Calibrations were performed for three types of neutron ambient dose equivalent rate meters, i.e., Aloka TPS-451C (Hitachi), KSAR1U.06 (Baltic Scientific Instruments), and Model 12-4 (Ludlum), using a standard field of...Calibrations were performed for three types of neutron ambient dose equivalent rate meters, i.e., Aloka TPS-451C (Hitachi), KSAR1U.06 (Baltic Scientific Instruments), and Model 12-4 (Ludlum), using a standard field of a 241Am–Be source. The measured total neutron ambient dose equivalent rates, H*(10)' tot, were analyzed to obtain the direct neutron ambient dose equivalent rates, H*(10)' dir, using the ISO 8529-2-recommended generalized- fit method, semiempirical fit method, and reducedfitting method (RFM) fit methods. The calibration factor (CF), defined as the ratio between the conventional true value of the neutron ambient dose equivalent rates in a free field, H*(10)' FF, and H*(10)' dir, was evaluated as one of the important characteristics of the neutron meters in the present work. The fitting results show that the H*(10)' dir values of the meters are in good agreement within the theoretical data within 4%. The averaged CFs of the three neutron meters were evaluated as 0:99 ± 0:01, 1:00 ± 0.03;and 0:99 ± 0:08, respectively. The largest standard uncertainty of these values was determined to be approximately 18.47%(k =1). The standard uncertainty of the CFs obtained using the RFM method was less than 4.23%(k=1), which is the smallest uncertainty among the three methods.展开更多
Background The neutron activation analysis(NAA)is a very powerful method for multi-element analysis of samples.NAA technique needs to be developed for low neutron flux in millicuries using the 241Am-Be neutron source....Background The neutron activation analysis(NAA)is a very powerful method for multi-element analysis of samples.NAA technique needs to be developed for low neutron flux in millicuries using the 241Am-Be neutron source.Aims To optimize sample and neutron source geometry for maximumγ-ray yield for neutron activation analysis.Method Gamma ray neutron activation analysis(NAA)has been set up where a 50-millicurie Am-Be neutron source is available.In this experimental setup,the neutron source is placed at the center of a cylindrical water tank of 40 x 40 cm in xyz plan,and thermal neutrons are produced at a distance of 1.2 cm from the source.The system is used for the activation analysis of sodium carbonate,sodium chloride and copper with the gamma ray emissions of 1.37,1.73,2.25 and 2.76 MeV for 24Na and 0.511 MeV for 64Cu having half lives of 15 hrs and 12.9 hrs,respectively.The thermal neutron activation analysis has been demonstrated by placing the samples at about 1.2 cm from the neutron source.HPGe and 3x3 inch NaI(Tl)gamma ray spectrometers have been used for the gamma ray spectrometry of these activated samples with the use of a Marinelli beaker.The geometry of the sample with respect to the neutron source has been optimized for the maximumγ-ray yield in NAA.Conclusion The geometry of the sample with respect to the neutron source has been optimized for the maximumγ-ray yield in NAA.The increase in gamma ray flux distribution in the medium of water,due to the neutron source inside the tank,has been observed by a GM detector which is due to the production of short-lived 16N on activation of 16O in water.This system can also be used for promptγ-ray analysis.展开更多
This paper presents the calibration of a neutron dose rate meter and the evaluation of its calibration factors(CFs)in several neutron standard fields(i.e.,two standard fields with bare sources of252Cf and241Am-Be,and ...This paper presents the calibration of a neutron dose rate meter and the evaluation of its calibration factors(CFs)in several neutron standard fields(i.e.,two standard fields with bare sources of252Cf and241Am-Be,and five simulated workplace fields with241Am-Be moderated sources).The calibration in standard fields with bare sources was conducted by following the recommendations of the ISO 8529 standard.The measured total neutron ambient dose equivalent rates,denoted as H*(10)tot,were analyzed to obtain direct components,denoted as H*(10)dir,using a reduced fitting method.The CF was then calculated as the ratio between the conventional true value of the neutron ambient dose equivalent rate in a free field,denoted as H*(10)FF,and the value of H*(10)dir.In contrast,in the simulated workplace neutron fields,the calibration of the neutron dose rate meter was conducted by following the ISO 12789 standard.The CF was calculated as the ratio between the values of H*(10)totmeasured by a standard instrument(i.e.,Bonner sphere spectrometer)and the neutron dose rate meter.The CF values were obtained in the range of 0.88–1.0.The standard uncertainties(k=1)of the CFs were determined to be in the range of approximately 6.6–13.1%.展开更多
