Interaction of Polyethylene and Tritium Gas as Monitored by Raman Spectroscopy

Abstract

Irradiation of high-density polyethylene by ~1 atm overpressure of T2 gas at 23+- 2 degrees C has been shown to produce severe damage, about 200 MRad dose, within 6 months. Production rate of H2 gas from irradiation due to polymer incorporation of tritium increased quickly within the first 2 months, after which it slowed considerably. It is proposed that outgassing of H2 acted to inhibit diffusion of solubilized HT or T2 into the bulk, thereby limiting increases in polymer T incorporation and thus damage rate. Damage to the HDPE sample was found to be nonuniform. Laser fluorescence from the sample surface irradiated by the supply of T2 gas was ~10{sup}3-fold greater in the energy deposition layer than the fluroescence from bulk polymer after 2 months. This factor was within an order of magnitude of calculated dosages to surface and bulk. Fluorescence from the bulk, apparently caused by unsaturated polyene groups formed during irradiation, grew in time about proportionally to H2 generation and thus dose. An appreciable concentration of radical or ion-radical polyenes at room temperature could be recombined by bleaching for 15 minutes at ~150 degrees C; these species appeared to reform over night at room temperature.