Shielding underground detectors

The detector was placed deep underground to shield against cosmic ray background reactions. 

Figure 1 Schematic drawing of the underground HPGe-detector and the Pb/Cu shield together with Marinelli beaker.

Table 1 List of background y-ray peaks for the underground HPGe-detector before (2003) and after (2005) the installation of the new endcap as well as with mercury shield (2006-...

The relative count rates, expressed in counts per day per kilogram of germanium, of various detectors of the CELLAR network are also plotted on Figure 13.17 for comparison. Count rates are plotted relative to an estimated count rate at ground level without shielding. (CELLAR is a pseudo-acronym for a collaboration of European Low-Level underground laboratories.) The deepest laboratory, LSCE, at Mondane in France, is at 4800 m w.e. 

Active shields in the form of veto detectors are undoubtedly worthwhile above ground and down to a depth of about 100 m w.e. underground. The plastic scintillator veto detector shielding the lAEA-MEL detectors (Povinec et al (2004)) installed at a depth of 35 m w.e. and referred to above, reduces the backgrounds to a level equivalent to 250 m w.e. depth. Reduction factors are between 4 and 11 for the various detectors. However, as depth increases the improvement is less. Above ground improvements of factors of 4 to 10 are achievable. At 500 m w.e., there might be only a 40 % reduction in background and only a few percent at 3000 m w.e. 

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