Nuclear Theory·nucl-th
5 papers—3 primary·2 cross-listed
The generation of fission fragments (FF) spins and of their relative orbital angular momentum has been debated for more than six decades and no consensus has been yet achieved so far. (The published abstract, being too long, can be found in the manuscript.)
A. O. Macchiavelli · H. L. Crawford · C. M. Campbell · R. M. Clark · M. Cromaz · P. Fallon · I. Y. Lee · A. Gade · A. Poves · E. Rice
Exclusive cross sections for the PSi reaction to the lowest and states, measured at NSCL with GRETINA and the S800, are interpreted in terms of a two-level mixing (collective) model of oblate and prolate co-existing shapes. Using the formalism developed for deformed nuclei we calculate the spectroscopic amplitudes and exclusive cross-sections in the strong coupling limit, where for P the schematic wavefunction includes the coupling of the Nilsson [211] proton orbit. Good agreement with the experimental data is obtained when the amplitude of the oblate configuration is 80\%, suggesting that both nuclei are predominantly oblate, in line with theoretical expectations.
M. Kimura · Y. Suzuki · T. Baba · Y. Taniguchi
Background: The isospin mixing is an interesting feature of atomic nuclei. It plays a crucial role in astrophysical nuclear reactions. However, it is not straightforward for variational nuclear structure models to describe it. Purpose: We propose a tractable method to describe the isospin mixing within a framework of the generator coordinate method and demonstrate its usability. Method: We generate the basis wave functions by applying the Fermi transition operator to the wave functions of isobars. The superposition of these basis wave functions and variationally obtained wave functions quantitatively describes the isospin mixing. Results: Using 14N as an example, we demonstrate that our method reasonably describes both T = 0 and 1 states and their mixing. Energy spectrum and E1 transition strengths are compared with the experimental data to confirm isospin mixing. Conclusion: The proposed method is effective enough to describe isospin mixing and is useful, for example, when we discuss {\alpha} capture reactions of N = Z nuclei.
Mark Alford🇺🇸 · Arus Harutyunyan🇦🇲 · Armen Sedrakian🇩🇪
In this work, we extend our previous study of the bulk viscosity of hot and dense matter induced by the Urca processes in the neutrino trapped regime to matter by adding the muonic Urca processes as well as the purely leptonic electroweak processes involving electron-muon transition. The nuclear matter is modeled in a relativistic density functional approach with two different parametrizations which predict neutrino dominated matter (DDME2 model) and antineutrino dominated matter (NL3 model) at temperatures for which neutrinos/antineutrinos are trapped. In the case of neutrino-dominated matter, the main equilibration mechanism is lepton capture, whereas in the case of antineutrino-dominated matter this is due to neutron decay. We find that the equilibration rates of Urca processes are higher than that of the pure leptonic processes, which implies that the Urca-process-driven bulk viscosity can be computed with the leptonic reactions assumed to be frozen. We find that the bulk viscosity decreases with temperature as at moderate temperatures. At high temperatures this scaling breaks down by sharp drops of the bulk viscosity close to the temperature where the proton fraction is density-independent and the matter becomes scale-invariant. This occurs also when the matter undergoes a transition from the antineutrino-dominated regime to the neutrino-dominated regime where the bulk viscosity attains a local maximum. We also estimate the bulk viscous dissipation timescales and find that these are in the range 1 s for temperatures above the neutrino trapping temperature. These timescales would be relevant only for long-lived objects formed in binary neutron star mergers and hot proto-neutron stars formed in core-collapse supernovas.
William J. Briscoe (GWU) · Michael Doring (GWU) · Helmut Haberzettl (GWU) · D. Mark Manley · (KSU) · Megumi Naruki (Kyoto University) · Greg Smith (JLab) · Igor Strakovsky (GWU) · Eric S. Swanson (University of Pittsburgh)
Over the past two decades, meson photo- and electroproduction data of unprecedented quality and quantity have been measured at electromagnetic facilities worldwide. By contrast, the meson-beam data for the same hadronic final states are mostly outdated and largely of poor quality, or even non-existent, and thus provide inadequate input to help interpret, analyze, and exploit the full potential of the new electromagnetic data. To reap the full benefit of the high-precision electromagnetic data, new high-statistics data from measurements with meson beams, with good angle and energy coverage for a wide range of reactions, are critically needed to advance our knowledge in baryon and meson spectroscopy and other related areas of hadron physics. To address this situation, a state-of-the-art meson-beam facility needs to be constructed. The present letter summarizes unresolved issues in hadron physics and outlines the vast opportunities and advances that only become possible with such a facility.
first authorsco-authorsvia INSPIRE