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以费米理论为指导,提出电子线的均整块制作与X线不同,可用最佳均整面积和最佳均整厚度的方法制作。在选用8MeV电子线,源皮距为2m的条件下,以透明X线胶片为材料,选出了均整块最佳面积为6cm×4.8cm,最佳总厚度为2.8mm。厚度再增加,对改善均匀度不起明显作用,但剂量损失和X线污染会显著提高。在此条件下,测得±10％的剂量区为25cm×21cm。中心轴深度5cm处的PDD为1.8％。在此长SSD时,低熔点铅制成的挡块对剂量影响很大,约与面积成正比。
Based on the Fermi theory, it is proposed that the uniform mass of the electron wire is produced differently from the X-ray, and the method can be produced by using the best uniform area and the best uniform thickness. In the selection of 8MeV electronic wire, the source skin from the 2m under the conditions of transparent X-ray film as the material, selected the best piece of the average area of 6cm × 4.8cm, the best total thickness of 2.8mm. Further increase in thickness, to improve the uniformity of no significant role, but dose loss and X-ray pollution will be significantly increased. Under this condition, a ± 10% dose zone was measured as 25 cm × 21 cm. The PDD at a center axis depth of 5 cm is 1.8%. In this long SSD, the low melting point lead made of a large impact on the dose, about proportional to the area.