triumf experiment e1104 study of halo effects in the ......15 olof tengblad: preparation experiment...

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TRIUMF experiment E1104

Study of halo effects in the Scattering of 11Li with heavy targets at energies around the Coulomb Barrier

16-30 July 2008

MINISTERIO DE EDUCACIÓNY CIENCIA

CONSEJO SUPERIORDE INVESTIGACIONESCIENTÍFICAS

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Olof Tengblad: Preparation experiment TRIUMF E1104 16-30 July 2008

TRIUMF EEC RESEARCH PROPOSALDetailed Statement of Proposed Research for Experiment S1104

The study of the elastic and break-up cross sections, performed at several collision energies, will allow understanding the role of the nuclear and Coulomb interaction in the collision of a weakly bound nucleus such as 11Li on 208Pb. We will also learn the role of the continuum of 11Li in the scattering process, in particular, which partial waves play a role, which break-up energies are more important, and if the 3-bodynature of 11Li has a special significance in this collision.

Scientific JustificationHalo nuclei are composed by a core nucleus and one or two loosely bound neutrons. Due to the loosely bound structure, they should be easily polarizable. Thus, in the presence of a strong electric field, the nucleus will be distorted, so that, with respect to the centre of mass of the nucleus, the halo neutrons will move opposite to the electric field, while the positively charged core will move in the direction of the field. The B(E1) distribution is a measurement of the importance of polarizability. Large B(E1) values at low excitation energies (close to the break-up threshold) indicate that the nucleus is easily polarizable. In terms of the ground state wavefunction, large B(E1) values at energies close to the break up threshold indicate a large probability that the halo neutrons are in the extreme asymptotic tail.The phenomenon of dipole polarizability should affect strongly the elastic scattering of halonuclei on heavy targets, even at energies below the Coulomb barrier, where the nuclearforce should not be important. Two effects are relevant: First, Coulomb break-up willreduce the elastic cross sections. Second, the distortion of the wave function generated bythe displacement of the charged core with respect to the centre of mass of the nucleus willreduce the Coulomb repulsion, and with it the elastic cross sections.

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The TRIUMF layout

ISAC-II

SEBT2

target

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Beamline from cyclotron towards primary target

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The two primary target positions

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Beam entering ISAC II

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The ISAC-II experimental hall

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The ISAC-II Linac

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ISAC-II experimental hall SEBT2 beam-line

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ISAC-II experimental hall

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SEBT2 beam-line

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SEBT2 beamline: our chamber superimposed

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SEBT2 beamline: possible experimental set-up

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The beam is entering through a 4mm collimator, in the centre of theset-up is the target positioned at about 45 degrees. The set-up consists of 6 particletelescopes; 20 – 40 micrometer thick Double Sided Silicon Strip detectors backedwith 1.500 micrometer thick E Si-Pad detectors.The DSSSDs give a pixilation of 3x3 mm2 and an angular resolution better than 3degrees.

Possible experimental set-up

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triumf experiment e1104 study of halo effects in the ......15 olof tengblad: preparation experiment...

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