Nuclear Theory·nucl-th

Wednesday·December 1, 2021

12 papers—7 primary·5 cross-listed

01
Beyond-mean-field calculations of allowed and first-forbidden $β^{-}$ decays of $r$ -process waiting-point nuclei
Caroline Robin · Elena Litvinova · Gabriel Martínez-Pinedo
$β$ -decay rates of neutron-rich nuclei, in particular those located at neutron shell closures, play a central role in simulations of the heavy-element nucleosynthesis and resulting abundance distributions. We present $β$ -decay half-lives of even-even $N = 82$ and $N = 126$ $r$ -process waiting-point nuclei calculated in the approach based on relativistic quasiparticle random phase approximation with quasiparticle-vibration coupling. The calculations include both allowed and first-forbidden transitions. In the $N = 82$ chain, the quasiparticle-vibration coupling has an important impact close to stability, as it increases the contribution of Gamow-Teller modes and improves the agreement with the available data. In the $N = 126$ chain, we find the decay to proceed dominantly via first-forbidden transitions, even when the coupling to vibrations is included.
nucl-thnucl-exEPJ Web Conf.(2022)·2 citations
02
Statistical Hauser-Feshbach model description of $(n, α)$ reaction cross sections for the weak s-process
Sema Küçüksucu · Mustafa Yiğit · Nils Paar
The $(n, α)$ reaction contributes in many processes of energy generation and nucleosynthesis in stellar environment. Since experimental data are available for a limited number of nuclei and in restricted energy ranges, at present only theoretical studies can provide predictions for all astrophysically relevant $(n, α)$ reaction cross sections. The purpose of this work is to study $(n, α)$ reaction cross sections for a set of nuclei contributing in the weak s-process nucleosynthesis. Theory framework is based on the statistical Hauser-Feshbach model implemented in TALYS code with nuclear masses and level densities based on Skyrme energy density functional. In addition to the analysis of the properties of calculated $(n, α)$ cross sections, the Maxwellian averaged cross sections are described and analyzed for the range of temperatures in stellar environment. Model calculations determined astrophysically relevant energy windows in which $(n, α)$ reactions occur in stars. In order to reduce the uncertainties in modeling $(n, α)$ reaction cross sections for the s-process, novel experimental studies are called for. Presented results on the effective energy windows for $(n, α)$ reaction in weak s-process provide a guidance for the priority energy ranges in the future experimental studies.
nucl-thastro-ph.SRnucl-exUniverse(2022)·3 citations
03
Microscopic analysis of induced nuclear fission dynamics
Z. X. Ren · J. Zhao · D. Vretenar · T. Niksic · P. W. Zhao · J. Meng
The dynamics of low-energy induced fission is explored using a consistent microscopic framework that combines the time-dependent generator coordinate method (TDGCM) and time-dependent nuclear density functional theory (TDDFT). While the former presents a fully quantum mechanical approach that describes the entire fission process as an adiabatic evolution of collective degrees of freedom, the latter models the dissipative dynamics of the final stage of fission by propagating the nucleons independently toward scission and beyond. By combining the two methods, based on the same nuclear energy density functional and pairing interaction, we perform an illustrative calculation of the charge distribution of yields and total kinetic energy for induced fission of $^{240}$ Pu. For the saddle-to-scission phase a set of initial points for the TDDFT evolution is selected along an iso-energy curve beyond the outer fission barrier on the deformation energy surface, and the TDGCM is used to calculate the probability that the collective wave function reaches these points at different times. Fission observables are computed with both methods and compared with available data. The relative merits of including quantum fluctuations (TDGCM) and the one-body dissipation mechanism (TDDFT) are discussed.
nucl-thnucl-exPRC(2022)·37 citations
04
Quadrupole-octupole coupling and the evolution of collectivity in neutron-deficient Xe, Ba, Ce, and Nd isotopes
K. Nomura · R. Rodríguez-Guzmán · L.M. Robledo
The evolution of quadrupole and octupole collectivity in neutron-deficient Xe, Ba, Ce, and Nd nuclei near the "octupole magic" neutron number $N = 56$ is investigated within the mapped $s df$ -IBM framework. Microscopic input is obtained via quadrupole and octupole constrained Hartree-Fock-Bogoliubov calculations, based on the parametrization D1M of the Gogny energy density functional. Octupole-deformed mean-field ground states are predicted for Ba and Ce isotopes near $N = 56$ . Excitation energies of positive- and negative-parity states as well as electric transition rates are computed with wave functions resulting from the diagonalization of the mapped IBM Hamiltonian. The parameters of the Hamiltonian are determined via the mapping of the mean-field potential energy surfaces onto the expectation value of the Hamiltonian in the condensate state of the $s$ , $d$ , and $f$ bosons. Enhanced octupolarity is predicted for Xe, Ba, and Ce isotopes near $N = 56$ . The shape/phase transition from octupole-deformed to strongly quadrupole-deformed near $N = 60$ is analyzed in detail.
