Measurement of the 232Th(n,f) cross section in the 1-200 MeV range at the CSNS Back-n

Zhi-Zhou Ren · Yi-Wei Yang · Yong-Hao Chen · Rong Liu · Bang-Jiao Ye · Jie Wen · Hai-Rui Guo ·Zi-Jie Han · Qi-Ping Chen · Zhong-Wei Wen · Wei-Li Sun · Han Yi · Xing-Yan Liu · Tao Ye · Jiang-Bo Bai ·Qi An,6 · Jie Bao · Yu Bao · Ping Cao · Hao-Lei Chen,6 · Zhen Chen,6 · Zeng-Qi Cui · Rui-Rui Fan,0 ·Chang-Qing Feng,6 · Ke-Qing Gao · Xiao-Long Gao · Min-Hao Gu3,0 · Chang-Cai Han · Guo-Zhu He ·Yong-Cheng He · Yang Hong, · Yi-Wei Hu · Han-Xiong Huang · Xi-Ru Huang,6 · Hao-Yu Jiang · Wei Jiang ·Zhi-Jie Jiang,6 · Han-Tao Jing · Ling Kang · Bo Li · Chao Li,6 · Jia-Wen Li6,3 · Qiang Li · Xiao Li ·Yang Li · Jie Liu · Shu-Bin Liu,6 · Ze Long · Guang-Yuan Luan · Chang-Jun Ning · Meng-Chen Niu ·Bin-Bin Qi,6 · Jie Ren · Xi-Chao Ruan · Zhao-Hui Song · Kang Sun, · Zhi-Jia Sun,0 · Zhi-Xin Tan ·Jing-Yu Tang · Xin-Yi Tang,6 · Bin-Bin Tian · Li-Jiao Wang, · Peng-Cheng Wang · Zhao-Hui Wang ·Xiao-Guang Wu · Xuan Wu · Li-Kun Xie6,3 · Xiao-Yun Yang · Li Yu · Tao Yu,6 · Yong-Ji Yu · Guo-Hui Zhang ·Lin-Hao Zhang, · Qi-Wei Zhang · Xian-Peng Zhang · Yu-Liang Zhang · Zhi-Yong Zhang,6 · Lu-Ping Zhou, ·Zhi-Hao Zhou, · Ke-Jun Zhu3,0,

Abstract The 232Th(n,f) cross section is very important in basic nuclear physics and applications based on the Th/U fuel cycle.Using the time-of-flight method and a multi-cell fast-fission ionization chamber, a novel measurement of the 232Th(n,f) cross section relative to 235U in the 1-200 MeV range was performed at the China Spallation Neutron Source Back-n white neutron source (Back-n).The fission event-neutron energy spectra of 232Th and 235U fission cells were measured in the single-bunch mode.Corrected 232Th/235U fission cross-sectional ratios were obtained, and the measurement uncertainties were 2.5-3.7%for energies in the 2-20 MeV range and 3.6-6.2% for energies in the 20-200 MeV range.The 232Th(n,f) cross section was obtained by introducing the standard cross section of 235U(n,f).The results were compared with those of previous theoretical calculations, measurements, and evaluations.The measured 232Th fission cross section agreed with the main evaluation results in terms of the experimental uncertainty, and 232Th fission resonances were observed in the 1-3 MeV range.The present results provide 232Th(n,f) cross-sectional data for the evaluation and design of Th/U cycle nuclear systems.

Keywords 232Th(n,f) cross section · Fast-fission ionization chamber · Back-n white neutron source

1 Introduction

Data on neutron-induced fission reactions are important in basic and applied nuclear physics [1].In a “generation IV”nuclear reactor and accelerator-driven system (ADS), a novel232Th-based fuel cycle has been proposed for improving the efficiency and safety of nuclear reactors as well as for transmuting nuclear waste, such as liquid fueled thorium molten salt reactor [2] and thorium-based molten salt fast energy amplifier [3].In these systems,232Th is converted to fissile233U after a neutron capture reaction and two β-decays[4], partially accounting for the emerging fission.Near the fission threshold,232Th plays a significant role in neutron delay, contributing up to 2%.In Th/U cycle-based nuclear systems, the232Th(n,f) cross section should have up to 5%of uncertainty [5].

