These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

[Effect of Saccharomyces cerevisiae RAD54 mutation on gamma ray-induced reciprocal mitotic recombination].  

PubMed

The effect of gamma-irradiation on mitotic segregation and intergenic reciprocal mitotic recombination between the centromere and the ade2 locus of rad sensitive Saccharomyces mutant has been studied in comparison with the wild type RAD. These strains homozygous for either RAD or rad54 gene, showed gamma-rays induced mitotic segregation and reciprocal mitotic recombination. Within a dose range resulting in an equal survival, fraction induced mitotic segregation and intergenic reciprocal recombination was greater for the RAD strain. Rad54 mutation increased the spontaneous mitotic segregation and mitotic reciprocal recombination in comparison with the rad strain. PMID:7007162

Kasinova, G V

1980-01-01

2

Did Gamma Ray Burst Induce Cambrian Explosion?  

E-print Network

One longstanding mystery in bio-evolution since Darwin's time is the origin of the Cambrian explosion that happened around 540 million years ago (Mya), where an extremely rapid increase of species occurred. Here we suggest that a nearby GRB event ~500 parsecs away, which should occur about once per 5 Gy, might have triggered the Cambrian explosion. Due to a relatively lower cross section and the conservation of photon number in Compton scattering, a substantial fraction of the GRB photons can reach the sea level and would induce DNA mutations in organisms protected by a shallow layer of water or soil, thus expediting the bio-diversification. This possibility of inducing genetic mutations is unique among all candidate sources for major incidents in the history of bio-evolution. A possible evidence would be the anomalous abundance of certain nuclear isotopes with long half-lives transmuted by the GRB photons in geological records from the Cambrian period. Our notion also imposes constraints on the evolution of ...

Chen, Pisin

2014-01-01

3

The measurement of gamma ray induced heating in a mixed neutron and gamma ray environment  

SciTech Connect

The problem of measuring the gamma heating in a mixed DT neutron and gamma ray environment was explored. A new detector technique was developed to make this measurement. Gamma heating measurements were made in a low-Z assembly irradiated with 14-Mev neutrons and (n, n{prime}) gammas produced by a Texas Nuclear Model 9400 neutron generator. Heating measurements were made in the mid-line of the lattice using a proportional counter operating in the Continuously-varied Bias-voltage Acquisition mode. The neutron-induced signal was separated from the gamma-induced signal by exploiting the signal rise-time differences inherent to radiations of different linear energy transfer coefficient, which are observable in a proportional counter. The operating limits of this measurement technique were explored by varying the counter position in the low-Z lattice, hence changing the irradiation spectrum observed. The experiment was modelled numerically to help interpret the measured results. The transport of neutrons and gamma rays in the assembly was modelled using the one- dimensional radiation transport code ANISN/PC. The cross-section set used for these calculations was derived from the ENDF/B-V library using the code MC{sup 2}-2 for the case of DT neutrons slowing down in a low-Z material. The calculated neutron and gamma spectra in the slab and the relevant mass-stopping powers were used to construct weighting factors which relate the energy deposition in the counter fill-gas to that in the counter wall and in the surrounding material. The gamma energy deposition at various positions in the lattice is estimated by applying these weighting factors to the measured gamma energy deposition in the counter at those locations.

Chiu, H.K.

1991-10-01

4

Molecular analysis of point mutations in a barley genome exposed to MNU and gamma rays.  

PubMed

We present studies aimed at determining the types and frequencies of mutations induced in the barley genome after treatment with chemical (N-methyl-N-nitrosourea, MNU) and physical (gamma rays) mutagens. We created M(2) populations of a doubled haploid line and used them for the analysis of mutations in targeted DNA sequences and over an entire barley genome using TILLING (Targeting Induced Local Lesions in Genomes) and AFLP (Amplified Fragment Length Polymorphism) technique, respectively. Based on the TILLING analysis of the total DNA sequence of 4,537,117bp in the MNU population, the average mutation density was estimated as 1/504kb. Only one nucleotide change was found after an analysis of 3,207,444bp derived from the highest dose of gamma rays applied. MNU was clearly a more efficient mutagen than gamma rays in inducing point mutations in barley. The majority (63.6%) of the MNU-induced nucleotide changes were transitions, with a similar number of G>A and C>T substitutions. The similar share of G>A and C>T transitions indicates a lack of bias in the repair of O(6)-methylguanine lesions between DNA strands. There was, however, a strong specificity of the nucleotide surrounding the O(6)-meG at the -1 position. Purines formed 81% of nucleotides observed at the -1 site. Scanning the barley genome with AFLP markers revealed ca. a three times higher level of AFLP polymorphism in MNU-treated as compared to the gamma-irradiated population. In order to check whether AFLP markers can really scan the whole barley genome for mutagen-induced polymorphism, 114 different AFLP products, were cloned and sequenced. 94% of bands were heterogenic, with some bands containing up to 8 different amplicons. The polymorphic AFLP products were characterised in terms of their similarity to the records deposited in a GenBank database. The types of sequences present in the polymorphic bands reflected the organisation of the barley genome. PMID:23085094

Kurowska, Marzena; Labocha-Paw?owska, Anna; Gnizda, Dominika; Maluszynski, Miroslaw; Szarejko, Iwona

2012-01-01

5

Determination of the elemental distribution in a sample using neutron induced gamma-ray emission tomography  

Microsoft Academic Search

The factors that affect accurate, quantitative results to be obtained by neutron induced gamma-ray emission tomography are stated. The technique, which is a combination of neutron activation analysis with computerised gamma-ray emission tomography, would be enhanced by the use of multiple detector assemblies, in geometrical configurations, which simultaneously record the gamma-rays emitted and improve detection efficiency. Developments in the past

N. M. Spyrou; J. M. Sharaf; S. Rajeswaran; E. Mesbahi

1997-01-01

6

Radiation-Induced Carcinogenesis: Mechanistically Based Differences between Gamma-Rays and Neutrons, and  

E-print Network

Radiation-Induced Carcinogenesis: Mechanistically Based Differences between Gamma-Rays and Neutrons: Mechanistically Based Differences between Gamma-Rays and Neutrons, and Interactions with DMBA. PLoS ONE 6(12): e dose/dose rate. Sparsely ionizing radiation (e.g. c-rays) generally produces linear or upwardly curving

Brenner, David Jonathan

7

Lymphocytes from wasted mice express enhanced spontaneous and {gamma}-ray-induced apoptosis  

SciTech Connect

Mice bearing the autosomal recessive mutation wasted (wst/wst) display a disease pattern including faulty repair of DNA damage in lymphocytes after radiation exposure, neurologic abnormalities, and immunodeficiency. Many of the features of this mouse model have suggested a premature or increased spontaneous frequency of apoptosis in thymocytes; past work has shown an inability to establish cultured T cell lines, an abnormally high death rate of stimulated T cells in culture, and an increased sensitivity of T cells to the killing effects of ionizing radiations in wst/wst mice relative to controls. The experiments reported here were designed to examine splenic and thymic lymphocytes from wasted and control mice for signs of early apoptosis. Our results revealed enhanced expression of Rp-8 mRNA (associated with apoptosis) in thymic lymphocytes and reduced expression in splenic lymphocytes of wst/wst mice relative to controls; expression of Rp-2 and Td-30 mRNA (induced during apoptosis) were not detectable in spleen or thymus. Higher spontaneous DNA fragmentation was observed in wasted mice than in controls; however, {gamma}-ray-induced DNA fragmentation peaked at a lower dose and occurred to a greater extent in wasted mice relative to controls. These results provide evidence for high spontaneous and {gamma}-ray-induced apoptosis in T cells of wasted mice as a mechanism underlying the observed lymphocyte and DNA repair abnormalities.

Woloschak, G.E. [Argonne National Lab., IL (United States)]|[Loyola Univ. Medical Center, Maywood, IL (United States); Chang-Liu, Chin-Mei [Argonne National Lab., IL (United States); Chung, Jen; Libertin, C.R. [Loyola Univ. Medical Center, Maywood, IL (United States)

1993-09-01

8

A revisit of mutation induction by gamma rays in rice ( Oryza sativa L . ): implications of microsatellite markers for quality control  

Microsoft Academic Search

Mutation techniques have been used for generating genetic variation and breeding new varieties during the past decades. However,\\u000a the skepticism has also persisted during the course on the sole mutational origin of genetic variation in mutated populations.\\u000a We addressed this issue using three unique rice genetic lines in this study. First, we confirmed that gamma rays had significant\\u000a effect on

Hao-Wei Fu; You-Fa Li; Qing-Yao Shu

2008-01-01

9

Detection of pulsed, bremsstrahlung-induced, prompt neutron capture gamma-rays with HPGe detector  

SciTech Connect

The Idaho National Engineering Laboratory (INEL) is developing a novel photoneutron-based nondestructive evaluation technique which uses a pulsed, high-energy (up to 8-MeV) electron accelerator and gamma-ray spectrometry. Highly penetrating pulses of bremsstrahlung photons are produced by each pulse of electrons. Interrogating neutrons are generated by the bremsstrahlung photons interacting within a photoneutron source material. The interactions of the neutrons within a target result in the emission of elemental characteristic gamma-rays. Spectrometry is performed by analyzing the photoneutron-induced prompt gamma-rays acquired between accelerator pulses with a unique, high-purity germanium (HPGe) gamma-ray detection system using a modified transistor reset preamplifier. The detection system, the experimental configuration, and the accelerator operation used to characterize the detection system performance are described. Using a 6.5 MeV electron accelerator and a beryllium metal photoneutron source, gamma-ray spectra were successfully acquired for Al, Cu, polyethylene, NaC1, and depleted uranium targets as soon as 30 {mu}s after each bremsstrahlung (or x-ray) flash.

Jones, J.L.

1996-08-01

10

a Model-Independent Method to Study Dark Matter Induced Leptons and Gamma Rays  

NASA Astrophysics Data System (ADS)

By using recent data, we directly determine the dark matter (DM)-induced e± spectrum at the source from experimental measurements at the earth, without reference to specific particle physics models. The DM-induced gamma rays emitted via inverse Compton scattering are then obtained in a model-independent way. However, the results depend on the choice of the astrophysical e± background, which is not reliably known. Nevertheless, we calculate, as an illustration, the fluxes of gamma rays from the Fornax cluster in the decaying DM scenario with various astrophysical e± backgrounds. Without any assumptions on details of the DM model, the predictions turn out to be either in disagreement with or only marginally below the upper limits measured recently by the Fermi-LAT Collaboration. In addition, these DM-induced ICS gamma rays in the GeV range are shown to be almost independent of choices of cosmic ray propagation model and of DM density profile, when a given astrophysical e± background is assumed. This provides a strong constraint on decaying DM scenario as the gamma rays may be produced in other processes besides inverse Compton scattering, such as the bremsstrahlung and neutral pion decays.

Luo, Mingxing; Wang, Liucheng; Zhu, Guohuai

2012-11-01

11

Hepatocyte growth factor protects endothelial cells against gamma ray irradiation-induced damage  

PubMed Central

Aim: To investigate the effect of HGF on proliferation, apoptosis and migratory ability of human vascular endothelial cells against gamma ray irradiation. Methods: ECV304 cells derived from adult human umbilical vein endothelial cells (HUVEC) were irradiated with a single gamma ray dose of 20 Gy. Immunocytochemistry and Western blot analysis were used to detect c-Met protein expression and HGF/c-Met signal pathway. In the HGF-treated groups, ECV304 cells were incubated with HGF (20 or 40 ng/mL) 3 h prior to irradiation. At 48 h post-irradiation, the proliferation of ECV304 cells was measured by MTT assay, the apoptosis was assessed by flow cytometry, and the migratory ability of ECV304 cells was measured by transwell chamber assay. Results: c-Met protein is expressed in ECV304 cells and can be activated by HGF. Gamma ray irradiation inhibits proliferation and migration of ECV304 cells in a dose-dependent manner. HGF significantly promoted the proliferation of ECV304 cells, and flow cytometry revealed that HGF can inhibit apoptosis of ECV304 cells. Transwell chamber assay also showed that HGF increases migration activity of endothelial cells. Conclusion: HGF may afford protection to vascular endothelial cells against gamma ray irradiation-induced damage. PMID:19749787

Hu, Shun-ying; Duan, Hai-feng; Li, Qing-fang; Yang, Yue-feng; Chen, Jin-long; Wang, Li-sheng; Wang, Hua

2009-01-01

12

Analysis of evolution of gamma-ray emission induced by MeV ions in JET  

Microsoft Academic Search

The paper investigates the temporal evolution of gamma-ray emission induced by nuclear reactions between energetic D-T fusion-born alpha particles with beryllium impurity ions in JET plasmas, 9Be(alpha, ngamma)12C. During and after tritium NBI blips into JET deuterium plasmas there occurs a delay between alpha production and gamma-emission. The delay time observed renders possible the assessment of alpha transport, e.g. loss

V. Yavorskij; V. Kiptily; C. Challis; V. Goloborod'ko; L. G. Eriksson; N. Hawkes; P. Neururer; S. Reznik; K. Schoepf; S. E. Sharapov; D. Stork; I. Voitsekhovitch; K.-D. Zastrow; JET-EFDA contributors

2010-01-01

13

Copolymerization of Styrene onto Polyethersulfone Films Induced By Gamma Ray Irradiation  

Microsoft Academic Search

Summary  Radiation-induced grafting of styrene into polyethersulfone (PES) films were investigated by simultaneous method in solution\\u000a using gamma-ray from a radio nuclide 60Co source. The starting materials were prepared via casting method of the polymeric solution. The grafted membranes have side\\u000a chains of polystyrene which may be sulfonated to become proton conductive to be used as polymer electrolyte membrane in fuel

A. A. M. Furtado Filho; A. S. Gomes

2006-01-01

14

Search for Neutrino-induced Cascades from Gamma-Ray Bursts with AMANDA  

Microsoft Academic Search

Using the neutrino telescope AMANDA-II, we have conducted two analyses searching for neutrino-induced cascades from gamma-ray bursts. No evidence of astrophysical neutrinos was found, and limits are presented for several models. We also present neutrino effective areas which allow the calculation of limits for any neutrino production model. The first analysis looked for a statistical excess of events within a

A. Achterberg; M. Ackermann; J. Adams; J. Ahrens; K. Andeen; J. Auffenberg; J. N. Bahcall; X. Bai; B. Baret; S. W. Barwick; R. Bay; K. Beattie; T. Becka; J. K. Becker; K.-H. Becker; P. Berghaus; D. Berley; E. Bernardini; D. Bertrand; D. Z. Besson; E. Blaufuss; D. J. Boersma; C. Bohm; J. Bolmont; S. Böser; O. Botner; A. Bouchta; J. Braun; C. Burgess; T. Burgess; T. Castermans; D. Chirkin; B. Christy; J. Clem; D. F. Cowen; M. V. D'Agostino; A. Davour; C. T. Day; C. De Clercq; L. Demirörs; F. Descamps; P. Desiati; T. De Young; J. C. Diaz-Velez; J. Dreyer; J. P. Dumm; M. R. Duvoort; W. R. Edwards; R. Ehrlich; J. Eisch; R. W. Ellsworth; P. A. Evenson; O. Fadiran; A. R. Fazely; K. Filimonov; M. M. Foerster; B. D. Fox; A. Franckowiak; T. K. Gaisser; J. Gallagher; R. Ganugapati; H. Geenen; L. Gerhardt; A. Goldschmidt; J. A. Goodman; R. Gozzini; T. Griesel; S. Grullon; A. Groß; R. M. Gunasingha; M. Gurtner; A. Hallgren; F. Halzen; K. Han; K. Hanson; D. Hardtke; R. Hardtke; J. E. Hart; Y. Hasegawa; T. Hauschildt; D. Hays; J. Heise; K. Helbing; M. Hellwig; P. Herquet; G. C. Hill; J. Hodges; K. D. Hoffman; B. Hommez; K. Hoshina; D. Hubert; B. Hughey; P. O. Hulth; K. Hultqvist; J.-P. Hülß; S. Hundertmark; M. Inaba; A. Ishihara; J. Jacobsen; G. S. Japaridze; H. Johansson; A. Jones; J. M. Joseph; K.-H. Kampert; T. Karg; A. Karle; H. Kawai; J. L. Kelley; N. Kitamura; S. R. Klein; S. Klepser; G. Kohnen; H. Kolanoski; L. Köpke; M. Kowalski; T. Kowarik; M. Krasberg; K. Kuehn; M. Labare; H. Landsman; H. Leich; D. Leier; I. Liubarsky; J. Lundberg; J. Lünemann; J. Madsen; K. Mase; H. S. Matis; T. McCauley; C. P. McParland; A. Meli; T. Messarius; P. Mészáros; H. Miyamoto; A. Mokhtarani; T. Montaruli; A. Morey; R. Morse; S. M. Movit; K. Münich; R. Nahnhauer; J. W. Nam; P. Nießen; D. R. Nygren; H. Ögelman; A. Olivas; S. Patton; C. Peña-Garay; C. Pérez de los Heros; A. Piegsa; D. Pieloth; A. C. Pohl; R. Porrata; J. Pretz; P. B. Price; G. T. Przybylski; K. Rawlins; S. Razzaque; E. Resconi; W. Rhode; M. Ribordy; A. Rizzo; S. Robbins; P. Roth; C. Rott; D. Rutledge; D. Ryckbosch; H.-G. Sander; S. Sarkar; S. Schlenstedt; T. Schmidt; D. Schneider; D. Seckel; B. Semburg; S. H. Seo; S. Seunarine; A. Silvestri; A. J. Smith; M. Solarz; C. Song; J. E. Sopher; G. M. Spiczak; C. Spiering; M. Stamatikos; T. Stanev; P. Steffen; T. Stezelberger; R. G. Stokstad; M. C. Stoufer; S. Stoyanov; E. A. Strahler; T. Straszheim; K.-H. Sulanke; G. W. Sullivan; T. J. Sumner; I. Taboada; O. Tarasova; A. Tepe; L. Thollander; S. Tilav; M. Tluczykont; P. A. Toale; D. Turcan; N. van Eijndhoven; J. Vandenbroucke; A. Van Overloop; V. Viscomi; B. Voigt; W. Wagner; C. Walck; H. Waldmann; M. Walter; Y.-R. Wang; C. Wendt; C. H. Wiebusch; G. Wikström; D. R. Williams; R. Wischnewski; H. Wissing; K. Woschnagg; X. W. Xu; G. Yodh; S. Yoshida; J. D. Zornoza

2007-01-01

15

Proton-induced X-ray and gamma ray emission analysis of biological samples  

NASA Astrophysics Data System (ADS)

A 4.1 MeV external proton beam was employed to simultaneously induce X-ray emission (PIXE) and gamma ray emission (PIGE) in biological samples that included human colostrum, spermatozoa, teeth, tree-rings, and follicular fluids. The analytical method was developed to simultaneously determine the elements lithium (Z = 3) through uranium (Z = 92) in the samples. PIXE-PIGE experimental design is described as well as applications in environmental and medical fields.

Hall, Gene S.; Navon, Eliahu

1986-04-01

16

Changes in optical transmission caused by gamma ray induced coloring in photoluminescence dosimeter.  

PubMed

Transmission of visible light and ultraviolet radiation was examined for a phosphate-glass photoluminescence dosimeter irradiated with Co source gamma rays in the dose range of 1-60 Gy (H2O). The transmission for the wavelengths (lambda) less than 600 nm decreased with increasing irradiation dose beginning at 6 Gy. An approximate 20% reduction of transmission was observed for a 60 Gy exposure at the wavelength of ultraviolet radiation used for excitation (lambda = 337 nm). However, no change of transmission was seen in longer wavelength region (lambda > 600 nm), which includes the range of photoluminescence (lambda = 610-710 nm). Relative efficiencies of measured photoluminescence agreed well with estimations that were calculated from the transmission reduction of ultraviolet radiation. This fact indicates that reduction of photoluminescence efficiency induced by high-dose gamma rays is attributable mostly to attenuation of the ultraviolet radiation from an excitation source, rather than saturation of trapping or recombination centers. PMID:16691104

Yasuda, Hiroshi; Takami, Michiko; Ishidoya, Tatsuyo

2006-06-01

17

Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses  

SciTech Connect

High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90 Degree-Sign collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF{sub 2} scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF{sub 2} scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

Taira, Y.; Toyokawa, H.; Kuroda, R. [Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568 (Japan); Yamamoto, N. [Nagoya University Synchrotron Radiation Research Center, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8603 (Japan); Adachi, M.; Tanaka, S.; Katoh, M. [UVSOR, Institute for Molecular Science, National Institutes of Natural Sciences, Myodaiji-cho, Okazaki, Aichi 444-8585 (Japan)

2013-05-15

18

Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses.  

PubMed

High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured. PMID:23742543

Taira, Y; Toyokawa, H; Kuroda, R; Yamamoto, N; Adachi, M; Tanaka, S; Katoh, M

2013-05-01

19

Chromosomal mutations and chromosome loss measured in a new human-hamster hybrid cell line, ALC: studies with colcemid, ultraviolet irradiation, and 137Cs gamma-rays  

NASA Technical Reports Server (NTRS)

Small mutations, megabase deletions, and aneuploidy are involved in carcinogenesis and genetic defects, so it is important to be able to quantify these mutations and understand mechanisms of their creation. We have previously quantified a spectrum of mutations, including megabase deletions, in human chromosome 11, the sole human chromosome in a hamster-human hybrid cell line AL. S1- mutants have lost expression of a human cell surface antigen, S1, which is encoded by the M1C1 gene at 11p13 so that mutants can be detected via a complement-mediated cytotoxicity assay in which S1+ cells are killed and S1- cells survive. But loss of genes located on the tip of the short arm of 11 (11p15.5) is lethal to the AL hybrid, so that mutants that have lost the entire chromosome 11 die and escape detection. To circumvent this, we fused AL with Chinese hamster ovary (CHO) cells to produce a new hybrid, ALC, in which the requirement for maintaining 11p15.5 is relieved, allowing us to detect mutations events involving loss of 11p15.5. We evaluated the usefulness of this hybrid by conducting mutagenesis studies with colcemid, 137Cs gamma-radiation and UV 254 nm light. Colcemid induced 1000 more S1- mutants per unit dose in ALC than in AL; the increase for UV 254 nm light was only two-fold; and the increase for 137Cs gamma-rays was 12-fold. The increase in S1- mutant fraction in ALC cells treated with colcemid and 137Cs gamma-rays were largely due to chromosome loss and 11p deletions often containing a breakpoint within the centromeric region.

Kraemer, S. M.; Waldren, C. A.; Chatterjee, A. (Principal Investigator)

1997-01-01

20

INDUCED MUTATION AND IN VITRO CULTURE OF ANTHURIUM ANDREANUM  

Microsoft Academic Search

The main aims of the project were to study the tissue culture response and the effect(s) of induced mutation through gamma-ray irradiation on Anthurium, an economically important crop of Mauritius. Tissue culture studies were carried out on Nitta, Osaki and Anouchka varieties and the Nitta variety was used for the induced mutation study. Different explants were used for investigating the

D Puchooa

21

THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS  

SciTech Connect

The recent Fermi observation of GRB 080916C shows that the bright photosphere emission associated with a putative fireball is missing, which suggests that the central engine likely launches a Poynting-flux-dominated (PFD) outflow. We propose a model of gamma-ray burst (GRB) prompt emission in the PFD regime, namely, the Internal-Collision-induced MAgnetic Reconnection and Turbulence (ICMART) model. It is envisaged that the GRB central engine launches an intermittent, magnetically dominated wind, and that in the GRB emission region, the ejecta is still moderately magnetized (e.g., 1 {approx}< {sigma} {approx}< 100). Similar to the internal shock (IS) model, the mini-shells interact internally at the radius R{sub IS} {approx} {Gamma}{sup 2} c{Delta}t. Most of these early collisions, however, have little energy dissipation, but serve to distort the ordered magnetic field lines entrained in the ejecta. At a certain point, the distortion of magnetic field configuration reaches the critical condition to allow fast reconnection seeds to occur, which induce relativistic MHD turbulence in the interaction regions. The turbulence further distorts field lines easing additional magnetic reconnections, resulting in a runway release of the stored magnetic field energy (an ICMART event). Particles are accelerated either directly in the reconnection zone, or stochastically in the turbulent regions, which radiate synchrotron photons that power the observed gamma rays. Each ICMART event corresponds to a broad pulse in the GRB light curve, and a GRB is composed of multiple ICMART events. This model retains the merits of IS and other models, but may overcome several difficulties/issues faced by the IS model (e.g., low efficiency, fast cooling, electron number excess, Amati/Yonetoku relation inconsistency, and missing bright photosphere). Within this model, the observed GRB variability timescales could have two components, one slow component associated with the central engine time history, and another fast component associated with relativistic magnetic turbulence in the emission region. The model predicts a decrease of gamma-ray polarization degree and E{sub p} in each ICMART event (broad pulse) during the prompt GRB phase, as well as a moderately magnetized external reverse shock. The model may be applied to the GRBs that have time-resolved, featureless Band-function spectra, such as GRB 080916C and most GRBs detected by Fermi LAT.

Zhang Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States); Yan Huirong [Kavli Institute of Astronomy and Astrophysics, Peking University, Beijing 100871 (China)

2011-01-10

22

Statistical methods for the chemical compound identification from neutron-induced gamma-ray spectra  

Microsoft Academic Search

The paper presents a list correlation method to identify specific high explosive (HE) compounds from the spectra derived from reconstructed images of a gamma- ray camera. The correlation method uses all the information of the characteristic gamma rays for the associated elements of a compound. We show that the method is able to identify HE material at the compound level

Randy C. Stevenson; Joonki Noh; Mark D. Hammig

2009-01-01

23

Ion-induced gamma-ray detection of fast ions escaping from fusion plasmasa)  

NASA Astrophysics Data System (ADS)

A 12 × 12 pixel detector has been developed and used in a laboratory experiment for lost fast-ion diagnostics. With gamma rays in the MeV range originating from nuclear reactions 9Be(?, n?)12C, 9Be(d, n?)12C, and 12C(d, p?)13C, a high purity germanium (HPGe) detector measured a fine-energy-resolved spectrum of gamma rays. The HPGe detector enables the survey of background-gamma rays and Doppler-shifted photo peak shapes. In the experiments, the pixel detector produces a gamma-ray image reconstructed from the energy spectrum obtained from total photon counts of irradiation passing through the detector's lead collimator. From gamma-ray image, diagnostics are able to produce an analysis of the fast ion loss onto the first wall in principle.

Nishiura, M.; Doi, K.; Taniike, A.; Matsuki, T.; Shimazoe, K.; Mushiake, T.; Yoshino, M.; Nagasaka, T.; Fujimoto, Y.; Fujioka, K.; Tanaka, T.; Kisaki, M.; Yamaoka, H.; Matsumoto, Y.; Wada, M.

2014-11-01

24

Comparison of the biological effectiveness of 45 MeV C-ions and {gamma}-rays in inducing early and late effects in normal human primary fibroblasts  

SciTech Connect

Investigation of the mechanisms underlying the biological effects induced by densely ionizing radiation has relevant implications in both radiation protection and therapy. In particular, the possible advantages of hadrontherapy with respect to conventional radiotherapy in terms of high conformal tumor treatment and sparing of healthy tissues are well known. Further improvements are limited by lack of radiobiological knowledge, particularly about the specific cellular response to the damage induced by particles of potential interest for tumor treatment. This study compares early and late effects induced in AG01522 normal human primary fibroblasts by {gamma}-rays and C-ions having E {approx} 45 MeV/u at the cell entrance, corresponding to LET (in water) {approx} 49 keV/{mu}m. Different end points have been investigated, namely: cell killing and lethal mutation, evaluated as early and delayed reproductive cell death, respectively; chromosome damage, as measured by micronuclei induction (MN); DNA damage, in terms of DSB induction and repair, as measured by the H2AX phosphorylation/dephosphorylation kinetics. Linear dose-response relationships were found for cell killing and induction of lethal mutations, with RBEs of about 1.3 and 1.6 respectively, indicating that the presence of genomic instability is greater in the progeny of C-ions irradiated cells. H2AX phosphorylation/dephosphorylation kinetics have shown a maximum foci number at 30 min after irradiation, higher for {gamma}-rays than for C-ions. However, in the first 12 h the fraction of residual {gamma}-H2AX foci was higher for C-ions irradiated cells, indicating a lower removal rate, possibly related to multiple/more complex damage along the particle track, with respect to the sparse lesions produced by {gamma}-rays. MN induction, observed after 72 h from irradiation, was also greater for C-ions. Overall, these data indicate a more severe DNA damage induced by 45 MeV/u C-ions with respect to {gamma}-rays, likely responsible of an increased cellular misrepair, leading to the greater observed levels of chromosome damage and, eventually, of genomic instability. They give strong support to the idea that higher damage severity at molecular level, determined by the typical deposition pattern of densely ionizing radiation, is the earliest relevant factor for the more severe late effects at cellular level.

Fratini, E. [Centro studi e ricerche e museo storico della fisica E. Fermi, Roma (Italy); Balduzzi, M. [ENEA, Roma, Italy and INFN, Sezione Roma1-Gruppo Collegato Sanita, Roma (Italy); Antonelli, F.; Sorrentino, E.; Esposito, G. [Istituto Superiore di Sanita, Roma, Italy and INFN, Sezione Roma1-Gruppo Collegato Sanita, Roma (Italy); Cuttone, G.; Romano, F. [INFN-LNS, Catania (Italy); Dini, V.; Simone, G.; Campa, A.; Tabocchini, M. A. [stituto Superiore di Sanita, Roma, Italy and INFN, Sezione Roma1-Gruppo Collegato Sanita, Roma (Italy); Belli, M. [INFN, Sezione Roma1-Gruppo Collegato Sanita, Roma (Italy)

2013-07-18

25

Mutation measurement in mammalian cells. IV: Comparison of gamma-ray and chemical mutagenesis.  

PubMed

The interaction of chemical mutagens with mammalian cells is much more complex than that of gamma-irradiation because of the different ways in which chemical agents react with cell and medium components. Nevertheless, the system previously described for analysis of mutagenesis by gamma-radiation appears applicable to chemical mutagenesis. The approach involves measurement of cell survival, use of caffeine to inhibit repair, analysis of mitotic index changes, and quantitation of microscopically visible structural changes in mitotic chromosomes. The behavior of a variety of chemical mutagens and nonmutagens in this system is described and compared with that of gamma-irradiation. The procedure is simple and the results reasonably quantitative though less so than those of gamma-irradiation. The procedure can be used for environmental monitoring, analysis of mutational events, and individual and epidemiological testing. Mutational events should be classified as primary or secondary depending on whether they represent initial genomic insult, or genomic changes resulting from primary mutation followed by structural changes due to metabolic actions. While caffeine has multiple effects on the mammalian genome, when used under the conditions specified here it appears to act principally as an inhibitor of mutation repair, and so affords a measure of the role of repair in the action of different mutagens on cells in the G2 phase of the life cycle. PMID:9776977

Puck, T T; Johnson, R; Webb, P; Yohrling, G

1998-01-01

26

First evidence for a gravitational lensing-induced echo in gamma rays with Fermi LAT  

E-print Network

Aims. This article shows the first evidence for gravitational lensing phenomena in high energy gamma-rays. This evidence comes from the observation of a gravitational lens induced echo in the light curve of the distant blazar PKS 1830-211. Methods. Traditional methods for the estimation of time delays in gravitational lensing systems rely on the cross-correlation of the light curves of the individual images. In this paper, we use 300 MeV-30 GeV photons detected by the Fermi-LAT instrument. The Fermi-LAT instrument cannot separate the images of known lenses. The observed light curve is thus the superposition of individual image light curves. The Fermi-LAT instrument has the advantage of providing long, evenly spaced, time series. In addition, the photon noise level is very low. This allows to use directly Fourier transform methods. Results. A time delay between the two compact images of PKS 1830-211 has been searched for both by the autocorrelation method and the â??double power spectrumâ? method. The d...

Barnacka, A; Moudden, Y

2010-01-01

27

Search for neutrino-induced cascades from gamma-ray bursts with AMANDA  

E-print Network

Using the neutrino telescope AMANDA-II, we have conducted two analyses searching for neutrino-induced cascades from gamma-ray bursts. No evidence of astrophysical neutrinos was found, and limits are presented for several models. We also present neutrino effective areas which allow the calculation of limits for any neutrino production model. The first analysis looked for a statistical excess of events within a sliding window of 1 or 100 seconds (for short and long burst classes, respectively) during the years 2001-2003. The resulting upper limit on the diffuse flux normalization times E^2 for the Waxman-Bahcall model at 1 PeV is 1.6 x 10^-6 GeV cm^-2 s^-1 sr^-1 (a factor of 120 above the theoretical prediction). For this search 90% of the neutrinos would fall in the energy range 50 TeV to 7 PeV. The second analysis looked for neutrino-induced cascades in coincidence with 73 bursts detected by BATSE in the year 2000. The resulting upper limit on the diffuse flux normalization times E^2, also at 1 PeV, is 1.5 x 10^-6 GeV cm^-2 s^-1 sr^-1 (a factor of 110 above the theoretical prediction) for the same energy range. The neutrino-induced cascade channel is complementary to the up-going muon channel. We comment on its advantages for searches of neutrinos from GRBs and its future use with IceCube.

IceCube Collaboration; A. Achterberg

2007-02-09

28

Early and Late Chromosome Damages in Human Lymphocytes Induced by Gamma Rays and Fe Ions  

NASA Technical Reports Server (NTRS)

Chromosomal translocations and inversions are considered stable, and cells containing these types of chromosome aberrations can survive multiple cell divisions. An efficient method to detect an inversion is multi-color banding fluorescent in situ hybridization (mBAND) which allows identification of both inter- and intrachromosome aberrations simultaneously. Post irradiation, chromosome aberrations may also arise after multiple cell divisions as a result of genomic instability. To investigate the stable or late-arising chromosome aberrations induced after radiation exposure, we exposed human lymphocytes to gamma rays and Fe ions ex vivo, and cultured the cells for multiple generations. Chromosome aberrations were analyzed in cells collected at first mitosis and at several time intervals during the culture period post irradiation. With gamma irradiation, about half of the damages observed at first mitosis remained after 7 day- and 14 day- culture, suggesting the transmissibility of damages to the surviving progeny. Detailed analysis of chromosome break ends participating in exchanges revealed a greater fraction of break ends involved in intrachromosome aberrations in the 7- and 14-day samples in comparison to the fraction at first mitosis. In particular, simple inversions were found at 7 and 14 days, but not at the first mitosis, suggesting that some of the aberrations might be formed days post irradiation. In contrast, at the doses that produced similar frequencies of gamma-induced chromosome aberrations as observed at first mitosis, a significantly lower yield of aberrations remained at the same population doublings after Fe ion exposure. At these equitoxic doses, more complex type aberrations were observed for Fe ions, indicating that Fe ion-induced initial chromosome damages are more severe and may lead to cell death. Comparison between low and high doses of Fe ion irradiation in the induction of late damages will also be discussed.

Sunagawa, Mayumi; Zhang, Ye; Yeshitla, Samrawit; Kadhim, Munira; Wilson, Bobby; Wu, Honglu

2014-01-01

29

EMISSION PATTERNS AND LIGHT CURVES OF GAMMA RAYS IN THE PULSAR MAGNETOSPHERE WITH A CURRENT-INDUCED MAGNETIC FIELD  

SciTech Connect

We study the emission patterns and light curves of gamma rays in the pulsar magnetosphere with a current-induced magnetic field perturbation. Based on the solution of a static dipole with the magnetic field induced by some currents (perturbation field), we derive the solutions of a static as well as a retarded dipole with the perturbation field in the Cartesian coordinates. The static (retarded) magnetic field can be expressed as the sum of the pure static (retarded) dipolar magnetic field and the static (retarded) perturbation field. We use the solution of the retarded magnetic field to investigate the influence of the perturbation field on the emission patterns and light curves, and apply the perturbed solutions to calculate the gamma-ray light curves for the case of the Vela pulsar. We find that the perturbation field induced by the currents will change the emission patterns and then the light curves of gamma rays, especially for a larger perturbation field. Our results indicate that the perturbation field created by the outward-flowing (inward-flowing) electrons (positrons) can decrease the rotation effect on the magnetosphere and makes emission pattern appear to be smoother relative to that of the pure retarded dipole, but the perturbation field created by the outward-flowing (inward-flowing) positrons (electrons) can make the emission pattern less smooth.

Li, X.; Zhang, L., E-mail: lizhang@ynu.edu.cn [Department of Physics, Yunnan University, Kunming (China)

2011-12-20

30

INVESTIGATION OF $gamma$-RAYS EMITTED IN THE FISSION OF U²³⁵ INDUCED BY 2.8 AND 14.7 Mev NEUTRONS  

Microsoft Academic Search

The gamma rays coinciding in time with fission fragments were recorded ; with a scintillation counter. It is shown that the gamma -ray spectrum is the ; same for U²³⁵ fission induced by 2.8 and 14.7 Mev neutrons as for fission ; induced by thermal neutrons. It is concluded that the total gamma -quantum ; energy per U²³⁵ fission event

A. N. Protopopov; B. M. Shiryaev

1958-01-01

31

Possible effects on avionics induced by terrestrial gamma-ray flashes  

NASA Astrophysics Data System (ADS)

Terrestrial gamma-ray flashes (TGFs) are impulsive (intrinsically sub-millisecond) events associated with lightning in powerful thunderstorms. TGFs turn out to be very powerful natural accelerators known to accelerate particles and generate radiation up to hundreds of MeV energies. The number ratio of TGFs over normal lightning has been measured in tropical regions to be near 10-4. We address in this Article the issue of the possible susceptibility of typical aircraft electronics exposed to TGF particle, gamma ray and neutron irradiation. We consider possible scenarios regarding the intensity, the duration, and geometry of TGFs influencing nearby aircraft, and study their effects on electronic equipment. We calculate, for different assumptions, the total dose and the dose-rate, and estimate single-event-effects. We find that in addition to the electromagnetic component (electrons/positrons, gamma rays) also secondary neutrons produced by gamma-ray photo production in the aircraft structure substantially contribute to single-event effects in critical semiconductors components. Depending on the physical characteristics and geometry, TGFs may deliver a large flux of neutrons within a few milliseconds in an aircraft. This flux is calculated to be orders of magnitude larger than the natural cosmic-ray background, and may constitute a serious hazard to aircraft electronic equipment. We present a series of numerical simulations supporting our conclusions. Our results suggest the necessity of dedicated measurement campaigns addressing the radiative and particle environment of aircraft near or within thunderstorms.

Tavani, M.; Argan, A.; Paccagnella, A.; Pesoli, A.; Palma, F.; Gerardin, S.; Bagatin, M.; Trois, A.; Picozza, P.; Benvenuti, P.; Flamini, E.; Marisaldi, M.; Pittori, C.; Giommi, P.

2013-04-01

32

Possible effects on avionics induced by Terrestrial Gamma-Ray Flashes  

NASA Astrophysics Data System (ADS)

We address the issue of the possible susceptibility of typical aircraft electronics exposed to particle, gamma-ray and neutron irradiation coming from Terrestrial Gamma-ray Flashes (TGF). We consider possible scenarios regarding the intensity, the duration, and geometry of TGFs influencing a nearby aircraft, and study their effects on electronic equipment. We calculate, for different assumptions, the total dose and the dose-rate, and estimate single-event effects. We find that in addition to the electromagnetic component (electrons/positrons, gamma-rays) also secondary neutrons produced by gamma-ray photoproduction in the aircraft structure substantially contribute to single-event effects in critical semiconductors components. Depending on the physical characteristics and geometry, TGFs may deliver a large flux of neutrons within a few milliseconds on an aircraft. This flux is calculated to be orders of magnitude larger than the natural cosmic-ray background, and may constitute a serious hazard to aircraft electronic equipment. We present a series of numerical simulations supporting our conclusions. Our results suggest the necessity of dedicated measurement campaigns addressing the radiative and particle environment of aircraft near or within thunderstorms.

Tavani, Marco; Argan, Andrea; Paccagnella, Alessandro; Pesoli, Alessandro; Palma, Francesco; Gerardin, Simone; Bagatin, Marta; Trois, Alessio; Picozza, Piergiorgio; Benvenuti, Piero; Flamini, Enrico; Marisaldi, Martino; Pittori, Carlotta; Giommi, Paolo

2013-04-01

33

PROTON INDUCED GAMMA-RAY ANALYSIS OF ATMOSPHERIC AEROSOLS FOR CARBON, NITROGEN, AND SULFUR COMPOSITION  

EPA Science Inventory

A technique for the simultaneous quantitative analysis of carbon, nitrogen, and sulfur using in-beam gamma-ray spectrometry has been developed for use with atmospheric aerosol samples. Samples are collected on quartz filters, and the aerosol composition is determined by analyzing...

34

Study of quasi-continuum gamma-ray deexcitation of 152-161Dy nuclei populated in alpha- and 12C-induced reactions  

Microsoft Academic Search

The influence of the reaction mechanism and of the nuclear structure at high angular momentum on the gamma-ray deexcitation process is studied for Dy nuclei produced in a (40-80 MeV) and 12C (80-110 MeV) induced reactions on 154, 155, 158, 160Gd and 146, 150Nd targets, respectively. The quasi-continuum (q.c.) gamma-ray spectra for selected exit channels are decomposed into collective and

J. Lukasiak; D. C. J. M. Hageman; R. V. F. Janssens; Z. Sujkowski; M. J. A. de Voigt

1982-01-01

35

High energy irradiations simulating cosmic-ray-induced planetary gamma ray production. I - Fe target  

NASA Technical Reports Server (NTRS)

Two thick Fe targets were bombarded by a series of 6 GeV proton irradiations for the purpose of simulating the cosmic ray bombardment of planetary objects in space. Gamma ray energy spectra were obtained with a germanium solid state detector during the bombardment, and 46 of the gamma ray lines were ascribed to the Fe targets. A comparison between observed and predicted values showed good agreement for Fe lines from neutron inelastic scattering and spallation reactions, and less satisfactory agreement for neutron capture reactions, the latter attributed to the difference in composition between the Fe target and the mean lunar abundance used in the modeling. Through an analysis of the irradiation results together with continuum data obtained in lunar orbit, it was found that 100 hours of measurement with a current instrument should generate a spectrum containing approximately 20 lines due to Fe alone, with a 2-sigma sensitivity for detection of about 0.2 percent.

Metzger, A. E.; Parker, R. H.; Yellin, J.

1986-01-01

36

Gamma Ray-Induced Loss of Expression of HLA and Glyoxalase I Alleles in Lymphoblastoid Cells  

Microsoft Academic Search

Gamma rays from a cesium source were used to generate human lymphoblastoid cell line variants that had lost expression of all major histocompatibility complex antigens coded for by a single haplotype. The cell line was heterozygous at the glyoxalase I locus and had the HLA haplotypes HLA-A1, B8, DRw3, and HLA-A2, B5, DRw1. We selected with anti-HLA-B8 antiserum in a

Paula Kavathas; Fritz H. Bach; Robert Demars

1980-01-01

37

High-energy gamma ray spectrometer for heavy-ion induced experiments  

Microsoft Academic Search

A gamma-ray detector system of large NaI(Tl) crystals has been constructed to investigated heavy ion reaction mechanisms and highly excited nuclear structure with heavy ion beams. The NaI(Tl) crystals have as a whole a cross section of hexagonal shape of 30 cm between the parallel sides and a length of 20 cm, and are composed of seven substructures based on

S. Kubono; M. H. Tanaka; H. Kawakami; K. Sueki; H. Miyatake; T. Nomura; K. Morita; M. Ishihara; S. Kato; C. Konno; A. Sakaguchi

1986-01-01

38

Charged-particle induced radiation damage of a HPGe gamma-ray detector during spaceflight  

Microsoft Academic Search

The Mars Observer spacecraft was launched on September 26, 1992 with a planned arrival at Mars after an 11-month cruise. Among the scientific instruments carried on the spacecraft was a Gamma-Ray Spectrometer (GRS) experiment to measure the composition of Mars. The GRS used a passively cooled high-purity germanium detector for measurements in the 0.2–10MeV region. The sensor was a closed-end

Larry G Evans; Richard Starr; Johannes Brückner; William V Boynton; S. H Bailey; J. I. Trombka

1999-01-01

39

High energy gamma ray astronomy  

NASA Technical Reports Server (NTRS)

The SAS-2 gamma ray experiment and its detection of celestial gamma rays are described. Data also cover intensity of high energy gamma rays, gamma ray distribution, gamma ray origin, and diffuse radiation.

