Shears bands in 112In

A new level scheme of 112In have been established up to 6.8 MeV in excitation energy and to a tentative spin of (21+) through the reaction 110Pd(7Li,5n)112In at a beam energy of 50 MeV. In-beam measurements involving γ-γ coincidences and directional correlation of oriented states were performed. M1 bands consisting of/△I = 1 dipole transitions have been observed. Possible quasiparticle configurations suggest that these bands are similar to the shears bands observed in Pb nuclei.     

Shears bands in 112In

A new level scheme of ¹¹²In have been established up to 6.8 MeV in excitation energy and to a tentative spin of (21⁺) through the reaction ¹¹⁰Pd(⁷Li,5n)¹¹²In at a beam energy of 50 MeV. In-beam measurements involving γ-γ coincidences and directional correlation of oriented states were performed. M1 bands consisting of ΔI=1 dipole transitions have been observed. Possible quasiparticle configurations suggest that these bands are similar to the shears bands observed in Pb nuclei.     

Superdeformed bands and ‘shears’ bands in 197Pb and 198Pb

Excited states in ¹⁹⁷Pb and ¹⁹⁸Pb, produced in the ¹⁸⁶W (¹⁸O,xn) reaction, were studied using the EUROGAM phase 2 γ ray spectrometer array. Two new superdeformed bands have been observed in ¹⁹⁷Pb, and the existence of a superdeformed band in ¹⁹⁸Pb has been confirmed. The increased statistics provided by the latest generation of arrays has resulted in the reordering of some of the previous known cascades of magnetic dipole transitions, with the first observation of the extremely weak E2 crossover transitions.     

Dipole bands in the oblate-shaped195Pb

The nucleus¹⁹⁵Pb has been populated with the¹⁸⁴W+¹⁶O reaction at 113 MeV. Two dipole γ-ray cascades have been observed using the EUROGAM spectrometer. A comprehensive level scheme related to these structures has been established. Multiparticle configurations are attributed to these high-spin structures from detailed comparison with the neighbouring nuclei,¹⁹³Hg,¹⁹⁴Pb and¹⁹⁵Tl. Band crossings due to i13/2 neutron pair breaking are observed in¹⁹⁵Pb at about the same frequencies as in the isotone¹⁹³Hg.

     

Crossing of shears bands in196Pb

High-spin states in¹⁹⁶Pb have been populated using the reaction¹⁷⁰Er(³⁰Si,4n). The previously observed shears bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin.     

Crossing of shears bands in 196Pb

High-spin states in 196Pb have been populated using the reaction ¹⁷⁰Er(³⁰Si,4n). The previously observed shears bands in this nucleus have been extended and some of their transitions have been reordered. They now form regular bands with band crossings. One of the bands splits into two pathways at high spin.     

Dipole bands and multi-quasiparticle excitations in 193Pb

The nucleus ¹⁹³Pb was populated via the ¹⁶⁸Er(³⁰Si,5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipole Δ I = 1 cascades have been found. These structures have been connected to the level scheme which has been considerably extended up to a spin of ? and an excitation energy of about 8 MeV. Angular distribution coefficients, a₂, have been measured and confirm the dipole character of the in-band transitions. B(M1)/B(E2) ratios have been extracted for the two most intense cascades. The ¹⁹³Pb dipole bands are discussed in comparison with those known in odd lead isotopic series and the structure of the band heads is analyzed in terms of microscopic HF+BCS calculations. The proposed configurations are based on a high-K two quasiproton excitation, π ([505]9/2^t? ? [606]13/2⁺)_K=11^t -, coupled to one or three rotation aligned quasineutrons involving the i_13/2, p _3/2, f_5/2 and/or h{9/2} subshells. The main difference, compared with the heavier lead isotopes, is the presence of large Ω orbitals from the ν (i_13/2) shell near the Fermi surface which are responsible for the increasing band-head spin as A decreases.     

Dipole bands and multi-quasiparticle excitations in193Pb

The nucleus¹⁹³Pb was populated via the¹⁶⁸Er(³⁰Si,5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipoleΔI=1 cascades have been found. These structures have been connected to the level scheme which has been considerably extended up to a spin of 61/2? and an excitation energy of about 8 MeV. Angular distribution coefficients,α ₂, have been measured and confirm the dipole character of the in-band transitions. B(M1)/B(E2) ratios have been extracted for the two most intense cascades. The¹⁹³Pb dipole bands are discussed in comparison with those known in odd lead isotopic series and the structure of the band heads is analyzed in terms of microscopic HF-BCS calculations. The proposed configurations are based on a high-K two quasiproton excitation,π([505]9/2^??[606]13/2⁺) _K =11^?, coupled to one or three rotation aligned quasineutrons involving thei _13/2,p _3/2,f _5/2 and/orh _9/2 subshells. The main difference, compared with the heavier lead isotopes, is the presence of largeΩ orbitals from theν (i _13/2) shell near the Fermi surface which are responsible for the increasing band-head spin as A decreases.     

