This project will support the development of a new method for determining the formation ages of minerals, especially those that cannot currently be dated with existing techniques. The method is based on the ingrowth of a rare isotope of neon - 21Ne - from the decay of uranium and thorium. This technique should be especially useful for dating of iron oxide minerals such as hematite and magnetite, and will likely be applicable to understanding the timing and origin of economically significant ore deposits produced by both sedimentary and hydrothermal processes.
Several important aspects of this dating system will be investigated. First, a set of experiments will be performed to determine the nuclear cross sections for the reaction 18O(α, n) 21Ne, which produces the daughter isotope. These experiments will involve implantation of a known dose of α particles of known energies into various target materials, followed by direct measurement of the 21Ne produced by isotope dilution mass spectrometry. Additional experiments will caharcterize the diffusivity of neon in likely minerals to be dated, which will establish under what temperature conditions neon retention is to be expected. Such data are necessary for accurate interpretation of the measured ages. A final set of experiments will be designed to identify the typical levels of uranium and thorium, as well as non-radiogenic neon, in minerals of interest for dating. These data will provide insight to what types of minerals are promising targets for the dating method.
