H. Irnich

Schottky mass measurements of stored and cooled neutron-deficient projectile fragments in the element range of 57≤Z≤84

Abstract A novel method for direct, high precision mass measurements of relativistic exotic nuclei has been successfully applied in the storage ring ESR at GSI. The nuclei of interest were produced by projectile fragmentation of 930 MeV / u bismuth ions, separated in-flight by the fragment separator FRS, stored and cooled in the ESR. The mass values have been deduced from the revolution frequencies of the coasting cooled ions. We have measured 104 new mass values with a precision of about 100 keV and a resolving power of 3.5×10 5 for the neutron-deficient isotopes of the elements 57≤Z≤84 . This paper presents the experimental method, the mass evaluation and a table of the experimental mass values.

Charge-changing nuclear reactions of relativistic light-ion beams (5 Z 10) passing through thick absorbers*

Abstract Light-ion beams of 20 Ne, 19 Ne, 18 F, 16 O, 15 O, 14 N, 12 C and 10 B in the energy range between 200 and 670 MeV/u were fragmented in thick targets of water, carbon, lucite, polyethylene, and aluminum. The nuclear charge composition of the fragmented beam was measured via energy loss in a large-area ionisation chamber. Using a water absorber of variable thickness up to 25 cm the elemental fragment yields were measured down to Z = 5. Their build-up and decay characteristics are described by a system of differential equations. From an analysis of the depth distributions of the surviving projectiles and the lower- Z projectile fragments, both total and partial charge-changing cross sections were obtained.

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.

Charge states and energy loss of relativistic heavy ions in matter

Abstract Relativistic heavy-ion collisions of few-electron projectiles ranging from argon up to uranium have been investigated in solid and gaseous media. Electron-loss and electron-capture cross sections, charge-state distributions, as well as energy loss and energy deposition have been measured and are compared with theoretical predictions. Especially fully-ionized heavy projectiles represent a unique possibility to test atomic-collision theories.

First spatial isotopic separation of relativistic uranium projectile fragments

Abstract Spatial isotopic separation of relativistic uranium projectile fragments has been achieved for the first time. The fragments were produced in peripheral nuclear collisions and spatially separated in-flight with the fragment separator FRS at GSI. A two-fold magnetic-rigidity analysis was applied exploiting the atomic energy loss in specially shaped matter placed in the dispersive central focal plane. Systematic investigations with relativistic projectiles ranging from oxygen up to uranium demonstrate that the FRS is a universal and powerful facility for the production and in-flight separation of monoisotopic, exotic secondary beams of all elements up to Z = 92. This achievement has opened a new area in heavy-ion research and applications.

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.

Energy-loss straggling of (200–1000) MeV/u uranium ions

Abstract The charge-exchange contribution can dominate the energy-loss straggling of partially stripped heavy ions depending on the charge-changing cross sections and the partial stopping powers. We have studied the energy-loss straggling of few-electron uranium ions in different solids in the energy range of (200–1000) MeV/u. Our experimental data are compared with a new model taking into account realistic screening for relativistic scattering of target electrons at close impacts to derive partial stopping powers. Screening of the projectile nucleus by inner-shell electrons reduces the charge-exchange straggling compared to that pertaining to a point-like charge distribution.

Vavilov-Cherenkov radiation emitted by heavy ions near the threshold

Abstract The Vavilov–Cherenkov radiation (VChR) emitted by the heavy ions 79 Au was studied by the photography method. The photographs of the radiation near and below the VChR threshold are published for the first time.

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.

Radiative double electron capture in heavy-ion atom collisions

Abstract Total cross sections for radiative double electron capture (RDEC) in collisions of fast highly charged ions with light target atoms were estimated. The applied method is based on the principle of detailed balance using the cross sections for the double photoionization process. Preliminary results of a dedicated RDEC experiment aiming at the observation of photons with twice the single REC photon energy, associated with double charge exchange, are discussed. Additionally, results of complementary measurements of double capture (without photon registration) by fully stripped U ions in collisions with C atoms at 295 MeV/u are presented. Here, a surprisingly enhanced cross section for double electron capture is found in accordance with observations reported in the literature.