To detect radioactive substances with low activity levels,an anticoincidence detector and a high-purity germanium(HPGe)detector are typically used simultaneously to suppress Compton scattering background,thereby resul...To detect radioactive substances with low activity levels,an anticoincidence detector and a high-purity germanium(HPGe)detector are typically used simultaneously to suppress Compton scattering background,thereby resulting in an extremely low detection limit and improving the measurement accuracy.However,the complex and expensive hardware required does not facilitate the application or promotion of this method.Thus,a method is proposed in this study to discriminate the digital waveform of pulse signals output using an HPGe detector,whereby Compton scattering background is suppressed and a low minimum detectable activity(MDA)is achieved without using an expensive and complex anticoincidence detector and device.The electric-field-strength and energy-deposition distributions of the detector are simulated to determine the relationship between pulse shape and energy-deposition location,as well as the characteristics of energy-deposition distributions for fulland partial-energy deposition events.This relationship is used to develop a pulse-shape-discrimination algorithm based on an artificial neural network for pulse-feature identification.To accurately determine the relationship between the deposited energy of gamma(γ)rays in the detector and the deposition location,we extract four shape parameters from the pulse signals output by the detector.Machine learning is used to input the four shape parameters into the detector.Subsequently,the pulse signals are identified and classified to discriminate between partial-and full-energy deposition events.Some partial-energy deposition events are removed to suppress Compton scattering.The proposed method effectively decreases the MDA of an HPGeγ-energy dispersive spectrometer.Test results show that the Compton suppression factors for energy spectra obtained from measurements on ^(152)Eu,^(137)Cs,and ^(60)Co radioactive sources are 1.13(344 keV),1.11(662 keV),and 1.08(1332 keV),respectively,and that the corresponding MDAs are 1.4%,5.3%,and 21.6%lower,respectively.展开更多
Two optical methods, namely crystal facet reflection and etching pits reflection, were used to orient and high-purity germanium crystals. The X-ray diffraction patterns of three slices that were cut from the oriented ...Two optical methods, namely crystal facet reflection and etching pits reflection, were used to orient and high-purity germanium crystals. The X-ray diffraction patterns of three slices that were cut from the oriented and crystals were measured by X-ray diffraction. The experimental errors of crystal facet reflection method and etching pits reflection method are in the range of 0.05° - 0.12°. The crystal facet reflection method and etching pits reflection method are extremely simple and cheap and their accuracies are acceptable for characterizing high purity detector-grade germanium crystals.展开更多
For a characteristic c-ray with interlaced overlap peak, and the case where its reliable and credible net count cannot be obtained using the current high-purity germanium(HPGe) multichannel γ-ray spectrum software, t...For a characteristic c-ray with interlaced overlap peak, and the case where its reliable and credible net count cannot be obtained using the current high-purity germanium(HPGe) multichannel γ-ray spectrum software, two new methods are proposed herein to obtain the γ-ray net peak count from the interlaced overlap peak in the HPGe cray spectrometer system, of which one is the symmetric conversion method based on Gaussian distribution and the other is where the energy average value of two close γ-rays is regarded as the γ-ray energy. The experimental results indicate that the two methods mentioned above are reliable and credible. This study is significant for the development of better γ-ray spectrum processing software for measuring complex γ-ray spectra concerning the nuclear reaction cross section, neutron activation analysis, and analysis of transuranium elements, using an HPGe detector.展开更多
Microsatellites have recently opened windows of frequent and low cost missions for planetary exploration. The performance of gamma-ray and neutron spectrometers on future microsatellite missions is simulated to assess...Microsatellites have recently opened windows of frequent and low cost missions for planetary exploration. The performance of gamma-ray and neutron spectrometers on future microsatellite missions is simulated to assess the possibility of observation of hydrogen and major elements, given their concentration on the observation target. The measured elemental abundance will provide important geological constraints, and some of them may serve as space resources. Four different types of target bodies with various hydrogen concentrations in the range of 0 - 20,000 ppm are assumed as target compositions;Earth’s core, C-type, S-type and Martian meteorites. Gamma-ray and neutron emission rates show unique footprints that are related to the different elemental compositions. The starting point is the solid angle subtended between observation target and spectrometers that allow estimating the gamma-ray and neutron count rates emitted by the celestial bodies. In this work, three types of gamma-ray detectors;high-purity germanium (HPGe), CeBr3 and LaBr3(Ce), a neutron spectrometer combining a lithium glass scintillator with a boron loaded plastic scintillator and a dual mode spectrometer Cs2LiYCl6(Ce) (CLYC) are simulated, focusing on their observation backgrounds as a model case for microsatellite based measurements. The background count level of both gamma-ray (except for the LaBr3 detector) and neutron count rates was negligible under these particular conditions. The gamma-ray detectors were compared by the figure of merit, which was determined by their efficiency and energy resolution. It was found that each detector has unique advantages. The HPGe detector has the highest figure of merit due to its excellent energy resolution, whereas the CLYC detector is low in weight and power consumption due to its dual sensitivity to gamma-ray and neutron. The CeBr3 detector is an intermediate choice. The neutron count rates are calculated separately in three energy ranges, i.e. , thermal (<0.5 eV), epithermal (0.5 eV - 500 keV), and fast (>500 keV), as a function of the hydrogen concentration in the 0 - 20,000 ppm range. The thermal and epithermal neutron count rates are found to decrease with hydrogen concentration, while the fast neutron count rate increases with the target average atomic mass. The optimal detector should be decided by the mission restraints on mass, power consumption, and heat thermal design.展开更多
