Neutron resonance imaging(NRI)has recently emerged as an appealing technique for neutron radiography.Its complexity surpasses that of conventional transmission imaging,as it requires a high demand for both a neutron s...Neutron resonance imaging(NRI)has recently emerged as an appealing technique for neutron radiography.Its complexity surpasses that of conventional transmission imaging,as it requires a high demand for both a neutron source and detector.Consequently,the progression of NRI technology has been sluggish since its inception in the 1980s,particularly considering the limited studies analyzing the neutron energy range above keV.The white neutron source(Back-n)at the China Spallation Neutron Source(CSNS)provides favorable beam conditions for the development of the NRI technique over a wide neutron energy range from eV to MeV.Neutron-sensitive microchannel plates(MCP)have emerged as a cutting-edge tool in the field of neutron detection owing to their high temporal and spatial resolutions,high detection efficiency,and low noise.In this study,we report the development of a 10B-doped MCP detector,along with its associated electronics,data processing system,and NRI experiments at the Back-n.Individual heavy elements such as gold,silver,tungsten,and indium can be easily identified in the transmission images by their characteristic resonance peaks in the 1–100 eV energy range;the more difficult medium-weight elements such as iron,copper,and aluminum with resonance peaks in the 1–100 keV energy range can also be identified.In particular,results in the neutron energy range of dozens of keV(Aluminum)are reported here for the first time.展开更多
We report an inelastic neutron scattering investigation on the spin resonance mode in the optimally hole-doped ironbased superconductor Ba_(0.67)K_(0.33)Fe_(2)As_(2)with T_c=38.2 K.Although the resonance is nearly two...We report an inelastic neutron scattering investigation on the spin resonance mode in the optimally hole-doped ironbased superconductor Ba_(0.67)K_(0.33)Fe_(2)As_(2)with T_c=38.2 K.Although the resonance is nearly two-dimensional with peak energy ER≈14 meV,it splits into two incommensurate peaks along the longitudinal direction([H,0,0])and shows an upward dispersion persisting to 26 meV.Such dispersion breaks through the limit of total superconducting gaps△_(tot)=|△k|+|△k+Q|(about 11-17 meV)on nested Fermi surfaces measured by high resolution angle resolved photoemission spectroscopy(ARPES).These results cannot be fully understood by the magnetic exciton scenario under s^(±)-pairing symmetry of superconductivity,and suggest that the spin resonance may not be restricted by the superconducting gaps in the multi-band systems.展开更多
The neutron-induced total cross-section of ^(209)Bi is crucial for the physical design and safety assessment of lead-based fast reactors, and the quality of experimental data should be improved for evaluation and appl...The neutron-induced total cross-section of ^(209)Bi is crucial for the physical design and safety assessment of lead-based fast reactors, and the quality of experimental data should be improved for evaluation and application.A recent experiment was conducted on the back-streaming white neutron beamline(Back-n) at the China Spallation Neutron Source(CSNS) using the neutron total cross-section spectrometer(NTOX). The neutron energy was determined using a fast multi-cell fission chamber and the time-of-flight technique. Two high-purity bismuth samples,6 mm and 20 mm in thickness, were chosen for neutron transmission measurements and comparisons. The neutron total cross-sections of ^(209)Bi, ranging from 0.3 e V to 20 Me V, were derived considering neutron flight time determination, flight path calibration, and background subtraction. A comparison of the experimental results with the data in the ENDF/B-VⅢ.0 library showed fair agreement, and the point-wise cross-sections were found to be consistent with existing experimental data. Special attention was given to the determination of resonance parameters, which were analyzed using the R-matrix code SAMMY and Bayesian method in the 0.5 ke V to 20 ke V energy range. The extracted resonance parameters were compared to previously reported results and evaluated data. This study is recognized as the first one where the neutron total cross-section of bismuth across such a broad energy spectrum is measured in a single measurement or experiment, and it provides valuable data for the assessment of related reaction information for evaluated libraries and the advancement of lead-bismuth-based nuclear systems.展开更多
Purpose Back-n is a white neutron beamline at China spallation neutron source,which was established in the year of 2018.It is a powerful facility for nuclear data measurement,neutron detector calibration,and radiation...Purpose Back-n is a white neutron beamline at China spallation neutron source,which was established in the year of 2018.It is a powerful facility for nuclear data measurement,neutron detector calibration,and radiation effect research.Method A series of detectors were built for different experiments,including beam monitoring,beam profile measurement,neutron induced secondaries(fission fragments,light charged particles and gamma)cross section measurement,and neutron resonance radiography,etc.A common digitization electronics and a cluster-based DAQ were developed for these detector systems.Most detectors have been employed at Back-n and serviced for experiments from the beginning of the beamline running.Results and conclusion As an overview of detectors of Back-n,the details of the detector design and the experiment performing are described in this paper.Some developing systems,e.g.,MTPC and B-MCP,are also included.展开更多
