PROFILE Series GEM HPGe Coaxial Detectors   
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• "Application-Matched" P-type HPGe Detectors, optimized for specific sample types, gamma energy ranges and measurement geometries.
• Range now includes "FX" series
• Know how your new HPGe detector will perform before you buy it!
• Best absolute efficiency for the given IEEE standard relative efficiency in your counting geometry.
• Warranted Crystal Dimensions ensure measurement performance.
• Reproducible dimensions mean reproducible performance. . . no surprises.
• Full range of PopTop Cryostats and options (contact factory for -Plus options).

PROFILE GEM detectors are a first in germanium detectors; a range of detectors from which you can choose the best solution for your application from specified crystal dimensions. They are available in 2 series of endcap sizes. Nominal relative efficiency specifications are provided in order to help relate relative efficiency to terms of crystal dimensions. The resolution is measured according to the IEEE standard. If a particular PROFILE series detector is available from the ORTEC detector stocklist, then the ACTUAL MEASURED specifications may be inspected before purchase.

PROFILE Series GEM Germanium Detector Selection Guide

F-Series PROFILE GEM Detectors
F-Series PROFILE detectors employ "over-square" (diameter > length) coaxial structures. For a given relative (IEEE) efficiency, the F-Series represents the "best use" of the germanium material in terms of producing the maximum absolute counting efficiency for on-endcap or "close geometry" extended samples, such as:

• Point sources on-endcap
• Filter Paper Samples on-endcap
• Samples presented in bottles and pots on-endcap
• Bio-Assay applications (e.g., lung monitoring)
• Waste Drum monitoring

In addition, the over-square geometry helps improve low-energy resolution by reduced crystal capacitance.

FX-Series PROFILE GEM Detectors

• All the advantages of the F-Series PROFILE detector with an ULTRA-thin Entrance Window.
• Excellent warranted performance specifications

FX-Series PROFILE GEM detectors employ a proprietary thin entrance window in order to improve low energy efficiency. The FX-series can extend the useful energy range down to 10 keV and below, which maintains the excellent peak shape and resolution characteristics of the PROFILE series.

Figure 1 shows absolute efficiency curves for a 70 mm diameter x 15 mm thick source on endcap for an 85 mm diameter GEM-FX8530, compared to a GEM80 76 mm diameter x 87 mm depth.¹ Note the much higher absolute efficiency of the FX85 at all energies below 160 keV. At 59 keV, the FX is SIX times more efficient, and below that the efficiency of the GEM80 falls off due to the thick (~700 µm) contact. The FX detector has an ultra thin contact (~10 µm Ge) allowing good transmission at 22 keV and below.

Figure 2 shows similar spectra from the three detectors compared, in the energy range up to ~130 keV. From the top they are the GEM-FX8530, a GMX40 and a GEM80. The spectra are taken from a mixed isotope calibration source. In all cases, the cursor is centered on the 59 keV ²⁴¹Am peak. To the right is the 88 keV peak from ¹⁰⁹Cd.In both the GEM-FX and the GMX, the thin entrance window clearly transmits the low-energy gammas in the 22–24 keV region. These peaks are entirely absent from the spectrum of the GEM80, even though the 88 keV is visible.

General Guidelines for Choosing an F-Series or FX-Series PROFILE GEM Detector
For a close or on-endcap sample, the detector diameter should ideally exceed the sample diameter by 20% or more. Beyond 30% the gain in efficiency is small. Another point, often missed, is if the detector diameter exceeds the sample diameter by 20% or more, then any errors due to irreproducibility of sample position will be minimal.

When budget limits are considered, first select the largest diameter up to the optimum diameter, then specify a deeper detector to further increase the absolute efficiency, specifically at higher energies. For samples to be counted in geometries similar to those listed above, choose an F-Series PROFILE detector with a diameter 20% (or more) larger than the sample to ensure the highest absolute efficiency for a given relative (IEEE) efficiency. Over-square detectors can often achieve better low-energy resolution than longer, smaller diameter detectors of the same relative efficiency.

M-Series PROFILE GEM Detectors
The M-Series detectors are designed specifically to provide optimum geometry for use with Marinelli beakers. These are made with the endcap diameter "filled with crystal" and the length slightly longer than the diameter, which maximizes the overall absolute efficiency for a Marinelli beaker. This is the most common beaker where the well diameter is equal to its length.

General Guidelines for Choosing an M-Series PROFILE GEM Detector
Choosing the optimum M-Series detector for use with a specific Marinelli beaker could not be easier: simply choose the detector with the tightest fit inside the Marinelli beaker well!

An F-Series detector may be used in a Marinelli geometry, but will have a lower efficiency than an M-Series of the same diameter. Correspondingly, an M-Series detector may be used as a substitute for an F-Series in an on-endcap type of geometry. For the same diameter, the M-Series will give slightly higher efficiency (improvement increasing with increasing energy).

Ordering Information

PROFILE GEM detectors are specified as follows: GEM-AABBCC, where "AA" is the series (currently F, FX, or M) and BB and CC are the nominal crystal diameter and length in mm respectively.

Notes

• GEM-MAABBP4 is an M-Series PROFILE Detector optimized for use with Marinelli Beakers. Choose the largest diameter which will fit within the Marinelli Well.
• GEM-FAABBP4 is an F-Series PROFILE Detector optimzed for “close geometry” samples such as filters, Petri dishes, and bottles. If possible, choose a crystal diameter >20% larger than your sample.
• GEM-FXAABBP4 is an FX-Series PROFILE Detector optimzed for the same geometries as the F-Series, but with thin contact³ and carbon fiber window for use down to below 15 keV.

¹FWHM = Full Width at Half Maximum; FW.1M = Full Width at One-Tenth Maximum; FW.02M = Full Width at One-Fiftieth Maximum; total system resolution for a source at 1000 counts/s measured in accordance with ANSI/IEEE Std. 325-1996, using ORTEC standard electronics.

²Measured at optimum shaping time using ORTEC analog or digital electronics.

³The proprietary contact employed in the FX-Series detectors offers exceptionally high transmission at energies below 40 keV. Some instability in transmission may occur below 20 keV if stored (uncooled) at room temperature for extended time periods (20–25°C or above). It is therefore recommended to keep FX-Series detectors cold, limiting the exposure to elevated ambient storage temperatures for applications which demand minimally varying efficiency below 20 keV.

Higher specification versions of these detectors may be available to special order. Contact the factory for details.

PROFILE Series GEM HPGe Coaxial Detectors are supplied in "P4" PopTop Capsules
The full specification for ordering consists of the capsule, cryostat, dewar (if applicable), and any other options.
For example:
GEM-M7080P4
CFG-PV4
DWR-30
Fully specifies a GEM-M7080P4 in PopTop capsule in a vertical dipstick configuration with a 30-liter dewar.