Low-energy pion double charge exchange on Ca isotopes.

Differential cross sections for the double-isobaric-analog-state transition in the /sup 42,44/Ca(..pi../sup +/,..pi../sup -/) reactions were measured at an incident energy of 35 MeV and 40 degrees. The /sup 42/Ca cross section (2.0 +- 0.5 ..mu..b/sr) is nearly as large as those of the lighter T = 1 nuclei and only slightly smaller than that previously measured for /sup 48/Ca (2.4 +- 0.7 ..mu..b/sr). The cross section for /sup 44/Ca (1.1 +- 0.3 ..mu..b/sr) is half of this amount. These results are surprising when compared with simple expectations and point to the importance of the nonanalog route contribution at low energies.