Hard X-ray Detector
It is harder to build X-ray mirrors for X-rays above an energy of
~10 keV, so we use the old-fashioned method of "collimation."
Imagine observing a star near bright city lights by looking through a
cardboard tube: the tube is a collimator, a device that shields you
from light coming from directions other than the star you are pointing at.
 |
The Hard
X-ray Detector
(HXD) is shown to the left. It is designed to
keep out X-rays coming from directions other than the X-ray source it is
pointing at. |
The HXD is a non-imaging instrument operating in the 10 to 700 keV
range; its novel design is expected to result in the highest
sensitivity yet in this spectral region.
In more technical terms, the HXD has 16 identical "Well-type Phoswich
Counter" units. The detector itself is made up of a material
called GSO. It glows (mostly in visible light) when it' is hit with
X-rays. Scientists call GSO and similar materials a "scintillator."
The collimator is made of a different
type of scintillator crystal (BGO), and is shaped like a well. BGO
does not actually stop extraneous X-rays, but it will allow you to
tell which X-rays are coming from the direction you're looking
at, and which X-rays are coming in from the side.
detect X-rays coming in sideways. On-board computer will
discard all the X-rays coming from the side. Scientists hope
that this clever design will allow
very sensitive observations for X-rays with energies up to 700 keV!
For more information, see
http://www-utheal.phys.s.u-tokyo.ac.jp/hxd2/
(note, however, most content in English - in their HXD-I section -
are over 5 years old and are for the original HXD on ASTRO-E)
You can now read about the first data taken with the HXD in orbit!
Follow the links to
the news item and
the gallery entry
about this.