A pair of excited superdeformed bands in196Pb

Two excited superdeformed bands have been found in¹⁹⁶Pb using the GASP-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 isotone¹⁹⁴Hg. The bands are probably built on an excited neutron configuration. They show an unusual incremental alignment of 1/2 with respect to the¹⁹⁴Pb core.Communicated by: B. Herskind     

Superdeformation in Pb: Observation of three additional excited bands

The superdeformed nucleus ¹⁹³Pb has been studied following a heavy-ion fusion-evaporation reaction with the Gammasphere spectrometer array. Three new superdeformed bands, two of them probably signature partners, have been observed, bringing the total number of superdeformed bands known in this nucleus to nine. An estimate of the g-factor associated with one of the previously known pairs of strongly coupled excited bands has been made, confirming their configuration. The properties of the bands are compared with the results of cranked shell model calculations; good agreement is found and configurations are assigned to each band. The two new signature partner bands are suggested to be based on the two signatures of the [512]5/2 neutron orbital. The third new band is probably based on the 7₃ intruder orbital. In addition, the high-energy region of the spectrum in coincidence with the yrast superdeformed bands has been carefully studied. The current data provide no evidence for the previously reported transitions linking the superdeformed and normal-deformed states with energies around 2.2–2.4 MeV.     

Excited rotational bands in the high-spin region of deformed nuclei

Rotational bands of deformed nuclei in the rare-earth region in the vicinity of the yrast line are investigated within the framework of the random phase approximation based on a self-consistent solution of the Hartree-Fock-Bogolyubov equations in the rotating system. For low angular momenta one finds the well-known β, δ and γ vibrational bands and non-collective two-quasiparticle bands. In the high-spin region additional aligned bands develop. They are dramatically lowered in energy by the Coriolis interaction. Several band crossings occur. The calculated spectra are in fair agreement with experimental measurements.     

Coexistence of terminating bands and more collective bands in the A ∼ 100 region of nuclei

Nilsson-Strutinsky cranking calculations on A ≥ 100 Ru and Pd nuclei suggest that, contrary to other mass regions, it should be possible to follow the ground state rotational bands to their termination at spins just above I = 30? and then also to observe other bands which terminate at higher spins.     

Particle-hole excitations in the208Pb mass region

Spectra, magnetic dipole moments and spectroscopic factors of a number ofA=205–209 nuclei as well asM1 transitions in²⁰⁸Pb are investigated in terms of large-scale shell-model calculations which include 1p ?1h excitations and for some nuclei 2p ?2h excitations. The calculated spectra agree well with the data. The calculatedg-factors are in fair agreement with the data in most cases. The predicted strength forM1 transitions to low-lying states in²⁰⁸Pb is less than that obtained from previous calculations. Spectroscopic factors forl=0 proton pick-up from²⁰⁸Pb and²⁰⁶Pb agree very well with recent experimental data from (e, e′p) reactions.     

Perpendicular bands of cyclopropane in the 3000 cm−1 region

The ν₈ and ν₂ + ν₉ bands of cyclopropane when studied with high resolution exhibit Q-branches at the band centers. The ζ constants calculated using these measured band spacings are +0.12 for ν₈ and +0.07 for ν₂ + ν₉.     

Coexistence of terminating bands and more collective bands in theA ∼ 100 region of nuclei

Nilsson-Strutinsky cranking calculations onA≥100 Ru and Pd nuclei suggest that, contrary to other mass regions, it should be possible to follow the ground state rotational bands to their termination at spins just aboveI=30? and then also to observe other bands which terminate at higher spins.     

Shears band in the 105Sn nucleus

The structure of ¹⁰⁵Sn has been investigated through the ⁵⁰Cr(⁵⁸Ni,2pn) reaction at a beam energy of 210 MeV. In addition to an extension of the spherical level scheme, a regular sequence of dipole transitions has been found. The experimental results are in agreement with the prediction of Tilted Axis Cranking calculations, which satisfactorily explain the properties of the band.