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

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