Effect of gauge invariance and fermi motion of nucleons on radiative pion capture by 16O

Partial transition rates and the γ-quanta spectrum have been calculated for the 16O(π-,γ)16N reaction using a new effective Hamiltonian. The Hamiltonian satisfies the requirements of gauge invariance and also regards for the nucleonic Fermi-motion effects in a nucleus. According to the estimates the total γ-quanta yield conforming to the nuclear spin-dipole excitations decreases by 10-15% and the γ-quanta yield conforming to the spin-quadrupolar branch of excitation decreases by 30%. The main differencies from the results obtained with the traditional form of the effective Hamiltonian are fully related to a new kinematical factor, but the nucleon velocity terms and the effective Hamiltonian constant renormalization play an important part in weak transitions