A method is proposed for high-resolution neutron spectrum regulation across the entire energy domain.It was applied to in-reactor transuranic isotope production.This method comprises four modules:a neutron spectrum pe...A method is proposed for high-resolution neutron spectrum regulation across the entire energy domain.It was applied to in-reactor transuranic isotope production.This method comprises four modules:a neutron spectrum perturbation module,a neutron spectrum calculation module,a neutron spectrum valuation module,and an intelligent optimization module.It makes it possible to determine the optimal neutron spectrum for transuranic isotope production and a regulation scheme to establish this neutron spectrum within the reactor.The state-of-the-art production schemes for^(252)Cf and^(238)Pu in the High Flux Isotope Reactor were optimized,improving the yield of^(252)Cf by 12.16%and that of^(238)Pu by 7.53-25.84%.Moreover,the proposed optimization schemes only disperse certain nuclides into the targets without modifying the reactor design parameters,making them simple and feasible.The new method achieves efficient and precise neutron spectrum optimization,maximizing the production of transuranic isotopes.展开更多
The neutron spectrum unfolding by Bonner sphere spectrometer(BSS) is considered a complex multidimensional model,which requires complex mathematical methods to solve the first kind of Fredholm integral equation. In or...The neutron spectrum unfolding by Bonner sphere spectrometer(BSS) is considered a complex multidimensional model,which requires complex mathematical methods to solve the first kind of Fredholm integral equation. In order to solve the problem of the maximum likelihood expectation maximization(MLEM) algorithm which is easy to suffer the pitfalls of local optima and the particle swarm optimization(PSO) algorithm which is easy to get unreasonable flight direction and step length of particles, which leads to the invalid iteration and affect efficiency and accuracy, an improved PSO-MLEM algorithm, combined of PSO and MLEM algorithm, is proposed for neutron spectrum unfolding. The dynamic acceleration factor is used to balance the ability of global and local search, and improves the convergence speed and accuracy of the algorithm. Firstly, the Monte Carlo method was used to simulated the BSS to obtain the response function and count rates of BSS. In the simulation of count rate, four reference spectra from the IAEA Technical Report Series No. 403 were used as input parameters of the Monte Carlo method. The PSO-MLEM algorithm was used to unfold the neutron spectrum of the simulated data and was verified by the difference of the unfolded spectrum to the reference spectrum. Finally, the 252Cf neutron source was measured by BSS, and the PSO-MLEM algorithm was used to unfold the experimental neutron spectrum.Compared with maximum entropy deconvolution(MAXED), PSO and MLEM algorithm, the PSO-MLEM algorithm has fewer parameters and automatically adjusts the dynamic acceleration factor to solve the problem of local optima. The convergence speed of the PSO-MLEM algorithm is 1.4 times and 3.1 times that of the MLEM and PSO algorithms. Compared with PSO, MLEM and MAXED, the correlation coefficients of PSO-MLEM algorithm are increased by 33.1%, 33.5% and 1.9%, and the relative mean errors are decreased by 98.2%, 97.8% and 67.4%.展开更多
The improved version of Los Alamos model with the multi-modal fission approach is used to analyse the prompt fission neutron spectrum and multiplicity for the neutron-induced fission of 237Np. The spectra of neutrons ...The improved version of Los Alamos model with the multi-modal fission approach is used to analyse the prompt fission neutron spectrum and multiplicity for the neutron-induced fission of 237Np. The spectra of neutrons emitted from fragments for the three most dominant fission modes （standard Ⅰ, standard Ⅱ and superlong） are calculated separately and the total spectrum is synthesized. The multi-modal parameters contained in the spectrum model are determined on the basis of experimental data of fission fragment mass distributions. The calculated total prompt fission neutron spectrum and multiplicity are better agreement with the experimental data than those obtained from the conventional treatment of the Los Alamos model.展开更多
The extended Bonner sphere spectrometer （EBSS） at the HL-2A tokamak for the neutron spectrum is described. This device was developed on the basis of previous Bonner sphere spectrometry （BSS）, aiming to obtain a mo...The extended Bonner sphere spectrometer （EBSS） at the HL-2A tokamak for the neutron spectrum is described. This device was developed on the basis of previous Bonner sphere spectrometry （BSS）, aiming to obtain a more accurate neutron spectrum in the HL-2A tokamak hall. The previous BSS contained eight Bonner spheres （BS）. This EBSS contains 13 3He-filled detectors embedded in polyethylene spheres （PS）, pre-amplifiers, and a parallel processing data acquisition system （DAQ）. A response matrix is simulated in Geant4 taking the effect of the environment into account.展开更多
Neutron spectrum should be measured before test samples are irradiated.Neutron spectrum in an irradiation chamber of a research reactor was measured by using activation method when the reactor is in normal operation u...Neutron spectrum should be measured before test samples are irradiated.Neutron spectrum in an irradiation chamber of a research reactor was measured by using activation method when the reactor is in normal operation under 2 MW.Sixteen kinds of non-fission foils(19 reaction channels) were selected,of which 10 were sensitive to thermal and intermediate energy regions,while the others were of different threshold energy and sensitive to fast energy regions.By measuring the foil radioactivity,the neutron spectrum was unfolded with the iterative methods SAND-Ⅱ and MSIT.Finally,shielding corrections of group cross-section and main factors affecting the calculation accuracy were studied and the uncertainty of solution was analyzed using the Monte Carlo method in the process of SAND-Ⅱ.展开更多
