Characterisation of the plutonium isotopic composition of a sediment core from Palomares, Spain, by low-energy AMS and alpha-spectrometry

TL;DR

This study demonstrates the use of low-energy accelerator mass spectrometry to analyze plutonium isotopic composition in a sediment core from Palomares, confirming the presence of weapon-grade plutonium from the 1966 nuclear accident and validating the AMS technique against alpha-spectrometry.

Contribution

First application of low-energy AMS for environmental plutonium isotope analysis, providing detailed isotopic profiles and source attribution in marine sediments.

Findings

Weapon-grade plutonium detected in marine sediments.

AMS results validated against alpha-spectrometry.

Isotopic ratios confirm nuclear accident source.

Abstract

The measurement of plutonium isotopes, 239Pu and 240Pu, at 670 kV on the compact accelerator mass spectrometry (AMS) system at the Centro Nacional de Aceleradores (CNA) in Seville, Spain, is now a reality. In this work, we present first Pu AMS results for environmental samples: a sediment core collected in a submarine canyon in the Mediterranean coast of the Spanish region of Palomares, affected by a nuclear accident in 1966. From the study of the 240Pu/239Pu atomic ratio profile, showing on average levels lower than 11%, we confirm that the weapon-grade plutonium released on land during the accident, with a characteristic 240Pu/239Pu atomic ratio of 5.8%, has found its way into the marine environment. A two-plutonium sources mixture model (Palomares and fallout) is used to elucidate the percentage of the plutonium coming from the accident. As a validation exercise of the Pu AMS measuring technique and in order to obtain the 238Pu/(239+240)Pu activity ratios, samples were also studied by alpha-spectrometry (AS). The obtained AS 239+240Pu activity concentration results fit in with the AMS ones in a wide dynamic range, thus validating the AMS technique.