer loss significantly correlated with visual acuity (R2 = 0.6, p < 0.001) and microperimetry findings for the first time in 22 eyes with Stargardt dystrophy. Visualization and quantification of photoreceptor inner and outer segment using ultrahigh resolution OCT has the potential to improve early ophthalmic diagnosis, contributes to a better understanding of pathogenesis of retinal diseases as well as might have impact in the development and monitoring of novel therapy approaches.

Drexler, Wolfgang; Hermann, Boris; Unterhuber, Angelika; Sattmann, Harald; Wirtitsch, Matthias; Stur, Michael; Scholda, Christoph; Ergun, Erdem; Anger, Elisabeth; Ko, Tony H.; Schubert, Christian; Ahnelt, Peter K.; Fujimoto, James G.; Fercher, Adolf F.

2004-07-01

217

Development of an ultrahigh resolution Si-PM based PET system for small animals.  

PubMed

Since a high resolution PET system is needed for small animal imaging, especially for mouse studies, we developed a new small animal PET system that decreased the size of the scintillators to less than 1 mm. Our developed PET system used 0.5 × 0.7 × 5 mm(3) LYSO pixels arranged in an 11 × 13 matrix to form a block with a 0.1 mm BaSO4 reflector between the pixels. Two LYSO blocks were optically coupled to two optical fiber based angled image guides. These LYSO blocks and image guides were coupled to a Si-PM array (Hamamatsu MPPC S11064-050P) to form a block detector. Eight block detectors (16 LYSO blocks) were arranged in a 34 mm inner diameter ring to form a small animal PET system. The block detector showed good separation for the 22 × 13 LYSO pixels in the two-dimensional position histogram. The energy resolution was 20% full-with at half-maximum (FWHM) for 511 keV gamma photons. The transaxial resolution reconstructed by filtered backprojection was 0.71 to 0.75 mm FWHM and the axial resolution was 0.70 mm. The point source sensitivity was 0.24% at the central axial field-of-view. High resolution mouse images were obtained using our PET system. The developed ultrahigh resolution PET system showed attractive images for small animal studies and has a potential to provide new findings in molecular imaging researches. PMID:24145308

Yamamoto, Seiichi; Watabe, Hiroshi; Kanai, Yasukazu; Watabe, Tadashi; Kato, Katsuhiko; Hatazawa, Jun

2013-11-01

218

Optimization of dual-band continuum light source for ultrahigh-resolution optical coherence tomography  

NASA Astrophysics Data System (ADS)

We demonstrate a dual-band continuum light source centered at 830 and 1300 nm for optical coherence tomography (OCT) generated by pumping a photonic crystal fiber having two closely spaced zero-dispersion wavelengths with a femtosecond laser at 1059 nm. By use of polarization control, sidelobe suppression can be improved up to approximately 7.7 dB. By employing compression of the pump pulses, the generated spectrum is smooth and near-Gaussian, resulting in a point-spread function with negligible sidelobes. We demonstrate ultrahigh-resolution OCT imaging of biological tissue in vivo and in vitro using this light source and compare it with conventional-resolution OCT imaging at 1300 nm.

Wang, Hui; Rollins, Andrew M.

2007-04-01

219

Ultra-high resolution imaging of the human brain using acquisition-weighted imaging at 9.4T.  

PubMed

One of the main goals of ultra-high field MRI is to increase the spatial resolution reached in structural and functional images. Here, the possibility to obtain in vivo images of the human brain with voxel volumes below 0.02mm(3) is shown at 9.4T. To optimize SNR and suppress ringing artifacts, an acquisition-weighted 3D gradient-echo sequence is used, which acquires more averages in the center than in the outer regions of k-space. The weighting function is adjusted to avoid losses in spatial resolution and scan duration compared to a conventional experiment with an equal number of scans and otherwise identical parameters. Spatial resolution and SNR of the weighted sequence are compared to conventionally acquired images by means of phantom and in vivo measurements, and show improved image quality with unchanged spatial resolution and an SNR increase of up to 36% in phantoms and 20%±5% in vivo. Ultra-high resolution images with a voxel volume of 0.014mm(3) (0.13×0.13×0.8mm(3)) from the human brain have sufficient SNR and show fine intracortical detail, demonstrating the potential of the technique. The combination of acquisition-weighted imaging and highly sensitive array coils at ultra-high fields thus makes it possible to obtain images with ultra-high spatial resolutions within acceptable scan times. PMID:23954486

Budde, Juliane; Shajan, G; Scheffler, Klaus; Pohmann, Rolf

2014-02-01

220

GLAST: a detector for high-energy gamma rays  

NASA Astrophysics Data System (ADS)

The gamma-ray large area space telescope (GLAST) is a proposed next-generation high-energy gamma-ray telescope for studying emission from astrophysical sources in the 10 MeV to 300 GeV energy range. GLAST is currently under study as a NASA new mission concept in astrophysics. The primary scientific targets for the GLAST mission include active galactic nuclei, gamma-ray bursts, neutron stars, and the diffuse galactic and extragalactic high-energy radiation. GLAST relies on the unambiguous identification of incident gamma-rays by detection of the electron and positron that result from pair creation in a thin converter material. Measurement of the energy and direction of the electron- positron pair shower provides information about the energy and direction of the incident gamma-ray. The GLAST design utilizes modern solid-state particle detector technology and recently developed space-qualified computers. Because of the technical approach, the telescope design can be easily optimized to a range of sizes. For example, accommodation of GLAST within a Delta II size launch system results in an instrument with capabilities well beyond those of the highly successful EGRET currently operating on the Compton Observatory; namely, a broader energy range, larger effective area, wider field of view, and single-photon angular resolution 2 to 5 times more precise than EGRET's resolution. GLAST will have an effective area of 8000 cm(superscript 2) above 300 MeV, a field of view of 2.6 sr, and single photon angular resolution (rms projected) of 0.3 degrees at 1 GeV, approaching 0.03 degrees above 20 GeV.

Michelson, Peter F.

1996-10-01

221

Gamma-ray burst spectra and time histories from 2 to 400 keV  

SciTech Connect

The Gamma-Ray burst detector on Ginga consisted of a proportional counter to observe the x-rays and a scintillation counter to observe the gamma-rays. Both instrument recorded the time histories in phase with each other and with 0.03125 s temporal resolution. The author compares the average of 21 gamma-ray bursts to determine the delay, in any, between the peak of the x-rays and the peak of the gamma-rays. The delay is less than or about equal to 30 msec. Thus, models must content with two average features of the temporal behavior. First, as a function of energy, the time structure scales as {approximately}E{sup {minus}0.45}. Second, the x-rays are not appreciable delayed relative to the gamma-rays. Some cooling models might have difficulties explaining these features.

Fenimore, E.E.

1998-07-01

222

Measurements of gamma-ray production cross sections for shielding materials of space nuclear systems  

NASA Technical Reports Server (NTRS)

Measurements of secondary gamma ray production from neutron interactions have been made over the entire energy range of interest in shielding applications. The epithermal capture gamma ray yields for both resolved gamma ray lines and continuum have been measured from thermal energies to 100 KeV for natural tungsten and U-238, two important candidate shield materials in SNAP reactor systems. Data are presented to illustrate the variation of epithermal capture gamma ray yields with neutron energy. The gamma ray production cross sections from (n,xy) reactions have been measured for Fe and Al from the threshold energies for inelastic scattering to approximately 16 MeV. Typical Fe and Al cross sections obtained with high-neutron energy resolution and averaged over broad neutron-energy groups are presented.

Orphan, V. J.; John, J.; Hoot, C. G.

1972-01-01

223

Gamma-Ray Astronomy Technology Needs  

NASA Technical Reports Server (NTRS)

In recent decades gamma-ray observations have become a valuable tool for studying the universe. Progress made in diverse 8re1lS such as gamma-ray bursts (GRBs), nucleosynthesis, and active galactic nuclei (AGNs) has complimented and enriched our astrophysical understanding in many ways. We present an overview of current and future planned space y-ray missions and discussion technology needs for- the next generation of space gamma-ray instruments.

Gehrels, N.; Cannizzo, J. K.

2012-01-01

224

Very High Energy Gamma-Ray Astronomy  

Microsoft Academic Search

We present a review of the current status of very high energy gamma-ray astronomy. The development of the atmospheric Cerenkov imaging technique for ground-based gamma-ray astronomy has led to a rapid growth in the number of observatories. The detection of TeV gamma-rays from active galactic nuclei was unexpected and is providing new insights into the emission mechanisms in the jets.

Michael Catanese; Trevor C. Weekes

1999-01-01

225

Gamma-Ray Pulsar Studies with GLAST  

NASA Technical Reports Server (NTRS)

This viewgraph presentation reviews the prospects of extending the understanding of gamma ray pulsars, and answering the open questions left from the limited observations that are available from current observatories. There are 2 new gamma ray observatories that are either on orbit or will be shortly launched: (1) Astro-rivelatore Gamma a Immagini LEggero (AGILE), and Gamma-ray Large Area Space Telescope (GLAST). On board GLAST there will be two instruments Large Area Telescope (LAT), and GLAST Burst Monitor (GBM).

Thompson, David J.

2007-01-01

226

Gamma rays from star-forming regions  

E-print Network

Star-forming regions have been tentatively associated with gamma-ray sources since the early days of the COS B satellite. After the Compton Gamma-Ray Observatory, the statistical evidence for such an association has became overwhelming. Recent results from Cherenkov telescopes indicate that some high-energy sources are produced in regions of active star formation like Cygnus OB2 and Westerlund 2. In this paper I will briefly review what kind of stellar objects can produce gamma-ray emission in star-forming regions and I will suggest that the formation process of massive stars could in principle result in the production of observable gamma rays.

Gustavo E. Romero

2008-10-15

227

Gamma rays from compact binary system  

E-print Network

Some of the very high energy (VHE) gamma-ray sources detected with the modern generation of Cherenkov telescopes have been identified with previously known X-ray binary systems. These detections demonstrate the richness of non-thermal phenomena in compact galactic objects containing relativistic outflows or winds produced near black holes and neutron stars. Recently, the well-known microquasar Cygnus X-3 seems to be associated with a gamma-ray source detected with AGILE. Here I summarise the main observational results on gamma-ray emission from X-ray binaries, as well as some of the proposed scenarios to explain the production of VHE gamma-rays.

Josep M. Paredes

2008-10-24

228

Fermi Large Area Telescope Measurements of the Diffuse Gamma-Ray Emission at Intermediate Galactic Latitudes  

SciTech Connect

The diffuse galactic {gamma}-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess {gamma}-ray emission {ge}1 GeV relative to diffuse galactic {gamma}-ray emission models consistent with directly measured CR spectra (the so-called 'EGRET GeV excess'). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse {gamma}-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10{sup o} {le} |b| {le} 20{sup o}. The LAT spectrum for this region of the sky is well reproduced by a diffuse galactic {gamma}-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.

Abdo, A.A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.; Ajello, M.; /SLAC; Anderson, B.; Atwood, W.B.; /UC, Santa Cruz; Axelsson, M.; /Stockholm U. /Stockholm U., OKC; Baldini, L.; /INFN, Pisa; Ballet, J.; /DAPNIA, Saclay; Barbiellini, G.; /INFN, Trieste /Trieste U.; Bastieri, D.; /INFN, Padua /Padua U.; Baughman, B.M.; /Taiwan, Natl. Taiwan U. /Ohio State U.; Bechtol, K.; /SLAC; Bellazzini, R.; /INFN, Pisa; Berenji, B.; Blandford, R.D.; Bloom, E.D.; /SLAC; Bonamente, E.; /INFN, Perugia /Perugia U.; Borgland, A.W.; /SLAC; Bregeon, J.; Brez, A.; /INFN, Pisa; Brigida, M.; /Bari U. /INFN, Bari /Ecole Polytechnique /Washington U., Seattle /Bari U. /INFN, Bari /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /IASF, Milan /DAPNIA, Saclay /INFN, Perugia /Perugia U. /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /Naval Research Lab, Wash., D.C. /George Mason U. /NASA, Goddard /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /INFN, Perugia /Perugia U. /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /Montpellier U. /Stockholm U. /Stockholm U., OKC /Royal Inst. Tech., Stockholm /Padua U. /Naval Research Lab, Wash., D.C. /Udine U. /INFN, Trieste /Bari U. /INFN, Bari /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /INFN, Pisa /UC, Santa Cruz /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /CENBG, Gradignan /CENBG, Gradignan /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /Montpellier U. /Bari U. /INFN, Bari /Ecole Polytechnique /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /Udine U. /INFN, Trieste /Hiroshima U. /Stanford U., HEPL /KIPAC, Menlo Park /SLAC /Bari U. /INFN, Bari /INFN, Pisa /INFN, Bari /NASA, Goddard /Maryland U.; /more authors..

2012-04-11

229

Fermi large area telescope measurements of the diffuse gamma-ray emission at intermediate galactic latitudes.  

PubMed

The diffuse galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission greater, > or approximately equal to 1 GeV relative to diffuse galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called "EGRET GeV excess"). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10 degrees < or = |b| < or = 20 degrees. The LAT spectrum for this region of the sky is well reproduced by a diffuse galactic gamma-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess. PMID:20366246

Abdo, A A; Ackermann, M; Ajello, M; Anderson, B; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cecchi, C; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; Dereli, H; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; Di Bernardo, G; Dormody, M; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Edmonds, Y; Farnier, C; Favuzzi, C; Fegan, S J; Focke, W B; Frailis, M; Fukazawa, Y; Funk, S; Fusco, P; Gaggero, D; Gargano, F; Gehrels, N; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Glanzman, T; Godfrey, G; Grenier, I A; Grondin, M-H; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hughes, R E; Jóhannesson, G; Johnson, A S; Johnson, R P; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocian, M L; Kuehn, F; Kuss, M; Lande, J; Latronico, L; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Nuss, E; Ohsugi, T; Okumura, A; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Panetta, J H; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Porter, T A; Rainò, S; Rando, R; Razzano, M; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rodriguez, A Y; Roth, M; Ryde, F; Sadrozinski, H F-W; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Sellerholm, A; Sgrò, C; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stecker, F W; Striani, E; Strickman, M S; Strong, A W; Suson, D J; Tajima, H; Takahashi, H; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M

2009-12-18

230

Gamma-ray burst spectra and the hardness-intensity correlation  

Microsoft Academic Search

We have performed a global study of gamma-ray burst spectra using the moderate time and energy resolution CONT data from BATSE. These data have 2 s temporal resolution in 16 energy channels that span the range of approximately 20 keV to 1.8 MeV. Spectral fits were created for a large ensemble of gamma-ray bursts. We present distributions of the peak

Robert S. Mallozzi; Geoffrey N. Pendleton; William S. Paciesas; Robert D. Preece; Michael S. Briggs

1998-01-01

231

Fast Super-Resolution Imaging with Ultra-High Labeling Density Achieved by Joint Tagging Super-Resolution Optical Fluctuation Imaging (JT-SOFI)  

E-print Network

Previous stochastic localization-based super-resolution techniques are largely limited by the labeling density and the fidelity to the morphology of specimen. We report on an optical super-resolution imaging scheme implementing joint tagging using multiple fluorescent blinking dyes associated with super-resolution optical fluctuation imaging (JT-SOFI), achieving ultra-high labeling density super-resolution imaging. To demonstrate the feasibility of JT-SOFI, quantum dots with different emission spectra were jointly labeled to the tubulin in COS7 cells, creating ultra-high density labeling. After analyzing and combining the fluorescence intermittency images emanating from spectrally resolved quantum dots, the microtubule networks are capable of being investigated with high fidelity and remarkably enhanced contrast at sub-diffraction resolution. The spectral separation also significantly decreased the frame number required for SOFI, enabling fast super-resolution microscopy through simultaneous data acquisition....

Zeng, Zhiping; Wang, Hening; Huang, Ning; Shan, Chunyan; Zhang, Hao; Teng, Junlin; Xi, Peng

2015-01-01

232

Gravitational Waves versus X and Gamma Ray Emission in a Short Gamma-Ray Burst  

E-print Network

The recent progress in the understanding the physical nature of neutron star equilibrium configurations and the first observational evidence of a genuinely short gamma-ray burst, GRB 090227B, allows to give an estimate of the gravitational waves versus the X and Gamma-ray emission in a short gamma-ray burst.

F. G. Oliveira; Jorge A. Rueda; Remo Ruffini

2012-05-31

233

117Fermi Detects Gamma-Rays from Messier 82 The Fermi Gamma-Ray Space  

E-print Network

117Fermi Detects Gamma-Rays from Messier 82 The Fermi Gamma-Ray Space Telescope has recently to the left shows the gamma-ray energy spectrum measured by Fermi. The data points are presented as crosses telescope is red; Hubble space telescope observations of hydrogen line emission is orange, and the bluest

234

The Universe Viewed in Gamma-Rays 1 Gamma-ray Signatures of Dark Matter Particles  

E-print Network

The Universe Viewed in Gamma-Rays 1 Gamma-ray Signatures of Dark Matter Particles Lars Bergstr@physto.se Abstract Indirect detection methods of dark matter particles are discussed. In particular, detection of supersymmetric dark matter through annihilation into gamma-rays is described. Aspects of the density structure

Enomoto, Ryoji

235

High-resolution microscope for tip-enhanced optical processes in ultrahigh vacuum  

NASA Astrophysics Data System (ADS)

An optical microscope based on tip-enhanced optical processes that can be used for studies on adsorbates as well as thin layers and nanostructures is presented. The microscope provides chemical and topographic informations with a resolution of a few nanometers and can be employed in ultrahigh vacuum as well as gas phase. The construction involves a number of improvements compared to conventional instruments. The central idea is to mount, within an UHV system, an optical platform with all necessary optical elements to a rigid frame that also carries the scanning tunneling microscope unit and to integrate a high numerical aperture parabolic mirror between the scanning probe microscope head and the sample. The parabolic mirror serves to focus the incident light and to collect a large fraction of the scattered light. The first experimental results of Raman measurements on silicon samples as well as brilliant cresyl blue layers on single crystalline gold and platinum surfaces in ultrahigh vacuum are presented. For dye adsorbates a Raman enhancement of ˜106 and a net signal gain of up to 4000 was observed. The focus diameter (˜?/2) was measured by Raman imaging the focal region on a Si surface. The requirements of the parabolic mirror in terms of alignment accuracy were experimentally determined as well.

Steidtner, Jens; Pettinger, Bruno

2007-10-01

236

High-resolution Mapping of Linear Antibody Epitopes Using Ultrahigh-density Peptide Microarrays*  

PubMed Central

Antibodies empower numerous important scientific, clinical, diagnostic, and industrial applications. Ideally, the epitope(s) targeted by an antibody should be identified and characterized, thereby establishing antibody reactivity, highlighting possible cross-reactivities, and perhaps even warning against unwanted (e.g. autoimmune) reactivities. Antibodies target proteins as either conformational or linear epitopes. The latter are typically probed with peptides, but the cost of peptide screening programs tends to prohibit comprehensive specificity analysis. To perform high-throughput, high-resolution mapping of linear antibody epitopes, we have used ultrahigh-density peptide microarrays generating several hundred thousand different peptides per array. Using exhaustive length and substitution analysis, we have successfully examined the specificity of a panel of polyclonal antibodies raised against linear epitopes of the human proteome and obtained very detailed descriptions of the involved specificities. The epitopes identified ranged from 4 to 12 amino acids in size. In general, the antibodies were of exquisite specificity, frequently disallowing even single conservative substitutions. In several cases, multiple distinct epitopes could be identified for the same target protein, suggesting an efficient approach to the generation of paired antibodies. Two alternative epitope mapping approaches identified similar, although not necessarily identical, epitopes. These results show that ultrahigh-density peptide microarrays can be used for linear epitope mapping. With an upper theoretical limit of 2,000,000 individual peptides per array, these peptide microarrays may even be used for a systematic validation of antibodies at the proteomic level. PMID:22984286

Buus, Søren; Rockberg, Johan; Forsström, Björn; Nilsson, Peter; Uhlen, Mathias; Schafer-Nielsen, Claus

2012-01-01

237

Future Gamma-Ray Imaging of Solar Eruptive Events  

NASA Technical Reports Server (NTRS)

Solar eruptive events, the combination of large solar flares and coronal mass ejections (CMEs), accelerate ions to tens of Gev and electrons to hundreds of MeV. The energy in accelerated particles can be a significant fraction (up to tens of percent) of the released energy and is roughly equipartitioned between ions and electrons. Observations of the gamma-ray signatures produced by these particles interacting with the ambient solar atmosphere probes the distribution and composition of the accelerated population, as well as the atmospheric parameters and abundances of the atmosphere, ultimately revealing information about the underlying physics. Gamma-ray imaging provided by RHESSI showed that the interacting approx.20 MeV/nucleon ions are confined to flare magnetic loops rather than precipitating from a large CME-associated shock. Furthermore, RHESSI images show a surprising, significant spatial separation between the locations where accelerated ions and electrons are interacting, thus indicating a difference in acceleration or transport processes for the two types of particles. Future gamma-ray imaging observations, with higher sensitivity and greater angular resolution, can investigate more deeply the nature of ion acceleration. The technologies being proven on the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS), a NASA balloon instrument, are possible approaches for future instrumentation. We discuss the GRIPS instrument and the future of studying this aspect of solar eruptive events.

Shih, Albert

2012-01-01

238

Galactic Diffuse Gamma Ray Emission Is Greater than 10 Gev  

NASA Technical Reports Server (NTRS)

AGILE and Gamma-ray Large Area Telescope (GLAST) are the next high-energy gamma-ray telescopes to be flown in space. These instruments will have angular resolution about 5 times better than Energetic Gamma-Ray Experiment Telescope (EGRET) above 10 GeV and much larger field of view. The on-axis effective area of AGILE will be about half that of EGRET, whereas GLAST will have about 6 times greater effective area than EGRET. The capabilities of ground based very high-energy telescopes are also improving, e.g. Whipple, and new telescopes, e.g. Solar Tower Atmospheric Cerenkov Effect Experiment (STACEE), Cerenkov Low Energy Sampling and Timing Experiment (CELESTE), and Mars Advanced Greenhouse Integrated Complex (MAGIC) are expected to have low-energy thresholds and sensitivities that will overlap the GLAST sensitivity above approximately 10 GeV. In anticipation of the results from these new telescopes, our current understanding of the galactic diffuse gamma-ray emission, including the matter and cosmic ray distributions is reviewed. The outstanding questions are discussed and the potential of future observations with these new instruments to resolve these questions is examined.

Hunter, Stanley D.; White, Nicholas E. (Technical Monitor)

2000-01-01

239

Light collection optimization in scintillator-based gamma-ray spectrometers  

NASA Astrophysics Data System (ADS)

Scintillator-based gamma-ray detectors are being actively pursued for homeland security applications. A key property of such detectors is their energy resolution which enables faster detection and more precise identification of gamma-ray sources. In order to obtain the best energy resolution with a given scintillator material, it is crucial to collect the largest fraction possible of the light emitted after gamma-ray absorption. Different techniques to maximize the light collection efficiency were investigated and tested experimentally. In particular, the effect of the scintillator geometry has been simulated with Detect2000. Also, a number of wrapping materials have been tested for their reflectivity and their performance in terms of improving the energy resolution in a BGO-based gamma-ray detector. The best results were obtained with a tapered cylinder geometry and the GORE DRP tape.

Hull, G.; Du, S.; Niedermayr, T.; Payne, S.; Cherepy, N.; Drobshoff, A.; Fabris, L.

2008-04-01

240

Ultra-high vacuum scanning thermal microscopy for nanometer resolution quantitative thermometry.  

PubMed

Understanding energy dissipation at the nanoscale requires the ability to probe temperature fields with nanometer resolution. Here, we describe an ultra-high vacuum (UHV)-based scanning thermal microscope (SThM) technique that is capable of quantitatively mapping temperature fields with ?15 mK temperature resolution and ?10 nm spatial resolution. In this technique, a custom fabricated atomic force microscope (AFM) cantilever, with a nanoscale Au-Cr thermocouple integrated into the tip of the probe, is used to measure temperature fields of surfaces. Operation in an UHV environment eliminates parasitic heat transport between the tip and the sample enabling quantitative measurement of temperature fields on metal and dielectric surfaces with nanoscale resolution. We demonstrate the capabilities of this technique by directly imaging thermal fields in the vicinity of a 200 nm wide, self-heated, Pt line. Our measurements are in excellent agreement with computational results-unambiguously demonstrating the quantitative capabilities of the technique. UHV-SThM techniques will play an important role in the study of energy dissipation in nanometer-sized electronic and photonic devices and the study of phonon and electron transport at the nanoscale. PMID:22530657

Kim, Kyeongtae; Jeong, Wonho; Lee, Woochul; Reddy, Pramod

2012-05-22

241

Ultrahigh-resolution endoscopic optical coherence tomography for in vivo mouse colonoscopy  

NASA Astrophysics Data System (ADS)

In vivo monitoring of mouse models of colon cancer promises to reduce the cost of research by improving sacrifice timing and allowing serial studies that observe the progression of disease and drug efficacy in a relatively small set of animals. Optical coherence tomography (OCT) is an optical analog of ultrasound imaging, capable of minimally-invasive mapping of light scatter intensity up to 2 mm deep in tissue. In this work, factors limiting resolution in OCT were examined and devices were created and applied to mouse colon imaging that extended the state-of-the-art in endoscopic ultrahigh-resolution OCT. First, axial chromatic aberration of the objective optics acts as a spectral filter in the sample arm limiting the effective bandwidth of the system. An achromatized endoscope design was demonstrated that achieved axial resolution of 2.3 mum in tissue and 4.4 mum lateral spot diameter with 101 dB sensitivity when interfaced with a time domain OCT system utilizing a 10-femtosecond laser (Deltalambda=150 nm FWHM, lambdac=800 nm). Second, dispersion matching between the sample and reference arms presents the practical resolution limit to endoscopic implementations including a separate, fiber-based reference arm. A second endoscope incorporated the reference arm into the tip of the endoscope using a novel custom beamsplitter prism and achieved 2.4 mum axial resolution in tissue without adjustments for pathlength or dispersion matching when interfaced with a spectrometer-based frequency domain OCT system and a similar laser. Third, non-linear dispersion of the sample media with respect to wavelength causes distortion and broadening of the axial point spread function when data are sampled uniformly in optical frequency. An experiment was performed on high dispersion glass to demonstrate that dispersion artifact free imaging can be achieved without post process corrections if the samples are acquired at equal intervals of media index of refraction divided by vacuum wavelength. Finally, other microscopic modalities that depend on tissue scatter intensity are used to find the origins of scatter in the mouse colonic mucosa. These observations are used to explain unexpected features found in ultrahigh-resolution tomograms collected with the two endoscopes presented.

Tumlinson, Alexandre Rex

242

The Compton Gamma Ray Observatory: mission status  

Microsoft Academic Search

The Arthur Holly Compton Gamma Ray Observatory (Compton) is the second in NASA's series of Great Observatories. Compton has now been operating for over two and a half years, and has given a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made and

N. Gehrels; E. Chipman; D. A. Kniffen

1994-01-01

243

Gamma ray lines from dark matter annihilation  

SciTech Connect

If direct annihilation of dark matter particles into a pair of photons occurs in the galactic halo, a narrow {gamma}-ray line can be discovered at future {gamma}-ray detectors sensitive to the GeV region. The signals predicted by different dark matter candidates are analyzed. 16 refs., 3 figs.

Giudice, G.F.

1989-08-01

244

Concept of new gamma ray detector  

E-print Network

We present a concept of a new gamma ray detector in order to observe undetected TeV gamma ray background. We measure a track of an electron-positron pair made by a pair creation in a magnet. By using Si as a tracker in a magnetic field 3 T, an energy range is up to 10 TeV.

S. Osone

2002-11-29

245

Atmospheric gamma-ray and neutron flashes  

SciTech Connect

Gamma-ray pulses are calculated from 2D numerical simulations of an upward atmospheric discharge in a self-consistent electric field using the multigroup approach to the kinetics of relativistic runaway electrons (REs). Computed {gamma}-ray numbers and spectra are consistent with those of terrestrial {gamma}-ray flashes (TGFs) observed aboard spacecrafts. The RE flux is concentrated mainly within the domain of the Blue Jet fluorescence. This confirms that exactly the domain adjacent to a thundercloud is the source of the observed {gamma}-ray flashes. The yield of photonuclear neutrons is calculated. One {gamma}-ray pulse generates {approx}10{sup 14}-10{sup 15} neutrons. The possibility of the direct deposition of REs to the detector readings and the origin of the lightning-advanced TGFs are discussed.