Fichtel, C. E.

1974-01-01

40

Rapid, non-destructive carbon analysis of forest soils using neutron-induced gamma-ray spectroscopy  

SciTech Connect

Forest soils are pivotal to understanding global carbon (C) cycling and evaluating policies for mitigating global change. However, they are very difficult to monitor because of the heterogeneity of soil characteristics, the difficulty of representative sampling, and the slow time scale of response to environmental change. Here we demonstrate that use of gamma-ray spectroscopy facilitates in situ non-destructive analysis of C and other elements in forest soils. In this approach the element-specific gamma-rays are induced by fast and thermal neutrons interacting with the nuclei of the elements present in the soil. Background gamma-rays emanating from naturally occurring radionuclides in the forest are recorded as well. We applied this approach in a mature northern hardwood forest on glacial till soils at the Bartlett Experimental Forest in New Hampshire, USA. The inelastic neutron scattering (INS) system yielded strong signals in gamma-ray counts/h, from C and other elements present in the soil matrix that included silicon, oxygen, hydrogen, iron, aluminum, manganese and potassium. The INS sensitivity for carbon was 20.656 counts h{sup -1} kg{sup -1} C m{sup -2} based on current net C gamma-ray counts and the data for the O horizon and mineral soil to a depth of 30 cm obtained from a nearby quantitative soil pit (7.35 kg C m{sup -2}). We estimate the minimum detectable change to be {approx}0.34 kg C m{sup -2}, which is {approx}5% of the current soil C content, and the minimum detectable limit to be {approx}0.23 kg C m{sup -1}. Eight % reproducibility from 11 measurements was limited, in part, by the large variability in the system counting geometry due to the uneven forest microtopography. The INS approach has the potential to revolutionize belowground monitoring of C and other elements, because the possibility of detecting a 5% change in forest soils has not been possible with destructive sampling methods.

Wielopolski, L.; Mitra, S.; Yanai, R. D.; Levine, C. R.; Vadeboncoeur, M. A.

2010-08-01

41

Comparison of protein expression profile changes in human fibroblasts induced by low doses of gamma rays and energetic protons  

NASA Astrophysics Data System (ADS)

Extrapolation of known radiation risks to the risks from low dose and low dose-rate exposures of human population, especially prolonged exposure of astronauts in the space radiation environment, relies in part on the mechanistic understanding of radiation induced biological consequences at the molecular level. While some genomic data at the mRNA level are available for cells or animals exposed to radiation, the data at the protein level are still lacking. Here, we studied protein expression profile changes using Panorama antibody microarray chips that contain antibodies to more than 200 proteins (or modified proteins) involved in cell signaling that included mostly apoptosis, cytoskeleton, cell cycle and signal transduction. Normal human fibroblasts were cultured till fully confluent and then exposed to 2 cGy of gamma rays at either low (1 cGy/hr) or high (0.2 Gy/min) dose-rate, or to 2 cGy of 150 MeV protons at high dose-rate. The proteins were isolated at 2 and 6 hours after exposure and labeled with Cy3 for the irradiated cells and with Cy5 for the control samples before loaded onto the protein microarray chips. The intensities of the protein spots were analyzed using ScanAlyze software and normalized by the summed fluorescence intensities and the housekeeping proteins. Comparison of the overall protein expression profiles in gamma-irradiated cells showed significantly higher inductions at the high dose-rate than at the low dose-rate. The protein profile in cells after the proton exposure showed a much earlier induction pattern in comparison to both the high and low dose-rate gamma exposures. The same expression patterns were also found in individual cell signaling cascades. At 6 hours post irradiation, high dose-rate gamma rays induced cellular protein level changes (ratio to control ˜2) mostly in apoptosis, cell cycle and cytoskeleton, while low dose-rate gamma rays induced similar changes with smaller fold-change values. In comparison, protons induced protein changes mainly in the cell cycle category. Thus, at the total dose of 2 cGy, high dose-rate gamma rays may generate more cellular responses through protein level and modification changes to regulate cell signaling and cell-cell communication. Protons presented the less effect, possibly due to the different track distribution compared with gamma radiation.

Zhang, Ye; Clement, Jade; Gridley, Diala; Rohde, Larry; Wu, Honglu

42

Chemical warfare agent and high explosive identification by spectroscopy of neutron-induced gamma rays  

SciTech Connect

This paper reports on a non-destructive assay method to identify chemical warfare (CW) agents and high explosive (HE) munitions which was tested with actual chemical agents and explosives at the Tooele Army Depot, Tooele, Utah, from 22 April 1991 through 3 May 1991. The assay method exploits the gamma radiation produced by neutron interactions inside a container or munition to identify the elemental composition of its contents. The characteristic gamma-ray signatures of the chemical elements chlorine, phosphorus, and sulfur were observed form the CW agent containers and munitions, in sufficient detail to enable us to reliably discern agents GB (sarin), HD (mustard gas), and VX from one another, and from HE-filled munitions. By detecting of the presence of nitrogen, the key indictor of explosive compounds, and the absence of elements Cl, P, and S, HE shells were also clearly identified.

Caffrey, A.J.; Cole, J.D.; Gehrke, R.J.; Greenwood, R.C. (Idaho National Engineering Lab., Idaho Falls, ID (United States))

1992-10-01

43

GAMMA-RAY POLARIZATION INDUCED BY COLD ELECTRONS VIA COMPTON PROCESSES  

SciTech Connect

The polarization measurement is an important tool to probe the prompt emission mechanism in gamma-ray bursts (GRBs). The synchrotron photons can be scattered by cold electrons in the outflow via Compton scattering (CS) processes. The observed polarization depends on both the photon energy and the viewing angle. With the typical bulk Lorentz factor {Gamma} {approx} 200, photons with energy E > 10 MeV tend to have smaller polarization than photons with energy E < 1 MeV. At the right viewing angle, i.e., {theta} {approx} {Gamma}{sup -1}, the polarization achieves its maximal value, and the polarization angle changes 90 Degree-Sign relative to the initial polarization direction. Thus, the synchrotron radiation plus CS model can naturally explain the 90 Degree-Sign change of the polarization angle in GRB 100826A.

Chang Zhe; Jiang Yunguo; Lin Hainan, E-mail: changz@ihep.ac.cn, E-mail: jiangyg@ihep.ac.cn, E-mail: linhn@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, 100049 Beijing (China)

2013-05-20

44

Coincidence measurements between alpha particles and gamma rays in reactions induced by 85 and 155 MeV ¹²C on ¹??Sm  

E-print Network

COINCIDENCE MEASUREMENTS BETWEEN ALPHA PARTICLES AND GAMMA RAYS 12 154 IN REACTIONS INDUCED BY 85 AND 155 MEV C ON Sm A Thesis by STEVEN EDWARD CALA Submitted to the Graduate College of Texas A&M University in partial fulfillment... of the requirement for the degree of MASTER OF SCIENCE August 1978 Major Subject: Chemistry COINCIDENCE MEASUREMENTS BETWEEN ALPHA PARTICLES AND GAMMA RAYS 12 154 IN REACTIONS INDUCED BY 85 AND 155 MEV C ON Sm A Thesis by STEVEN EDWARD CALA Approved...

Cala, Steven Edward

2012-06-07

45

Induced mutations – A new paradigm in plant breeding  

Microsoft Academic Search

The use of ionizing radiation, such as X-rays, gamma rays and neutrons and chemical mutagens for inducing variation, is well\\u000a established. Induced mutations have been used to improve major crops such as wheat, rice, barley,cotton, peanuts, and beans,\\u000a which are seed propagated. Since the establishment of the Joint FAO\\/IAEA Division of the Nuclear Techniques in Agriculture,\\u000a more than 1800 cultivars

B. S. Ahloowalia; M. Maluszynski

2001-01-01

46

Charged-particle induced radiation damage of a HPGe gamma-ray detector during spaceflight  

NASA Astrophysics Data System (ADS)

The Mars Observer spacecraft was launched on September 26, 1992 with a planned arrival at Mars after an 11-month cruise. Among the scientific instruments carried on the spacecraft was a Gamma-Ray Spectrometer (GRS) experiment to measure the composition of Mars. The GRS used a passively cooled high-purity germanium detector for measurements in the 0.2-10MeV region. The sensor was a closed-end co-axial detector, 5.5cm diameter by 5.5cm long, and had an efficiency along its axis of 28% at 1332keV relative to a standard NaI(Tl) detector. The sensor was surrounded by a thin (0.5cm) plastic charged-particle shield. This was the first planetary mission to use a cooled Ge detector. It was expected that the long duration in space of three years would cause an increase in the energy resolution of the detector due to radiation damage and could affect the expected science return of the GRS. Shortly before arrival, on August 21, 1993, contact was lost with the spacecraft following the pressurization of the propellent tank for the orbital-insertion rocket motor. During much of the cruise to Mars, the GRS was actively collecting background data. The instrument provided over 1200h of data collection during periods of both quiescent sun and solar flares. From the charged particle interactions in the shield, the total number of cosmic ray hits on the detector could be determined. The average cosmic ray flux at the MO GRS was about 2.5cm-2s-1. The estimated fluence of charged particles during cruise was about 108 particles cm-2 with 31% of these occurring during a single solar proton event of approximately 10 days duration. During cruise, the detector energy resolution determined from a background gamma-ray at 1312keV degraded from 2.4keV full-width at half-maximum shortly after launch to 6.4keV 11 months later. This result agrees well with measurements from ground-based accelerator irradiations (at 1.5GeV) on a similar size detector.

Evans, L. G.; Starr, R.; Brückner, J.; Boynton, W. V.; Bailey, S. H.; Trombka, J. I.

1999-02-01

47

Determination of total fluorine in five coal reference materials by proton-induced gamma-ray emission spectrometry.  

PubMed

The direct non-destructive proton-induced gamma-ray emission (PIGE) technique with a germanium detector was applied to the determination of total fluorine concentration in five coal reference materials (BCR 40, NIST 1632b, NIST 1635, SARM 20 and USGS CLB-1). Duplicate analyses were made from five randomly selected bottles of each coal. Individual data are presented and some problems (calibration, proton stopping power, effects of sample heating by the proton beam, background estimation) which were encountered during this study are discussed. Sensitivity and reproducibility of the determinations, and homogeneity of the coal samples with respect to fluorine contents by analysis of variance were investigated. The present data are also compared with the few published values for these reference samples, including other PIGE data. The use of synthetic standards and spiked samples in the present study suggested that the PIGE method was more accurate than other techniques. PMID:18966506

Roelandts, I; Robaye, G; Delbrouck-Habaru, J M; Weber, G

1996-03-01

48

Thermal and Gamma-ray induced relaxation in As-S glasses: modeling and experiment  

SciTech Connect

Enthalpy relaxation is measured in a series of As-S glasses irradiated with gamma rays and these samples are compared with a set of identical control samples kept in the dark. It is shown that gamma irradiation lifts the kinetic barrier for relaxation at room temperature and speeds up the enthalpy release. The measured values of thermal relaxation in the dark agree closely with modeling results obtained by fitting differential scanning calorimetry curves with the TNM equations. The measured values of activation energy for enthalpy relaxation are also in close agreement with that predicted by the TNM model therefore lending credence to the fitting results. These measurements permit extraction of the effect of gamma irradiation on the glass structure for a series of As-S glasses with increasing structural coordination, and gamma irradiation is shown to reduce the structural relaxation time. It is also shown that lower coordination glasses exhibit greater radiation sensitivity but also greater thermal relaxation due to their lower Tg. On the other end, over-coordinated glasses show lower relaxation and almost no radiation sensitivity. This behavior is similar to the glass response under sub-bandgap light irradiation.

Lucas, Pierre; King, Ellyn A.; Erdmann, Robert G.; Riley, Brian J.; Sundaram, S. K.; McCloy, John S.

2011-09-09

49

Thermal and gamma-ray induced relaxation in As-S glasses: modelling and experiment  

NASA Astrophysics Data System (ADS)

Enthalpy relaxation was measured in a series of As-S glasses irradiated with gamma rays and these samples are compared with a set of identical control samples kept in the dark. It is shown that gamma irradiation lifts the kinetic barrier for relaxation at room temperature and speeds up the enthalpy release. The measured values of thermal relaxation in the dark agree closely with modelling results obtained by fitting differential scanning calorimetry curves with the Tool-Narayanaswamy-Moynihan (TNM) equations. The measured values of activation energy for enthalpy relaxation are also in close agreement with that predicted by the TNM model, therefore lending credence to the fitting results. These measurements permit extraction of the effect of gamma irradiation on the glass structure for a series of As-S glasses with increasing structural coordination, and gamma irradiation is shown to reduce the structural relaxation time. It is also shown that lower coordination glasses exhibit greater radiation sensitivity but also greater thermal relaxation due to their lower Tg. On the other end, over-coordinated glasses show lower relaxation and almost no radiation sensitivity. This behaviour is similar to the glass response under sub-bandgap light irradiation.

Lucas, Pierre; King, Ellyn A.; Erdmann, Robert G.; Riley, Brian J.; Sundaram, S. K.; McCloy, John S.

2011-10-01

50

Neutron-induced gamma-ray production cross sections for the first excited-state transitions in Ne-20 and Ne-22  

E-print Network

Background: Neutron-induced reactions are a significant concern for experiments that require extremely low levels of radioactive backgrounds. Measurements of gamma-ray production cross sections over a wide energy range will help to predict and identify neutron backgrounds in these experiments. Purpose: Determine partial gamma-ray production cross sections for neutron-induced reactions in natural neon. Methods: The broad-spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE) was used for the measurement. Gamma rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE). Results: Partial gamma-ray cross sections were measured for the first excited-state transitions in Ne-20 and Ne-22. The measured cross sections were compared to the TALYS and CoH3 nuclear reaction codes. Conclusions: These are the first experimental data for (n,n') reactions in neon. In addition to providing data to aid in the prediction and identification of neutron backgrounds in low-background experiments, these new measurements will help refine cross-section predictions in a mass region where models are not well constrained.

S. MacMullin; M. Boswell; M. Devlin; S. R. Elliott; N. Fotiades; V. E. Guiseppe; R. Henning; T. Kawano; B. H. LaRoque; R. O. Nelson; J. M. O'Donnell

2012-10-03

51

Freshly induced short-lived gamma-ray activity as a measure of fission rates in lightly re-irradiated spent fuel  

NASA Astrophysics Data System (ADS)

A new measurement technique has been developed to determine fission rates in burnt fuel, following re-irradiation in a zero-power research reactor. The development has been made in the frame of the LIFE@PROTEUS program at the Paul Scherrer Institute, which aims at characterizing the interfaces between fresh and highly burnt fuel assemblies in modern LWRs. To discriminate against the high intrinsic gamma-ray activity of the burnt fuel, the proposed measurement technique uses high-energy gamma-rays, above 2000 keV, emitted by short-lived fission products freshly produced in the fuel. To demonstrate the feasibility of this technique, a fresh UO 2 sample and a 36 GWd/t burnt UO 2 sample were irradiated in the PROTEUS reactor and their gamma-ray activities were recorded directly after irradiation. For both fresh and the burnt fuel samples, relative fission rates were derived for different core positions, based on the short-lived 142La (2542 keV), 89Rb (2570 keV), 138Cs (2640 keV) and 95Y (3576 keV) gamma-ray lines. Uncertainties on the inter-position fission rate ratios were mainly due to the uncertainties on the net-area of the gamma-ray peaks and were about 1-3% for the fresh sample, and 3-6% for the burnt one. Thus, for the first time, it has been shown that the short-lived gamma-ray activity, induced in burnt fuel by irradiation in a zero-power reactor, can be used as a quantitative measure of the fission rate. For both fresh and burnt fuel, the measured results agreed, within the uncertainties, with Monte Carlo (MCNPX) predictions.

Kröhnert, H.; Perret, G.; Murphy, M. F.; Chawla, R.

2010-12-01

52

Effect of photobleaching on radiation-induced transmission loss of fused-silica-core optical fibres under gamma-ray and 14 MeV neutron irradiation  

Microsoft Academic Search

The effect of photobleaching on radiation-induced transmission loss of fused-silica-core optical fibres was examined under 60Co gamma-ray and 14 MeV neutron irradiation. In the visible wavelength range, the radiation-induced transmission loss could be reduced by photobleaching under both types of irradiation. It is considered that the number of radiation-induced defects such as E' centre and NBOHC that cause optical absorption

K. Toh; T. Shikama; S. Nagata; B. Tsuchiya; M. Yamauchi; T. Nishitani

2006-01-01

53

Gamma ray transients  

NASA Technical Reports Server (NTRS)

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

Cline, Thomas L.

1987-01-01

54

Gamma Ray Bursts Sudden, intense flashes of gamma rays  

E-print Network

Gamma Ray Bursts #12;The Case Sudden, intense flashes of gamma rays come from nowhere and disappear with out a trace. Incredibly powerful: A single gamma ray burst is hundreds of times brighter a supernova #12;Who Vela (1960's) Looking for arms testing, found gamma ray bursts Compton Gamma Ray Observatory

Washington at Seattle, University of - Department of Physics, Electroweak Interaction Research Group

55

Measurement of {sup 235}U content and flow of UF{sub 6} using delayed neutrons or gamma rays following induced fission  

SciTech Connect

Feasibility experiments conducted at Pacific Northwest National Laboratory demonstrate that either delayed neutrons or energetic gamma rays from short-lived fission products can be used to monitor the blending of UF{sub 6} gas streams. A {sup 252}Cf neutron source was used to induce {sup 235}U fission in a sample, and delayed neutrons and gamma rays were measured after the sample moved {open_quotes}down-stream.{close_quotes} The experiments used a UO{sub 2} powder that was transported down the pipe to simulate the flowing UF{sub 6} gas. Computer modeling and analytic calculation extended the test results to a flowing UF{sub 6} gas system. Neutron or gamma-ray measurements made at two downstream positions can be used to indicate both the {sup 235}U content and UF{sub 6} flow rate. Both the neutron and gamma-ray techniques have the benefits of simplicity and long-term reliability, combined with adequate sensitivity for low-intrusion monitoring of the blending process. Alternatively, measuring the neutron emission rate from (a, n) reactions in the UF{sub 6} provides an approximate measure of the {sup 235}U content without using a neutron source to induce fission.

Stromswold, D.C.; Peurrung, A.J.; Reeder, P.L.; Perkins, R.W.

1996-06-01

56

Photobleaching effect on gamma-ray and 14 MeV fast neutron induced transmission loss of fused silica core optical fiber  

Microsoft Academic Search

A photo-bleaching effect on radiation-induced transmission loss of fused silica core optical fibers was examined under 60Co gamma-ray and 14 MeV fast neutron irradiation. In the visible wavelength range, radiation induced loss could be reduced by the photo-bleaching under the both irradiation. For using optical fibers in visible wavelength range such as a light guide and an image guide, the

K. Toh; T. Shikama; S. Nagata; Bun Tsuchiya; M. Yamauchi; T. Nishitani

2005-01-01

57

Molecular characterization of mutations induced by gamma irradiation in rice.  

PubMed

In order to analyze mutations induced by gamma irradiation in higher plants, we irradiated rice with gamma rays and screened for mutations expressing phenotypes of glutinous endosperm (wx), chlorophyll b deficiency, endosperm protein deficiency, gibberellin-related dwarfism, and shortened plastochron-in order to clarify types of mutations. Nucleotide sequence analysis showed that the most frequent mutation induced by gamma rays was deletion, particularly small deletion. Of the 24 mutations, 15 were small deletions (1-16 bp), four were large deletions (9.4-129.7 kbp), three were single-base substitutions, and two were inversions. Deletions 100 bp-8 kbp in length were not found, suggesting that gamma irradiation is unlikely to induce deletions of 100 bp to 8 kbp but is more likely to induce deletions between 1 and several ten bp or those of around 10 kbp or more. Based on the results, reverse genetics applications may be possible for gamma irradiation-induced deletions in rice by mismatch cleavage analysis used in Targeting Induced Local Lesions IN Genomes (TILLING) to detect small deletions and base substitutions or by using array comparative genomic hybridization (aCGH) to detect large deletions. PMID:20154423

Morita, Ryouhei; Kusaba, Makoto; Iida, Shuichi; Yamaguchi, Hiroyasu; Nishio, Takeshi; Nishimura, Minoru

2009-10-01

58

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

59

Specificity of mutations induced by carbon ions in budding yeast Saccharomyces cerevisiae.  

PubMed

To investigate the nature of mutations induced by accelerated ions in eukaryotic cells, the effects of carbon-ion irradiation were compared with those of gamma-ray irradiation in the budding yeast Saccharomyces cerevisiae. The mutational effect and specificity of carbon-ion beams were studied in the URA3 gene of the yeast. Our experiments showed that the carbon ions generated more than 10 times the number of mutations induced by gamma-rays, and that the types of base changes induced by carbon ions include transversions (68.7%), transitions (13.7%) and deletions/insertions (17.6%). The transversions were mainly G:C-->T:A, and all the transitions were G:C-->A:T. In comparison with the surrounding sequence context of mutational base sites, the C residues in the 5'-AC(A/T)-3' sequence were found to be easily changed. Large deletions and duplications were not observed, whereas ion-induced mutations in Arabidopsis thaliana were mainly short deletions and rearrangements. The remarkable feature of yeast mutations induced by carbon ions was that the mutation sites were localized near the linker regions of nucleosomes, whereas mutations induced by gamma-ray irradiation were located uniformly throughout the gene. PMID:16949109

Matuo, Youichirou; Nishijima, Shigehiro; Hase, Yoshihiro; Sakamoto, Ayako; Tanaka, Atsushi; Shimizu, Kikuo

2006-12-01

60

Hyperthermia increases gamma-ray and fission neutron-induced translocations in Drosophila  

SciTech Connect

Hyperthermia has been reported in Drosophila melanogaster to increase radiation-induced chromosome rearrangements, chromosome loss, recessive and dominant lethals. To determine whether hyperthermia would also affect high linear energy transfer (LET)-induced genetic damage such as translocations, which involve breakage and reunion of chromosomes, a genetic system was employed not only allowing detection of ordinary 2;3 translocations, but also permitting a more accurate measure of Y-autosome translocations.

Mittler, S.

1984-01-01

61

mBAND Analysis of Late Chromosome Aberrations in Human Lymphocytes Induced by Gamma Rays and Fe Ions  

NASA Technical Reports Server (NTRS)

Chromosomal translocations and inversions are considered stable, and cells containing these types of chromosome aberrations can survive multiple cell divisions. An efficient method to detect an inversion is multi-color banding fluorescent in situ hybridization (mBAND) which allows identification of both inter- and intrachromosome aberrations simultaneously. Post irradiation, chromosome aberrations may also arise after multiple cell divisions as a result of genomic instability. To investigate the stable or late-arising chromosome aberrations induced after radiation exposure, we exposed human lymphocytes to gamma rays and Fe ions ex vivo, and cultured the cells for multiple generations. Chromosome aberrations were analyzed in cells collected at first mitosis and at several time intervals during the culture period post irradiation. With gamma irradiation, about half of the damages observed at first mitosis remained after 7 day- and 14 day- culture, suggesting the transmissibility of damages to the surviving progeny. Detailed analysis of chromosome break ends participating in exchanges revealed a greater fraction of break ends involved in intrachromosome aberrations in the 7- and 14-day samples in comparison to the fraction at first mitosis. In particular, simple inversions were found at 7 and 14 days, but not at the first mitosis, suggesting that some of the aberrations might be formed days post irradiation. In contrast, at the doses that produced similar frequencies of gamma-induced chromosome aberrations as observed at first mitosis, a significantly lower yield of aberrations remained at the same population doublings after Fe ion exposure. At these equitoxic doses, more complex type aberrations were observed for Fe ions, indicating that Fe ion-induced initial chromosome damages are more severe and may lead to cell death. Comparison between low and high doses of Fe ion irradiation in the induction of late damages will also be discussed.

Sunagawa, Mayumi; Zhang, Ye; Yeshitla, Samrawit; Kadhim, Munira; Wilson, Bobby; Wu, Honglu

2014-01-01

62

Gamma-ray Astronomy  

E-print Network

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

Jim Hinton

2007-12-20

63

Gamma-ray-induced mutagen sensitivity and risk of sporadic breast cancer in young women: a case-control study  

PubMed Central

Hypersensitivity to radiation exposure has been suggested to be a risk factor for the development of breast cancer. In this case–control study of 515 young women (?55 years) with newly diagnosed sporadic breast cancer and 402 cancer-free controls, we examined the radiosensitivity as measured by the frequency of chromatid breaks induced by gamma-radiation exposure in the G2 phase of phytohemagglutinin-stimulated and short-term cultured fresh lymphocytes. We found that the average chromatid breaks per cell from 50 well-spread metaphases were statistically significantly higher in 403 non-Hispanic White breast cancer patients (0.52 ± 0.22) than that in 281 non-Hispanic White controls (0.44 ± 0.16) (P value < 0.001), and in 60 Mexican American breast cancer patients (0.52 ± 0.19) than that in 65 Mexican American controls (0.44 ± 0.16) (P value = 0.021), but the difference was not significant in African Americans (52 cases [0.45 ± 0.16] versus 56 controls [0.47 ± 0.16], P = 0.651). The frequency of chromatid breaks per cell above the median of control subjects was associated with two-fold increased risk for breast cancer in non-Hispanic Whites and Mexican Americans. A dose–response relationship was evident between radiosensitivity and risk for breast cancer (Ptrend < 0.001) in these two ethnic groups. We concluded that gamma-ray-induced mutagen sensitivity may play a role in susceptibility to breast cancer in young non-Hispanic White and Mexican American women. PMID:22218884

Han, Chan H.; Xiong, Ping; Bondy, Melissa L.; Yu, Tse-Kuan; Brewster, Abenaa M.; Shete, Sanjay; Arun, Banu K.; Buchholz, Thomas A.; Wei, Qingyi

2012-01-01

64

Gamma Ray Pulsars: Observations  

NASA Technical Reports Server (NTRS)

High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The six or more pulsars seen by CGRO/EGRET show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. Unless a new pulsed component appears at higher energies, progress in gamma-ray pulsar studies will be greatest in the 1-20 GeV range. Ground-based telescopes whose energy ranges extend downward toward 10 GeV should make important measurements of the spectral cutoffs. The Gamma-ray Large Area Space Telescope (GLAST), now in planning for a launch in 2005, will provide a major advance in sensitivity, energy range, and sky coverage.

Thompson, David J.; White, Nicholas E. (Technical Monitor)

2000-01-01

65

Gamma ray astronomy  

NASA Technical Reports Server (NTRS)

Miscellaneous tasks related to the development of the Bursts and Transient Source Experiment on the Gamma Ray Observatory and to analysis of archival data from balloon flight experiments were performed. The results are summarized and relevant references are included.

Paciesas, William S.

1991-01-01

66

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

67

The gamma-ray observatory  

NASA Technical Reports Server (NTRS)

An overview is given of the Gamma Ray Observatory (GRO) mission. Detection of gamma rays and gamma ray sources, operations using the Space Shuttle, and instruments aboard the GRO, including the Burst and Transient Source Experiment (BATSE), the Oriented Scintillation Spectrometer Experiment (OSSE), the Imaging Compton Telescope (COMPTEL), and the Energetic Gamma Ray Experiment Telescope (EGRET) are among the topics surveyed.

1991-01-01

68

Theoretical treatment of the Cherenkov emission contribution to biological effects induced by gamma-rays in microorganisms  

Microsoft Academic Search

The contribution of Cherenkov emission in the formation of photoreactivatable damage (pyrimidine dimers) in E. coli cells has been analyzed. The mean quantity of Cherenkov photons in the wavelength range (200-600) nm produced in a suspension volume unit per absorbed dose unit was calculated by a Monte Carlo method for a point isotropic gamma-ray source with energy up to 30

V. A. Pitkevich; V. V. Duba; M. N. Myasnik; I. V. Petrova; V. G. Skvortzov

1986-01-01

69

Gamma Ray Bursts from Ordinary Cosmic Strings  

E-print Network

We give an upper estimate for the number of gamma ray bursts from ordinary (non-superconducting) cosmic strings expected to be observed at terrestrial detectors. Assuming that cusp annihilation is the mechanism responsible for the bursts we consider strings arising at a GUT phase transition and compare our estimate with the recent BATSE results. Further we give a lower limit for the effective area of future detectors designed to detect the cosmic string induced flux of gamma ray bursts.

R. H. Brandenberger; A. T. Sornborger; M. Trodden

1993-02-12

70

Choice of detectors for in vivo elemental analysis by counting natural and neutron-induced gamma rays for medical applications  

NASA Astrophysics Data System (ADS)

Body fat is measured by detecting C and O in vivo through fast neutron inelastic scattering. A sealed D?T neutron generator is used for the pulsed (4-10 kHz) production of fast neutrons. Carbon and oxygen are detected by counting the 4.44 and 6.13 MeV gamma rays resulting from the inelastic scattering of the fast neutrons from 12C and 16O. Large Bi 4Ge 3O 12 (BGO) crystal detectors (127 × 76 mm) are used for the gamma ray detection during the 10 ?s neutron burst. BGO detectors improved the signal to background ratio for the carbon detection by a factor of six compared to 152 × 152 mm NaI (Tl) detectors. Exposure to scattered neutrons did not affect the gain stability of the BGOs. Thermal neutrons from a moderated 238Pu?Be source are used for the measurement of total body nitrogen (and thus protein). The resulting high energy prompt gamma rays from nitrogen (10.83 MeV) are detected simultaneously with the irradiation. BGO detectors have superior stability operating in an environment of variable neutron exposure and high counting rates. However, the presence of neutrons creates a 10.2 MeV gamma ray peak from 73Ge in the BGO detector which interferes with the nitrogen peak. Whole body gamma ray counters, consisting of NaI(Tl) crystal detectors in a shielded room, are used to measure the natural radioactivity of the body due to 40K. They are also used to measure body Ca, P, Na and Cl, following total body exposure to thermal neutrons.

Kehayias, Joseph J.; Zhuang, Hong; Dowling, Lisa; Ma, Ruimei; Moore, Robert

1994-12-01

71

Simultaneous determination of Si, Al and Na concentrations by particle induced gamma-ray emission and applications to reference materials and ceramic archaeological artifacts  

NASA Astrophysics Data System (ADS)

A particle induced gamma ray emission (PIGE) method using 4 MeV proton beam was standardized for simultaneous determination of Si, Al and Na concentrations and has been applied for non-destructive analysis of several reference materials and archaeological clay pottery samples. Current normalized count rates of gamma-rays for the three elements listed above were obtained by an in situ method using Li as internal standard. The paper presents application of the in situ current normalized PIGE method for grouping study of 39 clay potteries, obtained from Rajasthan and Andhra Pradesh states of India. Grouping of artifacts was carried out using the ratios of SiO2 to Al2O3 concentrations, due to their non volatile nature. Powder samples and elemental standards in pellet forms (cellulose matrix) were irradiated using the 4 MeV proton beam (?10 nA) from the 3 MV tandem accelerator at IOP Bhubaneswar, and assay of prompt gamma rays was carried out using a 60% relative efficiency HPGe detector coupled to MCA. The concentration ratio values of SiO2/Al2O3 indicated that pottery samples fell into two major groups, which are in good agreement with their collection areas. Reference materials from IAEA and NIST were analyzed for quantification of Si, Al and Na concentrations as a part of validation as well as application of PIGE method.

Dasari, K. B.; Chhillar, S.; Acharya, R.; Ray, D. K.; Behera, A.; Lakshmana Das, N.; Pujari, P. K.

2014-11-01

72

Cultured mouse SR-1 cells exposed to low dose of gamma-rays become less susceptible to the induction of mutagenesis by radiation as well as bleomycin.  

PubMed

The effect of pre-exposure of cultured mouse SR-1 cells to a low dose of gamma-rays on the induction of mutations at the hprt locus by subsequent high dose radiation or bleomycin was studied. When cells were pre-exposed to 0.01 Gy gamma-rays, the induction of mutations by a 3 Gy gamma-ray dose given 18 or 24 h later was significantly reduced as compared with those which did not receive the low dose pre-exposure. When cells were challenged with 5 or 10 micrograms/ml bleomycin for 12 h, which can produce double-strand breaks in DNA, instead of 3 Gy gamma-rays, a similar mutagenetic adaptive response was observed. We conclude that this resistance to radiation- or bleomycin-induced mutation is attributed to the induction of a DNA double-strand break repair mechanism. PMID:7681929

Zhou, P K; Liu, X Y; Sun, W Z; Zhang, Y P; Wei, K

1993-03-01

73

Diffuse gamma-rays from galactic halos  

E-print Network

Here we review our current knowledge on diffuse gamma-rays from galactic halos. Estimates of the relative contribution of the various emission processes at low and high latitudes are compared to the data over 6 decades in energy. The observed spectral shape differs from what was expected, especially at ver low and very high energies. In the latter case, above 1 GeV, the sky emission related to gas exceeds the expected pi^0 decay spectrum. At energies below 1 MeV the relatively high gamma-ray intensity indicates at high density of nearly relativistic electrons which would have a strong influence on the energy and ionisation balance of the interstellar medium. Given the EGRET results for the Magellanic Clouds the gamma-ray emissivity in the outer halo is probably small, so that a substantial amount of baryonic dark matter may be hidden at 20-50 kpc radius without inducing observable gamma-ray emission.

M. Pohl

1996-03-12

74

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

75

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

76

MODELING PHOTODISINTEGRATION-INDUCED TeV PHOTON EMISSION FROM LOW-LUMINOSITY GAMMA-RAY BURSTS  

SciTech Connect

Ultra-high-energy cosmic-ray heavy nuclei have recently been considered as originating from nearby low-luminosity gamma-ray bursts that are associated with Type Ibc supernovae. Unlike the power-law decay in long duration gamma-ray bursts, the light curve of these bursts exhibits complex UV/optical behavior: shock breakout dominated thermal radiation peaks at about 1 day, and, after that, nearly constant emission sustained by radioactive materials for tens of days. We show that the highly boosted heavy nuclei at PeV energy interacting with the UV/optical photon field will produce considerable TeV photons via the photodisintegration/photo-de-excitation process. It was later predicted that a thermal-like {gamma}-ray spectrum peaks at about a few TeV, which may serve as evidence of nucleus acceleration. The future observations by the space telescope Fermi and by the ground atmospheric Cherenkov telescopes such as H.E.S.S., VERITAS, and MAGIC will shed light on this prediction.

Liu Xuewen [Physics Department, Sichuan University, Chengdu 610065 (China); Wu Xuefeng; Lu Tan, E-mail: astrolxw@gmail.com, E-mail: xfwu@pmo.ac.cn, E-mail: t.lu@pmo.ac.cn [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

2012-05-15

77

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

78

Gamma Ray Bursts  

NASA Technical Reports Server (NTRS)

Gamma-ray bursts (GRBs) are bright flashes of gamma-rays coming from the cosmos. They occur roughly once per day ,last typically lOs 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 afterglows.

Gehrels, Neil; Meszaros, Peter

2012-01-01

79

Gamma Ray Bursts  

E-print Network

Gamma-ray bursts have been detected at photon energies up to tens of GeV. We review some recent developments in the X-ray to GeV photon phenomenology in the light of Swift and Fermi observations, and some of the theoretical models developed to explain them, with a view towards implications for C.T.A.

Peter Mészáros

2012-04-09

80

Celestial gamma ray study  

NASA Technical Reports Server (NTRS)

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

Michelson, Peter F.

1995-01-01

81

Determination of Fluorine in Fourteen Microanalytical Geologic Reference Materials using SIMS, EPMA, and Proton Induced Gamma Ray Emission (PIGE) Analysis  

NASA Astrophysics Data System (ADS)

Fluorine (F) is a volatile constituent of magmas and hydrous minerals, and trace amounts of F are incorporated into nominally anhydrous minerals such as olivine and clinopyroxene. Microanalytical techniques are routinely used to measure trace amounts of F at both high sensitivity and high spatial resolution in glasses and crystals. However, there are few well-established F concentrations for the glass standards routinely used in microanalytical laboratories, particularly standards of low silica, basaltic composition. In this study, we determined the F content of fourteen commonly used microanalytical glass standards of basaltic, intermediate, and rhyolitic composition. To serve as calibration standards, five basaltic glasses with ~0.2 to 2.5 wt% F were synthesized and characterized. A natural tholeiite from the East Pacific Rise was mixed with variable amounts of CaF2. The mixture was heated in a 1 atmosphere furnace to 1440 °C at fO2 = NNO for 30 minutes and quenched in water. Portions of the run products were studied by electron probe microanalysis (EPMA) and secondary ion mass spectrometry (SIMS). The EPMA used a 15 µm diameter defocused electron beam with a 15 kV accelerating voltage and a 25 nA primary current, a TAP crystal for detecting FK? X-rays, and Biotite 3 as the F standard. The F contents by EPMA agreed with the F added to the basalts after correction for mass loss during melting. The SIMS analyses used a primary beam of 16O- and detection of low-energy negative ions (-5 kV) at a mass resolution that resolved 18OH. Both microanalytical techniques confirmed homogeneity, and the SIMS calibration defined by EPMA shows an excellent linear trend with backgrounds of 2 ppm or less. Analyses of basaltic glass standards based on our synthesized calibration standards gave the following F contents and 2? errors (ppm): ALV-519 = 83 ± 3; BCR-2G = 359 ± 6; BHVO-2G = 322 ± 15; GSA-1G = 10 ± 1; GSC-1G = 11 ± 1; GSD-1G = 19 ± 2; GSE-1G = 173 ± 1; KL2G (MPI-DING) = 101 ± 1; ML3B-G (MPI-DING) = 49 ± 17. These values are lower than published values for BCR-2 and BHVO-2 (unmelted powders) and the “information values” for the MPI-DING glass standards. Proton Induced Gamma ray Emission (PIGE) was tested for the high silica samples. PIGE analyses (1.7 MeV Tandem Accelerator; reaction type: 19F(p, ??)16O; primary current = 20-30 nA; incident beam voltage = 1.5 MeV) were calibrated with a crystal of fluor-topaz (F = 20.3 wt%) and gave F values of: NIST 610 = 266 ± 14 ppm; NIST 620 = 54 ± 5 ppm; and UTR-2 = 1432 ± 32 ppm. SIMS calibration defined by the PIGE analyses shows an excellent linear trend with low background similar to the basaltic calibration. The F concentrations of intermediate MPI-DING glasses were determined based on SIMS calibration generated from the PIGE analysis above. The F concentrations and 2? errors (ppm) are: T1G = 219.9 ± 6.8; StHs/680-G = 278.0 ± 2.0 ppm. This study revealed a large matrix effect between the high-silica and basaltic glasses, thus requiring the use of appropriate standards and separate SIMS calibrations when analyzing samples of different compositions.

Guggino, S. N.; Hervig, R. L.

2010-12-01

82

Molecular characterisation of murine acute myeloid leukaemia induced by 56Fe ion and 137Cs gamma ray irradiation  

PubMed Central

Exposure to sparsely ionising gamma- or X-ray irradiation is known to increase the risk of leukaemia in humans. However, heavy ion radiotherapy and extended space exploration will expose humans to densely ionising high linear energy transfer (LET) radiation for which there is currently no understanding of leukaemia risk. Murine models have implicated chromosomal deletion that includes the hematopoietic transcription factor gene, PU.1 (Sfpi1), and point mutation of the second PU.1 allele as the primary cause of low-LET radiation-induced murine acute myeloid leukaemia (rAML). Using array comparative genomic hybridisation, fluorescence in situ hybridisation and high resolution melt analysis, we have confirmed that biallelic PU.1 mutations are common in low-LET rAML, occurring in 88% of samples. Biallelic PU.1 mutations were also detected in the majority of high-LET rAML samples. Microsatellite instability was identified in 42% of all rAML samples, and 89% of samples carried increased microsatellite mutant frequencies at the single-cell level, indicative of ongoing instability. Instability was also observed cytogenetically as a 2-fold increase in chromatid-type aberrations. These data highlight the similarities in molecular characteristics of high-LET and low-LET rAML and confirm the presence of ongoing chromosomal and microsatellite instability in murine rAML. PMID:22987027

Bacher, Jeffery W.

2013-01-01

83

Solar Flares: Gamma Rays  

E-print Network

We briefly review the theory of gamma ray production in solar flares and present the highlights of the observations and their implications. Specifically: (i) the gamma ray data show that a large fraction of the released flare energy is in accelerated ions, mostly around 1 MeV/nucleon; (ii) the accelerated He-3, heavy ion, and relativistic electron abundances are enriched, implying that the particle acceleration is dominated by stochastic gyroresonant interactions with plasma turbulence; (iii) there is evidence for the enhancement of the abundances of ambient chromospheric elements with low first ionization potentials; (iv) the observed Li-7 and Be-7 lines, at 0.429 MeV and 0.478 MeV due to alpha-alpha interactions, show that both the accelerated alpha particle and the ambient He abundances are significantly enhanced.

Reuven Ramaty; Natalie Mandzhavidze

1998-10-06

84

Gamma ray astronomy  

NASA Technical Reports Server (NTRS)

The Burst and Transient Source Experiment (BATSE) is one of four instruments on the Compton observatory which was launched by the space shuttle Atlantis on April 5, 1991. As of mid-March, 1994, BATSE detected more than 925 cosmic gamma-ray bursts and more than 725 solar flares. Pulsed gamma rays have been detected from at least 16 sources and emission from at least 28 sources (including most of the pulsed sources) has been detected by the earth occultation technique. UAH participation in BATSE is extensive but can be divided into two main areas, operations and data analysis. The daily BATSE operations tasks represent a substantial level of effort and involve a large team composed of MSFC personnel as well as contractors such as UAH. The scientific data reduction and analysis of BATSE data is also a substantial level of effort in which UAH personnel have made significant contributions.

Paciesas, William S.

1994-01-01

85

Gamma-ray Bursts  

Microsoft Academic Search

Since their discovery in 1967, Gamma-ray bursts (GRBs) have been puzzling to astrophysicists. With the advent of a new generation\\u000a of X-ray satellites in the late 90’s, it was possible to carry out deep multi-wavelength observations of the counterparts\\u000a associated with the long duration GRBs class just within a few hours of occurrence, thanks to the observation of the fading

Alberto J. Castro-Tirado

86

Unidentified Gamma-Ray Sources: Hunting Gamma-Ray Blazars  

SciTech Connect

One of the main scientific objectives of the ongoing Fermi mission is unveiling the nature of the unidentified {gamma}-ray sources (UGSs). Despite the large improvements of Fermi in the localization of {gamma}-ray sources with respect to the past {gamma}-ray missions, about one third of the Fermi-detected objects are still not associated to low energy counterparts. Recently, using the Wide-field Infrared Survey Explorer (WISE) survey, we discovered that blazars, the rarest class of Active Galactic Nuclei and the largest population of {gamma}-ray sources, can be recognized and separated from other extragalactic sources on the basis of their infrared (IR) colors. Based on this result, we designed an association method for the {gamma}-ray sources to recognize if there is a blazar candidate within the positional uncertainty region of a generic {gamma}-ray source. With this new IR diagnostic tool, we searched for {gamma}-ray blazar candidates associated to the UGS sample of the second Fermi {gamma}-ray catalog (2FGL). We found that our method associates at least one {gamma}-ray blazar candidate as a counterpart each of 156 out of 313 UGSs analyzed. These new low-energy candidates have the same IR properties as the blazars associated to {gamma}-ray sources in the 2FGL catalog.

