Measurement of the neutron-induced total cross sections of ^(nat)Pb from 0.3 eV to 20 MeV on the Back-n at CSNS

The neutron-induced total cross sections of natural lead have been measured in a wide energy range(0.3 eV-20 MeV)on the back-streaming white neutron beamline(Back-n)at the China Spallation Neutron Source.Neutron energy was determined by the neutron total cross-section spectrometer using the time-of-flight technique.A fast multi-cell fission chamber was used as the neutron detector,and a 10-mm-thick high-purity natural lead sample was employed for the neutron transmission measurements.The on-beam background was determined using Co,In,Ag,and Cd filters.The excitation function of ^(nat)Pb(n,tot)reaction below 20 MeV was calculated using the TALYS-1.96 nuclear-reaction modeling program.The present results were compared with previous results,the evaluated data available in the five major evaluated nuclear data libraries(i.e.,ENDF/B-VIII.0,JEFF-3.3,JENDL-5,CENDL-3.2,and BROND-3.1),and the theoretical calculation curve.Good agreement was found between the new results and those of previous experiments and with the theoretical curves in the corresponding region.This measurement obtained the neutron total cross section of natural lead with good accuracy over a wide energy range and added experimental data in the resonance energy range.This provides more reliable experimental data for nuclear engineering design and nuclear data evaluation of lead.

In-beam gamma rays of CSNS Back-n characterized by black resonance filter

The back-streaming white-neutron beamline(Back-n)of the China Spallation Neutron Source is an essential neutronresearch platform built for the study of nuclear data,neutron physics,and neutron applications.Many types of cross-sectional neutron-reaction measurements have been performed at Back-n since early 2018.These measurements have shown that a significant number of gamma rays can be transmitted to the experimental stations of Back-n along with the neutron beam.These gamma rays,commonly referred to as in-beam gamma rays,can induce a non-negligible experimental background in neutron-reaction measurements.Studying the characteristics of in-beam gamma rays is important for understanding the experimental background.However,measuring in-beam gamma rays is challenging because most gamma-ray detectors are sensitive to neutrons;thus,discriminating between neutron-induced signals and those from in-beam gamma rays is difficult.In this study,we propose the use of the black resonance filter method and a CeBr_(3) scintillation detector to measure the characteristics of the in-beam gamma rays of Back-n.Four types of black resonance filters,^(181)Ta,^(59)Co,^(nat)Ag,and^(nat)Cd,were used in this measurement.The time-of-flight(TOF)technique was used to select the detector signals remaining in the absorption region of the TOF spectra,which were mainly induced by in-beam gamma rays.The energy distribution and flux of the in-beam gamma rays of Back-n were determined by analyzing the deposited energy spectra of the CeBr_(3) scintillation detector and using Monte Carlo simulations.Based on the results of this study,the background contributions from in-beam gamma rays in neutron-reaction measurements at Back-n can be reasonably evaluated,which is beneficial for enhancing both the experimental methodology and data analysis.

Comparison of displacement damage effects on the dark signal in CMOS image sensors induced by CSNS back-n and XAPR neutrons

This study investigates the effects of displacement damage on the dark signal of a pinned photodiode CMOS image sensor(CIS)following irradiation with back-streaming white neutrons from white neutron sources at the China spallation neutron source(CSNS)and Xi'an pulsed reactor(XAPR).The mean dark signal,dark signal non-uniformity(DSNU),dark signal distribution,and hot pixels of the CIS were compared between the CSNS back-n and XAPR neutron irradiations.The nonionizing energy loss and energy distribution of primary knock-on atoms in silicon,induced by neutrons,were calculated using the open-source package Geant4.An analysis combining experimental and simulation results showed a noticeable proportionality between the increase in the mean dark signal and the displacement damage dose(DDD).Additionally,neutron energies influence DSNU,dark signal distribution,and hot pixels.High neutron energies at the same DDD level may lead to pronounced dark signal non-uniformity and elevated hot pixel values.

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

The ^(232)Th(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^(232)Th(n,f)cross sec-tion relative to^(235)U 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^(232)Th and^(235)U 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^(232)Th(n,f)cross section was obtained by introducing the standard cross section of^(235)U(n,f).The results were compared with those of previous theoreti-cal 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^(232)Th(n,f)cross-sectional data for the evaluation and design of Th/U cycle nuclear systems.

