Fig. 4. ${}^{233}$U/${}^{236}$U ratio in the Irish Sea.

Depth profile of the ${}^{233}$U/${}^{236}$U atom ratio in the Irish Sea sediment core collected close to the Sellafield reprocessing plant and in Irish Sea water (IAEA-381) with ±1 $\sigma$ uncertainty. Increased uncertainties of three samples at depths 11 cm, 23 cm and 47 cm are caused by low counting statistics on ${}^{233}$U due to preceding dilution (1:100) of the material. The horizontal blue line marks the weighted average for the ${}^{233}$U/${}^{236}$U ratio in the Irish Sea with ±1 $\sigma$ uncertainty (s.e.m.).