Low Energy Germanium Detectors
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Features
- Spectroscopy from 3 keV up
- Wide range of sizes
- High resolution – good peak shape
- No slow pulses
- Thin front contact
- High energy rate capability
Description
The Low Energy Germanium Detector (LEGe) represents a new concept in Germanium Detector Geometry with major advantages over conventional planar or coaxial detectors in many applications. The LEGe detector is fabricated with a thin front contact. The rear contact is of less than full area and thus the capacitance of the detector is less than that of a planar device of similar size. Since preamplifier noise is a function of detector capacitance, the LEGe affords lower noise and consequently better resolution at low and moderate energies than any other detector geometry. Unlike grooved planar detectors, there is little dead germanium beyond the active region. This, and the fact that the side surface is charge collecting rather than insulating, results in fewer long-rise time pulses with improved count rate performance and peak-to-background ratios.
The LEGe detector is available with active areas from 50 mm2 to 38 cm2 and with thicknesses ranging from 5 to 25 mm. For applications involving moderate gamma-ray energies, the LEGe may well outperform an expensive large volume coaxial detector. The efficiency curve given below illustrates the performance of a typical LEGe detector.
To take full advantage of the low energy response of this intrinsically thin window detector, the LEGe is usually equipped with a thin Be window. For applications involving energies exclusively above 30 keV or so, the LEGe can be provided with a conventional 0.5 mm Aluminum window. Other window options are available. In any case, a wide range of CANBERRA cryostats is available to choose from.
LEGe Detector
Absolute Efficiency Curve for LEGe Detector with 2.5 cm
Spacing Between Source and End Cap
PREAMPLIFIERS
CANBERRA offers the choice of RC feedback preamplifiers or pulsed -optical preamplifiers on its LEGe detectors. The pulsed-optical type preamplifier affords better resolution at low energies and at low total energy rates. The RC preamplifier gives better performance at high total energy rates. It is, therefore, used exclusively on larger detectors which have greater stopping power for high energy photons. Block diagrams and descriptions of the operating principles of each type are illustrated.
RC Feedback
Charge impulses from the detector result in an equivalent charge stored on the feedback capacitor (Cf), producing the step function . V°=Qin/Cf. Rf discharges Cf with the time constant 1/RfCf. This signal is differentiated by C2-R2 and amplified X2 or X10 by amp A2.
Block Diagram - RC Preamp
PULSED-OPTICAL FEEDBACK PREAMPLIFIER
Charge impulses (Qin) from the detector result in equivalent charge stored on feedback capacitor Cf producing step function Vo = Qin/Cf. Subsequent impulses increase the output to a limit at which point the Schmitt trigger fires an LED directed at the FET. The light pulse momentarily shorts out the FET gate-source junction thus discharging Cf and resetting the preamplifier. An adjustable width monostable multivibrator provides a pulse which can be used to gate off the MCA during the transient reset time.
LEGe DETECTOR
General specifications and information Standard configuration includes:
- Vertical dipstick cryostat with Be window and 30 liter Dewar
- Pulsed optical feedback (P) or resistive feedback (R) preamplifier with cooled FET and 3 meter bias, signal and power cables
Resolution (FWTM) less than or equal to 2 times resolution (FWHM)
Model |
Area |
Thickness |
Be Window |
Resolution |
Preamp |
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| 5.9 keV | 122 keV | |||||
GL0055PS |
50 |
5 |
0.05 (2) |
145 |
500 |
PO |
GL0055P |
50 |
5 |
0.05 (2) |
155 |
500 |
PO |
GL0055R |
50 |
5 |
0.05 (2) |
175 |
500 |
RC |
GL0110P |
100 |
10 |
0.075 (3) |
160 |
500 |
PO |
GL0110R |
100 |
10 |
0.075 (3) |
180 |
500 |
RC |
GL0210P |
200 |
10 |
0.15 (6) |
170 |
520 |
PO |
GL0210R |
200 |
10 |
0.15 (6) |
195 |
520 |
RC |
GL0213R |
200 |
13 |
0.15 (6) |
195 |
510 |
RC |
GL0510P |
500 |
10 |
0.15 (6) |
200 |
550 |
PO |
GL0510R |
500 |
10 |
0.15 (6) |
250 |
550 |
RC |
GL0515R |
500 |
15 |
0.15 (6) |
250 |
550 |
RC |
GL1010R |
1000 |
10 |
0.5 (20) |
300 |
650 |
RC |
GL1015R |
1000 |
15 |
0.5 (20) |
300 |
650 |
RC |
GL2015R |
2000 |
15 |
0.5 (20) |
400 |
700 |
RC |
GL2020R |
2000 |
20 |
0.5 (20) |
400 |
700 |
RC |
GL2820R |
2800 |
20 |
0.5 (20) |
450 |
750 |
RC |
GL3825R |
3800 |
25 |
0.5 (20) |
475 |
750 |
RC |
OPTIONS
Cryostat - see options and accessories price list.
Window -0.5 mm (20 mil) aluminum, no charge.
Window - 0.6 mm (24 mil) carbon composite, consult factory.
Block Diagram - Pulsed Optical
Feedback Preamp
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Note to our International Customers: The CANBERRA Online Quoting System is only available for our US customers. If you would like a quote on this product, please contact your Local Sales Office for assistance. We apologize for the inconvenience. |
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| Models | ||
| GL0055P: LEGe GL0055P | Request a Quote | |
| GL0055PS: LEGe GL0055PS | Request a Quote | |
| GL0055R: LEGe GL0055R | Request a Quote | |
| GL0110P: LEGe GL0110P | Request a Quote | |
| GL0110R: LEGe GL0110R | Request a Quote | |
| GL0210P: LEGe GL0210P | Request a Quote | |
| GL0210R: LEGe GL0210R | Request a Quote | |
| GL0213R: LEGe GL0213R | Request a Quote | |
| GL0510P: LEGe GL0510P | Request a Quote | |
| GL0510R: LEGe GL0510R | Request a Quote | |
| GL0515R: LEGe GL0515R | Request a Quote | |
| GL1010R: LEGe GL1010R | Request a Quote | |
| GL1015R: LEGe GL1015R | Request a Quote | |
| GL2015R: LEGe GL2015R | Request a Quote | |
| GL2020R: LEGe GL2020R | Request a Quote | |
| GL2820R: LEGe GL2820R | Request a Quote | |
| GL3825R: LEGe GL3825R | Request a Quote | |
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