Note: This page contains sample records for the topic gamma-ray buildup factors from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Significant differences in reported gamma-ray buildup factors  

Microsoft Academic Search

Significant differences have been observed between Goldstein and Wilkins (moments method) and ASFIT (anisotropic source flux iteration technique) buildup factors in the materials of high atomic number (Z) for 6and 8-MeV gamma rays at depths greater than 10 mfp. Comparison has been made between the two, and quantitative differences are presented for tin, tungsten, lead, and uranium in the gamma-ray

A. Natarajan; D. V. Gopinath; K. V. Subbaiah

1983-01-01

2

Gamma-ray buildup factors for a point isotropic source in stratified spherical shields  

Microsoft Academic Search

A general review of investigations of gamma-ray buildup factors is presented. Gamma-ray buildup factors for a point isotropic source in stratified spherical shields have been calculated using the one-dimensional gamma-ray transport code BIGGI-4T. The behavior of the buildup factor for stratified shields with respect to the behavior for the component materials differs between spherical and slab geometry. In addition to

M. F. Su; S. H. Jiang

1989-01-01

3

Gamma-ray dose rate conversion and buildup factors. [1 to 10 MeV  

Microsoft Academic Search

The gamma-ray flux-to-dose-rate conversion factor set in the new American National Standard has a significantly different variation with energy than earlier sets. An evaluation was made of the effect that such differences have on gamma-ray dose rate buildup factors and on gamma-ray dose rates. 4 tables.

Shure

1979-01-01

4

Taylor Parameters for gamma-Ray Buildup Factors in the Proposed American National Standard.  

National Technical Information Service (NTIS)

Parameters have been determined for the Taylor two-exponential representation of the gamma-ray dose and energy absorption buildup factors contained in a proposed American National Standard on gamma-ray attenuation. These buildup factors are for 26 materia...

K. Shure O. J. Wallace

1988-01-01

5

Taylor parameters for gamma-ray buildup factors in the proposed American National Standard  

Microsoft Academic Search

Parameters have been determined for the Taylor two-exponential representation of the gamma-ray dose and energy absorption buildup factors contained in a proposed American National Standard on gamma-ray attenuation. These buildup factors are for 26 materials, 25 source energies, and 16 depths of penetration up to 40 mean-free-paths. 5 refs., 30 tabs.

K. Shure; O. J. Wallace

1988-01-01

6

GAMMA-RAY PENETRATION STUDIES FOR SEVERAL MATERIALS. I. MEASUREMENTS OF DOSE BUILDUP FACTORS  

Microsoft Academic Search

One of the most important data for shielding calculation of gamma rays ; is the buildup factor. The dose buildup factors of water, aluminum, iron, and ; lead for parallel beams or Co-60 gamma rays are determined experimentally. ; (T.F.H.);

Y. Furuta; A. Tsuruo; K. Tamura; Y. Kanemori; S. Miyasaka

1961-01-01

7

Calculated and measured dose buildup factors for gamma rays penetrating multilayered slabs  

Microsoft Academic Search

Dose buildup factors for normally incident 662-keV gamma rays ; penetrating multilayered aluminum-lead slabs were measured for various ; combinations using thermoluminescence dosimeters. The results were compared with ; calculated values obtained from a gamma-ray transport code and with values ; inferred from a semiempirical formula using single-layer slab buildup factors. ; This formula, a slightly modified version of the

G. d. Burke; H. L. Beck

1974-01-01

8

POLYNOMIAL APPROXIMATION OF GAMMA RAY BUILDUP FACTORS FOR A POINT ISOTROPIC SOURCE  

Microsoft Academic Search

Polynomial expressions were derived for approximation of the gamma ray ; dose, energy, and energy absorption build-up factors tabulated for a point ; isotropic source in NYO-3075. The expressions represent the build-up factor as a ; function of gamma ray energy and the number of relaxation lengths for a specified ; material. Bivariant polynomial coefficients are presented in tabular form

Capo

1959-01-01

9

A new approximating model for gamma-ray buildup factors of stratified shields  

Microsoft Academic Search

A new approximate expression for gamma-ray buildup factors of multilayered shields is proposed. The expression is formulated based on the vector form and considers the gamma-ray energy spectrum directly. It treats the gamma-ray transmission by a transmission matrix and the backscattering by an albedo matrix. Its capability of reproducing the buildup factors for multilayered shields is demonstrate by using double-layered

K. Shin; H. Hirayama

1994-01-01

10

A new approximating formula for calculating gamma-ray buildup factors in multilayer shields  

Microsoft Academic Search

This study proposes a new approximating formula for calculating gamma-ray buildup factors in multilayer shields. The formula combines the buildup factors of single-layer shields with products and quotients. The feasibility of the formula for reproducing the buildup factors was tested by using point isotropic buildup factors calculated with the SN1D discrete ordinates code as reference data. The dose buildup factors

A. Assad; M. Chiron; J. C. Nimal; C. M. Diop; P. Ridoux

1999-01-01

11

PLANE ISOTROPIC GAMMA RAY BUILDUP FACTORS IN LEAD AND WATER WITH APPLICATIONS TO SHIELDING CALCULATIONS  

Microsoft Academic Search

Plane isotropic dose (B\\/sub r\\/) and energy absorption (B\\/sub a\\/) buildup ; factors were calculated for gamma rays in lead and water for various initial ; energies from 0.5 to 10 Mev and for penetrations up to 15 mean free paths. These ; buildup factors, computed by numerical integration of point isotropic buildup ; factors, are compared with plane isotropic

S. Preiser; P. S. Mittelman; C. R. Berndtson

1954-01-01

12

Polynomial form of gamma-ray buildup factor functions  

Microsoft Academic Search

A three-paramerer polynomial form of the buildup factor function was introduced. The parameters were calculated for aluminum, water, and iron. It was found that buildup factors calculated by these polynomials, in most cases, were more accurate than those using the Taylor, Berger, Capo, or quadratic (Trubey) formulas when compareed with Goldstein-Wilkins data

Metghalchi

1979-01-01

13

An approximation of gamma-ray buildup factors for two-layer shields  

Microsoft Academic Search

An empirical formula for gamma-ray buildup factors in two-layer shields is proposed. The values of the parameters are given for the formula when fitted to the dose buildup factors, calculated by the invariant imbedding method, for normally incident gamma rays penetrating two-layer shields comprised of combinations of water, iron, or lead slabs. The results from the present formula are in

Harima

1983-01-01

14

Calculation of gamma-ray buildup factors including the contribution of bremsstrahlung  

Microsoft Academic Search

Buildup factors for gamma rays traversing slab shields have been ; obtained using the Monte Carlo method. Secondary particles produced inside the ; shield were taken into account, with special attention given to the contribution ; of bremsstrahlung which is produced by electrons and positrons. The results ; indicate that annihilation gamma rays from pair production do increase the ;

J. P. Kuspa; N. Tsoulfanidis

1973-01-01

15

Applicability of Geometrical Progression Approximation (G-P Method) of gamma-Ray Buildup Factors.  

National Technical Information Service (NTIS)

The G-P method formula B/sub r/ (X) = 1 + (B-1) center dot (K/sup X/-1)/(K-1) (X: optical length, B: buildup factor at X = 1, K: a gamma-ray multiplication factor per one mean free path) gives an accurate representation of the buildup factor for point iso...

Y. Harima Y. Sakamoto S. Tanaka

1986-01-01

16

Gamma-Ray Dose at Shield-Tissue Interfaces and Buildup Factor Implications.  

National Technical Information Service (NTIS)

Buildup factors continue to be widely used for gamma-ray shield design, but there are several problems in application. Shure has pointed out the need for buildup factors to be consistent with the ANSI standard flux-to-dose factors. However, consistent bui...

D. K. Trubey D. V. Gopinath K. V. Subbaiah

1982-01-01

17

Gamma-ray dose at shield-tissue interfaces and buildup factor implications  

Microsoft Academic Search

Buildup factors continue to be widely used for gamma-ray shield design, but there are several problems in application. Shure has pointed out the need for buildup factors to be consistent with the ANSI standard flux-to-dose factors. However, consistent buildup factor data cannot be obtained by simply integrating the ANSI response function over infinite-medium spectra, because this function gives the response

D. K. Trubey; D. V. Gopinath; K. V. Subbaiah

1982-01-01

18

An approximation of gamma-ray buildup factors by modified geometrical progression  

Microsoft Academic Search

The empirical formula of gamma-ray buildup factors by a geometric-progression (G-P) method was modified by presenting the K parameter as a function of the penetrating distance from the source. The values of the parameters are given for the modified G-P method fitted to the exposure and absorbed dose buildup factor data for air, water, concrete, and iron calculated by a

Harima

1983-01-01

19

Experimental Determination of Effective-Z from the Measurements of Gamma-Ray Buildup Factors  

Microsoft Academic Search

Buildup factors BN for the number of gamma-rays in C, H2O, Al, Cu and Pb absorbers have been measured and the variation of BN with the atomic number Z and the thickness of the absorber were investigated. Linear absorption coefficient and the buildup factor of a soil sample were measured and the effective-Z (Zeff) of the sample was estimated from

Güngör Yener; Özdemir Mersinoglu

1989-01-01

20

Effect of finite sample dimensions and total scatter acceptance angle on the gamma ray buildup factor  

Microsoft Academic Search

The simultaneous variation of gamma ray buildup factors with absorber thickness (up to 6.5mfp) and total scatter acceptance angle (which is the sum of incidence and exit beam divergence) in the media of high volume flyash concrete and water was studied experimentally using a point isotropic 137Cs source.

Sukhpal Singh; Ashok Kumar; Charanjeet Singh; Kulwant Singh Thind; Gurmel S. Mudahar

2008-01-01

21

ASPIS; gamma-ray source buildup factor calculations. [CDC6600; FORTRAN IV and ASCENT  

Microsoft Academic Search

ASPIS computes the energy, dose and energy deposition buildup factors for monoenergetic gamma rays for a plane isotropic, plane monodirectional, or plane slant source, in an arbitrary laminar array.CDC6600; FORTRAN IV and ASCENT; SCOPE 3.1; 140K (octal) memory and 3 tapes for scratch storage.

Lois

2008-01-01

22

Approximating model for multilayer gamma-ray buildup factors by transmission matrix method: Application to point isotropic source geometry  

Microsoft Academic Search

An approximating formula recently proposed by the authors for gamma-ray buildup factors of multilayered shields is applied to point isotropic source problems. The formula, which is formulated in vector form with a four-group approximation, handles the gamma-ray energy spectrum directly and uses the transmission and albedo matrices to take gamma-ray transmission and backscattering effects into consideration. The gamma-ray transmission and

Kazuo Shin; Hideo Hirayama

1995-01-01

23

Development of Fitting Methods Using Geometric Progression Formulae of Gamma-ray Buildup Factors  

Microsoft Academic Search

The gamma ray buildup factors are represented by an approximation method to speed up calculation using the point attenuation kernel method. The fitting parameters obtained by the GP formula and Taylor's formula are compiled in ANSI\\/ANS 6.4.3, available without any limitation. The GP formula featured high accuracy but required a high-level fitting technique. Thus the GP formula was divided into

Yoshitaka YOSHIDA

2006-01-01

24

Gamma-ray and neutron dose-equivalent buildup factors for infinite slabs  

Microsoft Academic Search

In this paper gamma-ray and neutron dose-equivalent buildup factors are calculated for six common shielding materials in a point-source, infinite-slab, point-detector geometry using a decomposition of the solution to the transport problem into single- and multiple-scatter components. A rigorous solution for the single-scatter component is constructed and a Monte Carlo model for the multiple-scatter component is employed. Simplified models are

W. L. Dunn; A. M. Yacout; F. OFoghludha; G. Riel

1992-01-01

25

Buildup factors of gamma rays including Bremsstrahlung and annihilation radiation for water, concrete, iron, and lead  

Microsoft Academic Search

Gamma-ray exposure buildup factors are calculated using a discrete ordinates direct integration code, PALLAS-PL, SP-Br, for water, concrete, iron, and lead, typifying materials of low, medium, and high atomic number. The radiation sources considered were both plane, at normal incidence, and at plane-isotropic. These data include the effects of secondary photon sources arising from Compton scattering, bremsstrahlung, and annihilation. Inclusion

K. Takeuchi; S. I. Tanaka

1984-01-01

26

Effects of incoherent and coherent scattering on the exposure buildup factors of low-energy gamma rays  

Microsoft Academic Search

The effects of including incoherent and coherent scattering in a calculation of the exposure buildup factors for plane normal gamma-ray sources have been investigated by using an electron-gamma-ray shower Monte Carlo code, EGS4, for water, iron, and lead in the 40- to 200-keV range. The ''true'' buildup factors for practical uses are defined to clarify the effects of bound-electron Compton

H. Hirayama; D. K. Trubey

1988-01-01

27

Calculation of Gamma-Ray Buildup Factors up to Depths of 100 mfp by the Method of Invariant Embedding, (I)  

Microsoft Academic Search

The method of invariant embedding has been applied to calculations of gamma-ray buildup factors for point isotropic sources in infinite homogeneous media up to depths of 100 mean free paths (mfp) without bremsstrahlung. A comprehensive survey of buildup factors was performed to estimate errors due to energy, angle and space meshes adopted in the transport calculations by the present method.

Akinao SHIMIZU

2002-01-01

28

The use of an expanded polynomial orthogonal set in approximations to gamma-ray buildup factor data  

Microsoft Academic Search

Buildup factors for various shielding materials exhibit large variations in magnitude and in curve shapes as a function of penetration depth as a result of the stochastic nature of the scattering processes for different incident photon energies. In a quest for adequate functional representation of point isotropic gamma-ray buildup factor data, a family of functions based on an expanded polynomial

Michieli

1994-01-01

29

New gamma-ray buildup factor data for point kernel calculations: ANS6. 4. 3 standard reference data  

Microsoft Academic Search

An American Nuclear Society Standards Committee Working Group, identified as ANS-6.4.3, has developed a set of evaluated gamma-ray isotropic point-source buildup factors and attenuation coefficients for a standard reference data base. The largely unpublished set of buildup factors calculated with the moments method has been evaluated by recalculating key values with Monte Carlo, integral transport, and discrete ordinates methods. Additional

Trubey

1991-01-01

30

New gamma-ray buildup factor data for point kernel calculations: ANS6. 4. 3 standard reference data  

Microsoft Academic Search

An American Nuclear Society Standards Committee Working Group, identified as ANS-6.4.3, has developed a set of evaluated gamma-ray isotropic point-source buildup factors and attenuation coefficients for a standard reference data base. The largely unpublished set of buildup factors calculated with the moments method has been evaluated by recalculating key values with Monte Carlo, integral transport, and discrete ordinates methods. Additional

Trubey

1988-01-01

31

Calculation of Gamma-Ray Buildup Factors up to Depths of 100 mfp by the Method of Invariant Embedding, (III)  

Microsoft Academic Search

An improved data set of gamma-ray buildup factors for point isotropic sources in infinite homogeneous media has been generated by the method of invariant embedding. The points of improvement compared with the standard data set ANSI\\/ANS-6.4.3 include (1) extension of the buildup factors up to depths of 100 mean free paths, (2) improved treatment of bremsstrahlung, (3) addition of the

Akinao SHIMIZU; Takashi ONDA; Yukio SAKAMOTO

2004-01-01

32

Calculation of Gamma-Ray Buildup Factors up to Depths of 100 mfp by the Method of Invariant Embedding, (II)  

Microsoft Academic Search

An improved method to calculate the gamma-ray buildup factors including bremsstrahlung has been developed. The exposure buildup factors with bremsstrahlung were computed by the present method for lead, iron and water at the source energy of 10.0 MeV up to depths of 100 mfp. The accuracy of the present method was checked by comparison with the calculations by use of

Akinao SHIMIZU; Hideo HIRAYAMA

2003-01-01

33

Evaluation of gamma-ray exposure buildup factors and neutron shielding for bismuth borosilicate glasses  

NASA Astrophysics Data System (ADS)

Gamma-ray exposure buildup factor (EBF) values and neutron shielding effectiveness of bismuth borosilicate (BBS) glass systems in composition (50-x)SiO2:15B2O3:2Al2O3:10CaO:23Na2O:xBi2O3 (where x=0, 5, 10, 15 and 20 mol%) were calculated. The EBF values were computed for photon energy 0.015-15 MeV up to penetration depths of 40 mfp (mean free path) by the geometrical progression (G-P) method. The EBF values were found dependent upon incident photon energy, penetration and bismuth molar concentration. In low- and high-energy photon regions, the EBF values were minimum whereas maximum in the intermediate-energy region. The fast neutron removal cross sections for energy 2-12 MeV were calculated by the partial density method. The BBS glass with 20 mol% Bi2O3 is found to be superior gamma-ray and neutron transparent shielding. The EBF values of the BBS glasses were compared with steel-magnetite concrete and lead. The investigation was carried out to explore the advantages of the BBS glasses in different radiation shielding applications.

Singh, Vishwanath P.; Badiger, N. M.; Chanthima, N.; Kaewkhao, J.

2014-05-01

34

New Gamma-Ray Buildup Factor Data for Point Kernel Calculations: ANS-6.4.3 Standard Reference Data.  

National Technical Information Service (NTIS)

An American Nuclear Society Standards Committee Working Group, identified as ANS-6.4.3, has developed a set of evaluated gamma-ray isotropic point-source buildup factors and attenuation coefficients for a standard reference data base. The largely unpublis...

D. K. Trubey

1991-01-01

35

An experimental study of gamma-ray buildup factors for a point isotropic source in stratified spherical shields  

Microsoft Academic Search

Gamma-ray buildup factors for a point isotropic source in stratified spherical shields have been studied experimentally. Energy absorption rates for an experimental setup of iron spheres in water have been measured using the thermoluminescent dosimeter (TLD)-200. The measured absorbed doses in the TLD have been converted to the absorbed doses in iron and water by using cavity ionization theory. The

U. T. Lin; C. C. Tseng; S. H. Jiang

1996-01-01

36

Improvement of MERCURE-6's General Formalism for Calculating Gamma-Ray Buildup Factors in Multilayer Shields  

Microsoft Academic Search

This study proposes an improvement of the general formalism for calculating gamma-ray buildup factors in multilayer shields developed by Assad et al. The main modification concerns the treatment of the double-layer shield formed by the two first layers of a multilayer shield. Instead of replacing the double-layer shield with an equivalent thickness of the layer of the second material, the

Christophe Suteau; Maurice Chiron; Gilles Arnaud

2004-01-01

37

A dedicated empirical formula for gamma-ray buildup factors for a point isotropic source in stratified shields  

Microsoft Academic Search

A dedicated empirical formula for evaluating gamma-ray buildup factors of double-layered shields for a point isotropic source has been proposed for the first time by fitting it to the data of Monte Carlo calculations using EGS4 code. The calculated results from the present formula were compared with those using other empirical formulae. The extension of the present formula in the

Lin Uei-Tyng; Jiang Shiang-Huei

1996-01-01

38

Interpolation of gamma-ray buildup factors for point isotropic source with respect to atomic number  

Microsoft Academic Search

The values of buildup factors for a specific energy above KAPPA edges and penetration distance vary smoothly with respect to atomic number. An interpolation of buildup factors for an arbitrary elemental material is examined using geometric-progression (G-P) parameters for an equivalent atomic number. The G-P parameters are data fitted to the proposed American National Standard Buildup factor data compilation of

Y. Sakamoto; S. I. Tanaka; Y. Harima

1988-01-01

39

Exposure buildup factors of high-energy gamma rays for water, concrete, iron, and lead  

Microsoft Academic Search

Exposure buildup factors for plane normal sources have been calculated with an electron gamma shower Monte Carlo code, EGS4, for water, concrete, iron, and lead in the 10 to 100 MeV range. Electron reactions like multiple scattering, collision, and continuous energy loss are taken into account together with bremsstrahlung. The buildup factors in this energy region are affected very much

Hirayama

1987-01-01

40

Buildup Factor Fitting Method and its Application for a Gamma-ray Shielding Calculation  

Microsoft Academic Search

This work developed atting method of buildup factors for shielding calculation to predict the radiation dose of emergency actions in a nuclear power plant (NPP). The deviation for buildup factors of deep penetration calculated by thetting were carefully estimated by varying the unit penetration depth, ˆtting range and method of inducing the error direction. Furthermore, as application examples of the

Yoshitaka YOSHIDA

2008-01-01

41

Detailed investigation of the buildup factors and spectra for point isotropic gamma-ray sources in the vicinity of the K edge in lead  

Microsoft Academic Search

Detailed calculations of the buildup factors and spectra of gamma rays including fluorescence radiations in lead are carried out using a discrete ordinates code, PALLAS-PL,SP-Br. The exposure and absorbed dose buildup factors with and without fluorescence are tabulated for 11 source energies from 0.09 to 0.3 MeV for penetration depths up to 40 mfp. Important characteristics of the gamma-ray transport

S. Tanaka; K. Takeuchi

1986-01-01

42

Validity of the geometric-progression formula in approximating gamma-ray buildup factors  

Microsoft Academic Search

A geometric-progression (G-P) method formula, B\\/sub r\\/ = 1 + (B-1) . (K\\/sup x\\/-1)\\/(K-1), accurately represents the buildup factor data as a function of distance for the following reasons: 1. The value of parameter B corresponds to that of the buildup factor at 1 mfp, which is the integration of a basic spectrum for a specified material and for a

Y. Harima; Y. Sakamoto; S. Tanaka; M. Kawai

1986-01-01

43

Evaluation of gamma ray buildup factor data in water with MCNP4C code  

Microsoft Academic Search

The exposure buildup factors for gamma and X-ray photons in water are computed using the MCNP4C code. The results are obtained for the energy range 0.04–6MeV and penetration depths up to 10mfp. The results are compared with the published buildup factor data during 1960–2010. Both agreements and discrepancies are observed between our results and the data appearing in the literature.

Dariush Sardari; Sassan Saudi; Maryam Tajik

2011-01-01

44

Development of New Gamma-Ray Buildup Factor and Application to Shielding Calculations  

Microsoft Academic Search

The PALLAS (discrete ordinates-integral transport) code was improved to include secondary sources, such as bremsstrahlung and fluorescence, to assure accurate and reliable results. The point buildup factors for high-Z materials were calculated with this code in the energy range of 0.015~15 MeV up to 40 mean free paths. The buildup factors for low-Z materials in the low energy range, which

Yoshiko HARIMA; Shun-ichi TANAKA; Yukio SAKAMOTO; Hideo HIRAYAMA

1991-01-01

45

Calculation of Gamma-Ray Buildup Factors up to Depths of 100 mfp by the Method of Invariant Embedding. (I). Analysis of Accuracy and Comparison with Other Data  

Microsoft Academic Search

The method of invariant embedding has been applied to calculations of gamma-ray buildup factors for point isotropic sources in infinite homogeneous media up to depths of 100 mean free paths (mfp) without bremsstrahlung. A com- prehensive survey of buildup factors was performed to estimate errors due to energy, angle and space meshes adopted in the transport calculations by the present

Akinao SHIMIZU

2002-01-01

46

Modeling of gamma-ray energy absorption buildup factors using neural network  

Microsoft Academic Search

This paper presents a new approach based on multilayered perceptrons (MLPs) to compute energy absorption buildup factors. The MLP has been trained by a Levenberg–Marquardt learning algorithm. The model is fast and does not require tremendous computational efforts. The results obtained by using the proposed model are in good agreement with the ANSI\\/ANS-6.4.3 standard data set.

Nil Kucuk

2008-01-01

47

Gamma ray buildup factors in lead-iron and iron-lead shields  

Microsoft Academic Search

Using the gamma transport code PIPE, buildup factors are evaluated in shields consisting of: iron layers of up to 40 cm thickness followed by thick lead layers; and lead layers of up to 10 cm thickness followed by thick iron layers. The source is assumed plane isotropic and four source energies were used, ranging from 0.66 MeV (caesium source) to

H. Penkuhn

1980-01-01

48

Gamma Ray Buildup Factors in Lead-Iron and Iron-Lead Shields.  

National Technical Information Service (NTIS)

Using the gamma transport code PIPE, buildup factors are evaluated in shields consisting of: iron layers of up to 40 cm thickness followed by thick lead layers; and lead layers of up to 10 cm thickness followed by thick iron layers. The source is assumed ...

H. Penkuhn

1980-01-01

49

Gamma-ray energy absorption and exposure buildup factor studies in some human tissues with endometriosis  

Microsoft Academic Search

Human tissues with endometriosis have been analyzed in terms of energy absorption (EABF) and exposure (EBF) buildup factors using the five-parameter geometric progression (G-P) fitting formula in the energy region 0.015–15MeV up to a penetration depth of 40mfp (mean free path). Chemical compositions of the tissue samples were determined using a wavelength dispersive X-ray fluorescence spectrometer (WDXRFS). Possible conclusions were

Murat Kurudirek; Bekir Do?an; Metin ?ngeç; Neslihan Ekinci; Yüksel Özdemir

2011-01-01

50

Monte Carlo calculation and analytical approximation of gamma-ray buildup factors in air  

Microsoft Academic Search

The photon fluence due to isotropic photon point sources in air has been calculated with a Monte Carlo code that accounts for photon absorption, Compton scattering, annihilation, and bremsstrahlung. Kerma buildup factors have been determined for ten energies in the 0.05- to 10-MeV range and for 72 distances in the 0.15- to 10-mfp range. The results agree with the moments

P. Jacob; H. G. Paretzke; J. Wolfel

1984-01-01

51

A 3D point-kernel multiple scatter model for parallel-beam SPECT based on a gamma-ray buildup factor  

Microsoft Academic Search

A three-dimensional (3D) point-kernel multiple scatter model for point spread function (PSF) determination in parallel-beam single-photon emission computed tomography (SPECT), based on a dose gamma-ray buildup factor, is proposed. This model embraces nonuniform attenuation in a voxelized object of imaging (patient body) and multiple scattering that is treated as in the point-kernel integration gamma-ray shielding problems. First-order Compton scattering is

Predrag Marinkovic; Radovan Ilic; Rajko Spaic

2007-01-01

52

Calculation of gamma-ray buildup factors for two-layered shields made of water, concrete and iron and application of approximating formula  

Microsoft Academic Search

Gamma-ray buildup factors that are the basic data for the point kernel calculations were calculated up to 40 mean free path (mfp) for double-layered shields consisting of water, concrete and iron by the EGS4 code using a special splitting technique at gamma-ray energies of 0.1, 0.3, 0.6, 1, 3, 6 and 10MeV. The assumed shields were 40mfp monolayer, 5mfp first

Kazuo Shin; Hideo Hirayama

2001-01-01

53

Analysis of some Earth, Moon and Mars samples in terms of gamma ray energy absorption buildup factors: Penetration depth, weight fraction of constituent elements and photon energy dependence  

Microsoft Academic Search

The Earth, Moon and Mars samples have been investigated in terms of gamma ray energy absorption buildup factors (EABF) depending on penetration depth, weight fraction of constituent elements and photon energy. The five parameter geometric progression (G-P) fitting approximation has been used to compute the buildup factors in the energy region 0.015–15MeV up to a penetration depth of 40 mean

Murat Kurudirek; Bekir Dogan; Yüksel Özdemir; Anderson Camargo Moreira; Carlos Roberto Appoloni

2011-01-01

54

Calculation of Gamma-Ray Buildup Factors up to Depths of 100 mfp by the Method of Invariant Embedding, (II) Improved Treatment of Bremsstrahlung  

Microsoft Academic Search

An improved method to calculate the gamma-ray buildup factors including bremsstrahlung has been developed. The exposure buildup factors with bremsstrahlung were computed by the present method for lead, iron and water at the source energy of 10.0 MeV up to depths of 100 mfp. The accuracy of the present method was checked by comparison with the calculations by use of

Akinao SHIMIZU; Hideo HIRAYAMA

2003-01-01

55

STRATIFIED SLAB GAMMA-RAY DOSE-RATE BUILDUP FACTORS FOR LEAD AND WATER SHIELDS  

Microsoft Academic Search

The ORACLE Monta Carlo code for the calculation of the penetration of ; gamma rays through stratified slabs was used to calculate a total of 512 problems ; for eight different lead and water configurations. The energy of the incident ; radiation, the angle of incidence, the thickness of the shield, and the ; percentage of lead preceding or following

L. A. Bowman; D. K. Trubey

1958-01-01

56

Gamma-ray transport in a shield-tissue composite system and the buildup factor implications  

Microsoft Academic Search

Transport computations in shield-tissue composite systems are presented. It is observed that the scattered gamma-ray spectra at the interface, which are governed by the reflectivities of different media, are significantly different from those of an infinite medium. The interface effects also extend back into the shield medium, the extent depending on the atomic number of the medium and energy of

D. V. Gopinath; K. V. Subbaiah; D. K. Trubey

1987-01-01

57

Exposure, Dose-Equivalent and Absorbed-Dose Buildup Factors of gamma Rays for Plane Normal and Isotropic Incidences on Water, Concrete, Iron and Lead.  

National Technical Information Service (NTIS)

Exposure, dose-equivalent and absorbed-dose buildup factors are calculated using a discrete-ordinates direct integration code, PALLAS-PL, SP-Br, for water, concrete, iron and lead, typifying materials of low, medium, high atomic number for gamma ray sourc...

S. Tanaka K. Takeuchi

1984-01-01

58

Calculation of Gamma-ray Exposure Buildup Factors up to 40mfp using the EGS4 Monte Carlo Code with a Particle Splitting  

Microsoft Academic Search

Gamma-ray exposure buildup factors up to 40 mfp have been calculated using the Monte Carlo code EGS4 for water, iron and lead for point isotropic sources. The new algorithm which applies particle-splitting at each preset depth to simulate almost same number of particles from the preset depth is developed in order to obtain reasonable results with EGS4 at deep-penetrations. Comparisons

Hideo HIRAYAMA

1995-01-01

59

[Approximation formulas on buildup factors as a function of the effective atomic number, gamma-ray energy and relaxation length (author's transl)].  

PubMed

Approximation formulas on energy, dose and energy absorption buildup factors were constructed to facilitate the computation of the values in a material irradiated with a point isotropic gamma-ray source. The approximation formulas were expressed as a function of the effective atomic number (Z), gamma-ray energy (E) and relaxation length in mean free path (micror), with 15 or 17 coefficients. The approximate values were compared with the buildup factors reported by Goldstein and Wilkins in the range of Z, E and micror adopted for gamma-ray irradiator design, that is in 7.42 less than or equal to Z less than or equal to 26, 0.5 less than or equal to E (MeV) less than or equal to 4 and 0 less than or equal to micror less than or equal to 10. It was shown that the maximum relative errors of the approximation formulas are +/- 5.2%, +/- 4.3% and +/- 3.5% for energy, dose and energy absorption buildup factor, respectively. PMID:7291612

Hoshi, T

1981-02-01

60

Interpolation of gamma-ray Buildup Factors in Atomic Number, Using the Geometrical Progression (G-P) Parameters.  

National Technical Information Service (NTIS)

The values of buildup factors for specified energy above K-edges and penetration distance vary smoothly with respect to atomic number, and the geometrical progression (G-P) parameters behave also similarly. An interpolation of buildup factors for an arbit...

Y. Sakamoto S. Tanaka Y. Harima

1988-01-01

61

Tchebycheff-fitted berger coefficients for Eisenhauer--Simmons gamma-ray buildup factors in ordinary concrete  

Microsoft Academic Search

Coefficients are given for the two-parameter Berger empirical formula fitted to air kerma and concrete kerma buildup factor data provided by Eisenhauer and Simmons (E--S). The fit is such as to minimize the maximum deviation of the resulting formula predictions from the basic E--S data. Comparison with similar work by others is provided.

1979-01-01

62

Description of Multilayered Gamma-Ray Exposure Buildup Factors up to 40 mfp by the Approximating Model  

Microsoft Academic Search

An approximating formula recently proposed by the authors for ?-ray buildup factors of multilayered shields was applied for very thick shields up to 40 mfp. For this purpose, modifications were made to the model and the fitting method to improve the data reproducibility. The previous model was expanded so that it included both the plane-normal and point isotropic geometries.The verification

Kazuo SHIN; Hideo HIRAYMA

1998-01-01

63

A 3D point-kernel multiple scatter model for parallel-beam SPECT based on a gamma-ray buildup factor.  

PubMed

A three-dimensional (3D) point-kernel multiple scatter model for point spread function (PSF) determination in parallel-beam single-photon emission computed tomography (SPECT), based on a dose gamma-ray buildup factor, is proposed. This model embraces nonuniform attenuation in a voxelized object of imaging (patient body) and multiple scattering that is treated as in the point-kernel integration gamma-ray shielding problems. First-order Compton scattering is done by means of the Klein-Nishina formula, but the multiple scattering is accounted for by making use of a dose buildup factor. An asset of the present model is the possibility of generating a complete two-dimensional (2D) PSF that can be used for 3D SPECT reconstruction by means of iterative algorithms. The proposed model is convenient in those situations where more exact techniques are not economical. For the proposed model's testing purpose calculations (for the point source in a nonuniform scattering object for parallel beam collimator geometry), the multiple-order scatter PSF generated by means of the proposed model matched well with those using Monte Carlo (MC) simulations. Discrepancies are observed only at the exponential tails mostly due to the high statistic uncertainty of MC simulations in this area, but not because of the inappropriateness of the model. PMID:17881800

Marinkovic, Predrag; Ilic, Radovan; Spaic, Rajko

2007-10-01

64

A 3D point-kernel multiple scatter model for parallel-beam SPECT based on a gamma-ray buildup factor  

NASA Astrophysics Data System (ADS)

A three-dimensional (3D) point-kernel multiple scatter model for point spread function (PSF) determination in parallel-beam single-photon emission computed tomography (SPECT), based on a dose gamma-ray buildup factor, is proposed. This model embraces nonuniform attenuation in a voxelized object of imaging (patient body) and multiple scattering that is treated as in the point-kernel integration gamma-ray shielding problems. First-order Compton scattering is done by means of the Klein-Nishina formula, but the multiple scattering is accounted for by making use of a dose buildup factor. An asset of the present model is the possibility of generating a complete two-dimensional (2D) PSF that can be used for 3D SPECT reconstruction by means of iterative algorithms. The proposed model is convenient in those situations where more exact techniques are not economical. For the proposed model's testing purpose calculations (for the point source in a nonuniform scattering object for parallel beam collimator geometry), the multiple-order scatter PSF generated by means of the proposed model matched well with those using Monte Carlo (MC) simulations. Discrepancies are observed only at the exponential tails mostly due to the high statistic uncertainty of MC simulations in this area, but not because of the inappropriateness of the model.

