LS301快中子探测器的效率刻度

主要介绍了利用252Cf标准裂变中子能谱刻度快脉冲LS301型液闪中子探测器的探测效率的实验方法和结果, 简要介绍了实验数据的处理过程, 得到了阈值分别为0.5, 0.7, 1.0和1.6 MeV, 以及中子能量在10 MeV以下的探测器效率, 并对测量结果进行了误差分析。同时为了检验实验结果的准确性, 将实验结果与理论计算结果进行比较, 两者在不确定度范围内符合得很好。Neutron detection efficiency of LS301 fast neutron detector was calibrated by measuring the neutron energy spectrum of 252Cf source, which has a standard fission neutron spectrum. A low mass, fast ionization chamber is used as the fission fragments detector in the time of flight(TOF) spectrometer and afforded the start signal of neutron flight. The stop signal was offered by the anode of LS301. A measured TOF spectrum was turned to the neutron energy spectrum which will be compared with the standard one. Consequently, the fast neutron detection efficiency of LS301 was obtained. Calibration procedures of experimental and data processing was given. Relative detection efficiencies were obtained separately for threshold settings of 0.5, 0.7, 1.0 and 1.6 MeV for neutron energies under 10 MeV. Experimental results accorded with theoretical efficiency curves which were calculated with the Monte Carlo code NEFF50.     

NE213 闪烁体探测器中子探测效率模拟

应用FLUKA 软件包对NE213 液体闪烁体中子探测器的探测效率进行了蒙特卡罗模拟,通过Birks 公式将中子产生的次级粒子的能量沉积转化为相应的光输出。根据不同探测阈值对模拟得到的光输出进行积分处理,计算出给定能量下探测器的中子探测效率。将模拟得到的闪烁体光输出、中心探测效率和平均探测效率随中子入射到探测器前表面位置的变化与实验数据进行比较,结果显示,FLUKA 模拟结果与实验值符合得很好,这为中子探测器的设计提供了可靠保证。A NE213 liquid scintillation neutron detector was simulated by using the FLUKA code. The light output of the detector was obtained by transforming the secondary particles energy deposition using Birks formula. According to the measurement threshold, detection efficiencies can be calculated by integrating the light output. The light output, central efficiency and the average efficiency as a function of the front surface radius of the detector, were simulated and the results agreed well with experimental results.     

2.8MeV中子诱发238U裂变的瞬发中子谱高能段实验测量

在中国原子能科学研究院的高压倍加器上利用中子飞行时间方法测量了2.8 MeV中子引起238U裂变的瞬发中子能谱,通过增大样品量和设计合适的屏蔽体提高了效应/本底比,使得测量数据的不确定度满足预期目标（在5.5～14 MeV能区内,能量间隔为0.5 MeV条件下能谱的不确定度小于10%）。将实验几何、中子源能量分布及角分布、探测效率、束流的时间结构等实验条件输入到MCNP程序里,模拟了出射的中子谱,模拟结果与测量结果在不确定度范围内一致,验证了在入射中子能量较低时238>U的裂变瞬发中子谱评价数据的可靠性。The Prompt Fission Neutron Spectrum (PFNS) of 238U induced by 2.8 MeV neutron was measured using the Cockcroft-Walton accelerator in China Institute of Atomic Energy (CIAE). The signal/background ratio was improved by increasing the amount of sample mass and using an appropriate shielding system. The final uncertainty of neutron energy spectrum in 5.5～14 MeV region is less than 10% with a bin size of 0.5 MeV which has reached this project's anticipation. The experimental geometry, the angular distribution and energy distribution of neutron source, the detection efficiency and time structure of deuteron beam were inputted into the MCNP code to simulate the outgoing neutron spectrum. The simulated results agree with the experimental ones within the uncertainty. The result indicates that the evaluated PFNS for 238U at low neutron energy is reliable.     

