Beam profile monitors provide position and ux distribution information to facilitate the configuration of an experimental apparatus and are an important component of any accelerator facilities beam diagnostic system. Nuclear physics experiments typically involve the incidence of high energy particles or gamma-rays on some target material and the detection of the products of the ensuing interactions. Therefore, knowing the profile of the incident radiation beam is desirable. To address the need for a profile monitor for the High-Intensity Gamma-Ray Source, development of a CCD-based gamma-ray beam profiler was undertaken. The profiler consisted of plastic scintillator, a lens system and a Starlight Express MX5 CCD camera, all contained within a light tight box. The scintillation pattern, created by the interaction between the incident gamma-rays and the scintillator, could be focused onto the CCD. Simulations were used to determine the amount of power that would be absorbed for different beam energies and scintillator thicknesses. The use of a converter material, placed directly against the scintillator to improve power deposition, was also investigated. The system was tested in order to and the camera noise characteristics, the optical resolution and magnification and the systems responsivity to power absorption in the scintillator. Using a 137Cs source, preliminary beam proles were obtained. By combining the results of the testing and simulation, predictions of the required length of exposure were made. It was determined that a beam with a flux of 10^6/s and a diameter of 2.5 cm could be profiled, using 6.0 mm of plastic scintillator and 0.6 mm of iron converter, to within 5% error per 0.64 mm x 0.91 mm resolving unit, in less than 1 minute.

The modern fields of 𝜸-ray astrophysics, multi-messenger astronomy, and particle astrophysics, have a shared history and future. This thesis will focus on the interconnectedness between them, and the role that measurements of very high-energy (VHE; 100 GeV < 𝐸 < 100 TeV) 𝜸 rays play in contributing to them. In particular, one confirmed and one putative source class for VHE 𝜸 rays will be explored: active galactic nuclei (AGN) and short gamma-ray bursts (sGRBs) (associated binary neutron star (BNS) merger progenitors), characterized by their variable and transient emission behavior respectively. The particle acceleration and radiative processes which can result in this energetic electromagnetic (EM) emission in these sources is described. Subsequently, the detection principles of VHE 𝜸-ray photons is detailed, highlighting the unique detection technique of imaging atmospheric Cherenkov telescopes (IACTs) to use the Earth’s atmosphere as an effective high-energy particle calorimeter. Advancements in the field of these detectors will be discussed, from the first-generation of detectors up to its current generation, which includes the VERITAS 𝜸-ray observatory, the principal instrument used to conduct the analyses in this thesis. Additionally, a prototype for the novel two-mirror Schwarzschild-Couder telescope (SCT) design will be introduced, which is proposed for inclusion in the future Cherenkov Telescope Array Observatory (CTAO), set to be the next-generation observatory for VHE 𝜸 rays. Finally, work from three projects, each demonstrating the contributions VHE ? rays can make to the initially listed fields, will be discussed. First, a multi-messenger search for VHE 𝜸-ray emission in VERITAS associated with sub-threshold gravitational wave (GW) signals. No VHE ?-ray emission is detected; the upper limit on the integral flux for all VERITAS observations is reported and compared to a sGRB model. Next, a search for the imprint of beyond-the-standard-model axion-like particles (ALPs) on the flaring VHE spectrum of the radio galaxy (RG) AGN NGC 1275, embedded in the cool-core Perseus cluster. No detection is made; limited exclusions on the mass and coupling strength to electromagnetism are reported. Finally, a VERITAS detection of a VHE ?-ray flare from the blazar AGN B2 1811+31 will be presented. Preliminary work from the broadband analysis of the source are shown, and the future of the project is discussed.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Physics / Master / Master of Philosophy

The detection of γ-rays from explosive astrophysical scenarios such as novae provides an excellent opportunity for the study of on-going nucleosynthesis in the Universe. Within this context, this work has addressed an uncertainty in the destruction rate of the 18F nucleus, thought to be the primary source of 511 keV γ-rays from novae. A direct measurement of the 18F(p,α )15O cross section has provided the opportunity to extract resonance parameters through the R-Matrix formalism. The inferred parameters of populated states in 19Ne include the observation of a broad 1/2+ state, consistent with a recent theoretical prediction, which will have a significant impact on the rate of destruction of this γ-ray producing radioisotope. The 18O(p,α )15N reaction follows similar nuclear and kinematic processes and is expected to occur in the hydrogen burning layers of AGB stars. Resonance widths have been extracted from a direct measurement in the region around a poorly constrained broad state close to the Gamow window. This has produced a new parameter set for future reference and provides new information on the reaction rate. The complex R-Matrix formalism used in these analyses is a crucial tool in the study of nuclear astrophysics reactions, and many codes have been written to implement the complex mathematics. This thesis presents a comparison of two publicly available codes from the JINA collaboration and a code used extensively by the University of Edinburgh. For this, the recent results of the 18F destruction reaction, presented here, have been used. A minor error was found within one of the codes, and corrected. The final parameters extracted, and the resulting cross sections calculations, are shown to be consistent between the three codes. A further γ-ray line of interest at 1.809 MeV, characteristic of 26Al decay, has been observed throughout the interstellar medium. If, however, this isotope is formed in a known isomeric state, its decay bypasses the emission of this γ-ray, thus complicating the interpretation of observed γ-ray fluxes. To this end, an experiment has been carried out, providing proof of principle of a direct measurement of the 26mAl(p,γ)27Si reaction. The calculation of the isomeric intensity is presented here.

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Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 107-113). Also available on the World Wide Web.