Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe kinks in charge radii across $N$ = 82 and 126 revisited
75
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We revisit the studies of the isotopic shift in the charge radii of {it even-even} isotopes of Sn and Pb nuclei at $N$ = 82, and 126, respectively, within the relativistic mean-field and Relativistic-Hartree-Bogoliubov approach. The shell model is also used to estimate isotopic shift in these nuclei, for the first time, to the best of our knowledge. The ground state single-particle energies ($spe$) are calculated for non-linear NL3 & NL3$^*$ and density-dependent DD-ME2 parameter sets compared with the experimental data, wherever available. We establish a correlation between the filling of single-particle levels and the isotopic shift in occupation probabilities. The obtained $spe$ from the relativistic mean-field and Relativistic-Hartree-Bogoliubov approaches are in line with those used in the shell model and experimental data for both the Sn and Pb isotopic chains. The shell model calculated isotopic shift agrees with relativistic mean-field and Relativistic-Hartree-Bogoliubov approaches that explain the experimental data quite well.
rate research
Read More
It is well known that most actinides fission into fragments of unequal size. The first attempt to understand this difference suggested that division leading to one of the fragments being near doubly magic $^{132}$Sn is favored by gain in binding energy. After the Strutinsky shell-correction method was developed an alternative idea that gained popularity was that the fission saddle might be lower for mass-asymmetric shapes and that this asymmetry was preserved until scission. Recently it was observed [Phys. Rev. Lett. {bf 105} (2010) 252502] that $^{180}$Hg preferentially fissions asymmetrically in contradiction to the fragment-magic-shell expectation which suggested symmetric division peaked around $^{90}$Zr, with its magic neutron number $N=50$, so it was presented as a new type of asymmetric fission. However, in a paper [Phys. Lett. 34B (1971) 349] a simple microscopic mechanism behind the asymmetry of the actinide fission saddle points was proposed to be related the coupling between levels of type [40$LambdaOmega$] and [51$LambdaOmega$]. The paper then generalizes this idea and made the remarkable prediction that analogous features could exist in other regions. In particular it was proposed that in the rare-earth region couplings between levels of type [30$LambdaOmega$] and [41$LambdaOmega$] would favor mass-asymmetric outer saddle shapes. In this picture the asymmetry of $^{180}$Hg is not a new type of asymmetric fission but of analogous origin as the asymmetry of actinide fission. This prediction has never been cited in the discussion of the recently observed fission asymmetries in the new region of asymmetry, in nuclear physics also referred to as the rare-earth region. We show by detailed analysis that the mechanism of the saddle asymmetry in the sub-Pb region is indeed the one predicted half a century ago.
The mean-square charge radii of $^{207,208}$Hg ($Z=80, N=127,128$) have been studied for the first time and those of $^{202,203,206}$Hg ($N=122,123,126$) remeasured by the application of in-source resonance-ionization laser spectroscopy at ISOLDE (CERN). The characteristic textit{kink} in the charge radii at the $N=126$ neutron shell closure has been revealed, providing the first information on its behavior below the $Z=82$ proton shell closure. A theoretical analysis has been performed within relativistic Hartree-Bogoliubov and non-relativistic Hartree-Fock-Bogoliubov approaches, considering both the new mercury results and existing lead data. Contrary to previous interpretations, it is demonstrated that both the kink at $N=126$ and the odd-even staggering (OES) in its vicinity can be described predominately at the mean-field level, and that pairing does not need to play a crucial role in their origin. A new OES mechanism is suggested, related to the staggering in the occupation of the different neutron orbitals in odd- and even-$A$ nuclei, facilitated by particle-vibration coupling for odd-$A$ nuclei.
The systematic trend in charge radii along isotopic chain is of great interest due to its distinctive aspect at the nucleon-shell closure and the odd-even staggering (OES) behavior. In this work, the modified root mean square (rms) charge radius formula to phenomenally account for the formation of neutron-proton short-range correlations (np-SRCs) is firstly extended to study the heavier odd-$Z$ copper and indium isotopic chains. The parabolic-like shape of rms charge radii can be remarkably reproduced between two strong closure shells. In addition, the OES and abrupt changes in the slope of the rms charge radii across $N=50$ and $82$ shell closure are also identified evidently, but the odd-even oscillation is slightly overestimated for cooper isotopes. This means the np-SRCs play an indispensable role to determine the fine structures of nuclear charge radii along isotopic chain quantitatively.
Octet hyperon charge radii are calculated in a chiral constituent quark model including electromagnetic exchange currents between quarks. In impulse approximation one observes a decrease of the hyperon charge radii with increasing strangeness. This effect is reduced by exchange currents. Due to exchange currents, the charge radius of the negatively charged hyperons are close to the proton charge radius.
We present a comprehensive study on the low-lying states of neutron-rich Er, Yb, Hf, and W isotopes across the $N=126$ shell with a multi-reference covariant density functional theory. Beyond mean-field effects from shape mixing and symmetry restoration on the observables that are relevant for understanding quadrupole collectivity and underlying shell structure are investigated. The general features of low-lying states in closed-shell nuclei are retained in these four isotopes around $N=126$, even though the shell gap is overall quenched by about 30% with the beyond mean-field effects. These effects are consistent with the previous generator-coordinate calculations based on Gogny forces, but much smaller than that predicted by the collective Hamiltonian calculation. It implies that the beyond mean-field effects on the $r$-process abundances before the third peak at $Asim195$ might be more moderate than that found in A. Arcones and G. F. Bertsch, Phys. Rev. Lett. 108, 151101 (2012).
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
