Electron-shell processes accompanying the US decay of nickel, and determination of the end-point energy of the US spectrum

We report the results of theoretical calculations which illustrate the reaction of the electron shell of atomic /sup 63/Ni to the US decay of its nucleus, and also the influence of this shell on the shape of the US spectrum near its end point. The calculations were carried out in the sudden approximation, and the atomic wave functions of the WTNi parent atom and the Cu daughter ion were calculated in the Hartree-Fock approximation. On the basis of our results, the experimentally observed drawing out of the high-energy tail of the /sup 63/Ni US spectrum is explained by redistribution of the energy of US decay into electronic degrees of freedom.