Formation of the Pulse-Height Spectrum of Diamond Detectors Irradiated with Electrons

The pulse-height spectrum of the diamond detectors irradiated with conversion electrons from 109Cd source (Eo=84keV) is calculated. The energy losses of electrons are taken into account with the help of an empirical expression that connects the range with the energy. The comparison with experimental data allowed to estimate the parameter of the detictor material, i.e. the value NS = 10-4 cm-1.     

Absorption of electrons in xenon for energies up to 200 keV: aMonte Carlo simulation study

Gas proportional scintillation counters are room-temperature, general-purpose X-ray detectors, which are used in many applications due to their good energy resolution, which can be better than standard proportional counters by a factor of ~2. However, for energies higher than ~20 keV, the experimentally measured energy resolution is found to deviate from the usual 1/√E law. Under these circumstances, it is of great interest to understand the mechanisms involved in the detection of higher energy X-rays. Since the photoelectrons will then carry most of the absorbed energy, we study in this work the response of xenon detectors to electrons with energies up to ~200 keV, using a Monte Carlo simulation technique. Distributions of the number of primary (subionization) electrons produced per parent electrons with energy E _e are calculated, and results are presented for the Fano factor, the w-value and the intrinsic energy resolution as a function of E_e in the range 20-200 keV. The influence of an applied reduced electric field on the results is assessed, showing that for 200 keV electrons an increase in the field from 0.1 to 0.8 Td causes an increase as high as 35% in the intrinsic energy resolution     

The Potential of Fast Ignition and Related Experiments with a Petawatt Laser Facility

A model of energy gain induced by fast ignition of thermonuclear burn in compressed deuterium-tritium fuel, is used to show the potential for 300× gain with a driver energy of 1 MJ, if the National Ignition Facility (NIF) were to be adapted for fast ignition. The physics of fast ignition has been studied using a petawatt laser facility at the Lawrence Livermore National Laboratory. Laser plasma interaction in a preformed plasma on a solid target leads to relativistic self-focusing evidenced by x-ray images. Absorption of the laser radiation transfers energy to an intense source of relativistic electrons. Good conversion efficiency into a wide angular distribution is reported. Heating by the electrons in solid density CD₂ produces 0.5 to 1 keV temperature, inferred from the D-D thermo-nuclear neutron yield.     

电子束与复合靶作用后辐射特性的数值模拟

建立了复合靶的蒙特卡罗粒子输运计算模型,以“闪光二号”加速器为电子束源,模拟了电子和光子在不同材料中的输运规律,研究了钽和聚乙烯组成的复合阳极靶对辐射X射线场的影响。模拟结果表明：随着钽厚度的增加,辐射X射线平均能量增大,能量转换效率先增大后减小;聚乙烯可明显减小辐射场中的电子份额。当钽和聚乙烯的厚度分别取20 μm、3 mm时,辐射场中平均光子能量为102.68 keV;光子总能量为88.62 J,远大于电子总能量0.02 J;X射线能量转换效率为0.57%。根据数值模拟结果和实验条件设计了复合靶,计算和测得的X射线平均能量分别为108和121 keV,二者符合得较好。     

Channeltron operating in coincidence mode

We have investigated channeltron operating in coincidence with silicon surface barrier detector for detection of extreme low energy particles. By use of Po-209 radionuclide and silver backing, a radioactive source was prepared as a fine emitter of released α particles, conversion electrons, recoil Pb-205 ions and knock out silver ions. To avoid parasite coincidence events mainly from channeltron anode RC circuit, we have applied appropriate Faraday screens. After getting proper counting rates, composite spectra were recorded. Based on time-of-flight and secondary electron emission coefficient arguments, particular spectra of mentioned particles were extracted. Final experimental data analysis enabled us to found channeltron efficiency curves for electrons, lead ions and silver ions with low detection thresholds at 40 eV, 4 keV and 1.7 keV, respectively.     

Development of a Double Layered Scintillator for Separating and Detecting Low Energy Protons and Electrons

A scintillator system consisting of a thin (5,000 ? - 15,000 ?) CsI(Tl) layer evaporated onto a plastic scintillator (NE-102) has been developed for the purpose of distinguishing low energy protons from electrons and measuring the energy of each species. Evaporations in a high vacuum (10-8 Torr) produced layers of CsI(Tl) that scintillate with an efficiency comparable to optimally doped bulk material, If the CsI(Tl) layer thickness is 15,000 ?, it stops protons with energies below 170 keV and electrons with energies below 18 keV. Thus, protons with energies between about 25 and 250 keV can be distinguished from electrons with energies above 18 keV by examining the shape of the light pulse generated in the dual scintillator. Results obtained with protons and electron beams will be presented.     

