The Shears Mechanism in 142Gd in the Skyrme-Hartree-Fock Method with the Tilted-Axis Cranking

We report on the first Skyrme-Hartree-Fock calculations with the tilted-axis cranking in the context of magnetic rotation. The mean field symmetries, differences between phenomenological and self-consistent methods and the generation of shears-like structures in the mean field are discussed. Significant role of the time-odd spin-spin effective interaction is pointed out. We reproduce the shears mechanism, but quantitative agreement with experiment is rather poor. It may have to do with too large core polarization, lack of pairing correlations or properties of the Skyrme force.Comment: Presented at the XXVII Mazurian Lakes School of Physics, September 2-9 2001, Krzyze, Poland, Submitted to Acta Physica Polonic

First observation of medium-spin excitations in the 138Cs nucleus

Medium-spin, yrast excitations in the 138Cs nucleus, populated in the spontaneous fission of 248Cm, were observed for the first time. 138Cs was studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. The newly observed yrast cascade, built on the known 6- isomer at 80 keV, was successfully described by shell model calculations. Analogously to the 136I isotone, the 6- isomer in 138Cs has the \ensuremath{(\pi g_{7/2} ^4 d_{5/2} \nu f_{7/2})_{6^-}} dominating configuration and the 7- excitation, located 175 keV above, corresponds to the \ensuremath{(\pi g_{7/2} ^3 d_{5/2}^2 \nu f_{7/2})_{7^-}} as dominating configuration. Similarly as in 136I, changing the position of the d 5/2 proton orbital improves the reproduction of the data. However, in 138Cs the energy of this orbital should be increased compared to its energy in 133Sb, to get the best description, in contrast to 136I and 135Sb, where it had to be decreased. The best reproduction of excitation energies in 138Cs is obtained assuming that the πd 5/2 orbital in 138Cs is located about 100 keV higher than in 133Sb. These observations suggest that the lowering of the d 5/2 s.p. energy in 135Sb is not a physical effect due to the appearance of a neutron skin, as proposed by other authors, but rather an artifact due to some deficiency of the input data used in the shell model calculations in the region of the doubly magic 132Sn core

New Spins for ground states and isomers in 115^{115}Pd and 117^{117}Pd

Levels in 115Pd and 117Pd nuclei, populated in the spontaneous fission of 248Cm were studied by means of prompt gamma spectroscopy using the EUROGAM2 array of Anti-Compton spectrometers. Negative-parity, I = 9/2 excitations were identified, which are associated with the long-lived isomers in these nuclei, reported previously as 11/2- excitations. The new data indicate spin and parity 3/2 + for ground states in 115Pd and 117Pd instead of 5/2 + proposed in previous works. This result implicates changes of spin assignments to other levels in both nuclei

The (n, gamma) campaigns at EXILL

At the PF1B cold neutron beam line at the Institut Laue Langevin, the EXILL array consisting of EXOGAM, GASP and ILL-Clover detectors was used to perform (n, gamma) measurements at very high coincidence rates. About ten different reactions were measured in autumn 2012 using a highly collimated cold neutron beam. In spring 2013, the EXOGAM array was combined with 16 LaBr3(Ce) scintillators in the EXILL&FATIMA campaign for the measurement of lifetimes using the generalised centroid difference method. We report on the properties of the set-ups and present first results from both campaigns

First observation of excited states in the 111Tc nucleus - A new region of deformation at 40 ≤ Z ≤ 46, N ≥ 68?

The 111Tc nucleus, populated in the spontaneous fission of 248Cm, was studied by means of prompt γ-ray spectroscopy using the EUROGAM2 array. Excited states in 111Tc were observed for the first time. Systematics of energy levels in odd-A Tc isotopes, obtained in our study of 107Tc and 109Tc provide a reliable spin and parity assignment I = 5/2+ to the head of the new band in 111Tc, interpreted as the π5/2+[422] orbital originating from the proton g 9/2 shell. This level is most likely the ground state. Therefore, the (9/2+,7/2+) spin-parity assignment to the ground state of 111Tc, reported previously, is unlikely. Properties of the yrast band in 111Tc suggest prolate deformation of this band. There are hints that the deformation of 111Tc is larger than that of 109Tc, possibly due to admixtures of oblate-deformed configurations, which lower their excitation energy with increasing neutron number

New information on medium-spin structure of 133Sb

Excited states in the nucleus 133Sb, populated in the fission of 235U induced by thermal neutrons were studied using the Lohengrin fission-fragment separator. A new 4191.8 keV level in 133Sb, populated in the decay of the 16.6 μs isomer, was observed. The level is interpreted as the 11/2+ member of the πg7/2 * core configuration, predicted by the shell model at 4095 keV. Levels corresponding to octupole excitation of the 132Sn core, identified previously in prompt-γ measurement, were now observed in the isomeric decay