Spin-isospin flip transitions in 40Ca(γ,π+)40K reaction

The energy and angular distribution of π+ produced by 40Ca(e,π+)40K reaction have been measured in order to study the spin-isospin excitation in the threshold region. The present experiment concerns the heaviest nucleus that has been studied so far. We found several strong transitions to the ground state and to the excited states at excitation energies of 0.9, 2.7, 4.4 and 6.1 MeV in 40K. The (γ,π+) cross sections leading to the lower 3 states are deduced. Results are compared with the theoretical estimates in the distorted-wave impulse approximation and with the data by other kinds of reactions. Qualitative agreement is obtained with a one-particle-one-hole model calculation, but normalization factors are needed. (orig.)