Marinkovic, Predrag; Ilic, Radovan; Spaic, Rajko

2007-09-01

65

Computation of gamma-ray exposure buildup factors up to 10 mfp using generalized feed-forward neural network  

Microsoft Academic Search

This paper presents an approach based on generalized feed-forward neural network (GFFNN) to compute exposure buildup factors (BD) for point isotropic sources in infinite homogeneous media at energies varying from 0.03MeV to 15MeV and up to depths of 10 mean free paths (mfp). The results obtained by using the proposed model have been compared with the ANSI standard data, the

Nil Kucuk

2010-01-01

66

Analysis of some Earth, Moon and Mars samples in terms of gamma ray energy absorption buildup factors: Penetration depth, weight fraction of constituent elements and photon energy dependence  

NASA Astrophysics Data System (ADS)

The Earth, Moon and Mars samples have been investigated in terms of gamma ray energy absorption buildup factors (EABF) depending on penetration depth, weight fraction of constituent elements and photon energy. The five parameter geometric progression (G-P) fitting approximation has been used to compute the buildup factors in the energy region 0.015-15 MeV up to a penetration depth of 40 mean free paths (mfp). The maximum values of EABF have been observed for the Earth, Mars and Moon samples at 0.2, 0.3 and 0.2 MeV, respectively. At the corresponding energies where maximum EABF occur, the Earth samples have the highest and the Mars samples have the lowest EABF values. There is no significant variation in EABF for the Earth, Moon and Mars samples beyond 1 MeV, hence the values of EABF remain constant with the variation in chemical composition for all the given materials. Finally, the buildup factors so obtained have been discussed in function of the penetration depth, weight fraction of constituent elements and photon energy.

Kurudirek, Murat; Dogan, Bekir; Özdemir, Yüksel; Moreira, Anderson Camargo; Appoloni, Carlos Roberto

2011-03-01

67

Modeling of gamma ray energy-absorption buildup factors for thermoluminescent dosimetric materials using multilayer perceptron neural network: A comparative study  

NASA Astrophysics Data System (ADS)

In this work, multilayered perceptron neural networks (MLPNNs) were presented for the computation of the gamma-ray energy absorption buildup factors (BA) of seven thermoluminescent dosimetric (TLD) materials [LiF, BeO, Na2B4O7, CaSO4, Li2B4O7, KMgF3, Ca3(PO4)2] in the energy region 0.015-15 MeV, and for penetration depths up to 10 mfp (mean-free-path). The MLPNNs have been trained by a Levenberg-Marquardt learning algorithm. The developed model is in 99% agreement with the ANSI/ANS-6.4.3 standard data set. Furthermore, the model is fast and does not require tremendous computational efforts. The estimated BA data for TLD materials have been given with penetration depth and incident photon energy as comparative to the results of the interpolation method using the Geometrical Progression (G-P) fitting formula.

Kucuk, Nil; Manohara, S. R.; Hanagodimath, S. M.; Gerward, L.

2013-05-01

68

Calculation of gamma-ray buildup factors for two-layered shields made of water, concrete and iron and application of approximating formula  

NASA Astrophysics Data System (ADS)

Gamma-ray buildup factors that are the basic data for the point kernel calculations were calculated up to 40 mean free path (mfp) for double-layered shields consisting of water, concrete and iron by the EGS4 code using a special splitting technique at gamma-ray energies of 0.1, 0.3, 0.6, 1, 3, 6 and 10 MeV. The assumed shields were 40 mfp monolayer, 5 mfp first layer +35 mfp second layer, 10 mfp first layer +30 mfp second layer and 20 mfp first layer +20 mfp second layer of these materials. All the possible combinations of single- and double-layered shields made up of two materials from water, concrete and iron were assumed in the calculations. The calculated data were parameterized by an empirical formula based on the transmission matrix method of recently proposed by the authors. The formula reproduced very well the reference data in all cases, except for those at 0.1 MeV where the small disagreement is now under investigation.

Shin, Kazuo; Hirayama, Hideo

2001-06-01

69

Determination of point isotropic buildup factors of gamma rays including incoherent and coherent scattering for aluminum, iron, lead, and water by discrete ordinates method  

Microsoft Academic Search

Exposure and energy absorption buildup factors for aluminum, iron, lead, and water are calculated by the SNID discrete ordinates code for an isotropic point source in a homogeneous medium. The calculation of the buildup factors takes into account the effects of both bound-electron Compton (incoherent) and coherent (Rayleigh) scattering. A comparison with buildup factors from the literature shows that these

S. Kitsos; A. Assad; C. M. Diop; J. C. Nimal; P. Ridoux

1994-01-01

70

Comparison of Gamma-Ray Point Isotropic Buildup Factors Including Fluorescence and Bremsstrahlung in Lead Using Discrete Ordinates and Point Monte Carlo Methods  

Microsoft Academic Search

Exposure buildup factors and energy spectra of ?-rays, including fluorescence or bremsstrahlung radiations, in Pb for a point isotropic source have been calculated in the vicinity of the K edge and at 10 MeV using a discrete ordinate code, PALLAS. Comparisons of PALLAS results with those by the point Monte Carlo code, EGS4 showed good agreement for exposure buildup factors

Hideo HIRAYAMA; Shun-ichi TANAKA; Yukio SAKAMOTO; K. V. SUBBAIAH; Yoshiko HARIMA

1990-01-01

71

Application of the EGS4 Monte Carlo Code to a Study of Multilayer Gamma-Ray Exposure Buildup Factors of up to 40 mfp  

Microsoft Academic Search

Multilayer ?-ray exposure buildup factors of up to 40 mfp were calculated using an electron-photon cascade Monte Carlo code, EGS4, as a point isotropic source. A kind of splitting technique was used in the EGS4 calculations in order to obtain reasonable results at very deep penetration problems, such as 40 mfp.The double-layer ?-ray exposure buildup factors were calculated for combinations

Hideo HIRAYAMA; Kazuo SHIN

1998-01-01

72

A comparison of gamma-ray buildup factors for low-Z material and for low energies using discrete ordinates and point Monte Carlo methods  

Microsoft Academic Search

This paper discusses the calculation of exposure and absorbed dose buildup factors for a photon point source in infinite beryllium in the low-energy range of 0.03 to 0.3 MeV, for penetration depth up to 40 mfp, using two discrete ordinates codes, PALLAS-PL, SP-Br, and ANISN. Comparisons of both result to values obtained by point Monte Carlo calculations using the electron

Y. Harima; H. Hirayama; T. Ishikawa; Y. Sakamoto; S. Tanaka

1987-01-01

73

Improvement of gamma-ray S{sub n} transport calculations including coherent and incoherent scatterings and secondary sources of bremsstrahlung and fluorescence: Determination of gamma-ray buildup factors  

Microsoft Academic Search

Improvements of gamma-ray transport calculations in S{sub n} codes aim at taking into account the bound-electron effect of Compton scattering (incoherent), coherent scattering (Rayleigh), and secondary sources of bremsstrahlung and fluorescence. A computation scheme was developed to take into account these phenomena by modifying the angular and energy transfer matrices, and no modification in the transport code has been made.

S. Kitsos; C. M. Diop; A. Assad; J. C. Nimal; P. Ridoux

1996-01-01

74

Reduction of the buildup contribution in gamma ray attenuation measurements and a new way to study this experiment in a student laboratory  

NASA Astrophysics Data System (ADS)

In continuation of our investigation into the buildup phenomenon appearing in gamma ray attenuation measurements in laboratory experiments we study the dependence of the buildup factor on the area of the absorber in an effort to reduce the buildup of photons. Detailed measurements are performed for up to two mean free paths of 60Co ?-rays through a lead absorber. A semi-empirical model on the attenuation of ?-rays studied in the laboratory, which includes the buildup effect, is developed. Finally, we propose a new procedure for studying laboratory ?-ray attenuation, which takes the buildup phenomenon into consideration.

Adamides, E.; Kavadjiklis, A.; Koutroubas, S. K.; Moshonas, N.; Tzedakis, A.; Yiasemides, K.

2014-01-01

75

Factors influencing in situ gamma-ray measurements  

Microsoft Academic Search

Introduction In situ passive gamma-ray sensors are very well suitable for mapping physical soil properties. In order to make a qualitative sound soil map, high quality input parameters for calibration are required. This paper will focus on the factors that affect the output of in situ passive gamma-ray sensors, the primary source, soil, not taken into account. Factors The gamma-ray

E. H. Loonstra; F. M. van Egmond

2009-01-01

76

An historical review and current status of buildup factor calculations and applications  

Microsoft Academic Search

The gamma-ray buildup factor is a multiplicative factor which corrects the response to uncollided photons so as to include the contribution of the scattered photons. Buildup factors are important data implemented in point kernel codes for use in shield design, together with attenuation coefficients. The Goldstein-Wilkins buildup factors calculated with the moments in 1954 were used as standard data until

Yoshiko Harima

1993-01-01

77

Formulas Giving Buildup Factor for Double-Layered Shields  

Microsoft Academic Search

Formulas that give absorbed dose buildup factors for two-layered shields have been developed based on gamma-ray absorption buildup factors computed with the Monte Carlo Neutral Particle Transport Code System (MCNP). The shielding materials considered were water, lead, steel, concrete, and some of their combinations for two-layered shields with thicknesses between 1 to 10 mfp. Gamma energy considered ranged from 0.5

Mevlut Guvendik; Nicholas Tsoulfanidis

2000-01-01

78

New Buildup Factor Data for Point Kernel Calculations.  

National Technical Information Service (NTIS)

An American Nuclear Society Standards Committee Working Group, ANS-6.4.3, is developing a set of evaluated gamma-ray isotropic point-source buildup factors and attenuation coefficients for a standard reference data base. A largely unpublished set of build...

D. K. Trubey Y. Harima

1986-01-01

79

Energy absorption buildup factors for thermoluminescent dosimetric materials and their tissue equivalence  

NASA Astrophysics Data System (ADS)

Gamma ray energy-absorption buildup factors were computed using the five-parameter geometric progression (G-P) fitting formula for seven thermoluminescent dosimetric (TLD) materials in the energy range 0.015-15 MeV, and for penetration depths up to 40 mfp (mean free path). The generated energy-absorption buildup factor data have been studied as a function of penetration depth and incident photon energy. Buildup factors determined in the present work should be useful in radiation dosimetry, diagnostics and therapy. The tissue equivalence of TLD materials is also discussed.

Manohara, S. R.; Hanagodimath, S. M.; Gerward, L.

2010-05-01

80

Dose buildup factor formula for double-layered shields  

SciTech Connect

In radiation shielding, health physics, and radioactive waste management, it is very important to know buildup factors for various materials and their combinations used as multilayer shields. In this work, a general formula that computes buildup factors for double-layer shields was developed on the basis of Monte Carlo photon transport using the MCNP code. Formulas for buildup factors for double-layer shields have been developed in the past with various degrees of success and limitations. The GP formula is excellent but applies to single-layer materials only. In this work, gamma-ray dose buildup factors for double-layer shields have been computed using the MCNP code. A point monoenergetic isotropic source was used with energy from 0.5 to 6 MeV. The source was placed at the center of the first spherical materials, surrounded by a second one. Detectors were placed on the surface of the second material and used to tally the photon flux in a six-energy-group structure. The shielding materials considered were water, lead, steel, concrete, and some of their combinations for double-layered shields ranging in thickness from 1 to 10 mean free paths (mfp).

Guvendik, M.; Tsoulfanidis, N.

1999-07-01

81

Gamma -Ray Shielding Effect of Various Building Materials.  

National Technical Information Service (NTIS)

It is necessary to know the gamma -ray attenuation coefficients and the dose buildup factors for various building materials in order to evaluate the gamma -ray shielding factor of the residential houses in a reactor accident. As a matter of fact, however,...

Y. Yamaguchi K. Minami S. Ohtani

1985-01-01

82

Factors influencing in situ gamma-ray measurements  

NASA Astrophysics Data System (ADS)

Introduction In situ passive gamma-ray sensors are very well suitable for mapping physical soil properties. In order to make a qualitative sound soil map, high quality input parameters for calibration are required. This paper will focus on the factors that affect the output of in situ passive gamma-ray sensors, the primary source, soil, not taken into account. Factors The gamma-ray spectrum contains information of naturally occurring nuclides 40K, 238U and 232Th and man-made nuclides like 137Cs, as well as the total count rate. Factors that influence the concentration of these nuclides and the count rate can be classified in 3 categories. These are sensor design, environmental conditions and operational circumstances. Sensor design The main elements of an in situ gamma-ray sensor that influence the outcome and quality of the output are the crystal and the spectrum analysis method. Material and size of the crystal determine the energy resolution. Though widely used, NaI crystals are not the most efficient capturer of gamma radiation. Alternatives are BGO and CsI. BGO has a low peak resolution, which prohibits use in cases where man-made nuclides are subject of interest. The material is expensive and prone to temperature instability. CsI is robust compared to NaI and BGO. The density of CsI is higher than NaI, yielding better efficiency, especially for smaller crystal sizes. More volume results in higher energy efficiency. The reduction of the measured spectral information into concentration of radionuclides is mostly done using the Windows analysis method. In Windows, the activities of the nuclides are found by summing the intensities of the spectrum found in a certain interval surrounding a peak. A major flaw of the Windows method is the limited amount of spectral information that is incorporated into the analysis. Another weakness is the inherent use of ‘stripping factors' to account for contributions of radiation from nuclide A into the peak of nuclide B. This can be overcome using Full Spectrum Analysis (FSA). This method incorporates virtually all data present in the measured gamma spectrum. In FSA, a Chi-squared algorithm is used to fit a set of "Standard Spectra" to the measured spectrum. The uncertainty in the FSA method is at least a factor 2 lower compared to the Windows method. Environmental conditions Environmental conditions can influence the signal output and therefore the quality. In general, the density of the medium through which gamma-radiation travels determines the interaction of the radiation with matter and thus affects the sensor readings. Excluding soil as being the source; water is the most important external factor in this respect. The amount of water in soil will affect the signal. In general, energy loss occurs as water content in soil increases. As a result, the nuclide concentrations will be lower. Monte Carlo simulations show a difference of 16% in nuclide concentration for completely dry and fully saturated sandy soils. Another water related issue is rainfall. With rain radon gas, a product of 238U, will precipitate. This causes spectral noise effects. Snow and fog have the same effect to a minor degree. Another aspect is the openness of soil. From experience we know that the concentration of 40K differs if soil is tilled. Finally, on earth there is always radioactive noise present from the galaxy. The "Standard Spectra" used in the FSA method can take noise and geometric effects into account. Operational circumstances During a survey an operator should be aware of the effects of driving speed and measurement height. In general, a larger crystal has better energy efficiency and is therefore more suitable for high speed. E.g. a 70 x 150 mm CsI crystal provides qualitative satisfactory output for soil mapping up to 10 km/hr. Sample locations, however, are best measured during a longer period (3 to 5 minutes). The measurement height affects the measurement resolution; the lower the sensor, the smaller the measured area. In addition, Monte Carlo simulations show that the m

Loonstra, E. H.; van Egmond, F. M.

2009-04-01

83

Factors that have an effect on degradation of diclofenac in aqueous solution by gamma ray irradiation  

Microsoft Academic Search

Purpose  Gamma ray irradiation is considered as an effective way to degrade diclofenac. However, due to the extensive coexisting substances\\u000a in natural waters, the use of gamma ray irradiation for degradation is often influenced by multiple factors. The various factors\\u000a that affect degradation efficiency, such as initial diclofenac concentration, initial pH, and the concentration of the additives\\u000a including H2O2 (·OH radical

Qun Liu; Xingzhang Luo; Zheng Zheng; Binguo Zheng; Jibiao Zhang; Yongjun Zhao; Xiaoying Yang; Jiaqi Wang; Lianhong Wang

84

Estimation of gamma- and X-ray photons buildup factor in soft tissue with Monte Carlo method.  

PubMed

Buildup factor of gamma- and X-ray photons in the energy range 0.2-2MeV in water and soft tissue is computed using Monte Carlo method. The results are compared with the existing buildup factor data of pure water. The difference between soft tissue and water buildup factor is studied. Soft tissue is assumed to have a composition as H(63)C(6)O(28)N. The importance of such work arises from the fact that in medical applications of X- and gamma-ray, soft tissue is usually approximated by water. It is shown that the difference between water and soft tissue buildup factor is usually more than 10%. On the other hand, buildup factor in water resulted from Monte Carlo method is compared with the experimental data appearing in references. It seems there is around 10% error in the reference data as well. PMID:19362488

Sardari, Dariush; Abbaspour, Ali; Baradaran, Samaneh; Babapour, Farshid

2009-01-01

85

Calculated photon KERMA factors based on the LLNL EGDL (Evaluated Gamma-Ray Data Library) data file  

SciTech Connect

Photon (Gamma-Ray) KERMA factors calculated from the LLNL EGDL (Evaluated Gamma-Ray Data Library) file are tabulated for the elements from Z=1 to Z=30 and for 15 composite materials. The KERMA factors are presented for 191 energy groups over the incident photon energy range from 100 eV to 100 MeV. 3 refs.

Howerton, R.J.

1986-10-10

86

Dose buildup factor formula for double-layered shields  

Microsoft Academic Search

In radiation shielding, health physics, and radioactive waste management, it is very important to know buildup factors for various materials and their combinations used as multilayer shields. In this work, a general formula that computes buildup factors for double-layer shields was developed on the basis of Monte Carlo photon transport using the MCNP code. Formulas for buildup factors for double-layer

M. Guvendik; N. Tsoulfanidis

1999-01-01

87

LORENTZ-FACTOR-ISOTROPIC-LUMINOSITY/ENERGY CORRELATIONS OF GAMMA-RAY BURSTS AND THEIR INTERPRETATION  

SciTech Connect

The bulk Lorentz factor of the gamma-ray burst (GRB) ejecta ({Gamma}{sub 0}) is a key parameter to understanding GRB physics. Liang et al. have discovered a correlation between {Gamma}{sub 0} and isotropic {gamma}-ray energy: {Gamma}{sub 0}{proportional_to}E{sup 0.25}{sub {gamma},iso,52}. By including more GRBs with updated data and more methods to derive {Gamma}{sub 0}, we confirm this correlation and obtain {Gamma}{sub 0} {approx_equal} 91E{sup 0.29}{sub {gamma},iso,52}. Evaluating the mean isotropic {gamma}-ray luminosities L{sub {gamma},iso} of the GRBs in the same sample, we discover an even tighter correlation {Gamma}{sub 0} {approx_equal} 249L{sup 0.30}{sub {gamma},iso,52}. We propose an interpretation to this later correlation. Invoking a neutrino-cooled hyperaccretion disk around a stellar mass black hole as the central engine of GRBs, we derive jet luminosity powered by neutrino annihilation and baryon loading from a neutrino-driven wind. Applying beaming correction, we finally derive {Gamma}{sub 0}{proportional_to}L{sup 0.22}{sub {gamma},iso}, which is consistent with the data. This suggests that the central engine of long GRBs is likely a stellar mass black hole surrounded by a hyper-accreting disk.

Lue Jing; Zou Yuanchuan; Lei Weihua; Wu Qingwen; Wang Dingxiong [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Zhang Bing; Lue Houjun [Department of Physics and Astronomy, University of Nevada Las Vegas, 4505 Maryland Parkway, Box 454002, Las Vegas, NV 89154-4002 (United States); Liang Enwei, E-mail: zouyc@hust.edu.cn, E-mail: leiwh@hust.edu.cn, E-mail: zhang@physics.unlv.edu [Department of Physics, Guangxi University, Nanning 530004 (China)

2012-05-20

88

Gamma Rays  

MedlinePLUS

... infrared, and ultraviolet light, are part of the electromagnetic spectrum. While gamma rays and x-rays pose the same kind of hazard, they differ in their origin. Gamma rays originate in the nucleus. X-rays originate in the electron fields surrounding the nucleus or are machine-produced. What ...

89

Analysis of 10B by PIGE with factor analytical gamma-ray peak identification.  

PubMed

Studying the biodistribution of boronated compounds for B neutron capture therapy (BNCT) requires the accurate detection of low levels of boron (10B) in biological samples. Proton induced gamma-ray emission analysis (PIGE) of 10B was found to be viable in a study of low density lipoprotein (LDL), in tissue and blood samples. However, the method is sensitive to Na present in the samples and can therefore not be used for accurate measurements of 10B concentrations below 5 ppm in samples containing Na. PIGE can be considered to be an appropriate reference method for chemical B analysis. The factor analytical method presented here is the most objective way to separate Na and B peaks from each other, and the factorizing method can be applied in different forms of spectral analysis. PMID:7581292

Savolainen, S; Räisänen, J; Eteläniemi, V; Abo Ramadan, U A; Kallio, M

1995-09-01

90

Gamma-ray buildup factors for concrete slab shields under slant incidence conditions  

Microsoft Academic Search

Monte Carlo calculations have been made for the penetration of slab shields by gamma radiation of monoenergetic character. The radiation is in the form of parallel, broad beams incident on the front face of the slab at various angles having cosines between 0.25 and 1.0. The beam photon energies vary between 0.661 and 6.13 MeV. The slab thicknesses extend to

E. M. Fournie; A. B. Chilton

1980-01-01

91

Energy absorption and exposure buildup factors for some polymers and tissue substitute materials: photon energy, penetration depth and chemical composition dependence.  

PubMed

The gamma ray energy absorption and exposure buildup factors have been calculated by using the five parameter geometric progression (GP) fitting formula for some polymers and tissue substitute materials in the energy region 0.015-15 MeV up to a penetration depth of 40 mean free paths. From the results, it is worth noting that significant variations occur in gamma ray buildup factors for the given polymers and tissue substitute materials depending on photon energy, penetration depth and chemical composition of the materials. Also, it was observed that there are significant variations between energy absorption (EABF) and exposure (EBF) buildup factors which may be due to the variations in chemical composition of the materials used. Finally, it is expected that the presented buildup factor data may be helpful in (a) estimating the effective dose to be given to patients in radiation therapy and diagnostics, hence allowing corrections to be made to the intensity of radiation, as it is somewhat problematic to evaluate the real absorbed dose in critical organs due to the probability of photon buildup somewhere inside the medium; (b) estimating the health hazards arising from the exposure of the human body to radiation, thus it will be helpful in controlling the exposure of the human body to radiation. PMID:21346285

Kurudirek, Murat; Özdemir, Yüksel

2011-03-01

92

Lorentz-factor-Isotropic-luminosity/Energy Correlations of Gamma-Ray Bursts and Their Interpretation  

NASA Astrophysics Data System (ADS)

The bulk Lorentz factor of the gamma-ray burst (GRB) ejecta (?0) is a key parameter to understanding GRB physics. Liang et al. have discovered a correlation between ?0 and isotropic ?-ray energy: ?0vpropE 0.25 ?, iso, 52. By including more GRBs with updated data and more methods to derive ?0, we confirm this correlation and obtain ?0 ~= 91E 0.29 ?, iso, 52. Evaluating the mean isotropic ?-ray luminosities L ?, iso of the GRBs in the same sample, we discover an even tighter correlation ?0 ~= 249L 0.30 ?, iso, 52. We propose an interpretation to this later correlation. Invoking a neutrino-cooled hyperaccretion disk around a stellar mass black hole as the central engine of GRBs, we derive jet luminosity powered by neutrino annihilation and baryon loading from a neutrino-driven wind. Applying beaming correction, we finally derive ?0vpropL 0.22 ?, iso, which is consistent with the data. This suggests that the central engine of long GRBs is likely a stellar mass black hole surrounded by a hyper-accreting disk.

Lü, Jing; Zou, Yuan-Chuan; Lei, Wei-Hua; Zhang, Bing; Wu, Qingwen; Wang, Ding-Xiong; Liang, En-Wei; Lü, Hou-Jun

2012-05-01

93

Linear attenuation coefficient and buildup factor of MCP-96 alloy for dose accuracy, beam collimation, and radiation protection.  

PubMed

The linear attenuation coefficients and buildup factor of MCP-96 alloy were determined for (60)Co, (54)Mn, and (137)Cs gamma emitters and a NaI detector. The thickness of the MCP-96 attenuator was varied from 1 to 4 cm. A collimated beam of gamma rays was allowed to pass through various thicknesses of the MCP-96 alloy. The attenuated beam was detected by a NaI detector, and data were recorded by a multichannel analyzer. The run was repeated without the collimator for broad-beam geometry. For each run, the attenuated beam intensity was normalized by the intensity of the unattenuated incident beam obtained by removing the attenuators. Linear attenuation coefficients were determined by plotting of the intensity of the collimated beam against the attenuator thickness. For every thickness of the alloy, the ratio of the attenuated to the unattenuated beam was found to be higher in broad-beam geometry as compared to the same ratio in narrow-beam geometry. We used the difference in these ratios in broad and narrow-beam geometries to calculate the buildup factor. The buildup factor was found to increase with beam energy and attenuator thickness. Variation in the source-to-detector distance gave a lower value of the buildup factor for a small and a large distance and a higher value for an intermediate distance. The buildup factor was found to be greater than 1 in all cases. We conclude that the buildup factor must be calculated and incorporated for dose correction and precision when the MCP-96 alloy is used for tissue compensation or radiation shielding and protection purposes. PMID:22585280

Hopkins, Deidre N; Maqbool, Muhammad; Islam, Mohammed S

2012-07-01

94

Absolute quantitation of radioactivity using the buildup factor.  

PubMed

A quantitation scheme for absolute activity measurements with the gamma camera is presented. The technique relies on the use of a set of derived buildup factors to correct for the effects of scatter. Only anterior and posterior view count rates of the region of interest are required for quantitation. The buildup factors are reported for various depths for two different source sizes using the parallel-hole collimator with a specific window setting. Phantom studies have shown that the method provides less than 5% error for activity determinations at all investigated depths. PMID:6328238

Wu, R K; Siegel, J A

1984-01-01

95

A study of the energy absorption and exposure buildup factors of some anti-inflammatory drugs.  

PubMed

Human radiation exposure is increasing due to radiation development in science and technology. The development of radioprotective agents is important for protecting patients from the side effects of radiotherapy and for protecting the public from unwanted irradiation. Radioprotective agents are used to reduce the damage caused by radiation in healthy tissues. There are several classes of radioprotective compounds that are under investigation. Analgesics and anti-inflammatory compounds are being considered for treating or preventing the effects of damage due to radiation exposure, or for increasing the chance of survival after exposure to a high dose of radiation. In this study, we investigated the radioprotective effects of some analgesic and anti-inflammatory compounds by evaluating buildup factors. The gamma ray energy absorption (EABF) and exposure buildup factors (EBF) were calculated to select compounds in a 0.015-15MeV energy region up to a penetration depth of 40mfp (mean free path). Variations of EABF and EBF with incident photon energy and penetration depth elements were also investigated. Significant variations in both EABF and EBF values were observed for several compounds at the moderate energy region. At energies below 0.15MeV, EABF and EBF values increased with decreasing equivalent atomic number (Zeq) of the samples. In addition, EABF and EBF were the largest for ibuprofen, aspirin, paracetamol, naproxen and ketoprofen at 0.05 and 0.06MeV, respectively, and the EABF value was 0.1MeV for aceclofenac. From these results, we concluded that the buildup of photons is less for aceclofenac compared to other materials. PMID:24859334

Ekinci, Neslihan; Kavaz, Esra; Ozdemir, Yüksel

2014-08-01

96

Amelioration de la modelisation du transport des gamma suivant la methode de l'attenuation en ligne droite. (Improvement of the gamma-ray transport model the point kernel attenuation method).  

National Technical Information Service (NTIS)

The gamma-ray buildup factor is a multiplicative factor which corrects the response of non-collided photons to include the contribution of the scattered photons. Buildup factors are very important data implemented in Point kernel codes for use in shield d...

A. Assad

1995-01-01

97

The Study of Equilibrium factor between Radon-222 and its Daughters in Bangkok Atmosphere by Gamma-ray Spectrometry  

NASA Astrophysics Data System (ADS)

To study the Equilibrium between radon-222 and its daughters in Bangkok atmosphere by Gamma-ray spectrometry, air sample were collected on 48 activated charcoal canister and 360 glass fiber filters by using a high volume jet-air sampler during December 2007 to November 2008.The Spectra of gamma-ray were measured by using a HPGe (Hyper Pure Germanium Detector). In the condition of secular equilibrium obtaining between Radon-222 and its decay products, radon-222 on activated charcoal canister and its daughters on glass fiber filters collected in the same time interval were calculated. The equilibrium factor (F) in the open air had a value of 0.38 at the minimum ,and 0.75 at the maximum. The average value of equilibrium factor (F) was 0.56±0.12. Based on the results, F had variations with a maximum value in the night to the early morning and decreased in the afternoon. In addition, F was higher in the winter than in the summer. This finding corresponds with the properties of the Earth atmosphere. The equilibrium factor (F) also depended on the concentration of dust in the atmosphere. People living in Bangkok were exposed to average value of 30 Bq/m3 of Radon-222 in the atmosphere. The equilibrium factor (0.56±0.12) and the average value of Radon-222 showed that people were exposed to alpha energy from radon-222 and its daughters decay at 0.005 WL(Working Level) which is lower than the safety standard at 0.02 WL. Keywords: Radon, Radon daughters , equilibrium factor, Gamma -ray spectrum analysis ,Bangkok ,Thailand

Rujiwarodom, Rachanee

2010-05-01

98

Energy absorption and exposure buildup factors of essential amino acids.  

PubMed

The effective atomic number and effective electron density in amino acids are of significant interest due to their use in various applications. The energy absorption buildup factors, exposure buildup factors, effective atomic numbers, and electron densities of essential amino acids such as Leucine (C6H13NO2), Lysine (C6H14N2O2), Methionine (C5H11NO2S), Phenylalanine (C9H11NO2), Threonine (C4H9NO3), Tryptophan (C11H12N2O2), Valine (C5H11NO2), Arginine (C6H14N4O2), and Histidine (C6H9N3O2) were determined theoretically in the energy range 0.015-15?MeV. PMID:24605325

Bursal?o?lu, Ertu?rul; Balkan, Begüm; Kavanoz, H Birtan; Okutan, Mustafa; ?çelli, Orhan; Yalç?n, Zeynel

2014-01-01

99

Stimulating effect of space flight factors on Artemia cysts: comparison with irradiation by gamma rays  

SciTech Connect

The Artemia cyst, a gastrula in dormant state, is a very suitable material to investigate the individual effects of HZE cosmic particles. Monolayers of Artemia cysts, sandwiched with nuclear emulsions, flew aboard the Soviet biosatellite Cosmos 1129. The space flight stimulated the developmental capacity expressed by higher percentages of emergence, hatching, and alive nauplii at day 4-5. A greater mean life span was reported in Artemias developed from Artemia cysts hit by the cosmic heavy ions. On Earth, Artemia cysts were exposed to 1, 10, 100, 200 and 400 Gy of gamma (gamma) rays. A stimulating effect on developmental capacity was observed for 10 Gy; the mean life span was significantly increased for this dose. These results are discussed in comparison with previous investigations performed on Earth and in space.

Gaubin, Y.; Pianezzi, B.; Gasset, G.; Plannel, H.; Kovalev, E.E.

1986-06-01

100

Gamma ray camera  

Microsoft Academic Search

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

1997-01-01

101

Gamma ray camera  

Microsoft Academic Search

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

Victor

1997-01-01

102

Gamma-ray waveguides  

SciTech Connect

We have developed an approach for gamma-ray optics using layered structures acting as planar waveguides. Experiments demonstrating channeling of 122 keV gamma rays in two prototype waveguides validate the feasibility of this technology. Gamma-ray waveguides allow one to control the direction of radiation up to a few MeV. The waveguides are conceptually similar to polycapillary optics, but can function at higher gamma-ray energies. Optics comprised of these waveguides will be able to collect radiation from small solid angles or concentrate radiation into small area detectors. Gamma-ray waveguides may find applications in medical imaging and treatment, astrophysics, and homeland security.

Tournear, D. M.; Hoffbauer, M. A.; Akhadov, E. A.; Chen, A. T.; Pendleton, S. J.; Williamson, T. L.; Cha, K. C.; Epstein, R. I. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2008-04-14

103

Verification of some building materials as gamma-ray shields.  

PubMed

The shielding properties for gamma rays of a few low Z materials were investigated. The values of the mass attenuation coefficient, equivalent atomic number, effective atomic number, exposure buildup factor and energy absorption buildup factor were calculated and used to estimate the shielding effectiveness of the samples under investigation. It has been observed that the shielding effectiveness of a sample is directly related to its effective atomic number. The shielding character of any sample is a function of the incident photon energy. Good shielding behaviour has been verified in soil samples in the photon energy region of 0.015-0.30 MeV and of dolomite in 3-15 MeV. The results have been shown graphically with more useful conclusions. PMID:22223719

Mann, Kulwinder Singh; Singla, Jyoti; Kumar, Vipan; Sidhu, G S

2012-08-01

104

Semi-empirical relationship for photon buildup factor in soft tissue and water.  

PubMed

Buildup factor of gamma and X-ray photons in the energy range of 0.2-2 MeV in water and soft tissue is computed using Monte Carlo code MCNP4C. The results are compared with the buildup factor data of pure water. A new relationship estimating buildup factor as a function of penetration depth, Compton scattering and energy absorption cross sections is introduced. The new relationship estimates buildup factor with 5 % deviation compared with the existing data. PMID:20823036

Sardari, D; Baradaran, S

2010-12-01

105

Gamma-Ray Pulsars  

Microsoft Academic Search

Gamma-ray photons from young pulsars allow the deepest insight into the properties and interactions of high-energy particles with magnetic and photon fields in a pulsar magnetosphere. Measurements with the Compton Gamma-Ray Observatory have led to the detection of nearly ten Gamma-ray pulsars. Although quite a variety of individual signatures is found for these pulsars, some general characteristics can be summarized:

Gottfried Kanbach

2002-01-01

106

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

107

Gamma Ray Bursts.  

National Technical Information Service (NTIS)

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 pion...

