P. G. Hansen

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

Thirty-two-fold segmented germanium detectors to identify γ-rays from intermediate-energy exotic beams

Abstract Thirty-two-fold segmented coaxial high-purity large-volume germanium detectors for use in intermediate-energy radioactive-ion-beam experiments have been developed and tested. This high degree of segmentation will allow a precise localization of the point of photon interaction in the detector, thus allowing accurate doppler reconstruction of the energy of a γ-ray emitted in flight. In this article we report on the design of these detectors and their operational characteristics.

Evidence for an l=0 ground state in 9He

Abstract The unbound nuclear systems 10 Li and 9 He were produced in direct reactions of 28 MeV/u 11 Be incident on a 9 Be target. The distributions of the observed velocity differences between the neutron and the charged fragment show a strong influence of final-state interactions. Since the neutron originates in a dominant l =0 initial state, a selection-rule argument allows a firm l =0 assignment for the lowest odd-neutron state in 10 Li. We report the results suggesting a very similar unbound state in 9 He, characterized by an s-wave scattering length more negative than −10 fm corresponding to an energy of the virtual state of less than 0.2 MeV. Shell-model calculations cast light on the reasons for the disappearance of the magic shell gap near the drip line.

Reactions and single-particle structure of nuclei near the drip lines

Abstract The techniques that have allowed the study of reactions of nuclei situated at or near the neutron or proton drip line are described. Nuclei situated just inside the drip line have low nucleon separation energies and, at most, a few bound states. If the angular momentum in addition is small, large halo states are formed where the wave function of the valency nucleon extends far beyond the nuclear radius. We begin with examples of the properties of nuclear halos and of their study in radioactive-beam experiments. We then turn to the continuum states existing above the particle threshold and also discuss the possibility of exciting them from the halo states in processes that may be thought of as “collateral damage”. Finally, we show that the experience from studies of halo states has pointed to knockout reactions as a new way to perform spectroscopic studies of more deeply bound non-halo states. Examples are given of measurements of l values and spectroscopic factors.

Neutrons from the breakup of C-19

Neutrons arising from the breakup of a 30 MeV/nucleon C-19 beam on a tantalum target have been measured using the 98 element array DEMON. A narrow, forward peaked neutron angular distribution, with a corresponding momentum spread considerably smaller than those measured simultaneously for N-21, O-22 and F-24 was observed for charged fragments with Z < Z(proj). Interpreted in terms of the core-breakup reaction model, the results support the existence of a one neutron halo in C-19.

Cross-shell excitation in two-proton knockout: Structure of Ca 52

Gade, A. Janssens, R. V. F. Bazin, D. Broda, R. Brown, B. A. Campbell, C. M. Carpenter, M. P. Cook, J. M. Deacon, A. N. Dinca, D. -C. Fornal, B. Freeman, S. J. Glasmacher, T. Hansen, P. G. Kay, B. P. Mantica, P. F. Mueller, W. F. Terry, J. R. Tostevin, J. A. Zhu, S.

Proton halos in the 1s0d shell

Abstract The shell-model properties of proton halo states in proton-rich 1 s 0 d shell nuclei are investigated. The most interesting cases appear to be those in 26,27 P and 27 S. The parallel-momentum distributions of core fragments from proton stripping reactions may provide experimental insight into the structure of the halo states and the role played by the reaction mechanism. The “generalized Coulomb shift”, defined as the difference between the neutron and proton separation energies for an analogue pair, is shown to vary smoothly as a function of proton-separation energy and provides a good tool for mass extrapolations. The relation between the total interaction cross section and the matter radius is discussed.

Two-neutron knockout from neutron-deficient Ar-34, S-30, and Si-26

Department of Physics, School of Electronics and Physical Sciences,University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom(Dated: February 8, 2008)Two-neutron knockout reactions from nuclei in the proximity of the proton dripline have beenstudied using intermediate-energy beams of neutron-deficient

Single proton knock-out reactions fromF24,25,26

The cross sections of the single proton knock-out reactions from

Shell structure at N=28 near the dripline: Spectroscopy of Si-42, P-43, and S-44

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