The impact of accidental immersion in selected liquids on the sensitivity and repeatability of MCP-N thermoluminescent detectors

Abstract

Thermoluminescent detectors (TLDs) are often used for personal and environmental dosimetry. The investigations of accidental immersion in liquids or washing TLDs on the dose response are limited. Detectors are placed in the dedicated card, which, may not provide full protection against liquids. Such accidental contact with liquids affects correctness of the TLDs read-out depending on the type of detector. The purpose of this study was to evaluate MCP-N response for the same dose after contact with different liquids.First, the stability of thirty four MCP-N detectors (LiF:Mg,Cu,P) manufactured at the Institute of Nuclear Physics in Krakow in a form of circular pellets ø 4.5 × 0.9 mm was checked. Then the procedure was as follows: weighting, annealing at 240 °C for 10 min, irradiation (dose 1.1 mGy), immersion in different liquids (water, tea, coffee, washing liquid) for 30 min, drying, reweighting, reannealing at 100 °C for 10 min, reweighting and read-out. Read-outs were performed using a RA-04 reader. Immersion was repeated 6 times in two phases. Six detectors were used as a reference group – they were not immersed at any liquid.After immersion in tea and coffee MCP-N read-out was lower than before immersion and the sensitivity after the experiment significantly decreased (in average 60% and 66%). After immersion in water and in washing liquid MCP-N read-out was higher than before immersion whereas the sensitivity after the experiment slightly decreased (in average 8% and 12%). This reduction was probably apparent as in the reference group it was equal to 21%. Detector mass changes were observed in the range of ±1%.Summarizing, dark liquids cause significant and immediate decrease of sensitivity while water or washing liquid cause apparent increase of sensitivity. This means in practice an underestimated or overestimated individual or environmental dose.