A. N. Ostrowski

Louvain-Edinburgh Detector Array (LEDA): a silicon detector array for use with radioactive nuclear beams

We discuss the design and implementation of the Louvain-Edinburgh Detector Array: a charged particle detector array composed of silicon-strip detectors which is used for the study of nuclear astrophysics and nuclear physics using radioactive nuclear beams at the Louvain-1a-Neuve radioactive nuclear beam facility

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.

Search for 28O and study of neutron-rich nuclei near the N = 20 shell closure

Abstract A search for 28 O with a 78 AMeV beam of the neutron-rich isotope 36 S has been performed for the first time. Evidence for the unbound character of 28 O was obtained. In the same experiment the half-lives of the very neutron-rich isotopes 27,29 F and 30 Ne were measured and those for 28,29 Ne and 30,31 Na reexamined. The results are compared to shell-model predictions and conclusions drawn regarding the extent of the region of deformation around N = 20.

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.

CD: A double sided silicon strip detector for radioactive nuclear beam experiments

A very compact double sided silicon strip detector array is described, designed for use in reaction studies involving radioactive nuclear beams. It is small enough to fit inside a large solid angle g-detector array and will enable Dopplershift corrections at energies in the vicinity of the Coulomb barrier. The detector provides sufficient energy and time-offlight resolution for the identification of light reaction products and can be set up to cover a substantial part of the scattering angular distribution with good resolution. The device is available in thicknesses of up to 500 mm to stop all interesting reaction products. Moreover, a very thin (35–40 mm) variant of this detector is described that can be used as an energy loss detector in a DE@E telescope geometry followed by a detector that measures the residual energy. This provides additional particle identification capabilities, e.g. in light exotic nuclei induced reactions. First results from a commissioning run using a post-accelerated radioactive beam are presented. r 2002 Elsevier Science B.V. All rights reserved.

Spectroscopy of 10He

Abstract The mass of 10 He has been measured with the double charge exchange reaction 10 Be( 14 C, 14 O) 10 He at E Lab = 334.4 MeV and a mass excess M.E. = 48.81 (7) MeV is obtained. It follows that 10 He is particle unstable against 2 n - emission by S 2n = −1.07(7) MeV . Two excited states are observed: a broad resonance at an excitation energy of E x = 3.24(20) MeV , and a strong resonance at E x = 6.80(7) MeV .

Coupling effects in the elastic scattering of the exotic nucleus 6He on protons

Abstract Cross sections for the elastic scattering of 6He radioactive nuclear beam on proton targets have been measured at 38.3 MeV/nucleon. With a view to test the ability of general optical potentials to reproduce the data for scattering of unstable nuclei, the present results, as well as other existing data for 6,8He, have been analyzed within the framework of the microscopic Jeukenne–Lejeune–Mahaux nucleon–nucleus potential. The angular distributions were found to be best reproduced by reducing the real part of the optical potential. This renormalization can be seen as a consequence of the complex polarization potential produced by the coupling to the continuum due to the weakly bound nature of the unstable nuclei. This effect can be simulated in a phenomenological analysis by a surface potential.

Spectroscopy of 13Be

Abstract Six quasi-stationary states of 13 Be populated in the 14 C( 11 B, 12 N) 13 Be reaction at E lab = 190 MeV are reported. A Q -value = −39.60(9) MeV and a mass excess, M.E.= 33.95(9) MeV, have been found for the lowest observed spectral line. The ground state is unstable with respect to one-neutron emission by 0.80(9) MeV. Excitation energies of 1.22(10), 2.10(16), 4.14(12), 5.09(14) and 7.0(2) MeV have been obtained for the observed spectral lines.

Stud of weakly bound and unbound states of exotic nuclei with binary reactions

Abstract Binary reactions using neutron-rich beams (and targets) give the best approach to study the level structure of exotic nuclei. Systematic cross section dependencies of multi-step transfer reactions are discussed. Some rections, for example the proton-neutron exchange ( 12 C, 12 N) and ( 13 C, 13 N) , have distinct selectivity for the population of unnatural or natural parity states, respectively. This selectivity has been applied to new spectroscopic studies of 10 Li using the 10 Be( 12 C, 12 N) and 9 Be)(P 13 C, 12 N) reactions. The lowest resonance of 10 Li observed at 0.24(6) MeV above the neutron threshold. The results are discussed together with other available data.

Elastic 2n-transfer in the 4He(6He,6He)4He scattering

The elastic scattering He-4(He-6,He-6)He-4 has been investigated at center-of-mass energies of 11.6 and 15.9 MeV. Differential cross sections are determined using a post-accelerated He-6 (T-1/2 = 0.807 s) beam in the center-of-mass angular range between 50 and 140 degrees. The comparison of the measured data with calculations using a double folding potential shows evidence for the 2n-transfer process in the He-4(He-6,He-6)He-4 elastic scattering