Inferring Soil Chemical and Physical Mobility Using 256-Channel Nai Radiometric Data

Abstract

The ²²⁸Ac gamma ray decay emission at ~900 keV from the thorium-232 decay series is produced approximately 1.9 years (half-life) before the formation of ²⁰⁸Tl and the 2614 keV (standard thorium) gamma ray decay emission. Because the difference between the daughter products is relatively small, it has been assumed that the two decay energies are in equilibrium. However, when ²²⁸Ac gamma ray energy at ~900 keV was isolated from standard 256-channel, high resolution radiometric data using a multispectral processing technique, a difference in the spatial distribution of the ²²⁸Ac ~900 keV and ²⁰⁸Tl 2614 keV was observed. This case study describes how the difference between the ²²⁸Ac ~900 keV and ²⁰⁸Tl 2614 keV was resolved, and considers how the spatial differences maybe used to infer and monitor soil chemical and physical mobility and identify potential radiometric disequilibrium conditions.

Technical Area: Regolith Geophysics