Nuclear Theory·nucl-th

Tuesday·June 9, 2020

17 papers—7 primary·10 cross-listed

01
Level density within a micro-macroscopic approach
A.G. Magner · A.I. Sanzhur · S.N. Fedotkin · A.I. Levon · S. Shlomo
Statistical level density $ρ (E, A)$ is derived for nucleonic system with a given energy $E$ , particle number $A$ and other integrals of motion in the micro-macroscopic approximation beyond the standard saddle-point method of the Fermi gas model. This level density reaches the two limits; the well-known Fermi gas grand-canonical ensemble limit for a large entropy $S$ related to large excitation energies, and the finite micro-canonical limit for a small combinatorical entropy $S$ at low excitation energies. The inverse level density parameter $K$ as function of the particle number $A$ in the semiclassical periodic orbit theory, taking into account the extended Thomas-Fermi and Strutinsky shell corrections, is calculated and compared with experimental data.
nucl-thnucl-exNPA(2022)·8 citations
02
Successful prediction of total $α$ -induced reaction cross sections at astrophysically relevant sub-Coulomb energies using a novel approach
P. Mohr · Zs. Fülöp · Gy. Gyürky · G. G. Kiss · T. Szücs
The prediction of stellar ( $γ$ , $α$ ) reaction rates for heavy nuclei is based on the calculation of ( $α$ , $γ$ ) cross sections at sub-Coulomb energies. These rates are essential for modeling the nucleosynthesis of so-called $p$ -nuclei. The standard calculations in the statistical model show a dramatic sensitivity to the chosen $α$ -nucleus potential. The present study explains the reason for this dramatic sensitivity which results from the tail of the imaginary $α$ -nucleus potential in the underlying optical model calculation of the total reaction cross section. As an alternative to the optical model, a simple barrier transmission model is suggested. It is shown that this simple model in combination with a well-chosen $α$ -nucleus potential is able to predict total $α$ -induced reaction cross sections for a wide range of heavy target nuclei above $A ≳ 150$ with uncertainties below a factor of two. The new predictions from the simple model do not require any adjustment of parameters to experimental reaction cross sections whereas in previous statistical model calculations all predictions remained very uncertain because the parameters of the $α$ -nucleus potential had to be adjusted to experimental data. The new model allows to predict the reaction rate of the astrophysically important $^{176}$ W( $α$ , $γ$ ) $^{180}$ Os reaction with reduced uncertainties, leading to a significantly lower reaction rate at low temperatures. The new approach could also be validated for a broad range of target nuclei from $A \approx 60$ up to $A ≳ 200$ .
nucl-thastro-ph.IMPRL(2020)·39 citations
03
Pairing, quasi-spin and seniority
Bijay Kumar Agrawal · Bhoomika Maheshwari
We present our concise notes for the lectures and tutorials on pairing, quasi-spin and seniority delivered at SERB school on Role of Symmetries in Nuclear Physics, AMITY University, $2019$ . Starting with some generic features of residual nucleon-nucleon interactions, we provide detailed derivation of the matrix elements for the $δ$ -interaction which is the basis for the standard pairing Hamiltonian. The eigen values for standard pairing Hamiltonian are then obtained within the quasi-spin formalism. The algebra involving quasi-spin operators is performed explicitly using the annihilation and creation operators for single nucleon together with the application of Wicks theorem. These techniques are expected to be helpful in deriving the mean-field equations for the $H a r t r ee - F oc k$ , $B a r d ee n - C oo p er - S c h r i e f f er$ and $H a r t r ee - F oc k$ Bogoliubov theories.
nucl-thEur.Phys.J.ST(2020)·1 citation
04
Radiative pion photoproduction in covariant chiral perturbation theory
J. Rijneveen🇩🇪 · N. Rijneveen🇩🇪 · H. Krebs🇩🇪 · A. M. Gasparyan🇩🇪 · E. Epelbaum🇩🇪
We present a calculation of radiative pion photoproduction in the framework of covariant chiral perturbation theory with explicit $Δ (1232)$ degrees of freedom. The analysis is performed employing the small scale expansion scheme adjusted for the $Δ$ region. Depending on the channel, we include contributions up to next-to-next-to-leading order. We fit the available experimental data for the reaction $γ p \to γ p π^{0}$ and extract the value of the $Δ^{+}$ magnetic moment. Errors from the truncation of the small scale expansion are estimated using the Bayesian approach. We compare our results both with the previous studies within the $δ$ -expansion scheme and with the $Δ$ -less theory. We also give predictions for radiative charged-pion photoproduction.