Massaro, F.; D'Abrusco, R.; Tosti, G.; Ajello, M.; Gasparrini, A.Paggi.D.

2012-04-02

87

UNIDENTIFIED {gamma}-RAY SOURCES: HUNTING {gamma}-RAY BLAZARS  

SciTech Connect

One of the main scientific objectives of the ongoing Fermi mission is unveiling the nature of unidentified {gamma}-ray sources (UGSs). Despite the major improvements of Fermi in the localization of {gamma}-ray sources with respect to the past {gamma}-ray missions, about one-third of the Fermi-detected objects are still not associated with low-energy counterparts. Recently, using the Wide-field Infrared Survey Explorer survey, we discovered that blazars, the rarest class of active galactic nuclei and the largest population of {gamma}-ray sources, can be recognized and separated from other extragalactic sources on the basis of their infrared (IR) colors. Based on this result, we designed an association method for the {gamma}-ray sources to recognize if there is a blazar candidate within the positional uncertainty region of a generic {gamma}-ray source. With this new IR diagnostic tool, we searched for {gamma}-ray blazar candidates associated with the UGS sample of the second Fermi {gamma}-ray LAT catalog (2FGL). We found that our method associates at least one {gamma}-ray blazar candidate as a counterpart to each of 156 out of 313 UGSs analyzed. These new low-energy candidates have the same IR properties as the blazars associated with {gamma}-ray sources in the 2FGL catalog.

Massaro, F.; Ajello, M. [SLAC National Laboratory and Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); D'Abrusco, R.; Paggi, A. [Harvard-Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Tosti, G. [Dipartimento di Fisica, Universita degli Studi di Perugia, 06123 Perugia (Italy); Gasparrini, D. [ASI Science Data Center, ESRIN, I-00044 Frascati (Italy)

2012-06-10

88

Temperature dependence of gamma-ray-induced luminescence of xylene-based liquid scintillator between 200 and 242 K  

NASA Astrophysics Data System (ADS)

The luminescence response of xylene-based liquid scintillator (scintillation grade), xylene + 1 g/l PPO + 0.1 g/l BBOT, has been studied as a function of temperature in the range 200 to 242 K. It has been observed that under gamma-ray excitation the light output increases with the decrease of temperature. The data are well described by the Arrhenius relation, I low- I= I 0 exp(- E/kT), where I is the count rate at temperature T. I low is a constant equal to 5600 counts per min, the I 0 factor is 3.3 × 106 counts/min, k is the Boltzmann constant. The activation energy E was found to be equal to 0.20 eV. It is typical for thermally activated diffusion controlled process.

Haq, Faizan Ul; Bashir, Shazia

2006-12-01

89

Evidence for an Inducible Repair-Recombination System in the Female Germ Line of Drosophila Melanogaster. II. Differential Sensitivity to Gamma Rays  

PubMed Central

In a previous paper, we reported that the reactivity level, which regulates the frequency of transposition of I factor, a LINE element-like retrotransposon, is enhanced by the same agents that induce the SOS response in Escherichia coli. In this report, we describe experimental evidence that, for identical genotypes, the reactivity levels correlate with the sensitivity of oogenesis to gamma rays, measured by the number of eggs laid and by frequency of dominant lethals. This strongly supports the hypothesis that the reactivity level is one manifestation of an inducible DNA repair system taking place in the female germ line of Drosophila melanogaster. The implications of this finding for the understanding of the regulation of I factor are discussed and some other possible biological roles of this system are outlined. PMID:8647394

Laurencon, A.; Bregliano, J. C.

1995-01-01

90

Gamma-Ray Bursts  

NASA Technical Reports Server (NTRS)

Gamma-ray burst (GRB) have been an unsolved mystery in high-energy astrophysics for the last 30 years. Immediately after GRB were discovered, scientists tried to understand the mechanism that causes these events and where they come from. Since than, many theories have been suggested to explain GRB which have durations spanning five orders of magnitude (ranging between a few milliseconds and minutes) and spectrals that peak generally in the range of 0.1 to 1 MeV. Given this numbers, most theorists would think of processes occurring near neutron stars in our galaxy, many of which are known sources of rapidly varying, high-energy photon emission.

Kouveliotou, Chryssa

1997-01-01

91

{gamma} ray astronomy with muons  

SciTech Connect

Although {gamma} ray showers are muon poor, they still produce a number of muons sufficient to make the sources observed by GeV and TeV telescopes observable also in muons. For sources with hard {gamma} ray spectra there is a relative {open_quotes}enhancement{close_quotes} of muons from {gamma} ray primaries as compared to that from nucleon primaries. All shower {gamma} rays above the photoproduction threshold contribute to the number of muons N{sub {mu}}, which is thus proportional to the primary {gamma} ray energy. With {gamma} ray energy 50 times higher than the muon energy and a probability of muon production by the {gamma}{close_quote}s of about 1{percent}, muon detectors can match the detection efficiency of a GeV satellite detector if their effective area is larger by 10{sup 4}. The muons must have enough energy for sufficiently accurate reconstruction of their direction for doing astronomy. These conditions are satisfied by relatively shallow neutrino detectors such as AMANDA and Lake Baikal, and by {gamma} ray detectors such as MILAGRO. TeV muons from {gamma} ray primaries, on the other hand, are rare because they are only produced by higher energy {gamma} rays whose flux is suppressed by the decreasing flux at the source and by absorption on interstellar light. We show that there is a window of opportunity for muon astronomy with the AMANDA, Lake Baikal, and MILAGRO detectors. {copyright} {ital 1997} {ital The American Physical Society}

Halzen, F. [Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)] [Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States); Stanev, T. [Bartol Research Institute, University of Delaware, Newark, Delaware 19716 (United States)] [Bartol Research Institute, University of Delaware, Newark, Delaware 19716 (United States); Yodh, G.B. [Department of Physics and Astronomy, University of California, Irvine, California 92715 (United States)] [Department of Physics and Astronomy, University of California, Irvine, California 92715 (United States)

1997-04-01

92

Intrinsic and dust-induced polarization in gamma-ray burst afterglows: the case of GRB 021004  

E-print Network

Polarization measurements for the optical counterpart to GRB 021004 are presented and discussed. Our observations were performed with the TNG and the VLT-UT3 (Melipal) during the first and fourth night after the gamma-ray burst discovery. We find robust evidence of temporal evolution of the polarization, which is therefore, at least partially, intrinsic to the optical transient. We do not find convincing evidence of wavelength dependence for the intrinsic polarization of the transient, in agreement with current polarization models for optical afterglows. We discuss the role of dust, both in our galaxy and in the host, in modifying the transmitted polarization vector, showing how a sizable fraction of the observed polarized flux is due to Galactic selective extinction, while it is not possible to single out any clear contribution from dust in the host galaxy. We discuss how our data compare to those obtained by different groups showing that a two-component model is required to describe the complete dataset. This is not surprising given the complex lightcurve of GRB 021004.

D. Lazzati; S. Covino; S. di Serego Alighieri; G. Ghisellini; J. Vernet; E. Le Floc'h; D. Fugazza; S. Di Tomaso; D. Malesani; N. Masetti; E. Pian; E. Oliva; L. Stella

2003-08-29

93

Digital Pulse Processing and Gamma Ray Tracking  

NSDL National Science Digital Library

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

2010-09-21

94

Cell cycle perturbations and genotoxic effects in human primary fibroblasts induced by low-energy protons and X/gamma-rays.  

PubMed

The effect of graded doses of high-linear energy transfer (LET) low-energy protons to induce cycle perturbations and genotoxic damage was investigated in normal human fibroblasts. Furthermore, such effects were compared with those produced by low-LET radiations. HFFF2, human primary fibroblasts were exposed to either protons (LET = 28.5 keV/microm) or X/gamma-rays, and endpoints related to cell cycle kinetics and DNA damage analysed. Following both type of irradiations, unsynchronized cells suffered an inhibition to entry into S-phase for doses of 1-4 Gy and remained arrested in the G(1)-phase for several days. The levels of induction of regulator proteins, such as TP53 and CDKN1A showed a clear LET-dependence. DSB induction and repair as measured by scoring for gamma-H2AX foci indicated that protons, with respect to X-rays, yielded a lower number of DSBs per Gy, which showed a slower kinetics of disappearance. Such result was in agreement with the extent of MN induction in binucleated cells after X-irradiation. No significant differences between the two types of radiations were observed with the clonogenic assay, resulting anyway the slope of gamma-ray curve higher than that the proton one. In conclusion, in normal human primary fibroblasts cell cycle arrest at the G(1)/S transition can be triggered shortly after irradiation and maintained for several hours post-irradiation of both protons and X-rays. DNA damage produced by protons appears less amenable to be repaired and could be transformed in cytogenetic damage in the form of MN. PMID:19755805

Antoccia, Antonio; Sgura, Antonella; Berardinelli, Francesco; Cavinato, Maria; Cherubini, Roberto; Gerardi, Silvia; Tanzarella, Caterina

2009-09-01

95

Polarization mesurements of gamma ray bursts and axion like particles  

E-print Network

A polarized gamma ray emission spread over a sufficiently wide energy band from a strongly magnetized astrophysical object like gamma ray bursts (GRBs) offers an opportunity to test the hypothesis of axion like particles (ALPs). Based on evidences of polarized gamma ray emission detected in several gamma ray bursts we estimated the level of ALPs induced dichroism, which could take place in the magnetized fireball environment of a GRB. This allows to estimate the sensitivity of polarization measurements of GRBs to the ALP-photon coupling. This sensitivity $\\gag\\le 2.2\\cdot 10^{-11} {\\rm GeV^{-1}}$ calculated for the ALP mass $m_a=10^{-3}~{\\rm eV}$ and MeV energy spread of gamma ray emission is competitive with the sensitivity of CAST and becomes even stronger for lower ALPs masses.

Andre Rubbia; Alexander Sakharov

2008-09-03

96

Gamma-ray burst observations  

Microsoft Academic Search

Gamma-ray bursts (GRBs) are the most luminous known objects in the Universe. Their brief, random appearance in the gamma-ray region had made their study difficult since their discovery, over thirty years ago. There is a rich diversity in the duration and morphology of GRB time profiles. The spectra are characterized by a smooth continuum, usually peaking in the range from

Gerald J. Fishman

2000-01-01

97

Genetic dissimilarity of putative gamma-ray-induced 'Preciosa-AAAB-Pome type' banana (Musa sp) mutants based on multivariate statistical analysis.  

PubMed

Bananas are among the most important fruit crops worldwide, being cultivated in more than 120 countries, mainly by small-scale producers. However, short-stature high-yielding bananas presenting good agronomic characteristics are hard to find. Consequently, wind continues to damage a great number of plantations each year, leading to lodging of plants and bunch loss. Development of new cultivars through conventional genetic breeding methods is hindered by female sterility and the low number of seeds. Mutation induction seems to have great potential for the development of new cultivars. We evaluated genetic dissimilarity among putative 'Preciosa' banana mutants generated by gamma-ray irradiation, using morphoagronomic characteristics and ISSR markers. The genetic distances between the putative 'Preciosa' mutants varied from 0.21 to 0.66, with a cophenetic correlation coefficient of 0.8064. We found good variability after irradiation of 'Preciosa' bananas; this procedure could be useful for banana breeding programs aimed at developing short-stature varieties with good agronomic characteristics. PMID:22033908

Pestana, R K N; Amorim, E P; Ferreira, C F; Amorim, V B O; Oliveira, L S; Ledo, C A S; Silva, S O

2011-01-01

98

High energy gamma ray astronomy  

NASA Technical Reports Server (NTRS)

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

Fichtel, Carl E.

1987-01-01

99

Cross sections relevant to gamma-ray line emission in solar flares: $^3$He-induced reactions on $^{16}$O nuclei  

E-print Network

Gamma-ray production cross sections have been measured for gamma-ray lines copiously emitted in the $^3$He bombardment of $^{16}$O nuclei: the 937, 1042 and 1081 keV lines of $^{18}$F and the 1887 keV line of $^{18}$Ne. Four Ge detectors with BGO shielding for Compton suppression were used to measure the angular distributions of the gamma-rays. The excitation functions have been obtained for $^3$He bombarding energies from 3.7 to 36 MeV. Total cross sections are tabulated for calculations relevant to gamma-ray astronomy. The importance of these lines as diagnosis for the presence and properties of accelerated $^3$He in solar flares is discussed in light of the measured cross sections.

V. Tatischeff; J. Duprat; J. Kiener; M. Assuncao; A. Coc; C. Engrand; M. Gounelle; A. Lefebvre; M. -G. Porquet; N. De Sereville; J. -P. Thibaud; C. Bourgeois; M. Chabot; F. Hammache; J. -A. Scarpaci

2003-08-25

100

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

101

Gamma-Ray Burst Lines  

E-print Network

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

Michael S. Briggs

1999-10-20

102

Application of time-series analysis to induced gamma ray spectroscopy logs from two Cold Lake heavy-oil observation wells  

SciTech Connect

This paper reports on induced gamma ray spectroscopy (IGRS) logs from two cyclic-steam-stimulation observation wells in Cold Lake that were analyzed to determine the vertical resolution and repeatability of data derived from gamma rays of inelastic and capture neutron reactions. Time-series analysis, a technique that uses the Fourier representation of the log data, was used to quantify the vertical resolution and the signal/noise characteristics of various IGRS log curves and to compute the coherence vs. spatial frequency of data collected on multiple IGRS passes. The coherence function ranges from 1.0 for perfect repeatability to 0.0 for incoherent noise. Because no real variations in the measured data were expected for the 12- to 24-hour data-collection period, andy deviation of the coherence function from 1.0 is attributed to incoherent noise. Generally, coherence is high at low frequencies (large vertical scales) and low at high frequencies (small vertical scales). By noting the frequency at which the coherence level decreases to the expected value of random noise, we can quantify the vertical resolution of a log curve. Data analysis from these wells indicates that both the vertical resolution and repeatability of individual capture and inelastic curves differ. We found that the H-yield and capture curves have the highest vertical resolution ({approx}0.3m) and the best signal/noise ratios (F{sub SN} {approx} 30:1). In contrast, the capture Ca and Si yields are of significantly lower quality (F{sub SN} {approx}2:1). Only a small difference exist between the vertical resolution of the inelastic C (1.0 m) and O (1.3 m) yields, but the F{sub SN} of the O yield is only one-half that of the C yield. Fortunately, the vertical resolution and the repeatability of the C/O ratio, F{sub CO}, are determined primarily by the quality of the inelastic C data.

Georgi, D.T. (Esso Resources Canada Ltd. (CA))

1991-12-01

103

Gamma Ray Bursts and CETI  

E-print Network

Gamma ray burst sources are isotropically distributed. They could be located at distances $\\sim 1000$ AU. (Katz \\cite{JK92}) GRB signals have many narrow peaks that are unresolved at the millisecond time resolution of existing observations. \\cite{JK87} CETI could use stars as gravitational lenses for interstellar gamma ray laser beam communication. Much better time resolution of GRB signals could rule out (or confirm?) the speculative hypothesis that GRB = CETI.

Frank D. Smith Jr

1993-02-10

104

Lightning Generated Gamma Ray Bursts  

NASA Technical Reports Server (NTRS)

The prime focus of this effort is to advance the state of understanding of correlation between lightning strokes and gamma-ray flashes. key issue addressed was the revision of the existing models of runaway breakdown in the stratosphere due to low altitude lightning, which are related to the source of gamma-ray flashes. The revision includes the assessment of the effect due to geomagnetic field on the development of runaway discharge.

Milikh, Gennady

1996-01-01

105

First Quantitative Imaging of Organic Fluorine within Angiogenic Tissues by Particle Induced Gamma-Ray Emission (PIGE) Analysis: First PIGE Organic Fluorine Imaging  

PubMed Central

PET (Positron Emission Tomography) allows imaging of the in vivo distribution of biochemical compounds labeled with a radioactive tracer, mainly 18F-FDG (2-deoxy-2-[18F] fluoro-D-glucose). 18F only allows a relatively poor spatial resolution (2-3 mm) which does not allow imaging of small tumors or specific small size tissues, e.g. vasculature. Unfortunately, angiogenesis is a key process in various physiologic and pathologic processes and is, for instance, involved in modern anticancer approaches. Thus ability to visualize angiogenesis could allow early diagnosis and help to monitor the response of cancer to specific chemotherapies. Therefore, indirect analytical techniques are required to assess the localization of fluorinated compounds at a micrometric scale. Multimodality imaging approaches could provide accurate information on the metabolic activity of the target tissue. In this article, PIGE method (Particle Induced Gamma-ray Emission) was used to determine fluorinated tracers by the nuclear reaction of 19F(p,p??)19F in tissues. The feasibility of this approach was assessed on polyfluorinated model glucose compounds and novel peptide-based tracer designed for angiogenesis imaging. Our results describe the first mapping of the biodistribution of fluorinated compounds in both vascularized normal tissue and tumor tissue. PMID:24310427

Lavielle, Sebastien; Gionnet, Karine; Ortega, Richard; Deves, Guillaume; Kilarski, Victor; Wehbe, Katia; Bikfalvi, Andreas; Deleris, Gerard

2011-01-01

106

Study of asymmetries of Cd(Zn)Te devices investigated using photo-induced current transient spectroscopy, Rutherford backscattering, surface photo-voltage spectroscopy, and gamma ray spectroscopies  

SciTech Connect

Despite these recent advancements in preparing the surface of Cd(Zn)Te devices for detector applications, large asymmetries in the electronic properties of planar Cd(Zn)Te detectors are common. Furthermore, for the development of patterned electrode geometries, selection of each electrode surface is crucial for minimizing dark current in the device. This investigation presented here has been carried out with three objectives. Each objective is oriented towards establishing reliable methods for the selection of the anode and cathode surfaces independent of the crystallographic orientation. The objectives of this study are (i) investigate how the asymmetry in I-V characteristics of Cd(Zn)Te devices may be associated with the TeO2 interfacial layer using Rutherford backscattering to study the structure at the Au-Cd(Zn)Te interface, (ii) develop an understanding of how the concentration of the active traps in Cd(Zn)Te varies with the external bias, and (iii) propose non-destructive methods for selection of the anode and cathode which are independent of crystallographic orientation. The spectroscopic methods employed in this investigation include Rutherford backscattering spectroscopy, photo-induced current transient spectroscopy, and surface photo-voltage spectroscopy, as well as gamma ray spectroscopy to demonstrate the influence on detector properties.

Crocco, J.; Bensalah, H.; Zheng, Q.; Dieguez, E. [Crystal Growth Laboratory, Universidad Autonoma de Madrid, Madrid Spain (Spain); Corregidor, V.; Avles, E. [Instituto Tecnologico e Nuclear UFA, Sacavem (Portugal); Castaldini, A.; Fraboni, B.; Cavalcoli, D.; Cavallini, A. [PHoS Laboratory, Department of Physics, University of Bologna, Bologna (Italy); Vela, O. [Centro de Investigacion Energeticas Medioambientales y Tecnologicas (CIEMAT), Madrid (Spain)

2012-10-01

107

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

108

Gamma ray bursts ROBERT S MACKAY  

E-print Network

Gamma ray bursts ROBERT S MACKAY COLIN ROURKE We propose that a gamma ray burst is a kinematic Gamma ray bursts are intense flashes of electromagnetic radiation of cosmic origin lasting from ten accepted mechanism. We propose that a gamma ray burst is simply a kinematic effect, namely the effect

Rourke, Colin

109

Radiation effect on PMMA POF under gamma-ray irradiation  

Microsoft Academic Search

An irradiation test was performed for polymethylmethacrylate plastic optical fibers under gamma-ray irradiation in order to use the fiber in low-level radiation environments. Under gamma-ray irradiation at a high dose rate, only a large radiation-induced transmission loss at wavelengths less than 700 nm was observed. Under irradiation at a low dose rate, the loss was small and other two characteristic

K. Toh; S. Nagata; B. Tsuchiya; T. Shikama

2007-01-01

110

Gamma-RayGamma-Ray Bursts: from SwiftBursts: from Swift  

E-print Network

Gamma-RayGamma-Ray Bursts: from SwiftBursts: from Swift to GLASTto GLAST Bing ZhangBing ZhangGehrels, et al), et al) #12;Gamma-ray bursts: the mostGamma-ray bursts: the most violent explosions fireball central photosphere internal external shocks engine (shocks) (reverse) (forward) gamma-ray UV

California at Santa Cruz, University of

111

Characterization of gamma-ray induced paramagnetic centers in bayerite by means of EPR and ENDOR spectroscopies  

Microsoft Academic Search

Four different paramagnetic centers, induced in bayerite samples by irradiation, have been characterized by EPR and ENDOR spectroscopies. Two of them, respectively, of V- and F-types, have been found to be mobile at room temperature and frozen at lower temperature. The first one, with g1= 2.021+\\/-0.002, g2=2.010+\\/-0.005, and g3=2.005+\\/-0.002, is identified with an O- species stemming from the ionization of

Eric G. Derouane; Jacques C. Vedrine

1976-01-01

112

Gamma rays induce a p53-independent mitochondrial biogenesis that is counter-regulated by HIF1?  

PubMed Central

Mitochondrial biogenesis is an orchestrated process that presides to the regulation of the organelles homeostasis within a cell. We show that ?-rays, at doses commonly used in the radiation therapy for cancer treatment, induce an increase in mitochondrial mass and function, in response to a genotoxic stress that pushes cells into senescence, in the presence of a functional p53. Although the main effector of the response to ?-rays is the p53-p21 axis, we demonstrated that mitochondrial biogenesis is only indirectly regulated by p53, whose activation triggers a murine double minute 2 (MDM2)-mediated hypoxia-inducible factor 1? (HIF1?) degradation, leading to the release of peroxisome-proliferator activated receptor gamma co-activator 1? inhibition by HIF1?, thus promoting mitochondrial biogenesis. Mimicking hypoxia by HIF1? stabilization, in fact, blunts the mitochondrial response to ?-rays as well as the induction of p21-mediated cell senescence, indicating prevalence of the hypoxic over the genotoxic response. Finally, we also show in vivo that post-radiotherapy mitochondrial DNA copy number increase well correlates with lack of HIF1? increase in the tissue, concluding this may be a useful molecular tool to infer the trigger of a hypoxic response during radiotherapy, which may lead to failure of activation of cell senescence. PMID:23764844

Bartoletti-Stella, A; Mariani, E; Kurelac, I; Maresca, A; Caratozzolo, M F; Iommarini, L; Carelli, V; Eusebi, L H; Guido, A; Cenacchi, G; Fuccio, L; Rugolo, M; Tullo, A; Porcelli, A M; Gasparre, G

2013-01-01

113

Mutagenic effectiveness and efficiency of EMS, DES and gamma-rays in rice  

Microsoft Academic Search

Data on chlorophyll mutation frequency after treatment with EMS, DES and gamma-rays and sequential administration of gamma-rays and the two alkylating agents in three varieties of rice have been used to work out quantitatively the effectiveness and efficiency of each mutagen and combination treatment. For effectiveness, the order is EMS > DES and for efficiency it is EMS > DES

M. L. H. Kaul; A. K. Bhan

1977-01-01

114

The Gamma-ray Sky with Fermi  

NASA Technical Reports Server (NTRS)

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

Thompson, David

2012-01-01

115

Apoptosis (cell death) induced in mouse bowel by 1,2-dimethylhydrazine, methylazoxymethanol acetate, and gamma-rays  

SciTech Connect

Apoptosis is a pattern of cell death involving nuclear pyknosis, cytoplasmic condensation, and karyorrhexis. The frequency of apoptosis after treatment with two colon carcinogens and radiation was studied in the crypts of five different portions of mouse bowel. When 1,2-dimethylhydrazine (DMH) was injected s.c., the earliest rise in apoptotic incidence after a high dose (200 mg/kg) was noted at 3 h in small intestine and at 6 h in large bowel. After i.p. administration of methylazoxymethanol (MAM) acetate, apoptotic cells were seen in large bowel after 3 h. When the plateau values attained after high doses of DMH were compared, many apoptotic cells were found in the lower part of the large bowel, whereas few such cells were observed in the small intestine and the upper part of the large bowel. This finding was reversed in the case of radiation-induced apoptosis. In the descending colon, a definite circadian rhythm in the apoptotic incidence was observed 6 h after injection of DMH or MAM acetate. Apoptosis showed a high incidence when these drugs were given between 2400 h and 0900 h, but a low incidence after administration between 1200 h and 2100 h. In the small intestine a rhythm was also noted for MAM acetate, but not significantly for DMH.

Ijiri, K. (Univ. of Tokyo (Japan))

1989-11-15

116

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

117

Neutrinos from Gamma Ray Bursts  

E-print Network

We show that the detection of neutrinos from a typical gamma ray burst requires a kilometer-scale detector. We argue that large bursts should be visible with the neutrino telescopes under construction. We emphasize the 3 techniques by which neutrino telescopes can perform this search: by triggering on i) bursts of muons from muon neutrinos, ii) muons from air cascades initiated by high energy gamma rays and iii) showers made by relatively low energy ($\\simeq 100\\,\\mev$) electron neutrinos. Timing of neutrino-photon coincidences may yield a measurement of the neutrino mass to order $10^{-5}$~eV, an interesting range in light of the solar neutrino anomaly.

F. Halzen; G. Jaczko

1996-02-07

118

Striking regression of subcutaneous fibrosis induced by high doses of gamma rays using a combination of pentoxifylline and ?-tocopherol: an experimental study  

Microsoft Academic Search

Purpose: To establish a successful treatment of subcutaneous fibrosis developing after high doses of gamma rays, suitable for use in clinical practice.Methods and Materials: We used an animal model of acute localized gamma irradiation simulating accidental overexposure in humans. Three groups of 5 Large White pigs were irradiated using a collimated 192Ir source to deliver a single dose of 160

Jean-Louis Lefaix; Sylvie Delanian; Marie-Catherine Vozenin; Jean-Jacques Leplat; Yves Tricaud; Michéle Martin

1999-01-01

119

Upgrade of the JET Gamma-Ray Cameras  

SciTech Connect

The JET gamma-ray camera diagnostics have already provided valuable information on the gamma-ray imaging of fast ion in JET plasmas /1,2/. The applicability of gamma-ray imaging to high performance deuterium and deuterium-tritium JET discharges is strongly dependent on the fulfilment of rather strict requirements for the characterisation of the neutron and gamma-ray radiation fields. These requirements have to be satisfied within very stringent boundary conditions for the design, such as the requirement of minimum impact on the co-existing neutron camera diagnostics. The JET Gamma-Ray Cameras (GRC) upgrade project deals with these issues with particular emphasis on the design of appropriate neutron/gamma-ray filters ('neutron attenuators'). Several design versions have been developed and evaluated for the JET GRC neutron attenuators at the conceptual design level. The main design parameter was the neutron attenuation factor. The two design solutions, that have been finally chosen and developed at the level of scheme design, consist of: a) one quasi-crescent shaped neutron attenuator (for the horizontal camera) and b) two quasi-trapezoid shaped neutron attenuators (for the vertical one). The second design solution has different attenuation lengths: a short version, to be used together with the horizontal attenuator for deuterium discharges, and a long version to be used for high performance deuterium and DT discharges. Various neutron-attenuating materials have been considered (lithium hydride with natural isotopic composition and {sup 6}Li enriched, light and heavy water, polyethylene). Pure light water was finally chosen as the attenuating material for the JET gamma-ray cameras. The neutron attenuators will be steered in and out of the detector line-of-sight by means of an electro-pneumatic steering and control system. The MCNP code was used for neutron and gamma ray transport in order to evaluate the effect of the neutron attenuators on the neutron field of the JET GRC. The modelling was dedicated to the estimation of neutron and (plasma-emitted) gamma-ray attenuation, neutron-induced gamma-ray background and the neutron in-scattering impact on the neutron detectors due to the attenuator in the parking location. A numerical study of the gamma-ray detector (CsI(Tl)) was done by means of the IST Monte Carlo code. It provided preliminary results on the detector efficiency and response function.

Soare, S.; Curuia, M.; Anghel, M.; Constantin, M.; David, E. [Association EURATOM-MEdC, National Institute for Cryogenics and Isotopic Technologies, Rm. Valcea (Romania); Zoita, V.; Craciunescu, T.; Falie, D.; Pantea, A.; Tiseanu, I. [Association EURATOM-MEdC, National Institute for Laser, Plasma and Radiation Physics, Bucharest (Romania); Kiptily, V.; Prior, P.; Edlington, T.; Griph, S.; Krivchenkov, Y.; Loughlin, M.; Popovichev, S.; Riccardo, V.; Syme, B.; Thompson, V. [Association EURATOM-UKAEA/JOC, Culham Science Centre, Abingdon (United Kingdom)] (and others)

2008-03-12

120

On Gamma-Ray Bursts  

E-print Network

(Shortened) 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 energy ion collisions. We then turn to the theory of vacuum polarization around a Kerr-Newman black hole, leading to the extraction of the blackholic energy, to the concept of dyadosphere and dyadotorus, and to the creation of an electron-positron-photon plasma. We then present a new theoretical approach encompassing the physics of neutron stars and heavy nuclei. It is shown that configurations of nuclear matter in bulk with global charge neutrality can exist on macroscopic scales and with electric fields close to the critical value near their surfaces. These configurations may represent an initial condition for the process of gravitational collapse, leading to the creation of an electron-positron-photon plasma: the basic self-accelerating system explaining both the energetics and the high energy Lorentz factor observed in GRBs. We then turn to recall the two basic interpretational paradigms of our GRB model. [...] We then turn to the special role of the baryon loading in discriminating between "genuine" short and long or "fake" short GRBs [...] We finally turn to the GRB-Supernova Time Sequence (GSTS) paradigm: the concept of induced gravitational collapse. [...] We then present some general conclusions.

Remo Ruffini; Maria Grazia Bernardini; Carlo Luciano Bianco; Letizia Caito; Pascal Chardonnet; Christian Cherubini; Maria Giovanna Dainotti; Federico Fraschetti; Andrea Geralico; Roberto Guida; Barbara Patricelli; Michael Rotondo; Jorge Armando Rueda Hernandez; Gregory Vereshchagin; She-Sheng Xue

2008-04-17

121

Cosmological gamma-ray bursts  

NASA Technical Reports Server (NTRS)

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

Paczynski, Bohdan

1991-01-01

122

Prospects for future very high-energy gamma-ray sky survey: Impact of secondary gamma rays  

NASA Astrophysics Data System (ADS)

Very high-energy gamma-ray measurements of distant blazars can be well explained by secondary gamma rays emitted by cascades induced by ultra-high-energy cosmic rays. The secondary gamma rays will enable one to detect a large number of blazars with future ground based gamma-ray telescopes such as Cherenkov Telescope Array (CTA). We show that the secondary emission process will allow CTA to detect 100, 130, 150, 87, and 8 blazars above 30 GeV, 100 GeV, 300 GeV, 1 TeV, and 10 TeV, respectively, up to z?8 assuming the intergalactic magnetic field (IGMF) strength B=10-17 G and an unbiased all sky survey with 0.5 h exposure at each field of view, where total observing time is ?540 h. These numbers will be 79, 96, 110, 63, and 6 up to z?5 in the case of B=10-15 G. This large statistics of sources will be a clear evidence of the secondary gamma-ray scenarios and a new key to studying the IGMF statistically. We also find that a wider and shallower survey is favored to detect more and higher redshift sources even if we take into account secondary gamma rays.

Inoue, Yoshiyuki; Kalashev, Oleg E.; Kusenko, Alexander

2014-02-01

123

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...

124

The Gamma-ray Universe through Fermi  

NASA Technical Reports Server (NTRS)

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

Thompson, David J.

2012-01-01

125

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

126

Light Curves of Swift Gamma Ray Bursts  

E-print Network

Recent observations from the Swift gamma-ray burst mission indicate that a fraction of gamma ray bursts are characterized by a canonical behaviour of the X-ray afterglows. We present an effective theory which allows us to account for X-ray light curves of both (short - long) gamma ray bursts and X-ray rich flashes. We propose that gamma ray bursts originate from massive magnetic powered pulsars.

Paolo Cea

2006-06-05

127

Continued study of the parameterization of the El gamma-ray strength function  

SciTech Connect

The parameterization of the magnitude and the energy dependence of the E1 gamma-ray strength function for the calculation of neutron- and proton-induced capture cross sections and capture gamma-ray spectra is investigated. The energy-dependent Breit-Wigner (EDBW) is reparameterized incorporating a more general expression for the Breit-Wigner line shape. Evaluation of the reparameterized E1 gamma-ray strength function is discussed. (WHK)

Gardner, M.A.; Gardner, D.G.

1981-06-19

128

Gamma ray astrophysics. [emphasizing processes and absorption  

NASA Technical Reports Server (NTRS)

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

Stecker, F. W.

1974-01-01

129

Differential Radiosensitivity Phenotypes of DNA-PKcs Mutations Affecting NHEJ and HRR Systems following Irradiation with Gamma-Rays or Very Low Fluences of Alpha Particles  

PubMed Central

We have examined cell-cycle dependence of chromosomal aberration induction and cell killing after high or low dose-rate ? irradiation in cells bearing DNA-PKcs mutations in the S2056 cluster, the T2609 cluster, or the kinase domain. We also compared sister chromatid exchanges (SCE) production by very low fluences of ?-particles in DNA-PKcs mutant cells, and in homologous recombination repair (HRR) mutant cells including Rad51C, Rad51D, and Fancg/xrcc9. Generally, chromosomal aberrations and cell killing by ?-rays were similarly affected by mutations in DNA-PKcs, and these mutant cells were more sensitive in G1 than in S/G2 phase. In G1-irradiated DNA-PKcs mutant cells, both chromosome- and chromatid-type breaks and exchanges were in excess than wild-type cells. For cells irradiated in late S/G2 phase, mutant cells showed very high yields of chromatid breaks compared to wild-type cells. Few exchanges were seen in DNA-PKcs-null, Ku80-null, or DNA-PKcs kinase dead mutants, but exchanges in excess were detected in the S2506 or T2609 cluster mutants. SCE induction by very low doses of ?-particles is resulted from bystander effects in cells not traversed by ?-particles. SCE seen in wild-type cells was completely abolished in Rad51C- or Rad51D-deficient cells, but near normal in Fancg/xrcc9 cells. In marked contrast, very high levels of SCEs were observed in DNA-PKcs-null, DNA-PKcs kinase-dead and Ku80-null mutants. SCE induction was also abolished in T2609 cluster mutant cells, but was only slightly reduced in the S2056 cluster mutant cells. Since both non-homologous end-joining (NHEJ) and HRR systems utilize initial DNA lesions as a substrate, these results suggest the possibility of a competitive interference phenomenon operating between NHEJ and at least the Rad51C/D components of HRR; the level of interaction between damaged DNA and a particular DNA-PK component may determine the level of interaction of such DNA with a relevant HRR component. PMID:24714417

Little, John B.; Kato, Takamitsu A.; Shih, Hung-Ying; Xie, Xian-Jin; Wilson Jr., Paul F.; Brogan, John R.; Kurimasa, Akihiro; Chen, David J.; Bedford, Joel S.; Chen, Benjamin P. C.

2014-01-01

130

Terrestrial Gamma-Ray Flashes (TGFs)  

NASA Technical Reports Server (NTRS)

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

Fishman, Gerald J.

2010-01-01

131

Gamma rays from globular clusters  

NASA Technical Reports Server (NTRS)

Globular clusters are known to contain a relatively large number of pulsars whose individual and collective emission in the X-ray and gamma-ray energy bands may be detectable by the instruments on board the Compton Gamma-Ray Observatory (CGRO), ROSAT, and possibly SIGMA. We discuss the several types of high-energy emission expected from isolated and interacting binary pulsars in globular clusters. Individual or collective high-energy emission from isolated pulsars is expected to be too low to be detected with current instruments. However, a class of high-luminosity hidden millisecond pulsars enshrouded in the evaporating material from irradiated companion stars can produce unpulsed shock emission detectable by the high-sensitivity instruments of ROSAT and CGRO. Establishing upper limits of high-energy emission from globular clusters will be valuable in constraining models for the formation of cluster millisecond pulsars.

Tavani, Marco

1993-01-01

132

Fission prompt gamma-ray multiplicity distribution measurements and simulations at DANCE  

SciTech Connect

The nearly energy independence of the DANCE efficiency and multiplicity response to {gamma} rays makes it possible to measure the prompt {gamma}-ray multiplicity distribution in fission. We demonstrate this unique capability of DANCE through the comparison of {gamma}-ray energy and multiplicity distribution between the measurement and numerical simulation for three radioactive sources {sup 22}Na, {sup 60}Co, and {sup 88}Y. The prospect for measuring the {gamma}-ray multiplicity distribution for both spontaneous and neutron-induced fission is discussed.

Chyzh, A; Wu, C Y; Ullmann, J; Jandel, M; Bredeweg, T; Couture, A; Norman, E

2010-08-24

133

Study of the characteristics of high-energy proton-induced gamma ray and neutron emission from materials that imitate surface of planets.  

SciTech Connect

A proposed ISTC Project is discussed in the present paper. The proposal is aimed at experiments to determine the space-energy characteristics of the neutron and gamma ray emission fields generated by 0.2-0.8 GeV proton irradiation of thick targets composed of various elements. At present, reliable data on physical properties of secondary radiation from materials irradiated by intennediate- and high-energy protons for some fundamental and applied researches in astrophysics, space physics, atomic and nuclear physics, as well as for designing and operating the latest accelerators are lacking.

Titarenko, Y. E. (Yury E.); Batyaev, V. F. (Vyacheslav F.); Karpikhin, E. I. (Evgeny I.); Zhivun, V. M. (Valery M.); Koldobsky, A. B. (Aleksander B.); Mulambetov, R. D. (Ruslan D.); Mulambetova, S. V.; Mashnik, S. G. (Stepan G.); Nekrasov, Y. V. (Yu V.); Trebukhovsky, Y. V. (Yury V.); Barashenkov, V. S. (Vladilen Sergeevich); Dmitrenko, V. V.; Ulin, S. E.; Hasebe, N.; Prael, R. E. (Richard E.)

2003-01-01

134

Standoff Performance of HPGe Detectors in Identification of Gamma-Ray Radiation Sources  

Microsoft Academic Search

The detection and identification of radiation sources at distances in the range of 15 meters or more is becoming increasingly important for illicit materials interdiction and the location of lost or orphan sources. In most locations, there is a considerable gamma-ray flux from natural background (NORM) and cosmic- induced nuclides. This gamma-ray flux varies with time, weather conditions, location, and

Ronald M. Keyser; Timothy R. Twomey; Sam Hitch

135

Cosmic Rays and Gamma Ray Bursts From Microblazars  

E-print Network

Highly relativistic jets from merger and accretion induced collapse of compact stellar objects, which may produce the cosmological gamma ray bursts (GRBs), are also very efficient and powerful cosmic ray accelerators. The expected luminosity, energy spectrum and chemical composition of cosmic rays from Galactic GRBs, most of which do not point in our direction, can explain the observed properties of Galactic cosmic rays.

Arnon Dar

1998-09-13

136

Can Fireball or Firecone Models Explain Gamma Ray Bursts?  

E-print Network

The observed afterglows of gamma ray bursts, in particular that of GRB 970228 six months later, seem to rule out relativistic fireballs and relativistic firecones driven by merger or accretion induced collapse of compact stellar objects in galaxies as the origin of GRBs. GRBs can be produced by superluminal jets from such events.

Arnon Dar

1997-09-24

137

Gamma-Ray Bursts: History and Observations  

Microsoft Academic Search

\\u000a Gamma-ray bursts (GRBs) are the most luminous objects known in the Universe. Their brief, random appearance in the gamma-ray\\u000a region had made their study difficult since their discovery over thirty years ago. The discovery of counterparts to gamma-ray\\u000a bursts and afterglow radiation in other wavelengths has provided the long-sought breakthrough in the direct determination\\u000a of their distance and luminosity scales.

G. J. Fishman

138

Gamma-Ray Bursts: an Overview  

Microsoft Academic Search

A history and overview of the observed properties of gamma-ray bursts are presented. The phenomenon of gamma-ray bursts is without precedence in astronomy, having no observed property that would be a direct indicator of their distance and no counterpart object in another wavelength region. Their brief, random appearance only in the gamma-ray region has made their study difficult. The observed

Gerald J. Fishman

1995-01-01

139

Gamma-Ray Astronomy Technology Needs  

NASA Technical Reports Server (NTRS)

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

Gehrels, N.; Cannizzo, J. K.

2012-01-01

140

GAMCIT: A gamma ray burst detector  

NASA Technical Reports Server (NTRS)

The origin of celestial gamma ray bursts remains one of the great mysteries of modern astrophysics. The GAMCIT Get-Away-Special payload is designed to provide new and unique data in the search for the sources of gamma ray bursts. GAMCIT consists of three gamma ray detectors, an optical CCD camera, and an intelligent electronics system. This paper describes the major components of the system, including the electronics and structural designs.

Surka, Derek M.; Grunsfeld, John M.; Warneke, Brett A.

1992-01-01

141

Black Stars and Gamma Ray Bursts  

E-print Network

Stars that are collapsing toward forming a black hole but are frozen near the Schwarzschild horizon are termed ``black stars''. Collisions of black stars, in contrast to black hole collisions, may be sources of gamma ray bursts, whose basic parameters are estimated quite simply and are found to be consistent with observed gamma ray bursts. Black star gamma ray bursts should be preceded by gravitational wave emission similar to that from the coalescence of black holes.

Tanmay Vachaspati

2007-06-08

142

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 and has put Europe in the lead in the field of gamma-ray astronomy INTEGRAL provides an unprecedented survey of the soft gamma-ray sky revealing hundreds of sources new classes of objects extraordinary views of antimatter annihilation in our Galaxy and fingerprints of recent nucleosynthesis processes While INTEGRAL has provided 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 satellite to the XMM Newton observatory 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

Knödlseder, J.; Gri Consortium

143

Future prospects for gamma-ray  

NASA Technical Reports Server (NTRS)

Astrophysical phenomena discussed are: the very energetic and nuclear processes associated with compact objects; astrophysical nucleo-synthesis; solar particle acceleration; the chemical composition of the planets and other bodies of the solar system; the structure of our galaxy; the origin and dynamic pressure effects of the cosmic rays; the high energy particles and energetic processes in other galaxies, especially active ones; and the degree of matter antimater symmetry of the universe. The gamma ray results of GAMMA-I, the gamma ray observatory, the gamma ray burst network, solar polar, and very high energy gamma ray telescopes on the ground provide justification for more sophisticated telescopes.

Fichtel, C.

1980-01-01

144

Cosmic gamma-ray bursts  

NASA Technical Reports Server (NTRS)

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

Hurley, K.

1991-01-01

145

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

E-print Network

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

Enomoto, Ryoji

146

Simulation fidelity issues when using gamma-ray simulators for tree testing  

SciTech Connect

Factors that influence the fidelity of gamma-ray TREE testing have been investigated. Specifically, package-induced dose enhancement in 256 K CMOS SRAMs and dose enhancement from finite-range electrons produced (by gamma-ray interactions) in materials external to the SRAM packages have been studied. Two gamma-ray simulators with significantly different spectra were used in the studies. The spectral differences produced less change in SRAM upset levels than did surrounding materials of equal mass density but differing atomic number. The implication for gamma-ray simulation testing is that individual devices within electronic systems may respond quite differently in gamma-ray TREE testing because of the structural materials within the system than when tests are performed on these individual devices without the system present.

