Search

For the Rrst time, using a unique finite-range interaction (D1M Gogny force), a fully coherent and time-feasible calculation of the Bohr Hamiltonian vibrational mass is envisioned in a Hartree-Fock-Bogoliubov + quasiparticle random-phase approximation (QRPA) framework. In order to reach a reasonable computation time, we evaluate the feasibility of this method by considering two restrictions for the QRPA: the Tamm-Dancoff approximation and the insertion of a valence space. We validate our approach in the even-even tin isotopes by comparing the convergence scheme of the mass parameter with those of built-in QRPA outputs: excited-state energy and reduced transition probability. The seeming convergence of these intrinsic quantities is shown to be misleading and the difference with the theoretical expected value is quantified. This work is a primary step towards the systematic calculation of mass parameters. [ABSTRACT FROM AUTHOR]

High-spin states in 139Ce have been populated using the 130Te(14C,5n) reaction. The level scheme has been extended to higher spins, including a new band of dipole transitions. The parity of several states has been changed from negative to positive, mainly based on the comparison with the level structure of the core nucleus 140Ce and the results of a realistic shell-model calculation. The dipole band is interpreted as a magnetic rotation band with πh11/2² ⊗ νh-111/2 configuration built on small deformation axial shape with (ɛ2 = 0.12,γ = 0°). [ABSTRACT FROM AUTHOR]

The 26Al radioisotope is of great importance for understanding the chemical and dynamical evolution of our galaxy. Among the possible stellar sources, massive stars are believed to be the main producer of this radioisotope. Understanding 26Al nucleosynthesis in massive stars requires estimates of the thermonuclear reaction rates of the 26Al(n,p)26Mg, 26Al(n,α)23Na, and 23Na(α,p)26Mg reactions. These reaction rates depend on the spectroscopic properties of 27Al states above the neutron and alpha thresholds. In this context, the 27Al(p,p)27Al* reaction was studied at 18 MeV using a high-resolution Enge Split-Pole spectrometer. States from the ground state up to excitation energies of ≈14 MeV were populated. While up to the 23Na + α threshold no additional states are observed, we report for the first time 30 new levels above the 23Na + α threshold and more than 30 new states above the 26Al + n threshold for which excitation energies are determined with an uncertainty of 4-5 keV. [ABSTRACT FROM AUTHOR]

The nucleus 35S has been studied by in-beam γ-ray spectroscopy using the 24Mg(14N,3p) fusion-evaporation reaction at Elab = 40 MeV. A level scheme extended up to Jπ = 17/2+ at 8023 keV and Jπ = 13/2- at 6352 keV has been established. Lifetimes of six excited states have been determined by applying the Doppler shift attenuation method. The experimental data have been compared with the results of large-scale shell model calculations performed using different effective interactions and model spaces allowing particle-hole excitations across the N = Z = 20 shell gap. [ABSTRACT FROM AUTHOR]

The high-spin states of the two neutron-rich nuclei 88Kr52 and 89Rb52 have been studied from the 18O+208Pb fusion-fission reaction. Their level schemes were built from triple β-ray coincidence data, and β-β angular correlations were analyzed in order to assign spin and parity values to most of the observed states. The two level schemes evolve from collective structures to single-particle excitations as a function of the excitation energy. Comparison with results of shell-model calculations gives the specific proton and neutron configurations which are involved to generate the angular momentum alongthe yrast lines. [ABSTRACT FROM AUTHOR]

Odd-odd 136Cs nuclei have been produced in the 18O + 208Pb and 12C + 238U fusion-fission reactions and their γ rays studied with the Euroball array. The high-spin level scheme was built up to ~4.7 MeV excitation energy and spin I ~ 16h from the triple γ-ray coincidence data. The configurations of the three structures observed above ~2 MeV excitation energy are first discussed bγ analogy with the proton excitations identified in the semimagic 137Cs82 nucleus, which involve the three high-j orbits lying above the Z = 50 gap, πg7/2, πd5/2, and πhn1/2- This is confirmed by the results of shell-model calculations performed in this work. [ABSTRACT FROM AUTHOR]