A position-sensitive detector with lithium glass and MaPMT

A position-sensitive detector is designed for neutron detection. It uses a single continuous screen of a self-made lithium glass scintillator, rather than discrete crystal implementations, coupling with a multi-anode PMT (MaPMT). The scintillator is fast and efficient; with a decay time of 34 ns and thermal neutron detection efficiency of around 95.8% for the 3 mm thick screen, and its light yield is around 5670 photons per neutron and 3768 photons per MeV γ rays deposition. The spatial resolution is around 1.6 mm (FWHM) with the energy resolution around 34.7% by using α (5.2 MeV) rays test.     

应用于热中子的nTHGEM探测器性能研究

随着脉冲强流中子源的发展,对高性能中子探测器提出了更大的挑战,3He气体资源严重短缺和高计数率中子探测器的迫切需求,已开始制约着中子源应用技术的发展。中国科学院高能物理研究所针对中子的特殊性,专门研发了一种陶瓷基材的nTHGEM（neutron Thick Gaseous Electron Multiplier）探测器用于中子探测。基于nTHGEM的中子探测器具有高计数率、高位置与时间分辨能力、增益大、制作工艺简单,且便于大面积制作的特点,是目前国际上发展替代3He探测技术的重要方向之一。为了详细研究nTHGEM探测器的本身性能,本工作使用55Fe放射源研究了nTHGEM探测器的增益、计数率稳定性、能量分辨率等关键参数与nTHGEM膜间电压、收集场强、漂移场强之间的关系,优化了nTHGEM探测器在不同工作气体中的工作参数,为后续进一步优化nTHGEM探测器设计和工艺奠定了基础。实验结果表明,单层nTHGEM探测器在Ar（90%）+CO₂（10%）混合气体中增益能达到103,探测器计数率稳定性良好。另外,还在中国原子能科学研究院的CARR反应堆（China Advanced Research Reactor）上进行了中子束流实验,通过狭缝测量到探测器位置分辨率为（3.01±0.03）mm（FWHM）,已经接近高气压3He MWPC中子探测器水平。With the development of pulsed intense neutron source, the high-performance neutron detector poses more challenges. The severe shortage of 3He gas resources and the urgent need of neutron detector with high counting rate have begun to restrict the neutron source application technology development. In response to the particularity of neutrons, the Institute of High Energy Physics of CAS developed a nTHGEM(neutron Thick Gaseous Electron Multiplier)of ceramic substrate for neutron detection. The neutron detector based on nTHGEM is one of the most important directions for the development of alternative 3He detection technology in the world at present because of its high counting rate, high position and time resolution, large gain, simple fabrication process and large area production. In order to study the properties of nTHGEM detector in detail, this paper studied the relationship between nTHGEM detector's gain, counting rate stability, energy resolution and other key parameters and nTHGEM film voltage, collection field strength and drift field strength using 55Fe radioactive source, Optimized the working parameters of nTHGEM detector in different working gases, which laid the foundation for further optimization of nTHGEM detector design and process. The experimental results show that the single-layer nTHGEM detector has a gain of 103 in a Ar(90%)+CO₂(10%) mixed gas with good counting rate stability. In addition, a neutron beam experiment was performed on the China Advanced Research Reactor at the China Institute of Atomic Energy, and the position resolution of the detector was (3.01±0.03) mm (FWHM) measured by slits. Its performance is close to the high pressure 3He MWPC neutron detector level.     

用于中子测量的俘获探测器研究

为了在弱中子场和有限小空间内测量绝对裂变率, 制作了俘获探测器, 研究了俘获探测器的性能。 介绍了用于中子测量的俘获探测器和铅屏蔽室, 以及该探测器系统在特定条件下测量裂变反应率的结果, 并与裂变室测量结果进行了比较。 探讨了铅屏蔽室大小对测量结果的影响。 To detect the absolute neutron flux in a weak neutron field and restricted space, the fission fragment trapping detector was fabricated and the properties of the detector were studied. In this paper, the detector and shielding chamber used in neutron detection were described and the experimental measurements of the fission rate in specific condition were performed with the detection system and the result has been compared with that obtained by fission chamber. The influence of the shielding chamber on the measured results was analyzed.     

