Neutron response calculation on the basis of variable track etch rates along the secondary particle trajectories in CR-39

The calculation of the response of CR-39 detectors exposed to neutrons is of high importance for their dosimetric application. A computer code system has been developed for this purpose. Whereas the generation of secondary charged particles is carried out using non-analogue Monte-Carlo techniques with variance reduction the simulation of the track formation process is treated without any free parameter starting from the etch rate ratio V(REL) only. Results are given for the contribution of recoil protons to the response as a function of the neutron energy and angle of incidence. Furthermore, the influence of an external radiator has been studied. The comparison of the calculated values with experimental data confirm the reliability of the track etch model applied.     

Fast Neutron Sensitivity of TL Detectors using Proton Radiator Techniques

TL materials have a small intrinsic sensitivity for fast neutrons. In order to increase this sensitivity one uses hydrogen containing radiators giving recoil protons as a result of the neutron interaction. By combining the proton radiator technique with the use of TL detectors having various glow peaks with a different response to recoil protons an additional sensitivity yield can be reached. The paper deals with the calculation procedure for the (radiator) sensitivity component. For the LiF phosphors TLD-600 and TLD-700 calculated and experimentally determined fast neutron sensitivities are presented for the glow peaks V and VII. The results show that for accident dosimetry a sufficient agreement of the dedector response with the dose-to-fluence conversion factors is obtained.     

塑料闪烁光纤在高能中子辐照下质子分布特性的数值模拟

 利用Geant4系统模拟了在高能中子照射下,塑料闪烁光纤中产生的反冲质子的分布特性,分析了入射中子能量分别为2,4,6,8 MeV时,产生的反冲质子能量和方向分布,给出了反冲质子在不同方向上的能量分布。结果表明:向前和向后出射的质子分布不对称;反冲质子的能量在零与入射中子能量之间连续地分布;接近垂直入射方向产生的质子数较多;入射中子能量越高,产生质子数越少;反冲质子的出射角度越小,其能量越大,即沿着入射中子方向的反冲质子能量较大,垂直入射方向的反冲质子能量较小。     

High-energy neutrons emitted after muon capture in 40Ca

The energy spectrum of neutrons emitted after ω-capture in ⁴⁰Ca has been measured up to the kinematical endpoint of 92 MeV using two recoil telescopes. The neutron energy was deduced from the energy and angle of recoiling protons which originate from interactions of neutrons in a liquid scintillator. The neutron spectrum above 30 MeV is reproduced fairly well by a simple calculation based upon a reaction mechanism in which the muon is adsorbed, like in pion capture, by a pair of nucleons.     

GEANT4 Monte Carlo simulation response of parallel plate avalanche counter for fast neutrons detection

In the present study, GEANT4 based Monte Carlo codes have been employed to evaluate parallel plate avalanche counter (PPAC) response for fast neutron detection. In order to detect fast neutrons, a thin polyethylene layer is coated on the surface of the electrode of the PPAC. Neutrons entering the converter produce protons which enter the counter and are detected. Fast neutrons in the energy range of 4.0 MeV–20.0 MeV have been transported onto the PPAC surface using GEANT4 MC code. The performance of the PPAC counter has been evaluated by means of simulation by employing QGSP_BERT_HP and QGSP_BIC_HP physics lists. The detection efficiencies of polyethylene-coated PPAC are 1.69 × 10^?2 and 1.86 × 10^?2 using converter thickness of 1 mm and 2 mm, respectively. The obtained results are discussed in detail.     

