X-Ray Detectors Using PILATUS3 Technology

The standards set by the established PILATUS X-ray detectors have been further raised by the PILATUS3 X-ray detector series. PILATUS3 detectors are based on an improved CMOS readout ASIC, with shorter readout time. They are equipped with DECTRIS instant retrigger technology (patent pending) and can be used with future cadmium telluride (CdTe) sensors, which are potential alternatives for silicon sensors and will considerably optimize quantum efficiency at high X-ray energies.

Instant retrigger technology facilitates highly accurate count rate correction and non-paralyzable counting. The improvements such as improved pixel uniformity, counter overflow handling, and reduced crosstalk enable the PILATUS3 detectors to deliver high-rate counting performance. Increased frame rates can be achieved with the reduced readout time.

Key Advantages of PILATUS3 X-Ray Detectors

The following are the main advantages of PILATUS X-ray detectors:

  • DECTRIS instant retrigger technology for non-paralyzable counting
  • Highest local and global count rates
  • Reduced readout time and increased frame rates
  • Compatibility with future CdTe sensors for high-energy applications
  • Highly accurate count rate correction for supreme data quality at high count rates

Instant Retrigger Technology

As a photon counting imaging technique, the instant retrigger technology combined with adjustable dead time enables non-paralyzable counting with enhanced high-rate counting performance. In a conventional single-photon counting X-ray detector, charge pulses generated by impinging photons are counted by digital circuits. Problems are faced by this type of detector when simultaneously generated pulses get piled up, thus leading to the loss of photon counts. The influence of the pulse pile-up on the observed count rate is noteworthy at high photon fluxes, resulting in complete paralyzation of the counting circuit.

The counting loss at high count rates is negated by the application of count rate correction in PILATUS single-photon counting hybrid pixel X-ray detectors. However, counter paralyzation limits the maximum usable count rate. The instant retrigger technology re-evaluates the pulse signal after a predetermined dead time interval subsequent to each count. In the case of a pulse pile-up, the instant retrigger technology can retrigger the counting circuit. The corresponding dead time interval is adjustable and is equal to the width of one single-photon pulse. This results in non-paralyzable counting and enables enhanced count rate correction so that enhanced data quality can be achieved at high count rates.

Signal waveforms illustrating instant retrigger technology

Figure 1. Signal waveforms illustrating instant retrigger technology. Image credit: Dectris Ltd.

Figure 1 presents the principle of instant retrigger technology. The first image shows the signal pulses generated by the impinging photons and the effective discriminator threshold level for single-photon counting. The pulse signal comprises of a chain of one single pulse, a pile-up of two pulses, and a pile-up of multiple pulses. The second image illustrates the respective digital discriminator output signal triggering the counting circuit. The third image represents the corresponding counts being registered by a conventional single-photon counting X-ray detector, revealing the loss of photon counts in case of pulse pile-up and subsequent paralyzation.

The corresponding dead-time generator output signal generated by a single-photon counting X-ray detector equipped with instant retrigger technology is shown in the fourth image. Here, a preset dead time interval is initiated whenever a count is registered. The final image represents the respective counts being registered, including possible retriggering of the counting circuit following the dead-time interval after each count. This data reveals the more accurate counting of the pulses during pile-up and that counting is non-paralyzable.

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Improved High-Rate Counting Performance

In comparison with the earlier PILATUS X-ray detectors, PILATUS3 X-ray detectors offer improved high-rate counting performance owing to the CMOS readout ASIC improvements, including an instant retrigger technology for non-paralyzable counting. The non-paralyzable counting is the foundation for enhanced high-rate counting performance. Furthermore, the implementation of counter overflow handling allows determination of the incoming photon rate unmistakably. In order to achieve improved count rate homogeneity over the complete modules, enhanced pixel uniformity is offered. Other advantages of this new design include better stability, reduced crosstalk, and higher local and global count rates.

Typical count rate characteristics of PILATUS3 X-ray detectors with DECTRIS instant retrigger technology compared to previous PILATUS X-ray detectors.

Figure 2. Typical count rate characteristics of PILATUS3 X-ray detectors with DECTRIS instant retrigger technology compared to previous PILATUS X-ray detectors. Image credit: Dectris Ltd.

Figure 2 shows the comparison of the typical count rate characteristics of PILATUS3 X-ray detectors equipped with DECTRIS instant retrigger technology against preceding PILATUS X-ray detectors. PILATUS3 X-ray detectors not only have considerably improved count rate capabilities but also involve more accurate application of count rate correction. This results in better data quality with rates more than 107 photons per second in a single pixel. Without any limitation for the global count rate, the new design can handle global rates of over 3 x 108 photons per second and mm2.

Compatibility with CdTe sensors

By optionally processing inverted polarity sensor signals, PILATUS3 X-ray detectors can be used with future CdTe sensors. CdTe sensors have the potential to be a replacement to silicon sensors in high-energy applications.

Shorter Readout Time

With a shorter readout time of below 1 ms, PILATUS3 X-ray detectors can achieve higher frame rates of 100–500 Hz.

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

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

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