GEM0 pages

ORTEC®
GEM Series Coaxial HPGe Detector
Product Configuration Guide
P-type Coaxial HPGe Detectors for High Performance
Gamma Spectroscopy in the Energy Range of ~40 kev
and Up.
The majority of gamma spectroscopy applications such as those found in
counting laboratories involve the energy range ~40 keV upward. ORTEC GEM
and Profile Series GEM detectors are designed to cover this energy range. The
Profile GEM-FX Series extends this lower energy cut off to 10 keV and above. (A
separate guide is available for the Profile GEM Series.)
All GEM Series feature:
• Efficiencies to 150%, higher on request.
• Excellent energy resolution and peak symmetry..
• Specified crystal dimensions in Profile models.
• SMART bias options.
• Harsh Environment (-HE) option.
• Low-background carbon fiber endcap options.
• PLUS preamplifier option for ultra-high-rate applications.
• Huge configuration flexibility: PopTop, Streamline and mechanically cooled
options.
ORTEC offers GEM Series HPGe detectors with relative efficiencies1 from 10% to
150% and beyond. The detectors are manufactured from ORTEC-grown
germanium crystals processed in our advanced manufacturing facility in Oak
Ridge, TN. The detectors are fabricated from P-type germanium with an outer
contact of diffused Li and an inner contact of ion-implanted boron.
ORTEC maintains a large stocklist of GEM detectors. Some of these have "super
specifications," that is, a warranted energy resolution better than the usual GEM
warranted specifications.
The Following Specifications are Provided for each GEM Detector
• Energy resolution full-width half-maximum (FWHM) at 1.33-MeV and optimum shaping time.
• Relative Photopeak efficiency at 1.33 MeV.
• Peak-to-Compton ratio at 1.33 MeV.
• Peak shape ratio for the full-width tenth-maximum to the full-width half-maximum at 1.33 MeV.
• Energy resolution at 122 keV at optimum shaping time.
Configuration Guidelines
PopTop or Streamline (non-PopTop) Configuration
The essence of a PopTop detector system is that the HPGe detector element cryostat, preamplifier, and high voltage filter are housed
in a detector “capsule” which is then attached to an appropriate cryostat (Figure 2.)
In so called Streamline systems, the detector capsule in NOT demountable. Detector capsule and cryostat share the same vacuum. In
configuration terms, this requires a cryostat or cryostat/dewar selection with the cryostat having a matching diameter to the capsule
endcap. A cryostat must always be ordered with a Streamline capsule, because they are integral.
The actual PopTop capsule has its own vacuum. It can be mounted on any of the available cryostats, cryostat/dewar combinations, or
the X-COOLER II mechanical cooling system.
Fig. 1. Configuration of GEM Coaxial
Germanium Crystal.
1By convention, HPGe detectors are characterized by “relative efficiency”. Relative efficiency is defined as the efficiency of a point Co-60 source at 25
cm from the face of a standard 3-inch x 3-inch right circular cylinder NaI(Tl) detector. “IEEE Test Procedures for Germanium Detectors for Ionizing
Radiatio,” ANSI/IEEE Standard 325-1986.