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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

Ultrahigh energy resolution gamma-ray spectrometers for precision measurements of uranium enrichment  

Microsoft Academic Search

Superconducting gamma-ray detectors offer an order of magnitude higher energy resolution than conventional high-purity germanium\\u000a detectors. This can significantly increase the precision of non-destructive isotope analysis for nuclear samples where line\\u000a overlap affects the errors of the measurement. We have developed gamma-detectors based on superconducting molybdenum-copper\\u000a sensors and bulk tin absorbers for nuclear science and national security applications. They have,

S. Ali; I. D. Hau; T. R. Niedermayr; S. Friedrich

2008-01-01

3

High resolution {gamma}-ray spectroscopy: The first 85 years  

SciTech Connect

This opening review attempts to follow the main trends in crystal diffraction spectrometry of nuclear {gamma} rays from its 1914 beginning in Rutherford's laboratory to the ultra-high resolution instrumentation realized in the current generation of spectrometers at the Institute Laue Langeven (ILL). The authors perspective is that of an instrumentalist hoping to convey a sense of intellectual debt to a number of predecessors, each of whom realized a certain elegance in making the tools that have enabled much good science, including that to which the remainder of this workshop is dedicated. This overview follows some of the main ideas along a trajectory toward higher resolution at higher energies, thereby enabling not only the disentangling of dense spectra, but also allowing detailed study of aspects of spectral profiles sensitive to excited state lifetimes and interatomic potentials. The parallel evolution toward increasing efficiency while preserving needed resolution is also an interesting story of artful compromise that should not be neglected. Finally, it is the robustness of the measurement chain connecting {gamma}-ray wavelengths with optical wave-lengths associated with the Rydberg constant that only recently has allowed {gamma}-ray data to contribute to determine of particle masses and fundamental constants, as will be described in more detail in other papers from this workshop.

Deslattes, R.D.

2000-02-01

4

A search for ultra-high energy gamma-rays from the supernova 1987A  

Microsoft Academic Search

A search for ultrahigh-energy gamma-rays emitted by the supernova 1987A was conducted with a new cosmic-ray facility installed at the Black Birch Range in New Zealand. The observaions from October 13 to December 3 suggest no clear clustering of events around the direction of the supernova. It is concluded that the upper limit on the flux of gamma-rays of energies

Masaki Mori

1989-01-01

5

A high resolution scintillating fiber gamma-ray telescope.  

NASA Astrophysics Data System (ADS)

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 electron or pair production point can be determined by the scintillation photons reaching the photomultipliers. A 3-dimensional conversion point accuracy is expected to be ?rms ? 1 mm. The authors are presenting 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.

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

6

Ultra-high Energy Source Contributions to the Extragalactic Gamma-Ray Background  

NASA Astrophysics Data System (ADS)

The ingredients of the extragalactic gamma-ray background (EGB) at GeV-TeV energies must contain contributions from all source classes that are known to emit at these energies, including blazars, radio galaxies, star-forming galaxies, pulsars, and gamma-ray bursts. An uncertain contribution should be provided by cosmic-rays accelerated in cluster formation shocks, as well as from exotic processes, including dark matter annihilation and decay. After presenting an overview, the focus of this talk will be on contributions to the EGB from blazars emitting at >>TeV energies as well as from ultra-high energy cosmic rays. These ultra-high energy sources induce secondary radiations that cascade into the TeV and GeV band. Measurements of the EGB at very high gamma-ray energies can be used to constrain the number and distribution of such sources.

Dermer, Charles D.

2012-05-01

7

Mechanism for generation of ultrahigh energy gamma rays in accreting X-ray pulsars  

Microsoft Academic Search

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

Yu. N. Gnedin; N. R. Ikhsanov

1990-01-01

8

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

Microsoft Academic Search

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

Yu. N. Gnedin; N. R. Ikhsanov

1991-01-01

9

Low-resolution gamma-ray measurements of uranium enrichment  

SciTech Connect

Facilities that process special nuclear material perform periodic inventories. In bulk facilities that process low-enriched uranium, these inventories and their audits are based primarily on weight and enrichment measurements. Enrichment measurements determine the {sup 211}U weight fraction of the uranium compound from the passive gamma-ray emissions of the sample. Both international inspectors and facility operators rely on the capability to make in-field gamma-ray measurements of uranium enrichment. These users require rapid, portable measurement capability. Some in-field measurements have been biased, forcing the inspectors to resort to high-resolution measurements or mass spectrometry to accomplish their goals.

Sprinkle, J.K. Jr.; Christiansen, A.; Cole, R.; Collins, M.L. [and others

1996-11-01

10

High Energy Gamma Rays from Ultrahigh Energy Cosmic Rays in Gamma Ray Bursts  

Microsoft Academic Search

It has recently been proposed that ultrahigh energy ($\\\\gtrsim 10^{19}$ eV)\\u000acosmic rays (UHECRs) are accelerated by the blast waves associated with GRBs.\\u000aWe calculate the observed synchrotron radiation spectrum from protons and\\u000aenergetic leptons formed in the cascades initiated by photopion production,\\u000ataking into account $\\\\gamma\\\\gamma$ attenuation at the source. Normalizing to\\u000athe emission characteristics of GRB~970508, we predict

M. Boettcher; C. D. Dermer

1998-01-01

11

A search for ultra-high energy gamma-rays from the supernova 1987A  

NASA Astrophysics Data System (ADS)

A search for ultrahigh-energy gamma-rays emitted by the supernova 1987A was conducted with a new cosmic-ray facility installed at the Black Birch Range in New Zealand. The observaions from October 13 to December 3 suggest no clear clustering of events around the direction of the supernova. It is concluded that the upper limit on the flux of gamma-rays of energies is greater than 100 TeV is 1.1 x 10 to the-12th/sq cm s for a differential spectral index, alpha = 2.0 and source distance d = 50 kpc.

Mori, Masaki

1989-03-01

12

Detector characteristics of CCDs for high resolution gamma ray imaging  

Microsoft Academic Search

We are developing a high resolution gamma ray imager for use in Nuclear Medicine at energies up to ?150 keV. The imager is based upon a charge coupled device (CCD) coated with a polycrystalline scintillator to improve the detection efficiency. Three CCDs from E2V Ltd, bearing 100 ?m, 300 ?m and 500 ?m layers of Gd2O2S(Tb) (GADOX) have been tested.

W. J. Ryder; R. J. Ott; J. E. Lees; A. Keay; D. Bassford; G. W. Fraser

2002-01-01

13

Minute-of-Arc Resolution Gamma ray Imaging Experiment -- MARGIE  

NASA Astrophysics Data System (ADS)

MARGIE (Minute-of-Arc Resolution Gamma-ray Imaging Experiment) is a large area ( ~ 10(4) cm(2) ), wide field-of-view ( ~ 1 sr), hard X-ray/gamma-ray ( ~ 20--500 keV) coded-mask imaging telescope capable of performing a sensitive survey of both steady and transient cosmic sources. MARGIE has been selected for a NASA mission-concept study for an Ultra Long Duration (100 day) Balloon flight. We describe our program to develop the instrument based on new detector technology of either cadmium-zinc-telluride (CZT) semiconductors or pixellated cesium iodide (CsI) scintillators viewed by fast-timing bi-directional charge-coupled devices (CCDs). The primary scientific objective is to image faint Gamma-Ray Bursts (GRB) in near-real-time at the low intensity end (high-redshift) of the logN--logS distribution, thereby extending the sensitivity of present observations. Other high-priority scientific goals include a wide field survey of the Galactic center, mapping the distribution of the Galactic 511 keV emission and performing high-resolution spectral and temporal studies of active galaxies.

Altice, P. P.; Cherry, M. L.; Guzik, T. G.; Kappadath, S. C.; Stacy, J. G.; Macri, J.; McConnell, M. L.; Ryan, J. M.; Band, D. L.; Matteson, J. L.; O'Neill, T. J.; Zych, A. D.; Buckley, J.; Hink, P. L.

1999-04-01

14

Ultrahigh Energy Gamma Ray Cascading in the Geomagnetic Field and Its Development in the Atmosphere  

NASA Astrophysics Data System (ADS)

Extensive simulations of the longitudinal development of air showers from ultrahigh (UHE) energy gamma rays have been carried out. The shower development is affected by the geomagnetic cascading before entering the atmosphere and by the Landau-Pomeranchuk-Migdal effect in the atmosphere. AIRES code as well as our original code have been used for cascade simulations in the atmosphere. The analysis of the results shows that the longitudinal development of the showers depend strongly on both primary energy and incident direction. This feature may provide reliable conclusions about the photon fraction in the UHE ( > 5 × 1019 eV) cosmic ray flux.

Vankov, H.; Inoue, N.; Shinozaki, K.; Konishi, E.; Kawaguchi, S.; Misaki, A.; Kato, M.

2003-07-01

15

High resolution in-beam. gamma. -ray spectroscopy  

SciTech Connect

An in-beam curved crystal facility has been installed at the SIN variable energy cyclotron. Using the (110) planes of a 3.0 mm thick quartz lamina bent at 3.15 m, diffraction peaks typically 6 arcsec wide (FWHM) are obtained. The energy resolution is thus, for instance, 110 eV at 170 keV in 3rd order. Due to a sophisticated detector system and heavy shielding, the sensitivity of the instrument is quite good. The facility proves quite useful in (p,xn..gamma..) reaction studies whenever the ..gamma..-ray spectrum is very complex, e.g. in the study of odd-odd deformed nuclei. Complicated multiplets appearing in the /sup 176/Yb(p,3n..gamma..)/sup 174/Lu spectrum could be successfully resolved. From the results we derive that the g-factors of the 142 d, J/sup ..pi../ = 6/sup -/ isomer, take anomalous values.

Kern, J.; Dousse, J.h.; Gasser, M.; Perny, B.; Rheme, C.

1985-01-15

16

The large area high resolution gamma ray astrophysics facility - HR-GRAF  

NASA Astrophysics Data System (ADS)

The long-term program is described in terms of its equipment, scientific objectives, and long-range scientific studies. A prototype of a space-based large-area high-resolution gamma-ray facility (HR-GRAF) is being developed to examine pointlike and diffuse gamma-ray sources in the range 1 MeV-100 GeV. The instrument for the facility is proposed to have high angular and energy resolution and very high sensitivity to permit the study of the proposed objects. The primary research targets include the mapping of galactic gamma radiation, observing the angular variations of diffuse gamma rays, and studying the Galactic center with particular emphasis on the hypothetical black hole. Also included in the research plans are obtaining data on gamma-ray bursters, investigating the transmission of gamma rays from cold dark matter, and studying nuclear gamma-ray lines.

Fenyves, E. J.; Chaney, R. C.; Hoffman, J. H.; Cline, D. B.; Atac, M.; Park, J.; White, S. R.; Zych, A. D.; Tumer, Q. T.; Hughes, E. B.

1990-03-01

17

Synchrotron X-Ray and Gamma-Ray Haloes of UltraHigh Gamma-Ray Sources  

Microsoft Academic Search

Previous work on electron-photon cascades through the cosmic-microwave-background radiation initiated by primary gamma-rays and electrons is extended to a three-dimensional calculation which includes synchrotron radiation. New functions which enable synchrotron photon spectra to be calculated more easily are described. These functions are used in a Monte Carlo cascade simulation to predict the size and intensity of synchrotron haloes surrounding sources

R. J. Protheroe

1990-01-01

18

Analytic Expressions for the Angular Resolution of Compton Gamma-ray Detectors.  

National Technical Information Service (NTIS)

This paper describes the derivation of analytic expressions for the angular resolution of reconstructing gamma rays detected via Compton interactions. We consider two types of gamma-ray detectors: Compton-ring and electron-tracking devices. In Compton-rin...

D. M. Wright

2004-01-01

19

Very-high-energy gamma-ray signal from nuclear photodisintegration as a probe of extragalactic sources of ultrahigh-energy nuclei  

SciTech Connect

It is crucial to identify the ultrahigh-energy cosmic-ray sources and probe their unknown properties. Recent results from the Pierre Auger Observatory favor a heavy nuclear composition for the ultrahigh-energy cosmic rays. Under the requirement that heavy nuclei survive in these sources, using gamma-ray bursts as an example, we predict a diagnostic gamma-ray signal, unique to nuclei--the emission of deexcitation gamma rays following photodisintegration. These gamma rays, boosted from MeV to TeV-PeV energies, may be detectable by gamma-ray telescopes such as VERITAS, HESS, and MAGIC, and especially the next-generation CTA and AGIS. They are a promising messenger to identify and study individual ultrahigh-energy nuclei accelerators.

Murase, Kohta [Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, 606-8502 (Japan); CCAPP, Ohio State University, Columbus, Ohio 43210 (United States); Beacom, John F. [CCAPP, Ohio State University, Columbus, Ohio 43210 (United States); Department of Physics, Ohio State University, Columbus, Ohio 43210 (United States); Department of Astronomy, Ohio State University, Columbus, Ohio 43210 (United States)

2010-08-15

20

High-resolution spectroscopy of fission fragments, neutrons, and (gamma)-rays. Proceedings.  

National Technical Information Service (NTIS)

This volume contains most of the contributions presented at the 'International Workshop on High-Resolution Spectroscopy of Fission Fragments, Neutrons, and (gamma)-Rays' held at Technische Universitaet Dresden. The scientific aim of the workshop was to ob...

H. Maerten K. D. Schilling

1993-01-01

21

CONSTRAINING THE EMISSIVITY OF ULTRAHIGH ENERGY COSMIC RAYS IN THE DISTANT UNIVERSE WITH THE DIFFUSE GAMMA-RAY EMISSION  

SciTech Connect

Ultrahigh cosmic rays (UHECRs) with energies {approx}> 10{sup 19} eV emitted at cosmological distances will be attenuated by cosmic microwave and infrared background radiation through photohadronic processes. Lower energy extragalactic cosmic rays ({approx}10{sup 18}-10{sup 19} eV) can only travel a linear distance smaller than {approx}Gpc in a Hubble time due to the diffusion if the extragalactic magnetic fields are as strong as nano-Gauss. These prevent us from directly observing most of the UHECRs in the universe, and thus the observed UHECR intensity reflects only the emissivity in the nearby universe within hundreds of Mpc. However, UHECRs in the distant universe, through interactions with the cosmic background photons, produce UHE electrons and gamma rays that in turn initiate electromagnetic cascades on cosmic background photons. This secondary cascade radiation forms part of the extragalactic diffuse GeV-TeV gamma-ray radiation and, unlike the original UHECRs, is observable. Motivated by new measurements of extragalactic diffuse gamma-ray background radiation by Fermi/Large Area Telescope, we obtained upper limit placed on the UHECR emissivity in the distant universe by requiring that the cascade radiation they produce not exceed the observed levels. By comparison with the gamma-ray emissivity of candidate UHECR sources (such as gamma-ray bursts (GRBs) and active galactic nuclei) at high redshifts, we find that the obtained upper limit for a flat proton spectrum is {approx_equal} 10{sup 1.5} times larger than the gamma-ray emissivity in GRBs and {approx_equal} 10 times smaller than the gamma-ray emissivity in BL Lac objects. In the case of iron nuclei composition, the derived upper limit of UHECR emissivity is a factor of 3-5 times higher. Robust upper limit on the cosmogenic neutrino flux is further obtained, which is marginally reachable by the Icecube detector and the next-generation detector JEM-EUSO.

Wang Xiangyu; Liu Ruoyu [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Aharonian, Felix [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, 69117 Heidelberg (Germany)

2011-08-01

22

Search on extraterrestrial gamma-ray lines from Southern Hemisphere sources with high energy resolution gamma-ray telescopes  

Microsoft Academic Search

The scope of the GEL 1 and 2 balloon-borne gamma ray telescope experiments is described. The gamma ray spectrometer to be used on GEL 1 is described. It is designed to study the nature of the Galactic center positron annihilation 511 KeV line. The telescope effect is achieved through the aperture angle formed by the gamma ray spectrometer anticoincidence crystals.

J. M. Dacosta; J. O. D. Jardim; F. Gonzalez-Blanco; D. J. R. Nordemann; I. M. Martin; S. L. G. Dutra; F. Albernhe; G. Vedrenne; D. Boclet; P. Durouchoux

1981-01-01

23

THE FIRST LIMITS ON THE ULTRA-HIGH ENERGY NEUTRINO FLUENCE FROM GAMMA-RAY BURSTS  

SciTech Connect

We set the first limits on the ultra-high energy (UHE) neutrino fluence at energies greater than 10{sup 9} GeV from gamma-ray bursts (GRBs) based on data from the second flight of the Antarctic Impulsive Transient Antenna (ANITA). During the 31 day flight of ANITA-II, 26 GRBs were recorded by Swift or Fermi. Of these, we analyzed the 12 GRBs which occurred during quiet periods when the payload was away from anthropogenic activity. In a blind analysis, we observe 0 events on a total background of 0.0044 events in the combined prompt window for all 12 low-background bursts. We also observe 0 events from the remaining 14 bursts. We place a 90% confidence level limit on the E{sup -4} prompt neutrino fluence between 10{sup 8} GeV < E < 10{sup 12} GeV of E{sup 4}{Phi} = 2.5 x 10{sup 17} GeV{sup 3} cm{sup -2} from GRB090107A. This is the first reported limit on the UHE neutrino fluence from GRBs above 10{sup 9} GeV, and the strongest limit above 10{sup 8} GeV.

Vieregg, A. G.; Belov, K. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Palladino, K.; Allison, P.; Baughman, B. M.; Beatty, J. J.; Connolly, A.; Grashorn, E. W. [Department of Physics, Ohio State University, Columbus, OH 43210 (United States); Besson, D. Z.; Detrixhe, M. [Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045 (United States); Bevan, S. [Department of Physics and Astronomy, University College London, London (United Kingdom); Binns, W. R.; Dowkontt, P. F. [Department of Physics, Washington University in St. Louis, St. Louis, MO 63130 (United States); Chen, C.; Chen, P. [Department of Physics, National Taiwan University, Taipei, Taiwan (China); Clem, J. M.; De Marco, D. [Department of Physics, University of Delaware, Newark, DE 19716 (United States); DuVernois, M.; Gorham, P. W.; Hill, B., E-mail: avieregg@cfa.harvard.edu [Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States)

2011-07-20

24

New high-resolution gamma-ray burst detector: all-sky x-ray and gamma-ray astronomy monitor (AXGAM)  

Microsoft Academic Search

A wide field-of-view, arcsecond imaging, high energy resolution x-ray and low energy gamma ray detector is proposed for a future space mission. It is specifically designed to monitor and study gamma ray bursts (GRBs) with high energy and angular resolution and also find counterparts at other wavelengths. Detection of GRBs requires wide field-of-view ((pi) to 2 (pi) field-of-view) and high

Tumay O. Tuemer; Terrence J. O'Neill; Kevin Hurley; Hakki Ogelman; Robert J. Paulos; Richard C. Puetter; Eric Beuville; William J. Hamilton; Ray Proctor

1997-01-01

25

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

26

Process diagnostics and non-destructive testing using high-resolution gamma-ray tomography  

Microsoft Academic Search

In this paper, a high-resolution gamma-ray computed tomography (CT) measurement system is presented that was developed to determine phase fractions and other flow parameters in industrial devices operated under real industrial conditions. From CT scans non-superimposed cross-sectional images are reconstructed, which show the local gamma-ray attenuation coefficients within the scanned object slice. An advanced fast read-out electronics facilitates 2-D visualization

André Bieberle; Dietrich Hoppe; Uwe Hampel

2010-01-01

27

Search for Ultrahigh Energy Gamma-Ray Emission from Supernova Remnants  

NASA Astrophysics Data System (ADS)

The majority of the cosmic rays in our galaxy with energies in the range of ~ 10(9) --10(14) eV are thought to be accelerated in supernova remnants (SNRs). Measurements of SNR gamma-ray spectra in this energy region could support or contradict this hypothesis. The Energetic Gamma-Ray Telescope Experiment (EGRET) has reported several sources of gamma rays in the energy range of ~ 10(8) --10(10) eV whose coordinates are correlated with SNRs. Five of these are within the field of view of the CYGNUS extensive air shower detector. No evidence of gamma-ray emission above ~ 10(14) eV is found for these five SNRs in the CYGNUS data set. The flux upper limits from the CYGNUS experiment and the fluxes measured with the EGRET instrument are compared. The implications for models of gamma-ray production in these five SNRs will be presented.

Allen, G. E.; Chang, C. Y.; Chen, M. L.; Dion, C. L.; Goodman, J. A.; Stark, M. J.; Berley, D.; Biller, S.; Burman, R. L.; Haines, T. J.; Hoffman, C. M.; Nagle, D. E.; Schmidt, D. M.; Sinnis, C.; Cavalli-Sforza, M.; Coyne, D.; Dorfan, D.; Kelley, L.; Schnee, R.; Williams, D. A.; Yang, T.; Chumney, P.; Shoup, A.; Yodh, G. B.; Ellsworth, R. W.; Klein, S.; Wu, J.-P.

1994-12-01

28

A search for point sources of ultrahigh energy gamma rays with the South Pole air shower array  

NASA Astrophysics Data System (ADS)

This dissertation describes the search for ultrahigh energy gamma rays from discrete sources with the South Pole Air Shower Experiment (SPASE) . The design, configuration, and performance of the telescope are discussed, followed by a description of the techniques used for data analysis. Two novel analysis methods were developed and subsequently applied to the SPASE data base was applied to the problem of air shower core location, and a CUSUM method was used to identify gamma-ray bursts. Three years worth of data (1988, 1989, and 1991) were searched for emission of ultrahigh energy gamma radiation from nine pre-defined point sources X1, 4U1626-67, 4U1145-61, the supernova SN1987A, the globular cluster 47 Tucanae, and BL-1, an unconfirmed source that was found by the SPASE group in an earlier all sky survey. No conclusive evidence was found for DC emission from any of the nine candidates. In light of this, upper limits have been set on the time averaged flux detectable by the SPASE array. The four X-ray binaries SMC X-1, LMC X-4, Cen X-S, and Vela X-1, which have well-established orbital periods, were investigated for gamma ray emission modulated with the orbital period. No evidence for a modulated gamma-ray signal was found. A search for sporadic emission from the nine sources was conducted at time scales of one hour, one day, and one week. A statistically significant excess from SMC X-1 (99.6% c.l.) was detected during one day in 1991 120 background events.

Vanstekelenborg, John

1993-01-01

29

A Search for Point Sources of Ultrahigh Energy Gamma Rays with the South Pole Air Shower Array.  

NASA Astrophysics Data System (ADS)

This dissertation describes the search for ultrahigh energy gamma rays from discrete sources with the South Pole Air Shower Experiment (SPASE). The design, configuration, and performance of the telescope are discussed, followed by a description of the techniques used for data analysis. Two novel analysis methods were developed and subsequently applied to the SPASE data base: a neural network was applied to the problem of air shower core location, and a CUSUM method was used to identify gamma-ray bursts. Three years worth of data (1988, 1989, and 1991) were searched for emission of ultrahigh energy gamma radiation from nine pre-defined point sources: the X-ray binaries SMC X-1, LMC X-4, Cen X-3, Vela X-1, 4U1626-67, 4U1145 -61, the super-nova SN1987A, the globular cluster 47 Tucanae, and BL-1, an unconfirmed source that was found by the SPASE group in an earlier all sky survey. No conclusive evidence was found for DC emission from any of the nine candidates. In light of this, upper limits have been set on the time averaged flux detectable by the SPASE array. The four X-ray binaries SMC X-1, LMC X-4, Cen X-3, and Vela X-1, which have well-established orbital periods, were investigated for gamma ray emission modulated with the orbital period. No evidence for a modulated gamma-ray signal was found. A search for sporadic emission from the nine sources was conducted at time scales of one hour, one day, and one week. A statistically significant excess from SMC X-1 (99.6% c.l.) was detected during one day in 1991: 178 events on-source versus 120 background events.

van Stekelenborg, John

1993-01-01

30

High spatial resolution X-ray and gamma ray imaging system using diffraction crystals  

DOEpatents

A method and a device for high spatial resolution imaging of a plurality of sources of x-ray and gamma-ray radiation are provided. The device comprises a plurality of arrays, with each array comprising a plurality of elements comprising a first collimator, a diffracting crystal, a second collimator, and a detector.

Smither, Robert K. (Hinsdale, IL)

2011-05-17

31

High resolution gamma-ray spectrometry of culverts containing transuranic waste at the Savannah River Site  

SciTech Connect

A number of concrete culverts used to retrievably store drummed, dry, radioactive waste at the Savannah River Site (SRS), were suspected of containing ambiguous quantities of transuranic (TRU) nuclides. These culverts were assayed in place for Pu-239 content using thermal and fast neutron counting techniques. High resolution gamma-ray spectroscopy on 17 culverts, having neutron emission rates several times higher than expected, showed characteristic gamma-ray signatures of neutron emitters other than Pu-239 (e.g., Pu-238, Pu/Be, or Am/Be neutron sources). This study confirmed the Pu-239 content of the culverts with anomalous neutron rates and established limits on the Pu-239 mass in each of the 17 suspect culverts by in-field, non-intrusive gamma-ray measurements.

Hofstetter, K.J.; Sigg, R.

1990-12-31

32

High resolution gamma-ray spectrometry of culverts containing transuranic waste at the Savannah River Site  

SciTech Connect

A number of concrete culverts used to retrievably store drummed, dry, radioactive waste at the Savannah River Site (SRS), were suspected of containing ambiguous quantities of transuranic (TRU) nuclides. These culverts were assayed in place for Pu-239 content using thermal and fast neutron counting techniques. High resolution gamma-ray spectroscopy on 17 culverts, having neutron emission rates several times higher than expected, showed characteristic gamma-ray signatures of neutron emitters other than Pu-239 (e.g., Pu-238, Pu/Be, or Am/Be neutron sources). This study confirmed the Pu-239 content of the culverts with anomalous neutron rates and established limits on the Pu-239 mass in each of the 17 suspect culverts by in-field, non-intrusive gamma-ray measurements.

Hofstetter, K.J.; Sigg, R.

1990-01-01

33

Search for point sources of ultrahigh energy gamma rays in the southern sky  

Microsoft Academic Search

A search for point sources of gamma rays with energies >~100 TeV which has been made by the JANZOS Collaboration using an array of plastic scintillators located at Black Birch mountain in New Zealand is reported. The physical characteristics of the array are described, and also the techniques which have been used to analyze the data. Measurements of the angular

W. H. Allen; I. A. Bond; E. Budding; M. J. Conway; A. Daniel; K. B. Fenton; H. Fujii; Z. Fujii; N. Hayashida; K. Hibino; M. Honda; J. E. Humble; S. Kabe; K. Kasahara; T. Kifune; G. D. Lythe; A. Masaike; Y. Matsubara; K. Mitsui; Y. Miura; M. Mori; Y. Muraki; M. Nagano; T. Nakamura; M. Nishizawa; P. M. Morris; S. Ogio; To. Saito; M. Sakata; H. Sato; H. M. Shimizu; M. Spencer; J. R. Storey; T. Tanimori; M. Teshima; S. Torii; A. Wadsworth; Y. Watase; M. D. Woodhams; Y. Yamamoto; P. C. Yock; T. Yuda

1993-01-01

34

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

SciTech Connect

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 BrLa{sub 3} 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.

Tardocchi, M.; Proverbio, L. I.; Gorini, G.; Grosso, G.; Locatelli, M. [Universita degli Studi di Milano-Bicoccae Istituto di Fisica del Plasma, EURATOM-ENEA-CNR Association, I-20125 Milan (Italy); Chugonov, I. N.; Gin, D. B.; Shevelev, A. E. [A. F. Ioffe Physico-Technical Institute, St. Petersburg 194021 (Russian Federation); Murari, A.; Kiptily, V. G.; Syme, B. [EURATOM-UKAEA Association, Culham Science Centre, OX14 3DB Abingdon (United Kingdom); Fernandes, A. M.; Pereira, R. C.; Sousa, J. [Associacao EURATOM/IST Centro de Fusao Nuclear, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal)

2008-10-15

35

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

36

Low-resolution gamma-ray measurements of uranium enrichment  

Microsoft Academic Search

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

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

1997-01-01

37

Underlying generation mechanisms for the extragalactic gamma ray background and their implications for high-resolution gamma ray cosmology  

Microsoft Academic Search

The cosmological effects and observational consequences of various proposed extragalactic gamma ray background (EGB) generation mechanisms are investigated. It is claimed that the fine-scale EGB anisotropies can form a unique test for the active galactic nuclei (AGN) mechanism. Some effects independent of the AGN evolution models are found. It is argued that more than one type of underlying generation mechanism

Yi-Tian Gao; Yitian

1991-01-01

38

A Search for Ultra-High Energy Gamma Rays from EGRET Blazars  

NASA Astrophysics Data System (ADS)

Recently, the EGRET experiment aboard the Compton Gamma Ray Observatory has reported the detection of strong episodic emission from over 15 extra-galactic sources, typically radio-loud quasars and BL Lac objects. These sources are generally classified as ``blazars'', with significant gamma-ray energy which may be beamed towards the observer. At least one of these objects, Mrk 421, has also been detected at energies ~ 1 TeV by the Whipple observatory. Depending on the details of intergalactic absorption, it may be possible to detect such sources at energies above 50 TeV with large air shower arrays. We present a progress report on a search for Ultra High Energy (UHE) gamma rays from extra-galactic sources, such as the EGRET blazars, using the UMC air shower facility at Dugway, Utah. The facility is comprised of the large-area Chicago Air Shower Array (CASA) operating in coincidence with the underground Michigan Muon array (MIA). We describe our analysis approach for Mrk 421 and other AGN which are under observation by CASA-MIA in the northern hemisphere. We anticipate a sensitivity of ~ 3*E(-14) ph cm(-2) s(-1) above 80 TeV to flux from Mrk 421 after one full year's observations.

Covault, C. E.; Borione, A.; Cronin, J. W.; Fick, B. E.; Gibbs, K. G.; Hauptfeld, S.; McKay, T. A.; Muller, D.; Newport, B. J.; Ong, R. A.; Rosenberg, L. J.; Catanese, M.; Green, K. D.; Matthews, J.; Nitz, D.; Sinclair, D.; van der Velde, J. C.; Kieda, D. B.

1992-12-01

39

Search for ultra-high energy radiation from gamma-ray bursts  

NASA Astrophysics Data System (ADS)

A recent class of models suggests that some gamma-ray bursters may produce ultra-high-energy (greater than or equal to 100 TeV) photons. Using data from the CYGNUS array, we have searched for evidence of emission of ultra-high-energy radiation coincident with gamma-ray bursts observed either by the third Interplanetary Network of satellites or by the Burst and Transient Source Experiment (BATSE) instrument on the Compton Gamma-Ray Observatory. No statistically significant excess was found for six bursts whose locations were accurately determined by the Network, or for any point in the sky within 2 sigma of the BATSE location coordinates of 52 additional bursts. Flux upper limits depend greatly on the zenith angles of the bursts, but typical limits above 100 TeV are approximately 4 x 10-10/sq cm(s). The flux upper limits for three of the bursts imply that the observed spectrum softens between 2 MeV and approximately 100 TeV. If the production spectrum does not soften between these energies, the bursts must have a cosmological origin.

Alexandreas, D. E.; Allen, G. E.; Berley, D.; Biller, S.; Burman, R. L.; Cavalli-Sforza, M.; Chang, C. Y.; Chen, M. L.; Chumney, P.; Coyne, D.; Dion, C.; Dion, G. M.; Dorfan, D.; Ellsworth, R. W.; Goodman, J. A.; Haines, T. J.; Harmon, M.; Hoffman, C. M.; Kelley, L.; Klein, S.; Nagle, D. E.; Schaller, S. C.; Schmidt, D. M.; Schnee, R.; Shoup, A.; Sinnis, C.; Stark, M. J.; Weeks, D. D.; Williams, D. A.; Wu, J.-P.; Yang, T.; Yodh, G. B.; Zhang, W.

1994-05-01

40

High spectral resolution measurement of gamma ray lines from the earth's atmosphere  

SciTech Connect

A search for gamma ray line features from the Earth's atmosphere has been conducted using data from the third High Energy Astronomy Observatory (HEAO 3) high spectral resolution gamma ray spectrometer. In addition to the strong line at 0.511 MeV, other intrinsically broadened line features have been observed at 1.63, 2.31, 3.67, 4.43, 5.09, and 6.13 MeV. Since the spectral resolution of the instrument is much finer than the width of the observed line features, the intrinsic width as well as the energy and intensity of each of these lines are reported. Several other predicted lines have also been observed. The characteristics of the lines seen by HEAO 3 are generally consistent with theoretical predictions as well as with previous measurements.

Willett, J.B.; Mahoney, W.A. (California Inst. of Tech., Pasadena (United States))

1992-01-01

41

High vertical resolution spectral gamma ray logging in shallow water carbonates  

Microsoft Academic Search

Spectral gamma-ray logs provide one of the best means to investigate the mineralogy of thin-bedded sedimentary sequences, to correlate among different logging runs, and to compare logging data and core measurements. Increasing vertical resolution over currently available tools provides new opportunities for: a) log analysis in reservoirs with rapidly changing lithology, and b) extracting high-frequency climate changes from sedimentary cycles.

H. Delius; D. Goldberg; A. Meltser; G. Eberli

2001-01-01

42

Improved yield of high resolution mercuric iodide gamma-ray spectrometers  

SciTech Connect

Mercuric iodide (HgI{sub 2}) exhibits properties which make it attractive for use as a solid state nuclear radiation detector. The wide bandgap (E{sub g} = 2.1 eV) and low dark current allow room temperature operation, while the high atomic number provides a large gamma-ray cross section. However, poor hole transport has been a major limitation in the routine fabrication of high-resolution spectrometers using this material. This paper presents the results of gamma-ray response and charge transport parameter measurements conducted during the past year at EG G/EM on 96 HgI{sub 2} spectrometers. The gamma-ray response measurements reveal that detector quality is correlated with the starting material used in the crystal growth. In particular, an increased yield of high-resolution spectrometers was obtained from HgI{sub 2} which was synthesized by precipitation from an aqueous solution, as opposed to using material from commercial vendors. Data are also presented which suggest that better spectrometer performance is tied to improved hole transport. Finally, some initial results on a study of detector uniformity reveal spatial variations which may explain why the correlation between hole transport parameters and spectrometer performance is sometimes violated. 6 refs., 3 figs.

Gerrish, V.; van den Berg, L.

1990-01-01

43

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

44

High resolution x-ray and gamma ray imaging using diffraction lenses with mechanically bent crystals  

DOEpatents

A method for high spatial resolution imaging of a plurality of sources of x-ray and gamma-ray radiation is provided. High quality mechanically bent diffracting crystals of 0.1 mm radial width are used for focusing the radiation and directing the radiation to an array of detectors which is used for analyzing their addition to collect data as to the location of the source of radiation. A computer is used for converting the data to an image. The invention also provides for the use of a multi-component high resolution detector array and for narrow source and detector apertures.

Smither, Robert K. (Hinsdale, IL)

2008-12-23

45

High-resolution observations of gamma-ray line emission from SN 1987A  

NASA Astrophysics Data System (ADS)

A balloon-borne gamma-ray spectrometer comprising an array of high-purity germanium (HPGE) detectors was flown from Alice Springs, Australia, on October 29-30-31, norminally 250 days after the observed neutrino pulse. High-resolution data, typically 2.5 keV at 1.33 MeV, for two transists of the supernova SN 1987A were obtained along with interspersed background data. A significant net flux of gamma rays with energy 847 keV was observed from the direction of SN 1987A on each transit. No prominent gamma-ray features were seen at other energies, although data analysis is still in progress. A preliminary estimate of the line flux at 847 keV is ~5×10-4 photons cm-2 s-1 with statistical significance greater than three sigma. This line may be interpreted as emission from the first excited state of 56Fe due to the radioactive decay of 56Co, providing strong evidence for nucleosynthesis in the supernova. No emission was seen from the second excited state of 56Fe at 1238 keV. A preliminary upper limit for the 1238-keV line is ~5×10-4 photons cm-2 s-1. The flux estimates may be considerably altered as the systematics of the experiment are better understood.

Sandie, W. G.; Nakano, G. H.; Chase, L. F.; Fishman, G. J.; Meegan, C. A.; Wilson, R. B.; Paciesas, W. S.; Lashe, G. P.

1988-09-01

46

High-resolution observations of gamma-ray line emission from SN 1987A  

SciTech Connect

A balloon-borne gamma-ray spectrometer comprising an array of high-purity germanium (HPGE) detectors was flown from Alice Springs, Australia, on October 29--30--31, norminally 250 days after the observed neutrino pulse. High-resolution data, typically 2.5 keV at 1.33 MeV, for two transists of the supernova SN 1987A were obtained along with interspersed background data. A significant net flux of gamma rays with energy 847 keV was observed from the direction of SN 1987A on each transit. No prominent gamma-ray features were seen at other energies, although data analysis is still in progress. A preliminary estimate of the line flux at 847 keV is approx.5 x 10/sup -4/ photons cm/sup -2/ s/sup -1/ with statistical significance greater than three sigma. This line may be interpreted as emission from the first excited state of /sup 56/Fe due to the radioactive decay of /sup 56/Co, providing strong evidence for nucleosynthesis in the supernova. No emission was seen from the second excited state of /sup 56/Fe at 1238 keV. A preliminary upper limit for the 1238-keV line is approx.5 x 10/sup -4/ photons cm/sup -2/ s/sup -1/. The flux estimates may be considerably altered as the systematics of the experiment are better understood.

Sandie, W.G.; Nakano, G.H.; Chase L.F. Jr.; Fishman, G.J.; Meegan, C.A.; Wilson, R.B.; Paciesas, W.S.; Lashe, G.P.

1988-09-25

47

Simulating gamma-ray energy resolution in scintillators due to electron-hole pair statistics  

NASA Astrophysics Data System (ADS)

The best-possible limit to gamma-ray energy resolution in scintillators is given by the statistics of the number of electron-hole pairs produced by an incident gamma-ray, characterized by the Fano factor. The Fano factor is primarily controlled by the inelastic scattering during the electron cascade, which could be modeled by Monte Carlo simulation. Commonly used radiation transport codes do not follow the electrons to low enough energies to calculate electron-hole pair distributions. A Monte Carlo simulation for inelastic electron scattering is introduced based on cross-sections derived from data measured by Electron Energy-Loss Spectroscopy (EELS) for fast electrons. This inelastic scattering model was incorporated into the radiation transport code Penelope so that it could accurately count the number of electron-hole pairs produced by a gamma-ray. The Fano factor was calculated for the scintillators cerium fluoride (CeF3) and lutetium oxyorthosilicate (Lu2SiO5).

Narayan, R. D.; Miranda, R.; Rez, P.

2011-11-01

48

In situ calibration of a high-resolution gamma-ray borehole sonde for assaying uranium-bearing sandstone deposits  

USGS Publications Warehouse

A method is presented for assaying radioactive sandstone deposits in situ by using a high-resolution borehole gamma-ray spectrometer. Gamma-ray photopeaks from the same spectrum acquired to analyze a sample are used to characterize gamma-ray attenuation properties, from which a calibration function is determined. Assay results are independent of differences between properties of field samples and those of laboratory or test-hole standards generally used to calibrate a borehole sonde. This assaying technique is also independent of the state of radioactive disequilibrium that usually exists in nature among members of the natural-decay chains. ?? 1985.

Day, Jr. , J. H.