The ^239Pu fission chambers are widely used to measure fission spectrum neutron flux due to a fiat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influen...The ^239Pu fission chambers are widely used to measure fission spectrum neutron flux due to a fiat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by using ^10B and Cd covers. At a column enriched uranium fast neutron critical assembly, the fission reaction rates of ^239gpu are measured as 1.791 × 10^-16 2.350 × 10^-16 and 1.385×10^-15 per second for 15 mm thick ^10B cover, 0.5 mm thick Cd cover, and no cover respectively, while the fission reaction rate of 239pu is rapidly increased to 2.569×10^-14 for a 20 mm thick polythene covering fission chamber. The average 239pu fission cross-section of thermal and resonance neutrons is calculated to be 500 b and 24.95 b with the assumption of 1/v and 1/E spectra respectively, then thermal, resonance and fast neutron flux are achieved to be 2.30×10^6, 2.24×10^6 and 1.04×10^8 cm^-2·s^-1.展开更多
The pygmy dipole resonance(PDR) of nickel isotopes is studied using the deformed random phase approximation method. The isoscalar character of the pygmy resonance is confirmed, and the correlation between the pygmy ...The pygmy dipole resonance(PDR) of nickel isotopes is studied using the deformed random phase approximation method. The isoscalar character of the pygmy resonance is confirmed, and the correlation between the pygmy resonance and neutron skin thickness is discussed. Our investigation shows a linear correlation between PDR integral cross section and neutron skin thickness when the excess neutrons lie in pf orbits, with a correlation rate of about 0.27 fm^(-1). However, in more neutron-rich nickel isotopes, the growth of the pygmy dipole resonance is stagnant. Although the neutron skin thickness increases, the whole skin is not active. There is an inertial part in the nuclei^(70-78)Ni which does not participate in the pygmy resonance actively and as a result, contributes little to the photo-absorption cross section.展开更多
基金supported by the National Natural Science Foundation of China(No.12035017)the Guangdong Basic and Applied Basic Research Foundation(No.2023A1515030074)。
文摘Neutron resonance imaging(NRI)has recently emerged as an appealing technique for neutron radiography.Its complexity surpasses that of conventional transmission imaging,as it requires a high demand for both a neutron source and detector.Consequently,the progression of NRI technology has been sluggish since its inception in the 1980s,particularly considering the limited studies analyzing the neutron energy range above keV.The white neutron source(Back-n)at the China Spallation Neutron Source(CSNS)provides favorable beam conditions for the development of the NRI technique over a wide neutron energy range from eV to MeV.Neutron-sensitive microchannel plates(MCP)have emerged as a cutting-edge tool in the field of neutron detection owing to their high temporal and spatial resolutions,high detection efficiency,and low noise.In this study,we report the development of a 10B-doped MCP detector,along with its associated electronics,data processing system,and NRI experiments at the Back-n.Individual heavy elements such as gold,silver,tungsten,and indium can be easily identified in the transmission images by their characteristic resonance peaks in the 1–100 eV energy range;the more difficult medium-weight elements such as iron,copper,and aluminum with resonance peaks in the 1–100 keV energy range can also be identified.In particular,results in the neutron energy range of dozens of keV(Aluminum)are reported here for the first time.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFA0704200,2018YFA0305602,2017YFA0303100,2017YFA0302900)the National Natural Science Foundation of China(Grant Nos.11822411 and 11961160699)+3 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(CAS)(Grant Nos.XDB25000000 and XDB07020300)K.C.Wong Education Foundation(Grant No.GJTD-2020-01)the Youth Innovation Promotion Association of CAS(Grant No.Y202001)the Beijing Natural Science Foundation,China(Grant No.JQ19002)。
文摘We report an inelastic neutron scattering investigation on the spin resonance mode in the optimally hole-doped ironbased superconductor Ba_(0.67)K_(0.33)Fe_(2)As_(2)with T_c=38.2 K.Although the resonance is nearly two-dimensional with peak energy ER≈14 meV,it splits into two incommensurate peaks along the longitudinal direction([H,0,0])and shows an upward dispersion persisting to 26 meV.Such dispersion breaks through the limit of total superconducting gaps△_(tot)=|△k|+|△k+Q|(about 11-17 meV)on nested Fermi surfaces measured by high resolution angle resolved photoemission spectroscopy(ARPES).These results cannot be fully understood by the magnetic exciton scenario under s^(±)-pairing symmetry of superconductivity,and suggest that the spin resonance may not be restricted by the superconducting gaps in the multi-band systems.
