Untitled document

PGT High-Purity Germanium
Detectors
Princeton Gamma-Tech has been a leader in the field of semiconductor gamma- and X-ray detectors for over 30 years. In the early days, this meant lithium-compensated ger-manium. Then, when General Electric first produced high-purity (intrinsic) germanium crystals in 1972-73, PGT manufactured the first commercial HPGe planar detectors, soon followed by the first HPGe coaxials. Since that time, PGT HPGe detectors have explored outer space, gone to the depths of mines in search of β β decay in enriched germanium, and found uses throughout the world in nuclear power plants, environmen-tal measurements, and aerospace studies.
HPGe has an impurity level of ~1010 impuri-ties per cubic centimeter and is designated either P-type or N-type, based on the type of impurity. One surface of the crystal has a Energy Range
lithium-diffusion N+ layer, ~0.5 mm thick; the other surface has a thinner P+ layer In general, IGC detectors are suitable for formed by boron ion implantation or gold energies of 40 keV to 10 MeV. N-type coax- ials extend the range down to 4 keV. For lower-energy gammas, planar detectors are When a bias voltage is applied to the crystal, incident ionizing radiation creates charge since they have better energy resolution and carriers that are swept toward oppositely less sensitivity to high energy background charged contacts. In P-type coaxial (IGC series) and well detectors (IGW series), the 109 eV to 60 keV, Si(Li) detectors are pre- applied voltage is positive, and holes are the primary charge carriers. In N-type coaxial (NIGC series) and planar crystals (IGP or Efficiency
NIGP detectors), the outer face is the thin P+ layer and the applied bias is negative. Elec- The IEEE Standards describe efficiency as trons are the main carriers. These detectors absolute, the ratio of photons detected to all
have lower trapping levels and are less sensi- photons emitted by the source, or relative,
which compares the number of photons detected to the number detected by a 7.62 mm × 7.62 mm (3" × 3") NaI(Tl) scintillation silicon, Si(Li), detectors for X-ray spectros- detector. Efficiency is also related to crystal size. Thus, coaxial detectors are frequently “sized” by percent relative efficiency. PGT Product Information
IGC detectors, for example, are available in Product Information
Selecting a Detector
All PGT HPGe and Si(Li) detectors can be temperature cycled and stored indefinitely at It is important to select the appropriate size. room temperature. Several parameters are An overly large detector wastes money and useful in the selection of a detector for a par- small detector will be less expensive, but can cost more in time required for an analysis.
Detector Performance Parameters
Resolution
Standard
Detector
Standard
Peak Shape
Energy Range
Type/Series
FWTM/FWHM
* with optional low-energy windows or well insert Energy Resolution
Energy resolution is a measure of how well neighboring or A variety of liquid-nitrogen cooled cryostats, including dip- overlapping peaks can be distinguished from one another. stick, unitary, and portable styles, along with the JT Cool The usual standard for energy resolution is the full width at cryocooler, can be selected. The PGT QUIET ONE™ ultra- half maximum (FWHM) for the full energy peak of the low microphonics mounting system assures the best possible Co60 1.33 MeV line. Usually, a second value, at one-tenth resolution even in the noisiest field deployment situations. the maximum (FWTM), is also determined. The ratio of Beryllium and low-Z organic windows and well inserts are these, FWTM/FWHM, is called peak shape, and is used in needed for lower energy ranges. Low-background materials, computer analysis of complex spectra. For lower-energy as well as lead shields, can be specified if needed.
regions, the FWHM of the 5.9 keV line of Fe55 or the 122 keV line of Co57 is reported.
PGT can design a system best suited to your nuclear spectros-copy needs.
Resolution may be limited by the multichannel analyzer (MCA) used. For example, if the MCA has only 4000 chan-nels available for a 2MeV energy range (i.e., only 2 chan- nels per keV), then the difference between a 2.2 keV FWHM detector and a more expensive 1.7 keV FWHM detector will hardly be noticed.
Other Factors
For More Information Contact:
The peak-to-Compton ratio is sometimes more important than resolution or efficiency. At the lowest energy ranges, the peak-to-background is the significant factor because PGT Oak Ridge
the Compton effect is small compared to scattering and 1010 Commerce Drive Suite G
window and edge effects. For planar detectors, the active Oak Ridge, TN 37830
area, depletion depth, and window thickness need to be Toll Free (800) 980-9284
Tel: (865) 482-1665
Fax: (865) 482-6253
All these measures of detector performance are dependent Web Site: www.pgt.com
also on the other system components. PGT offers three e-mail: sales@pgt.com
types of preamplifier: resistive feedback, optical reset, and transistor reset. Corporate Headquarters:
Princeton Gamma-Tech, Inc.
C/N 863
Princeton, NJ 08542-0863
Tel: (609) 924-7310
Fax: (609) 924-1729
Product Information

Source: http://www.savtek.com.tr/dosyalar/brosur/HPGeDetectors.pdf