In addition to its important applications in nuclear systems, the232Th(n,f) reaction is interesting owing to the“thorium anomaly” [6, 7].Möller and Nix [8] explained this phenomenon using a triple-humped barrier, owing to the difficulty associated with describing the structure using a double-humped barrier.By studying the resonances in the232Th(n,f) reaction, a profound understanding of the nuclear structure can be achieved.Therefore, it is very important to measure the high-precision232Th(n,f) cross section in a wide range of energies.

During the last few decades, various measurements of the232Th(n,f) cross section have been performed.Behrens [9] measured the232Th(n,f) cross section for energies in the 0.7-30 MeV range, using parallel plate ionization fission chambers and photoneutrons; these measurements were performed at the Lawrence Livermore National Laboratory in 1982.The overall uncertainty associated with that experiment was in the 2.5-61.7% range.In 1983,Meadows et al.[10] measured the232Th(n,f) cross section with an ionization chamber and monoenergetic neutron flux at Argonne Fast Neutron Generator Laboratory, for energies ranging from 1.2 to 9.9 MeV; the uncertainty was in the 1.5-10.8% range.In 1988, Lisowski et al.[11] measured the cross-sectional ratio232Th/235U(n,f) for energies in the 1-400 MeV range, using a multiple-plate gas ionization chamber at the Weapons Neutron Research Facility at Los Alamos National Laboratory; the uncertainty was in the 1.4-9.1% range.Fursov et al.[12] also measured the cross-sectional ratio for neutrons with energies in the 0.13-7.4 MeV range; the experimental uncertainty ranged from 2.2 to 15%.These measurements were performed using a fission chamber at the electrostatic accelerator at the Power Physics Institute.Using the time-of-flight(TOF) method and fast parallel plate ionization chambers, Shcherbakov et al.[13] measured energies in the 1-200 MeV range in 2002, using the neutron spectrometer GNEIS; the uncertainty was in the 0.5-9.9% range.

Recently, Michalopoulou et al.[7] measured the232Th(n,f) cross section using micromegas detectors with quasi-monoenergetic neutron beams with energies in the 2-18 MeV range; the uncertainty was in the 1.6-8.0% range.Using d-d neutron sources and back-to-back Th/238U samples, Gledenov et al.[14] performed measurements at 12 energy points, for energies ranging from 4.2 to 11.5 MeV;the uncertainty was in the 3.7-5.8% range.These measurements were performed at Peking University and China Institute of Atomic Energy.Chen et al.[15] measured the232Th(n,f) cross sections relative to the235U(n,f) cross section and n-p scattering, for energies in the 1-300 MeV range, using a fast-ionization chamber and a proton recoil telescope at the Back-n facility.The measurements were performed in the double-bunch mode at an Endstation 1.The measured results were normalized to the evaluation data at approximately 14 MeV, and the uncertainty was in the 3.9-27.4% range.

The upper limit of the232Th(n,f) cross section in the ENDF/B-VIII.0 evaluation was 60 MeV, and that obtained in other evaluations was 20 MeV [16-20].The different evaluations of the232Th(n,f) cross section exhibit large discrepancies, especially at the fission threshold and high-energy points.For energies up to 20 MeV, the differences reach 10%and are much larger near the threshold.For energies above 20 MeV, only the data of Shcherbakov et al., Lisowski et al.,and Chen et al.cover the range of energies up to 200 MeV.However, these datasets for energies above 20 MeV still exhibit significant discrepancies, reaching 30%.These discrepancies create obstacles for applications in both basic and applied nuclear physics.

To provide independent experimental data, a novel measurement of the232Th(n,f) cross section, for energies in the 1-200 MeV range, was performed at the China Spallation Neutron Source (CSNS) Back-n [21, 22].A multi-cell fission ionization chamber (MFIC) [23-25] and high-purity thorium and uranium samples were used for these measurements.The experimental method and setup are described in Sects.2 and 3, respectively.After a detailed introduction to the data analysis in Sect.4, 5 presents the results and discussion.Finally, Sect.6 summarizes this study.

