Calculating off-axis efficiency of coaxial HPGe detectors by Monte Carlo simulation. (September 2022)

• Record Type: Journal Article
• Authors: Omer, Mohamed; Shizuma, Toshiyuki; Hajima, Ryoichi; Koizumi, Mitsuo
• Is Part Of: Radiation physics and chemistry. Volume 198(2022)
• Publication Date: 2022-09
• Subjects: Coaxial HPGe detector efficiency -- Monte Carlo simulation -- Geant4 -- In-beam γ-ray spectroscopy -- Off-axis efficiency -- Nuclear resonance fluorescence -- Efficiency optimization; Radiation chemistry -- Periodicals; Radiometry -- Periodicals; Radiation -- Periodicals; Chimie sous rayonnement -- Périodiques; 539.2
• DOI: 10.1016/j.radphyschem.2022.110241
• Languages: English
• ISSNs: 0969-806X

Abstract

Abstract: In beam geometries where a directed γ -ray beam hits the surface of a coaxial high purity germanium detector (HPGe), the detector efficiency is sensitive to the position where γ -rays initially hit the detector surface because the structure of the detector is nonuniform. This may cause inaccuracy of the detector efficiency when measured using standard sources that are point-like sources emitting γ -rays isotropically. Obtaining a precise estimation of the full energy peak efficiency of the coaxial HPGe detector in the beam geometry for on-axis and off-axis measurements requires a Monte Carlo simulation. We performed Monte Carlo simulations that calculate the detector efficiency in the beam geometry. The effects of the off-axis distance and γ -ray beam size on the efficiency are quantitatively analyzed. We found that the intrinsic efficiency in the beam geometry is maximized when the beam hits the detector at specific off-axis distances. Our Monte Carlo calculations have been supported by nuclear resonance fluorescence experiments using laser Compton scattering γ -ray beams. Highlights: Calculating efficiency of coaxial HPGe detector for directed γ-ray beams by Geant4. Revealing the sensitivity of efficiency to γ-ray beam size and off-axis distance. Off-axis efficiency is higher than on-axis efficiency, depending on γ-ray energy. Maximizing efficiency by selecting the optimum off-axis distance. LCS γ-ray beams up to 3 MeV validate calculations experimentally.