Development of a passive fast-neutron spectrometer based on electrochemically etched CR-39 detectors with radiators and degraders

In the present paper we describe, first, our theoretical and experimental work to determine the registration properties of electrochemically etched (ECE) CR-39 detectors to protons. Here, we have irradiated CR-39 detectors with monoenergetic protons over the energy range of 0.6 to 6 MeV, at normal incidence, and found that the lower and upper limits of protons energies that can yield ECE spots in CR-39 are ~ 50 keV and ~ 2.2 MeV, respectively. The ECE registration limits at other angles have been determined by attuning the calculated response of bare CR-39 to the experimental response values. The paper then proceeds to describe a technique developed by us for the energy-selective fast-neutron detection. This technique is based on the ECE spot-density measurements in CR-39 detectors placed in conjunction with judiciously chosen thicknesses of a polyethylene radiator and a lead degrader (or absorber). The optimum thicknesses of the radiator and degrader. for a given neutron energy, are determined from computer calculations.     

Application of CR-39 Track Detector to Neutron Spectrum Measurement

A new technique for estimating the neutron energy spectrum with CR-39 track detectors has been proposed for application to a singly pulsed neutron field where prevailing counters cannot operate properly. The CR-39 sample exposed to neutrons was intermittently etched, then the major and minor radii of respective etch pits were measured for each etching stage and the growth curve was obtained. The analysis method of growth curves was also designed, with which both the energy and the angle of recoil protons could be evaluated and converted into the energy of neutrons incident normally.

The neutron irradiation experiments were carried out with the 46 MeV electron linear accelerator at the Research Reactor Institute, Kyoto University. It was confirmed from comparing with the reference spectrum measured by the neutron time-of-flight method that the present growth-curve method is useful for the estimation of the neutron energy distribution between about 0.3 and 2 MeV. Moreover, we have experimentally examined the unfolding method suggested by Matiullah and Durrani in order to extend the application of CR-39 detector to higher energies.     

An elgenvalue and eigenfunction study of time-dependent fast-neutron spectra in 232Th

The pulsed problem for fast neutrons in Th has been studied using the multigroup diffusion equation and eigenfunction expansion method. The time-dependent fast-neutron spectra have been obtained up to 8000 ns inside Th systems with buckling ranging from 0.0 to 0.015 cm⁻². The results have been obtained using the 27-group BARC data set. It has been shown that for a fast Th system, unlike a fast U system, all the time eigenvalues lie in the continuum and no discrete time eigenvalue exists. A fast Th system behaves more like a non-multiplying system. The spectra shift continuously to lower energies with increasing time. However, pseudo-asymptotic conditions are established in certain time intervals. The start of pseudo-equilibrium conditions and the duration for which they persist is seen to increase with decreasing buckling. The reason for the establishment of pseudo-equilibrium conditions has been discussed. The theoretical results for the instantaneous decay constant inside a 40 cm cube of Th have been compared with the experimental results of Moo et al. (1973). The present results are in good agreement with the above experimental results based on the ²³⁹Pu detector.     

Track formation in CR-39 detector exposed to D-T neutrons

The characteristic response of CR-39 track detectors exposed to a D-T neutron field has been investigated both experimentally and theoretically. In order to discriminate the etched tracks due to neutron-induced particles from those of protons secondarily generated near a tritium target, we developed a new technique based on intermittent chemical etching. The intrinsic efficiency for D-T neutron detection with bare CR-39 was thereby estimated to be about (7−8) × 10⁻⁵ pits/n. A theoretical calculation has also been carried out with a special attention to the angular dependence of differential cross sections for all constituent elements and the characteristic response to carbon and oxygen ions as well as protons and α-particles. These results suggest that the etch pits are mainly due to heavy recoils; in other words, the contribution of proton recoils to the efficiency is extremely small.     

Experimental Study of CR-39 Etched Track Detector for Fast Neutron Dosimetry

The CR-39 detectors were irradiated with three kinds of fast neutrons and etched in several alkaline solutions. Size distributions of etch-pits were obtained from analysis of micro- photographs. An automatic image analyzer was used to obtain the density of etch-pits. When etching conditions were kept at 30% KOH, 90°C and 1 h. the sensitivity was found to be 3.8xlO^?4, 4.9 xlO^?4 and 2.4 x10^?4for fission, Am-Be and 14 MeV neutrons, respectively. From analysis of increasing rate of the sensitivity, it was found that the track density in CR-39 roughly corresponded to the density of elastic scattering with H, C and O in the case of Am-Be and 14 MeV neutrons, however, the track density was somewhat smaller than the elastic scattering density in the case of fission neutrons. The size of etch-pits increased with neutron energy. The etching time could be reduced to less than 1/10 as a result of a rising from 60 to 90°C. After due consideration of background counts, a dose equivalent of 0.2 mSv could be measured with this system.     

