A study of track registration in the region of the critical energy

Abstract

Abstract A latent track in a plastic detector can be etched to a visible track, if the ratio of the track etching rate vt to the bulk etching rate vb is greater than 1. The etching rate in a specific material for a given particle depends on the particle's energy. For a given particle the critical energy Ec is defined by vt(Ec ) = vb The track etching rate approaches the bulk etching rate near the critical energy in an asymptotic manner. The critical energy of cellulose nitrate was determined by using vertical incident alpha particles. The relation of the track diameter, the etching time and the energy of the particle can be calculated using the track and the bulk etching rate. In the region E ≥ 3 MeV the curve vt (E) was unknown. For this calculation vt (E) was set to be vt = vb for E ≥ 5 MeV and as E decreases to 3 MeV vt (E) increases to vt (3 MeV) = 2vb . Comparing the measured and the calculated curves the critical energy of a-particles in cellulose nitrate was found to be higher than 5 MeV. The calculation predicts that the curves of track diameters as function of the etching time using the energy as parameter are parallel to each other as E increases beyond E. The measured curves are not parallel up to 6–7 MeV. The function vt (E) can be obtained by fitting the calculated curves to the measurements.