基于信赖域算法的中子解谱方法研究

提出了一种新的基于信赖域算法的中子能谱求解方法。使用O5S软件仿真了能量范围为0.25～16 MeV、能量间隔为0.25 MeV的BC501A液体闪烁体探测器响应函数。利用该响应函数仿真验证了入射中子能谱分别为单峰和多峰情况下算法的解谱效果，并通过D-T单能中子源、^{241Am-Be和252Cf连续中子源对解谱方法进行了实验验证。结果表明，使用信赖域算法求得的能谱与参考谱线具有较好的一致性，初步验证了解谱方法的有效性。}     

BC501液体闪烁体对n-γ及能量的分辨与其尺寸的关系

BC501液体闪烁体广泛应用于探测快中子，但测量伴随着很高的γ本底。为寻找具有较好的n-γ及能量分辨的BC501闪烁体，利用脉冲上升时间法，对几种不同尺寸的BC501闪烁体进行n-γ及能量分辨测量。在下阈0.75和1MeV下，分别测量了Am-Be中子源的n-γ分辨谱以及相同条件下的γ上升时间-幅度谱。测量了d-T中子源14MeV的反冲质子脉冲高度分布。对不同尺寸BC501闪烁体的n-γ及能量分辨进行了比较。实验表明，综合考虑n-γ和能量分辨，闪烁体的体积不应太大，长度应在保证效率的条件下适中选择。      

板状Bi样品泄漏中子和γ谱实验测量与模拟计算

通过飞行时间法,测量了氘氘脉冲中子与不同厚度209Bi样品作用后61°和119°方向的泄漏中子飞行时间谱和泄漏γ能谱,样品尺寸分别为30 cm×30 cm×5 cm、30 cm×30 cm×10 cm和30 cm×30 cm×15 cm。采用BC501A液体闪烁体探测器测量0.8～3.2 MeV能区的泄漏中子飞行时间谱,钾冰晶石探测器（CLYC）测量0.2～0.8 MeV的泄漏中子飞行时间谱和泄漏γ能谱。用MCNP-4C程序对泄漏中子飞行时间谱和泄漏γ能谱进行了模拟计算,²⁰⁹Bi的评价中子核数据分别采用了CENDL-3.1库、ENDF/B-Ⅷ.0库、JENDL-4.0库以及JEFF-3.3库中的数据,模拟结果分别与实验结果进行比较分析,研究结果表明,泄漏中子谱CENDL-3.1库的模拟结果在119°方向弹性峰位置有较严重的低估现象,JENDL-4.0库在1.5 MeV附近（第二非弹能区）有一定高估,而在低能区有明显低估;泄漏γ能谱JENDL-4.0库和JEFF-3.3库的模拟结果与实验结果偏差明显,而CENDL-3.1库符合较好。     

Measurements and Calculations of Neutron Energy Spectra Behind Polyethylene Shields Bombarded by 40- and 65-MeV Quasi-Monoenergetic Neutron Sources

Measurements of neutron energy spectra behind 30.5-, 61.0-, 122.0-, 183.0-cm-thick polyethylene shields bombarded by 40- and 65-MeV quasi-monoenergetic neutrons are performed at the 90-MeV AVF cyclotron of the TIARA (Takasaki Ion Accelerator for Advanced Radiation Application) at JAERI (Japan Atomic Energy Research Institute). Source neutrons are produced at 3.6- and 5.2-mm-thick⁷ Li targets bombarded by 43- and 68-MeV protons, respectively. A BC501A organic liquid scintillator and multi-moderator spectrometer with a ³He counter (Bonner ball) are used for spectrometry of transmitted neutrons and their energy spectra are obtained with the unfolding technique. The energy spectra from a few MeV up to a peak energy are obtained by the BC501A scintillator measurement and those below a few MeV down to thermal energy are obtained by the Bonner ball measurement. The measurements are performed on the neutron beam axis and at off-center positions, and attenuation profiles of neutron fluxes along the beam axis are obtained. The MORSE Monte Carlo calculations are performed with the DLC119/HIL086 multi-group cross section library for comparison with the measured data. The calculation generally gives a little overestimated fluxes, and a few % longer attenuation lengths of peak flux and dose equivalent.     

