/ !/ L“ IMP CONVERSION FACTOR DERIVATION 410161 Detector Air Soi1 z’ 4 i Source Element x Unscattered flux at height h given by / [lJ/p s“ exp - w ,/ ) a Par a+v/ps ) P~ r~j’ 21TX dx dz 1 (1) where s“ = activity per unit volume r = ra + ‘/p)a, ‘/P); rs = air and soil mass attenuation coefficients cm2 (— !3) Pa9 Ps = air and soil density (g/cm3) Assume an exponential source distribution sv = s~e -. ‘az (2) where s: = activity per unit volume at the sudface (~) a = reciprocal of the relaxation depth (cm-’) Rewrite Eq.1 in terms of ~and integrate over z. Leads to z, combine with Eq.2 and