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| The XR-100T-CdTe represents a breakthrough in x-ray detector technology by providing "off-the-shelf" performance previously available only from expensive cryogenically cooled systems. | |
Features
Additional Information |
Applications
Application Notes
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Model XR-100T-CdTe is a new high performance x-ray and gamma ray detector, preamplifier, and cooler system using a 3 x 3 x 1 mm Cadmium Telluride (CdTe) diode detector mounted on a two-stage thermoelectric cooler. Also on the cooler are the input FET feedback components to the charge sensitive preamplifier. The internal components are kept at approximately -30 ºC and can be monitored by a temperature sensitive integrated circuit. The hermetic TO-8 package of the detector has a light tight, vacuum tight 4 mil (100 µm) Beryllium window.
All the critical connections between the detector and the preamplifier have been made internally to the XR-100T-CdTe to ensure quick, first time operation by the user. The XR-100T-CdTe is provided complete with BNC connectors and power cable.
The XR-100T-CdTe is capable of detecting energies from a few keV to several hundreds of keV!
Figure 1. 57Co Spectrum.
X-rays & gamma rays interact with CdTe atoms to create an average of one electron/hole pair for every 4.43 eV of energy lost in the CdTe. Depending on the energy of the incoming radiation, this energy loss is dominated by either the photoelectric effect or Compton scattering. The probability or efficiency of the detector to "stop" the incoming radiation and create electron/hole pairs increases with the thickness of CdTe.
In order to facilitate the electron/hole collection process in the CdTe detector, a 400 volt potential is applied. This voltage is too high for operation at room temperature, as it will cause excessive leakage, and eventually a breakdown. Since the detector in the XR-100T-CdTe is cooled, the leakage current is reduced considerably, thus permitting the high bias voltage.
 Figure 2. 57Co Spectrum with RTD on and off. |
Electron/hole pairs created by radiation, which interact with the CdTe near the back contact of the detector, result in fluctuations of charge collection times. These fluctuations are observed as rise time variations of the voltage step at the output of the charge sensitive preamplifier. As a result, the acquired spectra suffer from increased background counts and degraded energy resolution. To reduce these effects, a Rise Time Discrimination (RTD) circuit has been developed for the PX2T amplifier. When the RTD is active, the shaped pulses are internally gated and only pulses corresponding to "full charge collection" events are allowed to be sent to the Multichannel Analyzer (MCA) for analysis.
NOTE: When using the PX4 instead of the PX2, RTD is not necessary since the PX4 has a variable High Voltage Supply. Increasing the HV to the detector reduces the hole/tailing by collecting more of the charge.
The thermoelectric cooler cools both the CdTe detector and the input FET transistor to the charge sensitive preamplifier. Cooling the FET reduces its leakage current and increases the transconductance, which in turn reduce the electronic noise of the system.
In order to further reduce electronic noise, the feedback capacitor and part of the current feedback network to the preamplifier are also placed on the same substrate as the detector and FET. This minimizes parasitic capacitance at the input.
A temperature monitoring integrated circuit is placed on the cooled substrate to provide a direct reading of the temperature of the internal components, which will vary with room temperature. Once the internal temperature gets below minus 10 °C the performance of the XR-100T-CdTe will not change with a temperature variation of a few degrees. Hence, accurate temperature control is not necessary when using the XR-100T-CdTe inside the laboratory.
The XR-100T-CdTe can be operated in air or in vacuum down to 10-8 Torr. There are two ways the XR-100T-CdTe can be operated in vacuum: 1) The entire XR-100T-CdTe detector and preamplifier box can be placed inside the chamber. In order to avoid overheating and dissipate the 1 Watt of power needed to operate the XR-100T-CdTe, good heat conduction to the chamber walls should be provided by using the four mounting holes. An optional Model 9DVF 9-Pin D vacuum feedthrough connector on a Conflat is available to connect the XR-100T-CdTe to the PX2T outside the vacuum chamber. 2) The XR-100T-CdTe can be located outside the vacuum chamber to detect X-Rays inside the chamber through a standard Conflat compression O-ring port. Optional Model EXV9 (9 inch) vacuum detector extender is available for this application. See photograph of XR-100T-CdTe with extender and Conflat and components for vacuum applications.
