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 Landé splitting factor $g_J=-1.9371\mathrm{}\left(10\right)\mathrm{}$. In addition, the magnetic-dipole and electric-quadrupole hyperfine-structure coupling constants have been found to be, respectively, $A=\pm 17.144\left(8\right)\mathrm{}$ Mc/sec and $B=\mp 123.82\left(10\right)\mathrm{}$ 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 ${\mathrm{}\left(5f\right)\mathrm{}}^7{\mathrm{}\left(7s\right)\mathrm{}}^2$. 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.