A new ground-level fallout record of uranium and plutonium isotopes for northern temperate latitudes Thorsten Warneke, Ian W. Croudace  , Phillip E. Warwick, Rex N. Taylor Southampton Oceanography Centre, Southampton SO14 3ZH, UK Received 26 April 2001; received in revised form 28 June 2002; accepted 14 August 2002 Abstract Plutonium and uranium isotope ratios can be used to differentiate the sources of nuclear contamination from nuclear weapon establishments (Environ. Sci. Technol. 34 (2000) 4496; Internal Report for AWRE Aldermaston, UK (1961)), weapon fallout (Geochim. Cosmochim. Acta 51 (1987) 2623; Earth Planet. Sci. Lett. 63 (1983) 202; Earth Planet. Sci. Lett. 22 (1974) 111; Geochim. Cosmochim. Acta 64 (2000) 989), reprocessing plants, reactor or satellite accidents (Science 105 (1979) 583; Science 238 (1987) 512) and in addition they provide markers for post-1952 geochronology of environmental systems. A good record of plutonium and uranium isotope ratios of the background resulting from atmospheric nuclear testing is essential for source characterisation studies. Using recently developed mass spectrometric techniques (J. Anal. At. Spectrom. 16 (2001) 279) we present here the first complete records between 1952 and the present day of northern temperate latitude 240 Pu/ 239 Pu and 238 U/ 235 U atom ratios for atmospheric deposition. Such information was not derived directly during the period of atmospheric testing because suitable mass spectrometric capability was not available. The currently derived records are based on an annual herbage archive and a core from an Alpine glacier. These studies reveal hitherto unseen fluctuations in the 238 U/ 235 U atmospheric fallout record, some of which are directly related to nuclear testing. In addition, they also provide the first evidence that plutonium contamination originating from Nevada Desert atmospheric weapon tests in 1952 and 1953 extended eastwards as far as northwestern Europe. The results presented here demonstrate that we now have the capability to detect and precisely identify sources of plutonium in the environment with implications for the development of atmospheric transport models, recent geochronology and environmental studies. ß 2002 Elsevier Science B.V. All rights reserved. Keywords: plutonium; uranium; isotope ratios; weapon fallout; multi-collector ICP-mass spectrometry; Rothamsted grass archive 1. Introduction The radioactive debris from nuclear explosions (Figs. 1 and 2) was partitioned into the tropo- sphere and stratosphere according to its particle size and the power of the explosion. The subse- quent fallout occurred on a time scale of minutes through to years. The amount of debris produced and its particle size distribution depended on the explosive yield of the device and its height above ground when detonated [9]. Fine debris from small yield tests ( 6 100 kt TNT equivalent) pro- duced fallout that was expected to have a maxi- 0012-821X / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII:S0012-821X(02)00930-5 * Corresponding author. Tel.: +44-2380-59-27-80; Fax: +44-2380-59-64-50. E-mail address: iwc@soc.soton.ac.uk (I.E. Croudace). Earth and Planetary Science Letters 203 (2002) 1047^1057 www.elsevier.com/locate/epsl