Screening cargo to detect nuclear materials at ports, airports, train terminals and other critical installations is one of
the major challenges facing the US Department of Homeland Security and similar organizations worldwide. An
effective method of identifying hidden radioactive materials is the detection of Gamma rays transmitted through the
cargo container. Accurate detection and identification can be only achieved using cryogenically- cooled High Purity
Germanium (HPGe) detectors. A Portal detection system developed and manufactured by ORTEC Corporation
contains several such cryogenically cooled sensors (see Fig 1).
This paper presents the main design considerations for selection of a cryo cooler for this application where long life,
reliability, operation over extreme outdoor temperatures and with a low vibration signature are the main technical
drivers. The paper further discusses the different cooling alternatives and the technical challenges of achieving a
minimal foot print and interchangeability.