CR-39 detector based thermal neutron flux measurements, in the photo neutron project

PhoNeS (photo neutron source) is a project aimed at the production and moderation of neutrons by exploiting high energy linear accelerators, currently used in radiotherapy. A feasibility study has been carried out with the scope in mind to use the high energy photon beams from these accelerators for the production of neutrons suitable for boron neutron capture therapy (BNCT). Within these investigations, it was necessary to carry out preliminary measurements of the thermal neutron component of neutron spectra, produced by the photo-conversion of X-ray radiotherapy beams supplied by three LinAcs: 15 MV, 18 MV and 23 MV. To this end, a simple passive thermal neutron detector has been used which consists of a CR-39 track detector facing a new type of boron-loaded radiator. Once calibrated, this passive detector has been used for the measurement of both the thermal neutron component and the cadmium ratio of different neutron spectra. In addition, bubble detectors with a response highly sensitive to thermal neutrons have also been used. Both thermal neutron detectors are simple to use, very compact and totally insensitive to low-ionizing radiation such as electrons and X-rays. The resultant thermal neutron flux was above 10⁶ n/cm²s and the cadmium ratio was no greater than 15 for the first attempt of photo-conversion of X-ray radiotherapy beams.     

热释光个人中子剂量计的刻度及性能试验

本文叙述了用作个人剂量监则的镉帽型热释光子中子剂量计的中子能响特性和刻度方法。用标准Ａｍ－Ｂｅ中子辐射场测量了剂量计的响应因子，检验了反平方律。给出了相对刻度的总不确定度为７．６％。对油田中子测井和使用中子水份测量仪等测量仪器的单位，可用该剂量计作个人中子防护剂监测。     

15MV医用电子直线加速器光核中子剂量分布的MC模拟及测量

医用电子直线加速器产生的X射线已广泛应用于放射治疗过程,X射线与机头中的高Z物质(铅、钨、铜和铁)发生(γ,n),(γ,2n)反应产生一定量的中子,引起与治疗无关的中子剂量。本文对工作在15MV能量档的Prim μs-M型医用电子直线加速器在标准照射野10cm×10cm内治疗平面的光中子剂量分布,进行了Monte-Carlo模拟,并使用CR39固体核径迹探测器和中子气泡探测器(NBD)进行了实验测量。研究发现,测量与模拟的中子剂量之间最大偏差约±30%,其最主要的原因是由于"加速器产生的光核中子与物质发生非弹性散射反应"而逐步降低能量,产生了低于上述两种探测器阈能(100keV)的中子,使测量值比模拟值偏低。研究结果为X射线放射治疗中减低污染中子剂量的优化设计提供了基础数据。     

一种新型中子剂量当量仪的能量响应性能分析

介绍了对一种新型中子剂量当量仪的能量响应性能的分析.用MCNP程序分别计算了它的各探测单元的中子注量能量响应,并按照中子剂量当量指示值的算法计算了它的中子周围剂量当量能量响应性能,从计算结果看,在热中子～15 MeV的能量范围内它的能量响应变化范围大约在0.55～1.95之间.计算了它在Am - Be源和Cf - 25...     

Interaction of 960 MeV/nucleon- 238U ions with light target atoms of CR-39 polycarbonate

CR-39 plastic track detectors have been employed both as the target and as the detector to study the interaction of 960 MeV/nucleon-²³⁸U ions with light target atoms (hydrogen, carbon, and oxygen), the constituents of CR-39. The experimental value of the mean free path (mfp) for the relativistic uranium ions has been obtained and compared with the value computed theoretically. The range of the uranium ions has been found to be 6.5 cm in the composite medium of CR-39 track detectors. The average multiplicity due to fission of the uranium projectiles in CR-39 track detecting medium has been found to be 2.1, which indicates that binary fission is the most common mode of interaction.     

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.     