Preparation of In low energy conversion electron sources

The preparation of ^114mIn sources of conversion electrons in the energy range 162-190 keV and β continuum with a 1989 keV endpoint via ion implantation of ¹¹³In into Al substrates and subsequent irradiation by thermal and epi-thermal neutrons in a nuclear reactor is described.     

惰性气体β-γ符合测量系统探测器能量及分辨率刻度

β-γ符合法是全面禁止核试验条约(CTBT)放射性核素核查中惰性气体氙测量的一种重要方法,探测器能量及分辨率刻度是其首要解决的关键技术。本工作详细介绍了β-γ符合测量系统NaI(Tl)闪烁体和塑料闪烁体探测器能量及分辨率刻度的方法和结果,采用γ放射性核素点源刻度NaI(Tl)γ射线能量及分辨率,利用137Cs661.66keVγ射线康普顿散射电子刻度塑料闪烁体β射线能量及分辨率,并与131Xem内转换电子刻度的β射线能量分辨率结果进行了比较。结果表明:用137Cs康普顿散射电子刻度塑料闪烁体β射线能量是一种简便可行的方法,但用其刻度的β射线分辨率比实际的大。     

Ionization and excitation collision processes of electrons in liquid water

This paper reports on Monte Carlo simulations of electrons in liquid water using a set of electron collision cross-sections constructed with data published recently. The track history of electrons having initial energy ranged from 1 keV to 10 keV is investigated looking at the ionization and excitation processes. The results show that the ratio of the ionization and excitation events per track history is unique independent of the initial electron energy above a couple of 100 eV and these inelastic processes occur with low energy electrons frequently below 100 eV. In particular, the excitation processes are dominated by the electrons below 50 eV. Flight distance distributions between the inelastic collisions are also discussed.     

Development of a radiographic method for measuring the discrete spectrum of the electron beam from a plasma focus device

An indirect method is proposed for measuring the relative energy spectrum of the pulsed electron beam of a plasma focus device. The Bremsstrahlung x-ray, generated by the collision of electrons against the anode surface, was measured behind lead filters with various thicknesses using a radiographic film system. A matrix equation was considered in order to explain the relation between the x-ray dose and the spectral amplitudes of the electron beam. The electron spectrum of the device was measured at 0.6 mbar argon and 22 k V charging voltage, in four discrete energy intervals extending up to 500 ke V. The results of the experiments show that most of the electrons are emitted in the 125–375 ke V energy range and the spectral amplitude becomes negligible beyond 375 ke V.?     

An algorithm for Monte Carlo simulation of bremsstrahlung emission by electrons

An algorithm for Monte Carlo simulation of bremsstrahlung emission by electrons based on the framework of SuperMC is presented in this paper with efficient and accurate methods to sample the angular distribution and energy of bremsstrahlung photons.The photon energy is sampled according to scaled energy-loss differential cross sections tabulated by Seltzer and Berger.A novel hybrid model for photon angular distribution by low-and high-energy incident electrons is developed.The model uses Tsai's full form of angular distribution function with atomic form factors for high-energy incident electrons.For electrons of ＜500 keV,a simple efficient and accurate analytical distribution function is developed,using adjustable parameters determined from the fitting of numerical values of the shape functions tabulated by Kissel et al.The efficiency of sampling photon energy is 80％.Our angular sampling algorithm for high-energy electron bremsstrahlung based on Tsai distribution function is very efficient (sampling efficiency ～ 70％) in the useful photon energy range.     

Kinetic electron emission in the interactions of slow ions with MgO surfaces

We report experimental energy distributions and yields of electrons emitted from MgO surfaces under the impact of slow noble gas and sodium singly charged ions at varying incident energies.

At impact energies below 1 keV, electron spectra are nearly independent of ion type and energy. A tail of high-energy electrons is observed to grow at higher impact energies.

The results are explained in terms of promotion of oxygen-2p electrons during binary projectile-oxygen collisions populating continuum and excitonic states. Excitons can significantly contribute to electron emission due to the negative electron affinity of the surface.     

