Isovector spin states observed in radiative pion capture in flight and at rest: recent results from SIN

At first glance, the difficulties inherent in using photopion reactions as compared to other charge exchange probes, make the use of such reactions a poor choice. But photopion reactions have contributed to the study of spin-isospin states since the late sixties. Photopion reactions single out isovector transitions with large spin-density matrix-elements, and the experimental photon spectra feature prominent peaks corresponding to analogs of magnetic dipole to octupole transitions in the target nucleus. The recent interest in magnetic quadrupole transitions stimulated the authors to extend the previous measurements on 12C7, 16C8 and 18O8 to other nuclei near the end of the 1p shell, namely 14C and 15N. The 14C data, along with the recent data on 13C9, 19F9 and 20Ne10 allow a rather complete interpretation of the isovector transitions. Also presented are the first results from an experiment searching for precursor phenomena in photopion reactions. The case selected is 13C(π+,r)13N