RADIATION-INDUCED CATHODOLUMINESCENT SIGNATURES IN CALCITE

At ambient temperatures, a permanent change due to neutron irradiation has been identified in the luminescent properties of the common mineral calcite. Calcite is one of many ubiquitous minerals that are known to exhibit luminescence under electron bombardment, a process known as cathodoluminescence (CL). The UV-Visible spectra of individual calcite grains were measured with CL spectroscopy before and after neutron irradiation. Exposure to natural and laboratory-induced radiation by neutrons causes additional crystal lattice defects (beyond those naturally occurring) that leave a permanent, readily-measurable CL signature in the 515 nm region of the spectrum. Dose-response results following irradiation have been measured and a spectroscopic signature is described that increases proportionately to neutron dose. The CL measurements are complicated by a dependence on the orientation relative to direction of excitation. When taken into account, the total dose to the crystal can be estimated, and possibly even the direction of the neutron source can be determined.

This signature could potentially be developed into a nuclear forensics tool to help identify locations where special nuclear materials have been stored, as well as a functional geological tool for dating. Development of this environmental dosimetry technique would provide a nondestructive, practical range of age paleodose measurements for important calcite minerals in question.