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Register a new userIsospin Dependence in the Odd-Even Staggering of Nuclear Binding Energies
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The FRS-ESR facility at GSI provides unique conditions for precision measurements of large areas on the nuclear mass surface in a single experiment. Values for masses of 604 neutron-deficient nuclides (30<=Z<=92) were obtained with a typical uncertainty of 30 microunits. The masses of 114 nuclides were determined for the first time. The odd-even staggering (OES) of nuclear masses was systematically investigated for isotopic chains between the proton shell closures at Z=50 and Z=82. The results were compared with predictions of modern nuclear models. The comparison revealed that the measured trend of OES is not reproduced by the theories fitted to masses only. The spectral pairing gaps extracted from models adjusted to both masses, and density related observables of nuclei agree better with the experimental data.
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We explore the systematics of odd-even mass staggering with a view to identifying the physical mechanisms responsible. The BCS pairing and mean field contributions have A- and number parity dependencies which can help disentangle the different contributions. This motivates the two-term parametrization c_1 + c_2/A as a theoretically based alternative to the inverse power form traditionally used to fit odd-even mass differences. Assuming that the A-dependence of the BCS pairing is weak, we find that mean-field contributions are dominant below mass number A~40 while BCS pairing dominates in heavier nuclei.
A unified theoretical model reproducing charge radii of known atomic nuclei plays an essential role to make extrapolations in the regions of unknown nuclear size. Recently developed new ansatz which phenomenally takes into account the neutron-proton short-range correlations (np-SRCs) can describe the discontinuity properties and odd-even staggering (OES) effect of charge radii along isotopic chains remarkably well. In this work, we further review the modified rms charge radii formula in the framework of relativistic mean field (RMF) theory. The charge radii are calculated along various isotopic chains that include the nuclei featuring the $N=50$ and $82$ magic shells. Our results suggest that RMF with and without considering correction term give almost similar trend of nuclear size for some isotopic chains with open proton shell, especially the shrink phenomena of charge radii at strong neutron closed shells and the OES behaviors. This suggests that the np-SRCs has almost no influence for some nuclei due to the strong coupling between different levels around Fermi surface. The weakening OES behavior of nuclear charge radii is observed generally at completely filled neutron shells and this may be proposed as a signature of magic indicator.
Atomic masses of the neutron-rich isotopes $^{121-128}$Cd, $^{129,131}$In, $^{130-135}$Sn, $^{131-136}$Sb, and $^{132-140}$Te have been measured with high precision (10 ppb) using the Penning trap mass spectrometer JYFLTRAP. Among these, the masses of four r-process nuclei $^{135}$Sn, $^{136}$Sb, and $^{139,140}$Te were measured for the first time. The data reveals a strong $N$=82 shell gap at $Z$=50 but indicates the importance of correlations for $Z>50$. An empirical neutron pairing gap expressed as the odd-even staggering of isotopic masses shows a strong quenching across $N$=82 for Sn, with the $Z$-dependence that is unexplainable by the current theoretical models.
``Beat patterns are shown to appear in the octupole bands of several actinides and rare earths, their appearance being independent from the formula used in order to isolate and demonstrate them. It is shown that the recent formalism, making use of discrete approximations to derivatives of the transition energies (or of the energy levels) gives results consistent with the traditional formulae. In both regions it is seen that the first vanishing of the staggering occurs at higher values of the angular momentum I in nuclei exhibiting higher staggering at low I. Since these nuclei happen to be good rotators, the observed slow decrease of the amplitude of the staggering with increasing I is in good agreement with the parameter independent predictions of the su(3) (rotational) limit of several algebraic models. In the actinides it has been found that within each series of isotopes the odd-even staggering exhibits minima at N=134 and N=146, while a local maximum is shown at N=142, these findings being in agreement with the recent suggestion of a secondary maximum of octupole deformation around N=146.
We have performed shell-model calculations of binding energies of nuclei around $^{132}$Sn. The main aim of our study has been to find out if the behavior of odd-even staggering across N=82 is explainable in terms of the shell model. In our calculations, we have employed realistic low-momentum two-body effective interactions derived from the CD-Bonn nucleon-nucleon potential that have already proved quite successful in describing the spectroscopic properties of nuclei in the $^{132}$Sn region. Comparison shows that our results fully explains the trend of the experimental staggering.
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