Berlin 2005 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 33: Kernphysik/Spektroskopie

HK 33.1: Gruppenbericht

Dienstag, 8. März 2005, 16:30–17:00, TU MA041

Electromagnetic Strength in Single-Particle Halo Nuclei — •Stefan Typel¹ and Gerhard Baur² — ¹GSI Darmstadt — ²Forschungszentrum Jülich

Nuclei close to the driplines often exhibit a pronounced nucleon+core structure that is well described by single-particle models. For low orbital angular momenta of the lowest bound valence nucleon an extended density distribution, a halo, develops resulting in a large size of the nucleus. Light exotic nuclei were studied extensively in recent years by electromagnetic excitation and a large transition strength was observed at low energies in the continuum that shows universal features when plotted in the appropriately scaled variables. The relevant matrix elements are essentially determined by the asymptotics of the wave functions and simple scaling laws apply for the transition strength [1]. Effects of the interaction in the continumm are conveniently described by the effective-range expansion since details of the interaction are not resolved at the relevant low energies. This is in the spirit of effective field theoretical approaches to halo nuclei. We introduce appropriate dimensionless scaling parameters and find explicit analytical scaling laws for several quantities like radii, probabilities, strength functions and corresponding sum rules. Electromagnetic strength functions are parametrized in terms of the separation energy of the halo nucleon, the asymptotic normalization coefficient of the bound state and the scattering length. A typical example is the neutron halo nucleus ¹¹Be [1]. The present approach provides a framework for future studies of heavier halo nuclei.

[1] S. Typel and G. Baur, Phys. Rev. Lett. 93, 142502 (2004).