Lab research demonstrates how iron artifacts sequester plutonium from their local environment

August 19, 2010—Plutonium released into the environment has a strong affinity for particulate and mineral surfaces. Iron oxides are of particular interest because iron and iron-containing alloys are ubiquitous and may function as high efficiency plutonium scavengers. Metals of this class, often covered with an oxide coating, could adsorb and sequester trace levels of plutonium encountered in the local environment.

Cody Lake, a LANL summer student from the New Mexico Institute of Mining and Technology, worked with Warren Oldham and Don Dry of Nuclear and Radiochemistry (C-NR) to test this intriguing idea. The researchers collected discarded iron artifacts, such as nails, washers, rebar, and saw blades; from the outdoor environment and analyzed their surfaces for adsorbed plutonium. The scientists used dilute acid to leach adsorbed plutonium that may be present on the surfaces of these metal objects. They purified the resulting solution, and then assayed the electroplated deposit using alpha spectrometry.

The figure below shows a typical collection of objects and associated analytical data. In this case, a sample collected at an historic mine site in the Zuni Mountains of western New Mexico gave a measured activity of plutonium-239 and -240 isotopes of 2.4 disintegrations per minute (dpm), corresponding to approximately 3 x 10¹⁰ total plutonium atoms. This activity level represents an approximate 10 to 100-fold enhancement in collection efficiency compared to plutonium measured in a typical gram of regional soil. Analyses of control samples that did not have environmental exposure, such as fully dissolved iron nails purchased from a local hardware store, gave no evidence for detectable levels of plutonium. The study demonstrates that trace levels of plutonium, which were produced in atmospheric nuclear tests more than 50 years ago, can be detected and quantified by exploiting the actinide-scavenging properties of certain metal oxide coatings. This development for extremely sensitive detection of actinides has potential applications for the Laboratory's Global Security mission area.

The NNSA Office of Nonproliferation Research and Development (Rebecca Chamberlin, LANL program manager) supported the work. Warren Oldham is the technical contact.

Click to enlarge

Rusty nails and other modern artifacts sequester plutonium from their local environment. This sample came from an historic mine site in the Zuni Mountains of west-central New Mexico.