Design of detector to monitor the Bragg peak location of carbon ions by means of prompt γ-ray measurements with Geant4

Real-time monitoring of the Bragg peak location of carbon ions is urgently required for the quality control of hadron therapy. In this study, we design an annular detector to monitor the Bragg peak location of carbon ions with Geant4 simulation. This 360° surrounding structure has a high detection efficiency for the small-dose situation. The detector consists of a multilayered collimator system and an Na I scintillator for prompt gamma counting. The multilayered collimator includes a lead layer to prevent unwanted gammas and the paraffin and boron carbide layers to moderate and capture fast neutrons. An inclination of the detector further diminishes the background signal caused by neutrons. The detector, with optimized parameters, is applicable to carbon ions of different energies. In addition, the scintillator is replaced by an improved EJ301 organic liquid scintillator to discriminate gammas and neutrons. Inserting thin Fe slices into the liquid scintillator improves the energy deposition efficiency. The Bragg peak location of 200 Me V/u carbon ions can be monitored by prompt gamma detection with the improved liquid scintillator.     

Ground-State Energy Shifts of H-Like Ti Under Dense and Hot Plasma Conditions

In this study, by adopting the ion sphere model, the self-consistent field method is used with the Poisson-Boltzmann equation and the Dirac equation to calculate the ground-state energies of H-like Ti at a plasma electron density from 10^22 cm^-3 to 10^24 cm^-3 and the electron temperature from 100 eV to 3600 eV. The ground-state energy shifts of H-like Ti show different trends with the electron density and the electron temperature. It is shown that the energy shifts increase with the increase in the electron density and decrease with the increase in the electron temperature. The energy shifts are sensitive to the electron density, but only sensitive to the low electron temperature. In addition, an accurately fitting formula is obtained to fast estimate the ground-state energies of H-like Ti. Such fitted formula can also be used to estimate the critical electron density of pressure ionization for the ground state of H-like Ti.     

Some characteristics of X-ray imaging for energy region of over 100 keV using plastic scintillation fiber array

In this work, characteristics of using PSFs （plastic scintillation fibers） coupled with CCD （charge-coupled devices ） to build area detectors for high energy X-ray imaging are studied with a Monte Carlo simulation, which cover an energy range of a few hundred keV to about 20 MeV. It was found that the efficiency of PSF in detecting X-ray with energy above a few hundred keV is low. We can use large incident flux to increase the output signal to noise ratio （SNR）. The performance can also be improved by coating PSF with X-ray absorption layers and the MTF of the system is presented. By optimizing the absorption layer thickness, the crosstalk of the area detector built with PSF decreases.     

LIGHT ION REFLECTION STUDIED BY MONTE CARLO SIMULATION AND TRANSPORT THEORY

The reflection of light ions, such as H+,3He+ and 4He+, with energies of 0.1- 10 keV, from Cu and Ni surface has been studied by Monte Carlo simulation and transport theory. The Monte Carlo simulation gives the detail energy spectra for the reflected particles and their angular distribution for different incident angles. It shows that the reflected particle energy spectra can be approximately described by an analytical formula for the whole energy range, all the incident angles and different ion- target combination studied here. The reflected particle energy vs its average reflection angle to the surface normal can almost be expressed by a universal curve for all cases studied here. The reflection energy spectra are used for the calculation of the reflection coefficient by transport theory including the realistic surface correction. The present work is compared with both experimental measurement and other simulation codes.     

A new method for position-sensitive measurement of beta surface contamination

In this paper, we propose a new method for position-sensitive measurement of beta surface contamination. With a position-sensitive detector of enlarged sensitive detection area, accurate information of the contamination distribution can be obtained. The positionsensitive detection is based on a large-area plastic scintillator and the wavelength shifting(WLS) fibers and adopts the ‘‘light center of gravity' method. Optical transmission of the detector is simulated with a preliminary detector model, and feasibility of the detector design and measurement method is evaluated using an experiment system.The simulation and experiment results at different beta-ray incident points on the scintillator surface show that there is a polynomial relationship between the average amplitude ratio of the output pulses from the two parallel WLS fibers in the same fiber layer and the relative distance from the incident point to the WLS fiber.     

Transmission Degradation of Femtosecond Laser Pulses in Opened Cone Targets

Irradiated by femtosecond laser pulses with different energies, opened cone targets behave very differently in the transmission of incident laser pulses. The targets, each with an opening angle of 71 and an opening of 5 μm, are fabricated using standard semiconductor technology. When the incident laser energy is low and no pre-plasma is generated on the side walls of the cones, the cone target acts like an optical device to reflect the laser pulse, and 15% of the laser energy can be transmitted through the cones. In contrast, when the incident laser energy is high enough to generate pre-plasmas by the pre-pulse of the main pulse that fills the inner cone, the cone with the plasmas will block the transmission of the laser, which leads to a decrease in laser transmission compared with the low-energy case with no plasma. Simulation results using optical software in the low-energy case, and using the particle-in-cell code in the high-energy case, are primarily in agreement with the experimental results.     

