Real-time monitoring of the 14-MeV D-T fusion neutron yield is urgently required for the triton burnup study on the Experimental Advanced Superconducting Tokamak (EAST). In this study, we developed an optimal design o...Real-time monitoring of the 14-MeV D-T fusion neutron yield is urgently required for the triton burnup study on the Experimental Advanced Superconducting Tokamak (EAST). In this study, we developed an optimal design of a fast-neutron detector based on the scintillating fiber (Sci-Fi) to provide D-T neutron yield through Geant4simulation. The effect on the detection performance is concerned when changing the number of the Sci-Fis embedded in the probe head, minimum distance between the fibers, length of the fibers, or substrate material of the probe head. The maximum number of scintillation photons generated by the n/γ source particles and output by the light guide within an event (event:the entire simulation process for one source particle) was used to quantify the n/γ resolution of the detector as the main basis. And the intrinsic detection efficiency was used as another evaluation criterion. The results demonstrate that the optimal design scheme is to use a 5 cm probe head whose substrate material is pure aluminum, in which 463 Sci-Fis with the same length of 5 cm are embedded, and the minimum distance between the centers of the two fibers is 2 mm. The optimized detector exhibits clear directionality in the simulation, which is in line with the expectation and experimental data provided in the literature. This study presents the variation trends of the performance of the SciFi detector when its main parameters change, which is beneficial for the targeted design and optimization of the Sci-Fi detector used in a specific radiation environment.展开更多
Chinese Spallation Neutron Source(CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the engineering material...Chinese Spallation Neutron Source(CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the engineering materials diffractometer(EMD) will be installed between 2019–2023. This instrument requires the neutron detectors with the cover area near3 m2in two 90° neutron diffraction angle positions, the neutron detecting efficiency is better than 40%@1A, and the spatial resolution is better than 4 mm×200 mm in horizontal and vertical directions respectively. We have developed a onedimensional position-sensitive neutron detector based on the oblique6Li F/Zn S(Ag) scintillators, wavelength shifting fibers,and Si PMs(silicon photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, needs to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20(beam line 20) of CSNS. Using water sample, the neutron beam with Φ5 mm exit hole was dispersed related evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one has been improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.展开更多
The detection of low-level light is a key technology in various experimental scientific studies. As a photon detector, the silicon photomultiplier （SiPM） has gradually become an alternative to the photomultiplier tu...The detection of low-level light is a key technology in various experimental scientific studies. As a photon detector, the silicon photomultiplier （SiPM） has gradually become an alternative to the photomultiplier tube （PMT） in many applications in high-energy physics, astroparticle physics, and medical imaging because of its high photon detection efficiency （PDE）, good resolution for single-photon detection, insensitivity to magnetic field, low operating voltage, compactness, and low cost. However, primarily because of the geometric fill factor, the PDE of most SiPMs is not very high; in particular, for those SiPMs with a high density of micro cells, the effective area is small, and the bandwidth of the light response is narrow. As a building block of the SiPM, the concept of the backside-illuminated avalanche drift detector （ADD） was first proposed by the Max Planck Institute of Germany eight years ago; the ADD is promising to have high PDE over the full energy range of optical photons, even ultraviolet light and X-ray light, and because the avalanche multiplication region is very small, the ADD is beneficial for the fabrication of large-area SiPMs. However, because of difficulties in design and fabrication, no significant progress had been made, and the concept had not yet been verified. In this paper, preliminary results in the design, fabrication, and performance of a backside-illuminated ADD are reported; the difficulties in and limitations to the backside-illuminated ADD are analyzed.展开更多
Onlineγ-spectrometry systems for inland waters,most of which extract samples in situ and in real time,are able to produce reliable activity concentration measurements for waterborne radionuclides only when they are d...Onlineγ-spectrometry systems for inland waters,most of which extract samples in situ and in real time,are able to produce reliable activity concentration measurements for waterborne radionuclides only when they are distributed relatively uniformly and enter into a steady-state diffusion regime in the measurement chamber.To protect residents’health and ensure the safety of the living environment,better timeliness is required for this measurement method.To address this issue,this study established a mathematical model of the online waterγ-spectrometry system so that rapid warning and activity estimates can be obtained for water under non-steady-state(NSS)conditions.In addition,the detection efficiency of the detector