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Abstract
Over the 100 years of their use, X-ray generators have proven to be indispensable in a wide array of applications. However, the methods for generating X-rays have not developed significantly, and the inherent size and power draw of existing X-ray generators limit the manufacture of more portable X-ray systems. The first demonstration of applying the pyroelectric effect for X-ray generation in 1992 made it a promising candidate for in-field and on-line analyses. This method of thermally cycling a pyroelectric material in a high vacuum exhibits advantages of being lightweight, compact and battery operated.
In this thesis, an X-ray generator that utilises the pyroelectric effect was developed and optimised to maximise its performance, in terms of X-ray flux and end-point energy. The generation of X-rays relied on the emission of electrons which was dependent on the electric field created between the pyroelectric crystal and the target placed at a gap distance. Evaluation of the material figures-of-merit and utilisation of electrostatics simulations to estimate the electric field in the gap determined a theoretical optimal combination of material properties, crystal thickness and gap distance.
An experimental system was built to simultaneously control the temperature of the pyroelectric crystal in a high vacuum chamber and collect time and energy-resolved X-ray emissions. The effects of various parametric combinations were then investigated and found to deviate from the theoretical findings. Thus, the most optimal combination of parameters was using the pyroelectric crystal, lithium tantalate, at a gap distance of 5 mm and pressure of 0.33 Pa. This produced an X-ray flux of 1.22e5 cm2/s and end-point energy of 40 keV.
The enhancement of the electric field at the crystal edges was exploited in an attempt to improve the X-ray generator’s performance by dicing the crystal to introduce more edges per unit area. Using lithium tantalate, a range of dicing combinations were assessed and found to underperform compared to its uniform counterpart.
Finally, the X-ray generator was operated over 200 cumulative hours and its output monitored. The X-ray flux and end-point energy fluctuated over this time and was found to correlate with the gradual surface degradation observed on the pyroelectric crystal.