The University of Washington X-Ray Imager:   How It Works

Figure 1

Figure 2

Figure 3

Figure 1.
  • Precipitating electrons produce X-rays through the bremsstrahlung process.
  • These X-rays can be observed by balloons, but do not penetrate all the way to the ground.
  • Typical auroral X-rays that reach balloon altitudes have energies between about 20 and 120 keV.
  • Figure 2.
  • The lead pinhole collimator focuses X-rays like a camera. (A different collimator uses multiple pinholes in a coded-aperture mask to allow more X-rays to be detected.)
  • The sodium iodide scintillator emits visible photons when hit by an X-ray.
  • Photomultiplier tubes (PMTs) detect photons and send signals to the electronics.
  • Figure 3.
  • The distribution of light among the PMTs tells the location of the X-ray.
  • The total of the four PMT responses tells the energy of the X-ray.
  • The spatial resolution is about 10 km for aurora at 100 km altitude.

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    Updated Nov 2011