Nuclear Moments of Americium-241 and 16-h Americium-242 and Analysis of the Hyperfine Fields

Abstract

The nuclear moments of americium-241 and 16-h americium-242 have been directly measured by the method of triple resonance in an atomic beam. They are ${\mu }_I\left({\mathrm{Am}}^{241}\right)=+1.58\mathrm{}\left(3\right)\mathrm{}$ nm and ${\mu }_I\left({\mathrm{Am}}^{242}\right)=+0.3808\mathrm{}\left(15\right)\mathrm{}$ nm, including a correction for diamagnetic shielding. On the collective model ${\mu }_I\left({\mathrm{Am}}^{242}\right)$ is a direct measure of the gyromagnetic ratio of the core ($g_R$), and the measured value of ${\mu }_I$ is in excellent agreement with the value $g_R=\frac{Z}{A}$. From these values for the magnetic moments and previous measurements of the hyperfine constants, values are deduced for the magnetic fields at the nucleus. It is shown that breakdown of Russell-Saunders coupling including relativistic effects gives contributions of the wrong sign to the magnetic field. Arguments are given which show that the residual effect is most probably due to core polarization.