基于10B4C转换体的多层多丝正比室中子探测器模拟

随着国内高通量中子源及中子散射谱仪的快速发展,对高探测效率、高位置分辨、低伽玛灵敏度的位置灵敏型热中子探测器需求日益迫切。目前国际上中子散射谱仪大多数采用了基于3He的热中子探测器,由于当前3He价格昂贵,寻求3He替代型热中子探测器的相关研究任务紧迫。提出了一种基于10B₄C转换体的多层多丝正比室新型二维位置灵敏型热中子探测器,并利用蒙特卡罗模拟软件Geant4和Garfield++对其探测效率、位置分辨、n/γ抑制比等性能展开了详细的模拟研究。结果表明,当多丝正比室单元为40层,阈值为200 keV时,热中子（E=0.025 eV）探测效率可达到~54%,位置分辨为2.6 mm （FWHM）,n/γ抑制比为~107,可以满足大多数中子散射谱仪的需求,为此类探测器设计及实验研究提供了理论依据。As the development of high flux neutron sources and neutron scattering spectrometers in China, more and more neutron detectors with high detection efficiency, high position resolution, high time resolution and low gamma sensitivity are need ungently. 3He based neutron detector is one of the best options. Recently, because of the 3He gas shortage and its expensive price, we must find a new replacement of 3He. A two-dimensional position sensitive neutron detector based on multi-layer Multi Wires Proportional Chambers (mMWPC) with 10B₄C converter was proposed in this paper. The neutron detection efficiency, position resolution and γ compression were simulated with Geant4 and Garfield++. The results show that with 40 layers of neutron convertor, high themal neutron (E=0.025 eV) detection of~54%, best position resolution of 2.6 mm (FWHM) and high n/γ rejection ratio of~107 with the threshold of 200 keV can be achieved, which can meet the requirements of most spectrometers. This simulation results lay a good foundation for the next step of detector construction and test.     

HPGe 探测器晶体尺寸及效率的研究

采用蒙特卡罗方法模拟计算光子的探测效率需对高纯锗( HPGe ) 探测器进行准确的建模。模拟计算研究了HPGe 晶体长度对探测效率的影响,并在空间不同的测量位置对放射源进行测量,将模拟计算与实验测量相结合,对探测器晶体的尺寸进行调整,获得了HPGe 探测器晶体的模拟计算的准确尺寸,并在122s1 332 keV 能量范围内对模拟结果进行了验证。结果表明,在此能量范围内HPGe 探测器的探测效率的模拟计算值与实验测量值的相对偏差大多数在5% 内,并建立点源探测效率与探测器轴向距离的关系。The accurate shape of HPGe detector is needed in order to calculate its detection efficiency with Monte Carlo methods. In our calculation, the influence of the HPGe crystal size on efficiency has been investigated; the final crystal sizes were determined by comparison with experiments and were validated by the experimental efficiency obtained at several source-to-detector positions. The results show that when the crystal dimensions determined are used to calculate the detection efficiency in the energy range 122s1 332 keV, the relative deviations between simulated and most experimental results were within 5%. In addition, the relationship between detection efficiency and axial distance to detector was established.     

Experimental study on scintillation efficiency of ZnO:In to proton response

Film ZnO:In crystal is a good candidate for a scintillation recoil proton neutron detection system and the response of ZnO:In to protons is a crucial point. The energy response of ZnO:In to mono-energetic protons in the range of 10 keV-8 MeV was measured. The experiment was carried out in current mode, and Au foil scattering was employed, where the forward scattering protons were used for exciting the sample, and the backward scattering protons were used for monitoring the beam intensity. According to the result, the yield of light non-linearly depends on proton energy, and drops significantly when proton energy is low. The scintillation efficiency as a function of proton energy was obtained, which is very useful for researching the scintillation recoil proton neutron detection system.     

