The National Institute of Standards and Technology (NIST) has developed a highly sensitive x-ray spectrometer called the Transition Edge Sensor Microcalorimeter. This device can measure the energy of individual x-ray photons with a resolution of about 5 electron volts (eV) over a wide range of energies from hundreds of eV to 8,000 eV.
The NIST microcalorimeter works by detecting the tiny amount of heat generated when an x-ray photon hits a block of normal (non-superconducting) metal. This heat pulse is converted into an electronic signal through a chain of superconducting elements, including a superconducting bimetal junction that is held at a critical temperature where small changes in temperature cause large changes in resistance.
The resistance changes are monitored by a superconducting quantum interference device (SQUID) amplifier, which converts the signal into voltage pulses. These pulses are then digitized and processed using an optimal filter to determine the energy of each individual x-ray photon. The NIST microcalorimeter can handle a few hundred x-ray photons per second.
To function properly, the sensor must be kept at extremely low temperatures, around 150 millionths of a degree above absolute zero (150 mK). This is achieved by cooling the device in three stages: first with liquid nitrogen, then with liquid helium, and finally using an adiabatic demagnetization refrigerator to reach the required temperature. The temperature is actively stabilized around 150 mK for durations of six to ten hours.
Source: https://www.nist.gov/laboratories/tools-instruments/microcalorimeter-detector
Keywords: x-ray spectrometer, superconducting elements, quantum interference device, adiabatic demagnetization, microcalorimeter
