Thermoluminescent method for the measurements of tritium production in neutronics experiments

Abstract

A European nuclear-fusion technology program is currently, except of other acivities, on the stage of validating the capability of neutronic codes and nuclear data for use in the ITER project. This requires a technique for reliable measurements of tritium produced by a neutron flux and these estimates must have a qualified uncertainty. The application of LiF TL detectors, calibrated by the direct measurement of tritium activity using the Liquid Scintillation Counting (LSC) technique, is a new approach to the assessment of the tritium production rate in fusion related benchmark experiments. Lithium Fluoride Thermoluminescent Detectors (TLD) are commonly used for measurements of thermal neutron dose using the 6 Li(n,α) 3 H reaction. The accumulation of radioactive tritium in the LiF detectors is usually considered as an undesired effect to the detectors, increasing intrinsic background after high-dose neutron exposure. The same effect may be exploited for the measurement of generated tritium activity. A TL signal corresponding to the energy deposited in the − β decay of 3 H, expressed as mGy/h to be recalculated to Bq/mg, requires calibration by an independent measurement of 3 H activity. This calibration can be performed by applying e.g. LSC-technique. A good correlation was obtained in the tested range of tritium activity: 17–25 Bq/mg of LiF (0.080–0.118 mGy/h) with a slope of regression line: 1.75 × 10 −4 [mGy/h]/[Bq], r 2 = 0.94. The thermal treatment of the TLDs after irradiation (annealing: 400 °C, 1 h) leads to a loss of 37% of the initial tritium content. Prolonged storage of the irradiated TLDs at room temperature, pressure and humidity causes the escape of less than 5% of the accumulated tritium after 100 days. Thus LiF TLDs after calibration can be used as one of techniques for the assessment of tritium production in neutronic experiments.