This paper is aimed at detecting the neutron spectrum of^(241)Am–Be, a widely used neutron source, with the SP9 ~3He proportional counter, which is a multi-sphere spectrometer system of eight thermal neutron detector...This paper is aimed at detecting the neutron spectrum of^(241)Am–Be, a widely used neutron source, with the SP9 ~3He proportional counter, which is a multi-sphere spectrometer system of eight thermal neutron detectors embedded in eight polyethylene(PE) spheres of varying diameters. The transport processes of a neutron in the multi-sphere spectrometer are simulated using the Geant4 code. Two sets of response functions of the PE spheres are obtained for calculating the^(241)Am–Be neutron spectrum.Response Function 1 utilizes the thermal neutron scattering model G4 Neutron HPThermal Scattering for neutron energies of ≤4 eV, and Response Function 2 has no thermal treatment. Neutron spectra of an^(241)Am–Be neutron source are measured and compared to those calculated by using the response functions. The results show that response function with thermal treatment is more accurate and closer to the real spectrum.展开更多
The acquisition of neutron time spectrum data plays a pivotal role in the precise quantification of uranium via prompt fission neutron uranium logging(PFNUL).However,the impact of the detector dead-time effect remains...The acquisition of neutron time spectrum data plays a pivotal role in the precise quantification of uranium via prompt fission neutron uranium logging(PFNUL).However,the impact of the detector dead-time effect remains paramount in the accurate acquisition of the neutron time spectrum.Therefore,it is imperative for neutron logging instruments to establish a dead-time correction method that is not only uncomplicated but also practical and caters to various logging sites.This study has formulated an innovative equation for determining dead time and introduced a dead-time correction method for the neutron time spectrum,called the“dual flux method.”Using this approach,a logging instrument captures two neutron time spectra under disparate neutron fluxes.By carefully selecting specific“windows”on the neutron time spectrum,the dead time can be accurately ascertained.To substantiate its efficacy and discern the influencing factors,experiments were conducted utilizing a deuterium-tritium(D-T)neutron source,a Helium-3(3He)detector,and polyethylene shielding to collate and analyze the neutron time spectrum under varying neutron fluxes(at high voltages).The findings underscore that the“height”and“spacing”of the two windows are the most pivotal influencing factors.Notably,the“height”(fd)should surpass 2,and the“spacing”twd should exceed 200μs.The dead time of the 3 He detector determined in the experiment was 7.35μs.After the dead-time correction,the deviation of the decay coefficients from the theoretical values for the neutron time spectrum under varying neutron fluxes decreased from 12.4%to within 5%.Similarly,for the PFNUL instrument,the deviation in the decay coefficients decreased from 22.94 to 0.49%after correcting for the dead-time effect.These results demonstrate the exceptional efficacy of the proposed method in ensuring precise uranium quantification.The dual flux method was experimentally validated as a universal approach applicable to pulsed neutron logging instruments and holds immense significance for uranium exploration.展开更多
Prompt fission neutron uranium logging(PFNUL)is an advanced method for utilizing pulsed neutron bombardment of the ore layer and a fission reaction with uranium(^(235)U)to detect the transient neutrons produced by fis...Prompt fission neutron uranium logging(PFNUL)is an advanced method for utilizing pulsed neutron bombardment of the ore layer and a fission reaction with uranium(^(235)U)to detect the transient neutrons produced by fission and then directly measure and quantify uranium;however,the stability and lifetime performance of pulsed neutron sources are the key constraints to its rapid promotion.To address these problems,this study proposes a PFNUL technique for acquiring the time spectrum of dual-energy neutrons(epithermal and thermal neutrons)from the upper and lower detection structures and establishes a novel uranium quantification algorithm based on the ratio of epithermal and thermal neutron time windows(E/T)via a mathematical-physical modeling derivation.Through simulations on well-logging models with di erent uranium contents,the starting and stopping times of the time window(Δt)for uranium quantification in the dual-energy neutron time spectrum are determined to be 200 and 800μs,respectively.The minimum radius and height of the model wells are 60 and 120 cm,respectively,and the E/T values in the time window show an excellent linear relationship with the uranium content.The scale factor is K_(E/T)=1.92 and R^(2)=0.999,which verifies the validity of the E/T uranium quantification algorithm.In addition,experiments were carried out in the Nu series of uranium standard model wells,and the results showed that under di erent neutron source yields,the E/T-based uranium quantification method reduced the relative standard deviation of the scale factor of the uranium content from 33.41%to 1.09%,compared with a single epithermal neutron quantification method.These results prove that the E/T value uranium quantification method is una ected by the change in the neutron source yield,e ectively improves the accuracy and service life of the logging instrument,and has great scientific and popularization value.展开更多
