A procedure for the preparation of thermoluminescent, manganese-activated calcium fluoride (CaF 2: Mn) that involves the activation of the coprecipitated mixed fluorides of calcium and manganese at 1200°C is described. The characteristics of the material are given, and a comparison is made between the coprecipitated product and that produced by procedures described in the literature. The coprecipitated phosphor has been thoroughly investigated in terms of radiation dosimetry and found to have a linear response ranging from 100 μr to at least 10 4r with an information loss of less than 3 percent per 2-month period.