(π+,π0) and (p,n) excitations

There has been considerable interest in using charge-exchange reactions in the medium energy regime to study nuclear structure. This has been delayed by difficulties in understanding the experimental results even when the structure appears to be understood. As a result, even the limited data available in the past have prompted considerable efforts at going beyond a first order treatment. Initially, some of the features of (p,n) and (π+,π0) reactions are contrasted. Then the published (π+,π0) treatments will be briefly sketched. Finally, some calculations for mass-7 and mass-14 will be discussed, indicating the way in which pion or nucleon charge exchange may be a particularly fruitful tool. 24 references