for radionuclides during the NSS diffusion process was determined by applying the computational fluid dynamics technique in conjunction with Monte Carlo simulations.On this basis,a method was developed that allowed the online waterγ-spectrometry system to provide rapid warning and activity concentration estimates for radionuclides in water.Subsequent analysis of the NSS-mode measurements of^(40)K radioactive solutions with different activity concentrations determined the optimum warning threshold and measurement time for producing accurate activity concentration estimates for radionuclides.The experimental results show that the proposed NSS measurement method is able to give warning and yield accurate activity concentration estimates for radionuclides 55.42 and 69.42 min after the entry of a 10 Bq/L^(40)K radioactive solution into the measurement chamber,respectively.These times are much shorter than the 90 min required by the conventional measurement method.Furthermore,the NSS measurement method allows the measurement system to give rapid(within approximately 15 min)warning when the activity concentrations of some radionuclides reach their respective limits stipulated in the Guidelines for Drinking-water Quality of the WHO,suggesting that this method considerably enhances the warning capacity of in situ online waterγ-spectrometry systems.展开更多
The nuclides inhaled during nuclear accidents usually cause internal contamination of the lungs with low activity.Although a parallel-hole imaging system,which is widely used in medical gamma cameras,has a high resolu...The nuclides inhaled during nuclear accidents usually cause internal contamination of the lungs with low activity.Although a parallel-hole imaging system,which is widely used in medical gamma cameras,has a high resolution and good image quality,owing to its extremely low detection efficiency,it remains difficult to obtain images of inhaled lung contamination.In this study,the Monte Carlo method was used to study the internal lung contamination imaging using the MPA-MURA coded-aperture collimator.The imaging system consisted of an adult male lung model,with a mosaicked,pattern-centered,and anti-symmetric MURA coded-aperture collimator model and a CsI(Tl)detector model.The MLEM decoding algorithm was used to reconstruct the internal contamination image,and the complementary imaging method was used to reduce the number of artifacts.The full width at half maximum of the I-131 point source image reconstructed by the MPAMURA coded-aperture imaging reached 2.51 mm,and the signal-to-noise ratio of the simplified respiratory tract source(I-131)image reconstructed through MPA-MURA coded-aperture imaging was 3.98 dB.Although the spatial resolution of MPA-MURA coded-aperture imaging is not as good as that of parallel-hole imaging,the detection efficiency of PMA-MURA coded-aperture imaging is two orders of magnitude higher than that of parallel-hole collimator imaging.Considering the low activity level of internal lung contamination caused by nuclear accidents,PMA-MURA coded-aperture imaging has significant potential for the development of lung contamination imaging.展开更多
To accurately reconstruct the tomographic gamma scanning(TGS)transmission measurement image,this study optimized the transmission reconstruction equation based on the actual situation of TGS transmission measurement.U...To accurately reconstruct the tomographic gamma scanning(TGS)transmission measurement image,this study optimized the transmission reconstruction equation based on the actual situation of TGS transmission measurement.Using the transmission reconstruction equation and the Monte Carlo program Geant4,an innovative virtual trajectory length model was constructed.This model integrated the solving process for the trajectory length and detection efficiency within the same model.To mitigate the influence of the angular distribution ofγ-rays emitted by the transmitted source at the detector,the transport processes of numerous particles traversing a virtual nuclear waste barrel with a density of zero were simulated.Consequently,a certain amount of information was captured at each step of particle transport.Simultaneously,the model addressed the nonuniform detection efficiency of the detector end face by considering whether the energy deposition of particles in the detector equaled their initial energy.Two models were established to validate the accuracy and reliability of the virtual trajectory length model.Model 1 was a simplified nuclear waste barrel,whereas Model 2 closely resembled the actual structure of a nuclear waste barrel.The results indicated that the proposed virtual trajectory length model significantly enhanced the precision of the trajectory length determination,substantially increasing the quality of the reconstructed images.For example,the reconstructed images of Model 2 using the“point-to-point”and average trajectory models revealed a signalto-noise ratio increase of 375.0%and 112.7%,respectively.Thus,the virtual trajectory length model proposed in this study holds paramount significance for the precise reconstruction of transmission images.Moreover,it can provide support for the accurate detection of radioactive activity in nuclear waste barrels.展开更多
基金supported by the Users with Excellence Program of Hefei Science Center CAS(No.2020HSC-UE012)the Comprehensive Research Facility for Fusion Technology Program of China(No.2018-000052-73-01-001228)the Institute of Energy,Hefei Comprehensive National Science Center(No.21KZS205,21KZL401).
