Projectile electron loss in collisions of light charged ions with helium

We investigate the single-electron loss processes of light charged ions （Li^1＋,2＋, C^2＋,3＋,5＋, and O^2＋,3＋） in collisions with helium. To better understand the experimental results, we propose a theoretical model to calculate the cross section of projectile electron loss. In this model, an ionization radius of the incident ion was defined under the classical over-barrier model, and we developed ＂strings＂ to explain the processes of projectile electron loss, which is similar with the molecular over-barrier model. Theoretical calculations are in good agreement with the experimental results for the cross section of single-electron loss and the ratio of double-to-single ionization of helium associated with one-electron loss.     

低电荷态离子原子碰撞过程中的转移电离机理的研究

介绍了使用位置灵敏技术和飞行时间方法研究中低能低电荷态离子-原子碰撞过程中转移电离与单电子俘获过程.对于确定的入射离子电荷态,通过理论分析及与实验数据对比给出了转移电离与单电子俘获截面比R_TS随着入射离子速度V_P的变化规律和转移电离过程中电离的电子主要来自靶原子的最外亚壳层. 关键词： 转移电离 逃离半径 电离半径 俘获半径     

Guided transmission of oxygen ions through Al2O3 nanocapillaries

The transmissions of oxygen ions through Al2O3 nanocapillaries each 50 nm in diameter and 10 μm in length at a series of different tilt angles are measured,where the ions with energies ranging from 10 to 60 keV and charge states from 1 up to 6 are involved.The angular distribution and the transmission yields of transported ions are investigated.Our results indicate both the existence of a guiding effect when ions pass through the capillary and a significant dependence of the ion transmission on the energy and the charge state of the ions.The guiding effects are observed to be enhanced at lower projectile energies and higher charge states.Meanwhile,the results also exhibit that the transmission yields increase as the tilt angle decreases at a given energy and charge state.     

Charge sharing effect on 600 μm pitch pixelated CZT detector for imaging applications

We are currently investigating the spatial resolution of highly pixelated Cadmium Zinc Telluride(CZT)detector for imaging application. A 20 mm×20 mm×5 mm CZT substrate was fabricated with 600 μm pitch pixels(500 μm anode pixels with 100 μm gap) and coplanar cathode. Charge sharing between two pixels was studied using collimated a 122 keV gamma ray source. Experiments show a resolution of 125 μm FWHM for double-pixel charge sharing events when the 600 μm pixelated and 5 mm thick CZT detector biased at-1000V. In addition, we analyzed the energy response of the 600 μm pitch pixelated CZT detector.     

Guiding of 150 keV O6＋ ions through nanocapillaries in an uncoated Al2O3 membrane： special time dependence of the transmission profile width

<正>This paper reports that the transmission of O⁶⁺ ions with energy of 150keV through capillaries in an uncoated Al₂O₃ membrane was measured,and agreements with previously reported results in general angular distribution of the transmitted ions and the transmission fractions as a function of the tilt angle well fitted to Gaussian-like functions were observed.Due to using an uncoated capillary membrane,ourψ_c is larger than that using a gold-coated one with a smaller value of（?）,which suggests a larger equilibrium charge Q_∞in our experiment.The observed special width variation with time and a larger width than that using a smaller（?） were qualitatively explained by using mean-field classical transport theory based on a classical-trajectory Monte Carlo simulation.     

Transmission of 18 keV negative ions Cl through nanocapillariesin Al2O3 membrane

We investigate the angular distribution of the transmitted 18keV negative ions Cl^- through Al₂O₃ nanocapillaries of 50 nm in diameter and 10 μm in length. Elastic scattering ions and inelastic scattering ions are obtained simultaneously. The experimental result is partially consistent with the guiding effect. We can qualitatively explain our experimental result through a dynamic process.     

Al_2O_3微孔膜对60keV O~+离子的“导向”效应

在不同入射角度条件下,研究了60keV的O+离子入射孔径分别为50nm和30nm,厚度为10μmAl2O3微孔膜的角分布.实验结果表明离子透射微孔膜时发生了导向效应,随着入射角度的增大,透射于孔径大的微孔膜离子计数下降比较快,透射于孔径小的微孔膜离子计数下降比较缓慢.建立了一个初步的理论模型,对以上现象给出了较好的解释.     

Single-and-double electron loss of O2+ in collisions with argon and helium

This paper reports that the ratios of double to single electron loss cross-section （R） of O^2＋ in collision with Ar and He at the velocity of 1 -4 vo（vo is the Bohr velocity） have been obtained by the coincidence technique. The trend of R - V in the experiment indicates that the effective charge varies with injected velocity. The effective charge can be obtained by the n-body classical trajectory Monte Carlo method, which is interpreted by the molecular Coulomb over barrier model.     

基于TPS和蒙特卡罗计算的12C肿瘤放射治疗In-beam PET剂量监测研究

In-beam PET成像是碳离子放射治疗剂量监测的有效手段,可以对碳离子放疗过程的物理剂量分布和生物剂量分布进行实时监测。结合放射治疗计划系统(TPS)和蒙特卡罗(MC)模拟分别对静态均匀水模体和腹部肿瘤CT图像进行治疗计划设计、MC计算和PET成像,比较TPS肿瘤靶区剂量分布、MC模拟剂量分布和PET成像三者之间的一致性。TPS和MC模拟中相对生物学效应(RBE)的计算均采用线性二次模型(LQ)。研究结果显示,TPS和MC计算的静态均匀水模体、单野治疗腹部肿瘤的物理剂量、RBE加权剂量在SOBP区域的平均误差均在0.5%和2%以内。碳离子束流能量为120~400 MeV/u时,束流方向剂量深度分布与PET成像在SOBP区域的位置差异均在8 mm以内。In-beam PET可作为碳离子放射治疗中位置验证和剂量验证的有效手段。     

Interaction of O3+ Ions with Al2O3 Nanocapillaries

We investigate angular distributions of the transmitted 60 keV and 120 keV O^3＋ ions through nanocapillaries with 50hm diameter and 10μm length. The experimental results are in agreement with the ＇guiding effect＇ found by Stolterfoht et al. For different tilted angles of the nanocapillary membrane with respect to the beam, the angular distributions of the transmitted ions are measured by a one-dimensional micro-channel plate （MCP） detector. Moreover, the dependence of this guiding effect on the projectile energy is studied.