Rare event search experiments are one of the most important topics in the field of fundamental physics,and high-purity germanium(HPGe)detectors with an ultralow radioactive background are frequently used for such expe...Rare event search experiments are one of the most important topics in the field of fundamental physics,and high-purity germanium(HPGe)detectors with an ultralow radioactive background are frequently used for such experiments.However,cosmogenic activation contaminates germanium crystals during transport and storage.In this study,we investigated the movable shielding containers of HPGe crystals using Geant4 and CRY Monte Carlo simulations.The production rates of 68Ge,65Zn,60Co,55Fe,and 3H were obtained individually for different types of cosmic rays.The validity of the simulation was confirmed through a comparison with the available experimental data.Based on this simulation,we found that the interactions induced by neutrons contribute to approximately 90%of the production rate of cosmogenic activation.In addition,by adding an optimized shielding structure,the production rates of cosmogenic radionuclides are reduced by about one order of magnitude.Our results show that it is feasible to use a shielding container to reduce the cosmogenic radioactivity produced during the transport and storage of high-purity germanium on the ground.展开更多
Most of the natural occurring radionuclides in both noodles and bread are found to have specific activities below the detectable limit of the high purity germanium (n-type) spectrometer system of the EG&G Ortec C...Most of the natural occurring radionuclides in both noodles and bread are found to have specific activities below the detectable limit of the high purity germanium (n-type) spectrometer system of the EG&G Ortec Company. For dried bread, 40K,137Cs and 60Co are found to be 44.45￣84.52, < 0.012 ￣0.052, < 0.018 ￣0.054 Bq/kg;for noodles, to be 29.55￣64.54, < 0.01 ￣0.069 and < 9.8× 10-3 ￣ 0.074 Bq/kg,respectively. The weighted committed dose equivalents due to the ingestion of 137Csfrom noodles and bread for a male and female adults have been estimated to be 0.5and 0.6μSv, respectively, being less than the values recommended by ICRP.展开更多
基金This work was supported by the National Key R&D Program of China(Nos.2022YFF0709503,2022YFB1902700,2017YFC0602101)the Key Research and Development Program of Sichuan province(No.2023YFG0347)the Key Research and Development Program of Sichuan province(No.2020ZDZX0007).
文摘To detect radioactive substances with low activity levels,an anticoincidence detector and a high-purity germanium(HPGe)detector are typically used simultaneously to suppress Compton scattering background,thereby resulting in an extremely low detection limit and improving the measurement accuracy.However,the complex and expensive hardware required does not facilitate the application or promotion of this method.Thus,a method is proposed in this study to discriminate the digital waveform of pulse signals output using an HPGe detector,whereby Compton scattering background is suppressed and a low minimum detectable activity(MDA)is achieved without using an expensive and complex anticoincidence detector and device.The electric-field-strength and energy-deposition distributions of the detector are simulated to determine the relationship between pulse shape and energy-deposition location,as well as the characteristics of energy-deposition distributions for fulland partial-energy deposition events.This relationship is used to develop a pulse-shape-discrimination algorithm based on an artificial neural network for pulse-feature identification.To accurately determine the relationship between the deposited energy of gamma(γ)rays in the detector and the deposition location,we extract four shape parameters from the pulse signals output by the detector.Machine learning is used to input the four shape parameters into the detector.Subsequently,the pulse signals are identified and classified to discriminate between partial-and full-energy deposition events.Some partial-energy deposition events are removed to suppress Compton scattering.The proposed method effectively decreases the MDA of an HPGeγ-energy dispersive spectrometer.Test results show that the Compton suppression factors for energy spectra obtained from measurements on ^(152)Eu,^(137)Cs,and ^(60)Co radioactive sources are 1.13(344 keV),1.11(662 keV),and 1.08(1332 keV),respectively,and that the corresponding MDAs are 1.4%,5.3%,and 21.6%lower,respectively.
文摘Two optical methods, namely crystal facet reflection and etching pits reflection, were used to orient and high-purity germanium crystals. The X-ray diffraction patterns of three slices that were cut from the oriented and crystals were measured by X-ray diffraction. The experimental errors of crystal facet reflection method and etching pits reflection method are in the range of 0.05° - 0.12°. The crystal facet reflection method and etching pits reflection method are extremely simple and cheap and their accuracies are acceptable for characterizing high purity detector-grade germanium crystals.
