alpha-decay spectroscopy of the N=130 isotones Ra-218 and Th-220: Mitigation of alpha-particle energy summing with implanted nuclei

An analysis technique has been developed in order to mitigate energy summing due to sequential short-lived alpha decays from nuclei implanted into a silicon detector. Using this technique, alpha-decay spectroscopy of the N = 130 isotones Ra-218 (Z = 88) and Th-220 (Z = 90) has been performed. The energies of the alpha particles emitted in the Ra-218 -> Rn-214 and Th-220 -> Ra-216 ground-state-to-ground-state decays have been measured to be 8381(4) keV and 8818(13) keV, respectively. The half-lives of the ground states of Ra-218 and Th-220 have been measured to be 25.99(10) mu s and 10.4(4) mu s, respectively. The half-lives of the ground states of the alpha-decay daughters, Rn-214 and Ra-216, have been measured to be 259(3) ns and 161(11) ns, respectively. Fine structure in the alpha decay of Ra-218 has been observed for the first time, populating the 695-keV 2(1)(+) state in Rn-214. The fine-structure a decay has an alpha-particle energy of 7715(40) keV and branching ratio b(alpha) = 0.123(11)%.