A pair of excited superdeformed bands in196Pb

Abstract

Abstract. Two excited superdeformed bands have been found in ~96Pb using the GASP 7-ray spectrometer array. They are signature-partner bands with a small signature splitting developing at higher frequencies, similar to bands 2 and 3 in the isotone 194Hg. The bands are probably built on an excited neutron configuration. They show an unusual incremental alignment of 1/2 h with respect to the a94Pb core. 21.10.-k; 23.20.-v; 27.80.+w The region of nuclei with mass numbers around A = 190 is now a well established area of superdeformation with about 50 superdeformed (SD) rotational bands known [1]. However, as long as the connections of the bands to the normal-deformed states are missing, no direct spin determination is possible and configuration assignments depend on a detailed study of the systematic properties of yrast and excited SD bands. In this work we report on the observation of the first two excited SD bands in 196pb. This nucleus is the isotone of 194Hg where two excited SD bands have been known [2-4] for some time. PACS:High-spin states in 196pb were populated in the reaction 17~176 at a beam energy of 143 MeV at the LNL XTU tandem accelerator. Gamma-ray coincidences were measured using the GASP array of 40 Compton-suppressed Ge detectors and an inner ball of 80 BGO scintillation counters. The target consisted of a stack of two selfsupporting foils of l~~ (enrichment 97%) with a thickness of 750 #g/cm 2 each. A total of about 109 two-and higher-fold coincidence events were recorded.In the first step of the off-line analysis all coincidences were unpacked into two-fold events and sorted into a two-dimensional En-E ~ matrix. These data confirmed and extended the known yrast SD band in 196Pb [5][6][7], but no further bands could be identified -probably because of the lank of clean coincidence gates. In the second step the threeand (unpacked) higher-fold events (94.5. 106 ) were sorted into a three-dimensional matrix of the "),-ray energies (E~-En-E ~ cube) and double-gated coincidence spectra were analysed. The search for new bands was guided by the dynamic moments of inertia of known SD bands in this region. In that way we could exclude that known bands in neighbouring nuclei are present in our data within the statistical limits. But when the starting energies of the bands were allowed to vary, two new bands were found that have moments of inertia which are similar to the yrast SD band in 194pb [8,9]. One of the new bands has transition energies close to those of one of the bands in 195T1 [10]. In our experiment, however, that nucleus is hardly produced at all.The three bands in 196pb are shown in Fig. 1. All combinations of clean double-gated spectra have been added. The two new bands have intensities of about 35% of that of the yrast SD band. The assignment of the new bands to 196pb is still somewhat tentative since the coincidences with the low-lying transitions are not conclusive. However, as we do not observe any of the known SD bands, in particular in a95pb or 193Hg which are the other nuclei populat...

New results on the superdeformed 196Pb nucleus: decay of the excited bands to the yrast band

“…The data were subsequently analysed by sorting and extracting triple-gated spectra with background substraction. The known yrast [9] and two first excited bands [10] in 196 Pb have been observed in the data. The assignment to 196 Pb is firmly confirmed by the observation of γ transitions located between low-lying 196 Pb yrast states in all the spectra gated by SD transitions.…”

“…10.Re Nearly all excitations observed in SD minima have been identified as particle, hole, or (multi-) particle-hole excitations. Calculations [1][2][3][4] suggested that the octupole vibrational mode is the lowest of the possible vibrational modes for superdeformed shapes in both the mass 150 and 190 regions.…”

Cranked relativistic Hartree–Bogoliubov theory: formalism and application to the superdeformed bands in the A∼190 region

“…The experimental data are taken from Refs [32]. ( 192 Pb) and[34] ( 196 Pb). The experimental J(1) values of the 192 Pb band are shown for the spin value of I0 = 8 for the lowest state in the SD band (the lowest transition with the energy 214.8 keV corresponds to a spin change 10 → 8).…”

Superdeformations in Relativistic and Non-Relativistic Mean Field Theories

“…The experimental data are taken from Refs. [82] ( 192 Pb), [83,84,85] ( 194 Pb), [86] ( 196 Pb), [87] ( 190 Hg), [88] ( 192 Hg) and [89,90] N=112 N=114 Figure 5: The same as Fig. 4 but for kinematic moments of inertia J (1) .…”