Radiation of X-rays Using Uniaxially Polarized LiNbO3 Single Crystal

Abstract

AbstractIt is well known that by changing the temperature for the polarized hemimorphy single crystal, such as LiNbO3 or BaTiO3, the electric field with high intensity is generated and then atmospheric gas atoms or molecules around the crystal are ionized. Using these phenomena, X-rays could be radiated by the bremsstrahlung radiation of electrons in low pressure [1,2]. However, this method has some disadvantages. For example, it is difficult to maintain the intensity of X-rays for a long term. The gas pressure range, where the intensity of X-rays is high, is narrow. The purpose of this study is to increase the intensity of X-rays in a high vacuum. In a low vacuum, positive charges generated by the ionization of gas molecules near the crystal weaken the electric field strength. Consequently, the intensity of X-rays also becomes weak. On the other hand, in a high vacuum, the number of electrons decreases. Thus, thermally emitted electrons are supplied to the X-rays radiation system in high vacuum to increase and stabilize the intensity of X-rays.The -z plane of the congruent LiNbO3 single crystal polarized in the z-axis direction of a 5 mm thickness and a 10 mm diameter was opposed to the Cu target of a 10 μm thickness placed at a distance of 21 mm from the –z plane in the gas pressure of 10-2-10-4 Pa. The temperature of crystal was changed between from -5 to 75 °C using Peltiert device. The temperature history of the crystal consists of a repetition of a series of the increasing and decreasing processes with the same period. Filament of thorium-added-tungsten as a thermal electrons source was placed at a distance of approximately 20 mm from the crystal side edge. DC current flowing in the filament was adjusted from 0 to 4 A.In the increasing process of the temperature, the characteristic X-ray of Nb was radiated. This result indicates that the sign of net charge on -z plane of the crystal is positive. Because thermally emitted electrons are supplied to the positively charged –z plane, the electric field strength generated by the crystal is very low. Thus, the intensity of characteristic X-ray of Nb is low. On the other hand, in the decreasing process of the temperature, the characteristic X-ray of Cu was radiated. At the pressure of approximately 10-2 Pa and the filament current of 2.5 A, the intensity of X-rays showed the local maximum. If electrons are supplied more, synthetic electric field strength is weakened by the electric field made by the electron. The intensity of X-rays using thermal electron source was ten or more times higher at the maximum than that without the source and was almost comparable as the case of a low vacuum or more than it. Using thermal electron source, the intensity of X-rays increased with decreasing the pressure down to approximately 10-2 Pa and became constant at lower pressure.