Doshisha University, Kyotanabe, Kyoto 610-0321, Japan.
IEEE Trans Ultrason Ferroelectr Freq Control. 2009 Sep;56(9):1850-5. doi: 10.1109/TUFFC.2009.1260.
The dependence of X-ray intensity on the pressure and type of ambient gas was investigated for LiNbO(3) single crystals polarized in the c-axis direction at pressures of approximately 1 to 30 Pa. Ionization of surrounding gas molecules by the electric field generated by the crystal led to the production of both positive ions and free electrons. The electrons were accelerated toward a Cu target, radiating both white X-rays and X-rays specific to the crystal or target material by bremsstrahlung. The integrated X-ray intensity per cycle in the energy range 1 to 20 keV showed a local maximum value at a pressure P(max). The logarithm of P(max) was proportional to the Boltzmann factor using the first ionization energy of each ambient gas molecule. The value of P(max) was found to be independent of the electrical surface area of the crystal. The integrated X-ray intensity was approximated qualitatively by a quadratic function with pressure, which was upwardly convex. It was found that one of the causes of the reduction in X-ray intensity at pressures P > P(max) is the adsorption of positive ions generated by the ionization of gas molecules on the negative electric surface. It was also discovered that the lifetime of the X-ray radiation device could be improved when the X-ray radiation case was covered with another hermetically sealed decompression case. The gas with the smallest first ionization energy, with a partial pressure of P(max), was enclosed inside the X-ray radiation case (inner case) and the gas with the largest first ionization energy was enclosed at a suitable pressure between the inner and outer cases.
研究了在约 1 至 30 Pa 的压力下，沿 c 轴方向极化的 LiNbO(3)单晶体中 X 射线强度对环境气体压力和类型的依赖性。晶体产生的电场使周围气体分子发生电离，从而产生正离子和自由电子。这些电子被加速到一个 Cu 靶上，通过韧致辐射产生既包括晶体或靶材特有的 X 射线，也包括白光 X 射线。在 1 至 20 keV 的能量范围内，每个周期的积分 X 射线强度在压力 P(max)处呈现局部最大值。P(max)的对数与每个环境气体分子的第一电离能的玻尔兹曼因子成正比。发现 P(max)的值与晶体的电表面积无关。积分 X 射线强度与压力的关系可以用二次函数近似，该函数是向上凸的。研究发现，在压力 P > P(max)时，X 射线强度降低的原因之一是气体分子电离产生的正离子被吸附在负电表面上。还发现，当 X 射线辐射装置的外壳用另一个密封减压外壳覆盖时，可以提高 X 射线辐射装置的寿命。在 X 射线辐射装置内（内壳）封闭具有最小第一电离能且分压为 P(max)的气体，在内外壳之间的合适压力下封闭具有最大第一电离能的气体。
