Alpha-decay-correlated mass measurement of 206,207Ra using an $\alpha$-TOF detector equipped MRTOF-MS system

TL;DR

This study measured the atomic masses of $^{206,207}$Ra isotopes using decay-correlated mass spectroscopy with an $ ext{α}$-TOF detector and MRTOF-MS, providing precise mass, excitation energy, and decay properties.

Contribution

The paper introduces a novel decay-correlated mass measurement method combining an $ ext{α}$-TOF detector with MRTOF-MS for high-accuracy isotope mass determination.

Findings

Mass excess of $^{206}$Ra measured as 3538(15) keV/c$^2$

Excitation energy of $^{207}$Ra determined as 552(42) keV

Decay branching ratio of $^{207m}$Ra found to be 0.26(20)

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 $\alpha$-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 $\alpha$-TOF detector provides for high-accuracy mass measurements by correlating time-of-flight signals with subsequent $\alpha$-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 $\alpha$-TOF detector. A mass excess of ME = 3538(15) keV/c$^2$ and an excitation energy of E$_{\rm ex}$ = 552(42) keV were determined. The $\alpha$-decay branching ratio of $^{207m}$Ra, b$\alpha$ = 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 $\delta^2$ = 50+62-41 keV from the branching ratio. The spin-parity of $^{207m}$Ra was confirmed to be $J^\pi$ = 13/2$^-$ from decay correlated mass measurement results.