[en] The π1/2⁺[411] ground band structure of ¹⁶³Lu shows a large signature splitting with inversion above the backbend suggesting a shape change associated with the triaxiality degree of freedom. The π1/2^-[541] band shows no backbending up to h bar ω = 0.4 MeV indicating a more deformed structure. 7 refs., 3 figs

[en] In-beam spectroscopic study of ¹³⁵Pr was made using 91 MeV ¹²⁰Sn(¹⁹F,4n) reaction. A strong negative parity proton band based on the h/sub 11/2^-/ 1/2[550] configuration with α = -1/2 was observed. Possibly α = +1/2 unfavored band is observed. Also two positive parity proton bands are observed most likely based on the g/sub 7/2⁺/ 5/2[413] configurations with α = +-1/2. In all cases (except for the (π,α) = (-,+1/2) band) the backbending is caused by alignment of two h/sub 11/2^-/ 9/2[514] quasi-neutrons. For the strongly decoupled π(-) bands the observed signature splitting decreases with increasing rotational frequency. The signature splitting of the positive parity bands increases with rotational frequency and then inverts above the backbending. This is interpreted to be caused by the quasi-neutrons, which drive the γ-deformation to the negative values. 18 refs., 6 figs

[en] The cross section for fusion of heavy ions below the Coulomb barrier can be orders of magnitude larger than the predictions of models that are quite successful above the barrier. Recent studies of γ-ray multiplicity have shown that the average l of the partial waves participating in subbarrier fusion is much higher than expected. The discrepancies become larger as the mass asymmetry of the projectile and target decreases. We have used the Spin Spectrometer in coincidence with identified products from two reactions leading to the same compound nucleus, ¹⁶⁴Yb, to study entry-state angular-momentum effects. The reactions were ⁶⁴Ni + ¹⁰⁰Mo and ¹⁶O + ¹⁴⁸Sm; the conditions of bombardment are listed. The O + Sm energies were chosen to match two of the Ni + Mo compound-nucleus excitation energies. Exit channels were identified by known γ-ray lines from the residual nuclei observed in six Compton-suppressed Ge detectors which replaced a like number of pentagonal NaI units of the Spin Spectrometer. Recording of events was triggered by detection of a ''clean'' Ge pulse (i.e., no γ ray detected in its surrounding Compton shield). 10 refs., 5 figs., 2 tabs

[en] Low- and medium-spin states in ¹⁹⁸Pb are studied using the reaction ¹⁹⁸Hg(³He,3n) at laboratory energy 27.5 MeV. The in-beam measurements comprise γ-ray singles, γ-RF timing, γ-ray angular distributions and γ-γ coincidences. Seven new levels are located and assigned spins and parities. The previously reported lifetimes are unambiguously assigned: T_1/2(5^-) = 50.4 ± 0.5 ns, T_1/2(7^-) = 4.19 ± 0.10 μs and T_1/2(9^-) = 240 ± 15 ns. The corresponding transition rates B(λ) are deduced. The new non-yrast levels are compared to the existing systematics. A tentative excited (collective) band structure is proposed and compared to a similar one in ¹⁹⁶Pb. Systematic trends in E1, E2 and E3 transition rates in light Pb isotopes are discussed. (orig.)

[en] The π9/2-[514] ground band structure of /sup 163/Lu shows a large signature splitting weight inversion above the backbend suggesting a shape change associated with the triaxiality degree of freedom. The πl/2-[541] band shows no backbending up to hω = 0.4 MeV indicating a more deformed structure

