Speaker
Description
The spectrum-shape method has been proposed to determine the effective value of the axial-vector coupling constant (g$_A$) with the vector coupling constant (g$_v$=1) in forbidden nonunique beta decays. $^{210}$Bi is an isotope undergoing a first-forbidden nonunique beta decay, and its shape function exhibits strong sensitivity to g$_A$.
Given the short half-life of $^{210}$Bi, the decay chain $^{210}$Pb ($\beta$, T$_{1/2}$=22.3 y) $\rightarrow$ $^{210}$Bi ($\beta$, T$_{1/2}$=5.0 d) $\rightarrow$ $^{210}$Po ($\alpha$, T$_{1/2}$=138 d) was utilized. PbMoO$_4$ cryogenic detectors were employed for their high detection efficiency (source = detector configuration) and excellent energy resolution. Two detectors of identical geometric design and crystal size (1 cm$^3$) were prepared. One PbMoO$_4$ crystal was grown using modern lead, yielding a $^{210}$Pb radioactivity of about 30 Bq/kg. The second PbMoO$_4$ crystal was made with archaeological lead, characterized by significantly reduced $^{210}$Pb radioactivity (about 0.2 Bq/kg), enabling background rejection with minimal systematic error. Both detectors were installed adjacently in a cryogen-free dilution refrigerator.
This presentation will outline the detection system's design and performance and present preliminary beta decay spectrum analysis results.
