Radiative Pion Capture in Medium Mass Nuclei: 32S, 40Ca+)

Abstract

The comparison between enelastic electron scattering, photo-absorption and radiative pion capture for 1p - shell nuclei has shed some light on the structure of the isovector M1 and spin-isospin transitions1. The principle reason for this is, that in the π−,γ -reaction the Tz = +1analog states to the ΔT = 1 excitations in the target nucleus are observed, whereas with conventional electromagnetic probes ΔT = 0 and ΔT = 1 can be excited. It is found thatin+ the impulse approximation matrix-elements of the type \( \) contribute to the radiative pion capture rate, and are thus identical to the spin-density part of the electromagnetic M1, the spin-isospin dipole or quadrupole operator for different JL, respectively. To test whether these ideas are still meaningful for nuclei in the s-d shell, we selected target nuclei with known Ml-levels. Good cases are 28Si, already discussed previously2 and 32S, for which we present preliminary results here. We also include some results on 40Ca, which had been measured previously with inferior resolution3 and which were obtained in the process of background studies for a radiative muon capture experiment4.