Babich, L. P., E-mail: babich@elph.vniief.ru; Kudryavtsev, A. Yu., E-mail: kay@sar.ru; Kudryavtseva, M. L., E-mail: kay@sar.ru; Kutsyk, I. M. [All-Russian Research Institute of Experimental Physics (VNIIEF), Russian Federal Nuclear Center (Russian Federation)

2008-01-15

246

Gamma-Ray Bursts: An Overview  

NASA Technical Reports Server (NTRS)

A history and overview of the observed properties of gamma-ray bursts are presented. The phenomenon of gamma-ray bursts is without precedent in astronomy, having no observed property that would be a direct indicator of their distance and no counterpart object in another wavelength region. Their brief, random appearance only in the gamma-ray region has made their study difficult. The observed time profiles, spectral properties, and durations of gamma-ray bursts cover a wide range. All proposed models for their origin must be considered speculative. It is humbling to think that even after 25 years since their discovery, the distance scale of gamma-ray bursts is still very much debatable.

Fishman, Gerald J.

1995-01-01

247

Research in particle and gamma-ray astrophysics  

NASA Technical Reports Server (NTRS)

This research program is directed toward the investigation of the astrophysical aspects of cosmic rays and gamma rays and of the radiation and electromagnetic field environment of the Earth and other planets. The emphasis was on precice measurements with high resolution in charge, mass and energy. These investigations were carried out by means of energetic particle and photon detector systems flown on spacecraft and balloons.

Stone, E. C.; Davis, L., Jr.; Mewaldt, R. A.; Prince, T. A.

1988-01-01

248

Analysis of protein hydration in ultrahigh-resolution structures of the SRP GTPase Ffh  

PubMed Central

Two new structures of the SRP GTPase Ffh have been determined at 1.1 Å resolution and provide the basis for comparative examination of the extensive water structure of the apo conformation of these GTPases. A set of well defined water-binding positions have been identified in the active site of the two-domain ‘NG’ GTPase, as well as at two functionally important interfaces. The water hydrogen-bonding network accommodates alternate conformations of the protein side chains by undergoing local rearrangements and, in one case, illustrates binding of a solute molecule within the active site by displacement of water molecules without further disruption of the water-interaction network. A subset of the water positions are well defined in several lower resolution structures, including those of different nucleotide-binding states; these appear to function in maintaining the protein structure. Consistent arrangements of surface water between three different ultrahigh-resolution structures provide a framework for beginning to understand how local water structure contributes to protein–ligand and protein–protein binding in the SRP GTPases. PMID:17139088

Ramirez, Ursula D.; Freymann, Douglas M.

2013-01-01

249

High-purity germanium Gamma-Ray Spectrometer with stirling cycle cryocooler  

NASA Astrophysics Data System (ADS)

The Japanese lunar polar orbiter SELENE carries a gamma-ray spectrometer which uses a high-purity Ge detector cooled to 80-90 K by a Stirling mechanical cooler. The Gamma-Ray Spectrometer (GRS) consists of a large volume n-type Ge detector (252 cc) as the main detector and bismuth-germanate (BGO) and plastic scintillators as an active shielding. The engineering model still maintains excellent energy resolution even after severe vibration testing. The Gamma-Ray Spectrometer will globally map of the Moon for the major elements of O, Mg, Al, Si, Ti, Fe, etc. and natural radioisotopes of K, Th and U with a high precision. The energy resolution of the GRS is such that it would identify prompt gamma-ray line from hydrogen and the location and the amount of ice, if it exists at the polar regions.

Kobayashi, M. N.; Hasebe, N.; Miyachi, T.; Doke, T.; Kikuchi, J.; Okada, H.; Oka, A.; Okudaira, O.; Souri, H.; Yamashita, N.; Shibamura, E.; Kashiwagi, T.; Takashima, T.; Narasaki, K.; Tsurumi, K.; Mori, K.; d'Uston, C.; Maurice, S.; Grande, M.; Reedy, R. C.

250

An imaging neutron/gamma-ray spectrometer  

NASA Astrophysics Data System (ADS)

We present the test results of a neutron/gamma-ray imaging spectrometer for the identification and location of radioactive and special nuclear materials. Radioactive materials that could be fashioned into a radiation dispersal device typically emit gamma rays, while fissile materials such as uranium and plutonium emit both neutrons and gamma rays via spontaneous or induced fission. The simultaneous detection of neutrons and gamma rays is a clear indication of the presence of fissile material. The instrument works as a double-scatter telescope, requiring a neutron or gamma ray to undergo an interaction in two detectors to be considered a valid event. While this requirement reduces the detector efficiency, it yields information about the direction and energy of the incident particle, which is then used to reconstruct an image of the emitting source. Because of this imaging capability background events can be rejected, decreasing the number of events required for high confidence detection and thereby greatly improving its sensitivity. The instrument is optimized for the detection of neutrons with energies from 1-20 MeV and gamma rays from 0.4 to 10 MeV. Images and energy spectra for neutron and gamma rays are reported for several sources including depleted uranium and plutonium. In addition, the effect of neutron source shielding is investigated.

Madden, Amanda C.; Bloser, Peter F.; Fourguette, Dominique; Larocque, Liane; Legere, Jason S.; Lewis, Matt; McConnell, Mark L.; Rousseau, Marissa; Ryan, James M.

2013-05-01

251

Observations of Gamma-Ray Bursts  

NASA Technical Reports Server (NTRS)

Some basic observed properties of gamma-ray bursts are reviewed. Although some properties were known 25 years ago, new and more detailed observations have been made by the Compton Observatory in the past three years. The new observation with the greatest impact has been the observed isotropic distribution of bursts along with a deficiency of weak bursts which would be expected from a homogeneous burst distribution. This is not compatible with any known Galactic population of objects. Gamma-ray bursts show an enormous variety of burst morphologies and a wide spread in burst durations. The spectra of gamma-ray bursts are characterized by rapid variations and peak power which is almost entirely in the gamma-ray energy range. Delayed gamma-ray burst photons extending to GeV energies have been detected for the first time. A time dilation effect has also been reported to be observed in gamma-ray, bursts. The observation of a gamma-ray burst counterpart in another wavelength region has yet to be made.

Fishman, G. J.

1995-01-01

252

A liquid xenon 3-dimensional imaging detector for MeV gamma-ray astrophysics  

Microsoft Academic Search

The experiment LXe-CAT (Liquid Xenon-Coded Aperture Telescope), which we have proposed for gamma-ray astrophysical observations in the 0.3-10 MeV energy range, uses a Liquid Xenon Time Projection Chamber (LXe-TPC) as a three-dimensional position sensitive gamma-ray detector, and a coded aperture mask to provide a telescope with an angular resolution of 30 arcmin over a field-of-view (FOV) of 19 deg x

Danli Chen

1994-01-01

253

Observation of SN 1987A with the gamma-ray spectrometer HEXAGONE  

Microsoft Academic Search

The HEXAGONE balloon-borne spectrometer was flown from Alice Springs (Australia) on 1989 May 22. HEXAGONE is a high-resolution gamma-ray spectrometer and consists of an array of twelve cooled germanium detectors. One of the observed targets was the supernova 1987A and it was seen during 9.9hr, 818 days after the initial optical outburst. No significant hard X-ray or gamma-ray emission is

C. G. L. Chapuis; P. Wallyn; Ph. Durouchoux; J. Matteson; M. Pelling; B. Bowman; M. Briggs; D. Gruber; L. Peterson; R. Lingenfelter; C. Cork; D. Landis; P. Luke; N. Madden; D. Malone; R. Pehl; M. Pollard; R. Lin; D. Smith; P. Feffer; K. Hurley; G. Vedrenne; M. Niel; P. von Ballmoos

1993-01-01

254

CdZnTe gamma-ray spectrometer for orbital planetary missions  

Microsoft Academic Search

We present the design and analysis of a new gamma-ray spectrometer for planetary science that uses an array of CdZnTe detectors to achieve the detection efficiency needed for orbital measurements. The use of CdZnTe will provide significantly improved pulse-height resolution relative to scintillation-based detectors, with commensurate improvement in the accuracy of elemental abundances determined by gamma-ray and neutron spectroscopy. The

Thomas H. Prettyman; William C. Feldman; Kenneth R. Fuller; Steven A. Storms; Stephen A. Soldner; Csaba Szeles; Frank P. Ameduri; David J. Lawrence; Michael C. Browne; Calvin E. Moss

2002-01-01

255

Fermi LAT measurements of diffuse gamma-ray emission: results at the first-year milestone  

SciTech Connect

For more than one year the Fermi Large Area Telescope has been surveying the gamma-ray sky from 20 MeV to more than 300 GeV with unprecedented statistics and angular resolution. One of the key science targets of the Fermi mission is diffuse gamma-ray emission. Galactic interstellar gamma-ray emission is produced by interactions of high-energy cosmic rays with the interstellar gas and radiation field. We review the most important results on the subject obtained so far: the non-confirmation of the excess of diffuse GeV emission seen by EGRET, the measurement of the gamma-ray emissivity spectrum of local interstellar gas, the study of the gradient of cosmic-ray densities and of the X{sub CO} = N(H{sub 2})/W{sub CO} ratio in the outer Galaxy. We also catch a glimpse at diffuse gamma-ray emission in the Large Magellanic Cloud. These results allow the improvement of large-scale models of Galactic diffuse gamma-ray emission and new measurements of the extragalactic gamma-ray background.

Tibaldo, Luigi [INFN-Sezione di Padova and Dipartimento di Fisica 'G. Galilei'-Universita di Padova, I-35131 Padova, Italy and Laboratoire AIM, CEA-IRFU/CNRS/Universite Paris Diderot, Service d'Astrophysique, CEA Saclay, 91191 Gif sur Yvette (France)

2010-03-26

256

Fermi Gamma-Ray Space Telescope  

NASA Technical Reports Server (NTRS)

The Fermi Gamma-ray Space Telescope, launched in June 2008, is an observatory designed to survey the high-energy gamma-ray sky. The primary instrument, the Large Area Telescope (LAT), provides observations from 20 MeV to greater than 300 GeV. A second instrument, the Gamma-ray Burst Monitor (GBM), provides observations of transients from less than 10 keV to 40 MeV. We describe the design and performance of the instruments and their subsystems, the spacecraft and the ground system.

McEnery, Julie E.; Michelson, Peter F.; Paclesas, William S.; Ritz, Steven

2012-01-01

257

Cosmic gamma-ray lines - Theory  

NASA Technical Reports Server (NTRS)

The various processes that lead to gamma-ray line emission and the possible astrophysical sources of such emission are reviewed. The processes of nuclear excitation, radiative capture, positron annihilation, and cyclotron radiation, which may produce gamma-ray line emission from such diverse sources as the interstellar medium, novas, supernovas, pulsars, accreting compact objects, the galactic nucleus and the nuclei of active galaxies are considered. The significance of the relative intensities, widths, and frequency shifts of the lines are also discussed. Particular emphasis is placed on understanding those gamma-ray lines that have already been observed from astrophysical sources.

Lingenfelter, R. E.; Ramaty, R.

1980-01-01

258

NEAR Gamma Ray Spectrometer Characterization and Repair  

NASA Technical Reports Server (NTRS)

This report covers the work completed in the third year of the contract. The principle activities during this period were (1) the characterization of the NEAR 2 Gamma Ray Spectrometer using a neutron generator to generate complex gamma ray spectra and a large Ge Detecter to identify all the major peaks in the spectra; (2) the evaluation and repair of the Engineering Model Unit of the Gamma Ray Spectrometer for the NEAR mission; (3) the investigation of polycapillary x-ray optics for x-ray detection; and (4) technology transfer from NASA to forensic science.

Groves, Joel Lee; Vajda, Stefan

1998-01-01

259

Detecting axionlike particles with gamma ray telescopes.  

PubMed

We propose that axionlike particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to a detectable signature in the spectra of high-energy gamma-ray sources. This occurs as a result of gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the "Hillas criterion", such as jets of active galactic nuclei or hot spots of radio galaxies. The discovery of such an effect is possible by GLAST in the 1-100 GeV range and by ground-based gamma-ray telescopes in the TeV range. PMID:18233353

Hooper, Dan; Serpico, Pasquale D

2007-12-01

260

Simulation of the ultrahigh energy resolution IXS analyzer system at NSLS-II  

NASA Astrophysics Data System (ADS)

The ultrahigh energy resolution IXS spectrometer being developed at the National Synchrotron Light Source II (NSLSII) employs an innovative optical design. Its analyzer system utilizes an L-shaped laterally graded multilayer mirror in tandem with a multi-crystal arrangement. The multi-crystal arrangement explores the angular dispersion effect in extremely asymmetric Bragg reflections to achieve sub-meV energy resolution at an energy about 9.1 keV. Its angular acceptance (~ 0.1 mrad) is about two orders of magnitude lower than the spherically-bent backscattering analyzers conventionally used in other IXS spectrometers. The L-shaped laterally graded multiplayer mirror was designed to increase the angular acceptance of this new multi-crystal optics to a comparable level. It performs angular collimation of the incoming beam from about 15 mrad down to 0.1 mrad in both vertical and horizontal directions. Here we present simulations of the mirror performance and study the positioning and stability requirements in conjunction with the multicrystal energy analyzer.

Suvorov, Alexey; Coburn, David S.; Cunsolo, Alessandro; Keister, Jeffrey W.; Cai, Yong Q.

2014-09-01

261

Evaluation of hypoxic swelling of human cornea with high speed ultrahigh resolution optical coherence tomography  

NASA Astrophysics Data System (ADS)

Hypoxia induced corneal swelling was observed and evaluated in healthy human volunteers by use of high speed, ultrahigh resolution optical coherence tomography (UHROCT). Two dimensional corneal images were acquired at a speed of 47,000 A-scans/s with 3µm x 10µm (axial x lateral) resolution in corneal tissue. The UHROCT tomograms showed clear visualization of all corneal layers, including the Bowman's layer and the Descemet's membrane - Endothelium complex. A segmentation algorithm was developed and used for automatic detection of the boundaries of the different corneal layers and evaluation the individual layer thickness as a function of location. Corneal hypoxia was induced by wear of a soft contact lens (SCL) and an eye patch by 2 healthy volunteers for duration of 3 hours. The thickness of all corneal layers was measured as a function of time, prior to, with and after removal of the SCL. Results from the hypoxia study showed different rates of swelling and de-swelling of the individual corneal layers. About 10% increase in the total cornea thickness was observed, similar to the changes in the stroma, the Bowman's membrane swelled by 20%, while no significant change in the thickness was observed in the Descemet's - Endothelium complex.

Bizheva, Kostadinka; Hyun, Chulho; Eichel, Justin; Hariri, Sepideh; Mishra, Akshaya; Clausi, David; Fieguth, Paul; Simpson, Trefford; Hutchings, Natalie

2009-02-01

262

Miniaturization in x ray and gamma ray spectroscopy  

NASA Technical Reports Server (NTRS)

The paper presents advances in two new sensor technologies and a miniaturized associated electronics technology which, when combined, can allow for very significant miniaturization and for the reduction of weight and power consumption in x-ray and gamma-ray spectroscopy systems: (1) Mercuric iodide (HgI2) x-ray technology, which allows for the first time the construction of truly portable, high-energy resolution, non-cryogenic x-ray fluorescence (XRF) elemental analyzer systems, with parameters approaching those of laboratory quality cryogenic instruments; (2) the silicon avalanche photodiode (APD), which is a solid-state light sensitive device with internal amplification, capable of uniquely replacing the vacuum photomultiplier tube in scintillation gamma-ray spectrometer applications, and offering substantial improvements in size, ruggedness, low power operation and energy resolution; and (3) miniaturized (hybridized) low noise, low power amplification and processing electronics, which take full advantage of the favorable properties of these new sensors and allow for the design and fabrication of advanced, highly miniaturized x-ray and gamma-ray spectroscopy systems. The paper also presents experimental results and examples of spectrometric systems currently under construction. The directions for future developments are discussed.

Iwanczyk, Jan S.; Wang, Yuzhong J.; Bradley, James G.

1993-01-01

263

Gamma-ray spectrometer (GRS) for lunar polar orbiter SELENE  

NASA Astrophysics Data System (ADS)

The high-precision gamma-ray spectrometer (GRS) on the lunar polar orbiter SELENE is designed to measure 200 keV—12 MeV gamma rays in order to determine elemental compositions of the lunar surface. The GRS consists of a large germanium (Ge) crystal as a main detector and a massive bismuth germanate crystal and a plastic scintillator as anticoincidence detectors. The Ge detector is cooled by a Stirling cryocooler with its compressor attached to a passive radiator facing the cold space. The cooling system maintains the Ge detector below 90 K during the observation. The flight model of the GRS has achieved an energy resolution of 3.0 keV (FWHM) at 1333 keV. Energy spectra obtained by the GRS will show sharp gamma-ray lines whose energies identify the elements and whose intensities determine the concentrations of the elements, permitting global mapping of the elemental abundances in the sub-surface of the Moon. The elemental maps obtained by the GRS with such high-energy resolution enable us to study lunar geoscience problems.

Hasebe, Nobuyuki; Shibamura, Eido; Miyachi, Takashi; Takashima, Takeshi; Kobayashi, Masanori; Okudaira, Osamu; Yamashita, Naoyuki; Kobayashi, Shingo; Ishizaki, Takeshi; Sakurai, Kunitomo; Miyajima, Mitsuhiro; Fujii, Masayuki; Narasaki, Keisuke; Takai, Shigeki; Tsurumi, Katsuhiro; Kaneko, Hiroshi; Nakazawa, Michio; Mori, Kunishiro; Gasnault, Olivier; Maurice, Sylvestre; d'Uston, Claude; Reedy, Robert C.; Grande, Manuel

2008-04-01

264

Terrestrial Gamma-ray Flash (TGFs) Above Thunderstorms  

NASA Technical Reports Server (NTRS)

Terrestrial gamma-ray flashes (TGFs) are being observed with the Gamma-ray Burst Monitor (GBM) detectors on Fermi about once every four weeks. These intense millisecond flashes of MeV photons have been observed with four space-borne experiments since their initial discovery by the BATSE-CGRO experiment in the early 1990s. TGFs have extremely hard spectra (harder than GRBs) and photons are seen to extend to over 30 MeV. The GBM-Fermi observations have the highest temporal resolution of any previous TGF observations and time-resolved coarse spectra can be derived. These features will be crucial for testing the leading current model of TGF production: relativistic run-away electron cascades formed in the intense electric fields within thunderstorms.

Fishman, Gerald J.

2009-01-01

265

High-energy gamma rays from the intense 1993 January 31 gamma-ray burst  

NASA Technical Reports Server (NTRS)

The intense gamma-ray burst of 1993 January 31 was detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. Sixteen gamma rays above 30 MeV were imaged in the telescope when only 0.04 gamma rays were expected by chance. Two of these gamma rays have energies of approximately 1 GeV, and the five bin spectrum of the 16 events is fitted by a power law of photon spectral index -2.0 +/- 0.4. The high-energy emission extends for at least 25 s. The most probable direction for this burst is determined from the directions of the 16 gamma rays observed by Egret and also by requiring the position to lie on annulus derived by the Interplanetary Network.

Sommer, M.; Bertsch, D. L.; Dingus, B. L.; Fichtel, C. E.; Fishman, G. J.; Harding, A. K.; Hartman, R. C.; Hunter, S. D.; Hurley, K.; Kanbach, G.

1994-01-01

266

The EGRET high energy gamma ray telescope  

NASA Technical Reports Server (NTRS)

The Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (GRO) is sensitive in the energy range from about 20 MeV to about 30,000 MeV. Electron-positron pair production by incident gamma photons is utilized as the detection mechanism. The pair production occurs in tantalum foils interleaved with the layers of a digital spark chamber system; the spark chamber records the tracks of the electron and positron, allowing the reconstruction of the arrival direction of the gamma ray. If there is no signal from the charged particle anticoincidence detector which surrounds the upper part of the detector, the spark chamber array is triggered by two hodoscopes of plastic scintillators. A time of flight requirement is included to reject events moving backward through the telescope. The energy of the gamma ray is primarily determined by absorption of the energies of the electron and positron in a 20 cm deep NaI(Tl) scintillator.

Hartman, R. C.; Bertsch, D. L.; Fichtel, C. E.; Hunter, S. D.; Kanbach, G.; Kniffen, D. A.; Kwok, P. W.; Lin, Y. C.; Mattox, J. R.; Mayer-Hasselwander, H. A.

1992-01-01

267

Thermal neutron capture gamma-rays  

SciTech Connect

The energy and intensity of gamma rays as seen in thermal neutron capture are presented. Only those (n,..cap alpha..), E = thermal, reactions for which the residual nucleus mass number is greater than or equal to 45 are included. These correspond to evaluations published in Nuclear Data Sheets. The publication source data are contained in the Evaluated Nuclear Structure Data File (ENSDF). The data presented here do not involve any additional evaluation. Appendix I lists all the residual nuclides for which the data are included here. Appendix II gives a cumulated index to A-chain evaluations including the year of publication. The capture gamma ray data are given in two tables - the Table 1 is the list of all gamma rays seen in (n,..gamma..) reaction given in the order of increasing energy; the Table II lists the gamma rays according to the nuclide.

Tuli, J.K.

1983-01-01

268

Gamma rays from giant molecular clouds  

NASA Technical Reports Server (NTRS)

Giant Molecular Clouds (GMCs) are massive, bounded, cool, dense regions containing mostly H2, but also H I, CO, and other molecules. These clouds occupy less than 1 percent of the galactic volume, but are a substantial part of the interstellar mass. They are irradiated by the high energy cosmic rays which are possibly modulated by the matter and magnetic fields within the clouds. The product of cosmic-ray flux and matter density is traced by the emission of high energy gamma-rays. A spherical cloud model is considered and the gamma ray flux from several GMCs within 1 kpc of the sun which should be detectable by the EGRET (Energetic Gamma-Ray Experimental Telescope) instrument on GRO (Gamma Ray Observatory).

Hunter, Stanley D.; Kanbach, Gottfried

1990-01-01

269

Gamma Rays in a Spectrum from the Mars Odyssey Gamma-Ray Spectrometer  

NASA Technical Reports Server (NTRS)

The gamma-ray spectrum from a long sum over the middle latitudes of Mars measured by the Mars Odyssey Gamma Ray Spectrometer was analyzed. About 250 peaks and features were observed, including many seen during the cruise to Mars. The sources of about 85% of these gamma rays were identified. Most were background lines from the Ge detector or from Ti, Mg, and Zn near the detector.

Reedy, R. C.; Evans, L. G.; Brueckner, J.; Kim, K. J.; Boynton, W. V.

2003-01-01

270

Particle Acceleration in Gamma-Ray Burst Jets  

E-print Network

Gradual shear acceleration of energetic particles in gamma-ray burst (GRB) jets is considered. Special emphasis is given to the analysis of universal structured jets, and characteristic acceleration timescales are determined for a power-law and a Gaussian evolution of the bulk flow Lorentz factor $\\gamma_b$ with angle $\\phi$ from the jet axis. The results suggest that local power-law particle distributions may be generated and that higher energy particles are generally concentrated closer to the jet axis. Taking several constraints into account we show that efficient electron acceleration in gradual shear flows, with maximum particle energy successively decreasing with time, may be possible on scales larger than $r \\sim 10^{15}$ cm, provided the jet magnetic field becomes sufficiently weak and/or decreases rapidly enough with distance, while efficient acceleration of protons to ultra-high energies $> 10^{20}$ eV may be possible under a wide range of conditions.

Frank M. Rieger; Peter Duffy

2005-11-02

271

The BATSE experiment on the Gamma Ray Observatory: Solar flare hard x ray and gamma-ray capabilities  

NASA Technical Reports Server (NTRS)

The Burst and Transient Source Experiment (BATSE) for the Gamma Ray Observatory (GRO) consists of eight detector modules that provide full-sky coverage for gamma-ray bursts and other transient phenomena such as solar flares. Each detector module has a thin, large-area scintillation detector (2025 sq cm) for high time-resolution studies, and a thicker spectroscopy detector (125 sq cm) to extend the energy range and provide better spectral resolution. The total energy range of the system is 15 keV to 100 MeV. These 16 detectors and the associated onboard data system should provide unprecedented capabilities for observing rapid spectral changes and gamma-ray lines from solar flares. The presence of a solar flare can be detected in real-time by BATSE; a trigger signal is sent to two other experiments on the GRO. The launch of the GRO is scheduled for June 1990, so that BATSE can be an important component of the Max '91 campaign.

Fishman, G. J.; Meegan, C. A.; Wilson, R. B.; Parnell, T. A.; Paciesas, W. S.; Pendleton, G. N.; Hudson, H. S.; Matteson, J. L.; Peterson, L. E.; Cline, T. L.

1989-01-01

272

GRI: The Gamma-Ray Imager mission  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe While at lower wavebands the observed emission is generally dominated by thermal processes the gamma-ray sky provides us with a view on the non-thermal Universe Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood and nuclear

Jürgen Knödlseder

2006-01-01

273

The Gamma-Ray Imager GRI  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear

Cornelia B. Wunderer

2006-01-01

274

Gamma-ray constraints on supernova nucleosynthesis  

NASA Technical Reports Server (NTRS)

Gamma-ray spectroscopy holds great promise for probing nucleosynthesis in individual supernova explosions via short-lived radioactivity, and for measuring current global Galactic supernova nucleosynthesis with longer-lived radioactivity. It was somewhat surprising that the former case was realized first for a Type II supernova, when both Co-56 and Co-57 were detected in SN 1987A. These provide unprecedented constraints on models of Type II explosions and nucleosynthesis. Live Al-26 in the Galaxy might come from Type II supernovae, and if it is eventually shown to be so, can constrain massive star evolution, supernova nucleosynthesis, and the Galactic Type II supernova rate. Type Ia supernovae, thought to be thermonuclear explosions, have not yet been detected in gamma-rays. This is somewhat surprising given current models and recent Co-56 detection attempts. Ultimately, gamma-ray measurements can confirm their thermonuclear nature, probe the nuclear burning conditions, and help evaluate their contributions to Galactic nucleosynthesis. Type Ib/c supernovae are poorly understood. Whether they are core collapse or thermonuclear events might be ultimately settled by gamma-ray observations. Depending on details of the nuclear processing, any of these supernova types might contribute to a detectable diffuse glow of Fe-60 gamma-ray lines. Previous attempts at detection have come very close to expected emission levels. Remnants of any type of age less that a few centuries might be detectable as individual spots of Ti-44 gamma-ray line emission. It is in fact quite surprising that previous surveys have not discovered such spots, and the constraints on the combination of nucleosynthesis yields and supernova rates are very interesting. All of these interesting limits and possibilities mean that the next mission, International Gamma-Ray Astrophysics Laboratory (INTEGRAL), if it has sufficient sensitivity, is very likely to lead to the realization of much of the great potential of gamma-ray spectroscopy for understanding supernovae.

Leising, Mark D.

1994-01-01

275

Neutrinos and Gamma Rays from Galaxy Clusters  

E-print Network

The next generation of neutrino and gamma-ray detectors should provide new insights into the creation and propagation of high-energy protons within galaxy clusters, probing both the particle physics of cosmic rays interacting with the background medium and the mechanisms for high-energy particle production within the cluster. In this paper we examine the possible detection of gamma-rays (via the GLAST satellite) and neutrinos (via the ICECUBE and Auger experiments) from the Coma cluster of galaxies, as well as for the gamma-ray bright clusters Abell 85, 1758, and 1914. These three were selected from their possible association with unidentified EGRET sources, so it is not yet entirely certain that their gamma-rays are indeed produced diffusively within the intracluster medium, as opposed to AGNs. It is not obvious why these inconspicuous Abell-clusters should be the first to be seen in gamma-rays, but a possible reason is that all of them show direct evidence of recent or ongoing mergers. Their identification with the EGRET gamma-ray sources is also supported by the close correlation between their radio and (purported) gamma-ray fluxes. Under favorable conditions (including a proton spectral index of 2.5 in the case of Abell 85, and sim 2.3 for Coma, and Abell 1758 and 1914), we expect ICECUBE to make as many as 0.3 neutrino detections per year from the Coma cluster of galaxies, and as many as a few per year from the Abell clusters 85, 1758, and 1914. Also, Auger may detect as many as 2 events per decade at ~ EeV energies from these gamma-ray bright clusters.

Brandon Wolfe; Fulvio Melia; Roland M. Crocker; Raymond R. Volkas

2008-07-04

276

Simulating The Gamma-Ray Observatory Spacecraft  

NASA Technical Reports Server (NTRS)

Gamma-Ray Observatory (GRO) spacecraft constitutes major advance in gamma-ray astronomy by offering first opportunity for comprehensive observations in range of 0.1 to 30,000 MeV. GRO Attitude Dynamics Simulator (GROSS) computer program designed to simulate mission. Consists of three separate programs: stand-alone profile program; simulator program, containing simulation control input/output (SCIO) subsystem, truth model (TM) subsystem, and on-board computer (OBC) subsystem; and postprocessor program. Written in FORTRAN 77.

Garrick, J.

