Evaluation of influence of surface barrier in solid on ion reflection by bipartition model of ion transport

The influence of surface barrier of solid upon ion reflection was studied in a few papers of other authors by using the Monte-Carlo simulation. Based on the bipartition model of ion transport, a new analytical theory has been developed instead of the MC simulation, due to important implication of the effect for fusion research. In the present paper we have calculated the number reflection coefficients of H , D , He and T normally incident on C, Al and Cu for ion energy from several eV to one hundred keV respectively. Our computational results accorded with the MC simulation. The results have shown that the effect of surface barrier on ion reflection becomes evident when the energy of incident ions is lower than one keV. In particular, for the ion energy from several eV to one hundred eV, the discrepancies of number reflection coefficients can increase up to 0.1-0.3, showing this influence to be very important.     

Study of pressure effects on ocean in-situ detection using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has attracted extensive attention as a new technique for in-situ marine application. In this work, the influence of deep-sea high pressure environment on LIBS signals was investigated by using a compact LIBS-sea system developed by Ocean University of China for the in-situ chemical analysis of seawater. The results from the field measurements show that the liquid pressure has a significant effect on the LIBS signals. Higher peak intensity and larger line broadening were obtained as the pressure increases. By comparing the variations of the temperature and salinity with the LIBS signals, a weak correlation between them can be observed. Under high pressure conditions, the optimal laser energy was higher than that in air environment. When the laser energy exceeded 17 mJ, the effect of laser energy on the signal intensity weakened. The signal intensity decreases gradually at larger delays. The obtained results verified the feasibility of the LIBS technique for the deep-sea in-situ detection, and we hope this technology can contribute to surveying more deep-sea environments such as the hydrothermal vent regions.     

Modelling swift heavy ion irradiation in iron

Swift heavy ions moving in metals lose most of their energy to inelastic scattering of electrons. The energy deposited in the electronic system is transferred into the atomic system via electron-ion interactions and can lead to melting and creation of new damage and also annealing of pre-existing atomic defects. Using a combination of molecular dynamics and a consistent treatment of electron energy transfer and transport we have modelled experiments performed in Fe to investigate the annealing effect and damage creation under electronic excitations. We observe both annealing and new damage creation at low and high electronic stopping, respectively. Rapid separation of interstitial atoms and vacant lattice sites is seen due to efficient transport via replacement collision sequences. Our results suggest that the role of electronic excitation can be significant in modeling of the behaviour of metals under swift heavy ion irradiation and attempts to modify metals via ion implantation.     

Energy deposition of y-ray in different instances and its influence on energy detection

In this paper, we simulate y-ray energy deposition for different incident energies with four different models using the tool GEANT4 ( Geant4.7.0, 2005 ) developed by CERN (the Center of European Research of Nucleus).The results we obtained indicate that there are different peak values for different incident energies. That is, we can differentiate the incident energy accurately if the detector can determine the peak value accurately. This is meaningful for the geometrical configuration of the detector to get the most probable distribution (MPD) of energy deposition for different incident energies. According to the simulation, we can insert certain slices with large absorption coefficient to obtain a better MPD of energy deposition which will not alter the shape of the energy deposition.     

Self-consistent Kinetic Description of the Low-Pressure Solenoidal Inductively Coupled Argon Discharge

Using an one-dimensional slab model, we have studied the electron energy distribution, the anomalous skin effect, and power absorption in the solenoidal-inductively-coupled argon discharge under low pressures (≤1.33 Pa). The electron energy distribution function and rf electromagnetic field in the plasma are determined self-consistently by the linearized Bolztmann equation incorporating with the Maxwell equations. The numerical results show that, at low pressures, the electron energy distribution function exhibits a non-Maxwellian distribution with a long high-energy tail. The anomalous skin effect is greatly enhanced under low pressures and the negative power absorption is also obtained.     

Geant4在中子辐射效应中的应用

中子辐射效应是半导体器件在辐射环境中损伤的重要因素。本文建立了中子在半导体材料中的电离和非电离能量沉积、原子空位密度的Geant4模拟方法。电离能量沉积可用于分析电离总剂量效应,非电离能量沉积可用于分析位移损伤效应。电离kerma因子的模拟结果定量解释了中子辐照在CMOS工艺单片机中引起的电离增强效应。通过原子空位密度计算了中子引入的附加陷阱密度,分析了位移损伤对电离效应的增强作用。实验和模拟结果表明,中子的电离能量沉积加剧了CMOS工艺单片机的退化。     

Are shocks to nuclear energy consumption per capita permanent or temporary? A global perspective

This paper aims to examine the integration properties of nuclear energy consumption per capita by applying the panel unit root test with structural breaks in 27 countries over the period 1993–2013. To obtain comprehensive and exhaustive information, we utilize the longitudinal clustering approach to segment the overall sample into four sub-samples. We find that for the overall sample, nuclear energy consumption is stationary, while two sub-samples contain unit roots. These results imply that shocks to global nuclear energy consumption will only result in temporary deviations from the long-run growth path; however, shocks have a permanent effect on nuclear energy consumption in two sub-samples. Several implications are provided: if shocks have a lasting effect on nuclear energy consumption, policy makers should design energy conservation and stabilization policies in these countries; otherwise, we do not intervene in the process of nuclear energy consumption.     

