Institutional Repository of Institute of Modern Physics, CAS
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Dynamics of He2++ H ionization with exponential cosine-screened Coulomb potential
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Dynamics of He2+ + H ionization in dense quantum plasmas (DQPs) has been studied by the classical trajectory Monte Carlo method. The interactions between charged particles have been described by the exponential cosine-screened Coulomb potential. It is found that ionization cross sections in plasma environments are obviously larger than those in plasma-free environments due to the screening effects. Cross sections for H+ also have been calculated for comparison. For H+, cross sections increase with the increase of screening effects. However, for He2+, cross sections begin to decrease in strong screening effects at intermediate energies. Furthermore, He2+ impact ionization cross sections in weakly coupled plasmas (WCPs) also have been calculated. The interactions have been described by the static screened Coulomb potential. It is found that when screening effects are weak, cross sections in DQPs and WCPs are approximately the same. As screening effects increase, cross sections in DQPs become larger than those in WCPs at high energies. However, when screening effects are strong enough, cross sections in DQPs become smaller than those in WCPs at low and intermediate energies.</span
Simulation of induced radioactivity for a heavy ion medical machine
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">The radioactivity induced by carbon ions of the Heavy Ion Medical Machine (HIMM) was studied to asses its radiation protection and environmental impact. Radionuclides in the accelerator component, and in the cooling water and air at the target area, which are induced from primary beam and secondary particles, are simulated by FLUKA Monte Carlo code. It is found that radioactivity in the cooling water and air is not very important at the required beam intensity and energy that is needed for treatment, while radionuclides in the accelerator component may cause some problems for maintenance work and, therefore, a suitable cooling time is needed after the machine is shut down.</span
Studies on low energy beam transport for high intensity high charged ions at IMP
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 20px; background-color: rgb(248, 248, 248);">Superconducting Electron Cyclotron Resonance ion source with Advanced design in Lanzhou (SECRAL) is an advanced fully superconducting ECR ion source at IMP designed to be operational at the microwave frequency of 18-24 GHz. The existing SECRAL beam transmission line is composed of a solenoid lens and a 110° analyzing magnet. Simulations of particle tracking with 3D space charge effect and realistic 3D magnetic fields through the line were performed using particle-in-cell code. The results of the beam dynamics show that such a low energy beam is very sensitive to the space charge effect and significantly suffers from the second-order aberration of the analyzing magnet resulting in large emittance. However, the second-order aberration could be reduced by adding compensating sextupole components in the beam line. On this basis, a new 110° analyzing magnet with relatively larger acceptance and smaller aberration is designed and will be used in the design of low energy beam transport line for a new superconducting ECR ion source SECRAL-II. The features of the analyzer and the corresponding beam trajectory calculation will be detailed and discussed in this paper.</span
氦离子低温预辐照对不锈钢中氦泡生长抑制作用的Monte Carlo模拟研究
No full text<span id="ChDivSummary" name="ChDivSummary">实验中已发现氦离子低温预辐照不锈钢材料能有效抑制高温辐照阶段的氦泡生长,但这一结果一直缺少理论解释.基于持续注入粒子的三维格子气模型,采用Monte Carlo模拟方法研究了不同温度模式对氦泡生长行为的影响.研究发现,计算结果能很好地再现氦离子低温预注入抑制高温氦泡生长的实验现象,其原理为低温预注入时材料中形成了较高数密度的小氦泡,由于氦泡数量较多从而限制了氦泡平均尺寸的增大.</span>Zhang Chong-Hong group has found that pre-irradiation of helium ions at low temperature with very low dose could effectively suppress helium bubble growth in materials. This experimental result lacks theoretical explanation. In this paper, we use Monte Carlo simulation to study the effects of different temperature modes on helium bubbles based on a three-dimensional lattice gas model under continued particle injection, and find that the phenomenon that pre-irradiation of helium atoms at low temperature can suppress the helium bubble growth occurs in simulation results as it does in the experiments. The reason is that small helium bubbles with high number density are produced by pre-irradiation at low temperature, and the high number density of bubbles controls the increase of sizes of helium bubbles
