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The success encountered in the systematic studies of the electric and magnetic strength functions for almost all even-even nuclei proves the quality of our HFB+QRPA calculations which use the Gogny interaction within the whole nuclear chart. In this paper, we study the dipole electromagnetic strength distribution in 158-166Dy. The scalar or the vector nature, in the isospin as well as in the spin space, is analysed according to transition density for some of the M1 excitations in 162Dy. [ABSTRACT FROM AUTHOR]

In this paper we present theoretical results on the dipole response in the proton spin-saturated Zr isotopes. The electric and magnetic dipole excitations are obtained in Hartree-Fock-Bogolyubov plus Quasi-particle Random Phase Approximation (QRPA) calculations performed with the D1M Gogny force. A pnQRPA charge exchange code is used to study the Gamow-Teller response. The results on the pygmy, the giant dipole resonances as well as those on the magnetic nuclear spin-flip excitation and the Gamow-Teller transitions are compared with available experimental or theoretical information. In our approach, the proton pairing plays a role in the phonon excitations, in particular in the M1 nuclear spin-flip resonance. [ABSTRACT FROM AUTHOR]

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]

The N = 52 Ga 83 β decay was studied at ALTO. The radioactive 83 Ga beam was produced through the ISOL photofission technique and collected on a movable tape for the measurement of γ -ray emission following β decay. While β -delayed neutron emission has been measured to be 56–85% of the decay path, in this experiment an unexpected high-energy 5–9 MeV γ -ray yield of 16(4)% was observed, coming from states several MeVs above the neutron separation threshold. This result is compared with cutting-edge QRPA calculations, which show that when neutrons deeply bound in the core of the nucleus decay into protons via a Gamow–Teller transition, they give rise to a dipolar oscillation of nuclear matter in the nucleus. This leads to large electromagnetic transition probabilities which can compete with neutron emission, thus affecting the β -decay path. This process is enhanced by an excess of neutrons on the nuclear surface and may thus be a common feature for very neutron-rich isotopes, challenging the present understanding of decay properties of exotic nuclei. [ABSTRACT FROM AUTHOR]

The response of a scintillation detector with a cylindrical 1.5-in. LaBr 3 :Ce crystal to incident neutrons has been measured in the energy range E n = 2–12 MeV. Neutrons were produced by proton irradiation of a Li target at E p = 5–14.6 MeV with pulsed proton beams. Using the time-of-flight information between target and detector, energy spectra of the LaBr 3 :Ce detector resulting from fast neutron interactions have been obtained at 4 different neutron energies. Neutron-induced γ rays emitted by the LaBr 3 :Ce crystal were also measured in a nearby Ge detector at the lowest proton beam energy. In addition, we obtained data for neutron irradiation of a large-volume high-purity Ge detector and of a NE-213 liquid scintillator detector, both serving as monitor detectors in the experiment. Monte-Carlo type simulations for neutron interactions in the liquid scintillator, the Ge and LaBr 3 :Ce crystals have been performed and compared with measured data. Good agreement being obtained with the data, we present the results of simulations to predict the response of LaBr 3 :Ce detectors for a range of crystal sizes to neutron irradiation in the energy range E n = 0.5–10 MeV. [ABSTRACT FROM AUTHOR]

A new β -decay station, COnversion electrons Chasing at Orsay (COeCO), has been developed at ALTO to perform conversion electron spectroscopy studies of neutron-rich nuclei produced by photo-fission of a uranium carbide target. It is based on the collection of a low-energy ISOL beam on a mylar tape, and the transportation of the electrons emitted by the produced radioactive source through a magnetic field induced by two copper coils, towards a cooled Si(Li) detector. In this article, a detailed description of the new decay station and its components is given. The magnetic field induced by the coils was measured and compared to simulations performed with the COMSOL ® software. The efficiency of the detection setup was estimated using a 207Bi and a 152Eu source as an off-line commissioning. Finally, the results obtained with a 96Rb radioactive beam for the on-line commissioning are presented. [ABSTRACT FROM AUTHOR]

Excited states in the mirror nuclei 31P and 31S were populated in the 1p and 1n exit channels of the reaction 20Ne + 12C, at a beam energy of 33 MeV. The 20Ne beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident γ -rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A = 31 mass region. Self-consistent beyond mean field calculations using Equation of Motion method based on a chiral potential and including two- and three-body forces reproduce well the experimental B(E1) strengths, reinforcing our conclusion. Coherent mixing from higher-lying states involving the Giant Isovector Monopole Resonance accounts well for the effect observed. The breaking of the isospin symmetry originates from the violation of the charge symmetry of the two- and three-body parts of the potential, only related to the Coulomb interaction. [ABSTRACT FROM AUTHOR]

