Technology of Pyroelectric X-ray Tubes

Authored by: Susumu Imashuku

Handbook of X-ray Imaging

Print publication date:  December  2017
Online publication date:  December  2017

Print ISBN: 9781498741521
eBook ISBN: 9781351228251
Adobe ISBN:

10.1201/9781351228251-6

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Abstract

Pyroelectric crystals, such as lithium niobate (LiNbO3) and lithium tantalite (LiTaO3), exhibit an electric dipole moment because the center of positive charge of the pyroelectric crystal does not coincide with the center of negative charge. The electric dipole moment in the pyroelectric crystal changes by heating or cooling the pyroelectric crystal. Thus, the surface of the pyroelectric crystal becomes electrically charged when its temperature is changed. The electrical charging on the surface of the pyroelectric crystal is immediately neutralized by suspended charges in air. In contrast, it takes a while, normally several minutes, for the electrical charge to be neutralized in a vacuum because the amount of suspended charges is quite small. Then, an electric field is produced between the surface of the pyroelectric crystal and other areas, such as components of the vacuum system. As a result, quite a small amount of the suspended charges (electrons and ions) is accelerated by the electric field of 106–108 V cm−1 (Rosenman et al. 2000). The accelerated charges impact on the pyroelectric crystal and components of the vacuum system such as stainless steel, which produces secondary electrons. The secondary electrons are also accelerated by the electric field. In this manner, an electron beam is generated by changing the temperature of the pyroelectric crystal in a vacuum.

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