T. Nilsson

Invariant-mass spectroscopy of 10Li and 11Li

Break-up of secondary Li-11 ion beams (280 MeV/nucleon) on C and Pb targets into Li-9 and neutrons is studied experimentally. Cross sections and neutron multiplicity distributions are obtained, characterizing different reaction mechanisms. Invariant-mass spectroscopy for Li-11 and Li-10 is performed. The E1 strength distribution, deduced from electromagnetic excitation of Li-11 up to an excitation energy of 4 MeV comprises similar to 8% of the Thomas-Reiche-Kuhn energy-weighted sumrule strength. Two low-lying resonance-like structures are observed for Li-10 at decay energies of 0.21(5) and 0.62(10) MeV, the former one carrying 26(10)% of the strength and likely to be associated with an s-wave neutron decay. A strong di-neutron correlation in Li-11 can be discarded. Calculations in a quasi-particle RPA approach are compared with the experimental results for Li-10 and Li-11

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

The REX-ISOLDE project

The Radioactive Beam Experiment REX-ISOLDE [1–3] is a pilot experiment at ISOLDE (CERN) testing the new concept of post acceleration of radioactive ion beams by using charge breeding of the ions in a high charge state ion source and the efficient acceleration of the highly charged ions in a short LINAC using modern ion accelerator structures. In order to prepare the ions for the experiments singly charged radioactive ions from the on-line mass separator ISOLDE will be cooled and bunched in a Penning trap, charge bred in an electron beam ion source (EBIS) and finally accelerated in the LINAC. The LINAC consists of a radiofrequency quadrupole (RFQ) accelerator, which accelerates the ions up to 0.3 MeV/u, an interdigital H-type (IH) structure with a final energy between 1.1 and 1.2 MeV/u and three seven gap resonators, which allow the variation of the final energy. With an energy of the radioactive beams between 0.8 MeV/u and 2.2 MeV/u a wide range of experiments in the field of nuclear spectroscopy, astrophysics and solid state physics will be addressed by REX-ISOLDE.

Facilities and methods for radioactive ion beam production

Radioactive ion beam facilities are transforming nuclear science by making beams of exotic nuclei with various properties available for experiments. New infrastructures and development of existing installations enlarges the scientific scope continuously. An overview of the main production, separation and beam handling methods with focus on recent developments is done, as well as a survey of existing and forthcoming facilities world-wide.

Accelerated radioactive beams from REX-ISOLDE

In 2001 the linear accelerator of the Radioactive beam EXperiment (REX-ISOLDE) delivered for the first time accelerated radioactive ion beams, at a beam energy of 2 MeV/u. REX-ISOLDE uses the method of charge-state breeding, in order to enhance the charge state of the ions before injection into the LINAC. Radioactive singly-charged ions from the on-line mass separator ISOLDE are first accumulated in a Penning trap, then charge bred to an A/q < 4.5 in an electron beam ion source (EBIS) and finally accelerated in a LINAC from 5 keV/u to energies between 0.8 and 2.2 MeV/u. Dedicated measurements with REXTRAP, the transfer line and the EBIS have been carried out in conjunction with the first commissioning of the accelerator. Thus the properties of the different elements could be determined for further optimization of the system. In two test beam times in 2001 stable and radioactive Na isotopes (Na-23-Na-26) have been accelerated and transmitted to a preliminary target station. There Ni-58- and Be-9- and H-2-targets have been used to study exited states via Coulomb excitation and neutron transfer reactions. One MINIBALL triple cluster detector was used together with a double sided silicon strip detector to detect scattered particles in coincidence with gamma-rays. The aim was to study the operation of the detector under realistic conditions with gamma-background from the beta-decay of the radioactive ions and from the cavities. Recently for efficient detection eight tripple Ge-detectors of MINIBALL and a double sided silicon strip detector have been installed. We will present the first results obtained in the commissioning experiments and will give an overview of realistic beam parameters for future experiments to be started in the spring 2002.

Two-neutron interferometry as a probe of the nuclear halo

The technique of intensity interferometry is proposed as a probe of the spatial configuration of two-Neutron haloes. After exploring the sensitivity of interferometry to the n-N configuration, it is demonstrated that the application of the standard method for constructing the correlation function is not valid for halo neutrons. A new iterative method is presented and applied to measurements of the dissociation of 6He, 11Li and 14Be. The correlation functions for these systems have thus been extracted for the first time and the corresponding root-Mean-Square n-n separations estimated. The results are in agreement with the predictions of available three-Body models

Three-body correlations in Borromean halo nuclei

Three-body correlations in the dissociation of Borromean halo nuclei are explored for the first time using a technique based on intensity interferometry and Dalitz plots. As an example, the breakup of

Study of charged particles emitted in the β-decay of 6,8He

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New results on the halo structure of 8B

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

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