N. Gehrels P. Meszaros

2012-01-01

108

Gamma-Ray Pulsars  

NASA Technical Reports Server (NTRS)

The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the detection of over 80 gamma-ray pulsars. Several new populations have been discovered, including 24 radio quiet pulsars found through gamma-ray pulsations alone and about 20 millisecond gamma-ray pulsars. The gamma-ray pulsations from millisecond pulsars were discovered by both folding at periods of known radio millisecond pulsars or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -35 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. The higher sensitivity and larger energy range of the Fermi Large Area Telescope has produced detailed energy-dependent light curves and phase-resolved spectroscopy on brighter pulsars, that have ruled out polar cap models as the major source of the emission in favor of outer magnetosphere accelerators. The large number of gamma-ray pulsars now allows for the first time meaningful population and sub-population studies that are revealing surprising properties of these fascinating sources.

Harding, Alice K.

2011-01-01

109

Gamma-ray Bursts  

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

110

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

111

Measurement of partial gamma-ray production cross-sections and k0-factors for radionuclides with chopped-beam PGAA—Part II  

NASA Astrophysics Data System (ADS)

As a continuation of our previously reported experiments, the partial gamma-ray production cross-sections ( ??) and k0-factors of 12 short- and medium-lived radionuclides were determined using a chopped beam of cold neutrons. This technique avoids several problems associated with epithermal activation, sample transportation and dead-time effects in neutron activation analysis (NAA) measurements. Our k0-values were determined with internal standardization, using stoichiometric compounds or water solutions of known compositions.

Szentmiklósi, L.; Révay, Zs.; Belgya, T.

2010-10-01

112

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

113

Gamma-Ray Detectors  

NASA Astrophysics Data System (ADS)

The common methods of analyzing gamma-ray spectra obtained from detectors capable of energy discrimination are discussed. Gamma-ray spectra generally are in the form of detector response versus discrete channel number. The methods considered for gamma-ray spectroscopy are somewhat general and can be applied to other types of spectroscopy. The general objective of spectroscopy is to obtain, at a minimum, the qualitative identification of the source (e.g., source energies or nuclides present). However, most spectroscopy applications seek quantitative information also, as expressed by, e.g., the source strength or the nuclide concentration. Various different methods for qualitative and quantitative analysis are summarized, and an illustrative example is provided. A review of detectors used for gamma-ray spectroscopy is included.

Dunn, William L.; McGregor, Douglas S.

114

Gamma ray pulsars: Observations  

Microsoft Academic Search

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

David J. Thompson

2001-01-01

115

gamma ray astronomy with muons  

Microsoft Academic Search

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 ``enhancement'' of muons from gamma ray primaries as compared to that from nucleon primaries. All shower gamma rays above the

Francis Halzen; Todor Stanev; Gaurang B. Yodh

1997-01-01

116

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

117

GRB 090510: A DISGUISED SHORT GAMMA-RAY BURST WITH THE HIGHEST LORENTZ FACTOR AND CIRCUMBURST MEDIUM  

SciTech Connect

GRB 090510, observed by both Fermi and AGILE satellites, is the first bright short-hard gamma-ray burst (GRB) with an emission from the keV up to the GeV energy range. Within the Fireshell model, we interpret the faint precursor in the light curve as the emission at the transparency of the expanding e {sup +} e {sup -} plasma: the Proper-GRB. From the observed isotropic energy, we assume a total plasma energy E{sup tot}{sub e{sup +}e{sup -}}=(1.10{+-}0.06) Multiplication-Sign 10{sup 53} erg and derive a Baryon load B = (1.45 {+-} 0.28) Multiplication-Sign 10{sup -3} and a Lorentz factor at transparency {Gamma}{sub tr} = (6.7 {+-} 1.6) Multiplication-Sign 10{sup 2}. The main emission {approx}0.4 s after the initial spike is interpreted as the extended afterglow, due to the interaction of the ultrarelativistic baryons with the CircumBurst Medium (CBM). Using the condition of fully radiative regime, we infer a CBM average spherically symmetric density of (n{sub CBM}) = (1.85 {+-} 0.14) Multiplication-Sign 10{sup 3} particles cm{sup -3}, one of the highest found in the Fireshell model. The value of the filling factor, 1.5 Multiplication-Sign 10{sup -10}{<=}R{<=}3.8 Multiplication-Sign 10{sup -8}, leads to the estimate of filaments with densities n{sub fil} = n{sub CBM}/R approx. (10{sup 6}-10{sup 14}) particles cm{sup -3}. The sub-MeV and the MeV emissions are well reproduced. When compared to the canonical GRBs with (n{sub CBM}) Almost-Equal-To 1 particles cm{sup -3} and to the disguised short GRBs with (n{sub CBM}) Almost-Equal-To 10{sup -3} particles cm{sup -3}, the case of GRB 090510 leads to the existence of a new family of bursts exploding in an overdense galactic region with (n{sub CBM}) Almost-Equal-To 10{sup 3} particles cm{sup -3}. The joint effect of the high {Gamma}{sub tr} and the high density compresses in time and 'inflates' in intensity the extended afterglow, making it appear as a short burst, which we here define as a 'disguised short GRB by excess'. The determination of the above parameter values may represent an important step toward the explanation of the GeV emission.

Muccino, M.; Ruffini, R.; Bianco, C. L.; Izzo, L.; Penacchioni, A. V.; Pisani, G. B. [Dip. di Fisica and ICRA, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Rome (Italy)

2013-07-20

118

Gamma ray optics  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

119

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

120

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

121

Gamma rays from the magellanic clouds  

NASA Technical Reports Server (NTRS)

Predicted gamma ray fluxes from the Megallanic Clouds, obtained by using updated parameters, are significantly above the values previously determined, and well within the capabilities of observation from COS-B satellite. Concepts relating galactic gamma ray production and other Population 1 phenomena in the Milky Way were used to postulate a factor of four increase in predicted flux, based on the galactic origin hypothesis. The values obtained provide a possible test of two interpretations of gamma ray emission: enhancement in the inner galaxy from gas and cosmic ray sources alone, or increases produced by the trapping of cosmic rays in spiral arms. Because spiral structure is absent in the small cloud, and questionable in the large cloud, and both clouds are classed as irregular galaxies, the predicted enhancement in gamma ray flux may not be as great in the absence of clear spiral structure.

Stecker, F. W.

1977-01-01

122

Gamma ray pulsars  

NASA Technical Reports Server (NTRS)

Recent data from the high energy gamma ray experiment have revealed the existence of four pulsars emitting photons above 35 MeV. An attempt is made to explain the gamma ray emission from these pulsars in terms of an electron-photon cascade that develops in the magnetosphere of the pulsar. Although there is very little material above the surface of the pulsar, the very intense magnetic fields correspond to many radiation lengths which cause electrons to emit photons via magnetic bremsstrahlung and these photons to pair produce. The cascade develops until the mean photon energy drops below the pair production threshold which happens to be in the gamma ray range; at this stage the photons break out from the source.

Oegelman, H.; Ayasli, S.; Hacinliyan, A.

1976-01-01

123

Gamma-ray Polarimetry  

SciTech Connect

An astrophysics application of a low noise Double-sided Silicon Strip Detector (DSSD) is described. A Semiconductor Multiple-Compton Telescope (SMCT) is being developed to explore the gamma-ray universe in the 0.1-20 MeV energy band. Excellent energy resolution and polarization sensitivity are key features of the SMCT. We have developed prototype modules for a low-noise DSSD system, which reached an energy resolution of 1.3 keV (FWHM) for 122 keV at 0 C. Results of a gamma-ray imaging test are also presented.

Tajima, Hiroyasu

2003-02-05

124

Possible existence of the Ep-Lp and Ep-Eiso correlations for short gamma-ray bursts with a factor 5-100 dimmer than those for long gamma-ray bursts  

NASA Astrophysics Data System (ADS)

We analysed correlations among the rest-frame spectral peak energy Ep, the observed frame 64 ms peak isotropic luminosity Lp and the isotropic energy Eiso for 13 short gamma-ray burst (SGRB) candidates having the measured redshift z, Tobs90/(1 + z) < 2 s and well-determined spectral parameters. An SGRB candidate is regarded as a misguided SGRB if it is located in the 3?int dispersion region from the best-fitting function of the Ep-Eiso correlation for long GRBs (LGRBs), while the others are regarded as secure SGRBs possibly from compact star mergers. Using 8 secure SGRBs out of 13 SGRB candidates, we tested whether the Ep-Eiso and Ep-Lp correlations exist for SGRBs. We found that the Ep-Eiso correlation for SGRBs (Eiso = 1051.42 ± 0.15 erg s-1(Ep/774.5 keV)1.58 ± 0.28) seems to exist with the correlation coefficient r = 0.91 and chance probability p = 1.5 × 10-3. We also found that the Ep-Lp correlation for SGRBs (Lp = 1052.29 ± 0.066 erg s-1(Ep/774.5 keV)1.59 ± 0.11) is tighter than the Ep-Eiso correlation since r = 0.98 and p = 1.5 × 10-5. Both correlations for SGRBs are dimmer than those of LGRBs for the same Ep by factors ˜100 (Ep - Eiso) and ˜ 5(Ep - Lp). Applying the tighter Ep-Lp correlation for SGRBs to 71 bright Burst and Transient Source Experiment SGRBs, we found that pseudo-redshift z ranges from 0.097 to 2.258 with the mean of 1.05. The redshifts of SGRBs apparently cluster at lower redshift than those of LGRBs ( ˜2.2), which supports the merger scenario of SGRBs.

Tsutsui, Ryo; Yonetoku, Daisuke; Nakamura, Takashi; Takahashi, Keitaro; Morihara, Yoshiyuki

2013-05-01

125

Gamma-ray telescopes  

Microsoft Academic Search

The last half-century has seen dramatic developments in ??ray telescopes, from their initial conception and development through to their blossoming into full maturity as a potent\\u000a research tool in astronomy. Gamma-ray telescopes are leading research in diverse areas such as ??ray bursts, blazars, Galactic transients, and the Galactic distribution of 26Al.

Neil Gehrels; John K. Cannizzo

2009-01-01

126

Gamma ray astronomy  

NASA Technical Reports Server (NTRS)

Miscellaneous tasks related to mission operations and data analysis for the Burst and Transient Source Experiment on the Gamma Ray Observatory, to collection, analysis, and interpretation of data from the Marshall Space Flight Center Very Low Frequency transient monitoring program, and to compilation and analysis of induced radioactivity data were performed. The results are summarized and relevant references are included.

Paciesas, William S.

1992-01-01

127

Gamma-Ray Bursts  

NASA Technical Reports Server (NTRS)

Gamma-Ray Bursts (GRBs) are now known to be the most powerful explosions in the Universe. I will summarize the history of observations of GRBs, and how we came to know that the sources are so distant. I will also give an overview of the most prominent theories as to the cause of bursts.

Meegan, Charles A.; Six, N. Frank (Technical Monitor)

2002-01-01

128

Gamma-ray Astronomy.  

National Technical Information Service (NTIS)

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...

W. S. Paciesas

1994-01-01

129

Gamma Ray Astronomy  

NASA Technical Reports Server (NTRS)

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

Wu, S. T.

2000-01-01

130

Liquid xenon gamma ray imager  

US Patent & Trademark Office Database

A gamma ray imager includes a chamber containing a scintillation liquid such as xenon and several mutually optically isolated interaction modules immersed in the scintillation liquid within the chamber. Multiple photodetectors optically coupled to the modules separately detect scintillation light resulting from gamma ray interactions in the modules. Charge readout devices coupled to the modules provide time projection chamber-class detection of ionization charges produced by gamma ray interactions within the modules. A signal processor connected to the multiple photodetectors and charge readout devices analyzes signals produced by gamma ray interactions within the modules and calculates from the signals gamma ray energy and gamma ray angle. The calculations use Compton scattering formula inversion and also use anti-correlation of prompt scintillation light signals from gamma ray interactions and charge signals from gamma ray interactions.

2013-07-02

131

Monte Carlo simulation of photon buildup factors for shielding materials in radiotherapy x-ray facilities  

SciTech Connect

Purpose: This paper presents the results of a series of calculations to determine buildup factors for ordinary concrete, baryte concrete, lead, steel, and iron in broad beam geometry for photons energies from 0.125 to 25.125 MeV at 0.250 MeV intervals.Methods: Monte Carlo N-particle radiation transport computer code has been used to determine the buildup factors for the studied shielding materials.Results: The computation of the primary broad beams using buildup factors data was done for nine published megavoltage photon beam spectra ranging from 4 to 25 MV in nominal energies, representing linacs made by the three major manufacturers. The first tenth value layer and the equilibrium tenth value layer are calculated from the broad beam transmission for these nine primary megavoltage photon beam spectra.Conclusions: The results, compared with published data, show the ability of these buildup factor data to predict shielding transmission curves for the primary radiation beam. Therefore, the buildup factor data can be combined with primary, scatter, and leakage x-ray spectra to perform computation of broad beam transmission for barriers in radiotherapy shielding x-ray facilities.

Karim Karoui, Mohamed [Faculte des Sciences de Monastir, Avenue de l'environnement 5019 Monastir -Tunisia (Tunisia); Kharrati, Hedi [Ecole Superieure des Sciences et Techniques de la Sante de Monastir, Avenue Avicenne 5000 Monastir (Tunisia)

2013-07-15

132

Estimation of gamma- and X-ray photons buildup factor in soft tissue with Monte Carlo method  

Microsoft Academic Search

Buildup factor of gamma- and X-ray photons in the energy range 0.2–2MeV in water and soft tissue is computed using Monte Carlo method. The results are compared with the existing buildup factor data of pure water. The difference between soft tissue and water buildup factor is studied. Soft tissue is assumed to have a composition as H63C6O28N. The importance of

Dariush Sardari; Ali Abbaspour; Samaneh Baradaran; Farshid Babapour

2009-01-01

133

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

134

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

135

Gamma-ray spectroscopy - Status and prospects  

NASA Technical Reports Server (NTRS)

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

Matteson, J. L.

1983-01-01

136

Gamma-ray localization of terrestrial gamma-ray flashes.  

PubMed

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by the AGILE Mini-Calorimeter. We detect 8 TGFs with gamma-ray photons of energies above 20 MeV localized by the AGILE gamma-ray imager with an accuracy of ?5-10° at 50 MeV. Remarkably, all TGF-associated gamma rays are compatible with a terrestrial production site closer to the subsatellite point than 400 km. Considering that our gamma rays reach the AGILE satellite at 540 km altitude with limited scattering or attenuation, our measurements provide the first precise direct localization of TGFs from space. PMID:20867680

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

2010-09-17

137

Noiseless coding for the Gamma Ray spectrometer  

NASA Technical Reports Server (NTRS)

The payload of several future unmanned space missions will include a sophisticated gamma ray spectrometer. Severely constrained data rates during certain portions of these missions could limit the possible science return from this instrument. This report investigates the application of universal noiseless coding techniques to represent gamma ray spectrometer data more efficiently without any loss in data integrity. Performance results demonstrate compression factors from 2.5:1 to 20:1 in comparison to a standard representation. Feasibility was also demonstrated by implementing a microprocessor breadboard coder/decoder using an Intel 8086 processor.

Rice, R.; Lee, J. J.

1985-01-01

138

Precise absolute gamma-ray wavelength measurements  

NASA Astrophysics Data System (ADS)

Gamma-ray wavelengths measured with the joint NIST/ILL GAMS4 facility at the High Flux Reactor, Grenoble, France, are discussed. This primary goal of these measurements is gamma-ray wavelengths which are consistent with the optical wavelength scale and the Rydberg constant with an uncertainty no larger than 0.1 ppm for energies up to 5 MeV. The current status of the Bragg angle and crystal lattice spacing measurements on reference energy values, the neutron mass, and the determination of fundamental constants is reviewed. Measurement of structure factors at high energies is also considered.

Kessler, E. G.; Dewey, M. S.; Greene, G. L.; Deslattes, R. D.; Börner, H.

1991-10-01

139

Gamma Ray Pulsars: Multiwavelength Observations  

Microsoft Academic Search

High-energy gamma rays are a valuable tool for studying particle acceleration\\u000aand radiation in the magnetospheres of energetic pulsars. The seven or more\\u000apulsars seen by instruments on the Compton Gamma Ray Observatory (CGRO) show\\u000athat: the light curves usually have double-peak structures (suggesting a broad\\u000acone of emission); gamma rays are frequently the dominant component of the\\u000aradiated power;

David J. Thompson

2003-01-01

140

The Gamma Ray Pulsar Population  

Microsoft Academic Search

We apply a likelihood analysis to pulsar detections, pulsar upper limits, and\\u000adiffuse background measurements from the OSSE and EGRET instruments on the\\u000aCompton Gamma Ray Observatory to constrain the luminosity law for gamma-ray\\u000apulsars and some properties of the gamma-ray pulsar population. We find that\\u000athe dependence of luminosity on spin period and dipole magnetic field is much\\u000asteeper

M. A. McLaughlin; J. M. Cordes

1999-01-01

141

{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

142

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

143

Gamma-ray bursters  

NASA Technical Reports Server (NTRS)

Current theoretical models developed to explain the observational data (from spaceborne detectors) on gamma-ray bursters are summarized and illustrated with drawings, diagrams, graphs, and photographic images. Although the data are fragmentary and often flawed by instrument defects, models involving neutron stars with strong magnetic fields are generally favored, and it is assumed that most observed bursters lie within the Galaxy. The neutron-star origin of the bursts is suggested by their intensity and rapid variability (implying a very compact high-energy source) and the presence in some burster spectra of a line at 420 keV which is explained by the combination of electron-positron annihilation and gravitational reddening. Consideration is also given to optical flashes observed to occur about once per year in the direction of gamma bursters, and the need for further searches for lower-energy emissions from bursters is stressed.

Schaefer, B. E.

1985-01-01

144

Astrophysical gamma-ray spectroscopy  

NASA Technical Reports Server (NTRS)

Observations of gamma-ray lines from solar flares, the Galactic Center, and transient celestial events are reviewed. The lines observed in each case are identified, and possible emission sources are considered. Future prospects for gamma-ray line astronomy are briefly discussed.

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

1979-01-01

145

Planetary gamma-ray spectroscopy  

NASA Technical Reports Server (NTRS)

The measured intensities of certain gamma rays of specific energies escaping from a planetary surface can be used to determine the abundances of a number of elements. The fluxes of the more intense gamma-ray lines emitted from 32 elements were calculated using current nuclear data and existing models for the source processes. The source strengths for neutron-capture reactions were modified from those previously used. The fluxes emitted form a surface of average lunar composition are reported for 292 gamma-ray lines. These theoretical fluxes were used elsewhere to convert the data from the Apollo gamma-ray spectrometers to elemental abundances and can be used with measurements from future missions to map the concentrations of a number of elements over a planet's surface. Detection sensitivities for these elements are examined and applications of gamma-ray spectroscopy for future orbiters to Mars and other solar-system objects are discussed.

Reedy, R. C.

1978-01-01

146

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

147

Astrophysical S factor of the {sup 3}He({alpha},{gamma}){sup 7}Be reaction measured at low energy via detection of prompt and delayed {gamma} rays  

SciTech Connect

Solar neutrino fluxes depend both on astrophysical and on nuclear physics inputs, namely on the cross sections of the reactions responsible for neutrino production inside the Solar core. While the flux of solar {sup 8}B neutrinos has been recently measured at Superkamiokande with a 3.5% uncertainty and a precise measurement of {sup 7}Be neutrino flux is foreseen in the next future, the predicted fluxes are still affected by larger errors. The largest nuclear physics uncertainty to determine the fluxes of {sup 8}B and {sup 7}Be neutrinos comes from the {sup 3}He({alpha},{gamma}){sup 7}Be reaction. The uncertainty on its S-factor is due to an average discrepancy in results obtained using two different experimental approaches: the detection of the delayed {gamma} rays from {sup 7}Be decay and the measurement of the prompt {gamma} emission. Here we report on a new high precision experiment performed with both techniques at the same time. Thanks to the low background conditions of the Gran Sasso LUNA accelerator facility, the cross section has been measured at E{sub c.m.}=170, 106, and 93 keV, the latter being the lowest interaction energy ever reached. The S-factors from the two methods do not show any discrepancy within the experimental errors. An extrapolated S(0)=0.560{+-}0.017 keV barn is obtained. Moreover, branching ratios between the two prompt {gamma}-transitions have been measured with 5-8% accuracy.

Confortola, F.; Costantini, H.; Corvisiero, P.; Lemut, A.; Prati, P. [Universita degli Studi Genova and INFN Genova, Via Dodecaneso 33, I-16146 Genova (Italy); Bemmerer, D.; Broggini, C.; Lozza, V.; Menegazzo, R.; Alvarez, C. Rossi [INFN Sezione di Padova, Via Marzolo 8, I-35131 Padova (Italy); Formicola, A.; Gustavino, C.; Junker, M.; Laubenstein, M. [INFN, Laboratori Nazionali del Gran Sasso, S.S. 17bis km 18.890, Assergi, L'Aquila (Italy); Gyuerky, Gy.; Elekes, Z.; Fueloep, Zs.; Somorjai, E. [ATOMKI, Debrecen (Hungary); Bezzon, P. [INFN, Laboratori Nazionali di Legnaro, Padova (Italy); Bonetti, R. [Istituto di Fisica Generale Applicata, Universita di Milano and INFN Milano, Milan (Italy)] (and others)

2007-06-15

148

HIGH-ENERGY GAMMA-RAY AFTERGLOWS FROM LOW-LUMINOSITY GAMMA-RAY BURSTS  

SciTech Connect

The observations of gamma-ray bursts (GRBs) such as 980425, 031203 and 060218, with luminosities much lower than those of other classic bursts, lead to the definition of a new class of GRBs-LL-GRBs. The nature of the outflow responsible for them is not yet clear. Two scenarios have been suggested: one is the conventional relativistic outflow with initial Lorentz factor of order of GAMMA{sub 0} approx> 10 and the other is a trans-relativistic outflow with GAMMA{sub 0} approx = 1-2. Here, we compare the high-energy gamma-ray afterglow emission from these two different models, taking into account both synchrotron self-inverse Compton (SSC) scattering and the external inverse Compton scattering due to photons from the cooling supernova or hypernova envelope (SNIC). We find that the conventional relativistic outflow model predicts a relatively high gamma-ray flux from SSC at early times (<10{sup 4} s for typical parameters) with a rapidly decaying light curve, while in the trans-relativistic outflow model, one would expect a much flatter light curve of high-energy gamma-ray emission at early times, which could be dominated by both the SSC emission and the SNIC emission, depending on the properties of the underlying supernova and the shock parameter epsilon{sub e} and epsilon{sub B}. The Fermi Gamma-ray Space Telescope should be able to distinguish between the two models in the future.

He Haoning; Wang Xiangyu; Yu Yunwei [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Meszaros, Peter [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)

2009-12-01

149

WIDE RADIO BEAMS FROM {gamma}-RAY PULSARS  

SciTech Connect

We investigate the radio and {gamma}-ray beaming properties of normal and millisecond pulsars (MSPs) by selecting two samples from the known populations. The first, Sample G, contains pulsars which are detectable in blind searches of {gamma}-ray data from the Fermi Large Area Telescope. The second, Sample R, contains pulsars detectable in blind radio searches which have spin-down luminosities E>10{sup 34} erg s{sup -1}. We analyze the fraction of the {gamma}-ray-selected Sample G which have detectable radio pulses and the fraction of the radio-selected Sample R which have detectable {gamma}-ray pulses. Twenty of our 35 Sample G pulsars have already observed radio pulses. This rules out low-altitude polar-cap beaming models if, as is currently believed, {gamma}-ray beams are generated in the outer magnetosphere and are very wide. We further find that, for the highest-E pulsars, the radio and {gamma}-ray beams have comparable beaming factors, i.e., the beams cover similar regions of the sky as the star rotates. For lower-E {gamma}-ray emitting pulsars, the radio beams have about half of the {gamma}-ray sky coverage. These results suggest that, for high-E young and MSPs, the radio emission originates in wide beams from regions high in the pulsar magnetosphere, probably close to the null-charge surface and to the {gamma}-ray emitting regions. Furthermore, it suggests that for these high-E pulsars, as in the {gamma}-ray case, features in the radio profile represent caustics in the emission beam pattern.

Ravi, V.; Manchester, R. N.; Hobbs, G. [Australia Telescope National Facility, CSIRO, Epping, NSW 1710 (Australia)

2010-06-10

150

Pulsars as gamma ray sources.  

NASA Astrophysics Data System (ADS)

Aspects of the physics of rotation powered pulsars as gamma ray sources are discussed. The shock excitation of pulsar powered nebulae (plerions) is discussed, based on recent theoretical work on the structure of relativistic, collisionless magnetosonic shock waves. This theory is used to outline a model in which the ?^-2^ injection spectrum of the Crab Nebula is satisfactorily accounted for. The same theory suggests a model of the ``wisp'' features in the Crab Nebula which accounts for these time variable features in the surface bightness as compressions associated with the magnetic overshoots within the shock structure. It is pointed out that this theory suggests observable variability in the high energy gamma rays from the Crab Nebula (?>50MeV.) The energetics of pulsed gamma ray emission from the six known EGRET pulsars are reviewed and shown to fit a simple efficiency {prop.to}{PHI}_open_^-k^ law, where k~0.8 and {PHI}_open_={OMEGA}_*_^2mu/c^2^=10^13^(?(P)_15_ /P^3^)^1/2^ is a measure of the total voltage available on a pulsar's open field lines. Here ?(P)_15_=?(P)/10^-15^. This result is used to define a criterion for cessation of gamma ray emission in voltage-P space, such that empirically pulsars should stop being gamma ray emitters when the total spindown luminosity falls to ~2x10^32^ergs/sec. A simple result of the same form as the empirical gamma ray emission efficency is derived for the acceleration efficiency of particle beams extracted from the polar cap, and for high voltage pulsars, where curvature radiation reaction is important, equated to the gamma ray efficiency. However, it is also argued that since radio emission from the polar caps continues to lower voltages and spin down luminosities than inferred for the gamma ray emission, that this correspondence is a coincidence and that the EGRET gamma rays come from the outer magnetosphere. The most popular of outer magnetosphere models are shown to be unable to simultanously account for gamma ray efficiencies approaching unity and having most of the gamma ray luminosity in sharp pulses, suggesting that the gamma ray emission has something to do with dense return current boundary layers whose physics has yet to be quantified.

Arons, J.

1996-11-01

151

GRB 090313 and the Origin of Optical Peaks in Gamma-ray Burst Light Curves: Implications for Lorentz Factors and Radio Flares  

NASA Astrophysics Data System (ADS)

We use a sample of 19 gamma-ray bursts (GRBs) that exhibit single-peaked optical light curves to test the standard fireball model by investigating the relationship between the time of the onset of the afterglow and the temporal rising index. Our sample includes GRBs and X-ray flashes for which we derive a wide range of initial Lorentz factors (40 < ? < 450). Using plausible model parameters, the typical frequency of the forward shock is expected to lie close to the optical band; within this low typical frequency framework, we use the optical data to constrain epsilon e and show that values derived from the early time light-curve properties are consistent with published typical values derived from other afterglow studies. We produce expected radio light curves by predicting the temporal evolution of the expected radio emission from forward and reverse shock components, including synchrotron self-absorption effects at early time. Although a number of GRBs in this sample do not have published radio measurements, we demonstrate the effectiveness of this method in the case of Swift GRB 090313, for which millimetric and centimetric observations were available, and conclude that future detections of reverse-shock radio flares with new radio facilities such as the EVLA and ALMA will test the low-frequency model and provide constraints on magnetic models.

Melandri, A.; Kobayashi, S.; Mundell, C. G.; Guidorzi, C.; de Ugarte Postigo, A.; Pooley, G.; Yoshida, M.; Bersier, D.; Castro-Tirado, A. J.; Jelínek, M.; Gomboc, A.; Gorosabel, J.; Kubánek, P.; Bremer, M.; Winters, J. M.; Steele, I. A.; de Gregorio-Monsalvo, I.; Smith, R. J.; García-Appadoo, D.; Sota, A.; Lundgren, A.

2010-11-01

152

Planar imaging quantification using 3D attenuation correction data and Monte Carlo simulated buildup factors.  

PubMed

A new method to correct for attenuation and the buildup of scatter in planar imaging quantification is presented. The method is based on the combined use of 3D density information provided by computed tomography to correct for attenuation and the application of Monte Carlo simulated buildup factors to correct for buildup in the projection pixels. CT and nuclear medicine images were obtained for a purpose-built nonhomogeneous phantom that models the human anatomy in the thoracic and abdominal regions. The CT transverse slices of the phantom were converted to a set of consecutive density maps. An algorithm was developed that projects the 3D information contained in the set of density maps to create opposing pairs of accurate 2D correction maps that were subsequently applied to planar images acquired from a dual-head gamma camera. A comparison of results obtained by the new method and the geometric mean approach based on published techniques is presented for some of the source arrangements used. Excellent results were obtained for various source-phantom configurations used to evaluate the method. Activity quantification of a line source at most locations in the nonhomogeneous phantom produced errors of less than 2%. Additionally, knowledge of the actual source depth is not required for accurate activity quantification. Quantification of volume sources placed in foam, Perspex and aluminium produced errors of less than 7% for the abdominal and thoracic configurations of the phantom. PMID:8858727

Miller, C; Filipow, L; Jackson, S; Riauka, T

1996-08-01

153

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 1-10 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 possible launch in 2005, will provide a major advance in sensitivity, energy range, and sky coverage.

Thompson, David J.

2000-01-01

154

Jet Shockwaves Produce Gamma Rays  

NASA Video Gallery

Theorists believe that GRB jets produce gamma rays by two processes involving shock waves. Shells of material within the jet move at different speeds and collide, generating internal shock waves th...

155

Gamma-ray spectrometer experiment  

NASA Technical Reports Server (NTRS)

The experiments in gamma-ray spectrometry to determine the geochemical composition of the lunar surface are reported. The theory is discussed of discrete energy lines of natural radioactivity, and the lines resulting from the bombardment of the lunar surface by high energy cosmic rays. The gamma-ray spectrometer used in lunar orbit and during transearth coast is described, and a preliminary analysis of the results is presented.

Arnold, J. R.; Peterson, L. E.; Metzger, A. E.; Trombka, J. I.

1972-01-01

156

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

157

Protection of spermatogenesis against gamma ray-induced damage by granulocyte colony-stimulating factor in mice.  

PubMed

The radioprotective effects of granulocyte colony-stimulating factor (GCSF) were further investigated with respect to the testicular system. Recombinant human GCSF (100 ?g kg(-1) body weight/day) was administrated to male C3H/HeN mice by subcutaneous injection for three consecutive days before pelvic irradiation (5 Gy) and histopathological parameters were assessed at 12 h and 21 days post-irradiation (pi). The GCSF protected the germ cells from radiation induced- apoptosis (P < 0.01 vs. irradiated group at 12 h pi). GCSF remarkably attenuated radiation-induced reduction in testis weight, seminiferous tubular diameter, seminiferous epithelial depth and sperm head count in the testes (P < 0.05 versus irradiated group at 21 days pi). Repopulation index and stem cell survival index of the seminiferous tubules were increased in the GCSF-treated group when compared with the radiation group (P < 0.01). The frequency of abnormal sperm in the GCSF group was lower than that in the irradiated group at 21 days pi (P < 0.01). The decrease in the sperm count and in sperm liability in the epididymis caused by irradiation was counteracted by GCSF. The present study suggests that GCSF protects from radiation-induced testicular dysfunction via an anti-apoptotic effect and recovery of spermatogenesis. PMID:21382061

Kim, J; Lee, S; Jeon, B; Jang, W; Moon, C; Kim, S

2011-04-01

158

Neutrino bursts from gamma-ray bursts  

NASA Technical Reports Server (NTRS)

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

Paczynski, Bohdan; Xu, Guohong

1994-01-01

159

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

160

Terrestrial gamma-ray flashes  

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

161

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

162

Hard Gamma Ray Emission from the Starburst Galaxy NGC 253  

NASA Technical Reports Server (NTRS)

We have completed the study to search for hard gamma ray emission from the starburst galaxy NGC 253. Since supernovae are thought to provide the hard gamma ray emission from the Milky Way, starburst galaxies, with their extraordinarily high supernova rates, are prime targets to search for hard gamma ray emission. We conducted a careful search for hard gamma ray emission from NGC 253 using the archival data from the EGRET experiment aboard the CGRO. Because this starburst galaxy happens to lie near the South Galactic Pole, the Galactic gamma ray background is minimal. We found no significant hard gamma ray signal toward NGC 253, although a marginal signal of about 1.5 sigma was found. Because of the low Galactic background, we obtained a very sensitive upper limit to the emission of greater than 100 MeV gamma-rays of 8 x 10(exp -8) photons/sq cm s. Since we expected to detect hard gamma ray emission, we investigated the theory of gamma ray production in a dense molecular medium. We used a leaky-box model to simulate diffusive transport in a starburst region. Since starburst galaxies have high infrared radiation fields, we included the effects of self-Compton scattering, which are usually ignored. By modelling the expected gamma-ray and synchrotron spectra from NGC 253, we find that roughly 5 - 15% of the energy from supernovae is transferred to cosmic rays in the starburst. This result is consistent with supernova acceleration models, and is somewhat larger than the value derived for the Galaxy (3 - 10%). Our calculations match the EGRET and radio data very well with a supernova rate of 0.08/ yr, a magnetic field B approx. greater than 5 x 10(exp -5) G, a density n approx. less than 100/sq cm, a photon density U(sub ph) approx. 200 eV/sq cm, and an escape time scale tau(sub 0) approx. less than 10 Myr. The models also suggest that NGC 253 should be detectable with only a factor of 2 - 3 improvement in sensitivity. Our results are consistent with the standard picture of gamma-ray acceleration by supernovae.

Jackson, James M.; Marscher, Alan M.

1996-01-01

163

Gamma-ray pulsar model  

Microsoft Academic Search

Extremely high energy bursts of pulsed gamma-rays have recently been detected from several binary X-ray pulsars and young radio pulsars. It is proposed that curvature synchrotron radiation from electrons (accelerated along the open magnetic field lines) is a possible origin of this emission. The electric and magnetic fields in the present model are computed in the near zone (close to

Jeffrey M. Cohen; Errol Mustafa

1987-01-01

164

Diffuse galactic gamma ray lines  

NASA Technical Reports Server (NTRS)

The production rate of 4.44-MeV line for a variety of assumed cosmic ray spectra is evaluated. These results are compared with reported galactic gamma-ray line intensities and are consistent with a low energy cosmic ray density which increases toward the galactic center in proportion to the molecular gas density.

Lingenfelter, R. E.; Ramaty, R.

