LOW-BACKGROUND COUNTING SYSTEMS COMPARED

A comparison of special low-background germanium counting systems used at the Pacific Northwest Laboratory will be presented. These vary from specially modified instruments in the laboratory to low-cosmic-exposure detectors operated deep underground. The underground detectors have copper cryostats completely electro formed from low-background copper. Electroforming is a process analogous to zone refining in its ability to remove chemical impurities. Shielding techniques and their merit are compared as to difficulty and benefit. Active cosmic veto is directly compared to passive overburden shielding. Special attention is paid to cosmic activation of the cryostat and the germanium crystal itself.