1985-01-01

49

High spectral resolution studies of gamma ray bursts on new missions  

SciTech Connect

Two new missions will be launched in 1996 and 1997, each carrying X-ray and gamma ray detectors capable of high spectral resolution at room temperature. The Argentine Satelite de Aplicaciones Cientificas (SAC-B) and the Small Spacecraft Technology Initiative (SSTI) Clark missions will each carry several arrays of X-ray detectors primarily intended for the study of solar flares and gamma-ray bursts. Arrays of small (1 cm{sup 2}) cadmium zinc telluride (CZT) units will provide x-ray measurements in the 10 to 80 keV range with an energy resolution of {approx_equal}6 keV. Arrays of both silicon avalanche photodiodes (APD) and P-intrinsic-N (PIN) photodiodes (for the SAC-B mission only) will provide energy coverage from 2-25 keV with {approx_equal}1 keV resolution. For SAC-B, higher energy spectral data covering the 30-300 keV energy range will be provided by CsI(Tl) scintillators coupled to silicon APDs, resulting in similar resolution but greater simplicity relative to conventional CsI/PMT systems. Because of problems with the Pegasus launch vehicle, the launch of SAC-B has been delayed until 1997. The launch of the SSTI Clark mission is scheduled for June 1996.

Desai, U. D.; Acuna, M. H.; Cline, T. L.; Dennis, B. R.; Orwig, L. E.; Trombka, J. I.; Starr, R. D. [NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Catholic University of America, Washington, District of Columbia 20064 (United States)

1996-08-01

50

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

2012-11-02

51

On Gamma Ray Burst and Blazar AGN Origins of the UltraHigh Energy Cosmic Rays in Light of First Results from Auger  

Microsoft Academic Search

The discoveries of the GZK cutoff with the HiRes and Auger Observatories and the discovery by Auger of clustering of >~60 EeV ultra-high energy cosmic rays (UHECRs) towards nearby <~75 Mpc) AGNs along the supergalactic plane establishes the astrophysical origin of the UHECRs. The likely sources of the UHECRs are gamma-ray bursts and radio-loud AGNs because: (1) they are extragalactic;

Charles D. Dermer

2007-01-01

52

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

53

A statistical approach to the choice of channel-width in gamma-ray spectrometry using empirical relations between resolution and gamma-ray energy  

Microsoft Academic Search

The problem of extra peak-broadening caused by the finite channel-width in multichannel gamma-ray spectrometry is discussed,\\u000a using empirical equations for the relations between resolution and energy for NaI(T1) scintillation detectors and Ge(Li) drift\\u000a detectors. Relations are derived and graphs designed to estimate the extra peak-broadening at a certain energy, caused by\\u000a the compromise necessary when using a chosen energy scale

R. Furler; H. Poppe

1974-01-01

54

High vertical resolution spectral gamma ray logging in shallow water carbonates  

NASA Astrophysics Data System (ADS)

Spectral gamma-ray logs provide one of the best means to investigate the mineralogy of thin-bedded sedimentary sequences, to correlate among different logging runs, and to compare logging data and core measurements. Increasing vertical resolution over currently available tools provides new opportunities for: a) log analysis in reservoirs with rapidly changing lithology, and b) extracting high-frequency climate changes from sedimentary cycles. Given known borehole geometry, optimal logging speed and sampling rate, the vertical resolution can only be enhanced by decreasing the detector length. The low counting efficiency and high statistical fluctuation inherent in small crystals, however, limit the improvement in resolution achievable in this manner. To overcome these limitations, we use an innovative approach based on real-time stacking of output signals from an array of small detectors that has been implemented in a Multi-sensor spectral Gamma ray Tool (MGT) developed for the Ocean Drilling Program. The MGT uses an array of independent, self-contained gamma spectrometry modules with 2-ft spacing. Each module comprises a 2"x4" NaI detector, a programmable 256-channel amplitude analyzer, and an individual spectrum stabilization system based on an Am241 calibration source. The spectral resolution of the stacked data is therefore the same as for each individual detector ( ~8%). The tool also includes an accelerometer to improve data stacking based on the precise measurement of logging speed. A specialized telemetry system developed for the MGT allows it to be combined with other commercial logging devices. The results of field tests using this tool are presented from the shallow water carbonates drilled by ODP Leg 194, Site 1194, offshore eastern Australia on the Marion Plateau. Comparison of MGT and Schlumberger gamma-ray tool data confirms that the MGT has vertical resolution 3 to 4 times better than conventional logging tools at common logging speeds. The improved vertical resolution enables the identification of high order cycles (<1 m thickness) in the thinly bedded successions of hemipelagic sediments. This result is of major interest for paleoceanographic studies of drilled sequences.

Delius, H.; Goldberg, D.; Meltser, A.; Eberli, G.

2001-05-01

55

DO ULTRAHIGH ENERGY COSMIC RAYS COME FROM ACTIVE GALACTIC NUCLEI AND FERMI {gamma}-RAY SOURCES?  

SciTech Connect

We study possible correlations between ultrahigh energy cosmic rays (UHECRs), observed by Auger, AGASA, and Yakutsk, and nearby active galactic nuclei (AGNs) and Fermi sources. We consider the deflection effects by a Galactic magnetic field (GMF) model constrained by the most updated measurements. We found that the average deflection angles of UHECRs by the Galactic magnetic fields are less than 4{sup 0}. A correlation between the Auger cosmic-ray events and nearby AGNs with a significance level of {approx}4{sigma} was found for the Auger UHECR data sets with or without deflection correction. No correlation was found between the AGASA/Yakutsk events with nearby AGNs. Marginal correlations between the Auger events and the Fermi sources, and between AGASA events and Fermi AGNs were found when the deflections calculated by the GMF model were considered. However, no correlation was found between the Yakutsk data and Fermi sources. Some Fermi sources are close to the arrival directions of UHECR events detected by Auger, AGASA, and Yakutsk, most of which are probably chance coincidences rather than objects producing UHECRs in the nearby universe. Four Fermi sources, NGC 4945, ESO 323-G77, NGC 6951, and Cen A, within 100 Mpc have UHECR events within 3.{sup 0}1 from their positions, which could potentially be cosmic-ray accelerators. However, the association can only be confirmed if more UHECRs are preferably detected in these directions.

Jiang Yunying; Hou, L. G.; Han, J. L.; Sun, X. H.; Wang Wei, E-mail: hjl@nao.cas.c [National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012 (China)

2010-08-10

56

High resolution gamma ray tomography scanner for flow measurement and non-destructive testing applications  

SciTech Connect

We report on the development of a high resolution gamma ray tomography scanner that is operated with a Cs-137 isotopic source at 662 keV gamma photon energy and achieves a spatial image resolution of 0.2 line pairs/mm at 10% modulation transfer function for noncollimated detectors. It is primarily intended for the scientific study of flow regimes and phase fraction distributions in fuel element assemblies, chemical reactors, pipelines, and hydrodynamic machines. Furthermore, it is applicable to nondestructive testing of larger radiologically dense objects. The radiation detector is based on advanced avalanche photodiode technology in conjunction with lutetium yttrium orthosilicate scintillation crystals. The detector arc comprises 320 single detector elements which are operated in pulse counting mode. For measurements at fixed vessels or plant components, we built a computed tomography scanner gantry that comprises rotational and translational stages, power supply via slip rings, and data communication to the measurement personal computer via wireless local area network.

Hampel, U.; Bieberle, A.; Hoppe, D.; Kronenberg, J.; Schleicher, E.; Suehnel, T.; Zimmermann, F.; Zippe, C. [Institute of Safety Research, Forschungszentrum Dresden-Rossendorf e.V., P.O. Box 51 01 19, 01314 Dresden (Germany); Institute of Safety Research, Forschungszentrum Dresden-Rossendorf e.V., P.O. Box 51 01 19, 01314 Dresden, Germany and AREVA NP GmbH, P.O. Box 3220, 91050 Erlangen (Germany); Institute of Safety Research, Forschungszentrum Dresden-Rossendorf e.V., P.O. Box 51 01 19, 01314 Dresden (Germany); AREVA NP GmbH, P.O. Box 3220, 91050 Erlangen (Germany); Institute of Safety Research, Forschungszentrum Dresden-Rossendorf e.V., P.O. Box 51 01 19, 01314 Dresden (Germany)

2007-10-15

57

Derivation of elemental abundance maps at intermediate resolution from optical interpolation of lunar prospector gamma-ray spectrometer data  

Microsoft Academic Search

We propose a technique that interpolates available lunar prospector gamma-ray spectrometer (GRS) data using Clementine UVVIS spectral reflectance images. The main idea is to use low resolution GRS data as a ``ground truth'' to establish relationships linking optical data and geochemical information maximizing the respective correlation coefficients. Then the relationships and Clementine UVVIS data are used to derive elemental abundance

Yuriy G. Shkuratov; Vadim G. Kaydash; Dmitriy G. Stankevich; Larissa V. Starukhina; Patrick C. Pinet; Serge D. Chevrel; Yves H. Daydou

2005-01-01

58

Derivation of elemental abundance maps at intermediate resolution from optical interpolation of lunar prospector gamma-ray spectrometer data  

Microsoft Academic Search

We propose a technique that interpolates available lunar prospector gamma-ray spectrometer (GRS) data using Clementine UVVIS spectral reflectance images. The main idea is to use low resolution GRS data as a “ground truth” to establish relationships linking optical data and geochemical information maximizing the respective correlation coefficients. Then the relationships and Clementine UVVIS data are used to derive elemental abundance

Yuriy G. Shkuratov; Vadim G. Kaydash; Dmitriy G. Stankevich; Larissa V. Starukhina; Patrick C. Pinet; Serge D. Chevrel; Yves H. Daydou

2005-01-01

59

On Gamma Ray Burst and Blazar AGN Origins of the UltraHigh Energy Cosmic Rays in Light of First Results from Auger  

Microsoft Academic Search

The discoveries of the GZK cutoff with the HiRes and Auger Observatories and\\u000athe discovery by Auger of clustering of >~60 EeV ultra-high energy cosmic rays\\u000a(UHECRs) towards nearby <~75 Mpc) AGNs along the supergalactic plane\\u000aestablishes the astrophysical origin of the UHECRs. The likely sources of the\\u000aUHECRs are gamma-ray bursts and radio-loud AGNs because: (1) they are\\u000aextragalactic;

Charles D. Dermer

2007-01-01

60

A high resolution gamma-ray spectrometer based on superconducting microcalorimeters  

NASA Astrophysics Data System (ADS)

Improvements in superconductor device fabrication, detector hybridization techniques, and superconducting quantum interference device readout have made square-centimeter-sized arrays of gamma-ray microcalorimeters, based on transition-edge sensors (TESs), possible. At these collecting areas, gamma microcalorimeters can utilize their unprecedented energy resolution to perform spectroscopy in a number of applications that are limited by closely-spaced spectral peaks, for example, the nondestructive analysis of nuclear materials. We have built a 256 pixel spectrometer with an average full-width-at-half-maximum energy resolution of 53 eV at 97 keV, a useable dynamic range above 400 keV, and a collecting area of 5 cm2. We have demonstrated multiplexed readout of the full 256 pixel array with 236 of the pixels (91%) giving spectroscopic data. This is the largest multiplexed array of TES microcalorimeters to date. This paper will review the spectrometer, highlighting the instrument design, detector fabrication, readout, operation of the instrument, and data processing. Further, we describe the characterization and performance of the newest 256 pixel array.

Bennett, D. A.; Horansky, R. D.; Schmidt, D. R.; Hoover, A. S.; Winkler, R.; Alpert, B. K.; Beall, J. A.; Doriese, W. B.; Fowler, J. W.; Fitzgerald, C. P.; Hilton, G. C.; Irwin, K. D.; Kotsubo, V.; Mates, J. A. B.; O'Neil, G. C.; Rabin, M. W.; Reintsema, C. D.; Schima, F. J.; Swetz, D. S.; Vale, L. R.; Ullom, J. N.

2012-09-01

61

A high resolution gamma-ray spectrometer based on superconducting microcalorimeters.  

PubMed

Improvements in superconductor device fabrication, detector hybridization techniques, and superconducting quantum interference device readout have made square-centimeter-sized arrays of gamma-ray microcalorimeters, based on transition-edge sensors (TESs), possible. At these collecting areas, gamma microcalorimeters can utilize their unprecedented energy resolution to perform spectroscopy in a number of applications that are limited by closely-spaced spectral peaks, for example, the nondestructive analysis of nuclear materials. We have built a 256 pixel spectrometer with an average full-width-at-half-maximum energy resolution of 53 eV at 97 keV, a useable dynamic range above 400 keV, and a collecting area of 5 cm(2). We have demonstrated multiplexed readout of the full 256 pixel array with 236 of the pixels (91%) giving spectroscopic data. This is the largest multiplexed array of TES microcalorimeters to date. This paper will review the spectrometer, highlighting the instrument design, detector fabrication, readout, operation of the instrument, and data processing. Further, we describe the characterization and performance of the newest 256 pixel array. PMID:23020368

Bennett, D A; Horansky, R D; Schmidt, D R; Hoover, A S; Winkler, R; Alpert, B K; Beall, J A; Doriese, W B; Fowler, J W; Fitzgerald, C P; Hilton, G C; Irwin, K D; Kotsubo, V; Mates, J A B; O'Neil, G C; Rabin, M W; Reintsema, C D; Schima, F J; Swetz, D S; Vale, L R; Ullom, J N

2012-09-01

62

A transportable high-resolution gamma-ray spectrometer and analysis system applicable to mobile, autonomous or unattended applications  

SciTech Connect

The Safeguards Technology Program at the Lawrence Livermore National Laboratory is developing systems based on a compact electro-mechanically cooled high-purity germanium (HPGe) detector. This detector system broadens the practicality of performing high- resolution gamma-ray spectrometry in the field. Utilizing portable computers, multi-channel analyzers and software these systems greatly improve the ease of performing mobile high-resolution gamma-ray spectrometry. Using industrial computers, we can construct systems that will run autonomously for extended periods of time without operator input or maintenance. These systems can start or make decisions based on sensor inputs rather than operator interactions. Such systems can provide greater capability for wider domain of safeguards, treaty verification application, and other unattended, autonomous or in-situ applications.

Buckley, W.M.; Neufeld, K.W.

1995-07-01

63

A First Application of the FRAM Isotopic Analysis Code to High-Resolution Microcalorimetry Gamma-Ray Spectra  

Microsoft Academic Search

Gamma-ray spectrometry systems based on High-Purity Germanium (HPGe) have been the long-standing leader in terms of resolution since their introduction many years ago. The application of this technology to the spectroscopic assay of special nuclear material led to the development of several isotopic analysis tools, including the advanced software package FRAM, which was, and continues to be, developed at Los

Pete J. Karpius; Duc Vo; Minesh Bacrania; James Beall; Douglas Bennett; Randy W. Doriese; Gene Hilton; Andrew Hoover; Robert Horansky; Kent Irwin; Michael Rabin; Carl Reintsema; Cliff Rudy; J. N. Ullom; Leila Vale

2009-01-01

64

The Calibration of an Ultra-High Energy Muon Hodoscope and Search for Cosmic Gamma Ray Anisotropies.  

NASA Astrophysics Data System (ADS)

The Homestake Deep Underground Hodoscope is a liquid scintillation detector that lies at a depth of 4200 mwe within a cavernous chamber of granite within the Homestake Gold Mine. At this depth, it is shielded from all but the most energetic elementary particles, in particular, muons with an energy of less than 27 TeV. Consequently, primaries with energies greater than 1 PeV are indirectly detected. The detector has two tiers of detectors each comprised of 40 scintillation modules of dimension.305 m x.305 m x 7.925 m, separated by a distance of 8.047 m. With this geometrical arrangement and the use of fast timing triggers (2.5 ns resolution), a directional study of ultra -high energy particles was conducted. By exploiting the fact that these particles enter the detector at very nearly the speed of light and that the trigger window has a fixed timing limit, a methodology was developed to fine tune the detector using these constraints. Once calibration was established, noisy events are easily eliminated and the resulting data is used to compute the flux of muons entering the detector, to plot the number of muons entering the detector as a function of angle and to compare this with theoretical profiles and, finally, to extrapolate the muon's velocity vector back onto the celestial sphere to search for anisotropies. The results of this study indicate a flux that is constant in time and is consistent with other, independent measurements. The angular profile is consistent with theoretical models, although a different scale factor was required to make a precise agreement. This may be due to the particular nature of the Homestake stratum. There was no indication for discrete gamma ray sources of cosmic origin, supporting earlier work using the same detector. Lastly, the methodology developed can be applied to similar detection facilities that are in operation on a long term basis. With its use of a personal computer, on site, a large facility could be monitored quite effectively.

McCarthy, Thomas K.

65

Dramatic resolution enhancement of gamma-ray spectra acquired with cadmium-zinc-telluride detectors via a patented pulse-shape-analysis methodology  

Microsoft Academic Search

We are developing a technique to correct for the resolution-degrading ballistic deficit in cadmium-zinc-telluride (CZT) gamma-ray detectors using our patent-pending pulse-shape analysis methodology. The pulse-shape-analysis methodology has already been demonstrated by LLNL for application in Compton rejection (technology being licensed) and possible application to gamma-ray imaging with Ge-based systems. If the extension of our technique to CZT detectors is successful,

S. A. Kreek; Y. Darsdenne; Dean Beckedahl; G. J. Schmid; Jerry J. Blair; J. Kammeraad; Allen Friensehner

2000-01-01

66

Constraining the Emissivity of Ultrahigh Energy Cosmic Rays in the Distant Universe with the Diffuse Gamma-Ray Emission  

Microsoft Academic Search

Ultrahigh cosmic rays (UHECRs) with energies >~ 1019 eV emitted at cosmological distances will be attenuated by cosmic microwave and infrared background radiation through photohadronic processes. Lower energy extragalactic cosmic rays (~1018-1019 eV) can only travel a linear distance smaller than ~Gpc in a Hubble time due to the diffusion if the extragalactic magnetic fields are as strong as nano-Gauss.

Xiang-Yu Wang; Ruo-Yu Liu; Felix Aharonian

2011-01-01

67

Use of an iterative convolution approach for qualitative and quantitative peak analysis in low resolution gamma-ray spectra  

NASA Astrophysics Data System (ADS)

In many applications, low resolution gamma-ray spectrometers, such as sodium iodide scintillation detectors, are widely used primarily due to their relatively low cost and high detection efficiency. There is widespread interest in improved methods for analyzing spectral data acquired with such devices, using inverse analysis. Peak means and peak areas in gamma- and X-ray spectra are needed for both qualitative and quantitative analysis. This paper introduces the PEAKSI code package that was developed at the Center for Engineering Applications of Radioisotopes (CEAR). The basic approach described here is to use accurate forward models and iterative convolution instead of direct deconvolution. Rather than smoothing and differentiation a combination of linear regression and non-linear searching is used to minimize the reduced chi-square, since this approach retains the capability of establishing uncertainties in the estimated peak parameters. The PEAKSI package uses a Levenberg–Marquardt (LM) non-linear search method combined with multiple linear regression (MLR) to minimize the reduced chi-square value for fitting single or multiple overlapping peaks to determine peak parameters, including peak means, peak standard deviations or full width at half maximum (FWHM), net peak counts, and background counts of peaks in experimental gamma-ray spectra. This approach maintains the natural error structure so that parameter uncertainties can be estimated. The plan is to release this code to the public in the near future.

Gardner, Robin P.; Ai, Xianyun; Peeples, Cody R.; Wang, Jiaxin; Lee, Kyoung; Peeples, Johanna L.; Calderon, Adan

2011-10-01

68

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

69

Arcminute Resolution Gamma-ray Images of Cosmic Sources Taken with the Balloon-borne GRATIS Payload  

Microsoft Academic Search

We present the first arcminute images of the gamma-ray sky. These images were taken with the Gamma Ray Arcminute Telescope and Imaging System (GRATIS). Using a combination of rotated one-dimensional coded aperture masks and a novel state of the art aspect reconstruction system we imaged a number of gamma ray sources, including CenA and GRS 1915 during the Fall 1995

W. W. Craig; C. J. Hailey; J. Hong; S. M. Kahn; J. W. Keck; R. McLean; M. J. Pivovaroff; G. Sprehn; R. E. Wurtz; K. P. Ziock; F. A. Harrison; J. G. Jernigan; P. M. Lubin; M. Seiffert

1996-01-01

70

Variable Gamma-Ray Emission Induced by Ultra-high Energy Neutral Beams: Application to 4C +21.35  

NASA Astrophysics Data System (ADS)

The flat-spectrum radio quasar 4C +21.35 (PKS 1222+216) displays prominent nuclear infrared emission from ?1200 K dust. A 70-400 GeV flare with ?10 minute variations during half an hour of observations was found by the MAGIC telescopes, and GeV variability was observed on sub-day timescales with the Large Area Telescope on Fermi. We examine 4C +21.35, assuming that it is a source of ultra-high energy cosmic rays (UHECRs). UHECR proton acceleration in the inner jet powers a neutral beam of neutrinos, neutrons, and ?-rays from p? photopion production. The radiative efficiency and production spectra of neutrals formed through photohadronic processes with isotropic external target photons of the broad-line region (BLR) and torus are calculated. Secondary radiations made by this process have a beaming factor vprop?5 D, where ?D is the Doppler factor. The pair-production optical depth for ?-rays and the photopion efficiency for UHECR neutrons as they pass through external isotropic radiation fields are calculated. If target photons come from the BLR and dust torus, large Doppler factors, ?D >~ 100, are required to produce rapidly variable secondary radiation with isotropic luminosity >~ 1047 erg s-1 at the pc scale. The ?-ray spectra from leptonic secondaries are calculated from cascades initiated by the UHECR neutron beam at the pc-scale region and fit to the flaring spectrum of 4C +21.35. Detection of >~ 100 TeV neutrinos from 4C +21.35 or other very high energy ?-ray blazars with IceCube or KM3NeT would confirm this scenario.

Dermer, Charles D.; Murase, Kohta; Takami, Hajime

2012-08-01

71

Digital pulse processing in high resolution, high throughput, gamma-ray spectroscopy  

Microsoft Academic Search

A new method for processing signals produced by high resolution, large volume semiconductor detectors is described. These detectors, to be used in the next generation of spectrometer arrays for nuclear research (i.e., EUROBALL, etc.), present a set of problems, such as resolution degradation due to charge trapping and ballistic deficit effects, poor resolution at a high count rate, long term

Andrey Georgiev; Werner Gast

1993-01-01

72

High resolution gamma ray spectroscopy with CdTe detector systems  

Microsoft Academic Search

Energy resolution and photopeak efficiency of the nowadays CdTe detector material can be improved using several detector shapes or electronic signal processing. Current results obtained in our laboratory with different detector geometries and pulse discrimination methods are presented and compared. Finally, we report on a new charge loss compensation method which improves both energy resolution and photopeak efficiency.

M. Richter; P. Siffert

1992-01-01

73

High resolution, high speed ultrahigh vacuum microscopy  

SciTech Connect

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 [National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2004-09-01

74

Effect of Gamma-Ray Detector Energy Resolution on the Ability to Identify Radioactive Sources.  

National Technical Information Service (NTIS)

This report describes the results of an initial study on radiation detector spectral resolution, along with the underlying methodology used. The study was done as part of an ongoing effort in Detection Modeling and Operational Analysis (DMOA) for the DNDO...

D. A. Knapp K. E. Nelson T. B. Goshell

2009-01-01

75

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

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, SrI{sub 2} 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 cm{sup 3} in size (with lower resolution). Our analysis indicates that SrI{sub 2}(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 SrI{sub 2}(Eu) scintillator device.

Cherepy, N J; Payne, S A; Hawrami, R; Burger, A; Boatner, L; Van Loef, E; Shah, K

2009-04-03

76

The effect of gain variation in micro-channel plates on gamma-ray energy resolution  

NASA Astrophysics Data System (ADS)

A Monte Carlo simulation of micro-channel plate (MCP) with particular interest in its effect on energy resolution performance is presented. Important physical processes occurring in MCP channels are described and modeled, including secondary electron (SE) yield, SE emission, and primary electron reflection. The effects causing channel saturation are also introduced. A two dimensional Monte Carlo simulation is implemented under the assumption of unsaturated channel. Simulation results about basic MCP performances and especially gain and energy resolution performances are presented and analyzed. It's found that energy resolution as an intrinsic property of MCP cannot be improved simply by adjusting system parameters; however it can be improved by increasing input signal or number of photoelectrons (PEs) in the context of image intensifier. An initial experiment with BazookaSPECT detector and CsI(Tl) scintillator is performed to validate and correlate with the simulation results and good agreement is achieved.

Han, Ling; Barrett, Harrison H.; Barber, H. Bradford; Furenlid, Lars R.

2013-09-01

77

An ISPA-camera for gamma rays with improved energy resolution  

Microsoft Academic Search

An Imaging Silicon Pixel Array (ISPA)-tube with nonfiber optic quartz window has been tested with respect to spatial and energy resolutions. The 122-keV ?-quanta of a Co57 source was converted in a planar YAP-disc or in optically separated YAP-pillars of 0.6×0.6-mm2 or 0.3×0.3-mm2 cross sections. The achieved intrinsic spatial resolution is worsened when compared to the ISPA-version with fiber optic

D. Puertolas; D. Piedigrossi; H. Leutz; T. Gys; F. De Notaristefani

1997-01-01

78

The Effect of Gamma-ray Detector Energy Resolution on the Ability to Identify Radioactive Sources  

SciTech Connect

This report describes the results of an initial study on radiation detector spectral resolution, along with the underlying methodology used. The study was done as part of an ongoing effort in Detection Modeling and Operational Analysis (DMOA) for the DNDO System Architecture Directorate. The study objective was to assess the impact of energy resolution on radionuclide identification capability, measured by the ability to reliably discriminate between spectra associated with 'threats' (defined as fissile materials) and radioactive 'non-threats' that might be present in the normal stream of commerce. Although numerous factors must be considered in deciding which detector technology is appropriate for a specific application, spectral resolution is a critical one for homeland security applications in which a broad range of non-threat sources are present and very low false-alarm rates are required. In this study, we have proposed a metric for quantifying discrimination capability, and have shown how this metric depends on resolution. In future work we will consider other important factors, such as efficiency and volume, and the relative frequency of spectra known to be discrimination challenges in practical applications.

Nelson, K E; Gosnell, T B; Knapp, D A

2009-03-05

79

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

80

Derivation of elemental abundance maps at intermediate resolution from optical interpolation of lunar prospector gamma-ray spectrometer data  

NASA Astrophysics Data System (ADS)

We propose a technique that interpolates available lunar prospector gamma-ray spectrometer (GRS) data using Clementine UVVIS spectral reflectance images. The main idea is to use low resolution GRS data as a "ground truth" to establish relationships linking optical data and geochemical information maximizing the respective correlation coefficients. Then the relationships and Clementine UVVIS data are used to derive elemental abundance maps with significantly improved spatial resolution. The main limitation of the technique is its dependence on how well the abundance of the elements correlates with the Clementine UVVIS data. The technique can also be applied to analysis of coming D-CIXS/Smart-1 and AMIE/Smart-1 data to increase resolution of lunar compositional maps. As an illustration of the suggested technique, maps for the elements Fe, Ti, O, Al, Ca, and Mg with pixel size 15 km×15 km are presented. The Fe and Ti distributions resemble qualitatively to the maps obtained with the well-known technique by lucey et al. (2000a. Lunar iron and titanium abundance algorithms based on final processing of Clementine ultraviolet-visible images. J. Geophys. Res. 105, 20,297-20,306), though in our case the ranges of Fe and Ti variations are, respectively, wider and narrower than for lucey's maps. New maps for the elements Fe, Ti, O, Al, Ca, and Mg appear to be informative. For instance, the map of oxygen abundance demonstrates an anomaly in the crater Tycho. The maps of Fe and Al contents show for highland regions slight variations related to maturity degree. Reliability of this relation is confirmed with lunar sample data. The reason of the correlation between chemical composition and exposition age of the lunar surface can be the global transport of the lunar surface material due to meteorite impacts.

Shkuratov, Yuriy G.; Kaydash, Vadim G.; Stankevich, Dmitriy G.; Starukhina, Larissa V.; Pinet, Patrick C.; Chevrel, Serge D.; Daydou, Yves H.

2005-10-01

81

The effect of energy resolution on the extraction of information content from gamma-ray spectra  

NASA Astrophysics Data System (ADS)

Rapid unambiguous identification of illicit radioactive materials is a matter of international concern that has yet to be fully attained. This is particularly true for shielded fissile materials in the presence of background radiation and routinely encountered benign radionuclides. We present a systematic treatment of the effect of detector resolution on the identification of nuclides in simple and complex shielded ?-ray spectra. Case studies of some problematic spectra with 1000 counts suggest that, at moderate count rates, near-unambiguous identification (<1% probability of misidentification) of potential fissile sources requires a detector with an energy resolution of at least 1-2% at 662 keV. While somewhat limited in scope, the study establishes a quantitative basis for the comparative evaluation of detectors of comparable efficiency.

Nelson, Karl E.; Gosnell, Thomas B.; Knapp, David A.

2011-12-01

82

An ISPA-camera for gamma rays with improved energy resolution  

SciTech Connect

An Imaging Silicon Pixel Array (ISPA)-tube with nonfiber optic quartz window has been tested with respect to spatial and energy resolutions. The 122-keV {gamma}-quanta of a Co{sup 57} source was converted in a planar YAP-disc or in optically separated YAP-pillars of 0.6 x 0.6-mm{sup 2} or 0.3 x 0.3-mm{sup 2} cross sections. The achieved intrinsic spatial resolution is worsened when compared to the ISPA-version with fiber optic glass window but is still in the submillimeter region. As the YAP emission spectrum is fully covered by the spectral transmission of the quartz window and well adapted to the photocathode quantum efficiency spectrum, the resulting improved energy resolution allows for triggering of ISPA-events within a selected energy window at the 122-keV total absorption peak. This mode of operation, since it strongly reduces the number of unwanted events, is essential for the application of a {gamma} camera in environmental conditions where a wider energy range from other background sources may be present.

Puertolas, D.; Notaristefani, F. de [INFN Section of Rome (Italy)]|[Third Univ. of Rome (Italy); Piedigrossi, D.; Leutz, H.; Gys, T.; D`Ambrosio, C. [CERN, Geneva (Switzerland)

1997-10-01

83

Imaging and background in low-energy gamma ray astronomy  

Microsoft Academic Search

The current status of low energy gamma ray astronomy is reviewed and the conclusion drawn that the next generation of low energy gamma ray telescopes will require high sensitivity, good timing, and spectral resolution. High angular resolution imaging capability is also considered essential. The imaging of low energy gamma rays is hampered by the difficulties encountered in developing high resolution

Fan Lei

1989-01-01

84

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

85

XUV Source for Ultra-High Resolution Photoionization Spectroscopy.  

National Technical Information Service (NTIS)

A tunable vuv-xuv laser system with good pulse energy (>100mJ in the visible) and narrow bandwidth (<210MHz in the xuv) was built in order to do ultra-high resolution photoionization spectroscopy. The capabilities of this system have been demonstrated wit...

E. Cromwell A. H. Kung T. Trickl Y. T. Lee

1988-01-01

86

XUV source for ultra-high resolution photoionization spectroscopy  

SciTech Connect

A tunable vuv-xuv laser system with good pulse energy (>100mJ in the visible) and narrow bandwidth (<210MHz in the xuv) was built in order to do ultra-high resolution photoionization spectroscopy. The capabilities of this system have been demonstrated with a study of isotope shifts and hyperfine splitting in Kr Rydbeg levels.

Cromwell, E.; Kung, A.H.; Trickl, T.; Lee, Y.T.

1988-01-01

87

High-Resolution Soft X-ray Spectroscopy of a Gamma-ray Burst X-ray Afterglow  

Microsoft Academic Search

We propose a deep TOO observation of a bright X-ray afterglow of a gamma-ray burst using the Chandra LETG\\/ACIS-S. The trigger will be based primarily on the X-ray flux, which will be monitored with the X-ray Telescope on board the Swift observatory. An additional constraint on the line-of-sight Galactic column density will be imposed as well to provide the highest

Masao Sako

2005-01-01

88

High-Resolution Soft X-ray Spectroscopy of a Gamma-ray Burst X-ray Afterglow  

Microsoft Academic Search

We propose a deep TOO observation of a bright X-ray afterglow of a gamma-ray burst using the Chandra LETG\\/ACIS-S. The trigger will be based primarily on the amount of X-ray variability observed during it's early afterglow phases, which will be monitored with the X-ray Telescope onboard the Swift satellite. Additional constraints including X-ray flux and line-of-sight Galactic column density will

Masao Sako

2003-01-01

89

High-Resolution Soft X-ray Spectroscopy of a Gamma-ray Burst X-ray Afterglow  

Microsoft Academic Search

We propose a deep TOO observation of a bright X-ray afterglow of a gamma-ray burst using the Chandra LETG\\/ACIS-S. The trigger will be based primarily on the amount of X-ray variability observed during it's early afterglow phases, which will be monitored with the X-ray Telescope onboard the Swift satellite. Additional constraints including X-ray flux and line-of-sight Galactic column density will

Masao Sako

2004-01-01

90

High-Resolution Soft X-ray Spectroscopy of a Gamma-ray Burst X-ray Afterglow  

Microsoft Academic Search

We propose a deep TOO observation of a bright X-ray afterglow of a gamma-ray burst using the Chandra LETG\\/ACIS-S. The trigger will be based primarily on the X-ray flux, which will be monitored with the X-ray Telescope on board the Swift observatory. An additional constraint on the line-of-sight Galactic column density will be imposed as well to provide the highest

Masao Sako

2006-01-01

91

a Quantitative Method for Analyzing Radioactive Nuclides in Infinite Composite Materials Using High-Resolution Gamma-Ray Spectroscopy  

Microsoft Academic Search

A theory is formulated in which the concentration of a radionuclide uniformly distributed throughout an infinite medium is related to the photopeak count rate of a signature gamma ray acquired by a detector within the medium. The mass fraction of the i('th) radionuclide in the medium is given by f(,i) = W(,i)(psi)(,i) (E)\\/(lamda)(,i)I(,I)(E)K(E); where (psi)(,i)(E) and I(,i)(E) are the observed

John Henry Day Jr.; J. H. Jr

1982-01-01

92

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

93

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

Microsoft Academic Search

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.

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

1984-01-01

94

Hard X-ray and Gamma-ray Emission Induced by UltraHigh Energy Protons in Cluster Accretion Shocks and their Detectability  

Microsoft Academic Search

Protons can be plausibly accelerated to $\\\\sim 10^{18}$-$10^{19}$ eV in strong accretion shocks surrounding massive clusters of galaxies. Such protons efficiently produce very high energy pairs through interactions with the CMB, which then radiate synchrotron and inverse Compton emission with hard spectra, peaking respectively in hard X-rays and TeV gamma-rays. We discuss the prospects for detecting this emission from nearby

Susumu Inoue; Felix A. Aharonian; Naoshi Sugiyama

2005-01-01

95

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

96

High-resolution integrated germanium Compton polarimeter for the {gamma}-ray energy range 80 keV--1 MeV  

SciTech Connect

Parameters which govern the choice of a detection system to measure the linear polarization of {gamma} rays at low energies are discussed. An integrated polarimeter is described which is constructed from a single crystal of germanium. It is a compact planar device with the sectors defined electrically, and which gives an energy resolution in the add-back mode of 1 keV at 300 keV. Its performance is demonstrated in a series of calibration measurements using both unpolarized radiation from radioactive sources and polarized {gamma} rays from the {sup 168}Er({alpha},2{ital n}){sup 170}Yb reaction at {ital E}{sub {alpha}}=25 MeV. Polarization measurements at energies as low as 84 keV have been achieved, where the sensitivity was 0.32{plus_minus}0.09. The sensitivity, efficiency, and energy resolution are reported. Our results indicate that energy resolution should be included in the definition of the figure of merit and we relate the new definition to earlier work. The comparisons show the advantages of the present design in the energy range below 300 keV and its competitiveness up to 1500 keV. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Sareen, R.A.; Urban, W.; Barnett, A.R.; Varley, B.J. [Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom)

1995-06-01

97

Ultrahigh-resolution optical coherence tomography  

Microsoft Academic Search

In the past two decades, optical coherence tomography (OCT) has been established as an adjunct diagnostic technique for noninvasive, high-resolution, cross-sectional imaging in a variety of medical fields. The rapid development of ultrabroad bandwidth light sources has recently enabled a significant improvement in OCT imag- ing resolution, demonstrating the potential of OCT to accomplish its original goal of performing noninvasive

Wolfgang Drexler

2004-01-01

98

The BATSE Gamma-Ray Burst Spectral Catalog. I. High Time Resolution Spectroscopy of Bright Bursts using High Energy Resolution Data  

Microsoft Academic Search

This is the first in a series of gamma-ray burst spectroscopy catalogs from\\u000athe Burst And Transient Source Experiment (BATSE) on the Compton Gamma Ray\\u000aObservatory, each covering a different aspect of burst phenomenology. In this\\u000apaper, we present time-sequences of spectral fit parameters for 156 bursts\\u000aselected for either their high peak flux or fluence. All bursts have at

R. D. Preece; M. S. Briggs; R. S. Mallozzi; G. N. Pendleton; W. S. Paciesas; D. L. Band

1999-01-01

99

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

2011-12-16

100

Energy resolution of gamma-ray spectroscopy of JET plasmas with a LaBr{sub 3} scintillator detector and digital data acquisition  

SciTech Connect

A new high efficiency, high resolution, fast {gamma}-ray spectrometer was recently installed at the JET tokamak. The spectrometer is based on a LaBr{sub 3}(Ce) scintillator coupled to a photomultiplier tube. A digital data acquisition system is used to allow spectrometry with event rates in excess of 1 MHz expected in future JET DT plasmas. However, at the lower rates typical of present day experiments, digitization can degrade the energy resolution of the system, depending on the algorithms used for extracting pulse height information from the digitized pulses. In this paper, the digital and analog spectrometry methods were compared for different experimental conditions. An algorithm based on pulse shape fitting was developed, providing energy resolution equivalent to the traditional analog spectrometry method.

Nocente, M.; Tardocchi, M.; Grosso, G.; Perelli Cippo, E.; Pietropaolo, A.; Proverbio, I.; Gorini, G. [Dipartimento di Fisica, Universita degli Studi di Milano-Bicocca and Istituto di Fisica del Plasma, Associazione EURATOM-ENEA-CNR, 20125 Milano (Italy); Chugunov, I.; Gin, D.; Shevelev, A. [A. F. Ioffe Physico-Technical Institute, St. Petersburg 194021 (Russian Federation); Pereira, R. C.; Fernandes, A. M.; Neto, A.; Sousa, J. [Associacao EURATOM/IST Centro de Fusao Nuclear, Instituto Superior Tecnico, 1049-001 Lisboa (Portugal); Edlington, T.; Kiptily, V.; Syme, B. [Culham Centre for Fusion Energy, Culham OX143DB (United Kingdom); Murari, A. [Consorzio RFX, 35127 Padova (Italy); Collaboration: JET-EFDA Contributors

2010-10-15

101

Advanced gamma-ray astronomy telescope experiment: AGATE  

Microsoft Academic Search

In order to continue the achievements in high energy (10 MeV - 100 GeV) gamma-ray astronomy made with the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma Ray Observatory (CGRO), a 'next generation' high energy gamma- ray telescope with a large increase in sensitivity coupled with improved angular resolution will be required. This 'next generation' telescope is envisioned

Brenda L. Dingus; D. L. Bertsch; Rajani Cuddapah; Carl E. Fichtel; Stanley D. Hunter; D. J. Thompson

1993-01-01

102

Ultrahigh resolution optical biopsy with endoscopic optical coherence tomography  

NASA Astrophysics Data System (ADS)

Optical coherence tomography (OCT) is an emerging medical imaging technology that can generate high resolution, cross-sectional images of tissue in situ and in real time. Although endoscopic OCT has been used successfully to identify certain pathologies in the gastrointestinal tract, the resolution of current endoscopic OCT systems has been limited to 10-15 µm for in vivo studies. In this study, in vivo imaging of the rabbit gastrointestinal tract is demonstrated at a three-fold higher resolution (< 5 µm), using a broadband Cr4+:Forsterite laser as the optical light source. Images acquired from the esophagus, trachea, and colon reveal high resolution details of tissue architecture. Definitive correlation of architectural features in OCT images and histological sections is shown. The ability of ultrahigh resolution endoscopic OCT to image tissue morphology at an unprecedented resolution in vivo advances the development of OCT as a potential imaging tool for the early detection of neoplastic changes in biological tissue.