nucl-thnucl-exPRC(2021)·16 citations
05
Two-pion exchange as a leading-order contribution in chiral effective field theory
Chinmay Mishra🇺🇸 · A. Ekström🇸🇪 · G. Hagen🇺🇸 · T. Papenbrock🇺🇸 · L. Platter🇺🇸
Pion exchange is the central ingredient to nucleon-nucleon interactions used in nuclear structure calculations, and one pion exchange (OPE) enters at leading order in chiral effective field theory. In the $^{2 S + 1} L_{J} =^{1} S_{0}$ partial wave, however, OPE and a contact term needed for proper renormalization fail to produce the qualitative, and quantitative, features of the scattering phase shifts. Cutoff variation also revealed a surprisingly low breakdown momentum of about 330 MeV in this partial wave. Here we show that potentials consisting of OPE, two pion exchange (TPE), and a single contact address these problems and yield accurate and renormalization group (RG) invariant phase shifts in the $^{1} S_{0}$ partial wave. We demonstrate that a leading-order potential with TPE can be systematically improved by adding a contact quadratic in momenta. For momentum cutoffs below about 500 MeV, the removal of relevant physics from TPE loops needs to be compensated by additional contacts to keep RG invariance. Inclusion of the $Δ$ isobar degree of freedom in the potential does not change the strong contributions of TPE.
nucl-thPRC(2022)·15 citations
06
Beyond-mean-field approaches for nuclear neutrinoless double beta decay in the standard mechanism
J. M. Yao🇨🇳 · J. Meng🇨🇳 · Y. F. Niu🇨🇳 · P. Ring🇩🇪
Nuclear weak decays provide important probes to fundamental symmetries in nature. A precise description of these processes in atomic nuclei requires comprehensive knowledge on both the strong and weak interactions in the nuclear medium and on the dynamics of quantum many-body systems. In particular, an observation of the hypothetical double beta decay without emission of neutrinos ( $0 ν β β$ ) would unambiguously demonstrate the Majorana nature of neutrinos and the existence of the lepton-number-violation process. It would also provide unique information on the ordering and absolute scale of neutrino masses. The next-generation tonne-scale experiments with sensitivity up to $1 0^{28}$ years after a few years of running will probably provide a definite answer to these fundamental questions based on our current knowledge on the nuclear matrix element (NME), the precise determination of which is a challenge to nuclear theory. Beyond-mean-field approaches have been frequently adapted for the study of nuclear structure and decay throughout the nuclear chart for several decades. In this review, we summarize the status of beyond-mean-field calculations of the NMEs of $0 ν β β$ decay assuming the standard mechanism of an exchange of light Majorana neutrinos. The challenges and prospects in the extension and application of beyond-mean-field approaches for $0 ν β β$ decay are discussed.
nucl-thhep-exhep-phnucl-exPPNP(2022)·66 citations
07
Scaling approach to nuclear structure in high-energy heavy-ion collisions
Jiangyong Jia🇺🇸 · Chun-Jian Zhang🇺🇸
In high-energy heavy-ion collisions, the initial condition of the produced quark-gluon plasma (QGP) and its evolution are sensitive to collective nuclear structure parameters describing the shape and radial profiles of the nuclei. We find a general scaling relation between these parameters and many experimental observables such as elliptic flow, triangular flow, and particle multiplicity distribution. In particular, the ratios of observables between two isobar systems depend only on the differences of these parameters, but not on the details of the final state interactions, hence offering a new way to constrain the QGP initial condition. Using this scaling relation, we show how the structure parameters of $_{44}^{96}$ Ru and $_{40}^{96}$ Zr conspire to produce the rich centrality dependences of these ratios, as measured by the STAR Collaboration. Our scaling approach demonstrates that isobar collisions are a precision tool to probe the initial condition of heavy-ion collisions, as well as the collective nuclear structures, including the neutron skin, of the atomic nuclei across energy scales.
nucl-thhep-exhep-phnucl-exPRC(2023)·61 citations

Affiliations

first authorsco-authorsvia INSPIRE

Beyond-mean-field calculations of allowed and first-forbidden β− decays of r-process waiting-point nuclei

Statistical Hauser-Feshbach model description of (n,α) reaction cross sections for the weak s-process

Microscopic analysis of induced nuclear fission dynamics

Quadrupole-octupole coupling and the evolution of collectivity in neutron-deficient Xe, Ba, Ce, and Nd isotopes

Two-pion exchange as a leading-order contribution in chiral effective field theory

Beyond-mean-field approaches for nuclear neutrinoless double beta decay in the standard mechanism

Scaling approach to nuclear structure in high-energy heavy-ion collisions

Affiliations

Beyond-mean-field calculations of allowed and first-forbidden $β^{-}$ decays of $r$ -process waiting-point nuclei

Statistical Hauser-Feshbach model description of $(n, α)$ reaction cross sections for the weak s-process