M. J. Brinkman

Level spin and moments of inertia in superdeformed nuclei near A = 194

Abstract Experimental transition energies in the superdeformed (SD) bands near A = 190 are least-squares fit to rotational model formulae in order to extract level spin. The data set includes 16 SD bands, which show no evidence of either irregular behavior near the bottom of the bands or abrupt angular momentum alignment at low ħw . The 9 transitions lowest in energy in each band are well described by the formulae. The fitted spin of the final state in the γ-ray cascade is within ±0.1 ħ of an integer or half-odd integer for 13 of the bands. The weight of the evidence suggests that meaningful level spins corresponding to these transitions can be inferred. The moment of inertia at ω = 0 is correlated, with J = 88.3(5) ħ 2 / MeV and J = 93.4(5) ħ 2 / MeV for the strong and weak bands, respectively.

Properties of superdeformed bands in the A = 194 region

At least eighteen superdeformed (SD) bands have been identified in mercury, thallium, and lead nuclei since the report of a SD band in {sup 191}Hg. Systematic information is beginning to emerge on the properties of the SD bands in this mass region, and comparisons with SD bands in the A = 150 region are now possible. Recently, data were obtained with the HERA spectrometer at the Lawrence Berkeley Laboratory 88 Cyclotron on SD bands in {sup 194}Pb and {sup 196}Pb. In these experiments, we bombarded {sup 176}Yb with {sup 24}Mg and {sup 26}Mg. The cross bombardment was necessary to make the assignment of the band to {sup 196}Pb certain. These bands are typical of other SD bands in the region in many ways. The gamma rays have energies that range from about 200 to 800 keV. The gamma-ray spacing decreases from about 40 to 30 keV as the transition energy increases. Their intensities gradually increase as the gamma-ray energies decrease over the upper half of of the sequence, and then sustain a constant value until the one or two lowest energy transitions. 18 refs., 4 figs.

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.

Very elongated nuclei near A = 194

Abstract A γ-ray cascade in 191Hg of 12 members with average energy spacing 37 keV and Qt= 18(3)eb was reported by Moore and co-workers in 1989. This was the first report of very elongated nuclei (superdeformation) in this mass region. Since then, some 25 γ-ray cascades have been observed in 11 (slightly neutron deficient) Hg, Pb and Tl nuclei. Our collaboration has investigated 7 of these nuclei. The bands have similar dynamic moments-of-inertia. Some nuclei exhibit multiple bands, and the backbending phenomenon has been observed. Level spins can be obtained from comparison of transition energies to rotational model formulas. Selected bands (in different nuclei) have equal transition energies (within 0.1%). Alignment in integer multiples of has been observed. Properties of these bands will be described.

Superdeformation in the Hg‐Tl‐Pb Region

Superdeformation in the Hg‐Tl‐Pb region is discussed, with concentration on the experimental results. At least twenty‐five superdeformed bands are known in this region, providing much new data to test theoretical calculations.

Pattern Recognition in Gamma‐Gamma Coincidence Data sets

Considerable amounts of tedious labor are required to manually scan high‐resolution 1D slices of two dimensional γ‐γ coincident matrices for relevant and exciting structures. This is particularly true when the interesting structures are of weak intensity. We are working on automated search methods for the detection of rotational band structures in the full 2D space using pattern recognition techniques. For nominal sized data sets (1024×1024), however, these techniques only become computationally feasible through the use of Fourier Transform methods. Furthermore the presentation of data matrices as images rather than series of 1D spectra has been shown to be useful. In this paper we will present the data manipulation techniques we have developed.

Analysis of High‐Multiplicity Gamma‐Ray Events

A significant improvement in the measured peak‐to‐background ratio of highly‐correlated gamma‐ray cascades can be achieved through the use of high‐multiplicity gamma‐ray coincident events. We studied this effect using data from the 176Yb(22Ne,6n)192Hg reaction at a beam energy of 122 MeV using HERA at the LBL 88‐Inch cyclotron facility. An enriched set of all four‐ and higher‐fold coincidences was culled from these data.

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.