Engineering topics

Giuliani, S. A.

Publications and source records attributed to Giuliani, S. A..

4 records

DOE OSTI2021

Precision mass measurement of lightweight self-conjugate nucleus 80 Zr

Protons and neutrons in the atomic nucleus move in shells analogous to the electronic shell structures of atoms. The nuclear shell structure varies due to changes of the nuclear mean field with the number of neutrons N and protons Z, and these variations can be probed by measuring mass differences between nuclei. The N=Z=40 self-conjugate nucleus 80 Zr is of particular interest as its proton and neutron shell structures are expected to be very similar, and its ground state is highly deformed. Here, we provide evidence for the existence of a deformed double shell closure in 80Zr through high precision Penning trap mass measurements of 80-83 Zr. Our mass values show that 80Zr is significantly lighter, and thus more strongly bound than predicted. This can be attributed to the deformed shell closure at N=Z=40 and the large Wigner energy. A statistical Bayesian model mixing analysis employing several global nuclear mass models demonstrates difficulties with reproducing the observed mass anomaly using current theory.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2019

Spallation-altered Accreted Compositions for X-Ray Bursts: Impact on Ignition Conditions and Burst Ashes

Model predictions of X-ray burst ashes and light curves depend on the composition of the material accreted from the companion star, in particular the abundance of CNO elements. It has previously been pointed out that spallation in the atmosphere of the accreting neutron star can destroy heavy elements efficiently. In this work we study this spallation using a realistic reaction network that follows the complete spallation cascade and takes into account not only destruction, but also production of elements by the spallation of heavier species. We find an increased survival probability of heavier elements compared to previous studies, resulting in significantly higher CNO abundances.We provide resulting compositions as a function of accretion rate, and explore their impact on 1D multi-zone X-ray burst models. Finally, we find significant changes in the composition of the burst ashes, which will affect the thermal and compositional structure of accreted neutron star crusts.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2019

Role of dynamic pairing correlations in fission dynamics

We study the role of dynamic pairing correlations in fission dynamics by considering intrinsic Hartree-Fock-Bogoliubov wave functions that are obtained by minimizing the particle number projected energy. For the restricted variational space, the set of self-consistent wave functions with different values of proton and neutron number particle fluctuations are considered. The particle number projected energy is used to define the potential energy surface for fission whereas collective inertias are computed within the traditional formulas for the intrinsic states. Here, the results show that the effect of the restricted variation after particle number projection in the potential energy surface is small while collective inertias substantially decrease. On the other hand, we show that this quenching is strongly mitigated when Coulomb antipairing is considered and therefore the final outcome of the complete calculation is close to the plain mean field result without Coulomb antipairing. In the light of these beyond-mean-field calculations, the validity of traditional fission calculations is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2019

Colloquium : Superheavy elements: Oganesson and beyond

During the last decade, six new superheavy elements were added into the seventh period of the periodic table, with the approval of their names and symbols. This milestone was followed by proclaiming 2019 the International Year of the Periodic Table of Chemical Elements by the United Nations General Assembly. According to theory, due to their large atomic numbers, the new arrivals are expected to be qualitatively and quantitatively different from lighter species. The questions pertaining to superheavy atoms and nuclei are in the forefront of research in nuclear and atomic physics and chemistry. Lastly, this Colloquium offers a broad perspective on the field and outlines future challenges.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