E. Rubel

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 ...

Superdeformed bands in195Tl

Two superdeformed (SD) bands have been found and assigned to195Tl on the basis of excitation function and cross bombardment results. The two bands are almost identical in transition energies to those observed in193Tl. They are signature partners with a splitting, presumably due to the proton i13/2 (Ω=5/2) orbital, characteristic of all known SD bands in the thallium isotopes. Their alignments relative to the193Tl bands were found to be zero.

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.

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.

Superdeformation in sup 198,196 Pb

A weakly populated rotational band with energy spacings characteristic of superdeformation has been found in the reaction {sup 154}Sm({sup 48}Ca,{ital xn}) at {ital E}({sup 48}Ca)=205 MeV. This band has seven transitions with an average {gamma}-ray energy spacing of approximately 42 keV. It is assigned to {sup 198}Pb on the basis of the excitation-function results. We also confirm the isotopic assignment of a previously reported superdeformed (SD) band in {sup 196}Pb via the cross bombardments {sup 176}Yb({sup 26}Mg,{ital xn}) and {sup 176}Yb({sup 24}Mg,{ital xn}). Three SD bands have now been identified in the Pb isotopes with neutron numbers 112, 114, and 116.

Superdeformation in lead nuclei

A rotational band, with energy spacings characteristic of superdeformed shapes, has been identified in194Pb.The band, which consists of 12 members, was produced in the bombardment of176Yb with24Mg. This band extends the mass-194 region of superdeformation to higher Z.

‘‘Identical’’ superdeformed bands in the mass A=190 region

Several new rotational bands with energy spacings typical for superdeformed shapes have been identified in Tl and Pb nuclei. Their γ‐ray transition energies are often identical or closely related to those of 192Hg or 193Tl. The resulting dynamic moments of inertia are much more similar than experienced in any other case. Spins, although not directly measured in any superdeformed band, can be assigned with the help of a rigid‐rotor expansion of the γ‐ray energies. The alignments obtained as spin differences with respect to the reference band are quantized for rotational frequencies above 0.2 MeV.

Superdeformed bands in194Tl

Two superdeformed (SD) bands have been found in194Tl using the reactions176Yb(23Na,5n) and181Ta(18O,5n). The mass assignments were made from excitation function data. These are the first SD bands found in the mass-190 region that are not in Hg nuclei. The energies of many of the transitions of one of these new SD bands are similar in energy to those in the SD band of192Hg.

Superdeformed bands in193Hg and194Hg

A superdeformed band, consisting of 12 transitions, is assigned to193Hg on the basis of excitation function and cross bombardment results. A second band is identified which may be the signature partner of this band. In addition, another rotational band is observed which is assigned as the third superdeformed band in194Hg. The similarities of these three bands to those already known in the mercury region are discussed briefly.

Observation of superdeformed bands in194Hg

Two rotational bands, with energy spacings characteristic of superdeformed shapes, have been observed following bombardment of150Nd with48Ca. The more intensively populated band consists of 18 transitions and is assigned to194Hg. The depopulation of this band occurs around spin 10. The second band, consisting of at least 16 transitions, was populated less strongly and is tentatively assigned to194Hg also. The lowest level in this band is assigned spin 8. The energy differences between transitions for both bands decrease from ∼40 keV at low rotational frequencies to ∼30 keV at the highest observed frequencies. The moments of inertia of the bands are similar to those of the two previously observed superdeformed bands in191,192Hg. The similarities and differences of the four known bands in the mercury region are discussed.