1989-01-01

277

High altitude balloons and gamma ray astronomy  

SciTech Connect

The author's experience with scientific high altitude ballooning will be presented. Usefulness of satellite versus balloon platforms will be contrasted in the context of gamma ray astronomy. General principles of gamma ray astronomy instrumentation will be discussed and illustrated in terms of our current instrument, GRIS. Some words about the supernova phenomenon and its necessity for the existence of life in the universe will be followed by a brief glimpse of our preliminary data from Supernova 1987a.

MacCallum, C.J.

1988-01-01

278

ICF gamma-ray reaction history diagnostics  

NASA Astrophysics Data System (ADS)

Reaction history measurements, such as nuclear bang time and burn width, are fundamental components of diagnosing ICF implosions and will be employed to help steer the National Ignition Facility (NIF) towards ignition. Fusion gammas provide a direct measure of nuclear interaction rate (unlike x-rays) without being compromised by Doppler spreading (unlike neutrons). Gas Cherenkov Detectors that convert fusion gamma rays to UV/visible Cherenkov photons for collection by fast optical recording systems have established their usefulness in illuminating ICF physics in several experimental campaigns at OMEGA. In particular, bang time precision better than 25 ps has been demonstrated, well below the 50 ps accuracy requirement defined by the NIF. NIF Gamma Reaction History (GRH) diagnostics are being developed based on optimization of sensitivity, bandwidth, dynamic range, cost, and NIF-specific logistics, requirements and extreme radiation environment. Implementation will occur in two phases. The first phase consists of four channels mounted to the outside of the target chamber at ~6 m from target chamber center (GRH-6m) coupled to ultra-fast photo-multiplier tubes (PMT). This system is intended to operate in the 1013-1017 neutron yield range expected during the early THD campaign. It will have high enough bandwidth to provide accurate bang times and burn widths for the expected THD reaction histories (> 80 ps fwhm). Successful operation of the first GRH-6m channel has been demonstrated at OMEGA, allowing a verification of instrument sensitivity, timing and EMI/background suppression. The second phase will consist of several channels located just inside the target bay shield wall at 15 m from target chamber center (GRH-15m) with optical paths leading through the cement shield wall to well-shielded streak cameras and PMTs. This system is intended to operate in the 1016-1020 yield range expected during the DT ignition campaign, providing higher temporal resolution for the expected burn widths of 10-20 ps associated with ignition. Multiple channels at each phase will allow for increased redundancy, reliability, accuracy and flexibility. In addition, inherent energy thresholding capability combined with this multiplicity will allow exploration of interesting gamma-ray physics well beyond the ignition campaign.

Herrmann, H. W.; Young, C. S.; Mack, J. M.; Kim, Y. H.; McEvoy, A.; Evans, S.; Sedillo, T.; Batha, S.; Schmitt, M.; Wilson, D. C.; Langenbrunner, J. R.; Malone, R.; Kaufman, M. I.; Cox, B. C.; Frogget, B.; Miller, E. K.; Ali, Z. A.; Tunnell, T. W.; Stoeffl, W.; Horsfield, C. J.; Rubery, M.

2010-08-01

279

The HAWC Gamma-Ray Observatory: Sensitivity to Steady and Transient Sources of Gamma Rays  

E-print Network

The High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory is designed to record air showers produced by cosmic rays and gamma rays between 100 GeV and 100 TeV. Because of its large field of view and high livetime, HAWC is well-suited to measure gamma rays from extended sources, diffuse emission, and transient sources. We describe the sensitivity of HAWC to emission from the extended Cygnus region as well as other types of galactic diffuse emission; searches for flares from gamma-ray bursts and active galactic nuclei; and the first measurement of the Crab Nebula with HAWC-30.

Abeysekara, A U; Alvarez, C; Álvarez, J D; Arceo, R; Arteaga-Velázquez, J C; Solares, H A Ayala; Barber, A S; Baughman, B M; Bautista-Elivar, N; Belmont, E; BenZvi, S Y; Berley, D; Rosales, M Bonilla; Braun, J; Caballero-Lopez, R A; Caballero-Mora, K S; Carramiñana, A; Castillo, M; Cotti, U; Cotzomi, J; de la Fuente, E; De León, C; DeYoung, T; Hernandez, R Diaz; Díaz-Vélez, J C; Dingus, B L; DuVernois, M A; Ellsworth, R W; Fernandez, A; Fiorino, D W; Fraija, N; Galindo, A; Garfias, F; González, L X; González, M M; Goodman, J A; Grabski, V; Gussert, M; Hampel-Arias, Z; Hui, C M; Hüntemeyer, P; Imran, A; Iriarte, A; Karn, P; Kieda, D; Kunde, G J; Lara, A; Lauer, R J; Lee, W H; Lennarz, D; Vargas, H León; Linares, E C; Linnemann, J T; Longo, M; Luna-GarcIa, R; Marinelli, A; Martinez, H; Martinez, O; Martínez-Castro, J; Matthews, J A J; Miranda-Romagnoli, P; Moreno, E; Mostafá, M; Nava, J; Nellen, L; Newbold, M; Noriega-Papaqui, R; Oceguera-Becerra, T; Patricelli, B; Pelayo, R; Pérez-Pérez, E G; Pretz, J; Rivière, C; Rosa-González, D; Salazar, H; Salesa, F; Sanchez, F E; Sandoval, A; Santos, E; Schneider, M; Silich, S; Sinnis, G; Smith, A J; Sparks, K; Springer, R W; Taboada, I; Toale, P A; Tollefson, K; Torres, I; Ukwatta, T N; Villaseñor, L; Weisgarber, T; Westerhoff, S; Wisher, I G; Wood, J; Yodh, G B; Younk, P W; Zaborov, D; Zepeda, A; Zhou, H

2013-01-01

280

The blazar gamma-ray luminosity function and the diffuse extragalactic gamma-ray background  

NASA Technical Reports Server (NTRS)

We have used the data from the new EGRET catalog on 'grazars' (blazers which are observed to be high-energy gamma-ray sources), together with radio data, to construct a new relation between radio and gamma-ray luminosity for these sources. Using this relation to construct a grazar gamma-ray luminosity function, we then calculate the contribution of unresolved grazars to the cosmic gamma-ray background radiation. We derive the energy spectrum of this background component above 100 MeV and the angular fluctuations in this background implied by our model.

Salamon, M. H.; Stecker, F. W.

1994-01-01

281

Gamma-ray Albedo of the Moon  

SciTech Connect

We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of gamma-rays from the Moon is very steep with an effective cutoff around 3 GeV (600 MeV for the inner part of the Moon disc). Since it is the only (almost) black spot in the gamma-ray sky, it provides a unique opportunity for calibration of gamma-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). The albedo flux depends on the incident CR spectrum which changes over the solar cycle. Therefore, it is possible to monitor the CR spectrum using the albedo gamma-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo -rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the GLAST LAT to monitor the CR spectrum near the Earth beyond the lifetime of PAMELA.

Moskalenko, Igor V.; Porter, Troy A.

2007-06-14

282

Gamma-ray albedo of the moon  

E-print Network

We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of gamma rays from the Moon is very steep with an effective cutoff around 4 GeV (600 MeV for the inner part of the Moon disc). Apart from other astrophysical sources, the albedo spectrum of the Moon is well understood, including its absolute normalisation; this makes it a useful "standard candle" for gamma-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). The albedo flux depends on the incident CR spectrum which changes over the solar cycle. Therefore, it is possible to monitor the CR spectrum using the albedo gamma-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo gamma rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the GLAST LAT to monitor the CR spectrum near the Earth beyond the lifetime of PAMELA.

Igor V. Moskalenko; Troy A. Porter

2007-08-15

283

Digital discrimination of neutrons and gamma-rays in organic scintillation detectors using moment analysis  

NASA Astrophysics Data System (ADS)

Digital discrimination of neutron and gamma-ray events in an organic scintillator has been investigated by moment analysis. Signals induced by an americium-beryllium (Am/Be) isotropic neutron source in a stilbene crystal detector have been sampled with a flash analogue-to-digital converter (ADC) of 1 GSamples/s sampling rate and 10-bit vertical resolution. Neutrons and gamma-rays have been successfully discriminated with a threshold corresponding to gamma-ray energy about 217 keV. Moment analysis has also been verified against the results assessed by a time-of-flight (TOF) measurement. It is shown that the classification of neutrons and gamma-rays afforded by moment analysis is consistent with that achieved by digital TOF measurement. This method has been applied to analyze the data acquired from the stilbene crystal detector in mixed radiation field of the HL-2A tokamak deuterium plasma discharges and the results are described.

Xie, Xufei; Zhang, Xing; Yuan, Xi; Chen, Jinxiang; Li, Xiangqing; Zhang, Guohui; Fan, Tieshuan; Yuan, Guoliang; Yang, Jinwei; Yang, Qingwei

2012-09-01

284

Digital discrimination of neutrons and gamma-rays in organic scintillation detectors using moment analysis.  

PubMed

Digital discrimination of neutron and gamma-ray events in an organic scintillator has been investigated by moment analysis. Signals induced by an americium-beryllium (Am/Be) isotropic neutron source in a stilbene crystal detector have been sampled with a flash analogue-to-digital converter (ADC) of 1 GSamples/s sampling rate and 10-bit vertical resolution. Neutrons and gamma-rays have been successfully discriminated with a threshold corresponding to gamma-ray energy about 217 keV. Moment analysis has also been verified against the results assessed by a time-of-flight (TOF) measurement. It is shown that the classification of neutrons and gamma-rays afforded by moment analysis is consistent with that achieved by digital TOF measurement. This method has been applied to analyze the data acquired from the stilbene crystal detector in mixed radiation field of the HL-2A tokamak deuterium plasma discharges and the results are described. PMID:23020376

Xie, Xufei; Zhang, Xing; Yuan, Xi; Chen, Jinxiang; Li, Xiangqing; Zhang, Guohui; Fan, Tieshuan; Yuan, Guoliang; Yang, Jinwei; Yang, Qingwei

2012-09-01

285

Four extended gamma-ray supernova remnants newly identified by Fermi-LAT Pass 8 data  

NASA Astrophysics Data System (ADS)

Identifying gamma-ray emission from supernova remnants is crucial to determine the origin of Galactic cosmic rays. Despite the excellent sensitivity and spatial resolution of the Fermi Gamma-ray Space Telescope, it has proven difficult to clearly identify these sources as they are buried in the bright diffuse Galactic background and may be confused with other gamma-ray sources, such as pulsars. Here we report the detection of extended emission from four supernova remnants - CTB 109, PKS 1209-51/52, CTB 37A, RCW 86 - using 5 years of observations with Fermi and the new Pass 8 event reconstruction developed by the LAT collaboration. The improvements with Pass 8 promise to rapidly grow the population of gamma-ray supernova remnants identified through their spatial extension.

Hewitt, John W.; Fermi-LAT Collaboration

2015-01-01

286

High-energy gamma-ray beams from Compton-backscattered laser light  

SciTech Connect

Collisions of light photons with relativistic electrons have previously been used to produce polarized ..gamma..-ray beams with modest (-10%) resolution but relatively low intensity. In contrast, the LEGS project (Laser + Electron Gamma Source) at Brookhaven will produce a very high flux (>2 x 10/sup 7/ s/sup -1/) of background-free polarized ..gamma.. rays whose energy will be determined to a high accuracy (..delta..E = 2.3 MeV). Initially, 300(420)-MeV ..gamma.. rays will be produced by backscattering uv light from the new 2.5(3.0)-GeV X-ray storage ring of the National Synchrotron Light Source (NSLS). The LEGS facility will operate as one of many passive users of the NSLS. In a later stage of the project, a Free Electron Laser is expectred to extend the ..gamma..-ray energy up to 700 MeV.

Sandorfi, A.M.; LeVine, M.J.; Thorn, C.E.; Giordano, G.; Matone, G.

1983-01-01

287

Recent results with a combined gamma-ray and neutron imaging detector  

NASA Astrophysics Data System (ADS)

Numerous instruments have been developed for performing gamma-ray imaging and neutron imaging for research, nondestructive testing, medicine and national security. However, none are capable of imaging gamma-rays and neutrons simultaneously while also discriminating gamma-rays from the neutron. This paper will describe recent experimental results obtained using a gamma/neutron camera based on Cs2LiYCl6:Ce (CLYC) scintillation crystals, which can discriminate gamma-rays from neutrons. The ability to do this while also having good energy resolution provides a powerful capability for detecting and identifying shielded special nuclear materials for security applications. Also discussed are results obtained using a LaBr3 scintillation crystal.

Soundara-Pandian, L.; Whitney, C. M.; Johnson, E. B.; Vinci, R.; Glodo, J.; Christian, J. F.; Gervais, J.; Vogel, Sam; Nagarkar, E.; Robertson, F.; Squillante, M. S.; Waer, P.; Squillante, M. R.

2014-09-01

288

Digital discrimination of neutrons and gamma-rays in organic scintillation detectors using moment analysis  

SciTech Connect

Digital discrimination of neutron and gamma-ray events in an organic scintillator has been investigated by moment analysis. Signals induced by an americium-beryllium (Am/Be) isotropic neutron source in a stilbene crystal detector have been sampled with a flash analogue-to-digital converter (ADC) of 1 GSamples/s sampling rate and 10-bit vertical resolution. Neutrons and gamma-rays have been successfully discriminated with a threshold corresponding to gamma-ray energy about 217 keV. Moment analysis has also been verified against the results assessed by a time-of-flight (TOF) measurement. It is shown that the classification of neutrons and gamma-rays afforded by moment analysis is consistent with that achieved by digital TOF measurement. This method has been applied to analyze the data acquired from the stilbene crystal detector in mixed radiation field of the HL-2A tokamak deuterium plasma discharges and the results are described.

Xie Xufei; Zhang Xing; Yuan Xi; Chen Jinxiang; Li Xiangqing; Zhang Guohui; Fan Tieshuan [School of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing (China); Yuan Guoliang; Yang Jinwei; Yang Qingwei [Southwestern Institute of Physics, Chengdu (China)

2012-09-15

289

A Low-Cost Approach to High-Resolution, Single-Photon Imaging Using Columnar Scintillators and Image Intensifiers  

Microsoft Academic Search

Results are presented for a low-cost, ultra-high resolution gamma camera for small-animal SPECT and molecular imaging. The detector, known as Bazooka SPECT, employs a second-generation image intensifier which is directly coupled to a columnar CsI(Tl) scintillator. Operating in photon-counting mode, individual gamma-ray interactions are seen as clusters of signal, and significant improvement in spatial resolution is obtained by estimating the

Brian W. Miller; H. Bradford Barber; Harrison H. Barrett; Donald W. Wilson; Liying Chen

2006-01-01

290

The Measurements of Gamma-ray Spectrometers from China's Chang'E-1/2 Spacecrafts  

NASA Astrophysics Data System (ADS)

Gamma ray spectrometers, as one of the major payloads onboard China's Chang'E-1/2 spacecrafts, were aimed to provide maps of the abundances of major elements, O, Si, Mg, Al, Ca, Ti, Na, and Fe, and of the natural radioactive elements, U, Th, and K, in the subsurface of the Moon. These elements presented on the lunar surface are the end products of a series of processes (i.e., accumulation, collision, and modification), their measurements, therefore, could provide many important clues to understand the formation and evolution of the Moon. Gamma ray spectrometer onboard Chang'E-1spacecraft used a large CsI(Tl) crystal as its main detector to measure gamma rays from the Moon with energy resolution of ˜9%@662 keV while Chang'E-2 gamma ray spectrometer firstly used big LaBr3 crystal in the planetary detection with energy resolution of ˜3.61%@662 keV. Both gamma ray spectrometers used coincident technique to suppress the Compton effects and reduce the background gamma rays from the interactions from GCRs with spacecraft materials. Gamma rays from the Moon were measured in the energy range of 0.3 ˜ 10 MeV with 512-channel spectrum every 3 seconds from a circle, polar-orbit but at a nominal altitude of 200 km and 100 km, respectively. Thorium and Potassium maps were derived from the one-year gamma ray measurements of Chang'E-1spacecraft. All these maps show good consistent with previous results from Lunar Prospector and Kaguya missions. Lunar terrains could be clearly classified on the basis of these compositions in relation with other characteristics. Chang'E-2 gamma ray spectrometer has only half-year detections, but since large LaBr3 crystal has higher energy resolution and higher detection efficiency, element distribution across the lunar surface could be obtained with higher precision. With the data set from Chang'E-2 gamma ray spectrometer, radioactive elements (K, and Th), and major elements (Fe, Ti, Si, Mg, Al, O, and Ca) distributions on the lunar surface have been derived. From present research, several new features have been found that are different from the results of Lunar Prospector gamma ray spectrometer.

Zhu, Meng-Hua; Chang, Jin; Ma, T.

2012-07-01

291

Ultrahigh resolution mass spectrometry and indicator species analysis to identify marker components of soil- and plant biomass-derived organic matter fractions  

Technology Transfer Automated Retrieval System (TEKTRAN)

The chemical properties of organic matter affect important soil processes such as speciation, solubilization, and transport of plant nutrients and metals. This work uses ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to determine the molecula...

292

Observing with a space-borne gamma-ray telescope: selected results from INTEGRAL  

E-print Network

The International Gamma-Ray Astrophysics Laboratory, i.e. the INTEGRAL satellite of ESA, in orbit since about 3 years, performs gamma-ray observations of the sky in the 15 keV to 8 MeV energy range. Thanks to its imager IBIS, and in particular the ISGRI detection plane based on 16384 CdTe pixels, it achieves an excellent angular resolution (12 arcmin) for point source studies with good continuum spectrum sensitivity. Thanks to its spectrometer SPI, based on 19 germanium detectors maintained at 85 K by a cryogenic system, located inside an active BGO veto shield, it achieves excellent spectral resolution of about 2 keV for 1 MeV photons, which permits astrophysical gamma-ray line studies with good narrow-line sensitivity. In this paper we review some goals of gamma-ray astronomy from space and present the INTEGRAL satellite, in particular its instruments ISGRI and SPI. Ground and in-flight calibration results from SPI are presented, before presenting some selected astrophysical results from INTEGRAL. In particular results on point source searches are presented, followed by results on nuclear astrophysics, exemplified by the study of the 1809 keV gamma-ray line from radioactive 26Al nuclei produced by the ongoing stellar nucleosynthesis in the Galaxy. Finally a review on the study of the positron-electron annihilation in the Galactic center region, producing 511 keV gamma-rays, is presented.

S. Schanne

2006-06-22

293

Nucleotide-binding flexibility in ultrahigh-resolution structures of the SRP GTPase Ffh  

PubMed Central

Two structures of the nucleotide-bound NG domain of Ffh, the GTPase subunit of the bacterial signal recognition particle (SRP), have been determined at ultrahigh resolution in similar crystal forms. One is GDP-bound and one is GMPPCP-bound. The asymmetric unit of each structure contains two protein monomers, each of which exhibits differences in nucleotide-binding conformation and occupancy. The GDP-bound Ffh NG exhibits two binding conformations in one monomer but not the other and the GMPPCP-bound protein exhibits full occupancy of the nucleotide in one monomer but only partial occupancy in the other. Thus, under the same solution conditions, each crystal reveals multiple binding states that suggest that even when nucleotide is bound its position in the Ffh NG active site is dynamic. Some differences in the positioning of the bound nucleotide may arise from differences in the crystal-packing environment and specific factors that have been identified include the relative positions of the N and G domains, small conformational changes in the P-loop, the positions of waters buried within the active site and shifts in the closing loop that packs against the guanine base. However, ‘loose’ binding may have biological significance in promoting facile nucleotide exchange and providing a mechanism for priming the SRP GTPase prior to its activation in its complex with the SRP receptor. PMID:18931411

Ramirez, Ursula D.; Focia, Pamela J.; Freymann, Douglas M.

2008-01-01

294

Vertical and horizontal corneal epithelial thickness profiles determined by ultra-high resolution optical coherence tomography  

PubMed Central

Purpose To measure vertical and horizontal thickness profiles of the central and peripheral corneal epithelium and determine if daytime changes occur. Methods Forty eyes of 20 normal subjects were imaged by ultra-high resolution spectral domain optical coherence tomography to profile the corneal epithelial thickness from the edge of Bowman’s layer to the central cornea across the vertical and horizontal meridians. Measurements were made at 10:00 AM and again at 6, 8 hours later. Results The baseline vertical meridional epithelial thickness was thinnest, 42.9±4.1 ?m, at the edge of Bowman’s layer in the superior region. It increased in thickness (p<0.01), towards the central cornea. The central epithelium averaged 52.5±2.4 ?m, becoming thickest, 55.2±2.5 ?m, in the inferior pericentral region. It thinned towards the inferior periphery, reaching 51.3±5.1 ?m at the edge of Bowman’s layer (p<0.01). Along the horizontal meridian, the epithelium was thickest at the nasal side, 58.6±5.1 ?m, and temporal side, 59.3±6.6 ?m, near the edges of Bowman’s layer. It thinned towards the central cornea. There were no significant changes in the epithelial thickness at any location over 8 hours. Conclusion Epithelial thickness varied over the horizontal and vertical meridians and appeared stable during the daytime. PMID:22357393

Du, Chixin; Wang, Jianhua; Cui, Lele; Shen, Meixiao; Yuan, Yimin

2011-01-01

295

Findings of secondary corneal amyloidosis with ultrahigh-resolution optical coherence tomography  

PubMed Central

Purpose To describe observations by ultrahigh-resolution optical coherence tomography (OCT) in a secondary corneal amyloidosis (SCA) patient with histological analysis of excised tissue. A unique finding under OCT of her fellow eye is also described. Case A 39-year-old female had suffered from trichiasis in both of her eyes for more than 30 years. Slit-lamp examination showed a milky-white soft mass on her left cornea and a linear opacity on the fellow cornea at the cilia-attached region. OCT demonstrated the presence of a mass region within a thin epithelial layer and no destruction of Bowman’s layer in her left cornea. In the fellow cornea, which exhibited a linear opacity, a high-density spot in Bowman’s layer was observed at the cilia-attached region covered by the epithelial layer, with normal thickness. Histological examination of the excised cornea showed that the mass was positive with both Congo red and antilactoferrin antibody. Conclusion SCA, amyloid gradually accumulates above Bowman’s layer, occupying the epithelial layer, with no destruction of Bowman’s layer until the advanced stage. A high-density spot in Bowman’s layer might be the first stage of SCA. PMID:25342882

Araki-Sasaki, Kaoru; Osakabe, Yasuhiro; Fukuoka, Hideki; Ideta, Ryuichi; Hirano, Koji

2014-01-01

296

Ultrahigh resolution total organic carbon analysis using Fourier Transform Near Infrarred Reflectance Spectroscopy (FT-NIRS)  

NASA Astrophysics Data System (ADS)

Fourier transform near infrared reflectance spectroscopy (FT-NIRS) is a cheap, rapid, and nondestructive method for analyzing organic sediment components. Here, we examine the robustness of a within lake FT-NIRS calibration using a data set of almost 400 core samples from Lake Suigetsu, Japan, as a means to rapidly reconstruct % total organic carbon (TOC). We evaluate the best spectra pretreatment, examine different statistical approaches, and provide recommendations for the optimum number of calibration samples required for accurate predictions. Results show that the most robust method is based on first-order derivatives of all spectra modeled with partial least squares regression. We construct a TOC model training set using 247 samples and a validation test set using 135 samples (for test set R2 = 0.951, RMSE = 0.280) to determine TOC and illustrate the use of the model in an ultrahigh resolution (e.g., 1 mm/annual) study of a long sediment core from a climatically sensitive archive.

Pearson, Emma J.; Juggins, Steve; Tyler, Jonathan

2014-01-01

297

Gamma-Ray Focusing Optics for Small Animal Imaging  

NASA Technical Reports Server (NTRS)

There is a well-established need for high-resolution radionuclide imaging techniques that provide non-invasive measurement of physiological function in small animals. We, therefore, have begun developing a small animal radionuclide imaging system using grazing incidence mirrors to focus low-energy gamma-rays emitted by I-125, and other radionuclides. Our initial prototype optic, fabricated from thermally-formed glass, demonstrated a resolution of 1500 microns, consistent with the performance predicted by detailed simulations. More recently, we have begun constructing mirrors using a replication technique that reduces low spatial frequency errors in the mirror surface, greatly improving the resolution. Each technique offers particular advantages: e.g., multilayer coatings are easily deposited on glass, while superior resolution is possible with replicated optics. Scaling the results from our prototype optics, which only have a few nested shells, to system where the lens has a full complement of several tens of nested shells, a sensitivity of approx. 1 cps/micro Ci is possible, with the exact number dependent on system magnification and radionuclide species. (Higher levels of efficiency can be obtained with multi-optic imaging systems.) The gamma-ray lens will achieve a resolution as good as 100 microns, independent of the final sensitivity. The combination of high spatial resolution and modest sensitivity will enable in vivo single photon emission imaging studies in small animals.

Pivovaroff, M. J.; Barber, W. C.; Craig, W. W.; Hasegawa, B. H.; Ramsey, B. D.; Taylor, C.

2004-01-01

298

Fast Super-Resolution Imaging with Ultra-High Labeling Density Achieved by Joint Tagging Super-Resolution Optical Fluctuation Imaging  

PubMed Central

Previous stochastic localization-based super-resolution techniques are largely limited by the labeling density and the fidelity to the morphology of specimen. We report on an optical super-resolution imaging scheme implementing joint tagging using multiple fluorescent blinking dyes associated with super-resolution optical fluctuation imaging (JT-SOFI), achieving ultra-high labeling density super-resolution imaging. To demonstrate the feasibility of JT-SOFI, quantum dots with different emission spectra were jointly labeled to the tubulin in COS7 cells, creating ultra-high density labeling. After analyzing and combining the fluorescence intermittency images emanating from spectrally resolved quantum dots, the microtubule networks are capable of being investigated with high fidelity and remarkably enhanced contrast at sub-diffraction resolution. The spectral separation also significantly decreased the frame number required for SOFI, enabling fast super-resolution microscopy through simultaneous data acquisition. As the joint-tagging scheme can decrease the labeling density in each spectral channel, thereby bring it closer to single-molecule state, we can faithfully reconstruct the continuous microtubule structure with high resolution through collection of only 100 frames per channel. The improved continuity of the microtubule structure is quantitatively validated with image skeletonization, thus demonstrating the advantage of JT-SOFI over other localization-based super-resolution methods. PMID:25665878

Zeng, Zhiping; Chen, Xuanze; Wang, Hening; Huang, Ning; Shan, Chunyan; Zhang, Hao; Teng, Junlin; Xi, Peng

2015-01-01

299

Gamma-ray identification of nuclear weapon materials  

SciTech Connect

There has been an accelerating national interest in countering nuclear smuggling. This has caused a corresponding expansion of interest in the use of gamma-ray spectrometers for checkpoint monitoring, nuclear search, and within networks of nuclear and collateral sensors. All of these are fieldable instruments--ranging from large, fixed portal monitors to hand-held and remote monitoring equipment. For operational reasons, detectors with widely varying energy resolution and detection efficiency will be employed. In many instances, such instruments must be sensitive to weak signals, always capable of recognizing the gamma-ray signatures from nuclear weapons materials (NWM), often largely insensitive to spectral alteration by radiation transport through intervening materials, capable of real-time implementation, and able to discriminate against signals from commonly encountered legitimate gamma-ray sources, such as radiopharmaceuticals. Several decades of experience in classified programs have shown that all of these properties are not easily achieved and successful approaches were of limited scope--such as the detection of plutonium only. This project was originally planned as a two-year LDRD-ER. Since funding for 1997 was not sustained, this is a report of the first year's progress.

Gosnell, T. B., LLNL; Hall, J. M.; Jam, C. L.; Knapp, D. A.; Koenig, Z. M.; Luke, S. J.; Pohl, B. A.; Schach von Wittenau, A.; Wolford, J. K.

1997-02-03

300

A cosmic gamma-ray burst on May 14, 1975  

NASA Technical Reports Server (NTRS)

A cosmic gamma-ray burst is reported that occurred at 29309.11 s UTC, May 14, 1975. The burst was detected at an atmospheric depth of 4 g/sq cm residual atmosphere with the University of California double scatter gamma-ray telescope launched on a balloon from Palestine, Texas at 1150 UTC, May 13, 1975. The burst was observed both in the single scatter mode by the top liquid scintillator tank in anti-coincidence with the surrounding plastic scintillator and in the double scatter mode from which energy and directional information are obtained. The burst is 24 standard deviations above the background for single scatter events. The total gamma-ray flux in the burst, incident on the atmosphere with photon energy greater than 0.5 MeV, is 0.59 + or - 0.15 photons/sq cm. The initial rise time to 90% of maximum is 0.015 + or - 0.005 s and the duration is 0.11 s. Time structure down to the 5 ms resolution of the telescope is seen. The mean flux over this time period is 5.0 + or - 1.3 photons/sq cm/s and the maximum flux is 8.5 + or - 2.1 photons/sq cm/s.