[en] In-beam spectroscopic study of /sup 135/Pr was made using 91 MeV /sup 120/Sn(/sup 19/F,4n) reaction. A strong negative parity proton band based on the h/sub 11/2/- 3/2[541] configuration with (π,α)=(-,-1/2) was observed. (-,+1/2) unfavored band is probably observed. Also two positive parity proton bands are observed and are based on the g/sub 7/2//sup +/ 3/2[422] configuration with (π,α)=(+,+-1/2). In the case of π(+) bands the backbending is caused by the alignment of two h/sub 11/2/- 3/2[541] protons. For the (-,-l/2) band the backbending is caused by the alignment of two h/sub 11/2/- protons: 3/2 [541] and 1/2[550]. This is considerably different than in /sup 134/Ce core, where the h/sub 11/2/ neutron-holes are aligning. Nuclei in the vicinity of La, Ce, Pr are predicted to be soft in γ-deformation. Ban investigation was undertaken to study the signature splitting between rotational bands in /sup 135/Pr, which is related to γ-deformation. /sup 135/Pr was produced by the /sup 120/Sn(/sup 19/F,4n) reaction at 91 MeV using the tandem accelerator at the Brookhaven National Laboratory. Coincidence data were recorded between 4 Compton-suppressed Ge detectors at -- 40⁰ relative to the beam and 2 unsuppressed Ge detectors at -- 85⁰. In addition an array of 11 NaI detectors around the target were used as a multiplicity selector

[en] Angular-momentum distributions σ/sub L/ for the compound nucleus ¹⁶⁴Yb were deduced from measurements of γ-ray multiplicity for all significant evaporation residues from fusion of ⁶⁴Ni and ¹⁰⁰Mo at and below the Coulomb barrier. The excitation functions can be reproduced with coupled-channels calculations only if additional coupling beyond the known inelastic strengths is included. Even with this augmented coupling, however, at the lowest bombarding energies the experimental σ/sub L/ extend to higher L values than the predictions. Single-barrier penetration models for a potential with an energy-dependent depth and shape fitted to the excitation function likewise underestimate the role of high-L partial waves. Somewhat better success is achieved with models in which fission is allowed to occur at distances comparable with or even larger than the Coulomb barrier radius. 24 refs., 3 figs., 2 tabs

[en] An in-beam spectroscopic study of /sup 135/Pr was made using a 91 MeV /sup 120/Sn(/sup 19/F,4n) reaction. Two positive parity bands were observed based on the g/sub 7/2/ proton orbital with (π,α) = (+, +- (1/2)). A strongly populated negative parity (-,-(1/2)) band was also seen (based on the h/sub 11/2/ proton orbital). The unfavored (-,+(1/2)) structure may also be present. In both the positive and negative parity bands the first backbend is attributed to the alignment of two h/sub 11/2/ protons on the basis of cranked shell model calculations. The crossing frequency was found to increase in the (-,-(1/2)) band because of blocking of the h/sub 11/2/ orbital. The alignment of protons in /sup 135/Pr causes a shift of γ towards --+10⁰ with nearly collective prolate deformation. Also, there is some evidence for a second backbend and an upbend in the case of positive and negative parity bands, respectively. They could result from the alignment of the h/sub 11/2/ neutrons

[en] The spin spectrometer in coincidence with identified products from two reactions leading to the same compound nucleus, ytterbium 164, has been used to study entry-state angular momentum effects in sub-barrier fusion. The systems nickel 64 + molybdenum 100 and oxygen 16 + samarium 148 were studied at energies from 81 Mev to 210 Mev. Cross sections for the four dominant exit channels, 2n, 4n, alpha2n and 3n, as well as fusion cross sections are presented. Results compare well to statistical model calculations

[en] High-spin states in ¹³⁰Xe were populated in the reaction ¹³⁰Te(α,4n)¹³⁰Xe and studied using conventional gamma-ray spectroscopy. The ground-state band was observed up to its 10⁺ member, and a high-spin quadrupole band built on the yrast 10⁺ state at 2973 keV was observed up to a proposed (18⁺) state at 6435 keV. A negative-parity band built on the yrast 7^- state at 2375 keV was observed to its (13^-) member at 4811 keV. Nine additional levels are reported below 4700 keV. The 7^- and 10⁺ band heads are proposed to be two-quasiparticle states of the configurations (νhsub(11/2)^-1dsub(3/2^-1)sub(7^-) and (sup)νsub(11/2)^-2)sub(10⁺), respectively. The ''odd'' levels are interpreted, based on shell-model calculations, to be mostly two- and four-neutron-hole states. A 10⁺ state at 3878 keV is proposed to be a proton excitation of the form (πhsub(11/2)²)sub(10⁺). (author)