Digital approaches to field neutron spectrometry

Miniature digitising electronics have been coupled to a detector based on an organic liquid scintillator to form a digital neutron and gamma spectrometer. The electronics used are small enough to be packaged with a detector to form an easily portable unit. This miniaturisation has some impact on the achievable sampling rate and resolution, in comparison with the bulkier devices often used for such an application, so it is not clear which of the many pulse shape discrimination algorithms reported in the literature is best suited for use with this device. To explore this, the spectrometer was exposed to a selection of the radiation fields available at NPL, and three different neutron/gamma discrimination algorithms were compared on an equal footing. The energy resolution of the device, and its ease of use, were compared with those of a conventional analogue system.     

Time-of-flight neutron spectrometer for micro sample studies under high pressure

Abstract

A new neutron spectrometer for investigations of elastic and inelastic neutron scattering on polycrystal microsamples under high pressure in diamond and sapphire anvils cells is described. The spectrometer is operating at the IBR-2 pulsed reactor at JINR. The time-of-flight method and ring-shaped multicounter detector are used to register the scattered neutrons. Parameters and methodical peculiarities of the device and the examples of experimental studies are given.     

Application of the Monte Carlo methods and variational procedure for optimizing time-of-flight neutron diffractometer characteristics

Based on variational calculus, a procedure for the optimal approximation of detector surface of the time-of-flight neutron diffractometer has been suggested. The exact solution for a point sample and zero thickness detector has been obtained. Using the shape of the detector surface, an optimized Monte Carlo simulation has been performed for the parameters of the spectrometer depending on the sample size and detector thickness, its azimuthal and Bragg’s angular dimensions, and taking into account the neutron absorption in the sample and detector.     

基于中子飞行时间法的ICF内爆热斑离子温度诊断技术北大核心CSCD

在惯性约束聚变研究中,内爆热斑离子温度反映了热斑能量的高低,对内爆对称性和内爆速度等物理量十分敏感,是理解内爆物理过程不可或缺的重要参数。介绍了一种基于中子飞行时间法的ICF内爆热斑离子温度诊断技术。建立了一种采用塑料闪烁探测器作为中子测量器件的快时间响应中子飞行时间谱仪。谱仪输出时间波形的半高全宽小于1.1ns,上升时间约为0.5ns。描述了基于反卷积运算和低通滤波的飞行时间谱解谱方法。在神光Ⅲ原型装置较低的中子产额和离子温度条件下通过这种诊断技术成功获得了内爆热斑离子温度。     

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根据第一壁后聚变中子通量和能谱的空间分布和 ITER 可能输出的聚变功率、聚变中子产额、第一壁(产氚包层)之后的中子通量的蒙塔-卡罗中子输运(MCNP)计算,对氦冷却固体增殖剂中子学和产氚包层模块(NT-TBM-HCSB)的聚变中子诊断提出概念性设计,本设计提出用固定位置微型裂变室探测器和可移动封装薄箔活化分析系统测量中子倍增器之后、固体氚增殖剂中及其后的中子通量;用可移动天然金刚石探测器的紧凑型能谱仪测量中子能谱。     

反冲质子磁分析技术用于氘氚中子能谱测量研究

介绍了一种基于反冲质子法和磁分析技术的氘氚聚变诊断方法, 适用于稳态及脉冲条件下的等离子体温度、燃料密度和中子产额的精确诊断. 设计了小型的原理性装置, 磁分析器使用高性能钕铁硼二极永磁铁, 焦平面上使用CR-39固体径迹探测器或PIN探测器测量质子位置分布. 使用²³⁹Pu α 源对磁分析器进行了实验标定, 建立了配套的模拟程序. 利用蒙特卡罗方法模拟分析了装置整体性能, 并在K-400加速器上进行了中子实验研究.     

Search for solar neutrons using the data of neutron detector of the PAMELA spectrometer

The study is devoted to the development of the technique for searching for neutrons of solar origin during solar flares using the neutron detector of the PAMELA magnetic spectrometer onboard the RESURS-DK1 satellite. The study of the neutron detector counting rates showed that it operates properly and background conditions are stable in the geomagnetic equator region. 27 solar events from December 2006 to September 2014 were analyzed. Some events contain indications of solar neutron detection. The final conclusion on the nature of these neutrons requires an increase in statistics; to this end, background conditions in polar regions should be analyzed to increase the observation interval.     

