Radiation shielding for underground low-background experiments
  The design task of creating an efficient radiation shield for the new COBRA double-beta decay experiment led to a comprehensive study of commercially available shielding materials. The aim was to find the most efficient combination of materials under the constraints of an extreme low-background experiment operating in a typical underground laboratory. All existing shield configurations for this type of experiment have been found to perform sub-optimally in comparison to the class of multilayered configurations proposed in this study. The method used here to create a specific shield configuration should yield a close to optimal result when applied to any experiment utilising a radiation shield. In particular, the survey of single material response to a given radiation source turns out to give a guideline for the construction of efficient multilayer shields. 
D.Y Stewart, P.F. Harrison, B. Morgan, Y.A. Ramachers