41Ca, 14C and 10Be concentrations in coral sand from the Bikini atoll.

Abstract Activation measurements of materials exposed to nuclear bomb explosions are widely used to reconstruct the neutron flux for retrospective dosimetry. In this study the applicability of coral CaCO 3 as a biogenic neutron fluence dosimeter is tested. The long-lived radioisotopes 41 Ca, 14 C and 10 Be, which had been produced in nuclear bomb explosions, are measured in several coral sand samples from the Bikini atoll at the 600 kV and 200 kV AMS facilities of ETH Zurich. Elevated concentrations of all studied isotopes are found in a sample from the crater that was initially formed by the high-yield nuclear explosion Castle Bravo in 1954 and that had been used as site for several tests afterward. The observed 14 C concentration is considered too large to originate from neutron irradiation of CaCO 3 alone. The relatively low concentration of 10 Be found in the crater sample indicates that production of 10 Be during nuclear bomb testing is generally minor. A simple neutron fluence reconstruction is performed on basis of the 41 Ca/ 40 Ca ratio.