G. Kraus

Nuclear radii of Na and Mg isotopes

Abstract The effective root-mean-square (rms) matter radii of ANa (A = 20–23, 25–32) and AMg (A = 20, 22, 23, 27, 29–32) have been deduced from the measured interaction cross sections using a Glauber-type calculation. It was found that the increase of rms matter radii in Na isotopes is primarily a consequence of the increase of rms neutron radii. A correlation between the radii, corrected for quadrupole deformation, and the Fermi-energy difference was observed for both Na and Mg isotopes. This correlation can be explained by a model that assumes the valence nucleons are responsible for the changes in nuclear radii. The presence of a neutron skin is suggested for neutron-rich Na and Mg isotopes. An application to the nuclear equation of state (EOS) is discussed.

Matter radii of Na and Mg isotopes

Abstract The interaction cross sections (σI) of ANa (A = 20–23, 25–32) and AMg (A = 20, 22–25, 27, 29–33) on carbon target have been measured at a beam energy of around 950 A MeV. The effective root-mean-square matter radii of these isotopes were deduced from σI by a Glauber-type calculation. Combining the isotope-shift data with the present Na data the radii of neutrons have been compared with those of protons for the first time along a chain of stable and unstable isotopes. A monotonic increase in the neutron skin thickness has been observed as the neutron number increases in Na isotopes. The Mg data are also consistent with the claim that the formation of a neutron/proton skin is a universal feature in β-unstable nuclei.

Schottky mass spectrometry at the ESR: a novel tool for precise direct mass measurements of exotic nuclei

Abstract Schottky mass spectrometry is a novel method of precision nuclear mass spectrometry based on the measurement of the revolution frequencies of ions in a storage ring. The measurements are performed by non-destructive detection and frequency analysis of the beam noise, the well-established Schottky diagnosis technique. Schottky mass spectrometry was applied for the first time at the Experimental Storage Ring ESR at GSI using electron-cooled, highly charged (mainly bare, H- and He-like) heavy ions at relativistic energies of up to 370 MeV/u. The performance of the method at the ESR is shortly reviewed and an overview of the results from our first mass measurements of radioactive neutron-deficient gold and bismuth fragments is given. Relative accuracies down to 3 × 10 −7 were achieved for the measured masses, corresponding to absolute uncertainties of 50 to 150 keV/ c 2 for these heavy isotopes (135 ≤ A ≤ 209). The typical mass resolving power of about 350 000 allows even the resolution of isomeric from ground state masses in some cases. Due to the required cooling time, the method is applicable, so far, to nuclei with half-lives of at least a few seconds.

TOF-Mass-Measurements of exotic nuclei at the ESR of the GSI

Abstract We plan to measure masses of very shortlived exotic nuclei far from β-stability by using the Experimental Storage Ring (ESR) of the GSI as an energy isochronous Time-of-Flight (TOF) mass-spectrometer which requires a special ion-optical setting of the quadrupoles in the ESR. Via projectile fragmentation a large variety of exotic nuclei can be produced. which can be separated in flight by the Fragment Separator (FRS) prior to being injected into the ESR. A special time-pick-off-detector has been developed, which uses secondary electron emission from a thin foil, which is penetrated by the ions under investigation. This detector has been designed for use in the ESR-vacuum of 10 −11 mbar and has an intrinsic time-resolution of ≈ 85ps. Also a Time Recording System (TRS) with a time-jitter of only ≈ 50ps has been build. The TRS is capable of recording time-marks for a few ions over a large number (> 500) of turns.

Neutron skin of Na isotopes and an application to the EOS

Abstract The effective root-mean-square ( rms ) matter radii of A Na ( A =20–23,25–32) were deduced from the measured interaction cross sections by a Glauber-type calculation. The presence of a neutron skin is suggested for neutron-rich Na isotopes. An application to the nuclear equation of state (EOS) is discussed.

Mass measurements of stored and cooled exotic nuclei at GSI

Abstract Recent results of mass measurements of exotic heavy nuclei using Schottky mass spectrometry are reported. The investigated nuclei were produced and separated by the fragment separator FRS, injected, stored and cooled in the experimental storage ring ESR. Their masses were determined from the frequency analysis of the beam noise. In the present experiment the masses of more than 150 proton-rich nuclei in the mass region A ∼- 200 have been determined for the first time. Representative results are given for proton-separation energies and shell corrections. For some elements the proton drip line can be determined.

Direct mass measurements of proton-rich nuclei in the region from tellurium to polonium

Abstract In recent experiments using the FRS-ESR facilities at GSI we have measured the masses of 225 proton-rich nuclei in the range of 135≤A≤209. Applying the new technique of Schottky-Mass Spectrometry an accuracy of about 100 keV and a resolving power of 4 · 10 5 was achieved. Masses for cooled projectile fragments with half-lives larger than a few seconds were determined by their revolution frequencies in the ESR. Reliable predictions for the proton-drip line can be made for elements from bismuth to protactinium using the precisely measured Q α -values from literature and our new mass values for the isotopes at the ends of the corresponding α-chains.