D. Cortina-Gil

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.

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

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

Production of neutron-rich isotopes by cold fragmentation in the reaction 197Au + Be at 950 A MeV

Abstract The production cross sections and longitudinal-momentum distributions of very neutron-rich isotopes have been investigated in the fragmentation of a 950 A MeV 179 Au beam in a beryllium target. Seven new isotopes ( 193 Re, 194 Re, 191 W, 192 W, 189 Tl, 187 Hf and 188 Hf) and the five-proton-removal channel were observed for the first time. The reaction mechanism leading to the formation of these very neutron-rich isotopes is explained in terms of the cold-fragmentation process. An analytical model describing this reaction mechanism is presented.

New results on the halo structure of 8B

The longitudinal momentum distribution of Be fragments after fragmentation of B and the one-proton removal cross section (σ-1p) in a carbon target were measured at 1440 MeV/u with the fragment separator FRS used as an energy-loss spectrometer. The results show a narrow momentum distribution with a FWHM value of 91 ± 5 MeV/c and a large cross-section, σ-1p = 98 ± 6 mb. Both these results support the interpretation of a spatially extended proton orbit forming a halo in the B ground state. The momentum distribution and the one-proton removal cross section are shown to be reproduced with a three-body wave function for 8B where the target is treated as a black disc in the breakup process.

Production of new neutron-rich isotopes of heavy elements in fragmentation reactions of 238U projectiles at 1A GeV

The production of heavy neutron-rich nuclei has been investigated using cold-fragmentation reactions of {sup 238}U projectiles at relativistic energies. The experiment performed at the high-resolving-power magnetic spectrometer Fragment Separator at GSI made it possible to identify 40 new heavy neutron-rich nuclei: {sup 205}Pt, {sup 207-210}Au, {sup 211-216}Hg, {sup 214-217}Tl, {sup 215-220}Pb, {sup 219-224}Bi, {sup 223-227}Po, {sup 225-229}At, {sup 230,231}Rn, and {sup 233}Fr. The production cross sections of these nuclei were also determined and used to benchmark reaction codes that predict the production of nuclei far from stability.

Total charge-changing cross sections for neutron-rich light nuclei

Abstract Total charge-changing cross sections at relativistic energies on a carbon target have been measured for the light stable and neutron-rich radioactive nuclei 14 Be, 10−19 B, 12−20 C, 14−23 N, 16−24 O, and 18−27 F. A combined analysis of interaction and total charge-changing cross sections allows to draw definite conclusions concerning the thickness of the neutron skins or the size of the neutron halos for very neutron-rich isotopes. The obtained cross sections are also important in astrophysical applications to describe the propagation of galactic cosmic rays through the interstellar medium. A simple parameterization can reproduce the total charge-changing cross section within an accuracy of 5% for light nuclei from the valley of β -stability up to the drip line. These systematics improve the predictive capability of the formulae used to describe the unknown cross sections.

8He-6He: a comparative study of electromagnetic fragmentation reactions

Dissociation of a 227 MeV/u 8He beam in a lead target has been studied in a kinematically complete experiment. The results are compared with similar data from the well-known halo nucleus 6He. Coulomb–nuclear interference in the inelastic channel gives evidence for a Iπ=1− resonance in 8He at Ex=4.15 MeV. The deduced B(E1) value of 0.38±0.07 e2 fm2 indicates a uniform distribution of the four neutrons around the greek small letter alpha-particle core.

Exploring the anomaly in the interaction cross section and matter radius of 23O

New measurements of the interaction cross sections of 22,23O at 900A MeV performed at the GSI, Darmstadt are reported that address the unsolved puzzle of the large cross section previously observed for 23O. The matter radii for these oxygen isotopes extracted through a Glauber model analysis are in good agreement with the new predictions of the ab initio coupled-cluster theory reported here. They are consistent with a 22O+neutron description of 23O as well.

Proton-proton correlations observed in two-proton decay of 19Mg and 16Ne

Proton-proton correlations were observed for the two-proton decays of the ground states of 19 Mg and 16 Ne. The trajectories of the respective decay products, 17 Ne + p + p and 14 O + p + p, were measured by using a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of fragments projected on planes transverse to the precursor momenta. The measured three-particle correlations reflect a genuine three-body decay mechanism and allowed us to obtain spectroscopic information on the precursors with valence protons in the sd shell.

Optimization of Energy Resolution Obtained With CsI(Tl) Crystals for the R3B Calorimeter

Studies with different CsI(Tl) crystals coupled to avalanche photodiodes were performed in the frame of the R+D programme for the design of the R3B calorimeter (CALIFA). The study of the energy resolution has been performed for crystals with lengths varying from 1 to 10 cm and square section (1 times 1 cm2), attending to different optimization of parameters (i.e., crystal wrapping, optical coupling to the avalanche photodiode and the electronic chain). The obtained results with avalanche photo-diodes are very promising and suggest CsI(Tl) as a suitable candidate for at least part of the calorimeter.