Re-Examination of the Paramagnetic Resonance ofNp239

The microwave paramagnetic resonance spectrum previously reported for 2.3-day ${\mathrm{Np}}^{239}$ activity incorporated into a crystal of U${\mathrm{O}}_2$Rb${\left(\mathrm{N}{\mathrm{O}}_3\right)}_3$ has been re-examined and determined to be due, not to ${\mathrm{Zp}}^{239}$, but to radiation-induced resonance centers. Experiments tentatively suggest that these resonance centers may be ${\mathrm{Pu}}^{239}$ in an unusual oxidation state. An experiment in which ${\mathrm{Np}}^{239}$ nuclei were aligned by static hfs interactions (Pound and Bleaney methods) showed an anisotropy of the $\gamma$-ray pattern; this proves that the nuclear spin $I\left({\mathrm{Np}}^{239}\right)>\mathrm{}\frac{1}{2}$, in contradiction to our earlier result.