Precision analysis of 198Au beta spectral shape

The investigation of the 965 keV transitions of 198Au shows that the same data analysed with the Fermi function taken from NBS tables and that from Dzhelepov and Zyrianova (corrected for finite size) differ by 3% in slope. With a shape factor C(W)=k(1+aW) the coefficient a has been determined to be -0.022+or-0.011 using Bhalla and Rose tables with Buhring's screening correction and the correct end point determined from the proper physical behaviour of the shape factor in the neighbourhood of the end point energy. The use of this coefficient through the PBS method gives alpha 412K=(301+or-3)10-4 in agreement with theory as well as the recent very accurate IEC methods. This means that the disagreement of the PBS method with theory and other accurate methods arises mainly through the occurrence of a shape factor in the electron energy spectrum and the use of the correct shape factor in the PBS method gives good agreement.