Characterization of actinide targets by low solid-angle alpha particle counting

Actinide samples were characterized in an interlaboratory comparison betwee n IRMM and NIST, including alpha-particle counting at defined low solid ang le and counting in a 2 pi proportional gas counter. For this comparison, ni ne (UF4)-U-233 samples with high uniformity in the layer thickness were pre pared at IRMM by deposition under vacuum. Polished silicon wafers were used as source substrates, and these were rotated during the deposition using a planetary rotation system. The estimated uncertainties' for the defined low solid-angle methods were a bout 0.1% at both NIST and IRMM. The agreement of reported alpha-particle e mission rates in the energy range 2.5-5.09 MeV was better than or equal to 0.02% for the defined solid-angle methods. When comparing total alpha-parti cle emission rates over the larger energy range 0-9 MeV (which includes all emissions from the daughter nuclides and the impurities), the agreement of the defined solid-angle methods was better than or equal to 0.05%. The 2 pi proportional gas counter results were about 0.75% higher than thos e of the defined solid-angle methods. A re-examination of the correction fo r scattering from the polished silicon wafer substrates was undertaken to e xplain this discrepancy. Preliminary results of the recalculated 2 pi propo rtional gas counter results are also given. (C) 1999 Elsevier Science B.V. All rights reserved.