π+ photoproduction from 28Si leaving low-lying residual states

Abstract The energy and angular distributions of π + photoproduced from 28 Si were measured to study spin-isospin-flip transitions leaving the residual nuclei in states up to 2.5 MeV excitation energy. Dominant contributions were found for M1 transitions at around 1.3 MeV and 2.2 MeV in 28 Al. The strengths of these transitions have been deduced and compared with the results of (e, e′), (γ, γ′), (p, p′), ( π − , γ), ( μ − , γ) and charge-exchange reactions. The (γ, π + ) result agrees with the electromagnetic interaction case but not with the (p, p′) case, which supports the contribution of exchange currents in electromagnetic transitions.