G. Münzenberg

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

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.

Invariant mass spectrum and alpha-n correlation function studied in the fragmentation of He-6 on a carbon target

Momentum distributions and invariant mass spectra from the breakup of He-6 ions with an energy of 240 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of He-6. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the He-5 resonance. The shape of the (alpha+n) two-body invariant mass spectrum is interpreted as mainly reflecting the 5He ground state which is a J(pi) = 3/2(-) resonance. However, no evidence for correlations between cu particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance

Neutron Momentum Distributions from Core Break-up Reactions of Halo Nuclei

Neutron angular distributions from violent break-up reactions of Li-11 and Be-11 have been measured at 28 MeV/u and 280 MeV/u and at 41 MeV/u and 460 MeV/u, respectively. The derived neutron momentum distributions show a narrow component in transverse momentum that is within uncertainties independent of beam energy and target charge. This component is suggested to be simply related to the momentum distribution of the loosely bound halo neutron(s) in the projectiles.

Precision experiments with exotic nuclei

Abstract Progress and modern developments of secondary nuclear beam facilities based on the in-flight and ISOL separation methods are outlined. Precision experiments with nuclear beams characterized by large emittances have been performed by using special ion-optical conditions in spectrometers. A new generation of experiments have been started with stored and cooled exotic nuclei at sub eV and at relativistic energies using the combination of an ISOL facility and an ion trap or the combination of an in-flight system with a storage and cooler ring, respectively. Both experimental scenarios are realized by ISOLDE and the ISOLTRAP at CERN and the fragment separator FRS in combination with the experimental storage ring ESR at GSI. The power and the potential of these devices are illustrated by direct mass and lifetime measurements.

Coulomb breakup of neutron-rich Na-29,Na-30 isotopes near the island of inversion

First results are reported on the ground state configurations of the neutron-rich Na-29,Na-30 isotopes, obtained via Coulomb dissociation (CD) measurements. The invariant mass spectra of these nuclei have been obtained through measurement of the four-momenta of all decay products after Coulomb excitation of those nuclei on a Pb-208 target at energies of 400-430 MeV/nucleon using the FRS-ALADIN-LAND setup at GSI, Darmstadt. Integrated inclusive CD cross-sections (CD) of 89 (7) mb and 167 (13) mb for one neutron removal from Na-29 and Na-30, respectively, have been extracted up to an excitation energy of 10 MeV. The major part of one neutron removal, CD cross-sections of those nuclei populate the core, in its ground state. A comparison with the direct breakup model, suggests the predominant occupation of the valence neutron in the ground state of Na-29 (3/2(+)) and Na-30 (2(+)) is the d-orbital with a small contribution from the s-orbital, which are coupled with the ground state of the core. One of the major components of the ground state configurations of these nuclei are Na-28(gs)(1(+)) circle times v(s,d) and Na-29(gs)(3/2(+)) circle times v(s,d), respectively. The ground state spin and parity of these nuclei obtained from this experiment are in agreement with earlier reported values. The spectroscopic factors for the valence neutron occupying the s and d orbitals for these nuclei in the ground state have been extracted and reported for the first time. A comparison of the experimental findings with shell model calculation using the MCSM suggests a lower limit of around 4.3 MeV of the sd-pf shell gap in Na-30.

Response of Multi-strip Multi-gap Resistive Plate Chamber

A prototype of Multi-strip Multi-gap Resistive Plate chamber (MMRPC) with active area 40 cm × 20 cm has been developed at SINP, Kolkata. Detailed response of the developed detector was studied with the pulsed electron beam from ELBE at Helmholtz-Zentrum Dresden-Rossendorf. In this report the response of SINP developed MMRPC with different controlling parameters is described in details. The obtained time resolution (σt) of the detector after slew correction was 91.5 ± 3 ps. Position resolution measured along (σx) and across (σy) the strip was 2.8±0.6 cm and 0.58 cm, respectively. The measured absolute efficiency of the detector for minimum ionizing particle like electron was 95.8±1.3 %. Better timing resolution of the detector can be achieved by restricting the events to a single strip. The response of the detector was mainly in avalanche mode but a few percentage of streamer mode response was also observed. A comparison of the response of these two modes with trigger rate was studied.

Excitation of the two-phonon giant dipole resonance in 238U studied via inclusive measurements of neutron-removal cross sections

Abstract As part of a comprehensive study of uranium fragmentation at relativistic energies at the GSI projectile fragment separator, FRS, inclusive neutron-removal cross sections have been measured for several xn channels at projectile energies of 600 and 950 A MeV. The electromagnetic cross sections agree surprisingly well with a semiclassical calculation based on measured photonuclear cross sections and do not require an extra enhancement of the two-phonon giant dipole excitation as concluded from similar measurements with 197 Au.