A modified REL track formation model and its application to registration of 1Â GeV/n Au and U ions in polycarbonate

Identification of heavy ions recorded in track detectors requires the knowledge of the physical processes which take place in each of the three steps involved in ion registration: (i) energy deposition by the incident particle in the detector; (ii) track formation; and (iii) the identification method itself. The amount of energy deposited by the incident particle per unit path length (dE/dx) is usually calculated by means of the Bethe-Bloch formula, which is described in terms of the so-called close and distant collisions. The REL track formation model excludes the contribution of close collisions when calculating the fraction of dE/dx leading to track formation. The identification method relates REL to a measurable signal S in the detector, so that S=g(REL)h where g and h are parameters to be obtained from calibration. In this work, we present a modified REL model in which the energy deposited by close collisions may contribute partially to track formation. This contribution is accounted for by means of a new coefficient κ, introduced in the modified REL expression, which can take values between 0 and 1. We estimate the value of κ from measurements of tracks originated in polycarbonate detectors by incident Au and U ions of ∼1GeV/n energy from accelerator. The results are consistent with a small contribution (κ∼0.3) of close collisions.