Preparation of two uranium glass reference materials for fission-track dating of geological samples

The European Commission produced and certified uranium glass for fission-tr ack dating in 1996 (Reference Material IRMM-540). This material is now out of stock and a project for the preparation of two new reference glasses is underway. The new glasses, containing nominally 15 and 55 mg kg(-1) uranium , were prepared from blended oxide powder, and cast using an improved metho d, which minimised micro-scale defects and optimised the yield. Glass rods were produced which were then cut into discs of 2 mm thickness and 15 mm di ameter and subsequently polished. Uranium homogeneity and fission-track stability are critical properties of the glass. An extensive study was carried out to verify the homogeneity by fission-track counting, investigating both within-disc and between disc eff ects, and to investigate potential track fading due to thermal annealing, N o evidence of uranium heterogeneity was detected. The stability study, usin g an "isochronous" method, in which all measurements are made at the end of exposure to artificial ageing, is still underway. The reference material will be certified for isotopic composition (natural) , uranium mass fraction and neutron fluence (one disc out of each set of th ree will be irradiated, together with a mica foil, to induce fission tracks in a certified fluence). The reference materials will be released as IRMM- 540R (15 mg kg(-1) U) and IRMM-541 (55 mg kg(-1) U). (C) 2001 Elsevier Scie nce Ltd. All rights reserved.