Spin Determination of Intermediate Structure in the Subthreshold Fission ofNp237

A polarized neutron beam and a polarized target have been used to determine spins of 15 intermediate structure groups observed in the fission of ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ below 1 keV and of 94 resonances observed in transmission below 102 eV. The pulsed neutron beam, from the Oak Ridge electron linear accelerator, was polarized by transmission through a dynamically polarized proton sample. The ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$, in the ferromagnetic compound Np${\mathrm{Al}}_2$, was cooled by a ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ dilution refrigerator. Nine individual fine-structure resonances comprising the first group at 40 eV were determined to have the same spin, $J=3\mathrm{}$, substantiating the current interpretation of intermediate structure in subthreshold fission in terms of the Strutinsky double-humped deformation barrier. Correlation of these results with existing data on the angular distribution of fission fragments from aligned ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ indicates an apparent admixing of transition states, as evidenced by nonintegral values of the projection quantum number, $K$.