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HK: Hadronen und Kerne
HK 17: Giant Resonances
HK 17.1: Gruppenbericht
Montag, 16. März 1998, 17:00–17:30, E
Excitation and decay of giant resonances in 48Ca studied with (e,e′n) and (p,p′n) coincidence experiments⋆ — •K. Schweda1, C. Bähr1, P. von Neumann-Cosel1, A. Richter1, G. Schrieder1, A. Stascheck1, S. Strauch1, J. Carter2, R. Fearick3, S.V. Förtsch4, J.J. Lawrie4, J.V. Pilcher4, F.D. Smit4, and G.F. Steyn4 — 1Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany — 2Physics Department, University of the Witwatersrand, Johannesburg, South Africa — 3Physics Department, University of Cape Town, South Africa — 4National Accelerator Centre, Faure, South Africa
The giant resonances in 48Ca have been studied using the (e,e′n) and (p,p′n) reactions. We present a 48Ca(e,e′n) measurement in the giant resonance region with kinematics that favour electric monopole, dipole and quadrupole excitations. A multipole analysis of the data is performed. The extracted B(E1) and B(E2) + B(E0) strength distributions are compared to photonuclear cross sections and microscopic calculations taking into account 1p-1h⊗phonon configurations and the coupling to the continuum.
The branching ratio for neutron decay into the ground state of 47Ca, Γn0/Γ, largely exceeds expectations from statistical model calculations and indicates the presence of a direct decay component. It can be demonstrated that these direct contributions are related to the giant dipole resonance, while the neutron emission out of the monopole and quadrupole resonances are compatible with expectations for statistical decay. In the (e,e′n) spectra a narrow resonance with considerable cross sections is observed at an excitation energy of Ex=24.2 MeV decaying exclusively into a low-lying T=9/2 state in 47Ca. It is suggested to be a T = 5 resonance which is analogue to an excited Jπ = 1− state in 48K.
The 48Ca(p,p′n) experiment was performed at an incident energy Ep = 100 MeV at four proton scattering angles between 21∘ and 36∘ which enhances the excitation of the isoscalar quadrupole strength and allows a separation from other multipoles. Neutron decay was measured with the time-of-flight method using liquid scintillator detectors for up to 12 angles relative to the 48Ca recoil axis. The deduced E2 strength distribution and an analysis of the 48Ca(p,p′n0) angular correlations are presented.
⋆ Supported by the DFG under contract Ri 242/12-1 and by the South African FRD.