Herz, Paul R.; Chen, Yu; Aguirre, Aaron D.; Fujimoto, James G.; Mashimo, Hiroshi; Schmitt, Joseph; Koski, Amanda; Goodnow, John; Petersen, Chris

2004-07-01

103

Intrinsic germanium gamma-ray data from the New American Petroleum Institute spectral gamma-ray calibration models  

Microsoft Academic Search

High-resolution gamma-ray spectra have been recorded at the new American Petroleum Institute (API) spectral gamma-ray logging calibration center with a US Department of Energy passive spectral gamma-ray logging unit. These measurements were completed before gamma-ray source concentrations were assigned to the calibration model zones. Analyses of spectra gathered from five of the calibration zones yielded linear relationships between: (1) tentative

C. J. Koizumi; W. H. Ulbricht; J. R. Brodeur

1991-01-01

104

Average Energies Required per Scintillation Photon and Energy Resolutions in NaI(Tl) and CsI(Tl) Crystals for Gamma Rays  

NASA Astrophysics Data System (ADS)

The average energies required to produce one scintillation photon Ws were determined for 662 keV gamma rays in NaI(Tl) and CsI(Tl) crystals to be 15.0± 1.3 and 13.3± 1.1 eV, respectively, from the absolute numbers of photoelectrons measured for several combinations of a crystal and a photomultiplier tube (PMT) used as a vacuum photodiode. The numbers of scintillation photons were obtained by calculating the collection efficiency of scintillation photons at the photocathode using Monte Carlo simulations and by determining experimentally the photon-to-photoelectron conversion efficiency at PMT photocathode. The values of Ws determined in the present study are in good agreement with the theoretical values presented recently. The factors affecting energy resolutions were also examined. The calculated resolution agrees well with that obtained experimentally.

Sasaki, Shinichi; Tawara, Hiroko; Saito, Kiwamu; Miyajima, Mitsuhiro; Shibamura, Eido

2006-08-01

105

Gamma ray detector shield  

DOEpatents

A gamma ray detector shield comprised of a rigid, lead, cylindrical-shaped vessel having upper and lower portions with an pneumatically driven, sliding top assembly. Disposed inside the lead shield is a gamma ray scintillation crystal detector. Access to the gamma detector is through the sliding top assembly.

Ohlinger, R.D.; Humphrey, H.W.

1985-08-26

106

Intracavity laser absorption measurements at ultrahigh spectral resolution  

NASA Astrophysics Data System (ADS)

Intracavity laser absorption spectroscopy with ultrahigh sensitivity and enhanced spectral resolution is demonstrated. It entails use of an intracavity talon that selects equally spaced modes of the cavity. These modes are reduced in intensity when they occur at spectral locations where absorption that is due to intracavity species also occurs. We obtained absorption spectra by tuning the talon in small steps across its free spectral range, recording intracavity spectra at each step, and summing the result. The maximum resolution is determined by the width of the talon peaks, which was 0.01 cm 1 . When the finesse of the talon is increased, the resolution equal to the width of a single laser mode can be achieved. With this technique, spectra at Doppler-free resolution such as that required for studies of high vibrational-overtone transitions of molecules in supersonic jets are possible.

Kachanov, Alexander A.; Stoeckel, Frédéric; Charvat, Ales; O'Brien, James J.

1997-06-01

107

Mercuric iodide room temperature gamma-ray detectors  

SciTech Connect

High resolution mercuric iodide room temperature gamma-ray detectors have excellent potential as an essential component of space instruments to be used for high energy astrophysics. Mercuric iodide detectors are being developed both as photodetectors used in combination with scintillation crystals to detect gamma-rays, and as direct gamma-ray detectors. These detectors are highly radiation damage resistant. The list of applications includes gamma-ray burst detection, gamma-ray line astronomy, solar flare studies, and elemental analysis. 3 refs.

Patt, B.E.; Markakis, J.M.; Gerrish, V.M. (EG and G Energy Measurements, Inc., Goleta, CA (USA)); Haymes, R.C. (National Aeronautics and Space Administration, Washington, DC (USA). Astrophysics Div.); Trombka, J.I. (National Aeronautics and Space Administration, Greenbelt, MD (USA). Goddard Space Flight Center)

1989-01-01

108

Initial studies of a new detector design for ultra-high resolution positron emission tomography  

Microsoft Academic Search

We are developing a novel detector concept for Positron Emission Tomography (PET) that will facilitate ultrahigh spatial resolution, high sensitivity and optimal light collection efficiency. Spatial resolution in PCT can be improved by using finer scintillation crystal array elements. Several groups are developing arrays with <2 mm crystal pixels for ultra-high resolution small animal PET systems. The challenge with finer

Craig S. Levin; Frezghi Habte

2002-01-01

109

Gamma-Ray Pulsar Studies With GLAST  

SciTech Connect

Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies.

Thompson, D.J.; /NASA, Goddard

2011-11-23

110

GAMMA-RAY DETECTION WITH PbO GLASS CONVERTERS IN MWPC: ELECTRON CONVERSION EFFICIENCY AND TIME RESOLUTION  

SciTech Connect

The development of glass tubing converters for efficient gamma-ray detection in multiwire proportional chambers (MWPC) has led to an investigation on the improvement of conductivity on glass surfaces and to an investigation of gas mixtures which will improve on the electron conversion efficiency and electron transit time within the tubes. Efforts to establish uniform electric field lines within small diameter tubes has resulted in an improved H{sub 2} reducing treatment. For a 0.91 mm I.D., 1.10 mm O.D., 2 cm thick converter the electron conversion efficiency {epsilon} was measured to be 9.0% and 10.4% at 511 keV, using Ar mixtures containing 10% CF{sub 4} and 30% isobutane, respectively. The effects of gas mixtures on {epsilon} and on {tau}, the mean transit time on conversion electrons within the converter, and the projection of these results on the performance of a modified MWPC positron camera will be presented.

Lum, G.K.; Perez-Mendez, V.; Sleaford, B.

1980-06-01

111

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

112

Gamma ray optics  

SciTech Connect

Via refractive or diffractive scattering one can shape {gamma} ray beams in terms of beam divergence, spot size and monochromaticity. These concepts might be particular important in combination with future highly brilliant gamma ray sources and might push the sensibility of planned experiments by several orders of magnitude. We will demonstrate the experimental feasibility of gamma ray monochromatization on a ppm level and the creation of a gamma ray beam with nanoradian divergence. The results are obtained using the inpile target position of the High Flux Reactor of the ILL Grenoble and the crystal spectrometer GAMS. Since the refractive index is believed to vanish to zero with 1/E{sup 2}, the concept of refractive optics has never been considered for gamma rays. The combination of refractive optics with monochromator crystals is proposed to be a promising design. Using the crystal spectrometer GAMS, we have measured for the first time the refractive index at energies in the energy range of 180 - 2000 keV. The results indicate a deviation from simple 1/E{sup 2} extrapolation of X-ray results towards higher energies. A first interpretation of these new results will be presented. We will discuss the consequences of these results on the construction of refractive optics such as lenses or refracting prisms for gamma rays and their combination with single crystal monochromators.

Jentschel, M.; Guenther, M. M.; Habs, D.; Thirolf, P. G. [Institut Laue-Langevin, F38042 Grenoble (France); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching, Germany and Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany); Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany)

2012-07-09

113

Gamma-ray emission from thermonuclear supernovae  

SciTech Connect

The explosion mechanism associated with thermonuclear supernovae (SNIa) is still a matter of debate. Nevertheless, there is a wide agreement that high amounts of radioactive nuclei are produced during these events and that they are expected to be strong {gamma}-ray emitters. In this paper we investigate the use of this {gamma}-rays as a diagnostic tool. For this purpose we have performed a complete study of the {gamma}-ray spectra associated with all the different scenarios currently proposed: detonation, deflagration, delayed detonation, and pulsating delayed detonation. Our study shows that the {gamma}-ray emission from SNIa is, effectively, a promising tool but that has to be carefully used since it can lead to misinterpretations. We also show that 3D effects can be relevant in some circumstances and that they can provide important information about the exploding system and the thermonuclear burning front mechanism if high resolution spectra could be obtained.

Isern, J. [Institut de Ciencies de l'Espai (CSIC - IEEC), Campus UAB, Torre C5-parells 2n, 08193 Bellaterra (Spain); Institut d'Estudis Espacials de Catalunya (Spain); Bravo, E.; Hirschmann, A. [Departament de Fisica i Enginyeria Nuclear UPC (Spain); Diagonal 647, 08028 Barcelona (Spain); Institut d'Estudis Espacials de Catalunya (Spain)

2007-08-21

114

The Gamma-Ray Imaging Spectrometer (GRIS): A new balloon-borne experiment for gamma-ray line astronomy  

Microsoft Academic Search

High resolution gamma-ray spectroscopy is a relatively new field that holds great promise for further understanding of high energy astrophysical processes. When the high resolution gamma-ray spectrometer (GRSE) was removed from the GRO payload, a balloon program was initiated to permit continued development and improvement of instrumentation in this field, as well as continued scientific observations. The Gamma-Ray Imaging Spectrometer

B. J. Teegarden; T. L. Cline; N. Gehrels; G. Porreca; J. Tueller; M. Leventhal; A. F. Huters; C. J. MacCallum; P. D. Stang

1985-01-01

115

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

116

Imaging of cartilage degeneration progression in vivo using ultrahigh-resolution OCT  

NASA Astrophysics Data System (ADS)

Ultrahigh resolution OCT is used to visualize experimentally induced osteoarthritis in a rat knee model. Using a Cr4+:Forsterite laser, ultrahigh image resolutions of 5um are achieved. Progression of osteoarthritic remodeling and cartilage degeneration are quantified. The utility of OCT for the assessment of cartilage integrity is demonstrated.

Herz, Paul R.; Bourquin, Stephane; Hsiung, Pei-lin; Ko, Tony H.; Schneider, Karl; Fujimoto, James G.; Adams, Samuel, Jr.; Roberts, Mark; Patel, Nirlep; Brezinski, Mark

2003-10-01

117

Imaging of cartilage degeneration progression in vivo using ultrahigh-resolution OCT  

Microsoft Academic Search

Ultrahigh resolution OCT is used to visualize experimentally induced osteoarthritis in a rat knee model. Using a Cr4+:Forsterite laser, ultrahigh image resolutions of 5um are achieved. Progression of osteoarthritic remodeling and cartilage degeneration are quantified. The utility of OCT for the assessment of cartilage integrity is demonstrated.

Paul R. Herz; Stephane Bourquin; Pei-lin Hsiung; Tony H. Ko; Karl Schneider; James G. Fujimoto; Samuel Adams Jr.; Mark Roberts; Nirlep Patel; Mark Brezinski

2003-01-01

118

Gamma-ray burst and spectroscopy instrumentation development at the Goddard Space Flight Center  

Microsoft Academic Search

This paper summarizes the activities that are specifically related to the development of instrumentation for gamma-ray astronomy. Three programs are described: (1) the Gamma-Ray Imaging Spectrometer (GRIS), a balloon-borne array of seven germanium detectors for high-resolution spectrographic studies of persistent gamma-ray sources; (2) the Transient Gamma-Ray Spectrometer (TGRS), a single radiatively-cooled germanium detector for the spectrographic study of gamma-ray bursts,

B. J. Teegarden

1986-01-01

119

Bridgman growth of LaBr3:Ce and LaCl3:Ce crystals for high-resolution gamma-ray spectrometers  

NASA Astrophysics Data System (ADS)

Single crystals of LaBr3:Ce and LaCl3:Ce have been grown by the vertical Bridgman technique. Crystals of these scintillators are used in the fabrication of high-resolution, gamma-ray spectrometers. The LaBr3:Ce and LaCl3:Ce crystals we have grown have high light outputs of ˜80,000 and 50,000 photons/MeV, respectively, and fast principal decay constants of <30 ns. The emission wavelength for the LaBr3:Ce and LaCl3:Ce scintillators are ?=360 and 350 nm, respectively. Both materials have excellent energy resolutions of ˜3% FWHM for 662 keV photons at room temperature. In this paper, we will report on our results to date for vertical Bridgman crystal growth and characterization of Ce-doped LaBr3 and LaCl3 crystals. We will also describe the handling and processing procedures developed for these oxygen and moisture sensitive materials.

Higgins, W. M.; Glodo, J.; van Loef, E.; Klugerman, M.; Gupta, T.; Cirignano, L.; Wong, P.; Shah, K. S.

2006-01-01

120

Correlation between Parsec-Scale Jet Behavior and Gamma-Ray Light Curves of Blazars  

NASA Astrophysics Data System (ADS)

I will present total and polarized intensity images at ultra-high resolution (0.1 milliarcseconds) of a sample of 33 gamma-ray blazars obtained monthly with the Very Long Baseline Array (VLBA) at 43 GHz, starting in Summer 2008 when the Fermi Gamma-Ray Space Telescope began to operate. The VLBA observations determine the flux and polarization of the millimeter-wave core and other features of the jet, as well as the motions of bright superluminal knots. Comparison of the variability in gamma-rays and in the mm-wave core indicates a similarity as measured by a variability index defined by Aller et al. (2003). Analysis of the variability along with the jet kinematics suggests that in blazars with high variability indices (e.g. AO 0235+164, 3C 279, and PKS 1510-089), strong gamma-ray activity, lasting more than a month, occurs as a new superluminal knot propagates down the inner jet and passes through the core. This research is funded in part by NASA through Fermi Guest Investigator grants NNX08AV65G and NNX08AV61G, and by the National Science Foundation through grant AST-0907893.

Jorstad, Svetlana G.; Marscher, A. P.

2010-02-01

121

Connection of Gamma-Ray Emission to the mm-Wave VLBI Core in Blazars  

NASA Astrophysics Data System (ADS)

I will present total and polarized intensity images at ultra-high resolution (0.1 milliarcseconds) of a sample of 33 gamma-ray blazars obtained monthly with the Very Long Baseline Array (VLBA) at 43 GHz, starting in Summer 2008 when the Fermi Gamma-Ray Space Telescope began to operate. The VLBA observations determine the flux and polarization of the millimeter-wave core and other features of the jet, as well as the motions of bright superluminal knots. Comparison of the variability in gamma-rays and in the mm-wave core indicates a similarity as measured by a variability index defined by Aller et al. (2003). Analysis of the variability along with the jet kinematics suggests that in blazars with high variability indices (e.g. AO 0235+164, 3C 279, and PKS 1510-089), strong gamma-ray activity, lasting more than a month, occurs as a new superluminal knot propagates down the inner jet and passes through the core. This research is funded in part by NASA through Fermi Guest Investigator grants NNX08AV65G and NNX08AV61G, and by the National Science Foundation through grant AST-0907893.

Jorstad, Svetlana; Marscher, Alan

122

Gamma ray optics  

NASA Astrophysics Data System (ADS)

Via refractive or diffractive scattering one can shape ? ray beams in terms of beam divergence, spot size and monochromaticity. These concepts might be particular important in combination with future highly brilliant gamma ray sources and might push the sensibility of planned experiments by several orders of magnitude. We will demonstrate the experimental feasibility of gamma ray monochromatization on a ppm level and the creation of a gamma ray beam with nanoradian divergence. The results are obtained using the inpile target position of the High Flux Reactor of the ILL Grenoble and the crystal spectrometer GAMS. Since the refractive index is believed to vanish to zero with 1/E2, the concept of refractive optics has never been considered for gamma rays. The combination of refractive optics with monochromator crystals is proposed to be a promising design. Using the crystal spectrometer GAMS, we have measured for the first time the refractive index at energies in the energy range of 180 - 2000 keV. The results indicate a deviation from simple 1/E2 extrapolation of X-ray results towards higher energies. A first interpretation of these new results will be presented. We will discuss the consequences of these results on the construction of refractive optics such as lenses or refracting prisms for gamma rays and their combination with single crystal monochromators.

Jentschel, M.; Günther, M. M.; Habs, D.; Thirolf, P. G.

2012-07-01

123

Gamma ray camera  

DOEpatents

A gamma ray camera is disclosed 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. 6 figs.

Perez-Mendez, V.

1997-01-21

124

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

125

GRI: the gamma-ray imager mission  

NASA Astrophysics Data System (ADS)

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 reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are the major science themes that are addressed in the gamma-ray regime. With the INTEGRAL observatory, ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction and multilayer-coated mirror techniques hav paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow to study particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Knödlseder, Jürgen

2006-07-01

126

The Gamma-Ray Imager GRI  

NASA Astrophysics Data System (ADS)

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 reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are the major science themes that are addressed in the gamma-ray regime. With the INTEGRAL observatory, ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction and multilayer coated mirror techniques have paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow to study particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Wunderer, Cornelia B.; GRI Collaboration

2006-09-01

127

Multiwavelength Study of Gamma-Ray Bright Blazars  

Microsoft Academic Search

We investigate total intensity radio images of 6 gamma-ray bright blazars (BL Lac, 3C 279, 3C 273, W Com, PKS 1510-089, and 3C 66A) and their optical and gamma-ray light curves to study connections between gamma-ray and optical brightness variations and changes in the parsec-scale radio structure. We use high-resolution maps obtained by the BU group at 43 GHz with

Daria Morozova; V. M. Larionov; V. A. Hagen-Thorn; S. G. Jorstad; A. P. Marscher; I. S. Troitskii

2011-01-01

128

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

129

Lifetime effects for high-resolution gamma-ray spectroscopy at relativistic energies and their implications for the RISING spectrometer  

Microsoft Academic Search

The lineshapes and peak position of Doppler corrected ?-ray spectra from in-beam experiments at relativistic energies are investigated with respect to the intrinsic energy resolution of the employed detectors, the particles’ velocities, and the photons’ emission angle uncertainties at the moment of ?-ray emission. The uncertainties in velocity and photon emission angle are dependent on the lifetime of the excited

P. Doornenbal; P. Reiter; H. Grawe; T. Saito; A. Al-Khatib; A. Banu; T. Beck; F. Becker; P. Bednarczyk; G. Benzoni; A. Bracco; A. Bürger; L. Caceres; F. Camera; S. Chmel; F. C. L. Crespi; H. Geissel; J. Gerl; M. Górska; H. Hübel; M. Kavatsyuk; O. Kavatsyuk; M. Kmiecik; I. Kojouharov; N. Kurz; R. Lozeva; A. Maj; S. Mandal; W. Meczynski; B. Million; Zs. Podolyák; A. Richard; N. Saito; H. Schaffner; M. Seidlitz; T. Striepling; J. Walker; N. Warr; H. Weick; O. Wieland; M. Winkler; H. J. Wollersheim

2010-01-01

130

Imaging brain morphology with ultrahigh-resolution optical coherence tomography  

NASA Astrophysics Data System (ADS)

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 ?m axial resolution) was achieved at different central wavelengths by interfacing three state-of-the-art broad bandwidth light sources (Ti:Al2O3, ?c = 790 nm, ?? = 260 nm and Pout = 50 mW; PCF based laser, ?c = 1150 nm, ?? = 350 nm and Pout = 2 W; Fiber laser based light source, ?c = 1350 nm, ?? = 470 nm and Pout = 4 mW) to a modular free-space OCT system, utilizing a dynamic focusing and designed for optimal performance in the appropriate wavelength regions. Images acquired from a fixed honeybee brain demonstrated the ability of UHR OCT to image the globular structure of the brain, some fine morphological details such as the nerve fiber bundles connecting the medulla (visual center) to the honeybee eyes, and the interfaces between different tissue layers in the medulla. Tomograms of various human neuropathologies demonstrated the feasibility of UHR OCT to visualize morphological details such as small (~20 ?m) calcifications typical for fibrous meningioma, and enlarged nuclei of cancer cells (~10-15 ?m) characteristic for many other neuropathologies. In addition UHR OCT was used to image cellular morphology in living ganglion cells.

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

2003-10-01

131

Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are the brightest transient sources in the gamma-ray sky. Since their discovery in the late 1960s, the investigation of the astrophysical sys- tems in which these phenomena take place, and the physical mechanisms that drive them, has become a vast and prolific area of modern astrophysics. In this work I will briefly describe the most relevant observations of these sources, and the models that describe their nature, emphasizing on the in- vestigations about the progenitor astrophysical systems. FULL TEXT IN SPANISH

Pellizza, L. J.

132

Gamma-ray bursts.  

PubMed

Gamma-ray bursts (GRBs) are bright flashes of gamma rays coming from the cosmos. They occur roughly once per day, typically last for tens of seconds, and are the most luminous events in the universe. More than three decades after their discovery, and after pioneering advances from space and ground experiments, they still remain mysterious. The launch of the Swift and Fermi satellites in 2004 and 2008 brought in a trove of qualitatively new data. In this Review, we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglow. PMID:22923573

Gehrels, Neil; Mészáros, Péter

2012-08-24

133

Gamma ray and pi0 production from hydrogen and complex nuclei by 270-375 MeV gamma rays  

Microsoft Academic Search

Measurements are reported on the differential cross section for secondary gamma ray production on hydrogen and nuclear targets at 90° in the laboratory through the interactions of primary gamma rays in the energy range 270-375 MeV. A difference method using bremsstrahlung beams at different end point energies was employed. The gamma ray detector was a high resolution Nal(Tl) spectrometer and

B. L. Beron; E. B. Hughes

1973-01-01

134

Gamma Ray Observatory survives  

Microsoft Academic Search

Right now the budgetary position of NASA science projects for fiscal year 1982 is shaky, outside of the Space Shuttle Program. Two scientifically crucial missions being planned are the Gamma Ray Observatory (GRO) and the Venus Orbiting Imaging Radar (VOIR). President Reagan's proposed budgetary cuts have left both programs intact but delayed. For FY 1982, GRO will be able to

Peter M. Bell

1981-01-01

135

Scission gamma rays  

SciTech Connect

Gamma rays probably emitted by the fissioning nucleus {sup 236}U* at the instant of the break of the neck or within the time of about 10{sup -21} s after or before this were discovered in the experiment devoted to searches for the effect of rotation of the fissioning nucleus in the process {sup 235}U(n,{gamma}f) and performed in a polarized beam of cold neutrons from the MEPHISTO Guideline at the FRM II Munich reactor. Detailed investigations revealed that the angular distribution of these gamma rays is compatible with the assumption of the dipole character of the radiation and that their energy spectrum differs substantially from the spectrum of prompt fission gamma rays. In the measured interval 250-600 keV, this spectrum can be described by an exponential function at the exponent value of {alpha} = -5 x 10{sup -3} keV{sup -1}. The mechanism of radiation of such gamma rays is not known at the present time. Theoretical models based on the phenomenon of the electric giant dipole resonance in a strongly deformed fissioning nucleus or in a fission fragment predict harder radiation whose spectrum differs substantially from the spectrum measured in the present study.

Danilyan, G. V., E-mail: danilyan@itep.r [Institute of Theoretical and Experimental Physics (Russian Federation); Klenke, J. [Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) (Germany); Krakhotin, V. A.; Kuznetsov, V. L.; Novitsky, V. V.; Pavlov, V. S.; Shatalov, P. B. [Institute of Theoretical and Experimental Physics (Russian Federation)

2009-11-15

136

Gamma-ray bursts  

Microsoft Academic Search

Gamma-ray bursts are the most luminous explosions in the Universe, and their origin and mechanism are the focus of intense research and debate. More than three decades after their discovery, and after pioneering breakthroughs from space and ground experiments, their study is entering a new phase with the recently launched Swift satellite. The interplay between these observations and theoretical models

P. Mészáros

2006-01-01

137

New ultrahigh-resolution picture of Earth's gravity field  

NASA Astrophysics Data System (ADS)

provide an unprecedented ultrahigh resolution picture of Earth's gravity over all continents and numerous islands within ±60° latitude. This is achieved through augmentation of new satellite and terrestrial gravity with topography data and use of massive parallel computation techniques, delivering local detail at ~200 m spatial resolution. As such, our work is the first-of-its-kind to model gravity at unprecedented fine scales yet with near-global coverage. The new picture of Earth's gravity encompasses a suite of gridded estimates of gravity accelerations, radial and horizontal field components, and quasi-geoid heights at over 3 billion points covering 80% of Earth's land masses. We identify new candidate locations of extreme gravity signals, suggesting that the Committee on Data for Science and Technology standard for peak-to-peak variations in free-fall gravity is too low by about 40%. The new models are beneficial for a wide range of scientific and engineering applications and freely available to the public.

Hirt, Christian; Claessens, Sten; Fecher, Thomas; Kuhn, Michael; Pail, Roland; Rexer, Moritz

2013-08-01

138

Ultra-high resolution and compact volume holographic spectrometers  

NASA Astrophysics Data System (ADS)

Compact and efficient spectrometers are of great interest for biological and environmental sensing. In this paper, we describe a new class of spectrometers that work based on diffractive properties of spherical beam volume holograms (SBVHs) and cylindrical beam volume holograms (CBVHs). The hologram in these spectrometers acts as a spectral diversity filter (SDF) that maps different input wavelengths onto different locations in the output plane. The main properties of these holographic SDFs and new techniques for removing the ambiguity between incident wavelength (or the input channel) and incident angle (or the input spatial mode) are discussed. By using CBVHs, we show that the spectral mapping of the input beam can be obtained in one direction and the beam can be independently modified in the perpendicular direction. Using this unique property, we demonstrate a spectral wrapping technique to considerably increase the operation spectral range of spectrometers, without sacrificing their resolution. Finally, it is also shown that by combining CBVHs with a Fabry-Perot interferometer, a true two-dimensional spatial-spectral mapping can be formed, and an ultra-high resolution of 0.2 nm with large spectral bandwidth is demonstrated for this tandem spectrometer.

Adibi, Ali; Hsieh, Chaoray; Momtahan, Omid; Badieirostami, Majid

2008-03-01

139

Broadband superluminescent diode-based ultrahigh resolution optical coherence tomography for ophthalmic imaging  

PubMed Central

Spectral domain optical coherence tomography (SD-OCT) with ultrahigh resolution can be used to measure precise structures in the context of ophthalmic imaging. We designed an ultrahigh resolution SD-OCT system based on broadband superluminescent diode (SLD) as the light source. An axial resolution of 2.2 ?m in tissue, a scan depth of 1.48 mm, and a high sensitivity of 93 dB were achieved by the spectrometer designed. The ultrahigh-resolution SD-OCT system was employed to image the human cornea and retina with a cross-section image of 2048 × 2048 pixels. Our research demonstrated that ultrahigh -resolution SD-OCT can be achieved using broadband SLD in a simple way.

Zhu, Dexi; Shen, Meixiao; Jiang, Hong; Li, Ming; Wang, Michael R.; Wang, Yuhong; Ge, Lili; Qu, Jia; Wang, Jianhua

2011-01-01

140

Delayed gamma Rays from Fission.  

National Technical Information Service (NTIS)

Studies of delayed gamma rays from fission at early times were conducted using the pulsed beams of neutrons and bremsstrahlung x rays from an electron linear accelerator to produce fissions. Measurements of the energy spectrum of isomeric gamma rays from ...

R. B. Walton R. E. Sund

1965-01-01

141

High Resolution X-ray Characterization Of Mosaic Crystals For Hard X- And Gamma-ray Astronomy  

NASA Astrophysics Data System (ADS)

For hard X-ray astronomy in the 70-1000 keV energy range Laue lenses have been proposed where the focusing elements are made of single mosaic crystals, in order to increase the diffraction efficiency with respect to perfect crystals. Suitable crystals to be used for such application should have a sufficient density to increase the diffraction efficiency and a mosaicity ranging between 30 arcsec and 1-2 arcmin, depending on the lens focusing distance and resolution. In the past germanium and copper crystals, often employed as monochromators for neutrons, have been considered. In this work we propose several crystalline materials of different degree of crystal perfection such as GaAs, Cu, CdTe, and CdZnTe as possible mosaic crystals for hard X-ray astronomy. They were analyzed by high resolution X-ray diffraction at 8 keV and by diffraction at energies up to 700 keV at synchrotron. It was found that: CdTe and CdZnTe crystals exhibit low angle grain boundaries preventing the formation of a single diffracted X-ray beam; Cu crystals exhibit mosaicity of the order of several arcmin, however a deep etching is needed to remove the cutting damage; GaAs crystals grown by LEC method show mosaicity between 15 and 30 arcsec and good diffraction efficiency up to energies of 700 keV. Annealing and surface damage were considered as possible methods to increase the GaAs crystal mosaicity.

Marchini, L.; Ferrari, C.; Buffagni, E.; Zappettini, A.

2011-09-01

142

High-resolution x-ray characterization of mosaic crystals for hard x-and gamma-ray astronomy  

NASA Astrophysics Data System (ADS)

We have analyzed GaAs, Cu, CdTe, and CdZnTe crystals as possible optical elements for hard x-ray lenses for x-ray astronomy. We used high resolution x-ray diffraction at 8keV in Bragg geometry and Laue transmission diffraction at synchrotron at energies up to 500 keV. A good agreement was found between the mosaicity evaluated in Bragg diffraction geometry with x-ray penetration of the order of few tens micrometers and in Laue transmission geometry at synchrotron. All the analyzed crystals showed mosaicity values in a range between a few to 150 arcseconds and suitable for the application. Nevertheless -CdTe and CdZnTe crystals exhibit non-uniformity due to the presence of low angle grain boundaries; -Cu crystals exhibit mosaicity of the order of several arcminutes; they indeed suffer by a severe cutting damage that had to be removed with a very deep etching. The FWHM was also rapidly decreasing with the x-ray energy showing that the mosaic spread is not the only origin of peak broadening; -GaAs crystals grown by Czochralski method show mosaicity up to 30 arcseconds and good diffraction efficiency up to energies of 500 keV. The use of thermal treatments as a possible method to increase the mosaic spread is also evaluated.

Ferrari, Claudio; Buffagni, Elisa; Marchini, Laura; Zappettini, Andrea

2011-09-01

143

The Gamma-Ray Imager GRI  

NASA Astrophysics Data System (ADS)

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 reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are major science themes that are addressed in the gamma-ray regime. ESA's INTEGRAL observatory currently provides the astronomical community with a unique tool to investigate the sky up to MeV energies and hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes have been discovered. NASA's GLAST mission will similarly take the next step in surveying the high-energy ( GeV) sky, and NuSTAR will pioneer focusing observations at hard X-ray energies (to 80 keV). There will be clearly a growing need to perform deeper, more focused investigations of gamma-ray sources in the 100-keV to MeV regime. Recent technological advances in the domain of gamma-ray focusing using Laue diffraction and multilayer-coated mirror techniques have paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow the study of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Wunderer, Cornelia B.; GRI Collaboration

2008-03-01

144

Gamma-Ray Burst Wallsheet  

NSDL National Science Digital Library

The Gamma-ray Burst Wallsheet was developed to illustrate the properties of light emanating from a gamma-ray burst as seen by three distant satellites, including NASA's Swift. The back of the wallsheet has one of the three activities in the accompanying educator guide (Angling for Gamma-ray Bursts).

2005-01-01

145

Connection between Gamma-Ray Variations and Disturbances in the Jets of Blazars  

NASA Astrophysics Data System (ADS)

I present total and polarized intensity images at ultra-high resolution (0.1 milliarcseconds) of a sample of 33 gamma-ray blazars obtained monthly with the Very Long Baseline Array (VLBA) at 43 GHz, starting in Summer 2008 when the Fermi Gamma-Ray Space Telescope began to operate. The VLBA observations determine the flux and polarization of the millimeter-wave core and other components of the jet, as well as the kinematics of bright superluminal knots. I will compare the gamma-ray light curves of the blazars, obtained with the Fermi Large Area Telescope, with flux variations in the core and knots, the times when new knots pass through the core, changes in the flux at millimeter, optical, and X-ray wavelengths, and variations in the optical and millimeter-wave polarization. The results of the analysis show that, for a number of the blazars (e.g. AO 0235+164, 3C 279, and PKS 1510-089), strong gamma-ray activity lasting more than a month can include multiple flares with different durations and amplitudes on time scales of days or weeks. Such events occur as a new superluminal knot propagates down the inner jet, with the most intense gamma-ray flare occurring as the disturbance interacts with the core. This research is funded in part by NASA through Fermi Guest Investigator grants NNX08AV65G and NNX08AV61G, and Astrophysical Data Analysis Program grant NNX08AJ64G, and by the National Science Foundation through grant AST-0907893.

Jorstad, Svetlana G.; Marscher, A. P.

2010-01-01

146

GRI: The Gamma-Ray Imager mission  

NASA Astrophysics Data System (ADS)

With the INTEGRAL observatory ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction have paved the way towards a new gamma-ray mission, providing major improvements regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow studies of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Knödlseder, Jürgen

147

Ultrahigh-resolution multicolor colocalization of single fluorescent probes  

PubMed Central

An optical ruler based on ultrahigh-resolution colocalization of single fluorescent probes is described in this paper. It relies on the use of two unique families of fluorophores, namely energy-transfer fluorescent beads (TransFluoSpheres) and semiconductor nanocrystal quantum dots, that can be excited by a single laser wavelength but emit at different wavelengths. A multicolor sample-scanning confocal microscope was constructed that allows one to image each fluorescent light emitter, free of chromatic aberrations, by scanning the sample with nanometer scale steps with a piezo-scanner. The resulting spots are accurately localized by fitting them to the known shape of the excitation point-spread function of the microscope. We present results of two-dimensional colocalization of TransFluoSpheres (40 nm in diameter) and of nanocrystals (3–10 nm in diameter) and demonstrate distance-measurement accuracy of better than 10 nm using conventional far-field optics. This ruler bridges the gap between fluorescence resonance energy transfer, near- and far-field imaging, spanning a range of a few nanometers to tens of micrometers.

Lacoste, Thilo D.; Michalet, Xavier; Pinaud, Fabien; Chemla, Daniel S.; Alivisatos, A. Paul; Weiss, Shimon

2000-01-01

148

Retinal oximetry using ultrahigh-resolution optical coherence tomography  

PubMed Central

Background The purpose of this study was to investigate the repeatability of retinal oximetry using slit-lamp adapted ultrahigh-resolution optical coherence tomography (SL-UHR-OCT). Methods SL-UHR-OCT was developed and fringe patterns were obtained for a major retinal artery and a major retinal vein. A-scans at the central wavelengths of 805 nm and 855 nm were analyzed for calculating optical density ratios (ODRs), from which the percentage oxygen saturation was calculated. Measurements were made on two occasions for each person. Repeatability and coefficients of repeatability were calculated. Results The mean ODRs of the artery were 0.79 ± 0.86 and 0.88 ± 0.97 in sessions 1 and 2, respectively. The mean ODRs of the vein were ?0.08 ± 0.69 and 0.14 ± 0.77 between the two sessions, and were significantly lower than that of the artery (P < 0.05). The coefficients of repeatability were 1.44 and 1.81 for the artery and vein, respectively. The mean oxygen saturation of the major retinal artery was 94% ± 45% and 98% ± 51% in sessions 1 and 2, respectively, and the mean oxygen saturation of the major retinal vein was 48% ± 36% and 60% ± 40% between sessions. Conclusion Optical coherence tomographic oximetry for evaluating retinal oxygen saturation was subject to variation, although the averaged measurements in repeated sessions were matched. Further work on reducing variation will be needed.

Ye, Yufeng; Jiang, Hong; Shen, Meixiao; Lam, Byron L; DeBuc, Delia Cabrera; Ge, Lili; Sehi, Mitra; Wang, Jianhua

2012-01-01

149

Developments in Mercuric Iodide gamma Ray Imaging.  

National Technical Information Service (NTIS)

A mercuric iodide gamma-ray imaging array and camera system previously described has been characterized for spatial and energy resolution. Based on this data, a new camera is being developed to more fully exploit the potential of the array. Characterizati...

B. E. Patt A. G. Beyerle R. C. Dolin C. Ortale

1987-01-01

150

Low-resolution Spectroscopy of Gamma-ray Burst Optical Afterglows: Biases in the Swift Sample and Characterization of the Absorbers  

Microsoft Academic Search

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

J. P. U. Fynbo; P. Jakobsson; J. X. Prochaska; D. Malesani; C. Ledoux; A. de Ugarte Postigo; M. Nardini; P. M. Vreeswijk; K. Wiersema; J. Hjorth; J. Sollerman; H.-W. Chen; C. C. Thöne; G. Björnsson; J. S. Bloom; A. J. Castro-Tirado; L. Christensen; A. De Cia; A. S. Fruchter; J. U. Gorosabel; J. F. Graham; A. O. Jaunsen; B. L. Jensen; D. A. Kann; C. Kouveliotou; A. J. Levan; J. Maund; N. Masetti; B. Milvang-Jensen; E. Palazzi; D. A. Perley; E. Pian; E. Rol; P. Schady; R. L. C. Starling; N. R. Tanvir; D. J. Watson; D. Xu; T. Augusteijn; F. Grundahl; J. Telting; P.-O. Quirion

2009-01-01

151

Gamma-ray localization of terrestrial gamma-ray flashes.  

PubMed

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 ?5-10° 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. PMID:20867680

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

2010-09-14

152

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

153

Gamma-ray luminosity properties of gamma-ray pulsars  

Microsoft Academic Search

Based on a new self-consistent outer gap model, we statistically study luminosity properties of gamma-ray pulsars with ages of <=2× 107 yr in the Galaxy as well as those with ages of <=5× 106 yr in the Gould belt using a Monte Carlo method, where the gamma-ray beaming effect has been included. Generally, the relation between gamma-ray luminosity, Lgamma, and

L. Zhang; Z. X. Han; Z. J. Jiang

2005-01-01

154

Mercuric iodide room temperature gamma-ray detectors.  

National Technical Information Service (NTIS)

High resolution mercuric iodide room temperature gamma-ray detectors have excellent potential as an essential component of space instruments to be used for high energy astrophysics. Mercuric iodide detectors are being developed both as photodetectors used...

