Grosswendt B
Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany.
Radiat Environ Biophys. 2002 Jun;41(2):103-12. doi: 10.1007/s00411-002-0155-6.
Despite the importance of ionization yield formation in sub-cellular structures a few nanometres in size, with regard to radiation damage our present knowledge in this respect is almost exclusively based on Monte Carlo simulations which in turn are based on cross section sets for water vapour or liquid water. Experimental data, although urgently needed, are still missing because the direct measurement of ionization yields in sub-cellular structures or, at least, in nanometric volumes of liquid water, is not yet possible. The best feasible way to overcome this problem of measurement at present, is the use of highly sophisticated counters filled with gases at low operating pressure to simulate target volumes a few nanometres in diameter at unit density. An indispensable prerequisite of the reliability of such measurements is, however, a check of the equivalence of the ionization yield produced in a specified target gas and the yield to be expected in liquid water or biological material. For this purpose, the ionization yield formation by electrons and alpha-particles in liquid water was simulated using the Monte Carlo method and compared with that produced in propane-based tissue-equivalent gas (composition by volume 55% C3H8, 39.6% CO2, 5.4% N2). After a short summary of the most important physical aspects of ionization cluster formation, new results are presented and discussed from the point of view of radiation physics and radiation biology.
尽管在尺寸为几纳米的亚细胞结构中电离产额形成很重要，但就辐射损伤而言，我们目前在这方面的知识几乎完全基于蒙特卡罗模拟，而这些模拟又基于水蒸气或液态水的截面集。实验数据虽然迫切需要，但仍然缺失，因为目前还无法直接测量亚细胞结构中或至少是纳米级液态水体积中的电离产额。目前克服这一测量问题的最佳可行方法是使用在低工作压力下填充气体的高度精密计数器，以模拟单位密度下直径为几纳米的目标体积。然而，这种测量可靠性的一个不可或缺的先决条件是检查在特定目标气体中产生的电离产额与液态水或生物材料中预期产额的等效性。为此，使用蒙特卡罗方法模拟了液态水中电子和α粒子的电离产额形成，并与基于丙烷的组织等效气体（体积组成：55% C3H8、39.6% CO2、5.4% N2）中产生的电离产额进行了比较。在简要总结了电离簇形成的最重要物理方面之后，从辐射物理学和辐射生物学的角度介绍并讨论了新结果。
