Hyperfine Structure of Americium-241

Abstract

Atomic-beam measurements on ${\mathrm{Am}}^{241}$ have confirmed that the nuclear spin is $I=\frac{5}{2}$, and have established that the electronic ground state is characterized by an angular momentum $J=\frac{7}{2}$ and a Land\'e splitting factor ${g}_{J}=\ensuremath{-}1.9371(10)$. In addition, the magnetic-dipole and electric-quadrupole hyperfine-structure coupling constants have been found to be, respectively, $A=\ifmmode\pm\else\textpm\fi{}17.144(8)$ Mc/sec and $B=\ensuremath{\mp}123.82(10)$ Mc/sec. It is hypothesized that these values arise from a state that is primarily formed from the Hund's rule term $^{8}S$ of the configuration ${(5f)}^{7}{(7s)}^{2}$. However, important contributions to the measured ${g}_{J}$, $A$, and $B$ values are shown to come from the admixture of other terms in the ground state by means of the spin-orbit interaction, and also from the excitation of $s$ electrons in the core to higher $s$ states.