2 Experimental method

In this study, the TOF method, relative method, and MFIC were used for measuring the232Th(n,f) cross section at the CSNS Back-n.The energies of the incident neutrons were obtained using the TOF method, and the neutron flux was canceled out owing to relative measurements.Various fission cells mounted in the chamber were used for measuring the fission signals owing to the different samples.

The235U(n,f) cross section was used as a neutron standard at 0.0253 eV, 7.8-11 eV, and 0.15-200 MeV, which is fundamental for measurements that use the relative method.The uncertainties of the neutron standards file increased from ＜ 1 to 4.5% for the 0.15-200 MeV range of energies [26].The232Th(n,f)/235U(n,f) cross-sectional ratios were determined using Eq.(1).

whereσis the cross section, andNFFis the number of fission events measured by the MFIC.In addition,εis the detection efficiency of each fission cell calculated using the amplitude spectra.Nis the number of atoms in each fission sample with an approximate uncertainty of 1%.A,Q, andηaccount for the neutron flux attenuation, nonuniformity, and sample contamination correction, respectively, of each cell.

3 Experimental setup

3.1 Back-n white neutron source

At the Back-n white neutron source [21, 22], 1.6-GeVenergy protons were projected onto a tungsten target, and neutrons with different energies were emitted in all directions via the spallation reaction.The measurements were performed in the single-bunch mode for 12 h.The power of the proton beam was 40 kW, and the frequency was 25 Hz.The detector was set in the neutron beam at Endstation 2 of Back-n.The neutron beam spot at Endstation 2 hadΦ= 60 mm and the full width at half maximum (FWHM) of each neutron bunch was approximately 60 ns.The neutron beam had approximately 2.81 × 106n/cm2/s at Endstation 2 with water serving as a coolant passing through the thick tungsten target, yielding an excellent wide-energy-spectrum distribution, with energies ranging from 1 eV to 200 MeV [27].In these measurements, thermal neutrons were absorbed by a 1-mm-thick Cd foil.

3.2 MFIC

Based on a previously described fission ionization chamber[23-25], a detection system was developed at Back-n, consisting of an MFIC with a faster response time, associated electronics, and a data acquisition and processing system[21].

The MFIC was carefully optimized, as follows.The stainless-steel cylindrical shell of the MFIC was replaced with an aluminum shell.The neutron beam window, gas interfaces,and cable connectors were optimized in terms of their structure and material.The improved chamber was lighter, more versatile, and had less electromagnetic noise.The structure of each fission cell was modified to reduce the capacitance between the electrodes.Simultaneously, the chamber was filled with the P10 gas (90% Ar and 10% CF4) at approximately 0.8 bar.Changes in the structure and working gas led to a fast response time (less than 30 ns).

The MSI-8 preamplifier was chosen for the multi-cell fast-fission ionization chamber owing to its large amplification, fast response, and low output noise.The preamplifier signals were digitized using the Back-n data acquisition(DAQ) system [28].Figure 1 shows the optimized MFIC for Endstation 2.

3.3 Samples

Fig.1 Optimized MFIC mounted at Endstation 2 in the present study

For the measurements, three232Th and two235U high-purity fission samples were used:235U-1,235U-5,232Th-1,232Th-2,and232Th-3.These fission nuclides were electroplated on the backings of aluminum steel or stainless (235U-1) in the form of U3O8and ThO2.The diameters of the backing and deposit were 80 mm and 50 mm, respectively.The masses of the samples were determined from their spontaneous-decay alpha-particle spectra, which were measured using a small solid-angle physical quantitative counting device [29].The quality uncertainty ranges of the samples were calculated using an error propagation formula.Figure 2 shows the measured particle spectrum of the232Th-1 sample.The characteristics of the different fission samples along the neutron beam used in this study are listed in Table 1.The abundance of impurities of the232Th sample was less than 10-6; thus,it was ignored.

