Study of magnetic excitations in sup(42,44,48)Ca by high-resolution electron scattering

In electron scattering experiments with high energy resolution in the nuclei 42Ca, 44Ca, and 48Ca magnetic dipole and quadrupole excitations were looked for. For this at the Darmstadt electron linear accelerator spectra at incident energies E0=30-58 MeV under scattering angles of theta=1050, 1170, and 1650 were taken up at low momentum transfer q<0.6 fm-1 and continued at the nucleus 48Ca to larger momentum transfer up to q=1.4 fm-1 at the 350-MeV electron accelerator in Mainz. These measurements led to the discovery of a magnetic dipole transition in 48Ca at the excitation energy Esub(x)=10.23 MeV which is with the transition strength B(M1)up=(3.9+-0.3) μsub(N)2 the strongest M1-transition in a nucleus heavier than 28Si. Beside this prominent M1-excitation in 48Ca further weaker magnetic dipole transitions are observed. Also in 42Ca and 44Ca a strong fragmentation of the M1 strength occurs. While in 44Ca and 48Ca scattering experiments with electrons and protons yield agreeing results for Jsup(π)=1+ states in 42Ca in the electron scattering the excitation of a Jsup(π)=1+ state at Esub(x)=11.24 MeV is observed which is not populated in (p, n) and (p, p') experiments. The magnetic quadrupole strength in the calcium isotopes exhibits a similarly strong fragmentation as the M1-strength. With the results of an earlier work on 48Ca up to Esub(x)=17 MeV the M2 sum strength exhausts 23% of an energy-weighted sum rule. In 42Ca and 44Ca at Esub(x)=9.75 and 14.43 MeV the excitation of the Jsup(π); T=2-; Tsub(>) analog states of the ground states of 42K and 44K is observed. (orig./HSI)