K. Riisager

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

Observation of forward neutrons from the break-up of the 11Li neutron halo

Abstract The cross-sections and forward angular distributions of fast neutrons have been studied for the reaction (11Li, 9Li) at 29 MeV/u on targets of Be, Ni and Au. The cross-sections are large and arise essentially from peripheral reactions. The angular distributions of the neutrons are very narrow and indicate the existence of a neutron halo with radius of about 12 fm.

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

Two-body halos

Abstract We examine bound two-body systems in the presence of a long-range repulsive potential and determine when halos (states of large spatial extent) can develop. Potentials that fall off slower than r −2 keep the system absolutely confined, potentials that fall off faster do not. The behaviour for the r −2 potential itself is more complex. This is illustrated by examples of nuclear halo states, including proton halos, halos in excited states and halos with non-zero angular momentum. We give a survey of experimental halo probes and discuss their relative sensitivity.

Observation of a proton halo in8B

The longitudinal momentum distribution of7Be was measured after the break-up reaction of8B in C, Al, and Pb targets at 1471 A·MeV. We observed a narrow distribution with a FWHM of (81±6) MeV/c in all targets. The experimental results indicate an extended spatial distribution of the loosely bound proton in8B, and agree with QRPA calculations.

Efimov states in halo nuclei

We investigate conditions for the occurrence of Efimov states in the recently discovered halo nuclei. These states could appear in systems, where one neutron is added to a pronounced one-neutron halo nucleus. Detailed calculations of the properties of the states are presented and promising candidates are discussed.

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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Halos and related structures

Be into