α-decay-correlated mass measurement of 206,207g,mRa using an α-TOF detector equipped multireflection time-of-flight mass spectrograph system

Abstract

The atomic masses of the isotopes Ra-206,Ra-207 have been measured via decay-correlated mass spectroscopy using a multireflection time-of-flight mass spectrograph equipped with an alpha-TOF detector. The Ra isotopes were produced as fusion-evaporation products in the V-51 + Tb-159 reaction system and delivered by the gas-filled recoil ion separator GARIS-II at RIKEN. The alpha-TOF detector provides for high-accuracy mass measurements by correlating time-of-flight signals with subsequent alpha-decay events. The masses of Ra-206 and (207)g,mRa were directly measured using a multireflection time-of-flight mass spectrograph equipped with an alpha-TOF detector. The mass excesses of (206,207)gRa and the excitation energy of Ra-207m were determined to be ME = 3540(50) keV/c(2), 3538(15) keV/c(2), and Eex = 552(42) keV, respectively. The alpha-decay branching ratio of 207mRa, b alpha = 0.26(20), was directly determined from decay-correlated time-of-flight signals, and the reduced alpha width of (207)mRa was calculated to be 82 = 43+68 -34 keV from the branching ratio. The spin-parity of (207)mRa was confirmed to be J(pi) = 13/2(-) from decay correlated mass measurement results.