The XR-100T-CZT represents a breakthrough in x-ray detector technology by providing "off-the-shelf" performance previously available only from expensive cryogenically cooled systems.

Features CZT Detector Peltier Cooler Cooled FET Amptek A250 Preamp Temperature Monitor Beryllium Window Hermetic Package (TO-8) Sample Spectra and Applications XR-100T-CZT Photographs XR-100T-CZT, PX2T-CZT, and MCA8000A Connection Diagram Mechanical Dimensions Vacuum Applications Collimator Kit

Applications Medical X-Ray and Gamma Ray Detection, Mamography, Radiology, Conventional X-Ray X-Ray Fluorescence Art and Archaeology Portable X-Ray and Gamma Ray Instruments X-Ray and Gamma Ray Research Teaching Nuclear Plant Monitoring Uranium and Plutonium Detection CZT Application Notes XR-100T-CZT Efficiency Application Note (ANCZT-1 Rev. 1) XR-100T-CZT Charge Transport Application Note (ANCZT-2 Rev. 1)

All the critical connections between the detector and the preamplifier have been made internally to the XR-100T-CZT to ensure quick, first time operation by the user. The XR-100T-CZT is provided complete with BNC connectors and power cable.

In order to facilitate the use of the detector, Model PX2T-CZT Power Supply and Shaping Amplifier was developed. The PX2T-CZT is AC powered and provides all four voltages needed to operate the XR-100T-CZT plus a shaping amplifier. The output from the PX2T-CZT can be connected directly to a Multichannel Analyzer (MCA)

The XR-100T-CZT is capable of detecting energies from a few keV to several hundreds of keV!

Theory of Operation

In order to facilitate the electron/hole collection process in the CZT 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-CZT is cooled, the leakage current is reduced considerably, thus permitting the high bias voltage.

Electron/hole pairs created by radiation, which interact with the CZT 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 degrade energy resolution. To reduce these effects, a Rise Time Discrimination (RTD) circuit has been developed for the PX2T-CZT 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.

The thermoelectric cooler cools both the CZT detector and the input FET transistor to the A250 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 A250 preamp 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 ºC the performance of the XR-100T-CZT will not change with a temperature variation of a few degrees. Hence, accurate temperature control is not necessary when using the XR-100T-CZT inside the laboratory.

Figure 1. XR-100T-CZT Connection Diagram

Figure 2. PX2T-CZT Amplifier Output

The output pulse produced by the PX2T-CZT Shaping Amplifier is optimum for most applications using cooled CZT detectors, and can be connected directly to the input of a Multichannel Analyzer (MCA). If different shaping time constants or gains are needed, an external NIM type shaping amplifier with base line restoration can be used.

XR-100-CZT Connections
Preamp output	BNC coaxial connector
Test input	BNC coaxial connector
Power	6-Pin, LEMO connector with 5 ft cable Pin 1: +8 volt temperature monitor power Pin 2: +H.V. detector bias, +400 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 +2.1 volt @ 0.7 A max.) Case: Ground and shield

PX2T-CZT Specifications
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-CZT	6 to 60 mV/keV
Output range	+6.0 volts into 500 ohm load
Output impedance	50 ohms

PX2T-CZT Connections
Input from XR-100T-CZT	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 +3 volt cooler power @ 0.7 A max. Pin 4: +8 volt temperature monitor power Pin 5: +H.V. detector bias, +400 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)

Options

• Other detector sizes (5x5x2 mm or 5x5x5 mm) are available on special order.
• Components for vacuum applications
• Collimator Kit for high flux applications

CZT Detection Efficiency

For 2mm thick CZT and 10 mil (250 µm) Be window (window dominates low energy response).

Log-log plot of interaction probability between 1 keV and 1 MeV.

Linear plot of interaction probability over the lower energy range.

For a more detailed explanation of the efficiency of CZT and the effects of Rise Time Discrimination see the Efficiency of XR-100T-CZT Detectors Application Note (ANCZT-1 Rev. 1)

Sample Spectra and Applications
Medical Applications
Uranium and Plutonium Detection
Art and Archaeology
X-Ray Fluorescence - A Description
XR-100T-CZT Photographs
XR-100T-CZT, PX2T-CZT, and MCA8000A Connection Diagram
Mechanical Dimensions
Vacuum Applications
Collimator Kit

CZT Application Notes

• XR-100T-CZT Efficiency Application Note (ANCZT-1 Rev. 1)
• XR-100T-CZT Charge Transport Application Note (ANCZT-2 Rev. 1)

See also the XR-100CR at 186 eV resolution, and the new ROVER---a completely portable detector system.

XR-100T-CZT Specifications in PDF format

Revised February 6, 2001