A PRECISE IONIZATION METHOD FOR DETERMINATION OF THE ENERGY DEPOSITEDIN SMALL SITES OF IRRADIATED OBJECTS

The ionization method for determination of the energy deposited in sen sitive sites of irradiated objects is usually used with the assumption that deposited energy is directly proportional to the number of ioniz ations in a site. This assumption fails in two cases important for nan ometer-sized sites: (1) when the fluctuation characteristics of deposi ted energy such as higher moments, probability distributions, etc. are determined instead of the mean value; (2) when the radiation field in a site is spatially non-uniform. In this paper both cases are investi gated. Exact formulae connecting energy and ionization quantities (mom ents, cumulants, probability distributions) are established as well as practical procedures to obtain energy quantities from those of ioniza tion. The validity of the direct proportionality principle is analyzed and approximate methods to correct it are proposed. Some microdosimet ric results are presented. The solution of these problems required tha t we refine some known notions and introduce new terms. In particular, in the paper the necessity of distinguishing two distinct types of ev ents and correspondingly two sets of microdosimetric quantities is not ed; new radiation parameters such as the fluctuation W value and non-e quivalence factor for the events are defined and investigated numerica lly.