B. E. Patt J. M. Markakis V. M. Gerrish R. C. Haymes J. I. Trombka

1989-01-01

155

Gamma ray energy tracking in GRETINA  

NASA Astrophysics Data System (ADS)

The next generation of stable and exotic beam accelerators will provide physics opportunities to study nuclei farther away from the line of stability. However, these experiments will be more demanding on instrumentation performance. These come from the lower production rate for more exotic beams, worse beam impurities, and large beam velocity from the fragmentation and inverse reactions. Gamma-ray spectroscopy will be one of the most effective tools to study exotic nuclei. However, to fully exploit the physics reach provided by these new facilities, better gamma-ray detector will be needed. In the last 10 years, a new concept, gamma-ray energy tracking array, was developed. Tracking arrays will increase the detection sensitivity by factors of several hundred compared to current arrays used in nuclear physics research. Particularly, the capability of reconstructing the position of the interaction with millimeters resolution is needed to correct the Doppler broadening of gamma rays emitted from high velocity nuclei. GRETINA is a gamma-ray tracking array which uses 28 Ge crystals, each with 36 segments, to cover .5ex1 -.1em/ -.15em.25ex4 of the 4? solid angle. The gamma ray tracking technique requires detailed pulse shape information from each of the segments. These pulses are digitized using 14-bit 100 MHz flash ADCs, and digital signal analysis algorithms implemented in the on-board FPGAs provides energy, time and selection of pulse traces. A digital trigger system, provided flexible trigger functions including a fast trigger output, and also allows complicated trigger decisions to be made up to 20 microseconds. Further analyzed, carried out in a computer cluster, determine the energy, time, and three-dimensional positions of all gamma-ray interactions in the array. This information is then utilized, together with the characteristics of Compton scattering and pair-production processes, to track the scattering sequences of the gamma rays. GRETINA construction is completed in March 2011, and extensive engineering runs were carried out using radioactive sources, and beams from the 88-Inch Cyclotron at LBNL. The data obtained will be used to optimize its performance. Then the first scientific campaign will start in March 2012 at NSCL MSU.

Lee, I. Y.

2011-10-01

156

Arcsec source location measurements in gamma-ray astronomy from a lunar observatory  

NASA Astrophysics Data System (ADS)

The physical processes typically used in the detection of high energy gamma-rays do not permit good angular resolution, which makes difficult the unambiguous association of discrete gamma-ray sources with objects emitting at other wavelengths. This problem can be overcome by placing gamma-ray detectors on the moon and using the horizon as an occulting edge to achieve arcsec resolution. For the purpose of discussion, this concept is examined for gamma rays above about 20 MeV for which pair production dominates the detection process and locally-generated nuclear gamma rays do not contribute to the background.

Koch, D. G.; Hughes, B. E.

1990-03-01

157

Determination of Spatial Distribution Patterns of Clay and Plant Available Potassium Contents in Surface Soils at the Farm Scale using High Resolution Gamma Ray Spectrometry  

Microsoft Academic Search

Variation in dryland crop yield is often related to underlying soil properties such as water availability and soil fertility.\\u000a There are often significant difficulties in adequately defining the spatial distribution of such properties at the farm scale.\\u000a Gamma ray spectrometry (radiometrics) is a relatively new soil sensing technique that can potentially address this by improving\\u000a the mapping of soil texture

Gabriella Pracilio; Matthew L. Adams; Keith R. J. Smettem; Richard J. Harper

2006-01-01

158

On the measurement of 40 K in natural and synthetic materials by the method of high-resolution gamma-ray spectrometry  

Microsoft Academic Search

In the measurement of natural occurring radioactive material (NORM) concentrations of 40K, 232Th and 238U are measured by passive gamma ray spectrometry with either HPGe or NaI(Tl) detectors. 40K is measured through its 1460.8keV? line. However, till now it has been ignored that this line is mixed with the 1459.2keV line of 228Ac from the chain of 232Th. A correction

N. Lavi; F. Groppi; Z. B. Alfassi

2004-01-01

159

Extragalactic Gamma-Rays Gamma Ray Bursts and Blazars  

Microsoft Academic Search

The extragalactic gamma-ray sky is dominated by two classes of sources: Gamma-Ray Bursts (GRBs) and radio loud active galactic nuclei whose jets are pointing at us (blazars). We believe that the radiation we receive from them originates from the transformation of bulk relativistic energy into random energy. Although the mechanisms to produce, collimate and accelerate the jets in these sources

Gabriele Ghisellini

2005-01-01

160

In vivo ultrahigh-resolution optical coherence tomography of mouse colon with an achromatized endoscope  

Microsoft Academic Search

Endoscopic ultrahigh-resolution optical coherence tomog- raphy OCT enables collection of minimally invasive cross-sectional images in vivo, which may be used to facilitate rapid development of reliable mouse models of colon disease as well as assess chemopre- ventive and therapeutic agents. The small physical scale of mouse colon makes light penetration less problematic than in other tissues and high resolution acutely

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

2006-01-01

161

Real-time ultrahigh-resolution OCT systems for in vivo imaging  

NASA Astrophysics Data System (ADS)

We demonstrate compact ultrahigh resolution OCT systems for in vivo studies, with broadband light sources based on a commercially available Nd:Glass femtosecond laser and nonlinear fiber continuum generation. In vivo OCT images of hamster cheek pouch and human skin acquired at 4 frames per second and with 5.5 ?m axial resolution are presented. These systems are robust, compact and portable.

Bourquin, Stephane; Aguirre, Aaron D.; Hartl, Ingmar; Hsiung, Pei-Lin; Ko, Tony H.; Birks, Tim A.; Wadsworth, William J.; Buenting, Udo; Kopf, Daniel; Fujimoto, James G.

2003-10-01

162

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

163

Delayed gamma Rays from Fission.  

National Technical Information Service (NTIS)

Measurements of the energy spectrum of delayed gamma rays from the neutron fission of PU239 and U235 were performed with a naI detector at a number of time intervals between 2 and 80 microsec. The data showed three new prominent gamma rays with energies o...

R. B. Walton R. E. Sund

1966-01-01

164

The gamma-ray cosmos  

NASA Astrophysics Data System (ADS)

NASA's Compton Observatory spacecraft and the Russian/French Granat satellite have yielded vast new knowledge concerning the gamma-ray universe, which is indicative of the most energetic events in existence. A survey is presently conducted of the state of observational and theoretical understanding of gamma-ray sources in active galaxies and within the Galaxy.

Chupp, Edward L.

1992-12-01

165

Gamma ray astrophysics  

NASA Astrophysics Data System (ADS)

A general review of cosmic energetic gamma particles is given. A discussion on the subject starting with the discovery of the PeV gamma rays by Sammorski and Stamm, passing to the super-nova SN1987A explosion when several groups waited for high energy gamma particles but none has come so far up to the measurements of TeV gamma incoming from the Crab Nebula. The discussion in this paper is a by product of the cosmic ray research done in the Chacaltaya Cosmic Rays Observatory in the past few years. A brief description of the facilities on Mount Chacaltaya (5,200 m above sea level (a.s.l.)) is also given.

Martinic, Nicholas J.

1994-04-01

166

Instrument Requirements for Type Ia Supernova Gamma-Ray Studies  

NASA Astrophysics Data System (ADS)

Thermonuclear supernovae are widely used as distance indicators, which yields profound implications, yet details of their progenitor systems and explosion physics remain elusive. It has been argued for thirty-five years that these thoroughly radioactive objects can be understood through detailed gamma-ray line studies, but despite twenty years of gamma-ray instruments in orbit, no Type Ia supernova (SN Ia) has been detected in gamma-ray lines. Still the great promise of gamma-ray studies of SN Ia remains, but the instrument requirements, especially on line sensitivity, are substantial. Finally, a second-generation gamma-ray spectrometer, known now as the Advanced Compton Telescope, is being planned. Considering current SN Ia models of various types, including deflagrations, delayed detonations, and sub-Chandrasekhar-mass detonations, we outline the gamma-ray instrument requirements, especially line flux sensitivity and energy resolution, needed to discriminate among the possible models. We consider realistic SN Ia rates and distributions in space, plausible observing intervals and durations, and the information available from both gamma-ray photometry and spectroscopy. For example, we find that a wide-field compton telescope with energy resolution E/? E= 100 in a scanning mode would require broad line sensitivity of 7×10-7 cm-2 s-1 at 847 keV to distinguish deflagration models from delayed detonation models at the rate of one per year.

Leising, M.; Milne, P.; Lara, J.; The, L.

2004-12-01

167

CdZnTe gamma ray spectrometer for orbital gamma ray spectroscopy.  

SciTech Connect

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 spectrometer can be flown either on the instrument deck of the spacecraft or on a boom. For deck-mounted systems, a BGO anticoincidence shield is included in the design to suppress the response of the CdZnTe detector to gamma rays that originate in the spacecraft. The BGO shield also serves as a backup spectrometer, providing heritage from earlier planetary science missions and reducing the risk associated with the implementation of new technology.

Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Fuller, K. R. (Kenneth R.); Storms, S. A. (Steven A.); Soldner, S. A.; Lawrence, David J. (David Jeffery),; Browne, M. C. (Michael C.); Moss, C. E. (Calvin E.)

2001-01-01

168

Multiwavelength Study of Gamma-Ray Bright Blazars  

NASA Astrophysics Data System (ADS)

We investigate total intensity radio images of 6 gamma-ray bright blazars (BL Lac, 3C 279, 3C 273, W Com, PKS 1510-089, and 3C 66A) and their optical and gamma-ray light curves to study connections between gamma-ray and optical brightness variations and changes in the parsec-scale radio structure. We use high-resolution maps obtained by the BU group at 43 GHz with the VLBA, optical light curves constructed by the St.Petersburg State U. (Russia) team using measurements with the 0.4 m telescope of St.Petersburg State U. (LX200) and the 0.7 m telescope of the Crimean Astrophysical Observatory (AZT-8), and gamma-ray light curves, which we have constructed with data provided by the Fermi Large Area Telescope. Over the period from August 2008 to November 2009, superluminal motion is found in all 6 objects with apparent speed ranging from 2c to 40c. The blazars with faster apparent speeds, 3C 273, 3C 279, PKS 1510-089, and 3C 66A, exhibit stronger variability of the gamma-ray emission. There is a tendency for sources with sharply peaked gamma-ray flares to have faster jet speed than sources with gamma-ray light curves with no sharp peaks. Gamma-ray light curves with sharply peaked gamma-ray flares possess a stronger gamma-ray/optical correlations. The research at St.Petersburg State U. was funded by the Minister of Education and Science of the Russian Federation (state contract N#P123). The research at BU was funded in part by NASA Fermi Guest Investigator grant NNX08AV65G and by NSF grant AST-0907893. The VLBA is an instrument of the National Radio Astronomy Observatory, a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Morozova, Daria; Larionov, V. M.; Hagen-Thorn, V. A.; Jorstad, S. G.; Marscher, A. P.; Troitskii, I. S.

2011-01-01

169

Gamma-ray polarimetry with Compton Telescope  

NASA Astrophysics Data System (ADS)

Compton telescope is a promising technology to achieve very high sensitivity in the soft gamma-ray band (0.1-10 MeV) by utilizing Compton kinematics. Compton kinematics also enables polarization measurement which will open new windows to study gamma-ray production mechanism in the universe. CdTe and Si semiconductor technologies are key technologies to realize the Compton telescope in which their high energy resolution is crucial for high angular resolution and background rejection capability. We have assembled a prototype module using a double-sided silicon strip detector and CdTe pixel detectors. In this paper, we present expected polarization performance of a proposed mission (NeXT/SGD). We also report results from polarization measurements using polarized synchrotron light and validation of EGS4 MC simulation.

Tajima, Hiroyasu; Madejski, Grzegorz; Mitani, Takefumi; Tanaka, Takaaki; Nakamura, Hidehito; Nakazawa, Kazuhiro; Takahashi, Tadayuki; Fukazawa, Yasushi; Kamae, Tuneyoshi; Kokubun, Motohide; Marlow, Daniel; Nomachi, Masaharu; do Couto e Silva, Eduardo

2004-10-01

170

The Highest Energy Gamma Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are equally likely to occur from any part of the sky, are detected by satellites about once per day, and emit most of their energy in a few seconds. Consequently, a detector with a large field of view and high duty factor is essential to observe gamma-ray bursts. EGRET was the 1st such detector sensitive enough to detect GeV gamma rays from gamma-ray bursts. While only 4 bursts were detected, these were the brightest bursts, as measured at < 1 MeV, in EGRET's field of view. Therefore, GeV emission may be characteristic of many bursts, and several models even predict emission extending to > TeV energies. Recently, a new TeV gamma-ray observatory, Milagro, has begun observing the Northern hemisphere sky. Milagro has > 1 sr field of view and operates 24 hours/day, 7 days/week. Milagrito, a smaller prototype of Milagro, operated for 15 months and 54 bursts were identified by BATSE, a sub-MeV detector in low Earth orbit, to be within Milagrito's field of view. One of the 54 bursts had marginal evidence of TeV gamma-ray emission. The prospect of observing gamma-ray bursts with Milagro will be discussed.

Dingus, Brenda L.

2000-04-01

171

Hydrocarbon characterization by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry  

SciTech Connect

The ultrahigh-resolution capabilities of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) have been demonstrated for accurate mass measurements of complex hydrocarbon mixtures. Ultrahigh resolution is achievable over a wide mass range by the use of stored waveform inverse Fourier transform (SWIFT) ejection to eliminate space-charge effects. The mass measurement stability under different ionization conditions eliminates the need of mass reference standards during acquisition of sample spectra, thereby increasing sensitivity of the accurate mass measurements under low-voltage electron ionization conditions. 27 refs., 4 figs., 2 tabs.

Hsu, C.S. (Exxon Research and Engineering Company, Annandale, NJ (United States)); Liang, Z. (Exxon Research and Engineering Company, Annandale, NJ (United States) Millipore Corporation, Madison, WI (United States)); Campana, J.E. (Millipore Corporation, Madison, WI (United States))

1994-03-15

172

The Advanced Gamma-ray Imaging System (AGIS): Simulation studies  

SciTech Connect

The Advanced Gamma-ray Imaging System (AGIS) is a next-generation ground-based gamma-ray observatory being planned in the U.S. The anticipated sensitivity of AGIS is about one order of magnitude better than the sensitivity of current observatories, allowing it to measure gamma-ray emission from a large number of Galactic and extra-galactic sources. We present here results of simulation studies of various possible designs for AGIS. The primary characteristics of the array performance - collecting area, angular resolution, background rejection, and sensitivity - are discussed.

Maier, G.; /McGill U.; Buckley, J.; /Washington U., St. Louis; Bugaev, V.; /Washington U., St. Louis; Fegan, S.; /UCLA; Funk, S.; /SLAC; Konopelko, A.; /Pittsburgh U.; Vassiliev, V.V.; /UCLA

2011-06-14

173

A study of the intergalactic magnetic field using extragalactic ultra-high-energy gamma-ray sources  

Microsoft Academic Search

The possibility of measuring the intergalactic magnetic field between an extragalactic ultrahigh-energy (UHE) gamma-ray source and the Galaxy is considered. It is found that, if there is a strong UHE gamma-ray source at a distance of less than about 100 kpc, the magnetic field between the Galaxy and the source can be studied by UHE gamma-ray observations. If the field

M. Honda

1989-01-01

174

GAMANAL. Interpretation of Gamma-Ray Spectra  

Microsoft Academic Search

GAMANAL provides a complete qualitative and quantitative analysis of mixtures of radioactive species such as fission products by computer interpretation of high-resolution gamma-ray spectra. The program first determines and removes the background or Compton continuum under the peaks in a spectrum to locate the peak regions. This is done by examining the pulse-height spectrum data for background and peak regions

Gunnink

1986-01-01

175

Spectral variations in gamma-ray bursts  

Microsoft Academic Search

We report the initial results of an analysis of 19 gamma-ray burst energy spectra recorded by the Venera-13 and 14 SIGNE experiments. The complete data-base includes some 150 events, with 5 channel energy spectra taken in the 50-700 keV range with 0.5 s time resolution, for 64 s. The observed spectra of each event analyzed were fitted with a power

K. Hurley; V. Kargatis; E. Liang; C. Barat; E. Eveno; M. Niel; V. Sh. Dolidze; A. A. Kozlenkov; I. G. Mitrofanov; A. S. Pozanenko

1991-01-01

176

Multicavity X-Ray Fabry-Perot Resonance with Ultrahigh Resolution and Contrast  

SciTech Connect

Realization of x-ray Fabry-Perot (FP) resonance in back-Bragg-reflection crystal cavities has been proposed and explored for many years, but to date no satisfactory performance has been achieved. Here we show that single-cavity crystal resonators intrinsically have limited finesse and efficiency. To break this limit, we demonstrate that monolithic multicavity resonators with equal-width cavities and specific plate thickness ratios can generate ultrahigh-resolution FP resonance with high efficiency, steep peak tails, and ultrahigh contrast simultaneously. The resonance mechanism is similar to that of sequentially cascaded single-cavity resonators. The ultranarrow-bandwidth FP resonance is anticipated to have various applications, including modern ultrahigh-resolution or precision x-ray monochromatization, spectroscopy, coherence purification, coherent diffraction, phase contrast imaging, etc.

Huang X. R.; Siddons D.; Macrander, A.T.; Peng, R.W.; Wu, X.S.

2012-05-31

177

High-pressure xenon detectors for gamma-ray spectrometry  

Microsoft Academic Search

The main results of long-term research on compressed xenon detector properties conducted at the laboratory of cosmic physics of MEPhI are given along with a description of the latest gamma-ray spectrometers based on this work. It is shown that using xenon as working substance, it is possible to create a gamma-ray spectrometer with high energy resolution. The construction and the

V. V. Dmitrenko; V. M. Gratchev; S. E. Ulin; Z. M. Uteshev; K. F. VIasik

2000-01-01

178

Low-level gamma-ray spectrometry for environmental samples  

Microsoft Academic Search

Low-level gamma-ray spectrometry with large volume HPGe detectors has been widely used in analysis of environmental radionuclides.\\u000a The reasons are excellent energy resolution and high efficiency that permits selective and non-destructive analyses of several\\u000a radionuclides in composite samples. Although the most effective way of increasing the sensitivity of a gamma-ray spectrometer\\u000a is to increase counting efficiency and the amount of

P. P. Povinec

2008-01-01

179

Development and performance of a gamma-ray imaging detector  

NASA Astrophysics Data System (ADS)

In the last few years we have been working on feasibility studies of future instruments in the gamma-ray range, from several keV up to a few MeV. The innovative concept of focusing gamma-ray telescopes in this energy range, should allow reaching unprecedented sensitivities and angular resolution, thanks to the decoupling of collecting area and detector volume. High sensitivities are essential to perform detailed studies of cosmic explosions and cosmic accelerators, e.g., Supernovae, Classical Novae, Supernova Remnants (SNRs), Gamma-Ray Bursts (GRBs), Pulsars, Active Galactic Nuclei (AGN). In order to achieve the needed performance, a gamma-ray imaging detector with mm spatial resolution and large enough efficiency is required. In order to fulfill the combined requirement of high detection efficiency with good spatial and energy resolution, an initial prototype of a gamma-ray imaging detector based on CdTe pixel detectors is being developed. It consists of a stack of several layers of CdTe detectors with increasing thickness, in order to enhance the gamma-ray absorption in the Compton regime. A CdTe module detector lies in a 11 x 11 pixel detector with a pixel pitch of 1mm attached to the readout chip. Each pixel is bump bonded to a fan-out board made of alumina (Al2O3) substrate and routed to the corresponding input channel of the readout ASIC to measure pixel position and pulse height for each incident gamma-ray photon. We will report the main features of the gamma-ray imaging detector performance such as the energy resolution for a set of radiation sources at different operating temperatures.

Gálvez, J. L.; Hernanz, M.; Álvarez, J. M.; La Torre, M.; Álvarez, L.; Karelin, D.; Lozano, M.; Pellegrini, G.; Ullán, M.; Cabruja, E.; Martínez, R.; Chmeissani, M.; Puigdengoles, C.

2012-09-01

180

A balloon-borne imaging gamma-ray telescope  

Microsoft Academic Search

A balloon-borne coded-aperture gamma-ray telescope for galactic and extragalactic astronomy observations is described. The instrument, called Gamma Ray Imaging Payload (GRIP), is designed for measurements in the energy range from 30 keV to 5 MeV with an angular resolution of 0.6 deg over a 20 deg field of view. Distinguishing characteristics of the telescope are a rotating hexagonal coded-aperture mask

W. E. Althouse; W. R. Cook; A. C. Cummings; M. H. Finger; T. A. Prince; S. M. Schindler; C. H. Starr; E. C. Stone

1985-01-01

181

Elemental mapping of planetary surfaces using gamma-ray spectroscopy  

SciTech Connect

The gamma rays escaping from a planet can be used to map the concentrations of various elements in its surface. In a planet, the high-energy particles in the galactic cosmic rays induce a cascade of particles that includes many neutrons. The {gamma} rays are made by the nuclear excitations induced by these cosmic-ray particles and their secondaries (especially capture or inelastic-scattering reactions induced by neutrons) and decay of the naturally-occurring radioelements. After a short history of planetary {gamma}-ray spectroscopy and its applications, the {gamma}-ray spectrometer planned for the Mars Observer mission is presented. The results of laboratory experiments that simulate the cosmic-ray bombardments of planetary surfaces or measure cross sections for the production of {gamma} rays and the status of the theoretical calculations for the processes that make and transport neutrons and {gamma} rays will be reviewed. The emphasis here is on studies of Mars and on new ideas, concepts, and problems that have arisen over the last decade, such as Doppler broadening and peaks from neutron scattering with germanium nuclei in a high-resolution {gamma}-ray spectrometer. 31 refs., 1 fig., 1 tab.

Reedy, R.C.

1990-01-01

182

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; C. Labanti; F. Fuschino; A. Bulgarelli; M. Trifoglio; G. Di Cocco; F. Gianotti; A. Argan; G. De Paris; A. Trois; E. Del Monte; E. Costa; G. Di Persio; I. Donnarumma; Y. Evangelista; M. Feroci; F. Lazzarotto; L. Pacciani; A. Rubini; S. Sabatini

2010-01-01

183

The Highest Energy Gamma Rays from Gamma-Ray Bursts  

Microsoft Academic Search

Gamma-ray bursts are equally likely to occur from any part of the sky, are detected by satellites about once per day, and emit most of their energy in a few seconds. Consequently, a detector with a large field of view and high duty factor is essential to observe gamma-ray bursts. EGRET was the 1st such detector sensitive enough to detect

Brenda L. Dingus

2000-01-01

184

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

185

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

186

The Ultrahigh Resolution Mass Spectrometry of Natural Organic Matter from Different Sources  

Microsoft Academic Search

Gas phase mass spectral analysis is now showing great promise in the characterization of natural organic matter. With the routine availability of the soft electrospray ionization (ESI) technique, volatilization and ionization of a sample is no longer a problem. Also, resolving power and mass accuracy of the mass spectrometers has increased greatly. Electrospray ionization combined with ultrahigh resolution Fourier transform-ion

Lori Beth Tremblay

2006-01-01

187

Ultrahigh-resolution FT-ICR mass spectrometry characterization of a -pinene ozonolysis SOA  

EPA Science Inventory

Secondary organic aerosol (SOA) of α-pinene ozonolysis with and without hydroxyl radical scavenging hexane was characterized by ultrahigh-resolution. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Molecular formulas for more than 900 negative ions were i...

188

Gamma rays at airplane altitudes  

SciTech Connect

An examination of the gamma ray flux above 1 TeV in the atmosphere is needed to better understand the anomalous showers from point sources. Suggestions are made for future experiments on board airplanes.

Iwai, J.; Koss, T.; Lord, J.; Strausz, S.; Wilkes, J.; Woosley, J. (University of Washington, Seattle, WA 98195 USA (US))

1990-03-20

189

Direct observation of hydrogen atom dynamics and interactions by ultrahigh resolution neutron protein crystallography  

PubMed Central

The 1.1 ?, ultrahigh resolution neutron structure of hydrogen/deuterium (H/D) exchanged crambin is reported. Two hundred ninety-nine out of 315, or 94.9%, of the hydrogen atom positions in the protein have been experimentally derived and resolved through nuclear density maps. A number of unconventional interactions are clearly defined, including a potential O?H…? interaction between a water molecule and the aromatic ring of residue Y44, as well as a number of potential C?H…O hydrogen bonds. Hydrogen bonding networks that are ambiguous in the 0.85 ? ultrahigh resolution X-ray structure can be resolved by accurate orientation of water molecules. Furthermore, the high resolution of the reported structure has allowed for the anisotropic description of 36 deuterium atoms in the protein. The visibility of hydrogen and deuterium atoms in the nuclear density maps is discussed in relation to the resolution of the neutron data.

Chen, Julian C.-H.; Hanson, B. Leif; Fisher, S. Zoe; Langan, Paul; Kovalevsky, Andrey Y.

2012-01-01

190

Gamma-ray Burst Cosmology  

Microsoft Academic Search

Gamma-ray bursts (GRBs) are brief flashes of gamma-rays occurring at cosmological distances. GRB was discovered by Vela satellite in 1967. The discovery of afterglows in 1997 made it possible to measure the GRBs' redshifts and confirmed the cosmological origin. GRB cosmology includes utilizing long GRBs as standard candles to constrain the dark energy and cosmological parameters, measuring the high-redshift star

F. Y. Wang

2011-01-01

191

Underground Gamma-Ray Spectrometry  

Microsoft Academic Search

Gamma-ray spectrometry using high purity Ge detectors has made significant advances in recent years because large crystals have become readily available and the importance of very radiopure materials in the construction of detectors has been understood. The combination of these improvements has made it possible to decrease detection limits in special low-background counting systems. Gamma-ray spectrometry systems located underground are

Mikael Hult; Matthias Köhler; Nova Gorica

192

Swift: Gamma-Ray Bursts  

NSDL National Science Digital Library

In the late 1960s, scientists accidentally discovered gamma-ray bursts, intense flashes of energy that typically last no more than a few seconds or minutes. For decades after the discovery of these powerful bursts, they remained one of the greatest mysteries in astronomy. This video segment discusses the Swift satellite mission, launched in 2004 to investigate gamma-ray bursts, and presents some theories as to their origins. The segment is four minutes fourteen seconds in length.

193

Gamma-ray burst afterglows  

Microsoft Academic Search

The discovery of counterparts in X-ray and optical to radio wavelengths has revolutionized the study of gamma-ray bursts, until recently the most enigmatic of astrophysical phenomena. We now know that gamma-ray bursts are the biggest explosions in nature, caused by the ejection of ultrarelativistic matter from a powerful energy source and its subsequent collision with its environment. We have just

Paradijs van J. A; Chryssa Kouveliotou; Ralph A. M. J. Wijers

2000-01-01

194

Supernovae and Gamma Ray Bursts  

Microsoft Academic Search

We review the observational status of the Supernova\\/Gamma-Ray Burst connection. Recent (and less recent) observations of long duration Gamma-ray bursts suggest that a significant fraction of them (but not all) are associated with bright SNe of type Ib\\/c. Current estimates of the SN and GRB rates yield a ratio GRB\\/SNe-Ibc in the range ~ 0.4% - 3%. An analysis of

M. Della Valle

2007-01-01

195

Directional detector of gamma rays  

DOEpatents

A directional detector of gamma rays comprises a strip of an electrical cuctor of high atomic number backed with a strip of a second electrical conductor of low atomic number. These elements are enclosed within an electrical conductor that establishes an electrical ground, maintains a vacuum enclosure and screens out low-energy gamma rays. The detector exhibits a directional sensitivity marked by an increased output in the favored direction by a factor of ten over the output in the unfavored direction.

Cox, Samson A. (Downers Grove, IL); Levert, Francis E. (Chicago, IL)

1979-01-01

196

A computational framework for ultra-high resolution cortical segmentation at 7Tesla.  

PubMed

This paper presents a computational framework for whole brain segmentation of 7Tesla magnetic resonance images able to handle ultra-high resolution data. The approach combines multi-object topology-preserving deformable models with shape and intensity atlases to encode prior anatomical knowledge in a computationally efficient algorithm. Experimental validation on simulated and real brain images shows accuracy and robustness of the method and demonstrates the benefits of an increased processing resolution. PMID:23623972

Bazin, Pierre-Louis; Weiss, Marcel; Dinse, Juliane; Schäfer, Andreas; Trampel, Robert; Turner, Robert

2013-04-25

197

Zone-Doubling Technique to Produce Ultrahigh-Resolution X-Ray Optics  

Microsoft Academic Search

A method for the fabrication of ultrahigh-resolution Fresnel zone plate lenses for x-ray microscopy is demonstrated. It is based on the deposition of a zone plate material (Ir) onto the sidewalls of a prepatterned template structure (Si) using an atomic layer deposition technique. This results in a doubling of the effective zone density, thus improving the achievable resolution of x-ray

K. Jefimovs; J. Vila-Comamala; T. Pilvi; J. Raabe; M. Ritala; C. David

2007-01-01

198

Ultrahigh-resolution seismic reflection imaging of the Alpine Fault, New Zealand  

Microsoft Academic Search

High-resolution seismic reflection surveys across active fault zones are capable of supplying key structural information required for assessments of seismic hazard and risk. We have recorded a 360 m long ultrahigh-resolution seismic reflection profile across the Alpine Fault in New Zealand. The Alpine Fault, a continental transform that juxtaposes major tectonic plates, is capable of generating large (M > 7.8)

A. E. Kaiser; A. G. Green; F. M. Campbell; H. Horstmeyer; E. Manukyan; R. M. Langridge; A. F. McClymont; N. Mancktelow; M. Finnemore; D. C. Nobes

2009-01-01

199

Ultrahigh resolution photographic films for X-ray\\/EUV\\/FUV astronomy  

Microsoft Academic Search

The quest for ultrahigh resolution full-disk images of the sun at soft X-ray\\/EUV\\/FUV wavelengths has increased the demand for photographic films with broad spectral sensitivity, high spatial resolution, and wide dynamic range. These requirements were made more stringent by the recent development of multilayer telescopes and coronagraphs capable of operating at normal incidence at soft X-ray\\/EUV wavelengths. Photographic films are

Richard B. Hoover; Arthur B. C. Walker Jr.; Craig E. Deforest; Richard Watts; Charles Tarrio

1993-01-01

200

Unveiling the secrets of gamma ray bursts  

Microsoft Academic Search

Gamma Ray Bursts are unpredictable and brief flashes of gamma rays that occur about once a day in random locations in the sky. Since gamma rays do not penetrate the Earth's atmosphere, they are detected by satellites, which automatically trigger ground-based telescopes for follow-up observations at longer wavelengths. In this introduction to Gamma Ray Bursts we review how building a

Andreja Gomboc

2012-01-01

201

Search for gamma rays from supernova 1987A at energies greater than 100 TeV  

Microsoft Academic Search

The authors searched for ultrahigh-energy gamma rays emitted by Supernova 1987A with a new cosmic-ray facility installed at the Black Birch Range in New Zealand. The observations from 13 October to 3 December 1987 suggest no clear clustering of events around the direction of the supernova. The authors conclude that an upper limit on the flux of gamma rays of

I. A. Bond; E. Budding; M. J. Conway; K. B. Fenton; H. Fujii; Z. Fujii; H. Hasegawa; N. Hayashida; M. Honda; N. Hotta; J. E. Humble; S. Kabe; K. Kasahara; T. Kifune; A. Masaike; Y. Matsubara; K. Mitsui; Y. Miura; M. Mori; K. Murakami; Y. Muraki; M. Nagano; K. Nakamura; T. Nakamura; P. M. Norris; Y. Ohashi; A. Okada; T. Saito; M. Sakata; H. Sato; S. Shibata; M. Shima; J. R. Storey; T. Tanimori; M. Teshima; S. Torii; K. Uchino; Y. Watase; M. D. Woodhams; Y. Yamamoto; P. C. M. Yock; T. Yuda

1988-01-01

202

Search for gamma rays from Supernova 1987A at energies greater than 100 TeV  

Microsoft Academic Search

Ultrahigh-energy gamma rays emitted by Supernova 1987A are searched for with a new cosmic-ray facility installed at the Black Birch Range in New Zealand. The observations from October 13 to December 3, 1987 suggest no clear clustering of events around the direction of the supernova. It is concluded that an upper limit on the flux of gamma rays of energies

I. A. Bond; M. J. Conway; E. Budding; K. B. Fenton; H. Fujii; Z. Fujii; H. Hasegawa; N. Hayashida; M. Honda; N. Hotta

1988-01-01

203

Gamma-ray measurements at the WNR white neutron source  

SciTech Connect

Photon production data have been acquired in the incident neutron energy range, 1 < E{sub n} < 400 MeV, for a number of target nuclei, gamma-ray energy ranges, and reactions, using the continuous-energy neutron beam of the WNR facility at Los Alamos. Gamma-ray production measurements using high resolution Ge detectors have been employed for gamma-rays in the energy range, 0.1 < E{sub {gamma}} < 10 MeV. These measurements allow identification of reactions from the known energies of the gamma-ray transitions between low-lying states in the final nucleus. Some of the targets studied include: N, O, Al, Na, {sup 56}Fe, and {sup 207,208}Pb. These data are useful both for testing nuclear reaction models at intermediate energies and for numerous applied purposes. BGO detectors do not have the good energy resolution of Ge detectors, but have much greater detection efficiency for gamma rays with energies greater than a few MeV. We have used an array of 5 BGO detectors to measure cross sections and angular distributions for photon production from C and N. A large, well-shielded BGO detector has been used to measure fast neutron capture in the giant resonance region with a maximum gamma-ray energy of 52 MeV. We present results of our study of the isovector giant quadrupole resonance in {sup 41}Ca via these capture measurements. Recent measurements of inclusive photon spectra from our neutron proton Bremsstrahlung experiment have been made using a gamma-ray telescope to detect gamma-rays in the energy range, 40 < E{sub {gamma}} < 300 MeV. This detector is briefly described. The advantages and disadvantages of these detector systems are discussed using examples from our measurements. The status of current measurements is presented.

Nelson, R.O.; Wender, S.A.; Mayo, D.R.

1994-12-31

204

Fission-gamma-Ray Coincidence Studies of ^238U Neutron-Induced Fission in the Range 1 < En < 200 MeV  

Microsoft Academic Search

Studies of prompt fission-gamma-ray coincidences are being carried out using the high-resolution gamma-ray detector array GEANIE at the WNR broad-spectrum neutron source at LANSCE. Thin Si solar cells with thin ^238U deposits are used to detect fission products in coincidence with their de-excitation gamma rays. Low-energy gamma rays and x-rays are detected with planar Ge detectors. Higher-energy gamma rays are

R. O. Nelson; T. Ethvignot; T. Granier; P. Casoli; N. Fotiades; M. Devlin; P. E. Garrett; W. Younes; J. A. Becker; L. A. Bernstein

2002-01-01

205

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

SciTech Connect

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.

Grenier, Isabelle (University Paris Diderot and CEA Saclay, France)

2009-04-01

206

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.

207

Optical observations of Gamma-Ray Bursts  

Microsoft Academic Search

We briefly review the status and recent progress in the field of optical observations of gamma-ray burst afterglows. We will focus on the fundamental observational evidence for the relationship between gamma-ray bursts and the final evolutionary phases of massive stars. In particular, we will address (i) gamma-ray burst host galaxies, (ii) optically dark gamma-ray burst afterglows, (iii) the gamma-ray burst–supernova

J. Hjorth; E. Pian; J. P. U. Fynbo

2004-01-01

208

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.

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

209

The Compton Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

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

210

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

211

Design and performance of the GAMMA-400 gamma-ray telescope for dark matter searches  

NASA Astrophysics Data System (ADS)

The GAMMA-400 gamma-ray telescope is designed to measure the fluxes of gamma-rays and cosmic-ray electrons + positrons, which can be produced by annihilation or decay of the dark matter particles, as well as to survey the celestial sphere in order to study point and extended sources of gamma-rays, measure energy spectra of Galactic and extragalactic diffuse gamma-ray emission, gamma-ray bursts, and gamma-ray emission from the Sun. GAMMA-400 covers the energy range from 100 MeV to 3000 GeV. Its angular resolution is ~0.01° (E? > 100 GeV), the energy resolution ~1% (E? > 10 GeV), and the proton rejection factor ~106. GAMMA-400 will be installed on the Russian space platform Navigator. The beginning of observations is planned for 2018.

Galper, A. M.; Adriani, O.; Aptekar, R. L.; Arkhangelskaja, I. V.; Arkhangelskiy, A. I.; Boezio, M.; Bonvicini, V.; Boyarchuk, K. A.; Fradkin, M. I.; Gusakov, Yu. V.; Kaplin, V. A.; Kachanov, V. A.; Kheymits, M. D.; Leonov, A. A.; Longo, F.; Mazets, E. P.; Maestro, P.; Marrocchesi, P.; Mereminskiy, I. A.; Mikhailov, V. V.; Moiseev, A. A.; Mocchiutti, E.; Mori, N.; Moskalenko, I. V.; Naumov, P. Yu.; Papini, P.; Picozza, P.; Rodin, V. G.; Runtso, M. F.; Sparvoli, R.; Spillantini, P.; Suchkov, S. I.; Tavani, M.; Topchiev, N. P.; Vacchi, A.; Vannuccini, E.; Yurkin, Yu. T.; Zampa, N.; Zverev, V. G.; Zirakashvili, V. N.

2013-02-01

212

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

213

Optical coherence tomography for ultrahigh resolution in vivo imaging  

Microsoft Academic Search

Optical coherence tomography (OCT) is an emerging biomedical optical imaging technique that performs high-resolution, cross-sectional tomographic imaging of microstructure in biological systems. OCT can achieve image resolutions of 1–15 ?m, one to two orders of magnitude finer than standard ultrasound. The image penetration depth of OCT is determined by the optical scattering and is up to 2–3 mm in tissue.

James G Fujimoto

2003-01-01

214

Quest for ultrahigh resolution in X-ray optics  

Microsoft Academic Search

A program of solar X-ray astronomy using grazing incidence optics has culminated in X-ray images of the corona having one arc second spatial resolution. These images have demonstrated that, in general, X-ray optics can be fabricated to their specifications and can provide the level of resolution for which they are designed. Several aspects of these programs relating to the performance

J. M. Davis; A. S. Krieger; J. K. Silk; R. C. Chase

1979-01-01

215

Taladon: a polarized and tagged gamma ray beam  

NASA Astrophysics Data System (ADS)

We present the first measurements of the gamma-ray beam energy resolution obtained with a new tagging system for the Ladon facility on the storage ring Adone at Frascati. A resolution of the order of 3% in the energy region of 30-80 MeV is obtained in accordance with predictions.

Babusci, D.; Cima, E.; Iannarelli, M.; Turri, E.; Basti, F.; Halpern, I.; Casano, L.; D'Angelo, A.; Moricciani, D.; Picozza, P. G.; Schaerf, C.; Girolami, B.

