Some studies of the neutron response, background, ageing and fading properties of two different types of CR-39 plastic processed by electrochemical etching

The neutron-energy response, background, ageing and fading properties of high-quality CR-39 plastic have been studied using identical processing conditions consisting of pre-etching followed by electrochemical etching. The normalised neutron energy-responses of the two types of plastic for normally-incident neutrons were found to be identical within experimental uncertainties. However, both types of plastic exhibited some loss of neutron sensitivity with age, although neither showed any fading of recorded tracks. Backgrounds showed a slow but steady increase with time at rates which were different for the two types of plastic. The loss of sensitivity with age was reduced by storage in a dry enriched nitrogen atmosphere, but this did not prevent the increase in backgrounds with time. (author)