Measurement of 236U in environmental media

The long-lived uranium isotope 236U (T1/2=23.4 Ma) is produced by 235U neutron capture and builds up to high levels in nuclear fuel. It has been distributed in the environment as a result of nuclear activities including nuclear explosions, accidents at nuclear plants, dumping of nuclear waste and releases from nuclear facilities. 236U is a potentially useful tracer of irradiated uranium for nuclear safeguards or other applications, due to its virtual absence in natural samples (236U:238U ratio ∼10-10 in uranium ore). We have measured 236U in soil and sediment reference materials (IAEA 375, 135 and 300) by accelerator mass spectrometry (AMS). The AMS system on the ANTARES accelerator has been upgraded to make such measurements possible. The system, including sample preparation procedures, is described and the results discussed