Simulation study of indirect positron generation by an ultra-short laser

Positron generation by an ultra-short ultra-intense laser in an indirect manner has been studied with two-dimensional particle-in-cell (PIC) and Monte Carlo (MC) simulations. In this generation scheme, positrons are produced with energetic electrons accelerated by an ultra-shot laser pulse propagating through an underdense plasma. The dependence of the positron beam properties on the plasma length and secondary target (converter) thickness was investigated in detail. The simulation results reveal that the positron yield is strongly correlated with the total energy of laser-accelerated electrons; both the temperature and divergence of the positron beam are sensitive to the plasma length; and the positron beam has a pulse duration comparable to the incident electron beam. In addition, it is indicated that even with the optimal converter thickness, only a small fraction (11.4%) of positrons can escape out and most of the detected positrons originate from the back edge of the converter

Design of Low Energy Beam Transport System for CSRe Molecular Ion Research Facility

<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);">本文完成了 CSRe分子离子研究装置低能传输线的物理设计。采用Poisson/Superfish软件对150 kV倍压型高压加速器的电场分布进行了模拟,结果显示,加速器各区域空间电场强度均远低于击穿电场强度限值。利用Beampath程序对离子源引出的分子离子束在高压加速器中的传输进行了模拟,束流包络显示,加速区电场对分子离子束具有较强的聚焦作用,加速管出口束斑尺寸较小。采用Trace-3D 程序设计了高分辨能力的磁分析系统和RFQ加速器的注入匹配段。通过Beampath程序的模拟,分析出了质量数为150的分子离子束,并由三单元四极透镜实现了分析束流与直线加速器RFQ的注入匹配。</span><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 design of a low energy beam transport system for CSRe molecular ion research facility was presented. The electric field distribution of the 150 kV high voltage accelerator was simulated by Poisson/Superfish code. The results show that the electric field strengths of various region spaces were far lower than the value of breakdown electric field. The transmission of the molecular ion beam from the ion source was simulated by Beampath in the high voltage accelerator. The beam envelope indicates that the electric field of acceleration section has a strong focusing effect on the molecular ion beam, and the beam size is small at the end of the accelerate tube. The Trace-3D code was used to design the magnetic analysis system with high resolution and the matching section for injecting into RFQ accelerator. Finally, through the simulation, the molecular ion beam with the mass number of 150 was analyzed and the injection matching of the RFQ accelerator by one triplet quadrupoles was achieved.</span

Monte-Carlo calculation of fission process for neutron-induced typical actinide nuclei fission

A global potential-driving model with well-determined parameters is proposed by uniting the empirical asymmetric fission potential and the empirical symmetric fission potential, which can precisely calculate the pre-neutron-emission mass distributions for neutron-induced actinide nuclei fission. Based on the developed potential-driving model, Monte-Carlo code calculates the characteristics of fission reaction process for neutron-induced 241 Am fission. Typical calculated results, including yields, kinetic energy distributions, fission neutron spectrum and decay γ-ray spectrum, are compared with experimental data and evaluated data. It shows that the Monte-Carlo calculated results agree quite well with the experiment data, which indicate that Monte-Carlo code with the developed potential-driving model can reproduce and predict the characteristics of fission reaction process at reasonable energy ranges. Given the well predictions on the characteristics of fission reaction process, Monte-Carlo code with the developed potential-driving model can guide for the physical design of nuclear fission engineering

Monte-Carlo calculation of fission process for neutron-induced typical actinide nuclei fission

A global potential-driving model with well-determined parameters is proposed by uniting the empirical asymmetric fission potential and the empirical symmetric fission potential, which can precisely calculate the pre-neutron-emission mass distributions for neutron-induced actinide nuclei fission. Based on the developed potential-driving model, Monte-Carlo code calculates the characteristics of fission reaction process for neutron-induced 241 Am fission. Typical calculated results, including yields, kinetic energy distributions, fission neutron spectrum and decay γ-ray spectrum, are compared with experimental data and evaluated data. It shows that the Monte-Carlo calculated results agree quite well with the experiment data, which indicate that Monte-Carlo code with the developed potential-driving model can reproduce and predict the characteristics of fission reaction process at reasonable energy ranges. Given the well predictions on the characteristics of fission reaction process, Monte-Carlo code with the developed potential-driving model can guide for the physical design of nuclear fission engineering

Measurement of differential and double-differential neutron emission cross-sections for

The secondary neutron emission differential and double-differential cross sections (DX and DDXs) of n + 9Be have been measured at the neutron energy of 21.94MeV using the multi-detector fast neutron time-of-flight (TOF) spectrometer. The data was derived by comparing the measured TOF spectra with detailed Monte Carlo simulation, and corrected with n-p scattering cross section. Meanwhile, theoretical calculations based on the Hauser-Feshbach and exciton model have been performed to compare with experimental data. Measured differential cross sections were also compared with other measurements. It was found that the experimental results were in agreement with other measurements and theoretical calculations, while discrepancies were also present in the whole energy region and at some angles

Study on grid inefficiency for mesh-type Frisch-grid ionization chambers

In this study, the grid inefficiency $$\sigma$$ for a mesh-type Frisch-grid ionization chamber (FGIC) was investigated using the finite element method and Monte Carlo method. A grid inefficiency $$\sigma$$ evaluation model was developed, which can determine the relationship between the physical parameters of the detector and the grid inefficiency with reasonable accuracy. An artificial neural network (ANN) was applied in the investigation of the grid inefficiency factor $$\sigma$$. The trained ANN was able to describe and predict the grid inefficiency factor $$\sigma$$ with different physical parameters for the mesh-type FGIC. Thus, it can serve as a reference for the development of mesh-type FGICs and correct grid inefficiency $$\sigma$$ measurements