J. A. Becker

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.

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 ...

SUPERDEFORMATION IN AU-191

A superdeformed band has been observed for the first time in an Au isotope. The reaction used was B-11 + W-186, demonstrating that very light ions can be used to populate superdeformed (SD) bands a ...

Electromagnetic decay of 10+ states and yrast isomers in 208Pb

Abstract Gamma decay of the four previously known 10 + states between 4.8 and 5.9 MeV of excitation in 208 Pb, and isomerism of the lowest 10 + [T 1 2 =500(50) ns ] and 8 + [T 1 2 =3.2(5) ns ] states have been established with α - γ coincidence measurements in 209 Bi(t, αγ ) 208 Pb. Wavefunctions for the 10 + states were deduced in the model space involving 1p-1h excitations only. These show that the π h 9 2 h 11 2 −1 strength is nearly evenly distributed among the 10 + states, in disagreement with results from (e, e′) data.

Quadrupole moments of low-energy isomers in 210Po

Abstract The quadrupole interaction frequencies of the 8 + , 11 − , 13 − and 16 + isomers in 210 Po have been measured in a Bi single crystal by the DPAD method with the 209 Bi(t, 2n) 210 Po reaction. The results for the quadrupole moments, normalized to Q (8 + 1 ) = −55.2 (20)fm 2 , are | Q (11 − )| = 86 (11)fm 2 , | Q (13−)| = 90(7)fm 2 and | Q (16 + )| = 129.7 (20) fm 2 . The quadrupole moment of the 0 i 13 2 proton orbital was deduced, and found to be surprisingly small. The results are compared with shell model calculations using the surface delta interaction as residual interaction.

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.

Scissors mode of Gd nuclei measured, with?the?DANCE?detector

Spectra of γ-rays following the neutron capture at isolated resonances of stable Gd nuclei were measured with the DANCE detector. The objectives were to obtain new information on the photon strength of 153,155−159Gd with emphasis on the role of the M1 scissors-mode vibration. An analysis of the data obtained clearly indicates that the scissors mode is built not only on the ground state, but also on all excited levels of the nuclei studied. Our approach allows estimating the summed scissors-mode strength even for odd product nuclei for which conventional nuclear resonance fluorescence measurements yield only limited information. Our data indicate that for 157,159Gd the strength is significantly higher compared to 156,158Gd.

Superdeformation in 198 Po

The 174Yb(29Si,5n) reaction at 148 MeV with thin targets was used to populate high-angular momentum states in 198Po. Resulting γ rays were observed with Gammasphere. A weakly-populated superdeformed band of 10 γ-ray transitions was found and has been assigned to 198Po. This is the first observation of a SD band in the A ≈ 190 region in a nucleus with Z > 83. The J (2) of the new band is very similar to those of the yrast SD bands in 194Hg and 196Pb. The intensity profile suggests that this band is populated through states close to where the SD band crosses the yrast line and the Present address: Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. Present address: Department of Physics, Royal Institute of Technology, Stockholm, Sweden.

Decay of the 21/2− isomer in211Bi and structure of thevg 9 2/2 πh9/2 levels

Gamma rays and conversion electrons have been measured in211Bi populated by the209Bi(t,p) reaction, and the near yrast levels were observed up to 21/2−. The 21/2− state is isomeric withT1/2=70(5) ns. No alpha decaying isomer was found in211Bi. ObservedM1 transitions reveal mixing of the210Pb parent states in the levels of211Bi. The levels and transitions are well reproduced by the shell model with experimental matrix elements and pure configurations.