70. Aging and Fading Effects on Registration Properties for Nuclear Tracks in CR-39

Hiroko Enomoto and Nobuhito Ishigure

Keywords: CR-39, aging, fading, temperature, -track, fission-track, bulk etch rate, sensitivity

The effect of storage on track registration property of CR-39 has been studied. Pieces of CR-39 plate were irradiated with normally incident -particles and fission fragments using a ²⁵²Cf source prior and after their storage in air for one to six months at different temperatures of -80°C, -23°C, 4°C, 23°C and 35°C. The pieces were etched in the solution of NaOH with 7 moll^-1 at 70°C for 4 hours.

Bulk etch rate(V_b) was obtained from the etch pit diameter (D_f) of fission tracks using the equation:

V_b =D_f /2t

where t is etching time (h). Alpha-track sensitivity (S) was obtained from the etch pit diameters of - tracks (D_a) and fission-tracks using the equation:



The observed changes in sensitivity of CR-39 during storage at different temperatures are shown in Fig.21: (a) shows the result for the aging experiment and (b) for the fading experiment.

It was found that both the bulk etch rate and -track sensitivity tended to decrease with storage time and storage temperatures. The most significant effect was observed on the -track sensitivity at 35°C, which was reduced by 55% for six months. It was found that the storage effect was attributable to some changes in the detector itself, and not to fading of latent tracks.

Fig.21. Changes in sensitivity of CR-39 during storage at different temperatures:
(a) shows the result for the aging experiment and (b) for the fading experiment.

Publications:
Enomoto, H. and Ishigure, N.: J. Health Physics, 33, 407-413, 1998 (in Japanese, English abstract available).