基金the National Natural Science Foundation of China(12375296)the Key Laboratory of Nuclear Data Foundation(JCKY2022201C153)+1 种基金the National Key Research and Development Plan(2022YFA1603303)the Natural Science Foundation of Hunan Province of China(2021JJ40444,2020RC3054)。
文摘The neutron-induced total cross-section of ^(209)Bi is crucial for the physical design and safety assessment of lead-based fast reactors, and the quality of experimental data should be improved for evaluation and application.A recent experiment was conducted on the back-streaming white neutron beamline(Back-n) at the China Spallation Neutron Source(CSNS) using the neutron total cross-section spectrometer(NTOX). The neutron energy was determined using a fast multi-cell fission chamber and the time-of-flight technique. Two high-purity bismuth samples,6 mm and 20 mm in thickness, were chosen for neutron transmission measurements and comparisons. The neutron total cross-sections of ^(209)Bi, ranging from 0.3 e V to 20 Me V, were derived considering neutron flight time determination, flight path calibration, and background subtraction. A comparison of the experimental results with the data in the ENDF/B-VⅢ.0 library showed fair agreement, and the point-wise cross-sections were found to be consistent with existing experimental data. Special attention was given to the determination of resonance parameters, which were analyzed using the R-matrix code SAMMY and Bayesian method in the 0.5 ke V to 20 ke V energy range. The extracted resonance parameters were compared to previously reported results and evaluated data. This study is recognized as the first one where the neutron total cross-section of bismuth across such a broad energy spectrum is measured in a single measurement or experiment, and it provides valuable data for the assessment of related reaction information for evaluated libraries and the advancement of lead-bismuth-based nuclear systems.
基金support provided by the National KeyR&DProgram of China(Grant No.2016YFA0401600).
文摘Purpose Back-n is a white neutron beamline at China spallation neutron source,which was established in the year of 2018.It is a powerful facility for nuclear data measurement,neutron detector calibration,and radiation effect research.Method A series of detectors were built for different experiments,including beam monitoring,beam profile measurement,neutron induced secondaries(fission fragments,light charged particles and gamma)cross section measurement,and neutron resonance radiography,etc.A common digitization electronics and a cluster-based DAQ were developed for these detector systems.Most detectors have been employed at Back-n and serviced for experiments from the beginning of the beamline running.Results and conclusion As an overview of detectors of Back-n,the details of the detector design and the experiment performing are described in this paper.Some developing systems,e.g.,MTPC and B-MCP,are also included.
基金Supported by National Natural Science Foundation of China(91326109)
文摘The ^239Pu fission chambers are widely used to measure fission spectrum neutron flux due to a fiat response to fast neutrons. However, in the meantime the resonance and thermal neutrons can cause a significant influence on the measurement if they are moderated, which could be eliminated by using ^10B and Cd covers. At a column enriched uranium fast neutron critical assembly, the fission reaction rates of ^239gpu are measured as 1.791 × 10^-16 2.350 × 10^-16 and 1.385×10^-15 per second for 15 mm thick ^10B cover, 0.5 mm thick Cd cover, and no cover respectively, while the fission reaction rate of 239pu is rapidly increased to 2.569×10^-14 for a 20 mm thick polythene covering fission chamber. The average 239pu fission cross-section of thermal and resonance neutrons is calculated to be 500 b and 24.95 b with the assumption of 1/v and 1/E spectra respectively, then thermal, resonance and fast neutron flux are achieved to be 2.30×10^6, 2.24×10^6 and 1.04×10^8 cm^-2·s^-1.
基金Supported by National Science Foundation of China
文摘The pygmy dipole resonance(PDR) of nickel isotopes is studied using the deformed random phase approximation method. The isoscalar character of the pygmy resonance is confirmed, and the correlation between the pygmy resonance and neutron skin thickness is discussed. Our investigation shows a linear correlation between PDR integral cross section and neutron skin thickness when the excess neutrons lie in pf orbits, with a correlation rate of about 0.27 fm^(-1). However, in more neutron-rich nickel isotopes, the growth of the pygmy dipole resonance is stagnant. Although the neutron skin thickness increases, the whole skin is not active. There is an inertial part in the nuclei^(70-78)Ni which does not participate in the pygmy resonance actively and as a result, contributes little to the photo-absorption cross section.