利用Γ－X混合在AlAs/GaAs异质结构实现光生电子、空穴对的持久存储

利用GaAs量子阱中Γ谷速缚态与AlAs层中X谷束缚态在异质结界面处的共振Γ－X混合，使得光生电子不仅在实空间而且在K空间与光生空穴分离开来，从而在结构中形成了持久的电荷极化。这一效应已被C－V特性上所观察到的电容阶跃和正反方向扫描时所出现的双稳滞迟现象所证实。如果将我们的器件用作存储单元，预期可以获得很长的存储时间T_s。同时，由于Γ－X混合隧穿速率很快，光子“读出”仍可以保持很快。

In situ annealing treatment and In-doping of GaN epilayers grown by MOVPE

The effects of in situ annealing treatment in the initial growth stage and In-doping during growth of the GaN on the material properties were investigated. GaN was grown by LP-MOVPE. In situ annealing reduced the full-width at half-maximum (FWHM) of X-ray rocking curves and reduced etch pit density of GaN films. It improved the optical properties of the epilayer. Undoped and In-doped GaN films of initial growth stage were investigated. It was found that morphology and optical properties were improved in In-doped samples. (C) 2000 Elsevier Science B.V. All rights reserved.

Initiation and development of water film by seepage

When water seeps upwards through a saturated soil layer, the soil layer may become instability and water films occur and develop. Water film serves as a natural sliding surface because of its very small friction. Accordingly, debris flow may happen. To investigate this phenomenon, a pseudo-three-phase media is presented first. Then discontinuity method is used to analyze the expansion velocity of water film. Finally, perturbation method is used to analyze the case that a water flow is forced to seep upwards through the soil layer while the movement of the skeleton may be neglected relative to that of water. The theoretical evolutions of pore pressure gradient, effective stress, water velocity, the porosity and the eroded fine grains are obtained. It can be seen clearly that with the erosion and re-deposited of fine grains, permeability at some positions in the soil layer becomes smaller and smaller and, the pore pressure gradient becomes bigger and bigger, while the effective stress becomes smaller and smaller. When the effective stress equals zero, e.f. liquefaction, the water film occurs. It is shown also that once a water film occurs, it will be expanded in a speed of (U)(t)/(1 - E >).

HIRFL-CSR实验环中束流损失机制及寿命研究

分析了在储存环中回旋的离子束与残余气体分子、内靶和冷却电子束相互作用时的损失机制及相应的束流寿命,针对兰州重离子加速器冷却储存环实验环内靶模式,计算了50—500MeV/u12C6+,36Ar18+,132Xe54+和238U92+等束流在各种损失机制影响下所对应的束流寿命和总的束流寿命。结果表明:影响束流寿命的主要因素是与内靶分子(原子)之间的电荷交换及与冷却电子束之间的辐射复合;对于重离子束132Xe54+和238U92+,与冷却电子束之间的辐射复合是影响其储存寿命的主要因素。

~(12)C离子束的剂量学研究

研究了L-α-丙氨酸剂量计测量12C离子辐射的剂量学特性,实验证明丙氨酸剂量计适用于12C离子辐射的剂量学测量。另外,还研究了12C离子照射人外周血诱发的染色体畸变(双着丝粒+着丝粒环)的剂量效应,在0—8.0 Gy范围内拟合的最佳回归方程为Y=0.858 503D+0.361 5×10-2D2。

同位素~(208)Pb靶的制备

介绍了一种弧形靶框夹芯208Pb靶的制备工艺,包括核靶的制备装置和制备方法、核靶厚度和均匀性的控制和测量方法,并对结果进行了讨论。制备采用旋转蒸镀法,该法可以大大提高材料的利用率。所制靶的结构为30μg/cm2C+361μg/cm2208Pb+15μg/cm2C,同一次所制的靶平均厚度为361μg/cm2,不均匀性小于9.8%。其性能能够很好地满足超重核实验研究的要求。