基于白光中子源的169Tm辐射俘获截面测量和共振参数分析

中子辐射俘获截面及共振参数在核工程设计、核天体物理等研究领域中有重要的应用价值。在中国散裂中子源（CSNS）反角白光中子束线（Back n）上,使用C6D6测量系统开展了169Tm辐射俘获反应测量。通过脉冲高度权重技术、共振吸收法和饱和归一法得到169Tm辐射俘获反应的产额。利用SAMMY程序拟合169Tm的产额数据,得到169Tm在1~100 eV能量区间的共振能量、中子宽度、辐射俘获宽度等共振参数。使用实验测得的共振参数和Reich Moore近似计算了169Tm在1~100 eV能量区间的辐射俘获截面。实验测量结果与ENDF/B Ⅷ.0数据库的推荐值总体符合较好,部分共振参数和截面存在一定的差异。产生这些差异的原因与Back n的源中子能谱结构、能量分辨率、实验本底的精度有关。     

Measurements of neutron capture cross-sections for ADS-related studies

Capture cross-sections on several isotopes relevant to accelerator driven systems for energy production and nuclear waste transmutation, and to stellar nucleosynthesis can be studied at the innovative neutron time of flight facility (n_TOF) at CERN. The experimental apparatus is based on a low-mass Si-based flux monitor and a set of C₆D₆ liquid scintillator detectors. The accurate reconstruction of the cross-sections relies on the pulse height weighting function technique. The set-up used in the measurements is here described. The first results on reference isotopes, Au, Ag and Fe, used to verify the accuracy of the method are presented.     

先进裂变核能的关键核数据测量和CSNS白光中子源

在设计加速器驱动的次临界系统（ADS）、核废料嬗变装置及钍基熔盐堆时亟需一些关键核数据,当前核数据库受实验条件或中子能区的限制,存在核数据精度不高甚至少部分核素数据缺失的情况。本文综述了国内外相关的核数据研究和相应的白光中子源情况。基于中国散裂中子源(CSNS)的反角通道白光中子源实验终端的中子束流具有非常宽的能谱（0.01 eV~200 MeV）和很好的时间特性。模拟得到距靶80 m处的实验终端的中子注量率为9.3×10⁶cm^-2•s^-1,1 eV ~ 1 MeV能量间隔内的中子数占总中子数的53%;同时,加速器运行在双束团模式或单束团模式,时间分辨率均在0.3%～0.9%之间,适合开展核数据测量。     

Recent progress in nuclear data measurement for ADS at IMP

Recent progress in nuclear data measurement for ADS at Institute of Modern Physics is reviewed briefly.Based on the cooler storage ring of the Heavy Ion Research Facility in Lanzhou, nuclear data terminal was established.The nuclear data measurement facility for the ADS spallation target has been constructed, which provides a very important platform for the experimental measurements of spallation reactions. A number of experiments have been conducted in the nuclear data terminal. A Neutron Time-of-Flight(NTOF)spectrometer was developed for the study of neutron production from spallation reactions related to the ADS project.The experiments of 400 MeV/u ~(16)O bombarded on a tungsten target were presented using a NTOF spectrometer.Neutron yields for 250 MeV protons incident on a thick grain-made tungsten target and a thick solid lead target have been measured using the water-bath neutron activation method. Spallation residual productions were studied by bombarding W and Pb targets with a 250 MeV proton beam using the neutron activation method. Benchmarking of evaluated nuclear data libraries was performed for D-T neutrons on ADS relevant materials by using the benchmark experimental facility at the China Institute of Atomic Energy.     

