-decay-correlated mass measurement of Ra using an -TOF detector equipped multireflection time-of-flight mass spectrograph system

Niwase, Toshitaka*; Ito, Yuta   ; 26 of others*

The atomic masses of the isotopes 206,207Ra have been measured via decay-correlated mass spectroscopy using a multireflection time-of-flight mass spectrograph equipped with an -TOF detector. The Ra isotopes were produced as fusion-evaporation products in the 51V+159Tb reaction system and delivered by the gas-filled recoil ion separator GARIS-II at RIKEN. The -TOF detector provides for high-accuracy mass measurements by correlating time-of-flight signals with subsequent -decay events. The masses of 206Ra and 207g,mRa were directly measured using a multireflection time-of-flight mass spectrograph equipped with an -TOF detector. The mass excesses of 206,207gRa and the excitation energy of 207mRa were determined to be ME=3540(50)keV/c, 3538(15)keV/c, and Eex=552(42) keV, respectively. The -decay branching ratio of 207mRa =0.26(20), was directly determined from decay-correlated time-of-flight signals, and the reduced width of 207mRa was calculated to be =43 keV from the branching ratio. The spin-parity of 207mRa was confirmed to be J=13/2 from decay correlated mass measurement results.