Nuclear Theory·nucl-th

Friday·March 6, 2015

7 papers—4 primary·3 cross-listed

01
Systematic calculations of $α$ -decay half-lives with an improved empirical formula
Z. Y. Wang · Z. M. Niu · Q.Liu · J. Y. Guo
Based on the recent data in NUBASE2012, an improved empirical formula for evaluating the $α$ -decay half-lives is presented, in which the hindrance effect resulted from the change of the ground state spins and parities of parent and daughter nuclei is included, together with a new correction factor for nuclei near the shell closures. The calculated $α$ -decay half-lives are found to be in better agreements with the experimental data, and the corresponding root-mean-square (rms) deviation is reduced to $0.433$ when the experimental $Q$ -values are employed. Furthermore, the $Q$ -values derived from different nuclear mass models are used to predict $α$ -decay half-lives with this improved formula. It is found that the calculated half-lives are very sensitive to the $Q$ -values. Remarkably, when mass predictions are improved with the radial basis function (RBF), the resulting rms deviations can be significantly reduced. With the mass prediction from the latest version of Weizsäcker-Skyrme (WS4) model, the rms deviation of $α$ -decay half-lives with respect to the known data falls to $0.697$ .
nucl-thJ.Phys.G(2015)·32 citations
02
Fission barriers and probabilities of spontaneous fission for elements with Z $\geq$ 100
A. Baran · M. Kowal · P.-G. Reinhard · L.M. Robledo · A. Staszczak · M. Warda
This is a short review of methods and results of calculations of fission barriers and fission half-lives of even-even superheavy nuclei. An approvable agreement of the following approaches is shown and discussed: The macroscopic-microscopic approach based on the stratagem of the shell correction to the liquid drop model and a vantage point of microscopic energy density functionals of Skyrme and Gogny type selfconsistently calculated within Hartree-Fock-Bogoliubov method. Mass parameters are calculated in the Hartree-Fock-Bogoliubov cranking approximation. A short part of the paper is devoted to the nuclear fission dynamics. We also discuss the predictive power of Skyrme functionals applied to key properties of the fission path of $^{266}$ Hs. It applies the standard techniques of error estimates in the framework of a $χ^{2}$ analysis.
nucl-thNPA(2015)·86 citations
03
About consistence between pi N Delta spin-3/2 gauge couplings and electromagnetic gauge invariance
D. Badagnani🇦🇷 · C. Barbero🇦🇷 · A. Mariano🇦🇷
We analyze the consistence between the recently proposed "spin 3/2 gauge" interaction for the Delta resonance with nucleons and pions, and the fundamental electromagnetic gauge invariance in any radiative amplitude. Chiral symmetric pion-derivative pi N Delta couplings can be substituted through a linear transformation to get Delta-derivative ones, which have the property of decoupling the 1/2 field components of the Delta propagator. Nevertheless, the electromagnetic gauge invariance introduced through minimal substitution in all derivatives, can only be fulfilled at a given order n without destroying the spin 3/2 one by dropping n+1 order terms within an effective field theory (EFT) framework with a defined power counting. In addition, we show that the Ward identity for the gamma Delta gamma vertex cannot be fulfilled with a trimmed 3/2 propagator, which should be necessary in order to keep the spin 3/2 gauge symmetry in the radiative case for the gamma Delta gamma amplitude. Finally, it is shown that radiative corrections of the spin 3/2 gauge strong vertexes at one loop, reintroduce the conventional interaction.
nucl-th1 citation
04
Charge symmetry breaking in $Λ$ hypernuclei revisited
Avraham Gal🇮🇱
The large charge symmetry breaking (CSB) implied by the $Λ$ binding energy difference $Δ B_{Λ}^{4} (0_{g.s.}^{+}) \equiv B_{Λ} (_{Λ}^{4}$ He) $-$ $B_{Λ} (_{Λ}^{4}$ H) = 0.35 $\pm$ 0.06 MeV of the $A = 4$ mirror hypernuclei ground states, determined from emulsion studies, has defied theoretical attempts to reproduce it in terms of CSB in hyperon masses and in hyperon-nucleon interactions, including one pion exchange arising from $Λ - Σ^{0}$ mixing. Using a schematic strong-interaction $Λ N \leftrightarrow Σ N$ coupling model developed by Akaishi and collaborators for $s$ -shell $Λ$ hypernuclei, we revisit the evaluation of CSB in the $A = 4$ $Λ$ hypernuclei and extend it to $p$ -shell mirror $Λ$ hypernuclei. The model yields values of $Δ B_{Λ}^{4} (0_{g.s.}^{+}) \sim 0.25$ MeV. Smaller size and mostly negative $p$ -shell binding energy differences are calculated for the $A = 7 - 10$ mirror hypernuclei, in rough agreement with the few available data. CSB is found to reduce by almost 30 keV the 110 keV $_{Λ}^{10}$ B g.s. doublet splitting anticipated from the hyperon-nucleon strong-interaction spin dependence, thereby explaining the persistent experimental failure to observe the $2_{exc}^{-} \to 1_{g.s.}^{-}$ $γ$ -ray transition.
nucl-thhep-phnucl-exPLB(2015)·74 citations

Affiliations

first authorsco-authorsvia INSPIRE

Systematic calculations of α-decay half-lives with an improved empirical formula

Fission barriers and probabilities of spontaneous fission for elements with Z≥100

About consistence between pi N Delta spin-3/2 gauge couplings and electromagnetic gauge invariance

Charge symmetry breaking in Λ hypernuclei revisited

Affiliations

Systematic calculations of $α$ -decay half-lives with an improved empirical formula

Fission barriers and probabilities of spontaneous fission for elements with Z $\geq$ 100

Charge symmetry breaking in $Λ$ hypernuclei revisited