Blazars, active galactic nuclei with relativistic jets pointed almost directly at Earth, are powerful and highly variable sources of nonthermal electromagnetic radiation, including very-high-energy gamma rays. We can detect these gamma rays with arrays of imaging atmospheric Cherenkov telescopes (IACTs), including the Very Energetic Radiation Imaging Telescope Array System (VERITAS) and the upcoming Cherenkov Telescope Array (CTA). After reviewing the science of blazars and the methods used by IACTs, we investigate how gamma-ray variability can provide insight into blazars' physical properties while also complicating efforts to understand these sources as a population. We first present a study of three flaring blazars observed with VERITAS and analyze these sources' spectral and variability characteristics, taking into account data at other wavebands, including that of the Large Area Telescope aboard the Fermi space telescope (Fermi-LAT). Next, after laying out how observing biases and intrinsic variability can confound blazar population studies with IACTs, we propose methods to account for these effects, and use simulated data to report expectations for a blazar luminosity function measurement with VERITAS. Sophisticated new instruments and data analysis methods can further expand the frontier of gamma-ray blazar science. To that end, we design a camera software system to enable safer and more efficient operations of a next-generation IACT being developed for CTA, the prototype Schwarzschild-Couder Telescope (pSCT). Finally, we develop methods to apply deep neural networks to the analysis of IACT data and employ these methods to reject background events detected by simulated arrays of IACTs.

The Clemson GRB Follow-Up program utilizes the SARA 0.9-m telescope to observe optical afterglows of Gamma Ray Bursts. SARA is not yet robotic; it operates under direct and Target-of-Opportunity (ToO) interrupt modes. To facilitate rapid response and timely reporting of data analysis results, we developed a software suite that operates in two phases: first, to notify observers of a burst and assist in data collection, and second, to quickly analyze the images.

>Magister Scientiae - MSc / In this work we have determined the spectroscopic or static quadrupole moment of the rst excited state (QS (2+1) lying at 2230.6 keV in 32S using the reorientation e ect. The Coulomb-excitation experiment at safe bombarding energies was performed at iThemba LABS's AFRODITE vault, where 32S beams at 120.3 MeV were bombarded onto a 194Pt target of 1 mg/cm2 thickness. The beam energy has been chosen such that the separation between nuclear surfaces is greater than 6.5 fm at all scattering angles, in order to avoid nuclear interactions. A double-sided CD-type S3 silicon detector, with 24 rings and 32 sectors, has been placed upstream (at backward angles) to detect the scattered particles. Gamma rays have been detected with the AFRODITE clover array. This particle-gamma coincidence experiment allows for an angular distribution and Doppler correction of the gamma rays emitted at 9% the speed of light. The cross sections (or gamma-ray integrated yields) measured as a function of scattering angle at backward angles are sensitive to second-order perturbation e ects in Coulomb excitation, i.e., diagonal matrix elements which are directly related to the spectroscopic quadrupole moment. The gamma-ray integrated yields obtained from this experiment are compared with the GOSIA simulations, yielding a new measurement of QS (2+1) = 􀀀0:10 0:7 eb, which corresponds to a prolate shape in the intrinsic frame of the nucleus. The uncertainty of this measurement is limited by statistics. This result agrees with previous measurements and con rms the zig zag of shapes at the end of the sd shell when approaching the doubly-magic nucleus 40Ca. Nonetheless, the mystery continues as a prolate shape for the rst 2+ disagrees with modern theoretical mean- eld calculations and the pairing coupling model.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20786号 / 理博第4330号 / 新制||理||1622(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 谷森 達, 教授 永江 知文, 教授 鶴 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

A study of ground state binding energy values listed in the Atomic Mass Evaluation 2012 (AME2012) using an interpretive approach, as opposed to the exploratory methods of previous models, is presented. This model is based on a postulate requiring all protons to pair with available neutrons to form bound alpha clusters as the ground state for anN = Z core upon which excess neutrons are added. For each core, the trend of the binding energy as a function of excess neutrons in the isotopic chain can be fit with a three-term quadratic function. The quadratic parameter reveals a smooth decaying exponential function. By re-envisioning the determination of mass excess, the constant-term fit parameters, representing N = Z nuclei, reveal a near-symmetry around Z = 50. The linear fit parameters exhibit trends which are linear functions of core size. A neutron drip-line prediction is compared against current models. By considering the possibility of an alpha-cluster core, a new ground-state structure grouping scheme is presented; nucleon-nucleon pairing is shown to have a greater role in level filling. This model, referred to as the Alpha-Deuteron-Neutron Model, yields promising first results when considering root-mean-square variances from the AME2012. The beta-decay of the neutron-rich isotope 74Cu has been studied using three highpurity Germanium clover detectors at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. A high-resolution mass separator greatly improved the purity of the 74Cu beam by removing isobaric contaminants, thus allowing decay through its isobar chain to the stable 74Ge at the center of the LeRIBSS detector array without any decay chain member dominating. Using coincidence gating techniques, 121 gamma-rays associated with 74Cu were isolated from the collective singles spectrum. Eighty-seven of these were placed in an expanded level scheme, and updated betaeeding level intensities and log(ft) values are presented based on multiple newly-placed excited states up to 6.8 MeV. The progression of simulated Total Absorption gamma-ray Spectroscopy (TAGS) based on known levels and beta feeding values from previous measurements to this evaluation are presented and demonstrate the need for a TAGS measurement of this isotope to gain a more complete understanding of its decay scheme.