The232Th samples were assumed to be 100% abundant,and the235U samples were enriched to 99.985% [30].The mass distributions of the fission samples were obtained using an α-sensitive imaging plate placed over the surfaces of the samples.The232Th sample and its mass distribution with 0.2 mm × 0.2 mm pixels are shown in Fig.3.Darker colors indicate more nuclides.Mass distribution images were used for the uniformity determination and correction of the studied samples.

4 Data analysis

4.1 Processing of raw data

When a neutron bunch was produced by the CSNS, a synchronous signalT0triggered the DAQ system, and all signals exceeding the threshold within 10 ms were collected.The experimental data were recorded as 0.5 TBsize raw files in the form of packets, including the information about the signal waveform and channel number.The original raw files were processed using various C++programs based on ROOT [31].Figure 4 shows the signalwaveform measured for the232Th fission cell.Contrastingly, the amplitudes of the different signals were recorded for obtaining the amplitude spectra, which were used for distinguishing fission signals from other signals.Furthermore, the time difference between the fission and γ-flash signals was used for computing the flight time of the neutrons that induced this fission event.

Fig.2 α-particle spectrum of the 232Th sample.The α decay chain of the 232Th sample is clearly seen

Table 1 Characteristics of the fission samples along the neutron beam used in the present work

Fig.3 232Th sample (a) and its mass distribution (b)

4.2 Amplitude spectrum

The signals of fission, γ-flash, α-particle, and electronic noise were recorded using the DAQ system.The fastfission ionization chamber was insensitive to γ signals.Therefore, only γ-flash could be detected.Figure 5 shows the amplitude spectra of the235U and232Th fission cells and the Al cell (background), measured using the MFIC within the neutron beam.In this figure, the background is mainly attributed to the α decay of the fissile isotopes and(n,lcp) reactions of the sample backing and the aluminum collector.

As shown in Fig.5, the background is distributed in the low-amplitude region.In addition, the fission signals are distributed throughout the observed region.Therefore, amplitude thresholds were set for each fission cell to distinguish fission signals from other noise.The amplitude thresholds for235U and232Th cells are marked with blue dotted lines.The signals of the fission cells are shown as colored solid lines and are widely distributed.The background signal (red solid line) is mainly below the amplitude thresholds, and the few events above the threshold can be neglected.

4.3 Detection efficiency

The MFIC detection efficiency ε can be calculated using Eq.(2) [32].Fission events are primarily lost owing to selfabsorption and amplitude threshold settings, which correspond to the first and second terms in the below equation:

Fig.4 A typical signal waveform measured for the 232Th fission cell.The horizontal coordinate is the time information about the waveform, while the vertical coordinate captures the signal amplitude.The 10-90%temporal window of the rising edge was approximately 30 ns

Fig.5 (Color online) Amplitude spectra of the 235U, 232Th fission cells and Al cell (background),measured using the MFIC.The amplitude thresholds were set for different fission cells to distinguish the fission signals from other noise sources

The average ranges of fission fragments (R) for the U3O8and ThO2deposits were 7.5 ± 0.5 mg/cm2[33] and 8.0 ± 0.5 mg/cm2, respectively.TheRvalue for ThO2was calculated using the approach described in Ref.[32],whereNLandNUrepresent the counts of fission events below and above the amplitude threshold, respectively.To calculateNL, a constant number was assumed using the“flat tail” assumption below the amplitude threshold.

The efficiencies of the two235U and three232Th fission cells were 94.90%, 94.65%, 95.94%, 95.68%, and 96.00%,respectively.The detection efficiencies with respect to different energy regions were analyzed and found to change weakly [34].The uncertainties of the efficiencies of the235U and232Th fission cells were 0.2-0.3% and 0.2-0.4%, respectively, mainly owing to the statistical uncertainty ofNL.

