Precision measurement of $^{\mathbf{210}}$Bi $\beta$-spectrum

TL;DR

This study precisely measured the beta spectrum of $^{210}$Bi using a Si(Li) detector, providing detailed form-factor data crucial for low-background physics involving $^{210}$Pb.

Contribution

First detailed measurement of the $^{210}$Bi beta spectrum shape with high precision, improving understanding of its form-factor for low-background physics applications.

Findings

Transition form-factor deviates significantly from unity.

Measured form-factor parameters are in good agreement with previous studies.

Parameter precision has been significantly improved.

Abstract

The precision measurement of the $\beta-$spectrum shape for $^{210}$Bi (historically RaE) have been performed with a spectrometer based on semiconductor Si(Li) detector. This first forbidden non-unique transition has the transition form-factor strongly deviated from unity and knowledge of its spectrum would play an important role in low-background physics in presence of $^{210}$Pb background. The measured transition form-factor could be approximated as $S(W) = 1 + (-0.4363 \pm 0.0037) W + (0.0523 \pm 0.0010) W^2$, that is in good agreement with previous studies and has significantly increased parameter precision.