The XR100T-CdTe is a thermoelectrically cooled X-ray detector and preamplifier using a CdTe diode.  The high stopping power of CdTe makes excellent for applications requiring high detection efficiency at energies up to 100 keV.  Its performance, small size, and low cost make it ideal for applications including monitoring of X-ray tubes and EDXRF on the K lines of rare earth metals, lead, gold, uranium, and other high Z materials.

The XR-100T-CdTe is a high performance x-ray and gamma ray detector, preamplifier, and cooler system using either a 3 x 3 x 1 mm or 5 x 5 x 1 mm Cadmium Telluride (CdTe) diode detector mounted on a two-stage thermoelectric cooler.  The XR-100T-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.

Amptek has recently introduced two new variations of the CdTe detectors.  The traditional -T option provides very good energy resolution but is limited to count rates of < 10 kcps.  The new reset option provides the same good energy resolution but up to 100 kcps.  A resistive feedback option permits operation at even higher rates but at slightly lower resolution.

Power to the XR-100T-CdTe 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-100T-CdTe/PX5 system ensures stable operation in less than one minute from power turn-on.

Spectrum from Cobalt-57 as Measured with Amptek CdTe Detector

Figure 1. 57Co Spectrum take with the Amptek XR-100T-CdTe and PX5.

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Applications

 

Features

  • CdTe Diode Detector
  • Thermoelectric (Peltier) Cooler
  • Cooled FET
  • Temperature Monitor
  • 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-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.

Vacuum Operation

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 PX5 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.

XR-100T-CdTe X-Ray and Gamma Ray Detector

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 3.00 x 1.75 x 1.13 in (7.6 x 4.4 x 2.9 cm)
Case weight 4.4 ounces (125 g)
Total power Less than 1 watt
Operation conditions 0°C to +40°C
Storage and Shipping Long term storage: 10+ years in dry environment Typical Storage and Shipping: -20°C to +50°C, 10 to 90% humidity non condensing
tuv TUV Certification Certificate #: CU 72072412 01 Tested to: UL 61010-1: 2004 R7 .05 CAN/CSA-C22.2 61010-1: 2004
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 PX5: direct reading in K through software.

XR-100T-CdTe Connectors

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 6-Pin LEMO (5 ft. length)

6-Pin Lemo Connector Pin Out

Pin 1 Temperature monitor diode
Pin 2 +H.V. detector bias, +500 volt
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

CdTe Detection Efficiency

For 1 mm thick CdTe and various Be window thicknesses (window dominates low energy response). Detection Efficiency for 1 mm thick CdTe and various Be window thicknesses (window dominates low energy response).

Figure 6. Log-log plot of interaction probability between 1 keV and 1 MeV. Linear plot of interaction probability between 10 keV and 250 keV

Figure 7. Linear plot of interaction probability between 10 keV and 250 keV. For more information on the efficiency of the CdTe detector see the AN-CdTe-001 application note. Efficiency Package: A ZIP file of coefficients and a FAQ about efficiency. This package is provided for general information. It should not be used as a basis for critical quantitative analysis.

PX5 Digital Pulse Processor, MCA, and Power Supply for the XR-100T-CdTe

Power to the XR-100T-CdTe is provided by the PX5. The PX5 is DC powered by an AC adaptor 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, RS232, or Ethernet to a PC.

The XR-100T-CdTe/PX5 system ensures stable operation in less than one minute from power turn-on.

Block Diagram with PX5 and XR-100SDD Silicon Drift Detector
Figure 4. 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 PX5.

PX5 Throughput with SDD
Figure 5. Throughput for various peaking times. The XR-100T-CdTe provides the best resolution between 1 and 6 µs peaking time.

Application Notes


Typical Countrate of XR-100T-CdTe 3x3x1 mm3 (5x5x1 mm3) from Selected Nuclides

Nuclide Activity Radiation Level on Contact (mR/hr) Countrate on Contact (CPS) Radiation Level at 10 cm away (mR/hr) Countrate at 10 cm away (CPS)
137Cs 0.1 mCi (3.7 MBq) 25 500 (1,400) 2.0 11 (30)
57Co 0.1 mCi (3.7 MBq) 10 5,500 (15,000) 0.5 50 (140)
Uranium Oxide (Natural UO3) 0.6 mCi (21 MBq) 1 22 (60) 0.3 5 (15)
241Am 10 µCi (0.37 MBq) 10 1,400 (3,800) 0.5 20 (50)

Modeling

Please refer to the TO-8 detector drawing.

  1. The TO-8 cover is made of Ni, 14 mm diameter, 0.250 mm thick.
  2. The Detector element is located 1.27 mm behind the 100 µm thick Be window.
  3. The detector cavity is vacuum.
  4. The size of the detector is either 3x3x1 mm3 or 5x5x1 mm3. (*)
  5. The top contact is Pt of 0.2 µm thickness (- side).
  6. The bottom contact is In of 1 µm thick (+ side).
  7. The detector is placed on a ceramic substrate of 0.75 mm thickness.
  8. The thickness of the cooler is 2.75 mm.
  9. The base of the TO-8 package is made of steel (Kovar), 1.5 mm thick.

(*) Depending on which options are selected. Typical Kovar Composition

  • Carbon – 0.02
  • Silicon – 0.20
  • Manganese – 0.30
  • Iron – 53.48
  • Cobalt – 17.0
  • Nickel – 29.0

Do NOT use RTD when trying to compare theoretical results to actual measurements. The following applications notes may be useful when modeling the XR-100T-CdTe response

Example Spectra

cdte_2 Figure 1. cdte_3 Figure 2. cdte_4 Figure 3. cdte_13 Figure 4. Spectrum from Cobalt-57 as Measured with Amptek CdTe Detector Figure 5. cdte_11 Figure 6. cdte_6 Figure 7. cdte_uo3 Figure 8. cdte_12 Figure 9.

XR-100T-CdTe Mechanical Dimensions

1.5 Inch Extender (standard)

cztmech All dimensions are in inches except as noted ±0.0005.