基金supported by the National Natural Science Foundation of China(Nos.11575090,11605099)the Young Key Teachers Training Program of He’nan Higher Education in China(No.2015GGJS-258)
文摘For a characteristic c-ray with interlaced overlap peak, and the case where its reliable and credible net count cannot be obtained using the current high-purity germanium(HPGe) multichannel γ-ray spectrum software, two new methods are proposed herein to obtain the γ-ray net peak count from the interlaced overlap peak in the HPGe cray spectrometer system, of which one is the symmetric conversion method based on Gaussian distribution and the other is where the energy average value of two close γ-rays is regarded as the γ-ray energy. The experimental results indicate that the two methods mentioned above are reliable and credible. This study is significant for the development of better γ-ray spectrum processing software for measuring complex γ-ray spectra concerning the nuclear reaction cross section, neutron activation analysis, and analysis of transuranium elements, using an HPGe detector.
基金This paper is a part of the outcome research performed under a Waseda University Grant for Special Research Project(Project number:2017B-208).
文摘Microsatellites have recently opened windows of frequent and low cost missions for planetary exploration. The performance of gamma-ray and neutron spectrometers on future microsatellite missions is simulated to assess the possibility of observation of hydrogen and major elements, given their concentration on the observation target. The measured elemental abundance will provide important geological constraints, and some of them may serve as space resources. Four different types of target bodies with various hydrogen concentrations in the range of 0 - 20,000 ppm are assumed as target compositions;Earth’s core, C-type, S-type and Martian meteorites. Gamma-ray and neutron emission rates show unique footprints that are related to the different elemental compositions. The starting point is the solid angle subtended between observation target and spectrometers that allow estimating the gamma-ray and neutron count rates emitted by the celestial bodies. In this work, three types of gamma-ray detectors;high-purity germanium (HPGe), CeBr3 and LaBr3(Ce), a neutron spectrometer combining a lithium glass scintillator with a boron loaded plastic scintillator and a dual mode spectrometer Cs2LiYCl6(Ce) (CLYC) are simulated, focusing on their observation backgrounds as a model case for microsatellite based measurements. The background count level of both gamma-ray (except for the LaBr3 detector) and neutron count rates was negligible under these particular conditions. The gamma-ray detectors were compared by the figure of merit, which was determined by their efficiency and energy resolution. It was found that each detector has unique advantages. The HPGe detector has the highest figure of merit due to its excellent energy resolution, whereas the CLYC detector is low in weight and power consumption due to its dual sensitivity to gamma-ray and neutron. The CeBr3 detector is an intermediate choice. The neutron count rates are calculated separately in three energy ranges, i.e. , thermal (<0.5 eV), epithermal (0.5 eV - 500 keV), and fast (>500 keV), as a function of the hydrogen concentration in the 0 - 20,000 ppm range. The thermal and epithermal neutron count rates are found to decrease with hydrogen concentration, while the fast neutron count rate increases with the target average atomic mass. The optimal detector should be decided by the mission restraints on mass, power consumption, and heat thermal design.
基金supported by the National Key Research and Development Program of China(No.2017YFA0402203)the National Natural Science Foundation of China(No.11975162)the Fundamental Research Funds for Central Universities(No.20822041C4030)。
文摘Rare event search experiments are one of the most important topics in the field of fundamental physics,and high-purity germanium(HPGe)detectors with an ultralow radioactive background are frequently used for such experiments.However,cosmogenic activation contaminates germanium crystals during transport and storage.In this study,we investigated the movable shielding containers of HPGe crystals using Geant4 and CRY Monte Carlo simulations.The production rates of 68Ge,65Zn,60Co,55Fe,and 3H were obtained individually for different types of cosmic rays.The validity of the simulation was confirmed through a comparison with the available experimental data.Based on this simulation,we found that the interactions induced by neutrons contribute to approximately 90%of the production rate of cosmogenic activation.In addition,by adding an optimized shielding structure,the production rates of cosmogenic radionuclides are reduced by about one order of magnitude.Our results show that it is feasible to use a shielding container to reduce the cosmogenic radioactivity produced during the transport and storage of high-purity germanium on the ground.
文摘Most of the natural occurring radionuclides in both noodles and bread are found to have specific activities below the detectable limit of the high purity germanium (n-type) spectrometer system of the EG&G Ortec Company. For dried bread, 40K,137Cs and 60Co are found to be 44.45￣84.52, < 0.012 ￣0.052, < 0.018 ￣0.054 Bq/kg;for noodles, to be 29.55￣64.54, < 0.01 ￣0.069 and < 9.8× 10-3 ￣ 0.074 Bq/kg,respectively. The weighted committed dose equivalents due to the ingestion of 137Csfrom noodles and bread for a male and female adults have been estimated to be 0.5and 0.6μSv, respectively, being less than the values recommended by ICRP.