4.4 Energy calibration

The neutron TOFnwas calculated using Eq.(3) [30]:

In the above equation,TfandTγare the detected time of the fission signal and γ-flash recorded using the MFIC detector;Tnis the production time of neutrons; and TOFγis the TOF of the γ-flash.In fact, the uncertainty ofTnwas 60 ns,owing to the FWHM of each neutron bunch.The TOFγvalue was inferred from the determined flight distance.TheTfandTγvalues were well determined in the 0.4 constant fraction timing point (40% of the rising edge of signals).

Many γ-flash signals were used for yielding a standardized γ-flash waveform.TheTγcalibration results for the two235U cells and three232Th cells were - 969 ns, - 999 ns,- 1000 ns, - 999 ns, and - 1000 ns.The averaged γ-flash waveform measured for the235U-1 cell is shown in Fig.6a.

Fig.6 Averaged γ-flash waveform (a) and the TOF spectrum of the 8.77-eV-energy resonance peak (b) measured for the 235U-1 fission cell

TOFγ was calculated by dividing the accurate flight distance by the speed of light.The 8.77-eV-energy resonance peak of the235U(n,f) reaction was chosen for the flight distance calculation, as shown in Fig.6b.A detailed description of the flight distance determination can be found in Ref.[30].The estimated flight distance for the235U-1 fission cell was 77.073 m, and the positioning uncertainty was 3 mm.The flight distances for the other fission cells were obtained using the geometric dimensions of the MFIC.

4.5 Fission event-neutron energy spectra

Figure 7 shows the fission event-neutron energy spectra obtained for the235U and232Th fission cells, with the preliminary results divided into 100 bins per decade.The resonance peaks attributed to the235U(n,f) reaction are clearly observed in the 1-1000 eV range.The distribution of second-chance fission is also observed for energies in the 6-8 MeV range.In the232Th spectrum, there are fewer fission events below 1 MeV, owing to the fission threshold at 1.3 MeV.As shown in Fig.7, the two235U spectra and three232Th datasets (normalized with mass) are concordant.These observations validate the reliability of our measurements.

4.6 Corrections

In the present experiments, the fast-ionization chamber contained various fission cells in the direction of the incident neutrons.The neutron flux gradually attenuated as it passed through the fission cells of the MFIC, owing to interactions with the backing and collectors.A Monte Carlo simulation[35] was used to assess the flux attenuation in different fission cells based on the geometric design of the detector and fission samples.The simulation results showed that the neutron flux decreased as the number of cells increased.In the last232Th-3 cell, the neutron flux attenuation was 1.0-2.5%,for energies in the 1-200 MeV range; the uncertainty was in the 0.2-2% range.

Fig.7 (Color online) Measured fission event-neutron energy spectra, shown on the log-log scale

The nonuniformities of the235U and232Th samples obtained with α-sensitive imaging plates are listed in Table 1 and that of the neutron beam was obtained from simulations.The nonuniformity correction factor is described in detail in Ref.[36].The correction factors for the232Th and235U samples were 1.0023-1.0028 and 1.0026-1.0046, respectively.The uncertainty of the Q values was approximately 0.1%.

The dead time was negligible because the signal counting rate (1.2 × 103/s) was much lower than the DAQ acquisition rate, and the frame overlap probability of each independent channel was below 10-5.In addition, the samples were corrected for impurities, based on the abundance of isotopes and their fission cross sections.The232Th sample was assumed to be 100% abundant, and the correction factor was 1.In addition, in the 1-200 MeV range, the correction factor of the235U sample was 0.99988-0.99999; the associated uncertainty was less than 0.01%, allowing to neglect the correction.

5 Results and discussion

5.1 232Th/235U(n,f) cross-sectional ratio

The232Th/235U(n,f) cross-sectional ratio for energies in the 1-200 MeV range was obtained in the single-bunch mode,according to Eq.(1).Six datasets were obtained using two235U and three232Th fission cells were used for obtaining averages.As shown in Fig.8, the experimental data were compared with those of previous experiments, and the ratio was extracted from the ENDF/B-VIII.0 evaluation[16].The average discrepancies between these data and the ENDF/B-VIII.0 [16] data were - 1.0-2.5% for energies inthe 2-60 MeV range.The average discrepancy between the final average ratio and that of ENDF/B-VIII.0 was 0.8% for energies in the 2-60 MeV range, confirming the accuracy of the ENDF/B-VIII.0 evaluation.The energy resolution of this measurement varied from 1.6 to 27% for energies in the 1-200 MeV, which was the same as that described in detail in Refs.[30, 37].To match the energy resolution, the data in this region were divided into 86 bins, and the energy point was the center point of the corresponding bin.

