A microcalorimeter is a device for measuring the
energy of X-rays. works by measuring the heat of a
single photon.
is basically a thermal
device. The energy of an X-ray photon is deposited in an absorber and
detected with a thermistor. An X-ray which hits the absorber knocks
an electron loose from an atom of the absorber material. This
photoelectron then rattles around in the absorber, ultimately raising
the temperature of the absorber by a few milliKelvin. The thermistor
is partially isolated from the absorber, to give the absorber time to
come into equilibrium before the thermistor begins to see the
temperature rise.
After a few milliseconds, the thermistor comes to the same temperature as the absorber, a few mK warmer than the heatsink. Then the thermistor begins to cool as the heat flows out the weak link (the "legs" of the detector) to the heatsink. After a few tens of milliseconds, the thermistor has returned to its normal operating temperature.
The temperature rise DT measured by the thermistor is approximately proportional to the energy of the X-ray photon:
DT ~ E/C
where E is the energy of the X-ray and C is the heat capacity of the absorber. So by measuring how much the temperature changes, we can determine the energy of the X-ray.
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