PHYSICAL REVIEW C VOLUME 47, NUMBER 2 FEBRUARY 1993 Highly deformed band in 13sPm and the anomalous dynamical moment of inertia behavior in the A ~135 superdeformed region M. A. Riley, T. Petters, J. Shick, D.E. Archer, J. Doring, J. W. Holcornb, G. D. Johns, T. D. Johnson, O. N. Tekyi-Mensah, S. L. Tabor, P. C. Womble, and V. A. Wood Department of Physics, Florida State University, Tallahassee, Florida M906 C. Baktash, M. L. Halbert, D. C. Hensley, and I. Y. I ee* Physics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 87882 R. J. Charity, D. G. Sarantites, and L. L. Wittmer Department of Chemistry, Washington University, St. Louis, Missouri 68180 J. Simpson Science and Engineering Research Council Daresbury Laboratory, Daresbury, Warrington, WAg United Kingdom (Received 22 September 1992) A highly deformed rotational band has been observed in the odd-odd nucleus Pm. This band sheds important new light on the anomalous behavior of the dynamical moments of inertia of rota- tional bands previously observed in the Ce-Nd-Sm A 135 superdeformed region which has been a theoretical puzzle for several years. PACS numbers: 23. 20.Lv, 21.10. Re, 23.20.-g, 27.60. +j The dynamical moments of inertia (Jisl) of superde- formed bands in the A 150 Gd-Dy and A ~190 Hg-Pb regions are fairly well reproduced by standard cranking calculations [1, 2]. However, for the superdeformed or highly deformed A~135 Ce-Nd-Sm region, this is not true at all, and has presented a theoretical problem for some time. Several solutions in terms of quenched proton pair- ing [3] and a strong residual proton-neutron interaction [4, 5 have been proposed. The present Rapid Communication reports on the ob- servation of a rotational band in 3 Pm possessing an enhanced moment of inertia consistent with other highly deformed structures in this latter region. The behavior of this band sheds new light on the alignment processes taking place in neighboring highly deformed nuclei and represents an important step forward in the understand- ing of the so-called anomalous J( l behavior found in this region. Up to the present time in the A 135 region highly deformed bands have been observed almost exclusively in even-Z nuclei, i.e. , Ce [6 — 8]» s s Nd [9 — 12], ~ss s s Sm [3, 13 — 16], and Gd [17 18] Only in ~soLa [19] has a highly deformed band been ob- served in an odd-Z nucleus. Unfortunately this band, due to its very irregular behavior below h~ = 0. 5 MeV and Present address: Nuclear Science Division, Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720. its cessation near hu = 0. 4 MeV, is not able to contribute significantly to the understanding of the anomalous 1( ) dependence on rotational frequency which centers around the behavior of the lowest h» proton levels near hw = 0. 4 MeV [3 — 5, 20). The aim of the present experiment was to observe a highly deformed band in the N=75 odd-Z nucleus Pm which lies in the middle of the region. Two experiments were performed, the first took place at the Holifield Heavy Ion Research Facility at Oak Ridge and used a 165 MeV s S beam on two stacked 500 pg/cm thick foils of Pd. High resolution p-p information was collected using 18 Compton suppressed Ge detectors which replaced elements within the Spin Spectrometer [21]. Total energy and fold information was recorded by the remaining 52 NaI elements of the Spin Spectrometer and the 18 anti-Compton shields. In addition, because charged particle emission competes on an equal footing with neutron evaporation in this mass region, the Wash- ington University Dwarf Ball [22] was used to detect the charged particles in coincidence with p rays. A total of 2.80 x 10s Ge-Ge-charged particle coincidences were recorded. Two dimensional 4096x4096 channel p-p matrices were created gated by p, 2p, pn, and n information from the Dwarf Ball and with a fold condition of greater than 10. Calculated fractions of the 2p and pn matrices were subtracted from the p gated matrix in order to produce a matrix containing only Pm nuclei. In this latter ma- trix a rotational cascade of eight transitions possessing an enhanced moment of inertia characteristic of superde- formation in this region was observed. In addition, the known highly deformed bands in ~ssNd [9] and ~ssNd [9, 47 R441 1993 The American Physical Society