液闪探测器中子光响应函数刻度研究

BC501A液体闪烁体在临近空间高能中子测量中具有重要的应用价值,其光响应和能量分辨率对测量结果影响较大。对中子与BC501A液体闪烁体作用产生的反冲质子的光响应函数以及液闪的能量分辨函数进行了研究。利用5SDH-2串列加速器通过核反应获得单能脉冲中子源,实验获得单能中子的脉冲幅度谱,应用GEANT4等MC软件对实验进行模拟计算得到光响应谱,并与脉冲幅度谱进行拟合得到各能点中子的光输出以及其对应的能量分辨率,应用最小二乘法对中子光响应函数以及能量分辨函数进行了计算,并将计算结果与推荐光响应函数进行了对比分析。结果显示:模拟计算反冲质子能谱与单能中子脉冲幅度谱在末端边沿处拟合效果较好,中子光响应函数与其他文献中的研究结果基本一致。     

Characterization of the neutron flux distribution at the Athens Tandem Accelerator NCSR “Demokritos”

Quasi-monoenergetic neutron beams, in the energy range 7-11.5 MeV, produced via the ²H(d,n) reaction, have been used at the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR “Demokritos”. The flux variation of the neutron beam is monitored with a BF₃ detector, while the absolute flux is obtained with respect to reference reactions. An investigation of the energy dependence of the neutron fluence has been carried out using two independent techniques: by a liquid scintillator BC501A detector and deconvolution of its recoil energy spectra performed by means of the DIFBAS code, as well as via the multiple foil activation technique in combination with the SULSA unfolding code. The neutron facility has also been characterized by means of Monte Carlo simulations with MCNP5.     

Proposal of an Effective Initial Guess Scheme for Higher Harmonic Mode Calculation of Boiling Water Reactor Cores

Response functions of a BC501A liquid organic scintillator for neutrons up to 800 MeV have been measured at the heavy-ion accelerator of the National Institute of Radiological Sciences, Japan. A thick graphite target was bombarded with 400-MeV/u C ions and 800-MeV/u Si ions to produce high-energy neutrons whose kinetic energy was determined by the time-of-flight method. The measured response functions were compared with the results obtained using SCINFUL-QMD code, and the accuracy of the code was experimentally verified up to 800 MeV. This work will contribute to extending the energies measurable with our new radiation dose-monitoring system (DARWIN), which is based on the BC501A scintillator.     

Boiling Detection by Acoustic Analysis Applying Linear Discriminant Function

A new inventive radiation dose monitor, designated as DARWIN (Dose monitoring system Applicable to various Radiations with WIde energy raNges), has been developed for monitoring doses in workspaces and surrounding environments of high energy accelerator facilities. DARWIN is composed of a phoswitch-type scintillation detector, which consists of liquid organic scintillator BC501A coupled with ZnS(Ag) scintillation sheets doped with ⁶Li, and a data acquisition system based on a Digital-Storage-Oscilloscope. Scintillations from the detector induced by thermal and fast neutrons, photons and muons were discriminated by analyzing their waveforms, and their light outputs were directly converted into the corresponding doses by applying the G-function method. Characteristics of DARWIN were studied by both calculation and experiment. The calculated results indicate that DARWIN gives reasonable estimations of doses in most radiation fields. It was found from the experiment that DARWIN has an excellent property of measuring doses from all particles that significantly contribute to the doses in surrounding environments of accelerator facilities—neutron, photon and muon with wide energy ranges. The experimental results also suggested that DARWIN enables us to monitor small fluctuation of neutron dose rates near the background-level owing to its high sensitivity.     

R&D progress of high power ion source on EAST-NBI

The neutral beam injector(NBI) system was designed and developed mainly for the plasma heating on the Experimental Advanced Superconducting Tokamak(EAST). The high power ion source is the key part of the NBI. A hot cathode ion source was used on the EAST-NBI. The ion source was conditioned on the ion source test bed with hydrogen gas and achieved the designed parameters. The deuterium gas was used when it moved to the EAST-NBI. The main performance of the ion source on EAST is presented in this paper. The highest beam power of 4.5 MW in NBI-1 and 2.75 MW in NBI-2 was achieved. The total neutral beam power is about 4.5 MW. The long pulse beam of 100 s is injected into the EAST plasma too.     

