Broad Energy Ge Detector

Features

• Large area
• Wide energy range
• Thin window
• High resolution at low energy
• High resolution at high energy
• Standardized geometries

Description

The CANBERRA 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 Detector and the resolution at high energy is comparable to that of good quality coaxial detectors.

Most importantly the BEGe 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 ⁶⁰ Co point source at 25 cm which is hardly a relevant test condition for real samples. See the adjacent figure comparing detector efficiencies for the extremes of coaxial vs. BEGe geometries each having approximately 50% relative efficiency.

In addition to higher efficiency for typical samples, the BEGe 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 represents a breakthrough in this respect. The BEGe 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 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 opti-mized for energy rates of less than 40 000 MeV/sec. Charge collection times prohibit the use of short amplifier shaping time constants. Reso-lution is specified with shaping time constants of 4-6 microseconds typically.

Another big advantage of the BEGe 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.

Absolute Efficiency of BE5030 compared to a Coaxial Detector of 60 mm diameter by 80 mm length for a source measuring 74 mm diameter by 21 mm thick located on the detector end cap. Both detectors have approximately 50% Relative Efficiency for a ⁶⁰Co point source at 25 cm.

With cross-sectional areas of 20 to 50 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 low background composite carbon windows. Beryllium or aluminum windows are also available.