Hartman, E.F.; Browning, J.S.; Drumm, C.R. (Sandia National Labs., Albuquerque, NM (USA))

1990-12-01

147

Gamma Rays from Classical Novae  

NASA Technical Reports Server (NTRS)

NASA at the University of Chicago, provided support for a program of theoretical research into the nature of the thermonuclear outbursts of the classical novae and their implications for gamma ray astronomy. In particular, problems which have been addressed include the role of convection in the earliest stages of nova runaway, the influence of opacity on the characteristics of novae, and the nucleosynthesis expected to accompany nova outbursts on massive Oxygen-Neon-Magnesium (ONeMg) white dwarfs. In the following report, I will identify several critical projects on which considerable progress has been achieved and provide brief summaries of the results obtained:(1) two dimensional simulation of nova runaway; (2) nucleosynthesis of nova modeling; and (3) a quasi-analytic study of nucleosynthesis in ONeMg novae.

1997-01-01

148

Concept of new gamma ray detector  

E-print Network

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

S. Osone

2002-11-29

149

Gamma rays from extragalactic astrophysical sources  

NASA Astrophysics Data System (ADS)

Presently there are several classes of detected gamma-ray extragalactic sources. They are mostly associated to active galactic nuclei (AGN) and (at soft gamma rays) to gamma-ray bursts (GRB), but not only.Active galactic nuclei consist of accreting supermassive black holeshosted by a galaxy that present in some cases powerful relativistic jet activity. Thesesources, which have been studied in gamma rays for several decades, areprobably the most energetic astrophysical objects, and their appearancedepends much on whether their jets point to us. Gamma-ray bursts, thought to be associated to collapsing or merging stellar-mass objects atcosmological distances, are also accreting highly relativistic jet sources that shine strongly at high energies. These are very short-duration events, but they are also the most luminous. Recently, star formation galaxies have turned out to be also gamma-ray emitters.On the other hand, clusters of galaxies have not been detected beyond X-rays yet. These are the largest knownstructures in the Universe; in their formation through accretion andmerging, shocks and turbulence are generated, which may lead to gamma-ray production. In thiswork, the gamma-ray physics of AGNs is briefly presented, as well as that of starburst galaxies, GRBs and clusters of galaxies.Afterwards, we consider some particular cases ofgamma-ray production in non-blazar AGN jets interacting with their medium at different scales.

Bosch-Ramon, V.

2011-11-01

150

What are gamma-ray bursters?  

Microsoft Academic Search

Gamma-ray bursters have defied explanation since their discovery over 15 years ago. These objects are luminous for only a few seconds at a time, mostly emitting gamma rays that are hundreds of thousands or even millions of times more energetic than photons of visible light. Then they lapse back into quiescence and remain invisible at all wavelengths for many years.

Kevin Hurley

1990-01-01

151

The Soft Gamma-Ray Repeaters  

Microsoft Academic Search

The Soft Gamma-Ray Repeaters (SGR) are sources of brief intense outbursts of low energy gamma rays. Most likely they are a new manifestation of neutron stars. Three sources were known prior to the launch of CGRO, and bursts from two of these have been seen by BATSE. However, no new sources have been discovered, which means that they are either

I. A. Smith

1997-01-01

152

Gamma ray lines from dark matter annihilation  

SciTech Connect

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

Giudice, G.F.

1989-08-01

153

Gamma rays from hidden millisecond pulsars  

NASA Technical Reports Server (NTRS)

The properties were studied of a new class of gamma ray sources consisting of millisecond pulsars totally or partially surrounded by evaporating material from irradiated companion stars. Hidden millisecond pulsars offer a unique possibility to study gamma ray, optical and radio emission from vaporizing binaries. The relevance of this class of binaries for GRO observations and interpretation of COS-B data is emphasized.

Tavani, Marco

1992-01-01

154

Unveiling the Secrets of Gamma Ray Bursts  

E-print Network

Gamma Ray Bursts (GRBs) 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 multi-wavelength picture of these events has revealed that they are the most energetic explosions since the Big Bang and are connected with stellar deaths in other galaxies. However, in spite of exceptional observational and theoretical progress in the last 15 years, recent observations raise many questions which challenge our understanding of these elusive phenomena. Gamma Ray Bursts therefore remain one of the hottest topics in modern astrophysics.

Gomboc, A

2012-01-01

155

Gamma-Ray Bursts: An Overview  

NASA Technical Reports Server (NTRS)

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

Fishman, Gerald J.

1995-01-01

156

Constraining axion by polarized prompt emission from gamma ray bursts  

E-print Network

A polarized gamma ray emission spread over a sufficiently wide energy band from a strongly magnetized astrophysical object like gamma ray bursts (GRBs) offers an opportunity to test the hypothesis of invisible axion. The axionic induced dichroism of gamma rays at different energies should cause a misalignment of the polarization plane for higher energy events relative to that one for lower energies events resulting in the loss of statistics needed to form a pattern of the polarization signal to be recognized in a detector. According to this, any evidence of polarized gamma rays coming from an object with extended magnetic field could be interpreted as a constraint on the existence of the invisible axion for a certain parameter range. Based on reports of polarized MeV emission detected in several GRBs we derive a constraint on the axion-photon coupling. This constraint $\\g_{a\\gamma\\gamma}\\le 2.2\\cdot 10^{-11} {\\rm GeV^{-1}}$ calculated for the axion mass $m_a=10^{-3} {\\rm eV}$ is competitive with the sensitivity of CAST and becomes even stronger for lower masses.

A. Rubbia; A. S. Sakharov

2007-08-20

157

Accretion-Induced Conversion of High-Velocity Neutron Stars to Strange Stars in Supernovae and Implications for Gamma-Ray Bursts  

E-print Network

We present a new model for gamma-ray bursts (GRBs) that are not only associated with supernovae but also have small baryon contamination. In this model, we assume a newborn neutron star to move outward at a kick velocity of $\\sim 10^3 {\\rm km} {\\rm s}^{-1}$ in the supernova ejecta. We find that such a neutron star still hypercritically accretes its surrounding supernova matter. Once the stellar mass increases to some critical mass, the neutron star will undergo a phase transition to become a strange star, leading to an energy release of a few $10^{52}$ ergs. The phase transition, if possibly occuring just near the supernova front, will first result in an ultra-relativistic fireball and then a GRB. This provides a plausible explanation for the GRB-supernova association. We estimate the burst rate to be $\\sim 10^{-6}$ per year per galaxy. Our model also predicts other possiblities. For example, if the resulting fireballs have a Lorentz factor of the order of a few, they will produce X-ray GRBs observed by BeppoSAX. We find the rate of such bursts to be $\\sim 10^{-5}$ per year per galaxy.

K. S. Cheng; Z. G. Dai

2001-05-10

158

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

159

Degradation of SiGe HBT with reactor pulse neutron and gamma rays irradiation  

NASA Astrophysics Data System (ADS)

The typical dc electronic parameters degradation of SiGe HBT irradiated by reactor pulse neutron and gamma rays were measured. The mechanisms of transient radiation-induced damage in SiGe HBT were preliminary analyzed.

Liu, Shu-huan; Lin, Dong-sheng; Guo, Xiao-qiang; Liu, Nan-nan; Jiang, Xin-biao; Zhu, Guang-ning; Li, Da; Wang, Zhu-jun; Tang, Ben-qi; Chen, Wei; Zhang, Wei; Zhou, Hui; Shao, Bei-bei; Li, Jun-li

2006-12-01

160

Observations of Gamma-Ray Bursts  

NASA Technical Reports Server (NTRS)

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

Fishman, G. J.

1995-01-01

161

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

162

Gamma-ray Astronomy and GLAST  

NASA Technical Reports Server (NTRS)

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

McEnery, Julie

2007-01-01

163

Radiation-induced mutation at minisatellite loci  

SciTech Connect

We are studying the radiation-induced increase of mutation rate in minisatellite loci in mice and humans. Minisatellite mutations were scored by multilocus DNA fingerprint analysis in the progeny of {gamma}-irradiated and non-irradiated mice. The frequency of mutation in offspring of irradiated males was 1.7 higher that in the control group. Germline mutation at human minisatellite loci was studied among children born in heavily polluted areas of the Mogilev district of Belarus after the Chernobyl accident and in a control population. The frequency of mutation assayed both by DNA fingerprinting and by eight single locus probes was found to be two times higher in the exposed families than in the control group. Furthermore, mutation rate was correlated with the parental radiation dose for chronic exposure {sup 137}Cs, consistent with radiation-induction of germline mutation. The potential use of minisatellites in monitoring germline mutation in humans will be discussed.

Dubrova, Y.E. [Univ. of Leicester (United Kingdom)]|[Vavilov Institute of General Genetics, Moscow (Russian Federation); Nesterov, V.N.; Krouchinsky, N.G. [Research Institute for Radiation Medicine, Mogilev (Belarus)] [and others

1997-10-01

164

IR observations in gamma-ray blazars  

NASA Technical Reports Server (NTRS)

The infrared photometric and spectral observation of five gamma ray blazars in coordination with the energetic gamma ray experiment telescope (EGRET) onboard the Compton Gamma Ray Observatory is reported. The infrared measurements were made with a Cassegrain infrared camera and the mid-infrared large well imager at the Mt. Palomar 5 m telescope. The emphasis is on the three blazars observed simultaneously by EGRET and the ground-based telescope during viewing period 519. In addition to the acquisition of broadband spectral measurements for direct correlation with the 100 MeV EGRET observations, near infrared images were obtained, enabling a search for intra-day variability to be carried out.

Mahoney, W. A.; Gautier, T. N.; Ressler, M. E.; Wallyn, P.; Durouchoux, P.; Higdon, J. C.

1997-01-01

165

Fermi Gamma-Ray Space Telescope  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

166

Cosmic gamma-ray lines - Theory  

NASA Technical Reports Server (NTRS)

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

Lingenfelter, R. E.; Ramaty, R.

1980-01-01

167

Interpretations and implications of gamma ray lines from solar flares, the galactic center in gamma ray transients  

NASA Technical Reports Server (NTRS)

Observations and theories of astrophysical gamma ray line emission are reviewed and prospects for future observations by the spectroscopy experiments on the planned Gamma Ray Observatory are discussed.

Ramaty, R.; Lingenfelter, R. E.

1980-01-01

168

T-odd angular correlations in the emission of prompt gamma rays and neutrons in nuclear fission induced by polarized neutrons  

SciTech Connect

Study of the T-odd three-vector correlation in the emission of prompt neutrons from {sup 235}U fission by polarized cold neutrons has been continued at the facility MEPHISTO of the FRM II reactor (Technical University of Munich). The sought correlation was not found within experimental error of 2.3 Multiplication-Sign 10{sup -5}. The upper limit for the asymmetry coefficient has been set to vertical bar D{sub n} vertical bar < 6 Multiplication-Sign 10{sup -5} at 99% confidence level, whereas for ternary fission correlation coefficient D{sub {alpha}} = (170{+-}20) Multiplication-Sign 10{sup -5}. This limit casts doubt on a model that explains the three-vector correlation in ternary fission by the Coriolis mechanism. At the same time, five-vector correlation in the emission of prompt fission neutrons has been measured, which describes the rotation of the fissioning nucleus at the moment it breaks (ROT effect). At the angle 22.5 Degree-Sign to the fission axis, the correlation coefficient was found to be (1.57 {+-} 0.20) Multiplication-Sign 10{sup -4}, while at the angle of 67.5 Degree-Sign it is zero within the experimental uncertainty. The existence of ROT effect in the emission of prompt fission neutrons can be explained by the anisotropy of neutron emission in the rest frame of the fragment (fission fragments are aligned with respect to the axis of deformation of the fissioning nucleus), similar to the mechanism of ROT effect in the emission of prompt {gamma}-rays.

Danilyan, G. V. [Institute for Theoretical and Experimental Physics (Russian Federation); Klenke, J. [Forschungs-Neutronenquelle Heinz Meier-Leibnitz (FRM II) (Germany); Krakhotin, V. A.; Kopach, Yu. N.; Novitsky, V. V.; Pavlov, V. S.; Shatalov, P. B. [Institute for Theoretical and Experimental Physics (Russian Federation)

2011-05-15

169

Geolocation of Terrestrial Gamma Ray Flashes in Gamma Rays Using the Fermi Large Area Telescope  

NASA Astrophysics Data System (ADS)

We derive geolocations of bright Terrestrial Gamma ray Flashes (TGFs) directly in gamma rays using the Fermi Large Area Telescope (LAT) and compare with geolocations derived from LF and VLF (radio) networks. Imaging of the gamma ray direction is made possible by the fine spatial resolution of the LAT instrument, which is intended to make maps of the high-energy gamma ray astrophysical sky. Simulations show that LAT can geolocate very bright TGFs in favorable geometries with accuracies of several tens of km. Recent work by Connaughton et al. (2013) strongly suggests that the broadband radio signal is produced by the same bulk flow of relativistic electrons that create the gamma ray signal through bremsstrahlung interactions in the atmosphere. Our analysis confirms this picture by establishing that the radio and gamma ray signals are both temporally and spatially coincident. This work was performed at NRL and sponsored by NASA DPR S-15633-Y.

Schaal, Meagan; Grove, J. E.; Chekhtman, A.; Xiong, S.; Fitzpatrick, G.; Cummer, S.; Holzworth, R. H.

2014-01-01

170

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

171

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

172

Prospects of gamma-ray laser development  

SciTech Connect

In this paper the authors briefly present the current thrust of gamma-ray laser research. The authors discuss the major proposals of developing such lasers based on nuclear transitions and electron and positron beams.

Gupta, G.; Husain, J. (Dept. of Applied Physics, Faculty of Engineering and Technology, A.M. Univ., Aligarh UP 202 002 (IN))

1991-06-01

173

Overview Animation of Gamma-ray Burst  

NASA Video Gallery

Gamma-ray bursts are the most luminous explosions in the cosmos. Astronomers think most occur when the core of a massive star runs out of nuclear fuel, collapses under its own weight, and forms a b...

174

Cosmic-ray effects on diffuse gamma-ray measurements.  

NASA Technical Reports Server (NTRS)

Evaluation of calculations and experimental evidence from 600-MeV proton irradiation indicating that cosmic-ray-induced radioactivity in detectors used to measure the diffuse gamma-ray background produces a significant counting rate in the energy region around 1 MeV. It is concluded that these counts may be responsible for the observed flattening of the diffuse photon spectrum at this energy.

Fishman, G. J.

1972-01-01

175

Trimethylpsoralen induces small deletion mutations in Caenorhabditis elegans.  

PubMed Central

To examine the mutagenic spectrum of 4,5',8-trimethylpsoralen (TMP) in Caenorhabditis elegans, we isolated mutations in the unc-22 and pal-1 genes following TMP mutagenesis and analyzed them for restriction fragment length polymorphisms by Southern blot. Eleven of 21 unc-22 mutations exhibited restriction fragment length polymorphisms, 8 of which were deletions of between 0.10 and 15 kb in length. Both of two pal-1 mutations were also small deletions within this size range. Comparison of our results with previous studies on mutagenesis by gamma-rays and x-rays suggests that the mutagenic spectrum of TMP may be similar. TMP should be useful in generating mutations that cause complete loss of function of single genes and that are likely to result in allele-specific DNA polymorphisms. Images PMID:7906415

Yandell, M D; Edgar, L G; Wood, W B

1994-01-01

176

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

177

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

2006-06-01

178

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

179

Research in cosmic and gamma ray astrophysics  

NASA Technical Reports Server (NTRS)

Research activities in cosmic rays, gamma rays, and astrophysical plasmas are covered. The activities are divided into sections and described, followed by a bibliography. The astrophysical aspects of cosmic rays, gamma rays, and of the radiation and electromagnetic field environment of the Earth and other planets are investigated. These investigations are performed by means of energetic particle and photon detector systems flown on spacecraft and balloons.

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

1989-01-01

180

Photoabsorption of Gamma Rays in Relativistic Jets  

E-print Network

A derivation of the \\gamma\\gamma --> e^+ e^- optical depth for \\gamma rays produced in a comoving spherical emitting region is presented. Employing a simplified expression for the \\gamma\\gamma absorption cross section, analytic expressions for the minimum Doppler factor implied by the requirement of gamma-ray transparency are derived for a broken power-law spectrum of target photons which are isotropically distributed in the comoving frame. Application to specific systems is illustrated.

Charles Dermer

2004-02-18

181

Standoff 3D Gamma-Ray Imaging  

Microsoft Academic Search

We present a new standoff imaging technique able to provide 3-dimensional (3D) images of gamma-ray sources distributed in the environment. Unlike standard 3D tomographic methods, this technique does not require the radioactive sources to be bounded within a predefined physical space. In the present implementation, the gamma-ray imaging system is based on two large planar HPGe double sided segmented detectors,

Lucian Mihailescu; Kai Vetter; Daniel Chivers

2009-01-01

182

Gamma-Ray Bursts: Old and New  

E-print Network

Gamma-ray bursts are sudden releases of energy that for a duration of a few seconds outshine even huge galaxies. 30 years after the first detection of a gamma-ray burst their origin remains a mystery. Here I first review the ``old'' problems which have baffled astronomers over decades, and then report on the ``new'' exciting discoveries of afterglow emission at longer wavelengths which have raised more new questions than answered old ones.

Jochen Greiner

1998-02-17

183

Sequence specificity of streptozotocin-induced mutations.  

PubMed Central

The isolation and characterization of streptozotocin (STZ)-induced mutations in the phage P22 mnt repressor gene is described. Cells carrying the plasmid-borne mnt gene were exposed to STZ to give 10-20 percent survival and at least an eleven-fold increase in mutation frequency. DNA sequence analysis showed that 50 of 51 STZ-induced mutations were GC to AT transitions, and one was an AT to GC transition. We have also compared the STZ mutational spectrum to that for N-methyl-N'-nitro-N-nitroso-guanidine (MNNG). There are sites in the mnt gene which are mutated only by STZ; only by MNNG, or by both agents. Sites at which only STZ induced GC to AT transition mutations occur were in sequences that are pyrimidine rich 5' to the mutated site and purine rich 3' to the mutated site. Induction of mutations by both STZ and MNNG should be considered to maximize the number of mutable sites. PMID:2972994

Mack, S L; Fram, R J; Marinus, M G

1988-01-01

184

Gamma-ray albedo of the moon  

E-print Network

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

Igor V. Moskalenko; Troy A. Porter

2007-05-25

185

Analysis of gamma ray displacement damage in Light Water Reactor pressure vessels  

SciTech Connect

In addition to fast neutrons, the copious energetic gamma rays, present in a reactor environment, induce displacement damage in the reactor pressure vessel. The contribution of gamma ray damage to embrittlement is most pronounced in reactors with large water gaps separating the core from the reactor pressure vessel. Water moderates the energies of fast neutrons much more effectively than it attenuates the high energy gamma flux, and thus enhances the high energy gamma flux, incident on the vessel relative to the fast neutron flux. In this paper, an analysis of computer transport calculations is presented which quantifies the relative contribution of gamma ray damage in various pressure vessels. The results indicate that gamma ray damage must be included for accurate predictions of radiation-induced embrittlement.

Alexander, D.E.; Rehn, L.E.

1995-05-01

186

Supernovae and Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Participants; Preface; Gamma-ray burst-supernova relation B. Paczynski; Observations of gamma-ray bursts G. Fishman; Fireballs T. Piran; Gamma-ray mechanisms M. Rees; Prompt optical emission from gamma-ray bursts R. Kehoe, C. Akerlof, R. Balsano, S. Barthelmy, J. Bloch, P. Butterworth, D. Casperson, T. Cline, S. Fletcher, F. Frontera, G. Gisler, J. Heise, J. Hills, K. Hurley, B. Lee, S. Marshall, T. McKay, A. Pawl, L. Piro, B. Priedhorsky, J. Szymanski and J. Wren; X-ray afterglows of gamma-ray bursts L. Piro; The first year of optical-IR observations of SN1998bw I. Danziger, T. Augusteijn, J. Brewer, E. Cappellaro, V. Doublier, T. Galama, J. Gonzalez, O. Hainaut, B. Leibundgut, C. Lidman, P. Mazzali, K. Nomoto, F. Patat, J. Spyromilio, M. Turatto, J. Van Paradijs, P. Vreeswijk and J. Walsh; X-ray emission of Supernova 1998bw in the error box of GRB980425 E. Pian; Direct analysis of spectra of type Ic supernovae D. Branch; The interaction of supernovae and gamma-ray bursts with their surroundings R. Chevalier; Magnetars, soft gamma-ray repeaters and gamma-ray bursts A. Harding; Super-luminous supernova remnants Y. -H. Chu, C. -H. Chen and S. -P. Lai; The properties of hypernovae: SNe Ic 1998bw, 1997ef, and SN IIn 1997cy K. Nomoto, P. Mazzali, T. Nakamura, K. Iwanmoto, K. Maeda, T. Suzuki, M. Turatto, I. Danziger and F. Patat; Collapsars, Gamma-Ray Bursts, and Supernovae S. Woosley, A. MacFadyen and A. Heger; Pre-supernova evolution of massive stars N. Panagia and G. Bono; Radio supernovae and GRB 980425 K. Weiler, N. Panagia, R. Sramek, S. Van Dyk, M. Montes and C. Lacey; Models for Ia supernovae and evolutionary effects P. Hoflich and I. Dominguez; Deflagration to detonation A. Khokhlov; Universality in SN Iae and the Phillips relation D. Arnett; Abundances from supernovae F. -K. Thielemann, F. Brachwitz, C. Freiburghaus, S. Rosswog, K. Iwamoto, T. Nakamura, K. Nomoto, H. Umeda, K. Langanke, G. Martinez-Pinedo, D. Dean, W. Hix and M. Strayer; Sne, GRBs, and the global properties of the Universe B. Schmidt; How good are SNe Ia as standard candles? A. Sandage, G. Tammann and A. Saha; Type Ia supernovae and their implications for cosmology M. Livio; Conference summary: supernovae and gamma-ray bursts J. Wheeler.

Livio, Mario; Panagia, Nino; Sahu, Kailash

2001-07-01

187

Historical aspects of gamma-ray astronomy  

NASA Astrophysics Data System (ADS)

Over the entire 20th century, Cosmic Rays proved to be the watershed of fundamental knowledge from which poured out several streams that made us familiar with aspects of the universe that could never have been known through optical and radio astronomies alone. Cosmic ray interaction studies opened up the field of elementary particles and high energy physical processes. Gamma-ray astronomy enabled us to study celestial environments characterised by the dominance of high energy particles and their interactions with matter, magnetic and electric fields in the neighbourhood of these special environments. While neutrino astronomy is still in its infancy, it has the potential of becoming the most exciting field of study in the current century. Gamma-ray astronomy has had a chequered career. In the early part of the 20th century, Millikan proposed that cosmic rays are merely gamma rays. This was disproved by Compton, through the establishment of the latitude effect. The soviet astrophysicist Shklovskii pointed out at the III International conference on cosmic rays held at Guanjuato, Mexico, the possibility of supernova remants like the Crab Nebula being sources of TeV gamma rays. This was based on his realisation that the high degree of polarized light from the Crab could be due to Synchrotron emission by TeV energy electrons spiralling round the filamentary magnetic fields of the nebula. He argued that the same mechanism that accelerated electrons could also accelerate the protons which through their interaction with the surrounding matter generate pi-zero measons that would immediately decay into gamma rays. However, the efforts by the soviet experimentalists, who used the night air cerenkov technique for detection of the TeV gamma rays, proved negative; only upper limits could be set on the fluxew of TeV gamma rays from several of the SN-remnants; the negative results were first reported at the 7th ICRC held at Jaipur, India in 1963. High energy gamma ray astronomy had a remarkable revival with the discovery of Pulsars in 1967 and their identification with Neutron stars. The field has thrived since then has been extended even to the PeV range. Beginning with 1965, gamma ray astronomy in the energy range MeV to tens of GeV has also been successfully pursued with ballons, and satellites. The most perplexing in this energy range has been the discovery of the Gamma ray bursts. In the keynote address the historical aspects of this field will be covered with some references to the work in India.

Sreekantan, B. V.

2002-03-01

188

The response characteristics of GafChromic dosimetry media to 60Co gamma rays  

Microsoft Academic Search

The dosimetric characteristics of GafChromic Dosimetry Media after being irradiated by 60Co gamma rays have been studied and the dependence of the radiation-induced absorbance on the temperature during irradiated and during reading and the postirradiated effect are reported. The dose-response characteristics of the films to 60Co gamma rays at the reading wavelengths of 400 and 580 nm have been analyzed,

Li Zhongying; Peng Shouyong; Chen Yundong; Zhang Lu

1995-01-01

189

Effects of neutrons and gamma-rays on polymethylmethacrylate plastic optical fiber  

Microsoft Academic Search

The effects of neutron and gamma-ray irradiation on a polymethylmethacrylate (PMMA) plastic optical fiber (POF) were investigated. An improvement in the optical transmission was observed at the beginning of irradiation, but radiation damage (radiation-induced transmission loss in the visible wavelength range) increased as the irradiation continued. To determine the effects of neutrons and gamma-rays, the amount of energy absorbed in

K. Toh; K. Sakasai; T. Nakamura; K. Soyama; T. Shikama

2011-01-01

190

Fission Product Gamma-Ray Line Pairs Sensitive to Fissile Material and Neutron Energy  

SciTech Connect

The beta-delayed gamma-ray spectra from the fission of {sup 235}U, {sup 238}U, and {sup 239}Pu by thermal and near-14-MeV neutrons have been measured for delay times ranging from 1 minute to 14 hours. Spectra at all delay times contain sets of prominent gamma-ray lines with intensity ratios that identify the fissile material and distinguish between fission induced by low-energy or high-energy neutrons.

Marrs, R E; Norman, E B; Burke, J T; Macri, R A; Shugart, H A; Browne, E; Smith, A R

2007-11-15

191

Distinguishing fissions of 232Th, 237Np and 238U with beta-delayed gamma rays  

NASA Astrophysics Data System (ADS)

Measurements of beta-delayed gamma-ray spectra following 14-MeV neutron-induced fissions of 232Th, 238U, and 237Np were conducted at Lawrence Berkeley National Laboratory's 88-Inch Cyclotron. Spectra were collected for times ranging from 1 min to 14 h after irradiation. Intensity ratios of gamma-ray lines were extracted from the data that allow identification of the fissioning isotope.

Iyengar, A.; Norman, E. B.; Howard, C.; Angell, C.; Kaplan, A.; Ressler, J. J.; Chodash, P.; Swanberg, E.; Czeszumska, A.; Wang, B.; Yee, R.; Shugart, H. A.

2013-06-01

192

CONSTRAINTS ON VERY HIGH ENERGY GAMMA-RAY EMISSION FROM GAMMA-RAY BURSTS R. Atkins,1,2  

E-print Network

CONSTRAINTS ON VERY HIGH ENERGY GAMMA-RAY EMISSION FROM GAMMA-RAY BURSTS R. Atkins,1,2 W. Benbow,3 11; accepted 2005 June 3 ABSTRACT The Milagro Gamma-Ray Observatory employs a water Cerenkov detector emission from gamma-ray bursts (GRBs) during the prompt emission phase. Detection of >100 GeV counterparts

California at Santa Cruz, University of

193

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

194

Astrophysics with the 3DTI Gamma-Ray Telescope  

Microsoft Academic Search

Despite notable progress in gamma-ray astronomy, understanding the astrophysical sources of medium energy (MeV-range) gamma-rays still remains somewhat of a mystery. Medium-energy gamma-ray observations require diverse measurement techniques since the objects that produce these gamma- rays are both extended and point-like, transient and steady, and include both continuum and line emissions. The challenge is to develop a future gamma-ray instrument

S. D. Hunter; L. M. Barbier; P. F. Bloser

2008-01-01

195

Mercuric iodine room temperature gamma-ray detectors  

NASA Technical Reports Server (NTRS)

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.

Patt, Bradley E.; Markakis, Jeffrey M.; Gerrish, Vernon M.; Haymes, Robert C.; Trombka, Jacob I.

1990-01-01

196

Molecular markers of ionizing radiation-induced gene mutations in mammalian cells.  

PubMed

We have isolated independent Chinese hamster ovary (CHO) cell mutants at the hypoxanthine guanine phosphoribosyltransferase (hprt) locus from untreated, 60Co gamma-ray-exposed, and 212Bi alpha-exposed cells and identified the molecular changes underlying the mutation determined by multiplex polymerase chain reaction (PCR)-based exon deletion analysis. Both the parental CHO-K1 cells and the X-ray-sensitive mutant xrs-5 cells were studied. The radiosensitive xrs-5 cells are defective in DNA double-strand break rejoining ability and in V(D)J recombination, which can be complemented by Ku protein. Of the 71 spontaneous CHO-K1 hprt mutants analyzed, 78% showed no change in exon number or size, 20% showed loss of one to eight exons (partial deletion), and 3% showed loss of all nine hprt exons (total deletion). Exposure of CHO-K1 cells to 6 Gy of gamma rays, which reduced survival levels to 10%, produced a high deletion spectrum with 45% of the 20 mutants analyzed showing a loss of one to eight exons and 30% showing total deletion. Exposure to an equitoxic dose of alpha radiation from 212Bi, a 220Rn daughter, resulted in a spectrum similar to the gamma-ray spectrum in that 75% of the 49 mutants analyzed were deletions. To alpha radiation, however, tended to produce larger intragenic deletions than gamma radiation. Of the 92 spontaneous xrs-5 mutants analyzed for deletions, 43% showed a loss of one to eight exons and 14% showed total deletion. This suggests that, in certain regions of the hprt gene, base alterations can be converted into large deletions and alteration in the Ku protein complex can influence this type of mutational process. Exposure to alpha radiation (10% survival) to xrs-5 cells resulted in a deletion spectrum similar to that seen in CHO-K1 cells. Of the 49 mutants analyzed, 43% showed on change in exon number or size, 16% showed a loss of one to eight exons, and 41% showed total deletion. While the defect in xrs-5 cells has a profound effect on spontaneous mutant spectra, this defect does not appear to affect alpha-induced mutation spectra. PMID:8781403

Hsie, A W; Porter, R C; Xu, Z; Yu, Y; Sun, J; Meltz, M L; Schwartz, J L

1996-05-01

197

Mutations induced by ultraviolet light  

Microsoft Academic Search

The different ultraviolet (UV) wavelength components, UVA (320–400nm), UVB (280–320nm), and UVC (200–280nm), have distinct mutagenic properties. A hallmark of UVC and UVB mutagenesis is the high frequency of transition mutations at dipyrimidine sequences containing cytosine. In human skin cancers, about 35% of all mutations in the p53 gene are transitions at dipyrimidines within the sequence 5?-TCG and 5?-CCG, and

Gerd P. Pfeifer; Young-Hyun You; Ahmad Besaratinia

2005-01-01

198

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

199

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

NASA Astrophysics Data System (ADS)

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) ionization chamber with 6 different thick caps incorporated with the unfolding technique, was used to determine the gamma-ray spectrum in the THOR epithermal neutron beam, which contains intense neutrons and gamma rays. The applied caps had nominal thicknesses from 1 to 6 mm. Detector response functions of the applied Mg(Ar) chamber with different caps were calculated using MCNP5 with a validated chamber model. The spectrum unfolding process was performed using the well-known SAND-II algorithm. The unfolded result was found much softer than the originally calculated spectrum at the design stage. A large portion of low energy continuum was shown in the adjusted spectrum. This work gave us a much deeper insight into the THOR epithermal neutron beam and also showed a way to determine the gamma-ray spectrum.

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

2011-10-01

200

Development Of A Prompt Gamma-ray Analysis Combined With Multiple Gamma-ray Detection  

SciTech Connect

By applying the multiple gamma ray detection method to PGA, the interference from strong gamma ray can be reduced, therefore quantification limits of trace elements are improved significantly. MPGA detector system is constructed at the guide-hall of JRR-3M in JAERI. Several standard samples were measured by MPGA detector system.

Toh, Y.; Oshima, M.; Koizumi, M.; Osa, A.; Kimura, A. [Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan)

2006-03-13

201

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

202

Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-Ray Background  

NASA Technical Reports Server (NTRS)

The intergalactic magnetic field (IGMF) may leave an imprint on the anisotropy properties of the extragalactic gamma-ray background, through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thus inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that the two extreme cases (zero IGMF and IGMF strong enough to completely isotropize cascade photons) would be separable by ten years of Fermi observations and reasonable model parameters for the gamma-ray background. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

Venters, T. M.; Pavlidou, V.

2012-01-01

203

Can the Ionospheric Disturbances of Gamma-Ray Bursts be Detected Using the VLF Method?  

NASA Technical Reports Server (NTRS)

Following the first detection of an ionospheric disturbance caused by a gamma-ray burst, we searched for amplitude changes induced by gamma-ray bursts in very low frequency radio waves (VLF) propagating in the earth-ionosphere waveguide. All VLF propagation paths end in Huntsville, Alabama and the transmitters are located in Australia, Puerto Rico, Maine, Maryland, Washington State, Hawaii and Nebraska. Out of 200 bursts, which could have been detectable along 600 different propagation paths, not a single confirmed ionospheric disturbance attributable to a gamma-ray burst was found. Thus, it has been showed that the VLF approach is most likely not a viable method to detect gamma-ray bursts unless it can be demonstrated that all sea paths lead to a significant number of detections.

Fitzgerald, J. Brodney; Wright, William; George, Philip; Doyle, Hezzick; McGruder, Charles H., III; Jennings, Johnny; Inan, U. S.

1997-01-01

204

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

205

Gamma-ray burster recurrence timescales  

NASA Technical Reports Server (NTRS)

Three optical transients have been found which are associated with gamma-ray bursters (GRBs). The deduced recurrence timescale for these optical transients (tau sub opt) will depend on the minimum brightness for which a flash would be detected. A detailed analysis using all available data of tau sub opt as a function of E(gamma)/E(opt) is given. For flashes similar to those found in the Harvard archives, the best estimate of tau sub opt is 0.74 years, with a 99% confidence interval from 0.23 years to 4.7 years. It is currently unclear whether the optical transients from GRBs also give rise to gamma-ray events. One way to test this association is to measure the recurrence timescale of gamma-ray events tau sub gamma. A total of 210 gamma-ray error boxes were examined and it was found that the number of observed overlaps is not significantly different from the number expected from chance coincidence. This observation can be used to place limits on tau sub gamma for an assumed luminosity function. It was found that tau sub gamma is approx. 10 yr if bursts are monoenergetic. However, if GRBs have a power law luminosity function with a wide dynamic range, then the limit is tau sub gamma 0.5 yr. Hence, the gamma-ray data do not require tau sub gamma and tau sub opt to be different.

Schaefer, B. E.; Cline, T. L.

1984-01-01

206

Gamma rays, cosmic rays and galactic structure  

NASA Technical Reports Server (NTRS)

Working primarily from the recent SAS-2 observations of galactic gamma rays, the relation of these observations to the large scale distribution of cosmic rays and interstellar gas in the galaxy is reviewed and reexamined. Starting with a discussion of production rates, the case for pion decay being the predominant production mechanism in the galactic disk above 100 MeV is reestablished and it is also pointed out that Compton gamma rays can be a significant source. To facilitate discussion, the concepts of four distinct galactic regions are defined, viz. the nebulodisk, ectodisk, radiodisk and exodisk. Bremsstrahlung and pion decay gamma rays are associated with the first two (primarily the first) regions, and Compton gamma rays and synchrotron radiation are associated with the latter two regions. On a large scale, the cosmic rays, interstellar gas (primarily H2 clouds in the inner galaxy) and gamma ray emissivity all peak in a region between 5 and 6 kpc from the galactic center. This correlation is related to correlation with other population I phenomena and is discussed in terms of the density wave concept of galactic structure. The singular nature of the HI distribution appears to follow the supernova remnant and pulsar distributions in the galaxy.

Stecker, F. W.

1976-01-01

207

Gamma-ray and neutron spectroscopy of planetary surfaces and atmospheres  

SciTech Connect

The neutrons and 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 decay of the naturally-occurring radioelements and by nuclear excitations induced by cosmic-ray particles and their secondaries (especially neutron capture or inelastic scattering reactions). After a short history of planetary ..gamma..-ray and neutron spectroscopy, the ..gamma..-ray spectrometer and active neutron detection system planned for the Mars Observer Mission are presented. The results of laboratory experiments that simulate the cosmic-ray bombardments of planetary surfaces and the status of the theoretical calculations for the processes that make and transport neutrons and ..gamma.. rays will be reviewed. Studies of Mars, including its atmosphere, are emphasized, as are 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 ..gamma..-ray spectrometer. 23 refs., 1 fig.

Reedy, R.C.

1987-01-01

208

Automated krypton-85 gamma ray stack monitor  

SciTech Connect

A Ge(Li) ..gamma..-ray detector, housed in a lead cave, was used in conjunction with a six-liter pressurized (60 psia) well spectroscopy cell to selectively detect /sup 85/Kr stack emissions. This system was calibrated so as to relate the 514 keV ..gamma..-ray counting rate to /sup 85/Kr concentration. Counting rate, or concentration, was continuously recorded using a count rate meter/strip chart recorder combination and was also time averaged over 15 minute intervals using a programmable multi-channel analyzer system with cassette readout. Being completely automated, this ..gamma..-analysis system required little more than liquid nitrogen service and data record retrieval throughout a four-month long sampling period. The sensitivity of this ..gamma..-ray analytical system was such as to achieve a minimum detectable /sup 85/Kr stack concentration of 2 ..mu..Ci/m/sup 3/ for 15 minute counting intervals.

Goles, R.W.; Brauer, F.P.

1980-09-01

209

Technology Needs for Gamma Ray Astronomy  

NASA Technical Reports Server (NTRS)

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

Gehrels, Neil

2011-01-01

210

Gamma rays from pulsar wind shock acceleration  

NASA Technical Reports Server (NTRS)

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

Harding, Alice K.

1990-01-01

211

THE fermi gamma-ray burst monitor  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

212

Ground-Based Gamma Ray Astronomy  

NASA Astrophysics Data System (ADS)

This paper is the write-up of a rapporteur talk given by the author at the 33rd International Cosmic Ray Conference in Rio de Janeiro, Brazil, in 2013. It attempts to summarize results and developments in ground-based gamma-ray observations and instrumentation from among the ˜300 submissions to the gamma-ray sessions of the meeting. Satellite observations and theoretical developments were covered by a companion rapporteur (Stawarz, L., 33rd ICRC, Rio de Janeiro, Brazil, Rapporteur talk: Space-based Gamma-Ray Astronomy, 2013). Any review of this nature is unavoidably subjective and incomplete. Nevertheless, the article should provide a useful status report for those seeking an overview of this exciting and fast-moving field.

Holder, Jamie

2014-10-01

213

Ground-Based Gamma Ray Astronomy  

NASA Astrophysics Data System (ADS)

This paper is the write-up of a rapporteur talk given by the author at the 33rd International Cosmic Ray Conference in Rio de Janeiro, Brazil, in 2013. It attempts to summarize results and developments in ground-based gamma-ray observations and instrumentation from among the ˜300 submissions to the gamma-ray sessions of the meeting. Satellite observations and theoretical developments were covered by a companion rapporteur (Stawarz, L., 33rd ICRC, Rio de Janeiro, Brazil, Rapporteur talk: Space-based Gamma-Ray Astronomy, 2013). Any review of this nature is unavoidably subjective and incomplete. Nevertheless, the article should provide a useful status report for those seeking an overview of this exciting and fast-moving field.

Holder, Jamie

2014-08-01

214

Gamma-ray binaries: pulsars in disguise?  

Microsoft Academic Search

Context: .LS 5039 and LS I+61°303 are unique amongst high-mass X-ray binaries (HMXB) for their spatially-resolved radio emission and their counterpart at >GeV gamma-ray energies, canonically attributed to non-thermal particles in an accretion-powered relativistic jet. The only other HMXB known to emit very high-energy (VHE) gamma-rays, PSR B1259-63, harbours a non-accreting millisecond pulsar. Aims: .The purpose is to investigate whether

Guillaume Dubus; Marie Curie

2006-01-01

215

VHE Gamma-ray Supernova Remnants  

SciTech Connect

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

Funk, Stefan; /KIPAC, Menlo Park

2007-01-22

216

Gamma ray spectrometer for Lunar Scout 2  

NASA Technical Reports Server (NTRS)

We review the current status of the Los Alamos program to develop a high-resolution gamma-ray spectrometer for the Lunar Scout-II mission, which is the second of two Space Exploration Initiative robotic precursor missions to study the Moon. This instrument will measure gamma rays in the energy range of approximately 0.1 - 10 MeV to determine the composition of the lunar surface. The instrument is a high-purity germanium crystal surrounded by an CsI anticoincidence shield and cooled by a split Stirling cycle cryocooler. It will provide the abundance of many elements over the entire lunar surface.

Moss, C. E.; Burt, W. W.; Edwards, B. C.; Martin, R. A.; Nakano, George H.; Reedy, R. C.

1993-01-01

217

The gamma-ray laser project  

NASA Astrophysics Data System (ADS)

Recent approaches to the problem of the gamma-ray laser have focused on upconversion techniques in which metastable nuclei are pumped with long wavelength radiation. At the nuclear level the storage of energy can approach tera-Joules (10 to the 12th power J) per liter for thousands of years. However, any plan to use such a resource for a gamma-ray laser poses problems of a broad interdisciplinary nature requiring the fusion of concepts taken from relatively unrelated fields of physics.

Collins, Carl B.

1987-07-01

218

A supersymmetric model of gamma ray bursts  

E-print Network

We propose a model for gamma ray bursts in which a star subject to a high level of fermion degeneracy undergoes a phase transition to a supersymmetric state. The burst is initiated by the transition of fermion pairs to sfermion pairs which, uninhibited by the Pauli exclusion principle, can drop to the ground state of minimum momentum through photon emission. The jet structure is attributed to the Bose statistics of sfermions whereby subsequent sfermion pairs are preferentially emitted into the same state (sfermion amplification by stimulated emission). Bremsstrahlung gamma rays tend to preserve the directional information of the sfermion momenta and are themselves enhanced by stimulated emission.

L. Clavelli; G. Karatheodoris

2004-03-22

219

Neutrinos and Nucleosynthesis in Gamma Ray Bursts  

SciTech Connect

Gamma-ray bursts, while rare, may be important contributors to galactic nucleosynthesis. Here we consider the types of nucleosynthesis that can occur as material is ejected from a gamma-ray burst accretion disk. We calculate the composition of material within the disk as it dissociates into protons and neutrons and then use a parameterized outflow model to follow nuclear recombination in the wind. From the resulting nucleosynthesis we delineate the disk and outflow conditions in which iron peak, r-process, or light p-process nuclei may form. In all cases the neutrinos have an important impact on the final abundance distributions.

Surman, Rebecca [Union College; Mclaughlin, Gail C [North Carolina State University; Hix, William Raphael [ORNL

2006-01-01

220

Gamma ray line observations with OSSE  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

221

Gamma-ray Burst Skymap Website  

NSDL National Science Digital Library

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

222

Nucleosynthesis in gamma-ray bursts outflows  

E-print Network

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

M. Lemoine

2002-05-07

223

Radiation induced dynamic mutations and transgenerational effects.  

PubMed

Many studies have confirmed that radiation can induce genomic instability in whole body systems. Although the molecular mechanisms underlying induced genomic instability are not known at present, this interesting phenomenon could be the manifestation of a cellular fail-safe system in which fidelity of repair and replication is down-regulated to tolerate DNA damage. Two features of genomic instability namely, delayed mutation and untargeted mutation, require two mechanisms of ;damage memory' and ;damage sensing, signal transduction and execution' to induce mutations at a non damaged-site. In this report, the phenomenon of transgenerational genomic instability and possible mechanisms are discussed using mouse data collected in our laboratory as the main bases. PMID:17019049

Niwa, Ohtsura

2006-01-01

224

Comparison of gamma-ray coincidence and low-background gamma-ray singles spectrometry.  

