中能重离子碰撞中前平衡核子发射的同位旋效应

利用同位旋相关的输运理论,研究了中能重离子碰撞中丰中子和缺中子碰撞系统在较宽能区范围内前平衡发射核子的同位旋效应.结果表明除低能区外,在100MeV/u以上核子–核子碰撞动力学效应起主要作用的能区,前平衡发射的中子–质子比仍然对介质中核子–核子碰撞截面的同位旋效应不灵敏,然而对于对称势的改变非常灵敏.故从低能量到较高能量的较大能区内,前平衡发射的中子–质子比的理论值与实验值的比较是提取对称势形式和强度的灵敏探针.     

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。     

Neutron fluences and dose equivalents measured with passive detectors on LDEF

Neutron fluences were measured on LDEF in the low energy (< 1 MeV) and high energy (> 1 MeV) ranges. The low energy detectors used the ⁶Li(n,)T reaction with Gd foil absorbers to separate thermal (< 0.2 eV) and resonance (0.2 eV−1 MeV) neutron response. High energy detectors contained sets of fission foils (¹⁸¹Ta, ²⁰⁹Bi, ²³²Th, ²³⁸U) with different neutron energy thresholds. The measured neutron fluences together with predicted spectral shapes were used to estimate neutron dose equivalents. The detectors were located in the A0015 and P0006 experiments at the west and Earth sides of LDEF under shielding varying from 1 to 19 g/cm².

Dose equivalent rates varied from 0.8 to 3.3 μSv/d for the low energy neutrons and from 160 to 390 μSv/d for the high energy neutrons. This compares with TLD measured absorbed dose rates in the range of 1000–3000 μGy/d near these locations and demonstrates that high energy neutrons contribute a significant fraction of the total dose equivalent in LEO.

Comparisons between measurements and calculations were made for high energy neutrons based on fission fragment tracks generated by fission foils at different shielding depths. A simple 1-D slab geometry was used in the calculations. Agreement between measurements and calculations depended on both shielding depth and threshold energy of the fission foils. Differences increased as both shielding and thereshold energy increased. The modeled proton/neutron spectra appeared deficient at high energies. A 3-D model of the experiments is needed to help resolve the differences.     

A pulsed neutron source on the proton beam for the Moscow Meson Factory

A new pulsed neutron source based on a beam-blanking device has been under construction and improvement at the Moscow Meson Factory of the Institute for Nuclear Research of the Russian Academy of Sciences. Neutrons are generated in the course of the spallation process in a water-cooled tungsten target by a proton beam with an energy of 209 MeV. After water moderator (3 cm), neutrons are guided in three horizontal and one vertical channels with a length varying from 4 to 50 m. The standard duration of the proton pulse from the accelerator is 60 μs. At present, the average proton current is as high as 150 μA for a repetition rate of 50 Hz. The neutron fluence in the target is equal to 0.9 × 10¹⁵ neutrons/s, which corresponds to the requirements imposed on the intensity of modern pulsed neutron sources.     

库仑作用对同位旋分馏过程的影响

利用同位旋相关的量子分子动力学模型研究了中能重离子碰撞中库仑作用对同位旋分馏过程的影响.研究结果表明,在所研究的能区,无论是丰(缺)中子碰撞系统或者轻(重)反应系统,库仑作用都使同位旋分馏过程减弱,而这种影响主要来自于库仑作用对质子的排斥作用,使更多的质子发射,从而降低了气相中子–质子比所导致     

Investigation of neutron emission in the interaction of relativistic protons and deuterons with lead targets

Measurements of neutron double-differential cross sections and yields in time-of-flight experiments with various lead targets and beams of protons and deuterons with an energy of about 2 GeV are discussed. Space and energy distribution of neutrons in an extended lead target is studied by threshold detectors in the proton energy range of 1–3.7 GeV. The average multiplicity of neutrons, neutron energy, and neutron multiplication in lead as functions of target dimension, type, and energy of the beam particle are analyzed.     