1977-01-01

165

The GRAD gamma ray spectrometer  

SciTech Connect

A gamma-ray spectrometer for an upcoming space shuttle mission is described. Consisting of a 150 cm/sup 3/ n-type germanium detector set inside active shielding of bismuth germanate and plastic scintillator, the instrument will be used in studies of the Orbiter background and the galactic center.

Rester, A.C.; Piercey, R.B.; Eichhorn, G.; Coldwell, R.L.; McKisson, J.M.; Ely, D.W.; Mann, H.M.; Jenkins, D.A.

1986-02-01

166

Gamma-ray camera flyby  

ScienceCinema

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

167

Gamma-ray camera flyby  

SciTech Connect

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

None

2010-01-01

168

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

169

Analytical expressions for the gate utilization factors of passive multiplicity counters including signal build-up  

SciTech Connect

In the realm of nuclear safeguards, passive neutron multiplicity counting using shift register pulse train analysis to nondestructively quantify Pu in product materials is a familiar and widely applied technique. The approach most commonly taken is to construct a neutron detector consisting of {sup 3}He filled cylindrical proportional counters embedded in a high density polyethylene moderator. Fast neutrons from the item enter the moderator and are quickly slowed down, on timescales of the order of 1-2 {micro}s, creating a thermal population which then persists typically for several 10's {micro}s and is sampled by the {sup 3}He detectors. Because the initial transient is of comparatively short duration it has been traditional to treat it as instantaneous and furthermore to approximate the subsequent capture time distribution as exponential in shape. With these approximations simple expressions for the various Gate Utilization Factors (GUFs) can be obtained. These factors represent the proportion of time correlated events i.e. Doubles and Triples signal present in the pulse train that is detected by the coincidence gate structure chosen (predelay and gate width settings of the multiplicity shift register). More complicated expressions can be derived by generalizing the capture time distribution to multiple time components or harmonics typically present in real systems. When it comes to applying passive neutron multiplicity methods to extremely intense (i.e. high emission rate and highly multiplying) neutron sources there is a drive to use detector types with very fast response characteristics in order to cope with the high rates. In addition to short pulse width, detectors with a short capture time profile are also desirable so that a short coincidence gate width can be set in order to reduce the chance or Accidental coincidence signal. In extreme cases, such as might be realized using boron loaded scintillators, the dieaway time may be so short that the build-up (thermalization transient) within the detector cannot be ignored. Another example where signal build-up might be observed is when a {sup 3}He based system is used to track the evolution of the time correlated signal created by a higher multiplying item within a reflective configuration such as the measurement of a spent fuel assembly. In this work we develop expressions for the GUFs which include signal build-up.

Croft, Stephen [Los Alamos National Laboratory; Evans, Louise G [Los Alamos National Laboratory; Schear, Melissa A [Los Alamos National Laboratory

2010-01-01

170

Continuous Energy gamma-Ray Spectrometry.  

National Technical Information Service (NTIS)

Compton recoil gamma-ray spectroscopy provides absolute measurements of continuous gamma-ray spectra. Peaks which possess sufficient intensity above the continuum level can be observed. Since the inception of this spectrometric method, this method has evo...

R. Gold B. J. Kaiser J. P. McNeece

1983-01-01

171

High Altitude Balloons and gamma Ray Astronomy.  

National Technical Information Service (NTIS)

The author's experience with scientific high altitude ballooning will be presented. Usefulness of satellite versus balloon platforms will be contrasted in the context of gamma ray astronomy. General principles of gamma ray astronomy instrumentation will b...

C. J. MacCallum

1988-01-01

172

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

173

New Fermi-LAT Event Reconstruction Reveals More High-energy Gamma Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Based on the experience gained during the four and a half years of the mission, the Fermi-LAT Collaboration has undertaken a comprehensive revision of the event-level analysis going under the name of Pass 8. Although it is not yet finalized, we can test the improvements in the new event reconstruction with the special case of the prompt phase of bright gamma-ray bursts (GRBs), where the signal-to-noise ratio is large enough that loose selection cuts are sufficient to identify gamma rays associated with the source. Using the new event reconstruction, we have re-analyzed 10 GRBs previously detected by the Large Area Telescope (LAT) for which an X-ray/optical follow-up was possible and found four new gamma rays with energies greater than 10 GeV in addition to the seven previously known. Among these four is a 27.4 GeV gamma ray from GRB 080916C, which has a redshift of 4.35, thus making it the gamma ray with the highest intrinsic energy (~147 GeV) detected from a GRB. We present here the salient aspects of the new event reconstruction and discuss the scientific implications of these new high-energy gamma rays, such as constraining extragalactic background light models, Lorentz invariance violation tests, the prompt emission mechanism, and the bulk Lorentz factor of the emitting region.

Atwood, W. B.; Baldini, L.; Bregeon, J.; Bruel, P.; Chekhtman, A.; Cohen-Tanugi, J.; Drlica-Wagner, A.; Granot, J.; Longo, F.; Omodei, N.; Pesce-Rollins, M.; Razzaque, S.; Rochester, L. S.; Sgrò, C.; Tinivella, M.; Usher, T. L.; Zimmer, S.

2013-09-01

174

NEW FERMI-LAT EVENT RECONSTRUCTION REVEALS MORE HIGH-ENERGY GAMMA RAYS FROM GAMMA-RAY BURSTS  

SciTech Connect

Based on the experience gained during the four and a half years of the mission, the Fermi-LAT Collaboration has undertaken a comprehensive revision of the event-level analysis going under the name of Pass 8. Although it is not yet finalized, we can test the improvements in the new event reconstruction with the special case of the prompt phase of bright gamma-ray bursts (GRBs), where the signal-to-noise ratio is large enough that loose selection cuts are sufficient to identify gamma rays associated with the source. Using the new event reconstruction, we have re-analyzed 10 GRBs previously detected by the Large Area Telescope (LAT) for which an X-ray/optical follow-up was possible and found four new gamma rays with energies greater than 10 GeV in addition to the seven previously known. Among these four is a 27.4 GeV gamma ray from GRB 080916C, which has a redshift of 4.35, thus making it the gamma ray with the highest intrinsic energy ({approx}147 GeV) detected from a GRB. We present here the salient aspects of the new event reconstruction and discuss the scientific implications of these new high-energy gamma rays, such as constraining extragalactic background light models, Lorentz invariance violation tests, the prompt emission mechanism, and the bulk Lorentz factor of the emitting region.

Atwood, W. B. [Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States); Baldini, L. [Universita di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy); Bregeon, J.; Pesce-Rollins, M.; Sgro, C.; Tinivella, M. [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy); Bruel, P. [Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS/IN2P3, Palaiseau (France); Chekhtman, A. [Center for Earth Observing and Space Research, College of Science, George Mason University, Fairfax, VA 22030 (United States); Cohen-Tanugi, J. [Laboratoire Univers et Particules de Montpellier, Universite Montpellier 2, CNRS/IN2P3, F-34095 Montpellier (France); Drlica-Wagner, A.; Omodei, N.; Rochester, L. S.; Usher, T. L. [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States); Granot, J. [Department of Natural Sciences, The Open University of Israel, 1 University Road, P.O. Box 808, Ra'anana 43537 (Israel); Longo, F. [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy); Razzaque, S. [Department of Physics, University of Johannesburg, Auckland Park 2006 (South Africa); Zimmer, S., E-mail: melissa.pesce.rollins@pi.infn.it, E-mail: nicola.omodei@stanford.edu, E-mail: granot@openu.ac.il [Department of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm (Sweden)

2013-09-01

175

Portable compton gamma-ray detection system  

SciTech Connect

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

176

Gamma-Ray Spectroscopy of 166Er  

Microsoft Academic Search

Relative intensities of gamma rays of 166Er from the decays of 166mHo were precisely measured with a calibrated Ge(Li) detector. Errors of relative gamma-ray intensities are about 0.5% for strong gamma rays. Angular correlations for 11 cascades were measured with Ge(Li) and NaI(T1) detectors. The B(E2) ratios were deduced from the relative gamma-ray intensities and the adopted values of the

Kazuo Kato; Masaharu Hoshi; Yasukazu Yoshizawa

1981-01-01

177

Gamma ray spectroscopy in astrophysics. [conferences  

NASA Technical Reports Server (NTRS)

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

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

1978-01-01

178

High altitude balloons and gamma ray astronomy  

Microsoft Academic Search

The author's experience with scientific high altitude ballooning will be presented. Usefulness of satellite versus balloon platforms will be contrasted in the context of gamma ray astronomy. General principles of gamma ray astronomy instrumentation will be discussed and illustrated in terms of our current instrument, the Gamma Ray Imaging Spectrometer (GRIS). Some words about the supernova phenomenon and its necessity

Crawford J. MacCallum

1988-01-01

179

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

180

Gamma Ray Spectroscopy of Mn54  

Microsoft Academic Search

Internal conversion electrons of 0.84 Mev gamma ray were measured by a two-directional focusing beta-ray spectrometer, and it was determined that Egamma{=}837.9± 0.3 kev and K\\/L+M{=}8.5± 0.7. Weak gamma rays were searched, using scintillation counters, but no gamma ray was observed.

Toshio Katoh; Masao Nozawa; Yasukazu Yoshizawa; Yujiro Koh

1958-01-01

181

Feasibility study of gamma-ray medical radiography.  

PubMed

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

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

2013-02-01

182

Compton Gamma Ray Observatory Guest Investigator Program  

NASA Technical Reports Server (NTRS)

This paper presents a final report for the Compton Gamma Ray Observatory Guest Investigator Program from 06/01/91-07/31/97. The topics include: 1) Solar Flare Neutron Spectra and Accelerated Ions; 2) Gamma Ray Lines From The Orion Complex; 3) Implications of Nuclear Line Emission From The Orion Complex; 4) Possible Sites of Nuclear Line Emission From Massive OB Associations; 5) Gamma-Ray Burst Repitition and BATSE Position Uncertainties; 6) Effects of Compton Scattering on BATSE Gamma-Ray Burst Spectra; and 7) Selection Biases on the Spectral and Temporal Distribution of Gamma Ray Bursts.

Lingenfelter, Richard E.

1997-01-01

183

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

184

Energy absorption buildup factors of human organs and tissues at energies and penetration depths relevant for radiotherapy and diagnostics.  

PubMed

Energy absorption geometric progression (GP) fitting parameters and the corresponding buildup factors have been computed for human organs and tissues, such as adipose tissue, blood (whole), cortical bone, brain (grey/white matter), breast tissue, eye lens, lung tissue, skeletal muscle, ovary, testis, soft tissue, and soft tissue (4-component), for the photon energy range 0.015-15 MeV and for penetration depths up to 40 mfp (mean free path). The chemical composition of human organs and tissues is seen to influence the energy absorption buildup factors. It is also found that the buildup factor of human organs and tissues changes significantly with the change of incident photon energy and effective atomic number, Z(eff). These changes are due to the dominance of different photon interaction processes in different energy regions and different chemical compositions of human organs and tissues. With the proper knowledge of buildup factors of human organs and tissues, energy absorption in the human body can be carefully controlled. The present results will help in estimating safe dose levels for radiotherapy patients and also useful in diagnostics and dosimetry. The tissue-equivalent materials for skeletal muscle, adipose tissue, cortical bone, and lung tissue are also discussed. It is observed that water and MS20 are good tissue equivalent materials for skeletal muscle in the extended energy range. PMID:22089011

Manohara, S R; Hanagodimath, S M; Gerward, L

2011-01-01

185

Pinhole imaging of gamma rays  

Microsoft Academic Search

An approximate calculation is made of the effective area of pinhole collimators allowing for penetration of the metal by gamma -rays of two energies (364 and 140 keV). The particular case of normally-incident rays is treated without approximation. At 364 keV the performance even of heavy alloy (90% tungsten) collimators is dominated by penetration. The effective radius may approach twice

D. Paix

1967-01-01

186

Which unidentified EGRET sources are gamma-ray pulsars?  

Microsoft Academic Search

We consider high energy gamma -ray radiation from the radio pulsars associated with some unidentified EGRET gamma -ray sources. Calculated efficiencies for the conversion of spin-down power to gamma -rays and the energy spectra of the high energy gamma -rays from these possible gamma -ray pulsars in outer gap models are compared with observed results. Of these possible gamma -ray

L. Zhang; K. S. Cheng

1998-01-01

187

Diffuse galactic gamma ray lines  

NASA Technical Reports Server (NTRS)

The origin and observability were studied of diffuse gamma ray line emission from the galaxy. It was found that such lines could be formed by nuclear excitation interactions of low energy cosmic rays with both interstellar gas and dust grains. The gamma ray emission lines from deexcitation of grain nuclei are sharp with Doppler widths of the order of 10 kev or less; the lines from gas nuclei are also relatively sharp with widths of the order of 100 kev for the most intense line; and the lines from cosmic ray nuclei are broad with widths of the order of several hundred kev. A detailed evaluation is presented of the production rate of the 4.44 Mev line for a variety of assumed cosmic ray spectra. Results are compared with reported galactic gamma ray line intensities and it is concluded that the measurements are consistent with a low energy cosmic ray density which increases toward the galactic center in proportion to the molecular gas density.

Lingenfelter, R. E.; Ramaty, R.

1976-01-01

188

Significance of medium energy gamma ray astronomy in the study of cosmic rays  

NASA Technical Reports Server (NTRS)

Medium energy (about 10 to 30 MeV) gamma ray astronomy provides information on the product of the galactic electron cosmic ray intensity and the galactic matter to which the electrons are dynamically coupled by the magnetic field. Because high energy (greater than 100 MeV) gamma ray astronomy provides analogous information for the nucleonic cosmic rays and the relevant matter, a comparison between high energy and medium energy gamma ray intensities provides a direct ratio of the cosmic ray electrons and nucleons throughout the galaxy. A calculation of gamma ray production by electron bremsstrahlung shows that: bremsstrahlung energy loss is probably not negligible over the lifetime of the electrons in the galaxy; and the approximate bremsstrahlung calculation often used previously overestimates the gamma ray intensity by about a factor of two. As a specific example, expected medium energy gamma ray intensities are calculated for the speral arm model.

Fichtel, C. E.; Kniffen, D. A.; Thompson, D. J.; Bignami, G. F.; Cheung, C. Y.

1975-01-01

189

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

190

Quasars, blazars, and gamma rays  

NASA Technical Reports Server (NTRS)

The paper discusses the extragalactic sources that have been discovered with the Energetic Gamma Ray Experiment Telescope. All of the sources demonstrate evidence of blazar properties at other wavelengths, including high optical polarization, extreme optical variability, flat-spectrum radio emission associated with a compact core, and apparent superluminal motion. These properties are believed to be produced by those few rare extragalactic quasars and radio galaxies that are favorably aligned to make it possible to observe almost directly down a relativistically outflowing jet of matter expelled from a supermassive black hole.

Dermer, Charles D.; Schlickeiser, Reinhard

1992-01-01

191

Gamma-ray pulsar studies with COMPTEL  

Microsoft Academic Search

Since the launch of the Compton Gamma-Ray Observatory (CGRO) the number of detected gamma-ray pulsars increased from two to six. COMPTEL, on-board CGRO and sensitive to gamma-rays with energies between approximately 0.7 and 30 MeV, detected three of these unambiguously. The classical Crab and Vela pulsars have been observed on several occasions and detailed pulse patterns and spectral parameters have

W. Hermsen; L. Kuiper; R. Diehl; G. Lichti; V. Schoenfelder; A. W. Strong; A. Connors; J. Ryan; K. Bennett; M. Busetta; A. Carraminana; R. Buccheri; I. A. Grenier

1994-01-01

192

Gamma-Ray Pulsar Studies with GLAST  

Microsoft Academic Search

Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests

D. J. Thompson; GAMMA-RAY PULSARS

2008-01-01

193

Gamma-Ray Pulsar Studies with GLAST  

NASA Technical Reports Server (NTRS)

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

Thompson, David J.

2007-01-01

194

Gamma-Ray Pulsar Candidates for GLAST  

Microsoft Academic Search

The Gamma-ray Large Area Space Telescope (GLAST) will be launched less than a year from now, and its Large Area Telescope (LAT) is expected to discover scores to hundreds of gamma-ray pulsars. This poster discusses which of the over 1700 known pulsars, mostly visible only at radio frequencies, are likely to emit >100 MeV gamma rays with intensities detectable by

David J. Thompson; D. A. Smith; D. Dumora; L. Guillemot; D. Parent; T. Reposeur; J. E. Grove; R. W. Romani; S. E. Thorsett

2006-01-01

195

Gamma-Ray Pulsar Candidates for GLAST  

Microsoft Academic Search

The Gamma-ray Large Area Space Telescope (GLAST) will be launched this year, and its Large Area Telescope (LAT) is expected to discover scores to hundreds of gamma-ray pulsars. This poster discusses which of the over 1700 known pulsars, mostly visible only at radio frequencies, are likely to emit >100; MeV gamma rays with intensities detectable by the LAT. The main

David John Thompson

2008-01-01

196

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

197

Very High Energy Gamma-Ray Astronomy  

Microsoft Academic Search

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

Michael Catanese; Trevor C. Weekes

1999-01-01

198

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

199

Astrophysical constraints from gamma-ray spectroscopy  

Microsoft Academic Search

Gamma-ray lines from cosmic sources provide unique isotopic information, since they originate from energy level transitions in the atomic nucleus. Gamma-ray telescopes explored this astronomical window in the past three decades, detecting radioactive isotopes that have been ejected in interstellar space by cosmic nucleosynthesis events and nuclei that have been excited through collisions with energetic particles. Astronomical gamma-ray telescopes feature

Roland Diehl; Nikos Prantzos; Peter von Ballmoos

2006-01-01

200

Non-association of a celestial gamma ray source with the new Milky Way satellite galaxy  

NASA Technical Reports Server (NTRS)

The newly discovered satellite galaxy located in the Milky Way galactic anti-center region is discussed along with the possibility that a nearby gamma ray source is associated with it. The factors which led to the conclusion that the gamma ray excess is not associated with the galaxy are considered.

Lamb, R. C.; Thompson, D. J.; Fichtel, C. E.

1975-01-01

201

Radon emanation and soil moisture effects on airborne gamma-ray measurements  

SciTech Connect

A theoretical model is developed to explain variations in airborne gamma-ray measurements over a calibration range near Ottawa, Ontario. The gamma-ray flux from potassium and the thorium decay series showed an expected decrease with increasing soil moisture. However, the gamma-ray flux from the uranium decay series was highest in the spring when the ground was water-saturated and even covered with snow. These results are explained through the build-up of radon and its associated gamma-ray-emitting decay products in the clay soil of the calibration range with increasing soil moisture. Similar results were found from airborne measurements over other clay soils. However, measurements over sandy soils showed that the count rates from all three radio elements increased with decreasing soil moisture. This difference between soil types was attributed to the lower radon emanation of the more coarse-grained sandy soils compared to finer-grained clay soils. The theoretical and experimental results demonstrate that any estimate of the natural gamma-ray field caused by radium in the ground must take into consideration the radon emanation coefficient of the soil. The radon diffusion coefficient of the soil must also be considered since it depends strongly on soil moisture. This has significant implications for the assessment of outdoor radiation doses using laboratory analyses of soil samples and the use of ground and airborne gamma-ray measurements for radon potential mapping.

Grasty, R.L. [Geological Survey of Canada, Ottawa, Ontario (Canada)] [Geological Survey of Canada, Ottawa, Ontario (Canada)

1997-09-01

202

GRETINA: A gamma ray energy tracking array  

NASA Astrophysics Data System (ADS)

A gamma-ray energy tracking array (GRETA) is a new concept for the detection of gamma radiation. In such an array, the individual interactions of all the gamma rays are identified by their energies and positions. Then, using tracking algorithms based on the properties of gamma ray interactions, the scattering sequences are reconstructed. GRETA will give high peak efficiency, peak-to-background ratio, and position resolution. Recent research and development efforts have demonstrated that the construction of a gamma ray tracking array is feasible, and a plan for constructing a US array GRETINA is in place.

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

2004-12-01

203

BATSE observations of gamma-ray bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are being detected with unprecedented sensitivity by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray observatory since its launch in April, 1991. The experiment is detecting about one gamma-ray burst per day. A brief description is presented of the on-orbit performance of BATSE, the methods of identification of bursts, and examples of the diverse time profiles of the gamma-ray bursts observed. The most significant finding thus far is the apparent isotropy of the bursts together with the observed inhomogeneity of the sources.

Fishman, G. J.; Meegan, C. A.; Wilson, R. B.; Horack, J. M.; Brock, M. N.; Paciesas, W. S.; Pendleton, G. N.; Kouveliotou, C.

1991-09-01

204

BATSE observations of gamma-ray bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are being detected with unprecedented sensitivity by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory since its launch in April, 1991. The experiment is detecting about one gamma-ray burst per day. A brief description is presented of the on-orbit performance of BATSE, the methods of identification of bursts, and examples of the diverse time profiles of the gamma-ray bursts observed. The most significant finding thus far is the apparent isotropy of the bursts together with the observed inhomogeneity of the sources.

Fishman, Gerald J.; Meegan, C. A.; Wilson, R. B.; Horack, J. M.; Brock, M. N.; Paciesas, William S.; Pendleton, G. N.; Kouveliotou, C.

205

Radio Observations of Gamma-ray Novae  

NASA Astrophysics Data System (ADS)

Recent detection of gamma-ray emission from classical novae by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope surprised many in the astronomical community. We present results from radio observations, obtained using the Karl G. Jansky Very Large Array (VLA), of three gamma-ray novae: Mon2012, Sco2012, and Del2013. Radio observations allow for the calculation of ejecta masses, place limits on the distances, and provide information about the gamma-ray emission mechanism for these sources.

Linford, Justin D.; Chomiuk, L.; Ribeiro, V.; project, E.-Nova

2014-01-01

206

Low-level gamma-ray spectrometry  

SciTech Connect

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

Brodzinski, R.L.

1990-10-01

207

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

208

Gamma-ray burst populations  

NASA Astrophysics Data System (ADS)

Over the last fifty years the field of gamma-ray bursts has shown incredible growth, but the amassing of data has also left observers and theorists alike wondering about some of the basic questions surrounding these phenomena. Additionally, these events show remarkable individuality and extrema, ranging in redshift throughout the observable universe and over ten orders of magnitude in energy. This work focuses on analyzing groups of bursts that are different from the general trend and trying to understand whether these bursts are from different intrinsic populations and if so, what can be said about their progenitors. This is achieved through numerical Monte Carlo simulations and statistical inference in conjunction with current GRB observations. Chapter 1 gives a general introduction of gamma-ray burst theory and observations in a semi-historical context. Chapter 2 provides an introduction to the theory and practical issues surrounding the numerical simulations and statistics. Chapters 3--5 are each dedicated to a specific problem relating to a different type of GRB population: high-luminosity v. low-luminosity bursts, constraints from high-redshift bursts, and Type I v. Type II bursts. Chapter 6 follows with concluding remarks.

Virgili, Francisco Javier

209

Solar abundances from gamma-ray spectroscopy  

NASA Technical Reports Server (NTRS)

Determinations of solar abundances from gamma-ray line observations are reviewed. The principal results are: (1) in flare loops, at atmospheric heights betwen the transition region and the upper photosphere, the Mg/O ratio is higher by about a factor of 3 than in the photosphere, while the C/O ratio is essentially photospheric; (2) in the same region, the Ne/O ratio is higher by about a factor of 3 than the Ne/O ratio in the corona; (3) the photospheric He-3/H ratio is less than 0.000035. These results, combined with other data, suggest abundance variations in the solar atmosphere, possibly resulting from charge and mass dependent transport.

Ramaty, R.

1989-01-01

210

Investigation of human teeth with respect to the photon interaction, energy absorption and buildup factor  

NASA Astrophysics Data System (ADS)

The effective atomic numbers and electron densities of human teeth have been calculated for total photon interaction (Z, Ne) and photon energy absorption (Z, Z Ne) in the energy region 1 keV-20 MeV. Besides, the energy absorption (EABF) and exposure (EBF) buildup factors have been calculated for these samples by using the geometric progression fitting approximation in the energy region 0.015-15 MeV up to 40 mfp (mean free path). Wherever possible the results were compared with experiment. Effective atomic numbers ( Z) of human teeth were calculated using different methods. Discrepancies were noted in Z between the direct and interpolation methods in the low and high energy regions where absorption processes dominate while good agreement was observed in intermediate energy region where Compton scattering dominates. Significant variations up to 22% were observed between Z and Z in the energy region 30-150 keV which is the used energy range in dental cone beam computed tomography (CBCT) X-ray machines. The Zeff values of human teeth were found to relatively vary within 1% if different laser treatments are applied. In this variation, the Er:YAG laser treated samples were found to be less effected than Nd:YAG laser treated ones when compared with control group. Relative differences between EABF and EBF were found to be significantly high in the energy region 60 keV-1 MeV even though they have similar variations with respect to the different parameters viz. photon energy, penetration depth.

Kurudirek, Murat; Topcuoglu, Sinan

2011-05-01

211

Possible Detection of Gamma Ray Air Showers in Coincidence with BATSE Gamma Ray Bursts  

Microsoft Academic Search

Project GRAND presents the results of a search for coincident high-energy gamma ray events in the direction and at the time of nine Gamma Ray Bursts (GRBs) detected by BATSE. A gamma ray has a non-negligible hadron production cross section; for each gamma ray of energy of 100 GeV, there are 0.015 muons which reach detection level (Fasso & Poirier,

T. F. Lin; J. Carpenter; S. Desch; J. Gress; J. Poirier; A. Roesch

2000-01-01

212

Possible Detection of Gamma Ray Air Showers in Coincidence with BATSE Gamma Ray Bursts  

Microsoft Academic Search

Project GRAND presents the results of a search for coincident high-energy gamma ray events in the direction and at the time of nine Gamma Ray Bursts (GRBs) detected by BATSE. A gamma ray has a non-negligible hadron production cross section; for each gamma ray of energy of 100 GeV, there are 0.015 muons which reach detection level (Fasso & Poirier,

Tzu-Fen Lin

1999-01-01

213

Gamma rays in a spectrum from the Mars Odyssey gamma-ray spectrometer.  

NASA Astrophysics Data System (ADS)

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. Many gamma rays from Mars are present.

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

2003-04-01

214

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

215

Cloaked Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

It is suggested that many gamma-ray bursts (GRBs) are cloaked by an ultrarelativistic baryonic shell that has high optical depth when the photons are manufactured. Such a shell would not fully block photons reflected or emitted from its inner surface, because the radial velocity of the photons can be less than that of the shell. This avoids the standard problem associated with GRBs that the thermal component should be produced where the flow is still obscured by high optical depth. The radiation that escapes high optical depth obeys the Amati relation. Observational implications may include (1) anomalously high ratios of afterglow to prompt emission, such as may have been the case in the recently discovered PTF 11agg, and (2) ultrahigh-energy neutrino pulses that are non-coincident with detectable GRB. It is suggested that GRB 090510, a short, very hard GRB with very little afterglow, was an exposed GRB, in contrast to those cloaked by baryonic shells.

Eichler, David

2014-06-01

216

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, M.

1993-01-01

217

Gamma-Ray Pulsar Candidates for GLAST  

NASA Technical Reports Server (NTRS)

The Gamma-ray Large Area Space Telescope (GLAST) will be launched less than a year from now, and its Large Area Telescope (LAT) is expected to discover scores to hundreds of gamma-ray pulsars. This poster discusses which of the over 1700 known pulsars, mostly visible only at radio Erequencies, are likely to emit greater than l00 MeV gamma rays with intensities detectable by the LAT. The main figure of merit used to select gamma-ray pulsar candidates is sqrt(E-dot)/d^2, where E-dot is the energy loss due to rotational spindown, and d is the distance to the pulsar. The figure of merit incorporates spin-down flux at earth (proportional to E-dot/d^2) times efficiency, assumed proportional to 1/sqrt(E-dot). A few individual objects are cited to illustrate the issues. Since large E-dot pulsars also tend to have large timing noise and occasional glitches, their ephemerides can become inaccurate in weeks to months. To detect and study the gamma-ray emission the photons must be accurately tagged with the pulse phase. With hours to days between gamma-ray photon arrival times from a pulsar and months to years of LAT exposure needed for good detections, GLAST will need timing measurements throughout the continuous gamma-ray observations. The poster will describe efforts to coordinate pulsar timing of the candidate gamma-ray pulsars.

Thompson, David J.; Smith, D. A.; Dumora, D.; Guillemot, L.; Parent, D.; Reposeur, T.; Grove, E.; Romani, R. W.; Thorsett, S. E.

2007-01-01

218

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

219

Fermi Gamma-Ray Space Telescope.  

National Technical Information Service (NTIS)

The nonthermal nature of high-energy gamma-ray emission almost assures that gamma-ray sources will be radio sources. The VLBA/Fermi cooperative effort has already produced some excellent science, and more is anticipated from ongoing programs. The Fermi Gu...

D. Thompson J. McEnery

2011-01-01

220

Gamma-Ray Pulsar Candidates for GLAST  

NASA Technical Reports Server (NTRS)

The Gamma-ray Large Area Space Telescope (GLAST) will be launched this year, and its Large Area Telescope (LAT) is expected to discover scores to hundreds of gamma-ray pulsars. This poster discusses which of the over 1700 known pulsars, mostly visible only at radio frequencies, are likely to emit greater than 100 MeV gamma rays with intensities detectable by the LAT. The main figure of merit used to select gamma-ray pulsar candidates is sqrt(E-dot)/d2, where E-dot is the energy loss due to rotational spin-down, and d is the distance to the pulsar. The figure of merit incorporates spin-down flux at earth (proportional to E-dot/d2) times efficiency, assumed proportional to l/sqrt(E-dot). A few individual objects are cited to illustrate the issues. Since large E-dot pulsars also tend to have large timing noise and occasional glitches, their ephemerides can become inaccurate in weeks to months. To detect and study the gamma-ray emission the photons must be accurately tagged with the pulse phase. With hours to days between gamma-ray photon arrival times from a pulsar and months to years of LAT exposure needed for good detections, GLAST will rely on radio and X-ray timing measurements throughout the continuous gamma-ray observations. The poster will describe efforts to coordinate pulsar timing of the candidate gamma-ray pulsars.

Thompson, D. J.

2008-01-01

221

Gamma-ray emission from slow pulsars  

Microsoft Academic Search

The gamma-ray flux to be expected from three slow pulsars is calculated, neglecting the problem of the reliability of the observations. The principal hypothesis here is that since the gamma-ray luminosity is a substantial fraction of the intrinsic energy loss, it should be produced in the vicinity of the speed of light radius. This is from the argument of simultaneous

M. Morini; A. Treves

1981-01-01

222

Gamma-Ray Astronomy Technology Needs.  

National Technical Information Service (NTIS)

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 astrophys...

J. K. Cannizzo N. Gehrels

2012-01-01

223

GAMMA-RAY SPECTROSCOPY IN WELL LOGGING  

Microsoft Academic Search

Thermal neutron capture gamma rays have been observed in boreholes ; drilled in shales, sandstones, and limestones. A capsuled source of neutrons and ; a scintillation crystal detector, connected through 5,000 ft of logging cable to ; a transistorized, multichannel, pulse-height analyzer, were used. Resolved peaks ; were identified on the basis of the known energies of expected gamma rays

Richard L. Caldwell; W. F. Baldwin; J. D. Bargainer; J. E. Berry; G. N. Salaita; R. W. Sloan

1963-01-01

224

SIMULATE Program: a gamma ray spectroscopy tool  

Microsoft Academic Search

A software package which simulates the virtual creation of gamma ray spectra emitted from a combination of radioactive sources, as seen by a semiconductor or scintillation detector, is presented . It partially utilizes Monte Carlo techniques based on the physics of gamma ray spectroscopy. In addition, certain algorithms are used to compensate for the premature termination of the fate of

C. A Kalfas; E. Tsoulou

2003-01-01

225

Neutron Capture gamma-Ray Facility.  

National Technical Information Service (NTIS)

A neutron capture gamma-ray facility was constructed for prompt gamma-ray spectrometry, and its characteristics were measured. In the facility, a neutron beam is extracted from the H-6 horizontal experimental hole of Japan Research Reactor No.3, JAERI, an...

T. Tojo C. Yonezawa S. Koura S. Arai T. Komori

1980-01-01

226

Atmospheric gamma-ray and neutron flashes  

SciTech Connect

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

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

2008-01-15

227

Instrumentation for gamma-ray astronomy  

NASA Astrophysics Data System (ADS)

The current status of gamma-ray-telescope technology for ground, airborne, and space observations is surveyed and illustrated with drawings, diagrams, and graphs and tables of typical data. For the low- and medium-energy ranges, consideration is given to detectors and detector cooling systems, background-rejection methods, radiation damage, large-area detectors, gamma-ray imaging, data analysis, and the Compton-interaction region. Also discussed are the gamma-ray interaction process at high energies; multilevel automated spark-chamber gamma-ray telescopes; the Soviet Gamma-1 telescope; the EGRET instrument for the NASA Gamma-Ray Observatory; and Cerenkov, air-shower, and particle-detector instruments for the TeV and PeV ranges. Significant improvements in resolution and sensitivity are predicted for the near future.

Bertsch, David L.; Fichtel, Carl E.; Trombka, Jacob I.

1988-03-01

228

Instrumentation for gamma-ray astronomy  

NASA Technical Reports Server (NTRS)

The current status of gamma-ray-telescope technology for ground, airborne, and space observations is surveyed and illustrated with drawings, diagrams, and graphs and tables of typical data. For the low- and medium-energy ranges, consideration is given to detectors and detector cooling systems, background-rejection methods, radiation damage, large-area detectors, gamma-ray imaging, data analysis, and the Compton-interaction region. Also discussed are the gamma-ray interaction process at high energies; multilevel automated spark-chamber gamma-ray telescopes; the Soviet Gamma-1 telescope; the EGRET instrument for the NASA Gamma-Ray Observatory; and Cerenkov, air-shower, and particle-detector instruments for the TeV and PeV ranges. Significant improvements in resolution and sensitivity are predicted for the near future.

Bertsch, David L.; Fichtel, Carl E.; Trombka, Jacob I.