Neutron radiography uses the unique interaction probabilities of neutrons to create images of materials. This imaging technique is non-destructive. MCNP Monte Carlo Code has been used to design an optimized neutron ra...Neutron radiography uses the unique interaction probabilities of neutrons to create images of materials. This imaging technique is non-destructive. MCNP Monte Carlo Code has been used to design an optimized neutron radiography system that utilizes 241Am-Be neutron source. Many different arrangements have been simulated to obtain a neutron flux with higher amplitude and more uniform distribution in the collimator outlet, next to image plane. In the final arrangement the specifications of neutron filter, Gamma-ray shield and beam collimator has been determined. Simulations has been carried out for a 5Ci 241Am-Be neutron source. In this case 43.8 n/cm2s thermal neutron flux has been achieved at a distance of 35 cm from neutron source.展开更多
In order to make further studies on fusion neutron diagnosis on HL-2A /HL-2M,we have developed and succeeded in the calculation of the Response Function for a Bonner sphere spectrometer,which consists of eight polyeth...In order to make further studies on fusion neutron diagnosis on HL-2A /HL-2M,we have developed and succeeded in the calculation of the Response Function for a Bonner sphere spectrometer,which consists of eight polyethylene spheres with ^3He proportional counters inside.The response function of the Bonner spectrometer to neutrons is of fundamental importance for its neutron spectrum unfolding procedure and is directly related to the quality of the unfolded spectrum.In this paper,we calculated the response function to neutrons from 10^-9 MeV to100 MeV by Geant4.In order to test the accuracy of the Geant4 simulation,we apply it to measure an ^241Am-Be neutron source,and the measured neutron counts of the spectrometer and simulated counts are found to be highly consistent,with a relative error up to 9.3%.This has proven the calculation of the neutron response of the Bonner sphere spectrometer by Geant4 to be quite accurate.展开更多
China Spallation Neutron Source （CSNS）, one project of the 12th Five-Year-Plan scheme of China, is under construction in Guangdong province. Three neutron spectrometers will he installed during the first phase of th...China Spallation Neutron Source （CSNS）, one project of the 12th Five-Year-Plan scheme of China, is under construction in Guangdong province. Three neutron spectrometers will he installed during the first phase of the project, and two-dimensional position sensitive thermal neutron detectors are required. Before the construction of the neutron detectors, a prototype of a two-dimensional 200 mm^200 mm Multi-wire Proportional Chamber （MWPC） with Ar/CO2 （90/10） flowing gas has been constructed. In 2009, the prototype was tested with the 55Fe X-ray using part of the electronics, and performed well. Following the test in 2009, the neutron detector was constructed with the complete electronics and filled with the 6 atm. 3He^2.5 atm. C3Hs gas mixture in 2010. The neutron detector has been primarily tested with an Am-Be source. In this paper, new developments of the neutron detector including the design of the high pressure chamber, the optimization of the gas purifying system and the gas filling process will be reported. The results and discussion are also presented in this paper.展开更多
In order to realize real-time fusion neutron spectrum diagnosis for the HL_2A Tokamak, a Bonner Sphere Spectrometer （BSS） array has been developed, consisting of eight polyethylene spheres （PS） with embedded aHe p...In order to realize real-time fusion neutron spectrum diagnosis for the HL_2A Tokamak, a Bonner Sphere Spectrometer （BSS） array has been developed, consisting of eight polyethylene spheres （PS） with embedded aHe proportional counters. To validate its spectrometric capability, spectrum measurement of an 241Am-Be neutron source was carried out and is described. The Monte Carlo code Geant4 was used to calculate the response functions, taking this interference into consideration. Finally, the neutron spectrum was unfolded in the energy range from 10-9 MeV to 20 MeV. The unfolded spectrum has remarkable consistency with the ISO 8529-1 standard 2alAm-Be neutron spectrum which is a preliminary demonstration that this BSS is reliable and practical.展开更多
A high-efficiency fast neutron detector prototype based on a triple Gas Electron Multiplier（GEM） detector, which, coupled with a novel multi-layered high-density polyethylene（HDPE） as a neutron-to-proton converter...A high-efficiency fast neutron detector prototype based on a triple Gas Electron Multiplier（GEM） detector, which, coupled with a novel multi-layered high-density polyethylene（HDPE） as a neutron-to-proton converter for improving the neutron detection efficiency, is introduced and tested with the Am-Be neutron source in the Institute of Modern Physics（IMP） at Lanzhou in the present work. First, the developed triple GEM detector is tested by measuring its effective gain and energy resolution with55 Fe X-ray source to ensure that it has a good performance.The effective gain and obtained energy resolution is 5.0×104and around 19.2%, respectively. Secondly, the novel multi-layered HDPE converter is coupled with the cathode of the triple GEM detector making it a high-efficiency fast neutron detector. Its effective neutron response is four times higher than that of the traditional single-layered conversion technique when the converter layer number is 38.展开更多
