Novel Fission Track Detection for Identification and Characterization of Special Nuclear Materials

Fission track detection and analysis is used primarily in nuclear safeguards to identify special nuclear material. Identification of isotopic ratios is a crucial step in understanding the intended use of nuclear material and the nature of the materials production cycle. Unfortunately, this methodology uses etchable track detectors that require significant expertise and intensive labor to process.

This study developed a novel method using lithium fluoride (LiF) as a fluorescing nuclear track detector to conduct fission track analysis for isotopic prediction of uranium enrichment. Individual latent tracks produced by fission products were observed in LiF for the first time. These tracks were identified using fluorescence microscopy with a confocal laser scanning microscope. Specifically, lithium fluoride’s F₂ and F₃⁺ defects were excited and observed for fluorescing emission. These observations required the use of highly sensitive detectors that could maintain at least a one to ten signal to noise ratio while detecting single photon signal. Fission tracks were verified with concurrent ²⁵²Cf alpha tracks and agreement with variations in exposure times.

Experiments with uranium fuel glued to LiF detectors were used to predict enrichment. These samples were exposed to 10¹⁴ neutrons in a custom irradiator and then particles were characterized based on the number of tracks observed by the confocal laser scanning microscope. Predictions of uranium isotopes required calculation of particle mass contributing significantly to error. Seven of ten particles fell with error of prediction, two of which were depleted uranium samples and had predicted track counts of less than one per fuel grain.

This work proves the viability for a new method of identifying particles with fission track analysis. It reduces the work hours required to analyze an environmental sample for fissionable material by removing the need to etch traditional solid state nuclear track detectors.