ICF中子产额测量中统计涨落分析及计算

 塑料闪烁探测器通常用来测量氘氘、氘氚聚变中子产额。中子在闪烁体中产生的质子数的统计涨落及质子在闪烁体中沉积能量的统计涨落为测量结果引入了两项不确定度分量。以氘氚聚变中子为例,分析了这两种统计涨落的概率密度函数的计算方法,该计算方法也适用于其它能量的单能快中子和塑料闪烁体作用的相应计算。     

Calibration factor for estimating personal dose equivalent with imaging plates

A personal imaging plate (IP) dosimeter is in the process of being developed for neutron fields using the BaFBr:Eu²⁺ phosphor. A configuration incorporating a polyethylene radiator placed before the IP detector is used to produce protons via (n,p) elastic scattering. For a dosimeter sensitive to thermal neutrons, a Nylon plate ( thick) is placed between the polyethylene (1.2 mm thick) radiator and the IP ( thick sensitive layer) detector to produce protons via the ¹⁴N(n,p)¹⁴C reaction. Dosimeters having these configurations have been exposed to neutrons from ²⁴¹Am–Be and ²⁵²Cf sources at the Institute for Radioprotection and Nuclear Safety of Cadarache at angles of 0 (normal incidence), 30 and 60 and several dose equivalents. The personal dose equivalent response in terms of H_p(10) is evaluated from the net measured photostimulated luminescence densities (). The calibration factor obtained for estimating the personal dose equivalent with this dosimeter is for ²⁴¹Am–Be and for ²⁵²Cf.     

介质型脉冲高能中子探测器

首次报道一种基于反冲质子法和高速带电粒子在物质表面引起二次电子发射的高能中子探测方法,研制成功的新一代强流脉冲高能中子探测器,即介质型脉冲高能中子探测器.与传统的强流脉冲中子探测器相比,该探测器对中子的探测及信号的传输过程是在介质中完成的,因而不需要真空和高压也可以正常工作,并具有多项优异的物理性能.该探测器的输出信号来自于高能中子在聚乙烯转换靶产生的高能反冲质子和这些质子穿越电荷收集极表面时产生的部分二次电子.选择适当的卡阈吸收片和电荷收集极材料,二次电子在探测灵敏度中的份额及其随能量的变化可由实验测定.     

Improvement of neutron detection efficiency with high sensitive CR-39 track detector

Two subjects have been studied for establishing an efficient detection technique applicable to neutrons with an energy higher than 20 MeV, for which personnel dosimetry becomes more important especially in space activities and radiation protection around high-energy accelerators.

A performance of a new sensitive detector, recently developed copolymer of CR-39 and N-isopropylacrylamide, was checked in a D–T neutron field. It was confirmed experimentally that its sensitivity was several times as high as a pure CR-39 in the radiator effect and more than twice in the total efficiency. In the other experiment, CR-39 samples were exposed to 65 MeV quasi-monoenergetic neutrons, and the registration characteristics have been investigated from a fundamental point of view. The particles recorded were divided into three groups of proton relatives, -particles and heavy ions by applying the growth curve method and the multi-step etching technique. The measured fractions were in good agreement with the values calculated by SSNERS code previously developed.     

Slow and fast neutron detection using bare CN-85 cellulose nitrate detectors

We report on the application of CN-85 cellulose nitrate track detectors to neutron dosimetry. CN-85 has the ability to register proton tracks and therefore can be used for neutron detection via neutron-induced recoil events within the detector matrix. The CN-85 detectors were used to study the distribution of the weakly moderated spallation neutrons, produced in the irradiation of an extended Pb-target with 1 GeV protons. The results obtained are compared with Monte Carlo simulations using the MCNPX-2.5.c code. The thermal and epithermal neutrons can also be detected by CN-85 detectors without the need for a neutron converter via the ¹⁴N(n, p)¹⁴C reaction, which has a positive Q-value of 626 keV.     

Quasifree photoproduction of eta mesons off the neutron

Quasifree photoproduction of eta mesons off nucleons bound in the deuteron has been measured with the CBELSA/TAPS detector for incident photon energies up to 2.5 GeV at the Bonn ELSA accelerator. The eta mesons have been detected in coincidence with recoil protons and recoil neutrons, which allows a detailed comparison of the quasifree n(gamma,eta)n and p(gamma,eta)p reactions. The excitation function for eta production off the neutron shows a pronounced bumplike structure at W=1.68 GeV (E{gamma} approximately 1 GeV), which is absent for the proton.     

