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

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

Isospin-symmetry breaking corrections for the description of triplet energy differences

The charge-independence breaking of the nuclear interaction is analyzed by means of energy differences among analog states in T=1 isobaric multiplets. Data on triplet energy differences in the sd, pf, and pfg shells, i.e., 18≤A≤66, are reproduced with very good accuracy by large-scale shell-model calculations taking into account, aside from the Coulomb interaction, a single isotensor schematic interaction of monopole-pairing type. It is shown that the effect on the triplet energy differences of this isospin-breaking interaction is of the same magnitude as the Coulomb one. Moreover, its strength is the same for every single-particle orbital of the considered model space

Cycling the hot CNO : A teaching methodology

An interactive activity to teach the hot Carbon, Nitrogen and Oxygen (HCNO) cycle is proposed. Justification for why the HCNO cycle is important is included via an example of x-ray bursts. The activity allows teaching and demonstration of half-life, nuclear isotopes, nuclear reactions, protons and α-particles, and catalytic processes. Whilst the process example is specific to astrophysics it may be used to teach more broadly about catalytic processes. This practical is designed for use with 10-20 participants, with the intention that the exercise will convey nuclear physics principles in a fun and interactive manner

Nucleosynthetic Yields from Neutron Stars Accreting in Binary Common Envelopes

© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. Massive-star binaries can undergo a phase where one of the two stars expands during its advanced evolutionary stage as a giant and envelops its companion, ejecting the hydrogen envelope and tightening its orbit. Such a common envelope phase is required to tighten the binary orbit in the formation of many of the observed X-ray binaries and merging compact binary systems. In the formation scenario for neutron star binaries, the system might pass through a phase where a neutron star spirals into the envelope of its giant star companion. These phases lead to mass accretion on to the neutron star. Accretion on to these common-envelope-phase neutron stars can eject matter that has undergone burning near to the neutron star surface. This paper presents nucleosynthetic yields of this ejected matter, using population synthesis models to study the importance of these nucleosynthetic yields in a galactic chemical evolution context. Depending on the extreme conditions in temperature and density found in the accreted material, both proton-rich and neutron-rich nucleosynthesis can be obtained, with efficient production of neutron-rich isotopes of low Z material at the most extreme conditions, and proton-rich isotopes, again at low Z, in lower density models. Final yields are found to be extremely sensitive to the physical modelling of the accretion phase. We show that neutron stars accreting in binary common envelopes might be a new relevant site for galactic chemical evolution, and therefore more comprehensive studies are needed to better constrain nucleosynthesis in these objects

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

The first spectroscopy of excited states in Ni52 (Tz=-2) and Co51 (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. � 2013 American Physical Society

New experimental 23^{23}Na(α,pα,p)26^{26}Mg Reaction Rate for Massive Star and Type-Ia Supernova models

The $^{23}$Na($\alpha,p$)$^{26}$Mg reaction has been identified as having a significant impact on the nucleosynthesis of several nuclei between Ne and Ti in type-Ia supernovae, and of $^{23}$Na and $^{26}$Al in massive stars. The reaction has been subjected to renewed experimental interest recently, motivated by high uncertainties in early experimental data and in the statistical Hauser-Feshbach models used in reaction rate compilations. Early experiments were affected by target deterioration issues and unquantifiable uncertainties. Three new independent measurements instead are utilizing inverse kinematics and Rutherford scattering monitoring to resolve this. In this work we present directly measured angular distributions of the emitted protons to eliminate a discrepancy in the assumptions made in the recent reaction rate measurements, which results in cross sections differing by a factor of 3. We derive a new combined experimental reaction rate for the $^{23}$Na($\alpha,p$)$^{26}$Mg reaction with a total uncertainty of 30% at relevant temperatures. Using our new $^{23}$Na($\alpha,p$)$^{26}$Mg rate, the $^{26}$Al and $^{23}$Na production uncertainty is reduced to within 8%. In comparison, using the factor of 10 uncertainty previously recommended by the rate compilation STARLIB, $^{26}$Al and $^{23}$Na production was changing by more than a factor of 2. In type-Ia supernova conditions, the impact on production of $^{23}$Na is constrained to within 15%

Mirrored one-nucleon knockout reactions to the T-z = +/- 3/2 A=53 mirror nuclei

Background: The study of excited states in mirror nuclei allows us to extract information on charge-dependent (i.e., isospin-nonconserving) interactions in nuclei. Purpose: To extend previous studies of mirror nuclei in the f72 region, investigating charge symmetry breaking of the strong nuclear force. Methods: γ-ray spectroscopy has been performed for the mirror (Tz=±32) pair Ni53 and Mn53, produced via mirrored one-nucleon knockout reactions. Results: Several new transitions have been identified in Ni53 from which a new level scheme has been constructed. Cross sections for knockout have been analyzed and compared with reaction model calculations where evidence is found for knockout from high-spin isomeric states. Mirror energy differences between isobaric analog states have been computed, compared to large scale shell-model calculations, and interpreted in terms of isospin-nonconserving effects. In addition, lifetimes for the long-lived Jπ=52−1 analog states in both Mn53 and Ni53 have been extracted through lineshape analysis, giving half-lives of t12=120(14) ps and t12=198(12) ps, respectively. Conclusions: The inclusion of a set of isovector isospin-nonconserving matrix elements to the shell-model calculations gave the best agreement with the experimental data