Angular Distribution of Alpha Particles Emitted by OrientedNp237Nuclei

${\mathrm{Np}}^{237}$ nuclei were aligned through the electric quadrupole and magnetic hyperfine couplings in Np${\mathrm{O}}_2$Rbz${\left(\mathrm{N}{\mathrm{O}}_3\right)}_3$, cooled to 0.2-4.2°K. A complete experiment, with rotatable monocrystalline sample, solid-state counter, thermometer, and goniometer, was enclosed in a copper container filled with ${\mathrm{He}}^3$ gas and thermally attached to ½ mole of paramagnetic salt which could be cooled magnetically. The measured temperature dependence of the $\alpha$-particle anisotropy gives $A<\mathrm{}0\mathrm{}$, $P>\mathrm{}0\mathrm{}$ for the signs of the hyperfine coupling constants in Np${\mathrm{O}}_2^{++}$. The $\alpha$ particles were observed to be emitted preferentially along the direction of the nuclear angular momentum vector. The results are consistent with $P-\pi$ bonding in the Np${\mathrm{O}}_2^{++}$ ion and with Hill and Wheeler's prediction of the role of barrier penetration in $\alpha$ emission from nonspherical nuclei.