SiC基中子探测器对热中子的响应

以SiC二极管和中子转换材料6LiF为基础,研制了SiC基中子探测器,并用241Am源与临界装置分别研究了SiC基中子探测器的粒子响应、热中子响应。结果表明:SiC基中子探测器能够满足241Am源粒子的计数测量,但由于SiC二极管灵敏区薄,故不能用于5.48 MeV的粒子能谱测量;SiC基中子探测器对热中子响应良好,不同功率下,脉冲幅度谱中可清晰看到由6Li(n,)3H的反应产物粒子、3H粒子形成的双峰;脉冲幅度甄别法可将射线及电子学噪声甄别掉;在直接测量与符合测量中,SiC基中子探测器的计数率均与临界装置功率成线性关系,且直接测量的线性度比符合测量的线性度好,最好可达0.999 97。研究表明:降低肖特基接触金属的厚度、增加其外延层厚度、提高其外延层品质,可将SiC二极管用于带电粒子能谱测量。     

Multifunctional pulsed neutron spectrometer IN-06 of INR RAS

The elements of multifunctional neutron spectrometer designed to simultaneously determine the parameters of atomic and supra-atomic structure and the dynamic parameters of the substance in a condensed state were tested. The neutron spectrum was measured by a direct-beam detector placed in the sample position on a 20-meter sample-source path length. Diffraction patterns of industrial diamond powder were obtained in a wide range of transmitted pulses. The resolutions of back-scattering and high-intensity diffractometers were determined.     

聚变中子能谱测量系统脉冲中子灵敏度的实验研究

为多种复杂环境下的稳态和脉冲DT聚变中子能谱测量建立了一种灵敏度优化反冲质子磁谱仪. 使用成像板和同位素α源测量了谱仪的反冲质子能量-位置投影关系. 利用稳态加速器中子源平台、通过单粒子计数方法结合三维带电粒子输运程序模拟,研究了谱仪脉冲中子灵敏度能量响应. 通过高探测效率参数设置使谱仪对DT中子的探测效率达到2×10^-5 cm²水平,从而在较弱中子源上获得了较高统计精度实验数据. 程序模拟结果与谱仪α粒子刻度和DT中子标定实验结果取得了良好的一致性,可由此发展精细解谱技术,以提高脉冲中子能谱测量的灵敏度和能量分辨. 关键词： 聚变中子能谱 磁反冲质子 脉冲中子灵敏度 粒子输运     

用于n,γ混合场的新型脉冲中子探测器研究

新型脉冲中子探测器采用特殊工艺将两个PIN半导体组合而成.利用脉冲γ辐射研究了探测器对γ的响应；利用脉冲中子源研究了探测器对DT中了的响应，并与闪烁探测器进行了比较 .结果表明：脉冲中子探测器对脉冲γ辐射基本不灵敏，对脉冲中子辐射的灵敏程度依赖于中子辐射体，是一种用于n，γ混合脉冲辐射场中子测量的新型探测器. 关键词： 硅半导体 差分补偿 脉冲中子探测器 n γ混合场     

A telescope detection system for direct and high resolution spectrometry of intense neutron fields

A high energy- and spatial-resolution telescope detector was designed and constructed for neutron spectrometry of intense neutron fields. The detector is constituted by a plastic scintillator coupled to a monolithic silicon telescope (MST), in turn consisting of a ΔE and an E stage. The scintillator behaves as an “active” recoil-proton converter, since it measures the deposited energy of the recoil-protons generated across. The MST measures the residual energy of recoil-protons downstream of the converter and also discriminates recoil-protons from photons associated to the neutron field. The lay-out of the scintillator/MST system was optimized through an analytical model for selecting the angular range of the scattered protons. The use of unfolding techniques for reconstructing the neutron energy distribution was thus avoided with reasonable uncertainty (about 1.6% in neutron energy) and efficiency (of the order of 10⁻⁶ counts per unit neutron fluence). A semi-empirical procedure was also developed for correcting the non-linearity in light emission from the organic scintillator. The spectrometer was characterized with quasi-monoenergetic and continuous fields of neutrons generated at the CN Van De Graaff accelerator of the INFN-Legnaro National Laboratory, Italy, showing satisfactory agreement with literature data.     

用于DPF装置中子测量的闪烁体探测器

 介绍了一种用于等离子体焦点装置(DPF装置)中子波形测量的塑料闪烁体探测器,该探测器由ST401型塑料闪烁体、XP2262B型光电倍增管构成。利用银活化中子探测器和DPF装置对该塑料闪烁体探测器进行标定,确定其中子灵敏度为0.022 5 pC每中子,,中子产额测量范围达到10⁹～10¹¹每脉冲,可以满足DPF装置中子参数测量的需要。     

Fast neutron scattering from cesium

A study was made of the(n, n), (n, n′) and (n, n′ γ) reactions which occur when a cesium scattering sample is exposed to mono-energetic neutrons of energies ranging from 120 to 1910 keV. Total cross sections, elastic scattering angular distributions and excitation functions for inelastic scattering were measured with a neutron time-of-flight spectrometer. Results are compared with statistical theory. A 40 cc Ge(Li) detector was used in the time gated mode to measure γ-rays from the (n, n′ γ) reaction. These data were used to refine and extend the energy level scheme derived from the neutron spectroscopy measurements and mainly confirm the results of recent, similar measurements.     

Prototype of a large neutron detector based on MWPC

A prototype of large-area position sensitive neutron detector was designed and constructed according to the requirements of the Small-Angle Scattering spectrometer of China Spallation Neutron Source(CSNS).The detector was based on the 3He neutron convertor and MWPC with an effective area of 650 mm×650 mm.A prototype was completed and tested with 55Fe X-ray.The high-pressure vessel was designed and constructed with high-strength aluminum alloy.A position resolution of about 4.6mm×2.3 mm(FWHM)and efficiency65%for neutrons with wavelength of 1.8?was determined after the operational gas filled.     

ICF中子发射时间诊断

 对ICF中子发射时间的诊断技术进行了研究,研制了基于快闪烁体和微通道板式光电倍增管的中子发射时间探测器。在某大型激光原型装置上进行了中子发射时间的实验测量,成功获得多发实验的中子发射时间与打靶激光脉冲的时间及中子发射时间之间的关系。实验结果表明：中子发射时间探测器对DT中子和DD中子都能够响应,中子产额测量下限达到10⁷,时间测量不确定度小于20 ps;CH烧蚀层越厚,中子发射时间越长。     

A Gorizont neutron reflectometer—small-angle spectrometer based on the IN-06 pulsed neutron source

The Gorizont time-of-flight neutron reflectometer—small-angle spectrometer has been designed, manufactured, and assembled to operate with the IN-0 6 pulsed neutron source. The instrument has a vertical neutron scattering plane enabling research on liquid surfaces and interfaces. Model calculations of neutron spectra, beam profiles, and spectrometer resolutions have been performed via the Monte Carlo method. The spectrometer operates at wavelengths from 1.5 to 9 Å and ensures measurements in the momentum-transfer range of 0.003—1.5 Å^-1.     

Study of a nTHGEM-based thermal neutron detector

With new generation neutron sources, traditional neutron detectors cannot satisfy the demands of the applications, especially under high flux. Furthermore, facing the global crisis in ~3He gas supply, research on new types of neutron detector as an alternative to ~3He is a research hotspot in the field of particle detection. GEM(Gaseous Electron Multiplier) neutron detectors have high counting rate, good spatial and time resolution, and could be one future direction of the development of neutron detectors. In this paper, the physical process of neutron detection is simulated with Geant 4 code, studying the relations between thermal conversion efficiency, boron thickness and number of boron layers. Due to the special characteristics of neutron detection, we have developed a novel type of special ceramic n THGEM(neutron THick GEM) for neutron detection. The performance of the n THGEM working in different Ar/CO_2 mixtures is presented, including measurements of the gain and the count rate plateau using a copper target X-ray source. A detector with a single n THGEM has been tested for 2-D imaging using a ~(252)Cf neutron source. The key parameters of the performance of the n THGEM detector have been obtained, providing necessary experimental data as a reference for further research on this detector.     

Fast neutron scattering from rubidium

A study was made of the (n, n), (n, n′), and (n, n′ γ) reactions which occur when a natural rubidium scattering sample is exposed to mono-energetic neutron fluxes of energies ranging from 120 to 1910 keV. Total cross sections, elastic scattering angular distributions and excitation functions for inelastic scattering were measured with a neutron time-of-flight spectrometer. Results are compared with Hauser-Feshbach theory. A 40 cc Ge(Li) detector was used in the time-gated mode to measure γ-rays from the (n, n′ γ) reaction. The latter measurements were used to refine and extend the energy level schemes derived from neutron spectroscopy. Several new levels were discovered in the low-lying (below 1900 keV) energy level spectra of⁸⁵Rb and⁸⁷Rb. Gamma decay schemes and branching ratios were determined for the low-lying levels of⁸⁵Rb and⁸⁷Rb.     

A capture-gated fast neutron detection method

To address the problem of the shortage of neutron detectors used in radiation portal monitors(RPMs),caused by the ~3He supply crisis, research on a cadmium-based capture-gated fast neutron detector is presented in this paper. The detector is composed of many 1 cm × 1 cm × 20 cm plastic scintillator cuboids covered by 0.1 mm thick film of cadmium. The detector uses cadmium to absorb thermal neutrons and produce capture γ-rays to indicate the detection of neutrons, and uses plastic scintillator to moderate neutrons and register γ-rays. This design removes the volume competing relationship in traditional ~3He counter-based fast neutron detectors, which hinders enhancement of the neutron detection efficiency. Detection efficiency of 21.66% ± 1.22% has been achieved with a 40.4 cm × 40.4cm × 20 cm overall detector volume. This detector can measure both neutrons and γ-rays simultaneously. A small detector(20.2 cm × 20.2 cm × 20 cm) demonstrated a 3.3 % false alarm rate for a ~(252)Cf source with a neutron yield of 1841 n/s from 50 cm away within 15 s measurement time. It also demonstrated a very low(0.06%) false alarm rate for a 3.21 × 10~5 Bq ~(137)Cs source. This detector offers a potential single-detector replacement for both neutron and the γ-ray detectors in RPM systems.