几种不同材料降能器对200 MeV质子放疗特性的蒙特卡罗模拟

能量选择系统是医用质子回旋加速器放疗系统中极其重要的部件,主要用来调节质子束能量,使得从加速器出来的质子束能量满足临床治疗计划的要求。能量选择系统的核心部件是降能器,目前降能器大多采用石墨作为降能材料。近些年提出用铍或者碳化硼替代石墨作为降能器材料的设想,以期望提高质子束流的传输效率。利用蒙特卡罗软件TOPAS模拟200 MeV质子在石墨、铍和碳化硼三种不同材料多楔形结构降能器中的输运过程,统计了穿过降能器后质子以及产生的次级中子的能量通量,并计算了质子束流在穿过不同降能器后的能量分散,据此得到了三种材料降能器厚度与质子能量之间的关系曲线,同时也分析了不同降能器对质子束传输效率的影响以及次级中子产额的情况。通过对比发现,三种材料降能器对束流的能量发散效果相当,而使用铍或者碳化硼都能提高束流传输效率,尤其铍降能器的性能较优。但铍和碳化硼与质子相互作用会产生更多的次级中子,因此在实际应用时需要更多地考虑次级中子对设备的辐射防护。Energy selection system (ESS) is an important component for medical proton cyclotron system. It has been widely used to modulate the proton energy in accordance with treatment requirements. ESS consists of the energy degrader which was mostly made of graphite. Recent years, to improve the transmission efficiency of the proton beams, beryllium and boron carbide have been proposed to substitute the graphite. In this work, the Monte Carlo code, TOPAS, was used to simulate the transport process of 200 MeV proton beams traversing the multi-wedge energy degrader made of graphite, beryllium and boron carbide, respectively. Energy fluxes of the protons and secondary neutrons after degrader, as well as the energy dispersion of the degraded proton beams, were calculated. It is found that the energy dissipation effect is nearly identical for all three kinds of degrader material, but using the beryllium or even boron carbide can improve the proton transmission efficiency. However, more secondary neutrons would be produced when proton beams interact with the beryllium and boron carbide, suggesting the need of additional consideration for radiation shielding to devices.     

Possibilities of using synthetic polymers in nuclear emulsions for the dosimetry of fast neutrons

The study contains the results obtained in the process of the preparation and study of the properties of nuclear emulsion of a new type made especially for fast neutron dosimetry.Synthetic hydrophilic polymers were used for the preparation of the emulsion and the sensitivity to fast neutrons — by the detection of recoil protons — was increased by enriching the emulsion with elementary hydrogen and by the use of additive recoil proton radiators.The dosimetric results obtained with this emulsion are compared with the results achieved by various authors with the gelatine emulsions used up to now.     

Modelling of fusion-reaction protons measurements within TEXTOR facility

This paper describes the computation of fusion protons detection efficiency, which has been carried out by means of the known GOURDON code. For this purpose an analytical model of the tokamak magnetic field has been used. Computer simulations of different trajectories of charged particle, on the basis of the motion equations, have been performed with the GOURDON code. Detection efficiency, defined as the ratio of the number of detected particles to that of particles emitted from plasma, has been calculated. The transparency function of the detector system has been derived for given geometry of the ion-pinhole camera. Calculations have been carried out for the detector position used in recent experiments. The poloidal-and toroidal-symmetry of plasma and standard fusion-product source profile have been assumed. The computed detection efficiency is presented as a function of the main radius and particle pitch-angle for different spatial orientations of the detector head.     