Table 2 Uncertainties of the measured ratios

The comparison indicates a good agreement between the results obtained in the present study and those obtained using the ENDF/B-VIII.0 evaluation.The ratio measured in this experiment was consistent with that reported by Shcherbakov et al.[13] for energies in the 1-200 MeV range and agreed well with the results reported by Behrens [9],Meadows [10], and Fursov [12] within the reported uncertainties.In addition, the data reported by Lisowski et al.[11]were lower than those reported by the other groups.

Table 2 lists the measurement uncertainties of the reported ratio values.The measurement uncertainties weremainly derived from statistical and quantification uncertainties.The fission threshold of the232Th(n,f) reaction and the decrease in the neutron flux for energies above 20 MeV increased the statistical uncertainty in the corresponding region.The 210 MeV-energy points in Table 2 represent the bins for energies in the 172-248 MeV range.

Fig.8 (Color online) Comparison of the measured data with previously reported experimental data, for energies in the 1-200 MeV range [9-13, 16]

5.2 232Th(n,f) cross section

The neutron-induced232Th fission cross section was obtained along with the235U(n,f) cross section [26] and the measured ratio, as explained in Sect.5.1.The experimental uncertainties were 2.9-4.0% for energies in the 2-20 MeV range and 4.0-7.7% for energies in the 20-200 MeV range,respectively.The calculation program UNF [38] was used to calculate the theoretical results for energies in the 1-20 MeV range.Several theoretical models have been used to calculate the reaction processes and different cross sections.The specific process of theoretical calculations is described in Ref.[30].

Figure 9 compares the232Th(n,f) cross-sectional measurements of the current study with those reported by previous studies.Figure 10 compares the measured data with the calculated and evaluated data.Figure 11 compares the results for the 1-7 MeV range of energies.The experimental results of the present study agreed with the data of Shcherbakov et al.[13] and Chen et al.[15] for energies in the 1-200 MeV range; the values were within the range of experimental uncertainties.The measured cross section agreed with the calculation and main evaluation results, except for a large discrepancy with the ADS-HE evaluation for energies exceeding 60 MeV, as shown in Fig.11.For energies in the 1-7 MeV range, the data obtained in this study were concordant with those reported by Gledenov et al.[14], which in turn were slightly lower than those reported by Meadows et al.[10] and higher than those reported by Michalopoulou et al.[7], as shown in Fig.11.The resonances of the232Th(n,f) reaction for energies in the 1-3 MeV range(thorium anomaly behavior) were observed in the present measurements and were consistent with previously reported results and evaluations, within the experimental uncertainty.

Fig.9 (Color online) Comparison of the measured 232Th(n,f)cross section with those reported by previous studies [7,10, 11, 13-15]

Fig.10 (Color online) Comparison of the measured 232Th(n,f)cross section with previously calculated and evaluated data[16-19, 39]

Fig.11 (Color online) Comparison of the measured 232Th(n,f)cross section with previous results, calculations, and main evaluations, for energies in the 1-7 MeV range; the results are shown on the logarithmic scale[7, 10, 13-19]

Figure 12 shows the ratios of the measured data to the calculation results and main evaluations.The average discrepancies between the measured data and corresponding evaluations were - 0.77%, 4.13%, - 1.36%, 1.91%, and- 0.77% for energies in the 2-20 MeV range.Evidently,there are large discrepancies for energies in the 1-2 MeV range.In the UNF calculation, a large discrepancy was observed for energies in the 1-3 MeV range, owing to the “thorium anomaly”.For most of the evaluated energy points, the results obtained in the present study agree with the ENDF/B-VIII.0 evaluation results more than with other evaluation results.For energies higher than 60 MeV, there is a sudden increase in the232Th fission cross section in the ADS-HE database, which was not observed in the present work.

