UK low-background infrastructure for delivering SuperNEMO

TL;DR

This paper describes the development of low-background detection facilities in the UK, including gamma spectroscopy and radon measurement systems, to support the SuperNEMO experiment's stringent purity requirements for neutrinoless double beta decay detection.

Contribution

It introduces new low-background measurement infrastructure, including a radon concentration line, to improve material screening for the SuperNEMO experiment.

Findings

First results from UK HPGe detectors for material screening.

Radon levels in samples measured down to 10 μBq/m3.

Successful commissioning of the Radon Concentration Line.

Abstract

SuperNEMO is a next generation neutrinoless double beta decay experiment with a design capability to reach a half-life sensitivity of $10^{26}$ years corresponding to an effective Majorana neutrino mass of $\langle m_{\beta\beta} \rangle$ $<$ 50 - 100 meV. To achieve this sensitivity, stringent radio-purity requirements are imposed resulting in an equally stringent screening programme. Dedicated facilities have been established in the UK for screening and selection of detector construction materials. Gamma ray spectroscopy using high-purity germanium (HPGe) detectors has been the standard method for the measurement of material contamination. A low-background facility has been established at Boulby Underground Laboratory. The first results from the 2 current HPGe detector are shown. Radon is one of the most critical backgrounds for SuperNEMO and most other low background experiments. It can enter the detector either through diffusion, contamination during construction or emanation from the detector materials resulting in radioactive daughter isotopes. To reach the target sensitivity, the $^{222}$Rn concentration inside the SuperNEMO tracker volume must be less than 150 $\mu$Bq/m3. A "Radon Concentration Line" (RnCL) was developed to be used in conjunction with a state-of-the-art radon detector to make a more sensitive measurement of large gas volumes. This apparatus has now been commissioned and is capable of measuring radon levels in large samples down to 10 $\mu$Bq/m3. The results from first measurements of radon content using the RnCL are presented. These measurements include gas bottles, boil-off nitrogen and a SuperNEMO sub-module during the early stages of construction.