Herzo, D.; Dayton, B.; Zych, A. D.; White, R. S.

1975-01-01

301

Focal plane actuation to achieve ultra-high resolution on suborbital balloon payloads  

NASA Astrophysics Data System (ADS)

Over the past few years there has been remarkable success flying imaging telescope systems suspended from suborbital balloon payload systems. These imaging systems have covered optical, ultraviolet, sub-­-millimeter and infrared passbands (i.e. BLAST, STO, SBI, Fireball and others). In recognition of these advances NASA is now considering ambitious programs to promote planetary imaging from high altitude at a fraction of the cost of similar fully orbital systems. The challenge with imaging from a balloon payload is delivering the full diffraction-­-limited resolution of the system from a moving payload. Good progress has been made with damping mechanisms and oscillation control to remove most macroscopic movement in the departures of the imaging focal plane from a static configuration, however a jitter component remains that is difficult to remove using external corrections. This paper reports on work to demonstrate in the laboratory the utility and performance of actuating a detector focal plane (of whatever type) to remove the final jitter terms using an agile hexapod design. The input to this demonstration is the jitter signal generated by the pointing system of a previously flown balloon mission (the Stratospheric Terahertz Observatory, STO). Our group has a mature jitter compensation system that thermally isolates the control head from the focal plane itself. This allows the hexapod to remain at ambient temperature in a vacuum environment with the focal plane cooled to cryogenic temperatures. Our lab design mounts the focal plane on the hexapod in a custom cryostat and delivers an active optical stimulus together with the corresponding jitter signal, using the actuation of the hexapod to correct for the departures from a static, stable configuration. We believe this demonstration will make the case for inclusion of this technological solution in future balloon-­-borne imaging systems requiring ultra-­-high resolution.

Scowen, Paul A.; Miller, Alex; Challa, Priya; Veach, Todd; Groppi, Chris; Mauskopf, Phil

2014-07-01

302

Ultrahigh resolution optical coherence tomography imaging of diseased rat lung using Gaussian shaped super continuum sources  

NASA Astrophysics Data System (ADS)

We have been investigating ultrahigh resolution optical coherence tomography (UHR-OCT) imaging of lung tissues using fiber super continuum sources. The high power, low-noise, Gaussian shaped supercontinuum generated with ultrashort pulses and optical fibers at several wavelengths were used as the broadband light sources for UHR-OCT. For the 800 nm wavelength region, the axial resolution was 3.0 um in air and 2.0 um in tissue. Since the lung consists of tiny alveoli which are separated by thin wall, the UHR-OCT is supposed to be effective for lung imaging. The clear images of alveoli of rat were observed with and without index matching effects by saline. In this work, we investigated the UHR-OCT imaging of lung disease model. The lipopolysaccharide (LPS) induced acute lung injury / acute respiratory distress syndrome (ALI/ARDS) model of rat was prepared as the sample with disease and the UHR-OCT imaging of the disease part was demonstrated. The increment of signal intensity by pleural thickening was observed. The accumulation of exudative fluid in alveoli was also observed for two samples. By the comparison with normal lung images, we can obviously show the difference in the ALI/ARDS models. Since the lung consists of alveolar surrounded by capillary vessels, the effect of red-blood cells (RBC) is considered to be important. In this work, ex-vivo UHR-OCT imaging of RBC was demonstrated. Each RBC was able to be observed individually using UHR-OCT. The effect of RBC was estimated with the rat lung perfused with PBS.

Nishizawa, N.; Ishida, S.; Kitatsuji, M.; Ohshima, H.; Hasegawa, Y.; Matsushima, M.; Kawabe, T.

2012-02-01

303

Fireball/Blastwave Model and Soft Gamma-ray Repeaters  

E-print Network

Soft gamma-ray repeaters are at determined distances and their positions are known accurately. If observed, afterglows from their soft gamma-ray bursts will provide important clues to the study of the so called "classical gamma-ray bursts". On applying the popular fireball/blastwave model of classical gamma-ray bursts to soft gamma-ray repeaters, it is found that their X-ray and optical afterglows are detectable. Monitoring of the three repeaters is solicited.

Y. F. Huang; Z. G. Dai; T. Lu

2005-02-24

304

Terrestrial Gamma-ray Flashes (TGFs) Observed with the Fermi-Gamma-ray Burst Monitor: Temporal and Spectral Properties  

NASA Technical Reports Server (NTRS)

The Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope Observatory (Fermi) was detecting 2.1 TGFs per week. This rate has increased by a factor of 8 since new flight software was uploaded to the spacecraft in November 2009 in order to increase the sensitivity of GBM to TGFs. Further upgrades to Fermi-GBM to allow observations of weaker TGFs are in progress. The high time resolution (2 s) allows temporal features to be resolved so that some insight may be gained on the origin and transport of the gamma-ray photons through the atmosphere. The absolute time of the TGFs, known to several microseconds, also allows accurate correlations of TGFs with lightning networks and other lightning-related phenomena. The thick bismuth germanate (BGO) scintillation detectors of the GBM system have observed photon energies from TGFs at energies above 40 MeV. New results on the some temporal aspects of TGFs will be presented along with spectral characteristics and properties of several electron-positron TGF events that have been identified.

Fishman, G. J.; Briggs, M. S.; Connaughton, W.; Wilson-Hodge, C.; Bhat, P. N.

2010-01-01

305

Terrestrial Gamma-Ray Flashes (TGFs) Observed with the Fermi-Gamma-Ray Burst Monitor: The First Hundred TGFs  

NASA Technical Reports Server (NTRS)

The Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope Observatory (Fermi) is now detecting 2.1 TGFs per week. At this rate, nearly a hundred TGFs will have been detected by the time of this Meeting. This rate has increased by a factor of 8 since new flight software was uploaded to the spacecraft in November 2009 in order to increase the sensitivity of GBM to TGFs. The high time resolution (2 microseconds) allows temporal features to be resolved so that some insight may be gained on the origin and transport of the gamma-ray photons through the atmosphere. The absolute time of the TGFs, known to several microseconds, also allows accurate correlations of TGFs with lightning networks and other lightning-related phenomena. The thick bismuth germanate (BGO) scintillation detectors of the GBM system have observed photon energies from TGFs at energies above 40 MeV. New results on the some temporal aspects of TGFs will be presented.

Fishman, G J.; Briggs, M. S.; Connaughton, V.; Bhat, P. N.

2010-01-01

306

Neutron induced gamma-ray emission tomography  

NASA Astrophysics Data System (ADS)

Radioactivity induced in a neutron irradiated material may be considered as a distributed radioactive source suitable for imaging using computerized gamma-ray emission tomography. The resulting image reveals the distribution of an element of interest in a given plane of the imaged object. Therefore the technique, neutron induced gamma-ray emission tomography, provides information about the elemental composition and distribution. This is demonstrated by imaging the distribution of sodium in a pellet of freeze-dried sea water and a section of human bone using the gamma-ray emitted by Na-24 produced in the presence of a number of other gamma-ray emitting nuclides. Application of a dual energy scattering correction algorithm developed for this purpose resulted in a 44% increase in contrast for the lower energy gamma-rays (1.36 MeV), where the effect of scattering was pronounced and only 14% for the higher energy line (2.75 MeV) emitted by the same nuclide.

Balogun, F. A.; Spyrou, N. M.; Adesanmi, C. A.

1996-07-01

307

Gamma-ray Emission from Nova Outbursts  

NASA Astrophysics Data System (ADS)

Classical novae produce radioactive nuclei which are emitters of gamma-rays in the MeV range. Some examples are the lines at 478 and 1275 keV (from 7Be and 22Na) and the positron-electron annihilation emission, with the 511 keV line and a continuum. Gamma-ray spectra and light curves are potential unique tools to trace the corresponding isotopes and to give insights on the properties of the expanding envelope. Another possible origin of gamma-rays is the acceleration of particles up to very high energies, so that either neutral pions or inverse Compton processes produce gamma-rays of energies larger than 100 MeV. MeV photons during nova explosions have not been detected yet, although several attempts have been made in the last decades; on the other hand, GeV photons from novae have been detected with the Fermi satellite in V407 Cyg, a nova in a symbiotic binary, where the companion is a red giant with a wind, instead of a main sequence star as in the cataclysmic variables hosting classical novae. Two more novae have been detected recently (summer 2012) by Fermi, apparently in non symbiotic binaries, thus challenging our understanding of the emission mechanism. Both scenarios (radioactivities and acceleration) of gamma-ray production in novae are discussed.

Hernanz, M.

2014-12-01

308

Inverse compton scattering gamma ray source  

NASA Astrophysics Data System (ADS)

Special Nuclear Materials (SNM) (e.g. U-235, Pu-239) can be detected by active interrogation with gamma rays (>6 MeV) through photofission. For long-range detection (˜1 km), an intense beam of gamma rays (˜10 14 per second) is required in order to produce measurable number of neutrons. The production of such fluxes of gamma rays, and in the pulse formats useful for detection, presents many technical challenges, and requires novel approaches to the accelerator and laser technology. RadiaBeam is currently designing a gamma ray source based on Inverse Compton Scattering (ICS) from a high-energy electron beam. To achieve this, improvements in photoinjector, linac, final focus, and laser system are planned. These enhanced sub-systems build on parallel work being performed at RadiaBeam, UCLA, and elsewhere. A high-repetition rate photoinjector, a high-gradient S-band linac, and a laser pulse recirculator will be used. The proposed system will be a transportable source of high-flux, high-energy quasi-monochromatic gamma rays for active interrogation of special nuclear materials.

Boucher, S.; Frigola, P.; Murokh, A.; Ruelas, M.; Jovanovic, I.; Rosenzweig, J. B.; Travish, G.

2009-09-01

309

Stellar Photon Archaeology with Gamma-Rays  

NASA Technical Reports Server (NTRS)

Ongoing deep surveys of galaxy luminosity distribution functions, spectral energy distributions and backwards evolution models of star formation rates can be used to calculate the past history of intergalactic photon densities and, from them, the present and past optical depth of the Universe to gamma-rays from pair production interactions with these photons. The energy-redshift dependence of the optical depth of the Universe to gamma-rays has become known as the Fazio-Stecker relation (Fazio & Stecker 1970). Stecker, Malkan & Scully have calculated the densities of intergalactic background light (IBL) photons of energies from 0.03 eV to the Lyman limit at 13.6 eV and for 0$ < z < $6, using deep survey galaxy observations from Spitzer, Hubble and GALEX and have consequently predicted spectral absorption features for extragalactic gamma-ray sources. This procedure can also be reversed. Determining the cutoff energies of gamma-ray sources with known redshifts using the recently launched Fermi gamma-ray space telescope may enable a more precise determination of the IBL photon densities in the past, i.e., the "archaeo-IBL.", and therefore allow a better measure of the past history of the total star formation rate, including that from galaxies too faint to be observed.

Stecker, Floyd W.

2009-01-01

310

Ultra-High Resolution Spectroscopic Remote Sensing: A Microscope on Planetary Atmospheres  

NASA Technical Reports Server (NTRS)

Remote sensing of planetary atmospheres is not complete without studies of all levels of the atmosphere, including the dense cloudy- and haze filled troposphere, relatively clear and important stratosphere and the upper atmosphere, which are the first levels to experience the effects of solar radiation. High-resolution spectroscopy can provide valuable information on these regions of the atmosphere. Ultra-high spectral resolution studies can directly measure atmospheric winds, composition, temperature and non-thermal phenomena, which describe the physics and chemistry of the atmosphere. Spectroscopy in the middle to long infrared wavelengths can also probe levels where dust of haze limit measurements at shorter wavelength or can provide ambiguous results on atmospheric species abundances or winds. A spectroscopic technique in the middle infrared wavelengths analogous to a radio receiver. infrared heterodyne spectroscopy [1], will be describe and used to illustrate the detailed study of atmospheric phenomena not readily possible with other methods. The heterodyne spectral resolution with resolving power greater than 1,000.000 measures the true line shapes of emission and absorption lines in planetary atmospheres. The information on the region of line formation is contained in the line shapes. The absolute frequency of the lines can be measured to I part in 100 ,000,000 and can be used to accurately measure the Doppler frequency shift of the lines, directly measuring the line-of-sight velocity of the gas to --Im/s precision (winds). The technical and analytical methods developed and used to measure and analyze infrared heterodyne measurements will be described. Examples of studies on Titan, Venus, Mars, Earth, and Jupiter will be presented. 'These include atmospheric dynamics on slowly rotating bodies (Titan [2] and Venus [3] and temperature, composition and chemistry on Mars 141, Venus and Earth. The discovery and studies of unique atmospheric phenomena will also be described, such as non-thermal and lasing phenomena on Mars and Venus, mid-infrared aurora on Jupiter [5], and results of small body impacts on Jupiter [6]. The heterodyne technique can also be applied for detailed study of the Earth's stratosphere and mesosphere by measuring trace constituent abundances and temporal and spatial variability as well as winds, which provide information of transport. All ground-based measurements will be described as complementary and supporting studies for on-going and future space missions [7] (Mars Express, Venus Express, Cassini Huygens, JUNO, ExoMars Trace Gas Orbiter, and the Europa Jupiter System Mission, an Earth Science Venture Class missions), Proposed instrument and technology development for a space flight infrared heterodyne spectrometer will be described.

Kostiuk, Theodor

2010-01-01

311

Neutron-induced gamma-ray spectroscopy: simulations for chemical mapping of planetary surfaces  

SciTech Connect

Cosmic rays interact with the surface of a planetary body and produce a cascade of secondary particles, such as neutrons. Neutron-induced scattering and capture reactions play an important role in the production of discrete gamma-ray lines that can be measured by a gamma-ray spectrometer on board of an orbiting spacecraft. These data can be used to determine the concentration of many elements in the surface of a planetary body, which provides clues to its bulk composition and in turn to its origin and evolution. To investigate the gamma rays made by neutron interactions, thin targets were irradiated with neutrons having energies from 14 MeV to 0.025 eV. By means of foil activation technique the ratio of epithermal to thermal neutrons was determined to be similar to that in the Moon. Gamma rays emitted by the targets and the surrounding material were detected by a high-resolution germanium detector in the energy range of 0.1 to 8 MeV. Most of the gamma-ray lines that are expected to be used for planetary gamma-ray spectroscopy were found in the recorded spectra and the principal lines in these spectra are presented. 58 refs., 7 figs., 9 tabs.

Brueckner, J.; Waenke, H.; Reedy, R.C.

1986-01-01

312

A search for optical counterparts of gamma-ray bursts. Final report  

SciTech Connect

Gamma Ray Bursts (GRBS) are mysterious flashes of gamma rays lasting several tens to hundreds of seconds that occur approximately once per day. NASA launched the orbiting Compton Gamma Ray Observatory to study GRBs and other gamma ray phenomena. CGRO carries the Burst and Transient Experiment (BATSE) specifically to study GRBS. Although BATSE has collected data on over 600 GRBS, and confirmed that GRBs are localized, high intensity point sources of MeV gamma rays distributed isotropically in the sky, the nature and origin of GRBs remains a fundamental problem in astrophysics. BATSE`s 8 gamma ray sensors located on the comers of the box shaped CGRO can detect the onset of GRBs and record their intensity and energy spectra as a function of time. The position of the burst on the sky can be determined to < {plus_minus}10{degrees} from the BATSE data stream. This position resolution is not sufficient to point a large, optical telescope at the exact position of a GRB which would determine its origin by associating it with a star. Because of their brief duration it is not known if GRBs are accompanied by visible radiation. Their seemingly large energy output suggests thatthis should be. Simply scaling the ratio of visible to gamma ray intensities of the Crab Nebula to the GRB output suggests that GRBs ought to be accompanied by visible flashes of magnitude 10 or so. A few photographs of areas containing a burst location that were coincidentally taken during the burst yield lower limits on visible output of magnitude 4. The detection of visible light during the GRB would provide information on burst physics, provide improved pointing coordinates for precise examination of the field by large telescope and provide the justification for larger dedicated optical counterpart instruments. The purpose of this experiment is to detect or set lower limits on optical counterpart radiation simultaneously accompanying the gamma rays from

Park, Hye-Sook

1995-03-09

313

COMBINED GAMMA-RAY AND NEUTRON DETECTOR FOR MEASURING THE CHEMICAL COMPOSITION OF AIRLESS PLANETARY BODIES.  

SciTech Connect

Galactic cosmic rays (GCR) constant1,y itnpinge all planetary bodies and produce characteristic gamma-ray lines and leakage neutrons as reaction products. Together with gamma-ray lines produced by radioactive decay, these nuclear emissions provide a powerful technique for remotely measuring the chemical composition of airless planetary surfaces. While lunar gamma-ray spectroscopy was first demonstrated with Apollo Gamma-Ray measurements, the full value of combined gamma-ray and neutron spectroscopy was shown for the first time with the Lunar Prospector Gamma-Ray (LP-GRS) and Neutron Spectrometers (LP-NS). Any new planetary mission will likely have the requirement that instrument mass and power be kept to a minimum. To satisfy such requirements, we have been designing a GR/NS instrument which combines all the functionality of the LP-GRS and LP-NS for a fraction of the mass and power. Specifically, our design uses a BGO scintillator crystal to measure gamma-rays from 0.5-10 MeV. A borated plastic scintillator and a lithium gliiss scintillator are used to separately measure thermal, epithermal, and fast neutrons as well as serve as an anticoincidence shield for the BGO. All three scintillators are packaged together in a compact phoswich design. Modifications to this design could include a CdZnTe gamma-ray detector for enhanced energy resolution at low energies (0.5-3 MeV). While care needs to be taken to ensure that an adequate count rate is achieved for specific mission designs, previous mission successes demonstrate that a cornbined GR/NS provides essential information about planetary surfaces.

Lawrence, David J. (David Jeffery),; Barraclough, B. L. (Bruce L.); Feldman, W. C. (William C.); Prettyman, T. H. (Thomas H.); Wiens, R. C. (Roger C.)

2001-01-01

314

LaCl{sub 3}:Ce scintillator for Gamma ray detection  

SciTech Connect

In this paper, we report on a relatively new cerium doped scintillator - LaCl3 for gamma ray spectroscopy. Crystals of this scintillator have been grown using Bridgman method. This material when doped with 10 percent cerium has high light output ({approx} 50,000 photons/MeV) and fast principal decay time constant ({approx}20 ns). Furthermore, it shows excellent energy resolution for gamma ray detection. For example, energy resolution as low as 3.2 percent (FWHM) has been achieved with 662 keV photons (137Cs source) at room temperature. Also high timing resolution (264 ps - FWHM) has been recorded with LaCl3-PMT and BaF2-PMT detectors operating in coincidence using 511 keV positron annihilation gamma ray pairs. Details of crystal growth, scintillation properties, and variation of these properties with cerium concentration are also reported.

Shah, K.S.; Glodo, J.; Klugerman, M.; Cirignano, L.; Moses, W.W.; Derenzo, S.E.; Weber, M.J.

2002-05-25

315

The Characterization of Dissolved Organic Nitrogen in Wetlands by Ultrahigh Resolution Mass Spectrometry  

NASA Astrophysics Data System (ADS)

Dissolved Organic Nitrogen (DON) in agricultural runoff water can prove to be troublesome to wetland ecosystems. Therefore, Water Quality Treatment Areas (WQTAs) have been developed to reduce total nitrogen (TN) concentrations, specifically, organic nitrogen. At present the only parameter available for judging the effectiveness of WQTAs is total DON. However, total DON does not account for the biogeochemistry of individual organic nitrogen compounds. There are no doubt many organic-N species that are refractory and present no threat to receiving waters, but they are nevertheless counted as TN. Unfortunately, there is no general method for determining which DON molecules are biodegradable and which are refractory. The purpose of this research is to provide an analytical method that will drive the design of WTQAs that more effectively reduce organic nitrogen concentrations. We coupled Atmospheric Pressure Photo-ionization (APPI) with Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) to specifically focus on the characterization of DON compounds. Atmospheric pressure photoionization (APPI) represents an attractive alternative to the more conventional electrospray ionization (ESI) method. APPI has the ability to ionize both polar and nonpolar compounds, many of which are unobservable by ESI. APPI coupled with the ultrahigh resolution and mass accuracy provided by FT-ICR MS allowed us to unambiguously assign molecular formulas to the specific DON compounds. Therefore, we were able to determine the degree of oxidation and presence of other hetero-atoms, such as sulfur, in these DON compounds. Comparative analysis of the influent and effluent waters from the WTQAs provided valuable data about what types of molecules are successfully removed during the treatment process. This molecular level information was previously unavailable with other analytical techniques, and it may be used to design more effective WQTAs in the future.

Podgorski, D. C.; Osborne, D.; Cooper, W. T.

2009-12-01

316

Non-Invasive Detection of Early Retinal Neuronal Degeneration by Ultrahigh Resolution Optical Coherence Tomography  

PubMed Central

Optical coherence tomography (OCT) has revolutionises the diagnosis of retinal disease based on the detection of microscopic rather than subcellular changes in retinal anatomy. However, currently the technique is limited to the detection of microscopic rather than subcellular changes in retinal anatomy. However, coherence based imaging is extremely sensitive to both changes in optical contrast and cellular events at the micrometer scale, and can generate subtle changes in the spectral content of the OCT image. Here we test the hypothesis that OCT image speckle (image texture) contains information regarding otherwise unresolvable features such as organelle changes arising in the early stages of neuronal degeneration. Using ultrahigh resolution (UHR) OCT imaging at 800 nm (spectral width 140 nm) we developed a robust method of OCT image analyses, based on spatial wavelet and texture-based parameterisation of the image speckle pattern. For the first time we show that this approach allows the non-invasive detection and quantification of early apoptotic changes in neurons within 30 min of neuronal trauma sufficient to result in apoptosis. We show a positive correlation between immunofluorescent labelling of mitochondria (a potential source of changes in cellular optical contrast) with changes in the texture of the OCT images of cultured neurons. Moreover, similar changes in optical contrast were also seen in the retinal ganglion cell- inner plexiform layer in retinal explants following optic nerve transection. The optical clarity of the explants was maintained throughout in the absence of histologically detectable change. Our data suggest that UHR OCT can be used for the non-invasive quantitative assessment of neuronal health, with a particular application to the assessment of early retinal disease. PMID:24776961

Tudor, Debbie; Kaji?, Vedran; Rey, Sara; Erchova, Irina; Považay, Boris; Hofer, Bernd; Powell, Kate A.; Marshall, David; Rosin, Paul L.; Drexler, Wolfgang; Morgan, James E.

2014-01-01

317

Solar gamma rays and neutron observations  

NASA Technical Reports Server (NTRS)

The present status of knowledge concerning the impulsive and the continuous emission of solar gamma rays and neutrons is reviewed in the light of the recent solar activity in early August 1972. The gamma ray spectrometer on OSO-7 has observed the sun continuously for most of the activity period except for occultation by the earth. In association with the 2B flare on 4 August 1972 and the 3B flare on 7 August 1972, the monitor provides evidence for solar gamma ray line emission in the energy range from 300 keV to 10 MeV. A summary of all the results available from preliminary analysis of the data will be given. Significant improvements in future experiments can be made with more sensitive instruments and more extensive time coverage of the sun.

Chupp, E. L.; Forrest, D. J.; Suri, A. N.

1972-01-01

318

Gamma-ray bursters at cosmological distances  

NASA Astrophysics Data System (ADS)

It is proposed that some, perhaps most, gamma-ray bursters are at cosmological distances, like quasars, with a redshift of about 1 or 2. This proposition requires a release of supernova-like energy of about 10 to the 51st ergs within less than 1 s, making gamma-ray bursters the brightest objects known in the universe, many orders of magnitude brighter than any quasars. This power must drive a highly relativistic outflow of electron-positron plasma and radiation from the source. It is proposed that three gamma-ray bursts, all with identical spectra, detected from B1900 + 14 by Mazets, Golenetskii, and Gur'yan and reported in 1979, were all due to a single event multiply imaged by a gravitational lens. The time intervals between the successive bursts, 10 hr to 3 days, were due to differences in the light travel time for different images.

Paczynski, B.

1986-09-01

319

Gamma-ray spectroscopy - Status and prospects  

NASA Astrophysics Data System (ADS)

Contemporary gamma-ray spectroscopy instruments and their results are reviewed. Sensitivities of 10 to the -4th to 10 to the -3rd ph/sq cm-sec have been achieved for steady sources and 10 to the -2nd to 1 ph/sq cm-sec for transient sources. This has led to the detection of gamma-ray lines from more than 40 objects representing 6 classes of astrophysical phenomena. The lines carry model-independent information and are of fundamental importance to theoretical modeling and our understanding of the objects. The objectives and anticipated results of future instruments are discussed. Several instruments in development will have a factor of 10 sensitivity improvement to certain phenomena over contemporary instruments. A factor of 100 improvement in sensitivity will allow the full potential of gamma-ray spectroscopy to be realized. Instrument concepts which would achieve this with both present and advanced techniques are discussed.

Matteson, J. L.

320

Gamma rays from pulsar wind shock acceleration  

NASA Technical Reports Server (NTRS)

A shock forming in the wind of relativistic electron-positron pairs from a pulsar, as a result of confinement by surrounding material, could convert part of the pulsar spin-down luminosity to high energy particles through first order Fermi acceleration. High energy protons could be produced by this mechanism both in supernova remnants and in binary systems containing pulsars. The pion-decay gamma-rays resulting from interaction of accelerated protons with surrounding target material in such sources might be observable above 70 MeV with EGRET (Energetic Gamma-Ray Experimental Telescope) and above 100 GeV with ground-based detectors. Acceleration of protons and expected gamma-ray fluxes from SN1987A, Cyg X-3 type sources and binary pulsars are discussed.

Harding, Alice K.

1990-01-01

321

The Fermi Gamma-ray Burst Monitor  

NASA Astrophysics Data System (ADS)

The Gamma-Ray Burst Monitor (GBM) will significantly augment the science return from the Fermi Observatory in the study of gamma-ray bursts (GRBs). The primary objective of GBM is to extend the energy range over which bursts are observed downward from the energy range of the Large Area Telescope (LAT) on Fermi into the hard X-ray range where extensive previous data sets exist. A secondary objective is to compute burst locations onboard to allow re-orienting the spacecraft so that the LAT can observe delayed emission from bright bursts. GBM uses an array of 12 sodium iodide scintillators and two bismuth germanate scintillators to detect gamma rays from ~8 keV to ~40 MeV over the full unocculted sky. The onboard trigger threshold is ~0.7 photons cm-2 s-1 (50-300 keV, 1 s peak). GBM generates onboard triggers for ~250 GRBs per year.

Meegan, Charles; Lichti, Giselher; Bhat, P. N.; Bissaldi, Elisabetta; Briggs, Michael S.; Connaughton, Valerie; Diehl, Roland; Fishman, Gerald; Greiner, Jochen; Hoover, Andrew S.; van der Horst, Alexander J.; von Kienlin, Andreas; Kippen, R. Marc; Kouveliotou, Chryssa; McBreen, Sheila; Paciesas, W. S.; Preece, Robert; Steinle, Helmut; Wallace, Mark S.; Wilson, Robert B.; Wilson-Hodge, Colleen

2009-09-01

322

The Apollo gamma-ray spectrometer  

NASA Technical Reports Server (NTRS)

A gamma-ray spectrometer has been flown on the Apollo 15 and 16 spacecraft to determine the lunar-surface composition and measure the cosmic gamma-ray flux. The instrument included a NaI(Tl) scintillation crystal coupled to a 7.6-cm photomultiplier tube, a plastic mantle for anti-coincidence rejection of charged particles, and 511 channels of analysis. Boom-mounted operation permitted a significant reduction in the background. The data were transmitted on an event-by-event basis. About 22% of the lunar surface was mapped and spectra of the cosmic gamma-ray flux over an energy range of 0.065-27.5 MeV have been obtained.

Harrington, T. M.; Marshall, J. H.; Arnold, J. R.; Peterson, L. E.; Trombka, J. I.; Metzger, A. E.

1974-01-01

323

A Ge/Li/ spectrometer for gamma ray astronomy  

NASA Technical Reports Server (NTRS)

A space-borne instrument to measure the spectral and temporal characteristics of astronomical gamma rays in the .05 to 10 Mev energy range is described. The spectrometer consists of four 60 cc Ge(Li) detectors with an energy resolution of 2.5 Kev (FWHM) at 1.33 Mev. The Ge(Li) detectors are actively shielded with CsI(Na) for angular collimation and background reduction. Cooling of the Ge(Li) detectors to 88 K for orbital lifetimes of up to two years is provided by a two-stage solid subliming refrigerator.

Hicks, D. B.; Jacobson, A. S.

1974-01-01

324

Gamma ray burst source locations with the new interplanetary network  

NASA Technical Reports Server (NTRS)

The celestial source fields of gamma ray bursts can now be determined with precision considerably greater than that provided by earlier interplanetary networks. A new burst timing array consists of the Ulysses mission and the Pioneer-Venus Orbiter at great distances and the Compton Observatory, Granat, and other burst-observing spacecraft near the Earth. With Ulysses providing a baseline approaching five astronomical units in its progress towards Jupiter, and given the timing resolution of the Compton Burst and Transient Source Experiment, source fields with dimensions as small as several arc seconds by less than one arc minute will be determined for many of the events to be studied within this network.

