Alpha-decay-correlated mass measurement of 206,207Ra using an $\hat{I}\pm$-TOF detector equipped MRTOF-MS system

Abstract

The atomic masses of the isotopes ${}^{206,207}$Ra have been measured via decay-correlated mass spectroscopy using a multi-reflection time-of-flight mass spectrograph equipped with an $\hat{I}\pm$-TOF detector. The Ra isotopes were produced as fusion-evaporation products in the ${}^{51}$V+${}^{159}$Tb reaction system and delivered by the gas-filled recoil ion separator GARIS-II at RIKEN. The $\hat{I}\pm$-TOF detector provides for high-accuracy mass measurements by correlating time-of-flight signals with subsequent $\hat{I}\pm$-decay events. The masses of ${}^{206}$Ra and ${}^{207g,m}$Ra were directly measured using a multi-reflection time-of-flight mass spectrograph equipped with an $\hat{I}\pm$-TOF detector. A mass excess of ME = 3538(15) keV/c${}^2$ and an excitation energy of E${}_{\mathrm{ex}}$ = 552(42) keV were determined. The $\hat{I}\pm$-decay branching ratio of ${}^{207m}$Ra, b$\hat{I}\pm$ = 0.26(20), was directly determined from decay-correlated time-of-flight signals, and the reduced alpha width of ${}^{207m}$Ra was calculated to be $\hat{I}{´}^2$ = 50+62-41 keV from the branching ratio. The spin-parity of ${}^{207m}$Ra was confirmed to be $J^{\ddot{I}}€$ = 13/2${}^{-}$ from decay correlated mass measurement results.