The BiPo detector for ultralow radioactivity measurements

TL;DR

The paper presents the development and initial results of the BiPo-1 detector for ultra-low radioactivity measurements, demonstrating its capability to measure radiopurity levels relevant for double beta decay experiments.

Contribution

It introduces the BiPo-1 detector prototype and reports its successful measurement of surface radiopurity of scintillators, paving the way for the larger BiPo3 detector for SuperNEMO.

Findings

Measured surface activity of scintillators: 1.5 μBq/m² for 208Tl

BiPo-1's background level enables future larger detector sensitivity

Projected BiPo3 detector will achieve required radiopurity qualification in six months

Abstract

The development of BiPo detectors is dedicated to the measurement of extremely high radiopurity in 208Tl and 214Bi for the SuperNEMO double beta decay source foils. A modular prototype, called BiPo-1, with 0.8 m2 of sensitive surface area, has been running in the Modane Underground Laboratory since February, 2008. The goal of BiPo-1 is to measure the different components of the background and in particular the surface radiopurity of the plastic scintillators that make up the detector. The first phase of data collection has been dedicated to the measurement of the radiopurity in 208Tl. After more than one year of background measurement, a surface activity of the scintillators of A(208Tl) = 1.5 \muBq/m2 is reported here. Given this level of background, a larger BiPo3 detector having 3.25 m2 of active surface area, will able to qualify the radiopurity of the SuperNEMO selenium double beta decay foils with the required sensitivity of A(208Tl) < 3-4 \mu Bq/kg (90% C.L.) with a six month measurement. This detector is actually under construction and will be installed in the Canfranc Underground Laboratory mid 2011.