Short-lived isomers in Po-192 and Po-194

Isomeric states in Po194 and Po192 were studied at the velocity filter SHIP. The isotopes were produced in the fusion-evaporation reactions Pr141(Fe56, p2n)Po194 and Sm144(V51, p2n)Po192. Several new γ-ray transitions were attributed to the isomers and γ−γ coincidences for both isomers were studied for the first time. The 459-keV transition earlier, tentatively proposed as de-exciting the isomeric level in Po194, was replaced by a new 248-keV transition, and the spin of this isomer was reassigned from (11−) to (10−). The de-excitation of the (11−) isomeric level in Po192 by the 154-keV transition was confirmed and a parallel de-excitation by a 733-keV (E3) transition to (8+) level of the ground-state band was suggested. Moreover, side feeding to the (4+) level of the ground-state band was proposed. The paper also discusses strengths of transitions de-exciting 11− isomers in neighboring Po and Pb isotopes

New gas-filled mode of the large-acceptance spectrometer VAMOS

Spectromètre VAMOSA new gas-filled operation mode of the large-acceptance spectrometer VAMOS at GANIL is reported. A beam rejection factor greater than 1010 is obtained for the 40Ca+150Sm system at 196 MeV. The unprecedented transmission efficiency for the evaporation residues produced in this reaction is estimated to be around 80% for ®xn channels and above 95% for xnyp channels. A detailed study of the performance of the gasfilled VAMOS and future developments are discussed. This new operation mode opens avenues to explore the potential of fusion reactions in various kinematics

First spectroscopy of 66^{66}Se and 65^{65}As: Investigating shape coexistence beyond the N = Z line

The experiment was performed at the National Superconducting Cyclotron Laboratory (NSCL), at Michigan State University (USA).We report on the first γ spectroscopy of 66Se and 65As from two-neutron removal at intermediate beam energies. The deduced excitation energies for the first-excited states in 66Se and 65As are compared to mean-field-based predictions within a collective Hamiltonian formalism using the Gogny D1S effective interaction and to state-of-the-art shell-model calculations restricted to the pf5/2 g9/2 valence space. The obtained Coulomb-energy differences for the first excited states in 66Se and 65As are discussed within the shell-model formalism to assess the shape-coexistence picture for both nuclei. Our results support a favored oblate ground-state deformation in 66Se and 65As. A shape transition for the ground state of even-odd As isotopes from oblate in 65As to prolate in 67,69,71As is suggested

Study of 124^{124}Sn+136^{136}Xe fusion-evaporation: analysis of a rare-event experiment

7 pages, 4 figuresFusion-evaporation in the $^{124}$Sn+$^{136}$Xe system is studied using a high intensity xenon beam provided by the Ganil accelerator and the LISE3 wien filter for the selection of the products. Due to the mass symmetry of the entrance system, the rejection of the beam by the spectrometer was of the order of $5times10^8$. We have thus performed a detailed statistical analysis to estimate random events and to infer the fusion-evaporation cross sections. No signicant decay events were detected and upper limit cross sections of 172~pb, 87~pb and 235~pb were deduced for the synthesis of $^{257}$Rf, $^{258}$Rf and $^{259}$Rf, respectively

In-beam spectroscopic study of 244Cf

The ground-state rotational band of the neutron-deficient californium (Z = 98) isotope 244Cf was identified for the first time and measured up to a tentative spin and parity of I = 20+. The observation of the rotational band indicates that the nucleus is deformed. The kinematic and dynamic moments of inertia were deduced from the measured gamma-ray transition energies. The behavior of the dynamic moment of inertia revealed an up-bend due to a possible alignment of coupled nucleons in high-j orbitals starting at a rotational frequency of about hw = 0.20 MeV. The results were compared with the systematic behavior of the even-even N = 146 isotones as well as with available theoretical calculations that have been performed for nuclei in the region

In-beam spectroscopic study of Cf-244

The ground-state rotational band of the neutron-deficient californium (Z = 98) isotope 244Cf was identified for the first time and measured up to a tentative spin and parity of I I-pi = 20(+). The observation of the rotational band indicates that the nucleus is deformed. The kinematic and dynamic moments of inertia were deduced from the measured gamma-ray transition energies. The behavior of the dynamic moment of inertia revealed an up-bend due to a possible alignment of coupled nucleons in high-j orbitals starting at a rotational frequency of about (h) over bar (omega) = 0.20 MeV. The results were compared with the systematic behavior of the even-even N = 146 isotones as well as with available theoretical calculations that have been performed for nuclei in the region.Peer reviewe