Positron study of alpha-uranium

The results of measurements of the positron lifetime and Doppler broadening of the annihilation line for natural uranium in the alpha-phase are presen ted. The deconvolution of the positron lifetime spectrum showed only one li fetime component equal to 159 +/- 1 ps which corresponds to the positron li fetime in the bulk. Theoretical calculations of the positron lifetime disag ree with this value. We also observed a poor agreement between the measured and calculated Doppler broadening spectra in the part where the core elect ron contribution dominates. It turns out that current theoretical approache s used for the calculation of positron annihilation characteristics are ina dequate for uranium. (C) 1999 Elsevier Science Ltd. All rights reserved.