Fig.12 (Color online) Ratios of the data measured in this study to calculated and evaluated data [16-19, 39]

6 Conclusion

The232Th(n,f) fission cross section, for energies ranging from 1 to 200 MeV, was measured relative to235U in the single-bunch mode at the CSNS Back-n.An MFIC with five high-purity fission samples was used in these measurements.In the energy calibration, the TOF of the neutrons was calculated using the fission and γ-flash signals.After the calibration of the detection efficiency and corrections of various influencing factors, absolute232Th/235U(n,f) crosssectional ratios were obtained for energies in the 1-200 MeV range, with the experimental uncertainty of 2.5-3.7% for energies in the 2-20 MeV range and 3.6-6.2% for energies in the 20-200 MeV range.The232Th(n,f) cross section was obtained by introducing the standard235U(n,f) cross section.Resonances of the232Th(n,f) reaction for energies in the 1-3 MeV range were observed and were consistent with those of previous experiments and evaluations.

The measured data were more consistent with the ENDF/B-VIII.0 evaluation than other evaluations.The data of the present experiment are in agreement with the data of Shcherbakov et al.[13] and Chen et al.[15] for energies in the 1-200 MeV range, within a range of experimental uncertainties.The data also exhibit the same trends as the theoretical results obtained using the UNF code.These novel measurements can provide experimental data for addressing the discrepancies among main evaluations.Specifically, for energies above 20 MeV, the measured data of the present study are important for improving evaluations, owing to the data paucity for energies in that range.

Author contributionsAll authors contributed to the study conception and design.Material preparation, data collection, and analysis were performed by Zhi-Zhou Ren, Yi-Wei Yang, Yong-Hao Chen, Rong Liu, Bang-Jiao Ye, Jie Wen, Hai-Rui Guo, Zi-Jie Han, Qi-Ping Chen,Zhong-Wei Wen, Wei-Li Sun, Han Yi, Xing-Yan Liu, Tao Ye, Jiang-Bo Bai, Qi An, Jie Bao, Yu Bao, Ping Cao, Hao-Lei Chen, Zhen Chen,Zeng-Qi Cui, Rui-Rui Fan, Chang-Qing Feng, Ke-Qing Gao, Xiao-Long Gao, Min-Hao Gu, Chang-Cai Han, Guo-Zhu He, Yong-Cheng He, Yang Hong, Yi-Wei Hu, Han-Xiong Huang, Xi-Ru Huang, Hao-Yu Jiang, Wei Jiang, Zhi-Jie Jiang, Han-Tao Jing, Ling Kang, Bo Li, Chao Li, Jia-Wen Li, Qiang Li, Xiao Li, Yang Li, Jie Liu, Shu-Bin Liu, Ze Long, Guang-Yuan Luan, Chang-Jun Ning, Meng-Chen Niu, Bin-Bin Qi, Jie Ren, Xi-Chao Ruan, Zhao-Hui Song, Kang Sun, Zhi-Jia Sun,Zhi-Xin Tan, Jing-Yu Tang, Xin-Yi Tang, Bin-Bin Tian, Li-Jiao Wang,Peng-Cheng Wang, Zhao-Hui Wang, Xiao-Guang Wu, Xuan Wu, Li-Kun Xie, Xiao-Yun Yang, Li Yu, Tao Yu, Yong-Ji Yu, Guo-Hui Zhang,Lin-Hao Zhang, Qi-Wei Zhang, Xian-Peng Zhang, Yu-Liang Zhang,Zhi-Yong Zhang, Lu-Ping Zhou, Zhi-Hao Zhou, and Ke-Jun Zhu.The first draft of the manuscript was written by Zhi-Zhou Ren, and all authors commented on previous versions of the manuscript.All authors read and approved the final manuscript.