基金supported by the Ministry of Science and Technology of Vietnam under Grant 07/HD/DTCB
文摘Calibrations were performed for three types of neutron ambient dose equivalent rate meters, i.e., Aloka TPS-451C (Hitachi), KSAR1U.06 (Baltic Scientific Instruments), and Model 12-4 (Ludlum), using a standard field of a 241Am–Be source. The measured total neutron ambient dose equivalent rates, H*(10)' tot, were analyzed to obtain the direct neutron ambient dose equivalent rates, H*(10)' dir, using the ISO 8529-2-recommended generalized- fit method, semiempirical fit method, and reducedfitting method (RFM) fit methods. The calibration factor (CF), defined as the ratio between the conventional true value of the neutron ambient dose equivalent rates in a free field, H*(10)' FF, and H*(10)' dir, was evaluated as one of the important characteristics of the neutron meters in the present work. The fitting results show that the H*(10)' dir values of the meters are in good agreement within the theoretical data within 4%. The averaged CFs of the three neutron meters were evaluated as 0:99 ± 0:01, 1:00 ± 0.03;and 0:99 ± 0:08, respectively. The largest standard uncertainty of these values was determined to be approximately 18.47%(k =1). The standard uncertainty of the CFs obtained using the RFM method was less than 4.23%(k=1), which is the smallest uncertainty among the three methods.
文摘Background The neutron activation analysis(NAA)is a very powerful method for multi-element analysis of samples.NAA technique needs to be developed for low neutron flux in millicuries using the 241Am-Be neutron source.Aims To optimize sample and neutron source geometry for maximumγ-ray yield for neutron activation analysis.Method Gamma ray neutron activation analysis(NAA)has been set up where a 50-millicurie Am-Be neutron source is available.In this experimental setup,the neutron source is placed at the center of a cylindrical water tank of 40 x 40 cm in xyz plan,and thermal neutrons are produced at a distance of 1.2 cm from the source.The system is used for the activation analysis of sodium carbonate,sodium chloride and copper with the gamma ray emissions of 1.37,1.73,2.25 and 2.76 MeV for 24Na and 0.511 MeV for 64Cu having half lives of 15 hrs and 12.9 hrs,respectively.The thermal neutron activation analysis has been demonstrated by placing the samples at about 1.2 cm from the neutron source.HPGe and 3x3 inch NaI(Tl)gamma ray spectrometers have been used for the gamma ray spectrometry of these activated samples with the use of a Marinelli beaker.The geometry of the sample with respect to the neutron source has been optimized for the maximumγ-ray yield in NAA.Conclusion The geometry of the sample with respect to the neutron source has been optimized for the maximumγ-ray yield in NAA.The increase in gamma ray flux distribution in the medium of water,due to the neutron source inside the tank,has been observed by a GM detector which is due to the production of short-lived 16N on activation of 16O in water.This system can also be used for promptγ-ray analysis.
基金by the National Foundation for Science and Technology Development of Vietnam(No.103.04-2017.37)。
文摘This paper presents the calibration of a neutron dose rate meter and the evaluation of its calibration factors(CFs)in several neutron standard fields(i.e.,two standard fields with bare sources of252Cf and241Am-Be,and five simulated workplace fields with241Am-Be moderated sources).The calibration in standard fields with bare sources was conducted by following the recommendations of the ISO 8529 standard.The measured total neutron ambient dose equivalent rates,denoted as H*(10)tot,were analyzed to obtain direct components,denoted as H*(10)dir,using a reduced fitting method.The CF was then calculated as the ratio between the conventional true value of the neutron ambient dose equivalent rate in a free field,denoted as H*(10)FF,and the value of H*(10)dir.In contrast,in the simulated workplace neutron fields,the calibration of the neutron dose rate meter was conducted by following the ISO 12789 standard.The CF was calculated as the ratio between the values of H*(10)totmeasured by a standard instrument(i.e.,Bonner sphere spectrometer)and the neutron dose rate meter.The CF values were obtained in the range of 0.88–1.0.The standard uncertainties(k=1)of the CFs were determined to be in the range of approximately 6.6–13.1%.
