Search

Over the past few decades, the scale and mass of rare-event search experiments have increased by several orders of magnitude. To maintain background-free large fiducial-volume searches, the radiopurity requirements of the materials from which these devices are constructed have improved by similar factors. High-purity germanium spectroscopy has long-been the workhorse of material screening and selection, providing information on trace radioactive gamma-ray-emitting impurities in the bulk of materials. The next generation of direct dark matter and neutrinoless double beta decay experiments demand the development of additional assay techniques to provide a more complete understanding of the full uranium (U) and thorium (Th) decay chains, including knowledge of alpha-emitting surface depositions. In this proceeding I highlight the challenging radiopurity requirements for the next generation of rare-event search experiments, as well as the extensive UK-based material-assay infrastructure in place to address these demands. Where requirements exceed current capability, additional R&D is needed. I will summarise where this R&D is already underway across the UK. [ABSTRACT FROM AUTHOR]

The SuperNEMO experiment aims to search for the neutrinoless double beta decay (0νββ) to T1/2 (0ν) > 1026 years, this corresponds to an effective neutrino mass of 50-100 meV. The extremely rare event rate means the minimisation of background is of critical concern. The stringent strategy instigated to ensure detector radiopurity is outlined here for all construction materials. In particular the large R&D programme undertaken to reach the challengingly low level of radon, < 0.15 mBq/m³, required inside the SuperNEMO gaseous tracker will be detailed. This includes an experiment designed to measure radon diffusion through various materials. A "Radon Concentration Line" (RnCL) was developed to be used in conjunction with a state-of-the-art radon detector in order to achieve world leading sensitivity to 222Rn content in large gas volumes at the level of a few μBq/m³. A radon purification system was developed and installed which has demonstrated radon suppression by several orders of magnitude depending on the carrier gas. This apparatus has now been commissioned and measurements of cylindered gas have been made to confirm radon suppression by a factor 20 when using nitrogen as the carrier gas. The results from measurements of radon content in various gases, used inside SuperNEMO, using the RnCL will be presented. [ABSTRACT FROM AUTHOR]