Experimental investigation on de-icing by an array of impact rod-type plasma synthetic jets

Since flight accidents due to aircraft icing occur from time to time,this paper proposes an array of impact rod-type plasma synthetic jet de-icing methods for aircraft icing problems.The impact rod-type plasma synthetic jet actuator(PSJA) is based on the traditional PSJA with an additional impact rod structure for better de-icing in the flight environment.In this work,we first optimize the ice-breaking performance of a single-impact rod-type PSJA,and then conduct an array of impact rod-type plas...     

Displacement cascades in polyatomic materials

Using a continuous slowing-down, random amorphous material model, we have studied displacement cascades in a number of diatomic materials. This paper reviews a number of previously obtained results that elucidate the effect of atomic mass, recoil energy, displacement energy, capture energy, and material stoichiometry on the numbers of displacements in a cascade. The displacement cascade reveals a complex structure that is dependent on the type of irradiation and the material properties. Conclusions related to damage analysis for fusion reactors are given.     

呈任意能量分布的核信号模拟

针对核信号在脉冲幅度和相邻脉冲产生的时间间隔上存在的随机性,探讨了核信号统计特性的模拟方法.在进行核信号的能量随机性模拟中,可将核信号的统计特性分解为均匀分布、高斯分布、指数分布、多项式分布和泊松分布等基本分布,并用本文所述方法来实现;对于不便于分解、呈任意能量分布的核信号也可用此法实现,模拟效果较好.     

Modeling and simulation of uniformity effects in Cd/sub 1-x/Zn/sub x/Te gamma-ray spectrometers

Monte Carlo simulations of pulse height spectra for Cd/sub 1-x/Zn/sub x/Te detectors are used to investigate the effect of variations in alloy composition and carrier drift lengths on energy resolution. The results, which are based on a simple phenomenological model, show that these nonuniformities can have significant detrimental effects on spectrometer performance. For the case of Bridgman-grown material, the orientation of the growth axis relative to the detector axis is shown to be an important consideration, especially for crystals which come from the heel end of a boule, where the composition gradient due to zinc segregation is large. Other effects which we have simulated include growth striations, zinc segregation at grain boundaries, and trapping by inclusions and grain boundaries; each of these effects is detrimental to energy resolution. We conclude that material nonuniformity is a major obstacle to achieving statistically limited energy resolution in cadmium zinc telluride detectors.     

Spatio-temporal evaluation of Zr plasma parameters in a single-beam-splitting double-pulse laser-induced plasma

The plasma shielding effect is one of the major weaknesses of laser-induced breakdown spectroscopy(LIBS) as it causes non-linearity in signal strength. Although LIBS is typically carried out in constant laser energy, this non-linearity causes a reduction in sensitivity. In this work, we systematically examine laser-induced plasma, formed by two different excitation source modes, i.e. single pulse(SP)-excitation and single-beam-splitting double-pulse(SBSDP)-excitation over Zr-2.5% Nb alloy. The two most important plasma parameters influencing the emission line intensity, plasma temperature(T_e) and electron density(N_e) were studied and compared for both modes of laser excitation. Comparison of the results conclusively demonstrates that due to the splitting of the laser energy in the SBS-DP mode, the plasma shielding effect is significantly reduced. The reduced plasma shielding translates to an increased laser–sample coupling under SBS-DP mode. Temporal imaging of the total intensity of the laserinduced plasma in both excitation modes was also studied. The study shows how the plasma shielding effect can be reduced to improve the analytical quality of the LIBS methodology.     

The solid-gas difference in stopping powers, and statistical analysis of stopping power data

For the purpose of treating the difference in stopping power between condensed and gaseous substances, we first discuss our method of statistical analysis of published experimental data. We distinguish between a positive effect where the difference between mass stopping powers S_solid − S_gas is positive and a negative effect where the opposite holds true. Experimentally, the positive effect has been found so far with heavy ions at high energy, and the negative effect with light ions at low energy. The positive effect is due to the difference in ionic charges and can be described by the CasP program by Grande and Schiwietz. An apparent persistence of the positive effect down to low energy is found to be mainly an artifact inherent in the stopping table of ICRU Report 73. The negative effect can be described by a difference in mean ionization potentials between gases and condensed matter. It is large for metals, much smaller for compounds. It should be possible to see both effects in one projectile - target combination.     

软X射线光束线能量分辨率测量中 气体压强对谱线的影响研究

同步辐射软X射线光束线通常利用气体电离室来标定单色仪的能量及测量能量分辨率,通过分析拟合所得谱线的半高宽,可以对光束线的能量分辨能力进行定量评估.然而,传统的分析方法往往忽略了谱线中气体碰撞展宽的影响,从而导致所得能量分辨率略低于真实值.通过讨论气压对测量所得的谱线宽度的影响,提出了一种考虑气压修正的能量分辨率计算方法...     

