The BiPo-3 detector for the measurement of ultra low natural radioactivities of thin materials

TL;DR

The BiPo-3 detector, operational since 2013 at LSC, measures ultra low natural radioactivity in thin materials, crucial for the SuperNEMO experiment's radiopurity assessment, demonstrating high sensitivity and validated performance.

Contribution

This paper presents the design, performance, and validation of the BiPo-3 detector for measuring ultra low radioactivity in thin materials, specifically for SuperNEMO's selenium foils.

Findings

Achieved sensitivity of <2 μBq/kg for $^{208}$Tl

Achieved sensitivity of <140 μBq/kg for $^{214}$Bi

Validated measurement accuracy with calibrated aluminium foil

Abstract

The BiPo-3 detector, running in the Canfranc Underground Laboratory (Laboratorio Subterr\'aneo de Canfranc, LSC, Spain) since 2013, is a low-radioactivity detector dedicated to measuring ultra low natural radionuclide contaminations of $^{208}$Tl ($^{232}$Th chain) and $^{214}$Bi ($^{238}$U chain) in thin materials. The total sensitive surface area of the detector is 3.6 m$^2$. The detector has been developed to measure radiopurity of the selenium double $\beta$-decay source foils of the SuperNEMO experiment. In this paper the design and performance of the detector, and results of the background measurements in $^{208}$Tl and $^{214}$Bi, are presented, and validation of the BiPo-3 measurement with a calibrated aluminium foil is discussed. Results of the $^{208}$Tl and $^{214}$Bi activity measurements of the first enriched $^{82}$Se foils of the double $\beta$-decay SuperNEMO experiment are reported. The sensitivity of the BiPo-3 detector for the measurement of the SuperNEMO $^{82}$Se foils is $\mathcal{A}$($^{208}$Tl) $<2$ $\mu$Bq/kg (90\% C.L.) and $\mathcal{A}$($^{214}$Bi) $<140$ $\mu$Bq/kg (90\% C.L.) after 6 months of measurement.