Personnel dosimetry for the mixed beta (Kr-85)/photon (gamma, X-ray) beams using Harshaw 8814 TL dosimeters: Performance Test Applicability Study

Abstract

Performance of Harshaw 8814 TL dosimeters was evaluated in the mixture of low energy beta (Kr-85, average energy 251 keV) and X-ray/gamma photon beams, when many doses obtained using existing dose calculation algorithms show a high bias. 264 TLDs were exposed at the Radiological and Environmental Sciences Laboratory to the pure Kr-85 energy beam as well as to different combinations of beta and photon beams of various energies (including Cs-137 and Co-60 gamma sources and M50, M200 and H300 X-ray beams). The TLDs were irradiated to different beta-to-photon dose ratios; 22 different combinations of radiation energy beams and beam dose ratios were tested. After exposure, the TLDs were readout at Brookhaven National Laboratory facility using a Harshaw 8800 reader. The doses were determined with the Harshaw Combined DOELAP dose calculation algorithm and compared to the known values. The results showed a significant deviation from the corresponding nominal values for some of the tested TLDs exposed to pure Kr-85 or a combination of Kr-85 and photon beam mixed energies. The different ratios of TL signals from chips 1–4 of the 8814 TL cards were analyzed, and an algorithm was proposed to identify the radiation beam energy to which each individual TLD was irradiated to. Finally, correction coefficients were developed which improves the performance of TL dosimetry dose calculation algorithm in the cases of exposure to a low energy beta beam and to a mixture of such beam with photons.