241AM AS A STRATIGRAPHIC MARKER FOR NUCLEAR WEAPONS TESTING AND OTHER THERMONUCLEAR REACTIONS

Americium-241 (²⁴¹Am) and Cesium-137 (¹³⁷Cs) are short-lived radioisotopes with half-lives of ~432 and ~30 years, respectively. Both are thermonuclear by-products, and therefore can be used as stratigraphic markers for the peak of nuclear weapons testing in the early to mid 1960s. Both ²⁴¹Am and ¹³⁷Cs easily adhere to fine-grained sediments, but ¹³⁷Cs is utilized more often because of its high detectability using gamma spectroscopy. However, ¹³⁷Cs tends to be more susceptible to migration in organic-rich sediments, which can restrict its geochronologic use in these types of environments. Americium-241 is less mobile, thus having the potential to be more applicable in peaty, organic-rich settings. This study utilizes ²⁴¹Am in collaboration with ¹³⁷Cs, to validate Lead-210 (²¹⁰Pb) age-dates in sediment cores from a variety of natural and anthropogenically impacted environments throughout the U.S. Virgin Islands. A positive relationship was found between ²⁴¹Am and ¹³⁷Cs profiles in some of the cores analyzed. After applying the CRS model to the ²¹⁰Pb profiles, which gave the dates for each data point, it was determined that the peaks agree well with an early 1960s date. In many cases the ²⁴¹Am peak was more well defined than the ¹³⁷Cs peak. This suggests that ²⁴¹Am can be used as a replacement, or paired with ¹³⁷Cs, in organic-rich sediments to validate the height of nuclear weapons testing in the early to mid 1960s, and/or potentially other nuclear disasters (e.g. Chernobyl, 1986).