PREIRRADATION FADE AND POSTIRRADIATION FADE FOR LIFMG,TI, TLD-600 ANDTLD-700, AS A FUNCTION OF TIME

Pre-irradiation fade and post-irradiation fade are two contributing fa ctors that affect the response of a thermoluminescent (TL) phosphor as a function of time. These phenomena have been extensively studied, ye t the results from both experimental and theoretical calculations vary considerably. The Naval Dosimetry Center conducted several studies ex amining pre-irradiation fade and post-irradiation fade in the Harshaw/ Bicron Radiation Measurement Product's multi-element (LiF)-Li-6 (TLD-6 00) and (LiF)-Li-7 (TLD-700) 8801 TLD cards. Photon and neutron irradi ations were conducted using Ra-226 and PuBe sources, respectively. Pre -irradiation fade and post-irradiation fade investigations were conduc ted for evaluation periods that varied from 1 to 40 weeks. Findings sh ow that the fade factor following neutron exposure is greater than fro m photon exposure alone. Further a fade algorithm based on a multiple regression model using two independent variables, the number of weeks of pre-irradiation fade and post-irradiation fade, gives a more accura te fade correction factor than Bicron's (our current) algorithm. This is especially true for neutron exposures.