Beryllium(^(9)Be)serves as a crucial neutron multiplier and reflection material,being extensively employed in the nuclear industry.The evaluated nuclear data are utilized in the design of the nuclear devices.Following...Beryllium(^(9)Be)serves as a crucial neutron multiplier and reflection material,being extensively employed in the nuclear industry.The evaluated nuclear data are utilized in the design of the nuclear devices.Following the interaction between neutrons and^(9)Be,all neutrons generated stem from the^(9)Be(n,2n)^(8)Be reaction channel,except for the elastic scattering reaction channel.Nevertheless,the data of the outgoing neutron double differential cross section of the reaction channel provided by the latest internationally evaluated libraries still exhibit considerable discrepancies.A shielding integral experiment based on slab^(9)Be samples with measurements of neutron spectra leaked from different angles is an effective approach to verify the double differential cross-section data.Hence,in this study,a shielding integral experiment of^(9)Be samples of different thicknesses was conducted using a nanosecond pulsed deuterium-tritium neutron source established by the China Institute of Atomic Energy.The neutron time-of-flight spectra of three thicknesses(4.4 cm,8.8 cm,and 13.2 cm)and six angles(47°,58°,73°,107°,122°,and 133°)were measured by the neutron time-of-flight method,and 18 sets of experimental data were obtained.Additionally,the MCNP-4C program was used to obtain the simulated results of the leakage neutron spectra using the evaluated nuclear data of^(9)Be from the CENDL-3.2,ENDF/B-Ⅷ.0,JENDL-5,and JEFF-3.3 libraries.The simulated results of the leakage neutron spectra were compared with the experimental results,and the results showed that in the elastic scattering energy region,the simulated results from the CENDL-3.2,ENDF/B-Ⅷ.0,and JENDL-5 libraries were slightly higher at small angles and slightly lower at large angles.In the(n,2n)energy region,the simulated results from the CENDL-3.2 library were significantly different from the experimental results in terms of spectral shape,and the simulated results from the ENDF/B-Ⅷ.0 and the JENDL-5 libraries were in good agreement with the experimental results at small angles but low at large angles.The simulated results from the JEFF-3.3 library showed serious underestimation at all angles.展开更多
The neutron energy spectrum was measured using a Bonner sphere spectrometer at six locations inside the containment vessel of a nuclear reactor at the Qinshan nuclear power plant. The structures of the neutron spectra...The neutron energy spectrum was measured using a Bonner sphere spectrometer at six locations inside the containment vessel of a nuclear reactor at the Qinshan nuclear power plant. The structures of the neutron spectra obtained by the maximum entropy, iteration, and genetic algorithm methods were consistent with one another and could be interpreted as the spectral superposition of different energy regions. The characteristic parameters of the neutron spectrum, including the fluence rate,average energy, and neutron ambient dose equivalent rate H^(*)(10), were in good agreement among the three methods. In addition, an LB6411 neutron ambient dose equivalent meter was employed to obtain the H^(*)(10) directly for comparison.These findings indicate that neutron spectrum unfolding methods can be used to overcome the problems associated with the response functions of dosimeters to provide more accurate H^(*)(10) values. In this study, the following three evaluation criteria were systematically addressed to ensure the accuracy of the unfolded spectra: count rates of the inverse solutions,neutron spectrum structures, and comparison of key parameters.展开更多
The neutron response function for a BC501A liquid scintillator （LS） has been measured using a series of monoenergetic neutrons produced by the p-T reaction. The proton energies were chosen such as to produce neutron...The neutron response function for a BC501A liquid scintillator （LS） has been measured using a series of monoenergetic neutrons produced by the p-T reaction. The proton energies were chosen such as to produce neutrons in the energy range of 1 to 20 MeV. The principles of the technique of unfolding a neutron energy spectrum by using the measured neutron response function and the measured Pulse Height （PH） spectrum is briefly described. The PH spectrum of neutrons from the Pu-C source, which will be used for the calibration of the reactor antineutrino detectors for the Daya Bay neutrino experiment, was measured and analyzed to get the neutron energy spectrum. Simultaneously the neutron energy spectrum of an Am-Be source was measured and compared with other measurements as a check of the result for the Pu-C source. Finally, an error analysis and a discussion of the results are given.展开更多
The prompt fission neutron spectra for the neutron-induced fission of 233U for low energy neutrons （below 6 MeV） are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition o...The prompt fission neutron spectra for the neutron-induced fission of 233U for low energy neutrons （below 6 MeV） are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the nth＋233U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.展开更多
This paper presents the neutron energy spectrum in the central position of a neutron flux trap assembled in the core center of the research nuclear reactor IPEN/MB-01, obtained by an unfolding method. To this end, we ...This paper presents the neutron energy spectrum in the central position of a neutron flux trap assembled in the core center of the research nuclear reactor IPEN/MB-01, obtained by an unfolding method. To this end, we have used several different types of activation foils （Au, Sc, Ti, Ni, and plates） which have been irradiated in the central position of the reactor core （setting number 203） at a reactor power level （64.57±2.91 watts）. The activation foils were counted by solid-state detector HPGe （high pure germanium detector） （gamma spectrometry）. The experimental data of nuclear reaction rates （saturated activity per target nucleus） and a neutron spectrum estimated by a reactor physics computer code are the main input data to get the most suitable neutron spectrum in the irradiation position obtained through SANDBP （spectrum analysis neutron detection code-version Budapest University） code： a neutron spectra unfolding code that uses an iterative adjustment method. the integral neutron flux, （2.41 ± 0.01） × 10^9 n·cm^-2·s^-1 for the thermal The adjustment resulted in （3.85 ± 0.14） × 10^9 n·cm^-2·s^-1 for neutron flux, （1.09 ±0.02） × 10^9n·cm^-2·s^-1 for intermediate neutron flux and （3.41 ± 0.02） × 10^8 n·cm^-2·s^-1 for the fast neutrons flux. These results can be used to verify and validate the nuclear reactor codes and its associated nuclear data libraries, besides, show how much effective it can be that the use of a neutron flux trap in the nuclear reactor core to increase the thermal neutron flux without increase the operation reactor power level. The thermal neutral flux increased 4.04 ± 0.21 times compared with the standard configuration of the reactor core.展开更多
