CHARACTERIZATION OF FLUORESCENT NUCLEAR TRACK DETECTORS AS CRITICALITY DOSIMETERS II.

Fluorescent nuclear track detectors (FNTDs) as criticality dosimeters for both neutrons and gamma are further characterized in terms of angular dependence and quick dose assessment. The power spectrum integral depth profiles obtained from stacks of fluorescent images acquired within FNTDs exposed to a broad spectrum neutron field at various angles are analyzed to determine a calibration curve for angular dependence. MCNPX simulations were shown to be in good agreement with experimental results. A prototype triage reader was also designed and tested for quick assessment of dose. An unfolding technique incorporating both energy dependence and angular dependence is discussed. The advantages and shortcomings of using FNTDs in the event of a criticality excursion accident are analyzed.

ENERGY RESPONSE OF FLUORESCENT NUCLEAR TRACK DETECTORS OF VARIOUS COLORATIONS TO MONOENERGETIC NEUTRONS.

The neutron-energy dependence of the track-counting sensitivity of fluorescent nuclear track detectors (FNTDs) at two ranges of Mg doping, resulting in different crystal colorations, was investigated. The performance of FNTDs was studied with the following converters: Li-glass for thermal to intermediate-energy neutrons, polyethylene for fast neutrons, and polytetrafluoroethylene (Teflon™) for photon- and radon-background subtraction. The irradiations with monoenergetic neutrons were performed at the National Physics Laboratory (NPL), UK. The energy range was varied from 144 keV to 16.5 MeV in the personal dose equivalent range from 1 to 3 mSv. Monte Carlo simulations were performed to model the response of FNTDs to monoenergetic neutrons. A good agreement with the experimental data was observed suggesting the development of a basic model for future MC studies. Further work will focus on increasing FNTD sensitivity to low-energy neutrons and developing a faster imaging technique for scanning larger areas to improve counting statistics.