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The Question
(Submitted February 23, 1998)
I'm a student from Belgium. I'm writing a paper on applications of
foil. Can you tell me why precisely you use foil for the making of the
X-ray telescope. Thank you.
The Answer
Thank you for your question. The basic reason why we use
foil for X-ray telescope mirrors is because X-rays only
bounce at shallow angles. So the mirrors must deflect the
X-rays just only a little from their path.
As you can imagine, this means that the mirrors must be
shaped like a cylindrical tube.
The problem, however, with this comes in collecting area. If you have a
tube shaped mirror, it will not collect very many X-rays.
The solution is to make many thin tube shaped mirrors and nest them.
Put one inside the other. If they were not thin, it would be hard to
put them inside each other --- hence the need for foil.
Pictures and other descriptions are at:
http://imagine.gsfc.nasa.gov/docs/science/how_l2/xray_telescopes.html
http://imagine.gsfc.nasa.gov/docs/introduction/xray_detectors.html
For more elementary information, try reading this:
http://heasarc.gsfc.nasa.gov/docs/xte/learning_center/universe/universe.html
Good luck,
Jonathan Keohane
for Ask a NASA scientist
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