Nuclear moments and differences in mean square charge radii of short-lived neon isotopes by collinear laser spectroscopy

Abstract

The nuclear moments and charge radii of short-lived neon isotopes were measured by the use of collinear laser spectroscopy at the on-line mass separator ISOLDE at CERN. After a general introduction the semiclassical theory of atomic spectra is given and the relevant properties are calculated for neon. The atomic physics section is followed by a description of the experimental setup of the collinear laser spectroscopy experiment at ISOLDE. From the mass separator an isotopically clean ion beam with a kinetic energy of 60 keV is delivered to the experiments. In collinear laser spectroscopy the incoming ion beam from the mass separator is superimposed to a single frequency cw laser beam. The frequency of the atomic transition $\nu\scriptstyle_{0}$ is given at resonance with the laser light frequency $\nu\scriptstyle_\textrm{L}$ by the Doppler shifted frequency $\nu\scriptstyle_\textrm{D}$ = $\nu\scriptstyle_{0}(1\pm\beta)$/$\scriptstyle\sqrt {1-\beta^2}$ = $\nu\scriptstyle_\textrm{L}$. Thus, the position of the resonance line is dependent on the kinetic enrgy of the incoming ion beam. The difference in the nuclear charge radii between two isotopes of an element causes the field shift contributing to the isotope shift which was measured in this experiment. As the field shift decreases with the nuclear charge Z, for neon a new method was needed to measure the kinetic beam energy to reach the required precision to determine the field shift / differences in nuclear charge radii. A variant of collinear laser spectroscopy using the Doppler shift caused by laser excitation in collinear and anticollinear geometry of closly lying atomic levels of neon was used to measure the ISOLDE ion beam energy with a precision of better than 1 V. The results of the measurements on the hyperfine structure parameters and the isotope shifts in the extended isotope chain $^{17-26,28}$Ne with the reference isotope $^{20}$Ne is discussed. From the hyerfine structure parameters of the odd-A neon isotopes the corresponding nuclear moments, from the isotope shifts the differences in the ms charge radii are calculated. The nuclear moments of the odd-A neon isotopes $^{19}$Ne, $^{21}$Ne, $^{23}$Ne and $^{25}$Ne are discussed in the framework of the nuclear shell model. $^{17}$Ne is an exception, beacuse it is a candidate of a proton-halo nucleus. Due to the lack of shell-model calculations its magentic moment is discussed in the framework of the isoscalar moment. The nuclear charge radii of $^{18-26,28}$Ne are compared with a number of collective models. Besided the comparison with data from the literature the droplet model is used to calculate charge radii as comparison, which gives surprisingly closely lying values compared to the experimental data. Again, the discussion for $^{17}$Ne is done separately and is compared with halo-theory calculations