文摘Real-time monitoring of the 14-MeV D-T fusion neutron yield is urgently required for the triton burnup study on the Experimental Advanced Superconducting Tokamak (EAST). In this study, we developed an optimal design of a fast-neutron detector based on the scintillating fiber (Sci-Fi) to provide D-T neutron yield through Geant4simulation. The effect on the detection performance is concerned when changing the number of the Sci-Fis embedded in the probe head, minimum distance between the fibers, length of the fibers, or substrate material of the probe head. The maximum number of scintillation photons generated by the n/γ source particles and output by the light guide within an event (event:the entire simulation process for one source particle) was used to quantify the n/γ resolution of the detector as the main basis. And the intrinsic detection efficiency was used as another evaluation criterion. The results demonstrate that the optimal design scheme is to use a 5 cm probe head whose substrate material is pure aluminum, in which 463 Sci-Fis with the same length of 5 cm are embedded, and the minimum distance between the centers of the two fibers is 2 mm. The optimized detector exhibits clear directionality in the simulation, which is in line with the expectation and experimental data provided in the literature. This study presents the variation trends of the performance of the SciFi detector when its main parameters change, which is beneficial for the targeted design and optimization of the Sci-Fi detector used in a specific radiation environment.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11975255 and 11875273)Guangdong Basic and Applied Basic Research Foundation (Grant No. 2020B1515120025)。
文摘Chinese Spallation Neutron Source(CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the engineering materials diffractometer(EMD) will be installed between 2019–2023. This instrument requires the neutron detectors with the cover area near3 m2in two 90° neutron diffraction angle positions, the neutron detecting efficiency is better than 40%@1A, and the spatial resolution is better than 4 mm×200 mm in horizontal and vertical directions respectively. We have developed a onedimensional position-sensitive neutron detector based on the oblique6Li F/Zn S(Ag) scintillators, wavelength shifting fibers,and Si PMs(silicon photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, needs to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20(beam line 20) of CSNS. Using water sample, the neutron beam with Φ5 mm exit hole was dispersed related evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one has been improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.
基金Project supported by the National Natural Science Foundation of China(Grant No.11005010)
文摘The detection of low-level light is a key technology in various experimental scientific studies. As a photon detector, the silicon photomultiplier （SiPM） has gradually become an alternative to the photomultiplier tube （PMT） in many applications in high-energy physics, astroparticle physics, and medical imaging because of its high photon detection efficiency （PDE）, good resolution for single-photon detection, insensitivity to magnetic field, low operating voltage, compactness, and low cost. However, primarily because of the geometric fill factor, the PDE of most SiPMs is not very high; in particular, for those SiPMs with a high density of micro cells, the effective area is small, and the bandwidth of the light response is narrow. As a building block of the SiPM, the concept of the backside-illuminated avalanche drift detector （ADD） was first proposed by the Max Planck Institute of Germany eight years ago; the ADD is promising to have high PDE over the full energy range of optical photons, even ultraviolet light and X-ray light, and because the avalanche multiplication region is very small, the ADD is beneficial for the fabrication of large-area SiPMs. However, because of difficulties in design and fabrication, no significant progress had been made, and the concept had not yet been verified. In this paper, preliminary results in the design, fabrication, and performance of a backside-illuminated ADD are reported; the difficulties in and limitations to the backside-illuminated ADD are analyzed.
基金supported by the National Natural Science Foundation of China(No.42127807)Natural Science Foundation of Sichuan Province of China(Project No.2023NSFSC0008)+1 种基金Uranium Geology Program of China Nuclear Geology(No.202205-6)the Sichuan Science and Technology Program(No.2021JDTD0018)。
文摘Onlineγ-spectrometry systems for inland waters,most of which extract samples in situ and in real time,are able to produce reliable activity concentration measurements for waterborne radionuclides only when they are distributed relatively uniformly and enter into a steady-state diffusion regime in the measurement chamber.To protect residents’health and ensure the safety of the living environment,better timeliness is required for this measurement method.To address this issue,this study established a mathematical model of the online waterγ-spectrometry system so that rapid warning and activity estimates can be obtained for water under non-steady-state(NSS)conditions.In addition,the detection efficiency of the detector for radionuclides during the NSS diffusion process was determined by applying the computational fluid dynamics technique in conjunction with Monte Carlo simulations.On this basis,a method was developed that allowed the online waterγ-spectrometry system to provide rapid warning and activity concentration estimates for radionuclides in water.Subsequent analysis of the NSS-mode measurements of^(40)K radioactive solutions with different activity concentrations determined the optimum warning threshold and measurement time for producing accurate activity concentration estimates for radionuclides.The experimental results show that the proposed NSS measurement method is able to give warning and yield accurate activity concentration estimates for radionuclides 55.42 and 69.42 min after the entry of a 10 Bq/L^(40)K radioactive solution into the measurement chamber,respectively.These times are much shorter than the 90 min required by the conventional measurement method.Furthermore,the NSS measurement method allows the measurement system to give rapid(within approximately 15 min)warning when the activity concentrations of some radionuclides reach their respective limits stipulated in the Guidelines for Drinking-water Quality of the WHO,suggesting that this method considerably enhances the warning capacity of in situ online waterγ-spectrometry systems.