CMOS图像传感器在质子辐照下热像素的产生和变化规律

应用于空间的图像传感器在辐射影响下产生的热像素严重影响空间光电探测性能,本文通过质子辐照试验研究了热像素的产生和变化规律。首先,使用3 MeV和10 MeV两种能量的质子对图像传感器进行辐照,分析不同能量、不同注量的质子辐照产生热像素的性质;其次,再对辐照后的器件进行退火试验,分析热像素的退火规律。对于相同注量辐照,3 MeV质子辐照下热像素产生率大约是10 MeV质子辐照下的2.3倍,但是10 MeV质子辐照产生热像素的灰度值高于3 MeV质子;辐照过程中热像素的数量都是随着注量的增加线性增加。退火过程中,热像素数量都不断减少,而3 MeV质子辐照产生的热像素相比于10 MeV质子,退火更为显著。结果表明,质子辐照下每个质子与器件之间的作用过程及产生缺陷的机制是相对独立的,不同质子的作用过程之间没有相关性。不同能量的质子辐照产生缺陷的类型不同,导致热像素具有不同特性。     

Assessment of cancer risk from neutron exposure – The ANDANTE project

The ANDANTE project began in January 2012 as a spin-off of results of an earlier Euratom project, ALLEGRO, designed to address the problems of medium- and long-term risks following radiotherapy. ANDANTE will investigate the relative risk of induction of cancer from exposure to neutrons compared to photons. The project will focus on three specific cancers that may be detected as second malignant neoplasms following paediatric radiotherapy: salivary gland, thyroid gland, and breast tissue. Stem cells from each of the types of tissue will be exposed to well characterised beams of both neutrons and photons. Biological markers of possible tumorigenesis will be used to develop RBE models for neutrons. The experimental beams will be measured in terms of fluence and energy spectra in order to provide date for a track structure model, which will be developed to simulate the exact experimental conditions and to explore the relationships between exposure parameters and response. The RBE model will be utilized in the assessment of follow-up data from paediatric photon radiotherapy patients. The out-of-beam mixed photon-neutron fields generated during proton therapy will be measured in phantoms, and an analytic algorithm will be developed for reconstructing the fields distant from the treatment site using data available from clinical records. One of the aims of the project is a critical analysis of the potential power of a multi-centre cohort of paediatric patients to give confidence in the neutron risk estimates in radiotherapy patients.This paper focuses on the challenges in the ANDANTE project posed by the need to know detailed neutron, photon, and charged particle fluences and energy spectra in order to determine the neutron RBE as a function of dose and energy.     

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。     

GEANT4 Simulation of the High-Energy Neutron Beam of the TOF Spectrometer GNEIS

Using the Geant4 software package, a numerical simulation of a neutron source of the time-offlight spectrometer GNEIS created on the basis of the SC-1000 synchrocyclotron with 1 GeV proton energy at the NRC Kurchatov Institute—PNPI (Gatchina) has been carried out. The influence of the structural features of the neutron source of the spectrometer on the spatial and energy distributions of neutrons has been studied. The intensity and spectral characteristics of the neutron flux in the range of 1–1000 MeV have been determined on the basis of the obtained information and detailed allowance for all elements of the neutron beam guide system. It is found that the best agreement between the experiment and calculation performed by means of Geant4 is observed when using the QGSP_INCLXX_HP model. In the neutron energy range of 1–200 MeV, the difference between the experimental and calculated shapes of the spectra is less than 25%.     

Effect of proton irradiation on the physical properties of PC/PBT blends

Samples from polycarbonate/poly (butylene terephthalate) (PC/PBT) blends film have been irradiated using different fluences (1?×?10¹⁵– 5?×?10¹⁷ H⁺/cm²) of 1?MeV protons at the University of Surrey Ion Beam Center, UK. The structural modi?cations in the proton irradiated samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction and UV spectroscopy. The results indicate that the proton irradiation reduces the optical energy gap that could be attributed to the increase in structural disorder of the irradiated samples due to crosslinking. Furthermore, the color intensity ΔE, which is the color difference between the non-irradiated sample and those irradiated with different proton fluences, increased with increasing the proton fluence up to 5?×?10¹⁷ H^+/cm², convoyed by an increase in the red and yellow color components. In addition, the resultant effect of proton irradiation on the thermal properties of the PC/PBT samples has been investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). It is found that the PC/PBT decomposes in one weight loss stage. Also, the variation of transition temperatures with proton fluence has been determined using DSC. The PC/PBT thermograms were characterized by the appearance of two endothermic peaks due to the glass transition and melting temperatures. The melting temperature of the polymer, T_m, was investigated to probe the crystalline domains of the polymer, since the proton irradiation destroys the crystalline structure so reducing the melting temperature.     

