Using a multireflection time-of-flight mass spectrograph located after a gas cell coupled with the gas-filled recoil ion separator GARIS-II, the masses of several α-decaying heavy nuclei were directly and precisely measured. The nuclei were produced via fusion-evaporation reactions and separated from projectilelike and targetlike particles using GARIS-II before being stopped in a helium-filled gas cell. Time-of-flight spectra for three isobar chains, Fr204-Rn204-At204-Po204, Fr205-Rn205-At205-Po205-Bi205, and Fr206-Rn206-At206, were observed. Precision atomic mass values were determined for Fr204-206, Rn204,205, and At204,205. Identifications of Bi205, Po204,205, Rn206, and At206 were made with N10 detected ions, representing the next step toward use of mass spectrometry to identify exceedingly low-yield species such as superheavy element ions.
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