Measurement of the neutron total cross section of carbon at the Back-n white neutron beam of CSNS

To verify the performance of the neutron total cross-sectional spectrometer, the neutron total cross section of carbon is initially measured in the energy range of 1 eV to 20 MeV using the time-of-flight method. The measurement is performed at the Back-n white neutron source with a 76-m time-of-flight path using the China Spallation Neutron Source. A multilayer fast fission chamber with 235U and 238U is employed as the neutron detector. The diameter and thickness of the natural graphite sample are 70 mm and 40 mm, respectively. Signal waveforms are collected using a data acquisition system. Off-line data processing was used to obtain the neutron time-of-flight spectra and transmissions. The uncertainty of the counting statistics is generally approximately 3% for each bin in the energy range of 1–20 MeV. It is determined that the results for the neutron total cross section of carbon obtained using ^235U cells are in good agreement with the results obtained using 238U cells within limits of statistical uncertainty. Moreover, the measured total cross sections show good agreement with the broadening evaluated data.

Measurements ofthe 197Au(n, γ) crosssectionupto100keV at the CSNSBack-nfacility

The neutron capture cross section of 197 Au was measured using the time-of-flight(TOF)technique at the Back-n facility of the China Spallation Neutron Source(CSNS)in the 1 eV to 100 keV range.Prompt c-rays originating from neutron-induced capture events were detected by four C_(6)D_(6) liquid scintillator detectors.Pulse height weighting technology(PHWT)was used to analyze the data.The results are in good agreement with ENDF/B-VIII.0,CENDL-3.1,and other evaluated libraries in the resonance region,and in agreement with both n TOF and GELINA experimental data in the 5–100 keV range.Finally,the resonance peaks in the energy range from 1eV to 1 keV were fitted by the SAMMY R-matrix code.

一种改进Go-Back-N ARQ策略研究

经典GBN协议在信道质量较为恶劣的情况下存在着大量包的重传现象,因此吞吐量和传输效率较低。针对经典GBN协议的不足,提出一种改进的GBN协议,通过在接收端引入超时机制,大大提升GBN协议的运行效率。仿真结果表明,改进后的GBN协议在吞吐量和传输效率上要优于经典的GBN协议。

Measurement of ^(232)Th(n,γ)cross section at the CSNS Back-n facility in the unresolved resonance region from 4 keV to 100 keV

The neutron capture cross section of ^(232)Th was measured at the neutron time-of-flight facility Back-n of China Spallation Neutron Source(CSNS)for the first time.The measurement was performed with 4 hydrogen-free deuterated benzene C6D6 liquid scintillation detectors,in the ES#2 experiment station on the beam line,at a distance of about 76 m from the neutron-production assembly.The total energy detection principle in combination with the pulse height weighting technique(PHWT)was applied to analyze the measured data.Results of the ^(232)Th(n,γ)reaction cross section in the unresolved resonance region from 4 keV to 100 keV were obtained,which shows a good agreement with the existing experimental data from EXFOR,as well as with the evaluated data from the ENDF/B-VIII.0 and CENDL-3.1.In addition,the excitation function of ^(232)Th(n,γ)^(233)Th reaction in the unresolved resonance region was theoretically calculated by using the code TALYS-1.95.By fitting the experimental cross section and theoretical data,the average parameters in the unresolved resonance region were extracted.

New experimental measurement of^(nat)Se(n,γ)cross section between 1 eV to 1 keV at the CSNS Back-n facility

The^(74)Se is one of 35 p-nuclei,and^(82)Se is a r-process only nucleus,and their(n,γ)cross sections are vital input parameters for nuclear astrophysics reaction network calculations.The neutron capture cross section in the resonance range of isotopes and even natural selenium samples has not been measured.Promptγ-rays originating from neutron-induced capture events were detected by four C_(6)D_(6) liquid scintillator detectors at the Back-n facility of China Spallation Neutron Source(CSNS).The pulse height weighting technique(PHWT)was used to analyze the data in the 1 e V to 100 ke V region.The deduced neutron capture cross section was compared with ENDF/B-VIII.0,JEFF-3.2,and JENDL-4.0,and some differences were found.Resonance parameters were extracted by the R-matrix code SAMMY in the 1 e V-1 ke V region.All the cross sections ofnatSe and resonance parameters are given in the datasets.The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00019.

Measurements of the ^(107)Ag neutron capture cross sections with pulse height weighting technique at the CSNS Back-n facility

Silver indium cadmium(Ag–In–Cd) control rod is widely used in pressurized water reactor nuclear power plants,and it is continuously consumed in a high neutron flux environment. The mass ratio of ^(107)Ag in the Ag–In–Cd control rod is 41.44%. To accurately calculate the consumption value of the control rod, a reliable neutron reaction cross section of the ^(107)Ag is required. Meanwhile,^(107)Ag is also an important weak r nucleus. Thus, the cross sections for neutron induced interactions with ^(107)Ag are very important both in nuclear energy and nuclear astrophysics. The(n, γ) cross section of ^(107)Ag has been measured in the energy range of 1–60 eV using a back streaming white neutron beam line at China spallation neutron source. The resonance parameters are extracted by an R-matrix code. All the cross section of ^(107)Ag and resonance parameters are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00010.