PubMed

Aerosol samples have been studied under different background conditions using gamma-ray coincidence and low-background gamma-ray singles spectrometric techniques with High-Purity Germanium detectors. Conventional low-background gamma-ray singles counting is a competitive technique when compared to the gamma-gamma coincidence approach in elevated background conditions. However, measurement of gamma-gamma coincidences can clearly make the identification of different nuclides more reliable and efficient than using singles spectrometry alone. The optimum solution would be a low-background counting station capable of both singles and gamma-gamma coincidence spectrometry. PMID:22037206

Konki, J; Greenlees, P T; Jakobsson, U; Jones, P; Julin, R; Juutinen, S; Ketelhut, S; Hauschild, K; Kontro, R; Leppänen, A-P; Lopez-Martens, A; Mattila, A; Nieminen, P; Nyman, M; Peräjärvi, K; Peura, P; Rahkila, P; Ruotsalainen, P; Sarén, J; Scholey, C; Sorri, J; Toivonen, H; Turunen, J; Uusitalo, J

2012-02-01

225

Ultrahigh Energy Cosmic Rays and Prompt TeV Gamma Rays from Gamma Ray Bursts  

E-print Network

Gamma Ray Bursts (GRBs) have been proposed as one {\\it possible} class of sources of the Ultrahigh Energy Cosmic Ray (UHECR) events observed up to energies $\\gsim10^{20}\\ev$. The synchrotron radiation of the highest energy protons accelerated within the GRB source should produce gamma rays up to TeV energies. Here we briefly discuss the implications on the energetics of the GRB from the point of view of the detectability of the prompt TeV gamma rays of proton-synchrotron origin in GRBs in the up-coming ICECUBE muon detector in the south pole.

Pijushpani Bhattacharjee; Nayantara Gupta

2003-05-12

226

Gamma-ray bursts: Restarting the Engine  

E-print Network

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

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

2005-08-04

227

Gamma Rays From Rotation-Powered Pulsars  

E-print Network

The seven known gamma-ray pulsars represent a very small fraction of the more than 1000 presently known radio pulsars, yet they can give us valuable information about pulsar particle acceleration and energetics. Although the theory of acceleration and high-energy emission in pulsars has been studied for over 25 years, the origin of the pulsed gamma rays is a question that remains unanswered. Characteristics of the pulsars detected by the Compton Gamma-Ray Observatory could not clearly distinguish between an emission site at the magnetic poles (polar cap models) and emission from the outer magnetosphere (outer gap models). There are also a number of theoretical issues in both type of model which have yet to be resolved. The two types of models make contrasting predictions for the numbers of radio-loud and radio-quiet gamma-ray pulsars and of their spectral characteristics. GLAST will probably detect at least 50 radio-selected pulsars and possibly many more radio-quiet pulsars. With this large sample, it will be possible to fully test the model predictions and finally resolve this longstanding question.

Alice K. Harding

2002-08-22

228

Gamma-Ray Pulsars: Models and Predictions  

E-print Network

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

Alice K. Harding

2000-12-12

229

GAMMA RAY IMAGING FOR ENVIRONMENTAL REMEDIATION  

EPA Science Inventory

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

230

Search for Soft Gamma-Ray Events  

NASA Technical Reports Server (NTRS)

The support provided under this grant covered several projects, based on observations made with the Compton Gamma Ray Observatory, particularly with the Burst And Transient Source Experiment BATSE. The results of our work were published in 23 papers, 18 Circulars of the International Astronomical Union, and one popular article. I report on these projects separately.

vanParadijs, J. A.

1998-01-01

231

Current segmented gamma-ray scanner technology  

SciTech Connect

A new generation of segmented gamma-ray scanners has been developed at Los Alamos for scrap and waste measurements at the Savannah River Plant and the Los Alamos Plutonium Facility. The new designs are highly automated and exhibit special features such as good segmentation and thorough shielding to improve performance.

Bjork, C.W.

1987-01-01

232

A Compton scatter attenuation gamma ray spectrometer  

NASA Technical Reports Server (NTRS)

Compton attenuation technique, utilizing semiconductor sum-Compton detectors, has been proposed for gamma ray spectrometer capable of gamma spectral measurements in radition fields of 100 R/hr to one million R/hr. Spectrometer consists of two or more separate detectors, with only primary detector exposed to primary incident photon flux.

Austin, W. E.

1972-01-01

233

Physics of Gamma Ray Emitting AGN  

NASA Astrophysics Data System (ADS)

The TANAMI program has been studying the physics of relativistic jets of gamma-ray emitting AGN since November 2007 and was converted to a 5-year Large Proposal from Oct 2009. We propose to continue VLBI monitoring of these sources contemporaneously with observations at gamma-ray frequencies by the Fermi satellite which is continuously monitoring the full sky for the next 5 to 10 years. TANAMI has met all goals of its first 2.5 years, in particular by producing high-quality dual-frequency images and setting up a baseline for morphological and kinematic studies of Southern-Hemisphere gamma-ray sources/candidates. With its associated optical/UV and X-ray programs and its unique VLBI dual-frequency characteristics, TANAMI has become one of the major multiwavelength resources for the Fermi mission and the only one covering sources south of -30 degrees. The continuation of our program will establish critical jet parameters, including speeds and Doppler factors, which all depend on multi-year VLBI data. Tracking new jet components and associating their ejection epochs with gamma-ray flares will be possible and promises to pin down the origin and nature of the elusive high energy emission from AGN.

Ojha, Roopesh; Lovell, Jim; Edwards, Philip; Kadler, Matthias; Monitoringteam, Gamma Ray Blazar; Tingay, Steven

2010-10-01

234

Gamma-ray bursts as cosmological probes  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts (GRBs) are short, intense burstsof gamma-rays which during seconds to minutes outshine all other sources of gamma-ray emission in the sky.Following the prompt gamma-ray emission, an `afterglow' of emission from the X-ray range to radio wavelengthspersists up to months after the initial burst. The association of the class of long GRBs with the explosion of broad-line type Ic SNe GRBs allow galaxies to be selected independently oftheir emission properties (independently of dust obscuration and, uniquely, independently of their brightnesses atany wavelength) and they also permit the study of the gas in the interstellar medium (ISM) systematically and at anyredshift by the absorption lines present in the afterglow spectra. Moreover, the fading nature of GRBs and theprecise localization of the afterglow allow a detailed investigation of the emission properties of the GRB hostgalaxy once the afterglow has vanished. GRBs therefore constitute a unique tool to understand the link between theproperties of the ISM in the galaxy and the star formation activity, and this at any redshift. This is a unique wayto reveal the physical processes that trigger galaxy formation. The SVOM space mission project is designed to improve the use GRBs as cosmological probes.

Vergani, S. D.

2013-11-01

235

Evaluation of gamma-Ray Intensities.  

National Technical Information Service (NTIS)

Results of literature survey and evaluation of relative intensities and intensities per decay of gamma rays are presented. Evaluations were made for exp 22 Na, exp 24 Na, exp 46 Sc, exp 48 Sc, exp 48 V, exp 54 Mn, exp 57 Co, exp 60 Co, exp 85 Sr, exp 88 Y...

Y. Yoshizawa, H. Inoue, M. Hoshi, K. Shzuma, Y. Iwata

1978-01-01

236

Study of gamma-ray strength functions  

SciTech Connect

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

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

1980-08-07

237

Delayed Nickel Decay in Gamma Ray Bursts  

E-print Network

Recently observed emission lines in the X-ray afterglow of gamma ray bursts suggest that iron group elements are either produced in the gamma ray burst, or are present nearby. If this material is the product of a thermonuclear burn, then such material would be expected to be rich in Nickel-56. If the nickel remains partially ionized, this prevents the electron capture reaction normally associated with the decay of Nickel-56, dramatically increasing the decay timescale. Here we examine the consequences of rapid ejection of a fraction of a solar mass of iron group material from the center of a collapsar/hypernova. The exact rate of decay then depends on the details of the ionization and therefore the ejection process. Future observations of iron, nickel and cobalt lines can be used to diagnose the origin of these elements and to better understand the astrophysical site of gamma ray bursts. In this model, the X-ray lines of these iron-group elements could be detected in suspected hypernovae that did not produce an observable gamma ray burst due to beaming.

G. C. McLaughlin; R. A. M. J. Wijers

2002-05-19

238

Gamma-ray Pulsars: Models and Predictions  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

239

Gamma Ray and Neutron Detector Interactive  

NSDL National Science Digital Library

This product illustrates how scientists learn about the composition of an asteroid by studying energy and neutrons that emanate from it. The Dawn spacecraft contains three instruments -- the Gamma Ray and Neutro Detector (GRaND), the Visible Infrared Spectrometer, and the Framing Camera -- that will provide answers to questions about the formation and evolution of the early solar system.

Ristvey, John

2009-04-22

240

TILLING to detect induced mutations in soybean  

PubMed Central

Background Soybean (Glycine max L. Merr.) is an important nitrogen-fixing crop that provides much of the world's protein and oil. However, the available tools for investigation of soybean gene function are limited. Nevertheless, chemical mutagenesis can be applied to soybean followed by screening for mutations in a target of interest using a strategy known as Targeting Induced Local Lesions IN Genomes (TILLING). We have applied TILLING to four mutagenized soybean populations, three of which were treated with ethyl methanesulfonate (EMS) and one with N-nitroso-N-methylurea (NMU). Results We screened seven targets in each population and discovered a total of 116 induced mutations. The NMU-treated population and one EMS mutagenized population had similar mutation density (~1/140 kb), while another EMS population had a mutation density of ~1/250 kb. The remaining population had a mutation density of ~1/550 kb. Because of soybean's polyploid history, PCR amplification of multiple targets could impede mutation discovery. Indeed, one set of primers tested in this study amplified more than a single target and produced low quality data. To address this problem, we removed an extraneous target by pretreating genomic DNA with a restriction enzyme. Digestion of the template eliminated amplification of the extraneous target and allowed the identification of four additional mutant alleles compared to untreated template. Conclusion The development of four independent populations with considerable mutation density, together with an additional method for screening closely related targets, indicates that soybean is a suitable organism for high-throughput mutation discovery even with its extensively duplicated genome. PMID:18218134

Cooper, Jennifer L; Till, Bradley J; Laport, Robert G; Darlow, Margaret C; Kleffner, Justin M; Jamai, Aziz; El-Mellouki, Tarik; Liu, Shiming; Ritchie, Rae; Nielsen, Niels; Bilyeu, Kristin D; Meksem, Khalid; Comai, Luca; Henikoff, Steven

2008-01-01

241

Neutron and Prompt Gamma Ray Emission in the Proton Induced Fission of 239Np and 243Am and Spontaneous Fission of 252Cf  

NASA Astrophysics Data System (ADS)

Average prescission < Mnpre > and postscission < Mnpost > neutron multiplicities as well as average ?-ray multiplicity , average energy emitted by ?-rays and average energy per one gamma quantum as a function of mass and total kinetic energy (TKE) of fission fragments were measured in proton induced reactions p+242Pu?243Am, p+238U?239Np (at proton energy Ep=13, 20 and 55 MeV) and spontaneous fission of 252Cf. The solid angle aberration and the Doppler shift in the laboratory angular distribution of ?-ray emission were utilized to obtain the number and energy of ?-rays as functions of single fragment mass. The results in the case of 252Cf, for both average number and average energy as functions of single fragment mass, are characterized by a sawtooth behavior similar to that which is well known for neutron emission. The similar behavior is seen for proton induced fission of 239Np and 243Am. The fragment mass dependence < Mnpost > (m) and (m) show a clear sawtooth structure that is gradually washed out with increasing proton energy Ep. Using the response matrix techniques we were able to distinguish between the statistical dipole (E1) and collective quadrupole (E2) ?-ray emission of single fission fragments.

Krupa, L.; Kniajeva, G. N.; Kliman, J.; Bogatchev, A. A.; Chubarian, G. M.; Dorvaux, O.; Itkis, I. M.; Itkis, M. G.; Khlebnikov, S.; Kondratiev, N. A.; Kozulin, E. M.; Lyapin, V.; Materna, T.; Rubchenia, W.; Pokrovsky, I. V.; Trzaska, W.; Vakhtin, D.; Voskressensky, V. M.

2005-09-01

242

Gamma ray constraints on the Galactic supernova rate  

NASA Technical Reports Server (NTRS)

We perform Monte Carlo simulations of the expected gamma ray signatures of Galactic supernovae of all types to estimate the significance of the lack of a gamma ray signal due to supernovae occurring during the last millenium. Using recent estimates of the nuclear yields, we determine mean Galactic supernova rates consistent with the historic supernova record and the gamma ray limits. Another objective of these calculations of Galactic supernova histories is their application to surveys of diffuse Galactic gamma ray line emission.

Hartmann, D.; The, L.-S.; Clayton, Donald D.; Leising, M.; Mathews, G.; Woosley, S. E.

1991-01-01

243

Gamma-Ray Pulsars in the GLAST Era  

Microsoft Academic Search

A gamma-ray pulsar is a rotating neutron star that emits gamma-ray photons. The EGRET experiment has found seven so far. Gamma-ray pulsars exhibit a range of characteristics with some emitting at radio wavelengths and others not at all. The upcoming GLAST mission will dramatically improve on EGRET's flux sensitivity and energy range. In this talk gamma-ray pulsar models will be

Marcus Ziegler

2006-01-01

244

Quasars, Blazars, and the Gamma-Ray Sky  

Microsoft Academic Search

The statistical properties of gamma-ray emitting AGN are discussed, based on radio sources stronger than 1 Jy at 5 GHz that have been detected by the EGRET experiment on the Compton Gamma Ray Observatory. Most strong gamma-ray sources are radio quasars; radio galaxies are a small component of the population. Among the 1 Jy quasars, gamma-ray detections have stronger than

Chris Impey

1996-01-01

245

Simultaneous optical/gamma-ray observations of GRBs  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

246

TILLING to detect induced mutations in soybean  

Microsoft Academic Search

BACKGROUND: Soybean (Glycine max L. Merr.) is an important nitrogen-fixing crop that provides much of the world's protein and oil. However, the available tools for investigation of soybean gene function are limited. Nevertheless, chemical mutagenesis can be applied to soybean followed by screening for mutations in a target of interest using a strategy known as Targeting Induced Local Lesions IN

Jennifer L Cooper; Bradley J Till; Robert G Laport; Margaret C Darlow; Justin M Kleffner; Aziz Jamai; Tarik El-Mellouki; Shiming Liu; Rae Ritchie; Niels Nielsen; Kristin D Bilyeu; Khalid Meksem; Luca Comai; Steven Henikoff

2008-01-01

247

Very High-Energy Gamma-Ray Sources.  

ERIC Educational Resources Information Center

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

Weekes, Trevor C.

1986-01-01

248

Gamma-ray spectra from neutron capture on Sr  

Microsoft Academic Search

The gamma-ray spectrum following neutron capture on Sr was measured at 3 neutron energies: E\\/sub n\\/ = thermal, 2 keV, and 24 keV. Gamma rays were detected in a three-crystal Ge(Li)-NaI-NaI pair spectrometer. Gamma-ray intensities deduced from these spectra by spectral unfolding are presented.

R. E. Sullivan; J. A. Becker; M. L. Stelts

1981-01-01

249

Results from the Milagro Gamma-Ray Observatory  

E-print Network

Results from the Milagro Gamma-Ray Observatory E. Blaufuss for the Milagro Collaboration a,1 , aUniversity of Maryland, College Park, MD 20742, USA Abstract The Milagro Gamma-Ray Observatory, located at an altitude- tor capable of continuously monitoring the overhead sky for sources of TeV gamma rays. At the center

California at Santa Cruz, University of

250

THE MILAGRO GAMMA RAY OBSERVATORY: Gaurang B. Yodh  

E-print Network

THE MILAGRO GAMMA RAY OBSERVATORY: Gaurang B. Yodh for the Milagro Collaboration Department from AGN's such as MRK 421. Milagro will be the first VHE detector capable of recording Gamma Ray meters. 1. Inroduction The EGRET detector on the Compton Gamma Ray Observatory(CGRO) has observed gamma

California at Santa Cruz, University of

251

Very High Energy Gamma Ray Observations with the MAGIC  

E-print Network

Very High Energy Gamma Ray Observations with the MAGIC Telescope (a biased selection) Nepomuk Otte The non-thermal universe in VHE gamma-rays GRBs AGNs Origin of cosmic rays Cosmology Dark matter Space Physik / Humboldt Universität Berlin VHE gamma-ray sources status ICRC 2007 Rowell 71 known sources

California at Santa Cruz, University of

252

How Far Away Are Gamma-Ray Bursters?  

Microsoft Academic Search

The positions of over 1000 gamma-ray bursts detected with the BATSE experiment on board of the Compton Gamma Ray Observatory are uniformly and randomly distributed in the sky, with no significant concentration to the galactic plane or to the galactic center. The strong gamma-ray bursts have an intensity distribution consistent with a number density independent of distance in Euclidean space.

Bohdan Paczynski

1995-01-01

253

Celestial Gamma Ray Bursts Detector Development and Model Simulations  

Microsoft Academic Search

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

Patrick Charles Mock

1993-01-01

254

Viewing the Sky at Nuclear Gamma-Ray Wavelengths  

Microsoft Academic Search

I discuss our changed view of the gamma -ray sky as a result of measurements made by the gamma -ray spectrometer (GRS) on the Solar Maximum Mission satellite. This highly successful instrument was developed at UNH and MPE (Germany) to study solar flares and operated from 1980 February to 1989 November. The number of flares detected in nuclear gamma -rays

Gerald H. Share

1992-01-01

255

Gamma-Ray Telescopes: 400 Years of Astronomical Telescopes  

NASA Technical Reports Server (NTRS)

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

Gehrels, Neil; Cannizzo, John K.

2010-01-01

256

Ultraviolet observations of the gamma-ray blazer 3C 279 following the gamma-ray flare of 1991 June  

Microsoft Academic Search

Ultraviolet observations of the gamma-ray blazar 3C 279 were carried out in 1991 July with the International Ultraviolet Explorer (IUE) satellite, 28 days after the outburst of intense gamma-ray emission detected from this source with the high-energy Energetic Gamma Ray Experiment Telescope (EGRET) instrument aboard the Compton Gamma-Ray Observatory. IUE observations were conducted over the wavelength range 1200-3200 A (5-10

Jerry T. Bonnell; W. Thomas Vestrand; J. Gregory Stacy

1994-01-01

257

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

E-print Network

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

Mori, Masaki

258

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

E-print Network

It has recently been proposed that ultrahigh energy ($\\gtrsim 10^{19}$ eV) cosmic rays (UHECRs) are accelerated by the blast waves associated with GRBs. We calculate the observed synchrotron radiation spectrum from protons and energetic leptons formed in the cascades initiated by photopion production, taking into account $\\gamma\\gamma$ attenuation at the source. Normalizing to the emission characteristics of GRB~970508, we predict $\\sim 10$ MeV - 100 GeV fluxes at a level which may have been observed with EGRET from bright GRBs, and could be detected with the proposed GLAST experiment or with ground-based air \\v Cerenkov telescopes having thresholds $\\lesssim $ several hundred GeV. The temporal decay of the UHECR-induced high-energy $\\gamma$-ray afterglows is significantly slower than that of the lower-energy burst and associated synchrotron self-Compton (SSC) radiation, which provides a direct way to test the hadronic origin of a high-energy GRB afterglow. Besides testing the UHECR origin hypothesis, the short wavelength emission and afterglows can be used to probe the level of the diffuse intergalactic infrared radiation field or constrain redshifts of GRB sources.

M. Boettcher; C. D. Dermer

1998-01-06

259

Active Neutron and Gamma-Ray Instrumentation for In Situ Planetary Science Applications  

NASA Technical Reports Server (NTRS)

We describe the development of an instrument capable of detailed in situ bulk geochemical analysis of the surface of planets, moons, asteroids, and comets. This instrument technology uses a pulsed neutron generator to excite the solid materials of a planet and measures the resulting neutron and gamma-ray emission with its detector system. These time-resolved neutron and gamma-ray data provide detailed information about the bulk elemental composition, chemical context, and density distribution of the soil within 50 cm of the surface. While active neutron scattering and neutron-induced gamma-ray techniques have been used extensively for terrestrial nuclear well logging applications, our goal is to apply these techniques to surface instruments for use on any solid solar system body. As described, experiments at NASA Goddard Space Flight Center use a prototype neutron-induced gamma-ray instrument and the resulting data presented show the promise of this technique for becoming a versatile, robust, workhorse technology for planetary science, and exploration of any of the solid bodies in the solar system. The detection of neutrons at the surface also provides useful information about the material. This paper focuses on the data provided by the gamma-ray detector.

Parsons, A.; Bodnarik, J.; Evans, L.; Floyd, A.; Lim, L.; McClanahan, T.; Namkung, M.; Nowicki, S.; Schweitzer, J.; Starr, R.; Trombka, J.

2011-01-01

260

Research in cosmic and gamma ray astrophysics  

NASA Technical Reports Server (NTRS)

Discussed here is research in cosmic ray and gamma ray astrophysics at the Space Radiation Laboratory (SRL) of the California Institute of Technology. The primary activities discussed involve the development of new instrumentation and techniques for future space flight. In many cases these instrumentation developments were tested in balloon flight instruments designed to conduct new investigations in cosmic ray and gamma ray astrophysics. The results of these investigations are briefly summarized. Specific topics include a quantitative investigation of the solar modulation of cosmic ray protons and helium nuclei, a study of cosmic ray positron and electron spectra in interplanetary and interstellar space, the solar modulation of cosmic rays, an investigation of techniques for the measurement and interpretation of cosmic ray isotopic abundances, and a balloon measurement of the isotopic composition of galactic cosmic ray boron, carbon, and nitrogen.

Stone, Edward C.; Mewaldt, Richard A.; Prince, Thomas A.

1992-01-01

261

The Gamma-Ray Burst Next Door  

NASA Technical Reports Server (NTRS)

I hesitate to spawn a thousand bad sci-fi flicks, but here it goes: Scientists now say that some gamma-ray bursts, the most powerful explosions in the universe, originate in nearby galaxy clusters. If one were to occur nearby, it could wipe out life on Earth. Fortunately, the chances of mass extinction are slimmer than the Chicago Cubs meeting the Boston Red Sox in the World Series (. . . and the Red Sox winning). But a new analysis of over 1400 archived gamma-ray bursts reveals that about 100 bursts originated within 325 million light-years of Earth, and not billions of light-years away as previously thought. If so, there's no reason why a burst couldn't go off in our galaxy.

Wanjek, Christopher

2003-01-01

262

EBT-P gamma ray shielding analysis  

SciTech Connect

First, a one-dimensional scoping study was performed for the gamma ray shield of the ELMO Bumpy Torus proof-of-principle device to define appropriate shielding material and determine the required shielding thickness. The dose equivalent results are analyzed as a function of the radiation shield thickness for different shielding options. A sensitivity analysis for the pessimistic case is given. The recommended shielding option based on the performance and cost is discussed. Next, a three-dimensional scoping study for the coil shield was performed for four different shielding options to define the heat load for each component and check the compliance with the design criterion of 10 watts maximum heat load per coil from the gamma ray sources. Also, a detailed biological dose survey was performed which included: a) the dose equivalent inside and outside the building, b) the dose equivalent from the two mazes of the building, and c) the skyshine contribution to the dose equivalent.

Gohar, Y.

1983-09-01

263

Phenomenology of Gamma-Ray Jets  

E-print Network

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

Amir Levinson

2007-09-10

264

Cosmic-Rays and Gamma Ray Bursts  

NASA Astrophysics Data System (ADS)

Cosmic-rays are subatomic particles of energies ranging between a few eV to hundreds of TeV. These particles register a power-law spectrum, and it seems that most of them originate from astrophysical galactic and extragalactic sources. The shock acceleration in superalfvenic astrophysical plasmas, is believed to be the main mechanism responsible for the production of the non-thermal cosmic-rays. Especially, the importance of the very high energy cosmic-ray acceleration, with its consequent gamma-ray radiation and neutrino production in the shocks of the relativistic jets of Gamma Ray Bursts, is a favourable theme of study. I will discuss the cosmic-ray shock acceleration mechanism particularly focusing on simulation studies of cosmic-ray acceleration occurring in the relativistic shocks of GRB jets.

Meli, A.

2013-07-01

265

Gamma Ray Observatory (GRO): Emergency support  

NASA Technical Reports Server (NTRS)

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

Schauer, K.; Madden, J.

1991-01-01

266

Gamma ray spectroscopic measurements of Mars.  

PubMed

A gamma ray spectrometer placed in orbit around Mars is expected to yield significant compositional data which can be related to the evolution of that planet. Components of the observable gamma ray flux come from the Martian surface, galactic and intergalactic space, and the spacecraft itself. The flux can be detected by a scintillation crystal or solid state detector, either of which combines efficiency of detection with energy resolution, and returns information to the earth as a pulse height distribution in order to detect characteristic energy line structure. The data will be evaluated for evidence of elemental differentiation with reference to terrestrial, meteoritic, solar, and lunar abundances. A lengthy mission will allow the surface of Mars to be mapped in a search for possible correlations between composition and topography or albedo. PMID:20076376

Metzger, A E; Arnold, J R

1970-06-01

267

Ground-Based Gamma-Ray Astronomy  

E-print Network

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

Michael Catanese

1999-11-09

268

Gamma rays and large scale galactic structure  

NASA Technical Reports Server (NTRS)

Gamma ray astronomy is now beginning to provide a new look at the galactic structure and the distribution of cosmic rays, both electrons and nucleons, within the galaxy. The observations are consistent with a galactic spiral-arm model in which the cosmic rays are linearly coupled to the interstellar gas on the scale of the spiral arms. The agreement between the predictions of the model and the observations for regions of the plane where both 21-cm and 2.6-mm CO surveys exist emphasizes the need to extend these observations to include the entire plane. Future gamma-ray observations with more sensitivity and better angular resolutions, combined with these radio surveys, should shed new light on the distribution of cosmic rays, the nature of the galaxy, and the location and intensity of the spiral arms.

Kniffen, D. A.; Fichtel, C. E.; Thompson, D. J.

1977-01-01

269

Nucleosynthesis and astrophysical gamma ray spectroscopy  

NASA Technical Reports Server (NTRS)

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

Jacobson, Allan S.

1987-01-01

270

Gamma rays, cosmic rays, and galactic structure  

NASA Technical Reports Server (NTRS)

Observations of cosmic and gamma radiation by SAS-2 satellite are summarized and analyzed to determine processes responsible for producing observed galactic radiation. In addition to the production of gamma rays in discrete galactic objects such as pulsars, there are three main mechanisms by which high-energy (greater than 100 MeV) radiation is produced by high-energy interactions involving cosmic rays in interstellar space. These processes, which produce what may be called diffuse galactic gamma-rays, are: (1) the decay of pi mesons produced by interactions of cosmic ray nucleons with interstellar gas nuclei; (2) the bremsstrahlung radiation produced by cosmic ray electrons interacting in the Coulomb fields of nuclei of interstellar gas atoms; and (3) Compton interactions between cosmic ray electrons and low-energy photons in interstellar space.

Stecker, F. W.

1977-01-01

271

Solar flare gamma-ray line shapes  

NASA Technical Reports Server (NTRS)

A computer code has been developed which is used to calculate ab initio the laboratory shapes and energy shifts of gamma-ray lines from (C-12)(p, gamma/4.438/)p-prime(C-12) and (O-16)(p, gamma/6.129/)p-prime(O-16) reactions and to calculate the expected shapes of these lines from solar flares. The sensitivity of observable solar flare gamma-ray line shapes to the directionality of the incident particles is investigated for several projectile angular distributions. Shapes of the carbon and oxygen lines are calculated assuming realistic proton energy spectra for particles in circular orbits at the mirror points of magnetic loops, for particle beams directed downward into the photosphere, and for isotropic particle distributions. Line shapes for flare sites near the center of the sun and on the limb are shown for both thin-target and thick-target interaction models.

Werntz, C.; Kim, Y. E.; Lang, Frederick L.

1990-01-01

272

The GAMCIT gamma ray burst detector  

NASA Technical Reports Server (NTRS)

The GAMCIT payload is a Get-Away-Special payload designed to search for high-energy gamma-ray bursts and any associated optical transients. This paper presents details on the design of the GAMCIT payload, in the areas of battery selection, power processing, electronics design, gamma-ray detection systems, and the optical imaging of the transients. The paper discusses the progress of the construction, testing, and specific design details of the payload. In addition, this paper discusses the unique challenges involved in bringing this payload to completion, as the project has been designed, constructed, and managed entirely by undergraduate students. Our experience will certainly be valuable to other student groups interested in taking on a challenging project such as a Get-Away-Special payload.

Mccall, Benjamin J.; Grunsfeld, John M.; Sobajic, Srdjan D.; Chang, Chinley Leonard; Krum, David M.; Ratner, Albert; Trittschuh, Jennifer E.

1993-01-01

273

Real time gamma-ray signature identifier  

DOEpatents

A real time gamma-ray signature/source identification method and system using principal components analysis (PCA) for transforming and substantially reducing one or more comprehensive spectral libraries of nuclear materials types and configurations into a corresponding concise representation/signature(s) representing and indexing each individual predetermined spectrum in principal component (PC) space, wherein an unknown gamma-ray signature may be compared against the representative signature to find a match or at least characterize the unknown signature from among all the entries in the library with a single regression or simple projection into the PC space, so as to substantially reduce processing time and computing resources and enable real-time characterization and/or identification.

Rowland, Mark (Alamo, CA); Gosnell, Tom B. (Moraga, CA); Ham, Cheryl (Livermore, CA); Perkins, Dwight (Livermore, CA); Wong, James (Dublin, CA)

2012-05-15

274

Gamma rays from active galactic nuclei  

NASA Technical Reports Server (NTRS)

The general properties of Active Galactic Nuclei (AGN) and quasars are reviewed with emphasis on their continuum spectral emission. Two general classes of models for the continuum are outlined and critically reviewed in view of the impending GRO (Gamma Ray Observatory) launch and observations. The importance of GRO in distinguishing between these models and in general in furthering the understanding of AGN is discussed. The very broad terms the status of the current understanding of AGN are discussed.

Kazanas, Demosthenes

1990-01-01

275

Benchmark gamma-ray skyshine experiment  

Microsoft Academic Search

A benchmark gamma-ray skyshine experiment is descibed in which ⁶°Co sources were either collimated into an upward 150-deg conical beam or shielded vertically by two different thicknesses of concrete. A NaI(Tl) spectrometer and a high pressure ion chamber were used to measure, respectively, the energy spectrum and the 4..pi..-exposure rate of the air-reflected gamma photons up to 700 m from

R. R. Nason; J. K. Shultis; R. E. Faw; C. E. Clifford

1982-01-01

276

EBT-P gamma ray shielding analysis  

Microsoft Academic Search

First, a one-dimensional scoping study was performed for the gamma ray shield of the ELMO Bumpy Torus proof-of-principle device to define appropriate shielding material and determine the required shielding thickness. The dose equivalent results are analyzed as a function of the radiation shield thickness for different shielding options. A sensitivity analysis for the pessimistic case is given. The recommended shielding

Gohar

1983-01-01

277

Prospects for Nuclear-gamma-ray Astronomy  

NASA Technical Reports Server (NTRS)

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

Clayton, D. D.

1973-01-01

278

Beacons at the gamma ray horizon  

Microsoft Academic Search

Blazars with redshifts z<=0.1 are likely candidates for detection at energies in the range 300GeV-50TeV with Cerenkov telescopes and scintillator arrays. We present gamma-ray flux predictions for a sample of 15 nearby flat-spectrum radio sources fitting the proton blazar model of Mannheim (1993A&A...269...67M) to their observed broad-band spectral energy distributions. At high energies, we use fluxes or flux limits measured

K. Mannheim; S. Westerhoff; H. Meyer; H.-H. Fink

1996-01-01

279

Status of the Milagro Gamma Ray Observatory  

Microsoft Academic Search

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

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

1999-01-01

280

Gamma-Ray Line Observations with RHESSI  

E-print Network

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

David M. Smith

2004-04-30

281

The cannonball model of gamma ray bursts  

E-print Network

The cannonball model (CB) of gamma ray bursts (GRBs) is incredibly more successful than the standard blast-wave models (SM) of GRBs, which suffer from profound inadequacies and limited predictive power. The CB model is falsifiable in its hypothesis and results. Its predictions are summarized in simple analytical expressions, derived, in fair approximations, from first principles. It provides a good description on a universal basis of the properties of long-duration GRBs and of their afterglows (AGs).

Arnon Dar

2003-01-20

282

Are Gamma-Ray Bursts Standard Candles?  

E-print Network

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

Li-Xin Li

2007-05-30

283

Gadolinium-doped water cerenkov-based neutron and high energy gamma-ray detector and radiation portal monitoring system  

DOEpatents

A water Cerenkov-based neutron and high energy gamma ray detector and radiation portal monitoring system using water doped with a Gadolinium (Gd)-based compound as the Cerenkov radiator. An optically opaque enclosure is provided surrounding a detection chamber filled with the Cerenkov radiator, and photomultipliers are optically connected to the detect Cerenkov radiation generated by the Cerenkov radiator from incident high energy gamma rays or gamma rays induced by neutron capture on the Gd of incident neutrons from a fission source. The PMT signals are then used to determine time correlations indicative of neutron multiplicity events characteristic of a fission source.

Dazeley, Steven A; Svoboda, Robert C; Bernstein, Adam; Bowden, Nathaniel

2013-02-12

284

Nucleosynthesis and Gamma Ray-Line Astronomy  

E-print Network

The most energetic part of the electromagnetic spectrum bears the purest clues to the synthesis of atomic nuclei in the universe. The decay of radioactive species, synthesized in stellar environments and ejected into the interstellar medium, gives rise to specific gamma ray lines. The observations gathered up to now show evidence for radioactivities throughout the galactic disk, in young supernova remnants (Cas A, Vela), and in nearby extragalactic supernovae (SN 1987A, SN 1991T and SN1998bu), in the form of specific gamma ray lines resulting, respectively, from the radioactive decay of 26Al, 44Ti and 56Co. The various astrophysical sites of thermal nucleosynthesis of the radioactive nuclei were discussed: AGB and Wolf-Rayet stars, novae, and type Ia and type II supernovae. Nuclear excitations by fast particles also produce gamma ray lines which have been observed in great detail from solar flares, and more hypothetically from active star forming regions where massive supernovae and WR stars abound. This non thermal process and its nucleosynthetic consequences was reviewed. The 511 keV line arising from e+ + e- annihilation also provides important information on explosive nucleosynthesis, as well as on the nature of the interstellar medium where the positrons annihilate. INTEGRAL, the main mission devoted to high resolution nuclear spectroscopy, should lead to important progress in this field.

Elisabeth Vangioni-Flam; Reuven Ramaty; Michel Casse

1999-02-04

285

The Most Remote Gamma-Ray Burst  

NASA Astrophysics Data System (ADS)

ESO Telescopes Observe "Lightning" in the Young Universe Summary Observations with telescopes at the ESO La Silla and Paranal observatories (Chile) have enabled an international team of astronomers [1] to measure the distance of a "gamma-ray burst", an extremely violent, cosmic explosion of still unknown physical origin. It turns out to be the most remote gamma-ray burst ever observed . The exceedingly powerful flash of light from this event was emitted when the Universe was very young, less than about 1,500 million years old, or only 10% of its present age. Travelling with the speed of light (300,000 km/sec) during 11,000 million years or more, the signal finally reached the Earth on January 31, 2000. The brightness of the exploding object was enormous, at least 1,000,000,000,000 times that of our Sun, or thousands of times that of the explosion of a single, heavy star (a "supernova"). The ESO Very Large Telescope (VLT) was also involved in trail-blazing observations of another gamma-ray burst in May 1999, cf. ESO PR 08/99. PR Photo 28a/00 : Sky field near GRB 000131 . PR Photo 28b/00 : The fading optical counterpart of GRB 000131 . PR Photo 28c/00 : VLT spectrum of GRB 000131 . What are Gamma-Ray Bursts? One of the currently most active fields of astrophysics is the study of the mysterious events known as "gamma-ray bursts" . They were first detected in the late 1960's by instruments on orbiting satellites. These short flashes of energetic gamma-rays last from less than a second to several minutes. Despite much effort, it is only within the last few years that it has become possible to locate the sites of some of these events (e.g. with the Beppo-Sax satellite ). Since the beginning of 1997, astronomers have identified about twenty optical sources in the sky that are associated with gamma-ray bursts. They have been found to be situated at extremely large (i.e., "cosmological") distances. This implies that the energy release during a gamma-ray burst within a few seconds is larger than that of the Sun during its entire life time (about 10,000 million years). "Gamma-ray bursts" are in fact by far the most powerful events since the Big Bang that are known in the Universe. While there are indications that gamma-ray bursts originate in star-forming regions within distant galaxies, the nature of such explosions remains a puzzle. Recent observations with large telescopes, e.g. the measurement of the degree of polarization of light from a gamma-ray burst in May 1999 with the VLT ( ESO PR 08/99), are now beginning to cast some light on this long-standing mystery. The afterglow of GRB 000131 ESO PR Photo 28a/00 ESO PR Photo 28a/00 [Preview - JPEG: 400 x 475 pix - 41k] [Normal - JPEG: 800 x 949 pix - 232k] [Full-Res - JPEG: 1200 x 1424 pix - 1.2Mb] ESO PR Photo 28b/00 ESO PR Photo 28b/00 [Preview - JPEG: 400 x 480 pix - 67k] [Normal - JPEG: 800 x 959 pix - 288k] [Full-Res - JPEG: 1200 x 1439 pix - 856k] Caption : PR Photo 28a/00 is a colour composite image of the sky field around the position of the gamma-ray burst GRB 000131 that was detected on January 31, 2000. It is based on images obtained with the ESO Very Large Telescope at Paranal. The object is indicated with an arrow, near a rather bright star (magnitude 9, i.e., over 1 million times brighter than the faintest objects visible on this photo). This and other bright objects in the field are responsible for various unavoidable imaging effects, caused by optical reflections (ring-shaped "ghost images", e.g. to the left of the brightest star) and detector saturation effects (horizontal and vertical straight lines and coloured "coronae" at the bright objects, and areas of "bleeding", e.g. below the bright star). PR Photo 28b/00 shows the rapid fading of the optical counterpart of GRB 000131 (slightly left of the centre), by means of exposures with the VLT on February 4 (upper left), 6 (upper right), 8 (lower left) and March 5 (lower right). It is no longer visible on the last photo. Techni

2000-10-01

286

The Properties of Gamma-ray Binaries  

NASA Astrophysics Data System (ADS)

There are a small but growing number of high mass X-ray binaries (HMXBs) that also exhibit emission above 100 MeV. All of these "gamma-ray binaries" exhibit variable emission across the electromagnetic spectrum, from radio to TeV energies, that is modulated with the binary orbital period. The optical stellar companions in these gamma-ray binaries fall into a range of spectral classes: Wolf-Rayet, O main sequence, B supergiant, and Be. Their high energy emission is probably powered by the collision of stellar wind or disk outflows with relativistic pulsar winds in a shock region. These sources present a unique opportunity to study particle acceleration in nearby, Galactic sources. I will review the observed multiwavelength properties of known gamma-ray binaries and discuss the population in the context of the late stages of massive star evolution. I am grateful for support from the Fermi Cycle 4 program through NASA grant NNX11AO41G and from NSF grant AST-1109247.

McSwain, M. Virginia

2013-06-01

287

Positron annihilation in gamma-ray bursts  

NASA Technical Reports Server (NTRS)

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

Harding, Alice K.

1990-01-01

288

THE FERMI GAMMA-RAY BURST MONITOR  

SciTech Connect

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

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

2009-09-01

289

Hadronic Gamma Rays from Supernova Remnants  

E-print Network

A gas cloud near a supernova remnant (SNR) provides a target for pp-collisions leading to subsequent gamma-ray emission through neutral pion decay. The assumption of a power-law ambient spectrum of accelerated particles with index near -2 is usually built into models predicting the spectra of very-high energy (VHE) gamma-ray emission from SNRs. However, if the gas cloud is located at some distance from the SNR shock, this assumption is not necessarily correct. In this case, the particles which interact with the cloud are those leaking from the shock and their spectrum is approximately monoenergetic with the injection energy gradually decreasing as the SNR ages. In the GLAST energy range the gamma-ray spectrum resulting from particle interactions with the gas cloud will be flatter than expected, with the cutoff defined by the pion momentum distribution in the laboratory frame. We evaluate the flux of particles escaping from a SNR shock and apply the results to the VHE diffuse emission detected by the HESS at the Galactic centre.

I. V. Moskalenko; T. A. Porter; M. A. Malkov; P. H. Diamond

2007-05-25

290

Solar gamma rays. [in solar flares  

NASA Technical Reports Server (NTRS)

The theory of gamma ray production in solar flares is treated in detail. Both lines and continuum are produced. Results show that the strongest line predicted at 2.225 MeV with a width of less than 100 eV and detected at 2.24 + or - 2.02 MeV, is due to neutron capture by protons in the photosphere. Its intensity is dependent on the photospheric He-3 abundance. The neutrons are produced in nuclear reactions of flare accelerated particles which also produce positrons and prompt nuclear deexcitation lines. The strongest prompt lines are at 4.43 MeV from c-12 and at approximately 6.2 from 0-16 and N-15. The gamma ray continuum, produced by electron bremsstrahlung, allows the determination of the spectrum and number of accelerated electrons in the MeV region. From the comparison of the line and continuum intensities a proton-to-electron ratio of about 10 to 100 at the same energy for the 1972, August 4 flare. For the same flare the protons above 2.5 MeV which are responsible for the gamma ray emission produce a few percent of the heat generated by the electrons which make the hard X rays above 20 keV.

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

1974-01-01

291

Physical constraints on models of gamma-ray bursters  

SciTech Connect

This report deals with the constraints that can be placed on models of gamma-ray burst sources based on only the well-established observational facts and physical principles. The premise is developed that the very hard x-ray and gamma-ray continua spectra are well-established aspects of gamma-ray bursts. Recent theoretical work on gamma-ray bursts are summarized with emphasis on the geometrical properties of the models. Constraints on the source models which are implied by the x-ray and gamma-ray spectra are described. The allowed ranges for the luminosity and characteristic dimension for gamma-ray burst sources are shown. Some of the deductions and inferences about the nature of the gamma-ray burst sources are summarized. 67 refs., 3 figs.

Epstein, R.I.

1985-01-01

292

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

NASA Technical Reports Server (NTRS)

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

Ryan, James M.; Lockwood, John A.

1989-01-01

293

The axion-photon interaction and gamma ray signals of dark matter  

NASA Astrophysics Data System (ADS)

We explore two scenarios where the axion-photon interaction could induce additional astrophysical gamma ray signals for the dark matter. In the first scenario, dark compact objects made of axions, named axion stars, could collide with neutron stars. The whole energy of the axion star can be dissipated in the magnetized conducting medium of the neutron star generating gamma rays. The second scenario is an indirect method for observing self-annihilating dark matter trapped in stars: Gamma rays produced by the self-annihilation of neutralinos in the interior of the Sun can be transformed into axions due to photon-axion conversion. Then, the axion will travel freely in the Sun and be converted into photons again. This process is often referred as 'shine light through walls', in this case, the wall will be the solar interior. Hence, GeV gamma rays might pass through the Sun. We may conclude that observation of GeV photons by gamma-ray observatories like HAWC, coming from the Sun, may be a signal of annihilation of neutralinos in the interior of the Sun.

Barranco, J.; Carrillo Monteverde, A.; Delepine, D.

