Grosswendt B
Department of Fundamentals of Dosimetry, Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany.
Radiat Prot Dosimetry. 2006;122(1-4):437-45. doi: 10.1093/rpd/ncl520. Epub 2006 Dec 12.
An indispensable prerequisite for a deeper understanding of specified physical, chemical or biological changes initiated in matter when being exposed to ionising radiation is a detailed knowledge of particle track structure. Here, the structure of electron tracks is of particular interest since electrons are set in motion in large numbers as secondary particles during the slow down of any kind of ionising radiation in matter. From the point of view of radiation induced early damage to genes and cells, which starts with the early damage to segments of the DNA molecule, the most effective secondary electrons are those at energies of a few hundred eV since the yield of double-strand breaks induced by such electrons in the DNA shows a maximum. This can be explained by the fact that in water cylinders, 2 nm in diameter and height (as a substitute to small segments of the DNA), the probability of the electron-induced formation of ionisation cluster sizes greater than or equal to two is highest also at initial electron energies of a few hundred eV. In view of this promising feature of ionisation cluster-size distributions formed by low-energy electrons in nanometric targets of liquid water for explaining particular radio-biological endpoints, it is the aim of the present work to investigate the properties of cluster-size formation by electrons as a function of target size. Here, main emphasis is laid on the behaviour of cluster-size distributions if the target size is reduced from macroscopic to nanometric volumes.
深入理解物质在受到电离辐射时所引发的特定物理、化学或生物变化的一个不可或缺的前提条件，是对粒子径迹结构有详尽的了解。在此，电子径迹的结构尤为引人关注，因为在任何类型的电离辐射在物质中减速的过程中，大量电子作为次级粒子开始运动。从辐射诱导对基因和细胞的早期损伤（这种损伤始于对DNA分子片段的早期损伤）的角度来看，最有效的次级电子是那些能量为几百电子伏特的电子，因为这种电子在DNA中诱导产生双链断裂的产额呈现最大值。这可以通过以下事实来解释：在直径和高度均为2纳米的水缸（作为DNA小片段的替代物）中，在几百电子伏特的初始电子能量下，电子诱导形成尺寸大于或等于两个的电离簇的概率也是最高的。鉴于低能电子在液态水的纳米靶中形成的电离簇尺寸分布对于解释特定的放射生物学终点具有这一有前景的特性，本工作的目的是研究电子形成簇尺寸的特性作为靶尺寸的函数。在此，主要重点在于当靶尺寸从宏观体积减小到纳米体积时簇尺寸分布的行为。