空间重离子的鉴别

采用地面加速的重离子模拟空间重离子标定了CR－39固体核径迹探测器，通过物理分析和计算方法获得了一个数学表达式，这样就可以通过CR－39固体核径迹探测器上径迹的测量进行离子鉴别和能量估计。     

A fast-neutron pulse reactor

In June, 1960, criticality was reached on the fast-neutron pulse reactor constructed at the United Institute of Nuclear Studies. The fast-neutron pulse reactor is designed to work under periodic pulse conditions at a mean power output of about 1 kw. The power pulses are developed from the multiplication of prompt neutrons during an interval in which the reactor is in a supercritical state. The half-width of the power pulses is 36 microseconds, and the pulse repetition frequency may be varied between the limits 8–80 pulses/sec.     

含硼织物与透明树脂板中子屏蔽性能研究

测量了含硼织物和透明树脂板的辐射屏蔽性能、浓缩硼树脂板的耐辐照性能及含钆树脂板的热中子俘获γ辐射效应，并对有关问题进行了讨论。     

Relative Yield and Period of Individual Groups of Delayed Neutrons in 233U, 235U, and 239Pu Fission by Epithermal Neutrons

The relative yield of delayed neutrons and the half-life of their precursor nuclei in fissioning of ²³³U, ²³⁵U, and ²³⁹Pu by epithermal neutrons are measured on a setup which is based on a KG-2.5 electrostatic accelerator. The experimental samples are irradiated in a polyethylene cube, one face of which is irradiated by a neutron beam consisting of T(p, n)³He neutrons. A procedure is developed for averaging the group parameters of delayed neutrons from different series of measurements, taking account of their correlation. A comparative analysis of the data of this work and in ENDF/BVI in terms of the average half-life of the precursor nuclei of the delayed neutrons and using the dependence of the reactivity on the asymptotic period of the reactor is performed.It is shown that the data of this work agree, to within the uncertainty limits, with the recommended experimental data and differ substantially from the ENDF/BVI data.     

CR-39 plastic for massive magnetic monopole search

A new CR-39 plastic containing a small amount of antioxidants (Naugard-445) has been developed for use in a search for massive magnetic monopoles. Its characteristics have been investigated from the standpoint of the “heavy etching method”, which was proposed several years ago. The results are compared with those of pure CR-39 plastics measured under the same conditions.     

Modular next generation fast-neutron detector for portal monitoring

Nuclear nonproliferation is of critical importance for global security.Dangerous fissile materials including highly enriched uranium and weapons-grade plutonium are especially important to detect.Active interrogation techniques may result in much better sensitivity but are difficult with conventional portal monitors that rely on detecting thermal neutrons.Also,most conventional portal monitoring systems rely on³He,which has a finite and continually decreasing supply.By designing a hig...     

γ-Ray spectra excited in inelastic scattering of fast neutrons on manganese,aluminum, iron,copper, tin,and antimony

The study of inelastic scattering of fast neutrons is an important problem of both theoretical and practical interest. From the theoretical point of view the importance of this work lies in the possibility of obtaining data concerning levels in stable nuclei. The practical value arises in connection with the important role played by inelastic scattering of neutrons in fast-neutron reactors as well as the fact that the extension of reactor theory to fast-neutron reactors requires data on the spectra of inelastically scattered neutrons [1, 2]. In this connection the necessity for developing a neutron spectrometer for fast neutrons and-spectroscopy for inelastic neutron scattering is obvious. In the last 5–7 years a great deal of work has been devoted to this problem.The present work reports on measurements of-ray spectra excited in inelastic scattering of 2.8 Mev neutrons by manganese, aluminum, iron, copper, tin and antimony. The measurements were carried out with a scintillation spectrometer consisting of an NaI(Tl) crystal, a FEU-1B photomultiplier and a 50-channel pulse-height analyzer with a magnetic-drum memory. The spectrometer resolution was 6.5–7% for-rays from Co⁶⁰.-Rays of the following energies (Mev) were found: in manganese 0.97, 1.41, 1.92, 2.3; in aluminum 0.84, 1.00, 1.80, 2.16; in iron 0.84, 1.25, 1.46, 1.70; in copper 0.63, 0.78. 0.96, 1.12, 1.38, 1.46, 1.72, 2.03; in tin 0.84, 1.16, 1.50, 1.80, 2.16; in antimony 1.04, 1.50, 1.84, 2.16.Abbreviated version of a paper appearing in the Ukrainian Journal of Physics.The authors wish to take this opportunity to thank L. M. Beliaev and G. F. Dorbrzkanskii of the Institute of Crystallography, Academy of Sciences, USSR for making the NaI(TI) crystal and for kndly allowing us to use it in carrying out the present work.