2014-03-01

294

Ultra-sensitive in-beam gamma-ray spectroscopy for nuclear astrophysics at LUNA  

E-print Network

Ultra-sensitive in-beam gamma-ray spectroscopy studies for nuclear astrophysics are performed at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator, deep underground in Italy's Gran Sasso laboratory. By virtue of a specially constructed passive shield, the laboratory gamma-ray background for E_\\gamma < 3 MeV at LUNA has been reduced to levels comparable to those experienced in dedicated offline underground gamma-counting setups. The gamma-ray background induced by an incident alpha-beam has been studied. The data are used to evaluate the feasibility of sensitive in-beam experiments at LUNA and, by extension, at similar proposed facilities.

A. Caciolli; L. Agostino; D. Bemmerer; R. Bonetti; C. Broggini; F. Confortola; P. Corvisiero; H. Costantini; Z. Elekes; A. Formicola; Zs. Fulop; G. Gervino; A. Guglielmetti; C. Gustavino; Gy. Gyurky; G. Imbriani; M. Junker; M. Laubenstein; A. Lemut; B. Limata; M. Marta; C. Mazzocchi; R. Menegazzo; P. Prati; V. Roca; C. Rolfs; C. Rossi Alvarez; E. Somorjai; O. Straniero; F. Strieder; F. Terrasi; H. P. Trautvetter

2008-12-17

295

Scientific considerations in the design of the Mars observer gamma-ray spectrometer  

SciTech Connect

Cosmic-ray primary and secondary particles induce characteristic gamma-ray and neutron emissions from condensed bodies in our solar system. These characteristic emissions can be used to obtain qualitative and quantitative elemental analyses of planetary surfaces from orbital altitudes. Remote sensing gamma-ray spectroscopy has been successfully used to obtain elemental composition of the Moon and Mars during United States Apollo 15 and 16 missions and the Soviet Luna and Mars missions. A remote sensing gamma-ray and neutron spectrometer will be included aboard the United States Mars Observer Mission. If proper care is not taken in the design of the spectrometer and choice of materials in the construction of the detector system and spacecraft, the sensitivity of these remote sensing spectrometers can be greatly degraded. A discussion of these design and material selection problems is presented. 16 refs., 5 figs., 3 tabs.

Arnold, J.R.; Boynton, W.V.; Englert, P.; Feldman, W.C.; Metzger, A.E.; Reedy, R.C.; Squyres, S.W.; Trombka, J.I.; Wanke, H.

1987-01-01

296

GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES  

SciTech Connect

Star formation in galaxies is observed to be associated with gamma-ray emission, presumably from non-thermal processes connected to the acceleration of cosmic-ray nuclei and electrons. The detection of gamma rays from starburst galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity. Since star formation is known to scale with total infrared (8-1000 {mu}m) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star-forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study, we apply the functional relationships between gamma-ray luminosity and radio and IR luminosities of galaxies derived by the Fermi Collaboration to a sample of the best candidate galaxy clusters for detection in gamma rays in order to place lower limits on the gamma-ray emission associated with star formation in galaxy clusters. We find that several clusters have predicted gamma-ray emission from star formation that are within an order of magnitude of the upper limits derived in Ackermann et al. based on non-detection by Fermi-LAT. Given the current gamma-ray limits, star formation likely plays a significant role in the gamma-ray emission in some clusters, especially those with cool cores. We predict that both Fermi-LAT over the course of its lifetime and the future Cerenkov Telescope Array will be able to detect gamma-ray emission from star-forming galaxies in clusters.

Storm, Emma M.; Jeltema, Tesla E.; Profumo, Stefano [Department of Physics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)

2012-08-20

297

The characteristics of the prompt gamma-ray analyzing system at the neutron beam guides of JRR-3M  

Microsoft Academic Search

A reactor-neutron-induced prompt gamma-ray analyzing system was constructed at JRR-3M. The system can be set at cold and thermal neutron beam guides with a neutron flux at the sample position of 1.1 × 108 and 2.4 × 107 n cm-2 s-1, respectively. The system was designed to achieve the lowest gamma-ray background. This is done by using lithium fluoride tiles

Chushiro Yonezawa; Abdul Khalik Haji Wood; Michio Hoshi; Yasuo Ito; Enzo Tachikawa

1993-01-01

298

Air pollution induces heritable DNA mutations  

PubMed Central

Hundreds of thousands of people worldwide live or work in close proximity to steel mills. Integrated steel production generates chemical pollution containing compounds that can induce genetic damage (1, 2). Previous investigations of herring gulls in the Great Lakes demonstrated elevated DNA mutation rates near steel mills (3, 4) but could not determine the importance of airborne or aquatic routes of contaminant exposure, or eliminate possible confounding factors such as nutritional status and disease burden. To address these issues experimentally, we exposed laboratory mice in situ to ambient air in a polluted industrial area near steel mills. Heritable mutation frequency at tandem-repeat DNA loci in mice exposed 1 km downwind from two integrated steel mills was 1.5- to 2.0-fold elevated compared with those at a reference site 30 km away. This statistically significant elevation was due primarily to an increase in mutations inherited through the paternal germline. Our results indicate that human and wildlife populations in proximity to integrated steel mills may be at risk of developing germline mutations more frequently because of the inhalation of airborne chemical mutagens. PMID:12473746

Somers, Christopher M.; Yauk, Carole L.; White, Paul A.; Parfett, Craig L. J.; Quinn, James S.

2002-01-01

299

Gamma ray burst outflows and afterglows  

NASA Astrophysics Data System (ADS)

We carry out a theoretical investigation of jet propagation in Gamma Ray Bursts and examine the jitter radiation mechanism as a means of producing prompt and afterglow emission. We study the long-term evolution of relativistic jets in collapsars and examine the effects of viewing angle on the subsequent gamma ray bursts. Our simulations allow us to single out three phases in the jet evolution: a precursor phase in which relativistic material turbulently shed from the head of the jet first emerges from the star; a shocked jet phase where a fully shocked jet of material is emerging; and an unshocked jet phase where the jet consists of a free-streaming, unshocked core surrounded by a thin boundary layer of shocked jet material. We also carry out a series of simulations with central engines that vary on long time periods comparable to the breakout time of the jet, on short time periods (0.1s) much less than the breakout time, and finally that decay as a power law at late times. We conclude that rapid variability seen in prompt GRB emission, as well as shallow decays and flares seen in the X-ray afterglow, can be caused by central engine variability. Finally, we present a detailed computation of the jitter radiation spectrum, including self-absorption, for electrons inside Weibel-like shock- generated magnetic fields. We apply our results to the case of the prompt and afterglow emission of gamma-ray bursts. We conclude that jitter and synchrotron afterglows can be distinguished from each other with good quality observations. However, it is unlikely that the difference can explain the peculiar behavior of several recent observations, such as flat X-ray slopes and uncorrelated optical and X-ray behavior.

Morsony, Brian J.

2008-08-01

300

Common Gamma-ray Glows above Thunderclouds  

NASA Astrophysics Data System (ADS)

Gamma-ray glows are continuous, long duration gamma- and x-ray emission seen coming from thunderclouds. The Airborne for Energetic Lightning Emissions (ADELE) observed 12 gamma-ray glows during its summer 2009 flight campaign over the areas of Colorado and Florida in the United States. For these glows we shall present their spectra, relationship to lightning activity and how their duration and size changes as a function of distance. Gamma-ray glows follow the relativistic runaway electron avalanche (RREA) spectrum and have been previously measured from the ground and inside the cloud. ADELE measured most glows as it flew above the screening layer of the cloud. During the brightest glow on August 21, 2009, we can show that we are flying directly into a downward facing relativistic runaway avalanche, indicative of flying between the upper positive and negative screening layer of the cloud. In order to explain the brightness of this glow, RREA with an electric field approaching the limit for relativistic feedback must be occurring. Using all 12 glows, we show that lightning activity diminishes during the onset of the glow. Using this along with the fact that glows occur as the field approaches the level necessary for feedback, we attempt to distinguish between two possibilities: that glows are evidence that RREA with feedback, rather than lightning, is sometimes the primary channel for discharging the cloud, or else that the overall discharging is still controlled by lightning, with glows simply appearing during times when a subsidence of lightning allows the field to rise above the threshold for RREA.

Kelley, Nicole; Smith, David; Dwyer, Joseph; Hazelton, Bryna; Grefenstette, Brian; Lowell, Alex; Splitt, Michael; Lazarus, Steven; Rassoul, Hamid

2013-04-01

301

Can Naked Singularities Yield Gamma Ray Bursts?  

E-print Network

Gamma-ray bursts are believed to be the most luminous objects in the Universe. There has been some suggestion that these arise from quantum processes around naked singularities. The main problem with this suggestion is that all known examples of naked singularities are massless and hence there is effectively no source of energy. It is argued that a globally naked singularity coupled with quantum processes operating within a distance of the order of Planck length of the singularity will probably yield energy burst of the order of M_pc^2\\approx2\\times 10^{16} ergs, where M_p is the Planck mass.

H. M. Antia

1998-07-09

302

High Energy Neutrinos from Gamma Ray Bursts  

E-print Network

We treat high-energy neutrino production in GRBs. Detailed calculations of photomeson neutrino production are presented for the collapsar model, where internal nonthermal synchrotron radiation is the primary target photon field, and the supranova model, where external pulsar-wind synchrotron radiation provides important additional target photons. Detection of > 10 TeV neutrinos from GRBs with Doppler factors > 200, inferred from gamma-ray observations, would support the supranova model. Detection of 3x10^{-4} erg/cm^2 offer a realistic prospect for detection of muon neutrinos.

Dermer, C D; Dermer, Charles D.; Atoyan, Armen

2003-01-01

303

Gamma-Ray Fuel Gauges for Airplanes  

NASA Technical Reports Server (NTRS)

Accurate system overcomes problems of capacitance gauges. Feasibility study conducted on use of attenuation of gamma rays to measure quantities of fuel in tanks. Studies with weak Am241 59.5-keV radiation source indicate it is possible to monitor continuously fuel quantity in tanks to accuracy of better than 1 percent. Measurements also indicate easily measurable differences in physical properties and resultant attenuation characteristics of JP-4, JP-5, and Jet A fuels. Am241-based densitometers currently in use aboard some aircraft . Estimated complete system, including microprocessor and associated display devices, assembled at cost of less than $10,000 per fuel tank.

Singh, Jag J.; Sprinkle, Danny R.; Mall, Gerald H.; Chegini, Hoshang

1987-01-01

304

Multiwavelength Studies of gamma-ray Binaries  

NASA Astrophysics Data System (ADS)

High mass X-ray binaries (HMXBs) consist of an O or B star orbited by either a neutron star or a black hole. Of the 114 known Galactic HMXBs, a handful of these objects, dubbed gamma-ray binaries, have been observed to produce MeV-TeV emission. The very high energy emission can be produced either by accretion from the stellar wind onto a black hole or a collision between the stellar wind and a relativistic pulsar wind. Both these scenarios make gamma-ray binaries valuable nearby systems for studying the physics of shocks and jets. Currently, the nature of the compact object and the high energy production mechanism is unknown or unconfirmed in over half of these systems. My goal for this dissertation is to constrain the parameters describing two of these systems: LS 5039 and HD 259440. LS 5039 exhibits gamma-ray emission modulated with its orbital period. The system consists of an ON6.5V((f)) star and an unidentified compact companion. Using optical spectra from the CTIO 1.5m telescope, we found LS 5039 to have an orbital period of 3.90608 d and an eccentricity of 0.337. Spectra of the Halpha line observed with SOAR indicate a mass loss rate of ˜ 1.9x10 -8 M yr-1. Observations taken with ATCA at 13 cm, 6 cm, and 3 cm indicate radio fluxes between 10--40 mJy. The measurements show variability with time, indicating a source other than thermal emission from the stellar wind. HD 259440 is a B0pe star that was proposed as the optical counterpart to the gamma-ray source HESS J0632+057. Using optical spectra from the KPNO CF, KPNO 2.1m, and OHP telescopes, we find a best fit stellar effective temperature of 27500--30000 K, a log surface gravity of 3.75--4.0, a mass of 13.2--19.0 Msolar, and a radius of 6.0--9.6 Rsolar. By fitting the spectral energy distribution, we find a distance between 1.1--1.7 kpc. We do not detect any significant radial velocity shifts in our data, ruling out orbital periods shorter than one month. If HD 259440 is a binary, it is likely a long period (> 100 d) system.

Aragona, Christina

305

Benchmark gamma-ray skyshine experiment  

SciTech Connect

A benchmark gamma-ray skyshine experiment is descibed in which /sup 60/Co sources were either collimated into an upward 150-deg conical beam or shielded vertically by two different thicknesses of concrete. A NaI(Tl) spectrometer and a high pressure ion chamber were used to measure, respectively, the energy spectrum and the 4..pi..-exposure rate of the air-reflected gamma photons up to 700 m from the source. Analyses of the data and comparison to DOT discrete ordinates calculations are presented.

Nason, R.R.; Shultis, J.K.; Faw, R.E.; Clifford, C.E.

1982-01-01

306

Gamma ray emission and solar flares  

NASA Technical Reports Server (NTRS)

Solar gamma ray line and continuum emission provide information about particle acceleration and its temporal behavior; the energy spectrum, composition and directivity of the accelerated particles; and the composition, density and temperatures of the ambient medium. These data, coupled with the comprehensive photon and particle observations available for the sun, give a detailed picture of the particle acceleration and flare energy release processes. Additional information on elemental and isotopic abundances, surface nuclear reactions and coronal heating mechanisms can be obtained. Implications of present observations and the potential return from future observational are discussed.

Lin, R. P.; Ramaty, R.

1978-01-01

307

Do gamma-ray burst sources repeat?  

NASA Technical Reports Server (NTRS)

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 analyze the angular distribution of 585 bursts of the second BATSE catalog (Meegan et al. 1994). We search for evidence of burst recurrence using the nearest and farthest neighbor statistic ad the two-point angular correlation function. We find the data to be consistent with the hypothesis that burst sources do not repeat; however, a repeater fraction of up to about 20% of the bursts cannot be excluded.

Meegan, C. A.; Hartmann, D. H.; Brainerd, J. J.; Briggs, M.; Paciesas, W. S.; Pendleton, G.; Kouveliotou, C.; Fishman, G.; Blumenthal, G.; Brock, M.

1994-01-01

308

Gamma Ray Bursts: an Enigma Being Unraveled  

SciTech Connect

The best astrophysical accelerators are quasars and the 'progenitors' of GRBs which, after decades of observations and scores of theories, we still do not understand. But, I shall argue, we now know quite well where GRBs come from, and we understand how their 'beams' behave, as they make short pulses of gamma rays and long-duration X-ray, optical and radio 'afterglows'. I shall argue that our understanding of these phenomena, based on the 'Cannonball Model', is unusually simple, precise and successful. The 'sociology' of GRBs is interesting per se and, in this sense, the avatars of the Cannonball Model in confronting the generally accepted 'fireball models' are also quite revealing.

De Rujula, Alvaro (Boston University and CERN) [Boston University and CERN

2003-05-14

309

Neutrino Event Rates from Gamma Ray Bursts  

E-print Network

We recalculate the diffuse flux of high energy neutrinos produced by Gamma Ray Bursts (GRB) in the relativistic fireball model. Although we confirm that the average single burst produces only ~10^{-2} high energy neutrino events in a detector with 1 km^2 effective area, i.e. about 10 events per year, we show that the observed rate is dominated by burst-to-burst fluctuations which are very large. We find event rates that are expected to be larger by one order of magnitude, likely more, which are dominated by a few very bright bursts. This greatly simplifies their detection.

F. Halzen; D. W. Hooper

1999-08-12

310

Beaming Effects in Gamma-Ray Bursts  

E-print Network

Based on a refined generic dynamical model, we investigate afterglows from jetted gamma-ray burst (GRB) remnants numerically. In the relativistic phase, the light curve break could marginally be seen. However, an obvious break does exist at the transition from the relativistic phase to the non-relativistic phase, which typically occurs at time 10 to 30 days. It is very interesting that the break is affected by many parameters, especially by the electron energy fraction (xi_e), and the magnetic energy fraction (xi_B^2). Implication of orphan afterglow surveys on GRB beaming is investigated. The possible existence of a kind of cylindrical jets is also discussed.

Y. F. Huang; T. Lu; Z. G. Dai; K. S. Cheng

2002-07-29

311

Gamma-Ray Bursts observed by INTEGRAL  

E-print Network

During the first six months of operations, six Gamma Ray Bursts (GRBs) have been detected in the field of view of the INTEGRAL instruments and localized by the INTEGRAL Burst Alert System (IBAS): a software for the automatic search of GRBs and the rapid distribution of their coordinates. I describe the current performances of IBAS and review the main results obtained so far. The coordinates of the latest burst localized by IBAS, GRB 031203, have been distributed within 20 s from the burst onset and with an uncertainty radius of only 2.7 arcmin.

S. Mereghetti

2003-12-12

312

High Energy Neutrinos from Gamma Ray Bursts  

E-print Network

We treat high-energy neutrino production in GRBs. Detailed calculations of photomeson neutrino production are presented for the collapsar model, where internal nonthermal synchrotron radiation is the primary target photon field, and the supranova model, where external pulsar-wind synchrotron radiation provides important additional target photons. Detection of > 10 TeV neutrinos from GRBs with Doppler factors > 200, inferred from gamma-ray observations, would support the supranova model. Detection of 3x10^{-4} erg/cm^2 offer a realistic prospect for detection of muon neutrinos.

Charles D. Dermer; Armen Atoyan

2003-01-02

313

Gamma Ray Bursts as Cosmological Probes  

E-print Network

We discuss the prospects of using Gamma Ray Bursts (GRBs) as high-redshift distance estimators, and consider their use in the study of two dark energy models, the Generalized Chaplygin Gas (GCG), a model for the unification of dark energy and dark matter, and the XCDM model, a model where a generic dark energy fluid like component is described by the equation of state, $p= \\omega \\rho$. Given that the GRBs range of redshifts is rather high, it turns out that they are not very sensitive to the dark energy component, being however, fairly good estimators of the amount of dark matter in the Universe.

O. Bertolami; P. T. Silva

2006-01-23

314

Comptonization of gamma rays by cold electrons  

NASA Technical Reports Server (NTRS)

An analytic method is developed for calculating the emergent spectrum of gamma-rays and X-rays scattered in a homogeneous medium with low-temperature electrons. The Klein-Nishina corrections of the scattering cross section and absorption processes are taken in account. The wavelength relaxation and the spatial diffusion problems are solved separately, and the emergent spectrum is calculated by convolving the evolution function of the spectrum in an infinite medium with the photon luminosity resulting from the spatial diffusion in a finite sphere. The analytic results are compared with that of Monte Carlo calculations and it is concluded that the analytic result is quite accurate.

Xu, Yueming; Ross, Randy R.; Mccray, Richard

1991-01-01

315

Gamma ray lines from interstellar grains  

NASA Technical Reports Server (NTRS)

The existence of very narrow (FWHM or approximately = 5 KeV) gamma ray line emission from interstellar grains is pointed out. The prime candidate for detection is the line at 6.129 Mev from O-16, but other very narrow lines could also be detected at 0.847, 1.369, 1.634, 1.779 and 2.313 Mev from Fe-56, Mg-24, Ne-20, Si-28 and N-14. Measurements of this line emission can provide information on the composition, size and spatial distribution of interstellar grains.

Lingenfelter, R. E.; Ramaty, R.

1976-01-01

316

Gamma-ray lines from interstellar grains  

NASA Technical Reports Server (NTRS)

The letter points out the existence of a hitherto unknown component of gamma-ray line emission: very narrow (FWHM less than 5 keV) lines from interstellar grains. The prime candidate for detection is the line at 6.129 MeV from O-16, but other very narrow lines could also be detected at 0.847, 1.369, 1.634, 1.779, and 2.313 MeV from Fe-56, Mg-24, Ne-20, Si-28, and N-14. Measurements of this line emission can provide information on the composition, size, and spatial distribution of interstellar grains.

Lingenfelter, R. E.; Ramaty, R.

1977-01-01

317

Highlights of GeV Gamma-Ray Astronomy  

NASA Technical Reports Server (NTRS)

Because high-energy gamma rays are primarily produced by high-energy particle interactions, the gamma-ray survey of the sky by the Fermi Gamma-ray Space Telescope offers a view of sites of cosmic ray production and interactions. Gamma-ray bursts, pulsars, pulsar wind nebulae, binary sources, and Active Galactic Nuclei are all phenomena that reveal particle acceleration through their gamma-ray emission. Diffuse Galactic gamma radiation, Solar System gamma-ray sources, and energetic radiation from supernova remnants are likely tracers of high-energy particle interactions with matter and photon fields. This paper will present a broad overview of the constantly changing sky seen with the Large Area Telescope (LAT) on the Fermi spacecraft.

Thompson, David J.

2010-01-01

318

A model of the diffuse galactic gamma ray emission  

NASA Technical Reports Server (NTRS)

The galaxy was observed to be a source of high energy gamma rays as shown by the two successful satellite experiments, SAS-2 and COS-B. It is generally understood that these diffuse gamma rays result from interactions between energetic cosmic rays and interstellar gas. This work makes use of the most recent data on the distribution of atomic and molecular hydrogen in the galaxy along with new estimates of gamma ray production functions to model the diffuse galactic gamma ray emission. The model allows various spatial distributions for cosmic rays in the Galaxy including non-axisymmetric ones. In the light of the expected data from EGRET (Energetic Gamma-Ray Experiment Telescope), an improved model of cosmic ray-matter-gamma ray interaction will provide new insights into the distribution of cosmic rays and the strength of its coupling to matter.

Sreekumar, Parameswaran

1990-01-01

319

SAS-2 galactic gamma ray results. 2. Localized sources  

NASA Technical Reports Server (NTRS)

Gamma-ray emission was detected from the radio pulsars PSR1818-04 and PSR1747-46, in addition to the previously reported gamma-ray emission from the Crab and Vela pulsars. Since the Crab pulsar is the only one observed in the optical and X-ray bands, these gamma-ray observations suggest a uniquely gamma-ray phenomenon occurring in a fraction of the radio pulsars. Using distance estimates it is found that PSR1818-04 has a gamma-ray luminosity comparable to that of the Crab pulsar, while the luminosities of PSR1747-46 and the Vela pulsar are approximately an order of magnitude lower. This survey of SAS-2 data for pulsar correlations has also yielded upper limits to gamma-ray luminosity for 71 other radio pulsars.

Hartman, R. C.; Fichtel, C. E.; Kniffen, D. A.; Lamb, R. C.; Thompson, D. J.; Bignami, G. F.; Oegelman, H.; Oezel, M. E.; Tuemer, T.

1976-01-01

320

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.

Isabelle Grenier

2009-04-01

321

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) [University Paris Diderot and CEA Saclay, France

2009-04-01

322

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

ScienceCinema

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

Isabelle Grenier

2010-01-08

323

Computational techniques in gamma-ray Skyshine analysis  

Microsoft Academic Search

Two computer codes were developed to analyze gamma-ray skyshine, the scattering of gamma photons by air molecules. A review of previous gamma-ray skyshine studies discusses several Monte Carlo codes, programs using a single-scatter model, and the MicroSkyshine program for microcomputers. A benchmark gamma-ray skyshine experiment performed at Kansas State University is also described. A single-scatter numerical model was presented which

Darin L. George

1988-01-01

324

Gamma Ray/neutron Spectrometers for Planetary Elemental Mapping  

NASA Technical Reports Server (NTRS)

Los Alamos has designed gamma ray and neutron spectrometers for Lunar Scout, two robotic missions to map the Moon from 100 km polar orbits. Knowledge of the elemental composition is desirable in identifying resources and for geochemical studies and can be obtained using gamma ray and neutron spectrometers. Measurements with gamma ray and neutron spectrometers complement each other in determining elemental abundances in a planet's surface. Various aspects of the instruments are discussed.

Reedy, R. C.; Auchampaugh, G. F.; Barraclough, B. L.; Burt, W. W.; Byrd, R. C.; Drake, D. M.; Edwards, B. C.; Feldman, W. C.; Martin, R. A.; Moss, C. E.

1993-01-01

325

Two Classes of Gamma-Ray--emitting Active Galactic Nuclei  

Microsoft Academic Search

We interpret recent gamma-ray observations of active galactic nuclei (AGNs) made with the Whipple Observatory, Granat and especially the Compton Gamma Ray Observatory. The gamma-ray data show that there are two distinct classes of AGNs defined by their redshift and luminosity distributions and high-energy spectral properties. Sources in the first class, which are generally associated with AGNs classified in other

Charles D. Dermer; Neil Gehrels

1995-01-01

326

Recommended standards for gamma-ray energy calibration  

Microsoft Academic Search

A consistent set of gamma-ray energies, generally with uncertainties of less than 10ppm, has been prepared for use in the energy calibration of gamma-ray spectra. The energy scale used for the previously recommended standards (1979) has been modified to take into account subsequent adjustments in the fundamental constants (-7.71ppm) and in the gamma-ray wavelengths deduced from a revised estimate of

R. G. Helmer; C. van der Leun

1999-01-01

327

Measurements of Gamma-Ray Bursts with GLAST  

Microsoft Academic Search

The next large NASA mission in the field of gamma-ray astronomy is the Gamma-Ray Large Area Space Telescope (GLAST), which is scheduled for a launch end of 2007. This satellite consists of the main instrument LAT (Large-Area Telescope) which is sensitive in the energy range between 10 MeV and >300 GeV, and a secondary instrument, the Gamma-Ray Burst Monitor (GBM),

Helmut Steinle; N. P. Bhat; M. S. Briggs; V. Connaughton; R. Diehl; G. J. Fishman; J. Greiner; R. M. Kippen; A. Von Kienlin; C. Kouveliotou; G. G. Lichti; C. A. Meegan; W. S. Paciesas; R. D. Preece; R. B. Wilson

2006-01-01

328

Gamma-Ray Bursts and Afterglows: The Fireball Shock Model  

Microsoft Academic Search

\\u000a Gamma-ray bursts (GRB) are detected about once a day, and while they are on, they outshine everything else in the gamma-ray\\u000a sky, including the Sun. A major advance occurred in 1992 with the launch of the Compton Gamma-Ray Observatory, whose superb\\u000a results were summarized in a review by Fishman & Meegan (1995; see also Fishman, these proceedings). The all-sky survey

P. Mészáros

2001-01-01

329

Recommended standards for gamma-ray energy calibration (1999)  

Microsoft Academic Search

A consistent set of gamma-ray energies, generally with uncertainties of less than 10ppm, is recommended for use in the energy calibration of gamma-ray spectra. The energy scale used for the previously recommended standards (1979) has been modified to take into account subsequent adjustments in the fundamental constants (-7.71ppm) and in the gamma-ray wavelengths deduced from a revised estimate of the

R. G. Helmer; C. van der Leun

2000-01-01

330

Neutron-Capture gamma Rays from Various Elements  

Microsoft Academic Search

Neutron-capture gamma-ray spectra have been measured in the energy range 0.3 to 3 Mev by means of a two-crystal Compton scintillation spectrometer. The efficiency of the instrument as a function of energy was determined experimentally. The uniqueness of the 2.23-Mev gamma ray following capture of a neutron by hydrogen has been confirmed, and this gamma ray was used as a

T. H. Braid

1956-01-01

331

Fermi GBM Observations of Terrestrial Gamma-Ray Flashes  

NASA Technical Reports Server (NTRS)

This slide presentation explores the relationship between Terrestrial Gamma-Ray Flashes (TGF) and lightning. Using data from the World-Wide Lightning Location Network (WWLLN), and the gamma ray observations from Fermi's Gamma-ray Burst Monitor (GBM), the study reviews any causal relationship between TGFs and lightning. The conclusion of the study is that the TGF and lightning are simultaneous with out a causal relationship.

Wilson-Hodge, Colleen A.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R.; Kippen, R. M.; vonKienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

2010-01-01

332

Gamma Ray Bursts, Neutron Star Quakes, and the Casimir Effect  

E-print Network

We propose that the dynamic Casimir effect is a mechanism that converts the energy of neutron starquakes into $\\gamma$--rays. This mechanism efficiently produces photons from electromagnetic Casimir energy released by the rapid motion of a dielectric medium into a vacuum. Estimates based on the cutoff energy of the gamma ray bursts and the volume involved in a starquake indicate that the total gamma ray energy emission is consonant with observational requirements.

C. Carlson; T. Goldman; J. Perez-Mercader

1994-11-25

333

Digital gamma-ray tracking algorithms in segmented germanium detectors  

Microsoft Academic Search

A gamma-ray tracking algorithm has been implemented and tested, using simulated data, for gamma rays with energies between 0.1 and 2 MeV, and its performance evaluated for a 90-mm-long, 60-mm-diameter, cylindrical, 36 (6 × 6) segment detector. The performance of the algorithm in two areas was determined: Compton suppression and Doppler shift correction. It was found that for gamma rays

C. J. Pearson; J. J. Valiente Dobón; P. H. Regan; P. J. Sellin; E. Morton; P. J. Nolan; A. Boston; M. Descovich; J. Thornhill; J. Cresswell; I. Lazarus; J. Simpson

2002-01-01

334

Nucleonic gamma-ray production in pulsar wind nebulae  

Microsoft Academic Search

\\u000a Observations of the inner radian of the Galactic disk at very high energy (VHE) gamma-rays have revealed at least 16 new sources.\\u000a Besides shell type super-nova remnants, pulsar wind nebulae (PWN) appear to be a dominant source population in the catalogue\\u000a of VHE gamma-ray sources. Except for the Crab nebula, the newly discovered PWN are resolved at VHE gamma-rays to

D. Horns; F. Aharonian; A. I. D. Hoffmann; A. Santangelo

335

Nucleonic gamma-ray production in pulsar wind nebulae  

Microsoft Academic Search

Observations of the inner radian of the Galactic disk at very high energy (VHE) gamma-rays have revealed at least 16 new sources.\\u000a Besides shell type super-nova remnants, pulsar wind nebulae (PWN) appear to be a dominant source population in the catalogue\\u000a of VHE gamma-ray sources. Except for the Crab nebula, the newly discovered PWN are resolved at VHE gamma-rays to

D. Horns; F. Aharonian; A. I. D. Hoffmann; A. Santangelo

2007-01-01

336

Sensitivity of Gamma-Ray Detectors to Polarization  

E-print Network

Previous studies have shown that the largest gamma-ray detector to date, EGRET, does not have useful polarization sensitivity. We have explored here some improved approaches to analyzing gamma-ray pair production events, leading to important gains in sensitivity to polarization. The performance of the next generation gamma-ray instrument GLAST is investigated using a detailed Monte Carlo simulation of the complete detector.

I. -A. Yadigaroglu

1996-12-13

337

Fermi Large Area Telescope Bright Gamma-ray Source List  

SciTech Connect

Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than {approx}10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.

Abdo, Aous A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.; /KIPAC, Menlo Park /SLAC; Ajello, M.; /KIPAC, Menlo Park /SLAC; Atwood, W.B.; /UC, Santa Cruz; Axelsson, M.; /Stockholm U., OKC /Stockholm U.; Baldini, L.; /INFN, Pisa; Ballet, J.; /DAPNIA, Saclay; Band, D.L.; /NASA, Goddard /NASA, Goddard; Barbiellini, Guido; /INFN, Trieste /Trieste U.; Bastieri, Denis; /INFN, Padua /Padua U.; Bechtol, K.; /KIPAC, Menlo Park /SLAC; Bellazzini, R.; /INFN, Pisa; Berenji, B.; /KIPAC, Menlo Park /SLAC; Bignami, G.F.; /Pavia U.; Bloom, Elliott D.; /KIPAC, Menlo Park /SLAC; Bonamente, E.; /INFN, Perugia /Perugia U.; Borgland, A.W.; /KIPAC, Menlo Park /SLAC; Bregeon, J.; /INFN, Pisa; Brigida, M.; /Bari U. /INFN, Bari; Bruel, P.; /Ecole Polytechnique; Burnett, Thompson H.; /Washington U., Seattle /Bari U. /INFN, Bari /KIPAC, Menlo Park /SLAC /IASF, Milan /IASF, Milan /DAPNIA, Saclay /ASDC, Frascati /INFN, Perugia /Perugia U. /KIPAC, Menlo Park /SLAC /George Mason U. /Naval Research Lab, Wash., D.C. /NASA, Goddard /KIPAC, Menlo Park /SLAC /INFN, Perugia /Perugia U. /KIPAC, Menlo Park /SLAC /Montpellier U. /Sonoma State U. /Stockholm U., OKC /Royal Inst. Tech., Stockholm /Stockholm U. /KIPAC, Menlo Park /SLAC /ASDC, Frascati /NASA, Goddard /Maryland U. /Naval Research Lab, Wash., D.C. /INFN, Trieste /Pavia U. /Bari U. /INFN, Bari /KIPAC, Menlo Park /SLAC /UC, Santa Cruz /KIPAC, Menlo Park /SLAC /KIPAC, Menlo Park /SLAC /KIPAC, Menlo Park /SLAC /Montpellier U. /Bari U. /INFN, Bari /Ecole Polytechnique /NASA, Goddard; /more authors.; ,

2009-05-15

338

Gamma ray constraints on the galactic supernova rate  

NASA Technical Reports Server (NTRS)

Monte Carlo simulations of the expected gamma-ray signatures of galactic supernovae of all types are performed in order to estimate the significance of the lack of a gamma-ray signal due to supernovae occurring during the last millenium. Using recent estimates of nuclear yields, we determine galactic supernova rates consistent with the historic supernova record and the gamma-ray limits. Another objective of these calculations of galactic supernova histories is their application to surveys of diffuse galactic gamma-ray line emission.

Hartmann, D.; The, L.-S.; Clayton, D. D.; Leising, M.; Mathews, G.; Woosley, S. E.

1992-01-01

339

Radio and gamma-ray emission from pulsars  

E-print Network

The radiation of pulsars have been observed for many years. A few pulsars are discovered to have both radio and gamma-ray emission. Many models on pulsar radiation have been developed, but so far we are still lacking an elaborate model which can explain the emission from radio to gamma-rays in detail. In this paper we present a joint model for radio and gamma-ray emission, in which both the dominate emission mechanisms are inverse Compton scattering. The pulse profiles at radio and gamma-ray bands are reproduced for the Crab-like, Vela-like and Geminga-like pulsars, in good agreement with observations.

G. J. Qiao; K. J. Lee; H. G. Wang; R. X. Xu

2003-03-11

340

Soft gamma rays from black holes versus neutron stars  

NASA Technical Reports Server (NTRS)

The recent launches of GRANAT and GRO provide unprecedented opportunities to study compact collapsed objects from their hard x ray and gamma ray emissions. The spectral range above 100 keV can now be explored with much higher sensitivity and time resolution than before. The soft gamma ray spectral data is reviewed of black holes and neutron stars, radiation, and particle energization mechanisms and potentially distinguishing gamma ray signatures. These may include soft x ray excesses versus deficiencies, thermal versus nonthermal processes, transient gamma ray bumps versus power law tails, lines, and periodicities. Some of the highest priority future observations are outlines which will shed much light on such systems.

Liang, Edison P.

1992-01-01

341

Systematic Effects in Extracting a "Gamma-Ray Haze" from Spatial Templates  

E-print Network

Recent claims of a gamma-ray excess in the diffuse galactic emission detected by the Fermi Large Area Telescope with a morphology similar to the WMAP haze were based on the assumption that spatial templates of the interstellar medium (ISM) column density and the 408 Mhz sky are good proxies for neutral pion and inverse Compton (IC) gamma-ray emission, respectively. We identify significant systematic effects in this procedure that can artificially induce an additional diffuse component with a morphology strikingly similar to the claimed gamma-ray haze. To quantitatively illustrate this point we calculate sky-maps of the ratio of the gamma-ray emission from neutral pions to the ISM column density, and of IC to synchrotron emission, using detailed galactic cosmic-ray models and simulations. In the region above and below the galactic center, the ISM template underestimates the gamma-ray emission due to neutral pion decay by approximately 20%. Additionally, the synchrotron template tends to under-estimate the IC emission at low energies (few GeV) and to over-estimate it at higher energies (tens of GeV) by potentially large factors that depend crucially on the assumed magnetic field structure of the Galaxy. The size of the systematic effects we find are comparable to the size of the claimed "Fermi haze" signal. We thus conclude that a detailed model for the galactic diffuse emission is necessary in order to conclusively assess the presence of a gamma-ray excess possibly associated to the WMAP haze morphology.

Tim Linden; Stefano Profumo

2010-02-26

342

Gamma ray bursts triggered by turbulent reconnection  

NASA Astrophysics Data System (ADS)

Understanding of the nature of gamma-ray bursts (GRBs) is one of the challenging problem facing the astrophysics community. Magnetic reconnection plays a crucial roles in the physics of GRBs, particularly, for those highly magnetized ones. Similar process can happen, as those on solar surface. I shall present our model of GRBs based on turbulent reconnection process. Turbulence fluctuations accumulates through shell collisions and triggers a bursty reconnection event once the turbulence reaches the critical condition, resulting in a runway release of the stored magnetic field energy. Particles are accelerated either directly in the reconnection zone, or stochastically in the turbulent regions, which radiate synchrotron photons that power the observed gamma rays. Within this model, the observed GRB variability timescales could have two components, one slow component associated with the central engine time history, and another fast component associated with relativistic magnetic turbulence in the emission region. The model may be applied to the GRBs that have time-resolved, featureless Band-function spectra.

Yan, Huirong

2012-07-01

343

Physics of Gamma Ray Burst Sources  

NASA Technical Reports Server (NTRS)

During this grant period, the physics of gamma-ray bursts was investigated. A number of new results have emerged. The importance of pair formation in high compactness burst spectra may help explain x-ray flashes; a universal jet shape is a likely explanation for the distribution of jet break times; gravitational waves may be copiously produced both in short bursts from compact mergers and in long bursts arising from collapsars; x-ray iron lines are likely to be due to interaction with the stellar atmosphere of the progenitor; prompt optical flashes from reverse shocks will give diagnostics on the Lorentz factor and the environment; GeV and TeV emission from bursts may be expected in the external shock; etc. The group working with the PI included postdocs Dr. Bing Zhang (now assistant professor at University of Nevada); Dr. Shiho Kobayashi; graduate student Lijun Gou; collaborators Drs. Tim Kallman and Martin Rees. Meszaros shared with Rees and Dr. Bohan Paczynsky the AAS Rossi Prize in 2000 for their work on the theory of gamma ray bursts. The refereed publications and conference proceedings resulting from this research are summarized below. The PI gave a number of invited talks at major conferences, also listed.

Meszaros, Peter

2004-01-01

344

The transient gamma-ray spectrometer  

NASA Astrophysics Data System (ADS)

The authors describe the Transient Gamma-Ray Spectrometer (TGRS) to be flown onboard the WIND spacecraft. This instrument is designed to detect cosmic gamma-ray bursts over the energy range of 20 keV to 10 MeV with an expected spectroscopic resolution of 2 keV at 1 MeV (E/Delta-E = 500). The active detection element is a 215-cu cm high-purity n-type Ge crystal cooled to cryogenic temperatures by a passive radiative cooler. The geometric field of view (FOV) defined by the cooler is 170 deg FWFM. Burst data are stored directly in an onboard 2.75-Mb burst memory with an absolute timing accuracy of +/-1.5 ms. This capacity is sufficient to store the entire spectral data set of all but the largest bursts. In addition to burst measurements, the instrument will also study solar flares, search for possible diffuse background lines, and monitor the 511-keV positron annihilation radiation from the galactic center. The experiment is scheduled to be launched on a Delta II launch vehicle from Cape Canaveral on December 31, 1992.

Owens, A.; Baker, R.; Cline, T. L.; Gehrels, N.; Jermakian, J.; Nolan, T.; Ramaty, R.; Smith, G.; Stilwell, D. E.; Teegarden, B. J.

1991-04-01

345

Gamma Ray Fresnel lenses - why not?  

E-print Network

Fresnel lenses offer the possibility of concentrating the flux of X-rays or gamma-rays flux falling on a geometric area of many square metres onto a focal point which need only be a millimetre or so in diameter (and which may even be very much smaller). They can do so with an efficiency that can approach 100%, and yet they are easily fabricated and have no special alignment requirements. Fresnel lenses can offer diffraction-limited angular resolution, even in a domain where that limit corresponds to less than a micro second of arc. Given all these highly desirable attributes, it is natural to ask why Fresnel gamma ray lenses are not already being used, or at least why there is not yet any mission that plans to use the technology. Possible reasons (apart from the obvious one that nobody thought of doing so) include the narrow bandwidth of simple Fresnel lenses, their very long focal length, and the problems of target finding. It is argued that none of these is a "show stopper" and that this technique should be seriously considered for nuclear astrophysics.

G. K. Skinner

2006-02-03

346

Iron K Lines from Gamma Ray Bursts  

NASA Technical Reports Server (NTRS)

We present models for reprocessing of an intense flux of X-rays and gamma rays expected in the vicinity of gamma ray burst sources. We consider the transfer and reprocessing of the energetic photons into observable features in the X-ray band, notably the K lines of iron. Our models are based on the assumption that the gas is sufficiently dense to allow the microphysical processes to be in a steady state, thus allowing efficient line emission with modest reprocessing mass and elemental abundances ranging from solar to moderately enriched. We show that the reprocessing is enhanced by down-Comptonization of photons whose energy would otherwise be too high to absorb on iron, and that pair production can have an effect on enhancing the line production. Both "distant" reprocessors such as supernova or wind remnants and "nearby" reprocessors such as outer stellar envelopes can reproduce the observed line fluxes with Fe abundances 30-100 times above solar, depending on the incidence angle. The high incidence angles required arise naturally only in nearby models, which for plausible values can reach Fe line to continuum ratios close to the reported values.

Kallman, T. R.; Meszaros, P.; Rees, M. J.

2003-01-01

347

Spectral modeling of gamma-ray blazars  

E-print Network

We present model calculations reproducing broadband spectra of $\\gamma$-ray blazars by a relativistic leptonic jet, combining the EIC and the SSC model. To this end, the evolution of the particle distribution functions inside a relativistic pair jet and of the resulting photon spectra is investigated. Inverse-Compton scattering of both external (EIC) as well as synchrotron photons (SSC) is treated using the full Klein-Nishina cross-section and the full angle-dependence of the external photon source. We present model fits to the broadband spectra of Mrk~421 and 3C279 and the X-ray and $\\gamma$-ray spectrum of PKS~1622-297. We find that the most plausible way to explain both the quiescent and the flaring states of these objects consists of a model where EIC and SSC dominate the observed spectrum in different frequency bands. For both Mrk~421 and 3C279 the flaring states can be reproduced by a harder spectrum of the injected pairs.

M. Boettcher; H. Mause; R. Schlickeiser

1997-06-23

348

Gamma-Ray Bursts and Cosmology  

NASA Technical Reports Server (NTRS)

The unrivalled, extreme luminosities of gamma-ray bursts (GRBs) make them the favored beacons for sampling the high redshift Universe. To employ GRBs to study the cosmic terrain -- e.g., star and galaxy formation history -- GRB luminosities must be calibrated, and the luminosity function versus redshift must be measured or inferred. Several nascent relationships between gamma-ray temporal or spectral indicators and luminosity or total energy have been reported. These measures promise to further our understanding of GRBs once the connections between the luminosity indicators and GRB jets and emission mechanisms are better elucidated. The current distribution of 33 redshifts determined from host galaxies and afterglows peaks near z $\\sim$ 1, whereas for the full BATSE sample of long bursts, the lag-luminosity relation predicts a broad peak z $\\sim$ 1--4 with a tail to z $\\sim$ 20, in rough agreement with theoretical models based on star formation considerations. For some GRB subclasses and apparently related phenomena -- short bursts, long-lag bursts, and X-ray flashes -- the present information on their redshift distributions is sparse or entirely lacking, and progress is expected in Swift era when prompt alerts become numerous.

