Mass of 18C by pion double-charge-exchange reaction

The first observation of the double-charge-exchange reaction (π-,π+) to discrete nuclear states is reported. The mass of 18C has been measured using the reaction 18O(π-π+)18C at T (π) = 164 MeV. The reaction 12C(π-,π+)12Be, with known Q0 = -25.078(19) MeV, was used as the calibration reaction to obtain Q0 = - 25.69(15) MeV for the reaction 18O(π-, π+)18C(g.s.). The mass excess of 18C is thus found to be 24.91(15) MeV