Spectral shape study of210Bi forbidden beta decay using PbMoO4 cryogenic detectors

초록

The spectrum-shape method has been proposed to determine the effective value of the axial-vector coupling constant, g<inf>A</inf> in forbidden non-unique β decays.210Bi is an isotope of first-forbidden non-unique beta decay, the shape function of which strongly depends on the g<inf>A</inf> value. Due to the short half-life of the210Bi, the210Pb (β, 22.3 y) →210Bi (β, 5.0 d) →210Po (α, 138 d) decay chain has been adopted by using PbMoO<inf>4</inf> crystals. We prepared a detection system with two PbMoO<inf>4</inf> crystals in the same crystal dimensions. One PbMoO<inf>4</inf> contains a modern lead and the210Pb radioactivity was measured about 30 Bq/kg. The other PbMoO<inf>4</inf> crystal consist of an archeological lead with low210Pb radioactivity of about 0.2 Bq/kg, which has been used to subtract the external backgrounds. This detection method with the two crystals has shown a good agreement with a previous beta spectrum study of210Bi. © 2025 American Institute of Physics Inc.. All rights reserved.