Norris, Jay P.

2003-01-01

349

IS CALVERA A GAMMA-RAY PULSAR?  

SciTech Connect

Originally selected as a neutron star (NS) candidate in the ROSAT All-Sky Survey, 1RXS J141256.0+792204 ('Calvera') was discovered to be a 59 ms X-ray pulsar in a pair of XMM-Newton observations by Zane et al. Surprisingly, their claimed detection of this pulsar in Fermi {gamma}-ray data requires no period derivative, severely restricting its dipole magnetic field strength, spin-down luminosity, and distance to small values. This implies that the cooling age of Calvera is much younger than its characteristic spin-down age. If so, it could be a mildly recycled pulsar, or the first 'orphaned' central compact object (CCO). Here we show that the published Fermi ephemeris fails to align the pulse phases of the two X-ray observations with each other, which indicates that the Fermi detection is almost certainly spurious. Analysis of additional Fermi data also does not confirm the {gamma}-ray detection. This leaves the spin-down rate of Calvera less constrained, and its place among the families of NSs uncertain. It could still be either an ordinary pulsar, a mildly recycled pulsar, or an orphaned CCO.

Halpern, J. P., E-mail: jules@astro.columbia.edu [Astronomy Department, Columbia University, 550 West 120th Street, New York, NY 10027-6601 (United States)

2011-07-20

350

Ultraviolet observations of the gamma-ray blazar 3C 279 following the gamma-ray flare of June 1991  

Microsoft Academic Search

Ultraviolet observations of the gamma-ray blazar 3C 279 were carried out in July 1991 with the International Ultraviolet Explorer (IUE) satellite, 28 d after the outburst of intense gamma-ray emission detected from this source with the high-energy EGRET instrument aboard the Compton Gamma Ray Observatory (CGRO). IUE observations were conducted over the wavelength range 1200 - 3200 Å (5 -

J. T. Bonnell; W. T. Vestrand; J. G. Stacy

1994-01-01

351

Ultraviolet observations of the Gamma-Ray Blazar 3C 279 following the gamma-ray flare of June 1991  

Microsoft Academic Search

Ultraviolet observations of the gamma-ray blazar 3C 279 were carried out in July 1991 with the International Ultraviolet Explorer (IUE) satellite, 28 days after the outburst of intense gamma-ray emission detected from this source with the high-energy EGRET instrument aboard the Compton Gamma Ray Observatory (CGRO). IUE observations were conducted over the wavelength range 1200–3200 A? (5–10 eV), and are

Jerry T. Bonnell; W. Thomas Vestrand; J. Gregory Stacy

1994-01-01

352

Radiation resistance testing of high-density polyethylene. [Gamma rays  

SciTech Connect

Mechanical tests following gamma inrradiation and creep tests during irradiation have been conducted on high-density polyethylene (HDPE) to assess the adequacy of this material for use in high-integrity containers (HICs). These tests were motivated by experience in nuclear power plants in which polyethylene electrical insulation detoriorated more rapidly than expected due to radiation-induced oxidation. This suggested that HDPE HICs used for radwaste disposal might degrade more rapidly than would be expected in the absence of the radiation field. Two types of HDPE, a highly cross-linked rotationally molded material and a non-cross-linked blow molded material, were used in these tests. Gamma-ray irradiations were performed at several dose rates in environments of air, Barnwell and Hanford backfill soils, and ion-exchange resins. The results of tensile and bend testing on these materials following irradiation will be presented along with preliminary results on creep during irradiation.

Dougherty, D.R.; Adams, J.W.

1983-01-01

353

MilagroA TeV Observatory for Gamma Ray Bursts  

E-print Network

Milagro­A TeV Observatory for Gamma Ray Bursts B.L. Dingus and the Milagro Collaboration Los- servatory sensitive to gamma-rays above 100 GeV. This unique detector is ideal for observing the highest energy gamma-rays from gamma-ray bursts. The highest energy gamma rays supply very strong constraints

California at Santa Cruz, University of

354

Search for GeV Emission from Gamma-Ray Bursts Using Milagro Scaler Data  

E-print Network

Search for GeV Emission from Gamma-Ray Bursts Using Milagro Scaler Data D. A. Williams to search for high energy emission from a sample of 98 gamma-ray bursts (GRB) detected from January 2000: gamma-ray sources; gamma-ray bursts; astronomical observations: gamma-ray PACS: 98.70.Rz,95.85.Pw Air

California at Santa Cruz, University of

355

GROSS- GAMMA RAY OBSERVATORY ATTITUDE DYNAMICS SIMULATOR  

NASA Technical Reports Server (NTRS)

The Gamma Ray Observatory (GRO) spacecraft will constitute a major advance in gamma ray astronomy by offering the first opportunity for comprehensive observations in the range of 0.1 to 30,000 megaelectronvolts (MeV). The Gamma Ray Observatory Attitude Dynamics Simulator, GROSS, is designed to simulate this mission. The GRO Dynamics Simulator consists of three separate programs: the Standalone Profile Program; the Simulator Program, which contains the Simulation Control Input/Output (SCIO) Subsystem, the Truth Model (TM) Subsystem, and the Onboard Computer (OBC) Subsystem; and the Postprocessor Program. The Standalone Profile Program models the environment of the spacecraft and generates a profile data set for use by the simulator. This data set contains items such as individual external torques; GRO spacecraft, Tracking and Data Relay Satellite (TDRS), and solar and lunar ephemerides; and star data. The Standalone Profile Program is run before a simulation. The SCIO subsystem is the executive driver for the simulator. It accepts user input, initializes parameters, controls simulation, and generates output data files and simulation status display. The TM subsystem models the spacecraft dynamics, sensors, and actuators. It accepts ephemerides, star data, and environmental torques from the Standalone Profile Program. With these and actuator commands from the OBC subsystem, the TM subsystem propagates the current state of the spacecraft and generates sensor data for use by the OBC and SCIO subsystems. The OBC subsystem uses sensor data from the TM subsystem, a Kalman filter (for attitude determination), and control laws to compute actuator commands to the TM subsystem. The OBC subsystem also provides output data to the SCIO subsystem for output to the analysts. The Postprocessor Program is run after simulation is completed. It generates printer and CRT plots and tabular reports of the simulated data at the direction of the user. GROSS is written in FORTRAN 77 and ASSEMBLER and has been implemented on a VAX 11/780 under VMS 4.5. It has a virtual memory requirement of 255k. GROSS was developed in 1986.

Garrick, J.

1994-01-01

356

Near-infrared and gamma-ray monitoring of TANAMI gamma-ray bright sources  

NASA Astrophysics Data System (ADS)

Context. Spectral energy distribution and its variability are basic tools for understanding the physical processes operating in active galactic nuclei (AGN). Aims: In this paper we report the results of a one-year near-infrared (NIR) and optical monitoring of a sample of 22 AGN known to be gamma-ray emitters, aimed at discovering correlations between optical and gamma-ray emission. Methods: We observed our objects with the Rapid Eye Mount (REM) telescope in J,H,K, and R bands nearly twice every month during their visibility window and derived light curves and spectral indexes. We also analyzed the gamma-ray data from the Fermi gamma-ray Space Telescope, making weekly averages. Results: Six sources were never detected during our monitoring, proving to be fainter than their historical Two micron all sky survey (2MASS) level. All of the sixteen detected sources showed marked flux density variability, while the spectral indexes remained unchanged within our sensitivity limits. Steeper sources showed, on average, a larger variability. From the NIR light curves we also computed a variability speed index for each detected source. Only one source (PKS 0208-512) underwent an NIR flare during our monitoring. Half of the sources showed a regular flux density trend on a one-year time scale, but do not show any other peculiar characteristic. The broadband spectral index ?ro appears to be a good proxy of the NIR spectral index only for BL Lac objects. No clear correlation between NIR and gamma-ray data is evident in our data, save for PKS 0537-441, PKS 0521-360, PKS 2155-304, and PKS 1424-418. The gamma-ray/NIR flux ratio showed a large spread, QSO being generally gamma-louder than BL Lac, with a marked correlation with the estimated peak frequency (?peak) of the synchrotron emission. A table of the photometry is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A2

Nesci, R.; Tosti, G.; Pursimo, T.; Ojha, R.; Kadler, M.

2013-07-01

357

Perspectives on Gamma-Ray Pulsar Emission  

SciTech Connect

Pulsars are powerful sources of radiation across the electromagnetic spectrum. This paper highlights some theoretical insights into non-thermal, magnetospheric pulsar gamma-ray radiation. These advances have been driven by NASA's Fermi mission, launched in mid-2008. The Large Area Telescope (LAT) instrument on Fermi has afforded the discrimination between polar cap and slot gap/outer gap acceleration zones in young and middle-aged pulsars. Altitude discernment using the highest energy pulsar photons will be addressed, as will spectroscopic interpretation of the primary radiation mechanism in the LAT band, connecting to both polar cap/slot gap and outer gap scenarios. Focuses will mostly be on curvature radiation and magnetic pair creation, including population trends that may afford probes of the magnetospheric accelerating potential.

Baring, Matthew G. [Department of Physics and Astronomy, MS-108, Rice University, P. O. Box 1892, Houston, TX 77251-1892 (United States)

2011-09-21

358

Gamma Ray Burst Discoveries with SWIFT  

NASA Technical Reports Server (NTRS)

Gamma-ray bursts are among the most fascinating occurrences in the cosmos. They are thought to be the birth cries of black holes throughout the universe. There has been tremendous recent progress in our understanding of bursts with the new data from the SWIFT mission. SWIFT was launched in November 2004 and is an international multiwavelength observatory designed to determine the origin of bursts and use them to probe the early Universe. Findings from the mission will be presented with emphasis on the relativistic outflows from GRBs. A huge step forward has been made in our understanding of the mysterious short GRBs. High redshift bursts have been detected from enormous explosions early in the universe. GRBs have been found with giant X-ray flares occurring in their afterglow, challenging predictions of the fireball model. These, and other topics, will be discussed.

Gehrels, Neil

2007-01-01

359

A Compton scatter attenuation gamma ray spectrometer  

NASA Technical Reports Server (NTRS)

A Compton scatter attenuation gamma ray spectrometer conceptual design is discussed for performing gamma spectral measurements in monodirectional gamma fields from 100 R per hour to 1,000,000 R per hour. Selectable Compton targets are used to scatter gamma photons onto an otherwise heavily shielded detector with changeable scattering efficiencies such that the count rate is maintained between 500 and 10,000 per second. Use of two sum-Compton coincident detectors, one for energies up to 1.5 MeV and the other for 600 keV to 10 MeV, will allow good peak to tail pulse height ratios to be obtained over the entire spectrum and reduces the neutron recoil background rate.

Austin, W. E.

1972-01-01

360

Gamma-ray bursts: nature's brightest explosions  

NASA Astrophysics Data System (ADS)

During the roughly 20 seconds it shines brightest, a gamma-ray burst (GRB) is over a billion times brighter, in electromagnetic radiation, than an ordinary supernova. The key difference is that GRBs emit some appreciable fraction of their kinetic energy in channeled ultra-relativistic outflows (Lorentz factor ? > 200). Currently credible models point to rotation as the key factor required to generate the outflows. We explore here the collapse of the core a massive, rotating star to a black hole and accretion disk and the subsequent propagation of relativistic jets through the star. A variety of high energy transients may be observed based upon the energy of the jet and the angle at which the explosion is observed, but there may be a minimum energy for GRBs that last only tens of seconds.

Zhang, W.; Woosley, S. E.; MacFadyen, A. I.

2006-09-01

361

Gamma Ray Bursts:. Some Facts and Ideas  

NASA Astrophysics Data System (ADS)

Gamma Ray Bursts (GRBs) are the most explosive events after the big bang: their energy output corresponds to a sizeable fraction of a solar mass entirely converted into energy in a few seconds. Although many questions about their progenitors remain to be answered, it is likely that they are generated by a newly formed and fast spinning black hole. The colossal power characterizing GRBs is carried by a surprisingly small amount of matter, which is accelerated to speeds differing from c by one part in ten thousands. GRBs are then the most (special and general) relativistic objects we know of. Since GRBs are the brightest sources at high redshift, albeit for a limited amount of time, they are also the best torchlights we have to shine the far universe.

Ghisellini, Gabriele

2003-01-01

362

Do gamma-ray burst sources repeat?  

NASA Technical Reports Server (NTRS)

The demonstration of repeated gamma-ray bursts from an individual source would severely constrain burst source models. Recent reports (Quashnock and Lamb, 1993; Wang and Lingenfelter, 1993) of evidence for repetition in the first BATSE burst catalog have generated renewed interest in this issue. Here, we analyze the angular distribution of 585 bursts of the second BATSE catalog (Meegan et al., 1994). We search for evidence of burst recurrence using the nearest and farthest neighbor statistic and the two-point angular correlation function. We find the data to be consistent with the hypothesis that burst sources do not repeat; however, a repeater fraction of up to about 20% of the observed bursts cannot be excluded.

Meegan, Charles A.; Hartmann, Dieter H.; Brainerd, J. J.; Briggs, Michael S.; Paciesas, William S.; Pendleton, Geoffrey; Kouveliotou, Chryssa; Fishman, Gerald; Blumenthal, George; Brock, Martin

1995-01-01

363

Host Galaxies of Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Host galaxies are an excellent means of probing the natal environments that generate gamma-ray bursts (GRBs). Recent work on the host galaxies of short-duration GRBs has offered new insights into the parent stellar populations and ages of their enigmatic progenitors. Similarly, surveys of long-duration GRB (LGRB) host environments and their ISM properties have produced intriguing new results with important implications for long GRB progenitor models. These host studies are also critical in evaluating the utility of LGRBs as potential tracers of star formation and metallicity at high redshifts. I will summarize the latest research on LGRB host galaxies, and discuss the resulting impact on our understanding of these events' progenitors, energetics, and cosmological applications.

Levesque, Emily M.

2012-09-01

364

The Swift Gamma Ray Burst Mission  

NASA Technical Reports Server (NTRS)

The Swift mission: scheduled for launch in early 2004: is a multiwavelength observatory for gamma-ray burst (GRB) astronomy. It is the first-of-its-kind autonomous rapid-slewing satellite for transient astronomy and pioneers the way for future rapid-reaction and multiwavelength missions. It will be far more powerful than any previous GRB mission, observing more than 100 bursts per year and performing detailed X-ray and UV/optical afterglow observations spanning timescales from 1 minute to several days after the burst. The objectives are to: 1) determine the origin of GFU3s; 2) classify GRBs and search for new types; 3) study the interaction of the ultra-relativistic outflows of GRBs with their surrounding medium; and 4) use GRBs to study the early universe out to z greater than 10. The mission is being developed by a NASA-led international collaboration. It will carry three instruments: a new-generation wide-field gamma-ray (15-150 keV) detector that will detect bursts, calculate 1-4 arcmin positions: and trigger autonomous spacecraft slews; a narrow-field X-ray telescope that will give 5 arcsec positions and perform spectroscopy in the 0.2 to 10 keV band; and a narrow-field UV/optical telescope that will operate in the 170-600 nm band and provide 0.3 arcsec positions and optical finding charts. Redshift determinations will be made for most bursts. In addition to the primary GRB science, the mission will perform a hard X-ray survey to a sensitivity of approx. 1 mCrab (approx. 2 x l0(exp -11) erg/sq cm s in the 15-150 keV band), more than an order of magnitude better than HEAO A-4. A flexible data and operations system will allow rapid follow-up observations of all types of high-energy transients. with rapid data downlink and uplink available through the NASA TDRSS system. Swift transient data will be rapidly distributed to the astronomical community and all interested observers are encouraged to participate in follow-up measurements. A Guest Investigator program for the mission will provide funding for community involvement. Innovations from the Swift program applicable to the future include: 1) a large-area gamma-ray detector us- ing the new CdZnTe detectors; 2) an autonomous rapid slewing spacecraft; 3) a multiwavelength payload combining optical, X-ray, and gamma-ray instruments; 4) an observing program coordinated with other ground-based and space-based observatories; and 5) immediate multiwavelength data flow to the community. The mission is currently funded for 2 years of operations and the spacecraft will have a lifetime to orbital decay of approx. 8 years.

Gehrels, N.; Chincarini, G.; Giommi, P.; Mason, K. O.; Nousek, J. A.; Wells, A. A.; White, N. E.; Barthelmy, S. D.; Burrows, D. N.; Cominsky, L. R.

2004-01-01

365

Gamma ray constraints on decaying dark matter  

NASA Astrophysics Data System (ADS)

We derive new bounds on decaying dark matter from the gamma ray measurements of (i) the isotropic residual (extragalactic) background by Fermi and (ii) the Fornax galaxy cluster by H.E.S.S. We find that those from (i) are among the most stringent constraints currently available, for a large range of dark matter masses and a variety of decay modes, excluding half-lives up to ˜1026 to few 1027seconds. In particular, they rule out the interpretation in terms of decaying dark matter of the e± spectral features in PAMELA, Fermi and H.E.S.S., unless very conservative choices are adopted. We also discuss future prospects for CTA bounds from Fornax which, contrary to the present H.E.S.S. constraints of (ii), may allow for an interesting improvement and may become better than those from the current or future extragalactic Fermi data.

Cirelli, Marco; Moulin, Emmanuel; Panci, Paolo; Serpico, Pasquale D.; Viana, Aion

2012-10-01

366

The High Altitude Gamma Ray Observatory, HAWC  

NASA Astrophysics Data System (ADS)

The Volcano Sierra Negra in Puebla, Mexico was selected to host HAWC (High Altitude Water Cherenkov), a unique obervatory of wide field of view (2? sr) capable of observing the sky continously at energies from 0.5 TeV to 100 TeV. HAWC is an array of 300 large water tanks (7.3 m diameter × 5 m depth) at an altitude of 4100 m. a. s. l. Each tank is instrumented with three upward-looking photomultipliers tubes. The full array will be capable of observing the most energetic gamma rays from the most violent events in the universe. HAWC will be 15 times more sensitive than its predecesor, Milagro. We present HAWC, the scientific case and capabilities.

González, M. M.

2011-10-01

367

Pulsar gamma rays from polar cap regions  

NASA Technical Reports Server (NTRS)

The production is studied of pulsar gamma rays by energetic electrons flowing in the open field region above pulsar polar caps. The propagation was followed of curvature radiation from primary electrons, as well as hard synchrotron radiation generated by secondary pairs, through the pulsar magnetosphere for vacuum dipole open field geometries. Using data from radio and optical observations, models were constructed for the specific geometries and viewing angles appropriate to particular pulsars. These detailed models produce normalized spectra above 10 MeV, pulse profiles, beaming fractions and phase resolved spectra appropriate for direct comparison with COS-B and GRO data. Models are given for the Crab, Vela, and other potentially detectable pulsars; general agreement with existing data is good, although perturbations to the simplified models are needed for close matches. The calculations were extended to the millisecond pulsar range, which allows the production of predictions for the flux and spectra of populations of recycled pulsars and search strategies are pointed out.

Chiang, James; Romani, Roger W.

1992-01-01

368

Constraining Lorentz violations with Gamma Ray Bursts  

E-print Network

Gamma ray bursts are excellent candidates to constrain physical models which break Lorentz symmetry. We consider deformed dispersion relations which break the boost invariance and lead to an energy-dependent speed of light. In these models, simultaneously emitted photons from cosmological sources reach Earth with a spectral time delay that depends on the symmetry breaking scale. We estimate the possible bounds which can be obtained by comparing the spectral time delays with the time resolution of available telescopes. We discuss the best strategy to reach the strongest bounds. We compute the probability of detecting bursts that improve the current bounds. The results are encouraging. Depending on the model, it is possible to build a detector that within several years will improve the present limits of 0.015 m_pl.

Maria Rodriguez Martinez; Tsvi Piran

2006-01-10

369

Super Luminous Supernova and Gamma Ray Bursts  

E-print Network

We use a simple analytical model to derive a closed form expression for the bolometric light-curve of super-luminus supernovae (SLSNe) powered by a plastic collision between the fast ejecta from core collapse supernovae (SNe) of types Ib/c and IIn and slower massive circum-stellar shells, ejected during the late stage of the life of their progenitor stars preceding the SN explosion. We demonstrate that this expression reproduces well the bolometric luminosity of SLSNe with and without an observed gamma ray burst (GRB), and requires only a modest amount ($M < 0.1\\,M_\\odot$) of radioactive $^{56}$Ni synthesized in the SN explosion in order to explain their late-time luminosity. Long duration GRBs can be produced by ordinary SNe of type Ic rather than by 'hypernovae' - a subclass of superenergetic SNeIb/c.

Shlomo Dado; Arnon Dar

2012-07-16

370

The GLAST Gamma-Ray Observatory  

SciTech Connect

GLAST is a space mission that will observe the gamma-ray sky between 20MeV and 1TeV with unprecedented resolution and sensitivity. The Large Area Telescope (LAT), the main instrument onboard the GLAST satellite, is built with state-of-the-art particle physics detectors, and combines a large area is-strip tracker-converter, that will measure direction of incoming photons to an imaging CsI e.m. calorimeter for measurements of photon energies; an outer, segmented Anti-Coincidence Detector will reject charged particle background. In this paper they give an overview of the many physics goals and potential reach of the GLAST observatory and describe in detail the instrument design and performance.

Latronico, L.

2004-10-27

371

Gamma-ray bursts and cosmology.  

PubMed

I review the current status of the use of gamma-ray bursts (GRBs) as probes of the early Universe and cosmology. I describe the promise of long GRBs as probes of the high redshift (z>4) and very high redshift (z>5) Universe, and several key scientific results that have come from observations made possible by accurate, rapid localizations of these bursts by Swift. I then estimate the fraction of long GRBs that lie at very high redshifts and discuss ways in which it may be possible to rapidly identify-and therefore study-a larger number of these bursts. Finally, I discuss the ways in which both long and short GRBs can be made 'standard candles' and used to constrain the properties of dark energy. PMID:17301023

Lamb, D Q

2007-05-15

372

Optical and Gamma Ray Space Observations  

NASA Technical Reports Server (NTRS)

Results of the first year of data acquired from several Earth observatories concerning the optical counterparts gamma ray bursts (GRB) are presented. From the present statistics, it seems to be obvious that typical GRB's have optical emission at the time of the burst at a level at least below 1/(F(sub gamma)/F(sub opt)) approximately equal to 1/0.5 and optical emission a few hours after the burst is lower by a factor of 10 to 200 than the simultaneous emission. Given the fact that GRB spectra are rather broad over the observed energy range of say 20 keV up to 100 MeV, the observations indicate that the broad spectral shape may not continue into the optical range. After the confirmation of the isotropic distribution of GRB's by the BATSE experiment the interpretation now tends to put the sources at cosmological distances.

1992-01-01

373

Gamma-ray bursts - The current status  

NASA Astrophysics Data System (ADS)

The field of gamma ray burst astronomy is reviewed with emphasis on the results obtained since 1978 by numerous spacecraft experiments. Burst energy spectra are now known to display complex and rapidly varying shapes; however, the detection of line emission poses both experimental and theoretical problems. The log N-log S curves, when properly corrected for instrumental effects, are substantially in agreement at high intensities, although the shape of the curves is inconsistent with the observed spatial distribution of the bursts. Precise localizations using the method of arrival time analysis between widely separated spacecraft have given small error boxes which have in many cases been searched down to magnitude 23.5 and beyond. The results of these searches, as well as those of archival and real-time optical searches, are reviewed.

Hurley, K.

374

SAS-2 galactic gamma ray results, 1  

NASA Technical Reports Server (NTRS)

Continuing analysis of the data from the SAS-2 high energy gamma-ray experiment has produced an improved picture of the sky at photon energies above 35 MeV. On a large scale, the diffuse emission from the galactic plane is the dominant feature observed by SAS-2. This galactic plane emission is most intense between galactic longitude 310 and 45 deg, corresponding to a region within 7kpc of the galactic center. Within the high-intensity region, SAS-2 observes peaks around galactic longitudes 315 deg, 330 deg, 345 deg, 0 deg, and 35 deg. These peaks appear to be correlated with such galactic features and components as molecular hydrogen, atomic hydrogen, magnetic fields, cosmic ray concentrations, and photon fields.

Thompson, D. J.; Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.; Bignami, G. F.; Lamb, R. C.; Oegelman, H.; Oezel, M. E.; Tuemer, T.

1976-01-01

375

Very High Energy Gamma Ray Extension of GRO Observations  

NASA Technical Reports Server (NTRS)

The membership, progress, and invited talks, publications, and proceedings made by the Whipple Gamma Ray Collaboration is reported for june 1990 through May 1994. Progress was made in the following areas: the May 1994 Markarian Flare at Whipple and EGRET (Energetic Gamma Ray Experiment Telescope) energies; AGN's (Active Galactic Nuclei); bursts; supernova remnants; and simulations and energy spectra.

Weekes, Trevor C.

1994-01-01

376

Discoveries by the Fermi Gamma Ray Space Telescope  

NASA Technical Reports Server (NTRS)

Fermi is a large space gamma-ray mission developed by NASA and the DOE with major contributions from France, Germany, Italy, Japan and Sweden. It was launched in June 2008 and has been performing flawlessly since then. The main instrument is the Large Area Telescope (LAT) operating in the 20 MeV to 300 GeV range and a smaller monitor instrument is the Gamma-ray Burst Monitor (GBM) operating in the 8 keV to 40 MeV range. New findings are occurring every week. Some of the key discoveries are: 1) Discovery of many new gamma-ray pulsars, including gamma-ray only and millisecond pulsars. 2) Detection of high energy gamma-ray emission from globular clusters, most likely due to summed emission from msec pulsars. 3) Discovery of delayed and extended high energy gamma-ray emission from short and long gamma-ray busts. 4) Detection of approximately 250 gamma-ray bursts per year with the GBM instrument. 5) Most accurate measurement of the cosmic ray electron spectrum between 30 GeV and 1 TeV, showing some excess above the conventional diffusion model. The talk will present the new discoveries and their implications.

Gehrels, Neil

2011-01-01

377

Discovery of Intense Gamma-Ray Flashes of Atmospheric Origin  

Microsoft Academic Search

Detectors aboard the Compton Gamma Ray Observatory have observed an unexplained terrestrial phenomenon: brief, intense flashes of gamma rays. These flashes must originate in the atmosphere at altitudes above at least 30 kilometers in order to escape atmospheric absorption and reach the orbiting detectors. At least a dozen such events have been detected over the past 2 years. The photon

G. J. Fishman; P. N. Bhat; R. Mallozzi; J. M. Horack; T. Koshut; C. Kouveliotou; G. N. Pendleton; C. A. Meegan; R. B. Wilson; W. S. Paciesas; S. J. Goodman; H. J. Christian

1994-01-01

378

GRAYSKY-A new gamma-ray skyshine code  

Microsoft Academic Search

This paper describes a new prototype gamma-ray skyshine code GRAYSKY (Gamma-RAY SKYshine) that has been developed at BNFL, as part of an industrially based master of science course, to overcome the problems encountered with SKYSHINEII and RANKERN. GRAYSKY is a point kernel code based on the use of a skyshine response function. The scattering within source or shield materials is

D. J. Witts; T. Twardowski; M. H. Watmough

1993-01-01

379

QUALITY CONTROL FOR ENVIRONMENTAL MEASUREMENTS USING GAMMA-RAY SPECTROMETRY  

EPA Science Inventory

This report describes the quality control procedures, calibration, collection, analysis, and interpretation of data in measuring the activity of gamma ray-emitting radionuclides in environmental samples. Included in the appendices are basic data for selected gamma ray-emitting ra...

380

The Gamma-Ray Luminosity Function of Radio Pulsars  

NASA Technical Reports Server (NTRS)

This final report is a study of gamma-ray luminosity function of radio pulsars. The goal is to constrain certain parameters in order to address such diverse issues as the high energy emission mechanism in pulsars and the fraction of the Galaxy's gamma ray emission attributable to these objects.

Helfand, David J.

1998-01-01

381

Gamma-ray astronomy: Promise for the future  

Microsoft Academic Search

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

Neil Gehrels; Daryl Macomb

1997-01-01

382

Coordinated UV Observations of Gamma-Ray Selected Blazars  

Microsoft Academic Search

We propose to use the unique capabilities of the IUE satellite to make UV observations as part of a large international multiwavelength campaign to monitor gamma-ray selected blazars. This program is being coordinated by Hartman with the Compton Gamma Ray Observatory (CGRO) phase 4 time line to obtain simultaneous observations of blazars over the entire electromagnetic spectrum. Multiwavelength observations are

Robert C. Hartman

1994-01-01

383

Science with the new generation high energy gamma- ray experiments  

Microsoft Academic Search

This Conference is the fifth of a series of Workshops on High Energy Gamma- ray Experiments, following the Conferences held in Perugia 2003, Bari 2004, Cividale del Friuli 2005, Elba Island 2006. This year the focus was on the use of gamma-ray to study the Dark Matter component of the Universe, the origin and propagation of Cosmic Rays, Extra Large

M. Alvarez; D. D'Armiento; G. Agnetta; A. Alberdi; A. Antonelli; A. Argan; P. Assis; E. A. Baltz; C. Bambi; G. Barbiellini; H. Bartko; M. Basset; D. Bastieri; P. Belli; G. Benford; L. Bergstrom; R. Bernabei; G. Bertone; A. Biland; B. Biondo; F. Bocchino; E. Branchini; M. Brigida; T. Bringmann; P. Brogueira; A. Bulgarelli; J. A. Caballero; G. A. Caliandro; P. Camarri; F. Cappella; P. Caraveo; R. Carbone; M. Carvajal; S. Casanova; A. J. Castro-Tirado; O. Catalano; R. Catena; F. Celi; A. Celotti; R. Cerulli; A. Chen; R. Clay; V. Cocco; J. Conrad; E. Costa; A. Cuoco; G. Cusumano; C. J. Dai; B. Dawson; B. De Lotto; G. De Paris; A. de Ugarte Postigo; E. Del Monte; C. Delgado; A. Di Ciaccio; G. Di Cocco; S. Di Falco; G. Di Persio; B. L. Dingus; A. Dominguez; F. Donato; I. Donnarumma; M. Doro; J. Edsjo; J. M. Espino Navas; M. C. Espirito Santo; Y. Evangelista; C. Evoli; D. Fargion; C. Favuzzi; M. Feroci; M. Fiorini; L. Foggetta; N. Fornengo; T. Froysland; M. Frutti; F. Fuschino; J. L. Gomez; M. Gomez; D. Gaggero; N. Galante; M. I. Gallardo; M. Galli; J. E. Garcia; M. Garczarczyk; F. Gargano; M. Gaug; F. Gianotti; S. Giarrusso; B. Giebels; N. Giglietto; P. Giommi; F. Giordano; A. Giuliani; J. Glicenstein; P. Goncalves; D. Grasso; M. Guerriero; H. L. He; A. Incicchitti; J. Kirk; H. H. Kuang; A. La Barbera; G. La Rosa; C. Labanti; G. Lamanna; I. Lapshov; F. Lazzarotto; S. Liberati; F. Liello; P. Lipari; F. Longo; F. Loparco; M. Lozano; P. G. Lucentini De Sanctis; J. M. Ma; M. C. Maccarone; L. Maccione; V. Malvezzi; A. Mangano; M. Mariotti; M. Marisaldi; I. Martel; A. Masiero; E. Massaro; M. Mastropietro; E. Mattaini; F. Mauri; M. N. Mazziotta; S. Mereghetti; T. Mineo; S. Mizobuchi; A. Moiseev; M. Moles; C. Monte; F. Montecchia; E. Morelli; A. Morselli; I. Moskalenko; F. Nozzoli; J. F. Ormes; M. A. Peres-Torres; L. Pacciani; A. Pellizzoni; F. Perez-Bernal; F. Perotti; P. Picozza; L. Pieri; M. Pietroni; M. Pimenta; A. Pina; C. Pittori; C. Pontoni; G. Porrovecchio; F. Prada; M. Prest; D. Prosperi; R. Protheroe; G. Pucella; J. M. Quesada; J. M. Quintana; J. R. Quintero; S. Raino; M. Rapisarda; M. Rissi; J. Rodriguez; E. Rossi; G. Rowell; A. Rubini; F. Russo; M. Sanchez-Conde; B. Sacco; V. Scapin; M. Schelke; A. Segreto; A. Sellerholm; X. D. Sheng; A. Smith; P. Soffitta; R. Sparvoli; P. Spinelli; V. Stamatescu; L. S. Stark; M. Tavani; G. Thornton; L. G. Titarchuk; B. Tome; A. Traci; M. Trifoglio; A. Trois; P. Vallania; E. Vallazza; S. Vercellone; S. Vernetto; V. Vitale; N. Wild; Z. P. Ye; A. Zambra; F. Zandanel; D. Zanello

2007-01-01

384

Images of Simultaneous Gamma-Ray Burst Optical Counterpart  

NSDL National Science Digital Library

Astronomers have observed a visible light emitted at the same time as a gamma-ray burst for the first time on January 27, 1999. Six images of this gamma-ray burst are provided at the University of Michigan site.

1999-01-01

385

Diagram of the Apollo 15 & 16 Gamma-ray Detector  

NSDL National Science Digital Library

This is a diagram of the Apollo 15 & 16 Gamma-ray Detector from the NASA website. Primarily intended to study the Moon's radioactivity, it made measurements of the cosmic gamma-ray background during its trip. It shows measurements in millimeters.

2010-05-05

386

Crystal diffraction lens telescope for focusing nuclear gamma rays  

Microsoft Academic Search

A crystal diffraction lens was constructed at Argonne National Laboratory for use as a telescope to focus nuclear gamma rays. It consists of 600 single crystals of germanium arranged in 8 concentric rings. The mounted angle of each crystal was adjusted to intercept and diffract the incoming gamma rays with an accuracy of a few arcsec. The performance of the

Robert K. Smither; Patricia B. Fernandez; Timothy Graber; Peter von Ballmoos; Juan E. Naya; Francis Albernhe; Gilbert Vedrenne; Mohamed Faiz

1996-01-01

387

Gamma rays from accretion onto rotating black holes  

NASA Technical Reports Server (NTRS)

Ionized matter falling onto an isolated, rotating black hole will be heated sufficiently that proton-proton collisions will produce mesons, including neutral pions, which decay into gamma rays. For massive (1000 M sub circled dot), black holes, the resulting gamma-ray luminosity may exceed 10 to the 36th power engs/s, with a spectrum peaked near 20 MeV.

Collins, M. S.

1978-01-01

388

Gamma-ray Bursts as Probes of Galaxy Evolution  

E-print Network

Gamma-ray Bursts as Probes of Galaxy Evolution Daniele Malesani, Dark Cosmology Centre and the X to ongoing star formation "Naked-eye" GRB 080319B GRBs explode within star-forming galaxies Gamma-ray bursts formation rate (you "only" need a redshift) Includes "invisible" star formation: - SF in faint galaxies

Â?umer, Slobodan

389

SAS-2 galactic gamma-ray results. 2: Localized sources  

NASA Technical Reports Server (NTRS)

Gamma ray emission was detected from the radio pulsars PSR 1818-04 and PSR 1747-46, in addition to the previously reported gamma ray emission from the Crab and Vela pulsars. Because the Crab pulsar is the only one observed in the optical and X-ray bands, these gamma ray observations suggest a uniquely gamma ray phenomenon occurring in a fraction of the radio pulsars. PSR 1818-04 has a gamma ray luminosity comparable to that of the Crab pulsar, whereas the luminosities of PSR 1747-46 and the Vela pulsar are approximately an order of magnitude lower. SAS-2 data for pulsar correlations yielded upper limits to gamma ray luminosity for 71 other radio pulsars. For five of the closest pulsars, upper limits for gamma ray luminosity are found to be at least three orders of magnitude lower than that of the Crab pulsar. Gamma ray enhancement near the Milky Way satellite galaxy and the galactic plane in the Cygnus region is also discussed.

Hartman, R. C.; Fichtel, C. E.; Kniffen, D. A.; Lamb, R. C.; Thompson, D. J.; Bignami, G. F.; Oegelman, H.; Oezel, M. E.; Tuemer, T.

1977-01-01

390

LONG GAMMA-RAY TRANSIENTS FROM COLLAPSARS  

SciTech Connect

In the collapsar model for common gamma-ray bursts (GRBs), the formation of a centrifugally supported disk occurs during the first {approx}10 s following the collapse of the iron core in a massive star. This only occurs in a small fraction of massive stellar deaths, however, and requires unusual conditions. A much more frequent occurrence could be the death of a star that makes a black hole and a weak or absent outgoing shock, but in a progenitor that only has enough angular momentum in its outermost layers to make a disk. We consider several cases where this is likely to occur-blue supergiants with low mass-loss rates, tidally interacting binaries involving either helium stars or giant stars, and the collapse to a black hole of very massive pair-instability supernovae. These events have in common the accretion of a solar mass or so of material through a disk over a period much longer than the duration of a common GRB. A broad range of powers is possible, 10{sup 47}-10{sup 50} erg s{sup -1}, and this brightness could be enhanced by beaming. Such events were probably more frequent in the early universe where mass-loss rates were lower. Indeed, this could be one of the most common forms of gamma-ray transients in the universe and could be used to study first generation stars. Several events could be active in the sky at any one time. Recent examples of this sort of event may have been the Swift transients Sw-1644+57, Sw-2058+0516, and GRB 101225A.

Woosley, S. E. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Heger, Alexander, E-mail: woosley@ucolick.org, E-mail: alex@physics.umn.edu [Minnesota Institute of Astrophysics, School of Physics and Astronomy, University of Minnesota, Twin Cities, Minneapolis, MN 55455 (United States)

2012-06-10

391

Gamma-Ray Bursts: Pulses and Populations  

NASA Astrophysics Data System (ADS)

We describe ongoing work on two projects that are enabling more thorough and accurate use of archival BATSE data for elucidating the nature of GRB sources; the methods and tools we are developing will also be valuable for analyzing data from other missions. The first project addresses modeling the spectro-temporal behavior of prompt gamma ray emission from GRBs by modeling gamma ray count and event data with a population of pulses, with the population drawn from one or more families of single-pulse kernels. Our approach is built on a multilevel nonparametric probabilistic framework we have dubbed "Bayesian droplets," and offers several important advances over previous pulse decomposition approaches: (1) It works in the pulse-confusion regime, quantifying uncertainty in the number, locations, and shapes of pulses, even when there is strong overlap. (2) It can self-consistently model pulse behavior across multiple spectral bands. (3) It readily handles a variety of spatio-temporal kernel shapes. (4) It reifies the idea of a burst as a population of pulses, enabling explicit modeling and estimation of the pulse population distribution. We describe the framework and present analyses of prototypical simple and complex GRB light curves. The second project aims to enable accurate demographic modeling of GRBs using the BATSE catalog. We present new calculations of the BATSE sky exposure, encompassing the full duration of the BATSE catalog for the first time, with many improvements over the currently available exposure map. A similar calculation of the detection efficiency is in progress. We also describe public Python software enabling access and accurate modeling of BATSE GRB data. The software enables demographic studies (e.g., modeling log N - log S distributions) with accurate accounting of both selection effects and measurement errors. It also enables spectro-temporal modeling of detailed data from individual GRBs. These projects are supported by NASA through the AISR and ADAP programs.

Loredo, Thomas J.; Hakkila, J. E.; Broadbent, M.; Wasserman, I. M.; Wolpert, R. L.

2013-04-01

392

Gamma-ray bursts and collisionless shocks  

E-print Network

Particle acceleration in collisionless shocks is believed to be responsible for the production of cosmic-rays over a wide range of energies, from few GeV to >10^{20}eV, as well as for the non-thermal emission of radiation from a wide variety of high energy astrophysical sources. A theory of collisionless shocks based on first principles does not, however, exist. Observations of gamma-ray burst (GRB) "afterglows" provide a unique opportunity for diagnosing the physics of relativistic collisionless shocks. Most GRBs are believed to be associated with explosions of massive stars. Their "afterglows," delayed low energy emission following the prompt burst of gamma-rays, are well accounted for by a model in which afterglow radiation is due to synchrotron emission of electrons accelerated in relativistic collisionless shock waves driven by the explosion into the surrounding plasma. Within the framework of this model, some striking characteristics of collisionless relativistic shocks are implied. These include the generation of downstream magnetic fields with energy density exceeding that of the upstream field by ~8 orders of magnitude, the survival of this strong field at distances ~10^{10} skin-depths downstream of the shock, and the acceleration of particles to a power-law energy spectrum, d\\log n/d\\log E ~ -2, possibly extending to 10^{20}eV. I review in this talk the phenomenological considerations, based on which these characteristics are inferred, and the challenges posed to our current models of particle acceleration and magnetic field generation in collisionless shocks. Some recent theoretical results derived based on the assumption of a self-similar shock structure are briefly discussed.

E. Waxman

2006-07-15

393

Magnetic Structures in Gamma-Ray Burst Jets Probed by Gamma-Ray Polarization  

NASA Astrophysics Data System (ADS)

We report polarization measurements in two prompt emissions of gamma-ray bursts, GRB 110301A and GRB 110721A, observed with the gamma-ray burst polarimeter (GAP) on borad the IKAROS solar sail mission. We detected linear polarization signals from each burst with polarization degree of ? = 70 ± 22% with statistical significance of 3.7? for GRB 110301A, and ? = 84+16 - 28% with 3.3? confidence level for GRB 110721A. We did not detect any significant change of polarization angle. These two events had shorter durations and dimmer brightness compared with GRB 100826A, which showed a significant change of polarization angle, as reported in Yonetoku et al. Synchrotron emission model can be consistent with the data of the three GRBs, while the photospheric quasi-thermal emission model is not favored. We suggest that magnetic field structures in the emission region are globally ordered fields advected from the central engine.

Yonetoku, Daisuke; Murakami, Toshio; Gunji, Shuichi; Mihara, Tatehiro; Toma, Kenji; Morihara, Yoshiyuki; Takahashi, Takuya; Wakashima, Yudai; Yonemochi, Hajime; Sakashita, Tomonori; Toukairin, Noriyuki; Fujimoto, Hirofumi; Kodama, Yoshiki

2012-10-01

394

The supernova-gamma-ray burst-jet connection.  

PubMed

The observed association between supernovae and gamma-ray bursts represents a cornerstone in our understanding of the nature of gamma-ray bursts. The collapsar model provides a theoretical framework for this connection. A key element is the launch of a bipolar jet (seen as a gamma-ray burst). The resulting hot cocoon disrupts the star, whereas the (56)Ni produced gives rise to radioactive heating of the ejecta, seen as a supernova. In this discussion paper, I summarize the observational status of the supernova-gamma-ray burst connection in the context of the 'engine' picture of jet-driven supernovae and highlight SN 2012bz/GRB 120422A--with its luminous supernova but intermediate high-energy luminosity--as a possible transition object between low-luminosity and jet gamma-ray bursts. The jet channel for supernova explosions may provide new insights into supernova explosions in general. PMID:23630379

Hjorth, Jens

2013-06-13

395

Gamma ray irradiation for sludge solubilization and biological nitrogen removal  

NASA Astrophysics Data System (ADS)

This study was conducted to investigate the effects of gamma ray irradiation on the solubilization of waste sewage sludge. The recovery of an organic carbon source from sewage sludge by gamma ray irradiation was also studied. The gamma ray irradiation showed effective sludge solubilization efficiencies. Both soluble chemical oxygen demand (SCOD) and biochemical oxygen demand (BOD 5) increased by gamma ray irradiation. The feasibility of the solubilized sludge carbon source for a biological nitrogen removal was also investigated. A modified continuous bioreactor (MLE process) for a denitrification was operated for 20 days by using synthetic wastewater. It can be concluded that the gamma ray irradiation was useful for the solubilization of sludge and the recovery of carbon source from the waste sewage sludge for biological nitrogen removal.

