Speaker
Description
Precise knowledge of forbidden transition beta-spectra plays a significant role in both nuclear and particle physics.
In this work we present a precision measurement of the beta-spectrum shape for $^{210}$Bi (historically RaE) performed with spectrometers based on semiconductor Si(Li) detectors. 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 studies were performed with spectrometers in target-detector and 4-$\pi$ geometries. The measured transition form-factor could be approximated as $H(W) = 1 + (-0.433 \pm 0.002) W + (0.0510 \pm 0.0004) W^2 $ and $H(W) = 1 + (-0.433 \pm 0.002) W + (0.0510 \pm 0.0004) W^2 $ for the target-detector and 4-$\pi$ spectrometer respectively that is in good agreement between the two experiments as well as with the previous studies. The form-factor parameter precision has been substantially increased with respect to the previous experimental results. This work was supported by the Russian Foundation for Basic Research (project nos. 16-29-13014 and 19-02-00097).