The influence of the Coulomb explosion on the energy loss of and molecules channeling along the Si 1 0 0 direction

In this work we have measured the contribution of the Coulomb explosion to the electronic stopping power of molecular hydrogen ions and channeling along the Si 1 0 0 direction. We have used a SIMOX target, consisting of crystalline Si 1 0 0 with a buried layer of SiO₂. The measurements of the energy loss of H⁺, and have been carried out using the standard channeling Rutherford backscattering spectrometry. The energy loss has been measured around the Si 1 0 0 channel at a fixed energy per nucleon (150 keV/amu) as a function of the tilt and azimuthal angles. The present results show the effect of Coulomb explosion, which enlarges the protons traversal energy and consequently the channeling energy loss. This heating effect due to ions is about two times larger than molecules and amounts to about 5% of the total stopping power.     

A new consecutive energy calibration method for X/γ detectors based on energy continuously tunable laser Compton scattering light source

In this paper, we present an energy calibration method based on steep Compton edges of the laser Compton scattered(LCS) photon energy spectra. It performs consecutive energy calibration in the neighborhood of certain energy, hence improves calibration precision in the energy region. It can also achieve direct calibration at high energy region(several MeV) where detectors can only be calibrated by extrapolation in conventional methods.These make it suitable for detectors that need wide-range energy calibration with high precision. The effects of systematic uncertainties on accuracy of this calibration method are studied by simulation, using the design parameters of a LCS device—SINAP Ⅲ. The results show that the SINAP Ⅲ device is able to perform energy calibration work over the energy region of 25–740 keV. The precision of calibration is better than 1.6% from 25 to 300 keV and is better than 0.5% from 300 to 740 keV.     

Restricted energy loss of ultrarelativistic particles in thin targets - A search for deviations from constancy

Experimental results for the restricted energy loss of ultrarelativistic electrons, with Lorentz factors up to 3×10⁵, in a thin silicon detector are presented. The combination of high Lorentz factors and thin targets, opens for the possibility to study two mutually excluding effects, both based upon theory and on scarce experimental observations. One is a disappearance of the density effect when the transit time becomes so short that the effect of plasma-oscillations becomes negligible. This would result in an increased energy loss as the Lorentz factor increases. The other is an effect based on the existence of a coherence length over which there are contributions to the energy loss. This effect leads to a substantially decreased energy loss for thin targets as the Lorentz factor increases. The latter is shown to be incompatible with our measurements, whereas the former may be present with a correction of a few percent to an otherwise constant energy loss. Furthermore, we point to significant effects related to synchrotron and transition radiation, that must be carefully considered in a possible future experiment, and may as well have been of significance for the conclusion in earlier experiments.     

逆滤波器法在能谱测量中的应用

由于传统测量能谱的方法是采用单道、多道的方法,其有一定的分辨时间,并且无法克服相近脉冲的叠加效应,提出了采用逆滤波器法测量能谱的方法。该方法将探测器系统看作具有某一传递函数的线性系统,对探测器系统的输出进行采样,构造系统的离散逆系统,使采样信号通过逆系统,即可取得原始入射粒子的能量与入射时间。仿真结果表明,采用该方法不仅能准确测量原始入射射线的能量,并能测出其入射时间,克服了传统单道、多道进行能谱测量的一些缺点。     

Thermal conductivity and the isotope effect in Li2O

The thermal conductivity of condensed matter can be reduced through the introduction of isotopic disorder as the different isotopes act as mass defects that scatter phonons responsible for the transfer of heat energy. Here we investigate, using classical molecular dynamic simulations, the magnitude of this effect in the ceramic oxide Li₂O, which will be artificially enriched with ⁶Li to improve tritium breeding potential in a future fusion reactor. The results show that while the isotope effect will be important at lower temperatures it has little influence at the expected operating temperatures of the breeder blanket.     

堆芯跌落事故下水力缓冲性能分析研究

对采用"水力缓冲+机械缓冲"技术的反应堆堆内构件二次支承结构缓冲性能进行分析,研究假想堆芯跌落事故(吊篮断裂)下反应堆堆内构件二次支承结构对吊篮组件的水力缓冲作用机理。基于Fluent动网格技术对吊篮组件跌落过程进行数值模拟,分析不同竖直间隙、冷却剂温度及初始流速下吊篮组件跌落过程的运动规律;基于LS-DYNA非线性动力分析程序分析跌落末端的冲击过程,研究二次支承结构水力缓冲作用效果。分析显示,堆芯跌落事故下,水力缓冲可以吸收缓解大部分跌落冲击能量,与传统缓冲结构相比,缓冲效果更佳,确保了反应堆压力容器(RPV)的结构完整性和堆芯稳定性。