Moments and mean square charge radii of short-lived argon isotopes

Abstract

We report on the measurement of optical isotope shifts for 32 40 Ar and for 46 Ar from which the changes in mean square nuclear charge radii across the N = 20 neutron shell closure are deduced. The investigations were carried out by collinear laser spectroscopy in fast beams of neutral argon atoms. The ultra-sensitive detection combines optical pumping, stateselective collisional ionization and counting of -radioactivity. By reaching far into the sd-shell, the results add new information to the systematics of radii in the calcium region (Z 20). Contrary to all major neutron shell closures with N 28, the N = 20 shell closure causes no signicant slope change in the development of the radii. Information from the hyperne structure of the odd-A isotopes includes the magnetic moments of 33 Ar (I = 1 = 2) and 39 Ar (I = 7 = 2), and the quadrupole moments of 35 Ar, 37 Ar (I = 3 = 2) and 39 Ar. The electromagnetic moments are compared to shell-model predictions for the sd-and fp-shell. Even far from stability a v ery good agreement between experiment and theory is found for these quantities. The mean square charge radii are discussed in the framework of spherical SGII Skyrme-type Hartree-Fock calculations.Keywords: NUCLEAR STRUCTURE 32 40;46 Ar; measured isotope shifts, hfs; deduced hyperne constants, spins I, magnetic dipole moments , electric quadrupole moments Q s , mean square charge radii hr 2 i; Collinear fast-beam laser spectroscopy, collisional ionization and -detection; shell model (sd-, fp-shell).

Charge radii of neon isotopes across thesdneutron shell

“…This is surprising in a region where single-particle orbitals and clustering are supposed to dominate the nuclear properties. It is in contrast to the behavior of other light nuclear systems such as the Ca and Ar isotopes [12] in the neighborhood of the Z = 20 shell closure, where deformation is small and single-particle contributions dominate over collective properties. Similarly, for heavier systems it was found that the semiempirical droplet description is most suitable in regions of strong deformation.…”

“…The experimental apparatus, procedure, and detection technique have already been described in our previous papers [8,12,16] (see Fig. 2).…”

“…1 In earlier works on collinear laser spectroscopy with noble gases it was estimated, based on the voltage applied to the plasma ion source, to be close to the anode potential with an uncertainty of about 20-30 V [12]. Equation (5) can then be used to determine the energy of an ion beam at resonance with the laser, if the transition frequencies are known with sufficient accuracy.…”

“…These uncertainties have in very good approximation the same mass dependence as the mass shift [12]. They can be expressed in terms of two parameters, k U and k U , accounting for deviations of the measured acceleration voltage U and postacceleration voltage differences U from their true values:…”

“…In the reported studies the accuracy requirement was met by an accurate determination of the beam kinetic energy [10] utilizing a novel method of comparing Doppler-shifted transition frequencies. At the same time, the high sensitivity and selectivity were achieved using ultrasensitive nonoptical detection based on optical pumping, state-selective collisional ionization, and observation of the β decay of collected radioactive ions [11,12].…”