First online multireflection time-of-flight mass measurements of isobar chains produced by fusion-evaporation reactions: Toward identification of superheavy elements via mass spectroscopy

Abstract

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 $\ensuremath{\alpha}$-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, $^{204}\mathrm{Fr}\ensuremath{-}^{204}\mathrm{Rn}\ensuremath{-}^{204}\mathrm{At}\ensuremath{-}^{204}\mathrm{Po}, ^{205}\mathrm{Fr}\ensuremath{-}^{205}\mathrm{Rn}\ensuremath{-}^{205}\mathrm{At}\ensuremath{-}^{205}\mathrm{Po}\ensuremath{-}^{205}\mathrm{Bi}$, and $^{206}\mathrm{Fr}\ensuremath{-}^{206}\mathrm{Rn}\ensuremath{-}^{206}\mathrm{At}$, were observed. Precision atomic mass values were determined for $^{204--206}\mathrm{Fr}, ^{204,205}\mathrm{Rn}$, and $^{204,205}\mathrm{At}$. Identifications of $^{205}\mathrm{Bi}, ^{204,205}\mathrm{Po}, ^{206}\mathrm{Rn}$, and $^{206}\mathrm{At}$ were made with $N\ensuremath{\lesssim}10$ detected ions, representing the next step toward use of mass spectrometry to identify exceedingly low-yield species such as superheavy element ions.