Cline, T. L.; Fishman, Gerald; Hurley, Kevin; Laros, John; Lund, Neils; Sommer, Michael

1992-01-01

325

Development of a gamma ray spectroscopy capability at LANSCE  

SciTech Connect

This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The goal of this project was to explore an upgrade to the GEANIE high-resolution gamma-ray spectrometer at the Los Alamos Neutron Science Center (LANSCE) to help build additional experimental capabilities. The improvements identified have significantly added to the capabilities of GEANIE and made the facility more attractive for studies supporting the core national security mission as well as for use by outside collaborators. These benefits apply to both basic and applied studies.

Nelson, R.O.; Strottman, D.D.; Sterbenz, S.M.

1998-12-31

326

High-revolution gamma-ray imaging from the moon  

NASA Technical Reports Server (NTRS)

An observatory is suggested for exploiting unique lunar features to perform sensitive, subarcsecond cosmic X-ray and gamma-ray imaging. The observatory would be built in an evolutionary manner and would eventually include several different position-sensitive detector systems which together would cover a broad energy range and address a wide variety of astrophysical problems. High angular resolution would be obtained by using a mobile crane on the flat lunar mare regions to move a coded aperture mask for source tracking with detector/mask separations of up to 5 kilometers.

Mahoney, William A.

1990-01-01

327

Gamma Ray Astronomy With IceCube  

E-print Network

We demonstrate that the South Pole kilometer-scale neutrino observatory IceCube can detect multi-TeV gamma rays continuously over a large fraction of the southern sky. While not as sensitive as pointing atmospheric Cerenkov telescopes, IceCube can roughly match the sensitivity of Milagro. Also, IceCube is complementary to Milagro because it will observe, without interruption, a relatively poorly studied fraction of the southern sky. The information which IceCube must record to function as a gamma ray observatory is only the directions and possibly energies of down-going muons.

Francis Halzen; Dan Hooper

2003-05-13

328

Radioactivities and gamma-rays from supernovae  

NASA Technical Reports Server (NTRS)

An account is given of the implications of several calculations relevant to the estimation of gamma-ray signals from various explosive astronomical phenomena. After discussing efforts to constrain the amounts of Ni-57 and Ti-44 produced in SN 1987A, attention is given to the production of Al-27 in massive stars and SNs. A 'delayed detonation' model of type Ia SNs is proposed, and the gamma-ray signal which may be expected when a bare white dwarf collapses directly into a neutron star is discussed.

Woosley, S. E.

1991-01-01

329

VHE Gamma-ray Supernova Remnants  

SciTech Connect

Increasing observational evidence gathered especially in X-rays and {gamma}-rays during the course of the last few years support the notion that Supernova remnants (SNRs) are Galactic particle accelerators up to energies close to the ''knee'' in the energy spectrum of Cosmic rays. This review summarizes the current status of {gamma}-ray observations of SNRs. Shell-type as well as plerionic type SNRs are addressed and prospect for observations of these two source classes with the upcoming GLAST satellite in the energy regime above 100 MeV are given.

Funk, Stefan; /KIPAC, Menlo Park

2007-01-22

330

Gamma ray line observations with OSSE  

NASA Technical Reports Server (NTRS)

Observations from the oriented scintillation spectrometer experiment of the gamma ray lines originating from a variety of Galactic center sources are reviewed. Extensive observations were acquired of the Galactic center region, including the 0.511 MeV positron annihilation line and associated positronium continuum and Al-26 emission. The results reviewed include: Co-57 from SN 1987A; limits on Co-56 from SN 1991T; gamma ray lines from solar flares; searches for Ti-44 emission from Cas A, and searches for C-12 and O-16 lines from the Orion region.

Kurfess, J. D.; Grove, J. E.; Johnson, W. N.; Murphy, R. J.; Share, G. H.; Purcell, W. R.; Leising, M. D.; Harris, M. J.

1997-01-01

331

Gamma-ray Burst Skymap Website  

NSDL National Science Digital Library

The Gamma-ray Burst Skymap website automatically updates for each gamma-ray burst as it occurs, whether detected by Swift or other orbiting satellites. For each burst, the location on the sky, star map, constellation and detecting mission are generated automatically. It is then quickly updated by hand to include a written description of the burst properties and scientific significance, as observations continue. Note: In order to view the content of the website, users need to download and install Silverlight on their computers.

332

Structural Characterization of Laboratory Made Tholins by IRMPD Action Spectroscopy and Ultrahigh Resolution Mass Spectrometry  

NASA Astrophysics Data System (ADS)

The complex organic material that is found on the surface and within the haze layer of Titan is attributed to chemistry occurring in its thick N2/CH4 atmosphere. Although several groups are producing in various laboratory setting the socalled tholins which have been investigated by using analytical methods including UV/Vis, fluorescence, IR, and MS1-5, these very complex organic mixtures still hold many unanswered questions, especially related to the potentiality for their prebiotic chemistry. In addition to tholins characterization and analysis, we recently investigated quantitatively the hydrolysis kinetics of tholins in pure and NH3 containing water at different temperatures.7-8 Our groups at UJF (Grenoble) and at U of Arizona (Tucson) have been collaborating on mass spectral analyses of tholins samples for several years.9 Here, we report our most recent results on the structural characterization of tholins by infrared multiphoton dissociation (IRMPD) action spectroscopy10 and ultrahigh resolution MS. IRMPD action spectroscopy is a recently developed technique that uses IR photons of variable wavelengths to activate ions trapped inside an ion trap. When photons are absorbed at a given wavelength, the selected ion fragments and this fragmentation is monitored as a function of wavelength, analog to an absorption spectrum (impossible to record otherwise because of the much reduced density). This technique can, therefore, be used to determine IR spectra of ions in the gas phase, and provides with very acute structural information. IRMPD action spectroscopy is often used to distinguish between structural isomers of isobaric ions. The drawback is that it requests for high power lasers. Only two Free Electron Lasers (FEL) are available in the world and allow to record spectra with reasonable resolution (20-25 cm-1). IRMPD action spectra of selected ions from tholins will be presented and discussed together with observed fragmentation processes that reveal structural features of the ions. We have studied ions in the mass range from 60 to 160 u, corresponding to particularly interesting species already characterized by other (e.g. tandem MS/MS) methods.

Thissen, R.; Somogyi, A.; Vuitton, V.; Bégué, D.; Lemaire, J.; Steinmetz, V.

2011-10-01

333

Retinal Structure of Birds of Prey Revealed by Ultra-High Resolution Spectral-Domain Optical Coherence Tomography  

PubMed Central

Purpose. To reveal three-dimensional (3-D) information about the retinal structures of birds of prey in vivo. Methods. An ultra-high resolution spectral-domain optical coherence tomography (SD-OCT) system was built for in vivo imaging of retinas of birds of prey. The calibrated imaging depth and axial resolution of the system were 3.1 mm and 2.8 ?m (in tissue), respectively. 3-D segmentation was performed for calculation of the retinal nerve fiber layer (RNFL) map. Results. High-resolution OCT images were obtained of the retinas of four species of birds of prey: two diurnal hawks (Buteo platypterus and Buteo brachyurus) and two nocturnal owls (Bubo virginianus and Strix varia). These images showed the detailed retinal anatomy, including the retinal layers and the structure of the deep and shallow foveae. The calculated thickness map showed the RNFL distribution. Traumatic injury to one bird's retina was also successfully imaged. Conclusions. Ultra-high resolution SD-OCT provides unprecedented high-quality 2-D and 3-D in vivo visualization of the retinal structures of birds of prey. SD-OCT is a powerful imaging tool for vision research in birds of prey. PMID:20554605

Ruggeri, Marco; Major, James C.; McKeown, Craig; Knighton, Robert W.; Puliafito, Carmen A.

2010-01-01

334

Gamma rays and interstellar gas in the Cepheus region - A new gamma-ray source?  

NASA Astrophysics Data System (ADS)

A recent CO survey of the Cep Flare region has allowed a detailed study of the diffuse gamma-ray emission and the gas content. The comparison of the H I and CO observations with the COS-B gamma-ray data yields estimates of the N(H2)/WCO ratio in this molecular complex and of the emissivity spectrum of the gas between 70 MeV and 5 GeV. A significant (3.9sigma) pointlike excess above the diffuse emission has been found and can be interpreted as a new gamma-ray source.

Grenier, I. A.; Lebrun, F.

335

Gamma-ray Pulsars: Models and Predictions  

NASA Technical Reports Server (NTRS)

Pulsed emission from gamma-ray pulsars originates inside the magnetosphere, from radiation by charged particles accelerated near the magnetic poles or in the outer gaps. In polar cap models, the high energy spectrum is cut off by magnetic pair production above an energy that is, dependent on the local magnetic field strength. While most young pulsars with surface fields in the range B = 10(exp 12) - 10(exp 13) G are expected to have high energy cutoffs around several GeV, the gamma-ray spectra of old pulsars having lower surface fields may extend to 50 GeV. Although the gamma-ray emission of older pulsars is weaker, detecting pulsed emission at high energies from nearby sources would be an important confirmation of polar cap models. Outer gap models predict more gradual high-energy turnovers of the primary curvature emission around 10 GeV, but also predict an inverse Compton component extending to TeV energies. Detection of pulsed TeV emission, which would not survive attenuation at the polar caps, is thus an important test of outer gap models. Next-generation gamma-ray telescopes sensitive to GeV-TeV emission will provide critical tests of pulsar acceleration and emission mechanisms.

Harding Alice K.; White, Nicholas E. (Technical Monitor)

2000-01-01

336

Study of gamma-ray strength functions  

SciTech Connect

The use of gamma-ray strength function systematics to calculate neutron capture cross sections and capture gamma-ray spectra is discussed. The ratio of the average capture width, GAMMA/sub ..gamma../-bar, to the average level spacing, D/sub obs/, both at the neutron separation energy, can be derived from such systematics with much less uncertainty than from separate systematics for values of GAMMA/sub ..gamma../-bar and D/sub obs/. In particular, the E1 gamma-ray strength function is defined in terms of the giant dipole resonance (GDR). The GDR line shape is modeled with the usual Lorentzian function and also with a new energy-dependent, Breit-Wigner (EDBW) function. This latter form is further parameterized in terms of two overlapping resonances, even for nuclei where photonuclear measurements do not resolve two peaks. In the mass ranges studied, such modeling is successful for all nuclei away from the N = 50 closed neutron shell. Near the N = 50 shell, a one-peak EDBW appears to be more appropriate. Examples of calculated neutron capture excitation functions and capture gamma-ray spectra using the EDBW form are given for target nuclei in the mass-90 region and also in the Ta-Au mass region. 20 figures.

Gardner, D.G.; Gardner, M.A.; Dietrich, F.S.

1980-08-07

337

Gamma-ray Burst Science with GLAST  

SciTech Connect

The recent observations of Gamma-ray bursts (GRBs) with Swift have provided unprecedented information about nature of GRBs. The launch of GLAST in late 2007 will unveil the final spectral regime of GRB prompt emission and afterglows. Here we briefly review various theoretical suggestions of producing high energy photons from GRB fireballs, and discuss what observatons are expected from the GLAST observatory.

Zhang Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States)

2007-07-12

338

Gamma-ray bursts: Restarting the Engine  

E-print Network

Recent gamma-ray burst observations have revealed late-time, highly energetic events which deviate from the simplest expectations of the standard fireball picture. Instead they may indicate that the central engine is active or restarted at late times. We suggest that fragmentation and subsequent accretion during the collapse of a rapidly rotating stellar core offers a natural mechanism for this.

Andrew King; Paul T. O'Brien; Michael R. Goad; Julian Osborne; Emma Olsson; Kim Page

2005-08-04

339

Gamma-ray Astrophysics with AGILE  

SciTech Connect

AGILE will explore the gamma-ray Universe with a very innovative instrument combining for the first time a gamma-ray imager and a hard X-ray imager. AGILE will be operational in spring 2007 and it will provide crucial data for the study of Active Galactic Nuclei, Gamma-Ray Bursts, unidentified gamma-ray sources. Galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. The AGILE instrument is designed to simultaneously detect and image photons in the 30 MeV - 50 GeV and 15 - 45 keV energy bands with excellent imaging and timing capabilities, and a large field of view covering {approx} 1/5 of the entire sky at energies above 30 MeV. A CsI calorimeter is capable of GRB triggering in the energy band 0.3-50 MeV AGILE is now (March 2007) undergoing launcher integration and testing. The PLSV launch is planned in spring 2007. AGILE is then foreseen to be fully operational during the summer of 2007.

Longo, Francesco [Department of Physics, University of Trieste (Italy)]|[INFN, Section of Trieste (Italy); Tavani, M.; Barbiellini, G.; Argan, A.; Basset, M.; Boffelli, F.; Bulgarelli, A.; Caraveo, P.; Cattaneo, P.; Chen, A.; Costa, E.; Del Monte, E.; Di Cocco, G.; Di Persio, G.; Donnarumma, I.; Feroci, M.; Fiorini, M.; Foggetta, L.; Froysland, T.; Frutti, M. (and others)

2007-07-12

340

The Supernova Gamma-Ray Burst Connection  

Microsoft Academic Search

The chief distinction between ordinary supernovae and long-soft gamma-ray bursts (GRBs) is the degree of differential rotation in the inner several solar masses when a massive star dies, and GRBs are rare mainly because of the difficulty achieving the necessary high rotation rate. Models that do provide the necessary angular momentum are discussed, with emphasis on a new single star

Stan Woosley; A. Heger

2006-01-01

341

Gamma Ray Burst Detectives (Elementary School)  

NSDL National Science Digital Library

This interactive resource invites students to join NASA to find the source of gamma ray bursts, the single biggest explosions in the Universe since the Big Bang. The web site features an animation, information on three possible star sources, and a check yes or no for each star with feedback.

WPSU

2010-04-29

342

Ultrahigh resolution spectral-domain optical coherence tomography at 1.3 ?m using a broadband superluminescent diode light source  

NASA Astrophysics Data System (ADS)

We present an ultrahigh resolution spectral-domain optical coherence tomography imaging system using a broadband superluminescent diode light source emitting at a center wavelength of 1.3 ?m. The light source consists of two spectrally shifted superluminescent diodes that are coupled together into a single mode fiber. The effective emission power spectrum has a full width at half maximum of 200 nm and the source output power is 10 mW. The imaging system has an axial resolution of 3.9 ?m in air (<3.0 ?m in biological tissue), and a lateral resolution of 6.5 ?m. The sensitivity and the maximum line rate are 95 dB and 46 kHz, respectively. Images of an infrared viewing card and a cornea from human eye suffering from glaucoma showing Schlemm's canal are presented to illustrate the performance of the system.

Bayleyegn, Masreshaw D.; Makhlouf, Houssine; Crotti, Caroline; Plamann, Karsten; Dubois, Arnaud

2012-11-01

343

Gamma Ray Telescope Senses High-Energy Radiation  

NSDL National Science Digital Library

This video from NASA describes the GLAST satellite, which is equipped with a gamma-ray telescope, and shares some background about the kinds of extreme universal phenomena indicated by the presence of gamma rays.

WNET

2011-11-02

344

Investigation of gamma rays from the galactic center  

NASA Technical Reports Server (NTRS)

Data from Argentine balloon flights made to investigate gamma ray emission from the galactic center are summarized. Data are also summarized from a Palestine, Texas balloon flight to measure gamma rays from NP 0532 and Crab Nebulae.

Helmken, H. F.

1973-01-01

345

Swift's 500th Gamma Ray Burst - Duration: 1:04.  

NASA Video Gallery

On April 13, 2010, NASA's Swift Gamma-ray Burst Explorer satellite discovered its 500th burst. Swift's main job is to quickly localize each gamma-ray burst (GRB), report its position so that others...

346

Studying the High Energy Gamma Ray Sky with Gamma Ray Large Area Space Telescope (GLAST)  

NASA Technical Reports Server (NTRS)

Building on the success of the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory, the Gamma Ray Large Area Space Telescope (GLAST) will make a major step in the study of such subjects as blazars, gamma Ray bursts, the search for dark matter, supernova remnants, pulsars, diffuse radiation, and unidentified high energy sources. The instrument will be built on new and mature detector technologies such as silicon strip detectors, low-power low-noise LSI, and a multilevel data acquisition system. GLAST is in the research and development phase, and one full tower (of 25 total) is now being built in collaborating institutes. The prototype tower will be tested thoroughly at Stanford Linear Accelerator Center (SLAC) in the fall of 1999.

Kamae, T.; Ohsugi, T.; Thompson, D. J.; Watanabe, K.

1998-01-01

347

Gamma-Ray, Cosmic Ray and Neutrino Tests of Lorentz Invariance and Quantum Gravity Models  

NASA Technical Reports Server (NTRS)

High-energy astrophysics observations provide the best possibilities to detect a very small violation of Lorentz invariance such as may be related to the structure of space-time near the Planck scale of approximately 10(exp -35) m. I will discuss here the possible signatures of Lorentz invariance violation (LIV) from observations of the spectra, polarization, and timing of gamma-rays from active galactic nuclei and gamma-ray bursts. Other sensitive tests are provided by observations of the spectra of ultrahigh energy cosmic rays and neutrinos. Using the latest data from the Pierre Auger Observatory one can already derive an upper limit of 4.5 x 10(exp -23) to the amount of LIV of at a proton Lorentz factor of approximately 2 x 10(exp 11). This result has fundamental implications for quantum gravity models. I will also discuss the possibilities of using more sensitive space based detection techniques to improve searches for LIV in the future.

Stecker, Floyd

2011-01-01

348

Preliminary observations of the SELENE Gamma Ray Spectrometer  

NASA Astrophysics Data System (ADS)

Introduction We analyze the spectra measured by the Gamma Ray Spectrometer (GRS) on board the SELENE satellite [1]. SELENE was inserted in lunar orbit on 4 Oct. 2007. After passing through a health check and a function check, the GRS was shifted to nominal observation on 21 Dec. 2007. The spectra consist in various lines of interest (O, Mg, Al, Si, Ti, Ca, Fe, K, Th, U, and possibly H) superposed on a continuum. The energies of the gamma rays identify the nuclides responsible for the gamma ray emission and their intensities relate to their abundance. Data collected through 17 Feb. 2008 are studied here, corresponding to an accumulation time (Fig. 1) sufficiently good to allow preliminary mapping. Analysis of the global gamma ray spectrum In order to obtain spectra with counting statistics sufficient for peak analysis, we accumulate all observations. The identification of lines is performed on this global lunar spectrum (Fig 2). Fit of individual lines The gamma ray lines that arise from decay of longlived radioactive species are among the easiest to analyze. So far the abundance of two species is studied thanks to such lines: potassium (1461 keV) and thorium (2614 keV). Secondary neutrons from cosmic ray interactions also produce gamma ray when reacting with the planetary material, according to scattering or absorption reactions. However these lines need substantial corrections before an interpretation in terms of abundance can be performed. Lines have been examined with different techniques. The simplest method consists in summing the spectra in a window containing the line of interest. The continuum is adjusted with a polynomial and removed. Such a method was used for the gamma ray spectra collected by Lunar Prospector [2]. This method is especially robust for isolated lines, such as those of K and Th mentioned above, or with very low statistics. The second method consists in fitting the lines by summing a quadratic continuum with Gaussian lines and exponential tails. We presently fit the spectra thanks to a program developed at CESR: Aquarius. Afterwards the areas associated with the parameters of these ideal lines are calculated. This method is welladapted for interfering lines, such as U, Al, and H around 2210 keV, but it requires good statistics. These two methods were used to analyze the Mars Odyssey gamma-ray spectra [3]. Prettyman et al. [4] applied a third method where theoretical spectra are simulated and matched against the observations. Below we propose a fourth approach based on statistical analyzes. Mapping of elemental abundances Data returned by the spacecraft are time-tagged records acquired with a resolution of 17 seconds. The angular distance covered by the spacecraft during this interval corresponds to about 1° at the surface. However the true resolution of the instrument is lower because gamma rays come from all directions onto the spacecraft. The resolution is therefore set by the field of view of the instrument, which depends on the spacecraft altitude and the geometry of the instrument. The full width half maximum of the instrumental response has been estimated to be 130 km at 1 MeV by the SELENE GRS team. We have tiled the data in agreement with the better resolution we could obtain depending on the intensity of a given line. The thorium line at 2614 keV was thus mapped at a resolution of 3° with the first method described above (sum over 2550-2640 keV). Then this map was smoothed with a 5° filter (152 km radius) to approximate the response function of the instrument. Finally the counting rate was converted into abundance (Fig. 3), using the compositions at landing sites and in the highlands as did Gillis et al. [5]. Statistical analysis We have also analysed the data with various multivariate techniques, one of them being the Independent Component Analysis (ICA) [6, 7]. ICA defines a generative model for the observed multivariate data, which is typically given as a large database of samples. In the model, the data variables are assumed to be linear mixtures of some unknown latent variables,

Forni, O.; Diez, B.; Gasnault, O.; Munoz, B.; D'Uston, C.; Reedy, R. C.; Hasebe, N.

2008-09-01

349

Report of the x ray and gamma ray sensors panel  

NASA Technical Reports Server (NTRS)

Overall five major areas of technology are recommended for development in order to meet the science requirements of the Astrotech 21 mission set. These are: detectors for high resolution gamma ray spectroscopy, cryogenic detectors for improved x ray spectral and spatial resolution, advanced x ray charge coupled devices (CCDs) for higher energy resolution and larger format, extension to higher energies, liquid and solid position sensitive detectors for improving stopping power in the energy range 5 to 500 keV and 0.2 to 2 MeV. Development plans designed to achieve the desired capabilities on the time scales required by the technology freeze dates have been recommended in each of these areas.

Szymkowiak, Andrew; Collins, S.; Kurfess, J.; Mahoney, W.; Mccammon, D.; Pehl, R.; Ricker, G.

1991-01-01

350

Cygnus X-3 and EGRET Gamma-Ray Observations  

Microsoft Academic Search

0!rQ1The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory observed the Cygnus region in 14 different viewing periods during 1991 May to 1994 July. We present here our results on unpulsed and pulsed emissions of gamma rays at E > 50 MeV from Cyg X-3. While we detect a gamma-ray source consistent with the position of

M. Mori; D. L. Bertsch; B. L. Dingus; J. A. Esposito; C. E. Fichtel; S. D. Hunter; G. Kanbach; D. A. Kniffen; Y. C. Lin; J. R. Mattox; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; R. Mukherjee; P. L. Nolan; P. V. Ramanamurthy; E. Schneid; P. Sreekumar; D. J. Thompson

1997-01-01

351

Observations of GRB 990123 by the Compton Gamma Ray Observatory  

Microsoft Academic Search

GRB 990123 was the first burst from which simultaneous optical, X-ray, and gamma-ray emission was detected; its afterglow has been followed by an extensive set of radio, optical, and X-ray observations. We have studied the gamma-ray burst itself as observed by the Compton Gamma Ray Observatory detectors. We find that gamma-ray fluxes are not correlated with the simultaneous optical observations

M. S. Briggs; D. L. Band; R. M. Kippen; R. D. Preece; C. Kouveliotou; J. van Paradijs; G. H. Share; R. J. Murphy; S. M. Matz; A. Connors; C. Winkler; M. L. McConnell; J. M. Ryan; O. R. Williams; C. A. Young; B. Dingus; J. R. Catelli; R. A. M. J. Wijers

1999-01-01

352

Simultaneous optical/gamma-ray observations of GRBs  

NASA Technical Reports Server (NTRS)

Details on the project to search for serendipitous time correlated optical photographic observations of Gamma Ray Bursters (GRB's) are presented. The ongoing photographic observations at nine observatories are used to look for plates which were exposed simultaneously with a gamma ray burst detected by the gamma ray instrument team (BATSE) and contain the burst position. The results for the first two years of the gamma ray instrument team operation are presented.

Greiner, J.; Wenzel, W.; Hudec, R.; Moskalenko, E. I.; Metlov, V.; Chernych, N. S.; Getman, V. S.; Ziener, Rainer; Birkle, K.; Bade, N.

1994-01-01

353

Gamma-ray Localization of Terrestrial Gamma-ray Flashes by AGILE  

NASA Astrophysics Data System (ADS)

We report the first direct localization of Terrestrial Gamma-ray Flashes (TGFs) in space by the AGILE gamma-ray imager above 20 MeV. AGILE is one of the three currently active space missions detecting TGFs. AGILE is detecting about 10 TGFs/month by the mini-calorimeter (MCAL) instrument sensitive in the energy range 0.35-100 MeV and was the first to clearly show the extension of the TGFs energy spectrum up to at least 40 MeV. Motivated by this initial discovery, we searched for detections in the AGILE Gamma-Ray Imaging Detector (GRID) data correlated with TGFs detected in MCAL. Among the 119 TGFs detected by MCAL at MeV energies during the period June, 2008 - December, 2009, we detect 8 TGFs with gamma-ray photons of energies above 20 MeV localized by the AGILE gamma-ray imager with a relatively good accuracy of 5-10 deg at 50 MeV. Remarkably, all TGF-associated gamma-rays are compatible with a terrestrial production site closer to the sub-satellite point than 400km, independently confirming the results obtained by combining space and ground measurements (sferics). Considering that our photons reach the AGILE satellite at 540 km altitude with limited scattering or attenuation, these results have deep implications for the study of TGFs.

Marisaldi, M.; Tavani, M.; Argan, A.; Trois, A.; Giuliani, A.; Labanti, C.; Fuschino, F.; Bulgarelli, A.; Longo, F.; Barbiellini, G.

2010-12-01

354

Hybrid pixel-waveform CdTe/CZT detector for use in an ultrahigh resolution MRI compatible SPECT system  

PubMed Central

In this paper, we will present a new small pixel CdTe/CZT detector for sub-500 ?m resolution SPECT imaging application inside MR scanner based on a recently developed hybrid pixel-waveform (HPWF) readout circuitry. The HPWF readout system consists of a 2-D multi-pixel circuitry attached to the anode pixels to provide the X–Y positions of interactions, and a high-speed digitizer to read out the pulse-waveform induced on the cathode. The digitized cathode waveform could provide energy deposition information, precise timing and depth-of-interaction information for gamma ray interactions. Several attractive features with this HPWF detector system will be discussed in this paper. To demonstrate the performance, we constructed several prototype HPWF detectors with pixelated CZT and CdTe detectors of 2–5 mm thicknesses, connected to a prototype readout system consisting of energy-resolved photon-counting ASIC for readout anode pixels and an Agilent high-speed digitizer for digitizing the cathode signals. The performances of these detectors based on HPWF are discussed in this paper. PMID:24371365

Cai, Liang; Meng, Ling-Jian

2013-01-01

355

Hybrid pixel-waveform CdTe/CZT detector for use in an ultrahigh resolution MRI compatible SPECT system.  

PubMed

In this paper, we will present a new small pixel CdTe/CZT detector for sub-500 ?m resolution SPECT imaging application inside MR scanner based on a recently developed hybrid pixel-waveform (HPWF) readout circuitry. The HPWF readout system consists of a 2-D multi-pixel circuitry attached to the anode pixels to provide the X-Y positions of interactions, and a high-speed digitizer to read out the pulse-waveform induced on the cathode. The digitized cathode waveform could provide energy deposition information, precise timing and depth-of-interaction information for gamma ray interactions. Several attractive features with this HPWF detector system will be discussed in this paper. To demonstrate the performance, we constructed several prototype HPWF detectors with pixelated CZT and CdTe detectors of 2-5 mm thicknesses, connected to a prototype readout system consisting of energy-resolved photon-counting ASIC for readout anode pixels and an Agilent high-speed digitizer for digitizing the cathode signals. The performances of these detectors based on HPWF are discussed in this paper. PMID:24371365

Cai, Liang; Meng, Ling-Jian

2013-02-01

356

Gamma-Ray Telescopes: 400 Years of Astronomical Telescopes  

NASA Technical Reports Server (NTRS)

The last half-century has seen dramatic developments in gamma-ray telescopes, from their initial conception and development through to their blossoming into full maturity as a potent research tool in astronomy. Gamma-ray telescopes are leading research in diverse areas such as gamma-ray bursts, blazars, Galactic transients, and the Galactic distribution of Al-26.

Gehrels, Neil; Cannizzo, John K.

2010-01-01

357

Very High-Energy Gamma-Ray Sources.  

ERIC Educational Resources Information Center

Discusses topics related to high-energy, gamma-ray astronomy (including cosmic radiation, gamma-ray detectors, high-energy gamma-ray sources, and others). Also considers motivation for the development of this field, the principal results to date, and future prospects. (JN)

Weekes, Trevor C.

