Charge radii and quadrupole-deformation parameters of high-spin isomers
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CLEI Experiment
Charge Radii and Quadrupole-Deformation Parameters of High-Spin Isomers Yu. P. Gangrsky* Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received October 5, 2007
Abstract—Experimental data on the differences of charge radii of nuclei in the ground and high-spin isomeric states are surveyed. High-resolution laser-spectroscopy methods were used for measurements. The results obtained for the differences of these radii by two methods—from measurements of isomeric shifts of the levels of atoms containing the nuclei being studied and from measurements of their quadrupole moments in both states under the assumption that the differences of the radii are determined by the difference in their quadrupole deformations—were compared. Two-particle isomers in odd–odd nuclei, isomers formed upon the break of one or several nucleon pairs, and isomers featuring the 1i13/2 configuration of the odd neutron in mercury nuclei were considered. The observed distinctions between the aforementioned differences of charged radii are discussed for isomeric states of different nature. PACS numbers: 21.10.Ft, 21.10.Ky DOI: 10.1134/S1063778808070077
INTRODUCTION
The mean-square charge radii r 2 and the quadrupole-deformation parameters β2 are among the main features that characterize the dimensions and shape of nuclei. In recent years, methods of highresolution laser resonance spectroscopy have been employed ever more frequently to determine them. These methods also make it possible to determine, in addition to the above features, the spin I and the magnetic dipole moment µ, as well as higher order moments in some cases—that is, to reconstruct a comprehensive pattern of collective and singleparticle properties of nuclei. Present-day laser methods have a high sensitivity and a high precision. They are based on precision measurements of perturbations that are caused by the spatial distribution of electric charges and currents in a nucleus—for example, the shift and splitting of atomic levels. Such perturbations are similar in nuclei of the isotopes of the same element; therefore, laser methods are the most efficient in measuring the dependence of the aforementioned parameters on the number of neutrons in a nucleus. Such dependences were already investigated for several tens of isotopic chains, and the results were presented in the review articles by Aufmuth et al. [1] and Nadjakov et al. [2]. The measurements revealed that the quadrupole deformation of nuclei has a strong effect on their mean *
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charge radii. Almost all of the irregularities in the dependences in question are explained by special features of the behavior of the quadrupole deformation— its decrease as closed shells are approached and its jumps at the boundaries of the regions of deformed nuclei. The growth of the mean-square charge radius of a nucleus with increasing quadrupole deformation is determined by the well-known expression 5 2 r 0 ∆ β22 . (1) ∆ r2 β = 4π The quadrupole-deformation parameter β2 is usuall
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