R.K. Kher

The development of thin CaSO4:Dy Teflon TL dosimeters for beta dosimetry in personnel monitoring

Abstract This paper describes the development of thin (0.1 and 0.2 mm) CaSO4:Dy Teflon dosimeters thermally bonded to thick (0.7 and 0.6 mm respectively) Teflon bases for application to β-dosimetry in personnel monitoring. The composite dosimeters (13 mm dia. and 0.8 mm thick) were found quite rigid and they do not deform during their readout. The TL response of the 0.1 mm TL dosimeter was found to be β-energy independent in the energy range 0.76–2.25 MeV. The TL response of the 0.2 mm dosimeter, however, decreased with decreasing β-energy in this range. The minimum detectable γ-dose with 0.1 mm TL dosimeters was found to be 0.13 mGy. Hence, due to their energy independence, mechanical strength, TL efficiency, and capability in low dose measurements, the 0.1 mm CaSO4:Dy Teflon dosimeters thermally bonded to 0.7 mm Teflon base were found suitable for β-dosimetry in personnel monitoring.

Gamma ray induced sensitization in CaSO4: Dy and competing trap model

Abstract Gamma ray induced sensitization in CaSO4 :Dy has been compared for different temperatures during irradiation (25° 120° and 250°C). Enhanced sensitization at elevated temperatures seems to support the competing trap model for supralinearity and sensitization in CaSO4 :Dy.

Fast neutron response of coumarin in water and heavy water

Abstract Response of coumarin in aqueous solution has been studied earlier for gamma rays and fast neutrons by fluorescence measurement. For further fast neutron studies, two systems viz. coumarin in H 2 O and coumarin in D 2 O, were irradiated with fast neutrons in snif facility in the swimming pool type apsara reactor at Trombay. Neutron fluence was estimated by measuring induced activity in sulphur pellet and associated gamma radiation was estimated using CaSO 4 :Dy TLD powder. The kerma values were calculated for H 2 O and D 2 O, assuming modified fission spectrum for fast neutron in snif position, and they were in the ratio of 2:1. Response of a chemical dosimetric system is expected to be proportional to the absorbed dose in the respective system for the same neutron fluence. This was experimentally found to be the case for coumarin in H 2 O or D 2 O. These results are likely to be true in general for any aqueous chemical system. The limitations of using such a dual system for dosimetry in a mixed field is discussed.

Fast neutron irradiation of aqueous solution of coumarin.

Abstract The response of aqueous solution of coumarin has been studied for fast neutrons from a reactor and for 60 Co gamma rays. Coumarin on irradiation yields fluorescent products which were measured by spectrophotofluorimetry. The ratio of neutron to gamma response was found to be 0.405 ±0.047. The effect of addition of dimethyl sulfoxide, cysteine and thymine on neutron response was studied. The reduction in the response matched with hydroxyl rate constants of these chemicals and of coumarin, indicating involvement of OH radicals.

Photon energy dependence of CaSO4: Dy embedded teflon TLD discs

Abstract The photon energy dependence of CaSo 4 : Dy TLD phosphor embedded in Teflon in various proportions has been studied and results are compared with calculated energy dependence for such mixtures. It is found that the energy response of a high effective Z TL phosphor could not be reduced by simply embedding it into a low effective Z binding matrix. The discrepancies in experimental and calculated values are explained.