The mar555 Flatpanel Detector

The mar555 flatpanel is a novel type of X-ray detector that consists of a TFT frame coated with a thin Selenium layer. Conventional X-ray detectors like the image plate or the CCDs count visible light photons. They need a phosphour that converts X-rays into light photons. This conversion process greatly contributes to degradation of the signal (spreading out, loss). In contrast, in a Se-coated flatpanel detector, X-rays directly produce charges in the Se-layer, where they are collected by the individual TFT pixel electrodes. The elimination of point spreading not only enables measurements of very large units cells but also enhances the signal-to-noise ratio.

Since the TFT panels are available in quite large sizes and Selenium can be coated on large areas using standard deposition techniques, building up an X-ray detector with a huge active area of 430 x 350 mm2 is relatively inexpensive compared to tiled CCD-detectors and - even more - to pixel detectors.

 

Highlights:

• Speed: Read-out time of only 1200 ms.
• Active area: With its diagonal of 555 mm (430 x 350 mm), the mar555 flatpanel is the largest X-ray detector on the market.
• Large number of pixels: 3072 x 2560 pixels @ 140 um pixel size
• Dynamic range: A propietary eletronics circuit enables a full 18-bit amplitude (1:260.000). The peak signal is 38.400.000 electrons with < 1% linearity deviation.
• Point spread: Due to the principle of direct conversion, THERE IS NO POINT SPREAD with the mar555 flatpanel detector. Depending on X-ray source properties and on crystal mosaicity, reflexions may consist of one single pixel.
• Sensitivity: The mar555 detector has been used succesfully on a broad range of energies, ranging from 100 keV (0.012 Ang.) down to 6 keV ( 2.06 Ang.). While the detector works even better at high energies (>=10 keV), also low energy data have already yielded interpretable anomalous maps (e.g. 6 keV data from insulin).
• No problem with Se-edge: Since the detector features an active Se layer, it has been argued, that MAD-data collection of Se-Met-proteins at wavelengths around the Se-absorption edge might be impossible. A nice demonstration of feasibility has been carried out at ESRF ID23 in December 2007 (see Application Note).
• Noise: Since the technology does not involve silicon, the mar555 detector has no dark current. The 6144 amplifiers coupled to 12 ADC-boards in the detector produce an amplifier noise of about 500 e- rms and a total noise of 750 e- rms per pixel (5 X-ray@12 keV). The signal charge of 12 keV X-rays at the detector is 150 e-. This has to be compared to typical values of 6-9 e- per X-ray photon in the case of a CCD detector.
• Design: The detector does not need a low-temperature cooling but is operated at room temperature. The detector itself that comes in the size of a large LCD monitor. A compact additional cabinet containing a closed-circuit temperature regulator and power supplies will fit anywhere on a beamline. The one and only connection to the outside world is a fiber optics cable from the cabinet to your computer.
• Calibration: Before being shipped, the detectors are carefully calibrated in our lab. In the course of that process a correction table is generated that compensates for detector inhomogeneities.
• Free software: Easy-to-use and versatile. Free updates for the lifetime of your detector. Plus state-of-the-art data processing software at no costs. Our software distribution policy really makes a difference!

 

 

 

 

Important notes:

• As of July 2008, the propietary PCI card comes with a Linux driver that work only on Linux 2.4 kernels. This kernel version is still being actively maintained by the Debian Sarge 3.1 distribution.

 

Downloads:

• Product brochure
• Drawing of dimensions of mar555 (pdf: 228 kb)
• Application note mar.AN13Dec07 (pdf: 485kB):
  “Selenomethionine phasing from MAD data collected with the mar555 flatpanel detector”
• Application note mar.AN22Sep08 (pdf: 1.9 MB):
  “SAD phasing from data collected with the mar555 flatpanel detector”