γ全吸收型探测装置探测效率的实验与模拟

为精确测量keV能区中子俘获反应截面,中国原子能科学研究院核数据重点实验室基于中国散裂中子源反角白光中子源建成了国内首套γ全吸收型BaF₂探测装置。为获得重要的实验参数装置对γ射线的探测效率曲线,对单个BaF₂探测器模块能谱的测量数据与模拟结果进行比较。结果表明,测量¹³⁷Cs和⁶⁰Co源得到的实验结果与MCNP和GEANT4的模拟结果吻合较好,验证了模拟计算得到的探测效率曲线的可靠性,可用于中子俘获反应截面的在线测量。     

中国散裂中子源反角白光中子束斑测量

中国散裂中子源（CSNS）反角白光中子（Back-n）束斑品质是核数据测量和其他物理实验的基础。利用像增器脉冲选通特性和飞行时间法搭建了一套具有时间分辨能力的成像系统,其空间分辨小于1 mm,初步实现了束斑轮廓、尺寸和非均匀性等特性参数的测量和定量分析。在距散裂靶约55、75 m处测得束斑FWHM分别为55、63 mm,对应峰值强度约75%处束斑直径分别为50、60 mm,且束斑边缘陡峭,呈台阶状。分析表明,束斑轮廓、尺寸和非均匀性等特性参数均与中子能量无关,在束斑中心区域80%范围内非均匀性小于10%。测量结果表明,CSNS反角白光中子源物理终端具有较好的中子束斑品质,可开展较高精度的核数据测量。     

An improved beam chopper setup at the Budapest PGAA facility

Modulating neutron beams with a beam chopper enables the investigation of time-dependent processes following neutron capture, such as emission of decay-gamma-radiation from short-lived nuclides. For this purpose, a redesigned beam chopper and controller electronics have been recently installed at the PGAA facility of the Budapest Research Reactor. The new electronics provides accurate timing and better control of routing of the signals. The upgraded instrumentation is capable of recording the events in the beam-on and beam-off phases in parallel. Simplified formulae were derived to relate the areas of prompt- and decay peaks to the partial γ-ray production cross-sections. Finally, preliminary results obtained with Ag- and Na-containing targets are presented.     

On the problem of monitoring the neutron parameters of the fast energy amplifier

The conceptual Fast Energy Amplifier, proposed by Rubbia et al. consists of a combination of a U-233/Th-232 fuelled fast-neutron subcritical facility with a proton accelerator. An intense beam of 1 GeV protons is injected into liquid lead at the core centre and drives the reactor by producing spallation neutrons. The burst of spallation neutrons produced by a single proton alters the basic neutron statistics which are well known for thermal neutrons in conventional nuclear reactors. A short assessment of standard neutron noise analysis methods is made with respect to monitoring neutron parameter data.     

Analysis of the FIC detector data at the n_TOF facility

Fission cross-section measurements with the Fast Ionization Chamber (FIC) at the CERN n_TOF facility were challenged by intense signals due to γ-rays and ultra-relativistic particles from the impact of the 20 GeV proton pulses on the neutron spallation target. A method for analyzing the data taken with Flash Analog to Digital Converters (FADC) was developed to treat these problems in an automated way to provide a reliable background subtraction and a fit routine for identifying fission events even at high energies. The analysis is illustrated at the example of the fission cross-section of ²³⁸U relative to that of ²³⁵U in the energy range from 40 keV to 300 MeV.     

利用瞬发γ射线法测量209Bi的中子非弹性散射截面

在铅铋快堆、空间堆等先进反应堆中,铋作为冷却剂和慢化剂材料被大量使用,其中子核反应截面,尤其是中子非弹性散射截面的准确性对这些核装置的安全性和经济性等具有重要的影响。基于中国原子能科学研究院HI 13串列加速器瞬发γ射线实验平台,通过瞬发γ射线法测量了209Bi在90、105和120 MeV 3个能点的中子非弹性散射截面。在相对于中子束30°、70°、110°和150°方向放置4个Clover探测器测量中子与样品相互作用产生的γ射线。实验采用相对测量,通过测量中子与48Ti发生非弹性散射发射的9835 keV γ射线的产生截面来确定209Bi的截面。209Bi金属样品的尺寸为50 mm×4 mm,参考样品为1块50 mm×1 mm的天然钛金属样品。将实验测量结果与已发表的实验数据、ENDF/B Ⅷ.0、JEFF 33、JENDL 40、ROSFOND 2010和CENDL 31等评价库数据以及Talys 195程序默认参数的计算结果进行对比,发现趋势一致,90、105 MeV能点的测量结果与Talys 195程序的计算结果符合得更好,120 MeV能点的测量结果与ROSFOND 2010评价库数据符合得更好。     