1988-01-01

229

A comprehensive study on energy absorption and exposure buildup factors for some essential amino acids, fatty acids and carbohydrates in the energy range 0.015-15 MeV up to 40 mean free path  

NASA Astrophysics Data System (ADS)

The gamma ray energy absorption ( EABF) and exposure buildup factors ( EBF) have been calculated for some essential amino acids, fatty acids and carbohydrates in the energy region 0.015-15 MeV up to a penetration depth of 40 mfp (mean free path). The five parameter geometric progression (G-P) fitting approximation has been used to calculate both EABF and EBF. Variations of EABF and EBF with incident photon energy, penetration depth and weight fraction of elements have been studied. While the significant variations in EABF and EBF for amino acids and fatty acids have been observed at the intermediate energy region where Compton scattering is the main photon interaction process, the values of EABF and EBF appear to be almost the same for all carbohydrates in the continuous energy region. It has been observed that the fatty acids have the largest EABF and EBF at 0.08 and 0.1 MeV, respectively, whereas the maximum values of EABF and EBF have been observed for aminoacids and carbohydrates at 0.1 MeV. At the fixed energy of 1.5 MeV, the variation of EABF with penetration depth appears to be independent of the variations in chemical composition of the amino acids, fatty acids and carbohydrates. Significant variations were also observed between EABF and EBF which may be due to the variations in chemical composition of the given materials.

Kurudirek, Murat; Özdemir, Yüksel

2011-01-01

230

The Build-up of Opacity in Impulsive Relativistic Sources  

NASA Astrophysics Data System (ADS)

Opacity effects in relativistic sources of high-energy gamma-rays, such as gamma-ray bursts (GRBs) or Blazars, can probe the Lorentz factor of the outflow as well as the distance of the emission site from the source, and thus help constrain the composition of the outflow (protons, pairs, magnetic field) and the emission mechanism. The attenuation of high energy photons will be probed by the Large Area Telescope (LAT) onboard the Gamma ray Large Area Space Telescope (GLAST), the next generation gamma-ray observatory to be launched in late 2007. While most previous works consider the opacity in steady state, we study here the time dependence of the opacity to pair production (?? ? e+e-), which may be especially relevant for impulsive relativistic sources, such as flares in Blazars or the prompt emission and flares in GRBs. We present a simple, yet rich, semi-analytic model that describes the build-up of the (target) photon field, and derive the time and energy dependence of the optical depth ?_{??}. Our model features a thin spherical shell that expands ultra-relativistically and emits isotropically in its own rest frame over a finite range of radii (R_0 ? R ? R_0 + ? R). We find that in an impulsive source (? R ? R_0), while the instantaneous spectrum has an exponential cutoff above the photon energy ?_1(t) where ?_{??}(?_1) = 1, the time integrated spectrum has a power-law high-energy tail above the photon energy ?_{1*} ˜ ?_1(? t) where ? t is the duration of the emission episode. Furthermore, photons with energies ? > ?_{1*} are expected to arrive mainly near the onset of the spike in the light curve or flare, which corresponds to the short emission episode. This arises since in such impulsive sources it takes time to build-up the (target) photon field, and thus the optical depth initially increases with time and ?_1(t) correspondingly decreases with time, so that photons of energy ? > ?_{1*} are able to escape the source mainly very early on while ?_1(t) > ?. As the source approaches a quasi-steady state (? R ? R_0), the time integrated spectrum develops an exponential cutoff, while the power-law tail becomes increasingly suppressed.

Cohen-Tanugi, Johann; Granot, Jonathan; Silva, Eduardo Do Couto E.

231

Search for Gamma-rays from Lightest Kaluza-Klein ParticleDark Matter with GLAST  

SciTech Connect

The Gamma-Ray Large Area Space Telescope (GLAST), scheduled to be launched in 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT), GLAST main instrument, has a wide field of view (> 2 sr), a large effective area and a 20 MeV-300 GeV energy range. It provides excellent high-energy gamma-ray observations for Dark-Matter searches. Here we study the possibility to detect gamma-rays coming from Lightest Kaluza-Klein Particle (LKP) annihilations in the context of the minimal Universal Extra Dimensions (UED) models. We perform the analysis for different LKP masses and for a Galactic Center (GC) Navarro, Frenk and White (NFW) halo model modified by a boost factor parameter. Finally we give an estimate of the background to obtain the expected total gamma-ray flux and the corresponding expected GLAST sensitivity.

Nuss, E.; Cohen-Tanugi, J.; Lionetto, A.; /Montpellier U. /SLAC /Rome U.,Tor Vergata

2006-05-16

232

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

NASA Astrophysics Data System (ADS)

Factors that influence the fidelity of gamma-ray TREE testing are investigated. Specifically, package-induced dose enhancement in 256K CMOS static-random-access-memories (SRAMs) and dose enhancement from finite-range electrons produced (by gamma-ray interactions) in materials external to the SRAM packages are studied. Two gamma-ray simulators with significantly different spectra are 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.

1990-12-01

233

Gamma-Ray Spectral Calculations for Uranium Borehole Logging.  

National Technical Information Service (NTIS)

Gamma-ray transport calculations were performed to determine the energy distribution of gamma rays inside a borehole introduced into an infinite medium. The gamma rays from the naturally occurring radioactive isotopes of potassium, thorium, and uranium we...

D. A. Close M. L. Evans M. Jain

1980-01-01

234

Exposure buildup factors for bakelite, perspex and magnox-A12 up to 40 m.f.p. using the interpolation method  

Microsoft Academic Search

The Geometric Progression (G-P) fitting parameters have been computed with respect to the equivalent atomic number for the composite materials of bakelite and perspex by the interpolation method. These parameters are then used to generate the exposure buildup factors up to 40 m.f.p. in the energy range of 0.015-15.0 MeV for these materials. The behaviour of buildup factors is shown

G. S. Brar; Apjit Kaur Sandhu; Makhan Singh; Gurmel S. Mudahar

1994-01-01

235

An imaging neutron/gamma-ray spectrometer  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

236

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

237

gamma. -ray diagnostic for the CIT  

SciTech Connect

We have examined the feasibility of a fusion ..gamma..-ray diagnostic for the Compact Ignition Tokamak (CIT), which is expected to produce 10/sup 20/ (d, t) fusion reactions per second. Gamma rays at 16.7 MeV are produced by the t(d, ..gamma..)He/sup 5/ fusion reaction. A Monte Carlo coupled neutron--photon transport code is used to model the expected ..gamma..-ray spectrum incident upon a Compton spectrometer backed by a Cerenkov detector. The results indicate that a signal of approx.3 x 10/sup 4/ counts/s and a signal-to-noise ratio of approx.30 can be achieved.

Petrasso, R.D.; Fiore, C.L.; Li, C.

1988-08-01

238

GRETA - Gamma Ray Energy Tracking Array  

NASA Astrophysics Data System (ADS)

Gamma ray energy tracking is a new concept for detecting gamma rays. It can be implemented as a 4? array of highly segmented Ge detector, which would advance detection sensitivity by three orders of magnitude in certain applications. Such an array will provide tremendous discovery potential at current stable and exotic beam facilities, as well as at future facilities. The development of a tracking array for nuclear structure physics has brought together scientists from different areas. Technical advances made in the last 5 years have demonstrated that the construction of a gamma ray energy-tracking array is feasible, and a plan for constructing a US array is in place.

Lee, I.-Yang

2003-03-01

239

NEAR Gamma Ray Spectrometer Characterization and Repair  

NASA Technical Reports Server (NTRS)

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

Groves, Joel Lee; Vajda, Stefan

1998-01-01

240

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

241

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

242

Gamma-Ray Spectroscopy of 42K  

Microsoft Academic Search

Decay of 42K was investigated by a Ge(Li) detector and a 5''phi× 4'' NaI scintillation counter. Two gamma-ray peaks were newly observed at 0.692 and 1.228 MeV in the gamma-gamma coincidence spectrum. The 0.587 MeV gamma-ray, previously reported by McCullen et al., could not be seen and the upper limit of the intensity of this gamma-ray relative to the 0.900

Kiyoshi Kawade; Hiroshi Yamamoto; Kanzo Yoshikawa; Katsuyuki Iizawa; Isao Kitamura; Susumu Amemiya; Toshio Katoh; Yasukazu Yoshizawa

1970-01-01

243

The AGILE gamma ray satellite  

NASA Astrophysics Data System (ADS)

AGILE (Light Imager for Gamma-ray Astrophysics) will be launched on an equatorial orbit in 2007 by the PSLV Indian launcher. It is a small scientific satellite for the detection of ?-ray cosmic sources in the energy range 50 MeV 30 GeV with a field of view of 15 of the sky, and will become the only detector in that energy range till the launch of GLAST. Three different detectors and an anticoincidence system are the components of the scientific instrument. The main detector is a silicon tungsten tracker. The second detector is a X-ray detector in the range 15 45 keV; its main aim is to highlight the X-ray emission associated to the gamma emissions. The third detector is a small calorimeter made of 30 CsI scintillating bars read out by photodiodes; its energy range is 150 300 keV. The large number of channels (about 37 000, with analog read out), requires very reliable components. Each part of the instrument has undergone several tests during the assembly phase; then the whole instrument has been calibrated on a dedicated photon tagged beam-line developed at the DAPHNE BTF (Beam Test Facility, INFN Frascati) and has been integrated with the satellite.

Basset, M.; AGILE Team

2007-03-01

244

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

245

Cosmological Evolution and Distributions of Gamma-ray Bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray Bursts (GRBs), in virtue of their large redshifts are good candidates for the probe of the early universe, in particular the history of star formation and the build-up of the so-called metalicity. Moreover, discovery of a tight relation between a distance independent property (e.g photon energy or timescale) and a distance dependent one (e.g luminosity or emitted power) will allow one to use GRBs as "standard candles" for measurements of the global cosmological parameters. The achievement of these potentials requires determination of the distributions and cosmological evolutions of the relevant characteristics and the correlations between them. We have applied the non-parametric methods developed by Efron and Petrosian to GRB data from Swift and earlier satellites to determine the cosmological evolutions of the gamma-ray and X-ray luminosities, timescales and their formation rate. We also have determined the correlations between some of these quantities to test the possibility of using GRBs as standard candles. The results using the most current data will be presented. This work is done in collaboration with M. Dainotti, E. Kitanidis and D. Kocevski all at Stanford University.

Petrosian, Vahe

2012-07-01

246

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

247

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, M.; Grove, J.; Chekhtman, A.; Xiong, S.; Fitzpatrick, G.; Cummer, S. A.; Holzworth, R. H.

2013-12-01

248

Gamma-Ray Heating in Power Reactors.  

National Technical Information Service (NTIS)

The objective of this work is to examine gamma ray heating in commercial nuclear power reactors. Design methods, computer codes, data libraries, and experimental data are examined. Some recommendations are made as to extensions of existing methods and cod...

A. P. Olson

1976-01-01

249

Gamma-Ray Pulsar Studies With GLAST  

SciTech Connect

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

Thompson, D.J.; /NASA, Goddard

2011-11-23

250

Gamma-Ray Burst Smashes a Record  

NSF Publications Database

... the most distant explosion ever seen The Birth of a Gamma-Ray Burst: one scenario Credit and ... via e-mail, Web sites and cell phone. One of the first groups to respond was Reichart's team from ...

251

Positron annihilation gamma rays from novae  

NASA Technical Reports Server (NTRS)

The potential for observing annihilation gamma rays from novae is investigated. These gamma rays, a unique signature of the thermonuclear runaway models of novae, would result from the annihilation of positrons emitted by beta(+)-unstable nuclei produced near the peak of the runaway and carried by rapid convection to the surface of the nova envelope. Simple models, which are extensions of detailed published models, of the expansion of the nova atmospheres are evolved. These models serve as input into investigations of the fate of nearby Galactic fast novae could yield detectable fluxes of electron-positron annihilation gamma rays produced by the decay of N-13 and F-18. Although nuclear gamma-ray lines are produced by other nuclei, it is unlikely that the fluxes at typical nova distances would be detectable to present and near-future instruments.

Leising, Mark D.; Clayton, Donald D.

1987-01-01

252

Gamma-Ray Pulsar Studies with GLAST  

SciTech Connect

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

Thompson, D. J. [Astrophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

2008-02-27

253

Gamma-ray bursts: An overview  

NASA Technical Reports Server (NTRS)

Gamma Ray Bursts were discovered by researchers studying data from gamma ray detectors aboard the Vela satellites. Since the original discovery, over 500 bursts have been observed by more than a dozen experiments on planetary spacecraft, earth orbiters, balloon flights, and even ground based instruments. Unfortunately, a description of the nature of these transient phenomena is no closer today than two decades ago. Part of the problem lies in the large variability in their physical characteristics. This variability has spawned more than 40 gamma ray burst models. Each model claims some subset of the 500 observed bursts that conclusively proves its validity. A very brief overview is presented of the gamma ray burst phenomenon.

Lestrade, John Patrick

1990-01-01

254

The EGRET high energy gamma ray telescope  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

255

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

256

Gamma-ray spectroscopy - Requirements and prospects  

NASA Technical Reports Server (NTRS)

The only previous space instrument which had sufficient spectral resolution and directionality for the resolution of astrophysical sources was the Gamma-Ray Spectrometer carried by HEAO-3. A broad variety of astrophysical investigations entail gamma-ray spectroscopy of E/Delta-E resolving power of the order of 500 at 1 MeV; it is presently argued that a sensitivity to narrow gamma-ray lines of a few millionths ph/sq cm, from about 10 keV to about 10 MeV, should typify the gamma-ray spectrometers of prospective missions. This performance is achievable with technology currently under development, and could be applied to the NASA's planned Nuclear Astrophysics Explorer.

Matteson, James L.

1991-01-01

257

The EGRET high energy gamma ray telescope  

NASA Astrophysics Data System (ADS)

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

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

1992-02-01

258

Gamma-Ray Pulsars Expected in the Outer Gap Model of Gamma-Ray Emission  

Microsoft Academic Search

We study the possibility of high-energy gamma-ray emission from the known 1130 radio pulsars based on the outer gap model of high-energy emission from pulsars. We estimate the fractional size of outer gap, the integrated flux, the gamma-ray luminosity for each known radio pulsar, and find that only 14% of the known radio pulsars are gamma-ray emitters according to the

Li Zhang; Jie Wu; Ze-Jun Jiang; Dong-Cheng Mei

2003-01-01

259

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

Microsoft Academic Search

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

Demosthenes Kazanas; Eric Perlman

1997-01-01

260

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

Microsoft Academic Search

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

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

261

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

Microsoft Academic Search

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

2009-01-01

262

First results on terrestrial gamma ray flashes from the Fermi Gamma-ray Burst Monitor  

Microsoft Academic Search

The Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Space Telescope detected 12 intense terrestrial gamma ray flashes (TGFs) during its first year of observation. Typical maximum energies for most of the TGFs are ?30 MeV, with one TGF having a 38 MeV photon; two of the TGFs are softer and longer than the others. After correcting for instrumental effects,

M. S. Briggs; G. J. Fishman; V. Connaughton; P. N. Bhat; W. S. Paciesas; R. D. Preece; C. Wilson-Hodge; V. L. Chaplin; R. M. Kippen; A. von Kienlin; C. A. Meegan; E. Bissaldi; J. R. Dwyer; D. M. Smith; R. H. Holzworth; J. E. Grove; A. Chekhtman

2010-01-01

263

Swift: A gamma ray burst MIDEX  

Microsoft Academic Search

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

2001-01-01

264

Swift gamma-ray burst MIDEX  

Microsoft Academic Search

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

Neil A. Gehrels

2000-01-01

265

The swift gamma-ray burst MIDEX  

Microsoft Academic Search

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

Neil Gehrels

2000-01-01

266

Compton scattering gamma-ray source optimization  

NASA Astrophysics Data System (ADS)

The interaction of a bright relativistic electron beam with an intense laser pulse via Compton scattering can generate tunable gamma-rays for precision nuclear photonics applications. The properties of the gamma-ray phase space will be outlined, in relation with the 6D electron bunch and 6D laser pulse phase space, along with collimation, nonlinear effects and other sources of spectral broadening. Optimization strategies will be outlines within the context of nuclear photonics applications.

Hartemann, Frederic; Wu, Sheldon; Albert, Félicie; Barty, Chris

2012-10-01

267

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

268

Very high energy gamma-ray spectroscopy  

Microsoft Academic Search

The cosmic gamma-ray spectrum in the relatively unexplored energy range 1 ⪅ E? ⪅ 103GeV may have several interesting features. It may contain the gamma-ray lines from photino annihilation in the galactic halo, if photinos indeed comprise the unidentified dark matter in typical galaxies. There could also be a detectable diffuse background at E? > 30 GeV. These and other

David Eichler; James H. Adams Jr.

1987-01-01

269

GAMMA-RAY BURSTS AS HYPERNOVAE  

Microsoft Academic Search

The energetics of optical and radio afterglows following BeppoSAX and BATSE gamma-ray bursts (GRBs) suggests that gamma-ray emission is not narrowly collimated, but a moderate beaming is possible, so the total energy of a GRB may be in the range ? 1050 1051 erg. All attempts to generate a fireball powered by neutrino-antineutrino annihilation have failed so far, and a

Bohdan Paczynski

270

Gamma-ray Albedo of the Moon  

SciTech Connect

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

Moskalenko, Igor V.; Porter, Troy A.

2007-06-14

271

Method and apparatus for gamma ray well logging  

Microsoft Academic Search

A radioactive logging source carried by a logging tool injects gamma rays into the formation. A detector generates a pulse for each gamma ray incident upon the detector having an amplitude proportional to the gamma ray energy. Electrical signals corresponding to each such amplitude are delivered to the surface. These incident gamma rays originate from the formation as well as

Hubner

1985-01-01

272

Gamma-Ray Heating in the Fast Breeder Blanket Facility  

Microsoft Academic Search

Gamma-ray heating rates in both stainless steel and lead have been measured in the Fast Breeder Blanket Facility using CaFâ:Dy thermoluminescent dosimeters. The TLD responses in stainless steel or lead holders were corrected by applying spectral-weighted f-factors. Corrections for neutron responses were based on CaFâ TLD neutron sensitivities. Radial experimental heating rates are presented and have been compared to results

K. R. Koch; F. M. Clikeman; R. H. Johnson

1980-01-01

273

The feasibility of periodicity searches in gamma-ray astronomy  

NASA Technical Reports Server (NTRS)

It is presently noted that, in some cases, the usually infeasible conduct of searches in gamma-ray astronomy can be rendered feasible by means of a time-smoothing technique that yields only a moderate sensitivity loss. The total observing time is subdivided into a convenient number m of subintervals, and summing the values of H of each of the subintervals. This will reduce the number of independent frequency values by a factor m due to the shorter observing time.

Buccheri, R.; Sacco, B.; Ozel, M. E.

1987-01-01

274

Gamma-Ray Pulsars: the 'Outer Gap' Perspective  

Microsoft Academic Search

Given that pulsars and AGN are the only identified GeV point sources, it isn't too bold to infer a substantial pulsar contribution to the Unidentified population. Specific models however predict differently the types of pulsars present in the observed sample. The dominant factors are the efficiency of spindown-gamma conversion, the high energy beam shape and the gamma ray spectrum. I'll

Roger W. Romani

2001-01-01

275

Cooled germanium spectrometers for X- and gamma-ray astronomy  

Microsoft Academic Search

The techniques of applying cooled germanium detectors to obtain high resolution measurements of hard X-ray and gamma-ray spectra from cosmic sources are discussed. Energy resolutions of better than 2 keV (FWHM) in the MeV region are achieved in the laboratory, representing an improvement of about a factor of 40 over conventional scintillators. Recent development of large intrinsic (pure) germanium detectors

G. H. Nakano; W. L. Imhof; J. B. Reagan

1976-01-01

276

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

277

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

278

Mercuric iodide room temperature gamma-ray detectors  

NASA Astrophysics Data System (ADS)

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.

1989-07-01

279

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

280

The Extraordinary Gamma-ray Flare of the Blazar 3C 454.3  

NASA Astrophysics Data System (ADS)

We present the gamma-ray data of the extraordinary flaring activity above 100 MeV from the flat spectrum radio quasar 3C 454.3 detected by AGILE during the month of 2009 December. 3C 454.3, which has been among the most active blazars of the FSRQ type since 2007, has been detected in the gamma-ray range with a progressively rising flux since 2009 November 10. The gamma-ray flux reached a value comparable with that of the Vela pulsar on 2009 December 2. Remarkably, between 2009 December 2 and 3, the source more than doubled its gamma-ray emission and became the brightest gamma-ray source in the sky with a peak flux of F ?,p = (2000 ± 400) × 10-8 ph cm-2 s-1 for a 1 day integration above 100 MeV. The gamma-ray intensity decreased in the following days with the source flux remaining at large values near F ? ~= (1000 ± 200) × 10-8 ph cm-2 s-1 for more than a week. This exceptional gamma-ray flare dissipated among the largest ever detected intrinsic radiated power in gamma-rays above 100 MeV (L ?,source,peak ~= 3 × 1046 erg s-1, for a relativistic Doppler factor of ? ~= 30). The total isotropic irradiated energy of the month-long episode in the range 100 MeV-3 GeV is E ?,iso ~= 1056 erg. We report the intensity and spectral evolution of the gamma-ray emission across the flaring episode. We briefly discuss the important theoretical implications of our detection.

Striani, E.; Vercellone, S.; Tavani, M.; Vittorini, V.; D'Ammando, F.; Donnarumma, I.; Pacciani, L.; Pucella, G.; Bulgarelli, A.; Trifoglio, M.; Gianotti, F.; Giommi, P.; Argan, A.; Barbiellini, G.; Caraveo, P.; Cattaneo, P. W.; Chen, A. W.; Costa, E.; De Paris, G.; Del Monte, E.; Di Cocco, G.; Evangelista, Y.; Feroci, M.; Ferrari, A.; Fiorini, M.; Fuschino, F.; Galli, M.; Giuliani, A.; Giusti, M.; Labanti, C.; Lazzarotto, F.; Lipari, P.; Longo, F.; Marisaldi, M.; Mereghetti, S.; Morelli, E.; Moretti, E.; Morselli, A.; Pellizzoni, A.; Perotti, F.; Piano, G.; Picozza, P.; Pilia, M.; Prest, M.; Rapisarda, M.; Rappoldi, A.; Sabatini, S.; Scalise, E.; Soffitta, P.; Trois, A.; Vallazza, E.; Zambra, A.; Zanello, D.; Pittori, C.; Verrecchia, F.; Santolamazza, P.; Lucarelli, F.; Colafrancesco, S.; Antonelli, L. A.; Salotti, L.

2010-07-01

281

Gamma-ray Burst Cosmology  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts (GRBs) are brief flashes of gamma-rays occurring at cosmological distances. GRB was discovered by Vela satellite in 1967. The discovery of afterglows in 1997 made it possible to measure the GRBs' redshifts and confirmed the cosmological origin. GRB cosmology includes utilizing long GRBs as standard candles to constrain the dark energy and cosmological parameters, measuring the high-redshift star formation rate (SFR), probing the metal enrichment history of the universe, dust, quantum gravity, etc. The correlations between GRB observables in the prompt emission and afterglow phases were discovered, so we can use these correlations as standard candles to constrain the cosmological parameters and dark energy, especially at high redshifts. Observations show that long GRBs may be associated with supernovae. So long GRBs are promising tools to measure the high-redshift SFR. GRB afterglows have a smooth continuum, so the extraction of IGM absorption features from the spectrum is very easy. The information of metal enrichment history and reionization can be obtained from the absorption lines. In this thesis, we investigate the high-redshift cosmology using GRBs, called GRB cosmology. This is a new and fast developing field. The structure of this thesis is as follows. In the first chapter, we introduce the progress of GRB studies. First we introduce the progress of GRB studies in various satellite eras, mainly in the Swift and Fermi eras. The fireball model and standard afterglow model are also presented. In chapter 2, we introduce the standard cosmology model, astronomical observations and dark energy models. Then progress on the GRB cosmology studies is introduced. Some of my works including what to be submitted are also introduced in this chapter. In chapter 3, we present our studies on constraining the cosmological parameters and dark energy using latest observations. We use SNe Ia, GRBs, CMB, BAO, the X-ray gas mass fraction in clusters and the linear growth rate of perturbations, and find that the ?CDM is the best fitted model. The transition redshift z_{T} is from 0.40_{-0.08}^{+0.14} to 0.65_{-0.05}^{+0.10}. This is the first time to combine GRBs with other observations to constrain the cosmological parameters, dark energy and transition redshift. In chapter 4, we investigate the early dark energy model using GRBs, SNe Ia, CMB and BAO. The negligible dark energy at high redshift will influence the growth of cosmic structures and leave observable signatures that are different from the standard cosmology. We propose that GRBs are promising tools to study the early dark energy. We find that the fractional dark energy density is less than 0.03 and the linear growth index of perturbations is 0.66. In chapter 5, we use a model-independent method to constrain the dark energy equation of state (EOS) w(z). Among the parameters describing the properties of dark energy, EOS is the most important. Whether and how it evolves with time are crucial in distinguishing different cosmological models. In our analysis, we include high-redshift GRBs. We find that w(z)<0 at z>1.7, and EOS deviates from the cosmological constant at z>0.5 at 95.4% confidence level. In chapter 6, we probe the cosmographic parameters to distinguish between the dark energy and modified gravity models. These two families of models can drive the universe to acclerate. We first derive the expressions of deceleration, jerk and snap parameters in the dark energy and modified gravity models. The snap parameters in these models are different, so they can be used to distinguish between the models. In chapter 7, we measure the high-redshift SFR using long GRBs. Swift observations reveal that the number of high-redshift GRBs is larger than the predication from SFR. We find that the evolving initial mass function can interpret this discrepancy. We study the high-redshift SFR up to z˜ 8.2 considering the Swift GRBs tracing the star formation history and the cosmic metallicity evolution in different background cosmological models. In chapter 8, we

Wang, F. Y.

2011-07-01

282

Simulating Terrestrial Gamma-ray Flashes using SWORD (Invited)  

NASA Astrophysics Data System (ADS)

We report on simulations of the relativistic feedback discharges involved with the production of terrestrial gamma-ray flashes (TGFs). The simulations were conducted using Geant4 using the SoftWare for the Optimization of Radiation Detectors (SWORD) framework. SWORD provides a graphical interface for setting up simulations in select high-energy radiation transport engines. Using Geant4, we determine avalanche length, the energy spectrum of the electrons and gamma-rays as they leave the field region, and the feedback factor describing the degree to which the production of energetic particles is self-sustaining. We validate our simulations against previous work in order to determine the reliability of our results. This work is funded by the Office of Naval Research.

Gwon, C.; Grove, J.; Dwyer, J. R.; Mattson, K.; Polaski, D.; Jackson, L.

2013-12-01

283

Gamma-ray bursts from sheared Alfven waves  

NASA Technical Reports Server (NTRS)

The physical process by which sheared Alfven waves can accelerate electrons to a Lorentz factor of 10,000 to 100,000 within 5 km of the stellar surface is applied to a study of gamma-ray bursts, taking both resonant and nonresonant scattering into account. Several very encouraging features of the model are discussed. Although the field is oscillatory, virtually all the charges are ejected from the system, resulting in very little backheating of the stellar surface. The particle number density is accounted for naturally in terms of BA0 and m, which in principle are known from the physical manifestation of the agent causing the crustal disturbance. The resulting gamma-ray spectrum compares very favorably with the observation. The model restricts the geometry of the emission region, in the sense that only the Compton upscattering of soft photons from a warm polar cap can produce the correct spectral shape.

Melia, Fulvio; Fatuzzo, Marco

1991-01-01

284

Gamma Rays in Spectra Measured by the Kaguya Gamma-Ray Spectrometer  

NASA Astrophysics Data System (ADS)

Of 200 peaks observed in spectra measured by the Kaguya Gamma Ray Spectrometer, the sources of 80% have been identified. Most are from the Ge detector, structural Al, and other local matter. Some gamma rays are from several elements in the Moon.

Reedy, R. C.; Hasebe, N.; Yamashita, N.; Karouji, Y.; Hareyama, M.; Kobayashi, S.; Okudaira, O.; Shibamura, E.; Kobayashi, M. N.; Kim, K. J.; D'Uston, C.; Diez, B.; Gasnault, O.; Forni, O.; Kaguya GRS Team

2009-03-01

285

Jets in Gamma-Ray Bursts  

NASA Technical Reports Server (NTRS)

In the afterglows of several gamma-ray bursts (GRBs), rapid temporal decay, which is inconsistent with spherical (isotropic) blast-wave models, is observed. In particular, GRB 980519 had the most rapidly fading of the well-documented GRB afterglows, with t(sup -2.05 +/- 0.04) in optical as well as in X-rays. We show that such temporal decay is more consistent with the evolution of a jet after it slows down and spreads laterally, for which t(sup -P) decay is expected (where p is the index of the electron energy distribution). Such a beaming model would relax the energy requirements on some of the more extreme GRBs by a factor of several hundred. It is likely that a large fraction of the weak- (or no-) afterglow observations are also due to the common occurrence of beaming in GRBs and that their jets have already transitioned. to the spreading phase before the first afterglow observations were made. With this interpretation, a universal value of p approx. = 2.4 is consistent with all data.

Sari, R.; Piran, T.; Halpern, Jules P.; Oliversen, Ronald (Technical Monitor)

2001-01-01

286

Sensitivity of HAWC to gamma ray bursts  

NASA Astrophysics Data System (ADS)

HAWC is a ground based very high-energy gamma ray detector under construction in Mexico at an altitude of 4100 m a.s.l. Higher altitude, improved design and a larger physical size used to reject CR background, make HAWC 10-20 times more sensitive than its predecessor Milagro. HAWC's large field of view, ~2sr, and over 90% duty cycle make it ideal to search for GRBs. We review the sensitivity of HAWC to GRBs with two independent data acquisition systems. We show that some of the brightest GRBs observed by Fermi LAT (e.g. GRB 090510) could result in >5 ? observation by HAWC. The observations (or limits) of GRBs by HAWC will provide information on the high-energy spectra of GRBs. The high-energy spectra will teach us about extra galactic background light, the Lorentz boost factor of the jets tha power GRBs and/or particle acceleration models of GRBs. Finally we present limits on > 10 GeV emission from GRB 111016B, recently studied with HAWC's engineering array VAMOS.

Taboada, Ignacio; HAWC Collaboration

2012-12-01

287

Gamma-ray Burst Energetics an the Gamma-ray Burst Hubble Diagram: Promises and Limitations  

NASA Technical Reports Server (NTRS)

We present a complete sample of 29 gamma-ray bursts (GRBs) for which it has been possible to determine temporal breaks (or limits) from their afterglow light curves. We interpret these breaks within the framework of the uniform conical jet model, incorporating realistic estimates of the ambient density and propagating error estimates on the measured quantities. In agreement with our previous analysis of a smaller sample, the derived jet opening angles of those 16 bursts with redshifts result in a narrow clustering of geometrically corrected gamma-ray energies about 1.33 x 10(exp 51) ergs; the burst-to-burst variance about this value is 0.35 dex, a factor of 2.2. Despite this rather small scatter, we demonstrate in a series of GRB Hubble diagrams that the current sample cannot place meaningful constraints upon the fundamental parameters of the universe. Indeed, for GRBs to ever be useful in cosmographic measurements, we argue the necessity of two directions. First, GRB Hubble diagrams should be based upon fundamental physical quantities such as energy, rather than empirically derived and physically ill-understood distance indicators (such as those based upon prompt burst time-profiles and spectra). Second, a more homogeneous set should be constructed by culling subclasses from the larger sample. These subclasses, although now first recognizable by deviant energies, ultimately must be identifiable by properties other than those directly related to energy. We identify a new subclass of GRBs (" f-GRBs ") that appear both underluminous by factors of at least 10 and exhibit a rapid fading (f(sub nu is proportional to t(sup -2) at early times (t < or = 0.5 day). About 10%-20% of observed long-duration bursts appear to be f-GRBs.

Bloom, J. S.; Frail, D. A.; Kulkarni, S. R.

2003-01-01

288

Two-Component Jet Models of Gamma-Ray Burst Sources  

Microsoft Academic Search

Recent observational and theoretical studies have raised the possibility that the collimated outflows in gamma-ray burst (GRB) sources have two distinct components: a narrow (opening half-angle thetaj,n), highly relativistic (initial Lorentz factor etan>~102) outflow, from which the gamma-ray emission originates, and a wider (thetaj,w<~3thetaj,n), moderately relativistic (etaw~10) surrounding flow. Using a simple synchrotron emission model, we calculate the R-band afterglow

Fang Peng; Arieh Königl; Jonathan Granot

2005-01-01

289

Natural gamma-ray spectrometry as a tool for radiation dose and radon hazard modelling  

Microsoft Academic Search

We reviewed the calibration procedures of gamma-ray spectrometry with particular emphasis to factors that affect accuracy, detection limits and background radiation in field measurements for dosimetric and radon potential mapping. Gamma-ray spectra were acquired in western Liguria (Italy). The energy windows investigated are centred on the photopeaks of 214Bi (1.76MeV), 208Tl (2.62MeV) and 40K (1.46MeV). The inferred absorbed dose rate

M. Verdoya; P. Chiozzi; P. De Felice; V. Pasquale; M. Bochiolo; I. Genovesi

2009-01-01

290

Low-state gamma-ray emission from blazars and the gamma-ray background  

NASA Technical Reports Server (NTRS)

The contribution of flat spectrum radio sources (FSRS) or blazars to the diffuse gamma ray background is examined. The basic assumptions of the investigation are: the existence of steady state gamma ray emission at the energetic gamma ray experiment telescope (EGRET) instrument energy band from the entire population of the FSRS; a proportionality between the FSRS' gamma ray luminosities and radio luminosities; and the production of the diffuse gamma ray background by the ensemble of blazars. Under these assumptions, the estimated average value of the proportionality constant in the luminosity relationship (vF(sub v))(sub 100 MeV) = f(vF(sub v))(sub 5 GHz) is approximately 70, compared to a mean observed value of 750. The implications of this result for the active galactic nuclei models are considered.

Kazanas, Demosthenes; Perlman, Eric

1997-01-01

291

Stellar Photon Archaeology with Gamma-Rays  

NASA Technical Reports Server (NTRS)

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

Stecker, Floyd W.

