Theory of Operation
When heated, a pyroelectric crystal exhibits spontaneous decrease of polarization. Hence, as the temperature increases, an electric field develops across the crystal. For a specific crystal orientation (-Z face pointing to the target), the top surface of the crystal gets positively charged and attracts electrons from the low pressure gas in the environment. As the electrons impinge on the surface of the crystal, they produce characteristic x-rays (Ta) as well as bremsstrahlung x-rays (see figure 1). When the cooling phase starts, the spontaneous polarization increases, and the electrons from the top surface of the crystal are accelerated towards the Cu target which is at ground potential. At this part of the cycle, Cu characteristic x-rays are produced as well as bremsstrahlung x-rays (see figure 2). When the crystal temperature reaches its low point, the heating phase starts again. The cycle time of the COOL-X can be varied from 2 to 5 minutes.
Figure 3 shows the typical x-ray spectrum of the COOL-X obtained from the sum of 300 cycles with the dominant 8 keV peak and the bremsstrahlung continuum. Figure 4 shows a typical COOL-X output count rate as a function of time for several heating and cooling phases. The x-ray flux varies throughout the cycle and may vary from cycle to cycle, see figure 4.
Figure 1.
Figure 2.
Figure 3.
Figure 4 is a typical COOL-X Output Flux vs Time. Specific units may have more counts in the heating or cooling phase, or all of the counts in one of the two phases.
Figure 5. Cool-X Output Flux vs. Angle
Figure 6. Amptek offers a version of the COOL-X without the tantalum (Ta) lines in the spectrum. This is the output spectrum without the Ta lines. Only the copper (Cu) lines are seen. This spectrum shape is similar to a traditional X-ray tube. This is the accumulation of 90 complete cycles.
References
J.D. Brownridge and S. Raboy “Investigations of pyroelectric generation of X-rays” Journal of Applied Physics, Vol. 86, No. 1, July 1999.
Hiroyuki Ida and Jun Kawai “Portable x-ray fluorescence spectrometer with a pyroelectric x-ray generator,” X-Ray Spectrometry, 34: 225-229, 2005.
CAUTION: The COOL-X is only one component of an X-ray instrument. It is the responsibility of the user, the OEM customer, or experimenter to provide a fail safe metal enclosure to prevent escaping radiation while using this product. The final product (turn-key system) must comply with local government regulations to protect personnel from exposure to radiation. Amptek Inc., bears no responsibility for the incorrect use of this product.