In this work, natural neutron spectra at nine sites in Tibet region were measured using a multi-sphere neutron spectrometer. The altitude-dependence of the spectra total fluence rate and ambient dose equivalent rate w...In this work, natural neutron spectra at nine sites in Tibet region were measured using a multi-sphere neutron spectrometer. The altitude-dependence of the spectra total fluence rate and ambient dose equivalent rate were analyzed. From the normalized natural neutron spectra at different altitudes, the spectrum fractions for neutrons of greater than 0.1 MeV do not differ obviously, while those of the thermal neutrons differ greatly from each other. The total fluence rate, effective dose rate and the ambient dose equivalent rate varied with the altitude according to an exponential law.展开更多
The characteristic gamma-ray spectrum of TNT in the soil induced by DT neutrons is measured by the PFTNA demining system. The GEANT4 toolkit is used to simulate the whole experimental procedure. The simulated spectra ...The characteristic gamma-ray spectrum of TNT in the soil induced by DT neutrons is measured by the PFTNA demining system. The GEANT4 toolkit is used to simulate the whole experimental procedure. The simulated spectra are compared with the experimental spectra, and they are mainly consistent. The share of the background sources such as neutrons and gamma is obtained and the contribution that the experimental apparatus to the background, such as shielding, detector sleeve and moderator, is analyzed. The effective gamma signal(from soil and TNT) is 29% of the full spectrum signal, and the background signal, more than 68%, this is mainly produced by shielding and the detector sleeve. By gradually optimizing the shielding and the cadmium sheet of the detector sleeve, the share of the effective gamma signal increases to 47%, and the background signal reduces to 18%.展开更多
The neutron radiation field has vital applications in areas such as biomedicine,geology,radiation safety,and many others for neutron detection and neutron metrology.Correcting neutron fluence rate perturbation accurat...The neutron radiation field has vital applications in areas such as biomedicine,geology,radiation safety,and many others for neutron detection and neutron metrology.Correcting neutron fluence rate perturbation accurately is an important yet challenging problem.This study proposes a correction method that analyzes three physical processes.This method,which transforms the detection process from point detection to area detection,is based on a novel physical model and has been validated through theoretical analyses,experiments,and simulations.According to the average differences between the calculated and experimental results,the new method(1.67%)demonstrated better accuracy than the traditional simulation(2.17%).In a closed thermal neutron radiation field,the detector or strong neutron absorption material significantly perturbs the neutron fluence rate,whereas its impact on the energy spectrum shape and neutron directionality is relatively minor.Furthermore,based on the calculation results of the perturbation rate formula for medium materials with different compositions and sizes,the larger the volume and capture cross section of the medium,the higher the perturbation rate generated in the closed radiation field.展开更多
It is a very complex and time-consuming process to simulate the nuclear reactor neutron spectrum from the reactor core to the export channel by applying a Monte Carlo program. This paper presents a new method to calcu...It is a very complex and time-consuming process to simulate the nuclear reactor neutron spectrum from the reactor core to the export channel by applying a Monte Carlo program. This paper presents a new method to calculate the neutron spectrum by using the convolution technique which considers the channel transportation as a linear system and the transportation scattering as the response function. It also applies Monte Carlo Neutron and Photon Transport Code （MCNP） to simulate the response function numerically. With the application of convolution technique to calculate the spectrum distribution from the core to the channel, the process is then much more convenient only with the simple numerical integral numeration. This saves computer time and reduces some trouble in re-writing of the MCNP program.展开更多
基金sponsored by the National Natural Science Foundation of China(No.12305190)the Lingchuang Research Project of the China National Nuclear Corporation(CNNC)。
文摘A method is proposed for high-resolution neutron spectrum regulation across the entire energy domain.It was applied to in-reactor transuranic isotope production.This method comprises four modules:a neutron spectrum perturbation module,a neutron spectrum calculation module,a neutron spectrum valuation module,and an intelligent optimization module.It makes it possible to determine the optimal neutron spectrum for transuranic isotope production and a regulation scheme to establish this neutron spectrum within the reactor.The state-of-the-art production schemes for^(252)Cf and^(238)Pu in the High Flux Isotope Reactor were optimized,improving the yield of^(252)Cf by 12.16%and that of^(238)Pu by 7.53-25.84%.Moreover,the proposed optimization schemes only disperse certain nuclides into the targets without modifying the reactor design parameters,making them simple and feasible.The new method achieves efficient and precise neutron spectrum optimization,maximizing the production of transuranic isotopes.
