ELECTRON AND GAMMA-RAY DOSIMETRY USING RADIATION-INDUCED COLOR-CENTERS IN LIF

Ionizing radiation produces relatively stable color centers in lithium fluoride. The values of the optical absorbance at the maxima of the resulting absorption bands are measured at the following wavelengths: λ = 247 nm (F-centers); 443 nm (M-centers); 315 nm (R1-centers); 374 nm (R2-centers); 517 nm (N1-centers); 547 nm (N2-centers). We show that the response expressed in terms of optical absorbance as a function of absorbed dose in LiF is approximately the same for electron beams at very high absorbed dose rates (<1012 rad · s-1) and for gamma radiation at intermediate dose rates (≈102 rad · s-1). A change in ambient temperature over the range from -78°C to +100°C during irradiation has only a small influence on response. The production of each type of color center is initially proportional to absorbed dose and then gradually tends toward saturation. By utilizing absorption bands corresponding to different types of color centers, an absorbed-dose range from 104 to 109 rad can be covered, with response regions overlapping at the doses of change-over from one to the other center. Commercially available cleaved LiF crystals, 6 mm × 6 mm × 2 mm in size and containing only very low amounts of impurities, proved to have satisfactory optical properties for high-level dosimetry applications. Commercially available LiF discs, 25 mm in diameter and 1.5 mm in thickness, supplied as vacuum-ultraviolet-transmitting window material, are also useful for dosimetry. Both types are of optical quality and may be reused by thermally bleaching the radiation-induced color centers. © 1979.