The X-ray Spectrometer
The X-ray Spectrometer (XRS) aboard Suzaku consists of an array of
X-ray microcalorimeters. The X-ray microcalorimeter determines
the energy of an X-ray by
measuring the temperature change in a piece of silicon when an X-ray
hits it. Just as the hood of an automobile warms up when left in
the Sun, the silicon heats up when it absorbs an X-ray. The amount
that it heats up is proportional to the energy of the incident
X-ray.
|
The X-ray Microcalorimeter Array. Click on the
image for a video clip of Dr. Caroline Kilbourne
explaining the array.
(Description)
|
The X-ray microcalorimeter consists of a 6 x 6 array of silicon
detectors. Silicon itself is not very good at absorbing X-rays. So
each detector has a tiny absorber made of mercury telluride. The
X-rays heat up the absorber, which heats up the silicon detector.
The entire array measures about 3.5 mm on a side.
The
temperature increase due to a single X-ray is very small, about 0.001
degrees. To detect this small change, the detector must be kept cold
in order to reduce its own natural thermal energy. So the detector must
be kept at very cold
temperatures - 0.06 K, i.e 0.06 degrees above absolute zero. This is
accomplished using a 3-stage cooling process, consisting of solid neon
(at 17 K), liquid helium (at 1.2 K) and an Adiabatic Demagnetization
Refrigerator (0.06 K). The ADR uses the magnetic properties of
certain types of salts to cool the microcalorimeter to its operating
temperature.
The result is that the XRS can determine the energy of an X-ray to
0.1%. If police had radar as accurate as the XRS, you could get a ticket
when driving at 100.1 km/hour when the posted speed limit is 100
km/hour. The XRS is sensitve to X-rays ranging in energy from 0.3
to 12 keV.
Publication Date: June 2005
| 
