Lead castles are passively contributing to the detectors low-backround level by protecting them from ambiant radioactivity. The outer part is made from low activity lead (LA : < 100 Bq/ kg) while the castle core is made from very low activity (VLA : < 50 Bq/ kg) selected lead. Such a design ensures a very low signal contribution from the lead castles to the detectors.
These 4 lead castles were specifically designed and made in northern France, at Gentilly’s foundries. Their thickness is 24 cm for a total mass of more than 2 tons: 1 cm plexiglas, 3 cm OFHC copper (from Carlier SA, certified 99.96% oxygen free high-conductivity; ISO designation Cu-OFE), 5 cm of VLA lead and 15 cm of LA lead. The lead castles were designed to minimise the air volume surrounding the detectors.
They were integrated into a cutsom-made autosampler. Opening is automated and controlled by jacks.
The lead castle of this detector supplied by Ortec-Ametek is 19 cm thick : 4 cm of ultra pure copper and 15 cm of VLA lead.