Kim, Tak-Hyun; Lee, Myunjoo; Park, Chulhwan

2011-12-01

396

Multiwavelength observations of unidentified high energy gamma-ray sources  

NASA Technical Reports Server (NTRS)

As was the case for COS B, the majority of high-energy (greater than 100 MeV) gamma-ray sources detected by the EGRET instrument on GRO are not immediately identifiable with catalogued objects at other wavelengths. These persistent gamma-ray sources are, next to the gamma-ray bursts, the least understood objects in the universe. This two year investigation is intended to support the analysis, correlation, and theoretical interpretation of data that we are obtaining at x-ray, optical, and radio wavelengths in order to render the gamma-ray data interpretable. This second year was devoted to studies of unidentified gamma-ray sources from the first EGRET catalog, similar to previous observations. Efforts have concentrated on the sources at low and intermediate Galactic latitudes, which are the most plausible pulsar candidates.

Halpern, Jules P.

1995-01-01

397

International Gamma-Ray Astrophysics Laboratory (INTEGRAL): a future ESA mission for gamma-ray astronomy  

Microsoft Academic Search

The INTEGRAL observatory, due for launch in 2001, will address the fine spectroscopy (2 keV FWHM 1 MeV) and accurate imaging (12 arcminute FWHM) of celestial gamma-ray sources in the important 15 keV to 10 MeV energy range. The fine spectroscopy will permit spectral features to be uniquely identified and line profiles to be determined for in-depth studies of the

Neil A. Gehrels; Christoph Winkler

1996-01-01

398

Gamma-ray lens development status for a European Gamma-Ray Imager  

E-print Network

A breakthrough in the sensitivity level of the hard X-/gamma-ray telescopes, which today are based on detectors that view the sky through (or not) coded masks, is expected when focusing optics will be available also in this energy range. Focusing techniques are now in an advanced stage of development. To date the most efficient technique to focus hard X-rays with energies above 100 keV appears to be the Bragg diffraction from crystals in transmission configuration (Laue lenses). Crystals with mosaic structure appear to be the most suitable to build a Laue lens with a broad passband, even though other alternative structures are being investigated. The goal of our project is the development of a broad band focusing telescope based on gamma-ray lenses for the study of the continuum emission of celestial sources from 60 keV up to >600 keV. We will report details of our project, its development status and results of our assessment study of a lens configuration for the European Gamma Ray Imager (GRI) mission now under study for the ESA plan "Cosmic Vision 2015-2025".

F. Frontera; A. Pisa; V. Carassiti; F. Evangelisti; G. Loffredo; D. Pellicciotta; K. H. Andersen; P. Courtois; L. Amati; E. Caroli; T. Franceschini; G. Landini; S. Silvestri; J. B. Stephen

2006-11-15

399

High Energy Gamma-Ray Emission from Gamma-Ray Bursts - Before GLAST  

SciTech Connect

Gamma-ray bursts (GRBs) are short and intense emission of soft {gamma}-rays, which have fascinated astronomers and astrophysicists since their unexpected discovery in 1960s. The X-ray/optical/radio afterglow observations confirm the cosmological origin of GRBs, support the fireball model, and imply a long-activity of the central engine. The high-energy {gamma}-ray emission (> 20 MeV) from GRBs is particularly important because they shed some lights on the radiation mechanisms and can help us to constrain the physical processes giving rise to the early afterglows. In this work, we review observational and theoretical studies of the high-energy emission from GRBs. Special attention is given to the expected high-energy emission signatures accompanying the canonical early-time X-ray afterglow that was observed by the Swift X-ray Telescope. We also discuss the detection prospect of the upcoming GLAST satellite and the current ground-based Cerenkov detectors.

Fan, Yi-Zhong; Piran, Tsvi

2011-11-29

400

Physics of Gamma-ray Bursts and Multi-messenger Signals from Double Neutron Star Mergers.  

E-print Network

??My dissertation includes two parts: Physics of Gamma-Ray Bursts (GRBs): Gamma-ray bursts are multi-wavelength transients, with both prompt gamma-ray emission and late time afterglow emission… (more)

Gao, He

2014-01-01

401

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

National Technical Information Service (NTIS)

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 indi...

A. A. Abdo, B. Anderson, M. Ackermann, M. Ajello, M. Axelsson, W. B. Atwood

2012-01-01

402

Time-resolved Neutron-gamma-ray Data Acquisition for in Situ Subsurface Planetary Geochemistry  

NASA Technical Reports Server (NTRS)

The current gamma-ray/neutron instrumentation development effort at NASA Goddard Space Flight Center aims to extend the use of active pulsed neutron interrogation techniques to probe the subsurface elemental composition of planetary bodies in situ. Previous NASA planetary science missions, that used neutron and/or gamma-ray spectroscopy instruments, have relied on neutrons produced from galactic cosmic rays. One of the distinguishing features of this effort is the inclusion of a high intensity 14.1 MeV pulsed neutron generator synchronized with a custom data acquisition system to time each event relative to the pulse. With usually only one opportunity to collect data, it is difficult to set a priori time-gating windows to obtain the best possible results. Acquiring time-tagged, event-by-event data from nuclear induced reactions provides raw data sets containing channel/energy, and event time for each gamma ray or neutron detected. The resulting data set can be plotted as a function of time or energy using optimized analysis windows after the data are acquired. Time windows can now be chosen to produce energy spectra that yield the most statistically significant and accurate elemental composition results that can be derived from the complete data set. The advantages of post-processing gamma-ray time-tagged event-by-event data in experimental tests using our prototype instrument will be demonstrated.

Bodnarik, Julie G.; Burger, Dan Michael; Burger, A.; Evans, L. G.; Parsons, A. M.; Schweitzer, J. S.; Starr R. D.; Stassun, K. G.

2013-01-01

403

Time-resolved neutron/gamma-ray data acquisition for in situ subsurface planetary geochemistry  

NASA Astrophysics Data System (ADS)

The current gamma-ray/neutron instrumentation development effort at NASA Goddard Space Flight Center aims to extend the use of active pulsed neutron interrogation techniques to probe the subsurface elemental composition of planetary bodies in situ. Previous NASA planetary science missions, that used neutron and/or gamma-ray spectroscopy instruments, have relied on neutrons produced from galactic cosmic rays. One of the distinguishing features of this effort is the inclusion of a high intensity 14.1 MeV pulsed neutron generator synchronized with a custom data acquisition system to time each event relative to the pulse. With usually only one opportunity to collect data, it is difficult to set a priori time-gating windows to obtain the best possible results. Acquiring time-tagged, event-by-event data from nuclear induced reactions provides raw data sets containing channel/energy, and event time for each gamma ray or neutron detected. The resulting data set can be plotted as a function of time or energy using optimized analysis windows after the data are acquired. Time windows can now be chosen to produce energy spectra that yield the most statistically significant and accurate elemental composition results that can be derived from the complete data set. The advantages of post-processing gamma-ray time-tagged event-by-event data in experimental tests using our prototype instrument will be demonstrated.

Bodnarik, J. G.; Burger, D. M.; Burger, A.; Evans, L. G.; Parsons, A. M.; Schweitzer, J. S.; Starr, R. D.; Stassun, K. G.

2013-04-01

404

In situ elemental analysis using neutron-capture gamma-ray spectroscopy  

NASA Astrophysics Data System (ADS)

In situ chemical analysis has become increasingly important in many areas of geochemical exploration and environmental monitoring. However, the determination of absolute or relative concentrations by neutron-gamma techniques can be difficult because of the variety of materials that can be encountered. Changes in concentration of neutron moderators, particularly water, and of strong absorbers, such as iron, can result in spatial and energy distribution variations of the neutron flux in the material. These lead to changes in the measured gamma-ray spectrum. We have been developing analytical procedures which allow the absolute and relative abundances of major and minor elements to be determined from the measured neutron-induced gamma-ray spectrum. Calculations are made using the one-dimensional neutron and gamma transport code ANISN. From the calculations, conversion factors are obtained that can be used to convert gamma-ray count rates to elemental concentrations. Once these conversion factors are determined as a function of water content and the macroscopic cross section, they can be used to determine compositions of unknown samples. To explore the application of these analytical methods, a number of different experimental test programs have been initiated to collect measured gamma-ray spectra. Field tests have been conducted in soils of various compositions using a 120 cm 3 HPGe detector and a 14 MeV pulsed neutron generator.

Evans, Larry G.; Lapides, Jeffrey R.; Trombka, Jacob I.; Jensen, Dal H.

405

Energy- and time-resolved detection of prompt gamma-rays for proton range verification  

NASA Astrophysics Data System (ADS)

In this work, we present experimental results of a novel prompt gamma-ray detector for proton beam range verification. The detection system features an actively shielded cerium-doped lanthanum(III) bromide scintillator, coupled to a digital data acquisition system. The acquisition was synchronized to the cyclotron radio frequency to separate the prompt gamma-ray signals from the later-arriving neutron-induced background. We designed the detector to provide a high energy resolution and an effective reduction of background events, enabling discrete proton-induced prompt gamma lines to be resolved. Measuring discrete prompt gamma lines has several benefits for range verification. As the discrete energies correspond to specific nuclear transitions, the magnitudes of the different gamma lines have unique correlations with the proton energy and can be directly related to nuclear reaction cross sections. The quantification of discrete gamma lines also enables elemental analysis of tissue in the beam path, providing a better prediction of prompt gamma-ray yields. We present the results of experiments in which a water phantom was irradiated with proton pencil-beams in a clinical proton therapy gantry. A slit collimator was used to collimate the prompt gamma-rays, and measurements were performed at 27 positions along the path of proton beams with ranges of 9, 16 and 23 g?cm-2 in water. The magnitudes of discrete gamma lines at 4.44, 5.2 and 6.13 MeV were quantified. The prompt gamma lines were found to be clearly resolved in dimensions of energy and time, and had a reproducible correlation with the proton depth-dose curve. We conclude that the measurement of discrete prompt gamma-rays for in vivo range verification of clinical proton beams is feasible, and plan to further study methods and detector designs for clinical use.

Verburg, Joost M.; Riley, Kent; Bortfeld, Thomas; Seco, Joao

2013-10-01

406

Gamma-ray astronomy: From Fermi up to the HAWC high-energy {gamma}-ray observatory in Sierra Negra  

SciTech Connect

Gamma-rays represent the most energetic electromagnetic window for the study of the Universe. They are studied both from space at MeV and GeV energies, with instruments like the Fermi{gamma}-ray Space Telescope, and at TeV energies with ground based instruments profiting of particle cascades in the atmosphere and of the Cerenkov radiation of charged particles in the air or in water. The Milagro gamma-ray observatory represented the first instrument to successfully implement the water Cerenkov technique for {gamma}-ray astronomy, opening the ground for the more sensitive HAWC {gamma}-ray observatory, currently under development in the Sierra Negra site and already providing early science results.

Carraminana, Alberto [Instituto Nacional de Astrofisica, Optica y Electronica Luis Enrique Erro 1, Tonantzintla, Puebla 72840 (Mexico); Collaboration: HAWC Collaboration

2013-06-12

407

Gamma-ray Astronomy: Implications for Fundamental Physics  

E-print Network

Gamma-ray Astronomy studies cosmic accelerators through their electromagnetic radiation in the energy range between ~100 MeV and ~100 TeV. The present most sensitive observations in this energy band are performed, from space, by the Large Area Telescope onboard the Fermi satellite and, from Earth, by the Imaging Air Cherenkov Telescopes MAGIC, H.E.S.S. and VERITAS. These instruments have revolutionized the field of Gamma-ray Astronomy, discovering different populations of gamma-ray emitters and studying in detail the non-thermal astrophysical processes producing this high-energy radiation. The scientific objectives of these observatories include also questions of fundamental physics. With gamma-ray instruments we study the origin of Galactic cosmic rays, testing the hypothesis or whether they are mainly produced in supernova explosions. Also, we obtain the most sensitive measurement of the cosmic electron-positron spectrum between 20 GeV and 5 TeV. By observing the gamma-ray emission from sources at cosmological distances, we learn about the intensity and evolution of the extragalactic background light, and perform tests of Lorentz Invariance. Moreover, we can search for dark matter by looking for gamma-ray signals produced by its annihilation or decay in over-density sites. In this paper, we review the most recent results produced with the current generation of gamma-ray instruments in these fields of research.

Javier Rico

2011-11-28

408

The Gamma-ray Albedo of the Moon  

E-print Network

We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of gamma rays from the Moon is very steep with an effective cutoff around 3-4 GeV (600 MeV for the inner part of the Moon disk) and exhibits a narrow pion-decay line at 67.5 MeV, perhaps unique in astrophysics. Apart from other astrophysical sources, the albedo spectrum of the Moon is well understood, including its absolute normalisation; this makes it a useful "standard candle" for gamma-ray telescopes. The steep albedo spectrum also provides a unique opportunity for energy calibration of gamma-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). Since the albedo flux depends on the incident CR spectrum which changes over the solar cycle, it is possible to monitor the CR spectrum using the albedo gamma-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter-Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo gamma rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the LAT to monitor the CR spectrum near the Earth beyond the lifetime of the PAMELA.

Igor V. Moskalenko; Troy A. Porter

2007-08-21

409

Gamma-Ray Observatory - The next great observatory in space  

NASA Technical Reports Server (NTRS)

The Gamma-Ray Observatory (GRO) which is part of NASA's Great Observatories space program is presented. The GRO is equipped with the Burst and Transient Source Experiment (which detects low-energy gamma-ray photons from 20 keV to 600 keV and locates sources of gamma-ray bursts), the Oriented Scintillation Spectrometer Experiment (which detects celestial gamma rays from 100 keV to 10 MeV and identifies the elements producing these rays by measuring the ray's spectra and time variability), the Imaging Compton Telescope (which images gamma rays with energies from 1 to 30 MeV created when cosmic rays interact with interstellar matter), and the Energetic Gamma-Ray Experiment Telescope (which detects high-energy photons associated with the most energetic processes occurring in nature). After the energies of photons from each source are classified, the gamma-ray mechanisms can be modelled. Nuclei, radioactive isotopes, and nuclear reactions can be identified, and the physical conditions at the radiation's source can also be modelled. From these models, theories can be developed about the creation of elements in the explosion and collapse of giant stars, the acceleration of charged particles to velocities approaching the speed of light, and the destruction of matter and antimatter.

Neal, Valerie; Fishman, Gerald; Kniffen, Donald

1990-01-01

410

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

411

Gamma-ray transfer and energy deposition in supernovae  

NASA Technical Reports Server (NTRS)

Solutions to the energy-independent (gray) radiative transfer equations are compared to results of Monte Carlo simulations of the Ni-56 and Co-56 decay gamma-ray energy deposition in supernovae. The comparison shows that an effective, purely absorptive, gray opacity, kappa(sub gamma) approximately (0. 06 +/- 0.01)Y(sub e) sq cm/g, where Y is the total number of electrons per baryon, accurately describes the interaction of gamma-rays with the cool supernova gas and the local gamma-ray energy deposition within the gas. The nature of the gamma-ray interaction process (dominated by Compton scattering in the relativistic regime) creates a weak dependence of kappa(sub gamma) on the optical thickness of the (spherically symmetric) supernova atmosphere: The maximum value of kappa(sub gamma) applies during optically thick conditions when individual gamma-rays undergo multiple scattering encounters and the lower bound is reached at the phase characterized by a total Thomson optical depth to the center of the atmosphere tau(sub e) approximately less than 1. Gamma-ray deposition for Type Ia supernova models to within 10% for the epoch from maximum light to t = 1200 days. Our results quantitatively confirm that the quick and efficient solution to the gray transfer problem provides an accurate representation of gamma-ray energy deposition for a broad range of supernova conditions.

Swartz, Douglas A.; Sutherland, Peter G.; Harkness, Robert P.

1995-01-01

412

GLAST and Ground-Based Gamma-Ray Astronomy  

NASA Technical Reports Server (NTRS)

The launch of the Gamma-ray Large Area Space Telescope together with the advent of a new generation of ground-based gamma-ray detectors such as VERITAS, HESS, MAGIC and CANGAROO, will usher in a new era of high-energy gamma-ray astrophysics. GLAST and the ground based gamma-ray observatories will provide highly complementary capabilities for spectral, temporal and spatial studies of high energy gamma-ray sources. Joint observations will cover a huge energy range, from 20 MeV to over 20 TeV. The LAT will survey the entire sky every three hours, allowing it both to perform uniform, long-term monitoring of variable sources and to detect flaring sources promptly. Both functions complement the high-sensitivity pointed observations provided by ground-based detectors. Finally, the large field of view of GLAST will allow a study of gamma-ray emission on large angular scales and identify interesting regions of the sky for deeper studies at higher energies. In this poster, we will discuss the science returns that might result from joint GLAST/ground-based gamma-ray observations and illustrate them with detailed source simulations.

McEnery, Julie

2008-01-01

413

X-ray and gamma ray astronomy detectors  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

414

BL Lac contribution to the Extragalactic Gamma-Ray Background  

E-print Network

Very high energy gamma-rays(E>20GeV) from blazars traversing cosmological distances through the metagalactic radiation field can convert to electron-positron pairs in photon-photon collisions. The converted gamma-rays initiate electromagnetic cascades driven by inverse-Compton scattering off the microwave background photons. The cascades shift the injected gamma ray spectrum to MeV-GeV energies. Randomly oriented magnetic fields rapidly isotropize the secondary electron-positron beams resulting from the beamed blazar gamma ray emission, leading o faint gamma-ray halo. Using a model for the time-dependent metagalactic radiation field consistent with all currently available far-infrared-to-optical data, we compute (i) the expected gamma-ray attenuation in blazar spectra, and (ii) the cascade contribution from faint, unresolved blazars to the extragalactic gamma-ray background as measured by EGRET, assuming a generic emitted spectrum extending to an energy of 10 TeV. The latter cascade contribution to the EGRET background is fed by the assumed >20 GeV emission from the hitherto undiscovered sources, and we estimate their dN-dz distribution taking into account that the nearby (z<0.2) fraction of these sources must be consistent with the known (low) numbers of sources above 300 GeV.

Tanja Kneiske; Karl Mannheim

2004-11-05

415

Dawn's Gamma Ray and Neutron Detector  

NASA Astrophysics Data System (ADS)

The NASA Dawn Mission will determine the surface composition of 4 Vesta and 1 Ceres, providing constraints on their formation and thermal evolution. The payload includes a Gamma Ray and Neutron Detector (GRaND), which will map the surface elemental composition at regional spatial scales. Target elements include the constituents of silicate and oxide minerals, ices, and the products of volcanic exhalation and aqueous alteration. At Vesta, GRaND will map the mixing ratio of end-members of the howardite, diogenite, and eucrite (HED) meteorites, determine relative proportions of plagioclase and mafic minerals, and search for compositions not well sampled by the meteorite collection. The large south polar impact basin may provide an opportunity to determine the composition of Vesta’s mantle and lower crust. At Ceres, GRaND will provide chemical information needed to test different models of Ceres’ origin and thermal and aqueous evolution. GRaND is also sensitive to hydrogen layering and can determine the equivalent H2O/OH content of near-surface hydrous minerals as well as the depth and water abundance of an ice table, which may provide information about the state of water in the interior of Ceres. Here, we document the design and performance of GRaND with sufficient detail to interpret flight data archived in the Planetary Data System, including two new sensor designs: an array of CdZnTe semiconductors for gamma ray spectroscopy, and a loaded-plastic phosphor sandwich for neutron spectroscopy. An overview of operations and a description of data acquired from launch up to Vesta approach is provided, including annealing of the CdZnTe sensors to remove radiation damage accrued during cruise. The instrument is calibrated using data acquired on the ground and in flight during a close flyby of Mars. Results of Mars flyby show that GRaND has ample sensitivity to meet science objectives at Vesta and Ceres. Strategies for data analysis are described and prospective results for Vesta are presented for different operational scenarios and compositional models.

Prettyman, Thomas H.; Feldman, William C.; McSween, Harry Y.; Dingler, Robert D.; Enemark, Donald C.; Patrick, Douglas E.; Storms, Steven A.; Hendricks, John S.; Morgenthaler, Jeffery P.; Pitman, Karly M.; Reedy, Robert C.

2011-12-01

416

Pair Production and Gamma-Ray Emission in the Outer Magnetospheres of Rapidly Spinning Young Pulsars  

NASA Technical Reports Server (NTRS)

Electron-positron pair production and acceleration in the outer magnetosphere may be crucial for a young rapidly spinning canonical pulsar to be a strong Gamma-ray emitter. Collision between curvature radiated GeV photons and soft X-ray photons seems to be the only efficient pair production mechanism. For Crib-like pulsars, the magnetic field near the light cylinder is so strong, such that the synchrotron radiation of secondary pairs will be in the needed X-ray range. However, for majority of the known Gamma-ray pulsars, surface emitted X-rays seem to work as the matches and fuels for a gamma-ray generation fireball in the outer magnetosphere. The needed X-rays could come from thermal emission of a cooling neutron star or could be the heat generated by bombardment of the polar cap by energetic particles generated in the outer magnetosphere. With detection of more Gamma-ray pulsars, it is becoming evident that the neutron star's intrisic geometry (the inclination angle between the rotation and magnetic axes) and observational geometry (the viewing angle with respect to the rotation axis) are crucial to the understanding of varieties of observational properties exhibited by these pulsars. Inclination angles for many known high energy Gamma-ray pulsars appear to be large and the distribution seems to be consistent with random orientation. However, all of them except Geminga are pre-selected from known radio pulsars. The viewing angles are thus limited to be around the respective inclination angles for beamed radio emission, which may induce strong selection effect. The viewing angles as well as the inclination angles of PSR 1509-58 and PSB 0656+14 may be small such that most of the high energy Gamma-rays produced in the outer accelerators may not reach the observer's direction. The observed Gamma-rays below 5 MeV from this pulsar may be synchrotron radiation of secondary electron-positron pairs produced outside the accelerating regions.

Ruderman, Malvin; Chen, Kaiyou

1997-01-01

417

NDA via gamma-ray active and passive computed tomography  

SciTech Connect

Gamma-ray-based computed tomography (CT) requires that two different measurements be made on a closed waste container. [MAR92 and ROB94] When the results from these two measurements are combined, it becomes possible to identify and quantify all detectable gamma-ray emitting radioisotopes within a container. All measurements are made in a tomographic manner, i.e., the container is moved sequentially through well- known and accurately reproducible translation, rotation, and elevation positions in order to obtain gamma-ray data that is reconstructed by computer into images that represent waste contents. [ROB94] The two measurements modes are called active (A) and passive (P) CT. In the ACT mode, a collimated gamma-ray source external to the waste container emits multiple, mono-energetic gamma rays that pass through the container and are detected on the opposite side. The attenuated gamma-rays transmitted are measured as a function of both energy and position of the container. Thus, container contents are `mapped` via the measured amount of attenuation suffered at each gamma-ray energy. In effect, a three dimensional (3D) image of gamma- ray attenuation versus waste content is obtained. In the PCT measurement mode, the external radioactive source is shuttered turned- off, and the waste container, is moved through similar positions used for the ACT measurements. However, this time the radiation detectors record any gamma-rays emitted by radioactive sources on the inside of the waste container. Thus, internal radioactive content is mapped or 3D-imaged in the same tomographic manner as the attenuating matrix materials were in the ACT measurement mode.

Decman, D.J.; Martz, H.E.; Roberson, G.P.; Johansson, E.

1996-10-01

418

Interactions between mutations for sensitivity to psoralen photoaddition (PSO) and to radiation (rad) in Saccharomyces cerevisiae  

Microsoft Academic Search

The mode of interaction in haploid Saccharomyces cerevisiae of two PSO mutations with each other and with rad mutations affected in their excision resynthesis (rad3), error-prone (rad6), and deoxyribonucleic acid double-strand break (rad52) repair pathways was determined for various double mutant combinations. Survival data for 8-methoxypsoralen photoaddition, 254-nm ultraviolet light and gamma rays are presented. For 8-methoxypsoralen photoaddition, which induces

J. A. P. Henriques; E. Moustacchi

1981-01-01

419

Energy sources in gamma-ray burst models  

NASA Technical Reports Server (NTRS)

The current status of energy sources in models of gamma-ray bursts is examined. Special emphasis is placed on the thermonuclear flash model which has been the most developed model to date. Although there is no generally accepted model, if the site for the gamma-ray burst is on a strongly magnetized neutron star, the thermonuclear model can qualitatively explain the energetics of some, but probably not all burst events. The critical issues that may differentiate between the possible sources of energy for gamma-ray bursts are listed and briefly discussed.

Taam, Ronald E.

1987-01-01

420

Spectral gamma-ray signatures of cosmological dark matter annihilations.  

PubMed

We propose a new signature for weakly interacting massive particle (WIMP) dark matter, a spectral feature in the diffuse extragalactic gamma-ray radiation. This feature, a sudden drop of the gamma-ray intensity at an energy corresponding to the WIMP mass, comes from the asymmetric distortion of the line due to WIMP annihilation into two gamma rays caused by the cosmological redshift. Unlike other proposed searches for a line signal, this method is not very sensitive to the exact dark matter density distribution in halos and subhalos. PMID:11736555

Bergström, L; Edsjö, J; Ullio, P

2001-12-17

421

HESS VHE Gamma-Ray Sources Without Identified Counterparts  

Microsoft Academic Search

The detection of gamma rays in the very-high-energy (VHE) energy range (100\\u000aGeV--100 TeV) provides a direct view of the parent population of\\u000aultra-relativistic particles found in astrophysical sources. For this reason,\\u000aVHE gamma rays are useful for understanding the underlying astrophysical\\u000aprocesses in non-thermal sources. We investigate unidentified VHE gamma-ray\\u000asources that have been discovered with HESS in the

F. Aharonian

2007-01-01

422

Pulsar gamma-rays: Spectra luminosities and efficiencies  

NASA Technical Reports Server (NTRS)

The general characteristics of pulsar gamma ray spectra are presented for a model where the gamma rays are produced by curvature radiation from energetic particles above the polar cap and attenuated by pair production. The shape of the spectrum is found to depend on pulsar period, magnetic field strength, and primary particle energy. By a comparison of numerically calculated spectra with the observed spectra of the Crab and Vela pulsars, it is determined that primary particles must be accelerated to energies of about 3 x 10 to the 7th power mc sq. A genaral formula for pulsar gamma ray luminosity is determined and is found to depend on period and field strength.

Harding, A. K.

1980-01-01

423

Directionality of continuum gamma rays from solar flares  

NASA Technical Reports Server (NTRS)

Using hard X-ray burst spectrometer total counts as calibration, the changes in the brightness of gamma rays above 300 keV as a function of the heliocentric angle of a flare are investigated. The normalized gamma-ray brightness, on the average, increases with the heliocentric angle; a flare at the limb is estimated to be 13 times brighter in beam gamma rays than a similar flare near the central meridian. Both pancakelike electron distributions and downward beam distributions can be adjusted to produce the deduced limb brightening.

Bai, Taeil

1988-01-01

424

Gamma-ray emission from young neutron stars  

NASA Technical Reports Server (NTRS)

The emission models of Cheng et al. (1986) and Harding (1981) are employed to determine likely candidates for pulsed gamma-ray emission on the basis of recent radio data of pulsars. The recent detection of pulsed gamma rays from PSR 1951+32 lends observational support to the scenario of Cheng et al. which also suggests that PSR 1855+09 might be another excellent gamma-ray pulsar candidate. The possible contribution of young neutron stars to the diffuse high energy glow is also discussed.

Hartmann, Dieter H.; Liang, Edison P.; Cordes, J. M.

1991-01-01

425

Gamma-Ray Burst Prompt Emission  

NASA Astrophysics Data System (ADS)

The origin of gamma-ray burst (GRB) prompt emission, bursts of ?-rays lasting from shorter than one second to thousands of seconds, remains not fully understood after more than 40 years of observations. The uncertainties lie in several open questions in the GRB physics, including jet composition, energy dissipation mechanism, particle acceleration mechanism and radiation mechanism. Recent broad-band observations of prompt emission with Fermi sharpen the debates in these areas, which stimulated intense theoretical investigations invoking very different ideas. I will review these debates, and argue that the current data suggest the following picture: A quasi-thermal spectral component originating from the photosphere of the relativistic ejecta has been detected in some GRBs. Even though in some cases (e.g. GRB 090902B) this component dominates the spectrum, in most GRBs, this component either forms a sub-dominant "shoulder" spectral component in the low energy spectral regime of the more dominant "Band" component, or is not detectable at all. The main "Band" spectral component likely originates from the optically thin region due to synchrotron radiation. The diverse magnetization in the GRB central engine is likely the origin of the observed diverse prompt emission properties among bursts.

Zhang, Bing

2014-12-01

426

Swift Observations of Gamma Ray Bursts  

SciTech Connect

Since its launch on 20 November 2004, the Swift mission is detecting {approx}100 gamma-ray bursts (GRBs) each year, and immediately (within {approx}90 s) starting X-ray and UV/optical observations of the afterglow. It has already collected an impressive database including prompt emission to higher sensitivities than BATSE, uniform monitoring of afterglows, and rapid follow-up by other observatories notified through the GCN. The detection of X-ray afterglows have been found to have complex temporal shapes including tails emission from the prompt phase and bright flares. X-ray afterglows from short bursts has led to accurate localizations. It is found that they can occur in non-star forming galaxies or regions, whereas long GRBs are strongly concentrated within star forming regions. This is consistent with the NS merger model. Swift has greatly increased the redshift range of GRB detection. The highest redshift GRBs, at z{approx}5-6, are approaching the era of reionization. Ground-based deep optical spectroscopy of high redshift bursts is giving metallicity measurements and other information on the source environment to much greater distance than other techniques. The localization of GRB 060218 to a nearby galaxy, and association with SN 2006aj, added a valuable member to the class of GRBs with detected supernova. The prospects for future progress are excellent give the >10 year orbital lifetime of the Swift satellite.

Gehrels, Neil [Astroparticle Physics Laboratory NASA/GSFC, Greenbelt, MD 20771 (United States)

2008-01-10

427

The electromagnetic model of Gamma Ray Bursts  

E-print Network

I describe electromagnetic model of gamma ray bursts and contrast its main properties and predictions with hydrodynamic fireball model and its magnetohydrodynamical extension. The electromagnetic model assumes that rotational energy of a relativistic, stellar-mass central source (black-hole--accretion disk system or fast rotating neutron star) is converted into magnetic energy through unipolar dynamo mechanism, propagated to large distances in a form of relativistic, subsonic, Poynting flux-dominated wind and is dissipated directly into emitting particles through current-driven instabilities. Thus, there is no conversion back and forth between internal and bulk energies as in the case of fireball model. Collimating effects of magnetic hoop stresses lead to strongly non-spherical expansion and formation of jets. Long and short GRBs may develop in a qualitatively similar way, except that in case of long bursts ejecta expansion has a relatively short, non-relativistic, strongly dissipative stage inside the star. Electromagnetic and fireball models (as well as strongly and weakly magnetized fireballs) lead to different early afterglow dynamics, before deceleration time. Finally, I discuss the models in view of latest observational data in the Swift era.

Maxim Lyutikov

2005-12-13

428

Effect of compound K, a metabolite of ginseng saponin, combined with gamma-ray radiation in human lung cancer cells in vitro and in vivo.  

PubMed

Pretreatment of NCI-H460 human lung cancer cells with compound K produced by intestinal bacteria enhances gamma-ray radiation-induced cell death. Increases in apoptosis induced by combined treatment are made apparent in the observation of nuclear fragmentation, loss of mitochondrial membrane potential (Deltapsi), and activation of caspase 3. Apoptosis induced by compound K and gamma-ray radiation is associated with reactive oxygen species (ROS) generation. Furthermore, compound K, in combination with gamma-ray radiation, has an enhanced effect in the regression of NCI-H460 tumor xenografts of nude mice. These results suggest that compound K has possible application for cancer therapy when used in combination with gamma-ray radiation. PMID:19526988

Chae, Sungwook; Kang, Kyoung Ah; Chang, Weon Young; Kim, Min Jung; Lee, Su Jae; Lee, Yun Sil; Kim, Hee Sun; Kim, Dong Hyun; Hyun, Jin Won

2009-07-01

429

Low and medium energy galactic gamma-ray observations  

NASA Technical Reports Server (NTRS)

Observation of 0.2-100 MeV diffuse gamma radiation emitted from the Galaxy can provide information on the intensities of 5-50 MeV/nucleon cosmic-rays and 50 MeV electrons in interstellar space. Recent measurements of gamma-rays emitted from the galactic center region provide evidence for a diffuse continuum between 10 and 100 MeV. The intensities of the recently reported nuclear line gamma rays, also observed in the direction of the galactic center, require the presence of intense fluxes of low-energy cosmic-rays in the inner Galaxy if the gamma-rays are produced on a galactic scale. Current detection techniques for 0.1-100 MeV gamma-ray measurements are summarized and their capabilities for measuring the diffuse galactic emission are evaluated.

Share, G. H.

1976-01-01

430

Low- and medium-energy galactic gamma-ray observations  

NASA Technical Reports Server (NTRS)

Observation of 0.2 to 100 MeV-diffuse gamma-radiation emitted from a galaxy provides information on the intensities of 5 to 50 MeV/nucleon cosmic-rays and approximately less than 50-MeV electrons in interstellar space. Recent measurements of gamma-rays emitted from the galactic center region provide evidence for a diffuse continuum between 10 and 100 MeV, which is dominant over the pi-decay emission generated in high-energy nuclear collisions. The intensities of the recently reported nuclear line gamma-rays, also observed in the direction of the galactic center, require the presence of intense fluxes of low energy cosmic rays in the inner galaxy if the gamma-ray are produced on a galactic scale. Current detection techniques for 0.1 to 100 MeV gamma-ray measurements are summarized, and their capabilities for measuring the diffuse galactic emission are evaluated.

Share, G. H.

1977-01-01

431

Gamma Ray Burst Discoveries with the Swift Mission  

NASA Technical Reports Server (NTRS)

This viewgraph presentation reviews the current understanding of Gamma Ray Bursts. It covers the Long GRBs, our current understanding of Collapsar, Short GRBs, afterglows, and reduced trigger threshold. It also discusses the Hard X-ray Sky Survey.

Gehrels, Neil

2007-01-01

432

Prompt Optical Observations of Gamma-ray Bursts  

E-print Network

The Robotic Optical Transient Search Experiment (ROTSE) seeks to measure simultaneous and early afterglow optical emission from gamma-ray bursts (GRBs). A search for optical counterparts to six GRBs with localization errors of 1 square degree or better produced no detections. The earliest limiting sensitivity is m(ROTSE) > 13.1 at 10.85 seconds (5 second exposure) after the gamma-ray rise, and the best limit is m(ROTSE) > 16.0 at 62 minutes (897 second exposure). These are the most stringent limits obtained for GRB optical counterpart brightness in the first hour after the burst. Consideration of the gamma-ray fluence and peak flux for these bursts and for GRB990123 indicates that there is not a strong positive correlation between optical flux and gamma-ray emission.

Carl Akerlof; Richard Balsano; Scott Barthelmy; Jeff Bloch; Paul Butterworth; Don Casperson; Tom Cline; Sandra Fletcher; Fillippo Frontera; Galen Gisler; John Heise; Jack Hills; Kevin Hurley; Robert Kehoe; Brian Lee; Stuart Marshall; Tim McKay; Andrew Pawl; Luigi Piro; John Szymanski; Jim Wren

2000-01-25

433

Gamma-ray bursts and radio pulsar glitches  

NASA Technical Reports Server (NTRS)

Upper limits to gamma-ray fluxes produced in conjunction with a radio pulsar glitch are presented. The glitch occurred on the Vela pulsar on December 24, 1988 and was the first to be observed as it occurred. Sensitive gamma-ray burst detectors aboard the Phobos 2 spacecraft were operating at this time, but recorded no significant burst at the time of the glitch. It is concluded that if a gamma-ray burst was generated in the energy range to which the Phobos detectors were sensitive, and if it was not beamed away from the spacecraft, the efficiency of glitch energy conversion into gamma-rays could not have exceeded 10 exp -4.

Hartmann, D.; Hurley, K.; Niel, M.

1992-01-01

434

Gamma-ray burst theory: Back to the drawing board  

NASA Technical Reports Server (NTRS)

Gamma-ray bursts have always been intriguing sources to study in terms of particle acceleration, but not since their discovery two decades ago has the theory of these objects been in such turmoil. Prior to the launch of Compton Gamma-Ray Observatory and observations by Burst and Transient Source Experiment (BATSE), there was strong evidence pointing to magnetized Galactic neutron stars as the sources of gamma-ray bursts. However, since BATSE the observational picture has changed dramatically, requiring much more distant and possibly cosmological sources. I review the history of gamma-ray burst theory from the era of growing consensus for nearby neutron stars to the recent explosion of halo and cosmological models and the impact of the present confusion on the particle acceleration problem.

Harding, Alice K.

1994-01-01

435

Recent developments in semiconductor gamma-ray detectors  

SciTech Connect

The successful development of lithium-drifted Ge detectors in the 1960's marked the beginning of the significant use of semiconductor crystals for direct detection and spectroscopy of gamma rays. In the 1970's, high-purity Ge became available, which enabled the production of complex detectors and multi-detector systems. In the following decades, the technology of semiconductor gamma-ray detectors continued to advance, with significant developments not only in Ge detectors but also in Si detectors and room-temperature compound-semiconductor detectors. In recent years, our group at Lawrence Berkeley National Laboratory has developed a variety of gamma ray detectors based on these semiconductor materials. Examples include Ge strip detectors, lithium-drifted Si strip detectors, and coplanar-grid CdZnTe detectors. These advances provide new capabilities in the measurement of gamma rays, such as the ability to perform imaging and the realization of highly compact spectroscopy systems.

Luke, Paul N.; Amman, Mark; Tindall, Craig; Lee, Julie S.

2003-10-28

436

Antimatter in the Universe: constraints from gamma-ray astronomy  

NASA Astrophysics Data System (ADS)

We review gamma-ray observations that constrain antimatter - both baryonic and leptonic - in the Universe. Antimatter is probed through ordinary matter, with the resulting annihilation gamma-rays providing indirect evidence for its presence. Although it is generally accepted that equal amounts of matter and antimatter have been produced in the Big Bang, gamma-rays have so far failed to detect substantial amounts of baryonic antimatter in the Universe. Conversely, positrons are abundantly observed through their annihilation in the central regions of our Galaxy and, although a wealth of astrophysical sources are plausible, their very origin is still unknown. As both antimatter questions - the source of the Galactic positrons and the baryon asymmetry in the Universe - can be investigated through the low energy gamma-ray channel, the mission concept of a dedicated space telescope is sketched out.

von Ballmoos, Peter

2014-02-01

437

History of gamma-ray telescopes and astronomy  

NASA Astrophysics Data System (ADS)

Gamma-ray astronomy is devoted to study nuclear and elementary particle astrophysics and astronomical objects under extreme conditions of gravitational and electromagnetic forces, and temperature. Because signals from gamma rays below 1 TeV cannot be recorded on ground, observations from space are required. The photoelectric effect is dominant <100 keV, Compton scattering between 100 keV and 10 MeV, and electron-positron pair production at energies above 10 MeV. The sun and some gamma ray burst sources are the strongest gamma ray sources in the sky. For other sources, directionality is obtained by shielding / masks at low energies, by using the directional properties of the Compton effect, or of pair production at high energies. The power of angular resolution is low (fractions of a degree, depending on energy), but the gamma sky is not crowded and sometimes identification of sources is possible by time variation. The gamma ray astronomy time line lists Explorer XI in 1961, and the first discovery of gamma rays from the galactic plane with its successor OSO-3 in 1968. The first solar flare gamma ray lines were seen with OSO-7 in 1972. In the 1980’s, the Solar Maximum Mission observed a multitude of solar gamma ray phenomena for 9 years. Quite unexpectedly, gamma ray bursts were detected by the Vela-satellites in 1967. It was 30 years later, that the extragalactic nature of the gamma ray burst phenomenon was finally established by the Beppo-Sax satellite. Better telescopes were becoming available, by using spark chambers to record pair production at photon energies >30 MeV, and later by Compton telescopes for the 1-10 MeV range. In 1972, SAS-2 began to observe the Milky Way in high energy gamma rays, but, unfortunately, for a very brief observation time only due to a failure of tape recorders. COS-B from 1975 until 1982 with its wire spark chamber, and energy measurement by a total absorption counter, produced the first sky map, recording galactic continuum emission, mainly from interactions of cosmic rays with interstellar matter, and point sources (pulsars and unidentified objects). An integrated attempt at observing the gamma ray sky was launched with the Compton Observatory in 1991 which stayed in orbit for 9 years. This large shuttle-launched satellite carried a wire spark chamber “Energetic Gamma Ray Experiment Telescope” EGRET for energies >30 MeV which included a large Cesium Iodide crystal spectrometer, a “Compton Telescope” COMPTEL for the energy range 1-30 MeV, the gamma ray “Burst and Transient Source Experiment” BATSE, and the “Oriented Scintillation-Spectrometer Experiment” OSSE. The results from the “Compton Observatory” were further enlarged by the SIGMA mission, launched in 1989 with the aim to closely observe the galactic center in gamma rays, and INTEGRAL, launched in 2002. From these missions and their results, the major features of gamma ray astronomy are: Diffuse emission, i.e. interactions of cosmic rays with matter, and matter-antimatter annihilation; it is found, “...that a matter-antimatter symmetric universe is empirically excluded....”

Pinkau, Klaus

2009-08-01

438

Gamma-Ray Pulse Tube Cooler Development and Testing  

NASA Technical Reports Server (NTRS)

For a variety of space-science applications, such as gamma-ray spectroscopy, the introduction of cryogenic cooling via a cryocooler can greatly increase the potential science return by allowing the use of more sensitive and lower noise detectors.

Ross, R.; Johnson, D.; Kotsubo, V.; Evtimov, B.; Olson, J.; Nast, T.; Rawlings, R.

2000-01-01

439

8th INTEGRAL Workshop "The Restless Gamma-ray Universe"  

NASA Astrophysics Data System (ADS)

The main goal of this workshop is to present and to discuss (via invited and contributed talks and posters) latest results obtained in the field of high energy astrophysics using the International Gamma-Ray Astrophysics Laboratory INTEGRAL, as well as results from related observations from other ground- and space-based high energy observatories. Topics: X-ray binaries (IGR sources, black holes, neutron stars, white dwarfs) Isolated neutron stars (gamma-ray pulsars, magnetars) Nucleosynthesis (SNe and SNRs), gamma-ray lines, diffuse line and continuum emission Massive black holes in AGNs, elliptical galaxies, nucleus of the Galaxy Surveys, source populations and unidentified sources Cosmic background radiation Gamma-ray bursts Coordinated observations with other ground- and space-based observatories Science data processing and analysis (posters only) Future instruments and missions (posters only)

440

VHE Gamma Rays from PKS 2155-304  

E-print Network

The close X-ray selected BL Lac PKS 2155-304 has been observed using the University of Durham Mark 6 very high energy (VHE) gamma ray telescope during 1996 September/October/November and 1997 October/November. VHE gamma rays with energy > 300 GeV were detected from this object with a time-averaged integral flux of (4.2 +/- 0.7 (stat) +/- 2.0 (sys)) x 10^(-11) per cm2 per s. There is evidence for VHE gamma ray emission during our observations in 1996 September and 1997 October/November, with the strongest emission being detected in 1997 November, when the object was producing the largest flux ever recorded in high-energy X-rays and was detected in > 100 MeV gamma-rays. The VHE and X-ray fluxes show evidence of a correlation.

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; S. E. Shaw; K. E. Turver; G. J. Wieczorek

1998-10-14