Thermoluminescent Internal Beta-Ray Dosimetry

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Abstract
The possibility of using ther-moluminescence for in vivo and in vitro direct dose measurements in tiny body cavities (for example, bone marrow) suggested investigation of the response to beta radiation of LiF and CaF2 powder and single crystals of different thicknesses (down to microns). Several beta-ray sources were made in the form of gelatin or polyester resin molds. The emitters consisted of 3H, 63Ni, 35S, 45Ca, 204T1, and 90Sr (90Y), and the absorbed dose rate was computed from the known concentration in each case. The thermoluminescent output/unit weight and/unit absorbed dose was essentially the same for 204Tl and 60Sr as for 60Co but dropped for the lower-energy beta-ray emitters. Among the factors considered which might account for the drop in light output were: the relation of the beta-ray range to the physical size of a grain of the compound; the existence of a "dead" surface layer; the effect of high specific ionization on light output. To check the latter possibility, monoenergetic conversion electrons of widely different energies were employed to irradiate single crystals in order to evaluate the light output/erg absorbed; this ratio was independent of the specific ionization existing under these conditions. This form of dosimetry is quite feasible, even for tritium, provided careful precalibration is carried out with a sample of the specific batch to be employed. Applications to the dosimetry of beta-ray applicators are described.