1991-07-01

216

Effect of Gamma-Ray Beaming on the Fluxes of Gamma-Ray Pulsars  

Microsoft Academic Search

We study the effect of gamma-ray beaming on gamma-ray emission of the pulsars in a self-sustained outer gap model. In this model, averaged gamma-ray flux is a function of period, magnetic field, magnetic inclination angle and solid angle of gamma-ray beaming for a gamma-ray pulsar. We generate a sample of gamma-ray pulsars with their ages less than 106 years by

Ze-Jun Jiang; Li Zhang

2005-01-01

217

The contribution of GRBs to the Cosmic Gamma-ray Background  

Microsoft Academic Search

The contribution to the cosmic diffuse gamma-ray background (CGB) from Gamma Ray Bursts (GRBs) has been studied in the 40 keV - 2 MeV regime. We utilized High Energy Resolution (HER) data obtained with the Burst And Transient Source Experiment (BATSE) abord the Compton Gamma-ray Observatory (CGRO). Data from the 4th BATSE catalog were used to generate an average GRB

K. Watanabe; D. H. Hartmann

2000-01-01

218

The high intensity gamma-ray source (HIgammaS) and recent results  

Microsoft Academic Search

The high intensity gamma-ray source (HIgammaS) utilizes intra-cavity backscattering of free electron laser photons from the Duke electron storage ring to produce a unique monoenergetic beam of high-flux gamma-rays with high polarization and selectable energy resolution. At present, gamma-ray beams with energies from 2 to 58 MeV are available with intensities as high as 105 5 × 106 gamma\\/s, energy

A. P. Tonchev; M. Boswell; C. R. Howell; H. J. Karwowski; J. H. Kelley; W. Tornow; Y. K. Wu

2005-01-01

219

Gamma-ray detectors; Proceedings of the Meeting, San Diego, CA, July 21, 22, 1992  

Microsoft Academic Search

The present status of research and development, and future trends in gamma-ray detectors for nuclear medical imaging, astrophysics, nuclear and particle physics, oil-well logging, and radiation monitoring and control are reviewed. Particular attention is given to well-type phoswich counters for low-flux X-ray\\/gamma-ray detection; energy resolution and other properties of CsI(TI) crystals; gamma-ray astronomy using a high-pressure gas scintillation drift chamber

Elena Aprile

1992-01-01

220

Imaging retinal nerve fiber bundles at ultrahigh-speed and ultrahigh-resolution using OCT with adaptive optics  

NASA Astrophysics Data System (ADS)

Ultrahigh speed line scan detectors based on CMOS technology have been recently demonstrated in ultrahigh resolution spectral-domain optical coherence tomography (UHR-SD-OCT) for retinal imaging. While successful, fundamental tradeoffs exist been image acquisition time, image sampling density, and sensitivity, all of which impact the extent of motion artifacts, visualization of fine spatial detail, and detection of faint reflections. Here we investigate these tradeoffs for imaging retinal nerve fiber bundles (RNFBs) using UHR-SD-OCT with adaptive optics (AO). Volume scans of 3°x3° and 1.5°x1.5° were acquired at retinal locations of 3° nasal and 6° superior to the fovea on a healthy subject. Dynamic AO compensation across a 6 mm pupil provided near-diffraction-limited performance. The acquisition rates were 22.5k lines/s and 125k lines/s with A-lines spaced at 0.9 ?m and 1.8 ?m and B-scans at 1.8 ?m and 9 ?m. Focus was optimized for visualizing the retinal nerve fiber bundles (RNFBs). En face projection and crosssectional views of the RNFBs were extracted from the volumes and compared to images acquired with established conventional CCD-based line-scan camera. The projection view was found highly sensitive to eye motion artifacts, yet could only be partially compensated with coarser sampling, since fine sampling was necessary to observe the microscopic features in the RNFBs. For the cross-sectional view, speckle noise rather than eye motion artifacts limited bundle clarity. The highest B-scan density (1.8 ?m spacing) coupled with B-scan averaging proved the best combination. Regardless of view, the higher line rate provided better RNFB clarity.

Kocaoglu, Omer Pars; Cense, Barry; Wang, Qiang; Bruestle, Jeremy; Besecker, Jason; Gao, Weihua; Jonnal, Ravi; Miller, Donald T.

2010-02-01

221

Gamma Rays from Heavy Neutralino Dark Matter  

SciTech Connect

We consider the gamma-ray spectrum from neutralino dark matter annihilations and show that internal bremsstrahlung of W pair final states gives a previously neglected source of photons at energies near the mass of the neutralino. For masses larger than about 1 TeV, and for present day detector resolutions, this results in a characteristic signal that may dominate not only over the continuous spectrum from W fragmentation, but also over the {gamma}{gamma} and {gamma}Z line signals which are known to give large rates for heavy neutralinos. Observational prospects thus seem promising.

Bergstroem, Lars; Bringmann, Torsten; Eriksson, Martin; Gustafsson, Michael [Department of Physics, Stockholm University, AlbaNova University Center, SE - 106 91 Stockholm (Sweden)

2005-12-09

222

Gamma-ray Imaging Methods  

SciTech Connect

In this document we discuss specific implementations for gamma-ray imaging instruments including the principle of operation and describe systems which have been built and demonstrated as well as systems currently under development. There are several fundamentally different technologies each with specific operational requirements and performance trade offs. We provide an overview of the different gamma-ray imaging techniques and briefly discuss challenges and limitations associated with each modality (in the appendix we give detailed descriptions of specific implementations for many of these technologies). In Section 3 we summarize the performance and operational aspects in tabular form as an aid for comparing technologies and mapping technologies to potential applications.

Vetter, K; Mihailescu, L; Nelson, K; Valentine, J; Wright, D

2006-10-05

223

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

224

Ultrahigh Resolution Imaging of Biomolecules by Fluorescence Photoactivation Localization Microscopy  

Microsoft Academic Search

Diffraction limits the biological structures that can be imaged by normal light microscopy. However, recently developed techniques are breaking the limits that diffraction poses and allowing imaging of biological samples at the molecular length scale. Fluorescence photoactivation localization microscopy (FPALM) and related methods can now image molecular distributions in fixed and living cells with measured resolution better than 30 nm.

Samuel T. Hess; Travis J. Gould; Mudalige Gunewardene; Joerg Bewersdorf; Michael D. Mason

2009-01-01

225

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

226

GRASP - Gamma ray astronomy with spectroscopy and positioning  

SciTech Connect

The GRASP telescope, which is currently under assessment by the European Space Agency as a future space mission, is designed to generate high resolution images of the gamma-ray sky with high sensitivity and fine spectral resolution. The telescope employs a coded aperture mask and the capability to function as a Spectral Imager is achieved by the incorporation of an array of discrete germanium solid state detectors within the matrix of a larger position sensitive (CsI(T1) gamma-ray detection plane.

Bignami, G.F.; Dean, A.J.; Durouchoux, P.; Lund, N.; McBreen, B.; Ramsden, D.; Staubert, R.; Taylor, B.G.; Vedrenne, G.

1987-02-01

227

Enhanced visualization of choroidal vessels using ultrahigh resolution ophthalmic OCT at 1050 nm  

NASA Astrophysics Data System (ADS)

In this article the ability of ultrahigh resolution ophthalmic optical coherence tomography (OCT) to image small choroidal blood vessels below the highly reflective and absorbing retinal pigment epithelium is demonstrated for the first time. A new light source (lc= 1050 nm, Dl = 165 nm, Pout= 10 mW), based on a photonic crystal fiber pumped by a compact, self-starting Ti:Al2O3 laser has therefore been developed. Ex-vivo ultrahigh resolution OCT images of freshly excised pig retinas acquired with this light source demonstrate enhanced penetration into the choroid and better visualization of choroidal vessels as compared to tomograms acquired with a state-of-the art Ti:Al2O3 laser (Femtolasers Compact Pro, lc= 780 nm, Dl= 160 nm, Pout= 400 mW), normally used in clinical studies for in vivo ultrahigh resolution ophthalmic OCT imaging. These results were also compared with retinal tomograms acquired with a novel, spectrally broadened fiber laser (MenloSystems, lc= 1350 nm, Dl= 470 nm, Pout = 4 mW) permitting even greater penetration in the choroid. Due to high water absorption at longer wavelengths retinal OCT imaging at ~1300 nm may find applications in animal ophthalmic studies. Detection and follow-up of choroidal neovascularization improves early diagnosis of many retinal pathologies, e.g. age-related macular degeneration or diabetic retinopathy and can aid development of novel therapy approaches.

Povazay, B.; Bizheva, K.; Hermann, B.; Unterhuber, A.; Sattmann, H.; Fercher, A. F.; Drexler, W.; Schubert, C.; Ahnelt, P. K.; Mei, M.; Holzwarth, R.; Wadsworth, W. J.; Knight, J. C.; Russell, P. St. J.

2003-08-01

228

A preliminary report on the determination of natural radioactivity levels of the State of Qatar using high-resolution gamma-ray spectrometry  

NASA Astrophysics Data System (ADS)

This study is aimed at the determination of the activity concentrations of naturally occuring and technically enhanced levels of radiation in soil samples collected across the landscape of Qatar. Representative soil samples from various locations across the Qatarian peninsula have been collected and analyzed in order to establish activity concentrations associated with the 235,8U and 232Th natural decay chains and also the long-lived naturally occurring radionuclide 40K. The activity concentrations have been measured using a hyper-pure germanium detector. Details of the sample preparation and the gamma-ray spectroscopic analysis techniques are presented, together with the preliminary values of the activity concentrations associated with the naturally occuring radionuclide chains for six soil samples collected from the Qatarian peninsula. Sample 228, which has been collected from an inshore oil-field area, was observed to have the highest observed value of 226Ra concentration among the six samples. The weighted mean values of the activity concentrations of the radionuclides 238U, 232Th and 40K in one particular sample (sample 228) were, respectively, found to be 213.9±1.4, 4.55±0.11 and 111.4±3.6 Bq/kg, which compare with the worldwide weighted mean values in soil samples, 33, 45 and 420 Bq/kg, respectively. The deduced activity concentration of 238U in sample 228 in the current work was found to be significantly higher than the worldwide average value and was also significantly higher than the values determined for the five other initial samples discussed here. The mean values of the activity concentration of the 232Th series, 40K and 137Cs in Bq/kg from the six investigated soil samples were found to be 9.4±1.3, 204±22 and 5.8±5.6, respectively, with the quoted uncertainty referring to the standard deviation among these measurements.

Al-Sulaiti, H.; Regan, P. H.; Bradley, D. A.; Malain, D.; Santawamaitre, T.; Habib, A.; Matthews, M.; Bukhari, S.; Al-Dosari, M.

2010-07-01

229

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

2012-11-09

230

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

231

Metal microelectromechanical oscillator exhibiting ultra-high water vapor resolution.  

PubMed

Water vapor sensing characterization of a metal resonator fabricated with an industrial 0.35 ?m CMOS technology is reported. The resonator frequency is ?13.2 MHz and exhibits a sensitivity magnitude of ?3.5 kHz per %RH without requiring any additional hygroscopic coating layer. An on-chip integrated oscillator circuit enables an unprecedented resolution of 0.005 %RH. PMID:21748145

Verd, J; Sansa, M; Uranga, A; Perez-Murano, F; Segura, J; Barniol, N

2011-07-11

232

Ultra-High Resolution Atom Imaging in a Light - Gradient  

NASA Astrophysics Data System (ADS)

In this thesis, we develop and demonstrate an all-optical technique for measuring the transverse positions of atoms moving in a beam. This technique is based on Raman induced resonance imaging in which a spatially varying potential correlates the atomic center-of-mass position with the resonance frequency of a Raman transition between two long-lived atomic states. The use of optical fields to induce atomic transitions permits access to very small volumes over which large potential gradients can be maintained. Under reasonable laboratory conditions, the spatial resolution of the technique can be two orders of magnitude smaller than an optical wavelength and is ultimately limited only by the Heisenberg uncertainty principle. We present a complete quantum mechanical calculation and analysis of the technique, including the limits placed on the spatial resolution by the motion of the atoms along the measurement direction. By using the Wigner phase space functions, we are able to treat the statistical velocity distribution of atoms in the beam on the same footing as the diffraction velocities of the atomic wavefronts. The results are given in terms of a spatial resolution function that predicts the shape of the measured spatial pattern in terms of the input phase space distribution. In the limit that the statistical velocities of the atoms dominate their diffractive velocities, this function is shown to take the form of a normalized gaussian sampling function that describes the shape of the spatial region in which Raman transitions occur. For an input atomic beam whose atomic distribution is initially uniform, we show that the outgoing beam has impressed in it a gaussian spatial distribution whose width Delta{x} is identical to the width of the gaussian resolution function. The measurement technique can be used to create spatial patterns as well as to measure them. For highly collimated atomic beams in which the transverse coherence length is large compared to the localization distance Delta{x}, the outgoing atomic distribution can take the form of minimum-uncertainty gaussian wavepacket for which Delta{x}Delta {p} = hbar/2. As an experimental demonstration of the technique, we have used a super-sonic beam of samarium atoms and a spatially varying light-shift potential to create and to measure localized atomic distributions. By using copropagating Raman fields to induce transitions between long-lived atomic ground states, we have achieved a spatial resolution of 200 nm, which is in excellent agreement with the theoretical predictions.

Gardner, Jeffrey Ray

233

Transient Gamma-Ray Spectrometer observation of the bright gamma-ray burst GRB 950822  

SciTech Connect

The Transient Gamma-Ray Spectrometer (TGRS) on the {ital Wind} satellite is designed to perform spectroscopy of bright gamma-ray bursts in the {approximately}20{endash}8000keV energy range, having a resolution 5{endash}30 times better than that of earlier generation detectors. GRB 950822 was the brightest burst observed by TGRS in its first year of operation, with a peak flux (1024 ms) of {approximately}78.3photonscm{sup {minus}2}s{sup {minus}1} and a fluence (50{endash}300 keV) of {approximately}1.4{times}10{sup {minus}4}ergscm{sup {minus}2}; therefore, the GRB data in this paper represent the first high-resolution spectroscopy ever performed on a burst of this brightness. The continuum spectrum of GRB 950822 has the classical gamma-ray burst shape and exhibits typical evolution from hard to soft over the course of the burst. We found no evidence of line features or any other spectral fine structure with significance greater than 3.5 {sigma} in our data. {copyright} {ital 1997} {ital The American Astronomical Society}

Seifert, H.; Teegarden, B.J.; Cline, T.L.; Gehrels, N.; in t Zand, J.J.; Palmer, D.M.; Ramaty, R. [NASA Goddard Space Flight Center, Greenbelt, Maryland20771 (United States); Hurley, K. [Space Sciences Laboratory, University of California at Berkeley, Berkeley, California94720 (United States); Madden, N.W.; Pehl, R. [Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California94720 (United States)

1997-12-01

234

Labr3:Ce scintillators for gamma ray spectroscopy  

SciTech Connect

In this paper, we report on a relatively new scintillator -LaBr3 for gamma ray spectroscopy. Crystals of this scintillator have beengrown using Bridgman process. This material when doped with cerium hashigh light output (~;60,000 photons/MeV) and fast principal decayconstant (less than 25 ns). Furthermore, it shows excellent energyresolution for gamma-ray detection. Energy resolution of 3.2 percent(FWHM) has been achieved for 662 keV photons (137Cs source) at roomtemperature. High timing resolution (260 ps - FWHM) has been recordedwith LaBr3-PMT and BaF2-PMT detectors operating in coincidence mode using511 keV positron annihilation gamma-ray pairs. Details of itsscintillation properties, and variation of these properties with changingcerium concentration are reported. Potential applications of thismaterial are also addressed.

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

2002-12-02

235

Waveguide image-slicers for ultrahigh resolution spectroscopy  

NASA Astrophysics Data System (ADS)

Waveguide image-slicer prototypes with resolutions up to 310.000 for the fiber fed PEPSI echelle spectrograph at the LBT and single waveguide thicknesses of down to 30 ?m have been manufactured. The waveguides were macroscopically prepared, stacked up to an order of 7 and thinned back to square stack cross sections. A high filling ratio was achieved by realizing homogenous adhesive gaps of 4.6 ?m, using index matching adhesives for TIR within the waveguides. The image-slicer stacks can be used in immersion mode and are miniaturized to be implemented in a set of four, measurements indicate an overall efficiency of above 80% for them.

Beckert, Erik; Strassmeier, Klaus G.; Woche, Manfred; Eberhardt, Ramona; Tünnermann, Andreas; Andersen, Michael

2008-07-01

236

Ultra-High Resolution Imaging by Fluorescence Photoactivation Localization Microscopy  

PubMed Central

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 small numbers of them at a time, at low excitation intensity. To control the number of visible fluorophores in the field of view and ensure that optically active molecules are separated by much more than the width of the point spread function, photoactivatable fluorescent molecules are used, in this case the photoactivatable green fluorescent protein (PA-GFP). For these photoactivatable molecules, the activation rate is controlled by the activation illumination intensity; nonfluorescent inactive molecules are activated by a high-frequency (405-nm) laser and are then fluorescent when excited at a lower frequency. The fluorescence is imaged by a CCD camera, and then the molecules are either reversibly inactivated or irreversibly photobleached to remove them from the field of view. The rate of photobleaching is controlled by the intensity of the laser used to excite the fluorescence, in this case an Ar+ ion laser. Because only a small number of molecules are visible at a given time, their positions can be determined precisely; with only ?100 detected photons per molecule, the localization precision can be as much as 10-fold better than the resolution, depending on background levels. Heterogeneities on length scales of the order of tens of nanometers are observed by FPALM of PA-GFP on glass. FPALM images are compared with images of the same molecules by widefield fluorescence. FPALM images of PA-GFP on a terraced sapphire crystal surface were compared with atomic force microscopy and show that the full width at half-maximum of features ?86 ± 4 nm is significantly better than the expected diffraction-limited optical resolution. The number of fluorescent molecules and their brightness distribution have also been determined using FPALM. This new method suggests a means to address a significant number of biological questions that had previously been limited by microscope resolution.

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

2006-01-01

237

FISSION PRODUCT GAMMA RAY SPECTRA  

Microsoft Academic Search

Uranium-235 fission product gamma spectra were calculated for various ; reactor operating histories. An IBM704 digital computer program was coded to ; compute the gamma energy contributed by each fission product gamma ray and to sum ; these results in energy groups. A representative curve showing the decay of ; various energy groups is presented. Comparisons are made with data

1958-01-01

238

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

239

Gamma-Ray Shielding Studies.  

National Technical Information Service (NTIS)

A monoenergetic beam of gamma rays was used to study the deep penetration of 10-MeV gamma radiation in aluminum. Recently a positron annihilation system was developed at General Atomic for the purpose of making shielding measurements in the energy range f...

J. A. Lonergan E. A. Beaver J. Parez D. F. Herring

1967-01-01

240

Periodicities in gamma ray bursts  

SciTech Connect

Gamma ray burst models based on magnetic neutron stars face a problem of account for the scarcity of observed periods. Both this scarcity and the typical period found when any is detected are explained if the neutron stars are accreting in binary systems

Wood, K.S.

1984-05-26

241

Cosmic gamma-ray bursts  

Microsoft Academic Search

The results of the observation of cosmic gamma-ray bursts are discussed and available theoretical models are presented. Emphasis is placed on a cosmological model in which a gamma burst results from a powerful (? 1051–1053 erg) and very short ( ?10 –100 s) energy release which occurs in a compact ( ? 106–107 cm) region and gives rise to a

Konstantin A Postnov

1999-01-01

242

On Gamma-Ray Bursts  

Microsoft Academic Search

We show by example how the uncoding of Gamma-Ray Bursts (GRBs) offers unprecedented possibilities to foster new knowledge in fundamental physics and in astrophysics. After recalling some of the classic work on vacuum polarization in uniform electric fields by Klein, Sauter, Heisenberg, Euler and Schwinger, we summarize some of the efforts to observe these effects in heavy ions and high

Remo Ruffini; M. G. Bernardini; C. L. Bianco; Letizia Caito; Pascal Chardonnet; Christian Cherubini; M. G. Dainotti; Federico Fraschetti; Andrea Geralico; Roberto Guida; Barbara Patricelli; Michael Rotondo; J. A. Rueda Hernandez; Gregory Vereshchagin; She-Sheng Xue

2008-01-01

243

The gamma Rays of Uranium  

Microsoft Academic Search

OUR knowledge of the gamma rays of uranium has until now been confined to their discovery by Rutherford (Phys. Zeit., 1902, 517) and to the observations of Eve (ibid., 1907, 185). The latter directed attention to their extraordinary feebleness and to their relatively low penetrating power. Eve found that uranium gives out only about one-tenth as much gamma radiation as

Frederick Soddy; Alexander S. Russell

1909-01-01

244

Photo-nuclear Science using laser Compton scattering gamma-rays in JAEA  

SciTech Connect

The laser Compton scattering gamma-rays are a new generation of gamma-rays which have advantages of tunable energy, high energy resolution, and almost 100% polarization. These gamma-rays have been used for wide fields as nuclear physics, nuclear astrophysics, and atomic energy engineering. One of the most important topics is a management of nuclear waste. We have proposed a novel non-destructive assay method for isotopes using nuclear resonance fluorescence measurement with the Compton scattering gamma-rays. This assay system is useful for the nuclear waste management. We have successfully demonstrated the detection of a target isotope hidden in heavy metals. We used these gamma-rays for the study of the nuclear physics and nuclear astrophysics. We also have developed a new Compton scattering gamma-ray source with an energy region of sub-MeV.

Hayakawa, Takehito [Kansai Photon Science Institute, Japan Atomic Energy Agency, Kizu, Kyoto 619-0215 (Japan); National Astronomical Observatory, Osawa, Mitaka, Tokyo 181-8588 (Japan); Hajima, Ryoichi [Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)

2008-06-24

245

Photo-nuclear Science using laser Compton scattering gamma-rays in JAEA  

NASA Astrophysics Data System (ADS)

The laser Compton scattering gamma-rays are a new generation of gamma-rays which have advantages of tunable energy, high energy resolution, and almost 100% polarization. These gamma-rays have been used for wide fields as nuclear physics, nuclear astrophysics, and atomic energy engineering. One of the most important topics is a management of nuclear waste. We have proposed a novel non-destructive assay method for isotopes using nuclear resonance fluorescence measurement with the Compton scattering gamma-rays. This assay system is useful for the nuclear waste management. We have successfully demonstrated the detection of a target isotope hidden in heavy metals. We used these gamma-rays for the study of the nuclear physics and nuclear astrophysics. We also have developed a new Compton scattering gamma-ray source with an energy region of sub-MeV.

Hayakawa, Takehito; Hajima, Ryoichi

2008-06-01

246

Ultrahigh-resolution spin-resolved photoemission spectrometer with a mini Mott detector  

SciTech Connect

We have developed an ultrahigh-resolution spin-resolved photoemission spectrometer with a highly efficient mini Mott detector and an intense xenon plasma discharge lamp. The spectrometer achieves the energy resolutions of 0.9 and 8 meV for non-spin-resolved and spin-resolved modes, respectively. Three-dimensional spin-polarization is determined by using a 90 deg. electron deflector situated before the Mott detector. The performance of spectrometer is demonstrated by observation of a clear Rashba splitting of the Bi(111) surface states.

Souma, S.; Sugawara, K. [WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Takayama, A.; Sato, T. [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Takahashi, T. [WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Department of Physics, Tohoku University, Sendai 980-8578 (Japan); CREST, Japan Science and Technology Agency (JST), Kawaguchi 332-0012 (Japan)

2010-09-15

247

Zone-doubling technique to produce ultrahigh-resolution x-ray optics.  

PubMed

A method for the fabrication of ultrahigh-resolution Fresnel zone plate lenses for x-ray microscopy is demonstrated. It is based on the deposition of a zone plate material (Ir) onto the sidewalls of a prepatterned template structure (Si) using an atomic layer deposition technique. This results in a doubling of the effective zone density, thus improving the achievable resolution of x-ray microscopes. Test structures with lines and spaces down to 15 nm were resolved in a scanning transmission x-ray microscope at 1 keV photon energy. PMID:18233580

Jefimovs, K; Vila-Comamala, J; Pilvi, T; Raabe, J; Ritala, M; David, C

2007-12-28

248

HIGH-RESOLUTION X-RAY OBSERVATIONS OF THE PULSAR WIND NEBULA ASSOCIATED WITH THE GAMMA-RAY SOURCE HESS J1640-465  

SciTech Connect

We present a Chandra X-ray observation of the very high energy gamma-ray source HESS J1640 - 465. We identify a point source surrounded by a diffuse emission that fills the extended object previously detected by XMM-Newton at the centroid of the HESS source, within the shell of the radio supernova remnant (SNR) G338.3 - 0.0. The morphology of the diffuse emission strongly resembles that of a pulsar wind nebula (PWN) and extends asymmetrically to the southwest of a point source presented as a potential pulsar. The spectrum of the putative pulsar and compact nebula are well characterized by an absorbed power-law model which, for a reasonable N{sub H} value of 14 x 10{sup 22} cm{sup -2}, exhibit an index of 1.1 and 2.5 respectively, typical of Vela-like PWNe. We demonstrate that, given the H I absorption features observed along the line of sight, the SNR and the H II surrounding region are probably connected and lie between 8 kpc and 13 kpc. The resulting age of the system is between 10 and 30 kyr. For a 10 kpc distance (also consistent with the X-ray absorption) the 2-10 keV X-ray luminosities of the putative pulsar and nebula are L{sub PSR} approx 1.3 x 10{sup 33} d {sup 2}{sub 10kpc} erg s{sup -1} and L{sub PWN} approx 3.9 x 10{sup 33} d {sup 2}{sub 10} erg s{sup -1} (d {sub 10} = d/10 kpc). Both the flux ratio of L {sub PWN}/L{sub PSR} approx 3.4 and the total luminosity of this system predict a pulsar spin-down power around E-dotapprox4 x 10{sup 36} erg s{sup -1}. We finally consider several reasons for the asymmetries observed in the PWN morphology and discuss the potential association with the HESS source in terms of a time-dependent one-zone leptonic model.

Lemiere, A.; Slane, P.; Murray, S. [Harvard-Smithonian Center For Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Gaensler, B. M. [Institute of Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia)

2009-12-01

249

Ultrahigh Resolution Imaging of Biomolecules by Fluorescence Photoactivation Localization Microscopy  

NASA Astrophysics Data System (ADS)

Diffraction limits the biological structures that can be imaged by normal light microscopy. However, recently developed techniques are breaking the limits that diffraction poses and allowing imaging of biological samples at the molecular length scale. Fluorescence photoactivation localization microscopy (FPALM) and related methods can now image molecular distributions in fixed and living cells with measured resolution better than 30 nm. Based on localization of single photoactivatable molecules, FPALM uses repeated cycles of activation, localization, and photobleaching, combined with high-sensitivity fluorescence imaging, to identify and localize large numbers of molecules within a sample. Procedures and pitfalls for construction and use of such a microscope are discussed in detail. Representative images of cytosolic proteins, membrane proteins, and other structures, as well as examples of results during acquisition are shown. It is hoped that these details can be used to perform FPALM on a variety of biological samples, to significantly advance the understanding of biological systems.

Hess, Samuel T.; Gould, Travis J.; Gunewardene, Mudalige; Bewersdorf, Joerg; Mason, Michael D.

250

Ultra-high resolution optical trap with single fluorophore sensitivity  

NASA Astrophysics Data System (ADS)

We present a new single-molecule instrument that combines ultra- high resolution optical tweezers with single-fluorophore fluorescence microscopy. 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). The optical tweezers portion of the instrument is based on a timeshared dual optical trap design and is interlaced with a confocal fluorescence microscope. In a demonstration experiment, individual single-fluorophore labeled DNA oligonucleotides can be 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 can be clearly observed.

Chemla, Yann

2011-03-01

251

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

252

Low-level gamma-ray spectrometry  

Microsoft Academic Search

Low-level gamma-ray spectrometry generally equates to high-sensitivity gamma-ray spectrometry that can be attained by background reduction, selective signal identification, or some combination of both. Various methods for selectively identifying gamma-ray events and for reducing the background in gamma ray spectrometers are given. The relative magnitude of each effect on overall sensitivity and the relative 'cost' for implementing them are given

R L Brodzinski

1991-01-01

253

High energy gamma ray balloon instrument  

Microsoft Academic Search

The High Energy Gamma Ray Balloon Instrument was built in part to verify certain subsystems' performance for the Energetic Gamma Ray Experiment Telescope (EGRET) instrument, the high energy telescope to be carried on the Gamma Ray Observatory. This paper describes the instrument, the performance of some subsystems, and some relevant results.

D. J. Thompson; R. G. Baker; D. L. Bertsch; J. R. Chesney; S. M. Derdeyn; C. H. Ehrmann; C. E. Fichtel; S. D. Hunter; J. S. Jacques; N. A. Laubenthal

1985-01-01

254

Faint Radio Sources and Gamma Ray Bursts  

Microsoft Academic Search

We calculate the number density of faint radio sources that are expected in radio source surveys due to the isotropic emission of Gamma Ray Burst sources. The calculation assumes the beamed supernovae model for gamma ray burst sources detected in gamma rays, x-rays, optical and radio wavelengths. Since the radio wavelength emission is expected to be more isotropically radiated, the

G. I. Langston; A. H. Minter; T. M. Freismuth

2002-01-01

255

Monte Carlo calibration of the SMM gamma ray spectrometer for high energy gamma rays and neutrons  

Microsoft Academic Search

The Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission spacecraft was primarily designed and calibrated for nuclear gamma ray line measurements, but also has a high energy mode which allows the detection of gamma rays at energies above 10 MeV and solar neutrons above 20 MeV. The GRS response has been extrapolated until now for high energy gamma rays

J. F. Cooper; C. Reppin; D. J. Forrest; E. L. Chupp; G. H. Share; R. L. Kinzer

1985-01-01

256

In situ gamma-ray spectrometry for the measurement of uranium in surface soils  

Microsoft Academic Search

The application of the technique of in situ gamma-ray spectrometry to the measurement of uranium isotopes in surface soils is described. A basic review of the in situ methodology using high resolution germanium gamma-ray spectrometers is given and specifics on calculated fluences, dose rates in air, and calibration factors are provided for relevant uranium isotopes and their progeny. The influence

K. M. Miller; P. Shebell; G. A. Klemic

1994-01-01

257

Development of an attitude control system for a balloon-borne gamma ray telescope  

Microsoft Academic Search

We describe the attitude control system employed by the MASCO balloon-borne gamma ray telescope and present the first laboratory tests of this system. The MASCO experiment is a low energy gamma ray imaging telescope that employs a MURA coded mask. Its angular resolution is 14? over a 13° field of view, which requires a pointing accuracy of some arcminutes in

T. Villela; R. A. Fonseca; P. de Souza; A. Alves; J. Mejía; R. Corrêa; J. Braga

2000-01-01

258

The semiconductor gamma-ray spectrometer as a neutron flux meter  

Microsoft Academic Search

A new method for measuring the flux densities of thermal and fast neutrons is described. The method is based on measuring the count rates of capture gamma rays produced by neutrons in suitable converters with a high resolution gamma-ray spectrometer. Two converters were used in the measurements: a converter for thermal neutrons and a converter for fast neutrons. By performing

M. Korun; R. MartinciC; B. Pucelj; M. Ravnik

1996-01-01

259

THE ORIGIN OF GAMMA RAYS FROM GLOBULAR CLUSTERS  

SciTech Connect

Fermi has detected gamma-ray emission from eight globular clusters (GCs). It is commonly believed that the energy sources of these gamma rays are millisecond pulsars (MSPs) inside GCs. Also it has been standard to explain the spectra of most Fermi Large Area Telescope pulsars including MSPs resulting from the curvature radiation (CR) of relativistic electrons/positrons inside the pulsar magnetosphere. Therefore, gamma rays from GCs are expected to be the collection of CR from all MSPs inside the clusters. However, the angular resolution is not high enough to pinpoint the nature of the emission. In this paper, we calculate the gamma rays produced by the inverse Compton (IC) scattering between relativistic electrons/positrons in the pulsar wind of MSPs in the GCs and background soft photons including cosmic microwave/relic photons, background star lights in the clusters, the galactic infrared photons, and the galactic star lights. We show that the gamma-ray spectrum from 47 Tucanae can be explained equally well by upward scattering of either the relic photons, the galactic infrared photons, or the galactic star lights, whereas the gamma-ray spectra from the other seven GCs are best fitted by the upward scattering of either the galactic infrared photons or the galactic star lights. We also find that the observed gamma-ray luminosity is correlated better with the combined factor of the encounter rate and the background soft photon energy density. Therefore, the IC scattering may also contribute to the observed gamma-ray emission from GCs detected by Fermi in addition to the standard CR process. Furthermore, we find that the emission region of high-energy photons from GCs produced by the IC scattering is substantially larger than the cores of GCs with a radius >10 pc. The diffuse radio and X-rays emitted from GCs can also be produced by the synchrotron radiation and IC scattering, respectively. We suggest that future observations including radio, X-rays, and gamma rays with energy higher than 10 GeV and better angular resolution can provide better constraints for the models.

Cheng, K. S. [Department of Physics, University of Hong Kong, Pokfulam Road (Hong Kong); Chernyshov, D. O. [Moscow Institute of Physics and Technology, Institutskii lane, 141700 Moscow Region, Dolgoprudnii (Russian Federation); Dogiel, V. A. [I. E. Tamm Theoretical Physics Division of P. N. Lebedev Institute, Leninskii pr, 53, 119991 Moscow (Russian Federation); Hui, C. Y. [Department of Astronomy and Space Science, Chungnam National University, Daejeon (Korea, Republic of); Kong, A. K. H. [Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu, Taiwan (China)

2010-11-10

260

Electron tomographic resolution of microns-thick specimens in the ultrahigh voltage electron microscope.  

PubMed

In this study, we determine the electron tomography (ET) resolution for microns-thick specimens by experiment in the ultra-high voltage electron microscope. A tilt series of projection images of a tilted 8?m thick epoxy-resin film are first acquired. Tomographic reconstructions are then calculated and the resolution is evaluated with the Fourier shell correlation method. The ET resolution of 32nm is achieved under the condition of 2MV accelerating voltage. We also demonstrate that some high tilt angle projections may be little useful for improving the final ET resolution because of the corresponding poor image qualities. These results are helpful to understand the possibility and limitation of ET applications in microns-thick specimens. PMID:23528481

Cao, Meng; Wang, Fang; Qiao, Zhi-Wei; Zhang, Hai-Bo; Nishi, Ryuji

2013-03-14

261

Space experiments on-board of lomonosov mission to study gamma-ray bursts and UHECRS  

NASA Astrophysics Data System (ADS)

The number of experiments on-board Lomonosov spacecraft are preparing now at SINP MSU in co-operation with other organisations. The main idea of Lomonosov mission is to study extreme astrophysical phenomena, such as cosmic gamma-ray bursts and ultra-high energy cosmic rays. These phenomena connect with processes occurred in very distant astrophysical objects of the Early Universe and give us information about first stages of Universe evolution. Thus, the Lomonosov mission scientific equipment includes several instruments for gamma-ray burst observation in optics, ultra-violet, X-rays and gamma-rays and the wide aperture telescope for ultra-high energy particle study by detection of ionisation light along its tracks in the atmosphere. The main parameters and a brief description of these instruments are presented.

Amelushkin, A. M.; Bogomolov, V. V.; Benghin, V. V.; Garipov, G. K.; Gorbovskoy, E. S.; Grossan, B.; Klimov, P. A.; Khrenov, B. A.; Lee, J.; Lipunov, V. M.; Na, G.; Panasyuk, M. I.; Park, I. H.; Petrov, V. L.; Smoot, G. F.; Svertilov, S. I.; Shprits, Yu.; Vedenkin, N. N.; Yashin, I. V.

2013-07-01

262

Visualization of 3D cell migration using high speed ultrahigh resolution optical coherence tomography  

NASA Astrophysics Data System (ADS)

Using high speed ultrahigh resolution optical coherence tomography (OCT) at 800nm, non-invasive 3D cellular imaging has been accomplished. Cellular resolution imaging on and within these types of substrates is not possible with conventional microscopy techniques such as interference contrast microscopy, and requires the use of fluorescent staining. It is possible to achieve data acquisition rates of 20,000 samples per second with OCT which, in combination with its high axial and transverse resolution (>2-3?m), allows it to be used as a non-invasive technique to analyze cell migration in 3D with time. Comparatively high penetration depth also makes OCT a uniquely suited imaging technique for visualization of cells within a 3D construct. In this paper it is demonstrated that it is possible to resolve ~10?m Dictyostelium discoideum cells, a well established and useful model for investigation of cell motility and chemotaxis, in 3D and follow them in time lapse using an 800nm ultrahigh resolution high speed frequency domain based OCT microscope. Ultimately, these visualization techniques could enable monitoring of cell behavior in regenerative medicine, for example tracking of individual cells within a cell scaffold.

Rey, Sara; Harwood, Adrian; Povazay, Boris; Hofer, Bernd; Unterhuber, Angelika; Hermann, Boris; Drexler, Wolfgang

2009-02-01

263

Determination of the gamma-ray spectrum in a strong neutron\\/gamma-ray mixed field  

Microsoft Academic Search

The knowledge of gamma-ray spectrum highly affects the accuracy of the correspondingly derived gamma-ray dose and the correctness of calculated neutron dose in the neutron\\/gamma-ray mixed field dosimetry when using the paired ionization chambers technique. It is of our interest to develop a method to determine the gamma-ray spectrum in a strong neutron\\/gamma-ray mixed field. The current type detector, Mg(Ar)

Yuan-Hao Liu; Yi-Chun Lin; Sander Nievaart; Wen-Tsae Chou; Hong-Ming Liu; Shiang-Huei Jiang

2011-01-01

264

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

265

Advanced gamma ray technology for scanning cargo containers.  

PubMed

The shipping industry is striving to increase security for cargo containers without significantly impeding traffic. Three Science Applications International Corporation (SAIC) development programs are supporting this effort. SAIC's ICIS system combines SAIC's VACIS gamma ray imaging, radiation scanning, OCR, elemental analysis and other technologies to scan containers for nuclear materials and other hazards in normal terminal traffic. SAIC's enhanced gamma ray detector improves VACIS image resolution by a factor of three. And SAIC's EmptyView software analyzes VACIS images to automatically verify empty containers. PMID:15996470

Orphan, Victor J; Muenchau, Ernie; Gormley, Jerry; Richardson, Rex

2005-06-29

266

Low-level single and coincidence gamma-ray spectrometry  

Microsoft Academic Search

Analyses of anthropogenic and natural gamma-ray emitters in the environment require high sensitive detector systems operating\\u000a in coincidence-anticoincidence modes. Thanks to an excellent energy resolution and a high efficiency, large volume HPGe detectors\\u000a have been widely used in low-level gamma-ray spectrometry. In the present paper we discuss the characteristics of single and\\u000a coincidence (HPGe-NaI(Tl)) arrangements suitable for analysis of environmental

I. Sýkora; M. Ješkovský; R. Janik; K. Holý; M. Chudý; P. P. Povinec

2008-01-01

267

Gamma-ray diagnostics of D-T fusion reactions  

SciTech Connect

The development of D-T fusion-energy sources requires intimate and precise measurement of fusion-burn conditions in reactor-development experiments. Some of the limitations inherent in presently available diagnostics based on massive particle emissions can be overcome by measuring fusion-generated high-energy gamma rays. Although gamma-ray intensities are low, gamma rays offer diagnostic advantages of dispersion-free propagation and low intrinsic backgrounds. This paper describes two detector systems developed to study D-T fusion reactions by measuring the associated 16.7-MeV gamma-ray emissions. The first system is a Compton-recoil spectrometer and features good energy resolution of the 16.7-MeV photons. This system uses a sector-magnet spectrometer to isolate electrons forward-scattered by the high-energy gamma rays. The second system is a threshold Cerenkov detector and features a higher net sensitivity. A chamber filled with CO/sub 2/ gas acts as a Cerenkov medium for electrons scattered by the 16.7-MeV photons. The gas pressure is adjusted so that electrons scattered by photons having energies less than 16.7 MeV do not have sufficient energy to generate Cerenkov light in the gas.

Moran, M.J.

1984-09-01

268

Applications of in Situ gamma-Ray Spectrometry.  

National Technical Information Service (NTIS)

Gamma-ray spectrometric methods using high-resolution Ge(Li) and high purity Ge detectors have been used to quantify the concentrations and external exposure rates of radionuclides in the soil. These in situ methods have been used to study radionuclide de...

