RADIATION DETECTOR FOR THE ISRAELI FIRST RESPONDERS-METHODOLOGY OF SELECTION.

This paper presents the rationale and development of a methodology of selection of a radiation detector that can be used by first responders arriving to a terror event scene, not knowing if the event involves any radioactive materials. This detector can be used to detect and quantify the presence of gamma radiation. The role of this detector in a radiological terror event is reviewed via the operational concept for handling radiological terror in Israel. The development of the methodology of selection included a literature survey of relevant radiation detector categories, followed by a user-side survey of requirements based on the first responders' experience along with the Israeli Ministry of Defense perspective on the management of radiological events, supplemented by the input from experts in aspects of radiation detection, radiation protection and dosimetry from the Israel Atomic Energy Commission's Soreq Nuclear Research Center. The general qualitative characterisation of requirements was then quantified using a scoring method, enabling the methodological evaluation and numerical ranking of available detectors. Plans to evaluate candidate detector models according to the developed methodology are outlined. The detectors evaluation will be conducted as part of the procurement procedure of future detectors for first responders.

SEARCH FOR EXPERIMENTAL EVIDENCE OF DOSE-RATE AND WALL SCATTERING EFFECTS IN THE THERMOLUMINESCENCE RESPONSE OF LIF:MG,TI (TLD-100).

An experimental investigation into the possibility of dose-rate effects and wall scatter in the thermoluminescent response of LiF:Mg,Ti (TLD-100) was carried out. The investigation was motivated by theoretical simulations predicting the possible presence of dose-rate effects coupled with the lack of detailed experimental studies. The dose rate was varied by changing the source to sample distance, by the use of attenuators, sources of 137Cs of various activities, filtration and the construction of identical geometrical irradiators of Teflon and stainless steel. Four levels of dose in the linear dose response region were studied at 10-2 Gy, 1.5 × 10-2 Gy, 0.1 Gy and 0.5 Gy to avoid complications in interpretation due to supralinearity above 1 Gy. At the dose of 1.5 × 10-2 Gy, the dose rate was varied by five orders of magnitude from 4.9 × 10-3 Gy s-1 to 4.9 × 10-8 Gy s-1. At the other levels of dose, a one to two orders of magnitude in dose rate was achieved. Within the measurement uncertainty of 5-10%, no dose-rate effects were observed in any of the experimental measurements and no changes in the shape of the glow curve were observed. The maximum wall scatter effect (Teflon to stainless steel) was measured at ~8% within the experimental uncertainty and well below expectations. The results are encouraging with respect to the accurate and reproducible use of LiF:Mg,Ti under various experimental conditions of irradiation.