Low-Background Materials

PGT offers a variety of low-background materials, as shown in the Table below. When incorporated into the low-background cryostat designs, with or without a lead radiation chamber, background radiation is significantly reduced.

In selecting a low-background system, there are some general factors that should be considered:

An external preamplifier is generally better than an in-line preamp, because the naturally occurring residual radioactive materials found in the circuit board are not in direct "line-of-sight" with the detector.

the molecular sieve getter, which may have a slightly higher residual radioactivity than charcoal, is significantly more effective in adsorbing contaminants and maintaining the vacuum. the NPR cryostat, with or without a shield, is a better way to keep the getter from shining on the detector.

PGT recommends the low-background beryllium entrance window, rather than magnesium, because the latter is  much more readily corroded. A Vespel window is also available. For the same window thickness, Vespel has a lower energy transmission (~10% at the 14.4 keV line of Co57); however, it is less costly.

If you are ordering a new detector with no restrictions (spatial constraints, e.g.), the following suggestions, in order, would result in increasingly low background counts:

• NPR cryostat, preferably with an external preamp, and
• A lead shield
• Replace the endcap and internal metal parts with OFHC copper or low-background aluminum (more expensive)
• Use low-background beryllium or Vespel window for lower energy spectroscopy
• If you must have a dipstick cryostat, consider the following:
• Lead shield
• lnternal shield between the back of the cryostat and the preamp and dewar. Copper-clad lead is preferable, but tungsten is more compact; therefore, the choice may depend on how much space is available.