基金supported by the National Natural science Foundation of China (No. 42127807)the Sichuan Science and Technology Program (No. 2020YJ0334)the Sichuan Science and Technology Breeding Program (No. 2022041)。
文摘The neutron spectrum unfolding by Bonner sphere spectrometer(BSS) is considered a complex multidimensional model,which requires complex mathematical methods to solve the first kind of Fredholm integral equation. In order to solve the problem of the maximum likelihood expectation maximization(MLEM) algorithm which is easy to suffer the pitfalls of local optima and the particle swarm optimization(PSO) algorithm which is easy to get unreasonable flight direction and step length of particles, which leads to the invalid iteration and affect efficiency and accuracy, an improved PSO-MLEM algorithm, combined of PSO and MLEM algorithm, is proposed for neutron spectrum unfolding. The dynamic acceleration factor is used to balance the ability of global and local search, and improves the convergence speed and accuracy of the algorithm. Firstly, the Monte Carlo method was used to simulated the BSS to obtain the response function and count rates of BSS. In the simulation of count rate, four reference spectra from the IAEA Technical Report Series No. 403 were used as input parameters of the Monte Carlo method. The PSO-MLEM algorithm was used to unfold the neutron spectrum of the simulated data and was verified by the difference of the unfolded spectrum to the reference spectrum. Finally, the 252Cf neutron source was measured by BSS, and the PSO-MLEM algorithm was used to unfold the experimental neutron spectrum.Compared with maximum entropy deconvolution(MAXED), PSO and MLEM algorithm, the PSO-MLEM algorithm has fewer parameters and automatically adjusts the dynamic acceleration factor to solve the problem of local optima. The convergence speed of the PSO-MLEM algorithm is 1.4 times and 3.1 times that of the MLEM and PSO algorithms. Compared with PSO, MLEM and MAXED, the correlation coefficients of PSO-MLEM algorithm are increased by 33.1%, 33.5% and 1.9%, and the relative mean errors are decreased by 98.2%, 97.8% and 67.4%.
基金Project supported by the State Key Development Program for Basic Research of China (Grant Nos 2008CB717803 and 2007ID103)the Research Fund for the Doctoral Program of Higher Education of China (Gant No 200610001023)
文摘The improved version of Los Alamos model with the multi-modal fission approach is used to analyse the prompt fission neutron spectrum and multiplicity for the neutron-induced fission of 237Np. The spectra of neutrons emitted from fragments for the three most dominant fission modes （standard Ⅰ, standard Ⅱ and superlong） are calculated separately and the total spectrum is synthesized. The multi-modal parameters contained in the spectrum model are determined on the basis of experimental data of fission fragment mass distributions. The calculated total prompt fission neutron spectrum and multiplicity are better agreement with the experimental data than those obtained from the conventional treatment of the Los Alamos model.
基金supported by National Natural Science Foundation of China (No. 11375195, No. 11575184)the National Magnetic Confinement Fusion Energy Development Research (2013GB104003)
文摘The extended Bonner sphere spectrometer （EBSS） at the HL-2A tokamak for the neutron spectrum is described. This device was developed on the basis of previous Bonner sphere spectrometry （BSS）, aiming to obtain a more accurate neutron spectrum in the HL-2A tokamak hall. The previous BSS contained eight Bonner spheres （BS）. This EBSS contains 13 3He-filled detectors embedded in polyethylene spheres （PS）, pre-amplifiers, and a parallel processing data acquisition system （DAQ）. A response matrix is simulated in Geant4 taking the effect of the environment into account.