The 10,000,000,000-Volt question: What is the best choice of proton energy to drive a pulsed spallation neutron source?

In pulsed spallation neutron sources, higher proton beam current or higher proton energy brings higher proton beam power, and from greater beam power come more neutrons. Consequently, accelerator scientists and target systems designers conceive systems to produce ever-higher intensities of neutrons, and the question arises: What is the best choice of proton energy to drive a pulsed spallation neutron source? Meanwhile target engineering, radiation shielding, and neutronic coupling to moderators must be accomplished effectively. This paper addresses the title question from the target side, assessing the neutron yield, the distribution of leakage neutrons, and the power density distribution as functions of proton energy.     

Detecting neutrons by forward recoil protons at the Energy &amp; Transmutation facility: Detector development and calibration with 14.1-MeV neutrons

As part of the Energy & Transmutation project, we are developing a detector for neutrons with energies in the 10–100 MeV range emitted from the target irradiated by a charged-particle beam. The neutron is detected by measuring the time-of-flight and total kinetic energy of the forward-going recoil proton [1] knocked out at a small angle from a thin layer of plastic scintillator, which has to be selected against an intense background created by γ quanta, scattered neutrons, and charged particles. On the other hand, neutron energy has to be measured over the full range with no extra tuning of the detector operation regime. Initial measurements with a source of 14.1-MeV neutrons are reported.     

Neutron yields from massive lead and uranium targets irradiated with relativistic protons

Long-lived isotopes can be transmuted into stable or short-lived elements either by neutron captures or neutron induced fission. The need of a large excess of neutrons has led to the use of accelerator driven sources (ADS). A series of experiments were carried out at the Synchrophasotron/Nuclotron of the Joint Institute for Nuclear Research (JINR) Dubna, using protons of 1.0 GeV. Solid Lead and Uranium targets surrounded by paraffin moderator were irradiated. On the outer surface of the moderator a number of Solid State Track Detectors were placed to monitor neutron spatial distribution. The results showed that the maximum neutron production was reached within the range of one to two proton mean free paths in the target. Then decreasing neutron production follows the proton beam attenuation along the target. Moreover, the results showed both targets neutron production evolution along the target, to be the same. However, neutron flux per incident proton is depended on the target mass, which was found to be higher for the heavier target.     

Dosimetry and fast neutron energies characterization of photoneutrons produced in some medical linear accelerators

This work focusses on the estimation of induced photoneutrons energy, fluence, and strength using nuclear track detector (NTD) (CR-39). Photoneutron energy was estimated for three different linear accelerators, LINACs as an example for the commonly used accelerators. For high-energy linear accelerators, neutrons are produced as a consequence of photonuclear reactions in the target nuclei, accelerator head, field-flattening filters and beam collimators, and other irradiated objects. NTD (CR-39) is used to evaluate energy and fluence of the fast neutron. Track length is used to estimate fast photoneutrons energy for linear accelerators (Elekta 10 MV, Elekta 15 MV, and Varian 15 MV). Results show that the estimated neutron energies for the three chosen examples of LINACs reveals neutron energies in the range of 1–2 MeV for 10 and 15 MV X-ray beams. The fluence of neutrons at the isocenter (Φ_total) is found to be (4×10⁶ n cm² Gy^?1) for Elekta machine 10 MV. The neutron source strengths Q are calculated. It was found to be 0.2×10¹² n Gy^?1 X-ray at the isocenter. This work represents simple, low cost, and accurate methods of measuring fast neutrons dose and energies.     