镓样品泄漏中子谱的测量与分析

基于中国原子能科学研究院的中子学积分实验装置，利用BC501A液体闪烁体探测器，结合飞行时间法（TOF）测量了镓样品的泄漏中子谱。采用MCNP 4C程序进行了模拟并与实验泄漏中子谱进行了比较，对ENDF/B-Ⅶ.1、JEFF-3.2、TENDL-2015数据库中镓核中子评价数据进行了宏观基准检验分析，并与TALYS程序计算结果作对比。研究结果显示：在9 MeV以下能区，TENDL-2015库与实验结果符合很好；在弹性散射能区，JEFF-3.2和TENDL-2015库与实验结果符合较好；对于12 MeV左右的非弹性散射峰，JEFF-3.2库与实验结果符合较好，TALYS计算结果显示该部分主要来自镓核分离能级的贡献。     

Application of local Monte Carlo method in neutronics calculation of EAST radial neutron camera

The Local Monte Carlo (LMC) method is used to solve the problems of deep penetration and long time in the neutronics calculation of the radial neutron camera (RNC) diagnostic system on the experimental advanced superconducting tokamak (EAST), and the radiation distribution of the RNC and the neutron flux at the detector positions of each channel are obtained. Compared with the results calculated by the global variance reduction method, it is shown that the LMC calculation is reliable within the reasonable error range. The calculation process of LMC is analyzed in detail, and the transport process of radiation particles is simulated in two steps. In the first step, an integrated neutronics model considering the complex window environment and a neutron source model based on EAST plasma shape are used to support the calculation. The particle information on the equivalent surface is analyzed to evaluate the rationality of settings of equivalent surface source and boundary. Based on the characteristic that only a local geometric model is needed in the second step, it is shown that the LMC is an advantageous calculation method for the nuclear shielding design of tokamak diagnostic systems.     

Activation and shutdown dose-rate analyses for the EAST NBI test facility

An analysis of the neutron activation and shutdown dose rates was performed for the EAST high-power deuterium neutral beam injector test facility(EAST NBITF) by using the multiparticle transport code FLUKA2011.2. Also, the neutron and neutron-induced gamma spectra of the facility's vacuum vessel were evaluated. The results identified the major radionuclides~(99) Mo,~(65)Ni,~(58) Co,~(56)Mn, and~(51) Cr for the vacuum vessel and the primary nuclide~(64) Cu for both the ion dump and the calorimeter.The simulated results indicated that, when the EAST NBITF operates within the design parameters of deuterium energy 80 ke V, current 50 A, and pulse 100 s, the neutron intensity will achieve 10~(11)n/s with no radiation safety problems after the EAST NBITF shuts down.     

直径30 cm的等高圆柱形载钆液闪探测性能

载钆液闪探测器是高能物理及核物理实验中重要的粒子探测工具。通过研制得到了一台大体积的直径为30 cm等高圆柱形载钆液闪探测器,载钆液闪溶液的载钆量为0.5%wt;利用252Cf中子源进行了中子与γ分辨性能实验测试,结果表明,直径30 cm等高圆柱形载钆液闪的中子与γ分辨性能较差;利用飞行时间技术通过符合测量的方法,分别测量了中子与伽马分辨谱中的中子与γ信号的时间分布,两者峰位之间的时间差为2 ns;利用252Cf裂变电离室的裂变碎片信号作为开门信号,通过符合测量的方法,获得了直径30 cm等高圆柱形载钆液闪的中子俘获时间分布实验数据,中子俘获平均时间为11μs。对于较大体积条件下,载钆液闪的中子与γ分辨性能较差的物理现象,通过实验给出了合理解释和分析。     

Neutronic performance of the MEGAPIE spallation target under high power proton beam

The MEGAPIE project, aiming at the construction and operation of a megawatt liquid lead-bismuth spallation target, constitutes the first step in demonstrating the feasibility of liquid heavy metal target technologies as spallation neutron sources. In particular, MEGAPIE is meant to assess the coupling of a high power proton beam with a window-concept heavy liquid metal target. The experiment has been set at the Paul Scherrer Institute (PSI) in Switzerland and, after a 4-month long irradiation, has provided unique data for a better understanding of the behavior of such a target under realistic irradiation conditions. A complex neutron detector has been developed to provide an on-line measurement of the neutron fluency inside the target and close to the proton beam. The detector is based on micrometric fission chambers and activation foils. These two complementary detection techniques have provided a characterization of the neutron flux inside the target for different positions along its axis. Measurements and simulation results presented in this paper aim to provide important recommendations for future accelerator driven systems (ADS) and neutron source developments.     