The National Nuclear Data Center (NNDC) contains a compilation of information on the beta decays of Gallium isotopes. In the mass range A = 74 to 77, the Germanium daughters lie close to or at the valley of stability leading us to believe the decays would have been well studied. However, closer inspection indicates significant conflict for placement of gamma rays and energy levels between different measurements, especially for upper-lying states. Detailed beta-decay studies for the 74-77Ga isotopes were performed using a high resolution four clover Hyper-Pure Germanium (HPGe) detector system with two beta scintillators in the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL) to better understand the structure of the corresponding 74-77Ge daughter nuclei. In our experiments, use of a high-resolution mass separator greatly improved the purity of the samples in comparison to previous measurements. Besides that, the efficiency of the detector system we utilized was much higher than used in previous studies. We also established a method to determine statistically significant gamma gamma coincidence relationships to add reliability to the placement of gamma rays to energy levels and avoid experimental biases. From our analysis, we have established comprehensive decay schemes for all four Germanium nuclei in this study. In most cases, we have extended the energy levels to cover more of the energy window available for beta decay. Our proposed 74Ge decay scheme contains 44 energy levels occupying up to 4.36-MeV with the placement of 99 gamma rays. Similarly, 75Ga decay scheme contains 72 gamma rays with 29 energy levels occupying up to 2.75 MeV. The 76Ga decay scheme has 49 excited states with 100 gamma rays occupying up to 4.81 MeV. And, the 77Ge decay scheme has 68 gamma rays and 34 energy levels occupying up to 3.14 MeV. Based on the expanded level schemes, betaeeding intensity and log(ft) value lower limits were calculated and attempts were made to assign the spin-parity of the observed states. The resulting level schemes were then compared with the Nushellx theoretical predictions.

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No description available.

Gamma-ray bursts (GRBs) are the most luminous phenomena in the Universe, explosions whoseenergy is generated by supernovae or mergers of dense objects such as neutron stars. The GRBemission is divided into the prompt emission phase characterized by γ-ray radiation and the afterglowof lower energy radiation. The prompt emission phase is still not understood; as of now, there aretwo leading descriptions: the photospheric- and the synchrotron models. The synchrotron model hashad great success in describing GRB spectra, and specifically some of the brightest ones, although notwithout issues such as some observations being at odds with theory. On the other hand, photosphericmodels have had problems too of how to broaden the spectrum in order to explain the observeddata. One explanation for this broadening is that Radiation Mediated Shocks (RMSs) dissipate energybelow the photosphere. In this report, a time resolved spectral analysis of the prompt emission of GRB160625B – a very bright GRB known to produce synchrotron-like emission – is done. Komrad is animplementation of the Kompaneets RMS Approximation (KRA), which is a dissipative photosphericmodel. Komrad is then used to fit a photospheric model to the prompt emission of GRB 160625Bin order to explore whether photospheric models can account for synchrotron-like emission spectra.Great statistical support is found for the photospheric model in comparison to standard GRB fittingfunctions as well as a synchrotron function which is indicative of the photospheric model being able toexplain a synchrotron-like spectra.

<p> This thesis deals with the changes, in the response of a Ge(Li) gamma ray detector, arising from damage caused by its exposure to high energy neutrons. The phenomenon of charge trapping is considered and included in a model explaining the collection of electron-hole pairs in a Ge(Li) detector. From this model a response function for the output of the detector is obtained and then applied to a description of the changes in FWHM of pulse height spectra peaks with energy and neutron irradiation.</p> <p> Described are experiments in which three detectors were exposed to fast neutrons and their changing response was related to the response function. Finally the number of damage centres produced by the neutrons is discussed.</p> / Thesis / Master of Science (MSc)