2009-01-01

292

The Gamma Ray Large Area Space Telescope:. AN Astro-Particle Mission to Explore the High Energy Gamma Ray Sky  

NASA Astrophysics Data System (ADS)

The Gamma Ray Large Area Space Telescope (GLAST) is a space mission that will detect photons from the gamma ray sky, in the rich yet poorly explored high energy band between 20MeV and 1TeV. Main instrument on board is the Large Area Telescope (LAT), a gamma-ray pair-conversion telescope, that will measure direction and energy of incoming photons by means of a very large (11.000 sensors), low pitch (228 ?m) Silicon strip Tracker and an imaging CsI e.m. calorimeter, supported in the rejection of charged particles background by an outer, segmented Anti-Coincidence Detector built with plastic scintillators. The superior angular resolution of the LAT, coupled to its very large field of view, results in a sensitivity advance of a factor 30 or more with respect to previously flown instruments. This will allow GLAST to locate currently unresolved gamma ray sources and to detect potential new classes of sources. Study of the residual gamma ray background will have a crucial role in connection to cosmological models, supersymmetric dark matter and relics of exotic particle decay searches. An accurate spectroscopy of all gamma ray emitters will be possible with the high energy resolution of the calorimeter, improving our knowledge of the mechanisms that power the cores of blazars and AGNs, and enabling tens of different pulsar emission models. The GLAST mission will have the instrumental capabilities to locate and analyse sources of cosmic rays and investigate on their acceleration mechanism. As for transient phenomena studies, like the spectacular GRBs, known to be the most energetic natural events, GLAST is in a prominent position. This is due to the minimum detection dead time (<100 ?s), typical of the silicon detectors used for the LAT tracker, and to the increased field of view and alert capabilities of the second GLAST instrument, the Gamma Burst Monitor (GBM), essentially conceived as a fast transients trigger for the more accurate observations from the LAT and from other space and earth missions sensitive to other wavelengths. In this paper we give an overview of the many physics goals and potential reach of the GLAST observatory, we describe in detail the detector design and performances and report on the status of the LAT tracker construction.

Bellazzini, R.; Spandre, G.

2003-09-01

293

ON THE RECENTLY DISCOVERED CORRELATIONS BETWEEN GAMMA-RAY AND X-RAY PROPERTIES OF GAMMA-RAY BURSTS  

SciTech Connect

Recently, many correlations between the prompt {gamma}-ray emission properties and the X-ray afterglow properties of gamma-ray bursts (GRBs) have been inferred from a comprehensive analysis of the X-ray light curves of more than 650 GRBs measured with the Swift X-Ray Telescope (Swift/XRT) during the years 2004-2010. We show that these correlations are predicted by the cannonball (CB) model of GRBs. They result from the dependence of GRB observables on the bulk motion Lorentz factor and viewing angle of the jet of highly relativistic plasmoids (CBs) that produces the observed radiations by interaction with the medium through which it propagates. Moreover, despite their different physical origins, long GRBs (LGRBs) and short-hard bursts (SHBs) in the CB model share similar kinematic correlations, which can be combined into triple correlations satisfied by both LGRBs and SHBs.

Dado, Shlomo; Dar, Arnon [Physics Department, Technion, Haifa 32000 (Israel)

2013-09-20

294

Monte Carlo simulation of x-ray buildup factors of lead and its applications in shielding of diagnostic x-ray facilities  

SciTech Connect

X-ray buildup factors of lead in broad beam geometry for energies from 15 to 150 keV are determined using the general purpose Monte Carlo N-particle radiation transport computer code (MCNP4C). The obtained buildup factors data are fitted to a modified three parameter Archer et al. model for ease in calculating the broad beam transmission with computer at any tube potentials/filters combinations in diagnostic energies range. An example for their use to compute the broad beam transmission at 70, 100, 120, and 140 kVp is given. The calculated broad beam transmission is compared to data derived from literature, presenting good agreement. Therefore, the combination of the buildup factors data as determined and a mathematical model to generate x-ray spectra provide a computationally based solution to broad beam transmission for lead barriers in shielding x-ray facilities.

Kharrati, Hedi; Agrebi, Amel; Karaoui, Mohamed-Karim [Ecole Superieure des Sciences et Techniques de la Sante de Monastir, Avenue Avicenne 5000 Monastir (Tunisia); Faculte des Sciences de Monastir (Tunisia)

2007-04-15

295

Tabulated data from the SAS-2 high energy gamma ray telescope  

NASA Technical Reports Server (NTRS)

The second small astronomy satellite (SAS-2) carried a high energy gamma ray telescope into an equitorial orbit with a 2 D inclination, an apogee of 610 km, and a perigee of 440 km. The energy threshold of the instrument was about 30 MeV, the energy of the gamma rays could be measured up to about 200 MeV, and the integral intensity above 200 MeV could also be measured. Summary tables of the gamma ray data are presented in two energy bands, 35-100 MeV and 100 MeV. The sky was divided into 144 solid angle elements, and, in each solid angle element for which data exist, the number of gamma rays observed is given and also the exposure factor. Information is provided to permit conversion of these data into approximate intensities.

Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.; Thompson, D. J.; Ogelman, H. B.; Tuner, T.; Ozel, M. E.

1978-01-01

296

Microsecond flares in gamma-ray bursts  

NASA Technical Reports Server (NTRS)

It has been suggested that gamma-ray burst light curves may consist of many superposed flares with a duration shorter than 30/microsec. If true, the implications for the interpretation of burst data are enormous. With the launch of the Compton Gamma-Ray Observatory, four predictions of Mitrofanov's (1989) suggestion can be tested. Our results which contradict this suggestion are (1) the photon arrival times are not correlated between independent detectors, (2) the spectral hardness and intensity does not depend on the detector area, (3) the bursts seen by detectors which measure photon positions do not see microsecond flares, and (4) burst positions deduced from detectors with different projected areas are close to the positions deduced from time-of-flight differences between separated spacecraft. We conclude, therefore, that gamma-ray bursts are not composed of microsecond flares.

Schaefer, Bradley E.; Cohen, Justin; Teegarden, Bonnard J.; Cline, Thomas L.; Fishman, Gerald J.; Meegan, Charles A.; Wilson, Robert B.; Paciesas, William S.; Pendleton, Geoffrey N.; Matteson, James L.

1993-01-01

297

Gamma-Ray Imaging for Explosives Detection  

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

298

Gamma-ray imaging for explosives detection  

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

299

Gamma ray pulsars. [electron-photon cascades  

NASA Technical Reports Server (NTRS)

Data from the SAS-2 high-energy gamma-ray experiment reveal the existence of four pulsars emitting photons above 35 MeV. An attempt is made to explain the gamma-ray emission from these pulsars in terms of an electron-photon cascade that develops in the magnetosphere of the pulsar. Although there is very little material above the surface of the pulsar, the very intense magnetic fields (10 to the 12th power gauss) correspond to many radiation lengths which cause electrons to emit photons by magnetic bremsstrahlung and which cause these photons to pair-produce. The cascade develops until the mean photon energy drops below the pair-production threshold which is in the gamma-ray range; at this stage, the photons break out from the source.

Oegelman, H.; Ayasli, S.; Hacinliyan, A.

1977-01-01

300

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

301

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

302

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

303

Study of SMM flares in gamma-rays and neutrons  

NASA Technical Reports Server (NTRS)

This report summarizes the results of the research supported by NASA grant NAGW-2755 and lists the papers and publications produced through the grant. The objective of the work was to study solar flares that produced observable signals from high-energy (greater than 10 MeV) gamma-rays and neutrons in the Solar Maximum Mission (SMM) Gamma-Ray Spectrometer (GRS). In 3 of 4 flares that had been studied previously, most of the neutrons and neutral pions appear to have been produced after the 'main' impulsive phase as determined from hard x-rays and gamma-rays. We, therefore, proposed to analyze the timing of the high-energy radiation, and its implications for the acceleration, trapping, and transport of flare particles. It was equally important to characterize the spectral shapes of the interacting energetic electrons and protons - another key factor in constraining possible particle acceleration mechanisms. In section 2.0, we discuss the goals of the research. In section 3.0, we summarize the results of the research. In section 4.0, we list the papers and publications produced under the grant. Preprints or reprints of the publications are attached as appendices.

Dunphy, Philip P.; Chupp, Edward L.

1992-01-01

304

Integrated neutron/gamma-ray portal monitors for nuclear safeguards  

SciTech Connect

Radiation monitoring is one nuclear-safeguards measure used to protect against the theft of special nuclear materials (SNM) by pedestrians departing from SNM access areas. The integrated neutron/gamma-ray portal monitor is an ideal radiation monitor for the task when the SNM is plutonium. It achieves high sensitivity for detecting both bare and shielded plutonium by combining two types of radiation detector. One type is a neutron-chamber detector, comprising a large, hollow, neutron moderator that contains a single thermal-neutron proportional counter. The entrance wall of each chamber is thin to admit slow neutrons from plutonium contained in a moderating shield, while the other walls are thick to moderate fast neutrons from bare or lead-shielded plutonium so that they can be detected. The other type of detector is a plastic scintillator that is primarily for detecting gamma rays from small amounts of unshielded plutonium. The two types of detector are easily integrated by making scintillators part of the thick back wall of each neutron chamber or by inserting them into each chamber void. The authors compared the influence of the two methods of integration on detecting neutrons and gamma rays, and they examined the effectiveness of other design factors and the methods for signal detection as well.

Fehlau, P.E. (Los Alamos National Lab., NM (United States))

1994-08-01

305

Continuum Background in Space-Borne Gamma-Ray Detectors  

NASA Technical Reports Server (NTRS)

The background measured with space-borne gamma-ray spectrometers (GRS) in the 100 keV-10 MeV energy region consists of both discrete lines and continuum. The discrete lines originate in the decay of radioactive species. The continuum originates from a number of different processes and can be an important factor in the detection, for example, of weak gamma-ray lines from a planetary surface. Measurements of the gamma-ray background have been made during the cruise portion of a number of planetary missions. The three missions described here are the Apollo 15 and 16 missions each of which carried a 7 cm x 7 cm NaI scintillation detector, the Mars Observer (MO) mission which used a 5.5 cm X 5.5 cm high-purity germanium (HPGe) detector, and the Near Earth Rendezvous Asteroid (NEAR) mission that has a 2.54 cm x 7.6 cm NaI detector. A comparison of the intensity and spectral shape of these background spectra can be useful to help understand how these backgrounds vary with spacecraft size, detector position, and detector size. The use of shields to reduce the background components on these three missions is a test of the effectiveness of different shield designs.

Evans, Larry G.; Trombka, Jacob I; Starr, Richard; Boyton, William V.; Bailey, S.

1997-01-01

306

Integrated neutron/gamma-ray portal monitors for nuclear safeguards  

NASA Astrophysics Data System (ADS)

Radiation monitoring is one nuclear-safeguards measure used to protect against the theft of special nuclear materials (SNM) by pedestrians departing from SNM access areas. The integrated neutron/gamma-ray portal monitor is an ideal radiation monitor for the task when the SNM is plutonium. It achieves high sensitivity for detecting both bare and shielded plutonium by combining two types of radiation detector. One type is a neutron-chamber detector, comprising a large, hollow, neutron moderator that contains a single thermal-neutron proportional counter. The entrance wall of each chamber is thin to admit slow neutrons from plutonium contained in a moderating shield, while the other walls are thick to moderate fast neutrons from bare or lead-shielded plutonium so that they can be detected. The other type of detector is a plastic scintillator that is primarily for detecting gamma rays from small amounts of unshielded plutonium. The two types of detector are easily integrated by making scintillators part of the thick back wall of each neutron chamber or by inserting them into each chamber void. We compared the influence of the two methods of integration on detecting neutrons and gamma rays, and we examined the effectiveness of other design factors and the methods for signal detection as well.

Fehlau, Paul E.

1994-08-01

307

Large gamma-ray detector arrays and electromagnetic separators  

NASA Astrophysics Data System (ADS)

The use of large gamma-ray detector arrays with electromagnetic separators is a powerful combination. Various types of gamma-ray detectors have been used; some provide high detector efficiency such as scintillation detector array, others use Ge detectors for good energy resolution, and recently developed Ge energy tracking arrays gives both high peak-to-background ratio and position resolution. Similarly, different types of separators were used to optimize the performance under different experimental requirements and conditions. For example, gas-filled separators were used in heavy element studies for their large efficiency and beam rejection factor. Vacuum separators with good isotope resolution were used in transfer and fragmentation reactions for the study of nuclei far from stability. This paper presents results from recent experiments using gamma-ray detector arrays in combination with electromagnetic separators, and discusses the physics opportunities provided by these instruments. In particular, we review the performance of the instruments currently in use, and discuss the requirements of instruments for future radioactive beam accelerator facilities.

Lee, I.-Yang

2013-12-01

308

Neutron and Gamma-ray Measurements  

SciTech Connect

Due to high neutron and gamma-ray yields and large size plasmas many future fusion reactor plasma parameters such as fusion power, fusion power density, ion temperature, fuel mixture, fast ion energy and spatial distributions can be well measured by various fusion product diagnostics. Neutron diagnostics provide information on fusion reaction rate, which indicates how close is the plasma to the ultimate goal of nuclear fusion and fusion power distribution in the plasma core, which is crucial for optimization of plasma breakeven and burn. Depending on the plasma conditions neutron and gamma-ray diagnostics can provide important information, namely about dynamics of fast ion energy and spatial distributions during neutral beam injection, ion cyclotron heating and generated by fast ions MHD instabilities. The influence of the fast particle population on the 2-D neutron source profile was clearly demonstrated in JET experiments. 2-D neutron and gamma-ray source measurements could be important for driven plasma heating profile optimization in fusion reactors. To meat the measurement requirements in ITER the planned set of neutron and gamma ray diagnostics includes radial and vertical neutron and gamma cameras, neutron flux monitors, neutron activation systems and neutron spectrometers. The necessity of using massive radiation shielding strongly influences the diagnostic designs in fusion reactor, determines angular fields of view of neutron and gamma-ray cameras and spectrometers and gives rise to unavoidable difficulties in the absolute calibration. The development, testing in existing tokomaks and a possible engineering integration of neuron and gamma-ray diagnostic systems into ITER are presented.

Krasilnikov, Anatoly V. [RRC 'Kurchatov Institute', Academician Kurchatov squarel, Moscow, 123182 (Russian Federation); SRC RF TRINITI, Troitsk, 142190 (Russian Federation); Sasao, Mamiko [Tohoku University, Sendai (Japan); Kaschuck, Yuri A. [SRC RF TRINITI, Troitsk, 142190 (Russian Federation); Kiptily, Vasily G.; Popovichev, Sergey V. [UKAEA, Abingdon (United Kingdom); Nishitani, Takeo [Japan Atomic Energy Agency, Tokai (Japan); Bertalot, Luciano [ITER Organization, Cadarach (France)

2008-03-12

309

Neutron and Gamma-ray Measurements  

NASA Astrophysics Data System (ADS)

Due to high neutron and gamma-ray yields and large size plasmas many future fusion reactor plasma parameters such as fusion power, fusion power density, ion temperature, fuel mixture, fast ion energy and spatial distributions can be well measured by various fusion product diagnostics. Neutron diagnostics provide information on fusion reaction rate, which indicates how close is the plasma to the ultimate goal of nuclear fusion and fusion power distribution in the plasma core, which is crucial for optimization of plasma breakeven and burn. Depending on the plasma conditions neutron and gamma-ray diagnostics can provide important information, namely about dynamics of fast ion energy and spatial distributions during neutral beam injection, ion cyclotron heating and generated by fast ions MHD instabilities. The influence of the fast particle population on the 2-D neutron source profile was clearly demonstrated in JET experiments. 2-D neutron and gamma-ray source measurements could be important for driven plasma heating profile optimization in fusion reactors. To meat the measurement requirements in ITER the planned set of neutron and gamma ray diagnostics includes radial and vertical neutron and gamma cameras, neutron flux monitors, neutron activation systems and neutron spectrometers. The necessity of using massive radiation shielding strongly influences the diagnostic designs in fusion reactor, determines angular fields of view of neutron and gamma-ray cameras and spectrometers and gives rise to unavoidable difficulties in the absolute calibration. The development, testing in existing tokomaks and a possible engineering integration of neuron and gamma-ray diagnostic systems into ITER are presented.

Krasilnikov, Anatoly V.; Sasao, Mamiko; Kaschuck, Yuri A.; Kiptily, Vasily G.; Nishitani, Takeo; Popovichev, Sergey V.; Bertalot, Luciano

2008-03-01

310

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

USGS Publications Warehouse

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

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

1984-01-01

311

Gamma ray pulsars: Models and observations  

NASA Technical Reports Server (NTRS)

The two known gamma ray pulsars, the Crab and Vela, were used as guides for the development of models of high-energy radiation from spinning neutron stars. Two general classes of models were developed: those with the gamma radiation originating in the pulsar magnetosphere far from the neutron star surface (outer gap models) and those with the gamma radiation coming from above the polar cap (polar cap models). The goal is to indicate how EGRET can contribute to understanding gamma-ray pulsars, and especially how it can help distinguish between models for emission.

Thompson, David J.

1990-01-01

312

Gamma-Ray Burst Detection with Icecube  

NASA Astrophysics Data System (ADS)

With their narrow emission window gamma-ray bursts (GRBs) are among the most promising objects for the first identification of high-energy cosmic neutrinos. If a considerable fraction of the ultra-high energy cosmic rays is indeed produced in GRBs, IceCube, which is now more than half-way completed, should be able to detect the associated neutrinos in the next few years. Furthermore, optical follow-up observations of neutrino multiplets will enhance IceCube's sensitivity to choked GRBs which do not produce a gamma-ray signal.

Kappes, Alexander

313

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

314

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

315

Gamma ray bursts from magnetospheric plasma oscillations  

NASA Technical Reports Server (NTRS)

Neutron star Magnetospheric Plasma Oscillations (MPO), can account for the energetics, decay time scale, and spectra of typical Gamma Ray Bursts (GRBs). The soft photon source is likely to be due to backwarming of the reprocessing boundary by the incipient gamma rays. It is shown that the observed fraction of bursts displaying low energy absorption features may be understood in the context of an MPO model. Moreover, it is found that GRB spectra should display these cyclotron lines about 18 percent of the time, which is consistent with the KONUS and Ginga sets of data.

Melia, Fulvio

1989-01-01

316

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.

317

Radioactivities and gamma-rays from supernovae  

NASA Technical Reports Server (NTRS)

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

Woosley, S. E.

1991-01-01

318

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

319

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

320

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

321

Historical aspects of gamma-ray astronomy  

Microsoft Academic Search

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

B. V. Sreekantan

2002-01-01

322

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

323

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

324

Observations of Gamma-Ray Bursts  

NASA Technical Reports Server (NTRS)

Observations of Gamma-ray bursts (GRBs) remain one of the most baffling phenomena in astrophysics. This talk will summarize the observations of GRBs with particular emphasis on those that present the greatest difficulty for theoretical interpretation. These include the short and highly variable temporal structure, the hard non-thermal spectra, and the enormous total energy output.

Meegan, C. A.; Six, N. Frank (Technical Monitor)

2001-01-01

325

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

326

Prompt Signals of Gamma Ray Bursts.  

National Technical Information Service (NTIS)

We introduce a new model of gamma ray burst (GRB) that explains its observed prompt signals, namely, its primary thermal spectrum and high energy tail. This mechanism can be applied to either assumption of GRB pro-genitor: coalescence of compact objects o...

P. Chen

2001-01-01

327

Gamma-ray astronomy comes of age  

NASA Astrophysics Data System (ADS)

The 'spark chamber' detector used for energies greater than 10 MeV in gamma-ray astronomy is a pictorial device in which the ionization trails left by an electron-positron pair can be seen as a series of sparks. Such a detector, although yielding comparatively low angular resolution, has been used in the COS-B satellite observations of pulsars and molecular clouds that began in 1975. Preliminary COS-B analysis results indicate an abundance of cosmic ray protons in the Milky Way 60,000 light years from the galactic center; some of these protons may be of extragalactic origin. Another significant discovery of the COS-B mission has been a population of unidentified gamma-ray objects (UGOs). UGOs are unique in emitting gamma rays preferentially over all other forms of electromagnetic radiation, thereby posing many theoretical problems and compelling efforts toward their identification with objects emitting at other wavelengths. The only probable identification of this type that has thus far been accomplished is of the 'Geminga' gamma-ray source in Gemini; both an X-ray counterpart and possible optical counterparts have been proposed.

Bignami, G. F.

1985-10-01

328

A Gamma-Ray Burst Trigger Toolkit  

NASA Technical Reports Server (NTRS)

The detection rate of a gamma-ray burst detector can be increased by using a count rate trigger with many accumulation times DELTAt and energy bands DELTAE Because a burst's peak flux varies when averaged over different DELTAt and DELTAE the nominal sensitivity (the numerical value of the peak flux) of a trigger system is less important than how much fainter a burst could be at the detection threshold as DELTAt and DELTAE are changed. The relative sensitivity of different triggers can be quantified by referencing the detection threshold back to the peak flux for a fiducial value of DELTAt and DELTA E. This mapping between peak flux values for different sets of DELTAt and DELTAE varies from burst to burst. Quantitative estimates of the burst detection rate for a given detector and trigger system can be based on the observed rate at a measured peak flux value in this fiducial trigger. Predictions of a proposed trigger's burst detection rate depend on the assumed burst population, and these predictions can be wildly in error for triggers that differ significantly from previous missions. I base the fiducial rate on the BATSE observations: 550 bursts per sky above a peak flux of 0.3 ph per square centimeter per second averaged over DELTAt=1.024 sec and DELTAE=50-300 keV. Using a sample of 100 burst lightcurves I find that triggering on any value of DELTAt that is a multiple of 0.064 sec decreases the average threshold peak flux on the 1.024 sec timescale by a factor of 0.6. Extending DELTAE to lower energies includes the large flux of the X-ray background, increasing the background count rate. Consequently a low energy DELTAE is advantageous only for very soft bursts. Whether a large fraction of the population of bright bursts is soft is disputed; the new population of X-ray Flashes is soft but relatively faint.

Band, David L.; White, Nicholas E. (Technical Monitor)

2002-01-01

329

Observations of cosmic gamma ray sources and their contribution to the diffuse gamma ray background  

NASA Astrophysics Data System (ADS)

The objective is to study soft gamma ray emission in the 0.1 to 10 MeV energy band for selected active galactic nuclei and explore how much they contribute to the total diffuse gamma ray background. A series of imaging observations of extragalactic objects in the low energy gamma-ray region were carried out by the Coded Aperture Directional Gamma-ray Telescope (DGT). The DGT was successfully flown at stratospheric balloon altitudes, and observations were made of the Crab, NGC 1275, MKN 421, and NGC 4151. The measured Crab spectrum is consistent with a featureless power-law of the form. Significant emission was detected up to 500 keV from the Seyfert galaxy, NGC 4151. To increase the total sky exposure the extragalactic field images were analyzed, including the 3C 273 region, obtained by the DGT.

Bhattacharya, Debadarshi

330

Investigation of gamma rays from the galactic center  

NASA Technical Reports Server (NTRS)

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

Helmken, H. F.

1973-01-01

331

Precise gamma-ray Timing and Radio Observations of 17 Fermi gamma-ray Pulsars  

Microsoft Academic Search

We present precise phase-connected pulse timing solutions for 16 gamma-ray-selected pulsars recently discovered using the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope plus one very faint radio pulsar (PSR J1124-5916) that is more effectively timed with the LAT. We describe the analysis techniques including a maximum likelihood method for determining pulse times of arrival from unbinned photon

P. S. Ray; M. Kerr; D. Parent; A. A. Abdo; L. Guillemot; S. M. Ransom; N. Rea; M. T. Wolff; A. Makeev; M. S. E. Roberts; F. Camilo; M. Dormody; P. C. C. Freire; J. E. Grove; C. Gwon; A. K. Harding; S. Johnston; M. Keith; M. Kramer; P. F. Michelson; R. W. Romani; P. M. Saz Parkinson; D. J. Thompson; P. Weltevrede; K. S. Wood; M. Ziegler

2011-01-01

332

Gamma ray spectroscopy in astrophysics: Solar gamma ray astronomy on solar maximum mission. [experimental design  

NASA Technical Reports Server (NTRS)

The SMM gamma ray experiment and the important scientific capabilities of the instrument are discussed. The flare size detectable as a function of spectrum integration time was studied. A preliminary estimate indicates that a solar gamma ray line at 4.4 MeV one-fifth the intensity of that believed to have been emitted on 4 August 1972 can be detected in approximately 1000 sec with a confidence level of 99%.

Forrest, D. J.

1978-01-01

333

Terrestrial gamma-ray flash production by lightning  

Microsoft Academic Search

Terrestrial gamma-ray flashes (TGFs) are brief flashes of gamma-rays originating in the Earth's atmosphere and observed by satellites. First observed in 1994 by the Burst And Transient Source Experiment on board the Compton Gamma-Ray Observatory, TGFs consist of one or more ˜1 ms pulses of gamma-rays with a total fluence of ˜1\\/cm2, typically observed when the satellite is near active

Brant E. Carlson

2010-01-01

334

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

335

Solar gamma-ray experiment on Astro-A satellite  

Microsoft Academic Search

The instrumentation and performance parameters of the Japanese Astro-A satellite for measuring solar gamma ray lines and continua associated with solar flares are described. A gamma ray spectrometer which is a phoswich scintillator covers the gamma ray range from 0.24-6.48 MeV with a resolution of 10 percent at 662 keV. Techniques to discern gamma ray from particle events are discussed,

K. Okudaira; Y. Hirasima; M. Yoshimori; I. Kondo

1981-01-01

336

Wide energy range gamma-ray calibration source  

Microsoft Academic Search

Calibration source with monoenergetic gamma-ray lines in wide energy range designed for gamma-ray detector energetic calibration and testing has been built. Gamma-rays are obtained from thermal neutron capture, which is a suitable and cost efficient way how to provide discrete gamma-ray lines with energies above 3 MeV with reasonable intensity. With appropriate and interchangeable targets the source can generate different

M Kroupa; C Granja; Z Janout; M Kralik; F Krejci; A Owens; S Pospisil; F Quarati; J Solc; M Vobecky

2011-01-01

337

The origin and implications of gamma rays from solar flares  

NASA Technical Reports Server (NTRS)

Solar flares studied in the gamma ray region provide essential information on accelerated nuclei that can be obtained in no other way. A multitude of physical processes, such as particle acceleration, nuclear reactions, positron and neutron physics, and kinematical line broadening, come into consideration at gamma ray energies. Gamma ray observations are complementary to hard X ray observations, since both provide information on accelerated particles. It appears that only in the gamma ray region do these particles produce distinct spectral lines.

Ramaty, R.

1975-01-01

338

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

339

Calibration of the RLS HPGe spectral gamma ray logging system  

Microsoft Academic Search

Gamma-ray spectral data have been recorded with the Radionuclide Logging System (RLS) high purity germanium (HPGe) system at (1) the American Petroleum Institute (API) spectral gamma-ray calibration center in Houston, Texas; (2) the US Department of Energy (DOE) spectral gamma-ray field calibration facility in Spokane, Washington; and (3) the DOE spectral gamma-ray primary calibration center in Grand Junction, Colorado. Analyses

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

1991-01-01

340

Theory and Modeling of Gamma-Ray Pulsars  

Microsoft Academic Search

Newborn neutron stars from supernovae explosions radiate brightly in gamma rays, outshining all other objects in the Galaxy. The gamma rays are emitted in a beam, and a flash of emission is observed at every rotation of the star; hence these objects are called gamma-ray pulsars. A great amount of energy is radiated in this form (~ 1035 erg\\/s), originating

Ion-Alexis George Yadigaroglu

1997-01-01

341

Probing the Radio Emission from Gamma Ray Blazars  

Microsoft Academic Search

The Energetic Gamma Ray Experiment Telescope on the Compton Gammay Ray Observatory discovered nearly 70 blazars with high confidence. The mechanics that results in the detectable gamma ray emission from these sources, is not completely understood, however. We obtained high resolution VLBA polarization imaging of two such gamma ray sources. We present our analysis of the superluminal motions discovered in

R. J. Cool; G. A. Moellenbrock

2003-01-01

342

Chemist's gamma-ray table. [9299 energy entries  

Microsoft Academic Search

An edited listing of gamma-ray information has been prepared. Prominent gamma rays originating from nuclides with half lives long enough to be seen in radiochemical experiments are included. Information is ordered by nuclide in one section and by energy in a second section. This shorter listing facilitates identification of nuclides responsible for gamma rays observed in experiments.

I. Binder; R. Kraus; R. Klein; D. Lee; M. M. Fowler

1977-01-01

343

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

344

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

345

Lunar Elemental Abundances from Gamma-Ray and Neutron Measurements  

NASA Astrophysics Data System (ADS)

The determination of elemental abundances is one of the highest science objectives of most lunar missions. Such multi-element abundances, ratios, or maps should include results for elements that are diagnostic or important in lunar processes, including heat-producing elements (such as K and Th), important incompatible elements (Th and rare earth elements), H (for polar deposits and regolith maturity), and key variable elements in major lunar provinces (such as Fe and Ti in the maria). Both neutron and gamma-ray spectroscopy can be used to infer elemental abundances; the two complement each other. These elemental abundances need to be determined with high accuracy and precision from measurements such as those made by the gamma-ray spectrometer (GRS) and neutron spectrometers (NS) on Lunar Prospector. As presented here, a series of steps, computer codes, and nuclear databases are needed to properly convert the raw gamma-ray and neutron measurements into good elemental abundances, ratios, and/or maps. Lunar Prospector (LP) is the first planetary mission that has measured neutrons escaping from a planet other than the Earth. The neutron spectrometers on Lunar Prospector measured a wide range of neutron energies. The ability to measure neutrons with thermal (E < 0.1 eV), epithermal (E about equal 0.1 - 1000 eV), and fast (E about 0.1-10 MeV) energies maximizes the scientific return, being especially sensitive to both H (using epithermal neutrons) and thermal-neutron-absorbing elements. Neutrons are made in the lunar surface by the interaction of galactic-cosmic-ray (GCR) particles with the atomic nuclei in the surface. Most neutrons are produced with energies above about 0.1 MeV. The flux of fast neutrons in and escaping from the Moon depends on es the intensity of the cosmic rays (which vary with solar activity) and the elemental composition of the surface. Variations in the elemental composition of the lunar surface can affect the flux of fast neutrons by about 25% , with Ti and Fe emitting more fast neutrons than light elements like O and Si. Most elements moderate neutrons to thermal energies at similar rates. The main exception is when neutrons scatter from H, in which case neutrons can be rapidly thermalized. The cross sections for the absorption of thermal neutrons can vary widely among elements, with major elements like Ti and Fe having high-capture cross sections. Some trace elements, such as Sm and Gd, have such large neutron-absorption cross sections that, despite their low abundances, can absorb significant amounts of thermal neutrons in the Moon. Because the processes affecting neutrons are complicated, good modeling is needed to properly extract elemental information from measured neutron fluxes. The LAHET Code System (LCS) can be use to calculate neutron fluxes from GCR interactions in the Moon. Lunar Gamma-Ray Spectroscopy: The main sources of planetary gamma-rays are the decay of the naturally occurring radioactive isotopes of K, Th, and U and the interactions of GCRs with atomic nuclei in the planet's surface. Most "cosmogenic" gamma-rays are produced by fast and thermal neutrons made in the planet's surface by GCRs, and their production rates can vary with time. Over 300 gamma-ray lines have been identified that can be emitted from planetary surfaces by a variety of production mechanisms. There exist nuclear databases that can be used to identify and quantify other gamma-ray lines. Use will be made of gamma-rays from major elements, particularly those from Si and O, that have not been routinely used in the past. The fluxes of gamma-rays from a given element can vary depending on many factors besides the concentration of that element. For example, the fluxes of neutron-capture gamma-rays in the planetary region of interest depend on (1) the total cross section for elements to absorb thermalized neutrons and (2) the H content of the top meter of the surface. The fluxes of the fast neutrons that induce inelastic-scattering and other nonelastic-scattering reactions can vary with the composition of

Reedy, R. C.; Vaniman, D. T.

1999-01-01

346

A Search for Gamma-Ray Bursts and Pulsars, and the Application of Kalman Filters to Gamma-Ray Reconstruction  

Microsoft Academic Search

Part I describes the analysis of periodic and transient signals in EGRET data. A method to search for the transient flux from gamma-ray bursts independent of triggers from other gamma-ray instruments is developed. Several known gamma-ray bursts were independently detected, and there is evidence for a previously unknown gamma-ray burst candidate. Statistical methods using maximum likelihood and Bayesian inference are

Brian Jones

2002-01-01

347

A search for gamma-ray bursts and pulsars, and the application of Kalman filters to gamma-ray reconstruction  

Microsoft Academic Search

High-energy gamma-ray astronomy was revolutionized in 1991 with the launch of the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma-Ray Observatory. In addition to unprecedented instrument effective area and a narrow point-spread function, EGRET provided photon time-tagging to an absolute accuracy of 100 mus. The opportunity to analyze high-quality gamma-ray data requires sophisticated statistical and analytic tools. Part

Brian Butler Jones

1999-01-01

348

Analysis of gamma-ray burst spectra with cyclotron lines  

NASA Technical Reports Server (NTRS)

Motivated by the recent developments in the cyclotron resonance upscattering of soft photons or CUSP model of Gamma Ray Burst (GBR) continuum spectra, we revisit a select database of GRBs with credible cyclotron absorption features. We measure the break energy of the continuum, the slope below the break and deduce the soft photon energy or the electron beam Lorentz factor cutoff. We study the correlation (or lack of) between various parameters in the context of the CUSP model. One surprise result is that there appears to be marginal correlation between the break energy and the spectral index below the break.

Kargatis, Vincent; Liang, Edison P.

1992-01-01

349

Experimental derivation of wall correction factors for ionization chambers used in high dose rate 192Ir source calibration.  

