Consistent calculation of the screening and exchange effects in allowed β- transitions.

The atomic exchange effect has previously been demonstrated to have a great influence at low energy on the 241 Pu β- transition. The screening effect has been given as a possible explanation for a remaining discrepancy. Improved calculations have been made to consistently evaluate these two atomic effects, compared here to the recent high-precision measurements of 241 Pu and 63Ni β spectra. In this paper a screening correction has been defined to account for the spatial extension of the electron wave functions. Excellent overall agreement of about 1% from 500 eV to the end-point energy has been obtained for both β spectra, which demonstrates that a rather simple ß decay model for allowed transitions, including atomic effects within an independent-particle model, is sufficient to describe well the current most precise measurements. [ABSTRACT FROM AUTHOR]