基金Supported by"Strategic Priority Research Program"of the Chinese Academy of Science(No.XDA02001003)
文摘Neutron spectrum should be measured before test samples are irradiated.Neutron spectrum in an irradiation chamber of a research reactor was measured by using activation method when the reactor is in normal operation under 2 MW.Sixteen kinds of non-fission foils(19 reaction channels) were selected,of which 10 were sensitive to thermal and intermediate energy regions,while the others were of different threshold energy and sensitive to fast energy regions.By measuring the foil radioactivity,the neutron spectrum was unfolded with the iterative methods SAND-Ⅱ and MSIT.Finally,shielding corrections of group cross-section and main factors affecting the calculation accuracy were studied and the uncertainty of solution was analyzed using the Monte Carlo method in the process of SAND-Ⅱ.
基金supported by ITER Plan National Major Project(No.2008GB109000)the Introduces Talents Scientific Research Project of Guizhou University(2014,No.32)
文摘This paper is aimed at detecting the neutron spectrum of^(241)Am–Be, a widely used neutron source, with the SP9 ~3He proportional counter, which is a multi-sphere spectrometer system of eight thermal neutron detectors embedded in eight polyethylene(PE) spheres of varying diameters. The transport processes of a neutron in the multi-sphere spectrometer are simulated using the Geant4 code. Two sets of response functions of the PE spheres are obtained for calculating the^(241)Am–Be neutron spectrum.Response Function 1 utilizes the thermal neutron scattering model G4 Neutron HPThermal Scattering for neutron energies of ≤4 eV, and Response Function 2 has no thermal treatment. Neutron spectra of an^(241)Am–Be neutron source are measured and compared to those calculated by using the response functions. The results show that response function with thermal treatment is more accurate and closer to the real spectrum.
基金supported by the National Natural Science Foundation of China(No.42374226)Jiangxi Provincial Natural Science Foundation(Nos.20232BAB201043 and 20232BCJ23006)+2 种基金Nuclear Energy Development Project(20201192-01)National Key Laboratory of Uranium Resource Exploration-Mining and Nuclear Remote Sensing(ECUT)(2024QZ-TD-09)Fundamental Science on Radioactive Geology and Exploration Technology Laboratory(2022RGET20).
文摘The acquisition of neutron time spectrum data plays a pivotal role in the precise quantification of uranium via prompt fission neutron uranium logging(PFNUL).However,the impact of the detector dead-time effect remains paramount in the accurate acquisition of the neutron time spectrum.Therefore,it is imperative for neutron logging instruments to establish a dead-time correction method that is not only uncomplicated but also practical and caters to various logging sites.This study has formulated an innovative equation for determining dead time and introduced a dead-time correction method for the neutron time spectrum,called the“dual flux method.”Using this approach,a logging instrument captures two neutron time spectra under disparate neutron fluxes.By carefully selecting specific“windows”on the neutron time spectrum,the dead time can be accurately ascertained.To substantiate its efficacy and discern the influencing factors,experiments were conducted utilizing a deuterium-tritium(D-T)neutron source,a Helium-3(3He)detector,and polyethylene shielding to collate and analyze the neutron time spectrum under varying neutron fluxes(at high voltages).The findings underscore that the“height”and“spacing”of the two windows are the most pivotal influencing factors.Notably,the“height”(fd)should surpass 2,and the“spacing”twd should exceed 200μs.The dead time of the 3 He detector determined in the experiment was 7.35μs.After the dead-time correction,the deviation of the decay coefficients from the theoretical values for the neutron time spectrum under varying neutron fluxes decreased from 12.4%to within 5%.Similarly,for the PFNUL instrument,the deviation in the decay coefficients decreased from 22.94 to 0.49%after correcting for the dead-time effect.These results demonstrate the exceptional efficacy of the proposed method in ensuring precise uranium quantification.The dual flux method was experimentally validated as a universal approach applicable to pulsed neutron logging instruments and holds immense significance for uranium exploration.
基金supported by the National Natural Science Foundation of China(No.42374226)Jiangxi Provincial Natural Science Foundation(Nos.20232BAB201043,gpyc20240073,and 20232BCJ23006)+2 种基金Nuclear Energy Development Project(20201192-01)Fundamental Science on Radioactive Geology and Exploration Technology Laboratory(2022RGET20)National Key Laboratory of Uranium Resource Exploration-Mining and Nuclear Remote Sensing(ECUT)(2024QZ-TD-09)。
文摘Prompt fission neutron uranium logging(PFNUL)is an advanced method for utilizing pulsed neutron bombardment of the ore layer and a fission reaction with uranium(^(235)U)to detect the transient neutrons produced by fission and then directly measure and quantify uranium;however,the stability and lifetime performance of pulsed neutron sources are the key constraints to its rapid promotion.To address these problems,this study proposes a PFNUL technique for acquiring the time spectrum of dual-energy neutrons(epithermal and thermal neutrons)from the upper and lower detection structures and establishes a novel uranium quantification algorithm based on the ratio of epithermal and thermal neutron time windows(E/T)via a mathematical-physical modeling derivation.Through simulations on well-logging models with di erent uranium contents,the starting and stopping times of the time window(Δt)for uranium quantification in the dual-energy neutron time spectrum are determined to be 200 and 800μs,respectively.The minimum radius and height of the model wells are 60 and 120 cm,respectively,and the E/T values in the time window show an excellent linear relationship with the uranium content.The scale factor is K_(E/T)=1.92 and R^(2)=0.999,which verifies the validity of the E/T uranium quantification algorithm.In addition,experiments were carried out in the Nu series of uranium standard model wells,and the results showed that under di erent neutron source yields,the E/T-based uranium quantification method reduced the relative standard deviation of the scale factor of the uranium content from 33.41%to 1.09%,compared with a single epithermal neutron quantification method.These results prove that the E/T value uranium quantification method is una ected by the change in the neutron source yield,e ectively improves the accuracy and service life of the logging instrument,and has great scientific and popularization value.
