Ageing of and environmental effects on PADC (CR-39)

The observed responses of poly allyl diglycol carbonate (PADC) detectors to radiation may be greatly influenced by the environment in which the material is stored between the time of manufacture and radiation exposure, the environment at the time of exposure and that during the time elapsing between exposure and processing. These environmental effects are that: (i) PADC plastic stored in air 'ages' during the time between manufacture and exposure to radiation: the background increases with time and the sensitivity decreases. This effect is much reduced for storage in nitrogen. (ii) High temperatures and relative humidities at the time of exposure can modify the detector response. (iii) The radiation response is critically dependent on the presence of oxygen at the time of exposure to irradiation or shortly after. (iv) Whereas some variation in observed responses of detectors on time elapsing between radiation exposure and processing may be observed, fading of the stored signal is not a significant consideration for operational use. Consideration of environmental effects, in particular the role of oxygen, can lead to insights into the mechanisms of track formation and stability, and into the more general properties of the plastic. Optimistically, such insights may help direct fundamental research on plastic properties and lead to improvements in performance of PADC as a radiation detector. (author)