Ph.D. Thesis Defense by Heather J. Gepford
January 3, 2001

(Dr. Nolan Hertel, advisor)

"Development and Implementation of a System for Reading Nuclear Etched Tracks in PADC (CR-39) Using Coherent Light Scattering"


Personnel neutron dosimetry remains a challenge despite years of research into various methodologies. One of the most effective techniques for neutrons energies greater than 100 keV employs the use of solid-state nuclear track detectors to monitor the passage of neutron induced charged particle tracks in the polymer CR-39. The systems currently available for reading the etched tracks in CR-39 experience difficulty quantifying the number of tracks when doses exceed 5 mSv. Operationally, dosimeters capable of assessing doses up to 50 mSv are required.

Early studies at the Universite de Franche-Compte and Los Alamos National Laboratory (LANL) have indicated the potential for using coherent light scattering from a Helium-Neon laser to read CR-39 track-etch dosimeters. Los Alamos National Laboratory initiated this work through the development of the Laser Illuminated Track Etch System (LANL-LITES), which quantifies the total scattered light produced by tracks in etched CR-39 dosimeters. An extension of this work was performed at Georgia Tech by combining the principles of LANL-LITES with those employed by J.E. Groetz at Universite de Franche-Compte resulting in the development of Buzz LITE.

The purpose of this thesis was to develop a system that uses coherent light scattering by nuclear etched tracks to ascertain personnel neutron doses. The research encompassed three objectives: a) Validation of the LANL-LITES system response through experimental measurements of CR-39 dosimeters irradiated by bare and D2O moderated 252Cf neutron fields on a mock-up system developed at Georgia Tech; b) Evaluation of the potential for using the Buzz LITE system to obtain neutron quality data from the etched CR-39 dosimeters; and c) Development of a theoretical model describing the angular light scatter distribution from neutron-induced proton tracks in CR-39.

This thesis work verifies the validity of a linear response of scattered light intensity to dose equivalent for dosimeters irradiated up to 50 mSv and theoretically establishes the potential for extraction of neutron quality information with experimental results suggesting agreement with the premise.