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The difference in isotope production between 1 and 1.4 GeV proton projectiles was investigated at ISOLDE/CERN during the year 1999. As target materials uranium carbide, thorium carbide, lead and lanthanum oxide were used and the ratio of the measured production yields for the two different projectile energies were determined for isotopes of the elements francium, mercury, thallium, xenon, cesium, krypton, rubidium and neon. A comparison of these experimental results with the predictions from a two-step reaction model Monte-Carlo code shows good agreement. (C) 2002 Elsevier Science B.V. All rights reserved.

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 deducted. The investigations were carried out by collinear laser spectroscopy in fast beams of neutral argon atoms. The ultra-sensitive detection combines optical pumping, state-selective collisional ionization and counting of $\beta$-radioactivity. By reaching far into the sd-shell, the results add new information to the systematics of radii in the calcium region (Z $\approx$ 20). Contrary to all major neutron shell closures with N $\geq$ 28, the N = 20 shell closure causes no significant slope change in the development of the radii. Information from the hyperfine structure of the odd-A isotopes includes 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 very 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.

The spins, moments and radii of krypton isotopes have been investigated by collinear fast-beam laser spectroscopy in combination with ultra-sensitive collisional ionization detection. The sequence of isotopes under study ranges from the neutron-deficient N = Z = 36 isotope 72 Kr to the neutron-rich 96 Kr ( N = 60). The mean-square charge radii in the neighbourhood of the N = 50 neutron-shell closure exhibit a pronounced shell effect which has recently been explained in the framework of relativistic mean-field theory. The results for the neutron-deficient nuclei are related to the shape coexistence of strongly prolate and near-spherical states which is known from nuclear spectroscopy. Here, an inversion of the odd-even staggering is observed below the neutron number N = 45. The neutron-rich transitional nuclei are influenced by the N = 56 subshell closure. In contrast to the N = 60 isotones 97 Rb, 98 Sr and 100 Zr, the new isotope 96 Kr is not strongly deformed.