Data availabilityThe data that support the findings of this study are openly available in Science Data Bank at https:// www.doi.org/ 10.57760/ scien cedb.09535 and https:// cstr.cn/ 31253.11.scien cedb.09535.

Declarations

Conflict of interestJing-Yu Tang, Ke-Jun Zhu, and Chang-Qing Feng are editorial board members for Nuclear Science and Techniques and were not involved in the editorial review, or the decision to publish this article.All authors declare that there are no competing interests.

Authors and Affiliations

Zhi-Zhou Ren1,2· Yi-Wei Yang2· Yong-Hao Chen3,4· Rong Liu2· Bang-Jiao Ye1· Jie Wen2· Hai-Rui Guo5·Zi-Jie Han2· Qi-Ping Chen2· Zhong-Wei Wen2· Wei-Li Sun5· Han Yi3,4· Xing-Yan Liu2· Tao Ye5· Jiang-Bo Bai2·Qi An1,6· Jie Bao7· Yu Bao3,4· Ping Cao6,8· Hao-Lei Chen1,6· Zhen Chen1,6· Zeng-Qi Cui9· Rui-Rui Fan3,4,10·Chang-Qing Feng1,6· Ke-Qing Gao3,4· Xiao-Long Gao3,4· Min-Hao Gu3,10· Chang-Cai Han11· Guo-Zhu He7·Yong-Cheng He3,4· Yang Hong3,4,12· Yi-Wei Hu9· Han-Xiong Huang7· Xi-Ru Huang1,6· Hao-Yu Jiang9· Wei Jiang3,4·Zhi-Jie Jiang1,6· Han-Tao Jing3,4· Ling Kang3,4· Bo Li3,4· Chao Li1,6· Jia-Wen Li6,13· Qiang Li3,4· Xiao Li3,4·Yang Li3,4· Jie Liu9· Shu-Bin Liu1,6· Ze Long3,4· Guang-Yuan Luan7· Chang-Jun Ning3,4· Meng-Chen Niu3,4·Bin-Bin Qi1,6· Jie Ren7· Xi-Chao Ruan7· Zhao-Hui Song11· Kang Sun3,4,12· Zhi-Jia Sun3,4,10· Zhi-Xin Tan3,4·Jing-Yu Tang6,8· Xin-Yi Tang1,6· Bin-Bin Tian3,4· Li-Jiao Wang3,4,12· Peng-Cheng Wang3,4· Zhao-Hui Wang7·Xiao-Guang Wu7· Xuan Wu3,4· Li-Kun Xie6,13· Xiao-Yun Yang3,4· Li Yu3,4· Tao Yu1,6· Yong-Ji Yu3,4· Guo-Hui Zhang9·Lin-Hao Zhang3,4,12· Qi-Wei Zhang7· Xian-Peng Zhang11· Yu-Liang Zhang3,4· Zhi-Yong Zhang1,6· Lu-Ping Zhou3,4,12·Zhi-Hao Zhou3,4,12· Ke-Jun Zhu3,10,12

✉ Rong Liu liurongzy@163.com

1Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China

2Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900, China

3Institute of High Energy Physics, Chinese Academy of Sciences (CAS), Beijing 100049, China

4Spallation Neutron Source Science Center,Dongguan 523803, China

5Institute of Applied Physics and Computational Mathematics,Beijing 100088, China

6State Key Laboratory of Particle Detection and Electronics,University of Science and Technology of China,Hefei 230027, China

7Key Laboratory of Nuclear Data, China Institute of Atomic Energy, Beijing 102413, China

8School of Nuclear Science and Technology, University of Science and Technology of China, Hefei 230027, China

9State Key Laboratory of Nuclear Physics and Technology,School of Physics, Peking University, Beijing 100871, China

10State Key Laboratory of Particle Detection and Electronics,Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China

11Northwest Institute of Nuclear Technology, Xi’an 710024,China

12University of Chinese Academy of Sciences, Beijing 100049,China

13Department of Engineering and Applied Physics, University of Science and Technology of China, Hefei 230026, China