Spin measurements for $^{147}$Sm$+n$ resonances: Further evidence for non-statistical effects

We have determined spins of resonances in the $^{147}$Sm ($n,\gamma $) reaction by using the DANCE detector at LANSCE to measure multiplicities of $\gamma $-ray cascades following neutron capture. These new spin assignments, together with previously determined resonance parameters, allowed us to extract separate level spacings and neutron strength functions for $J=3$ and 4 resonances. Furthermore, although all the evidence indicates that very few resonances of either spin have been missed below $E_{n}=700$eV, reduced-neutron-width and level- spacing distributions do not agree with the expected distributions for resonances in the energy range $350<$ $E_{n} <700$ eV. The new spin assignments also allowed us to reanalyze $^{147}$Sm($n,\alpha $) data and obtain more reliable $\alpha $ widths. Although our new $\alpha $ widths are somewhat different from previous work, recently reported non-statistical effects revealed by these widths remain. Taken together, the neutron- width, $\alpha $-width, and level-spacing data indicate the onset of some non-statistical effect near $E_{n}=350$eV. We will discuss possible explanations for these effects and their possible relation to similar effects previously observed in $^ {232}Th+n$ resonances.