Ultra-low background germanium assay at the Boulby Underground Laboratory

As we move to an era where next generation ultra-low background particle physics experiments begin to be designed and constructed, the ability to assay materials with high sensitivity and at speed with a variety of techniques will be key. This paper describes the Mirion Technologies (Canberra) specialty ultra-low background detectors installed and commissioned at the Boulby Underground Laboratory between 2017 and 2021. The low background levels of the detectors combine with low background shielding and a radon-reduced dry nitrogen purge system to give sensitivity approaching the best in the world without the need for intricate shielding solutions. For an optimised sample geometry, run for 100 d, it would be possible to reach close to 10 μBq kg-1 (10-12 g/g) for background radionuclides of interest in neutrinoless double-beta decay.