A novel method for the measurement of half-lives and decay branching ratios of exotic nuclei

Abstract

A novel method for simultaneous measurement of masses, Q-values, isomer excitation energies, half-lives and decay branching ratios of exotic nuclei has been demonstrated. The method includes first use of a stopping cell as an ion trap, combining storage of mother and daughter nuclides for variable durations in a cryogenic stopping cell (CSC), and afterwards the identification and counting of them by a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). We utilized our method to record the decay and growth of the ²¹⁶Po and²¹²Pb isotopes (alpha decay) and of the ^119m2Sb isomer (<em>t</em>_1/2=850&plusmn;90 ms) and ^119gSb isotope (isomer transition), obtaining half-lives consistent with literature values. The amount of non-nuclear-decay losses in the CSC up to &sim;10 s is negligible, which exhibits its extraordinary cleanliness. For ¹¹⁹Sb isotopes, we present the first direct measurements of the mass of its ground state, and the excitation energy and decay branching ratios of its second isomeric state (^119m2Sb). This resolves discrepancies in previous excitation energy data, and is the first direct evidence that the ^119m2Sb isomer decays dominantly via &gamma; emission. These results pave the way for the measurement of branching ratios of exotic nuclei.