Impact of pairing correlations on the chemical composition of the inner crust of a neutron star

We investigate the impact of the role of pairing correlation on the energy per particles of Wigner-Seitz cells in the inner crust of a neutron star. In particular, we compare some common approximations done to treat pairing effects and we estimate the possible error. To reduce the computational cost of the calculations required to determine the chemical composition of the crust, we present a new numerical method based on Gaussian Emulator Process

Isospin-breaking interactions studied through mirror energy differences

Background: Information on charge-dependent (i.e., isospin-non-conserving) interactions is extracted from excited states of mirror nuclei. Purpose: Specifically, the purpose of the study is to extract effective isovector (Vpp 12Vnn) interactions which, in general, can either be of Coulomb or nuclear origin. Methods: A comprehensive shell-model description of isospin-breaking effects is used to fit data on mirror energy differences in the A = 42\u201354 region. The angular-momentum dependence of isospin-breaking interactions was determined from a systematic study of mirror energy differences. Results: The results reveal a significant isovector term, with a very strong spin dependence, beyond that expected of a two-body Coulomb interaction. Conclusions: The isospin-breaking terms that are extracted have a J dependence that is not consistent with the known CSB properties of the bare nucleon-nucleon interaction

Decay of low-lying 12C resonances within a 3alpha cluster model

We compute energy distributions of three $\alpha$-particles emerging from the decay of $^{12}$C resonances by means of the hyperspherical adiabatic expansion method combined with complex scaling. The large distance continuum properties of the wave functions are crucial and must be accurately calculated. The substantial changes from small to large distances determine the decay mechanisms. We illustrate by computing the energy distributions from decays of the $1^{+}$ and $3^-$-resonances in $^{12}$C. These states are dominated by direct and sequential decays into the three-body continuum respectively.Comment: 5 pages, 3 figures. Proceedings of the Clusters '07 conference held in Stratford-upon-Avon in September 200

Mirror Energy Differences at Large Isospin Studied through Direct Two-Nucleon Knockout

The first spectroscopy of excited states in 52Ni (Tz=2) and 51Co (Tz=-3/2) has been obtained using the highly selective two-neutron knockout reaction. Mirror energy differences between isobaric analogue states in these nuclei and their mirror partners are interpreted in terms of isospin nonconserving effects. A comparison between large scale shell-model calculations and data provides the most compelling evidence to date that both electromagnetic and an additional isospin nonconserving interactions for J=2 couplings, of unknown origin, are required to obtain good agreement.Comment: Accepted for publication in Physical Review Letter

Two-neutron transfer reaction mechanisms in 12^{12}C(6^6He,4^{4}He)14^{14}C using a realistic three-body 6^{6}He model

The reaction mechanisms of the two-neutron transfer reaction $^{12}$C($^6$He,$^4$He) have been studied at 30 MeV at the TRIUMF ISAC-II facility using the SHARC charged-particle detector array. Optical potential parameters have been extracted from the analysis of the elastic scattering angular distribution. The new potential has been applied to the study of the transfer angular distribution to the 2$^+_2$ 8.32 MeV state in $^{14}$C, using a realistic 3-body $^6$He model and advanced shell model calculations for the carbon structure, allowing to calculate the relative contributions of the simultaneous and sequential two-neutron transfer. The reaction model provides a good description of the 30 MeV data set and shows that the simultaneous process is the dominant transfer mechanism. Sensitivity tests of optical potential parameters show that the final results can be considerably affected by the choice of optical potentials. A reanalysis of data measured previously at 18 MeV however, is not as well described by the same reaction model, suggesting that one needs to include higher order effects in the reaction mechanism.Comment: 9 pages, 9 figure

Study of the break-up channel in 11Li+208Pb collisions at energies around the Coulomb barrier

We present a study of 11Li+208 Pb collisions at energies around the Coulomb barrier (Elab = 24.3 and 29.8 MeV), measured at the post-accelerated beam facility, ISAC II, at TRIUMF (Vancouver, Canada). A remarkably large yield of 9Li has been observed, a result that is attributed to the weak binding of the 11Li nucleus. The angular distribution of this 9Li yield, relative to the elastic one, has been analysed in terms of first-order semiclassical calculations as well as four-body and three-body Continuum-Discretized Coupled-Channels (CDCC) calculations, based on a three-body and di-neutron model of the 11Li nucleus, respectively. The calculations reproduce well the trend of the data and support the existence of a large concentration of B (E1) strength at very low excitation energies. The connection of this large B (E1) with a possible low-lying dipole resonance is discussed

Characterization of the proposed 4-α cluster state candidate in O 16

The O16(α,α′) reaction was studied at θlab=0 at an incident energy of Elab=200 MeV using the K600 magnetic spectrometer at iThemba LABS. Proton decay and α decay from the natural parity states were observed in a large-acceptance silicon strip detector array at backward angles. The coincident charged-particle measurements were used to characterize the decay channels of the 06+ state in O16 located at Ex=15.097(5) MeV. This state is identified by several theoretical cluster calculations to be a good candidate for the 4-α cluster state. The results of this work suggest the presence of a previously unidentified resonance at Ex≈15 MeV that does not exhibit a 0+ character. This unresolved resonance may have contaminated previous observations of the 06+ state