K. Sümmerer

The GSI projectile fragment separator (FRS): A Versatile magnetic system for relativistic heavy ions

The projectile fragment separator FRS designed for research and applied studies with relativistic heavy ions was installed at GSI as a part of the new high-energy SIS/ESR accelerator facility. This high-resolution forward spectrometer has been successfully used in first atomic and nuclear physics experiments using neon, argon, krypton, xenon, and gold beams in the energy range from 500 to 2000 MeV/u. For the first time relativistic xenon and gold fragments have been isotopically separated. In this contribution we describe first experiments characterizing the performance of this spectrometer.

The super-FRS project at GSI

The GSI projectile fragment separator FRS has demonstrated with many pioneering experiments the research potential of in-flight separators at relativistic energies. Although the present facility has contributed much to the progress in the field of nuclear structure physics, major improvements are desirable in the future. The characteristics of the proposed next-generation facility at GSI, the Super-FRS, will be presented and compared to other projects. The Super-FRS is a large-acceptance superconducting fragment separator followed by different experimental branches including a combination with a new storage-cooler ring system. This system consists of a collector ring (CR) and a new experimental storage ring (NESR) which allow precision mass and lifetime measurements as well as in-ring reaction studies. The NESR can be operated in combination with an electron ring to measure electron scattering with exotic nuclei. This electron heavy-ion collider will open up new fields for nuclear structure research.

Measurements of interaction cross sections for light neutron-rich nuclei at relativistic energies and determination of effective matter radii

Abstract We measured the interaction cross sections ( σ I ) of 10,11B, 12–20C, 14–23N, 16–24O and 18–26F on carbon targets at energies of around 950 A MeV. We then deduced the effective matter radii of the nuclei by a Glauber-model analysis. Based on the assumption of a core plus a valence neutron structure, we applied a Glauber-model analysis for a few-body system adapted for nuclei with an odd neutron number. We also deduced the effective nucleus-matter densities as well as some spectroscopic information for selected nuclei. Evidence for a one-neutron halo structure was found for 22N, 23O and 24F, as well as 19C.

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.

Discovery and cross-section measurement of 58 new fission products in projectile-fission of 750 · A MeV

Abstract The projectile fission of uranium at relativistic energy impinging on a Be target was investigated with the fragment separator, FRS, in order to produce and identify new isotopes and to measure their production yields. Fifty eight new fragments have been observed with a neutron excess of (N - Z)/Z reaching 0.8 and cross sections as small as 0.3 nb.

^{238}

We have measured the Coulomb dissociation of 8B into 7Be and proton at 254 MeV/nucleon using a large-acceptance focusing spectrometer. The astrophysical S17 factor for the 7Be(p,gamma)8B reaction at E{c.m.} = 0.25-2.78 MeV is deduced yielding S17(0)=20.6 \pm 1.2 (exp.) \pm 1.0 (theo.) eV-b. This result agrees with the presently adopted zero-energy S17 factor obtained in direct-reaction measurements and with the results of other Coulomb-dissociation studies performed at 46.5 and 51.2 MeV/nucleon.

U

The fragment separator FRS at GSI was used as an energy-loss spectrometer to measure the longitudinal momentum distributions of C-16,C-18 fragments after one-neutron removal reactions in C-17,C-19 impinging on a carbon target at about 910 MeV/u. The distributions in the projectile frames are characterized by a FWHM of 141 +/- 6 MeV/c for C-16 and 69 +/- 3 MeV/c for C-18. Th, results are compared with experimental data obtained at lower energies and discussed within existing theoretical models

MEASUREMENT OF THE COULOMB DISSOCIATION OF 8B AT 254 MEV/NUCLEON AND THE 8B SOLAR NEUTRINO FLUX

Abstract Cross sections of iridium and platinum isotopes have been measured, which were produced as fragments from 197 Au projectiles interacting with aluminum target nuclei at 1 A GeV. The fragments were identified by a kinematic analysis ( ΔE − Bρ -time-of-flight) and by an ion-optical separation at the projectile-fragment separator FRS at GSI. Indications are found for high excitation energies and weak proton-neutron correlations in the peripheral nuclear-collision process.

Longitudinal momentum distributions of 16,18C fragments after one-neutron removal from 17,19C

Abstract The interaction cross sections ( σ I ) of light radioactive nuclei close to the neutron drip line ( 17,19 B, 14 Be) have been measured at around 800 A MeV. The effective root-mean-square (r.m.s.) matter radii of these nuclei have been deduced from σ I by two different methods, a Glauber-type calculation based on the optical limit approximation and a few-body reaction model. The deduced radii from both approaches agree with each other within experimental uncertainty. The r.m.s. radii of 17 B (2.99±0.09 fm) and of 14 Be (3.10±0.15 fm) in this work are consistent with the previously determined values, and have a higher accuracy. The r.m.s. radius of 19 B (3.11±0.13 fm) was newly determined. Assuming a “core plus 2n” structure in 17 B and 14 Be, the mixing of ν (2 s 1/2 ) and ν (1 d 5/2 ) was studied and the s -wave spectroscopic factor is found to be 36±19% and 47±25%, respectively. A valence radius analysis suggests a “core plus 4n” structure in 19 B.

Distribution of Ir and Pt isotopes produced as fragments of 1 A GeV 197Au projectiles: a thermometer for peripheral nuclear collisions

We have measured the interaction cross sections (σI) of 31–40Ar and 31–37Cl on carbon targets at energies of around 950 A MeV. The effective matter radii for these nuclei were deduced by a Glauber-model analysis. Combining our matter radii with measured charge radii for Ar isotopes, we could deduce the proton-skin thicknesses for the 32–40Ar isotopes, which were found to increase monotonically with decreasing neutron number. The larger radius of the proton drip-line nucleus 31Ar suggests an anomalous structure for this nucleus. In addition, using NaI(Tl) arrays surrounding the carbon target, we measured γ-rays emitted from excited states in these isotopes. In this way we could deduce the upper limits for the inelastic cross sections (σinela) on carbon targets at energies of around 950 A MeV.