核セキュリティ応用のためのLaBr3(Ce)検出器による核共鳴散乱測定に関する研究

京都大学0048新制・課程博士博士(エネルギー科学)甲第17918号エネ博第290号新制||エネ||60(附属図書館)30738京都大学大学院エネルギー科学研究科エネルギー応用科学専攻(主査)教授 大垣 英明, 教授 白井 康之, 教授 松田 一成学位規則第4条第1項該当Doctor of Energy ScienceKyoto UniversityDGA

Validating polarization effects in γ-rays elastic scattering by Monte Carlo simulation

The polarization properties of γ-rays elastically scattered by atoms have become more observable with the development of polarized photon beams. However, systematic studies are required to explore the elastic scattering in the MeV-energy range of the spectrum where Delbrück scattering becomes more significant, especially at large scattering angles. We implement a new Monte Carlo simulation to account for the polarization effects of elastic scattering. The simulation is based on explicit expressions driven in the formalism of Stokes parameters. The scattering amplitudes of Rayleigh, nuclear Thomson, and Delbrück scattering processes are superimposed onto a two orthogonal set of complex amplitudes. This set is then exploited to construct the core of the simulation in such a way that the simulation can handle arbitrary polarization states of the incoming beam and correspondingly generate polarization states of the outgoing beam. We demonstrate how the polarization of scattered photons is affected by the polarization of incoming photons. In addition, we explain the dependence of depolarization on the azimuthal angle

Compton scattering of quasi-monochromatic -ray beam

Compton scattering of a single-energy γ-ray results in a one-to-one relationship between the incident and scattered photon energies. This relationship is altered when the incident beam has a definite energy distribution because of the broadening occurring in the energy distribution upon Compton scattering. This broadening causes a change in the spectral density of the Compton-scattered spectra. To restore the spectral density, the energy distribution of the scattered radiation must be manifested as a function of the scattering kinematics. Here, we propose a simple analytic way to calculate the energy spread of the scattered photons in terms of the geometry of the scattering process and the energy spread of the incident photon beam. The predictions of the model agree with measurements of Compton scattering of quasi-monochromatic γ-ray beams, carried out at the High Intensity γ-ray Source (HIγS) facility, Duke University. As a benchmark of our method, we measured the intensity profile of energy-distributed -ray beams by direct measurements as well as by Compton scattering. We found that only when the spectral density of the scattered radiation is restored, the measured intensity profile agrees with the actual profile of the incident beam. The proposed method can continuously measure the flux of an energy-distributed γ-ray beams in real time and on a bin-by-bin basis. Such online monitoring of γ-ray beams is indispensable for in-beam measurements and applications