X-Ray Detectors

Since the 1970s, new semiconductor detectors have been developed (silicon or germanium doped with lithium: Si(Li) or Ge(Li), which allows to detect directly X-ray energy spectrum. This method is called energy dispersive X-ray spectroscopy (EDX or EDS).

The principle of operation is based on the absorption of X-ray photon in special semiconductor structure and direct correlation between amplitude of resulted electric signal to energy of the X-ray photon. This provides possibility of spectral analysis of absorbed X-rays. Such detectors are sometimes called solid state X-Ray detectors.

Devices based on the detection principle find many applications now – X-ray Fluorescence Analyzers (RFA).  The use of these analytical methods and equipment is wide from mining and industries (analysis of the composition of the materials), science (electron microscopy, etc.) and security needs.

The great impact to the X-ray spectroscopy method was done with development of special semiconductor structures of the detectors which made possible applications of the method very wide - from Si-PIN to Silicon Drift Detectors (SDD) and CdTe detectors.

Unlike conventional X-ray detectors, such as Si(Li), new semiconductor structures do not need cooling with liquid nitrogen. Relatively slight cooling to -20…-50°C is enough to provide perfect performance of X-ray detectors.

Here it does not need rejecting large amount of heat. These detectors have low power and emit little heat. However, they should be cooled: the lower the temperature, the better detector performance.

Cooling solves several tasks:

• to suppress heat-activated generation electron-hole pairs, giving the main contribution to noise and reduction of energy resolution
• to stifle the diffusion of Li atoms (dopiness) in the field of applied voltage, which destroyed the p-i-n structure.
• to suppress the noise field-effect transistor (FET), which is directly in contact with a sensing semiconductor structure and is a first pre-amp cascade.

The most successful for these tasks is to use thermoelectric Peltier coolers (TECs). It makes semiconductor x-ray detectors miniature, affordable and greatly expanded their scope of applications.

TECs have unique reliability of several hundred thousand hours of continuous operation. It is more than 20-25 years of operation without maintenance and replacement, which is important for telecommunication systems.

The company RMT produces several series of multi-stage TECs suitable for in X-ray detectors.

• For cooling to temperature range -20…-30°C different types of optimal two-stage TECs are advised in series 2MC04 and 2MD04.
• For deeper cooling to temperatures -50…-60°C four-stage TECs are suitable – series 4MC04 and 4MD04.

The most popular packages for state-of-art X-ray detectors are TO-Style packages. The company RMT offers complete solutions – thermoelectric cooling modules mounted in standard or customized TO-style packages suitable for X-ray detectors.

All the products are manufactured in whole conformity with the standard of reliability Telcordia GR468 Core. The modules of RMT are fully compliant with RoHS и REACH requirements.

To select a suitable solution and the optimal TEC for an application, the supporting Online TEC Assistance is available at RMT’s website. For detailed modeling and calculations the company RMT provides our customers by free software TEC Cad or iTECPad.