基金supported by the National Natural Science Foundation of China(Nos.11775311,U2167203,U2067205 and 12075105)Research and development project of China National Nuclear Corporation(FD010241222552)+2 种基金Continuous-Support Basic Scientific Research Project(BJ010261223282)Major Science and Technology Projects of Gansu Province(22ZD6GB020)Fundamental Research Funds for the Central Universities(lzujbky-2024-jdzx10)。
文摘Beryllium(^(9)Be)serves as a crucial neutron multiplier and reflection material,being extensively employed in the nuclear industry.The evaluated nuclear data are utilized in the design of the nuclear devices.Following the interaction between neutrons and^(9)Be,all neutrons generated stem from the^(9)Be(n,2n)^(8)Be reaction channel,except for the elastic scattering reaction channel.Nevertheless,the data of the outgoing neutron double differential cross section of the reaction channel provided by the latest internationally evaluated libraries still exhibit considerable discrepancies.A shielding integral experiment based on slab^(9)Be samples with measurements of neutron spectra leaked from different angles is an effective approach to verify the double differential cross-section data.Hence,in this study,a shielding integral experiment of^(9)Be samples of different thicknesses was conducted using a nanosecond pulsed deuterium-tritium neutron source established by the China Institute of Atomic Energy.The neutron time-of-flight spectra of three thicknesses(4.4 cm,8.8 cm,and 13.2 cm)and six angles(47°,58°,73°,107°,122°,and 133°)were measured by the neutron time-of-flight method,and 18 sets of experimental data were obtained.Additionally,the MCNP-4C program was used to obtain the simulated results of the leakage neutron spectra using the evaluated nuclear data of^(9)Be from the CENDL-3.2,ENDF/B-Ⅷ.0,JENDL-5,and JEFF-3.3 libraries.The simulated results of the leakage neutron spectra were compared with the experimental results,and the results showed that in the elastic scattering energy region,the simulated results from the CENDL-3.2,ENDF/B-Ⅷ.0,and JENDL-5 libraries were slightly higher at small angles and slightly lower at large angles.In the(n,2n)energy region,the simulated results from the CENDL-3.2 library were significantly different from the experimental results in terms of spectral shape,and the simulated results from the ENDF/B-Ⅷ.0 and the JENDL-5 libraries were in good agreement with the experimental results at small angles but low at large angles.The simulated results from the JEFF-3.3 library showed serious underestimation at all angles.
基金supported by the Fundamental Research Funds of the National Institute of Metrology,China(No.AKYZZ2113)National Key Research and Development Program of China(No.2017YFF0206205).
文摘The neutron energy spectrum was measured using a Bonner sphere spectrometer at six locations inside the containment vessel of a nuclear reactor at the Qinshan nuclear power plant. The structures of the neutron spectra obtained by the maximum entropy, iteration, and genetic algorithm methods were consistent with one another and could be interpreted as the spectral superposition of different energy regions. The characteristic parameters of the neutron spectrum, including the fluence rate,average energy, and neutron ambient dose equivalent rate H^(*)(10), were in good agreement among the three methods. In addition, an LB6411 neutron ambient dose equivalent meter was employed to obtain the H^(*)(10) directly for comparison.These findings indicate that neutron spectrum unfolding methods can be used to overcome the problems associated with the response functions of dosimeters to provide more accurate H^(*)(10) values. In this study, the following three evaluation criteria were systematically addressed to ensure the accuracy of the unfolded spectra: count rates of the inverse solutions,neutron spectrum structures, and comparison of key parameters.
文摘The neutron response function for a BC501A liquid scintillator （LS） has been measured using a series of monoenergetic neutrons produced by the p-T reaction. The proton energies were chosen such as to produce neutrons in the energy range of 1 to 20 MeV. The principles of the technique of unfolding a neutron energy spectrum by using the measured neutron response function and the measured Pulse Height （PH） spectrum is briefly described. The PH spectrum of neutrons from the Pu-C source, which will be used for the calibration of the reactor antineutrino detectors for the Daya Bay neutrino experiment, was measured and analyzed to get the neutron energy spectrum. Simultaneously the neutron energy spectrum of an Am-Be source was measured and compared with other measurements as a check of the result for the Pu-C source. Finally, an error analysis and a discussion of the results are given.
