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Evaluation of the passivation effect and the first-principles calculation on surface termination of germanium detector

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Nuclear Science and Techniques 2021年第9期32卷 40-51页

作者： Sha-Sha Lv Yuan-Yuan Liu Wei-You Tang Li He Xiu-Xia Li Jian-Ping Cheng Key Laboratory of Beam Technology of Ministry of Education College of Nuclear Science and TechnologyBeijing Normal UniversityBeijing 100875China Department of Engineering Physics Tsinghua UniversityBeijing 100084China Joint Research Center Nuctech Company LimitedBeijing 100084China

The point-contact high-purity germanium detector(HPGe)has the advantages of low background,low energy threshold,and high energy resolution and can be applied in the detection of rare-event physics.However,the performance of HPGe must be further improved to achieve superior energy resolution,low noise,and long-term reliability.In this study,we combine computational simulations and experimental comparisons to deeply understand the passivation mechanism of Ge.The surface passivation effect is calculated and inferred from the band structure and density of interface states,and further con-firmed by the minority carrier lifetime.The first-principles method based on the density functional theory was adopted to systematically study the lattice structure,band structure,and density of state(DOS)of four different systems:Ge–H,Ge–Ge-NH 2,Ge-OH,and Ge-SiO_(x).The electronic char-acteristics of the Ge(100)unit cell with different passi-vation groups and Si/O atomic ratios were compared.This shows that H,N,and O atoms can effectively reduce the surface DOS of the Ge atoms.The passivation effect of the SiO_(x) group varied with increasing O atoms and Si/O atomic ratios.Experimentally,SiO and SiO_(2) passivation films were fabricated by electron beam evaporation on a Ge substrate,and the valence state of Si and resistivity was measured to characterize the film.The minority carrier lifetime of Ge-SiO_(2) is 21.3 ls,which is approximately quadruple that of Ge-SiO.The passivation effect and mechanism are discussed in terms of hopping conduction and surface defect density.This study builds a relationship between the passivation effect and different termination groups,and provides technical support for the potential passivation layer,which can be applied in Ge detectors with ultralow energy thresholds and especially in HPGe for rare-event physics detection experiments in future.

关键词： germanium detector Passivation Surface termination

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High‑accuracy measurement of Compton scattering in germanium for dark matter searches

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Nuclear Science and Techniques 2022年第12期33卷 75-87页

作者： Hai‑Tao Jia Shin‑Ted Lin Shu‑Kui Liu Hsin‑Chang Chi Muhammed Deniz Chang‑Hao Fang Peng Gu Xi Jiang Yi‑Ke Shu Qian‑Yun Li Yu Liu Ren‑Ming‑Jie Li Chen‑Kai Qiao Chang‑Jian Tang Henry Tsz‑King Wong Hao‑Yang Xing Li‑Tao Yang Qian Yue Yu‑Lu Yan Kang‑Kang Zhao Jing‑Jun Zhu College of Physics Sichuan University610065 ChengduChina Department of Physics National Dong Hwa University97401 ShoufengHualienChina Department of Physics Dokuz Eylül University35160 BucaİzmirTurkey Institute of Physics Academia Sinica11529 TaipeiChina Key Laboratory of Particle and Radiation Imaging(Ministry of Education)and Department of Engineering Physics Tsinghua University100084 BeijingChina Institute of Nuclear Science and Technology Sichuan University610065 ChengduChina

Compton scattering with bound electrons contributes to a significant atomic effect in low-momentum transfer,yielding background structures in direct light dark matter searches as well as low-energy rare event experiments.We report the measurement of Compton scattering in low-momentum transfer by implementing a 10-g germanium detector bombarded by a^(137)Cs source with a radioactivity of 8.7 mCi and a scatter photon captured by a cylindrical NaI(Tl)detector.A fully relativistic impulse approximation combined with multi-configuration Dirac–Fock wavefunctions was evaluated,and the scattering function of Geant4 software was replaced by our calculation results.Our measurements show that the Livermore model with the modified scattering function in Geant4 is in good agreement with the experimental data.It is also revealed that atomic many-body effects significantly influence Compton scattering for low-momentum transfer(sub-keV energy transfer).