An ENDF-6 compatible evaluation for neutron induced reactions of Th in the unresolved resonance region

An evaluation for neutron induced reactions of ²³²Th has been performed in the unresolved resonance region from 4 to 100 keV. A generalized single-level representation compatible with the energy-dependent options of the ENDF-6 format has been used. The average partial cross sections have been expressed in terms of transmission coefficients by applying the Hauser–Feschbach statistical reaction theory including width-fluctuations. The evaluation is based on a combined analysis of experimental average cross section data (including the most recent capture cross section data obtained at the time-of-flight facilities GELINA and n_TOF), and results of dispersive coupled-channel optical model calculations. Experimental data on transmission and self-indication measurements as well as integral benchmark calculations have been used for validation. The evaluation also includes covariance information.     

Benchmark experiment of large-angle scattering reaction cross section of iron at 14 MeV using two shadow bars – Comparison of experimental results with ENDF/B-VIII –

ABSTRACT

It is important to perform neutron transport simulations with accurate nuclear data in the neutronics design of a fusion reactor. However, absolute values of large-angle scattering cross sections vary among nuclear data libraries even for well-examined nuclide of iron. Benchmark experiments focusing on large-angle scattering cross sections were thus performed to confirm the correctness of nuclear data libraries. The series benchmark experiments were performed at a DT neutron source facility, OKTAVIAN of Osaka University, Japan, by the unique experimental system established by the authors’ group, which can extract only the contribution of large-angle scattering reactions. This system consists of two shadow bars, target plate (iron), and neutron detector (niobium). Two types of shadow bars were used and four irradiations were conducted for one experiment, so that contribution of room-return neutrons was effectively removed and only large-angle scattering neutrons were extracted from the measured four Nb reaction rates. The obtained experimental results were compared with calculations for five nuclear data libraries including JENDL-4.0, JEFF.-3.3, FENDL-3.1, ENDF/B- VII, and recently released ENDF/B-VIII. It was found from the comparison that ENDF/B-VIII showed the best result, though ENDF/B-VII showed overestimation and others are in large underestimation at 14 MeV.     

回旋加速器快中子治癌装置的研究

就30MeV回旋加速器上建立快中子治癌装置的几个主要方面,如中子束特性参数、中子屏蔽准直器、中子靶、中子剂量监测及中子治癌控制等进行了可行性的研究。     

启明星Ⅱ号双堆芯零功率装置

启明星Ⅱ号是针对我国新型先进核能系统基础性研发及工程化设计验证而研制的双堆芯零功率装置。启明星Ⅱ号拥有两个堆芯,水堆堆芯侧重于开展热中子能谱环境下的原理性验证实验研究,铅堆堆芯侧重于重金属冷却的快中子反应堆及加速器驱动的次临界系统（ADS）等先进核能系统的中子物理特性实验研究。启明星Ⅱ号通过一套仪控系统实现了两个堆芯的集成化控制和测量数据采集,每个堆芯均配备了多套非能动安全停堆系统,固有安全性强。在启明星Ⅱ号上获取了多种堆芯的基准性临界实验数据,可为我国轻水堆的技术创新、重金属冷却反应堆工程化设计及新型核能系统的集成研发提供支持。     

Optimization of a neutron detector for pulsed photonuclear monitoring of fissile materials

The objective of the present work is optimization of the geometry of a multilayer detector used in the pulsed photonuclear method of remote monitoring of fissile materials. Numerical simulation of the conversion of an electron beam into bremsstrahlung and the interaction of the latter radiation with components of the facility and the contents of the object of monitoring, resulting in neutron emission, is performed. The spectral-time parameters of the neutron flux arriving at the detector are obtained and the probability of detecting neutrons with different energy is calculated as a function of the thickness of the layers for moderation and absorption. The construction of the detector giving high fission-neutron detection efficiency and low sensitivity to background neutrons is chosen. The data obtained were used to build the neutron detector used in the experimental model of a facility for detecting fuel-cycle materials by the photonuclear method based on the U-28 accelerator. Translated from Atomnaya énergiya, Vol. 106, No. 1, pp. 48–52, January, 2009.     

