J.P. Vivien

Single step links of the superdeformed band in Pb-194 : A measure of the absolute excitation energy, spin and parity of the superdeformed states

Abstract The EUROGAM array has been used to investigate the decay out of the yrast superdeformed (SD) band in 194 Pb. Six single step decays from the lowest observed SD states to low-lying states at normal deformation (ND) have been identified. From this observation, the excitation energy of the SD band in 194 Pb is established at 4877 ± 1.5 keV for the 6 + SD state. The most probable spins and parities of all members of the SD band are also deduced assuming that the SD states have even spin and positive parity.

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.

Excited bands in the doubly-magic superdeformed 152Dy nucleus: evidence for the first N = 7 proton hyper-intruder orbital

Abstract Five excited superdeformed bands have been observed in the doubly closed-shell superdeformed nucleus 152 Dy. Three of the new bands are interpreted in terms of single neutron excitations across the N = 86 shell gap. One of these bands appears to partly decay into the yrast superdeformed band. Another band involves a single proton excitation across the Z = 66 shell gap into the N = 7 hyper-intruder orbital. This is the first evidence of the influence of this deformation driving orbital on superdeformed structures in any mass region.

Multidimensional analysis of high resolution γ-ray data

Abstract Algorithms are developed to analyze high-fold γ-ray coincidences. Performances of the programs have been tested in 3, 4 and 5 dimensions using events generated with a Monte Carlo simulation.

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.

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.