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Effect of coaxial HPGe detector structure on [formula omitted]-ray beam measurements.

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Title: Effect of coaxial HPGe detector structure on [formula omitted]-ray beam measurements.
Authors: Omer, M.1 (AUTHOR) omer.mohamed@jaea.go.jp, Shizuma, T.1,2 (AUTHOR), Koizumi, M.1 (AUTHOR), Taira, Y.3,4 (AUTHOR), Zen, H.5 (AUTHOR), Ohgaki, H.5 (AUTHOR), Hajima, R.2 (AUTHOR)
Source: Radiation Physics & Chemistry. Mar2026, Vol. 240, pN.PAG-N.PAG. 1p.
Subjects: Gamma ray spectroscopy, Germanium radiation detectors, Sensitivity analysis, Spectral sensitivity, Pair production, Detectors, Monte Carlo method
Abstract: Coaxial high-purity germanium detectors are widely used in applications requiring high-resolution γ -ray spectroscopy. However, the internal structure of these detectors, particularly the geometry of the inactive volumes inside the detector core, can significantly influence their performance in beam detection configurations. This study investigates the impact of detector structure on the spectral response to pencil-like γ -ray beams, based on a comparison of γ -ray spectra measured with two coaxial high-purity germanium detectors that have similar active volumes but distinct internal geometries. Experimental measurements were conducted at the UVSOR synchrotron facility using collimated laser Compton scattered γ -ray beams with an energy of 5. 5 3 − 0. 580 + 0. 016 MeV. Monte Carlo simulations using the Geant4 toolkit were performed to refine the detector models and replicate experimental results. The results reveal that the front layer thickness and the presence of structural elements such as the cold finger strongly affect the spectral features, particularly the appearance of a coincidence sum peak of the annihilation radiation at 1.022 MeV. Off-axis irradiation significantly improves the detection efficiency and reduces undesired induced interactions within inactive volumes. Additionally, the observed pair production signatures are validated through the available theoretical cross section data, confirming the dominant role of internal structures in shaping the detector response under beam geometry. These findings are essential for optimizing detector configurations in precision γ -ray beam experiments. • HPGe detectors with different structures show distinct spectral responses. • Off-axis beam geometry enhances efficiency and reduces inactive region interactions. • Annihilation sum peak observed from pair production in detector inactive region. • Monte Carlo simulations accurately reproduce experimental γ -ray spectra. • Validation of pair production cross section through coincidence summing analysis. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:Coaxial high-purity germanium detectors are widely used in applications requiring high-resolution γ -ray spectroscopy. However, the internal structure of these detectors, particularly the geometry of the inactive volumes inside the detector core, can significantly influence their performance in beam detection configurations. This study investigates the impact of detector structure on the spectral response to pencil-like γ -ray beams, based on a comparison of γ -ray spectra measured with two coaxial high-purity germanium detectors that have similar active volumes but distinct internal geometries. Experimental measurements were conducted at the UVSOR synchrotron facility using collimated laser Compton scattered γ -ray beams with an energy of 5. 5 3 − 0. 580 + 0. 016 MeV. Monte Carlo simulations using the Geant4 toolkit were performed to refine the detector models and replicate experimental results. The results reveal that the front layer thickness and the presence of structural elements such as the cold finger strongly affect the spectral features, particularly the appearance of a coincidence sum peak of the annihilation radiation at 1.022 MeV. Off-axis irradiation significantly improves the detection efficiency and reduces undesired induced interactions within inactive volumes. Additionally, the observed pair production signatures are validated through the available theoretical cross section data, confirming the dominant role of internal structures in shaping the detector response under beam geometry. These findings are essential for optimizing detector configurations in precision γ -ray beam experiments. • HPGe detectors with different structures show distinct spectral responses. • Off-axis beam geometry enhances efficiency and reduces inactive region interactions. • Annihilation sum peak observed from pair production in detector inactive region. • Monte Carlo simulations accurately reproduce experimental γ -ray spectra. • Validation of pair production cross section through coincidence summing analysis. [ABSTRACT FROM AUTHOR]
ISSN:0969806X
DOI:10.1016/j.radphyschem.2025.113467