J.C. Merdinger

High-spin excitations of 187, 188Hg

Abstract High-spin states in 187, 188 Hg have been investigated via the 163, 164 Dy ( 28 Si , x n ) reactions by in-beam γ-ray spectroscopic techniques using the “Chateau de Cristal” 4π-multidetector array. Level schemes have been established. Spins and parities of the states have been deduced from transition multipolarities obtained from measurements of the angular distribution and linear polarization of the γ-rays. The shape coexistence of both prolate and oblate band structures has been observed for the first time in 187 Hg. In 188 Hg negative-parity bands are well developed. The band structure is interpreted within the frame of the Strutinsky method with the deformed Woods-Saxon average field. Pairing behaviour with increasing spin and general features of shape coexistence in mercury nuclei are illustrated.

γ rays in the 2–18 MeV range from the reaction 120Sn(28Si, 4n)144Gd

Abstract Unresolved γ radiation preceding the decay of the I π = 10 + isomer in 144 Gd has been studied via the 120 Sn + 28 Si reaction using a large NaI detector. The γ-ray multiplicity and anisotropy have been measured for 2 ⩽E⩽ 18MeV . At energies above 8 MeV a broad shoulder, presumably arising from the giant dipole resonance, is observed on top of the statistical tail. These high-energy γ rays are shown to deexcite high spin states and have a nearly isotropic angular distribution.

A comparative study of superdeformation in 146,147,148Gd. Possible manifestations of the pseudo-SU3 symmetry, octupole shape susceptibility and superdeformed deep-hole excitations

Abstract Two discrete superdeformed (SD) bands have been identified in the nucleus 147Gd and the twin-band mechanism studied by comparison with SD results for 146,148Gd. Theoretical interpretation in terms of nucleonic orbitals with the Woods-Saxon potential is consistent with the pseudo-spin symmetry picture and the octupole susceptibility mechanism predicted by theory.

Multi-particle excitations in the superdeformed 149Gd nucleus

Abstract Six rotational bands built on superdeformed intrinsic configurations have been observed in the 149 Gd nucleus with the Eurogam spectrometer. Orbital configuration assignments have been suggested on the basis of their effective alignments calculated with the Nilsson-Strutinsky cranking model. Most of the excited bands have identical partners in neighboring nuclei including one case differing by four mass units. Measurements of feeding patterns indicate that the 149 Gd yrast superdeformed band is fed over a wider range of angular momentum than other yrast superdeformed bands in this mass region whereas weaker excited bands in the same nucleus are populated in narrower spin windows.

Second backbending in the yrast line of 156Er

Abstract High spin yrast states of 156 Er were investigated using the reactions 141 Pr( 19 F,4nγ) and 123 Sb( 37 Cl, 4nγ), the latter in connection with a sum-crystal. In addition to the backbending at I = 12 h , a second one is found at I = 26 h ; and the yrast band is extended up to I = 32 h ; . These results are interpreted in terms of a Hartree-Fock-Bogolyubov Cranking (HFBC) method. It is demonstrated that for deformations in the vicinity of the Strutinsky equilibrium deformation, both a 2qp proton band crossing the yrast band or a 4qp neutron band crossing the yrast band can cause strong secondary backbending.

Collective band structures and particle alignments in 124Ba, 125Ba and 125Cs

Abstract High-spin states of 124Ba, 125Ba and 125Cs have been populated in the reactions 110Cd + 18O at 80MeV and 96Zr + 34S at 160 MeV and studied using nuclear spectroscopy techniques. Several bands have been established in 124Ba and previously known band structures in125Ba and 125Cs extended up to ( 43 2 − ) levels. Results concerning crossing frequencies and quasiparticle configurations are deduced from experimental routhians and aligned angular momenta. We propose that the two positive-parity bands in 124Ba are generated by h 11 2 proton and h 11 2 neutron alignments and the three negative-parity bands by the coupling of h 11 2 , g 7 2 neutrons and h 11 2 , g 7 2 or g 9 2 protons.

Very high spin states and isomerism in 153Ho

Abstract The level scheme of 153Ho has been studied to a spin of J= 81 2 and Ex=12.5 MeV using γ-ray and conversion-electron spectroscopy techniques. Two isomeric levels, with (J π , T 1 2 )=( 31 2 + , 229 (2) ns ) and ( 61 2 + , 2.98 (15) ns ) are observed. Above 2.7 MeV the yrast line displays the irregular level spacing characteristic of single particle alignment. Shell-model configurations are suggested for most states below 9.1 MeV, in which the 3− octupole vibration may play a major role.

Magnetic moments of the Iπ = 10+ isomers in Ce and Nd N = 80 isotones

Abstract Nuclear g -factors have been measured for the I π = 10 + isomers in 138 Ce and 140 Nd by the pulsed-beam time-differential spin-rotation method. The 3538 keV level in 138 Ce and 3621 keV level in 140 Nd were excited by the 130 Te( 12 C, 4nγ) and 128 Te( 16 O, 4nγ) reactions, respectively. The nuclear g -factors of these 10 + states were measured to be g = −0.176(10) and g = −0.192(12) for 138 Ce and 140 Nd respectively. These values are well explained by a two neutron-hole h 11 2 −2 configuration for these states.

Feeding of the superdeformed yrast band in 149Gd

Abstract The feeding pattern of the superdeformed yrast band in 149 Gd has been found to remain essentially the same, using the 124 Sn+ 30 Si reaction at beam energies of 150, 155 and 160 MeV leading to different input angular momenta and excitation energies in the compound nuclear system. This similarity as well as the relative yields of the superdeformed states as a function of beam energy may be understood in terms of the nuclear level density dependence on deformation and the onset of fission. In addition, it has been shown that, at all three beam energies, the selection of high-energy gamma rays does not enhance the yield of the superdeformed yrast states.

Multipolarity of the continuum γ-rays in 152Dy and 160Er via linear polarisation measurements

Abstract The multipolarity of the continuum transitions in 152 Dy and 160 Er has been deduced from γ-ray linear polarisation and angular distribution measurements. The yrast part for 160 Er agrees with the predicted stretched E2 cascade. The statistical parts for both 152 Dy and 160 Er consist of a mixture of dipolar stretched and non-stretched transitions, predominantly of electrical character. Below 1.5 MeV, the data of 152 Dy exhibit a different structure, and reveal a stretched M1 component in the low-energy region.