New measurement of the neutron-induced total cross-sections of^(nat)Cr in a wide energy range on the Back-n at CSNS

The neutron total cross-section of ^(nat)Cr plays a crucial role in new nuclear engineering design and fundamental science.A new measurement of the neutron-induced total cross-sections of ^(nat)Cr was performed using the transmission method on the back-streaming white neutron beamline(Back-n)at the China Spallation Neutron Source(CSNS).The neutron energy was determined using the time-of-flight technique.The neutron total cross-sections of ^(nat)Cr were obtained across a broad energy range(0.3 eV−20 MeV)in one experiment for the first time.The resulting effective total cross-sections were compared with the existing experimental data in different energy ranges,which revealed good agreement with the evaluated libraries.Theoretical calculation of the total cross-section in the energy range of 1.5 to 20 MeV was then conducted using TALYS-1.96 and compared with the present results.The measurement provides a high-quality total cross-section of ^(nat)Cr,including detailed uncertainty data across a wide energy range,offering a valuable reference for nuclear data re-evaluation and nuclear engineering design.

Measurement of the neutron total cross section of^(9)Be at the Back-n white neutron source of CSNS

The neutron total cross section data of^(9)Be are essential in the nuclear structure model research of light nuclei and nuclear power installations.The neutron total cross section of^(9)Be in the 0.3 eV−120 MeV energy region has been measured using time-of-flight and transmission methods with the Neutron Total Cross Sectional Spectrometer(NTOX)based on the multi-cell fast fission chamber at the China Spallation Neutron Source(CSNS)-Back-n white neutron source(Back-n).The fission count-neutron energy distributions of ^(235)U and ^(238)U without samples and with Be samples with three thicknesses were measured in the double-bunch operation mode for a beam power of 100 kW.The Bayesian method was used to eliminate the influence of the double-bunch problem on neutron measurement in the energy region above 10 keV.The neutron total cross section of^(9)Be results was consistent with ENDF/B-VIII.0 evaluation library data in the 0.3 eV−20 MeV energy region.In the energy ranges of 0.3 eV to 10 keV and 0.01 to 20 MeV,the deviations between our results and the evaluation results of ENDF/B-VIII.0 were within 2.5%and 15%,respectively.In the resonance energy region,the measured resonance energies in our experiment were 0.63,0.82,and 2.8 MeV,respectively.The results showed that the total cross section uncertainties of three Be samples were within 2.2%in the energy region below 1 MeV.The total cross section uncertainty of 30 mm Be from ^(235)U was the smallest and less than 5%in the energy region of 0.3 eV−120 MeV.The results of this experiment can provide technical support for further data analysis and related nuclear data evaluation.

Measurement and analysis of the neutron-induced total cross-sections of 209Bi from 0.3 eV to 20 MeV on the Back-n at CSNS

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.

不同神经类型大学生工作记忆的特点及神经机制

为探讨不同神经类型大学生工作记忆加工的特点,用80-8神经类型量表筛选灵活型、安静型、兴奋型和抑制型四组典型的神经类型大学生并让其完成ERP版的N-back任务。结果发现灵活型大学生的正确率显著高于兴奋型和抑制型;在任务所诱发的P3波幅上,灵活型被试大于抑制型,在P3的潜伏期上不同类型之间无差异。说明灵活型个体与抑制型个体之间的差异不是来源于工作记忆加工的匹配子任务阶段,而是由于工作记忆的刷新子任务上,灵活型个体比抑制型个体加工能力更强。

Neutron capture cross section of ^(169)Tm measured at the CSNS Back-n facility in the energy region from 30 to 300 keV

The capture cross sections of the ^(169)Tm(n,γ)reaction were measured at the back streaming white neutron beam line(Back-n)of the China Spallation Neutron Source(CSNS)using four C_(6)D_(6) liquid scintillation detectors.The background subtraction,normalization,and correction were carefully considered in the data analysis to obtain accurate cross sections.For the resonance at 3.9 eV,the R-matrix code SAMMY was used to determine the resonance parameters with the internal normalization method.The average capture cross sections of ^(169)Tm for energy between 30 and 300 keV were extracted relative to the ^(197)Au(n,γ)reaction.The measured cross sections of the ^(169)Tm(n,γ)reaction were reported in logarithmically equidistant energy bins with 20 bins per energy decade with a total uncertainty of 5.4%-7.0% in this study and described in terms of average resonance parameters using a Hauser-Feshbach calculation with fluctuations.The point-wise cross sections and the average resonance parameters showed fair agreement with the evaluated values of the ENDF/B-Ⅷ.0 library in the energy region studied.