NaI探测器对23.8 MeVγ射线的效率刻度方法

低能D(d,γ)4He辐射俘获反应截面的研究在聚变领域和天体物理等领域中起到非常重要的作用。由于受到标准γ源能量的制约,在研究D(d,γ)4He反应高能γ射线产额实验过程中不能用标准源进行效率刻度。采用实验测量与计算相结合的方法实现NaI探测器对23.8 MeV γ射线的效率刻度,先对6.13MeVγ射线效率进行实验刻度,然后用蒙卡程序MCNP－4C模拟计算出NaI探测器的效率曲线,再用实验数据与模拟结果进行对比校正,计算出NaI探测器在23.8MeV能量点对γ射线的探测效率。该方法对高能γ射线效率刻度给出了一种参考依据。In the study of D(d,γ)4He radiative capture reactions research, which is very important for fusion and astrophysics, the efficiency calibration of the detector is necessary. Due to the restriction on energy of the standard gamma source, the efficiency calibration of high-energy gamma-rays can not be calibrated by a standard source. In this paper, the method combining the experimental measurements and calculations for the efficiency calibrations of high energy gamma rays is given in the experiment of 6.13MeV gamma rays efficiency calibration using NaI detector, the efficiency curve of which is calculated by MCNP-4C and corrected experimentally. In this case, the detection efficiency of 23.8MeV gamma ray is known. The method provides a reference to high energy gamma ray efficiency calibration.     

Experimental neutron flux measurements with a diamond detector at the QUINTA setup

The operational capability of a diamond detector used to measure the neutron spectrum by the response function on the QUINTA setup [1] installed at the proton beam of the phasotron [2] (Laboratory of Nuclear Problems, Joint Institute for Nuclear Research) was demonstrated in the energy interval of 2.1–20 MeV. The neutron-flux count rate was measured. The energy of neutrons was estimated at 7.4–25.7 MeV based on the diamond-detector response spectrum. The dependence of the diamond-detector response spectra on the angle between the proton beam and the line going through the detector and the center of the QUINTA setup was investigated. The angular anisotropy of the neutron flux was demonstrated. Measurements at different distances from the detector to the QUINTA setup were performed.     

Low energy gamma rays from thermal neutron capture

The beam tubeP2 of the 4 MW FRM pool reactor was used as the neutron source for this nuclear spectroscopy study. An 8.5 and 13.5 cm lithium drifted germanium detector were used as gamma ray detector to measure the low energy prompt photon emissions from thermal neutron capture in 18 elements (12 rare earth elements) having aσ/A value greater than 0.1. The energy region was from 50–500 keV. Energy and intensity of the gamma ray lines are given.     

中国散裂中子源反角白光中子束流参数的初步测量

中国散裂中子源(CSNS)已于2018年5月建设完工,随后进行了试运行.其中的反角白光中子束线(Back-n)可用于中子核数据测量、中子物理研究和核技术应用等多方面的实验.本文报道对该中子束的品质参数测量实验过程以及最终实验结果.实验主要采用中子飞行时间法,利用~(235)U,~(238)U裂变室和~6Li-Si探测器测量了中子能谱和中子注量率,又利用闪烁体-互补金属氧化物半导体探测系统测量了中子束斑的剖面,得到了该束线的初步实验测量结果.其中白光中子的全能谱测量范围eV—100 MeV,给出了不确定度分析;给出了中子注量率两个实验厅位置的满功率值;给出了白光中子在直径60 mm情况下的全能区束斑.通过与模拟结果的比较探讨了以上结果的合理性,并提出了改进计划.这些实验结果为以后该束线的核数据测量和探测器标定实验奠定了基础.     

双层并联碲锌镉探测器制备及性能测试

实验采用并联方法制备了叠层(双层)碲锌镉探测器,并利用241Am@59.54 keV和57Co@122 keV γ射线源测试了其γ能谱特性。相比单层探测器,对于较高能量的57Co@122 keV γ射线,叠层碲锌镉探测器表现出较高的探测效率和光峰值效率,较好地改善了康普顿连续统一体。叠层CZT探测器较之单层探测器,能谱分辨率发生轻微恶化。实验初步表明,通过并联叠加方法制备叠层碲锌镉探测器是可行的,并可推断制备更大厚度的叠层探测器将有利于中高能γ射线能谱测量。     