基于GDT的14MeV中子源初步设计研究

为满足聚变材料测试对D-T聚变中子源的需要,本文首先根据国际上对用于聚变材料测试的中子源的要求给出设计目标,然后基于Gas Dynamic Trap(GDT)装置的实验进展,提出了基于GDT装置的14MeV中子源的设计初步方案,并建立了GDT中子源的物理模型。计算分析给出了两套中子源参数初步方案,其中FDS-GDT2中子壁负载为2MW/m2,可用于聚变材料的测试。     

液闪探测器的几种n/γ甄别方法研究

利用液闪探测器研究了几种数字化波形甄别方法的n/γ甄别能力。以Am-Be源作为混合场源,用示波器对EJ-301和BC501A两种液闪探测器信号进行数字化采集,分别用上升时间法、电荷比较法、脉冲梯度分析和频率梯度分析等数字化波形甄别方法对采集的信号进行了n/γ离线甄别分析,比较了4种方法的甄别效果,并用MPD-4甄别单元从实验上验证了各方法的可靠性。结果表明：对于液闪探测器,4种数字化方法具有较好的甄别一致性和准确性,上升时间法的甄别效果最好,是实时甄别系统甄别算法的理想选择。     

Simulations of scattered neutrons for the time-of-flight enhanced diagnostics(TOFED)neutron spectrometer on EAST

The time-of-flight enhanced diagnostics(TOFED) neutron spectrometer has been installed in TOFED house, which is a newly-built neutron diagnostic lab outside the EAST experimental hall. The line of sight(LOS) of TOFED is defined by the collimator going through the 150 cm biological shielding wall, which can reduce background neutrons very effectively for the neutron spectral measurements. The Monte Carlo code MCNP5 is used in the simulations to characterize collimation effects and the radiation safety of the new house. The collimator makes neutron flux almost fully perpendicular to S1 detectors. In addition, the proportion of scattered neutrons in the LOS of the TOFED is obtained for the measured spectral data interpretation. The simulation results show that the TOFED house satisfies the requirement for the TOFED operations at EAST and gives a safe environment for personnel access during the EAST operation.     

Determination of the absolute number of neutrons emitted by a radium-beryllium source by comparison with a photoneutron deuterium source

A method for standardizing neutron sources which Is comparatively simple and which may be realized in any laboratory has been developed. A photoneutron deuterium source, consisting of a chamber filled with heavy water with a source of -rays at the center, is used as the primary standard. The number of photoneutrons emitted by this standard is determined from the absolute number of photoprotons produced in a deuterium-gas ionization chamber which has the same geometry and is irradiated under the same conditions as the primary neutron standard. A comparison of the intensity of the primary standard and the source being calibrated is carried out by measuring the areas under the curves which give the spatial distribution of neutrons slowed-down in water. The method has been used to determine the absolute number of neutrons emitted by a Ra--Be source.     

Time Dependent DD Neutrons Measurement Using a Single Crystal Chemical Vapor Deposition Diamond Detector on EAST

A single crystal chemical vapor deposition(scCVD) diamond detector has been successfully employed for neutron measurements in the EAST(Experimental Advanced Superconducting Tokamak) plasmas.The scCVD diamond detector coated with a 5 μm ~6LiF(95%~6Li enriched) layer was placed inside a polyethylene moderator to enhance the detection efficiency.The time-dependent neutron emission from deuteron plasmas during neutral beam injection(NBI)heating was obtained.The measured results are compared with that of fission chamber detectors,which always act as standard neutron flux monitors.The scCVD diamond detector exhibits good reliability,stability and the capability to withstand harsh radiation environments despite its low detection efficiency due to the small active volume.     

Neutron and gamma ray heating in the grazing incident liquid metal mirrors for laser inertial fusion energy power plants

A thin film of liquid metal can serve as final optics of a laser inertial fusion energy (IFE) power plant. Calculations of pulsed neutron and gamma-ray heating are presented for a grazing incident liquid metal mirror (GILMM) used for robust final optics of a laser IFE power plant. Different liquid films (Li, Na, Mg, Al, Si, K, Ga, Ag, Au, Pb, Bi and Flibe “Li₂BeF₄”) are considered at a distance of 30 m from a nominal 1 GJ fusion source as well as different substrate materials (SS-304 and SiC). The effect of neutron heating both in the liquid metal film as well as in the subsrate material will be by around three to four orders of magnitude lower than the laser heating limit. Hence the nuclear heating will not be a limiting factor for grazing incident liquid metal mirror (GILMM) of a laser IFE power plant.