基金the Ministry of Science and Technology,People’s Republic of China(No.2012YQ180118)the National Natural Science Foundation of China(No.41874121)the Sichuan Science and Technology Program(No.2018JY0181).
文摘The nuclides inhaled during nuclear accidents usually cause internal contamination of the lungs with low activity.Although a parallel-hole imaging system,which is widely used in medical gamma cameras,has a high resolution and good image quality,owing to its extremely low detection efficiency,it remains difficult to obtain images of inhaled lung contamination.In this study,the Monte Carlo method was used to study the internal lung contamination imaging using the MPA-MURA coded-aperture collimator.The imaging system consisted of an adult male lung model,with a mosaicked,pattern-centered,and anti-symmetric MURA coded-aperture collimator model and a CsI(Tl)detector model.The MLEM decoding algorithm was used to reconstruct the internal contamination image,and the complementary imaging method was used to reduce the number of artifacts.The full width at half maximum of the I-131 point source image reconstructed by the MPAMURA coded-aperture imaging reached 2.51 mm,and the signal-to-noise ratio of the simplified respiratory tract source(I-131)image reconstructed through MPA-MURA coded-aperture imaging was 3.98 dB.Although the spatial resolution of MPA-MURA coded-aperture imaging is not as good as that of parallel-hole imaging,the detection efficiency of PMA-MURA coded-aperture imaging is two orders of magnitude higher than that of parallel-hole collimator imaging.Considering the low activity level of internal lung contamination caused by nuclear accidents,PMA-MURA coded-aperture imaging has significant potential for the development of lung contamination imaging.
基金supported by The Youth Science Foundation of Sichuan Province(Nos.2022NSFSC1230,2022NSFSC1231,and 23NSFSC5321)the Science and Technology Innovation Seedling Project of Sichuan Province(No.MZGC20230080)+2 种基金the General project of national Natural Science Foundation of China(No.12075039)the Youth Science Foundation of China(No.12105030)the Key project of the National Natural Science Foundation of China(No.U19A2086)。
文摘To accurately reconstruct the tomographic gamma scanning(TGS)transmission measurement image,this study optimized the transmission reconstruction equation based on the actual situation of TGS transmission measurement.Using the transmission reconstruction equation and the Monte Carlo program Geant4,an innovative virtual trajectory length model was constructed.This model integrated the solving process for the trajectory length and detection efficiency within the same model.To mitigate the influence of the angular distribution ofγ-rays emitted by the transmitted source at the detector,the transport processes of numerous particles traversing a virtual nuclear waste barrel with a density of zero were simulated.Consequently,a certain amount of information was captured at each step of particle transport.Simultaneously,the model addressed the nonuniform detection efficiency of the detector end face by considering whether the energy deposition of particles in the detector equaled their initial energy.Two models were established to validate the accuracy and reliability of the virtual trajectory length model.Model 1 was a simplified nuclear waste barrel,whereas Model 2 closely resembled the actual structure of a nuclear waste barrel.The results indicated that the proposed virtual trajectory length model significantly enhanced the precision of the trajectory length determination,substantially increasing the quality of the reconstructed images.For example,the reconstructed images of Model 2 using the“point-to-point”and average trajectory models revealed a signalto-noise ratio increase of 375.0%and 112.7%,respectively.Thus,the virtual trajectory length model proposed in this study holds paramount significance for the precise reconstruction of transmission images.Moreover,it can provide support for the accurate detection of radioactive activity in nuclear waste barrels.
