terms ot i.e, the size of the fon cascade, the “hit size" or cell dose. distributiodn of is taken as Thus, the magnitude of one obtains not only the the the stochastically delivered hit sizes, but also the number of discrete hits for the given amount of exposure. instrument represents a single cell, the readout can be hit, Since tyutal the in terms of hits/exposed cell. The microdosimeter registers essentially all impinging charged particles. However, extremely small exposures, cells, t.e., the with scaling factors as large as 103 | and with it provides the ratio hic/(hit plus unhit) fraction of exposed cells hit at least once. It can quantify "interspersed" partial body radiation, in which some contiguous cells are hit and otners are An additional not, important characteristic of stochastic cell particle encounters is time rate. dose deliveries can be varted at will. The mean time between Thus a single cell TCV can be subjected to from none up to a very large number of encounters, in an arbitrarily short period of time. Examples of microdosimetric distributions, LET's are shown in Figure 4. for radiations of three The amount of eneryy deposited has been designated the “specific energy” (4-6), with dimensions the same as those of absorbed dose, namely, energy/mass. However, because of the need the noun additionally as both an adjective and verb, and for brevity, TT F TAT . a3 YT Fr mee] TF if + FT mnt ~ . L . _ t Sre . ; ‘s : - 2 3 £ = ook r ~ ‘ L / \ i r / Ory 4 : i : " i | 4 Pr = ' \ ] a it ff‘ ' i: 14 MeVn e 7 Torn to use 2 fo . 4 Con 4 liy f io"> 0.9 C Lusi LA pital io2 =107! id. Sol i al 4 HIT SIZE 2 (rad) 10! LL. Oetial ak, 1o* ELS Fig. 4 Microdostmetric z distributions for three radiations of different qualities. Note that the varfance of the mean value can be quite large, and that the distributions overlap. -214- 90124 b restore ut cel l 103 at a &sse, & = oe. tox C Known lespo,