A. V. Ramayya

Octupole deformation in 142,143Ba and 144Ce: new band structures in neutron-rich Ba-isotopes

Abstract New, high spin band structures are established for the neutron-rich nuclei 142,143,145,147Ba, and 144Ce, and levels of 144,146Ba extended to higher spins from the study of γ-γ and γ-γ-γ coincidence studies in spontaneous fission. Alternating parity sequences connected by strong electric dipole transitions are identified in 142,143Ba and 144Ce but not in 145,147Ba to confirm theoretical predictions of stable octupole deformation for N = 86.

High-Spin Structure in Neutron-Rich 108Ru Nucleus

High spin states in the neutron-rich 108Ru nucleus have been studied through measuring prompt γ-ray coincidences following the spontaneous fission of 252Cf with the Gammasphere detector array. The yrast band has been confirmed. The one-phonon γ-vibrational band and the two-quasiparticle band based on the 5− level have been extended up to 13+ and 15−, respectively. In addition, two levels at 1644.8 keV and 1826.5 keV excitation energies are newly identified and proposed to be the members of a two-phonon γ-vibrational band. It is shown that the 108Ru nucleus has triaxial deformation with parameters β2~0.29 and γ = −22 degrees from the total Routhian surface calculations. The observed band crossing in the yrast band is due to the alignment of a pair of h11/2 neutrons according to the cranked shell model calculations. The possible configuration for the two-quasiparticle band has been discussed.

High Spin Band Structure in 112Ru

Levels in the neutron-rich 112Ru nucleus have been investigated by observing prompt gamma-rays from the spontaneous fission of 252Cf with the Gammasphere detector array. The ground-state band and the one-phonon γ-vibrational band have been confirmed and extended with spin up to 16xa0 and 15xa0, respectively. The other two side bands, one proposed as two-phonon γ-vibrational band and the other proposed as two-quasiparticle band, have been observed for the first time. The total-Routhian-surface calculations show that rotational 112Ru nucleus has triaxial deformation with parameters β2~0.27 and γ = −29°. The observed band crossing in the yrast band is due to the alignment of a pair of h11/2 neutrons according to the cranked shell model calculations. The possible configuration for the quasiparticle band has also been discussed.

Observation of Rotational Bands in Neutron-Rich 106Mo Nucleus

The rotational bands up to a spin of 16 in the neutron-rich 106Mo nucleus have been investigated by measuring high-fold prompt γ-ray coincidence events following spontaneous fission of 252Cf with a Gammasphere detector array. The ground-state band, the one-phonon and two-phonon γ-vibrational bands, as well as a quasi-particle band have been confirmed and expanded. The other four collective rotational bands, three proposed as two-quasi-particle bands and one proposed as a β-vibrational band, have been newly observed. The characteristics of these collective bands and the possible configurations for the quasi-particle bands are discussed.

Shape transitions and triaxiality in neutron-rich odd-mass Y and Nb isotopes

Abstract.New level schemes of 99, 101Y and 101, 105Nd are established based on the measurement of prompt γ-rays from the fission of 252Cf at Gammasphere. Triaxial-rotor-plus-particle model calculations and fitting suggest that in the A ≈ 100 neutron-rich nuclei triaxial shape is prevalent in the region with Z > 41.

Collective Band Structures in the Neutron-Rich 107,109Ru Nuclei

The levels in neutron-rich odd-A 107,109Ru nuclei have been investigated by using γ-γ- and γ-γ-γ-coincidence studies of the prompt γ-rays from the spontaneous fission of 252Cf. The ground state bands and the negative parity bands are identified and expanded in both nuclei. Triaxial rotor plus particle model calculations indicate the ground state bands originate from ν(d5/2 + g7/2) quasiparticle configurations and the negative parity bands are from νh11/2 orbital.

Reflection Asymmetric Shapes in the Neutron-Rich 140,143Ba Isotopes

Level schemes for the neutron-rich 140,143Ba nuclei have been determined by study of prompt γ-rays in spontaneous fission of 252Cf. The level pattern and enhanced E1 transitions between π = + and π = - bands show reflection asymmetric shapes with simplex quantum number s = +1 in 140Ba and s = ±i in 143Ba, respectively. The octupole deformation stability with spin variation has been discussed.

Two-Quasiparticle Bands and Isomers in 98Sr

Rotational bands in neutron-rich 98Sr nucleus have been investigated by measuring high-fold prompt γ-ray coincidence events of the spontaneous fission of 252Cf with the Gammasphere detector array. A deformed K = 3 band built on the 1838 keV level has been confirmed and extended. Another deformed K = 6 band based on the 2535 keV level has been established. Both the bands originate most probably from the ν9/2[404]⊗ν3/2[411] two-quasiparticle configuration with Ω = |Ω1−Ω2| and Ω = |Ω1+Ω2|, respectively. Based on the delay-coincidence measurements, the half-lives for the K = 3 and K = 6 band head levels have been obtained to be 13±3 ns and 4.5±1.0 ns, respectively.

High spin octupole correlations in the N = 85, 139Xe and 141Ba isotones

High spin states in and have been investigated using - and - coincidence studies of spontaneous fission of . Alternating parity bands built on a 7/2-level are assigned up to spin I = (37/2) and I = (29/2) in and , respectively. Another possible octupole band based on multiplet with spin up to (29/2) also is observed in both nuclei. Cascades of enhanced E1 transitions and ratios indicate strong octupole correlations. Systematics of the , and multiplets and bands in N = 85 isotones are presented.