The estimation of thorium and uranium at the submicrogram level in bone by neutron activation

A method for determining thorium and uranium at the sub-microgram level (down to 10−3 μg) is described. Bone which has previously been ashed at 600°C is irradiated in a neutron flux of 2 × 1013 cm−2 sec−1 for 20 min. After chemical separation which involves elution from an anion exchange column using a mixture of hydrochloric and hydrofluoric acids, the induced Pa223 and Np239 activities were measured and compared to a standard. The method was tested using samples of ashed cow bone to which were added known concentrations of uranium and thorium and results for the analysis of several bones with widely differing histories are presented.