1986-01-01

358

Blood oxygenation level-dependent functional MRI signal turbulence caused by ultrahigh spatial resolution: numerical simulation and theoretical explanation.  

PubMed

High-spatial-resolution functional MRI (fMRI) can enhance image contrast and improve spatial specificity for brain activity mapping. As the voxel size is reduced, an irregular magnetic fieldmap will emerge as a result of less local averaging, and will lead to abnormal fMRI signal evolution with respect to the image acquisition TE. In this article, we report this signal turbulence phenomenon observed in simulations of ultrahigh-spatial-resolution blood oxygenation level-dependent (BOLD) fMRI (voxel size of less than 50?×?50?×?50 µm³). We present a four-level coarse-to-fine multiresolution BOLD fMRI signal simulation. Based on the statistical histogram of an intravoxel fieldmap, we reformulate the intravoxel dephasing summation (a form of Riemann sum) into a new formula that is a discrete Fourier transformation of the intravoxel fieldmap histogram (a form of Lebesgue sum). We interpret the BOLD signal formation by relating its magnitude (phase) to the even (odd) symmetry of the fieldmap histogram. Based on multiresolution BOLD signal simulation, we find that the signal turbulence mainly emerges at the vessel boundary, and that there are only a few voxels (less than 10%) in an ultrahigh-resolution image that reveal turbulence in the form of sparse point noise. Our simulation also shows that, for typical human brain imaging of the cerebral cortex with millimeter resolution, TE?< 30 ms and B? ?=?3 T, we are unlikely to observe BOLD signal turbulence. Overall, the main causes of voxel signal turbulence include a high spatial resolution, high field, long TE and large vessel. PMID:22927163

Chen, Zikuan; Chen, Zeyuan; Calhoun, Vince

2013-03-01

359

Gamma-ray imaging probes  

SciTech Connect

External nuclear medicine diagnostic imaging of early primary and metastatic lung cancer tumors is difficult due to the poor sensitivity and resolution of existing gamma cameras. Nonimaging counting detectors used for internal tumor detection give ambiguous results because distant background variations are difficult to discriminate from neighboring tumor sites. This suggests that an internal imaging nuclear medicine probe, particularly an esophageal probe, may be advantageously used to detect small tumors because of the ability to discriminate against background variations and the capability to get close to sites neighboring the esophagus. The design, theory of operation, preliminary bench tests, characterization of noise behavior and optimization of such an imaging probe is the central theme of this work.

Wild, W.J.

1988-01-01

360

The IBIS\\/ISGRI Survey of the Galactic Plane - Global Characteristics of the Gamma-Ray Sources  

Microsoft Academic Search

INTEGRAL is the first gamma-ray astronomy mission with a sufficient sensitivity and angular resolution combination appropriate to the detection and identification of considerable numbers of gamma-ray emitting sources. The large field of view enables INTEGRAL to survey the Galactic Plane on a regular (˜weekly) basis as part of the core programme. The first source catalogue, based on the 1st year

A. J. Dean; A. Bazzano; A. B. Hill; J. B. Stephen; L. Bassani; E. J. Barlow; A. J. Bird; F. Lebrun; V. Sguera; S. E. Shaw; P. Ubertini; R. Walter; D. R. Willis

2006-01-01

361

Preliminary results from the 1999 balloon flight of the Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT)  

Microsoft Academic Search

LXeGRIT is a balloon-borne Compton telescope employing a large volume liquid xenon time projection chamber (LXe-TPC) as the central (gamma) -ray detector. It is designed to image (gamma) - rays in the energy range of approximately 200 keV to 20 MeV, with an angular resolution of about 3 degrees (1 sigma) at 2 MeV, within a field-of-view (FOV) of about

Elena Aprile; Uwe G. Oberlack; Alessandro Curioni; Valeri Egorov; Karl-Ludwig Giboni; Sandro Ventura; Tadayoshi Doke; Jun Kikuchi; Kyoko Takizawa; Edward L. Chupp; Philip P. Dunphy

2000-01-01

362

A new approach in the detection of weak {\\gamma}-ray peak of the radioactive waste in tomography {\\gamma} scanning  

E-print Network

We demonstrate a new approach to efficiently detect weak {\\gamma}-ray peak of the radioactive waste in tomographic {\\gamma} scanning (TGS). In the TGS measurement, {\\gamma}-ray peak identification is usually difficult due to the short measurement time that results in a lower {\\gamma}-ray energy produced by the decay. Consequently, the resulting significant scattering in the low-energy side leads to strong statistical fluctuations and low detection efficiency that overwhelm the {\\gamma}-ray peak. Here, we propose the use of shift invariance wavelet algorithm for low-energy part of the spectrum for weak {\\gamma}-ray peak smoothing. The proposed algorithm not only overcomes the pseudo-Gibbs in the high-resolution {\\gamma}-ray spectrum de-noising by the traditional wavelet transform, but also keeps quality of the weak {\\gamma}-ray characteristic peak as well. Our new approach shows a significantly improved performance of the figure of merit (FOM) together with lower limit of quantitation (LLOQ) compared with the ...

Jinzha, Zhang

2014-01-01

363

Gamma-Ray Bursts: A Mystery Story  

NASA Technical Reports Server (NTRS)

With the success of the Swift Gamma-Ray Burst Explorer currently in orbit, this is quite an exciting time in the history of Gamma Ray Bursts (GRBs). The study of GRBs is a modern astronomical mystery story that began over 30 years ago with the serendipitous discovery of these astronomical events by military satellites in the late 1960's. Until the launch of BATSE on the Compton Gamma-ray Observatory, astronomers had no clue whether GRBs originated at the edge of our solar system, in our own Milky Way Galaxy or incredibly far away near the edge of the observable Universe. Data from BATSE proved that GRBs are distributed isotropically on the sky and thus could not be the related to objects in the disk of our Galaxy. Given the intensity of the gamma-ray emission, an extragalactic origin would require an astounding amount of energy. Without sufficient data to decide the issue, a great debate continued about whether GRBs were located in the halo of our own galaxy or were at extragalactic - even cosmological distances. This debate continued until 1997 when the BeppoSAX mission discovered a fading X-ray afterglow signal in the same location as a GRB. This discovery enabled other telescopes, to observe afterglow emission at optical and radio wavelengths and prove that GRBs were at cosmological distances by measuring large redshifts in the optical spectra. Like BeppoSAX Swift, slews to new GRB locations to measure afterglow emission. In addition to improved GRB sensitivity, a significant advantage of Swift over BeppoSAX and other missions is its ability to slew very quickly, allowing x-ray and optical follow-up measurements to be made as early as a minute after the gamma-ray burst trigger rather than the previous 6-8 hour delay. Swift afterglow measurements along with follow-up ground-based observations, and theoretical work have allowed astronomers to identify two plausible scenarios for the creation of a GRB: either through core collapse of super massive stars or colliding compact objects in distant galaxies. The pieces of the puzzle are beginning to fall into place and yet the story isn't quite finished. I will frame the history of gamma-ray bursts as a mystery story and will end with a description of what we still don't know and what we'll have to do to get the next clues.

Parsons, Ann

2007-01-01

364

The Universe Viewed in Gamma-Rays 1 Galactic Diffuse Gamma-ray Spectrum from Cosmic-ray In-  

E-print Network

The Universe Viewed in Gamma-Rays 1 Galactic Diffuse Gamma-ray Spectrum from Cosmic-ray In- teractions with Gas Clouds Michiko OHISHI and Masaki MORI Institute for Cosmic Ray Research, University, Australia Abstract Gamma-ray spectra from cosmic-ray proton and electron interactions with gas clouds have

Mori, Masaki

365

Computer model for calculating gamma-ray pulse-height spectra for logging applications  

SciTech Connect

A generalized computer model has been devised to simulate the emission, transport, and detection of natural gamma radiation from various logging environments. The model yields high-resolution gamma-ray pulse-height spectra that can be used to correct both gross gamma and spectral gamma-ray logs. The technique can help provide corrections to airborne and surface radiometric survey logs for the effects of varying altitude, formation composition, and overburden. Applied to borehole logging, the model can yield estimates of the effects of varying borehole fluid and casing attenuations, as well as varying formation porosity and saturation.

Evans, M.L.

1981-01-01

366

On the observability of the gamma-ray line flux from dark matter annihilation  

SciTech Connect

The limits on the possible cosmic gamma-ray line flux from the two-photon annihilation of dark matter in the Galaxy are discussed. These limits are derived using both particle physics and cosmological constraints on dark matter candidates which arise in supersymmetric extensions of the standard model of particle physics. Results are given in terms of allowed and prescribed areas in the flux-energy plane. Then these bounds are used to consider the observability of the line flux above continuum background fluxes using future high-resolution gamma-ray telescopes. 25 refs.

Rudaz, S.; Stecker, F.W. (Minnesota Univ., Minneapolis (USA) NASA, Goddard Space Flight Center, Greenbelt, MD (USA))

1991-02-01

367

On the observability of the gamma-ray line flux from dark matter annihilation  

NASA Technical Reports Server (NTRS)

The limits on the possible cosmic gamma-ray line flux from the two-photon annihilation of dark matter in the Galaxy are discussed. These limits are derived using both particle physics and cosmological constraints on dark matter candidates which arise in supersymmetric extensions of the standard model of particle physics. Results are given in terms of allowed and prescribed areas in the flux-energy plane. Then these bounds are used to consider the observability of the line flux above continuum background fluxes using future high-resolution gamma-ray telescopes.

Rudaz, S.; Stecker, F. W.

1991-01-01

368

A field-deployable gamma-ray spectrometer utilizing xenon at high pressure  

SciTech Connect

Prototype gamma-ray spectrometers utilizing xenon gas at high pressure, suitable for applications in the nuclear safeguards, arms control, and nonproliferation communities, have been developed at Brookhaven National Laboratory (BNL). These spectrometers function as ambient-temperature ionization chambers detecting gamma rays with good efficiency in the energy range 50 keV - 2 MeV, with an energy resolution intermediate between semiconductor (Ge) and scintillation (NaI) spectrometers. They are capable of prolonged, low-power operation without a requirement for cryogenic fluids or other cooling mechanisms, and with the addition of small quantities of {sup 3}He gas, can function simultaneously as efficient thermal neutron detectors.

Smith, G.C.; Mahler, G.J.; Yu, B.; Salwen, C.; Kane, W.R.; Lemley, J.R.

1996-10-01

369

Can Galactic Cosmic Rays Account for Solar 6Li Without Overproducing Gamma Rays?  

E-print Network

Cosmic-ray interactions with interstellar gas produces both 6Li, which accumulates in the interstellar medium (ISM), and $\\pi^0$ mesons, which decay to gamma-rays which propagate throughout the cosmos. Local 6Li abundances and extragalactic gamma-rays thus have a common origin which tightly links them. We exploit this connection to use gamma-ray observations to infer the contribution to 6Li nucleosynthesis by standard Galactic cosmic-ray (GCR) interactions with the ISM. Our calculation uses a carefully propagated cosmic-ray spectrum and accounts for 6Li production from both fusion reactions ($\\alpha \\alpha \\to ^6Li$) as well as from spallation channels (${p,\\alpha+CNO \\to ^6Li$). We find that although extreme assumptions yield a consistent picture, more realistic ones indicate that solar 6Li cannot be produced by standard GCRs alone without overproducing the hadronic gamma rays. Implications for the primordial 6Li production by decaying dark matter and cosmic rays from cosmological structure formation are discussed. Upcoming gamma-ray observations by GLAST will be crucial for determining the resolution of this problem.

T. Prodanovic; B. D. Fields

2006-05-26

370

Contribution to diffuse gamma-rays in the Galactic center region from unresolved millisecond pulsars  

E-print Network

The diffuse gamma-rays in the Galactic center region have been studied. We propose that there exists a population of millisecond pulsars (MSPs) in the Galactic Center, which will emit GeV gamma-rays through the synchrotron-curvature radiation as predicted by outer gap models. These GeV gamma-rays from unresolved millisecond pulsars probably contribute to the diffuse gamma-ray spectrum detected by EGRET which displays a break at a few GeV. We have used the Monte Carlo method to obtain the simulated samples of millisecond pulsars in the Galactic center region covered by EGRET ($\\sim 1.5^\\circ$) according to the different period and magnetic field distributions from the observed millisecond pulsars in the Galactic field and globular clusters, and superposed their synchrotron-curvature spectra to derive the total GeV flux. Our simulated results suggest that there probably exist about 6000 unresolved millisecond pulsars in the region of the angular resolution for EGRET, whose emissions could contribute significantly to the observed diffuse gamma-rays in the Galactic center.

W. Wang; Z. J. Jiang; K. S. Cheng

2005-01-13

371

Dark Matter and the CACTUS Gamma-Ray Excess from Draco  

E-print Network

The CACTUS atmospheric Cherenkov telescope collaboration recently reported a gamma-ray excess from the Draco dwarf spheroidal galaxy. Draco features a very low gas content and a large mass-to-light ratio, suggesting as a possible explanation annihilation of weakly interacting massive particles (WIMPs) in the Draco dark-matter halo. We show that with improved angular resolution, future measurements can determine whether the halo is cored or cuspy, as well as its scale radius. We find the relevant WIMP masses and annihilation cross sections and show that supersymmetric models can account for the required gamma-ray flux. The annihilation cross section range is found to be not compatible with a standard thermal relic dark-matter production. We compute for these supersymmetric models the resulting Draco gamma-ray flux in the GLAST energy range and the rates for direct neutralino detection and for the flux of neutrinos from neutralino annihilation in the Sun. We also discuss the possibility that the bulk of the signal detected by CACTUS comes from direct WIMP annihilation to two photons and point out that a decaying-dark-matter scenario for Draco is not compatible with the gamma-ray flux from the Galactic center and in the diffuse gamma-ray background.

Stefano Profumo; Marc Kamionkowski

2006-02-16

372

Search for TeV gamma rays from Geninga. [2CG 195+04  

SciTech Connect

Recently the Tata group have reported (1) the detection of TeV [gamma]-rays from Geminga. Results of a search by the Whipple observatory Collaboration are presented here, based on observations made during 1989--90 and 1990--91, using the 10 m high resolution imaging cerenkov camera.

Fegan, D.J. (Physics Department, University College, Dublin (Ireland)); Akerlof, C.W. (Physics Department, University of Michigan, Ann Arbor, Michigan (United States)); Breslin, A.C. (Physics Department, University College, Dublin (Ireland)); Cawley, M.F. (Physics Department, St. Patricsk College, Maynooth, Co. Kildare (Ireland)); Chantell, M. (Whipple Observatory, Harvard-Smithsonian CfA, Amado, Arizona (United States)); Fennell, S. (Physics Department, University College, Dublin (Ireland) Whipple Observatory, Harvard-Smithsonian CfA, Amado, Arizona (United States)); Gaidos, J.A.; Hagan, J. (Physics Department, Purdue University, West Lafayette, Indiana (United States)); Hillas, A.M. (Physics department, University of Leeds, Leeds (United Kingdom)); Kerrick, A.D.; Lamb, R.C. (Physics Department, Iowa State University, Ames, Iowa (United States)); Lawrence, M.A. (Whipple Observatory, Harvard-Smithsonian CfA, Amado, Arizona (United States)); Lewis, D.A. (Physics Department, Io

1993-07-05

373

A multiple-plate, multiple-pinhole camera for X-ray gamma-ray imaging  

NASA Technical Reports Server (NTRS)

Plates with identical patterns of precisely aligned pinholes constitute lens system which, when rotated about optical axis, produces continuous high resolution image of small energy X-ray or gamma ray source. Camera has applications in radiation treatment and nuclear medicine.

Hoover, R. B.

1971-01-01

374

Observation of SN 1987A with the gamma-ray spectrometer HEXAGONE  

NASA Astrophysics Data System (ADS)

The HEXAGONE balloon-borne spectrometer was flown from Alice Springs (Australia) on 1989 May 22. HEXAGONE is a high-resolution gamma-ray spectrometer and consists of an array of twelve cooled germanium detectors. One of the observed targets was the supernova 1987A and it was seen during 9.9hr, 818 days after the initial optical outburst. No significant hard X-ray or gamma-ray emission is detected in the final spectrum of SN 1987A. We report the upper limits of the flux values for the gamma-ray lines coming from the decay of radionuclides synthesized in this star such as Co56, Co-57, or Ti-44. The results are consistent with models incorporating mixing of the radioactive nuclei in the ejecta, 0.073 solar mass of Co-56, 3.1 10 exp -3 solar mass of Co-57, and 1.2 10 expo -4 solar mass of Ti-44.

Chapuis, C. G. L.; Wallyn, P.; Durouchoux, Ph.; Matteson, J.; Pelling, M.; Bowman, B.; Briggs, M.; Gruber, D.; Peterson, L.; Lingenfelter, R.; Cork, C.; Landis, D.; Luke, P.; Madden, N.; Malone, D.; Pehl, R.; Pollard, M.; Lin, R.; Smith, D.; Feffer, P.; Hurley, K.; Vedrenne, G.; Niel, M.; von Ballmoos, P.

1993-01-01

375

The future of high energy gamma ray astronomy and its potential astrophysical implications  

NASA Technical Reports Server (NTRS)

Future satellites should carry instruments having over an order of magnitude greater sensitivity than those flown thus far as well as improved energy and angular resolution. The information to be obtained from these experiments should greatly enhance knowledge of: the very energetic and nuclear processes associated with compact objects; the structure of our galaxy; the origin and dynamic pressure effects of the cosmic rays; the high energy particles and energetic processes in other galaxies; and the degree of matter-antimatter symmetry of the universe. The relevant aspects of extragalactic gamma ray phenomena are emphasized along with the instruments planned. The high energy gamma ray results of forthcoming programs such as GAMMA-1 and the Gamma Ray Observatory should justify even more sophisticated telescopes. These advanced instruments might be placed on the space station currently being considered by NASA.

Fichtel, C. E.

1982-01-01

376

The high precision gamma-ray spectrometer for lunar polar orbiter SELENE  

NASA Astrophysics Data System (ADS)

The high precision gamma-ray spectrometer (GRS) is scheduled to be launched on the lunar polar orbiter of the SELENE mission in 2007. The GRS consists of a large Ge crystal as a main detector and massive bismuth germanate crystals as an anticoincidence detector. A Stirling cryocooler was adopted in cooling the Ge detector. The flight model of SELENE GRS has been completed and an energy resolution of 3.0 keV (FWHM) at 1.332 MeV has been achieved. The spectrometer aims to observe nuclear line gamma rays emitted from the lunar surface in a wide energy range from 100 keV to 12 MeV for one year and more to obtain chemical composition on the entire lunar surface. The gamma-ray data enable us to study lunar geoscience problems including crust and mantle composition, and volatile reservoirs at polar regions.

Hasebe, N.; Yamashita, N.; Okudaira, O.; Kobayashi, S.; Yamamoto, H.; Ishizaki, T.; Hirano, K.; Sakurai, K.; Miyachi, T.; Miyajima, M.; Fujii, M.; Kobayashi, M.-N.; Takashima, T.; Shibamura, E.; Gasnault, O.; Maurice, S.; D'Uston, C.; Reedy, R.; Grande, M.

2008-07-01

377

Fermi Large Area Telescope Measurements of the Diffuse Gamma-Ray Emission at Intermediate Galactic Latitudes  

NASA Astrophysics Data System (ADS)

The diffuse galactic ?-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess ?-ray emission ?1GeV relative to diffuse galactic ?-ray emission models consistent with directly measured CR spectra (the so-called “EGRET GeV excess”). The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse ?-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements for energies 100 MeV to 10 GeV and galactic latitudes 10°?|b|?20°. The LAT spectrum for this region of the sky is well reproduced by a diffuse galactic ?-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.

Abdo, A. A.; Ackermann, M.; Ajello, M.; Anderson, B.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B. M.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; Burnett, T. H.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Cecchi, C.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Dereli, H.; Dermer, C. D.; de Angelis, A.; de Palma, F.; Digel, S. W.; di Bernardo, G.; Dormody, M.; Do Couto E Silva, E.; Drell, P. S.; Dubois, R.; Dumora, D.; Edmonds, Y.; Farnier, C.; Favuzzi, C.; Fegan, S. J.; Focke, W. B.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gaggero, D.; Gargano, F.; Gehrels, N.; Germani, S.; Giebels, B.; Giglietto, N.; Giordano, F.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Johnson, R. P.; Johnson, T. J.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kawai, N.; Kerr, M.; Knödlseder, J.; Kocian, M. L.; Kuehn, F.; Kuss, M.; Lande, J.; Latronico, L.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Meurer, C.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nolan, P. L.; Nuss, E.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Pesce-Rollins, M.; Piron, F.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Rodriguez, A. Y.; Roth, M.; Ryde, F.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Saz Parkinson, P. M.; Scargle, J. D.; Sellerholm, A.; Sgrò, C.; Smith, D. A.; Smith, P. D.; Spandre, G.; Spinelli, P.; Starck, J.-L.; Stecker, F. W.; Striani, E.; Strickman, M. S.; Strong, A. W.; Suson, D. J.; Tajima, H.; Takahashi, H.; Tanaka, T.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Uchiyama, Y.; Usher, T. L.; Vasileiou, V.; Vilchez, N.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Ylinen, T.; Ziegler, M.

2009-12-01

378

SNM gamma-ray fingerprint monitor functional requirements and design specifications  

SciTech Connect

A number of DOE facilities need to perform confirmatory inventory measurements on items of special nuclear material (SNM). The DOE Office of Safeguards and Security (OSS) has tasked the Safeguards, Safety and Nonproliferation Division (SSN) of the Department of Advanced Technology at Brookhaven National Laboratory (BNL) to develop a high-resolution gamma-ray-spectroscopy-based instrument for performing confirmatory inventory measurements on such materials, a ``gamma-ray fingerprint monitor`` (GRFM). This document is a conceptual design for the SSN GRFM system. This conceptual design is based on previous experience with measurements of plutonium-bearing materials and comparison of gamma-ray spectrum features, not on actual tests of the procedures or hardware described. As a result, modifications may be necessary when actual prototype hardware and software are tested in realistic circumstances on actual materials of interest.

Bieber, A.M. Jr.; Kane, W.R.

1994-07-01

379

Nuclear isomer suitable for gamma ray laser  

NASA Technical Reports Server (NTRS)

The operation of gamma ray lasers (gasers) are studied. It is assumed that the nuclear isomers mentioned in previously published papers have inherent limitations. It is further assumed that the judicious use of Bormann effect or the application of the total external reflection of low energy gamma radiation at grazing angle of incidence may permit the use of a gaser crystal sufficiently long to achieve observable stimulated emission. It is suggested that a long lived 0(+) isomer decaying by low energy gamma ray emission to a short lived 2(+) excited nuclear state would be an attractive gaser candidate. It is also suggested that the nuclear isomer be incorporated in a matrix of refractory material having an electrostatic field gradient whose principal axis lies along the length of the medium. This results in the preferential transmission of electric quadrupole radiation along the length of the medium.

Jha, S.

1979-01-01

380

Phenomenology of Gamma-Ray Jets  

E-print Network

We discuss some phenomenological aspects of $\\gamma$-ray emitting jets. In particular, we present calculations of the $\\gamma$-sphere and $\\pi$-sphere for various target photon fields, and employ them to demonstrate how $\\gamma$-ray observations at very high energies can be used to constraint the Doppler factor of the emitting plasma and the production of VHE neutrinos. We also consider the implications of the rapid TeV variability observed in M87 and the TeV blazars, and propose a model for the very rapid TeV flares observed with HESS and MAGIC in some blazars,that accommodates the relatively small Doppler factors inferred from radio observations. Finally, we briefly discuss the prospects for detecting VHE neutrinos from relativistic jets.

Amir Levinson

2007-09-10

381

Spectral evolution in gamma-ray bursts  

NASA Technical Reports Server (NTRS)

The Hard X-ray Burst Spectrometer (HXRBS) and the Gamma-Ray Spectrometer (GRS) on NASA's Solar Maximum Mission satellite have independently monitored cosmic gamma-ray bursts since launch in February 1980. Several bursts with relatively simple pulse structure and sufficient intensity have been analyzed for evidence of spectral variability on time scales shorter than the pulse durations. In many of these bursts pulse structures are found, ranging in duration from 1 to 10 seconds, which exhibit a trend of hard-to-soft spectral evolution. No significant evidence for soft-to-hard evolution has been found. The HXRBS data above 100 keV and the GRS data above 1 MeV indicate that the spectral evolution generally is not due to time-varying absorption features at energies below 100 keV.

Norris, J. P.; Share, G. H.; Messina, D. C.; Matz, M.; Kouveliotou, C.; Dennis, B. R.; Desai, U. D.; Cline, T. L.

1986-01-01

382

Ground-Based Gamma-Ray Astronomy  

E-print Network

Ground-based gamma-ray astronomy has become an active astrophysical discipline with four confirmed sources of TeV gamma rays, two plerionic supernova remnants (SNRs) and two BL Lac objects (BL Lacs). An additional nine objects (one plerion, three shell-type SNRs, one X-ray binary, and four BL Lacs) have been detected but have not been confirmed by independent detections. None of the galactic sources require the presence of hadronic cosmic rays, so definitive evidence of their origin remains elusive. Mrk 421 and Mrk 501 are weak EGRET sources but they exhibit extremely variable TeV emission with spectra that extend beyond 10 TeV. They also exhibit correlations with lower energy photons during multi-wavelength campaigns, providing tests of emission models. Next generation telescopes like VERITAS hold the promise of moving this field dramatically forward.

Michael Catanese

1999-11-09

383

Lorentz violation from gamma-ray bursts  

NASA Astrophysics Data System (ADS)

The constancy of light speed is a basic assumption in Einstein’s special relativity, and consequently the Lorentz invariance is a fundamental symmetry of space-time in modern physics. However, it is speculated that the speed of light becomes energy-dependent due to the Lorentz invariance violation (LV) in various new physics theories. We analyse the data of the energetic photons from the gamma-ray bursts (GRBs) by the Fermi Gamma-Ray Space Telescope, and find more events to support the energy dependence in the light speed with both linear and quadratic form corrections. We provide two scenarios to understand all the new-released Pass 8 data of bright GRBs by the Fermi-LAT Collaboration, with predictions from such scenarios being testable by future detected GRBs.

Zhang, Shu; Ma, Bo-Qiang

2015-02-01

384

Neutron-driven gamma-ray laser  

DOEpatents

A lasing cylinder emits laser radiation at a gamma-ray wavelength of 0.87 .ANG. when subjected to an intense neutron flux of about 400 eV neutrons. A 250 .ANG. thick layer of Be is provided between two layers of 100 .ANG. thick layer of .sup.57 Co and these layers are supported on a foil substrate. The coated foil is coiled to form the lasing cylinder. Under the neutron flux .sup.57 Co becomes .sup.58 Co by neutron absorption. The .sup.58 Co then decays to .sup.57 Fe by 1.6 MeV proton emission. .sup.57 Fe then transitions by mesne decay to a population inversion for lasing action at 14.4 keV. Recoil from the proton emission separates the .sup.57 Fe from the .sup.57 Co and into the Be, where Mossbauer emission occurs at a gamma-ray wavelength.

Bowman, Charles D. (Los Alamos, NM)

1990-01-01

385

The Compton Gamma Ray Observatory: mission status.  

NASA Astrophysics Data System (ADS)

The Arthur Holly Compton Gamma Ray Observatory (Compton) is the second in NASA's series of Great Observatories. Compton has now been operating for over two and a half years, and has given a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made and continue to be made. The authors describe the capabilities of the four scientific instruments and the observing programs for the first three years of the mission. During Phases 2 and 3 of the mission a Guest Investigator program has been in progress with the Guest Observers' time share increasing from 30% to over 50% for the later mission phases.

Gehrels, N.; Chipman, E.; Kniffen, D. A.

386

Intergalactic thermonuclear gamma-ray line  

NASA Technical Reports Server (NTRS)

The possibility of thermonculear reactions occurring in dilute space is briefly considered. X-ray emission from clusters of galaxies demonstrates that perhaps as much as 10 to the 14th solar masses of hot gas (T of about 100 million K) may often surround galaxies in clusters with a density of perhaps 0.004/cu cm. If the ion temperature is 100 million K, the thermonuclear reaction p + d to He-3 + gamma ray should emit gamma rays at a rate of roughly 4 x 10 to the 41st/sec with energy 5.516 + or -0.016 MeV. Such a source in teh virgo cluster at 15.7 Mpc would present a line flux of 1 x 10 to the -11th/sq cm/sec.

Clayton, D. D.

