GAMMA-DOSIMETRY AND NEUTRON-DOSIMETRY USING CAF2-TM THERMOLUMINESCENTDOSIMETERS FOR FUSION-REACTOR SHIELDING EXPERIMENTS

TLD-300 (CaF2:Tm) dosimeters were used to measure the absorbed dose in an experimental assembly simulating the shield and the superconductin g coils of a fusion reactor irradiated by 14-MeV neutrons. The shield was formed by plates of Type 316 stainless steel and by a water-equiva lent material (Perspex), while a second block made of Type 316 stainle ss steel and copper plates simulated the superconducting coils of the tokamak. Since the TLD-300 shows two main peaks, one of which is more sensitive to neutrons, the neutron and gamma doses were separated usin g the two-peak method. The resulting absorbed neutron dose was 30% of the total in positions close to the neutron source, while its contribu tion was negligible (<7%) in the superconducting coils. The total dose level to be studied ranged from a few tens of micrograys to 10 Gy. Be cause the latter value was expected to be out of the linear response r ange for the TLD-300, the supralinear effects for the TLD-300 were stu died as well as its sensitivity to determine the possibility of its us e for doses as low as 10 mu Gy. Since the detector background can intr oduce an uncertainty of less than +/-10%, the measurement of very low doses was performed with a total error lower than +/-15%.