Effect of neutron irradiation on dosimetric properties of TLD-600H (6LiF:Mg,Cu,P)

Ideally, dosimeters should measure the dose without their dosimetric properties being affected by the radiation type being measured. Industry-wide occupational radiation workers that can be potentially exposed to neutron radiation fields are routinely monitored by thermoluminescent (TLD) dosimeters. The neutron dose measured by these devices is obtained from the interaction products of thermal (slow) neutrons and 6Li. The number of alpha particle and 3H− ions (tritium) released in the (n, 6Li) reaction is proportional to the dose received by the dosimeter. It is a common practice to evaluate the neutron dose indirectly from these products. In this work we present for the first time direct evidence that the neutron exposure to LiF:Mg,Cu,P (TLD-600H) can have deleterious effects on the dosimetric properties of one of the most commonly utilized dosimeters in the world. The interstitial non-negligible tritium dose contribution to the dosimeter is a result of the beta decay of the tritium nuclei interstitially present in the material. If not accounted for the effect of this self irradiation can directly affect the measured occupational dose to workers. In order to estimate the significance of these effects, tritium dose buildup was measured in the TLD-600H irradiated to different neutron doses from a reactor and a 252Cf source and then calculated in terms of a daily dose buildup rate. The effect of the self irradiation on these dosimeters resulting from tritium decay was extensively studied. The TLD dosimeters that were exposed to neutron doses show a significant dose buildup even after they have been annealed, i.e. even after the signal produced by the incident neutron dose is completely erased from the lower energy trap states of the dosimeter. The other discovered effect of neutron irradiation on TLD-600H is a significant loss in the detection sensitivity (up to 15%).