PubMed

At present there are no specific primary standards for 192Ir high dose rate sources used in brachytherapy. Traceability to primary standards is guaranteed through the method recommended by the AAPM that derives the air kerma calibration factor for the 192Ir gamma rays as the average of the air kerma calibration factors for x-rays and 137Cs gamma-rays or the Maréchal et al. method that uses the energy-weighted air kerma calibration factors for 250 kV x rays and 60Co gamma rays as the air kerma calibration factor for the 192Ir gamma rays. In order to use these methods, it is necessary to use the same buildup cap for all energies and the appropriate wall correction factor for each chamber. This work describes experimental work used to derive the A(W) for four different ionization chambers and different buildup cap materials for the three energies involved in the Maréchal et al. method. The A(W) for the two most common ionization chambers used in hospitals, the Farmer NE 2571 and PTW N30001 is 0.995 and 0.997, respectively, for 250 kV x rays, 0.982 and 0.985 for 192Ir gamma rays, and 0.979 and 0.991 for 60Co gamma rays, all for a PMMA build-up cap of 0.550 gm cm(-2). A comparison between the experimental values and Monte Carlo calculations shows an agreement better than 0.9%. Availability of the A(W) correction factors for all commercial chambers allows users of the in-air calibration jig, provided by the manufacturer, to alternatively use the Maréchal et al. method. Calibration laboratories may also used this method for calibration of a well-type ionization chamber with a comparable accuracy to the AAPM method. PMID:11833542

Maréchal, M H; de Almeida, C E; Ferreira, I H; Sibata, C H

2002-01-01

350

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

SciTech Connect

Non-destructive gamma-ray analysis is a fundamental part of nuclear safeguards, including nuclear energy safeguards technology. Developing safeguards capabilities for nuclear energy will certainly benefit from the advanced use of gamma-ray spectroscopy as well as the ability to model various reactor scenarios. There is currently a wide variety of nuclear data that could be used in computer modeling and gamma-ray spectroscopy analysis. The data can be discrepant (with varying uncertainties), and it may difficult for a modeler or software developer to determine the best nuclear data set for a particular situation. To use gamma-ray spectroscopy to determine the relative isotopic composition of nuclear materials, the gamma-ray energies and the branching ratios or intensities of the gamma-rays emitted from the nuclides in the material must be well known. A variety of computer simulation codes will be used during the development of the nuclear energy safeguards, and, to compare the results of various codes, it will be essential to have all the {gamma}-ray libraries agree. Assessing our nuclear data needs allows us to create a prioritized list of desired measurements, and provides uncertainties for energies and especially for branching intensities. Of interest are actinides, fission products, and activation products, and most particularly mixtures of all of these radioactive isotopes, including mixtures of actinides and other products. Recent work includes the development of new detectors with increased energy resolution, and studies of gamma-rays and their lines used in simulation codes. Because new detectors are being developed, there is an increased need for well known nuclear data for radioactive isotopes of some elements. Safeguards technology should take advantage of all types of gamma-ray detectors, including new super cooled detectors, germanium detectors and cadmium zinc telluride detectors. Mixed isotopes, particularly mixed actinides found in nuclear reactor streams can be especially challenging to identify. The super cooled detectors have a marked improvement in energy resolution, allowing the possibility of deconvolution of mixtures of gamma rays that was unavailable with high purity germanium detectors. Isotopic analysis codes require libraries of gamma rays. In certain situations, isotope identification can be made in the field, sometimes with a short turnaround time, depending on the choice of detector and software analysis package. Sodium iodide and high purity germanium detectors have been successfully used in field scenarios. The newer super cooled detectors offer dramatically increased resolution, but they have lower efficiency and so can require longer collection times. The different peak shapes require software development for the specific detector type and field application. Libraries can be tailored to specific scenarios; by eliminating isotopes that are certainly not present, the analysis time may be shortened and the accuracy may be increased. The intent of this project was to create one accurate library of gamma rays emitted from isotopes of interest to be used as a reliable reference in safeguards work. All simulation and spectroscopy analysis codes can draw upon this best library to improve accuracy and cross-code consistency. Modeling codes may include MCNP and COG. Gamma-ray spectroscopy analysis codes may include MGA, MGAU, U235 and FRAM. The intent is to give developers and users the tools to use in nuclear energy safeguards work. In this project, the library created was limited to a selection of actinide isotopes of immediate interest to reactor technology. These isotopes included {sup 234-238}U, {sup 237}Np, {sup 238-242}Pu, {sup 241,243}Am and {sup 244}Cm. These isotopes were examined, and the best of gamma-ray data, including line energies and relative strengths were selected.

Parker, W

2009-09-18

351

Cascaded Gamma Rays as a Probe of Cosmic Rays  

NASA Astrophysics Data System (ADS)

Very-high-energy (VHE) and ultra-high-energy (UHE) gamma rays from extragalactic sources experience electromagnetic cascades during their propagation in intergalactic space. Recent gamma-ray data on TeV blazars and the diffuse gamma-ray background may have hints of the cascade emission, which are especially interesting if it comes from UHE cosmic rays. I show that cosmic-ray-induced cascades can be discriminated from gamma-ray-induced cascades with detailed gamma-ray spectra. I also discuss roles of structured magnetic fields, which suppress inverse-Compton pair halos/echoes but lead to guaranteed signals - synchrotron pair halos/echoes.

Murase, Kohta

2014-06-01

352

THE REMARKABLE {gamma}-RAY ACTIVITY IN THE GRAVITATIONALLY LENSED BLAZAR PKS 1830-211  

SciTech Connect

We report the extraordinary {gamma}-ray activity (E > 100 MeV) of the gravitationally lensed blazar PKS 1830-211 (z = 2.507) detected by AGILE between 2010 October and November. On October 14, the source experienced a factor of {approx}12 flux increase with respect to its average value and remained brightest at this flux level ({approx}500 x 10{sup -8} photons cm{sup -2} s{sup -1}) for about four days. The one-month {gamma}-ray light curve across the flare showed a mean flux F(E > 100 MeV) = 200 x 10{sup -8} photons cm{sup -2} s{sup -1}, which resulted in a factor of four enhancement with respect to the average value. Following the {gamma}-ray flare, the source was observed in near-IR (NIR)-optical energy bands at the Cerro Tololo Inter-American Observatory and in X-Rays by Swift/X-Ray Telescope and INTEGRAL/IBIS. The main result of these multifrequency observations is that the large variability observed in {gamma}-rays does not have a significant counterpart at lower frequencies: no variation greater than a factor of {approx}1.5 appeared in the NIR and X-Ray energy bands. PKS 1830-211 is then a good '{gamma}-ray only flaring' blazar showing substantial variability only above 10-100 MeV. We discuss the theoretical implications of our findings.

Donnarumma, I.; De Rosa, A.; Vittorini, V.; Tavani, M.; Striani, E.; Pacciani, L. [INAF/IASF-Roma, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy); Miller, H. R.; Eggen, J.; Maune, J. [Department of Physics and Astronomy Georgia State University, GA 30303-3083 (United States); Popovic, L. C. [Astronomical Observatory, Volgina 7, 11160, Belgrade 74 (Serbia); Simic, S. [Isaac Newton Institute of Chile, Yugoslavia Branch, Belgrade (Serbia); Kuulkers, E. [European Space Astronomy Centre, SRE-O, Villanueva de la Canada, Madrid (Spain); Vercellone, S. [INAF/IASF Palermo Via Ugo La Malfa 153, 90146 Palermo (Italy); Pucella, G. [ENEA-Frascati, Via E. Fermi 45, I-00044 Frascati, Roma (Italy); Verrecchia, F.; Pittori, C.; Giommi, P. [ASI-ASDC, Via G. Galilei, I-00044 Frascati, Roma (Italy); Barbiellini, G. [Dipartimento di Fisica and INFN Trieste, Via Valerio 2, I-34127 Trieste (Italy); Bulgarelli, A. [INAF/IASF-Bologna, Via Gobetti 101, I-40129 Bologna (Italy); Cattaneo, P. W., E-mail: immacolata.donnarumma@iasf-roma.inaf.it [INFN-Pavia, Via Bassi 6, I-27100 Pavia (Italy)

2011-08-01

353

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

354

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

355

Neutron-driven gamma-ray laser  

DOEpatents

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

Bowman, Charles D. (Los Alamos, NM)

1990-01-01

356

Morphological study of short gamma ray bursts  

NASA Astrophysics Data System (ADS)

Gamma Ray Bursts (GRB) of duration less than about 2 s, detected by the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory have been selected for temporal analysis. These bursts constitute nearly 25% of the total and presumably form a separate class. Several parameters to describe the complexity and rapidity based on the burst temporal structure are derived and their dependence on other temporal and spectral properties are explored. A parameter is derived for each burst to characterize its spectral evolution based on its light curves in 4 energy channels. Bursts detected during April 1991 and March 1993 have been analysed yielding a sample size of 51 bursts. It has been found that the burst complexity is independent of its spectral content. The spectral evolution of short bursts is same as that of longer bursts. Also a systematic search for a coherent emission of ?-rays in short bursts yielded a negative result.

Bhat, P. N.; Fishman, G. J.; Meegan, C. A.; Wilson, R. B.; Paciesas, W. S.

1996-08-01

357

Spectral evolution in gamma-ray bursts  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

358

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

359

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

360

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

361

Gamma-ray multiplicity measurements using STEFF  

NASA Astrophysics Data System (ADS)

An ongoing investigation into the angular momentum generated during the fission of 252Cf is currently under way using the SpecTrometer for Exotic Fission Fragments (STEFF). Measurements have been made of the fold distribution (measured multiplicity) with STEFF. These have been compared to a Monte-carlo simulation to determine a value for the average angular momentum Jrms = 6hslash which is comparable to previous measurements [1]. Measurements of the gamma-ray multiplicity were performed whilst gating on different fragment mass regions. The result was compared with a sum of the lowest 2+ energies from both fragment and complementary in the mass gate. The results support the view that gamma-ray multiplicity is largely determined by the decay of the nucleus through near yrast transitions that follow the statistical decay.

Pollitt, A. J.; Smith, A. G.; Tsekhanovich, I.; Dare, J. A.

2012-09-01

362

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

363

The gamma ray north-south effect  

NASA Technical Reports Server (NTRS)

Theoretical calculations are presented that explain the balloon observations by O'Neill et al. (1987) of a strong north-south anisotropy of atmospheric gamma rays over the Southern Hemisphere, and to predict the north-south ratios. It is shown that the gamma rays that originate at the longest distances from the telescopes give the largest north-south ratios. Comparisons are made of the experimental north-south ratios measured on balloons launched from Alice Springs, Australia, and from Palestine, Texas, U.S., and predictions are made for ratios at other geomagnetic latitudes and longitudes. It is pointed out that observers who measure backgrounds for celestial sources may be misled unless they correct for the north-south effect.

White, R. S.; O'Neill, T. J.; Tumer, O. T.; Zych, A. D.

1988-01-01

364

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

365

Gamma-Ray Burst Progenitors: Merger Model  

NASA Astrophysics Data System (ADS)

The mergers of neutron stars and black holes remain a viable model for gamma-ray burst central engines, at least for the class of short bursts: their time scales, occurrence rates and energy output seem to be consistent with observations. We will present results of our latest simulations showing how the orbit of a neutron star around a black hole shrinks due to gravitational radiation, how the neutron star's matter gets accreted by the black hole, and how the tidal forces of the black hole finally shred the neutron star into a thick disk. In this process, huge amounts of energy are radiated away by gravitational waves and by neutrinos emitted from the hot disk. The neutrino luminosities are so large that an appreciable fraction (some few percent!) of neutrinos annihilate with antineutrinos creating the clean fireball necessary to power gamma-ray bursts.

Ruffert, Maximilian

2002-04-01

366

Gamma-Ray Polarimetry with Compton Telescope  

SciTech Connect

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

Tajima, H

2004-07-06

367

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

368

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

369

The gamma-ray telescope Gamma-1  

NASA Astrophysics Data System (ADS)

The telescope 'Gamma-1' is designed to investigate cosmic gamma rays in the energy range from 50 MeV to 5000 MeV. The geometrical sensitive area of the telescope amounts to 1500 cm2, the angular resolution in each direction is equal to 1.2° at the energy 300 MeV and is about 20arcmin when including a coded mask in the telescope, the energy resolution changes from 70% at 100 MeV to 35% at 550 MeV. The characteristics of the telescope and its systems have been determined by the Monte-Carlo method as well as by accelerator calibrations. Discrete sources at the intensity level of 10-7quanta cm-2s-1 may be recorded in a year of observations with the gamma-ray telescope 'Gamma-1' with a source location accuracy of ?10 arc min.

Akimov, V. V.; Balebanov, V. M.; Belousov, A. S.; Blokhintsev, I. D.; Veselova, G. V.

370

The Blackholic energy: long and short Gamma-Ray Bursts (New perspectives in physics and astrophysics from the theoretical understanding of Gamma-Ray Bursts, II)  

Microsoft Academic Search

We outline the confluence of three novel theoretical fields in our modeling of Gamma-Ray Bursts (GRBs): 1) the ultrarelativistic regime of a shock front expanding with a Lorentz gamma factor ~ 300; 2) the quantum vacuum polarization process leading to an electron-positron plasma originating the shock front; and 3) the general relativistic process of energy extraction from a black hole

Remo Ruffini; Maria Grazia Bernardini; Carlo Luciano Bianco; Pascal Chardonnet; Federico Fraschetti; Vahe Gurzadyan; Luca Vitagliano; She-Sheng Xue

2005-01-01

371

The gamma-ray telescope Gamma1  

Microsoft Academic Search

The telescope ‘Gamma-1’ is designed to investigate cosmic gamma rays in the energy range from 50 MeV to 5000 MeV. The geometrical sensitive area of the telescope amounts to 1500 cm2, the angular resolution in each direction is equal to 1.2° at the energy 300 MeV and is about 20' when including a coded mask in the telescope, the energy

V. V. Akimov; V. M. Balebanov; A. S. Belousov; I. D. Blokhintsev; G. V. Veselova; M. B. Dobrijan; L. F. Kalinkin; S. V. Kovalenko; V. D. Kozlov; N. G. Leikov; N. K. Mordvov; Y. I. Nagornih; V. E. Nesterov; O. F. Prilutsky; V. L. Prohin; V. G. Rodin; S. R. Tabaldiev; V. N. Chuprov; V. I. Fuks; I. A. Gerasimov; V. S. Ovtchinnikov; V. P. Poluektov; A. V. Serov; V. Y. Tugaenko; L. V. Kurnosova; M. A. Rusakovich; N. P. Topchiev; M. I. Fradkin; I. F. Bugakov; G. M. Gorodinsky; E. I. Chuikin; S. A. Voronov; A. M. Galper; V. A. Grigoriev; M. V. Guzenko; V. G. Kirillov-Ugriumov; S. V. Koldashov; M. G. Korotkov; B. I. Luchkov; A. A. Moiseev; Yu. V. Ozerov; A. V. Popov; V. A. Rud'ko; M. F. Runtso; B. Yu. Chesnokov; B. Agrinier; A. Bouere; M. Gros; J. P. Leray; A. Leconte; P. Masse; B. Mougin; P. Keirle; J. Cretolle; J. Paul; A. Raviart; B. Parlier; M. Poiviller; C. Hugot; F. Soroka; G. Serra; A. R. Bazer-Bachi; C. Doulade; J. Ducros; G. Vedrenne; F. Cotin; Y. M. Lavigne; P. Mandrou; E. Orsal; M. Avignon; J. Durand; J. Joli; F. Gardon; J. Mouli; M. Nobileau; D. Fournier

1989-01-01

372

GAMANAL. Interpretation of Gamma-Ray Spectra  

Microsoft Academic Search

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

Gunnink

1986-01-01

373

A portable gamma ray spectrometer/computer  

SciTech Connect

A state-of-the-art portable gamma ray spectrometer has been developed commercially. The instrument is available with NaI or hand-held Germanium detectors and can collect and analyze up to 4K channels of PHA or MCS spectra. An integral LCD provides graphic and character readout. Dual microprocessors are operated in a tightly-coupled multi-programming environment providing unique operator interface capability.

Roberts, H.

1984-02-01

374

Gamma-ray energy tracking array: GRETINA  

NASA Astrophysics Data System (ADS)

A Gamma-ray energy tracking array can provide higher efficiency, better peak-to-total ratio and higher position resolution than the current generation of detector arrays. Particularly, the capability of reconstructing the position of the interaction with millimetre resolution is needed to fully exploit the physics opportunities provided by current and next generation radioactive beam facilities. This paper presents the basic concepts of energy tracking, examples of physics opportunities, and the status of the GRETINA/GRETA project.

Lee, I.-Yang

2013-03-01

375

Gamma Ray Observatory over Baja California, Mexico  

NASA Technical Reports Server (NTRS)

In this view of the Gamma Ray Observatory over Baja California, Mexico (31.5N, 113.0W), the Salton Sea and Imperial Valley region of California where the mouth of the Colorado River empties into the Sea of Cortez is clearly visible. The Los Angeles basin is partially visible below the GRO's left solar panel. Looking due east, across Mexico and south Texas, toward the Earth limb, the Texas Gulf coast is faintly visible.

1991-01-01

376

Gamma -ray irradiation head for panoramic irradiation  

SciTech Connect

The invention relates to a gamma -ray irradiation head for panoramic irradiation comprising a tungsten target revolving about an axis, and means for deflecting electrons around the same axis for producing photons in several directions either successively or simultaneously. When the beam of electrons is deflected in its entirety and when the impact zone moves on the target about the axis, the axis of the radiation lobe moves in the same way and permits irradiation according to a variable azimuth.

Azam, G.; Bensussan, A.

1980-10-21

377

Gamma rays from extragalactic radio sources  

NASA Technical Reports Server (NTRS)

It is proposed that the important connection between 3C 273 and 3C 279, the first two extragalactic sources detected at greater than 100 MeV energies, is their superluminal nature. In support of this conjecture, we propose a radiation mechanism that focuses gamma rays in the superluminal direction, due to Compton scattering of accretion-disk photons by relativistic nonthermal electrons in the jet.

Dermer, Charles D.; Schlickeiser, Reinhard; Mastichiadis, Apostolos

1992-01-01

378

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

379

Gamma rays produce superior seedless citrus  

SciTech Connect

Using gamma radiation, seedless forms of some varieties of oranges and grapefruit are being produced. Since it has long been known that radiation causes mutations in plants and animals, experiments were conducted to determine if seediness could be altered by exposing seeds or budwood to higher than natural doses of gamma radiation. Orange and grapefruit seeds and cuttings exposed to gamma rays in the early 1970's have produced trees that bear fruit superior to that now on the market.

Pyrah, D.

1984-10-01

380

Gamma-ray spectroscopy of 126Ba  

Microsoft Academic Search

States of 126Ba up to spin 36+ were populated in the reaction 96Zr(34S, 4n)126Ba at 155 MeV and up to spin 20+ in the reaction 116Sn(13C, 3n)126Ba at 56 MeV. Gamma-ray spectroscopy was performed with the 8pi spectrometer, an instrument comprising 20 Campton-suppressed HPGe detectors and 71 BGO ball elements. A level scheme organized into fifteen rotational bands is proposed

D. Ward; V. P. Janzen; H. R. Andrews; D. C. Radford; G. C. Ball; D. Horn; J. C. Waddington; J. K. Johansson; F. Banville; J. Gascon; S. Monaro; N. Nadon; S. Pilotte; D. Prevost; P. Taras; R. Wyss

1991-01-01

381

Hypernovae and Gamma-Ray Bursts  

Microsoft Academic Search

Recently, there have been a number of candidates for the gamma-ray burst (GRB)\\/supernova (SN) connection (see Nomoto et al.\\u000a 2001 for references). Among the SNe with a possible GRB counterpart, the Type Ic SNe 1998bw and 1997ef are characterised by\\u000a a very large kinetic explosion energy, EK \\u000a >~1052\\\\gtrsim 10^{52}\\u000a erg. This is more than one order of magnitude larger than

P. Mazzali; K. Nomoto; K. Maeda; T. Nakamura

2001-01-01

382

Gamma-ray bursts as hypernovae  

Microsoft Academic Search

A standard fireball\\/afterglow model of a gamma-ray burst (GRB) relates the event to a merging neutron star binary, or a neutron star-black hole binary, which places the events far away from star-forming regions, and is thought to have an energy of ~1051 erg. A hypernova, the death of a massive and rapidly spinning star, may release ~1054 erg of kinetic

Bohdan Paczynski

1998-01-01

383

Hypernovae and Gamma-Ray Bursts  

Microsoft Academic Search

The nature of very energetic supernovae (hypernovae) is discussed. They are the explosive death of stars more massive than\\u000a ?20–25M?, probably linked to the enigmatic Gamma-Ray Bursts. The optical properties of hypernovae indicate that they are significantly\\u000a aspherical. Synthetic light curves and late-phase spectra of aspherical supernova\\/hypernova models are presented. These models\\u000a can account for the optical observations of SNe

Ken’ichi Nomoto; Keiichi Maeda; Nozomu Tominaga; Takuya Ohkubo; Jinsong Deng; Paolo A. Mazzali

2010-01-01

384

Hypernovae and Gamma-Ray Bursts  

Microsoft Academic Search

The nature of very energetic supernovae (hypernovae) is discussed. They are the explosive death of stars more massive than ~20–25M?, probably linked to the enigmatic Gamma-Ray Bursts. The optical properties of hypernovae indicate that they are significantly aspherical. Synthetic light curves and late-phase spectra of aspherical supernova\\/hypernova models are presented. These models can account for the optical observations of SNe

Ken’ichi Nomoto; Keiichi Maeda; Nozomu Tominaga; Takuya Ohkubo; Jinsong Deng; Paolo A. Mazzali

2005-01-01

385

Cosmic very high-energy gamma rays  

Microsoft Academic Search

The article gives a brief overview, aimed at nonspecialists, about the goals and selected recent results of the detection of very-high energy gamma-rays (energies above 100 GeV) with ground based detectors. The stress is on the physics questions, especially the origin of Galactic Cosmic Rays and the emission of TeV gamma-radiation from active galaxies. Moreover some particle-physics questions which are

R. Plaga

1998-01-01

386

Afterglow Radiation from Gamma Ray Bursts  

SciTech Connect

Gamma-ray bursts (GRB) are huge fluxes of gamma rays that appear randomly in the sky about once a day. It is now commonly accepted that GRBs are caused by a stellar object shooting off a powerful plasma jet along its rotation axis. After the initial outburst of gamma rays, a lower intensity radiation remains, called the afterglow. Using the data from a hydrodynamical numerical simulation that models the dynamics of the jet, we calculated the expected light curve of the afterglow radiation that would be observed on earth. We calculated the light curve and spectrum and compared them to the light curves and spectra predicted by two analytical models of the expansion of the jet (which are based on the Blandford and McKee solution of a relativistic isotropic expansion; see Sari's model [1] and Granot's model [2]). We found that the light curve did not decay as fast as predicted by Sari; the predictions by Granot were largely corroborated. Some results, however, did not match Granot's predictions, and more research is needed to explain these discrepancies.

Desmond, Hugh; /Leuven U. /SLAC

2006-08-28

387

Gamma Ray Burst All-Sky Spectrometer  

NASA Astrophysics Data System (ADS)

The Gamma Ray Burst All-Sky Spectrometer Experiment (GASE) is designed to detect radio emission from gamma ray bursts (GRB's). Radio emission from GRB's could help us better understand the plasma physics of the blast and might also help us measure dark energy. GASE uses short-baseline interferometry with eight dipole antennas located at the MIT Haystack Observatory. These antennas measure the radiofrequency sky at 30 MHz over a 4 MHz bandwidth and are able to collect information from the entire sky. Since the entire sky is surveyed, radio frequency interference occurring at the horizon can be eliminated as a transient source. Along with the SWIFT satellite and the Gamma Ray Burst Coordinate system, we will be able measure blast time, duration and position. We are currently designing techniques to calibrate and image the full sky in radio. In addition to locating and measuring GRB's, GASE may be able to measure dark energy due to the dispersion by the IGM. The pulse of radio emission is delayed as it travels through the intergalactic plasma, with longer wavelengths taking longer to arrive than shorter wavelengths. With the known free electron density (?m) we will use the dispersion measure to calculate the line of sight distance to the GRB and compare to the observed redshift to measure dark energy.

Steger, Arielle

2011-05-01

388

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

389

Nuclear gamma rays from solar flares  

NASA Technical Reports Server (NTRS)

The theory of gamma ray line emission from solar flares is reviewed and revised. It is shown that the recently observed (Chupp et al., 1972) line emissions at 0.5, 2.2, 4.4 and 6.1 MeV are due to positron annihilation, deuterium deexcitation following neutron capture on hydrogen, and the deexcitation of excited states in carbon and oxygen. From the observed relative line intensities it is possible to determine the spectrum of accelerated protons in the flare region. This spectrum is found to be very similar to that the charged particles from the flare observed near earth. The total numbers of protons at the sun is deduced from the observed absolute line intensities for various interaction models. It is found that if the protons at the sun have a spectrum which is an exponential in rigidity, the total energy in protons is a few times 10 to the 28th power ergs if the gamma rays are produced by protons moving down into the sun; and about 10 to the 30th power ergs if the gamma rays are produced at the site of the acceleration.

Ramaty, R.; Lingenfelter, R. E.

1973-01-01

390

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

391

Distribution of Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Gamma-Ray Bursts (GRBs) are known to be bright, irregular flashes of gamma rays that typically last just a few seconds, believed to be caused by stellar collapse or the merger of a pair of compact objects. Through previous work, it has been found that GRBs are distributed roughly uniformly over the entire sky, rather than being confined to the relatively narrow band of the Milky Way. Using the Python programming language, we generated a model of GRBs over cosmological distances, based on current empirical GRB distributions. The grbsim python module uses the acceptance-rejection Monte Carlo method to simulate the luminosity and redshift of a large population of GRBs, including cosmological effects such as dark energy and dark matter terms that modify the large-scale structure of space-time. The results of running grbsim are demonstrated to match the distribution of GRBs observed by the Burst Alert Telescope on NASA’s Swift satellite. The grbsim module will subsequently be used to simulate gamma ray and neutrino events for the Astrophysical Multimessenger Observatory Network.

Diaz Rodriguez, Mariangelly; Smith, M.; Tešic, G.

2014-01-01

392

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

393

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

394

Jet simulations and gamma-ray burst afterglow jet breaks  

NASA Astrophysics Data System (ADS)

The conventional derivation of the gamma-ray burst afterglow jet break time uses only the blast wave fluid Lorentz factor and therefore leads to an achromatic break. We show that in general gamma-ray burst afterglow jet breaks are chromatic across the self-absorption break. Depending on circumstances, the radio jet break may be postponed significantly. Using high-accuracy adaptive mesh fluid simulations in one dimension, coupled to a detailed synchrotron radiation code, we demonstrate that this is true even for the standard fireball model and hard-edged jets. We confirm these effects with a simulation in two dimensions. The frequency dependence of the jet break is a result of the angle dependence of the emission, the changing optical depth in the self-absorbed regime and the shape of the synchrotron spectrum in general. In the optically thin case the conventional analysis systematically overestimates the jet break time, leading to inferred opening angles that are underestimated by a factor of ˜1.3 and explosion energies that are underestimated by a factor of ˜1.7, for explosions in a homogeneous environment. The methods presented in this paper can be applied to adaptive mesh simulations of arbitrary relativistic fluid flows. All analysis presented here makes the usual assumption of an on-axis observer.

van Eerten, H. J.; Meliani, Z.; Wijers, R. A. M. J.; Keppens, R.

2011-01-01

395

Implications of Gamma-Ray Transparency Constraints in Blazars: Minimum Distances and Gamma-Ray Collimation  

NASA Technical Reports Server (NTRS)

We develop a general expression for the gamma - gamma absorption coefficient, alpha(sub gamma(gamma)) for gamma-rays propagating in an arbitrary direction at an arbitrary point in space above an X-ray-emitting accretion disk. The X-ray intensity is assumed to vary as a power law in energy and radius between the outer disk radius, R(sub 0), and the inner radius, R(sub ms) which is the radius of marginal stability for a Schwarzschild black hole. We use our result for alpha(sub gamma(gamma)) to calculate the gamma - gamma optical depth, tau(sub gamma(gamma)) for gamma - rays created at height z and propagating at angle Phi relative to the disk axis, and we show that for Phi = 0 and z greater than or approx equal to R(sub 0), tau(sub gamma(gamma)) proportional to Epsilon(sup alpha)z(sup -2(alpha) - 3), where alpha is the X-ray spectral index and Epsilon is the gamma - ray energy. As an application, we use our formalism to compute the minimum distance between the central black hole and the site of production of the gamma-rays detected by EGRET during the 1991 June flare of 3C 279. In order to obtain an upper limit, we assume that all of the X-rays observed contemporaneously by Ginga were emitted by the disk. Our results suggest that the observed gamma - rays may have originated within less than or approx equal to 45 GM/sq c from a black hole of mass greater than or approx equal to 10(exp 9) solar mass, perhaps in active plasma located above the central funnel of the accretion disk. This raises the possibility of establishing a direct connection between the production of the observed gamma - rays and the accretion of material onto the black hole. We also consider the variation of the optical depth as a function of the angle of propagation Phi. Our results indicate that the "focusing" of the gamma - rays along the disk axis due to pair production is strong enough to explain the observed degree of alignment in blazar sources. If the gamma - rays are produced isotropically in gamma - ray blazars, then these objects should appear as bright MeV sources when viewed along off-axis lines of sight.

Becker, Peter A.; Kafatos, Menas

1995-01-01

396

CdZnTe gamma ray spectrometer for orbital planetary missions  

SciTech Connect

Knowledge of surface elemental composition is needed to understand the formation and evolution of planetary bodies. Gamma rays and neutrons produced by the interaction of galactic cosmic rays with surface materials can be detected from orbit and analyzed to determine composition. Using gamma ray spectroscopy, major rock forming elements such as Fe, Ti, Al, Si, Mg, and Ca can be detected. The accuracy of elemental abundance is limited by the resolution of the spectrometer. For space missions, scintillators such as BGO and NaI(Tl) have been used for gamma ray spectroscopy. New planetary science missions are being planned to explore Mars, Mercury, the asteroid belt, and the outer planets. Significant improvements in the pulse height resolution relative to scintillation detectors can be made using CdZnTe, a new room temperature detector technology. For an orbiting instrument, a CdZnTe detector at least 16 cm{sup 3} in size is needed. A 4 x 4 array of 1-cm{sup 3} coplanar grid detectors can be manufactured that meets requirements for resolution and counting efficiency. The array will shielded from gamma rays produced in the spacecraft by a BGO detector. By improving pulse height resolution by a factor of three at low energy, the CdZnTe detector will be able to make accurate measurements of elements that are currently difficult to measure using scintillation technology. The BGO shield will provide adequate suppression of gamma rays originating in the spacecraft, enabling the gamma ray spectrometer to be mounted on the deck of a spacecraft. To test this concept, we are constructing a flight qualified, prototype CdZnTe detector array. The prototype consists of a 2 x 2 array of coplanar grid detectors. We will present the results of mechanical and electronic testing and radiation damage tests, and the performance of the array for gamma ray spectroscopy.

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

2001-01-01

397

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

398

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

NASA Astrophysics Data System (ADS)

The Large Area Telescope on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST), with its large field of view and effective area, combined with its excellent timing capabilities, is poised to revolutionize the field of gamma-ray astrophysics. The large improvement in sensitivity over EGRET is expected to result in the discovery of many new gamma-ray pulsars, which in turn should lead to fundamental advances in our understanding of pulsar physics and the role of neutron stars in the Galaxy. Almost immediately after launch, Fermi clearly detected all previously known gamma-ray pulsars and is producing high precision results on these. An extensive radio and X-ray timing campaign of known (primarily radio) pulsars is being carried out in order to facilitate the discovery of new gamma-ray pulsars. In addition, a highly efficient time-differencing technique is being used to conduct blind searches for radio-quiet pulsars, which has already resulted in new discoveries. I present some recent results from searches for pulsars carried out on Fermi data, both blind searches, and using contemporaneous timing of known radio pulsars.

Saz Parkinson, P. M.

2009-04-01

399

EGRET Measurements of Energetic Gamma Rays from the Gamma-Ray Bursts of 1992 June 22 and 1994 March 1  

NASA Astrophysics Data System (ADS)

Energetic gamma-ray emissions from the gamma-ray bursts on 1992 June 22 (GRB 920622) and on 1994 March 1 (GRB 940301) were detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma Ray Observatory (CGRO). Spectral data for both bursts were measured by EGRET's large NaI detector. Gamma rays up to 160 MeV were observed for GRB 94030t with its spark chamber telescope. Time-integrated, high-energy spectra for both bursts were fitted by single-power-law models having spectral indexes of 3.0 and 2.5 for GRB 920622 and GRB 940301, respectively.

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

1995-11-01

400

Gamma-ray constraints on dark matter annihilation into charged particles  

SciTech Connect

Dark matter annihilation into charged particles is necessarily accompanied by gamma rays, produced via radiative corrections. Internal bremsstrahlung from the final state particles can produce hard gamma rays up to the dark matter mass, with an approximately model-independent spectrum. Focusing on annihilation into electrons, we compute robust upper bounds on the dark matter self-annihilation cross section <{sigma}{sub A}v>{sub e{sup +}}{sub e{sup -}} using gamma-ray data from the Milky Way spanning a wide range of energies {approx}10{sup -3}-10{sup 4} GeV. We also compute corresponding bounds for the other charged leptons. We make conservative assumptions about the astrophysical inputs, and demonstrate how our derived bounds would be strengthened if stronger assumptions about these inputs are adopted. The fraction of hard gamma rays near the end point accompanying annihilation to e{sup +}e{sup -} is only a factor of < or approx. 10{sup 2} lower than for annihilation directly to monoenergetic gamma rays. The bound on <{sigma}{sub A}v>{sub e{sup +}}{sub e{sup -}} is thus weaker than that for <{sigma}{sub A}v>{sub {gamma}}{sub {gamma}} by this same factor. The upper bounds on the annihilation cross sections to charged leptons are compared with an upper bound on the total annihilation cross section defined by neutrinos.

Bell, Nicole F.; Jacques, Thomas D. [School of Physics, University of Melbourne, Victoria 3010 (Australia)

2009-02-15

401

GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy  

NASA Astrophysics Data System (ADS)

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range (COMPTEL, INTEGRAL; see Fig. 1). These gamma-ray observations will be complemented by observations in the soft X-ray and (near-)infrared region with the corresponding telescopes placed on a separate satellite. The Gamma-Ray Imaging, Polarimetry and Spectroscopy (" GRIPS") mission with its three instruments Gamma-Ray Monitor (GRM), X-Ray Monitor (XRM) and InfraRed Telescope (IRT) addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate ?-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts.