Directed flow of isospin sensitive fragments within a modified clusterization algorithm in heavy-ion collisions

By extending the minimum spanning tree （MST） clusterization algorithm for the binding energy cut, the isospin asymmetry dependence of directed flow for isospin sensitive isobar pairs （neutrons-protons, 3H-3He） is studied from low towards high incident energies. The modified clusterization method （MSTB） has the advantage to identify the fragments at quite early time. It enhances （reduces） the production of free nucleons （fragments） over MST method. The directed flow of isobaric pair 3H-3He is more sensitive towards isospin asymmetry caused by MSTB than isobaric pair n-p. This sensitivity becomes quite strong towards the high incident energy and neutron-rich reaction system. In conclusion, the inclusion of binding energy in clusterization method for the flow studies has been uniquely important for understanding the isospin physics, especially for high density behavior of symmetry energy.     

Performance Calibration Using Cosmic Rays for the Multi-Neutron Correlation Spectrometer

Efficient calibration methods have been applied to a complex neutron detector array by using the cosmic-ray muons. Through a differential operation on the time difference spectrum, the two edges of this spectrum can be precisely determined, corresponding to the geometrical two ends of the bar, and therefore the relationship between the position and time difference spectrum can be deduced for each bar. The alignment between different bars is realized by choosing cosmic-rays which are perpendicular to the bars. The position resolutions are extracted through a track fitting procedure which uses all tracks detected coincidently by the whole system, together with a simulation analysis. A method is also developed to calibrate the deposited energy by using cosmicrays at different incident angles.     

Numerical Simulation of Radial and Angular Distribution of γ-Ray＇s Energy Deposition in Scintillation Optical Fibre

Angular and radial distributions of the energy deposition of γ-ray radiation in scintillation optical fibres are simulated and analysed using the Geant4 system. The results show a linear relation between the energy deposition and the radius of the fibres. The deposition is roughly inversely proportional to sinθ with θ the incident angle relative to the fibre axis. The results could provide corrections to the measurements of the scintillation fibres used in monitoring the γ-ray radiation.     

A Simulation Study on the Flash X-Ray Spectra Spatial Distribution

Accurate measurement of flash X-ray energy spectra plays an important role in highenergy flash radiography. In this paper, by virtue of Geant4 toolkit, we simulated the generation and transport of X-ray photons resulting from the interaction of a high-energy electron beam with a solid thin target. We obtained the flash X-ray energy spectral distribution in the plane perpendicular to the electron beam incident direction. Our results indicate that the flash X- ray spectrum is almost uniform in the azimuthal direction but is quite different in the radius direction. Specifically, as the radius increases, the incident X-ray dose decreases significantly. Our work paves a theoretical basis for selecting appropriate structures and layout of the spectrometer and facilitates the measurements of flash X-ray energy spectra.     

Design of 3B3 beamline control system

1 Introduction BSRF-3B3 Beamline is a middle-energy (1.5~6 keV), monochromatic, focusable X-ray beam-line constructed in the Beijing Synchrotron Radiation Facility (BSRF) of the Beijing Electron Positron Col-lider (BEPC) in order to develop the work of demarca-tion of detectors for laser diagnosis and middle-energy X ray spectroscopy. Fig.1 is the optical layout of the 3B3 Beamline.Fig.1 Optical layout of 3B3 Beamline. 2 Design of control system The 3B3 Beamline control system (s…     

常量稀土存在时DEHDTP萃取Am~(3+)、Nd~(3+)、Eu~(3+)和Tm~(3+)的研究

研究了二（２－乙基己基）二硫代磷酸在常量稀土存在时对Ａｍ＾３＋、Ｎｄ＾３＋、Ｅｕ＾３＋和Ｔｍ＾３＋的萃取。研究结果表明，当萃取剂起始浓度为０．１ｍｏｌ／Ｌ时，平衡ＰＨ值越大，分离因数越大；萃取剂皂化度和起始ＰＨ相同时，萃取剂浓度越小，分离因素越大；平衡ＰＨ值固定时，稀土离子浓度越大，分离因数越大；ＤＥＨＤＴＰ和三辛基氧膦协同萃取时，分离因数β（Ａｍ／Ｅｕ）可提高到７１．４。     

三苯基膦还原制备ReOCl_3(PPh_3)_2的研究

用三苯基膦（PPh3)为还原剂，制得了单一价态的Re(V)化合物ReOCl3(PPh3)。通过独立变量法确定了ReOCl3(PPh3）2的最佳制备条件，对化合物进行了表征并测定其稳定性。结果表明，化合物在室温下性质稳定；控制盐酸浓度、PPh3和萃取剂的量等条件，ReOCL3(PPh3)的产率可达到95％以上。说明在制备ReOCl3(PPh3)中PPh3可望取代常用的还原剂Sn(Ⅱ）。     

3×3棒束间湍流流动的3D激光多普勒方法实验研究

子通道或者子通道间的流动搅混显著影响热传递性能。采用5光束3D激光多普勒测速(LDV)系统对3×3棒束间的流动速度进行测量。棒束组件带有简单的定位格架,格架中没有安装搅混装置。棒束的直径与棒间距根据真实燃料组件确定。测量区域选择在近出口段的位置,此位置距离定位格架较远,流动已是充分发展。测量窗口选择在侧边。采用2D LDV测量了1/4的子通道截面,试验记录了测试区域中的主流速度和湍流强度。