Studying X-ray burst nucleosynthesis in the laboratory

Type I X-ray bursts are the most common explosions in the Galaxy; however, the nucleosynthesis that occurs during the thermonuclear runaway and explosion is poorly understood. In this proceedings we discuss current experimental efforts and techniques that are being used to study X-ray burst nucleosynthesis in the laboratory. Specifically, radioactive ion beam techniques that have recently been developed have allowed the study of some of the most important (α, p) reactions in X-ray bursts for the first time. © Published under licence by IOP Publishing Ltd

Direct Evidence for Octupole Deformation in 146^{146}Ba and the Origin of Large E1E1 Moment Variations in Reflection-Asymmetric Nuclei

Despite the more than one order of magnitude difference between the measured dipole moments in $^{144}$Ba and $^{146}$Ba, the strength of the octupole correlations in $^{146}$Ba are found to be as strong as those in $^{144}$Ba with a similarly large value of $B(E3;3^- \rightarrow 0^+)$ determined as 48($^{+21}_{-29}$) W.u. The new results not only establish unambiguously the presence of a region of octupole deformation centered on these neutron-rich Ba isotopes, but also manifest the dependence of the electric dipole moments on the occupancy of different neutron orbitals in nuclei with enhanced octupole strength, as revealed by fully microscopic calculations.Comment: 6 pages, 5 figures, accepted for publication in Phys. Rev. Let

Quantum Monte Carlo calculations of spectroscopic overlaps in A≤7A \leq 7 nuclei

We present Green's function Monte Carlo calculations of spectroscopic overlaps for $A \leq 7$ nuclei. The realistic Argonne v18 two-nucleon and Illinois-7 three-nucleon interactions are used to generate the nuclear states. The overlap matrix elements are extrapolated from mixed estimates between variational Monte Carlo and Green's function Monte Carlo wave functions. The overlap functions are used to obtain spectroscopic factors and asymptotic normalization coefficients, and they can serve as an input for low-energy reaction calculations

Effect of shell structure on the fission of sub-lead nuclei

Fission of atomic nuclei often produces mass asymmetric fragments. However, the origin of this asymmetry was believed to be different in actinides and in the sub-lead region [A. Andreyev {\it et al.}, Phys. Rev. Lett. {\bf 105}, 252502 (2010)]. It has recently been argued that quantum shell effects stabilising pear shapes of the fission fragments could explain the observed asymmetries in fission of actinides[G. Scamps and C. Simenel, Nature {\bf 564}, 382 (2018)]. This interpretation is tested in the sub-lead region using microscopic mean-field calculations of fission based on the Hartree-Fock approach with BCS pairing correlations. The evolution of the number of protons and neutrons in asymmetric fragments of mercury isotope fissions is interpreted in terms of deformed shell gaps in the fragments. A new method is proposed to investigate the dominant shell effects in the pre-fragments at scission. We conclude that the mechanisms responsible for asymmetric fissions in the sub-lead region are the same as in the actinide region, which is a strong indication of their universality.Comment: Accepted as a rapid communication by Phys. Rev.

Penning trap mass measurements on (99-109)$Cd with ISOLTRAP and implications on the rp process

Penning trap mass measurements on neutron-deficient Cd isotopes (99-109)Cd have been performed with the ISOLTRAP mass spectrometer at ISOLDE/CERN, all with relative mass uncertainties below 3*10^8. A new mass evaluation has been performed. The mass of 99Cd has been determined for the first time which extends the region of accurately known mass values towards the doubly magic nucleus 100Sn. The implication of the results on the reaction path of the rp process in stellar X-ray bursts is discussed. In particular, the uncertainty of the abundance and the overproduction created by the rp-process for the mass A = 99 is demonstrated by reducing the uncertainty of the proton-separation energy of 100In Sp(100In) by a factor of 2.5.Comment: 14 pages, 9 figure

Nuclear Astrophysics with Radioactive Beams

The quest to comprehend how nuclear processes influence astrophysical phenomena is driving experimental and theoretical research programs worldwide. One of the main goals in nuclear astrophysics is to understand how energy is generated in stars, how elements are synthesized in stellar events and what the nature of neutron stars is. New experimental capabilities, the availability of radioactive beams and increased computational power paired with new astronomical observations have advanced the present knowledge. This review summarizes the progress in the field of nuclear astrophysics with a focus on the role of indirect methods and reactions involving beams of rare isotopes.Comment: 121 pages, 27 figures, 510 references, to appear in Physics Reports. Minor typos and references fixe

Fine structure of helium-like ions and determination of the fine structure constant

We report a calculation of the fine structure splitting in light helium-like atoms, which accounts for all quantum electrodynamical effects up to order \alpha^5 Ry. For the helium atom, we resolve the previously reported disagreement between theory and experiment and determine the fine structure constant with an accuracy of 31 ppb. The calculational results are extensively checked by comparison with the experimental data for different nuclear charges and by evaluation of the hydrogenic limit of individual corrections.Comment: 4 pages, 3 tables, with a typo in Eq. (9) correcte

R-matrix Methods with an application to 12C(alpha,gamma)16O

We review some aspects of R-matrix theory and its application to the semi-empirical analysis of nuclear reactions. Important applications for nuclear astrophysics and recent results for the ${}^{12}{\rm C}(\alpha,\gamma){}^{16}{\rm O}$ reaction are emphasized.Comment: 7 pages. Published in the Proceedings of the Fifth European Summer School on Experimental Nuclear Astrophysics, Santa Tecla, Sicily, Italy, 20-27 September 2009, Editors Claudio Spitaleri, Claus Rolfs, and Rosario Gianluca Pizzone, AIP Conference Proceedings number 1213 (AIP, New York, 2010), pp. 35-4