Imaging uranium distributions in fossil bones by fission track etching

In the course of our work within the framework of an interdisciplinary project dealing with the absolute dating of fossil bones from Austrian caves by means of the U-series method we became interested in possible U-concentration gradients in the bone samples. A successful attempt is reported to make the U-distribution in bones directly visible by irradiating the samples with thermal neutrons and detecting the emitted fission products of²³⁵U in a plastic foil using the track etch method. This turns out to be possible also for relatively small U-concentrations of the order of 1 ppm. The uranium seems to concentrate near the surfaces which is in qualitative agreement with earlier results from the literature obtained by means of neutron activation analysis.