Nuclear Theory·nucl-th

Friday·March 3, 2023

5 papers—4 primary·1 cross-listed

01
[Submitted on 1 Mar 2023]
Systematic Analysis of Double-Beta Decay Half Lives
B. Pritychenko
Evaluated $2 β^{-} (2 ν)$ half-lives and their systematics were reexamined in the framework of a phenomenological approach. Decay rate dependence on nuclear deformation, decay energy, shape coexistence, and forbidden transitions was observed. The following analysis showed distinct impacts of decay energy on half-lives and deformation parameters on effective nuclear matrix elements. These findings were used to predict $T_{1/2}$ for 36 isotopes of interest. Present work results were compared with published data.
Comments:
14 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2303.00838 [pdf]
NPA(2023)·14 citations
02
[Submitted on 2 Mar 2023]
Realistic evaluation of Coulomb potential in spherical nuclei and test of the traditional approach
L. Xayavong · Y. Lim
A realistic evaluation of Coulomb potential has been made for some selected nuclei using the available model-independent data for the charge density and the recent development of Coulomb energy-density functional. Within the Woods-Saxon potential as a nuclear component, we are able to quantify the differences in proton single-particle energies due to the differences from the model-independent data of the uniform distribution, the two-parameter Fermi function, as well as the charge density obtained from a microscopic Hartree-Fock calculation using the effective Skyrme interaction. The obtained energy differences are generally small in magnitude, namely about 100~keV or less if the parameters of the charge density models are appropriately determined. Considerable larger differences appear when the last occupied state is highly filled and, at the same time, has a small orbital angular momentum. Sulfur isotopes ( $Z = 16$ ) are a perfect example of these nuclei. Unfortunately, despite its simplicity, the uniform distribution cannot be used for evaluating the Coulomb exchange term within a well-established method because it is not differentiable at the surface of a nucleus. Traditionally, the missing of exchange term is corrected for by simply excluding the last-proton contribution to the direct term. %% We also investigate this approach and find that its effect is simply an introduction of the factor $(Z - 1) / Z$ into the Coulomb direct term. From medium to heavy nuclei (typically beyond the $s d$ shell) the resulting proton levels are 300-800~keV higher than those obtained with the exact Fock term. The result for lighter nuclei tends to be opposite because the factor $(Z - 1) / Z$ decreases rapidly towards the limit of $Z \to 1$ . Therefore, this traditional approach should be avoided for a precision nuclear structure calculation.
Comments:
13 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2303.00945 [pdf]
PRC(2023)·4 citations
03
[Submitted on 2 Mar 2023]
Impact of the quenching of shell effects with excitation energy on Nuclear Level Density
Mamta Aggarwal
We investigate the nature and impact of shell effects on nuclear level density (NLD) and particle emission probability as a function of temperature in a microscopic theoretical framework of Statistical Model for nuclei ranging from neutron deficient to neutron rich isotopes of Z $=$ 27 $-$ 35. Critical temperatures are traced for neighbouring even, odd, closed shell and mid $-$ shell nuclei which respond to excitations differently due to their varying stability and structural effects. Importance of the shell effects and shell correction energy is reflected significantly in NLD variation which slowly diminishes with increasing excitation energy indicating the quenching of shell effects. The enhancement of LD parameter with the deformation and rotation and the fade out of enhancement with increasing excitations has been shown. The weakening of magicity of N $=$ 28 near the proton drip line has been observed in the inverse level density parameter 'K'( $=$ A/a) and $β$ variation though it is usually uncommon to see this effect in excited nuclei. Variation of our calculated NLD for odd $^{69}$ As and even $^{70}$ Ge exhibits structural effects and agrees very well with the variation of experimental values. Our evaluated level density parameter 'a' values are compared with RIPL-2 (Reference Input Parameter Library) data which show good agreement.
Comments:
11 pages 15 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2303.01044 [pdf]
NPA(2023)·4 citations
04
[Submitted on 2 Mar 2023]
Single-particle spectroscopic strength from nucleon transfer reactions with a three-nucleon force contribution
N. K. Timofeyuk · L. Moschini · M. Gómez-Ramos
The direct reaction theory widely used to study single-particle spectroscopic strength in nucleon transfer experiments is based on a Hamiltonian with two-nucleon interactions only. We point out that in reactions with a loosely-bound projectile, where clustering and breakup effects are important, an additional three-body force arises due to three-nucleon ( $3 N$ ) interaction between two nucleons belonging to different clusters in the projectile and a target nucleon. We study the effects of this force on nucleon transfer in $(d, p)$ and $(d, n)$ reactions on $^{56}$ Ni, $^{48}$ Ca, $^{26 m}$ Al and $^{24}$ O targets at deuteron incident energies between 4 and 40 MeV/nucleon. Deuteron breakup is treated exactly within a continuum discretized coupled-channel approach. It was found that an additional three-body force can noticeably alter the angular distributions at forward angles, with consequences for spectroscopic factors' studies. Additional study of transfer to $2 p$ continuum in the $^{25}$ F $(p, 2 p)^{24}$ O reaction, involving the same overlap function as in the $^{24}$ O( $d, n)^{25}$ F case, revealed that $3 N$ force affects the $(d, n)$ and $(p, 2 p)$ reactions in a similar way, increasing the cross sections and decreasing spectroscopic factors, although its influence at the main peak of $(p, 2 p)$ is weaker. The angle-integrated cross sections are found to be less sensitive to the 3N force contribution, they increase by less than 20 $%$ . Including 3N interactions in nucleon removal reactions makes an essential step towards bringing together nuclear structure theory, where 3N force is routinely used, and nuclear direct reaction theory, based on two-nucleon interactions only.
Comments:
Accepted in Physics Letters B
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2303.01176 [pdf]
PLB(2023)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE

Systematic Analysis of Double-Beta Decay Half Lives

Realistic evaluation of Coulomb potential in spherical nuclei and test of the traditional approach

Impact of the quenching of shell effects with excitation energy on Nuclear Level Density

Single-particle spectroscopic strength from nucleon transfer reactions with a three-nucleon force contribution

Affiliations