Sodium pyrophosphate- a new thermoluminescent detector

Abstract

Sodium pyrophosphate doped with dysprosium oxide in the ratio of 1000 : 1 by weight has been developed as a thermoluminescent detector. The gamma ray response characteristics of the prepared phosphor along with the thermal and fast neutron responses are reported in this paper. The phosphor has an emission spectrum consisting of two peaks at 480 nm and 580 nm. It has three glow peaks at 90°C, 181°C and 228°C. The low temperature peak decays rapidly on storage and the glow peak at 181°C is stable and useful for dosimetry purposes. The integrated thermoluminescence has always been measured three days after irradiation. The trap depths for the three glow peaks have been determined as 0.89 eV, 1.24 eV and 1.58 eV respectively. The optimum annealing temperature of the phosphor is found to be 400°C. The photon energy response of the new phosphor was estimated theoretically and experimentally and found to be similar to that of LiF (TLD-100). The exposure range covered was from 0.41 C·kg⁻¹ to 3.30 C·kg⁻¹ of ⁶⁰Co gamma radiation and the TL output is found to be linear in this range. The response of the phosphor per unit thermal neutron fluence is equivalent to 1.3 × 10⁻¹⁴ C·kg⁻¹ of ⁶⁰Co gamma radiation. The kerma in sodium pyrophosphate for various neutron energies were computed. A fast neutron exposure of 10 mSv gives a TL output equivalent to 1.95×10⁻⁶ C·kg⁻¹ of ⁶⁰Co gamma rays.