gFactor of the 90-KeV Level inRu99and the Paramagnetic Correction in Transition Atoms

Abstract

Using the decay of 16.1-day ${\mathrm{Rh}}^{99}$, the half-life of the 90-keV state in ${\mathrm{Ru}}^{99}$ has been measured by observing delayed coincidences for the (354-90)- and the (529-90)-keV cascades. The result $t_{\frac{1}{2}}=(20.7\mathrm{}\pm 0.3)$ nsec, is very suitable for a measurement of the Larmor precession in this level by means of the time-differential angular-correlation technique. To overcome the difficult problem of correcting for paramagnetic shielding, the $g$ factor was determined with the Ru atoms in three magnetically different environments: (1) with a liquid source, (2) with Ru embedded in a copper lattice, and (3) with Ru dissolved in Ni. In the last case the product $g{H}_{\mathrm{eff}}$ was measured as a function of an external polarizing field, yielding both the $g$ factor and the magnetic hyperfine field of Ru in Ni. The method of using cubic metal lattices [case (2) above] is demonstrated to be a reliable way of measuring $g$ factors of excited nuclear states, as there are no interfering perturbation effects due to time-dependent and/or static quadrupole interactions. The final result for the $g$ factor is $g=-0.189\mathrm{}\pm 0.004$, which gives, with a spin of $\frac{3}{2}$ for the 90-keV level, a magnetic moment of $\mu =-0.284\mathrm{}\pm 0.006$ nm. Paramagnetic shielding in liquid sources of transition elements is discussed, and $g$ factors previously determined for such sources are shown to be in doubt by 5 to 10%.