Measurement of 248Cm/252Cf Cf Spontaneous Prompt Fission Neutron Spectrum

In order to treat the waste material of nuclear power and develop new type of clean nuclear power,it is necessary to measure the neutron adta of long half life nuclei existed in the waste material.The prompt spontaneous neutron spectrum is one of the most important unclear data for new type nuclear power facilities as well as for understanding the mechanism of fission neutron emission.The measurements of ²⁴⁸Cm/²⁵²Cf spontaneous prompt fission neutron spectrum in the neutron energy range form 200keV to 12MeV wer performed by using TOF method.A micro-ionization chamber aws used as fission fragment detector and stibene crystal as neutron detector.The flying paths of neutrons for the measurements were 30cm,50cm and 100cm respectively.The spontaneous prompt fission neutron spectrum of ²⁴⁸Cm was fitted by the Maxwellian distribution and the temperature was determined as (1.401±0.006)MeV in the corresponding neutron energy range.     

Calibration of a Bonner sphere extension (BSE) for high-energy neutron spectrometry

In a recent work, we constructed modular multisphere system which expands upon the design of an existing, commercially available Bonner sphere system by adding concentric shells of copper, tungsten, or lead. Our modular multisphere system is referred to as the Bonner Sphere Extension (BSE). The BSE was tested in a high energy neutron beam (thermal to 800 MeV) at Los Alamos Neutron Science Center and provided improvement in the measurement of the neutron spectrum in the energy regions above 20 MeV when compared to the standard BSS (Burgett, 2008 and Howell et al., 2009).However, when the initial test of the system was carried-out at LANSCE, the BSE had not yet been calibrated. Therefore the objective of the present study was to perform calibration measurements. These calibration measurements were carried out using monoenergetic neutron ISO 8529-1 reference beams at the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany. The following monoenergetic reference beams were used for these experiments: 14.8 MeV, 1.2 MeV, 565 keV, and 144 keV. Response functions for the BSE were calculated using the Monte Carlo N-Particle Code, eXtended (MCNPX). The percent difference between the measured and calculated responses was calculated for each sphere and energy. The difference between measured and calculated responses for individual spheres ranged between 7.9 % and 16.7 % and the arithmetic mean for all spheres was (10.9 ± 1.8) %. These sphere specific correction factors will be applied for all future measurements carried-out with the BSE.     

Be(d,n)反应中子源能谱测量及应用

 利用中子飞行时间技术和BC501A液体闪烁探测器的粒子分辨特性,测量了0°方向、20 MeV氘束轰击厚金属铍靶反应产生的中子源能谱,测量的中子能谱范围为0.7～25.0 MeV。在60°方向放置芪晶体闪烁探测器,由刻度好的BC501A液体闪烁探测器归一校正后,用于中子源强度监测。利用Be(d, n) 反应中子源,采用单粒子灵敏度标定方法,实验标定了0.75~15.75 MeV能量范围内的薄膜闪烁探测器中子能量响应曲线,实验结果与蒙特卡罗模拟计算结果在8%的不确定度范围内一致。     

Small-angle neutron scattering from Pb and 238U between 0.6 and 2.2 MeV

Differential cross sections for neutrons scattered from natural Pb and 99.9 % isotopically pure ²³⁸U have been measured at 0.5°, 1.0°, and 1.5°. A neutron energy continuum was produced by bombarding a thick natural lithium target with a 4 MeV, nanosecond-pulsed proton beam. Neutron energies were determined by time-of-flight techniques. Flight paths from the neutron source to the scatterer and from the scatterer to the detector were each about 5 m. For the 0.5° measurements an annular detector geometry with an angular resolution of ± 0.1° was developed to maximize detection solid angle. Data were averaged over 100 keV intervals from 0.6 to 2.2 MeV and were corrected for backgrounds, multiple scattering and inelastic scattering. Measured cross sections were compared to optical-model calculations which included electromagnetic interactions of neutrons with the nuclear Coulomb field. Inclusion of an induced neutron electric dipole moment interaction was not warranted by the data. The angular dependence of the cross section was fitted with a function $\text{A + B}\text{cot}{}^2\text{case1}\text{2}$θ at each energy. Mean values of B for ²³⁸U are in agreement with theoretical predictions. Values of B for Pb are apparently 15 % too low.