Amptek - Model CdTe -X-Ray & Gamma Ray Detector

Now available with Graphite Windows that are 1 mil (25 µm) thick, made of 100% carbon, and equivalent in Energy Transmission to 4 mil (100 µm) Be windows.

The XR-100CdTe is a high performance x-ray and gamma ray detector, preamplifier, and cooler system using 5 x 5 x 1 mm Cadmium Telluride (CdTe) diode detector mounted on a two-stage thermoelectric cooler.  The XR-100-CdTe is capable of detecting energies from a few keV to several hundreds of keV, with an efficiency that peaks from 10 to 100 keV.

Power to the XR-100CdTe is best provided by the PX5. The PX5 is DC powered by an AC adapter and provides a variable Digital Pulse Shaping Amplifier (0.2 µs to 100 µs peaking time), the MCA function, and all necessary power supplies for the detector and preamplifier. The PX5 connects via USB, RS-232, or Ethernet to a PC.  The XR-100CdTe/PX5 system ensures stable operation in less than one minute from power turn-on.

The X-123CdTe combines in a single package Amptek’s standard, high performance X-ray spectroscopy components: the CdTe detector, a preamplifier, a DP5digital pulse processor (DPP) and MCA, and a PC5 power supply. The result is a complete integrated system which can fit in your hand.

X-123 represents the culmination of 14 years of X-ray detector development at Amptek. Our philosophy has always been to create small, low power, high performance instruments while keeping them simple to operate. The X-123CdTe exemplifies this philosophy in a single package. All that is needed is a +5 Volts DC input and a USB or RS-232 connection to your computer.

• Medical X-Ray and Gamma Ray Detection: Mammography and Radiology
• Characterization of x-ray tubes: direct output spectrum, current stability
• 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

• CdTe Diode Detector
• Thermoelectric (Peltier) Cooler
• Cooled FET
• Temperature Monitor
• Graphite or Beryllium Window
• Hermetic Package (TO-8)

Theory of Operation

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 + 500 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.

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 sensor 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-100CdTe will not change with a temperature variation of a few degrees. Hence, accurate temperature control is not necessary when using the XR-100CdTe inside the laboratory.

Vacuum Operation

The XR-100CdTe can be operated in air or in vacuum down to 10^-8 Torr. There are two ways the XR-100CdTe can be operated in vacuum: 1) The entire XR-100CdTe 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-100CdTe, 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-100CdTe to the PX5 outside the vacuum chamber. 2) The XR-100CdTe 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-100CdTe with extender and Conflat and components for vacuum applications.