Charge and Energy Dependences of Ionization and Transfer for Helium in Collisions with Fast Charged Projectiles

The classical method within the independent electron model is employed to investigate （i） charge dependences of single and double ionization for helium by various charged ions A^q＋ （q = 1 - 8） at impact energies of 0.64 and 1.44 MeV/u, respectively, （ii） energy dependences of transfer ionization for helium by 0.5-3 MeV/u A^8.9＋ ions impact. The Lenz-Jensen model of the atom is applied instead of the Bohr model of the atom, and the impact-parameter dependences are also introduced into the calculations. Satisfactory agreement is found between theoretical and experimental data.     

Particle-in-Cell/Monte Carlo Collision simulation of planar DC magnetron sputtering

In this paper a numerical simulation of a planar DC magnetron discharge is performed with the Particle-in Cell/Monte Carlo Collision （PIC/MCC） method. The magnetic field used in the simulation is calculated with finite element method according to experimental configuration. The simulation is carried out under the condition of gas pressure of 0.665 Pa and voltage magnitude of 400V. Typical results such as the potential distribution, charged particle densities, the discharge current density and ion flux onto the target are calculated. The erosion profile from the simulation is compared with the experimental data. The maximum erosion position corresponds to the place where the magnetic field lines are parallel to the target surface.     

飞秒激光激发空气电离的阈值研究

报道在脉宽50fs—22ps，波长800nm脉冲激光作用下的空气电离阈值的研究结果.利用探测等离子体发光信号的方法，实验测量了激发空气电离所需的阈值激光强度.结果表明，当激光脉冲宽度从50fs增加到22ps时，阈值光强I_th从8.7×10¹⁴W/cm²下降到2.7×10¹³W/cm²；I_th经历了由迅速降低逐渐发展为缓慢降低的过程.在50fs—1p     

氧离子与氦、氖原子碰撞中转移电离过程的研究

采用位置灵敏探测和散射离子-反冲离子飞行时间测量技术,测量了氧离子与氖和氦原子碰撞过程中转移电离截面与单电子俘获截面之比.通过比较发现测量结果与文献结果的趋势一致,并对测量结果进行了讨论.     

高能重离子物理进展与展望

介绍了高能重离子碰撞物理的基本要领指出这一领域的中心课题是研究实现夸克一胶子等离子体相变的条件，文章了对各种可能的ＱＧＰ相变信号的理论分析及实验探测的最新进展，并展望了该领域实现了理论研究进展的未来前景。     

重提玻密子

 当粒子在世界的原子打碎器中心彼此相撞破裂出现一些奇异事例时,物理学家也引出一些同等奇异的解释。取所谓“软碰撞”的情况为例,两个快速质子相撞,彼此擦边而过,其中一粒子破裂为粒子喷注,而另一质子实际上未受损伤。在直觉上对顶碰撞较易了解如何被打破,但在交换中擦边而过撕碎如何产生令人遗憾的粒子散失?1961年物理学家提出一决定性非传统的回答:存在一种力的携带粒子称为玻密子(Pomeron),它冲击另一粒子而且将它震裂。     

科苑快讯

 美国将发射探测小行星的飞船据《科技日报》报道为了揭开小行星的奥秘,寻找对付可能撞击地球的小型天体的方法,美国航空航天局计划本月16日发射一艘名为“尼尔”的小型飞船,对“厄洛斯”小行星进行为期3年的探测。