Evaluation of radiation hardening in ion-irradiated Fe based alloys by nanoindentation
No full textNanoindentation in combination with ion irradiation offers the possibility to quantify irradiation hardening due to radiation damage. Irradiation experiments for Fe-1.0wt.%Cu alloys, China A508-3 steels, and 16MND5 steels were carried out at about 100 degrees C by proton and Fe-ions with the energy of 240 key, 3 MeV respectively. The constant stiffness measurement (CSM) with a diamond Berkovich indenter was used to obtain the depth profile of hardness. The results showed that under 240 key proton irradiation (peak damage up to 0.5 dpa), Fe-1.0wt.%Cu alloys exhibited the largest hardening (similar to 55%), 16MND5 steels resided in medium hardening (similar to 46%), and China A508-3(2) steels had the least hardening (similar to 10%). Under 3 MeV Fe ions irradiation (peak damage up to 1.37 dpa), both China A508-3(1) and 16MND5 steels showed the same hardening (similar to 26%). The sequence of irradiation tolerance for these materials is China A508-3(2) > 16MND5 approximate to China A508-3(1) > Fe-1.0wt.%Cu. Based on the determination of the transition depth, the nominal hardness H-0(irr) was also calculated by Kasada method. (C) 2013 Elsevier B.V. All rights reserved
Effects of irradiation defects on the nucleation of silver nanoparticles in spinel
No full textComposites with embedded metal nanoparticles attract much interest due to their unique physical properties, which considerably depend on size and shape of the nanoparticles, and on interparticle distance and dispersity of these parameters. Crystal defects can have an effect on the nucleation of nanoparticles. In this paper, the effect of defects on the nucleation and growth of silver nanoparticles was investigated. Argon ions with kinetic energy of 110 keV were implanted into spinet crystals, to produce defects in the surface-near region, and silver ions were then implanted into the region rich in defects. UV-VIS spectroscopy and TEM were used to analyze the samples. It is found that the introduction of defects can enhance the nucleation of silver nanoparticles and mediate their size distribution, and that the size of these nanoparticles for the sample with argon pre-implantation is larger than that in the sample without argon pre-implantation. During an annealing process, defects can improve the growth efficiency of nanoparticles. (c) 2013 Elsevier Ltd. All rights reserved
Irradiation hardening of ODS ferritic steels under helium implantation and heavy-ion irradiation
No full text研发可以承受聚变反应堆内部苛刻的辐照条件的结构材料是建造聚变堆的重要技术问题之一，为此需要首先澄清辐照损伤机理。低活化钢是聚变堆首选的结构材料，其中氧化物弥散强化铁素体钢（oxide-dispersion-strengthened ferritic steel，即ODS铁素体钢）是通过机械冶金和热压工艺，在铁基合金基体中掺杂纳米级别的氧化物颗粒（Y2O3），以增强其高温强度和抗辐照能力。ODS铁素体钢以其优越的的高温强度、高导热率和低膨胀系数等性能成为聚变堆重要的候选结构材料。ODS铁素体钢主要有以下特征：（1）高密度的氧化物纳米颗粒，（2）μm量级的晶粒，（3）高密度的位错。本文研究了氧化物弥散强化（ODS）的三种铁素体钢，包括： 19Cr-3.5Al ODS铁素体钢（MA956）、16Cr-0.1Ti ODS和16Cr-0.1Zr ODS铁素体钢，在多能量的He离子和MeV能量的Bi、Xe离子辐照条件下的硬化效应。获得了辐照硬化与原子离位损伤水平(dpa)、He注入浓度的关系。结果表明，材料的硬度在低剂量范围会随着辐照剂量迅速增加，而在高剂量范围逐渐趋于饱和，可以用1/2次的幂函数拟合辐照硬化与离位损伤水平之间的关系。不同入射离子——Bi离子和Xe离子都引起ODS钢的硬化，而He离子还会在材料中导致氦泡形成，造成更加明显的硬化。实验结果表明，16Cr-0.1Ti ODS和16Cr-0.1Zr ODS铁素体钢较19Cr-3.5Al ODS钢（MA956）具有更强的抗辐照硬化能力，原因可归于其含有更高数密度的细化氧化物粒子——能够有效俘获点缺陷和氦原子——从而有效抑制晶粒内部和晶界处缺陷的长大。The present work investigates the irradiation hardening of ODS ferritic steels after multi-energy He-ion implantation, or energetic Bi-ion and Xe-ion irradiation, to get an understanding of dependence of irradiation-hardening on atomic displacement damage and gas accumulation. Three kinds of high-Cr ODS ferritic steels including the commercial MA956 (19Cr-3.5Al), the 16Cr-0.1Ti and the 16Cr-0.1Zr ODS ferritic steels wereused. The results show that the hardness increases rapidly at the lower doses but tends to saturate at the higher dose. An 1/2-power law dependence on dpa value is obtained. Helium implantation contributes significantly to the irradiation hardening, possibly due to the impediment of the motion dislocations by helium bubbles.16Cr-ODS (Ti or Zr added) steels which contains finer oxide particles in higher number density show higher resistance to irradiation hardening than the MA956.