1985-01-01

387

Gamma Ray Observatory (GRO): Emergency support  

NASA Technical Reports Server (NTRS)

The Gamma Ray Observatory (GRO) is an Earth orbiting satellite that studies sources of localized, galactic, and extragalactic gamma rays. It will be carried into a near-circular orbit by the Space Shuttle, following which it will be placed in its operational orbit by its on-board hydrazine propulsion system. Formal orbit parameters are 350 km x 450 km x 28.5 degrees with a period of 93 minutes. Deep Space Network coverage will be provided during emergencies that would prevent communications via the normal Tracking and Data Relay Satellite System (TDRSS)-White Sands data link. Emergency support will be provided by the DSN's 26-meter antenna subnetwork. Information is given in tabular form for DSN support, frequency assignments, telemetry, and command.

Schauer, K.; Madden, J.

1991-01-01

388

THE HIGH ENERGY BUDGET ALLOCATIONS IN SHOCKS AND GAMMA RAY BURSTS  

SciTech Connect

The statistical distribution of energies among particles responsible for long gamma-ray burst (GRB) emission is analyzed in light of recent results of the Fermi Observatory. The all-sky flux, F{sub {gamma}}, recorded by the Gamma-Ray Burst Monitor (GBM) is shown, despite its larger energy range, to be not significantly larger than that reported by the Burst and Transient Explorer, suggesting a relatively small flux in the 3-30 MeV energy range. The present-day energy input rate in {gamma}-rays recorded by the GBM from long GRBs is found, assuming star formation rates in the literature, to be W-dot(0)=0.5 F{sub {gamma}H}/c=5x10{sup 42}erg Mpc{sup -3} yr{sup -1}. The Large Area Telescope fluence, when observed, is about 5%-10% per decade of the total, in good agreement with the predictions of saturated, nonlinear shock acceleration. The high-energy component of long GRBs, as measured by Fermi, is found to contain only {approx}10{sup -2.5} of the energy needed to produce ultrahigh-energy cosmic rays (UHECRs) above 4 EeV, assuming the latter to be extragalactic, when various numerical factors are carefully included, if the cosmic-ray source spectrum has a spectral index of -2. The observed {gamma}-ray fraction of the required UHECR energy is even smaller if the source spectrum is softer than E {sup -2}. The AMANDA II limits rule out such a GRB origin for UHECRs if much more than 10{sup -2} of the cosmic-ray energy goes into neutrinos that are within, and simultaneous with, the {gamma}-ray beam. It is suggested that 'orphan' neutrinos out of the {gamma}-ray beam might be identifiable via orphan afterglow or other wide angle signatures of GRBs in lieu of coincidence with prompt {gamma}-rays, and it is recommended that feasible single neutrino trigger criteria be established to search for such coincidences.

Eichler, David [Physics Department, Ben-Gurion University, Be'er-Sheva 84105 (Israel); Guetta, Dafne [Osservatorio astronomico di Roma, v. Frascati 33, 00040 Monte Porzio Catone (Italy); Pohl, Martin [Institut fuer Physik und Astronomie, Universitaet Potsdam, 14476 Potsdam-Golm (Germany)

2010-10-10

389

Prospects for Nuclear-gamma-ray Astronomy  

NASA Technical Reports Server (NTRS)

An analysis was made of prospects for gamma rays coming from two sources outside the solar system: (1) radioactive decay of fresh nuclear products to explosive nucleosynthesis, and (2) scattering of low energy cosmic rays. The former should be detectable and will provide a factual base for many suppositions about the site and history of nucleosynthesis. The latter may be detectable and, if so, will probably provide factual information about high-flux regions of cosmic radiation.

Clayton, D. D.

1973-01-01

390

Status of the Milagro Gamma Ray Observatory  

Microsoft Academic Search

The Milagro Gamma Ray Observatory is the world's first large-area water Cherenkov detector capable of continuously monitoring the sky at TeV energies. Located in the mountains of northern New Mexico, Milagro will perform an all sky survey of the Northern Hemisphere at energies between 250 GeV and 50 TeV. With ± a high duty-cycle, large detector area, and wide field-of-view

Joseph McCullough; W. Benbow; D. Berley; M.-L. Chen; D. G. Coyne; R. S. Delay; B. L. Dingus; D. E. Dorfan; R. W. Ellsworth; D. Evans; A. Falcone; L. Fleysher; R. Fleysher; G. Gisler; J. A. Goodman; T. J. Haines; C. M. Hoffman; S. Hugenberger; L. A. Kelley; I. Leonor; J. Macri; M. McConnell; J. E. McEnery; R. S. Miller; A. I. Mincer; M. F. Morales; P. Nemethy; J. M. Ryan; M. Schneider; B. Shen; A. Shoup; G. Sinnis; A. J. Smith; G. W. Sullivan; T. N. Thompson; O. T. Tumer; K. Wang; M. O. Wascko; S. Westerhoff; D. A. Williams; T. Yang; G. B. Yodh

1999-01-01

391

Supernovae and Gamma-Ray Bursts  

Microsoft Academic Search

I review the observational status of the Supernova\\/Gamma-Ray Burst (GRB) connection. Available data suggest that Supernovae (SNe) associated with GRBs form an heterogeneous class of objects including bright and faint hypernovae (Hyp) and perhaps also `standard' Ib\\/c events. Current estimates of SN and GRB rates and beaming angles yield ratios GRB\\/SNe-Ibc ?2% and GRB\\/Hyp ?25%. In the few SN\\/GRB associations

Massimo Della Valle

2006-01-01

392

Gamma-Ray Line Observations with RHESSI  

E-print Network

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has been observing gamma-ray lines from the Sun and the Galaxy since its launch in February 2002. Here I summarize the status of RHESSI observations of solar lines (nuclear de-excitation, neutron capture, and positron annihilation), the lines of $^{26}$Al and $^{60}$Fe from the inner Galaxy, and the search for positron annihilation in novae.

David M. Smith

2004-04-30

393

Are Gamma-Ray Bursts Standard Candles?  

E-print Network

By dividing a sample of 48 long-duration gamma-ray bursts (GRBs) into four groups with redshift from low to high and fitting each group with the Amati relation log Eiso = a + b log Epeak, I find that parameters a and b vary with the mean redshift of the GRBs in each group systematically and significantly. The results suggest that GRBs evolve strongly with the cosmic redshift and hence are not standard candles.

Li-Xin Li

2007-05-30

394

THE FERMI GAMMA-RAY BURST MONITOR  

SciTech Connect

The Gamma-Ray Burst Monitor (GBM) will significantly augment the science return from the Fermi Observatory in the study of gamma-ray bursts (GRBs). The primary objective of GBM is to extend the energy range over which bursts are observed downward from the energy range of the Large Area Telescope (LAT) on Fermi into the hard X-ray range where extensive previous data sets exist. A secondary objective is to compute burst locations onboard to allow re-orienting the spacecraft so that the LAT can observe delayed emission from bright bursts. GBM uses an array of 12 sodium iodide scintillators and two bismuth germanate scintillators to detect gamma rays from {approx}8 keV to {approx}40 MeV over the full unocculted sky. The onboard trigger threshold is {approx}0.7 photons cm{sup -2} s{sup -1} (50-300 keV, 1 s peak). GBM generates onboard triggers for {approx}250 GRBs per year.

Meegan, Charles [Universities Space Research Association, NSSTC, 320 Sparkman Drive, Huntsville, AL 35805 (United States); Lichti, Giselher; Bissaldi, Elisabetta; Diehl, Roland; Greiner, Jochen; Von Kienlin, Andreas; Steinle, Helmut [Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse Postfach 1312, Garching 85748 (Germany); Bhat, P. N.; Briggs, Michael S.; Connaughton, Valerie; Paciesas, W. S.; Preece, Robert; Wilson, Robert B. [University of Alabama in Huntsville, NSSTC, 320 Sparkman Drive, Huntsville, AL 35805 (United States); Fishman, Gerald; Kouveliotou, Chryssa [Space Science Office, VP62, NASA/Marshall Space Flight Center, Huntsville, AL 35812 (United States); Hoover, Andrew S.; Kippen, R. Marc; Wallace, Mark S. [Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545 (United States); Van der Horst, Alexander J. [NSSTC, 320 Sparkman Drive, Huntsville, AL 35805 (United States); McBreen, Sheila [University College, Dublin, Belfield, Stillorgan Road, Dublin 4 (Ireland)] (and others)

2009-09-01

395

Gravitational Waves and gamma-ray Bursts  

NASA Technical Reports Server (NTRS)

If the gamma-ray burst sources detected by GRO are coalescing binaries at cosmological distances there should be a coincident gravitational radiation signal. Using the GRBs rate we predict the gravitational radiation detection rate as a function of the gravitational wave strain at Earth. This method of predicting the rate avoids the large statistical uncertainties in the current estimates that are based on the three neutron star binaries containing pulsars found, so far, in the Galaxy. The brightest gamma-ray bursts should be accompanied by a gravitational pulse detectable by LIGO or VIRGO, and by using the bursts as triggers for LIGO/VIRGO their sensitivity can be improved by 50% and the detection rate increases by a factor of 3. LIGO/VIRGO must reach a strain sensitivity of 10(sup-20.7)h(sub 0) to detect one burst per decade, and a failure to find coincidences at a rate of one per year with a strain sensitivity of 10(sup -20.6)h(sub 0) will rule out the binary hypothesis. If they are detected as gravitational wave sources, the time delay between the gamma-rays and the gravitational waves will help to determine the burst mechanism, and the polarization of the gravitational waves will help to determine the burst geometry.

Kochanek, Christopher S.; Piran, Tsvi

1993-01-01

396

Positron annihilation in gamma-ray bursts  

NASA Technical Reports Server (NTRS)

Emission features appear at energies of 350 to 450 keV in the spectra of a number of gamma ray burst sources. These features were interpreted as electron-positron annihilation lines, redshifted by the gravitational field near the surface of a neutron star. Evidence that gamma ray bursts originate at neutron stars with magnetic field strengths of approx. 10(exp 12) Gauss came from recent observations of cyclotron scattering harmonics in the spectra of two bursts. Positrons could be produced in gamma ray burst sources either by photon-photon pair production or by one-photon pair production in a strong magnetic field. The annihilation of positrons is affected by the presence of a strong neutron star magnetic field in several ways. The relaxation of transverse momentum conservation causes an intrinsic broadening of the two-photon annihilation line and there is a decrease in the annihilation cross section below the free-space value. An additional channel for one-photon annihilation also becomes possible in high magnetic fields. The physics of pair production and annihilation near strongly magnetized neutron stars will be reviewed. Results from a self-consistent model for non-thermal synchrotron radiation and pair annihilation are beginning to identify the conditions required to produce observable annihilation features from strongly magnetized plasmas.

Harding, Alice K.

1990-01-01

397

Neutrino bursts from gamma-ray bursts  

NASA Technical Reports Server (NTRS)

If gamma-ray bursts originate at cosmological distances, as strongly indicated by the results from Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO), then ultrarelativistic ejecta are the likely consequence of the highly super-Eddington luminosity of the sources. If the energy injection rate varies with time, then the Lorentz factor of the wind also varies, and the shells of ejected matter collide with each other. The collisions between baryons produce pions which decay into high-energy photons, electrons, electron positron pairs, and neutrino pairs. The bulk Lorentz factor of approximately 300 is required if our model is to be compatible with the observed millisecond variability. The strongest gamma-ray bursts are observed to deliver approximately 10(exp -4) ergs/sq cm in 100-200 keV photons. In our scenario more energy may be delivered in a neutrino burst. Typical neutrinos may be approximately 30 GeV if the protons have a Maxwellian energy distribution, and up to approximately TeV if the protons have a power-law distribution. Such neutrino bursts are close to the detection limit of the DUMAND II experiment.

Paczynski, Bohdan; Xu, Guohong

1994-01-01

398

Gamma-Ray Bursts are Observed Off-axis  

NASA Astrophysics Data System (ADS)

We constrain the jet opening angle and, for the first time, the off-axis observer angle for gamma-ray bursts in the Swift-XRT catalog by using the ScaleFit package to fit afterglow light curves directly to hydrodynamic simulations. The ScaleFit model uses scaling relations in the hydrodynamic and radiation equations to compute synthetic light curves directly from a set of high-resolution two-dimensional relativistic blast wave simulations. The data sample consists of all Swift-XRT afterglows from 2005 to 2012 with sufficient coverage and a known redshift, 226 bursts in total. We find that the jet half-opening angle varies widely but is commonly less than 0.1 rad. The distribution of the electron spectral index is also broad, with a median at 2.30. We find the observer angle to have a median value of 0.57 of the jet opening angle over our sample, which has profound consequences for the predicted rate of observed jet breaks and affects the beaming-corrected total energies of gamma-ray bursts.

Ryan, Geoffrey; van Eerten, Hendrik; MacFadyen, Andrew; Zhang, Bin-Bin

2015-01-01

399

Simulated observations of gamma-ray bursts with GLAST  

SciTech Connect

The Gamma-ray Large Area Space Telescope (GLAST) will incorporate high sensitivity, large field of view, and precision tracker technology, providing arc-minute localizations of gamma-ray bursts (GRBs) and exploring GRB physics up to {approx}100 GeV. We have simulated the response of GLAST to GRBs with power-law spectra extending to GeV energies to determine the detailed burst localization capability. The simulated properties of GRBs are based on the BATSE peak flux and duration distributions. GLAST's hodoscopic calorimeter design has sufficiently good angular resolution and discrimination power against cosmic rays that >1 GeV gammas which are only detected in the calorimeter may be utilized for bright sources such as GRBs. Our results indicate that GLAST will detect and image {approx}230 GRBs yr{sup -1} with sensitivity to {approx}100 GeV for {approx}20 bursts yr{sup -1}. Many bright burst localizations will be comparable in size to the current InterPlanetary Network error boxes thus probing the cosmological burst parameter space at nearby redshifts and enabling counterpart searches at all lower energies.

Bonnell, J. T.; Norris, J. P. [Code 661, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Dingus, B. L. [Department of Physics, University of Utah, Salt Lake City, Utah 84112 (United States); Scargle, J. D. [NASA Ames Research Center, MS 245-3, Moffett Field, California 94035 (United States)

1998-05-16

400

SN2014J gamma rays from the 56Ni decay chain  

NASA Astrophysics Data System (ADS)

Context. The detection and measurement of gamma-ray lines from the decay chain of 56Ni provides unique information about the explosion in supernovae. SN2014J at 3.3 Mpc is a sufficiently-nearby supernova of type Ia so that such measurements have been feasible with the gamma-ray spectrometer SPI on ESA's INTEGRAL gamma-ray observatory. Aims: The 56Ni freshly produced in the supernova is understood to power the optical light curve, because it emits gamma rays upon its radioactive decay first to 56Co and then to 56Fe. Gamma-ray lines from 56Co decay are expected to become directly visible through the white dwarf material several weeks after the explosion, as they progressively penetrate the overlying material of the supernova envelope, which is diluted as it expands. The lines are expected to be Doppler-shifted or broadened from the kinematics of the 56Ni ejecta. We aim to exploit high-resolution gamma-ray spectroscopy with the SPI spectrometer on INTEGRAL toward constraining the 56Ni distribution and kinematics in this supernova. Methods: We use the observations with the SPI spectrometer on INTEGRAL, together with an improved instrumental background method. Results: We detect the two main lines from 56Co decay at 847 and 1238 keV, which are significantly Doppler-broadened, and at intensities (3.65 ± 1.21) × 10-4 and (2.27 ± 0.69) × 10-4 ph cm-2 s-1, respectively, at their brightness maximum. We measure their rise toward a maximum after about 60-100 days and a decline thereafter. The intensity ratio of the two lines is found to be consistent with expectations from 56Co decay (0.62 ± 0.28 at brightness maximum, the expected ratio is 0.68). We find that the broad lines seen in the late, gamma-ray transparent phase are not representative of the early gamma-ray emission, and notice instead that the emission spectrum is complex and irregular until the supernova is fully transparent to gamma rays, with progressive uncovering of the bulk of 56Ni. We infer that the explosion morphology is not spherically symmetric, both in the distribution of 56Ni and in the unburnt material which occults the 56Co emission. After we compare light curves from different plausible models, the resulting 56Ni mass is determined to be 0.49 ± 0.09 M?.

Diehl, Roland; Siegert, Thomas; Hillebrandt, Wolfgang; Krause, Martin; Greiner, Jochen; Maeda, Keiichi; Röpke, Friedrich K.; Sim, Stuart A.; Wang, Wei; Zhang, Xiaoling

2015-02-01

401

The Gamma-ray Large Area Space Telescope and Gamma-Ray Bursts  

SciTech Connect

The Gamma-ray Large Area Telescope (GLAST) is a satellite-based observatory to study the high energy gamma-ray sky. The main instrument on GLAST, the Large Area Telescope (LAT) is a pair-conversion telescope that will survey the sky from 20 MeV to greater than 300 GeV With the GLAST launch in 2007, the LAT will open a new and important window on a wide variety of high energy phenomena, including supermassive black holes and active galactic nuclei, gamma-ray bursts, supernova remnants and cosmic ray acceleration and dark matter. A second instrument, the GLAST Burst Monitor (GBM), greatly enhances GLAST's capability to study GRB by providing important spectral and timing information in the 10 keV to 30 MeV range. We describe how the instruments, spacecraft and ground system work together to provide observations of gamma-ray bursts from 8 keV - 300 GeV and to provide rapid notification of bursts to the wider gamma-ray burst community.

McEnery, Julie; Ritz, Steve [NASA/GSFC, Lab for Astroparticle Physics, MailCode 661, Greenbelt, MD 20771 (United States)

2006-05-19

402

Development of a telescope for medium-energy gamma-ray astronomy  

NASA Astrophysics Data System (ADS)

The Advanced Energetic Pair Telescope (AdEPT) is being developed at GSFC as a future NASA MIDEX mission to explore the medium-energy (5-200 MeV) gamma-ray range. The enabling technology for AdEPT is the Three- Dimensional Track Imager (3-DTI), a gaseous time projection chamber. The high spatial resolution 3-D electron tracking of 3-DTI enables AdEPT to achieve high angular resolution gamma-ray imaging via pair production and triplet production (pair production on electrons) in the medium-energy range. The low density and high spatial resolution of 3-DTI allows the electron positron track directions to be measured before they are dominated by Coulomb scattering. Further, the significant reduction of Coulomb scattering allows AdEPT to be the first medium-energy gamma-ray telescope to have high gamma-ray polarization sensitivity. We review the science goals that can be addressed with a medium-energy pair telescope, how these goals drive the telescope design, and the realization of this design with AdEPT. The AdEPT telescope for a future MIDEX mission is envisioned as a 8 m3 active volume filled with argon at 2 atm. The design and performance of the 3-DTI detectors for the AdEPT telescope are described as well as the outstanding instrument challenges that need to be met for the AdEPT mission.

Hunter, Stanley D.; Bloser, Peter F.; Dion, Michael P.; DeNolfo, Georgia A.; Legere, Jason; McConnell, Mark L.; Nowicki, Suzanne F.; Ryan, James M.; Son, Seunghee; Stecker, Floyd W.

2012-09-01

403

Response of AGATA Segmented HPGe Detectors to Gamma Rays up to 15.1 MeV  

E-print Network

The response of AGATA segmented HPGe detectors to gamma rays in the energy range 2-15 MeV was measured. The 15.1 MeV gamma rays were produced using the reaction d(11B,ng)12C at Ebeam = 19.1 MeV, while gamma-rays between 2 to 9 MeV were produced using an Am-Be-Fe radioactive source. The energy resolution and linearity were studied and the energy-to-pulse-height conversion resulted to be linear within 0.05%. Experimental interaction multiplicity distributions are discussed and compared with the results of Geant4 simulations. It is shown that the application of gamma-ray tracking allows a suppression of background radiation following neutron capture by Ge nuclei. Finally the Doppler correction for the 15.1 MeV gamma line, performed using the position information extracted with Pulse-shape Analysis, is discussed.

F. C. L. Crespi; R. Avigo; F. Camera; S. Akkoyun; A. Atac; D. Bazzacco; M. Bellato; G. Benzoni; N. Blasi; D. Bortolato; S. Bottoni; A. Bracco; S. Brambilla; B. Bruyneel; S. Cerutia; M. Ciemala; S. Coelli; J. Eberth; C. Fanin; E. Farnea; A. Gadea; A. Giaz; A. Gottardo; H. Hess; M. Kmiecik; S. Leoni; A. Maj; D. Mengoni; C. Michelagnoli; B. Million; D. Montanari; L. Pellegri; F. Recchia; P. Reiter; S. Riboldi; C. A. Ur; V. Vandone; J. J. Valiente-Dobon; O. Wieland; A. Wiens; The AGATA Collaboration

2012-09-06

404

50--500 MeV. gamma. -ray emission in the early phase of SN1987A  

SciTech Connect

SN1987A was observed on 19th April 1987 with a combined high energy ..gamma..-ray and hard x-ray payload, flown on a stratospheric balloon from Alice Springs, Australia. The ..gamma..-ray detector, sensitive in the energy range 50--500 MeV, was an optical spark chamber with 400cm/sup 2/ area, a field of view of 60/sup 0/ FWHM and a time resolution of 10 ..mu..s. The counting rate profile at approx.2.2 mb float altitude has lead to a 3sigma upper limit to the steady ..gamma..-ray flux of 7 x 10/sup -4/ ph cm/sup -2/ s/sup -1/ in the 50--500 MeV range. This upper limit is compared to our predictions for the time profile of ..gamma..-ray emission from SN1987A resulting from pulsar acceleration of particles to cosmic ray energies.

Sood, R.K.; Thomas, J.A.; Waldron, L.; Manchanda, R.K.; Ubertini, P.; Bazzano, A.; La Padula, C.D.; Rochester, G.K.; Sumner, T.J.; Frye, G.; and others

1988-09-25

405

Solar gamma ray and neutron observations. [analysis of gamma ray spectrometer data obtained on OSO-7  

NASA Technical Reports Server (NTRS)

The present status of knowledge concerning the impulsive and the continuous emission of solar gamma rays and neutrons is reviewed in the light of the recent solar activity in early August 1972. The gamma ray spectrometer on Orbiting Solar Observatory-7 (OSO-7) has observed the sun continuously for most of the activity period except for occultation by the earth. In association with the 2B flare on August 4, 1972, and the 3B flare on August 7, 1972, the monitor provides evidence for solar gamma ray line emission in the energy range from 300 keV to 10 MeV. A summary of all the results available from preliminary analysis of the data will be given.

Chupp, E. L.; Forrest, D. J.; Suri, A. N.

1973-01-01

406

182 OPTICS LETTERS / Vol. 28, No. 3 / February 1, 2003 Ultrahigh-resolution optical coherence tomography  

E-print Network

fiber is used to produce high longitudinal resolution. Longitudinal resolution of 1.3-mm has been a dynamic-focusing tracking method to maintain high lateral resolution over a large imaging depth tomography (OCT) can be used for in vivo high-resolution cross-sectional imaging of biological tissues.1 ­ 3

Chen, Zhongping

407

GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES  

SciTech Connect

Star formation in galaxies is observed to be associated with gamma-ray emission, presumably from non-thermal processes connected to the acceleration of cosmic-ray nuclei and electrons. The detection of gamma rays from starburst galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity. Since star formation is known to scale with total infrared (8-1000 {mu}m) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star-forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study, we apply the functional relationships between gamma-ray luminosity and radio and IR luminosities of galaxies derived by the Fermi Collaboration to a sample of the best candidate galaxy clusters for detection in gamma rays in order to place lower limits on the gamma-ray emission associated with star formation in galaxy clusters. We find that several clusters have predicted gamma-ray emission from star formation that are within an order of magnitude of the upper limits derived in Ackermann et al. based on non-detection by Fermi-LAT. Given the current gamma-ray limits, star formation likely plays a significant role in the gamma-ray emission in some clusters, especially those with cool cores. We predict that both Fermi-LAT over the course of its lifetime and the future Cerenkov Telescope Array will be able to detect gamma-ray emission from star-forming galaxies in clusters.

Storm, Emma M.; Jeltema, Tesla E.; Profumo, Stefano [Department of Physics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)

2012-08-20

408

GeV and higher energy photon interactions in gamma-ray burst fireballs and surroundings  

E-print Network

We have calculated the opacities and secondary production mechanisms of high energy photons arising in gamma-ray burst internal shocks, using exact cross-sections for the relevant processes. We find that for reasonable choices of parameters, photons in the range of 10's to 100's of GeV may be emitted in the prompt phase. Photons above this range are subject to electron-positron pair production with fireball photons and would be absent from the spectrum escaping the gamma-ray burst. We find that, in such cases, the fireball becomes optically thin again at ultra-high energies ($\\gtrsim$ PeV). On the other hand, for sufficiently large fireball bulk Lorentz factors, the fireball is optically thin at all energies. Both for $\\gamma\\gamma$ self-absorbed and optically thin cases, the escaping high energy photons can interact with infra-red and microwave background photons to produce delayed secondary photons in the GeV-TeV range. These may be observable with GLAST, or at low redshifts with ground-based air Cherenkov telescopes. Detection of the primary prompt spectrum constrains the bulk Lorentz factor, while detection of delayed secondary gamma-rays would provide a consistency check for the primary spectrum and the bulk Lorentz factor as well as constraints on the intergalactic magnetic field strength.

Soebur Razzaque; Peter Meszaros; Bing Zhang

2004-06-09

409

Radiation measurement above the lunar surface by Kaguya gamma-ray spectrometer  

NASA Astrophysics Data System (ADS)

The lunar surface is filled with various ionizing radiations such as high energy galactic particles, albedo particles and secondary radiations of neutrons, gamma rays and other elementary particles. A high-resolution Kaguya Gamma-Ray Spectrometer (KGRS) was carried on the Japan’s lunar explorer SELENE (Kaguya), the largest lunar orbiter since the Apollo missions. The KGRS instrument employed, for the first time in lunar exploration, a high-purity Ge crystal to increase the identification capability of elemental gamma-ray lines. The Ge detector is surrounded by BGO and plastic counters as for anticoincidence shields. The KGRS measured gamma rays in the energy range from 200 keV to 13 MeV with high precision to determine the chemical composition of the lunar surface. It provided data on the abundance of major elements over the entire lunar surface. In addition to the gamma-ray observation by the KGRS, it successfully measured the global distribution of fast neutrons. In the energy spectra of gamma-rays observed by the KGRS, several saw-tooth- peaks of Ge are included, which are formed by the collision interaction of lunar fast neutrons with Ge atoms in the Ge crystal. With these saw-tooth-peaks analysis, global distribution of neutrons emitted from the lunara surface was successfully created, which was compared with the previous results obtained by Lunar Prospector neutron maps. Another anticoincidence counter, the plastic counter with 5 mm thickness, was used to veto radiation events mostly generated by charged particles. A single photomultiplier serves to count scintillation light from the plastic scintillation counter. The global map of counting rates observed by the plastic counter was also created, implying that the radiation counting rate implies the geological distribution, in spite that the plastic counter mostly measures high energy charged particles and energetic neutrons. These results are presented and discussed.

Hasebe, Nobuyuki; Nagaoka, Hiroshi; Kusano, Hiroki; Hareyama, Matoko; Ideguchi, Yusuke; Shimizu, Sota; Shibamura, Eido

410

Atmospheric organic matter in clouds: exact masses and molecular formula identification using ultrahigh-resolution FT-ICR mass spectrometry  

NASA Astrophysics Data System (ADS)

Clouds alter the composition of atmospheric aerosol by acting as a medium for interactions between gas- and particulate-phase substances. To determine the cloud water atmospheric organic matter (AOM) composition and study the cloud processing of aerosols, two samples of supercooled clouds were collected at the Storm Peak Laboratory near Steamboat Springs, Colorado (3220 m a.s.l.). Approximately 3000 molecular formulas were assigned to ultrahigh-resolution mass spectra of the samples after using a reversed-phase extraction procedure to isolate the AOM components from the cloud water. Nitrogen-containing compounds (CHNO compounds), sulfur-containing compounds (CHOS and CHNOS compounds) and other oxygen-containing compounds (CHO compounds) with molecular weights up to 700 Da were observed. Average oxygen-to-carbon ratios of ∼0.6 indicate a slightly more oxidized composition than most water-soluble organic carbon identified in aerosol studies, which may result from aqueous oxidation in the clouds. The AOM composition indicates significant influences from biogenic secondary organic aerosol (SOA) and residential wood combustion. We observed 60% of the cloud water CHO molecular formulas to be identical to SOA samples of ?-pinene, ?-pinene, d-limonene, and ?-caryophyllene ozonolysis. CHNO compounds had the highest number frequency and relative abundances and are associated with residential wood combustion and NOx oxidation. Multiple nitrogen atoms in the assigned molecular formulas for the nighttime cloud sample composite were observed, indicating the significance of nitrate radical reactions on the AOM composition. Several CHOS and CHNOS compounds with reduced sulfur (in addition to the commonly observed oxidized sulfur-containing compounds) were also observed; however further investigation is needed to determine the origin of the reduced sulfur-containing compounds. Overall, the molecular composition determined using ultrahigh-resolution Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry provides an unambiguous identification of the cloud water organic anion composition in the Rocky Mountain area that could help to improve the understanding of aqueous-phase processes.