文摘Neutron radiography uses the unique interaction probabilities of neutrons to create images of materials. This imaging technique is non-destructive. MCNP Monte Carlo Code has been used to design an optimized neutron radiography system that utilizes 241Am-Be neutron source. Many different arrangements have been simulated to obtain a neutron flux with higher amplitude and more uniform distribution in the collimator outlet, next to image plane. In the final arrangement the specifications of neutron filter, Gamma-ray shield and beam collimator has been determined. Simulations has been carried out for a 5Ci 241Am-Be neutron source. In this case 43.8 n/cm2s thermal neutron flux has been achieved at a distance of 35 cm from neutron source.
基金supported by National Natural Science Foundation of China(Nos.10976028,11375195)National Magnetic Confinement Fusion Science Program of China(No.2013GB104003)
文摘In order to make further studies on fusion neutron diagnosis on HL-2A /HL-2M,we have developed and succeeded in the calculation of the Response Function for a Bonner sphere spectrometer,which consists of eight polyethylene spheres with ^3He proportional counters inside.The response function of the Bonner spectrometer to neutrons is of fundamental importance for its neutron spectrum unfolding procedure and is directly related to the quality of the unfolded spectrum.In this paper,we calculated the response function to neutrons from 10^-9 MeV to100 MeV by Geant4.In order to test the accuracy of the Geant4 simulation,we apply it to measure an ^241Am-Be neutron source,and the measured neutron counts of the spectrometer and simulated counts are found to be highly consistent,with a relative error up to 9.3%.This has proven the calculation of the neutron response of the Bonner sphere spectrometer by Geant4 to be quite accurate.
基金Supported by National Natural Science Foundation of China (11127508)
文摘China Spallation Neutron Source （CSNS）, one project of the 12th Five-Year-Plan scheme of China, is under construction in Guangdong province. Three neutron spectrometers will he installed during the first phase of the project, and two-dimensional position sensitive thermal neutron detectors are required. Before the construction of the neutron detectors, a prototype of a two-dimensional 200 mm^200 mm Multi-wire Proportional Chamber （MWPC） with Ar/CO2 （90/10） flowing gas has been constructed. In 2009, the prototype was tested with the 55Fe X-ray using part of the electronics, and performed well. Following the test in 2009, the neutron detector was constructed with the complete electronics and filled with the 6 atm. 3He^2.5 atm. C3Hs gas mixture in 2010. The neutron detector has been primarily tested with an Am-Be source. In this paper, new developments of the neutron detector including the design of the high pressure chamber, the optimization of the gas purifying system and the gas filling process will be reported. The results and discussion are also presented in this paper.
基金Supported by National Natural Science Foundation of China(11375195)National Magnetic Confinement Fusion Science Program of China(2013GB104003)
文摘In order to realize real-time fusion neutron spectrum diagnosis for the HL_2A Tokamak, a Bonner Sphere Spectrometer （BSS） array has been developed, consisting of eight polyethylene spheres （PS） with embedded aHe proportional counters. To validate its spectrometric capability, spectrum measurement of an 241Am-Be neutron source was carried out and is described. The Monte Carlo code Geant4 was used to calculate the response functions, taking this interference into consideration. Finally, the neutron spectrum was unfolded in the energy range from 10-9 MeV to 20 MeV. The unfolded spectrum has remarkable consistency with the ISO 8529-1 standard 2alAm-Be neutron spectrum which is a preliminary demonstration that this BSS is reliable and practical.
基金Supported by National Natural Science Foundation of China(11135002,11305232,11175076)
文摘A high-efficiency fast neutron detector prototype based on a triple Gas Electron Multiplier（GEM） detector, which, coupled with a novel multi-layered high-density polyethylene（HDPE） as a neutron-to-proton converter for improving the neutron detection efficiency, is introduced and tested with the Am-Be neutron source in the Institute of Modern Physics（IMP） at Lanzhou in the present work. First, the developed triple GEM detector is tested by measuring its effective gain and energy resolution with55 Fe X-ray source to ensure that it has a good performance.The effective gain and obtained energy resolution is 5.0×104and around 19.2%, respectively. Secondly, the novel multi-layered HDPE converter is coupled with the cathode of the triple GEM detector making it a high-efficiency fast neutron detector. Its effective neutron response is four times higher than that of the traditional single-layered conversion technique when the converter layer number is 38.
