Abstract
The dependence of the nuclear resonance fluorescence (NRF) yield on the target thickness was studied. To this end, an NRF experiment was performed on U-238 using a laser Compton back-scattering (LCS) gamma-ray beam at the High Intensity gamma-ray Source facility at Duke University. Various thicknesses of depleted uranium targets were irradiated by an LCS gamma-ray beam with an incident beam energy of similar to 2.475 MeV. The scattering NRF gamma-rays were measured using an High-purity Germanium (HPGe) detector array positioned at scattering angles of 90 degrees relative to the incident gamma-beam. An analytical model for the NRF reaction yield (NRF RY model) is introduced to interpret the experimental data. Additionally, a Monte Carlo simulation using GEANT4 was performed to simulate the NRF interaction for a wide range of target thicknesses of the U-238. The measured NRF yield shows the saturation behavior. The results of both of the simulation and the analytical model can reproduce the saturation curve of the scattering NRF yield of U-238 against the target thickness. In addition, we propose a method to deduce the precise integral cross section of the NRF reaction by fitting the NRF yield dependency on the target thickness without any absolute measurements.