High-precision measurement of $^{215}$Po half-life via delayed-coincidence analysis

TL;DR

This study delivers a high-precision measurement of the $^{215}$Po half-life by exploiting a delayed-coincidence analysis of the $^{219}$Rn → $^{215}$Po → $^{211}$Pb alpha-decay chain within a LaBr$_{3}$ detector containing intrinsic $^{227}$Ac contamination. The experiment, conducted in the Gran Sasso Underground Laboratory, achieves high statistics and a careful systematic assessment, using optimized energy windows, a Poisson likelihood fit to the time-difference distribution, and extensive toy-data studies to validate the fit. The result, $T_{1/2}=1.77804\,\pm0.00091$ (stat) $\pm0.00067$ (syst) ms, represents the most precise determination to date and substantially improves the previous precision, with systematic sources well quantified. The approach confirms the viability of intrinsic contamination-based delayed-coincidence methods for precision measurements of short-lived alpha decays and can be extended to other nuclei.

Abstract

We performed a high-precision study of the $^{215}$ Po $α$-decay using a LaBr$_3$ scintillating detector in a low-background environment. The $^{227}$Ac intrinsic contamination in the LaBr$_3$ crystal undergoes a decay chain, producing the intermediate pair of $^{219}$Rn$\rightarrow^{215}$Po$\rightarrow^{211}$Pb decays. The fast time response and good energy resolution of the detector allow for extracting the short half-life of $^{215}$Po from the time correlation of the two subsequent $α$-decays by using the delayed coincidence method. Thanks to high statistics and a comprehensive uncertainty assessment, we obtain the most precise half-life value to date of $^{215}$Po, corresponding to $1.77804\pm0.00091$(stat.)$\pm0.00067$(syst.) ms.

Figures (3)

• Figure 1: Physics energy spectrum measured for 23.5$\,$days with basic cuts applied. A high energy threshold of around 1200$\,$keV was applied during the acquisition. The most prominent peak at around 1460$\,$keV is from $^{40}$K contamination. The $\alpha$ events lie in separate peaks at higher energies, corresponding to the decay of $^{227}$Ac and its progeny.
• Figure 2: $\Delta t$ distribution with the exponential fit plus a constant background to determine the half-life $T_{1/2}$.
• Figure 3: Half-life values taken from Ref. Takacs:2023bie as a function of publication year. The black circular points represent the previous published results. The red square indicates the value obtained in this work, with the error bar hidden by the marker. The weighted mean is calculated by using the method described in Ref. rajput1992techniques. The uncertainties associated with the weighted mean are shown in the shaded area.