The Mirion Broad Energy Ge (BEGe) Detector covers the energy range of 3 keV to 3 MeV like no other. The resolution at low energies is equivalent to that of our Low Energy Ge (LEGe™) Detector and the resolution at high energy is comparable to that of good quality coaxial (SEGe™) detectors.
Most importantly the BEGe detector has a short, fat shape which greatly enhances the efficiency below 1 MeV for typical sample geometries. This shape is chosen for optimum efficiency for real samples in the energy range that is most important for routine gamma analysis. This is in stark contrast to the traditional relative efficiency measurement – a 60Co point source at 25 cm which is hardly a relevant test condition for real samples. See the figures below comparing absolute detector efficiencies of a 5000 mm² and 6500 mm² BEGe Detector to coaxial detectors with approximately 60% relative efficiency.
In addition to higher efficiency for typical samples, the BEGe detector exhibits lower background than typical coaxial detectors because it is more transparent to high energy cosmogenic background radiation that permeates above ground laboratories and to high energy gammas from naturally occurring radioisotopes such as 40K and 208Tl (thorium). This aspect of thin detector performance has long been recognized in applications such as actinide lung burden analysis.
Most Low Energy Detectors are aptly named because they do not give good resolution at higher energies. In fact resolution is not usually specified above 122 keV. The BEGe detector represents a breakthrough in this respect. The BEGe unit is designed with an electrode structure that enhances low energy resolution and is fabricated from select germanium having an impurity profile that improves charge collection (thus resolution and peak shape) at high energies. Indeed, this ensures good resolution and peak shape over the entire mid-range which is particularly important in analysis of the complex spectra from uranium and plutonium.
In addition to routine sample counting, there are many applications in which the BEGe Detector really excels. In internal dosimetry the BEGe unit gives the high resolution and low background need for actinide lung burden analysis and the efficiency and resolution at high energy for whole body counting. The same is true of certain waste assay systems particularly those involving special nuclear materials.
The BEGe detector and associated preamplifier are normally optimized for energy rates of less than 60 000 MeV/sec. Charge collection times prohibit the use of short amplifier shaping time constants. Resolution is specified with an optimum shaping time constant and Lynx® digital peaking time equivalent.
Another big advantage of the BEGe unit is that the detector dimensions are virtually the same on a model by model basis. This means that like units can be substituted in an application without complete recalibration and that computer modeling can be done once for each detector size and used for all detectors of that model.
With cross-sectional areas of 20 to 65 cm2 and thickness' of 20 to 30 mm, the nominal relative efficiency is given below along with the specifications for the entire range of models. BEGe detectors are normally equipped with our composite carbon windows which are robust and provide excellent transmission to below 10 keV. Beryllium or aluminum windows are also available. Aluminum is preferred when there is no interest in energies below 30 keV and improved ruggedness is desired. Beryllium should be selected to take full advantage of the low energy capability (down to 3 keV) of the BEGe detector.
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