FT values measured to ±0.1 for superallowed beta transitions: Metrology at sub-second time scales

摘要

Because of angular-momentum conservation, superallowed β decay between 0~+ analog states involves only the vector part of the weak interaction, so its measured ft value can be used to determine the vector coupling constant, G_V. If many such transitions are measured, then the constancy of G_V can be established and several important tests made on fundamentals of the electroweak Standard Model. We have developed apparatus that allows us to measure half-lives to ±0.03% and branching ratios to ±0.1% or better, for cyclotron-produced activities with half-lives as short as 100 ms. We present an overview of the equipment and a summary of more than 10 years of results.