Compton scattering of quasi-monochromatic -ray beam

Omer, M.; 静間 俊行*; 羽島 良一*

Nuclear Instruments and Methods in Physics Research A, 951, p.162998_1 - 162998_6, 2020/01

https://doi.org/10.1016/j.nima.2019.162998

Compton scattering of a single-energy -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 -ray beams, carried out at the High Intensity -ray Source (HIS) 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 -ray beams in the real time and on a bin-by-bin basis. Such online monitoring of -ray beams is indispensable for in-beam measurements and applications. This work was supported by the subsidiary for promotion of strengthening nuclear security or the like of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan.