Use of the EUR LiB 15/5 data set for radiation shielding calculations in iron

Abstract

The shielding effect of an iron sphere assembly has been tested for a Pu-α-Be neutron source placed in the center of the shield assembly. Emergent neutron and gamma spectra were measured with a stilbene scintillation counter. Discrimination between neutrons and gammas was achieved by the pulse shape discrimination technique based on the zero crossing method. Calculations have been made using the one-dimensional transport code ANISN-Westinghouse version (ANISN-W) and the EUR LiB 15/5 cross section data set. The agreement between measurements and calculations indicates that the cross section set and the calculation model are suitable for studying the iron shielding experiments over the neutron energy range 1.35–10 MeV and the gamma energy range 0.3–6 MeV. Total macroscopic cross sections for fast neutrons, linear attenuation coefficients for gamma rays and half-value thicknesses for neutrons and gammas for the whole energy range and at different energies have been obtained.     

A neutron beam spectrometer based on a scintillation detector with n-γ pulse shape discrimination

A scintillation spectrometer with pulse shape separation of signals from neutrons and gamma quanta, installed on the RADEX neutron beam channel at the Institute for Nuclear Research is described. The need for n-γ separation is due to the presence of a substantial gamma background at the location of the spectrometer. To optimize n-γ separation, new parameters of the pulse shape separation and methods for calculating them are proposed. Significant improvement in the n-γ separation is obtained. Applying new parameters allows us to use information about only part of the scintillation pulse, enabling the operation of the spectrometer at high count rates and pulse pileup. Such a spectrometer can be used to monitor the RADEX neutron beam channel and determine the energy distribution of neutrons in the beam.     

Radiation attenuation and nuclear properties of high density concrete made with steel aggregates

Abstract

The fast neutron and gamma ray spectra measured behind different thickness of steel scrap concrete with density of 4 g/cm³ have been studied. The mix proportions by weight of this type of concrete were 1 cement: 6.89 steel scrap: 2.9 sand and 0.5 Water. Comparison with a standard ordinary concrete of density 2.3 g/cm³ have been carried out. The measurements were made using a collimated beam of both gamma rays and neutrons emitted from one of the horizontal channel of the Egyptian Research Reactor-1. A fast neutron and gamma ray spectrometer with a stilbene crystal was used to measure the spectra of fast neutrons and gamma rays. Pulse shape discrimination using the zero cross over technique was used to separate the photon pulses from the electron pulses. The equation due to Schmidt has been modified and applied for determining the neutron effective removal cross sections (～_R) for steel scrap, ordinary, hematite–serpentine, ilmenite–limonite and ilmenite concretes. This equation gives results which are in good agreement with the measured values. The derived empirical equation in a previous work to calculate the neutron integral flux behind different thicknesses of different types of concretes, gives good results for steel scrap concrete under investigation comparing with the corresponding experimental data. Total neutron macroscopic cross sections, linear attenuation coefficients for gamma rays and the half-value layers for both radiations at different energies have been obtained for steel scrap concrete and comparing with the corresponding values of ordinary concrete. The results show that steel scrap concrete is better than ordinary, hematite–serpentine, ilmenite–limonite and ilmenite concretes from the radiation shielding point of view.     

Stilbene crystalline powder in polymer base as a new fast neutron detector

A new organic scintillation material consisting of stilbene grains in a polymer glue base is presented. The crystalline grains of stilbene are obtained by mechanical grinding of stilbene single crystals. The resulting composite scintillators have been studied as detectors for fast neutrons.     

Toward a fractal spectrum approach for neutron and gamma pulse shape discrimination

Accurately selecting neutron signals and discriminating 7 signals from a mixed radiation field is a key research issue in neutron detection.This paper proposes a fractal spectrum discrimination approach by means of different spectral characteristics of neutrons and 7 rays.Figure of merit and average discriminant error ratio are used together to evaluate the discrimination effccts.Different neutron and γ signals with various noise and pulse pile-up are simulated according to real data in the literature.The proposed approach is compared with the digital charge integration and pulse gradient methods.It is found that the fractal approach exhibits the best discrimination performance,followed by the digital charge integration method and the pulse gradient method,respectively.The fractal spectrum approach is not sensitive to high frequency noise;and pulse pile-up.This means that the proposed approach has superior performance for effective and efficient anti-noise and high discrimination in neutron detection.     

Neutron light output function and resolution investigation of the deuterated organic liquid scintillator EJ-315

In this paper we investigate the light response to fast neutrons and estimate the pulse height resolution of a deuterated liquid organic scintillator, EJ-315, considering the detector's non-linear light response to gamma-rays. Initially, collision data and a neutron beam trigger are recorded in coincidence mode, and incident neutron energy is calculated with a time-of-flight technique. Fast neutrons are further discriminated from gamma-ray background based on the scintillation material decay patterns using a pulse shape discrimination algorithm. A light response matrix composed of multiple neutron energy and their corresponding light outputs is derived. The pulse height resolution property of the EJ-315 is characterized utilizing the derivatives of the pulse height distributions with corrections of the measurements setup uncertainties. Additionally, the EJ-315's pulse height resolution is also characterized by comparing the smoothed derivatives of quasi-monoenergetic neutron pulse height distributions, given by the Peierls-formula-based analytic model, to match the measurement data. Results show rather consistent 10–13% pulse resolution for mono-energetic neutrons with kinetic energy above 2 MeV. The resolution decreases slightly with an increase in neutron energy indicating the improved resolution performance of EJ-315 in the higher energy events.     

Digital discrimination of neutrons and γ rays with organic scintillation detectors in an 8-bit sampling system using frequency gradient analysis

The feasibility of using frequency gradient analysis (FGA), a digital method based on Fourier transform, to discriminate neutrons and γ rays in the environment of an 8-bit sampling system has been investigated. The performances of most pulse shape discrimination methods in a scintillation detection system using the time-domain features of the photomultiplier tube anode signal will be lower or non-effective in this low resolution sampling system. However, the FGA method using the frequency-domain features of the anode signal exhibits a strong insensitivity to noise and can be used to discriminate neutrons and γ rays in the above sampling system. A detailed study of the quality of the FGA method in BC501A liquid scintillators is presented using a 5 G samples/s 8-bit oscilloscope and a 14.1 MeV neutron generator. A comparison of the discrimination results of the time-of-flight and conventional charge comparison (CC) methods proves the applicability of this technique. Moreover, FGA has the potential to be implemented in current embedded electronics systems to provide real-time discrimination in standalone instruments.     

Digital discrimination of neutrons and γ rays with organic scintillation detectors in an 8-bit sampling system using frequency gradient analysis

The feasibility of using frequency gradient analysis (FGA), a digital method based on Fourier transform, to discriminate neutrons and γ rays in the environment of an 8-bit sampling system has been investigated. The performances of most pulse shape discrimination methods in a scintillation detection system using the time-domain features of the photomultiplier tube anode signal will be lower or non-effective in this low resolution sampling system. However, the FGA method using the frequency-domain features of the anode signal exhibits a strong insensitivity to noise and can be used to discriminate neutrons and γ rays in the above sampling system. A detailed study of the quality of the FGA method in BC501A liquid scintillators is presented using a 5 G samples/s 8-bit oscilloscope and a 14.1 MeV neutron generator. A comparison of the discrimination results of the time-of-flight and conventional charge comparison (CC) methods proves the applicability of this technique. Moreover, FGA has the potential to be implemented in current embedded electronics systems to provide real-time discrimination in standalone instruments.     

Digital pulse shape discrimination methods for n-γ separation in an EJ-301 liquid scintillation detector

A digital pulse shape discrimination system based on a programmable module NI-5772 has been established and tested with an EJ-301 liquid scintillation detector. The module was operated by running programs developed in Lab VIEW, with a sampling frequency up to 1.6 GS/s. Standard gamma sources22 Na,137Cs and60 Co were used to calibrate the EJ-301 liquid scintillation detector, and the gamma response function was obtained. Digital algorithms for the charge comparison method and zero-crossing method have been developed. The experimental results show that both digital signal processing(DSP) algorithms can discriminate neutrons from γ-rays. Moreover,the zero-crossing method shows better n-γ discrimination at 80 ke Vee and lower, whereas the charge comparison method gives better results at higher thresholds. In addition, the figure-of-merit(FOM) for detectors of two different dimensions were extracted at 9 energy thresholds, and it was found that the smaller detector presented better n-γseparation for fission neutrons.     

Study of the Reflected (Albedo) Secondary Gamma Radiation from Different Materials

The experimental measurements of the reflected (albedo) component of the secondary gamma radiation have been carried out for cylindrical samples of graphite, ilmenite limonite concrete and iron of different thicknesses. A collimated beam of neutrons emitted from one of the horizontal channels of the ET-RR-1 reactor have been used. A single stilbene crystal scintillator applying zero crossover technique for the differentiation between gamma and neutron pulses have been utilized. The measured pulse height spectra were transformed to energy spectra. It was shown that the reflected secondary gamma rays increase with the increase of the material thickness then becomes constant. The reflected secondary gamma rays increase also with the increase of the used material density.

Die refleklierte (Albedo) Kompononte der sekundären Gammastrahlung wurde an zylindrischen Proben unterschiedlicher Dicke von Graphit, Ilmenit-Limonit-Zement und Eisen gemessen. Dazu iwurde cin gerichteter Neutronenstrahl verwendet, der aus cinem der horizontalen Kanäle des ET-RR-1 Reaktors emittiert wurde. Ein einzelner Stilbenkristall-Szintillalor wurde zur Unterscheidung der Gamma- und Neutronenimpulse eingesetzt. Es konnte gezeigt werden, daβ die reflektieten sekundaren Gammastrahlen mit der Materialdicke zunächst zunehmen und schlieβlich einen konstanten Wert errcichen. Der reflektierte Anteil der sekundären Gammastrahlen steigt ebenfalls mit der Dichte des verwendeten Materials an.     

电流型探测器单粒子灵敏度标定的原理及应用

采用电荷模数转换记录单个脉冲电荷的方法,标定了单能射线在电流型闪烁探测器中产生的平均电流,从而得到其灵敏度。标定结果与传统的电流法在±8%的范围内一致。该标定方法准确度高,扣除本底容易,对标定源的强度要求也大大降低。加上飞行时间法,还可对粒子进行甄别,能在中子-γ射线混合场中将中子和γ射线的电荷贡献分开,得到探测器对每种射线单独的灵敏度。该方法适用于在单个脉冲电荷信噪比较高的场合下标定脉冲电流型探测器。     

Baseline drift effect on the performance of neutron and γ ray discrimination using frequency gradient analysis

Frequency gradient analysis (FGA) effectively discriminates neutrons and γ rays by examining the frequency-domain features of the photomultiplier tube anode signal. This approach is insensitive to noise but is inevitably affected by the baseline drift similar to other pulse shape discrimination methods. The baseline drift effect is attributed to factors such as power line fluctuation, dark current, noise disturbances, hum, and pulse tail in front-end electronics. This effect needs to be elucidated and quantified before the baseline shift can be estimated and removed from the captured signal. Therefore, the effect of baseline shift on the discrimination performance of neutrons and γ rays with organic scintillation detectors using FGA is investigated in this paper. The relationship between the baseline shift and discrimination parameters of FGA is derived and verified by an experimental system consisting of an americium-beryllium source, a BC501A liquid scintillator detector, and a 5 GSample/s 8-bit oscilloscope. The theoretical and experimental results both show that the estimation of the baseline shift is necessary, and the removal of baseline drift from the pulse shapes can improve the discrimination performance of FGA.     

电流型探测器单粒子灵敏度标定的原理及应用

 采用电荷模数转换记录单个脉冲电荷的方法,标定了单能射线在电流型闪烁探测器中产生的平均电流,从而得到其灵敏度。标定结果与传统的电流法在±8%的范围内一致。该标定方法准确度高,扣除本底容易,对标定源的强度要求也大大降低。加上飞行时间法,还可对粒子进行甄别,能在中子-γ射线混合场中将中子和γ射线的电荷贡献分开,得到探测器对每种射线单独的灵敏度。该方法适用于在单个脉冲电荷信噪比较高的场合下标定脉冲电流型探测器。     

Stilbene composite scintillators as detectors of fast neutrons emitted by a 252Cf source

The results of the measurements are presented of the relative efficiency ε for ²⁵²Cf fast neutron detection by composite detectors based on stilbene crystalline grains. The effects of the grain size and height of the composite detector on its scintillation properties were studied. It is shown that the efficiency of fast neutron detection of stilbene composite scintillators ranges up to 60% of that of bulk single crystals. The results are also presented for relative light output measurements of stilbene composite detectors irradiated by gamma photons of ¹³⁷Cs, as well as transmittance data of samples in the range of their transparency absorption.     

Die Energieverteilung der Neutronen aus einer Po-α-Be-Quelle

The neutrons from a Po-α-Be source were detected via the recoil protons in a stilbene scintillator. The pulse height spectrum of the scintillations produced in the stilbene crystal by the recoil protons is analysed to yield the incident neutron energy distribution. Theγ-ray background was eliminated through pulse shape discrimination. Separately the spectrum of neutrons coincident withγ-rays, i.e. of neutrons from the Be⁹(α,n)C^12* reaction, has been determined. The resulting spectra are compared to previous measurements. The structure of the spectra is not compatible with an isotropic angular distribution of the neutrons relative to theα-direction. Furthermore it could be shown that the fraction of reactions leading to the 7,65 MeV state of C¹² is only about 10^?3.     

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。     

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。     

Fast-neutron spectrum measurement by a stilbene scintillation spectrometer

A stilbene scintillation spectrometer for continuous fast-neutron spectra measurement is described in this paper. Discrimination of gamma rays is achieved by utilizing differences in the shapes of scintillation pulses produced by recoiled protons and electrons. In addition, results of measurements of fast-neutron spectra of the reactor beam are given.     

A comparison of different discrimination parameters for the DFT-based PSD method in fast scintillators

Although the discrete Fourier transform (DFT) based pulse shape discrimination (PSD) method, realized by transforming the digitized scintillation pulses into frequency coefficients by using DFT, has been proven to effectively discriminate neutrons and γ rays, its discrimination performance depends strongly on the selection of the discrimination parameter obtained by the combination of these frequency coefficients. In order to thoroughly understand and apply the DFT-based PSD in organic scintillation detectors, a comparison of three different discrimination parameters, i.e. the amplitude of zero-frequency component, the amplitude difference between the amplitude of zero-frequency component and the amplitude of base-frequency component, and the ratio of the amplitude of base-frequency component to the amplitude of zero-frequency component, is described in this paper. An experimental setup consisting of an Americium–Beryllium (Am–Be) source, a BC501A liquid scintillator detector, and a 5Gsample/s 8-bit oscilloscope was built to assess the performance of the DFT-based PSD with each of these discrimination parameters in terms of the figure-of-merit (based on the separation of the event distributions). The third technique, which uses the ratio of the amplitude of base-frequency component to the amplitude of zero-frequency component as the discrimination parameter, is observed to provide the best discrimination performance in this research.     

Analog states of 7He observed via the 6He(p,n) reaction

Isobaric analog states of 7He have been investigated by a novel technique involving the observation of the resonant yield of neutrons from the 6He(p,n) reaction in coincidence with gamma rays from the decay of the (0(+),T=1) state in 6Li. The gamma rays provide a clean signature for the isospin-conserving neutron decay of the low-lying isobaric analog resonances. It is conclusively shown that the analog of the recently observed low-lying spin-orbit partner of the 7He ground state does not exist. Evidence is presented that this state lies at much higher energies, in agreement with microscopic calculations.