A. Scherillo

'Safe' Coulomb excitation of Mg-30

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient gamma spectrometer MINIBALL. Using 30Mg ions accelerated to an energy of 2.25 MeV/u together with a thin (nat)Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation gamma-ray yields the B(E2;0(+)gs-->2(+)1) value of 30Mg was determined to be 241(31)e2 fm4. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope 30Mg resides outside the island of inversion.

19/2+ isomer of 125Cd and realistic shell-model calculations of neutron-rich Cd isotopes

The decay of a T1/2 = 19(3) μs isomeric state from 125Cd has been observed using γ-ray spectroscopy at the Lohengrin mass spectrometer of the Institut Laue-Langevin, Grenoble. Two coincident γ rays were observed to be emitted from the decay of this isomeric state, contradicting recently published data on this nucleus. Realistic shell-model calculations have been performed to interpret the decay scheme, allowing a spin and parity of 19/2+ to be assigned to the isomeric state. All configurations contributing to this isomeric state have amplitudes less than 7 %. Experimental data have recently been published on the decays of μs isomeric states in 127,128,130Cd. Realistic shell-model calculations for these nuclei are presented which reproduce the known experimental decay schemes reasonably well.

New information on excited states below the μs isomer in 136Sb

New experimental information has been obtained on the μs isomeric cascade in the very neutron-rich 136 Sb using γ-ray and conversion-electron spectroscopy at the Lohengrin mass spectrometer of the Institut Laue-Langevin. Two new transitions have been observed and their multipolarities determined, resolving the question of the origin of the isomerism. The new level scheme is in good agreement with predictions of a realistic shell-model calculation. The isomeric state is tentatively assigned a spin and parity of 6- and a proposed πg7/2 ν( f 7/2 ) 3 dominant configuration.

Excitation energy and deformation of the 1/2{sup +}[431] intruder band in {sup 107}Tc

The already detailed study of {sup 107}Tc nucleus was complemented by a search for microsecond isomers at very low energy. For this purpose, this neutron-rich nucleus was produced by thermal-neutron-induced fission of {sup 241}Pu. We have found a new 30.1 keV microsecond isomeric state which deexcites to the ground state by a strongly-hindered E1 transition. This isomer was identified as the 3/2{sup +} level of the 1/2{sup +}[431] intruder band in {sup 107}Tc and is also the lowest-lying member of the band. The very low energy of the band head suggests a large quadrupole deformation. From a comparison with {sup 105}Tc, where more information is known about the intruder band, it is deduced that the 1/2{sup +}[431] band has a quadrupole deformation, {epsilon}{sub 2}{>=}0.35 and a possible triaxial shape, {gamma}{approx_equal}20 degrees.