一种用于DT聚变诊断的新型中子谱仪的设计

介绍了一种基于反冲质子法和磁分析技术的新型DT聚变中子谱仪, 能够以高信噪比对9—17MeV的中子能谱进行精确测量, 适用于稳态及脉冲条件下的等离子体温度（T_i）和燃料面密度（<ρR）的诊断, 对14 MeV的初级DT中子具有约4%的能量分辨率和约10-8的探测效率。谱仪的磁分析系统使用高性能钕铁硼二极永磁铁建造, 焦平面上使用CR-39固体径迹探测器测量反冲质子的位置分布。使用239Pu α源对磁分析系统进行了实验研究,并建立了配套的粒子输运模拟程序。 结合实验和程序模拟结果,使用蒙特卡罗软件模拟分析了谱仪整体性能。 谱仪结构紧凑、性能良好且适用于稳态及脉冲辐射场,可望在未来的聚变研究中得到有效应用。 Design of a novel spectrometer for measurements of neutrons in the energy range 9—17 MeV has been proposed. Based on proton recoil method and magnetic analyzing technigue, the spectrometer can be used to determine DT fuel areal density(<ρR) and ion temperature under steady state and pulsed radiation field. The detection efficiency is about 10-8 for measuring 14 MeV neutrons with an energy resolution of about 4%. A neodymium iron boron permanent dipole was used for the magnetic analyzing system and CR-39 track detectors were used in the focal plane. The system has been tested with 239Pu α suorce and a corresponding particle transport simulation program has been worked out. Performance of the spectrometer was investigated with Monte Carlo simulation, experiment data and the transport simulation. Due to its good performance, compact structure,and availability for both steady state and pulsed radiation field, the spectrometer can be effectively used for fusion research in the future.     

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.     

Computer studies of detection efficiency of fast-neutron spectrum based on PADC using the Monte Carlo method

A FORTRAN code for simulation of SSNTD detection efficiency is designed using the Monte Carlo method in this work. The theoretical basis for the fast-neutron spectrum measurement based on the assembly of PADC¹ detector+radiator+degrader is described. The main principle of this technique is that, the recoiled protons produced in the radiator by fast-neutrons can be slowed down in the degrader and only protons of energies within a limited range can be detected by PADC (proton energy within the PADC detection energy window). Therefore with a set of different-thickness degraders one can measure the fast-neutron spectrum. Studies show that the program can give reasonable results.     

Radiator effect on plastic nuclear track detectors for high-energy neutrons

The effect of radiators supplying charged particles to plastic nuclear track detectors has been investigated both experimentally and theoretically in order to apply them to personal dosimeters for high-energy neutrons. Performance of four types of radiator materials, CH₂, CD₂ (deuterized hydrocarbon), LiF (lithium fluoride) and C (graphite), was checked in a quasi-monoenergetic neutron field generated by p-Li reactions. The efficiency has been numerically calculated based on a model with a special attention to the angular dependence of cross sections and data of characteristic response to light ions. The effect of respective radiator candidates has been evaluated as a function of the neutron energy. A two-layer radiator has also been proposed to adjust the energy dependence of the relative sensitivity to conversion factor for dose-equivalent.     

Centrality of the collision and random matrix theory

I discuss the results from a study of the central 12CC collisions at 4.2 A GeV/c.The data have been analyzed using a new method based on the Random Matrix Theory.The simulation data coming from the Ultra Relativistic Quantum Molecular Dynamics code were used in the analyses.I found that the behavior of the nearest neighbor spacing distribution for the protons,neutrons and neutral pions depends critically on the multiplicity of secondary particles for simulated data.I conclude that the obtained results offer the possibility of fixing the centrality using the critical values of the multiplicity.     

质子和中子在硅中位移损伤等效性计算

基于蒙特卡罗软件Geant4,探讨质子与硅的库仑散射和核反应及中子与硅的核反应产生反冲原子沉积非电离能量的过程,建立质子和中子在硅中的非电离能量阻止本领计算方法。在此方法中,描述了原子间库仑散射的物理过程,模拟带电粒子与晶格原子之间的屏蔽库仑散射。计算得到不同能量质子和中子在硅中因库仑散射和核反应产生反冲原子的非电离能量沉积及阻止本领的等效性,计算结果与中子ASTM标准及文献计算得到的质子数据符合很好。