不同认知风格小学生的言语和视觉空间工作记忆

目的:探讨不同认知风格小学生言语和视觉空间工作记忆的发展特点。方法:使用镶嵌图形测验测试2、4、6年级学生的认知风格,通过2(认知风格:场独立、场依存)×3(年级:2、4、6年级)×2(任务类型:字母任务、空间任务)的三因素混合实验,采用2-back任务测查不同认知风格学生的工作记忆特点,对175名有效被试的字母和空间任务正确率进行重复测量方差分析。结果:场独立型小学生字母和空间任务正确率都高于场依存型小学生(P<0.001);场独立型小学生字母任务正确率高于空间任务正确率(P<0.001)。6年级场独立型学生两种任务正确率都高于2年级和4年级场独立型学生(P<0.05)。结论:不同认知风格小学生的言语和视觉空间工作记忆的发展存在差异,这种差异还可能与任务类型和年龄有关。

社会助长效应对认知负荷影响的神经表征分析

为探究数字化人机交互作业中,社会助长效应对操作人员认知负荷和行为绩效的影响,模拟单独在场、他人在场、有监控3种不同的作业场景,借助事件相关电位的脑电实验设计和NASA-TLX量表进行神经表征分析。研究结果表明:3种不同作业场景下,他人在场及有监控场景可显著提高个体进行简单任务的作业绩效,但会降低困难任务的作业绩效;个体的主观认知负荷在他人在场与有监控场景下较大,且随任务复杂度的增加而增加;他人在场、有监控场景诱发个体更高的P200,N200,P300波幅,且在不同任务类型下,个体的认知机制作用不同,字母任务可诱发更大的P200,N200波幅及更小的P300波幅;社会助长效应通过影响个体认知负荷进而影响作业绩效,研究结果可为相关企业优化人机交互作业管理模式提供参考。

应用于白光中子束线的低气压纯氦气正比计数器

通过蒙特卡罗模拟和实验测试,研究了不同工作气压下纯^(3)He气体正比计数器的基本性能,包括幅度响应和时间响应;开展了低气压纯^(3)He气体正比计数器α信号的探测实验。实验结果表明,当正比计数器内部^(3)He气压为0.25~1 atm(1 atm=1.013×10^(5)Pa)时,该探测器具有良好的正比计数功能,探测器内中子反应计数为数百每秒,满足中国散裂中子源的反角白光中子源(Back-n)开展中子与^(3)He反应截面测量实验的应用需求,可为未来Back-n配置^(3)He相关探测器、开展^(3)He截面的测量工作及进行白光中子的极化实验等提供参考。

基于ERPs技术探讨长期负性情绪累积肝失疏泄对正常人群工作记忆的影响及机制

目的运用事件相关电位技术(ERPs),研究负性情绪累积肝失疏泄对正常人群工作记忆的影响及机制。方法对情绪不稳定组和情绪稳定对照组各50例被试进行N-back范式两种记忆负荷任务,记录反应时和正确率,检测ERPs成分N200、P300在相关脑区的潜伏期和波幅并进行比较。结果①与情绪稳定对照组相比,情绪不稳定组反应时更长(P<0.05)。②与情绪稳定对照组相比,情绪不稳定组被试的N200潜伏期延长、P300波幅下降显著(P<0.05),P300潜伏期有延长趋势(P<0.1)。结论长期负性情绪累积肝失疏泄的正常人群存在工作记忆水平下降;工作记忆加工过程中的注意资源分配减少和工作记忆容量减小可能是其机制之一。

k元(n-1)方体子网络可靠性的近似评估方法

多处理器系统互连网络的拓扑性质对系统功能的实现起着重要的作用。k元n方体网络的子网络可靠性是以k元n方体为拓扑结构构建的多处理器系统处理计算任务时需要考虑的一个重要因素。为了精确高效地度量概率故障条件下k元n方体中k元(n-1)方体子网络的可靠性,提出基于反向传播(BP)神经网络的k元(n-1)方体子网络可靠性的近似评估方法。首先,利用蒙特卡洛仿真方法和k元(n-1)方体子网络可靠性的已有上下界给出用于训练BP神经网络的数据集的生成方法;其次,基于生成的训练数据集构造用于评估k元(n-1)方体子网络可靠性的BP神经网络模型;最后,对BP神经网络模型得出的k元(n-1)方体子网络可靠性的近似评估结果进行了分析,并与近似计算公式和基于蒙特卡洛的评估方法的结果进行了对比。与近似计算公式相比,所提方法得出的结果更为精确;与基于蒙特卡洛的评估方法相比,所提方法的评估耗时平均减少了约59%。实验结果表明,所提方法在兼顾精度和效率方面具有一定优势。