Mirion has years of experience in building custom low-background detectors for low level gamma spectroscopy. The most important features of these custom detectors have been incorporated into standardized cryostat designs which can be produced quickly and economically and which produce predictable results. There are two basic Ultra Low-Background cryostat designs available, a vertical dipstick and a U-style™ integral. Both have the following design and construction features in common:
- Low background materials are used for detector chamber, holder, and internal hardware.
- Design offsets are used to allow the use of shielding materials between the detector element and hotter materials such as the preamplifier and adsorber (molecular sieves).
- Direct streaming paths for external (to shield) sources of radiation are eliminated.
- Materials having high cross-section for cosmic neutrons are avoided in construction.
- Designs do not compromise ease of use or long-term reliability.
Among the select materials used in ULB cryostats are the following:
- Aluminum - 99.999% pure with guaranteed thorium and uranium less than 1 ppb.
- Copper - 99.99% pure (better than standard OFHC grade).
- Stainless Steel - selected low Co-60 content.
- Composite Carbon - Virtually zero background substitute for Be in low energy and wide range detectors.