Detecting radioactive material with the greatest detection efficiency and resolution is realized with Germanium-based gamma-ray detectors. To attain the resolution, Ge semiconductors must be cooled to ~100K under vacuum. In laboratory spectroscopy this is accomplished through the use of liquid nitrogen which makes the detector stationary—too large and heavy for field use. Cooling is also accomplished in portable systems through electromechanical methods making the detector smaller and lighter, but can take 12 hours or more to attain the required temperature.


LLNL has developed a radiation detector that cools to operating temperatures in 1-2 hours using two separate cooling stages. The first cooling brings the instrument to operating temperature. The embedded second cooling system achieves portable detection that can be sustained for 8-12 hours.

In addition, an integrated, hermetically-sealed package has been developed complete with user interface, shock mounting, LCD display, and a USB port for communication to a PC. The display is run by an embedded processor and shows spectroscopy, isotope identification, system health and status as well as other features. The entire packaged system weighs 10.1 lbs including batteries.

The integrated GeMini system has undergone extensive field testing and is at a Technical Readiness Level (TRL) of 5.


  • Fast Cooling—the instrument can be cooled to operating temperatures in 1-2 hours!
  • Lightweight—the cooling and Ge detector components weigh 3.5 lbs.
  • Low Power Consumption—the portable instrument has a lifetime of 8-12 hours.
  • Wide Energy Range Detection—30 keV to 3 MeV
  • High Resolution—2.5 keV fwhm at 1332 keV
Potential Applications

Hand-held radiation detectors are essential in identifying illicit radioactive materials. The fast-cooling of the LLNL detection system allows for nearly immediate inspections of suspicious areas.

Development Status

LLNL inventors have developed and are testing a prototype. U. S. Patent 7,732,781, "Hand-held, Mechanically-Cooled, Radiation Detection System, for Gamma-Ray Spectroscopy".

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