关键词： Compton scattering experiment germanium detector Atomic many-body effects Geant4 Dark matter

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Study of the material photon and electron background and the liquid argon detector veto efficiency of the CDEX-10 experiment

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Chinese Physics C 2015年第3期39卷 30-37页

作者：苏健曾志马豪岳骞程建平常建平陈楠陈宁陈庆豪陈云华庄又澄邓智杜强宫辉郝喜庆何庆驹黄瀚雄黄腾锐江灏康克军李浩斌李荐民李金李军李霞李新颖李学潜李玉兰李元景廖恒毅林枫凯林欣德刘书魁吕岚春毛绍基覃建强任杰任婧阮锡超申满斌 SINGH Lakhwinder SINGH Manoj Kumar SOMA Arun Kumar 唐昌建曾昭雄王继敏王力王青王子敬吴世勇吴玉成幸浩洋徐音薛涛杨丽桃杨松纬易难喻纯旭于昊余训臻曾雄辉张岚张蕴华赵明刚赵伟周祖英朱敬军朱维彬朱雪洲朱忠华 Key Laboratory of Particle and Radiation Imaging (Ministry of Education) and Department of Engineering Physics Tsinghua University Beijing 100084 China China Institute of Atomic Energy Beijing 102413 China Nankai University Tianjin 300071 China NUCTECH Company Beijing 100084 China Sichuan University Chengdu 610065 China Yalong River Hydropower Development Company Chengdu 610051 China Department of Physics Banaras Hindu University Varanasi 221005 India

The China Dark Matter Experiment （CDEX） is located at the China Jinping Underground Laboratory （CJPL） and aims to directly detect the weakly interacting massive particles （WIMP） flux with high sensitivity in the low mass region. Here we present a study of tile predicted photon and electron backgrounds including the background contribution of the structure materials of the germanium detector, the passive shielding materials, and the intrinsic radioactivity of the liquid argon that serves as an anti-Compton active shielding detector. A detailed geometry is modeled and the background contribution has been simulated based on the measured radioactivities of all possible components within tile GEANT4 program. Then the photon and electron background level in the energy region of interest （〈10-2events-kg1·day 1·keV-1 （cpkkd）） is predicted based on Monte Carlo simulations. The simulated result is consistent with the design goal of the CDEX-10 experiment, 0.1cpkkd, which shows that the active and passive shield design of CDEX-10 is effective and feasible.

关键词： CDEX-IO material photon and electron background germanium detector liquid argon veto coincidentcut Monte Carlo simulation

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Radiometric and Geophysical Investigations on Exposure Levels and Excess Cancer Risk in Kargi-Kenya

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Journal of Geoscience and Environment Protection 2023年第4期11卷 37-51页

作者： Willis O. Aguko Robert Kinyua John G. Githiri Physics Department School of Physical Sciences College of Pure & Applied Sciences Jomo Kenyatta University of Agriculture and Technology Nairobi Kenya

Radiation is considered one of the possible causes of cancer disease with natural background sources including cosmic, terrestrial and internal radiation. A number of cancer disease cases have been reported in Kargi with their causes not properly documented. The present work characterized the radioactivity in soil and water, to find out possible causes of radiation in KARGI-KENYA by studying magnetic intensities, anomalous zones with depth to magnetic sources and delineating subsurface structures. A total of 117 soil and 14 water samples were collected from the entire area and analysed for radionuclides due to 40K, 232Th and 226Ra. Measurement methods of proton magnetometer and gamma spectrometry employing a high purity germanium (HPGe) detector were employed basically to evaluate the magnetic survey and radiological hazard of radioactivities respectively. A total of 51 magnetic field measurements were taken on the eastern part of Kargi, a place suspected to have more concentration of radionuclides. The results showed that there could have been a fractionation during weathering period or metasomatic activity of the radioelements involvement. This study also reveals that the mining activities in the nearby study area could have affected the geologic formation causing more fracturing in rocks and pronounced subsurface structures as a result of mining that could have served as passage for leachates from pollutants as well as the level of radiation in the study area.

关键词： Kargi Magnetic Survey Anomalous zones Geologic germanium detector

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