Derivation of V function for LR 115 SSNTD from its sensitivity to 220Rn in a diffusion chamber

The sensitivity of the LR 115 detector inside a diffusion chamber to 220Rn gas concentration is dependent on the removed active layer thickness during chemical etching. This dependence is related to the V function for the LR 115 detector (where V is the ratio between the track etch velocity Vt and the bulk etch velocity Vb) and the geometry of the diffusion chamber. The present paper presents the experimentally determined relationship between the sensitivity of the LR 115 detector inside a Karlsruhe diffusion chamber (determined from the number of etched tracks completely penetrating the active cellulose nitrate layer) and the removed active layer thickness. These data were used to derive the V function for the LR 115 detector, which took the functional form of the Durrani-Green's function, i.e., V=1+(a1e-a2R+a3e-a4R)(1-e-a5R), with the best-fitted constants as a1=14.50, a2=0.50, a3=3.9 and a4=0.066.