A preliminary study enabled us, following a comparison with other electrets classically recognized as such (PE, PTFE, etc.), to show the interesting behaviour of the CR 39 (which is an allyl diglycol carbonate principally utilised as a solid state track detector) as an electret. Charged by Corona method and placed in a Faraday cage, conservation of the charges situates CR 39 between the classical electrets teflon and mylar. We studied the response (in charge terms) of the CR 39 submitted to an X radiation of average energy (77 keV) for dose between O and 8 rads. The discharge curves obtained are very significant and they enable us to prove the possibility of using the CR 39 in electret dosimetry.