We have measured the γ -ray line production cross sections in proton-induced nuclear reactions on various target nuclei (12C, 16O, 24Mg, 28Si, 56Fe) of chemical elements abundant in astrophysical sites (solar flares, the interstellar medium, cosmic compact objects) over the incident energy range of E p = 30 – 200 MeV. We carried out experimental campaigns in joint collaboration at the K = 200 separated sector cyclotron of iThemba LABS using a high-energy resolution, high-efficiency detection array composed of 8 Compton-suppressed clover detectors comprising 32 HP-Ge crystals for recording the γ -ray energy spectra. In the current paper, we focus on γ -ray de-excitation lines produced in proton irradiations of n a t C and Mylar targets, in particular, on the prominent 4.439 and 6.129 MeV lines of 12C and 16O which are among the strongest lines emitted in solar flares and in interactions of low-energy cosmic rays (LECRs) with the gas and dust of the inner galaxy. We report new γ -ray production experimental cross section data for ten nuclear γ -ray lines that we compare to previous low-energy data sets from the literature, to the predictions of the TALYS code of nuclear reactions and to a semi-empirical compilation. In the first approach, performing calculations with default input parameters of TALYS we observed substantial deviations between the predicted cross sections and experimental data. Then, using modified optical model potential (OMP) and nuclear level deformation parameters as input data we generated theoretical excitation functions for the above two main lines fully consistent with experimental data. In contrast, the experimental data sets for the other eight analyzed lines from the two proton-irradiated targets exhibit significant deviations with the predicted cross section values. We also report line-shape experimental data for the line complex observed at E γ = 4.44 MeV in irradiations of the two targets. Finally, we emphasize the astrophysical implications of our results. [ABSTRACT FROM AUTHOR]

The lifetimes of eight lower spin levels of the yrast band in 168 Yb, populated via the 154 Sm( 18 O,4n) and 124 Sn( 48 Ca,4n) reactions, were measured, six of them for the first time, by means of the recoil-distance Doppler-shift method. Two versions of the differential decay-curve method have been applied for the data analysis resulting in a very good agreement. The reduced transition probabilities indicate some reduction of the collectivity for states just above the 6 1 + level, i.e. well below the band-crossing. The reasons of this effect are discussed in terms of an interaction between the ground-state band and yet unknown part of the two-quasiparticle ( ν 13 / 2 ) spin-aligned S-band by invoking the shell-structure or alternatively/additionally, as changes in the internal structure/shape induced by the rotation. [ABSTRACT FROM AUTHOR]

We present the first experimental evidence of the scissors mode in the superheavy nucleus 254No produced in the 208Pb(48Ca, 2 n γ))254No reaction. The spectrum of γ rays emitted by the excited 254No nuclei shows an enhanced γ -ray yield for transition energies of ≈2.5 MeV. By measuring the linear polarization properties of the emitted γ rays, we confirm that the transitions in the enhancement region are predominantly of magnetic-dipole character, characteristic for the scissors mode. To further characterize the enhanced γ -ray yield, simulations of the electromagnetic decay of 254No were performed. The observed enhancement is reproduced by including an M 1 component in the γ strength function with total strength B (M 1 ↑) = 11.8 (19) μ N 2. This is in good agreement with the integrated M 1 strength from sum-rule estimates and new calculations within the quasi-particle random-phase approximation presented here. Our results provide a stringent test of phenomenological formulae for the scissors mode currently used in stellar nucleosynthesis calculations. We find that those formulae are not satisfactory, and we recommend using sum-rule estimates assuming a rigid-body moment of inertia instead for describing the scissors mode in superheavy nuclei. [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]

Five new 2+ levels have been established in the semimagic 210Po nucleus from a 208Pb(12C,10Be) two-proton transfer experiment, performed at energies close to the Coulomb barrier at JAEA Tokai. A setup combining Ge, LaBr3, and Si telescopes was used to detect both in-beam γ rays and ejectile residues. The new 2+ states have been established by means of the transitions toward the 0+ ground state which are present in the γ spectra produced by properly selecting the excitation energy in 210Po after kinematical reconstruction. (f7/2)², h9/2⊗f5/2, (i13/2)², f7/2⊗p3/2, and f7/2⊗f5/2 two-proton configurations are assigned to these states. In addition, a new 3-level has also been established in this nucleus, very likely originating from the f7/2⊗i13/2 configuration. Shell-model calculations strongly support these assignments. [ABSTRACT FROM AUTHOR]

The structure of low-lying excited states in 251Fm, populated by the α decay of 255No, has been investigated by means of combined γ and internal conversion electron spectroscopy. The values for the internal conversion coefficients for the 1/2+→5/2+ and 5/2+→9/2- transitions have been measured. The determined M2/E3 mixing ratio and lifetime for the 5/2+ decay to the ground state allowed to determine the corresponding reduced transitions strengths of B(E3)=18(6) W.u. and B(M2)=3.0(6)×10-3 W.u. These results, as well as the results of previous studies in N=151 isotopes, are compared to theoretical calculations beyond the mean-field approach, including the first QRPA calculations using the Gogny D1M parametrization for such heavy odd-N nuclei. The comparison points to the importance of accounting for the octupole vibrations for a proper understanding of the low-lying nuclear structure of some of the heaviest elements. [ABSTRACT FROM AUTHOR]

Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we extend our large-scale calculations of the E1 γ-ray strength function, obtained in the framework of the axially- symmetric-deformed quasiparticle random phase approximation (QRPA) based on the finite-range D1M Gogny force, to the calculation of the M1 strength function. We compare our QRPA prediction of the M1 strength with available experimental data and show that a relatively good agreement is obtained provided the strength is shifted globally by about 2 MeV and increased by an empirical factor of 2. Predictions of the M1 strength function for spherical and deformed nuclei within the valley of ß stability as well as in the neutron-rich region are discussed. Its impact on the radiative neutron capture cross section is also analyzed. [ABSTRACT FROM AUTHOR]