Other Electronics

In reply to a nzoomed's question on radmon.org: Im wanting to build an outdoor monitoring station with an SBM20 and not sure if its good to use a PVC pipe to place the tube inside? Obviously im wanting something as thin as possible to let as many particles through as possible. Are there some materials I should avoid? Are beta particles typically encountered much in the environment? Should I only be worried about cosmic rays? Im not sure how much background radiation is from other sources, but im expecting there is a great deal from alpha decay from the likes of radon etc which will never be