T.-F. Wang

Oblate collectivity in sup 197 Pb

Evidence for collective behavior in the high-spin region of lead nuclei is provided by the observation of two collective structures in {sup 197}Pb. One of these bands is interpreted as an oblate collective structure built on oblate proton and possibly neutron states. A second more irregular band is suggested to be most likely a triaxial rotational band. Neutron and proton configurations for these bands are suggested from the results of quasiparticle Routhians and total Routhians surface calculations. A partial level scheme up to {ital I}{approx}69/2 and {ital E}{sub {ital x}}{approx}8 MeV is presented.

ONSET OF COLLECTIVITY IN NEUTRON-DEFICIENT PO-196,PO-198

We have studied via in-beam gamma-ray spectroscopy Po-196 and Po-198, which are the first neutron-deficient Po isotopes to exhibit a collective low-lying structure. The ratios of yrast state energi ...

2H induced reactions on 8Li and primordial nucleosynthesis

Cross sections for the [sup 8]Li([ital d],[ital n])[sup 9]Be (ground state) and [sup 8]Li([ital d],[ital t])[sup 7]Li reactions, both important to primordial nucleosynthesis in the inhomogeneous models, have been measured using a radioactive beam technique. The cross section for the former reaction is found to be small, so it is important only for synthesis of [sup 9]Be. The cross section for the latter reaction, however, is found to be large enough to destroy significant quantities of [sup 8]Li, and thus could affect predictions of primordial nucleosynthesis yields.

HIGH-K BANDS IN THE YB-166 REGION

High-[ital K] bands have been observed in the [sup 166,167,168]Yb isotopes following the [sup 124]Sn([sup 48]Ca,[ital xn][gamma]) reaction. The [nu][ital h][sub 11/2] band in [sup 167]Yb has been extended to higher spins. The high-[ital K] bands in the even-even isotopes were observed for the first time and show very high [ital B]([ital M]1)/[ital B]([ital E]2) ratios. Configuration assignments for the new bands are proposed. The results are interpreted within the Tilted Cranking model.

Cross sections and reaction rates of d + 8Li reactions involved in Big Bang nucleosynthesis

Abstract We have measured angular distributions of the 2 H( 8 Li, 7 Li) 3 H and 2 H( 8 Li, 9 Be)n reactions at E c.m. = 1.5 to 2.8 MeV using an 8 Li- radioactive-beam technique. Astrophysical S -factors and reaction rates were calculated form the measured cross sections. Although the 2 H( 8 Li, 9 Be)n cross section is small, it can contribute to 9 Be synthesis. The 2 H( 8 Li, 7 Li) 3 H reaction has a sufficiently large cross section to destroy 8 Li, which may decrease the synthesis of heavier elements. No products from the 2 H( 8 Li, 9 Li)p reaction were detected. We also present the results of calculations using the inhomogeneous model of primordial nucleosynthesis in several regions of parameter space.

High-[ital K] bands in the [sup 166]Yb region

High-[ital K] bands have been observed in the [sup 166,167,168]Yb isotopes following the [sup 124]Sn([sup 48]Ca,[ital xn][gamma]) reaction. The [nu][ital h][sub 11/2] band in [sup 167]Yb has been extended to higher spins. The high-[ital K] bands in the even-even isotopes were observed for the first time and show very high [ital B]([ital M]1)/[ital B]([ital E]2) ratios. Configuration assignments for the new bands are proposed. The results are interpreted within the Tilted Cranking model.

LIFETIMES OF SUPERDEFORMED STATES IN 194PB

Lifetimes of members of the superdeformed band in 194Pb were measured by the Doppler-shift attenuation method. Quadrupole moments around 20 eb that are constant over the whole frequency range were derived. The results rule out large centrifugal stretching effects.

Transition quadrupole moments of superdeformed states in194Pb

Lifetimes of superdeformed states in194Pb were measured by the Doppler-shift attenuation method. Quadrupole moments around 20 eb, that are constant over the observed frequency range, are derived. The results rule out large centrifugal stretching effects.

New oblate band in [sup 196]Hg with quenched [ital M]1 strength

High-spin states in the nucleus [sup 196]Hg were populated in the reaction [sup 192]Os([sup 9]Be,5[ital n]) at a beam energy of 65 MeV. A regular rotational-like [Delta][ital I]=1 band has been observed up to an excitation energy of [ital E][sup *][approx]8.7 MeV and spin [ital I][approx]30[h bar]. This is the second observation of a band of this character in a mercury isotope. The experimental results are compared with mean field calculations and semiclassical estimates based on the Doenau-Frauendorf formalism. The mercury bands show significantly lower [ital B]([ital M]1)/[ital B]([ital E]2) branching ratios as compared with similar bands in light lead nuclei. This difference may be more readily explained by a difference in single-particle structure rather than by large differences in deformation between the lead and mercury configurations.

Oblate L=1 bands in 194,196–201Pb and 193Hg

Abstract Reports of recent experiments have included observations of regular and irregular bands in neutron deficient Pb isotopes with A =194, 196–201. The bands are populated strongly in (HI, xn ) reactions. The shared characteristics of the bands include: 1) bandhead energies of a few MeV; 2) high bandhead spin; 3) large alignments; 4) small dynamic moments of inertia, and 5) strong L =1 transitions and weaker L =2 crossover transitions, with B( M 1) B( E 2) ≈ 20 μ 2 e 2 b 2 . Lifetimes of band members in the 198 Pb regular band are B (M1) ≈ 1 W.u. and B (E2) ≈ 12 W.u. (with large errors). These observations are consistent with an interpretation of the regular structures as collective oblate bands with both proton and neutron excitations involved; the closed proton shell at Z =82 is broken, and coupled to v( i 13 2 ) −n excitations. The irregular structures may correspond to triaxial shapes, with similar orbits involved. A similar structure has been also found in 193 Hg.