Abstract
<sec>The electron microbeam is useful for modifying certain fragments of biomolecule. It is successful to apply the guiding effect to making the microbeam of positively charged particles by using single glass capillary. However, the mechanism for the electron transport through insulating capillaries is unclear. Meanwhile, previous researches show that there are oscillations of the transmission intensity of electrons with time in the glass capillaries with outer serface having no grounded conductive shielding, So, the application of glass capillary to making the microbeam of electrons is limited.</sec><sec>In this paper, the transmission of 1.5 and 0.9 keV electrons through the glass capillary without/with the grounded conductive-coated outer surface are investigated, respectively. This study aims to understand the mechanism for low energy electron transport in the glass capillaries, and find the conditions for the steady transport of the electrons. Two-dimensional angular distribution of the transported electrons and its time evolution are measured. It is found that the intensity of the transported electrons with the incident energy through the glass capillaries for the glass capillaries without and with the grounded conductive-coated outer surface show the typical geometrical transmission characteristics. The time evolution of the 1.5- keV electron transport presents an extremely complex variation for the glass capillary without the grounded conductive-coated outer surface. The intensity first falls, then rises and finally oscillates around a certain mean value. Correspondingly, the angular distribution center experiences moving towards positive-negative-settlement. In comparison, the charge-up process of the 0.9 keV electron transport through the glass capillary with the grounded conductive-coated outer surface shows a relatively simple behavior. At first, the intensity declines rapidly with time. Then, it slowly rises till a certain value and stays steady subsequently. The angular distribution of transported electrons follows the intensity distribution in general, but with some delay. It quickly moves to negative direction then comes back to positive direction. Finally, it regresses extremely slowly and ends up around the tilt angle. To better understand the physics behind the observed phenomena, the simulation for the interaction of the electrons with SiO<sub>2</sub> material is performed to obtain the possible deposited charge distribution by the CASINO code. Based on the analysis of the experimental results and the simulated charge deposition, the conditions for stabilizing the electron transport through glass capillary arepresented.</sec>
Highlights
The microbeam of the electrons is useful for modifying certain fragment of biomolecule
These two reasons limit the application of using glass capillary to make the microbeam of electrons
Skog P, Soroka I L, Johansson A, Schuch R 2007 Nucl
Summary
低能电子穿越高硼硅玻璃圆形毛细管的实验在兰州大学的低能粒子实验平 台完成。实验平台的详细介绍可参考我们之前发表的工作[36, 37]。能量为0.9 keV 或1.5 keV的电子束从电子枪发出后经过偏转、聚焦、准直后进入μ金属制作的靶 室。该靶室对外部磁场有屏蔽作用。靶架上的束斑大小为2 ×2 mm2。束流的发散 角被控制在0.5°以内。0.9 keV和1.5keV电子束的束流密度分别为-0.75 pA/mm2 和-3.75 pA/mm2。靶室的真空度优于5 ×10-8 mbar。穿越玻璃毛细管的电子被二维 微通道板荧光屏探测器(详见文献[36, 37])探测,可同时获取计数和角分布信息。 The tilt angle α between the axis of the glass capillary and the electron beam, the observation angles ф and θ relative to the direction of the electron beam are indicated. (b) A schematic drawing of the glass capillary, bare (above), silver conductive paint brushed (below). 于 1.5 keV 的穿透电子(图 2 中黑点),其穿透率分布不呈高斯分布。穿透电子强 度在倾角为 0°时达到最大,且在倾角为 0°(玻璃管中心)和玻璃管几何张角 边界处有很尖锐的转折点。在大于几何穿透半高宽角度的倾角上,绝大部分 1.5 keV 的电子被阻止。而对于 0.9 keV 的穿透电子(图 2 中的红圈),穿透电子强度 随倾角的变化可以用高斯函数拟合,其半高宽为 0.3°,远小于几何穿透的半高 宽角度,同时也比 1.5 keV 电子的倾角分布更窄。但毛细管倾角从 0.3°增加到 0.8°的过程中,电子穿透强度变化很微弱。
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