An experimental investigation of the 15.1 keV M1 + E2 nuclear transition in 227 Th from the β^- decay of 227 Ac

. Using the internal conversion electron spectroscopy, the energy of the 15.1 keV M1+E2 nuclear transition in 227 Th populated in the β^- decay of 227 Ac was determined to be 15098.6 ± 1.0 eV. This value is more accurate than the present accepted one by a factor of 200. The present uncertainty in the transition multipolarity was removed and it was found to be M1+E2 with the admixture |δ (E2/M1)| = 0.035 ± 0.006 .