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.
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 efficiencies
1
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 Streamline systems, the detector capsule is 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 or an integrated cryocooling system (ICS). A
cryostat or ICS 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 III or
ICS-P4 mechanical cooling systems.
Certain cryostat configurations are available only as PopTop and others are available only as Streamline.
Fig. 1. Configuration of GEM Coaxial Germanium
Crystal.
1
By 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 Radiation,” ANSI/IEEE Standard 325-1986.
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