A Study of the Strong Interaction Effects of Deeply Bound Pionic Levels in Pionic Atoms

The pionic X-ray spectra of 181Ta, natRe, natPt, 197Au, 208Pb, 209Bi and 237Np have been investigated to obtain data which provide for a systematical investigation of the pionic 3d and 4f levels. Special attention was paid to experimental methods for obtaining clearly improved results as compared to earlier experiments, by using an array of Compton suppression BGO-shields and by using neutron time-of-flight discrimination to reduce background. Also to explore X-rays populating deeply bound pionic 1s-levels in 24Mg, 27A1, 28Si and 2p-orbits in 93Nb, natRu, respectively, coincidence techniques in combination with these high resolution Ge-BGO Compton suppression spectrometers were applied. Only deviations in the width of the pionic 3d-levels are observed. They are narrower by a factor 1.5 as compared to theoretical predictions. The same deviation as for Γ0(3d) is found for the strong interaction quadrupole shift, e2, for both the 4f- and 3d-orbits. An explanation for the difference in Γ0(3d) can be found by adding an isovector absorption term to the optical potential with a negative value for the parameters ImB1 or ImC1.