Zhao, Y.; Hallar, A. G.; Mazzoleni, L. R.

2013-12-01

411

Atmospheric organic matter in clouds: exact masses and molecular formula identification using ultrahigh resolution FT-ICR mass spectrometry  

NASA Astrophysics Data System (ADS)

Clouds alter the composition of atmospheric aerosol by acting as a medium for interactions between gaseous and particulate phase substances. To determine the cloud water atmospheric organic matter (AOM) composition and study the cloud processing of aerosols, two samples of supercooled clouds were collected at Storm Peak Laboratory near Steamboat Spring, Colorado (3220 m a.s.l.). Approximately 3000 molecular formulas were assigned to ultrahigh resolution mass spectra of the samples after using a reverse phase extraction procedure to isolate the AOM components from the cloud water. Nitrogen containing compounds (CHNO compounds), sulfur containing compounds (CHOS and CHNOS compounds) and other oxygen containing compounds (CHO compounds) with molecular weights up to 700 Da were observed. Average oxygen-to-carbon ratios of ~0.6 indicate a slightly more oxidized composition than most water-soluble organic carbon identified in aerosol studies, which may result from aqueous oxidation in the clouds. The AOM composition indicates significant influences from biogenic secondary organic aerosol (SOA) and residential wood combustion. We observed 60% of the cloud water CHO molecular formulas to be identical to SOA samples of ?-pinene, ?-pinene, d-limonene, and ?-caryophyllene ozonolysis. CHNO compounds had the highest number frequency and relative abundances and are associated with residential wood combustion and NOx oxidation. We observed multiple nitrogen atoms in the assigned molecular formulas for the nighttime cloud sample composite indicating the significance of nighttime emissions or NOx oxidation on the AOM composition. Several CHOS and CHNOS compounds with reduced sulfur (in addition to the commonly observed oxidized sulfur containing compounds) were also observed, however further investigation is needed to determine the origin of the reduced sulfur containing compounds. Overall, the molecular composition determined using ultrahigh resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry provides an unambiguous identification of the cloud water organic composition in the Rocky Mountain area which could help to improve the understanding of aqueous phase processes.

Zhao, Y.; Hallar, A. G.; Mazzoleni, L. R.

2013-08-01

412

Design concept for a high altitude rotating modulator gamma-ray imager  

Microsoft Academic Search

A rotating modulator (RM) is capable of imaging hard x-rays and gamma rays by the temporal modulation of incident photons. It combines a single mask of equally-wide slats and slits, rotating above an array of detectors with diameter equal to the slats. Since the RM works in the temporal domain, appropriate analysis of the measured data enables super-resolution (resolution better

B. Budden; G. L. Case; M. L. Cherry; T. G. Guzik; J. Isbert; M. F. Stewart

2010-01-01

413

Common Gamma-ray Glows above Thunderclouds  

NASA Astrophysics Data System (ADS)

Gamma-ray glows are continuous, long duration gamma- and x-ray emission seen coming from thunderclouds. The Airborne for Energetic Lightning Emissions (ADELE) observed 12 gamma-ray glows during its summer 2009 flight campaign over the areas of Colorado and Florida in the United States. For these glows we shall present their spectra, relationship to lightning activity and how their duration and size changes as a function of distance. Gamma-ray glows follow the relativistic runaway electron avalanche (RREA) spectrum and have been previously measured from the ground and inside the cloud. ADELE measured most glows as it flew above the screening layer of the cloud. During the brightest glow on August 21, 2009, we can show that we are flying directly into a downward facing relativistic runaway avalanche, indicative of flying between the upper positive and negative screening layer of the cloud. In order to explain the brightness of this glow, RREA with an electric field approaching the limit for relativistic feedback must be occurring. Using all 12 glows, we show that lightning activity diminishes during the onset of the glow. Using this along with the fact that glows occur as the field approaches the level necessary for feedback, we attempt to distinguish between two possibilities: that glows are evidence that RREA with feedback, rather than lightning, is sometimes the primary channel for discharging the cloud, or else that the overall discharging is still controlled by lightning, with glows simply appearing during times when a subsidence of lightning allows the field to rise above the threshold for RREA.

Kelley, Nicole; Smith, David; Dwyer, Joseph; Hazelton, Bryna; Grefenstette, Brian; Lowell, Alex; Splitt, Michael; Lazarus, Steven; Rassoul, Hamid

2013-04-01

414

A portable gamma-ray spectrometer using compressed xenon  

SciTech Connect

An ionization chamber using compressed xenon has been designed and built for gamma-ray spectrometry. The device is based on signal measurement from a parallel plate detector, with the gas enclosure constructed specifically for packaging into a portable instrument; thus, appropriate engineering practices comprises two small containers that can be setup for operation in just a few minutes. Its sensitivity is 100 keV to over 1 MeV, with a resolution at 662 keV of 2.5% FWHM for uniform irradiation, and 2% FWHM for collimated irradiation, comparable to the best ever with compressed xenon. It also exhibits greater specificity that most scintillators, such as NaI. The device is insensitive to neutron damage and has a low power requirement.

Mahler, G.J.; Yu, B.; Smith, G.C.; Kane, W.R.; Lemley, J.R.

1997-10-01

415

The Earth's Gamma-ray Albedo as observed by EGRET  

SciTech Connect

The Earth's high energy gamma-ray emission is caused by cosmic ray interactions with the atmosphere. The EGRET detector on-board the CGRO satellite is only the second experiment (after SAS-2) to provide a suitable dataset for the comprehensive study of this emission. Approximately 60% of the EGRET dataset consist of gamma photons from the Earth. This conference contribution presents the first results from the first analysis project to tackle this large dataset. Ultimate purpose is to develop an analytical model of the Earth's emission for use in the GLAST project. The results obtained so far confirm the earlier results from SAS-2 and extend them in terms of statistical precision and angular resolution.

Petry, Dirk [Joint Center for Astrophysics, University of Maryland Baltimore County, Baltimore, MD 21250 (United States); NASA, Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2005-02-21

416

Gamma-ray bursts with ROSAT  

E-print Network

I review the use of ROSAT over the last years for the investigation of well localized gamma-ray burst (GRB) error boxes. In particular, I cover (i) the systematic study of several dozens of IPN locations using the ROSAT All-Sky-Survey data, (ii) results of deep ROSAT pointings of selected small GRB error boxes, (iii) the attempts for and results of quick follow-up observations after GRB events including the three GRBs localized with BeppoSAX, (iv) the correlation of GRB locations with serendipitous ROSAT pointings and (v) the search for X-ray flashes in the database of pointed ROSAT observations.

J. Greiner

1997-04-01

417

Gamma Ray Bursts: an Enigma Being Unraveled  

SciTech Connect

The best astrophysical accelerators are quasars and the 'progenitors' of GRBs which, after decades of observations and scores of theories, we still do not understand. But, I shall argue, we now know quite well where GRBs come from, and we understand how their 'beams' behave, as they make short pulses of gamma rays and long-duration X-ray, optical and radio 'afterglows'. I shall argue that our understanding of these phenomena, based on the 'Cannonball Model', is unusually simple, precise and successful. The 'sociology' of GRBs is interesting per se and, in this sense, the avatars of the Cannonball Model in confronting the generally accepted 'fireball models' are also quite revealing.

De Rujula, Alvaro (Boston University and CERN) [Boston University and CERN

2003-05-14

418

A Model of Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

We present a model that reproduces the basic spectral properties of classical gammaray bursts with essentially no free parameters. It is an elaboration of the scenario for cosmological gamma-ray bursts outlined by Duncan & Thompson. The starting point is a Poynting-flux-dominated, relativistic, MHD wind of extremely high luminosity, L 1050 erg s- . The compactness parameter measured at the base of the wind exceeds that of the Crab pulsar, or that of a luminous AGN, by a factor of 1012. The wind emanates from a rapidly rotating neutron star, or neutron disc, in which a poloidal field > 1014 G has been generated by a helical dynamo. Scenarios that could produce such an object include a failed Type Ib supernova, accretion-induced collapse of a white dwarf, or perhaps a binary neutron star merger. The wind is safely in the MHD limit as the result of neutrino-driven and centrifugally driven mass loss. Mildly relativistic Alfven turbulence is excited in the wind by reconnection, or by hydrodynamical instabilities triggered by magnetic tension. Gamma-rays are generated via Comptonization at moderate to high scattering depth. The amplitude of the turbulence is itself limited by Compton drag, and the y-parameter of the Alfven motions is regulated to a value near 114, with a weak dependence on parameters such as radius, luminosity and the amount of baryon loading. The resulting spectrum is a power law with spectral index close to = -2 (VFv = constant), extending from an energy Ebreak - 1 (Ly/1050 erg S - 1)1/4 MeV (close to the spectral peak of a thermal fireball carrying the same flux) up to an energy as high as - 10 meG2. This power law steepens when the amplitude of the turbulence declines, or when the turbulence is generated outside the scattering photosphere. The spectrum below energy Ebreak is also a power law, with index a = - 1, which is cut off from below by stimulated scattering terms. Heavy baryon loading causes much less adiabatic softening of the spectrum than in thermal fireballs, so long as the Alfve'n turbulence is generated out to the scattering photo sphere. We show explicitly that the broken power law spectrum is an attractor, and that neither power law is altered by relativistic corrections to the Kompane'ets equation (except near the high-energy cut-off). The emergent gamma-ray spectrum is generated at a distance as small as - 1 0 cm from the source, without the need for any interaction with an external medium. Key words: MHD - radiation mechanisms: non-thermal - radiative transfer - turbulence - stars: neutron - gamma-rays: bursts.

Thompson, C.

1994-10-01

419

Gamma ray bursts from extragalactic sources  

NASA Technical Reports Server (NTRS)

The properties of gamma ray bursts of classical type are found to be explicable in terms of high speed collisions between stars. A model is proposed in which the frequency of such collisions can be calculated. The model is then applied to the nuclei of galaxies in general on the basis that galaxies, or at least some fraction of them, originate in the expulsion of stars from creation centers. Evidence that low level activity of this kind is also taking place at the center of our own Galaxy is discussed. The implications for galactic evolution are discussed and a negative view of black holes is taken.

Hoyle, Fred; Burbidge, Geoffrey

1992-01-01

420

Comptonization of gamma rays by cold electrons  

NASA Technical Reports Server (NTRS)

An analytic method is developed for calculating the emergent spectrum of gamma-rays and X-rays scattered in a homogeneous medium with low-temperature electrons. The Klein-Nishina corrections of the scattering cross section and absorption processes are taken in account. The wavelength relaxation and the spatial diffusion problems are solved separately, and the emergent spectrum is calculated by convolving the evolution function of the spectrum in an infinite medium with the photon luminosity resulting from the spatial diffusion in a finite sphere. The analytic results are compared with that of Monte Carlo calculations and it is concluded that the analytic result is quite accurate.

Xu, Yueming; Ross, Randy R.; Mccray, Richard

1991-01-01

421

Gamma-Ray Bursts observed by INTEGRAL  

E-print Network

During the first six months of operations, six Gamma Ray Bursts (GRBs) have been detected in the field of view of the INTEGRAL instruments and localized by the INTEGRAL Burst Alert System (IBAS): a software for the automatic search of GRBs and the rapid distribution of their coordinates. I describe the current performances of IBAS and review the main results obtained so far. The coordinates of the latest burst localized by IBAS, GRB 031203, have been distributed within 20 s from the burst onset and with an uncertainty radius of only 2.7 arcmin.

S. Mereghetti

2003-12-12

422

Gamma-ray burster counterparts - Radio  

NASA Technical Reports Server (NTRS)

Many observers and theorists have suggested that gamma-ray bursters (GRBs) are related to highly magnetized rotating, neutron stars, in which case an analogy with pulsars implies that GRBs would be prodigious emitters of polarized radio emission during quiescence. The paper reports on a survey conducted with the Very Large Array radio telescope of 10 small GRB error regions for quiescent radio emission at wavelengths of 2, 6, and 20 cm. The sensitivity of the survey varied from 0.1 to 0.8 mJy. The observations did indeed reveal four radio sources inside the GRB error regions.

Schaefer, Bradley E.; Cline, Thomas L.; Desai, U. D.; Teegarden, B. J.; Atteia, J.-L.; Barat, C.; Estulin, I. V.; Evans, W. D.; Fenimore, E. E.; Hurley, K.

1989-01-01

423

Highlights of GeV Gamma-Ray Astronomy  

NASA Technical Reports Server (NTRS)

Because high-energy gamma rays are primarily produced by high-energy particle interactions, the gamma-ray survey of the sky by the Fermi Gamma-ray Space Telescope offers a view of sites of cosmic ray production and interactions. Gamma-ray bursts, pulsars, pulsar wind nebulae, binary sources, and Active Galactic Nuclei are all phenomena that reveal particle acceleration through their gamma-ray emission. Diffuse Galactic gamma radiation, Solar System gamma-ray sources, and energetic radiation from supernova remnants are likely tracers of high-energy particle interactions with matter and photon fields. This paper will present a broad overview of the constantly changing sky seen with the Large Area Telescope (LAT) on the Fermi spacecraft.

Thompson, David J.

2010-01-01

424

The gamma-ray light curves of SN 1987A  

NASA Technical Reports Server (NTRS)

Observations of the SN 1987A ejecta in four Co-56-decay gamma-ray lines, obtained using the SMM gamma-ray spectrometer between February 1987 and May 1989, are reported and analyzed. The instrument characteristics and data-reduction procedures are described, and the results are presented in extensive tables and graphs and discussed with reference to theoretical models. Gamma-ray fluxes significantly above possible instrumental levels (as determined from analysis of pre-1987 data) were detected in the second half of 1987 and the first half of 1988. The data are found to favor a model with some Co-56 in regions of low gamma-ray optical depth by 200 d after the SN outburst over models with all Co-56 at one depth within a uniform expanding envelope. Also investigated are the gamma-ray contribution to the total bolometric luminosity and the escape (and potential observability) of Co-57 gamma rays.

Leising, Mark D.; Share, Gerald H.

1990-01-01

425

Theoretical fluxes of gamma rays from the Martian surface  

NASA Astrophysics Data System (ADS)

Theoretical fluxes of gamma rays escaping the surface of Mars were calculated. These and other calculated fluxes are needed to model the counting rates in the Mars Odyssey gamma ray spectrometer that are used to determine elemental compositions and other results using these measurements. Cross sections for the formation of gamma rays by both thermal and fast neutrons were compiled and evaluated. These evaluated cross sections were used with neutron fluxes calculated with the Monte Carlo N Particle Extended (MCNPX) code to get gamma ray production rates as a function of depth in the Martian surface. The fluxes of these gamma rays as a function of angle at the Martian surface were then calculated using gamma ray attenuation coefficients.

Kim, Kyeong J.; Drake, Darrell M.; Reedy, Robert C.; Williams, Remo M. S.; Boynton, William V.

2006-12-01

426

Fermi gamma-ray imaging of a radio galaxy.  

PubMed

The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields. PMID:20360067

Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cavazzuti, E; Cecchi, C; Celik, O; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Colafrancesco, S; Cominsky, L R; Conrad, J; Costamante, L; Cutini, S; Davis, D S; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Farnier, C; Favuzzi, C; Fegan, S J; Finke, J; Focke, W B; Fortin, P; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Georganopoulos, M; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hughes, R E; Jackson, M S; Jóhannesson, G; Johnson, A S; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocian, M L; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Porter, T A; Rainò, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rochester, L S; Rodriguez, A Y; Romani, R W; Roth, M; Ryde, F; Sadrozinski, H F-W; Sambruna, R; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Sgrò, C; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stawarz, ?; Strickman, M S; Suson, D J; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wallace, E; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M; Hardcastle, M J; Kazanas, D

2010-05-01

427

Label-free evaluation of angiogenic sprouting in microengineered devices using ultrahigh-resolution optical coherence microscopy  

PubMed Central

Abstract. Understanding the mechanism of angiogenesis could help to decipher wound healing and embryonic development and to develop better treatment for diseases such as cancer. Microengineered devices were developed to reveal the mechanisms of angiogenesis, but monitoring the angiogenic process nondestructively in these devices is a challenge. In this study, we utilized a label-free imaging technique, ultrahigh-resolution optical coherence microscopy (OCM), to evaluate angiogenic sprouting in a microengineered device. The OCM system was capable of providing ?1.5-?m axial resolution and ?2.3-?m transverse resolution. Three-dimensional (3-D) distribution of the sprouting vessels in the microengineered device was imaged over 0.6×0.6×0.5??mm3, and details such as vessel lumens and branching points were clearly visualized. An algorithm based on stretching open active contours was developed for tracking and segmenting the sprouting vessels in 3-D-OCM images. The lengths for the first-, second-, and third-order vessels were measured as 127.8±48.8???m (n=8), 67.3±25.9???m (n=9), and 62.5±34.7???m (n=10), respectively. The outer diameters for the first-, second-, and third-order vessels were 13.2±1.0, 8.0±2.1, and 4.4±0.8???m, respectively. These results demonstrate OCM as a promising tool for nondestructive and label-free evaluation of angiogenic sprouting in microengineered devices. PMID:24395588

Li, Fengqiang; Xu, Ting; Nguyen, Duc-Huy T.; Huang, Xiaolei; Chen, Christopher S.; Zhou, Chao

2014-01-01

428

Global Characteristics of Gamma-Ray Bursts Observed with INTEGRAL  

Microsoft Academic Search

The gamma-ray instruments on board INTEGRAL have detected and localized 62 gamma-ray bursts (GRBs) to date. The peak flux distribution of these bursts shows that INTEGRAL detects proportionally more weak GRBs than Swift because of its higher sensitivity in a smaller field of view. Spectral lags, i.e., the time delay in the arrival of low-energy gamma rays with respect to

S. Foley; S. McGlynn; L. Hanlon; S. McBreen; A. Martin-Carrillo; B. McBreen; M. Topinka; S. Meehan

2009-01-01

429

Gamma Ray Bursts: Explaining the Universe's Biggest Bangs  

NSDL National Science Digital Library

This radio broadcast discusses research into gamma ray bursts, the largest explosions in the universe. Topics include the SWIFT satellite mission and discoveries; the immense energy output of a gamma ray burst, and the causes of long and short gamma ray bursts (long bursts caused by core collapse into a black hole, and the short bursts from binary stellar system mergers, such as a neutron star colliding with a black hole). The broadcast is 28 minutes and 50 seconds in length.

430

EGRET Observations of the Extragalactic Gamma-Ray Emission  

Microsoft Academic Search

The all-sky survey in high-energy gamma rays (E > 30 MeV) carried out by EGRET aboard the Compton Gamma Ray Observatory provides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, as well as an almost uniformly distributed component

P. Sreekumar; D. L. Bertsch; B. L. Dingus; J. A. Esposito; C. E. Fichtel; R. C. Hartman; S. D. Hunter; G. Kanbach; D. A. Kniffen; Y. C. Lin; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; A. Muecke; R. Mukherjee; P. L. Nolan; M. Pohl; O. Reimer; E. Schneid; J. G. Stacy; F. W. Stecker; D. J. Thompson; T. D. Willis

1998-01-01

431

Gamma Ray/neutron Spectrometers for Planetary Elemental Mapping  

NASA Technical Reports Server (NTRS)

Los Alamos has designed gamma ray and neutron spectrometers for Lunar Scout, two robotic missions to map the Moon from 100 km polar orbits. Knowledge of the elemental composition is desirable in identifying resources and for geochemical studies and can be obtained using gamma ray and neutron spectrometers. Measurements with gamma ray and neutron spectrometers complement each other in determining elemental abundances in a planet's surface. Various aspects of the instruments are discussed.

Reedy, R. C.; Auchampaugh, G. F.; Barraclough, B. L.; Burt, W. W.; Byrd, R. C.; Drake, D. M.; Edwards, B. C.; Feldman, W. C.; Martin, R. A.; Moss, C. E.

1993-01-01

432

Gamma-ray measurements for simultaneous calorimetric assay  

SciTech Connect

Gamma-ray measurements obtained in the course of developing a simultaneous calorimetric assay system are described. Gamma-ray measurements of the isotopic composition of six, well-characterized plutonium oxide samples were obtained while the samples were in the calorimeter. These samples represent a range of plutonium masses from 19 to 231 g and two isotopic compositions. The values of effective specific power determined from the gamma-ray measurements agree with the values determined from destructive assay.

Rakel, D.A.

1982-03-02

433

Fermi GBM Observations of Terrestrial Gamma-Ray Flashes  

NASA Technical Reports Server (NTRS)

This slide presentation explores the relationship between Terrestrial Gamma-Ray Flashes (TGF) and lightning. Using data from the World-Wide Lightning Location Network (WWLLN), and the gamma ray observations from Fermi's Gamma-ray Burst Monitor (GBM), the study reviews any causal relationship between TGFs and lightning. The conclusion of the study is that the TGF and lightning are simultaneous with out a causal relationship.

Wilson-Hodge, Colleen A.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R.; Kippen, R. M.; vonKienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

2010-01-01

434

The Gamma-Ray Background from Blazars: A New Look  

Microsoft Academic Search

We present the results of a new model calculation of the gamma-ray background\\u000aproduced by unresolved blazars, using the second EGRET catalogue and taking\\u000aaccount of flaring. These results are compared to the preliminary gamma-ray\\u000abackground spectrum reported recently by the EGRET team. We find that blazars\\u000acan account for the entire extragalactic gamma-ray background observed by\\u000aEGRET. In addition,

F. W. Stecker; M. H. Salamon

1996-01-01

435

Development of CDZNTE Detectors for Low-Energy Gamma-Ray Astronomy  

NASA Technical Reports Server (NTRS)

Under this grant the UC Berkeley PI, K. Hurley, joined a Goddard-led effort to develop large area, multi-pixel Cadmium-Zinc-Telluride (CdZnTe, or CZT) detectors for gamma-ray astronomy. His task was to advise the project of new developments in the area of cosmic gamma-ray bursts, in order to focus the detector development effort on the construction of an instrument which could be deployed on a spacecraft to localize and measure the energy spectra of bursts with good angular and energy resolution, respectively. UC Berkeley had no hardware role in this proposal. The result of this effort was the production, at Goddard, of five CZT prototype modules. A proposal was written for SWIFT, a MIDEX mission to study cosmic gamma-ray bursts. One experiment aboard SWIFT is the Burst Arcminute Telescope (BAT), which consists of a 5200 sq cm hard X-ray detector and a coded mask. The detector comprises 256 CZT modules, each containing 128 4 x 4 x 2 mm CZT detectors. Each detector is read out using an ASIC. The angular resolution achieved with this mask/array combination is 22 arcminutes, and a strong gamma-ray burst can be localized to an accuracy of 4 arcminutes in under 10 seconds. The energy resolution is typically 5 keV FWHM at 60 keV, and the energy range is 10 - 150 keV. The BAT views 2 steradians, and its sensitivity is such that the instrument can detect 350 gamma-ray burst/year, localizing 320 of them to better than 4 arcminute accuracy. The BAT concept therefore met the science goals for gamma-ray bursts. The UCB effort in the SWIFT proposal included the scientific objectives for gamma-ray bursts, and the assembly of a team of optical and radio observers who would use the BAT data to perform rapid multi-wavelength searches for the counterparts to bursts. This proposal was submitted to NASA and peer-reviewed. In January 1999 it was one of five such proposals selected for a Phase A study. This study was completed in June, and SWIFT was formally presented to NASA in September. It appeared that a final selection of two MIDEX missions for flight was imminent. However, the final selection was deferred at the last minute due to the uncertainty in NASA's OSS budget.

Gehrels, N.

1999-01-01

436

Inelastic cross sections from gamma-ray measurements  

SciTech Connect

Measurements of gamma rays following neutron induced reactions have been studied with the Germanium Array for Neutron-induced Excitations (GEANIE) at the Los Alamos Neutron Science Center (LANSCE) for many years. Gamma-ray excitation functions and coincidence studies provide insight into nuclear reaction mechanisms as well as expanding our knowledge of energy levels and gamma-rays. Samples studied with Ge detectors at LANSCE range from Be to Pu. Fe, Cr and Ti have been considered for use as reference cross sections. An overview of the measurements and efforts to create a reliable neutron-induced gamma-ray reference cross section will be presented.

Nelson, Ronald Owen [Los Alamos National Laboratory

2010-12-06

437

Measurement of Disintegration Rates and Absolute {gamma}-ray Intensities  

SciTech Connect

The majority of practical radioactive materials decay by modes that include {gamma}-ray emission. For questions of 'how much' or 'how pure', one must know the absolute intensities of the major radiations. We are using liquid scintillation counting (LSC) to measurements of disintegration rates, coupled with {gamma}-ray spectroscopy to measure absolute {gamma}-ray emission probabilities. Described is a study of the 227Th chain yielding absolute {gamma}-ray intensities with {approx}0.5% accuracy and information on LSC efficiencies.

DeVries, Daniel J.; Griffin, Henry C. [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109 (United States)

2006-03-13

438

GAMMA-RAY BURST PREDICTIONS FOR THE FERMI GAMMA RAY SPACE TELESCOPE  

SciTech Connect

Results of a phenomenological model to estimate the gamma-ray burst (GRB) detection rate by the Fermi Gamma-Ray Space Telescope are reported. This estimate is based on the Burst and Transient Source Experiment (BATSE) 4B GRB fluence distribution, the mean ratio of fluences measured at 100 MeV-5 GeV with Energetic Gamma-Ray Experiment Telescope (EGRET) and at 20 keV-2 MeV with BATSE, and the mean EGRET GRB spectrum for the five EGRET spark-chamber GRBs. For a 10% fluence ratio and a number spectral index {alpha}{sub 1} = -2 at 100 MeV- 5 GeV energies, we estimate a rate of {approx}20 and 4 GRBs yr{sup -1} in the Fermi Large Area Telescope field of view (FOV) with at least five photons with energy E>100 MeV and E>1 GeV, respectively. We also estimate {approx}1.5 GRBs yr{sup -1} in the Fermi FOV where at least one photon with energy E>10 GeV is detected. For these parameters, we estimate {approx}1-2 GRBs yr{sup -1} detected with the Fermi telescope with more than 100 {gamma}-rays with E {approx}> 100 MeV. Comparison predictions for {alpha}{sub 1} = -2.2, different fluence ratios, and the AGILE {gamma}-ray satellite are made. Searches for different classes of GRBs using a diagram plotting 100 MeV-10 GeV fluence versus 20 keV- 20 MeV fluence is considered as a way to search for separate classes of GRBs and, specifically, spectral differences between the short-hard and long-duration GRB classes, and for hard components in GRBs.

Le, Truong; Dermer, Charles D. [Space Science Division, Code 7653, Naval Research Laboratory, Washington, DC 20375 (United States)], E-mail: tle@ssd5.nrl.navy.mil, E-mail: charles.dermer@nrl.navy.mil

2009-08-01

439

Physics of Gamma Ray Burst Sources  

NASA Technical Reports Server (NTRS)

During this grant period, the physics of gamma-ray bursts was investigated. A number of new results have emerged. The importance of pair formation in high compactness burst spectra may help explain x-ray flashes; a universal jet shape is a likely explanation for the distribution of jet break times; gravitational waves may be copiously produced both in short bursts from compact mergers and in long bursts arising from collapsars; x-ray iron lines are likely to be due to interaction with the stellar atmosphere of the progenitor; prompt optical flashes from reverse shocks will give diagnostics on the Lorentz factor and the environment; GeV and TeV emission from bursts may be expected in the external shock; etc. The group working with the PI included postdocs Dr. Bing Zhang (now assistant professor at University of Nevada); Dr. Shiho Kobayashi; graduate student Lijun Gou; collaborators Drs. Tim Kallman and Martin Rees. Meszaros shared with Rees and Dr. Bohan Paczynsky the AAS Rossi Prize in 2000 for their work on the theory of gamma ray bursts. The refereed publications and conference proceedings resulting from this research are summarized below. The PI gave a number of invited talks at major conferences, also listed.

Meszaros, Peter

2004-01-01

440

Iron K Lines from Gamma Ray Bursts  

NASA Technical Reports Server (NTRS)

We present models for reprocessing of an intense flux of X-rays and gamma rays expected in the vicinity of gamma ray burst sources. We consider the transfer and reprocessing of the energetic photons into observable features in the X-ray band, notably the K lines of iron. Our models are based on the assumption that the gas is sufficiently dense to allow the microphysical processes to be in a steady state, thus allowing efficient line emission with modest reprocessing mass and elemental abundances ranging from solar to moderately enriched. We show that the reprocessing is enhanced by down-Comptonization of photons whose energy would otherwise be too high to absorb on iron, and that pair production can have an effect on enhancing the line production. Both "distant" reprocessors such as supernova or wind remnants and "nearby" reprocessors such as outer stellar envelopes can reproduce the observed line fluxes with Fe abundances 30-100 times above solar, depending on the incidence angle. The high incidence angles required arise naturally only in nearby models, which for plausible values