R. C. Ragaini J. A. Kirby

1978-01-01

269

Gamma-ray bursts – a puzzle being resolved  

Microsoft Academic Search

For a few seconds a gamma-ray burst (GRB) becomes the brightest object in the universe, over-shining the rest of the universe combined! Clearly, this reflects extreme conditions that are fascinating and worth exploring. The recent discovery of GRB afterglow have demonstrated that we are on the right track towards the resolution of this long standing puzzle. These observations have confirmed

Tsvi Piran

2000-01-01

270

Technical evaluation of software for gamma-ray logging system  

SciTech Connect

This report contains results of a technical review of software, identified as LGCALC, that processes data collected by a high-resolution gamma-ray borehole logging system. The software presently operates within Westinghouse Hanford Company, Department of Geosciences, to process data collected by the Radionuclide Logging System. The software has been reviewed for its suitability for processing data to be collected by new high-resolution gamma-ray logging trucks scheduled to begin operational tests within Westinghouse Tank Waste Remediation Systems during 1994. Examination of the program code and hands-on operational tests have shown that this software is suitable for its intended use of processing high-resolution gamma-ray data obtained from borehole logging. Most of the code requires no changes, but in a few limited cases, suggestions have been made to correct errors or improve operation. Section 4 describes these changes. The technical review has confirmed the appropriateness, correctness, completeness, and coding accuracy of algorithms used to process spectral gamma-ray data, leading to a calculation of subsurface radionuclide contaminants. Running the program with test data from calibration models has confirmed that the program operates correctly. Comparisons with hand calculations have shown the correctness of the output from the program, based on known input data. Section 3 describes these tests. The recommended action is to make the near term programming changes suggested in Section 4.1 and then use the LGCALC analysis program with the new high-resolution logging systems once they have been properly calibrated.

Stromswold, D.C.

1994-05-01

271

The imaging compton telescope COMPTEL on the gamma ray observatory  

SciTech Connect

This instrument is based on a newly established concept of ..gamma..-ray detection in the very difficult 1-30 MeV range. It employs the unique feature of a two-step interaction of the ..gamma..-ray: a Compton scattering collision in a first detector followed by an interaction in a second detector element. COMPTEL has been designed to perform a very sensitive survey of the ..gamma..-ray sky. Extreme care has been taken to minimize background so that the detection limits of COMPTEL will be dominated by source counting statistics. It combines a wide field of view (about 1 steradian) with a good angular resolution. The design criteria of COMPTEL and the performance of a Science Model are described.

Schonfelder, V.; Aarts, H.; Deerenberg, A.J.M.; Diehl, R.; Lichti, G.G.; Lockwood, J.; Steinle, H.; Swanburg, B.N.

1984-02-01

272

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

273

Miniature gamma-ray camera for tumor localization  

SciTech Connect

The overall goal of this LDRD project was to develop technology for a miniature gamma-ray camera for use in nuclear medicine. The camera will meet a need of the medical community for an improved means to image radio-pharmaceuticals in the body. In addition, this technology-with only slight modifications-should prove useful in applications requiring the monitoring and verification of special nuclear materials (SNMs). Utilization of the good energy resolution of mercuric iodide and cadmium zinc telluride detectors provides a means for rejecting scattered gamma-rays and improving the isotopic selectivity in gamma-ray images. The first year of this project involved fabrication and testing of a monolithic mercuric iodide and cadmium zinc telluride detector arrays and appropriate collimators/apertures. The second year of the program involved integration of the front-end detector module, pulse processing electronics, computer, software, and display.

Lund, J.C.; Olsen, R.W.; James, R.B.; Cross, E. [and others

1997-08-01

274

Spectral analysis of young gamma-ray pulsars with Fermi  

NASA Astrophysics Data System (ADS)

The Large Area Telescope (LAT) is the main instrument on board the Fermi Gamma-ray Space Telescope, launched on June 11, 2008. Thanks to its large effective area, good resolution and excellent sensitivity, Fermi has opened a new era for gamma-ray astronomy, in particular it has identified many new gamma-ray pulsars, that will help to study in detail the emission mechanism of these sources. We present a study on the spectrum emission and common features of J0007+7303, J0205+6449, J1833-1034 and J1124-5916 that, together with the Crab, are among the youngest pulsars in the galaxy, with an estimated age <15000 yr.

Gargano, Fabio; Fermi LAT Collaboration; Pulsar Timing Consortium

2011-02-01

275

Probing the gamma-ray sky  

NASA Astrophysics Data System (ADS)

The observational results of the NASA's Compton Gamma Ray Observatory (GRO) are reviewed with attention given to the results from solar flares and gamma-ray bursts. The observatory is described emphasizing the Burst and Transient Source Experiment, the Oriented Scintillation Spectrometer Experiment, and the Energetic Gamma Ray Experiment Telescope. Increases in gamma-ray emission are noted in solar observations, and the pulsar in the Crab nebula was studied extensively. More gamma-ray pulsars were observed, and a total of 261 gamma-ray bursts are recorded as a result of the GRO observations. A gamma-ray galaxy was discovered by the GRO instruments, and the source - 3C 279 - is estimated to be 7 billion light years from earth. The GRO is shown to be of use in the characterization of astronomical phenomena that cannot be observed from earth.

Hurley, Kevin

1992-12-01

276

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.

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

2011-01-01

277

The Impact of Multiple-Site Interactions on the Energy Resolution of a High-Pressure Xenon Gamma-Ray Spectrometer  

SciTech Connect

High-pressure xenon (HPXe) ionization chambers have generated interest as a radiation detection medium for purposes requiring good energy resolution, high detection efficiency, and uniform response over a broad temperature range, such as homeland security and well logging applications. These chambers generally exhibit a substantial degradation of the measured energy resolution relative to theoretical limits. This investigation studies the impact of the number of interaction sites in an event sequence on the measured energy resolution using a benchmarked simulation package. The prominence of single and multiple-site interactions is investigated in addition to the photopeak broadening due to each event class. A radial position-sensing technique developed for coplanar-anode HPXe chambers is shown to have benefit for only single-site events.

Kiff, Scott D.; He, Zhong

2007-11-30

278

Position Profiling of the Gamma-Ray Beam at the High Intensity Gamma-Ray Source (HIGS)  

NASA Astrophysics Data System (ADS)

A multi-wire proportional chamber has been constructed to be used as a gamma-ray position profiling device at the High Intensity Gamma-Ray Source (HIGS) located in the Duke Free Electron Laser Laboratory. The chamber will provide a means of locating the central axis of the gamma-ray beam with an enhanced position resolution as compared to current methods. The determination of the gamma-beam's position will enable symmetrical collimation of the gamma-beam about the central axis. This in turn, for a given diameter of collimator, will maximize the beam's intensity while simultaneously minimizing the beam's energy spread. Design specifications, construction procedures, projected performance and preliminary test results will be presented.

Westerly, David

2002-10-01

279

Ultrahigh-resolution in-vivo versus ex-vivo OCT imaging and tissue preservation  

NASA Astrophysics Data System (ADS)

Many studies have been performed which compare ex-vivo OCT imaging to histopathology in a wide range of tissues and organ systems. While some tissues, such as arterial pathology or cartilage, are relatively stable post mortem, others, such as epithelial tissues, exhibit rapid degradation. It is important to preserve these tissues with minimal changes in morphology relative to their in vivo state in order to enable meaningful ex vivo OCT imaging studies. In this paper, we investigate the differences between in vivo and ex vivo OCT imaging and the effect of different tissue preservation solutions on tissue degradation and image quality. Ultrahigh resolution OCT imaging was preformed using a Ti:Al2O3 light source with 2 micrometers axial and 5 micrometers transverse resolution, using the hamster cheek pouch as a model for epithelial tissue. Tissue preservation solutions examined included: low temperature saline, room temperature saline, phosphate buffered sucrose, University of Wisconsin solution, and 10% formalin. Results of in vivo versus ex vivo ultrahigh resolution OCT imaging indicate that changes in optical properties and image degradation occur on a rapid time scale (in minutes) for all preservation solutions except formalin.

Pitris, Constantinos; Ko, Tony H.; Drexler, Wolfgang; Ghanta, Ravi K.; Li, Xingde; Chudoba, Christian C.; Hartl, Ingmar; Fujimoto, James G.; Weinstein, Michael E.

2001-05-01

280

Simultaneous dual wavelength eye-tracked ultrahigh resolution retinal and choroidal optical coherence tomography.  

PubMed

We demonstrate an optical coherence tomography device that simultaneously combines different novel ultrabroad bandwidth light sources centered in the 800 and 1060 nm regions, operating at 66 kHz depth scan rate, and a confocal laser scanning ophthalmoscope-based eye tracker to permit motion-artifact-free, ultrahigh resolution and high contrast retinal and choroidal imaging. The two wavelengths of the device provide the complementary information needed for diagnosis of subtle retinal changes, while also increasing visibility of deeper-lying layers to image pathologies that include opaque media in the anterior eye segment or eyes with increased choroidal thickness. PMID:24177081

Unterhuber, A; Považay, B; Müller, A; Jensen, O B; Duelk, M; Le, T; Petersen, P M; Velez, C; Esmaeelpour, M; Andersen, P E; Drexler, W

2013-11-01

281

Fabrication and characterization of ultra-high resolution multilayer-coated blazed gratings  

SciTech Connect

Multilayer coated blazed gratings with high groove density are the most promising candidate for ultra-high resolution soft x-ray spectroscopy. They combine the ability of blazed gratings to concentrate almost all diffraction energy in a desired high diffraction order with high reflectance soft x-ray multilayers. However in order to realize this potential, the grating fabrication process should provide a near perfect groove profile with an extremely smooth surface of the blazed facets. Here we report on successful fabrication and testing of ultra-dense saw-tooth substrates with 5,000 and 10,000 lines/mm.

Voronov,, Dmitriy; Anderson, Erik; Cambie, Rossana; Dhuey, Scott; Gullikson, Eric; Salmassi, Farhad; Yashchuk, Tony; Padmore, Howard

2011-07-26

282

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.

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

2011-01-01

283

High-resolution integrated germanium Compton polarimeter for the gamma-ray energy range 80 keV1 MeV  

Microsoft Academic Search

Parameters which govern the choice of a detection system to measure the linear polarization of γ rays at low energies are discussed. An integrated polarimeter is described which is constructed from a single crystal of germanium. It is a compact planar device with the sectors defined electrically, and which gives an energy resolution in the add-back mode of 1 keV

R. A. Sareen; W. Urban; A. R. Barnett; B. J. Varley

1995-01-01

284

Novel ultrahigh resolution data acquisition and image reconstruction for multi-detector row CT  

SciTech Connect

We present and evaluate a special ultrahigh resolution mode providing considerably enhanced spatial resolution both in the scan plane and in the z-axis direction for a routine medical multi-detector row computed tomography (CT) system. Data acquisition is performed by using a flying focal spot both in the scan plane and in the z-axis direction in combination with tantalum grids that are inserted in front of the multi-row detector to reduce the aperture of the detector elements both in-plane and in the z-axis direction. The dose utilization of the system for standard applications is not affected, since the grids are moved into place only when needed and are removed for standard scanning. By means of this technique, image slices with a nominal section width of 0.4 mm (measured full width at half maximum=0.45 mm) can be reconstructed in spiral mode on a CT system with a detector configuration of 32x0.6 mm. The measured 2% value of the in-plane modulation transfer function (MTF) is 20.4 lp/cm, the measured 2% value of the longitudinal (z axis) MTF is 21.5 lp/cm. In a resolution phantom with metal line pair test patterns, spatial resolution of 20 lp/cm can be demonstrated both in the scan plane and along the z axis. This corresponds to an object size of 0.25 mm that can be resolved. The new mode is intended for ultrahigh resolution bone imaging, in particular for wrists, joints, and inner ear studies, where a higher level of image noise due to the reduced aperture is an acceptable trade-off for the clinical benefit brought about by the improved spatial resolution.

Flohr, T. G.; Stierstorfer, K.; Suess, C.; Schmidt, B.; Primak, A. N.; McCollough, C. H. [Siemens Medical Solutions, Computed Tomography CTE PA Siemensstr. 1, 91301 Forchheim (Germany) and Department of Diagnostic Radiology, Eberhard-Karls-Universitaet Tuebingen (Germany); Siemens Medical Solutions, Computed Tomography CTE PA Siemensstr. 1, 91301 Forchheim (Germany); Mayo Clinic College of Medicine, Department of Radiology, Rochester, Minnesota (United States)

2007-05-15

285

New crossbeam inspection tool combining an ultrahigh-resolution field emission SEM and a high-resolution FIB  

NASA Astrophysics Data System (ADS)

The combination of field emission scanning electron microscopy (FESEM) and focused ion beam (FIB) is a future key technology for semiconductor and material science related applications. A new CrossBeam tool is discussed in this presentation. Through the combination of the well known Gemini ultrahigh resolution field emission SEM column and the well known Canion31 + high performance FIB column a wide field of applications can now be accessed. This includes structural cross-sections for SEM and transmission electron microscopy (TEM) applications, device modification, failure analysis, sublayer measurement and examination, as well as SEM and FIB related analytical techniques such as energy dispersive x-ray spectroscopy (EDS), wavelength dispersive x-ray spectroscopy (WDS), secondary ion mass spectrometry (SIMS) etc. Real time high resolution SEM imaging of the cutting and deposition process enables the researcher to perform very accurate three dimensional structural examinations and device modifications.

Gnauck, Peter; Hoffrogge, Peter; Greiser, Jens

2002-07-01

286

Portable high energy gamma ray imagers  

NASA Astrophysics Data System (ADS)

To satisfy the needs of high energy gamma ray imagers for industrial nuclear imaging applications, three high energy gamma cameras are presented. The RMD-Pinhole camera uses a lead pinhole collimator and a segmented BGO detector viewed by a 3 in. square position sensitive photomultiplier tube (PSPMT). This pinhole gamma camera displayed an energy resolution of 25.0% FWHM at the center of the camera at 662 keV and an angular resolution of 6.2° FWHM at 412 keV. The fixed multiple hole collimated camera (FMCC), used a multiple hole collimator and a continuous slab of NaI(Tl) detector viewed by the same PSPMT. The FMCC displayed an energy resolution of 12.4% FWHM at 662 keV at the center of the camera and an angular resolution of 6.0° FWHM at 412 keV. The rotating multiple hole collimated camera (RMCC) used a 180° antisymmetric rotation modulation collimator and CsI(Tl) detectors coupled to PIN silicon photodiodes. The RMCC displayed an energy resolution of 7.1% FWHM at 662 keV and an angular resolution of 4.0° FWHM at 810 keV. The performance of these imagers is discussed in this paper.

Guru, S. V.; He, Z.; Wehe, D. K.; Knoll, G. F.; Redus, R. H.; Squillante, M. R.

1996-02-01

287

Observations of the Highest Energy Gamma Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to TeV gamma rays from gamma-ray bursts are beginning operation.

Dingus, Brenda L.

2003-04-01

288

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.

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

2012-01-01

289

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

290

Ultra-high resolution imaging of DNA and nucleosomes using non-contact atomic force microscopy.  

PubMed

Visualisation of nano-scale biomolecules aids understanding and development in molecular biology and nanotechnology. Detailed structure of nucleosomes adsorbed to mica has been captured in the absence of chemical-anchoring techniques, demonstrating the usefulness of non-contact atomic force microscopy (NC-AFM) for ultra-high resolution biomolecular imaging. NC-AFM offers significant advantages in terms of resolution, speed and ease of sample preparation when compared to techniques such as cryo-electron microscopy and X-ray crystallography. In the absence of chemical modification, detailed structure of DNA deposited on a gold substrate was observed for the first time using NC-AFM, opening up possibilities for investigating the electrical properties of unmodified DNA. PMID:15757664

Davies, Emma; Teng, Kar Seng; Conlan, Robert Steven; Wilks, Stephen Patrick

2005-03-14

291

Recommended standards for gamma ray intensities  

NASA Astrophysics Data System (ADS)

Gamma ray data are used in more and more areas of application, and so over the years the demand for recommended gamma ray energies and intensities has increased. This paper proposes a list of gamma rays whose intensity is sufficiently well-known and they can be used for the calibration of gamma ray spectrometers and other applications; it is based on studies carried out by an international group of evaluators: the Decay Data Evaluation Project. One goal of this paper is to gather this set of data together in order to facilitate and generalize their use. In the first part, a brief description of the methodology followed throughout the evaluations is given, different methods of gamma ray intensity evaluation are presented, some typical examples of evaluations are shown; in the second part, the list of chosen nuclides is given along with their applications, and finally a list of recommended gamma ray intensities is presented.

Bé, Marie-Martine; Chechev, Valery P.

2013-11-01

292

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

NASA Astrophysics Data System (ADS)

Optical coherence tomography (OCT) is an emerging technology for non-invasive cross-sectional imaging of biological tissue and material with um resolution. In the field of pulmonary medicine, non-invasive high resolution cross-sectional imaging is desired for investigation of diseases in lung. So far, a few works have been reported about OCT imaging of lung. Since the lung consists of alveoli separated by thin wall, ultrahigh resolution (UHR) OCT is supposed to be effective for the imaging of fine structure in lung tissue. In this work, ex vivo cross-sectional imaging of isolated rat and hamster lungs was demonstrated using UHR-OCT. A 120 nm-wide, high-power, Gaussian-like supercontinuum (SC) was generated at wavelength of 0.8 um region. The generated SC was used in a time-domain OCT system, and UHR-OCT imaging was demonstrated. An ultrahigh resolution of 2.9 um in air and 2.1 um in tissue was obtained. The achieved sensitivity was 105 dB. Using this system, ex vivo UHR-OCT imaging of isolated rat and hamster lungs was demonstrated for the first time. The structures of the trachea, visceral pleura, and alveoli were observed clearly. When saline was instilled into the lung, the penetration depth was improved, and clear images of the fine structure of the lung, including alveoli, were observed owing to the index matching effect. We have also demonstrated the UHR-OCT imaging of lung tissue using 1.3 um and 1.7 um SC sources. As the results, owing to the precise structures of lung tissues and index matching by saline, the finest images were observed with 0.8 um UHR-OCT system.

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

2011-02-01

293

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

294

GRETINA: A gamma ray energy tracking array  

Microsoft Academic Search

A gamma-ray energy tracking array (GRETA) is a new concept for the detection of gamma radiation. In such an array, the individual interactions of all the gamma rays are identified by their energies and positions. Then, using tracking algorithms based on the properties of gamma ray interactions, the scattering sequences are reconstructed. GRETA will give high peak efficiency, peak-to-background ratio,

I. Y. Lee; R. M. Clark; M. Cromaz; M. A. Deleplanque; M. Descovich; R. M. Diamond; P. Fallon; A. O. Macchiavelli; F. S. Stephens; D. Ward

2004-01-01

295

The physics of gamma-ray bursts  

Microsoft Academic Search

Gamma-ray bursts (GRB's), short and intense pulses of low-energy gamma rays, have fascinated astronomers and astrophysicists since their unexpected discovery in the late sixties. During the last decade, several space missions---BATSE (Burst and Transient Source Experiment) on the Compton Gamma-Ray Observatory, BeppoSAX and now HETE II (High-Energy Transient Explorer)---together with ground-based optical, infrared, and radio observatories have revolutionized our understanding

Tsvi Piran

2004-01-01

296

The Supernovae\\/Gamma-Ray Burst Connection  

Microsoft Academic Search

The correlation of SN 1998bw and GRB 980425 shows that some supernovae produce gamma-ray bursts. SN 1998bw resembled previous Type Ic supernovae in terms of its spectral evolution and finite polarization. A check of correlations between the Asiago supernova catalog and the BATSE catalog of gamma-ray bursts suggests that a correlation of gamma-ray bursts with Type Ic supernovae cannot be

J. C. Wheeler; L. Wang; P. Hoflich

1998-01-01

297

Hard gamma-ray background from the coding collimator of a gamma-ray telescope during in conditions of a space experiment  

Microsoft Academic Search

Coding collimators are used to improve the angular resolution of gamma-ray telescopes at energies above 50 MeV. However, the interaction of cosmic rays with the collimator material can lead to the appearance of a gramma-ray background flux which can have a deleterious effect on measurement efficiency. An experiment was performed on the Salyut-6-Soyuz spacecraft system with the Elena-F small-scale gamma-ray

A. P. Aleksandrov; A. N. Berezovoi; A. M. Galper; V. M. Grachev; V. V. Dmitrenko; V. G. Kirillov-Ugriumov; V. V. Lebedev; V. A. Liakhov; A. A. Moiseev; S. E. Ulin

1984-01-01

298

Gamma-ray irradiated polymer optical waveguides  

SciTech Connect

Optical waveguides fabricated by gamma-ray irradiation on polymer through a gold mask are presented. The gamma-ray induced index change is found almost linearly dependent on the dose of the irradiation. And the measured propagation losses are low enough for practical application. Due to the high penetrability of gamma ray, uniform refractive index change in depth can be easily achieved. Moreover, due to large-area printing, the uniformity of waveguide made by gamma-ray irradiation is much better than that by e-beam direct writing.

Lai, C.-C.; Wei, T.-Y.; Chang, C.-Y.; Wang, W.-S.; Wei, Y.-Y. [Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, No. 1, Roosevelt Road Sec. 4, Taipei 10617, Taiwan (China); Nuclear Science and Technology Development Center, National Tsing-Hua University, No. 101, Sec. 2, Kuang-Fu Road, Hsin-Chu 30043, Taiwan (China)

2008-01-14

299

Using Gamma Rays as Intergalactic Magnetometers  

NASA Astrophysics Data System (ADS)

Gamma rays from distant blazars interact with the extragalactic background light, creating electron-positron pairs, and reducing the amount of gamma-rays seen by ground-based atmospheric Cherenkov telescopes. These pairs can Compton-scatter the cosmic microwave background, creating a gamma-ray signature observable by the Fermi Large Area Telesope (LAT). The signature is also dependent on the intergalactic magnetic field (IGMF), since it can deflect the pairs from our line of sight, reducing the gamma-ray emission. We present preliminary constraints on the IGMF using Fermi-LAT and Cherenkov telescope observations, ruling out both very large and very small values of the IGMF strength.

Finke, Justin; Reyes, L. C.; Georganopoulos, M.; Fermi-LAT Collaboration

2013-04-01

300

Low-level gamma-ray spectrometry  

SciTech Connect

Low-level gamma-ray spectrometry generally equates to high-sensitivity gamma-ray spectrometry that can be attained by background reduction, selective signal identification, or some combination of both. Various methods for selectively identifying gamma-ray events and for reducing the background in gamma-ray spectrometers are given. The relative magnitude of each effect on overall sensitivity and the relative cost'' for implementing them are given so that a cost/benefit comparison can be made and a sufficiently sensitive spectrometer system can be designed for any application without going to excessive or unnecessary expense. 10 refs., 8 figs.

Brodzinski, R.L.

1990-10-01

301

Gamma rays from compact binary systems  

NASA Astrophysics Data System (ADS)

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.

Paredes, Josep M.

2008-12-01

302

Gamma ray bursts inner engines  

NASA Astrophysics Data System (ADS)

Long gamma ray bursts (GRBs) are brief durations of intense, highly variable gamma radiation coming from point like sources in the Universe. GRBs have been seen in connection with Type 1c supernovae. Their isotropical equivalent energy released in gamma rays is in some cases above 10 54 erg, but the engine creating this energy is unknown. In this thesis several models for the engine are explored. It is shown that cannonballs can in principle form from hyperaccreting disks, however the cannonball model requires almost all supernovae to create cannonballs, and our finding then implies that a hyperaccreting disk is a natural consequence in most supernovae, a notion which remains to be confirmed. General relativistic magnetohydrodynamic simulations of the collapsar model have been performed. Within our setup we found that the duration of the collapsar is too short to explain GRBs, and the energy output is not sufficient. Also the supernova connection could not be explained. I find that the more likely candidate for the GRB engine is an accreting quark star. A quark star has a maximum mass, if the mass increases above this the star will collapse to a black hole. This allows for a two stage engine that might be able to explain features observed in GRBs.

Staff, Jan Erling

303

Gamma-ray burst models.  

PubMed

I consider various possibilities for making gamma-ray bursts, particularly from close binaries. In addition to the much-studied neutron star+neutron star and black hole+neutron star cases usually considered good candidates for short-duration bursts, there are also other possibilities. In particular, neutron star+massive white dwarf has several desirable features. These systems are likely to produce long-duration gamma-ray bursts (GRBs), in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation and occur close to the host galaxy. However, rare members of the class need not be near star-forming regions and could have any type of host galaxy. Thus, a long-duration burst far from any star-forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that this type of GRB may be quite common, in agreement with the fact that the absence of a supernova can only be established in nearby bursts. PMID:17293332

King, Andrew

2007-05-15

304

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

2009-12-16

305

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

306

Response of ionization chambers filled with liquid xenon doped with organic molecules to gamma rays  

NASA Astrophysics Data System (ADS)

The charge collection and energy resolution in liquid rare gas ionization chambers can be improved by doping the liquid with photoionization molecules. We have observed the improvement in liquid Xe doped with triethylamine (TEA). The improvement is remarkable especially at a low electric field region. This effect is used to develop gamma-ray detectors with good energy resolution as well as high detection efficiency for gamma rays.

Masuda, Kimiaki

1992-12-01

307

Observations of the Highest Energy Gamma-Rays from Gamma-Ray Bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2002-01-01

308

Observations of the Highest Energy Gamma Rays from Gamma-Ray Bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2003-01-01

309

Observations of the highest energy gamma-rays from gamma-ray bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2001-01-01

310

Hand-Held Gamma-Ray Imaging Sensors Using Room-Temperature 3Dimensional Position-Sensitive Semiconductor Spectrometers  

Microsoft Academic Search

This paper demonstrates the capability of compact gamma-ray imaging devices using 3-dimensional position sensitive CdZnTe semiconductor gamma-ray spectrometers, developed at the University of Michigan. A prototype imager was constructed and tested using two 1 cm cube 3-dimensional position sensitive CdZnTe detectors. Energy resolutions of 1.5% FWHM for single pixel events at 662 keV gamma-ray energy were obtained on both detectors,

Zhong He; Carolyn Lehner; Feng Zhang; David K. Wehe; Glenn F. Knoll; James Berry; Yanfeng Du

2002-01-01

311

Gamma rays from the interactions of reactor fast neutrons ordered by increasing gamma-ray energy  

Microsoft Academic Search

Radioactive material handled in nuclear safeguards often emits both gamma rays and neutrons. The gamma rays emitted by the radioactive isotopes are listed in several compilations, which can be used for identification and quantitative analysis of the radioactive isotopes present. Some of the neutrons are moderated and undergo thermal capture. The capture gamma rays are also listed in several compilations

1982-01-01

312

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

PubMed

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 approximately 10(6) and a net signal gain of up to 4000 was observed. The focus diameter ( approximately lambda2) 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. PMID:17979403

Steidtner, Jens; Pettinger, Bruno

2007-10-01

313

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

314

Future Gamma-Ray Imaging of Solar Eruptive Events  

NASA Astrophysics Data System (ADS)

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 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 Y.; Lin, R. P.; Hurford, G. J.; Duncan, N. A.; Saint-Hilaire, P.; Bain, H. M.; Smith, D. M.

2012-05-01

315

Gamma Ray Measurement Information Barriers for the FMTT Demonstration System  

SciTech Connect

The gamma ray attribute measurement information barrier discussion directly complements the discussion of gamma ray measurement, presented in the measurements paper by Gosnell and the general discussion of information barriers (IBs) by MacArthur. It focuses on the information barrier features applied specifically to the gamma-ray measurement and attribute analysis system. The FMTT demonstration instrument represents the second application of an IB design paradigm developed in conjunction with the Joint DOE/DoD Information Barriers Working Group (IBWG) as well as representatives from the Russian Federation's delegations to the Trilateral Initiative and meetings on the agreement for transparency at the Mayak Fissile Storage Facility (FMSF). It is also the second evolutionary step in constructing hardware to embody these jointly developed ideas. The first step was the prototype instrument developed for the Trilateral Initiative, the so-called Attribute Verification System with Information Barriers for Plutonium with Classified Characteristics utilizing Neutron Multiplicity Counting and High-Resolution Gamma-ray Spectroscopy (AVNG), that was demonstrated at Los Alamos National Laboratory in June 1999. Several improvements are evident in this second effort, and will be discussed. Improved, though this information barrier may be, it is still a prototype meant only for demonstration purposes. Its evolving specification and design are appropriately a subject for joint discussion and development. Part of that development must include creating components that the respective governments can trust enough to certify.

Wolford Jr., J.K.

2000-08-16

316

Large-scale components of radio galaxies in gamma rays  

NASA Astrophysics Data System (ADS)

The populations of relativistic electrons and high-energy cosmic rays in the extended components of radio-loud active galaxies-kiloparsec-scale jets, hotspots and lobes-make them, in principle, interesting sources of gamma-ray photons up to the highest (TeV) energies. Here I discuss the few detections of extended gamma-ray emission with Fermi and show what constraints they put on the physical conditions in radio galaxies. Although detections of radio galaxies at TeV energy are rare, I show that the information we do have can already put interesting constraints on radio galaxy physics: the CTA should have the sensitivity and resolution to improve this situation considerably, and to resolve the expected arcmin-scale gamma-ray jet in the nearest radio galaxy, Centaurus A. Finally, I review the connection between the gamma-ray observations and the acceleration of ultra-high-energy cosmic rays, and suggest that, while radio galaxies may well be the sources of the highest-energy cosmic rays observed, they may constitute a `disappointing' population in the sense that only very nearby sources, such as Cen A, will ever be identified as discrete cosmic-ray sources.

Hardcastle, Martin J.

2012-12-01

317

Optical analysis of an ultra-high resolution two-mirror soft x-ray microscope.  

PubMed

Promoted by the successful application of multilayer coated optics in soft x-ray imaging experiments in solar physics and projection lithography, several groups have designed, analyzed, fabricated, and are testing Schwarzschild multilayer soft x-ray microscopes. Simulations have indicated that diffraction limited performance of a spherical Schwarzschild microscope operating near 100 Å will be limited to systems with a small numerical aperture of approximately 0.15 and a corresponding resolution, based on the Rayleigh criterion, of 3.3 times the wavelength of the incident radiation. In principle, a two aspherical mirror Head microscope, which satisfies the constant optical path length condition and the Abbé sine condition, should achieve diffraction limited performance for very large numerical apertures. For a practical soft x-ray microscope, surface contour errors, microroughness, reflectance of multilayer coatings, and variation of the angle of incidence over the multilayer substrates become significant factors in degrading system resolution and must be controlled before an ultra-high resolution, two-mirror microscope will be realized. For a 30x reflecting microscope with a numerical aperture ranging from 0.15 to 0.35, the effects on resolution of surface contour errors, tilts, and misalignments of the optics have been studied. Graded spacing of the multilayer coatings on the mirror substrates are required of a fast, two-mirror microscope. PMID:21307473

Shealy, D L; Wang, C; Hoover, R B

1995-01-01

318

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

319

Oligomers, organosulfates, and nitrooxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry  

Microsoft Academic Search

Wet deposition is an important removal mechanism for atmospheric organic matter, and a potentially important input for receiving ecosystems, yet less than 50% of rainwater organic matter is considered chemically characterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Elemental compositions of 552

K. E. Altieri; B. J. Turpin; S. P. Seitzinger

2009-01-01

320

Oligomers, organosulfates, and nitroxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry  

Microsoft Academic Search

Wet deposition is an important removal mechanism for atmospheric organic matter, and a potentially important input for receiving ecosystems, yet less than 50% of rainwater organic matter is considered chemically characterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Elemental compositions of 552

K. E. Altieri; B. J. Turpin; S. P. Seitzinger

2008-01-01

321

Oligomers, organosulfates, and nitrooxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry  

Microsoft Academic Search

Wet deposition is an important removal mecha- nism for atmospheric organic matter, and a potentially im- portant input for receiving ecosystems, yet less than 50% of rainwater organic matter is considered chemically char- acterized. Precipitation samples collected in New Jersey, USA, were analyzed by negative ion ultra-high resolution electrospray ionization Fourier transform ion cyclotron reso- nance mass spectrometry (FT-ICR MS).

K. E. Altieri; B. J. Turpin; S. P. Seitzinger

2009-01-01

322

Cerebral blood flow imaged with ultrahigh-resolution optical coherence angiography and Doppler tomography  

PubMed Central

Speckle contrast based optical coherence angiography (OCA) and optical coherence Doppler tomography (ODT) have been applied to image cerebral blood flow previously. However, the contrast mechanisms of these two methods are not fully studied. Here, we present both flow phantom and in vivo animal experiments using ultrahigh-resolution OCA (?OCA) and ODT (?ODT) to investigate the flow sensitivity differences between these two methods. Our results show that the high sensitivity of ?OCA for visualizing minute vasculature (e.g., slow capillary beds) is due to the enhancement by random Brownian motion of scatterers (e.g., red and white blood cells) within the vessels; whereas, ?ODT permits detection of directional flow below the Brownian motion regime (e.g., laser-induced microischemia) and is, therefore, more suitable for brain functional imaging.

Ren, Hugang; Du, Congwu; Pan, Yingtian

2013-01-01

323

Ultrahigh-resolution crystallography and related electron density and electrostatic properties in proteins.  

PubMed

With an increasing number of biological macromolecular crystal structures measured at ultrahigh resolution (1 A or better), it is necessary to extend to large systems the experimental valence electron density modelling that is applied to small molecules. A database of average multipole populations has been built, describing the electron density of chemical groups in all 20 amino acids found in proteins. It allows calculation of atomic aspherical scattering factors, which are the starting point for refinement of the protein electron density, using the MoPro software. It is shown that the use of non-spherical scattering factors has a major impact on crystallographic statistics and results in a more accurate crystal structure, notably in terms of thermal displacement parameters and bond distances involving H atoms. It is also possible to obtain a realistic valence electron density model, which is used in the calculation of the electrostatic potential and energetic properties of proteins. PMID:18421138

Lecomte, Claude; Jelsch, Christian; Guillot, Benoît; Fournier, Bertrand; Lagoutte, Angélique

2008-04-18

324

Vegetation Density Determinations by Gamma Ray Absorption.  

National Technical Information Service (NTIS)

A method of non-destructive determination of vegetation density in place is presented. This method utilizes a gamma ray absorption technique. The 122 keV gamma rays from Cobalt-57 were used for this work. The determinations are made using the principle of...

C. M. Cialella J. G. Dante

1971-01-01

325

The science of gamma-ray spectroscopy  

Microsoft Academic Search

The explosion mechanism associated with thermonuclear supernovae (SNIa) is still a matter of debate. Nevertheless, there is a wide agreement that high amounts of radioactive nuclei are produced during these events, that are expected to be strong gamma-ray emitters. In this paper we investigate the use of gamma-rays as a diagnostic tool. For this purpose we have performed a complete

J. Isern; E. Bravo; A. Hirschmann

2006-01-01

326

A review of gamma ray bursts  

Microsoft Academic Search

Gamma-ray bursts have continued to puzzle astronomers since their discovery thirty years ago. The sources and emission mechanisms are still uncertain. The instruments on the Compton Gamma Ray Observatory, most notably BATSE, have produced a revolution in our understanding of bursts. BATSE found that the burst spatial distribution was isotropic but inhomogeneous, a result inconsistent with any disk population of

Charles Meegan; Kevin Hurley; Alanna Connors; Brenda Dingus; Steven Matz

1997-01-01

327

On The Origin of Gamma Ray Bursts  

Microsoft Academic Search

We propose that repeated photoexcitation\\/ionization of high Z atoms of highly relativistic flows by star light in dense stellar regions followed by emission of decay\\/recombination photons, which are beamed and boosted to gamma ray energies in the observer frame, produce gamma ray bursts (GRBs). We show that this overlooked mechanism, which is able to convert efficiently baryonic kinetic energy release

Nir J. Shaviv; Arnon Dar

1996-01-01

328

Gamma ray observation with emulsion hybrid telescope  

Microsoft Academic Search

A new gamma ray observation project with balloon borne emulsion chambers is presented. A new technique based on the accelerator emulsion experiments was implemented for studying high energy stellar objects with cosmic gamma rays. This paper provides the aim and concept of this project as well as some results of test experiments.

S. Aoki; K. Kodam; J. Kawada; N. Nonaka; A. Suzuki; T. Hara; Y. Watanabe; H. Rokujyo; A. Ariga; M. Kazuyama; H. Kubota; M. Komatsu; T. Sako; O. Sato; Y. Taira; S. Takahashi; N. Naganawa; T. Nakano; M. Nakamura; K. Niwa; Y. Nonoyama; K. Hamada; T. Fukuda; T. Furukawa; K. Hoshino; M. Miyanishi; S. Miyamoto; K. Morishima; T. Yoshioka; J. Yoshida; A. Iyono; Y. Sato; I. Tezuka

2009-01-01

329

The Supernova-Gamma-Ray Burst Connection  

Microsoft Academic Search

SN 1998bw and its corresponding relativistically expanding radio source are coincident with the gamma -ray burst source GRB 980425. We searched for other possible supernova- gamma -ray burst associations among 101 recent Type Ia and 17 Type Ib\\/c supernovae (SNe) for which the dates of optical maximum are relatively well known. We show that Type Ia SNe can be excluded

Lifan Wang; J. Craig Wheeler

1998-01-01

330

Supernova and Gamma-Ray Burst Remnants  

Microsoft Academic Search

The connection between Supernovae and Gamma-Ray Bursts has provided insights to extend our understanding of both these phenomena beyond what was known from studying them separately. A unique window into the connections between the progenitors and mechanisms of supernova and gamma-ray burst explosions is provided by their remnants. This meeting brings together experts of the remnants of both Supernovae and

Roger Chevalier; Una Hwang; Martin Laming

2006-01-01

331

Hybrid gamma ray imaging—Model and results  

NASA Astrophysics Data System (ADS)

We report on a hybrid gamma-ray radiation imaging system for industrial applications that combine the advantages of a multi-aperture mechanical collimator with electronic collimation. The combination offers both efficiency and good angular resolution, and is unique since a single gamma ray can contribute information to both modalities simultaneously. The mechanically collimated camera is most effective for imaging lower energy photons while electronic collimation uncouples spatial resolution from efficiency for higher energies. Our proposed Hybrid Gamma Ray Imager combines a high-resolution URA coded aperture with a Compton scatter camera to provide a broader range of energy response suitable for a wider range of industrial applications (50 keV 2 MeV). The primary detector is a large-area LaCl3:Ce scintillator coupled directly to a Hammamatsu PSPMT, chosen to provide portability, efficiency and energy resolution. A pixellated CsI(Na)/PSPMT combination serves as the secondary absorption detector. Point and ring-shaped radiation sources (140, 364, 662 and 1275 keV) are simulated. The results show coverage over a broad energy range of radiation and better images than either a mechanical or an electronic imager at intermediate energies. The sensitivity loss of the electronic imager due to the introduction of the mechanical collimator is recognized.

Lee, Wonho; Wehe, David

2007-08-01

332

The effect of water dispersion and absorption on axial resolution in ultrahigh-resolution optical coherence tomography  

NASA Astrophysics Data System (ADS)

We examine the effects of dispersion and absorption in ultrahigh-resolution optical coherence tomography (OCT), particularly the necessity to compensate for high dispersion orders in order to narrow the axial point-spread function envelope. We present a numerical expansion in which the impact of the various dispersion orders is quantified; absorption effects are evaluated numerically. Assuming a Gaussian source spectrum (in the optical frequency domain), we focus on imaging through water as a first approximation to biological materials. Both dispersion and absorption are found to be most significant for wavelengths above ~ 1µm, so that optimizing the system effective resolution (ER) requires choosing an operating wavelength below this limit. As an example, for 1-µm source resolution (FWHM), and propagation through a 1-mm water cell, if up to third-order dispersion compensation is applied, then the optimal center wavelength is 0.8µm, which generates an ER of 1.5µm (in air). The incorporation of additional bandwidth yields no ER improvement, due to uncompensated high-order dispersion and long-wavelength absorption.