基金Supported by National Natural Science Foundation of China(11205246,91126010,91226102)
文摘The prompt fission neutron spectra for the neutron-induced fission of 233U for low energy neutrons （below 6 MeV） are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the nth＋233U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.
文摘This paper presents the neutron energy spectrum in the central position of a neutron flux trap assembled in the core center of the research nuclear reactor IPEN/MB-01, obtained by an unfolding method. To this end, we have used several different types of activation foils （Au, Sc, Ti, Ni, and plates） which have been irradiated in the central position of the reactor core （setting number 203） at a reactor power level （64.57±2.91 watts）. The activation foils were counted by solid-state detector HPGe （high pure germanium detector） （gamma spectrometry）. The experimental data of nuclear reaction rates （saturated activity per target nucleus） and a neutron spectrum estimated by a reactor physics computer code are the main input data to get the most suitable neutron spectrum in the irradiation position obtained through SANDBP （spectrum analysis neutron detection code-version Budapest University） code： a neutron spectra unfolding code that uses an iterative adjustment method. the integral neutron flux, （2.41 ± 0.01） × 10^9 n·cm^-2·s^-1 for the thermal The adjustment resulted in （3.85 ± 0.14） × 10^9 n·cm^-2·s^-1 for neutron flux, （1.09 ±0.02） × 10^9n·cm^-2·s^-1 for intermediate neutron flux and （3.41 ± 0.02） × 10^8 n·cm^-2·s^-1 for the fast neutrons flux. These results can be used to verify and validate the nuclear reactor codes and its associated nuclear data libraries, besides, show how much effective it can be that the use of a neutron flux trap in the nuclear reactor core to increase the thermal neutron flux without increase the operation reactor power level. The thermal neutral flux increased 4.04 ± 0.21 times compared with the standard configuration of the reactor core.
基金Supported by the National Natural Science Foundation of China(No.11575294)
文摘In this work, natural neutron spectra at nine sites in Tibet region were measured using a multi-sphere neutron spectrometer. The altitude-dependence of the spectra total fluence rate and ambient dose equivalent rate were analyzed. From the normalized natural neutron spectra at different altitudes, the spectrum fractions for neutrons of greater than 0.1 MeV do not differ obviously, while those of the thermal neutrons differ greatly from each other. The total fluence rate, effective dose rate and the ambient dose equivalent rate varied with the altitude according to an exponential law.
文摘The characteristic gamma-ray spectrum of TNT in the soil induced by DT neutrons is measured by the PFTNA demining system. The GEANT4 toolkit is used to simulate the whole experimental procedure. The simulated spectra are compared with the experimental spectra, and they are mainly consistent. The share of the background sources such as neutrons and gamma is obtained and the contribution that the experimental apparatus to the background, such as shielding, detector sleeve and moderator, is analyzed. The effective gamma signal(from soil and TNT) is 29% of the full spectrum signal, and the background signal, more than 68%, this is mainly produced by shielding and the detector sleeve. By gradually optimizing the shielding and the cadmium sheet of the detector sleeve, the share of the effective gamma signal increases to 47%, and the background signal reduces to 18%.
基金supported by the Fundamental Research Funds of the National Institute of MetrologyChina(No.AKYZZ2113)+1 种基金National Key Research and Development Program of China(No.2017YFF0206205)the Team Building Program of Nanjing University(No.1480604114)。
文摘The neutron radiation field has vital applications in areas such as biomedicine,geology,radiation safety,and many others for neutron detection and neutron metrology.Correcting neutron fluence rate perturbation accurately is an important yet challenging problem.This study proposes a correction method that analyzes three physical processes.This method,which transforms the detection process from point detection to area detection,is based on a novel physical model and has been validated through theoretical analyses,experiments,and simulations.According to the average differences between the calculated and experimental results,the new method(1.67%)demonstrated better accuracy than the traditional simulation(2.17%).In a closed thermal neutron radiation field,the detector or strong neutron absorption material significantly perturbs the neutron fluence rate,whereas its impact on the energy spectrum shape and neutron directionality is relatively minor.Furthermore,based on the calculation results of the perturbation rate formula for medium materials with different compositions and sizes,the larger the volume and capture cross section of the medium,the higher the perturbation rate generated in the closed radiation field.
文摘It is a very complex and time-consuming process to simulate the nuclear reactor neutron spectrum from the reactor core to the export channel by applying a Monte Carlo program. This paper presents a new method to calculate the neutron spectrum by using the convolution technique which considers the channel transportation as a linear system and the transportation scattering as the response function. It also applies Monte Carlo Neutron and Photon Transport Code （MCNP） to simulate the response function numerically. With the application of convolution technique to calculate the spectrum distribution from the core to the channel, the process is then much more convenient only with the simple numerical integral numeration. This saves computer time and reduces some trouble in re-writing of the MCNP program.
