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

• Established metrology facility for accelerator-produced short-lived activities.
• Measured half-lives and beta branching ratios to high precision.
• Precision is 0.03% for half-lives and ~0.1% for branching ratios.
• Results have important impact on electroweak Standard Model.

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, GV. If many such transitions are measured, then the constancy of GV 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.