Selecting the Right Sensor for X-Ray Energy Ranges

DECTRIS provides alternative sensors for the MYTHEN and PILATUS3 detector families to attain optimal performance over a high range of X-ray energies.

Further to the standard 450µm silicon sensors, which encompass a broad X-ray energy range, DECTRIS offers silicon sensors of thickness 1000 µm and 320 µm for PILATUS3 and MYTHEN.

Cadmium telluride sensors offered by the PILATUS3 X CdTe series of detectors improve the energy range to 100keV.

Choosing the Right Sensor for the Specific Application

The sensor and its thickness need to be chosen based on the typical X-ray energy range of a particular application. DECTRIS suggests the 450µm standard silicon sensor for all applications at X-ray energies below 12.5keV.

Silicon Sensors

Silicon sensor transforms X-ray photons into electrical charge. In the case of high-energy applications, the detection efficiency is restricted by the silicon sensor thickness. At high-energies, the high-energy sensors with a large sensor thickness of 1000µm compensate for silicon’s low absorption efficiency.

All silicon sensors from DECTRIS are based on the company’s proven silicon technology, and are offered for all DECTRIS detectors of the PILATUS and MYTHEN detector families, from the MYTHEN 1K to the PILATUS 6M. EIGER detectors are offered with the standard 450µm silicon sensors.

High-Energy Sensors

For achieving the right sensitivity at high X-ray energies, the 1000µm silicon sensors exhibit improved quantum efficiencies at energies of more than 10keV, while maintaining the well-known noise-free operation of DECTRIS detectors. The 1000µm silicon sensor provides a very good quantum efficiency of 76% and 50% for Mo and Ag Ka radiation respectively. For all high-energy applications, the improved X-ray sensitivity offered by the 1000µm sensors is suitable.

Low-Energy Sensors

DECTRIS offers the 320µm sensors for low-energy applications. These sensors allow the least possible energy thresholds, and are offered with special low- energy calibrations and for in-vacuum solutions.

The quantum efficiency(QE) for 320µm, 450µm and 1000µm sensors as a function of energy is shown in Figure 1. The QR values were determined in the PTB laboratory at BESSY II and exactly match values deduced by calculations. At high energies more than 10keV, the QE is restricted by sensor thickness and considerably improved for thicker sensors.

Table 1 provides QE values for the various sensors at normally used X-ray energies.

Figure 1. Quantum efficiency of 320, 450 and 1000 µm sensors measured at the PTB laboratory at BESSY II. Image credit: Dectris Ltd.

Table 1. Quantum efficiency at typical X-ray energies

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Cadmium Telluride Sensors for Hard X-Ray Radiation

In order to directly convert the hard X-ray radiation, the PILATUS3 X CdTe detector series uses cadmium telluride (CdTe) crystals as the sensor material for direct conversion of the hard X-ray radiation. Very good stopping power is offered by this high-Z semiconductor material (Cd with Z=48, Te with Z=52), causing high detection efficiency at high X-ray energies.

CdTe material is obtained by DECTRIS from a leading manufacturer in probably the largest size presently available. Two large CdTe sensors constitute each PILATUS3 CdTe detector module and the sensor dimensions are of dimensions 42×34mm, leaving just 3pixel gap between them. The 1000µm CdTe thickness enables high quantum efficiency for up to 100keV hard X-ray energies.

The QE for the 1000µm cadmium telluride sensors is shown in Figure 2 and Table 2 as a function of energy. For the PILATUS3 pixel size and geometry, QE values were simulated and determined in the PTB laboratory at BESSY II from 20 to 60 keV. The values deduced by simulation were confirmed by the measurements.

Figure 2. Quantum efficiency of PILATUS3 X CdTe module measured at the PTB laboratory at BESSY II. Image credit: Dectris Ltd.

The drop in the QE from above 26keV is due to fluorescence losses happening for photon energies above the Cd and Te K-edges. The QE is quantified for energy threshold set to 50% of the photon energy.

Table 2. Quantum efficiency of PILATUS3 CdTe sensors.

Benefits of Using DECTRIS Sensors

The advantages of using DECTRIS sensors are:

• Good data quality
• Optimal performance at low energies
• Rapid measurements
• Improved sensitivity at energies more than 10keV
• Superior sensor technology
• Noise-free photon-counting operation for all sensors

Applications

The applications of DECTRIS Sensors are:

• Powder diffraction
• Diffuse scattering experiments
• Non-destructive testing
• Pre-clinical imaging
• Pair distribution function analysis
• Small molecule crystallography
• High-pressure studies
• In-vacuum SAXS/GI-SAXS/aSAXS

This information has been sourced, reviewed and adapted from materials provided by Dectris Ltd.

For more information on this source, please visit Dectris Ltd.