If the answer is yes , then a Low-, Extra-Low-, or Very-Low-background detector  is needed to achieve detection limits. It can be provided in a wide choice of configurations.

If the answer is no, consider this next: Will the count rates of the peaks to be quantified be comparable with the Compton background counts created by the radioactive isotopes that are present at low levels in a standard cryostat? If the answer to this question is yes, observe the spectra (taken on 55% efficiency detectors — one low-background, one standard). This is an example of the reduction in background count rate that can be achieved with a low-background cryostat.

The low-background cryostat is substantially better than the standard one for energies below ~500 keV, somewhat better between 500 and 1500 keV, and little better above that. If your peaks of interest are below 500 keV, you should invest next in a low-background cryostat. Between 500 and 1500 keV, the low-background cryostat may help to lower the MDA, but the same amount of investment in a higher-efficiency detector will produce about the same MDA improvement. (Obtaining both the low-background cryostat and the high-efficiency detector will produce the best possible results.) For measurements of lines at energies above 1500 keV, a low-background cryostat is of little value.

There are two popular cryostat configurations often chosen for ultra-low MDA. They are (a) the J configuration, which makes it possible to shield the dewar, much of the cryostat, and the cryosorption material from the detector element, and (b) the HJ configuration, which, in addition, allows the preamplifier to be shielded from the detector element. These are available at modest additional cost in "streamline" (non-PopTop) cryostats.

Applications that have count rates sufficiently high that the total of background counts from all sources is insignificant need neither special shielding nor a low-background detector. However, if high sample throughput and low MDA must be obtained for low-level samples, the contribution from background radiation (the outside world and the cryostat) is of definite concern.

A good quality, low-background lead shield (containing ~4 inches of low-radiogenic lead) that will accommodate the detector is essential.

Graded Shielding