nucl-thhep-phPRC(2021)·5 citations
05
Far From Equilibrium Hydrodynamics and the Beam Energy Scan
Travis Dore🇺🇸 · Emma McLaughlin🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸
The existence of hydrodynamic attractors in rapidly expanding relativistic systems has shed light on the success of relativistic hydrodynamics in describing heavy-ion collisions at zero chemical potential. As the search for the QCD critical point continues, it is important to investigate how out of equilibrium effects influence the trajectories on the QCD phase diagram. In this proceedings, we study a Bjorken expanding hydrodynamic system based on DMNR equations of motion with initial out of equilibrium effects and finite chemical potential in a system with a critical point. We find that the initial conditions are not unique for a specific freeze-out point, but rather the system can evolve to the same final state freeze-out point with a wide range of initial baryon chemical potential, $μ_{B}$ . For the same initial energy density and baryon density, depending on how far out of equilibrium the system begins, the initial $μ_{B}$ can vary by $Δ μ_{B} \sim 350$ MeV. Our results indicate that knowledge of the out-of-equilibrium effects in the initial state provide vital information that influences the search for the QCD critical point.
nucl-thhep-phnucl-exJ.Phys.Conf.Ser.(2020)·9 citations
06
Markov Chain Monte Carlo Predictions of Neutron-rich Lanthanide Properties as a Probe of $r$ -process Dynamics
Nicole Vassh · Gail C. McLaughlin · Matthew R. Mumpower · Rebecca Surman
Lanthanide element signatures are key to understanding many astrophysical observables, from merger kilonova light curves to stellar and solar abundances. To learn about the lanthanide element synthesis that enriched our solar system, we apply the statistical method of Markov Chain Monte Carlo to examine the nuclear masses capable of forming the $r$ -process rare-earth abundance peak. We describe the physical constraints we implement with this statistical approach and demonstrate the use of the parallel chains method to explore the multidimensional parameter space. We apply our procedure to three moderately neutron-rich astrophysical outflows with distinct types of $r$ -process dynamics. We show that the mass solutions found are dependent on outflow conditions and are related to the $r$ -process path. We describe in detail the mechanism behind peak formation in each case. We then compare our mass predictions for neutron-rich neodymium and samarium isotopes to the latest experimental data from the CPT at CARIBU. We find our mass predictions given outflows that undergo an extended (n, $γ$ ) $⇄$ ( $γ$ ,n) equilibrium to be those most compatible with both observational solar abundances and neutron-rich mass measurements.
nucl-thastro-ph.HEApJ(2021)·26 citations
07
Resonance structure of $^{8}$ Be with the two-cluster resonating group method
V. O. Kurmangaliyeva · N. Kalzhigitov · N. Takibayev · V. S. Vasilevsky
A two-cluster microscopic model is applied to study elastic alpha-alpha scattering and resonance structure of $^{8}$ Be. The model is an algebraic version of the Resonating Group Method, which makes use complete set of oscillator functions to expand wave function of two-cluster system. Interaction between clusters is determined by well-known semi-realistic nucleon-nucleon potentials of Hasegawa-Nagata, Minnesota and Volkov. Detail analysis of resonance wave functions is carried out in oscillator, coordinate and momentum spaces. Effects of the Pauli principle on wave functions of the $^{8}$ Be continuous spectrum states are thoroughly studied.
nucl-thUkr.J.Phys.(2023)·7 citations

Affiliations

first authorsco-authorsvia INSPIRE

Level density within a micro-macroscopic approach

Successful prediction of total α-induced reaction cross sections at astrophysically relevant sub-Coulomb energies using a novel approach

Pairing, quasi-spin and seniority

Radiative pion photoproduction in covariant chiral perturbation theory

Far From Equilibrium Hydrodynamics and the Beam Energy Scan

Markov Chain Monte Carlo Predictions of Neutron-rich Lanthanide Properties as a Probe of r-process Dynamics

Resonance structure of 8Be with the two-cluster resonating group method

Affiliations

Successful prediction of total $α$ -induced reaction cross sections at astrophysically relevant sub-Coulomb energies using a novel approach

Markov Chain Monte Carlo Predictions of Neutron-rich Lanthanide Properties as a Probe of $r$ -process Dynamics

Resonance structure of $^{8}$ Be with the two-cluster resonating group method