engleski

Fast neutron response of LiF TL dosimeters

Generally, the intensity of the main dosimetric peak i.e. the sensitivity of the most thermoluminescence (TL) dosimeters (expressed as the TL response/absorbed dose) decreases with increasing LET. However, it is known that the 'high temperature peak' (HTP) of LiF:Mg, Ti TL detectors increases with increasing LET, while the 'low temperature peak' (LTP) of LiF:Mg, Ti decreases. HTP, also called peak 7, appears between 240-270 oC, while LTP can be found in the literature as peak 5 or 'dosimetric' peak and appears in the temperature range 180-240 oC. The dose response results of LTP and HTP of LiF:Mg, Ti in the literature are ambiguous in high LET radiation field. The reason in most cases is that the gamma component in the mixed field is not taken properly into consideration. In the every day practice work place monitoring it is necessary to measure low LET (gamma) and both low and high LET (e.g. gamma-neutron) radiation in the mixed fields. TLD-100 (Harshaw) and MTS-N (Poland) LiF:Mg, Ti dosimeters produced from natural LiF are easily available and widely used in the practical dosimetry tasks. The aim of this study was to compare the LET sensitivity of LTP and HTP for TLD-100 (Harshaw) and MTS-N (Poland) LiF detectors for 14.5 MeV neutrons in the dose range 50 mGy-300 mGy (expressed in tissue kerma). At the same time the effect of the holder type to the dosimeter response was also studied. 14.5 MeV fast neutrons produced by Texas Nuclear Corporation 300 keV electrostatic accelerator using 3H(d, n)4He nuclear reaction was used for neutron irradiation. The gamma component in the mixed field was measured by Geiger-Muller counter calibrated in standard dosimetry laboratory. Gamma irradiation was carried out by 137Cs source. It was found, that while the gamma sensitivity of MTS-N compared to TLD-100 is about 2.5, the fast neutron sensitivity is much lower, equal to about 0.7. The responses of the low and high temperature TL peaks are linear for both kinds of LiF detectors in the dose range investigated. Adequate analytical peak separation and curve fitting programme enabled estimation of the relative neutron sensitivity of both peaks and the assessment of changes on the structure of glow curves by changes of LET of radiation. With respect to different sensitivities of HTP and LTP both MTS-N and TLD-100 are suitable for simultaneous measurement of neutron and gamma component of the dose in a mixed neutron-gamma radiation field using single dosimeter.

Fast neutron dosimetry; LiF detectors; TL

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