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

The measurement of plutonium isotopes, Pu-239 and Pu-240, 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 Pu-240/Pu-239 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 Pu-240/Pu-239 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 Pu-238/Pu(239+240) activity ratios, samples were also studied by alpha-spectrometry (AS). The obtained AS(239+240)Pu activity concentration results fit in with the AMS ones in a wide dynamic range, thus validating the AMS technique. (C) 2009 Elsevier B.V. All rights reserved.