Electron Response of Nal(Tl) and a Comparison with Anthracene and Pilot B

An investigation was made of the relative response of NaI(Tl) to electrons over an energy range of 6 keV to 1 MeV. The light output at 6 keV is quite sensitive to the nature of the exposed surface. The results are given for the two best cleaved NaI(Tl) crystals and compared to the electron response deduced from photon data. There is good agreement above 20 keV, where little sensitivity to changes in surface condition was observed. Similar measurements were made for anthracene and Pilot B. The relative light output per unit energy is shown for all three scintillators. Their merit as low energy electron detectors was found to be significantly affected by the amount of backscattering and the intensity and duration of long lived excitation states arising from ionizing events.     

超短脉冲激光与固体靶相互作用的硬X射线能谱

本实验使用高纯锗探测器，运用单光子法，对超短脉冲激光与固体铜靶相互作用产生的硬X射线能谱进行测量。实验结果表明：在激光强度I≈8×10¹⁶W/cm²的P极化光以45°入射角照射5 mm铜靶、探测立体角为4.5×10^－6的实验条件下，产生的硬X射线的能量主要集中在低于100keV能量范围内，超热电子温度分别为(7.4±0.7)keV和(19.5±1.6)keV。     

A new electron spectrometer for depth-selective conversion electron Mössbauer spectroscopy

The construction and performance of a new electron spectrometer for depth-selective conversion electron Mössbauer spectroscopy (DSCEMS) is described, based on a design of a retarding-field analyser. The spectrometer is suited for energies up to 25 keV, for samples with diameters up to 10 mm, it has an energy resolution which can be varied between almost 0.1 and 6% and has a total transmission of 10% of 2π. Also the angle at which the electrons are detected can be varied. The temperature of the sample can be controlled between 25 and 1000 K. The spectrometer is mounted in a UHV chamber with a base pressure of 2 × 10⁻⁸ Pa. Results are shown of measurements of a thin iron layer on a stainless steel substrate, both nonenriched with ⁵⁷Fe. The results can be well described with the DSCEMS theory of Liljequist et al.     

Monte Carlo study of ion-induced secondary electron emission from SiO2

Here we describe a recently developed direct Monte Carlo program to study kinetic electron emission from SiO₂ target. The program includes excitation of the target electrons (by projectile ions, recoiling target atoms and fast primary electrons), subsequent transport and escape of these electrons from the target surface. The program can be used to calculate the electron yields, distribution of electron excitation points in the target and other physical parameters of the emitted electrons. In order to demonstrate the capabilities of this program, we report a study on the kinetic electron emission from SiO₂ induced by fast (1-10 keV) rare gas ions. The calculated kinetic electron yield for various ion energies and masses is in good agreement with the predictions of most frequently applied theoretical model. In addition, the effects of projectile energy, mass and impact angle on the depth distribution of electron excitation points and average escape depth of the outgoing electrons were investigated. It is important to mention that the existing experimental techniques are not capable to measure these parameters.     

Calculations of specific cellular doses for low-energy electrons

The objectives of this work were to calculate the cellular doses and the lineal energies of low-energy electrons in liquid water for different source-target geometry in a cell. Calculated specific cellular doses and their variations were analyzed for the dependences on electron energy, source-target geometry, elastic interaction, and type of energy depositions, i.e. starter, stopper, insider and crosser. Two approaches, i.e. the probabilistic method and the mixed method, were applied. In the probabilistic method, the Monte Carlo Penelope code was used. In the mixed method, the range-energy relation and the sampling of electron paths were applied. It was found that for N ← Cy elastic interactions led to a change of the specific cellular dose by about 30% for electron energies below 10 keV. Here N ← Cy denotes electrons emitted from the source region, Cy (cytoplasm), to deposit energy in the target region, N (cell nucleus). The variation of specific cellular dose was found greater (more than 10%) for N ← Cy than N ← N, C ← C and C ← CS, where C and CS denote the cell and cell surface, respectively. The lineal energy distribution varied substantially with electron energy, source-target geometry, and target size. The maximum values of the relative dose-mean lineal energy for 1, 5 and 10 keV electrons, relative to 36 keV reference electrons used to define the relative biological effectiveness, occurred at target radii of several tens, hundreds and thousands nanometers, respectively.     

低空气比释动能率和窄谱系列过滤X射线参考辐射能谱测量和分析

利用HPGe探测器能谱仪对已经建立的低空气比释动能率和窄谱两个系列的过滤X射线参考辐射进行了实验测定,通过蒙卡模拟方法建立了探测系统的模型,模拟计算能量6 keV～305 keV间隔1 keV的响应矩阵,利用反卷能谱法得到参考辐射场的注量谱,进而计算了各参考辐射的平均能量、能量分辨率、半值层、同质系数、从空气比释动能到...