Effect of (γ, n) Reactions of Heavy Water Moderator on Beam Quality in Biomedical Irradiation Facility

The effect of (γ, n) reactions of heavy water on beam quality of a biomedical irradiation facility was studied. In an irradiation facility using thermal neutrons from a nuclear reactor, heavy water is widely employed as neutron moderator because of its good nuclear characteristics. It is well known that the threshold energy of (γ, n) reactions of heavy water is 2.2 MeV and fast neutrons are generated from the reactions. In 1982, we proposed a technique for the evaluation of (γ,n) reactions using a computer code ANISN-JR. In the present work, with further improved ANISN-JR for the proper estimation of the leakage, the comparison calculations both with and without (γ, n) reactions were carried out and their results were compared with those of the foil activation experiments at the KUR Heavy Water Facility. In the ignorance of (γ, n) reactions, fast and epithermal neutron fluxes are extremely underestimated for deeper penetration than 80 cm, while the calculated results including (γ, n) reactions give good agreements with experiments.     

Concept of electron accelerator-driven system based on subcritical cascade reactor

A concept of accelerator-driven system consisting of electron accelerator, neutron-generating target and two-core subcritical blanket with fast and thermal neutron spectrum has been presented. Some general features of the cascade neutron multiplication in the two-core subcritical blanket are discussed. Calculation results are demonstrated for the processes of electron–photon–neutron interactions of electron beam with the target material. Neutronic and heat engineering characteristics of the facility are also described. It has been shown that with the system's subcritical level of 2% and electron beam power of 4 MW, the facility power is as high as 50 MW.     

MCNPX, MONK, and ERANOS analyses of the YALINA Booster subcritical assembly

This paper compares the numerical results obtained from various nuclear codes and nuclear data libraries with the YALINA Booster subcritical assembly (Minsk, Belarus) experimental results. This subcritical assembly was constructed to study the physics and the operation of accelerator-driven subcritical systems (ADS) for transmuting the light water reactors (LWR) spent nuclear fuel. The YALINA Booster facility has been accurately modeled, with no material homogenization, by the Monte Carlo codes MCNPX (MCNP/MCB) and MONK. The MONK geometrical model matches that of MCNPX. The assembly has also been analyzed by the deterministic code ERANOS. In addition, the differences between the effective neutron multiplication factor and the source multiplication factors have been examined by alternative calculational methodologies. The analyses include the delayed neutron fraction, prompt neutron lifetime, generation time, neutron flux profiles, and spectra in various experimental channels. The accuracy of the numerical models has been enhanced by accounting for all material impurities and the actual density of the polyethylene material used in the assembly (the latter value was obtained by dividing the total weight of the polyethylene by its volume in the numerical model). There is good agreement between the results from MONK, MCNPX, and ERANOS. The ERANOS results show small differences relative to the other results because of material homogenization and the energy and angle discretizations.The MCNPX results match the experimental measurements of the ³He(n,p) reaction rates obtained with the californium neutron source.     

Consideration about the Single-neutron Microbeam Facility

A conception of the single-neutron microbeam facility was put forward in this paper. The specific particle (e.g. H^ , ^2d^ or α ) bombarding a specific target can generate neutron, when the particle energy is more than a threshold (e.g., H^ energy is more than 2 MeV). And if the specific beam spot on the target is very small, the neutron beam along the direction of the specific beam spot will be very small too. If the neutron beam is weak and a neutron detector is mounted after the specific neutron collimator, the single- neutron will be obtained. Therefore, if the specific target and the neutron detector are installed after the proton accelerator and the microbeam system, the single-neutron microbeam will probably be obtained.     

Evaluation of neutron beam characteristics for D-BNCT01 facility

An accelerator-based Boron Neutron Capture Therapy （AB-BNCT） experimental facility called D-BNCT01 has been recently completed and is currently able to generate a high-intensity neutron beam for BNCT-related research.In this study,we perform several experiments involving water phantoms to validate the Monte Carlo simulation results and analyze the neutron beam characteristics.According to our measurements,D-BNCT01 can generate a neutron flux about 1.2×10⁸n/cm²/s at the beam...