Greiner, Jochen; Mannheim, Karl; Aharonian, Felix; Ajello, Marco; Balasz, Lajos G.; Barbiellini, Guido; Bellazzini, Ronaldo; Bishop, Shawn; Bisnovatij-Kogan, Gennady S.; Boggs, Steven; Bykov, Andrej; DiCocco, Guido; Diehl, Roland; Elsässer, Dominik; Foley, Suzanne; Fransson, Claes; Gehrels, Neil; Hanlon, Lorraine; Hartmann, Dieter; Hermsen, Wim; Hillebrandt, Wolfgang; Hudec, Rene; Iyudin, Anatoli; Jose, Jordi; Kadler, Matthias; Kanbach, Gottfried; Klamra, Wlodek; Kiener, Jürgen; Klose, Sylvio; Kreykenbohm, Ingo; Kuiper, Lucien M.; Kylafis, Nikos; Labanti, Claudio; Langanke, Karlheinz; Langer, Norbert; Larsson, Stefan; Leibundgut, Bruno; Laux, Uwe; Longo, Francesco; Maeda, Kei'ichi; Marcinkowski, Radoslaw; Marisaldi, Martino; McBreen, Brian; McBreen, Sheila; Meszaros, Attila; Nomoto, Ken'ichi; Pearce, Mark; Peer, Asaf; Pian, Elena; Prantzos, Nikolas; Raffelt, Georg; Reimer, Olaf; Rhode, Wolfgang; Ryde, Felix; Schmidt, Christian; Silk, Joe; Shustov, Boris M.; Strong, Andrew; Tanvir, Nial; Thielemann, Friedrich-Karl; Tibolla, Omar; Tierney, David; Trümper, Joachim; Varshalovich, Dmitry A.; Wilms, Jörn; Wrochna, Grzegorz; Zdziarski, Andrzej; Zoglauer, Andreas

2012-10-01

402

On the bimodal distribution of gamma-ray bursts  

NASA Technical Reports Server (NTRS)

Kouveliotou et al. recently confirmed that gamma-ray bursts are bimodal in duration. In this paper we compute the statistical properties of the short (less than or = 2 s) and long (greater than 2 s) bursts using a method of analysis that makes no assumption regarding the location of the bursts, whether in the Galaxy or at a cosmological distance. We find the 64 ms channel on Burst and Transient Source Experiment (BATSE) to be more sensitive to short bursts and the 1024 ms channel to be more sensitive to long bursts. We show that all the currently available data are consistent with the simple hypothesis that both short and long bursts have the same spatial distribution and that within each population the sources are standard candles. The rate of short bursts per unit volume is about 40% of the rate of long bursts. Although the durations of short and long gamma-ray bursts span several orders of magnitude and the total energy of a typical short burst is smaller than that of a typical long burst by a factor of about 20, surprisingly the peak luminosities of the two kinds of bursts are equal to within a factor of about 2.

Mao, Shude; Narayan, Ramesh; Piran, Tsvi

1994-01-01

403

EGRET - The high energy gamma ray telescope for NASA's Gamma Ray Observatory  

NASA Technical Reports Server (NTRS)

The EGRET high energy gamma-ray telescope under development for NASA's Gamma Ray Observatory will have an energy range of approximately 12 to 30,000 MeV, energy resolution of about 15 percent FWHM over most of that range, an effective area of about 2000 sq cm at high energies, and single photon angular accuracy of approximately 2 deg at 100 MeV, less than 0.1 deg above 5 GeV. This instrument can locate strong sources to an accuracy of about 5 arc min. The instrument utilizes a set of digital spark chambers interleaved with tantalum foils for detection and identification of gamma-ray events, and a large NaI(Tl) scintillator for energy determination. The system is triggered by a coincidence matrix using two arrays of plastic scintillation counters and a large plastic scintillator anticoincidence dome that rejects incident charged particles.

Fichtel, C. E.; Bertsch, D. L.; Hartman, R. C.; Kniffen, D. A.; Thompson, D. J.; Hofstadter, R.; Hughes, E. B.; Campbell-Finman, L. E.; Pinkau, K.; Mayer-Hasselwander, H.

1983-01-01

404

CdZnTe gamma ray spectrometer for orbital gamma ray spectroscopy.  

SciTech Connect

We present the design and analysis of a new gamma ray spectrometer for planetary science that uses an array of CdZnTe detectors to achieve the detection efficiency needed for orbital measurements. The use of CdZnTe will provide significantly improved pulse height resolution relative to scintillation-based detectors, with commensurate improvement in the accuracy of elemental abundances determined by gamma ray and neutron spectroscopy. The spectrometer can be flown either on the instrument deck of the spacecraft or on a boom. For deck-mounted systems, a BGO anticoincidence shield is included in the design to suppress the response of the CdZnTe detector to gamma rays that originate in the spacecraft. The BGO shield also serves as a backup spectrometer, providing heritage from earlier planetary science missions and reducing the risk associated with the implementation of new technology.

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

2001-01-01

405

Modeling Gamma-Ray Attenuation in High Redshift GeV Spectra  

NASA Astrophysics Data System (ADS)

We present two models for the cosmological UV background light, and calculate the opacity of GeV gamma-rays out to redshift 9. The contributors to the background include 2 possible quasar emissivities, and output from star-forming galaxies as determined by recent a semi-analytic model (SAM) of structure formation. The SAM used in this work is based upon a hierarchical build-up of structure in a ?CDM universe and is highly successful in reproducing a variety of observational parameters. Above 1 Rydberg energy, ionizing radiation is subject to reprocessing by the IGM, which we treat using our radiative transfer code, CUBA. The two models for quasar emissivity differing above z = 2.3 are chosen to match the ionization rates observed using flux decrement analysis and the higher values of the line-of-sight proximity effect. We also investigate the possibility of aflat star formation rate density at z>5. We conclude that observations of gamma-rays from 10 to 100 GeV by Fermi (GLAST) and the next generation of ground based experiments should confirm a strongly evolving opacity from 1gamma-ray bursts at higher redshift could constrain emission of UV radiation at these early times, either from a flat or increasing star-formation density or an unobserved population of sources.

Gilmore, Rudy C.; Madau, Piero; Primack, Joel R.; Somerville, Rachel S.

2008-12-01

406

GeV Gamma-Ray Astronomy in the Era of GLAST  

NASA Technical Reports Server (NTRS)

The Gamma Ray Large Area Space Telescope (GLAST) is a high energy astronomy mission planned for launch in 2005. GLAST features two instruments; the Large Area Telescope (LAT) operating from 20 MeV - 300 GeV and the Gamma-ray Burst Monitor (GBM) operating from 10 keV - 25 MeV. GLAST observations will contribute to our understanding of active galactic nuclei and their jets, gamma-ray bursts, extragalactic and galactic diffuse emissions, dark matter, supernova remnants, pulsars, and the unidentified high energy gamma-ray sources. The LAT sensitivity is 4 x 10(exp -9) photons per square centimeter per second (greater than 100 MeV) for a one year all-sky survey, which is a factor of greater than 20 better than CGRO/EGRET. GLAST spectral observations of gamma-ray bursts cover over 6 orders of magnitude in energy thanks to the context observations of the GBM. The upper end of the LAT energy range merges with the low energy end of ground-based observatories to provide a remarkable new perspective on particle acceleration in the Universe.

Gehrels, Neil; White, Nicholas E. (Technical Monitor)

2000-01-01

407

GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES  

SciTech Connect

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

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

2012-08-20

408

Opacity Build-up in Impulsive Relativistic Sources  

SciTech Connect

Opacity effects in relativistic sources of high-energy gamma-rays, such as gamma-ray bursts (GRBs) or Blazars, can probe the Lorentz factor of the outflow as well as the distance of the emission site from the source, and thus help constrain the composition of the outflow (protons, pairs, magnetic field) and the emission mechanism. Most previous works consider the opacity in steady state. Here we study the effects of the time dependence of the opacity to pair production ({gamma}{gamma} {yields} e{sup +}e{sup -}) in an impulsive relativistic source, which may be relevant for the prompt gamma-ray emission in GRBs or flares in Blazars. We present a simple, yet rich, semi-analytic model for the time and energy dependence of the optical depth, {tau}{gamma}{gamma}, in which a thin spherical shell expands ultra-relativistically and emits isotropically in its own rest frame over a finite range of radii, R{sub 0} {le} R {le} R{sub 0}+{Delta}R. This is particularly relevant for GRB internal shocks. We find that in an impulsive source ({Delta}R {approx}< R{sub 0}), while the instantaneous spectrum (which is typically hard to measure due to poor photon statistics) has an exponential cutoff above the photon energy {var_epsilon}1(T) where t{gamma}{gamma}({var_epsilon}1) = 1, the time integrated spectrum (which is easier to measure) has a power-law high-energy tail above the photon energy {var_epsilon}1* {approx} {var_epsilon}1({Delta}T) where {Delta}T is the duration of the emission episode. Furthermore, photons with energies {var_epsilon} > {var_epsilon}1* are expected to arrive mainly near the onset of the spike in the light curve or flare, which corresponds to the short emission episode. This arises since in such impulsive sources it takes time to build-up the (target) photon field, and thus the optical depth {tau}{gamma}{gamma}({var_epsilon}) initially increases with time and {var_epsilon}1(T) correspondingly decreases with time, so that photons of energy {var_epsilon} > {var_epsilon}1* are able to escape the source mainly very early on while {var_epsilon}1(T) > {var_epsilon}. As the source approaches a quasi-steady state ({Delta}R >> R0), the time integrated spectrum develops an exponential cutoff, while the power-law tail becomes increasingly suppressed.

Granot, Jonathan; Cohen-Tanugi, Johann; Silva, Eduardo do Couto e

2007-09-28

409

Development patterns and controlling factors of Tertiary carbonate buildups: Insights from high-resolution 3D seismic and well data in the Malampaya gas field (Offshore Palawan, Philippines)  

Microsoft Academic Search

The comprehensive subsurface database of the Malampaya buildup (Late Eocene to Early Miocene, offshore NW Palawan) provides a rare insight into the development of South-East Asian Cenozoic carbonate systems and their controlling factors. The newly acquired high-resolution three-dimensional seismic survey, combined with facies and well-log analysis, allowed a better understanding of the internal architecture of a carbonate platform whose development

F. Fournier; J. Borgomano; L. F. Montaggioni

2005-01-01

410

Simulation of prompt gamma-ray emission during proton radiotherapy.  

PubMed

The measurement of prompt gamma rays emitted from proton-induced nuclear reactions has been proposed as a method to verify in vivo the range of a clinical proton radiotherapy beam. A good understanding of the prompt gamma-ray emission during proton therapy is key to develop a clinically feasible technique, as it can facilitate accurate simulations and uncertainty analysis of gamma detector designs. Also, the gamma production cross-sections may be incorporated as prior knowledge in the reconstruction of the proton range from the measurements. In this work, we performed simulations of proton-induced nuclear reactions with the main elements of human tissue, carbon-12, oxygen-16 and nitrogen-14, using the nuclear reaction models of the GEANT4 and MCNP6 Monte Carlo codes and the dedicated nuclear reaction codes TALYS and EMPIRE. For each code, we made an effort to optimize the input parameters and model selection. The results of the models were compared to available experimental data of discrete gamma line cross-sections. Overall, the dedicated nuclear reaction codes reproduced the experimental data more consistently, while the Monte Carlo codes showed larger discrepancies for a number of gamma lines. The model differences lead to a variation of the total gamma production near the end of the proton range by a factor of about 2. These results indicate a need for additional theoretical and experimental study of proton-induced gamma emission in human tissue. PMID:22864267

Verburg, Joost M; Shih, Helen A; Seco, Joao

2012-09-01

411

Gamma-ray burst spectral diagnostics for GLAST  

NASA Astrophysics Data System (ADS)

One of the principal results obtained by the EGRET experiment aboard the Compton Gamma-Ray Observatory was the detection of several gamma-ray bursts (GRBs) above 100 MeV. The broad-band spectra obtained for these bursts gave no indication of any spectral attenuation that might preclude detection of bursts at higher energies. With the discovery of optical afterglows and counterparts to bursts in the last few years, enabling the determination of significant redshifts for these sources, it is anticipated that profound spectral attenuation will arise in the GLAST energy band of 30 MeV- 300 GeV for many if not most bursts. An important goal will be to discriminate between such extrinsic absorption, due to the cosmic infra-red background, and that which arises internally in GRBs. This paper explores the expectations for the spectral properties in the GLAST band for bursts, in particular how attenuation of photons by pair creation internal to the source modifies the spectrum to produce distinctive signatures. The energy of spectral breaks and the associated spectral indices provide valuable information that can constrain the bulk Lorentz factor of the GRB outflow at a given time. Moreover, distinct temporal behavior is present for internal attenuation, and is easily distinguished from extrinsic absorption. These characteristics define palpable observational goals for both the GLAST mission and ground-based ?Cerenkov telescopes, and strongly impact the observability of bursts above 1 GeV.

Baring, M. G.

2001-08-01

412

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

413

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

414

PRECURSORS OF SHORT GAMMA-RAY BURSTS  

SciTech Connect

We carried out a systematic search of precursors on the sample of short gamma-ray bursts (GRBs) observed by Swift. We found that {approx}8%-10% of short GRBs display such early episodes of emission. One burst (GRB 090510) shows two precursor events, the former {approx}13 s and the latter {approx}0.5 s before the GRB. We did not find any substantial difference between the precursor and the main GRB emission, and between short GRBs with and without precursors. We discuss possible mechanisms to reproduce the observed precursor emission within the scenario of compact object mergers. The implications of our results on quantum gravity constraints are also discussed.

Troja, E.; Gehrels, N. [NASA, Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Rosswog, S. [School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen (Germany)

2010-11-10

415

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

416

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

417

Gamma Ray Bursts: an Enigma Being Unraveled  

SciTech Connect

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

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

2003-05-14

418

Gamma-Ray Spectroscopy of 76As  

Microsoft Academic Search

Decay of 76As was investigated by using a Ge(Li) detector and Ge(Li)-NaI(Tl) coincidence methods. Sixteen new gamma-rays were observed and eleven of them were assigned in a proposed decay scheme. Four new levels were found at 2026.4, 2348, 2365.1 and 2514 keV. Spins and parities of levels at 2026.4, 2655.7 and 2669.8 keV were estimated from log ft values of

Katsuyuki Iizawa; Isao Kitamura; Kiyoshi Kawade; Hiroshi Yamamoto; Kanzo Yoshikawa; Susumu Amemiya; Toshio Katoh

1971-01-01

419

Directions in gamma-ray spectroscopy  

NASA Technical Reports Server (NTRS)

Current and future instrumentation for gamma-ray spectroscopy in the spectral range from 10 keV to 10 MeV is described. New technologies for Germanium (Ge) spectrometers and emerging detector technologies are highlighted. Scientific objectives are considered, with emphasis on capabilities beyond those of the Nuclear Astrophysics Explorer (NAE). A list of instrument requirements is given. Technologies under development for an NAE-era spectrometer are presented. Spectrometers beyond NAE and other types of future technologies are discussed, and a partial list of current and future spectrometers is provided.

Gehrels, Neil; Candey, Robert M.

1990-01-01

420

Status of the Compton Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

The Compton Gamma Ray Observatory and three of its four experiment packages continue to function in a nearly flawless manner now well into the eighth year of mission operations. Only the EGRET instrument is operating with reduced capability due mainly to the depleted spark-chamber gas, but it is nonetheless still expected to make significant contributions, notably in the area of Solar flares and AGN variability. We discuss the status of the mission as of mid-1999 as well as the prospects of an extended mission lasting well into the first decade of the next century. .

Gehrels, Neil; Shrader, Chris

2000-04-01

421

Fermi gamma-ray imaging of a radio galaxy.  

PubMed

The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields. PMID:20360067

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

2010-05-01

422

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

423

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

424

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

425

MGGPOD: a Monte Carlo Suite for Modeling Instrumental Line and Continuum Backgrounds in Gamma-Ray Astronomy  

NASA Technical Reports Server (NTRS)

Intense and complex instrumental backgrounds, against which the much smaller signals from celestial sources have to be discerned, are a notorious problem for low and intermediate energy gamma-ray astronomy (approximately 50 keV - 10 MeV). Therefore a detailed qualitative and quantitative understanding of instrumental line and continuum backgrounds is crucial for most stages of gamma-ray astronomy missions, ranging from the design and development of new instrumentation through performance prediction to data reduction. We have developed MGGPOD, a user-friendly suite of Monte Carlo codes built around the widely used GEANT (Version 3.21) package, to simulate ab initio the physical processes relevant for the production of instrumental backgrounds. These include the build-up and delayed decay of radioactive isotopes as well as the prompt de-excitation of excited nuclei, both of which give rise to a plethora of instrumental gamma-ray background lines in addition t o continuum backgrounds. The MGGPOD package and documentation are publicly available for download. We demonstrate the capabilities of the MGGPOD suite by modeling high resolution gamma-ray spectra recorded by the Transient Gamma-Ray Spectrometer (TGRS) on board Wind during 1995. The TGRS is a Ge spectrometer operating in the 40 keV to 8 MeV range. Due to its fine energy resolution, these spectra reveal the complex instrumental background in formidable detail, particularly the many prompt and delayed gamma-ray lines. We evaluate the successes and failures of the MGGPOD package in reproducing TGRS data, and provide identifications for the numerous instrumental lines.

Weidenspointner, G.; Harris, M. J.; Sturner, S.; Teegarden, B. J.; Ferguson, C.

2004-01-01

426

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.

427

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

428

Improved Gamma-Ray Flux Monitoring at the High Intensity Gamma-Ray Source (HIGS)  

NASA Astrophysics Data System (ADS)

An improved gamma-ray beam flux monitor has been built for use at the High Intensity Gamma-Ray Source at the Duke University Free Electron Laser Laboratories. It is important to know precisely the gamma-ray flux of this beam. It is also important to limit beam attenuation to a minimum while making an accurate flux measurement. The improvements from a more accurate gamma-ray intensity monitor will allow for more precise cross-section measurements and will be valuable to many of the experiments conducted at HIGS. The detector consists of a thin scintillator optically coupled to two photomultiplier tubes, a thin foil, and then another thin scintillator attached to two photomultiplier tubes. The front scintillator is used to veto counts from charged particles emitted upstream in the beam-line. The preliminary tests of the monitor show very promising results and after slight adjustments and calibrations, the detector will be ready to acquire accurate beam intensity measurements while contributing very little to beam attenuation.

Reynolds, Robert

2002-10-01

429

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

NASA Astrophysics Data System (ADS)

About 250 peaks and broad features were observed in a long spectrum from the Mars Odyssey Gamma-Ray Spectrometer, most of which have been identified. Many are background lines from Ge, Mg, Ti, Zn, and other elements near the GRS.

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

2003-03-01

430

Missing High-Energy Gamma-ray Afterglows of Gamma-ray Bursts  

NASA Astrophysics Data System (ADS)

The largest explosions in the Universe, gamma-ray bursts (GRBs), are short-lived signatures of a rare type of end stage stellar evolution. We study the X-ray and gamma-ray emission with the Swift and Fermi observatories. High energy gamma-ray (>100 MeV) emission from these objects is rare, only present in ~8% of GRBs. We investigate whether or not there are bursts in the Swift sample that should have been detectable by Fermi-LAT, assuming the same emission component. By using the well-studied Swift X-ray afterglows, we extrapolate from the soft X-ray energy range (0.3 keV-10 keV) to the LAT energy range (100 MeV-100 GeV), to search for bursts which should have had high-energy afterglows, but must have breaks or cutoffs in their spectra. We compare the extrapolated gamma-ray fluxes to upper limits measured while the GRBs were in the LAT field of view, and find candidates for cutoff spectra requiring full broadband modeling. By characterizing the missing LAT afterglows, we can gain a better understanding of the emission mechanism, environment, and microphysical parameters.

Holt, Carrie; Racusin, J. L.; Kocevski, D.; Fermi Large Area Telescope Collaboration

2014-01-01

431

Wolf-Rayet Stars and Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Observational properties of Gamma-Ray bursts, WR stars and their CO-cores at the end of evolution are analysed. Distribution of Gamma-Ray burst energies N(?E) has a wide range from 7?1051 to 2?1054 ergs. There are some evidences for bimodality of energy distribution N(?E) if we take into account Gamma-Ray burst GRB980425, associated with peculiar Ic-type supernova SN1998bw for which ?E?1048 ergs. These characteristics for Gamma-Ray bursts are in agreement with the distribution of the final masses of CO-cores of WR stars which is wide and continuous: MfCO=(1-2)Msolardiv(20- 44)Msolar. Possible bimodality of distribution of Gamma-Ray burst energies (? E1=1048 ergs; ? E2=7?1051div2?1054 ergs) is in agreement with bimodal distribution of relativistic objects: MNS=(1.35±0.15)Msolar, MBM=(4-15)Msolar. Arguments are given favoring possible connection of Gamma-Ray bursts with core collapses of WR stars. Expected frequency of collapses of CO-cores of WR stars in Galaxy is ~10-3 year-1 which is 3-4 order of magnitude higher than that of Gamma-Ray bursts calculated per one galaxy. WO stars can be considered as most probable candidates for progenitors of Gamma-Ray bursts. For these WR stars the frequency of collapses is ~10-5 years-1. Models of Paczynski (1998) and Gershtein (2000) can be considered as realistic models for Gamma-Ray burst phenomenon. For both models taking into account jet-like structure of Gamma-Ray formation region as well as random outcome of collapse of CO-core of WR star can explain observed Gamma-Ray burst frequencies. Investigation of WR galaxies (Conti, 1991) in connection with Gamma-Ray bursts seems to be very promising.

Cherepashchuk, A. M.

432

EGRET observations of high energy gamma ray pulsars  

Microsoft Academic Search

Observations with the EGRET instrument on CGRO have so far revealed gamma ray emission at E>100 MeV from 6, possibly 7 pulsars: 5 (6) radio pulsars and the radio quiet pulsar Geminga. The observed gamma ray lightcurves show mostly two peaked emission patterns; only PSR B1706-44 has a more complex lightcurve. The gamma ray photon number spectra between 30 MeV

G. Kanbach

1998-01-01

433

Multi-wavelength emission region of gamma-ray pulsars  

Microsoft Academic Search

Recent obserbations by Fermi Gamma-Ray Space Telescope of gamma-ray pulsars have revealed further details of the structure of the emission region. We investigate the emission region for the multi-wavelength light curve using outer gap model. We assume that gamma-ray and non-thermal X-ray photons are emitted from a particle acceleration region in the outer magnetosphere, and UV\\/optical photons originate above that

Shota Kisaka; Yasufumi Kojima

2011-01-01

434

Radio search for gamma-ray pulsar counterparts  

Microsoft Academic Search

The Fermi gamma-ray satellite, launched in June 2008 is already returning remarkable results. In particular, it has discovered a large number of gamma-ray pulsars without any known radio counterpart (where only 1 was known prior to launch) and has detected unknown sources of gamma-ray radiation in the galactic plane with arcmin positional accuracy. Here we request time to (a) search

Michael Keith; Simon Johnston; Roger W. Romani; David J. Thompson; Patrick Weltevrede; Peter Michelson

2009-01-01

435

On the energetics and number of gamma-ray pulsars  

Microsoft Academic Search

We examine a nearly aligned pulsar model with polar cap acceleration in order to explain the energetics and number of the known gamma-ray pulsars. In this model, the efficiency of converting spin-down luminosity to gamma-ray luminosity increases with decreasing spin-down luminosity, a trend recently emphasized by Ulmer. The predicted gamma-ray flux is proportional to dot P3\\/4\\/P5\\/4 d2, where P is

Charles D. Dermer; Steven J. Sturner

1994-01-01

436

Neutron-Insensitive Proportional Counter for Gamma-Ray Dosimetry  

Microsoft Academic Search

A gamma-ray dosimeter with low sensitivity to neutrons has been developed for radiation dosimetry in mixed fields of neutrons and gamma rays. Neutron sensitivity in a 2.5- to 3-Mev H2(d,n)He3 neutron field has been shown experimentally to be ?1.2% on the basis of first collision dose in tissue. Gamma-ray sensitivity is independent of energy to within ±5% from 1.25 Mev

Randall S. Caswell

1960-01-01

437

Gamma Rays in the Decay of Barium131  

Microsoft Academic Search

Gamma rays accompanying electron capture of 12-day Ba131 have been studied with a single-channel scintillation spectrometer. Relative intensities have been determined for the 122 kev (198), 214 kev (148), 372 kev (100), 496 kev plus satellite (360), and 620 kev (33) gamma-rays. Three new gamma-rays have been found at 823+\\/-20 kev (2.0), 917+\\/-15 kev (7.2), and 1032+\\/-15 kev (11.0), and

William C. Beggs; Berol L. Robinson; Richard W. Fink

1956-01-01

438

The Radio and Gamma-Ray Luminosities of Blazars  

Microsoft Academic Search

Based on the gamma-ray data of blazars in the third EGRET catalog and radio data at 5 GHz, we studied the correlation between the radio and gamma-ray luminosities using two statistical methods. The first method was the partial correlation analysis method, which indicates that there exist correlations between the radio and gamma-ray luminosities in both high and low states as

L. Zhang; K. S. Cheng; J. H. Fan

2001-01-01

439

The Radio and Gamma-Ray Luminosities of Blazars  

Microsoft Academic Search

Based on the $\\\\gamma$-ray data of blazars in the third EGRET catalog and\\u000aradio data at 5 GHz, we studied the correlation between the radio and\\u000a$\\\\gamma$-ray luminosities using two statistical methods. The first method was\\u000athe partial correlation analysis method, which indicates that there exist\\u000acorrelations between the radio and $\\\\gamma$-ray luminosities in both high and\\u000alow states as

L. Zhang; K. S. Cheng; J. H. Fan

2001-01-01

440

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

441

Interpretation of the pulsed gamma-ray emission from Vela  

NASA Technical Reports Server (NTRS)

A model is proposed for the Vela pulsar in which the radio emission originates near the surface of the neutron star while the pulsed gamma-ray emission is produced by synchrotron radiation near the speed-of-light cylinder. This model can explain the energy flux, double pulse structure, and phase shift (with respect to the radio) of the gamma-ray emission, and offers approximate quantitative predictions for other X- and gamma-ray fluxes.

Thompson, D. J.

1975-01-01

442

The new prompt gamma-ray catalogue for PGAA  

Microsoft Academic Search

A new catalogue of subthermal neutron-induced prompt gamma rays has been created for 79 elements, from hydrogen to uranium (including fission), on the basis of recent measurements at the Budapest guided-neutron PGAA facility. New energy values have been measured using 35Cl neutron-capture gamma rays, while the gamma-ray production cross-sections have been determined with respect to the 1H thermal capture cross-section.

G. L. Molnár; Zs. Révay; T. Belgya; R. B. Firestone

2000-01-01

443

Goddard Contributions to the Workshop on Gamma Ray Transients  

NASA Technical Reports Server (NTRS)

Six articles addressing cosmic and solar gamma ray transients are presented. The topics covered include: gamma ray lines from solar flares and cosmic transients including burst spectra; a review of the 1979 March 5 transient; time variation in the 511 KeV flux observed by the ISEE spectrometer; time variations of an absorption feature in the spectrum of the burst on 1980 April 19; and the theory of gamma ray amplification through stimulated annihilation radiation.

1981-01-01

444

Capture Gamma-ray Spectroscopy Using Cold Neutron Beams  

NASA Astrophysics Data System (ADS)

The availability of cold neutron beams can improve the quality of results obtainable from a capture gamma-ray measurement. Although capture gamma-ray instruments that use cold neutrons are less susceptible to problems that limit the capabilities of thermal instruments, new design parameters become important to consider. We discuss some of the questions that relate to neutron beam handling and present techniques for improving the quality of the capture gamma-ray instrument.

Stone, C. A.; Mildner, D. F. R.; Zeisler, R.; Cranmer, D. C.

1991-10-01

445

Multi-energy gamma-ray automated scanning system  

SciTech Connect

A CAMAC-based gamma-ray scanning system was used to measure the transmission through stacked attenuators for up to 16 different gamma rays. For each measurement, we obtained the transmission for gamma rays ranging in energy from 77 to 2614 keV. These transmission measurements were used to produce a set of linear equations that may be solved for either thickness or density of the discrete attenuators comprising a given stacked assembly.

Hsu, H.H.; Pratt, J.C.; Shunk, E.R.

1981-01-01

446

Interpretation of the pulsed gamma ray emission from Vela  

NASA Technical Reports Server (NTRS)

A model is proposed for the Vela pulsar in which the radio emission originates near the surface of the neutron star while the pulsed gamma ray emission is produced by synchrotron radiation near the speed of light cylinder. This model can explain the energy flux, double pulse structure, and phase shift with respect to the radio of the gamma ray emission and offers approximate quantitative predictions for other X-ray and gamma-ray fluxes.

Thompson, D. J.

1975-01-01

447

Planetary gamma-ray spectroscopy of the surface of Mercury  

Microsoft Academic Search

To approach basic scientific questions on the origin and evolution of Mercury one needs data on its chemical composition. Gamma-rays emitted from the surface can be measured by a gamma-ray spectrometer on board an orbiting spacecraft. The gamma-ray flux emitted by the surface of Mercury is simulated by Monte-Carlo codes that calculate the interaction of cosmic-ray particles with the surface

J. Brückner; J. Masarik

1997-01-01

448

Analytical applications of neutron capture gamma-ray spectroscopy  

Microsoft Academic Search

Prompt gamma rays from thermally induced nuclear reactions have been used to estimate the boron, chlorine and phosphorus contents in industrial and reference materials. A neutron capture gamma-ray spectroscopy facility for analytical purposes using 252Cf sources has been designed and calibrated and is described in this paper. The facility is principally designed for measurement of the prompt gamma-ray spectra obtained

A. M. Hassan; E. Gantner; E. Mainka; H. Ruf; U. Kuhnes; M. Mostafa

1983-01-01

449

Analysis of fissionable material using delayed gamma rays from photofission  

Microsoft Academic Search

The energetic gamma-ray spectra from the fission products of photofission have been investigated to determine whether photofission can identify heavily shielded fissionable material. Target samples of natural thorium, 93% enriched ²³⁵U, natural uranium, and 93% enriched ²³⁹Pu were irradiated with bremsstrahlung gamma rays produced by 10-MeV electrons from a small linear accelerator. The gamma-ray spectra for each of the four

C. L. Hollas; D. A. Close; C. E. Moss

1986-01-01

450

Analysis of fissionable material using delayed gamma rays from photofission  

Microsoft Academic Search

The energetic gamma-ray spectra from the fission products of photofission have been investigated to determine whether photofission can identify heavily shielded fissionable material. Target samples of natural thorium, 93% enriched 235U, natural uranium, and 93% enriched 239Pu were irradiated with bremsstrahlung gamma rays produced by 10-MeV electrons from a small linear accelerator. The gamma-ray spectra for each of the four

C. L. Hollas; D. A. Close; C. E. Moss

1987-01-01

451

Gamma Rays from Short-Lived Fission-Fragment Isomers  

Microsoft Academic Search

Measurements of the energy spectra of isomeric gamma rays from the neutron fission of U235 and Pu239 at a number of time intervals between 50 and 600 musec showed six prominent gamma rays for both cases of fission. The intensities and half-lives for these gamma rays indicate that there are three fission-fragment isomers, each giving rise to a pair of

R. E. Sund; R. B. Walton

1966-01-01

452

High energy gamma-ray observations of SN 1987A  

NASA Technical Reports Server (NTRS)

Results are presented from observations of SN 1987A made with a combined high energy gamma ray and hard X-ray payload carried on a balloon flight over Alice Springs, Australia on April 5, 1988. The payload instrumentation is described, emphasizing the characteristics of the gamma-ray detector. The gamma-ray emission profile is illustrated and the preliminary results of the observations are summarized.

Sood, R. K.; Thomas, J. A.; Waldron, L.; Manchanda, R. K.; Rochester, G. K.

1988-01-01

453

Future Facilities for Gamma-Ray Pulsar Studies  

NASA Technical Reports Server (NTRS)

Pulsars seen at gamma-ray energies offer insight into particle acceleration to very high energies, along with information about the geometry and interaction processes in the magnetospheres of these rotating neutron stars. During the next decade, a number of new gamma-ray facilities will become available for pulsar studies. This brief review describes the motivation for gamma-ray pulsar studies, the opportunities for such studies, and some specific discussion of the capabilities of the Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) for pulsar measurements.

Thompson, D. J.

2003-01-01

454

Gamma-ray/neutron spectroscopy from the Mars observer  

NASA Technical Reports Server (NTRS)

The Gamma-Ray Spectrometer (GRS) experiment on Mars Observer will measure gamma rays and neutrons that escape from Mars. The intensities of gamma-ray lines and of the thermal and epithermal neutrons can be used to study many problems related to Martian volcanism and volatiles. The results of theoretical calculations for the production and transport of gamma rays and neutrons indicate that the GRS should be able to determine the abundances of many elements and the amounts and stratigraphy of H2O and CO2 on and in the top meter of the Martian surface. Design considerations of the GRS are discussed.

Englert, P.; Reedy, R. C.; Drake, D. M.; Feldman, W. C.; Squyres, S. W.; Evans, L. G.; Boynton, W. V.

1987-01-01

455

Nonrelativistic phase in gamma-ray burst afterglows  

Microsoft Academic Search

The discovery of multiband afterglows definitely shows that most $\\\\gamma$-ray\\u000abursts are of cosmological origin. $\\\\gamma$-ray bursts are found to be one of\\u000athe most violent explosive phenomena in the Universe, in which astonishing\\u000aultra-relativistic motions are involved. In this article, the multiband\\u000aobservational characteristics of $\\\\gamma$-ray bursts and their afterglows are\\u000abriefly reviewed. The standard model of $\\\\gamma$-ray bursts,

HUANG Yongfeng; T. Lu; K. S. Cheng

2007-01-01

456

Inelastic cross sections from gamma-ray measurements  

SciTech Connect

Measurements of gamma rays following neutron induced reactions have been studied with the Germanium Array for Neutron-induced Excitations (GEANIE) at the Los Alamos Neutron Science Center (LANSCE) for many years. Gamma-ray excitation functions and coincidence studies provide insight into nuclear reaction mechanisms as well as expanding our knowledge of energy levels and gamma-rays. Samples studied with Ge detectors at LANSCE range from Be to Pu. Fe, Cr and Ti have been considered for use as reference cross sections. An overview of the measurements and efforts to create a reliable neutron-induced gamma-ray reference cross section will be presented.

Nelson, Ronald Owen [Los Alamos National Laboratory

2010-12-06

457

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

458

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

459

Experiment on gamma-ray generation and application  

NASA Astrophysics Data System (ADS)

An experimental setup of gamma-ray generation through laser Compton scattering has been built on the NewSUBARU storage ring. The aim is to study nuclear transmutation, which is regarded as the first stage to explore the feasibility of developing a nuclear waste disposal system based on the concept of ir