Front-back effect of plastic film detectors

The detection efficiency of plastic film detectors, namely cellulose nitrate (CN, Daicel) and cellulose triacetate (CTA, Fuji), was investigated. The relation between the growth rate of etch pits (Vt) and the restricted energy loss (REL) was obtained. A stack of the CN detector consists of 520 CN films with about 190 μm thickness, and that of the CTA detector 410 films with about 250 μm thickness. The stacks were irradiated by the Ar-40 beam of 400 MeV/n with a Bevalac. The results were compared with the results obtained with N-14 beam. In case of the CN films, both results were in good agreement, and the difference between the front surface and the back one was not able to be observed. In case of the CTA, however, the difference between both surfaces was clearly seen. The linear relation of the track etching rate and the REL was found in both surfaces. It is necessary to calibrate the front surface and the back surface separately. (Kato, T.)