General | |
| Detector type | Cadmium Telluride (CdTe) Diode |
| Detector areas | 3 x 3 mm (9 mm2), 5 x 5 mm (25 mm2) |
| Detector thickness | 1 mm |
| Energy resolution @ 122 keV, 57Co | 9 mm2: <1.2 keV FWHM, typical 25 mm2: <1.5 keV FWHM, typical |
| Dark counts | <5 x 10-3 counts/sec @ 10 keV < E < 1 MeV |
| Detector window | Be, 4 mil thick (100 µm) |
| Preamplifier | Charge Sensitive, with Current Divider Feedback |
| Case Size | 3.75 x 1.75 x 1.13 in (9.5 x 4.4 x 2.9 cm) |
| Case weight | 4.4 ounces (125 g) |
| Total power | Less than 1 watt |
Inputs | |
| Preamp power | ±8 volts @ 25 mA |
| Detector power | +500 volts @ 1 µA |
| Cooler power | Current = 350 mA maximum Voltage = 4 V maximum |
Outputs | |
| Preamplifier: Sensitivity Polarity |
0.82 mV/keV Negative signal out (1 kohm max. load) |
| Temperature monitor: Sensitivity |
PX2T-CdTe: 770 mV = -50 °C PX4: direct reading in K through software. |
| Preamp output | BNC coaxial connector |
| Power and Signal | 6-Pin LEMO connector (Part# ERA.1S.306.CLL) |
| Interconnect Cable | 6-Pin LEMO (Part# FFA.1S.306.CLAC57) to 9-Pin D (5 ft length) |
| Pin 1 | +8 volt temperature monitor power |
| Pin 2 | +H.V. detector bias, +500 volt max. |
| Pin 3 | -8 volt preamp power |
| Pin 4 | +8 volt preamp power |
| Pin 5 | Cooler power return |
| Pin 6 | Cooler power (0 to +4 volt @ 0.350 A max.) |
| Case | Ground and shield |
Power to the XR-100T-CdTe is provided by either the PX4 or the PX2T-CdTe:
A) The PX4 is DC powered by an AC adaptor and provides both a variable Digital Pulse Shaping Amplifier (0.330 µs to 45 µs shaping time) and the MCA function. The PX4 connects via USB to a PC.
B) The PX2T-CdTe is AC powered and also includes a spectroscopy grade Analog Shaping Amplifier with fixed shaping time constant (3 µs). The output of the PX2CR must then go to an external MCA such as the MCA8000A.
The XR-100T-CdTe/PX2T-CdTe or XR-100T-CdTe/PX4 systems ensures stable operation in less than one minute from power turn-on.
The PX4 Digital Pulse Processor, MCA, and Power Supply for the XR-100T-CdTe is DC powered by an AC adaptor. It provides a variable Digital Shaping Amplifier (0.330 µs to 45 µs shaping time), the MCA function, and all necessary power supplies for the XR-100T-CdTe.
Figure 3. This diagram shows the internal connections between the AXR hybrid sensor and the electronics within the case, as well as the external connections to the PX4.
Figure 4. Throughput for various peaking times. The XR-100T-CdTe provides the best resolution between 3 and 6 µs peaking time.
The PX2T-CdTe Shaping Amplifier and Power Supply for the XR-100T-CdTe is AC powered. It includes a spectroscopy grade shaping amplifier with a fixed shaping time constant (3 µs) and all the necessary power supplies for the XR-100T-CdTe. The output of the PX2T-CdTe must then go to an external MCA such as the MCA8000A.
Figure 5. XR-100T-CdTe Connection Diagram
Figure 6. PX2T Amplifier Output
General | |
| Size | 6 x 6 x 3.5 inches (15.3 x 15.3 x 8.9 cm) |
| Weight | 2.5 lbs (1.15 kg) |
Shaping amplifer | |
| Polarity | Positive unipolar |
| Shaping Time | 3 µs |
| Pulse width | 7.2 µs FWHM, see Figure 2 |
| Shaping type | 7 pole "Triangular" with Base Line Restoration, Pileup Rejection, and Rise Time Discrimination (RTD) |
| Sensitivity with XR-100T-CdTe | 6 to 60 mV/keV |
| Output range | +6.0 volts into 500 ohm load |
| Output impedance | 50 ohms |
| Input from XR-100T-CdTe | Front panel BNC |
| Output to MCA | Front panel BNC |
| Pileup Rejection (PU) | Rear panel BNC, Positive TTL For the duration of this output gate, any detected pulse must be rejected by the MCA. |
| Input Count Rate (ICR) | Rear panel BNC, Positive TTL < 2µs When connected to a counter, the ICR countrate corresponds to the total number of x ray events that strike the detector. |
| Probe power | 9-pin D-connector (cable provided) Pin 1: +8 volt preamp power Pin 2: -8 volt preamp power Pin 3: 0 to +4 V @ 350 mA cooler power Pin 4: +8 volt temperature monitor power Pin 5: +H.V. detector bias, +500 volt max. Pin 6: Ground and case Pin 7: Cooler power return Pin 8: Ground and case Pin 9: Ground and case |
| AC power | Standard IEC 320 receptacle, 110-250 VAC, 50/60 Hz (cable provided) |
Amptek no longer uses 2 mm thick CZT in the XR-100T. The CZT detector has been replaced by the 1 mm thick CdTe diode detector. The CdTe detector system provides improved performance over the CZT.
For 1 mm thick CdTe and various Be window thicknesses (window dominates low energy response).
Figure 7. Log-log plot of interaction probability between 1 keV and 1 MeV.
Figure 8. Linear plot of interaction probability between 10 keV and 250 keV.
For more information on the efficiency of the CdTe detector see the ANCZT-1 application note. This note includes the numeric table of efficiencies that created the figures above .
See also the XR-100CR at 149 eV resolution.
XR-100T-CdTe Specifications in PDF format (105 k)
Revised February 5, 2008