Hillman, Timothy R.; Sampson, David D.

2005-03-01

333

Very high-energy gamma rays from gamma-ray bursts.  

PubMed

Very high-energy (VHE) gamma-ray astronomy has undergone a transformation in the last few years, with telescopes of unprecedented sensitivity having greatly expanded the source catalogue. Such progress makes the detection of a gamma-ray burst at the highest energies much more likely than previously. This paper describes the facilities currently operating and their chances for detecting gamma-ray bursts, and reviews predictions for VHE gamma-ray emission from gamma-ray bursts. Results to date are summarized. PMID:17293337

Chadwick, Paula M

2007-05-15

334

Observations of the highest energy gamma-rays from gamma-ray bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to gamma-ray bursts are beginning operation, and one recently reported evidence for TeV emission from a burst. .

Dingus, Brenda L.

2001-04-01

335

Observations of the Highest Energy Gamma-Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to gamma-ray bursts are beginning operation, and one recently reported evidence for TeV emission from a burst.

Dingus, Brenda L.

2002-12-01

336

Ultrahigh-Resolution Measurement by Optical Coherence Tomography of Dynamic Tear Film Changes on Contact Lenses  

PubMed Central

Purpose. To determine the dynamic pre- and postlens tear film (PLTF and PoLTF) thicknesses by using optical coherence tomography (OCT). Methods. Ultrahigh-resolution OCT was used to image the tear film of 22 subjects before and after contact lens wear. A soft lens with 1 drop of artificial tears on its concave surface was inserted onto one randomly selected eye. OCT images were taken before insertion, immediately afterward, and every 2 minutes for 10 minutes. For the contralateral eye, the lens inserted was not prewetted on the concave surface. OCT images were taken before insertion, immediately afterward, and at 3 minutes. Then another drop was instilled, and images were taken immediately afterward and every 2 minutes for 10 minutes. Images were processed by custom software to yield tear film thickness. Results. The thickness of precorneal tear film (PCTF) was 1.9 ± 0.9 ?m. The PoLTF was visualized clearly in all cases immediately after lens insertion, with 1 drop on the lens concave surface. Through the first 6 minutes after insertion, the PoLTF was greater than the PCTF. The PLTF (n = 12) and PoLTF (n = 9) were visualized immediately after lens insertion. After 3 minutes, the PLTF in most subjects and PoLTF in all subjects were invisible. The thickness of the PLTF increased after the instillation of artificial tears, whereas the PoLTF did not at any checkpoint for 10 minutes. Conclusions. Ultrahigh-resolution OCT is a promising tool for measuring the tear film. The PoLTF did not increase after instillation of artificial tears.

Chen, Qi; Tao, Aizhu; Shen, Meixiao; Jiao, Shuliang; Lu, Fan

2010-01-01

337

The GLAST Gamma-Ray Telescope Mission  

SciTech Connect

The Gamma-ray Large Area Space Telescope, GLAST, is an orbital mission under construction to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. With its launch in 2007, GLAST will open a new and important window on a wide variety of high energy phenomena, including black holes and active galactic nuclei; gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark-matter annihilations, Lorentz-invariance violation, and exotic relics from the Big Bang. In addition to a short review of the science opportunities, this talk will describe the high-energy gamma-ray telescope and its components and review the mission status.

Johnson, Robert P. [Institute for Particle Physics, University of California, Santa Cruz, CA 95065 (United States)

2006-07-11

338

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

2013-10-21

339

Probing the ultra-high resolution structure of aldose reductase with molecular modelling and noncovalent mass spectrometry  

Microsoft Academic Search

Aldose reductase, the first and rate-limiting enzyme of the polyol pathway, is a target for drug design for the treatment of diabetes complications. The structures of aldose reductase in complex with the cyclic imide inhibitors Fidarestat and Minalrestat were recently determined at ultra-high resolution (Proteins2004, 55, 805). We have used the detailed structural information revealed at atomic resolution, including the

Connie Darmanin; Guillaume Chevreux; Noelle Potier; Alain Van Dorsselaer; Isabelle Hazemann; Alberto Podjarny; Ossama El-Kabbani

2004-01-01

340

ICF burn-history measurments using 17-MeV fusion gamma rays  

SciTech Connect

Fusion reaction rate for inertial-confinement fusion (ICF) experiments at the Nova Laser Facility is measured with 30-ps resolution using a high-speed neutron detector. We are investigating a measurement technique based on the 16.7-MeV gamma rays that are released in deuterium-tritium fusion. Our concept is to convert gamma-ray energy into a fast burst of Cerenkov light that can be recorded with a high-speed optical detector. We have detected fusion gamma rays in preliminary experiments conducted at Nova where we used a tungsten/aerogel converter to generate Cerenkov light and an optical streak camera to record the signal.

Lerche, R.A.; Cable, M.D.; Dendooven, P.G.

1995-04-12

341

Observations of cosmic gamma-ray bursts by HEND instrument on NASA's Mars Odyssey  

NASA Astrophysics Data System (ADS)

High Energy Neutron Detector HEND operates more than 7 years onboard NASA‘s Mars Odyssey. More than 150 cosmic gamma-ray bursts and soft gamma-ray repeaters were detected during the long period of space operations, which have often used for bursts localization program "The Third Interplanetary Network". This instrument is capable to perform continuous monitoring of gamma-ray background with temporal resolution of 0.25 sec. The HEND events are studied in comparison with the data from another space instruments taking into account the capability of HEND to measure time profiles in the continuous mode of operations.

Mitrofanov, Igor; Sanin, Anton; Litvak, Maxim; Hurley, Kevin; Boynton, William; Golovin, Dmitrij

342

Cosmic Connections: from Cosmic Rays to Gamma Rays, Cosmic Backgrounds and Magnetic Fields  

NASA Astrophysics Data System (ADS)

Combined data from gamma-ray telescopes and cosmic-ray detectors have produced some new surprising insights regarding intergalactic and galactic magnetic fields, as well as extragalactic background light. We review some recent advances, including a theory explaining the hard spectra of distant blazars and the measurements of intergalactic magnetic fields based on the spectra of distant sources. Furthermore, we discuss the possible contribution of transient galactic sources, such as past gamma-ray bursts and hypernova explosions in the Milky Way, to the observed flux of ultrahigh-energy cosmic-rays nuclei. The need for a holistic treatment of gamma rays, cosmic rays, and magnetic fields serves as a unifying theme for these seemingly unrelated phenomena.

Kusenko, Alexander

2013-01-01

343

Search for gamma rays from Supernova 1987A at energies greater than 100 TeV  

NASA Astrophysics Data System (ADS)

Ultrahigh-energy gamma rays emitted by Supernova 1987A are searched for with a new cosmic-ray facility installed at the Black Birch Range in New Zealand. The observations from October 13 to December 3, 1987 suggest no clear clustering of events around the direction of the supernova. It is concluded that an upper limit on the flux of gamma rays of energies greater than 100 TeV is 1.1 x 10 to the -12th/sq cm per sec (95 percent confidence limit) for a differential spectral index a = 2.0 and source distance d = 50 kpc. This value gives an upper bound on the gamma-ray luminosity of the supernova of 5.5 x 10 to the 38th erg/sec for 10 to the 14th to 10 to the 17th eV.

Bond, I. A.; Conway, M. J.; Budding, E.; Fenton, K. B.; Fujii, H.

1988-03-01

344

In vivo volumetric imaging of the human upper eyelid with ultrahigh-resolution optical coherence tomography  

NASA Astrophysics Data System (ADS)

The upper eyelid is a biological tissue with complex structure, essential for the maintenance of an optically clear ocular surface due to its physical (blinking) effect. The Meibomian glands (MGs) are structures that lie beneath the surface of the inner eyelid and are partially responsible for the production of the superficial oily layer of the tear film. The MGs are only superficially visible under magnification when the eyelid is everted. We present for the first time in vivo 3-D images of healthy and inflamed human MGs. Tomograms were acquired from the tarsal plate of everted human eyelids with a 1060-nm ultrahigh-resolution optical coherence tomography (UHOCT) system, with ~3 ?m×10 ?m (axial×lateral) resolution in biological tissue at the rate of 91,911 A-scans/s. Comparison with histology shows that the UHOCT images reveal a spatial distribution of structures that appear to correspond with the MGs' acini and ducts (in healthy subjects), and accumulation of heterogeneous, highly scattering biological material and clear fluids in the visibly blocked glands. Noninvasive, volumetric high-resolution morphological imaging of the human tarsal area could have a significant impact in the clinical diagnosis of inflammatory and noninflammatory lid pathologies.

Bizheva, Kostadinka; Lee, Patrick; Sorbara, Luigina; Hutchings, Natalie; Simpson, Trefford

2010-07-01

345

Direct surface analysis of time-resolved aerosol impactor samples with ultrahigh-resolution mass spectrometry.  

PubMed

Aerosol particles in the atmosphere strongly influence the Earth's climate and human health, but the quantification of their effects is highly uncertain. The complex and variable composition of atmospheric particles is a main reason for this uncertainty. About half of the particle mass is organic material, which is very poorly characterized on a molecular level, and therefore it is challenging to identify sources and atmospheric transformation processes. We present here a new combination of techniques for highly time-resolved aerosol sampling using a rotating drum impactor (RDI) and organic chemical analysis using direct liquid extraction surface analysis (LESA) combined with ultrahigh-resolution mass spectrometry. This minimizes sample preparation time and potential artifacts during sample workup compared to conventional off-line filter or impactor sampling. Due to the high time resolution of about 2.5 h intensity correlations of compounds detected in the high-resolution mass spectra were used to identify groups of compounds with likely common sources or atmospheric history. PMID:23110367

Fuller, Stephen J; Zhao, Yongjing; Cliff, Steven S; Wexler, Anthony S; Kalberer, Markus

2012-10-30

346

Recent improvements in plutonium gamma-ray analysis using MGA  

Microsoft Academic Search

MGA is a gamma-ray spectrum analysis program for determining relative plutonium isotopic abundances. It can determine plutonium isotopic abundances better than 1% using a high-resolution, low-energy, planar germanium detector and measurement times ten minutes or less. We have modified MGA to allow determination of absolute plutonium isotopic abundances in solutions. With calibration of a detector using a known solution concentration

W. D. Ruhter; R. Gunnink

1992-01-01

347

Quantum Calorimeter Gamma-ray Detectors: New Tools for Nonproliferation  

Microsoft Academic Search

High resolution gamma-ray spectroscopy is an important tool for non-destructive analysis of nuclear materials and is often used by safeguards inspectors to help verify the inventories of nuclear materials held around the world. The energy spectrum of photons emitted from isotopes of uranium or plutonium in the 40-1000 keV energy range give unique signatures that, if accurately measured, give inspectors

Barry Zink

2007-01-01

348

CdWO4 crystal in gamma-ray spectrometry  

Microsoft Academic Search

The properties of CdWO4 (CWO) crystals in gamma spectrometry were studied. Several small samples of 10×10×3 mm size, typically used in CT X-ray detectors, were tested and then compared to the performance of a larger crystal of 20 mm in diameter and 20 mm in height. The light output, energy resolution, and non-proportionality of the CWO response versus gamma-ray energy,

M. Moszynski; M. Balcerzyk; M. Kapusta; A. Syntfeld; D. Wolski; G. Pausch; J. Stein; P. Schotanus

2004-01-01

349

ATCA data acquisition system for gamma-ray spectrometry  

Microsoft Academic Search

The gamma-ray spectrometer JET EP2 (Joint European Torus enhancement project 2) project aims to perform high-resolution gamma spectroscopy at very high count rate (up to few MHz). Traditional analogue electronic has count rate and pulse processing limitations (long dead-time, pile-up challenge). Digital pulse processing (DPP) systems have been shown to have better performance than analogue ones for processing neutrons or\\/and

R. C. Pereira; J. Sousa; A. M. Fernandes; F. Patrício; B. Carvalho; A. Neto; C. A. F. Varandas; G. Gorini; M. Tardocchi; D. Gin; A. Shevelev

2008-01-01

350

ISGRI: The INTEGRAL Soft Gamma-Ray Imager  

Microsoft Academic Search

For the first time in the history of high energy astronomy, a large CdTe gamma-ray camera is operating in space. ISGRI is the low-energy camera of the IBIS telescope on board the INTEGRAL satellite. This paper details its design and its in-flight behavior and performances. Having a sensitive area of 2621 cm2 with a spatial resolution of 4.6 mm, a

F. Lebrun; J. P. Leray; P. Lavocat; J. Crétolle; M. Arquès; C. Blondel; C. Bonnin; A. Bouère; C. Cara; T. Chaleil; F. Daly; F. Desages; H. Dzitko; B. Horeau; P. Laurent; O. Limousin; F. Mathy; V. Mauguen; F. Meignier; F. Molinié; E. Poindron; M. Rouger; A. Sauvageon; T. Tourrette

2003-01-01

351

Portable wide-angle {gamma}-ray vision systems  

SciTech Connect

The characteristics of two portable {gamma}-ray vision systems, which could be transported by a robot, have been explored and compared. The detector of the first system (CSPMT) consists of an array of 37 CsI(Na) scintillation crystals viewed by a single 5 inch diameter position-sensitive photomultiplier tube (PSPMT), while the second system (CSPD) employs an array of 40 CsI(Tl) scintillation detectors coupled to PIN silicon photodiodes. These devices are designed to operate in the energy range from 70 keV to 1.5 MeV, which encompasses most energies of {gamma}-ray radiation from the radioactive nuclides of interest to the nuclear industry. These systems have good angular resolutions of about 3{degree} FWHM at the central field of view of 10{degree} x 10{degree} or better when image reconstruction is employed, and coarser angular resolutions of about 10{degree} FWHM elsewhere within a wide field of view of 50{degree} x 50{degree}. The energy resolution of both systems have been tested using individual detector elements, and the imaging performance of proposed full systems have been simulated using a prototype. The results show that these devices should be good candidates for the next generation portable {gamma}-ray imaging systems.

He, Z.; Guru, S.V.; Wehe, D.K.; Knoll, G.F. [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Nuclear Engineering; Truman, A.; Ramsden, D. [Southampton Univ. (United Kingdom). Physics Dept.

1995-08-01

352

Modeling gamma-ray bursts  

NASA Astrophysics Data System (ADS)

Discovered serendipitously in the late 1960s, gamma-ray bursts (GRBs) are huge explosions of energy that happen at cosmological distances. They provide a grand physical playground to those who study them, from relativistic effects such as beaming, jets, shocks and blastwaves to radiation mechanisms such as synchrotron radiation to galatic and stellar populations and history. Through the Swift and Fermi space telescopes dedicated to observing GRBs over a wide range of energies (from keV to GeV), combined with accurate pinpointing that allows ground based follow-up observations in the optical, infrared and radio, a rich tapestry of GRB observations has emerged. The general picture is of a mysterious central engine (CE) probably composed of a black hole or neutron star that ejects relativistic shells of matter into intense magnetic fields. These shells collide and combine, releasing energy in "internal shocks" accounting for the prompt emission and flaring we see and the "external shock" or plowing of the first blastwave into the ambient surrounding medium has well-explained the afterglow radiation. We have developed a shell model code to address the question of how X-ray flares are produced within the framework of the internal shock model. The shell model creates randomized GRB explosions from a central engine with multiple shells and follows those shells as they collide, merge and spread, producing prompt emission and X-ray flares. We have also included a blastwave model, which can constrain X-ray flares and explain the origin of high energy (GeV) emission seen by the Fermi telescope. Evidence suggests that gamma-ray prompt emission and X-ray flares share a common origin and that at least some flares can only be explained by long-lasting central engine activity. We pay special attention to the time history of central engine activity, internal shocks, and observed flares. We calculate the gamma-ray (Swift/BAT band) and X-ray (Swift/XRT band) lightcurves for arbitrary central engine activity and compare the model results with the observational data. We show that the observed X-ray flare phenomenology can be explained within the internal shock model. The number, width and occurring time of flares are then used to diagnose the central engine activity, putting constraints on the energy, ejection time, width and number of ejected shells. We find that the observed X-ray flare time history generally reflects the time history of the central engine, which reactivates multiple times after the prompt emission phase with progressively reduced energy. This shell model code can be used to constrain broadband observations of GRB 090926A, which showed two flares in both the Swift UVOT and XRT bands. Using the prompt emission fluence to constrain the total energy contained in the blastwave, the internal shock model requires that Lorentz factors of the shells causing flares must be less than the Lorentz factor of the blastwave when the shells are ejected. Recent observations of Gamma-Ray Bursts (GRBs) by the Fermi Large Area Telescope (LAT) revealed a power law decay feature of the high energy emission (above 100 MeV), which led to the suggestion that it originates from an external shock. We analyze four GRBs (080916C, 090510, 090902B and 090926A) jointly detected by Fermi LAT and Gamma-ray Burst Monitor (GBM), which have high quality lightcurves in both instrument energy bands. Using the MeV prompt emission (GBM) data, we can record the energy output from the central engine as a function of time. Assuming a constant radiative efficiency, we are able to track energy accumulation in the external shock using our internal/external shell model code and show that the late time lightcurves fit well within the external shock model, but the early time lightcurves are dominated by the internal shock component which has a shallow decay phase due to the initial pile-up of shells onto the blast wave.

Maxham, Amanda

353

Radioactivity Levels and Gamma-Ray Dose Rate in Soil Samples from Kohistan (Pakistan) Using Gamma-Ray Spectrometry  

Microsoft Academic Search

The analysis of naturally occurring radionuclides (226Ra, 232Th and 40K) and an anthropogenic radionuclide 137Cs is carried out in some soil samples collected from Kohistan district of N.W.F.P. (Pakistan), using gamma-ray spectrometry. The gamma spectrometry is operated using a high purity Germanium (HPGe) detector coupled with a computer based high resolution multi channel analyzer. The specific activity in soil ranges

M. Khan Hasan; M. Ismail; K. Khan; P. Akhter

2011-01-01

354

Gamma-Ray Burst Physics with Glast  

NASA Astrophysics Data System (ADS)

The Gamma-ray Large Area Space Telescope (GLAST) is an international space mission that will study the cosmos in the energy range 10 keV-300 GeV, the upper end of which is one of the last poorly observed region of the celestial electromagnetic spectrum. The ancestor of the GLAST/LAT was the Energetic Gamma Ray Experiment Telescope (EGRET) detector, which flew onboard the Compton Gamma Ray Observatory (CGRO). The amount of information and the step forward that the high energy astrophysics made thanks to its 9 years of observations are impressive. Nevertheless, EGRET uncovered the tip of the iceberg, raising many questions, and it is in the light of EGRET's results that the great potential of the next generation gamma-ray telescope can be appreciated. GLAST will have an imaging gamma-ray telescope, the Large Area Telescope (LAT) vastly more capable than instruments flown previously, as well as a secondary instrument, the GLAST Bursts Monitor, or GBM, to augment the study of gamma-ray bursts. Gamma-Ray Bursts (GRBs) science is one of the most exciting challenges for the GLAST mission, exploring the high energy emission of one of the most intense phenomena in the sky, shading light on various problems: from the acceleration of particles to the emission processes, to more exotic physics like Quantum Gravity effect. In this paper we report the work done so far in the simulation development as well as the study of the LAT sensitivity to GRB.

Omodei, N.

2006-04-01

355

Gamma-Ray Burst Physics with GLAST  

SciTech Connect

The Gamma-ray Large Area Space Telescope (GLAST) is an international space mission that will study the cosmos in the energy range 10 keV-300 GeV, the upper end of which is one of the last poorly observed region of the celestial electromagnetic spectrum. The ancestor of the GLAST/LAT was the Energetic Gamma Ray Experiment Telescope (EGRET) detector, which flew onboard the Compton Gamma Ray Observatory (CGRO). The amount of information and the step forward that the high energy astrophysics made thanks to its 9 years of observations are impressive. Nevertheless, EGRET uncovered the tip of the iceberg, raising many questions, and it is in the light of EGRET's results that the great potential of the next generation gamma-ray telescope can be appreciated. GLAST will have an imaging gamma-ray telescope, the Large Area Telescope (LAT) vastly more capable than instruments own previously, as well as a secondary instrument, the GLAST Bursts Monitor, or GBM, to augment the study of gamma-ray bursts. Gamma-Ray Bursts (GRBs) science is one of the most exciting challenges for the GLAST mission, exploring the high energy emission of one of the most intense phenomena in the sky, shading light on various problems: from the acceleration of particles to the emission processes, to more exotic physics like Quantum Gravity effect. In this paper we report the work done so far in the simulation development as well as the study of the LAT sensitivity to GRB.

Omodei, N.; /INFN, Pisa

2006-10-06

356

A study of the intergalactic magnetic field using extragalactic ultra-high-energy gamma-ray sources  

SciTech Connect

The possibility of measuring the intergalactic magnetic field between an extragalactic ultrahigh-energy (UHE) gamma-ray source and the Galaxy is considered. It is found that, if there is a strong UHE gamma-ray source at a distance of less than about 100 kpc, the magnetic field between the Galaxy and the source can be studied by UHE gamma-ray observations. If the field strength is less than 10 to the -12th G, the gamma-ray flux for E(gamma) greater than or equal to 10 to the 15th is enhanced about 10 times over that expected from the source energy spectrum and the absorption with the 3 K microwave background photons alone. 15 refs.

Honda, M.

1989-04-01

357

Gamma Rays from the 75As(n, gamma)76As Reaction  

Microsoft Academic Search

Neutron capture gamma rays from 76As have been studied. In this study 2 kg of 75As were irradiated with thermal neutrons from a 5-Ci Pu-Be source. Graphite and paraffin were used to thermalize the fast neutrons. The As nearly surrounded an encapsulated Ge-Li detector, which detected the high-energy gamma rays from the As with an energy resolution of 12 keV.

N. A. Morcos; R. O. Barnes; J. de Melo; B. E. Lee; J. R. van Hise

1968-01-01

358

Multiple gamma-ray detection method and its application to nuclear chemistry  

Microsoft Academic Search

A new radionuclide quantification method is proposed on the basis of multiple gamma-ray detection, which is two or higher\\u000a fold gamma-ray coincidence method. The coincidence method has so far been used for nuclear structure study. We apply this\\u000a method for quantification of radioactive nuclei. The advantage of this method consists of high energy resolution and high\\u000a sensitivity. It is successfully

M. Oshima; Y. Toh; Y. Hatsukawa; M. Koizumi; A. Kimura; A. Haraga; M. Ebihara; K. Sushida

2008-01-01

359

All-sky X-ray and gamma-ray monitor (AXGAM)  

Microsoft Academic Search

A wide field-of-view, arcsecond imaging, high energy resolution X-ray and low energy gamma ray detector is proposed for a future space mission. It is specifically designed to detect and find counterparts at other wavelengths for gamma ray bursts (GRBs). Detection of GRBs require wide field-of-view (? to 2? field-of-view) and high sensitivity. This will be achieved by using high quantum

T. O. Tumer; T. J. O'Neill; K. Hurley; H. Ogelman; R. J. Paulos; R. C. Puetter; I. Kipnis; W. J. Hamilton; R. Proctor

1996-01-01

360

Gamma-ray measurements of naturally occurring radioactive samples from Cyprus characteristic geological rocks  

Microsoft Academic Search

Using high-resolution gamma-ray spectroscopy, the terrestrial gamma radiation in all the predominant types of geological rock formations appearing in Cyprus was measured. Soil samples were collected from each rock type, sealed in 1-litre plastic Marinelli beakers, and measured in the laboratory for 24 hours each. From the measured gamma-ray spectra, activity concentrations were determined for Th-232 (range from 1.3 to

M. Tzortzis; H. Tsertos; S. Christofides; G. Christodoulides

2002-01-01

361

The energy spectrum of high energy gamma rays from Mrk501 by the stereoscopic analysis  

NASA Astrophysics Data System (ADS)

We have developed the energy measurement method which based on stereoscopic observation with multiple telescopes for TeV gamma rays. Energy resolution obtained by this method was 23%. The energy spectrum of the gamma-ray flares of Markarian 501 in 1997 was also obtained using this techniques. We have confirmed the bending or the cutoff of the energy spectrum around several TeV.

Yamamoto, T.

1999-08-01

362

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

363

Application of nondestructive gamma-ray and neutron techniques for the safeguarding of irradiated fuel materials  

SciTech Connect

Nondestructive gamma-ray and neutron techniques were used to characterize the irradiation exposures of irradiated fuel assemblies. Techniques for the rapid measurement of the axial-activity profiles of fuel assemblies have been developed using ion chambers and Be(..gamma..,n) detectors. Detailed measurements using high-resolution gamma-ray spectrometry and passive neutron techniques were correlated with operator-declared values of cooling times and burnup.

Phillips, J.R.; Halbig, J.K.; Lee, D.M.; Beach, S.E.; Bement, T.R.; Dermendjiev, E.; Hatcher, C.R.; Kaieda, K.; Medina, E.G.

1980-05-01

364

Maintaining Accuracy in Gamma-Ray Spectrometry at High Count Rates  

Microsoft Academic Search

Gamma-ray spectrometry losses through pulse processing dead time and pile-up are best assayed with an external pulse technique. In this work, the virtual pulse generator technique as implemented commercially with the Westphal loss free counting (LFC) module is set up and tested with four high resolution gamma-ray spectrometers. Dual source calibration and decaying source techniques are used in the evaluation

R. Zeisler

2000-01-01

365

Gamma-ray measurements of naturally occurring radioactive samples from Cyprus characteristic geological rocks  

Microsoft Academic Search

Using high-resolution gamma-ray spectroscopy, the terrestrial gamma radiation in all the predominant types of geological rock formations appearing in Cyprus was measured. Soil samples were collected from each rock type, sealed in 1l plastic Marinelli beakers, and measured in the laboratory for 24h each. From the measured gamma-ray spectra, activity concentrations were determined for 232Th (range from 1.3 to 52.8Bqkg?1),

Michalis Tzortzis; Haralabos Tsertos; Stelios Christofides; George Christodoulides

2003-01-01

366

A Gas-Cerenkov Telescope Experiment to Observe Cosmic Gamma Rays  

Microsoft Academic Search

The gas-Cerenkov balloon-borne cosmic gamma ray detector described here has a variable energy threshold and is sensitive down to 15 MeV with a half-angle resolution of 5° to 7°. Gamma rays are detected by a coincidence between light pulses in a scintillator at the top of the detector and pulses of Cerenkov light collected by a mirror at the bottom

J. A. Hoffman

1971-01-01

367

The nuclear compton telescope: A balloon-borne soft gamma-ray spectrometer, polarimeter, and imager  

Microsoft Academic Search

Our collaboration has begun the design and development of a prototype high resolution Compton telescope utilizing 3-D imaging germanium detectors. The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma-ray (0.2-15 MeV) telescope designed to study astrophysical sources of nuclear line emission and polarization. NCT is a prototype design for the Advanced Compton Telescope, to study gamma-ray radiation with very

S. E. Boggs; P. Jean; R. P. Lin; D. M. Smith; P. von Ballmoos; N. W. Madden; P. N. Luke; M. Amman; M. T. Burks; E. L. Hull; W. Craig; K. Ziock

2001-01-01

368

Gamma-Ray Astronomy Starts to see CLAIRE: First Light for a Crystal Diffraction Telescope  

Microsoft Academic Search

CLAIRE is a balloon-borne experiment dedicated to validating the concept of a diffraction gamma-ray lens. This new concept for high energy telescopes is very promising and could significantly increase sensi- tivity and angular resolution in nuclear astrophysics. CLAIRE's lens consists of 556 Ge-Si crystals, focusing 170 keV gamma-ray photons onto a 3x3 matrix of HPGe detectors, each detector element being

H. Halloin; P. von Ballmoos; J. Evrard; G. K. Skinner; J. M. Alvarez; M. Hernanz; N. Abrosimov; P. Bastie; B. Hamelin; P. Jean; J. Knödlseder; R. K. Smither; G. Vedrenne

2004-01-01

369

Simulated Performance of the Nuclear Compton Telescope as a Gamma-Ray Polarimeter  

Microsoft Academic Search

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma-ray (0.2-10 MeV) telescope designed to study astrophysical sources of nuclear line emission and gamma-ray polarization. NCT is sensitive to polarization in the range 0.2-1 MeV. NCT consists of 3D position-sensitive germanium strip detectors. The ultra-compact design and new technologies allow NCT to achieve high efficiencies with excellent spectral resolution and

Jau-Shian Liang; E. C. Bellm; S. E. Boggs

2008-01-01

370

A nuclear medicine gamma-ray detector based on germanium strip detector technology  

Microsoft Academic Search

Recent advances in germanium strip detector technology have opened up the possibility to produce a novel gamma-ray detector for use in nuclear medicine. The advantages of position sensitivity coupled with the fine spectral resolution from high-purity germanium can be exploited to produce a tracking detector for use with a variety of biochemically useful isotopes. The tracking ability of the gamma-ray

C. J Hall; W. I. Helsby; R. A Lewis; P. Nolan; A. Boston

2003-01-01

371

Utilization of the PC for analysis of gamma-ray spectra for reactor applications  

Microsoft Academic Search

A computer program has been developed for using the IBM PC and PC compatibles for gamma-ray spectrum analysis, including computation of photopeak areas from high-resolution spectra, identification of radioisotopes, and computation of absolute activity, based on absolute detector efficiency calibration. The program utilizes the direct transfer of gamma-ray spectra from any multichannel pulse-height analyzer with RS-232 serial output into the

George W

1986-01-01

372

Two-stage gas amplifier for ultrahigh resolution low vacuum scanning electron microscopy  

SciTech Connect

We describe a magnetic field assisted, two-stage secondary electron gas amplification process for low vacuum scanning electron microscopy. The field of an ultrahigh resolution magnetic immersion objective lens and the electric field of an annular electrode configuration partition the amplification volume into two regions in which the electric and magnetic fields are parallel and crossed, respectively. The fields confine secondary electrons to axial and radial oscillations within the detector volume, until all of the kinetic energy imparted by an anode is dissipated through inelastic collisions with gas molecules. The electron confinement yields high gas amplification efficiency at short working distances and low gas pressures, facilitating high resolution imaging at low electron beam energies. Charging of insulating specimens is stabilized by positive ions produced in the gas ionization cascade. Furthermore, the signal to background level and bandwidth of this detector are superior to those of earlier generations of environmental secondary electron detectors. The combination of low vacuum, short working distance, and low beam energy is attractive to the semiconductor metrology industry, in particular, for critical dimension measurements on photolithographic masks.

Thiel, B.L.; Toth, M.; Schroemges, R.P.M.; Scholtz, J.J.; Veen, G. van; Knowles, W.R. [College of Nanoscale Science and Engineering, State University of New York at Albany, 255 Fuller Road, Albany, New York 12203 (United States); FEI Company, 1 Corporation Way 2, Peabody, Massachusetts 01960 (United States)

2006-03-15

373

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

374

How to Make a Gamma-ray  

NASA Video Gallery

Animation showing a proton traveling near the speed of light striking a slower-moving proton. The protons survive the collision, but their interaction creates an unstable particle, a pion, with only 14 percent of the proton's mass. In 10 millionths of a billionth of a second, the pion decays into a pair of gamma-ray photons. Years of data collected by NASA's Fermi Gamma-Ray Space Telescope reveal that the shattered remains of a supernova first observed in 1572 shine in high-energy gamma-rays.

Holly Zell

2011-12-12

375

Detecting Axionlike Particles with Gamma Ray Telescopes  

SciTech Connect

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.

Hooper, Dan; Serpico, Pasquale D. [Center for Particle Astrophysics, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States)

2007-12-07

376

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

2007-12-06

377

The MILAGRO Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

MILAGRO will be the first water-\\v{C}erenkov detector specifically built to study extensive air showers. It is being built in an existing man-made pond 60m x 80m by 8m, located in the Jemez mountains near Los Alamos, NM. Unlike conventional air shower detectors, which sample less than 1% of the particles which reach detector level, MILAGRO will be totally sensitive to the electrons, photons, hadrons, and muons in the air shower. The energy threshold of the MILAGRO detector is comparable to atmospheric \\v{C}erenkov detectors, however it has several advantages over these optical detectors. MILAGRO is operational 24 hours a day in all weather conditions and it has an open aperture which allows it to view the entire northern sky every day. These capabilities allow for a systematic all-sky survey to be done for the first time at VHE energies. MILAGRO will measure the Crab spectrum with high significance. In addition, it will detect and measure the spectra from AGN's such as MRK 421. MILAGRO will be the first VHE detector capable of recording Gamma Ray Bursts at energies above 250 GeV. MILAGRO will search for point sources of VHE gamma radiation, both steady and episodic. The scientific merits of this detector together with its design and current status will be discussed.

Shoup, A.; Barwick, S.; Chumney, P.; Yodh, G. B.; Chang, C. Y.; Chen, M. L.; Dion, C.; Goodman, J. A.; Berley, D.; Haines, T. J.; Hoffman, C. M.; Nagle, D. E.; Sandberg, V. D.; Sanders, G.; Schaller, S.; White, D. H.; Schmidt, D. M.; Sinnis, C.; Cavalli-Sforza, M.; Coyne, D.; Dorfan, D.; Kelley, L.; Klein, S.; Schnee, R.; Williams, D. A.; Yang, T.; Mincer, A. I.; Nemethy, P.; Bauer, D.; Caldwell, D.; Lu, A.; Yellin, S.; O'Neill, T. J.; Tumer, O. T.; Zych, A.; Freedman, S. J.; Fujikawa, B. K.; Ellsworth, R. W.; Biller, S.; Dingus, B. L.; Ahulwalia, H. S.

1994-12-01

378

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, N.; Shibamura, E.; Miyachi, T.; Takashima, T.; Kobayashi, M.; Okudaira, O.; Yamashita, N.; Kobayashi, S.; Ishizaki, T.; Sakurai, K.; Miyajima, M.; Fujii, M.; Narasaki, K.; Takai, S.; Tsurumi, K.; Kaneko, H.; Nakazawa, M.; Mori, K.; Gasnault, O.; Maurice, S.; D'Uston, C.; Reedy, R. C.; Grande, M.

2008-04-01

379

Further development of IDGS: Isotope dilution gamma-ray spectrometry  

SciTech Connect

The isotope dilution gamma-ray spectrometry (IDGS) technique for determining the plutonium concentration and isotopic composition of highly radioactive spent-fuel dissolver solutions has been further developed. Both the sample preparation and the analysis have been improved. The plutonium isotopic analysis is based on high-resolution, low-energy gamma-ray spectrometry. The plutonium concentration in the dissolver solutions then is calculated from the measured isotopic differences among the spike, the dissolver solution, and the spiked dissolver solution. Plutonium concentrations and isotopic compositions of dissolver solutions analyzed from this study agree well with those obtained by traditional isotope dilution mass spectrometry (IDMS) and are consistent with the first IDGS experimental result. With the current detector efficiency, sample size, and a 100-min count time, the estimated precision is {approximately}0.5% for {sup 239}Pu and {sup 240}Pu isotopic analyses and {approximately}1% for the plutonium concentration analysis. 5 refs., 2 figs., 7 tabs.

Li, T.K.; Parker, J.L. (Los Alamos National Lab., NM (United States)); Kuno, Y.; Sato, S.; Kamata, M.; Akiyama, T. (Power Reactor and Nuclear Fuel Development Corp., Tokai, Ibaraki (Japan))

1991-01-01

380

Gamma-ray Burst Monitor for the CALET Mission  

NASA Astrophysics Data System (ADS)

We propose to provide a gamma-ray burst monitor (GBM) for the CALET mission to monitor gamma-ray bursts (GRBs) simultaneously with the CALET main detector. The major purpose is to derive a wide-band energy spectrum of GRB over an unprecedented 9 decades of energy (from a few keV to 10 TeV) in combination with the CALET tower detector. Hence it is desirable to have the CALET-GBM covering an energy range from a few keV to about 20 MeV to avoid a gap in observational energy band. The design of GBM is underway to fulfill this requirement. The current detector candidate is LaBr3(Ce) scintillator which has a superior energy resolution to that of NaI(Tl). The design and expected performance of the CALET-GBM will be presented in this paper.

Yamaoka, K.; Yoshida, A.; Nakagawa, Y. E.; et al.

381

Seabed gamma-ray spectrometry: applications at IAEA-MEL.  

PubMed

The technique of underwater gamma-ray spectrometry has been developed to complement or replace the traditional sampling-sample analysis approach for applications with space-time constraints, e.g. large areas of investigation, emergency response or long-term monitoring. IAEA-MEL has used both high-efficiency NaI(Tl) and high-resolution HPGe spectrometry to investigate contamination with anthropogenic radionuclides in a variety of marine environments. Surveys at the South Pacific nuclear test sites of Mururoa and Fangataufa have been used to guide sampling in areas of high contamination around ground zero points. In the Irish Sea offshore from the Sellafield nuclear reprocessing plant, a gamma-ray survey of seabed sediment was carried out to obtain estimates of the distribution and subsequently, for the inventory of 137Cs in the investigated area. PMID:11379061

Osvath, I; Povinec, P P

2001-01-01

382

Solar gamma rays powered by secluded dark matter  

SciTech Connect

Secluded dark matter models, in which weakly interacting massive particles annihilate first into metastable mediators, can present novel indirect detection signatures in the form of gamma rays and fluxes of charged particles arriving from directions correlated with the centers of large astrophysical bodies within the Solar System, such as the Sun and larger planets. This naturally occurs if the mean free path of the mediator is in excess of the solar (or planetary) radius. We show that existing constraints from water Cerenkov detectors already provide a novel probe of the parameter space of these models, complementary to other sources, with significant scope for future improvement from high angular resolution gamma-ray telescopes such as Fermi-LAT. Fluxes of charged particles produced in mediator decays are also capable of contributing a significant solar system component to the spectrum of energetic electrons and positrons, a possibility which can be tested with the directional and timing information of PAMELA and Fermi.

Batell, Brian; Shang Yanwen [Perimeter Institute for Theoretical Physics, Waterloo, Ontario, N2J 2W9 (Canada); Pospelov, Maxim [Perimeter Institute for Theoretical Physics, Waterloo, Ontario, N2J 2W9 (Canada); Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, V8P 1A1 (Canada); Ritz, Adam [Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, V8P 1A1 (Canada)

2010-04-01

383

Experimental investigation of wavelength dependence of penetration depth and imaging contrast for ultrahigh-resolution optical coherence tomography  

NASA Astrophysics Data System (ADS)

Optical coherence tomography (OCT) is a non invasive optical imaging technology for micron-scale cross-sectional imaging of biological tissue and materials. Although OCT has many advantages in medical equipments, low penetration depth is a serious limitation for other applications. To realize the ultrahigh resolution and the high penetration depth at the same time, it is effective to choose the proper wavelength to maximize the light penetration and enhance the image contrast at deeper depths. Recently, we have demonstrated ultrahigh resolution and high penetration depth OCT by use of all-fiber based Gaussian shaped supercontinuum source at 1.7 ?m center wavelength. Gaussian-like supercontinuum with 360 nm bandwidth at center wavelength of 1.7 ?m was generated by ultrashort pulse Er doped fiber laser based system. In this paper, using 0.8 ?m and 1.3 ?m SC sources in addition to the 1.7 ?m SC source, we have investigated the wavelength dependence of ultrahigh resolution OCT in terms of penetration depth. Longitudinal resolutions at each wavelength region are almost 4.6 ?m in air. The obtained sensitivity was 95 dB for all wavelength regions. We confirmed the difference of imaging contrast and penetration depth with hamster's cheek pouch and so on. As the wavelength was increased, the magnitude of penetration depth was increased for these samples.

