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Coupled multi-group neutron photon transport for the simulation of high-resolution gamma-ray spectroscopy applicationsBurns, Kimberly Ann. January 2009 (has links)
Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Hertel, Nolan; Committee Member: Kulp, William David; Committee Member: Lee, Eva; Committee Member: Pagh, Richard; Committee Member: Petrovic, Bojan; Committee Member: Rahnema, Farzad; Committee Member: Smith, Eric; Committee Member: Wang, Chris. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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High-energy emission and recent afterglow studies of gamma-ray burstsBarniol Duran, Rodolfo Jose 16 June 2011 (has links)
Gamma-ray Bursts (GRBs) are powerful explosions that emit
most of their energy, as their name suggests, in gamma-rays of typical energies
of about 1 MeV. This emission lasts for about two minutes or less and it is called the prompt emission. The isotropic energy radiated in GRBs is equivalent to the energy that the
Sun will radiate in its entire lifetime. After decades of studying
this cosmological phenomenon, we have come to learn that it involves
a collimated and relativistic jet. Also, we know that they
radiate energy in the X-ray, optical and radio bands for days, weeks and years, respectively, which is called the
afterglow. Recently, NASA's Fermi Satellite was launched and,
in addition to MeV photons, it detected GeV photons from these astrophysical sources.
We show that these GeV photons are produced when the GRB jet interacts with the medium
that surrounds it: the external forward shock model. We arrive at this conclusion
not only by studying the GeV emission, but also by studying the afterglow observations
(Chapter 2). We corroborate this model by studying the electron acceleration
in the external forward shock model and find that electrons can radiate at the maximum observed
energy of ~ 10 GeV (Chapter 3). We also provide an extensive analysis of the most recent
afterglow observations of GRB 090902B within the same
framework of an external forward shock origin. We find
that the data for this burst requires a small deviation from the
traditionally used power-law electron energy distribution, however,
our previous results remain unchanged (Chapter 4). To conclude,
we use the end of the prompt emission phase, which exhibits a
steep X-ray temporal decay, to constrain the behavior of the
central engine responsible for launching the relativistic jet (Chapter 5). / text
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A model for the production of galactic gamma rays above 10 MeV戚堅鏗, Chik, Kin-hang. January 1982 (has links)
published_or_final_version / Physics / Master / Master of Philosophy
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A multiwavelength investigation of blazar-type active galactic nuclei.Bastin, Fane Troy January 2013 (has links)
A multiwavelength investigation is conducted for nineteen blazar-type active galactic nuclei. Studies of variability timescales and flux duty cycles are performed at x- and gamma-rays for each source, with the relationship between flux and spectral index also being probed at gamma wavelengths. The correlation between these two energy ranges is also investigated, by utilising the Discrete Correlation Function with both one and ten day binning. The sources were chosen for their availability over a range of different x- and gamma-ray data sources: observations utilised include 0.2 - 150 keV x-ray data from the Swift mission and 200 MeV- 300 GeV gamma-ray data from the Fermi mission.
Daily-binned Fermi data is used to calculate the smallest rise and decay e-folding times in gamma for each source. The results range from 0.4 to 21 days, corresponding to limits on the size of the gamma emission region ranging from Rd^-1 = 4.39 x 10^12 to Rd^-1 = 5.14 x 10^14 m.
Flux duty cycles for fourteen sources are created from Fermi data, with six displaying structure at high fluxes that indicate flaring states have occured. Five of these six sources also display clear flares in their light curves, confirming these results. The relationship between the flux and the spectral index shows eight of nineteen sources exhibit harder-when-brighter behaviour. Four of these eight have been previously confirmed to display such behaviour.
Results from the Discrete Correlation Function show a correlation at a time lag of ~ 600 days for H 1426+428, of uncertain origin. Gaussian functions are fitted to possible near-zero peaks in 3C 66A, 3C 454.3 and Mrk 421, which could be indicative of a synchrotron self-Compton component to the emission of these objects.
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The distribution and zoning of the radioelements potassium, uranium, and thorium in selected porphyry copper depositsDavis, Jerry Dean, 1944- January 1971 (has links)
No description available.
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Coded-Aperture Compton Camera for Gamma-Ray ImagingFarber, Aaron M. January 2013 (has links)
This dissertation describes the development of a novel gamma-ray imaging system concept and presents results from Monte Carlo simulations of the new design. Current designs for large field-of-view gamma cameras suitable for homeland security applications implement either a coded aperture or a Compton scattering geometry to image a gamma-ray source. Both of these systems require large, expensive position-sensitive detectors in order to work effectively. By combining characteristics of both of these systems, a new design can be implemented that does not require such expensive detectors and that can be scaled down to a portable size. This new system has significant promise in homeland security, astronomy, botany and other fields, while future iterations may prove useful in medical imaging, other biological sciences and other areas, such as non-destructive testing. A proof-of-principle study of the new gamma-ray imaging system has been performed by Monte Carlo simulation. Various reconstruction methods have been explored and compared. General-Purpose Graphics-Processor-Unit (GPGPU) computation has also been incorporated. The resulting code is a primary design tool for exploring variables such as detector spacing, material selection and thickness and pixel geometry. The advancement of the system from a simple 1-dimensional simulation to a full 3-dimensional model is described. Methods of image reconstruction are discussed and results of simulations consisting of both a 4 x 4 and a 16 x 16 object space mesh have been presented. A discussion of the limitations and potential areas of further study is also presented.
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A procedure for gamma-ray spectroanalysis of neutron-activated materialsHemler, John Vaughn, 1929- January 1960 (has links)
No description available.
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Magnetic tape data handling in a mini-computer based gamma-ray spectroscopy systemRadda, George John, 1952- January 1976 (has links)
No description available.
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Structure of unstable nuclei in the g92 shellOxorn, Kenneth Warren January 1983 (has links)
The level structures of ('94)Ru, ('90)Mo, ('88)Zr, ('89)Mo and ('89)Nb have been studied via the decay of two isomers of ('94)Rh, two of ('90)Tc, two of ('88)Nb, one of ('89)Tc and one of ('89)Mo, respectively. These nuclides were produced via the proton bombardment of isotopically-enriched ('96)Ru and ('92)Mo as well as naturally-occurring Zr. Using gamma and beta spectroscopy techniques, detailed level schemes have been produced. / High-spin states in ('89)Nb, ('88)Zr and ('88)Nb have been studied with in-beam gamma-ray spectroscopy techniques. These nuclides were produced with alpha particle-induced reactions on ('89)Y. A neutron-multiplicity experiment was used to identify the nucleus to which several gamma-rays belong. / The systematics of the N = 48 and 47 nuclei, along with theoretical descriptions based on the nuclear shell model, are discussed. Contributions to original knowledge are summarized in Chapter V.
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Radiometric study of soil: the systematic effects.Joseph, Angelo Daniel. January 2007 (has links)
<p>The natural ² / ³ / â¸U, ² / ³ / ² / Th and â´° / K radioactive content of vineyard soil was measured with an in-situ gamma-ray detector. The activity concentration measured with the in-situ detector are normalized using the laboratory-determined activity concentrations of several samples from the vineyard site. To determine the activity concentration of a particular soil sample, the gamma-ray photopeak detection efficiencies are required. In this work, the detection efficiencies were derived for each soil sample using gamma-ray photopeaks associated with the radionuclide of ² / ³ / â¸U, ² / ³ / ² / Th present in the sample, and the â´° / K, 1460.8 keV gamma-ray peak, from KCl salt.</p>
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