The effect of fast neutrons on the conductance of single-crystal silicon

The dependence of variation of the specific conductance of single-crystal silicon on the fast neutron fluence is calculated. The results of calculations are compared with the experimental data obtained in two channels of an IRT-T reactor with different neutron spectra. These experimental data are also discussed. The fast neutron fluence was controlled using threshold sulfur activation detectors. The specific electrical resistance was measured by a 4-probe method. The calculation data are in good agreement with experiment and show that the variation of the specific conductance due to exposure to fast neutrons is in direct proportion to the fluence of these neutrons. The proportionality coefficient depends on the neutron spectrum, but is independent of the initial specific conductance. In so doing, it makes no difference, whether silicon was previously irradiated or not.     

Double-differential cross sections for the production of neutrons from Pb, W, Zr, Cu, and Al targets irradiated with 0.8-, 1.0-, and 1.6-GeV protons

Experimental results obtained by determining the double-differential cross sections for neutron production in Pb, W, Zr, Cu, and Al targets irradiated with 0.8-, 1.0-, and 1.6-GeV protons are presented. The spectra of neutrons were measured at 15°, 30°, 60°, 90°, 120°, and 150° with a time-of-flight spectrometer by using a proton beam extracted from the 10-GeV synchrotron at the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The neutrons are recorded with 5MAB-1F6BC501A/5L liquid scintillation detectors and NE110 solid-state scintillators. The experimental data in question are compared with the results of simulations based on the CEM97, LAHET, and CASCADE codes.     

Simulation of high fluence fast neutron damage with heavy ion bombardment

316 stainless steel has been irradiated with 5 MeV Cu ions to a fluence of 2 × 10¹⁶ ions/cm² at 500°C. Transmission electron microscopy of this sample reveals that 6 × 10¹⁵ voids/cm² of average diameter equal to 180 Å were produced. A method for correlating the fluence of ions with equivalent neutron fluences is described. This method predicts that the Cu bombardment in this study should produce a microstructure similar to that found in steel irradiated with 2–5 × 11²² neutrons/cm². A comparison of the ion produced voids with those found after previous neutron irradiation experiments confirms this prediction.     

CiADS中LBE散裂靶的放射性核素研究

铅铋合金(LBE)作为中国加速器驱动系统(CiADS)散裂靶的候选材料,长期辐照使其具有很强的放射性。散裂靶放射性核素的研究仅考虑了质子束的散裂反应,而忽略了反应堆裂变中子的活化作用。本文采用FLUKA和MCNP耦合计算LBE和及其结构件的放射性产物。比较了裂变中子和高能质子在放射性产物的活度、主要放射性核素、毒性和衰变光子等方面的贡献。裂变中子的活化作用对主壳、导管和射束管有显著影响。当反应堆趋于临界状态时,裂变中子对LBE的活化作用是高于质子束流的。在LBE中,96.66%的 210Po是由裂变中子诱导的。这些结果表明,裂变中子在LBE及其结构部件的活化计算中是必不可少的。此外,本研究为CiADS的辐射防护提供了参考数据,也为ADS系统中散裂靶的放射性核素研究提供了更准确的方法。     

Modification induced by proton irradiation in polyallyldiglycol carbonate (PADC)

Swift heavy ions interact predominantly through inelastic scattering while traversing through any polymeric medium producing excited/ionised atoms. Beyond a certain threshold, they affect the lattice structure leading to remarkable flexibility in engineering many physical and mechanical properties of the polymer. Polyallyldiglycol carbonate (PADC) is a class of polymeric detectors which finds its applications in various fields. In the present work, PADC samples were irradiated by four different fluences (≈10¹²–10¹³ cm⁻²) of 62 MeV protons from heavy ion accelerator (ISL) at HMI, Berlin. The modifications in the proton irradiated polymers as a function of fluence have been studied through different characterisation techniques such as Fourier Transform IR, UV-Vis, Electron Spin resonance, Thermogravimetric analysis, Differential Scanning Calorimetry and Track studies. The optical band-gap was found to be constant while a decrease in transmittance of PADC was observed with the increase in proton fluence. The thermal stability of PADC was found to be an inverse function of fluence. Further, these proton irradiated PADCs were exposed to fission fragments from ²⁵²Cf source and the bulk etch-rate was improved with the increase in proton fluence and was found to be increased by 90% for the PADC irradiated at the highest fluence as compared to the pristine. Thus, proton irradiation has led to degradation of the polymer by chain scission converting it into an easily etchable material.