The influence of thermochemical effects on the response of nuclear track detectors

We have investigated the effect on track detector sensitivity of those thermochemical or environmental parameters such as etchant concentration and temperature which affect both the bulk- and track-etch rates. We describe track response by a new, simple threshold model based on activation energy from chemical reaction-rate theory and we show it is possible to define, for any track, a unique diameter growth function, which we call the diameter response function and which completely characterises the response of the track. As an experimental illustration of this model we describe the effect of adding methanol to alkali etchants. We show that in CR 39 increasing the proportion of methanol or the temperature of certain etchants increases both the track- and bulk-etch rates along the tracks of 6.1 MeV α-particles, but that Vsub(T) → Vsub(B) along the track, completely desensitising part of it and giving rise to an apparent threshold in its response. We conclude that the location of the threshold along the track depends on the values of the environmental parameters. As an application we show how the dependence of the location of the threshold on the environmental parameters can be used to greatly increase the energy-resolution of the detector for short-range particles. (author)