Excited states up to Jπ = 11- at 10 296 keV and Jπ = 10+ at 10 707 keV have been populated in the odd-odd 36C1 nucleus using the 24Mg(14N,2p) fusion-evaporation reaction at Elab = 31 MeV. Twenty new states and 62 new γ transitions have been identified by employing γ-γ and γ-γ-γ coincidences. Lifetimes have been investigated by the Doppler shift attenuation method. The experimental data have been compared with the results of large-scale shell-model calculations performed using different effective interactions and model spaces allowing particle-hole excitations across the N = Z = 20 shell gap. [ABSTRACT FROM AUTHOR]

Five N = 82 isotones have been produced in two fusion-fission reactions and their &ggr; rays studied with the Euroball array. The high-spin states of 139La have been identified, while the high-spin yrast and near-to-yrast structures of the four others have been greatly extended. From angular correlation analysis, spin values have been assigned to some states of 136Xe and 137Cs. Several cascades involving &ggr; rays of 139La have been found to be delayed; they deexcite an isomeric state with T1/2 = 315(35) ns located at 1800 keV excitation energy. The excited states of these five N = 82 isotones are expected to be due to various proton excitations involving the three high-j subshells located above the Z = 50 shell closure. This is confirmed by the results of shell-model calculations performed in this work. In addition, high-spin states corresponding to the excitation of the neutron core have been unambiguously identified in 136Xe, 137Cs, and 138Ba. [ABSTRACT FROM AUTHOR]

The 119_126Sn nuclei have been produced as fission fragments in two reactions induced by heavy ions: 12C + 238U at a bombarding energy of 90 MeV and 18O + 208Pb at 85 MeV. Their level schemes have been built from γ rays detected using the Euroball array. High-spin states located above the long-lived isomeric states of the evenand odd-A 120-126Sn nuclei have been identified. Moreover, isomeric states lying around 4.5 MeV have been established in 120,122,124,126Sn from delayed coincidences between the fission fragment detector SAPhIR and the Euroball array. The states located above 3 MeV excitation energy are ascribed to several broken pairs of neutrons occupying the vh11/2 orbit. The maximum value of angular momentum available in such a high-j shell, i.e., for midoccupation and the breaking of the three neutron pairs, has been identified. This process is observed for the first time in spherical nuclei. [ABSTRACT FROM AUTHOR]

The 83, 81As nuclei have been produced as fission fragments in the fusion reaction 18O + 208Pb at 85 MeV bombarding energy and studied with the Euroball array. Medium-spin states of 83, 81As have been established up to ~3.5 MeV excitation energy. From angular correlation analysis, spin values have been assigned to most of the 81As excited states. The behaviors of the yrast structures identified in this work are discussed in comparison with the general features known in the mass région. Then they are compared to the results of two theoretical approaches: the "rotor + quasiparticle" for 81As and the shell model using the effective interactions JUN45 for 83, 81Ks. [ABSTRACT FROM AUTHOR]

γ-ray production cross sections have been measured in proton irradiations of N, Ne, and Si and α-particle irradiations of N and Ne. In the same experiment we extracted also line shapes for strong γ-ray lines of 16O produced in proton and α-particle irradiations of O. For the measurements gas targets were used for N, O, and Ne and a thick foil for Si. All targets were of natural isotopic composition. Beams in the energy range up to 26 MeV for protons and 39 MeV for α particles were delivered by the Institut de Physique Nucléaire-Orsay tandem accelerator. The γ rays were detected with four high-purity Ge detectors in the angular range 30° to 135°. We extracted 36 cross-section excitation functions for proton reactions and 14 for α-particle reactions. For the majority of the excitation functions no other data exist to our knowledge. Where comparison with existing data was possible, usually a very good agreement was found. It is shown that these data are very interesting for constraining nuclear reaction models. In particular, the agreement of cross section calculations in the nuclear reaction code talys with the measured data could be improved by adjusting the coupling schemes of collective levels in the target nuclei 14N, 20,22Ne, and 28Si. The importance of these results for the modeling of nuclear γ-ray line emission in astrophysical sites is discussed. [ABSTRACT FROM AUTHOR]