Graphite-mixed non-transparent LiF and Li2B4O7:Mn TL dosimeters combined with a two side reading system for beta-gamma dosimetry

Hot sintered LiF and Li2B4O7:Mn TL dosimeters are now in use for beta-gamma monitoring in Poland and Denmark. Both kinds of dosimeters show good energy characteristics for gamma radiation but their response to beta-rays are highly dependent on the energy of the beta particles. Improvement of the energy-response curves for beta radiation is normally achieved by minimizing the dosimeter thickness. A similar effect can be obtained by using TL dosimeters made of mixtures of LiF or Li2B4O7:Mn materials with different amounts of graphite (0.5, 1, 2, 4 and 8%) have been prepared and studied for beta-gamma dosimetry. A special design of a read-out chamber with two photomultipliers and with nitrogen as the heating medium enables simultaneous determination of emitted TL from both sides of the dosimeter separately. By using this method together with dosimeters prepared with graphite, good accuracy can be obtained for the determination of doses from soft beta emitters. This method enables also the determination of beta and gamma doses independently, applying only one sintered TL dosimeter. Experimental data, including sensitivity, energy response and re-use of the graphite-mixed dosimeters are presented and the capability of the two side read-out technique is described. (author)