Ishida, S.; Nishizawa, N.; Itoh, K.

2011-02-01

384

Ultrahigh-resolution full-field optical coherence tomography using spatial coherence gating and quasi-monochromatic illumination.  

PubMed

We developed an ultrahigh-resolution full-field optical coherence tomography (FF-OCT) microscope that is based on the spatial, rather than the temporal, coherence gating. The microscope is capable of observing three-dimensional microbiological structures as small as 0.4 ?m × 0.4 ?m × 1.0 ?m (xyz) using quasi-monochromatic light and a liquid crystal retarder. Unlike traditional FF-OCT systems, this microscope can be operated in high resolution for any preferable wavelength with minimized defocusing and dispersion effects. High-resolution images of an onion cell are presented. PMID:22344072

Safrani, Avner; Abdulhalim, Ibrahim

2012-02-15

385

High-Definition and 3-dimensional Imaging of Macular Pathologies with High-speed Ultrahigh-Resolution Optical Coherence Tomography  

PubMed Central

Objective To assess high-speed ultrahigh-resolution optical coherence tomography (OCT) image resolution, acquisition speed, image quality, and retinal coverage for the visualization of macular pathologies. Design Retrospective cross-sectional study. Participants Five hundred eighty-eight eyes of 327 patients with various macular pathologies. Methods High-speed ultrahigh-resolution OCT images were obtained in 588 eyes of 327 patients with selected macular diseases. Ultrahigh-resolution OCT using Fourier/spectral domain detection achieves ~3-?m axial image resolutions, acquisition speeds of ~25 000 axial scans per second, and >3 times finer resolution and >50 times higher speed than standard OCT. Three scan protocols were investigated. The first acquires a small number of high-definition images through the fovea. The second acquires a raster series of high-transverse pixel density images. The third acquires 3-dimensional OCT data using a dense raster pattern. Three-dimensional OCT can generate OCT fundus images that enable precise registration of OCT images with the fundus. Using the OCT fundus images, OCT results were correlated with standard ophthalmoscopic examination techniques. Main Outcome Measures High-definition macular pathologies. Results Macular holes, age-related macular degeneration, epiretinal membranes, diabetic retinopathy, retinal dystrophies, central serous chorioretinopathy, and other pathologies were imaged and correlated with ophthalmic examination, standard OCT, fundus photography, and fluorescein angiography, where applicable. High-speed ultrahigh-resolution OCT generates images of retinal pathologies with improved quality, more comprehensive retinal coverage, and more precise registration than standard OCT. The speed preserves retinal topography, thus enabling the visualization of subtle changes associated with disease. High-definition high-transverse pixel density OCT images improve visualization of photoreceptor and pigment epithelial morphology, as well as thin intraretinal and epiretinal structures. Three-dimensional OCT enables comprehensive retinal coverage, reduces sampling errors, and enables assessment of 3-dimensional pathology. Conclusions High-definition 3-dimensional imaging using high-speed ultrahigh-resolution OCT improves image quality, retinal coverage, and registration. This new technology has the potential to become a useful tool for elucidating disease pathogenesis and improving disease diagnosis and management.

Srinivasan, Vivek J.; Wojtkowski, Maciej; Witkin, Andre J.; Duker, Jay S.; Ko, Tony H.; Carvalho, Mariana; Schuman, Joel S.; Kowalczyk, Andrzej; Fujimoto, James G.

2007-01-01

386

Gamma-ray astronomy: Promise for the future  

NASA Astrophysics Data System (ADS)

We are in a very active period in gamma-ray astronomy due primarily to new discoveries from the Compton Gamma Ray Observatory (CGRO). While the near future looks bright with the ESA INTEGRAL mission scheduled for launch in ~2001, there are currently no major missions being planned beyond INTEGRAL and none being planned at all by NASA. This paper reviews current missions and then looks beyond INTEGRAL to see what mission concepts are being considered. Based on new technologies that are under development such as Si strip detectors for tracking electron-positron pairs in high-energy instruments, CdZnTe strip detectors for fine spatial resolution of hard x-rays, and grazing incidence mirrors with multilayer coatings that work in the 10-100 keV range, several exciting new concepts for future instruments and missions are under study. These include intermediate class high-energy gamma-ray missions (30 MeV-300 GeV) with two order-of-magnitude better point-source sensitivity than the current EGRET instrument on CGRO, intermediate class focusing-optics hard x-ray missions with micro-Crab sensitivities (two order-of-magnitude better than the Rossi X-ray Timing Explorer), MIDEX class hard x-ray (10-200 keV) all-sky survey missions with much better sensitivity and angular resolution than previous surveys, and SMEX and MIDEX class gamma-ray burst missions that can locate bursts to arcsecond accuracies to allow deep counterpart searches at other wavelengths.

Gehrels, Neil; Macomb, Daryl

1997-01-01

387

Gamma-ray Emission from HMXBs  

NASA Astrophysics Data System (ADS)

During the last ten years, high-mass X-ray binaries (HMXB) have consolidated their status of gamma-ray sources. Even before the first EGRET detection candidates, HMXB seemed to be interesting sources to look for gamma rays, and study the processes giving rise to such an energetic photons. Presently, there is already a well established population of gamma-ray emittings HMXB found or confirmed by the current GeV and TeV instruments. These objects have turned out to be very efficient as accelerators, and also channelling the available energy budget into relativistic particles. Their emission is strongly variable and typically periodical, with a low-energy counterpart that is intimately related to the processes at the highest energies. In this talk, I will review the main processes associated to the production of gamma-rays in high-mass X-ray binaries.

Bosch-Ramon, Valenti

2012-07-01

388

Gamma Ray Bursts from Magnetospheric Plasma Oscillations.  

National Technical Information Service (NTIS)

Neutron star Magnetospheric Plasma Oscillations (MPO), can account for the energetics, decay time scale, and spectra of typical Gamma Ray Bursts (GRBs). The soft photon source is likely to be due to backwarming of the reprocessing boundary by the incipien...

F. Melia

1989-01-01

389

Neutron Detection Gamma Ray Sensitivity Criteria  

SciTech Connect

The shortage of 3He has triggered the search for effective alternative neutron detection technologies for national security and safeguards applications. Any new detection technology must satisfy two basic criteria: (1) it must meet a neutron detection efficiency requirement, and (2) it must be insensitive to gamma-ray interference at a prescribed level, while still meeting the neutron detection requirement. It is the purpose of this paper to define measureable gamma ray sensitivity criteria for neutron detectors. Quantitative requirements are specified for: intrinsic gamma ray detection efficiency and gamma ray absolute rejection. The ratio GARRn is defined, and it is proposed that the requirement for neutron detection be 0.9 < GARRn < 1.1 at a 10 mR/h exposure rate. An example of results from a 3He based neutron detector are provided showing that this technology can meet the stated requirements. Results from tests of some alternative technologies are also reported.

Kouzes, Richard T.; Ely, James H.; Lintereur, Azaree T.; Mace, Emily K.; Stephens, Daniel L.; Woodring, Mitchell L.

2011-10-21

390

GRAPE - The Gamma Ray Polarimeter Experiment  

NASA Astrophysics Data System (ADS)

We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), has been successfully demonstrated in the lab using partially polarized gamma-ray sources and using fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model was flown on a high altitude balloon flight to demonstrate the design and to collect background data. We are currently working on the development of a much larger balloon payload that would provide a significant level of sensitivity for gamma-ray bursts on a long-duration balloon flight and, if flown near solar max, would also provide significant sensitivity for solar flare polarization measurements. We shall review the history, status and future potential of the GRAPE project and summarize the potential for making polarization measurements of gamma-ray bursts and solar flares.

McConnell, Mark L.; Bloser, P. F.; Legere, J.; Ryan, J. M.; Connor, T.

2009-01-01

391

Do Gamma-ray Burst Sources Repeat.  

National Technical Information Service (NTIS)

The demonstration of repeated gamma-ray bursts from an individual source would severely constrain burst source models. Recent reports of evidence for repetition in the first BATSE burst catalog have generated renewed interest in this issue. Here, we analy...

C. A. Meegan D. H. Hartmann J. J. Brainerd M. Briggs W. S. Paciesas

1994-01-01

392

Radio counterparts of gamma-ray pulsars  

NASA Astrophysics Data System (ADS)

Observations of pulsars with the Large Area Telescope (LAT) on the Fermi satellite have revolutionized our view of the gamma-ray pulsar population. For the first time, a large number of young gamma-ray pulsars have been discovered in blind searches of the LAT data. More generally, the LAT has discovered many new gamma-ray sources whose properties suggest that they are powered by unknown pulsars. Radio observations of gamma-ray sources have been key to the success of pulsar studies with the LAT. For example, radio observations of LAT-discovered pulsars provide constraints on the relative beaming fractions, which are crucial for pulsar population studies. Also, radio searches of LAT sources with no known counterparts have been very efficient, with the discovery of over forty millisecond pulsars. I review radio follow-up studies of LAT-discovered pulsars and unidentified sources, and discuss some of the implications of the results.

Guillemot, L.

2013-03-01

393

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

394

Gamma-ray Burst Predictions for the Fermi Gamma Ray Space Telescope  

Microsoft Academic Search

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,

Truong Le; Charles D. Dermer

2009-01-01

395

Low-State Gamma-Ray Emission from Blazars and the Gamma-Ray Background  

Microsoft Academic Search

We examine the contribution of flat spectrum radio sources (FSRSs), or blazars, to the diffuse gamma-ray background (DGRB), prompted by the association of the extragalactic gamma -ray sources detected by the EGRET instrument aboard the Compton Gamma Ray Observatory (CGRO) with this class of objects by using their well-studied log N--log S distribution. The basic assumption of our study are

Demosthenes Kazanas; Eric Perlman

1997-01-01

396

Gamma-Ray Library and Uncertainty Analysis: Passively Emitted Gamma Rays Used in Safeguards Technology  

Microsoft Academic Search

Non-destructive gamma-ray analysis is a fundamental part of nuclear safeguards, including nuclear energy safeguards technology. Developing safeguards capabilities for nuclear energy will certainly benefit from the advanced use of gamma-ray spectroscopy as well as the ability to model various reactor scenarios. There is currently a wide variety of nuclear data that could be used in computer modeling and gamma-ray spectroscopy

2009-01-01

397

Fermi Gamma-ray Space Telescope Observations of Gamma-ray Pulsars  

Microsoft Academic Search

The Large Area Telescope on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST), with its large field of view and effective area, combined with its excellent timing capabilities, is poised to revolutionize the field of gamma-ray astrophysics. The large improvement in sensitivity over EGRET is expected to result in the discovery of many new gamma-ray pulsars, which in turn

P. M. Saz Parkinson

2009-01-01

398

Pair-Signatures and High-Energy Gamma-Ray Emission from Gamma-Ray Bursts  

Microsoft Academic Search

We discuss high-energy gamma-ray emission from gamma-ray bursts (GRBs). When such high-energy gamma rays are expected, e+\\/- pairs may play an important role both inside and outside the source. e+\\/- pair-signatures inside the source (the pair-annihilation bump and the cutoff due to the pair-creation process) are useful for diagnosing the fireball of GRBs. The recipes for diagnoses are largely model-independent

Kohta Murase; Kunihito Ioka; Shigehiro Nagataki

2008-01-01

399

Constraints on the Luminosity Function of Gamma-Ray Bursts from the Gamma Ray Background  

Microsoft Academic Search

The width of the gamma-ray burst (GRB) luminosity function is presently not well constrained. A wide luminosity function might be expected were GRBs associated with supernovae, for example. The possibility that a large number of undetected GRBs might make a contribution to the diffuse soft gamma-ray background is investigated. If gamma-ray bursts (GRBs) create supernova-like remnants, the width of the

H. Che

1999-01-01

400

Solar Two Gamma-Ray Observatory  

Microsoft Academic Search

The field of high energy gamma-ray astronomy grew tremendously in the last decade due to the launch of the EGRET detector on the Compton Gamma-Ray Observatory in 1991 and the proliferation of ground-based air ?herenkov telescopes (ACTs) such as the Whipple 10 meter reflector. Interestingly, the ground-based telescopes only see 4–5 of the over 170 objects detected by EGRET. A

T. Tümer; D. Bhattacharya; U. Mohideen; R. Rieben; V. Souchkov; H. Tom; J. Zweerink

1999-01-01

401

Gamma-Ray Burst Physics with GLAST  

Microsoft Academic Search

The Gamma-ray Large Area Space Telescope (GLAST), scheduled to be launched in late of 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT), the main instrument of GLAST, will survey the sky in the energy range between 20 MeV to more than 300 GeV, shedding light on many issues left open by its highly

Nicola Omodei

2007-01-01

402

A General Gamma-Ray Source Catalog  

NASA Astrophysics Data System (ADS)

The past several years have seen unprecedented growth in the field of gamma-ray astronomy. Highly successful missions such as the Compton Gamma-Ray Observatory (CGRO) have led to both a great increase in the number of detected gamma-ray sources and a more fundamental understanding of the basic physical processes involved for those sources. New ground-based observatories, the Rossi X-Ray Timing Explorer (RXTE), and the SIGMA instrument aboard the GRANAT spacecraft have all contributed to this explosion. Detailed observations of active galaxies, pulsars, accreting binaries, and diffuse emission have had a tremendous impact on our view of the universe. Given that new experiments that will provide a similar increase in source numbers are several years away, it is a good time to take inventory of the state of gamma-ray astronomy. To this end, we have developed a general gamma-ray point-source catalog containing 309 objects that summarize the field. Gamma-ray astronomy, as we define it, includes photon energies from 50 keV to about 1 TeV. While many catalogs concentrate on a single type of astronomical object and/or a very restricted energy range, the nature of this catalog is somewhat different. The large variety of objects and the many orders of magnitude in energy space covered by gamma-ray astronomy presents an organizational challenge. We focus on two main types of information: a general listing of the basic characteristics of each source, and detailed tables of a representative sample of high-energy observations. We also summarize the gamma-ray instruments whose observations are included in the catalog.

Macomb, D. J.; Gehrels, N.

1999-02-01

403

Gamma-Ray Bursts: the Four Crises  

Microsoft Academic Search

We discuss some open problems concerning the origin and the emission\\u000amechanism of gamma-ray bursts (GRBs) in light of recent developments. If GRBs\\u000aoriginate at extragalactic distances, we are facing four crises: (1) an energy\\u000acrisis, models have to account for more than 10^{53} ergs of energy emitted in\\u000athe gamma-ray energy band; (2) a spectral crisis, emission models have

Marco Tavani

1998-01-01

404

Gamma-Ray Bursts: the Four Crises  

Microsoft Academic Search

We discuss some open problems concerning the origin and the emission mechanism of gamma-ray bursts (GRBs) in light of recent developments. If GRBs originate at extragalactic distances, we are facing four crises: (1) an energy crisis, models have to account for more than 10^{53} ergs of energy emitted in the gamma-ray energy band; (2) a spectral crisis, emission models have

M. Tavani

1999-01-01

405

Swift's 500th Gamma Ray Burst  

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 can immediately conduct follow-up observations, and then study the burst using its X-ray and Ultraviolet/Optical telescopes. Some notable bursts are identified in the video.

Katherine Lewis

2010-04-19

406

Swift gamma-ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well a using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

Neil A. Gehrels

2000-01-01

407

Gamma Ray Bursts Cook Book I: Formulation  

Microsoft Academic Search

Since the suggestion of relativistic shocks as the origin of gamma-ray bursts\\u000a(GRBs) in early 90's, the mathematical formulation of this process has stayed\\u000aat phenomenological level. One of the reasons for the slow development of\\u000atheoretical works in this domain has been the simple power-law behaviour of the\\u000aafterglows hours or days after the prompt gamma-ray emission. Nowadays with

Houri Ziaeepour

2008-01-01

408

Swift: A gamma ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

2001-01-01

409

Classification of Swift's gamma-ray bursts  

Microsoft Academic Search

Context. Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 s. There are, however, some indications for the existence of a third class. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for gamma-ray bursts. Therefore we reanalyze the durations and their distribution and also the classi-

I. Horváth; L. G. Balázs; Z. Bagoly; P. Veres

2008-01-01

410

First Gamma Ray Burst Observations with Swift  

Microsoft Academic Search

Swift is a NASA Explorer mission that was launched on November 20, 2004. It is a multiwavelength observatory for transient astronomy. The goals of the mission are to determine the origin of gamma-ray bursts and their afterglows and use bursts to probe the early Universe. A wide-field gamma-ray camera will detect more than a hundred GRBs per year to 3

Neil Gehrels

2005-01-01

411

The swift gamma-ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

Neil Gehrels

2000-01-01

412

Gamma-ray bursts and Swift  

Microsoft Academic Search

Discovered by accident using satellites monitoring the nuclear test-ban treaty, gamma-ray bursts (GRBs) are the most powerful explosive events in the Universe. Several GRBs per day occur randomly on the sky, typically lasting a few seconds as a gamma-ray source. This abrupt burst is followed by emission across the entire electromagnetic spectrum which can last for several weeks or more.

Paul O'Brien; Julian Osborne; Keith Mason

2005-01-01

413

GeV gamma-ray sources  

NASA Astrophysics Data System (ADS)

We report on the preliminary extension of our work on cataloging the GeV sky to approximately 7 years of CGRO/EGRET observations with special emphasis on a search for transient sources. The search method and significance levels are presented. Our initial results on 13 possible transients indicate that 3 may be new gamma-ray sources. Sixteen new steady GeV sources are also detected, 3 of which have never been reported as gamma-ray sources. .

Lamb, R. C.; Macomb, D. J.

2000-06-01

414

Mining Gamma-Ray Burst Data  

Microsoft Academic Search

Gamma-ray bursts provide what is probably one of the messiest of all astrophysical data sets. Burst class properties are indistinct,\\u000a as overlapping characteristics of individual bursts are convolved with effects of instrumental and sampling biases. Despite\\u000a these complexities, data mining techniques have allowed new insights to be made about gamma-ray burst data. We demonstrate\\u000a how data mining techniques have simultaneously

Jon Hakkila; Richard J. Roiger; David J. Haglin; Robert S. Mallozzi; Geoffrey N. Pendleton; Charles A. Meegan

415

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

416

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

2008-01-01

417

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

418

Gamma-Ray Bursts from Minijets  

Microsoft Academic Search

Striking similarities exist between high-energy gamma-ray emission from active galactic nuclei (AGNs) and gamma-ray bursts (GRBs). They suggest that GRBs are generated by inverse Compton scattering from highly relativistic electrons in transient jets. Such jets may be produced along the axis of an accretion disk formed around stellar black holes (BHs) or neutron stars (NSs) in BH-NS and NS-NS mergers

Nir J. Shaviv; Arnon Dar

1995-01-01

419

Cataclysmic Variables and Gamma-Ray Sources  

NASA Astrophysics Data System (ADS)

The cataclysmic variables are associated with high energy events and probably many of them could be potential gamma-ray sources. Up to now Fermi-LAT detected 3 gamma-ray transients, which belong to CVs and related objects: V407 Cyg, N Sco 2012 and N Mon 2012 = V959 Mon. We present the first multicolour observations of the slow classical nova V959 Mon.

Pavlenko, E.; Malanushenko, V.; Shugarov, S.; Chochol, D.

2013-07-01

420

Observing Gamma-ray Bursts with GLAST  

Microsoft Academic Search

The Gamma-ray Large Area Telescope (GLAST) is a satellite-based observatory to study the high-energy gamma-ray sky. The Large Area Telescope, the main instrument, is a pair-conversion telescope which will survey the sky in the energy range 20 MeV to greater than 300 GeV. The LAT's wide field of view (>2; sr), large effective area and low deadtime combine to provide

Julie E. McEnery

2007-01-01

421

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

422

Observing cosmic nuclei in gamma rays  

NASA Astrophysics Data System (ADS)

Nucleosynthesis events in cosmic objects create new nuclei, admixtures of radioactive isotopes being part of the matter ejected into interstellar space by these events. Gamma rays are emitted in radioactive decays, and can be measured with space-based gamma-ray telescopes. Four mission years of INTEGRAL have led to discoveries of new sources and to detailed astronomical refinements of already-known gamma-ray line emission. As part of the main science objectives of INTEGRAL's spectrometer SPI, diffuse emission from annihilation of positrons has presented a new puzzle, as the Galactic distribution of their presumed sources does not agree with the gamma-ray image. Recent massive-star nucleosynthesis is traced throughout the Galaxy with radioactivites seen in 26Al and now also 60Fe gamma rays; precision line spectroscopy now reveals Doppler shifts for the 26Al line, separately for different parts of the Galaxy. This provides new insights into the dynamics of hot interstellar gas. The processes generating new atomic nuclei in stars and supernovae are reflected in the abundances of the ejected radioactivities. For individual supernovae, measurements of 44Ti with its 85 year decay time probes the symmetry of the supernova interior. Since such gamma-ray measurements probe the generation of new nuclei in cosmic sites through a radiation process which is independent of environmental parameters such as temperature or ionization, it will remain worthwhile to further develop instrumentation in this window to the nuclear-physics universe.

Diehl, Roland

2008-01-01

423

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

424

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

425

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

426

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

427

Correcting for the effects of natural abundance in stable isotope resolved metabolomics experiments involving ultra-high resolution mass spectrometry  

Microsoft Academic Search

BACKGROUND: Stable isotope tracing with ultra-high resolution Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) can provide simultaneous determination of hundreds to thousands of metabolite isotopologue species without the need for chromatographic separation. Therefore, this experimental metabolomics methodology may allow the tracing of metabolic pathways starting from stable-isotope-enriched precursors, which can improve our mechanistic understanding of cellular metabolism. However, contributions to the

Hunter N. B. Moseley

2010-01-01

428

Ultrahigh-resolution structure of high-potential iron-sulfur protein from Thermochromatium tepidum.  

PubMed

Crystals of the high-potential iron-sulfur protein (HiPIP) from Thermochromatium tepidum diffract X-rays to 0.80 A using synchrotron radiation at 100 K. The crystal structure of this HiPIP was refined at this ultrahigh resolution with anisotropic temperature factors for all atoms to conventional crystallographic R factors of 0.092 and 0.101 for F(o) > 4sigma(F(o)) and all reflections, respectively. The present structure provides a more precise picture than the previous 1.5 A structure and allows location of the positions of most H atoms. The structure revealed a partly hydrophobic cavity near the main hydrophobic area and a much larger inter-cluster approach distance (23.454 A, the c constant of the unit cell) in the crystal packing than other types of HiPIPs. The structural features involved in the electron-transfer reaction of HiPIP are discussed. PMID:12077426

Liu, Lijun; Nogi, Terukazu; Kobayashi, Masayuki; Nozawa, Tsunenori; Miki, Kunio

2002-06-20

429

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

SciTech Connect

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.

Ramirez, U.D.; Focia, P.J.; Freymann, D.M. (Fox Chase); (NWU)

2008-10-24

430

Imaging Retinal Capillaries Using Ultrahigh-Resolution Optical Coherence Tomography and Adaptive Optics  

PubMed Central

Purpose. Ultrahigh-resolution optical coherence tomography (UHR-OCT) with adaptive optics (AO) provides micrometer-scale 3D resolution that is attractive for imaging the retinal microvasculature. Such imaging may be useful for early detection of pathologic changes as in diabetic retinopathy. Here the authors investigate this potential for detecting individual capillaries in healthy subjects. Methods. UHR-AO-OCT volumes centered on the fovea were acquired from seven subjects (age range, 25–61 years) with three preselected with no foveal avascular zone (FAZ). Images were compared with entoptic diagrams using the capillaries at the rim of the FAZ. Methods of comparison were testing for the presence of a FAZ, noting distinct features in the capillary pattern, and measuring the size of the FAZ. Additional analysis included measurements of capillary diameter and depth range with retinal eccentricity. Results. UHR-AO-OCT results are consistent with entoptic observations for all three methods of comparison. FAZ diameters measured by UHR-AO-OCT and entoptic imaging are strongly correlated (R2 = 0.86). Average capillary diameter near the FAZ rim is 5.1 (4.6) ± 1.4 ?m, with the value in parentheses accounting for axial image blur. This is consistent with histology (average, ?4.7 ?m). Depth range of the capillaries increases monotonically with eccentricity (0°–1.25°) and is larger and more variable for subjects without FAZ. Conclusions. UHR-AO-OCT permits observation of many of the capillaries proximal to the FAZ, including those of average size based on published histology. This supports the view that the vast majority of capillaries in the retina are likely detectable with UHR-AO-OCT.

Kocaoglu, Omer P.; Cense, Barry; Bruestle, Jeremy; Jonnal, Ravi S.; Gao, Weihua; Miller, Donald T.

2011-01-01

431

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

432

Ultrahigh-resolution seismic reflection imaging of the Alpine Fault, New Zealand  

NASA Astrophysics Data System (ADS)

High-resolution seismic reflection surveys across active fault zones are capable of supplying key structural information required for assessments of seismic hazard and risk. We have recorded a 360 m long ultrahigh-resolution seismic reflection profile across the Alpine Fault in New Zealand. The Alpine Fault, a continental transform that juxtaposes major tectonic plates, is capable of generating large (M > 7.8) damaging earthquakes. Our seismic profile across a northern section of the fault targets fault zone structures in Holocene to late Pleistocene sediments and underlying Triassic and Paleozoic basement units from 3.5 to 150 m depth. Since ultrashallow seismic data are strongly influenced by near-surface heterogeneity and source-generated noise, an innovative processing sequence and nonstandard processing parameters are required to produce detailed information on the complex alluvial, glaciofluvial and glaciolacustrine sediments and shallow to steep dipping fault-related features. We present high-quality images of structures and deformation within the fault zone that extend and complement interpretations based on shallow paleoseismic and ground-penetrating radar studies. Our images demonstrate that the Alpine Fault dips 75°-80° to the southeast through the Quaternary sediments, and there is evidence that it continues to dip steeply between the shallow basement units. We interpret characteristic curved basement surfaces on either side of the Alpine Fault and deformation in the footwall as consequences of normal drag generated by the reverse-slip components of displacement on the fault. The fault dip and apparent ˜35 m vertical offset of the late Pleistocene erosional basement surface across the Alpine Fault yield a provisional dip-slip rate of 2.0 ± 0.6 mm/yr. The more significant dextral-slip rate cannot be determined from our seismic profile.

Kaiser, A. E.; Green, A. G.; Campbell, F. M.; Horstmeyer, H.; Manukyan, E.; Langridge, R. M.; McClymont, A. F.; Mancktelow, N.; Finnemore, M.; Nobes, D. C.

2009-11-01

433

Investigation of Nuclear Gamma Ray Line Emission Associated with Lightning  

NASA Astrophysics Data System (ADS)

The first conclusive observations of X-rays associated with thunderstorm activity were made in the 1980's and the prompt emission has been interpreted as bremsstrahlung produced by lightning-accelerated electrons. In 2004, Greenfield et al. reported the first detection of delayed gamma ray emission, with flux peaking 70 minutes after a lightning stroke and decaying exponentially over 50 minutes. They suggested the delayed gamma rays are a result of nuclear reactions in the atmosphere, creating excited Chlorine-39 and decaying with a 56-minute half-life. These results are compelling, but inconclusive; instrumentation capable of measuring the energy spectrum with high precision is necessary to confirm the existence of nuclear line emission associated with lightning. During June-September 2005, we used a spare RHESSI 7 cm-diameter segmented coaxial germanium spectrometer to continuously monitor gamma radiation on South Baldy Peak (10,800 ft) in New Mexico. The detector monitors gamma rays between ~18 keV-10 MeV with an energy resolution of ~2 keV@835 keV. South Baldy is the site of Langmuir Lab and was chosen to take advantage of other lightning research instrumentation located there, including New Mexico Tech's 3D Lightning Mapping Array (LMA) which can determine the location of a lightning stroke to within about 50m. We describe the experiment and present the initial results.

Boggs, S. E.; Millan, R. M.; Eack, K.; Aulich, G. D.

2005-12-01

434

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

435

Prompt gamma rays from thermal-neutron capture  

Microsoft Academic Search

A catalog of ..gamma..-rays emitted following thermal-neutron capture in natural elements is presented. In Table I, ..gamma..-rays are arranged in order of increasing energy. Each line contains the ..gamma..-ray energy, intensity, element identification, thermal-neutron radiative-capture cross section, and the energies and intensities of two of the more abundant ..gamma..-rays associated with that element. In Table II, ..gamma..-rays are arranged by

M. A. Lone; R. A. Leavitt; D. A. Harrison

1981-01-01

436

The Supernovae Associated with Gamma-Ray Bursts  

Microsoft Academic Search

Supernovae were long suspected as possible progenitors of gamma-ray bursts. The arguments relied on circumstantial evidence. Several recent gamma-ray bursts, notably GRB 030329, have provided direct, spectroscopic evidence that supernovae and gamma-ray bursts are related. The supernovae associated with gamma-ray bursts are all of Type Ic, implying a compact progenitor, which has implications for gamma-ray burst models. Other peculiar Type

T. Matheson

2005-01-01

437

The 1979 March 5 gamma-ray transient: Was it a classic gamma-ray burst?  

Microsoft Academic Search

The 1979 March 5 gamma-ray transient has long been thought to be fundamentally different from the classic gamma-ray bursts (GRBs). It had recurrences, pulsations, and a soft spectral component unlike classic GRBs. With the exception of the soft component reported from the KONUS experiment, the unusual characteristics of the March 5 transient were detectable primarily because it was extremely bright.

E. E. Fenimore; R. W. Klebesadel; J. G. Laros

1996-01-01

438

The 1979 March 5 Gamma-Ray Transient: Was It a Classic Gamma-Ray Burst?  

Microsoft Academic Search

The 1979 March 5 gamma-ray transient has long been thought to be fundamentally different from the classic gamma-ray bursts (GRBs). It had recurrences, pulsations, and a soft spectral component unlike classic GRBs. With the exception of the soft component reported from the KONUS experiment, the unusual characteristics of the March 5 transient were detectable primarily because it was extremely bright.

E. E. Fenimore; R. W. Klebesadel; J. G. Laros

1996-01-01

439

Low energy {gamma}-rays scintillation detection with large area avalanche photodiodes  

SciTech Connect

Energy resolution of NaI(Tl), CsI(Tl), LSO and YAP crystals coupled to 16 mm diameter Large Area Avalanche Photodiodes (LAAPD) was studied for low energy {gamma}-rays. Energy resolutions of 11.3% and 8.4% were obtained for 59.6 keV {gamma}-rays from {sup 241}Am and 122 keV {gamma}-rays from {sup 57}Co sources, respectively, as measured with a 10 mm diameter by 10 mm high NaI(Tl) crystal. The optimization of the LAAPD performance is presented, being essential for improvement of energy resolution at low energy {gamma}-rays. Measured numbers of primary electron-hole pairs produced in LAAPDs and evaluation of noise contribution of these devices allowed for quantitative discussion of the results. Particularly, the intrinsic energy resolution of the crystals vs. energy of {gamma}-rays has been evaluated. Obtained data for NaI(Tl) crystal showed a good agreement (within 30%) with calculated component due to nonproportional light yield for energies above 50 keV.

Moszynski, M.; Kapusta, M.; Zalipska, J.; Balcerzyk, M.; Wolski, D. [Soltan Inst. for Nuclear Studies, Swierk-Otwock (Poland); Szawlowski, M. [Advanced Photonix, Inc., Camarillo, CA (United States); Klamra, W. [Royal Inst. of Tech., Stockholm (Sweden). Dept. of Physics

1999-08-01

440

Searching for Gamma-ray Pulsars using the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope  

Microsoft Academic Search

The Large Area Telescope (LAT) on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST) has greatly increased the sensitivity to astrophysical gamma-ray sources over previous gamma-ray telescope missions such as the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory (CGRO). The LAT has a much larger effective area and field of view, helping to increase the

Michael Dormody

2009-01-01

441

Hand-Held Gamma-Ray Imaging Sensors Using Room-Temperature 3-Dimensional Position-Sensitive Semiconductor Spectrometers  

NASA Astrophysics Data System (ADS)

This paper demonstrates the capability of compact gamma-ray imaging devices using 3-dimensional position sensitive CdZnTe semiconductor gamma-ray spectrometers, developed at the University of Michigan. A prototype imager was constructed and tested using two 1 cm cube 3-dimensional position sensitive CdZnTe detectors. Energy resolutions of 1.5% FWHM for single pixel events at 662 keV gamma-ray energy were obtained on both detectors, and an angular resolution of about 5° FWHM was demonstrated. The capabilities of proposed devices, which can cover a wider energy range up to 2.6 MeV, are discussed.

He, Zhong; Lehner, Carolyn; Zhang, Feng; Wehe, David K.; Knoll, Glenn F.; Berry, James; Du, Yanfeng

2002-10-01

442

Luminosity Evolution of Gamma-Ray Pulsars  

NASA Astrophysics Data System (ADS)

We investigate the electrodynamic structure of a pulsar outer-magnetospheric particle accelerator and the resulting gamma-ray emission. By considering the condition for the accelerator to be self-sustained, we derive how the trans-magnetic-field thickness of the accelerator evolves with the pulsar age. It is found that the thickness is small but increases steadily if the neutron-star envelope is contaminated by sufficient light elements. For such a light element envelope, the gamma-ray luminosity of the accelerator is kept approximately constant as a function of age in the initial 10,000 yr, forming the lower bound of the observed distribution of the gamma-ray luminosity of rotation-powered pulsars. If the envelope consists of only heavy elements, on the other hand, the thickness is greater, but it increases less rapidly than a light element envelope. For such a heavy element envelope, the gamma-ray luminosity decreases relatively rapidly, forming the upper bound of the observed distribution. The gamma-ray luminosity of a general pulsar resides between these two extreme cases, reflecting the envelope composition and the magnetic inclination angle with respect to the rotation axis. The cutoff energy of the primary curvature emission is regulated below several GeV even for young pulsars because the gap thickness, and hence the acceleration electric field, is suppressed by the polarization of the produced pairs.

Hirotani, Kouichi

2013-04-01

443

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 (˜1014 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

444

Gamma-ray Emission in GPS Quasars  

NASA Astrophysics Data System (ADS)

In this paper, it is argued that the relativistic jets in gigahertz peaked spectrum (GPS) quasars are oriented at small angle to the line of sight and are powerful gamma-ray sources. Besides luminous hard gamma-ray emission, most of them may have significant soft gamma-ray and X-ray emission due to infrared photons from very dense and dusty nuclear interstellar media in GPS quasars, which is consistent with ASCA X-ray observations. Because Compton cooling in GPS quasars is stronger than in flat spectrum radio quasars (FSRQs), synchrotron emission in GPS quasars may less dominate over thermal emission of the accretion disk and hot dust than in FSRQs, hence most GPS quasars show low optical polarization and small variability. We suggest that it is the significant radio emission of electron/positron pairs produced by the interaction of gamma-rays with the dense gas and dust grains in GPS quasars that makes GPS quasars show steep radio spectra, low radio polarization, and relatively faint VLBI/VLBA cores. The gamma-ray emission in GPS quasars can be tested by the observation of the INTEGRAL and GLAST in the near future.

Bai, Jin-Ming

2005-06-01

445

Simulated Performance of the Nuclear Compton Telescope as a Gamma-Ray Polarimeter  

NASA Astrophysics Data System (ADS)

The Nuclear Compton Telescope (NCT) is a balloon-borne soft gamma-ray (0.2-10 MeV) telescope designed to study astrophysical sources of nuclear line emission and gamma-ray polarization. NCT is sensitive to polarization in the range 0.2-1 MeV. NCT consists of 3D position-sensitive germanium strip detectors. The ultra-compact design and new technologies allow NCT to achieve high efficiencies with excellent spectral resolution and background reduction. We are currently preparing a balloon flight of the NCT instrument in New Mexico in September 2008. For studying the gamma-ray polarization capability of NCT during the upcoming balloon flight, detailed Monte Carlo simulations of sources predicted to be polarized in the MeV regime (the Crab nebula, Crab pulsar, and gamma-ray bursts) and of the expected background were performed with the MGGPOD suite. The data analysis, including event reconstruction and polarization analysis, was performed by using the Medium Energy Gamma-ray Astronomy library (MEGAlib). Here we present the results of our Crab and gamma-ray burst simulations and discuss the NCT performance as a polarimeter.

Liang, Jau-Shian; Bellm, E. C.; Boggs, S. E.; NCT Collaboration

2008-03-01

446

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

447

Celestial Gamma Ray Bursts Detector Development and Model Simulations  

NASA Astrophysics Data System (ADS)

Celestial gamma-ray bursts are a poorly understood astrophysical phenomenon. These transient events were discovered over twenty years ago, yet their origin is still an unsolved mystery. At present no quiescent counterpart to a gamma ray burst source has been conclusively identified, partly because the poor angular resolution of gamma ray detectors and the short durations of the bursts make it difficult to determine precise source positions. (A few precise source positions have been determined by analysis of burst arrival times at widely separated detectors.) The High Energy Transient Experiment (HETE), described by Ricker, et al. (1992), is a new gamma ray astronomy satellite designed to overcome these difficulties. It can determine precise source positions by simultaneously observing a gamma ray burst with gamma ray x-ray, and ultraviolet (UV) instruments and utilizing the better angular resolutions available with the x-ray and UV instruments. In the first part of this dissertation I present experimental research which contributes to the development of a UV-sensitive solid-state imaging detector for the HETE satellite. The detector is a thinned, backside-illuminated charge-coupled device (CCD). The UV quantum efficiency (QE) is very sensitive to the results of the back-surface treatment, which stabilizes and protects that surface. As part of the detector development I designed and built an instrument to measure the quantum efficiency of a CCD over the wavelength range of 200--500~nm. With this instrument I measured the QE of seven prototype devices that were manufactured with three different back-surface technologies. I derived a statistical test to measure the mean number of electrons per photon, which increases from unity with increasing photon energy above a threshold of ~3.65~eV (340 nm). This effect is critically important when making photometric measurements at these wavelengths with solid state detectors. I also developed a simple physically-motivated model of the back surface, which provides adequate fits to the measured QE. I find that the best back-surface technology yields CCDs that have stable QEs of >40\\% in the HETE UV band of 220-310 nm. This is significantly better than the QE of 20% required by the HETE UV instrument (Ricker, et al. 1992). This encouraging result enhances the ability of the HETE UV instrument to detect a gamma-ray burst, which will ultimately lead to the discovery of the underlying physical sources. While the origin of gamma-ray bursts is unknown, the rapid variability and hard spectra indicate that the sources are compact objects. Many different models of gamma-ray bursts assume that the bursts originate from neutrons stars. Blaes, et al. (1990) put forth the idea that the natural evolution of a slowly-accreting, isolated neutron star leads to the formation of density inversions which might become unstable and thereby lead to a gamma-ray burst. However, the recent measurements of the gamma-ray burst distribution reported by Meegan, et al. (1992) rule out many galactic models. Recent theoretical work is split between galactic halo models and cosmological models, many of which still associate gamma-ray bursts with neutron stars. In any event, slowly-accreting neutron stars should exist in the galaxy. Their evolution is the focus of the second part of this dissertation. I present computational research on the evolution of this class of slowly