Isospin mixing in the electric-dipole He(γ, n) and He(γ, p) reactions

Possible isospin mixing of the J^π = 1⁻ excited states of ⁴He leading to sizable differences in the ⁴He(γ, n)³He and⁴He(γ, p)³H cross sections in the giant-resonance region is examined in a bound-state approximation. Results indicate that the general features of certain experimental data can be accounted for by the presence of Coulomb mixing of the (S = 1, T = 0) and (S = 1, T = 1) states in addition to the usual spin-orbit mixing of the (S = 0, T = 1) and (S = 1, T = 1) states.