Excited states in ²¹⁷Ra populated in the decay of ²²¹Th

Fine structure in the alpha decay of Th-221(90) , populating excited states in( 88)(217)Ra, was studied using alpha gamma-coincidence spectroscopy. Two alpha-decay branches from Th-221 have been newly observed, with E-alpha(keV)[b(alpha)(%)] = 7951(8)[0.14(3)] and 8247(3)[1.51(12)], together with three previously known branches. Also, two new states in Ra-217 were identified at E = 177 and 227 keV. The ground-state configurations of the odd-A, N = 131 transitional isotones above Pb-208 are interpreted from their a-decay fine structure systematics and considered in terms of predictions using spherical shell and reflection-asymmetric models.