Biggs P J, Russell M D
Phys Med Biol. 1983 Sep;28(9):1033-43. doi: 10.1088/0031-9155/28/9/003.
The presence of secondary electrons in photon beams of 60Co and 4, 8, 10, 15 and 25 MV x-rays has been studied by measuring surface charge using thin window ionisation chambers. Measurements have been made for square fields from 4 X 4 cm2 to 35 X 35 cm2 for locations from the collimator head to a distance of 4 m from the target. In addition, measurements have been made for rectangular fields at 10 MV and 25 MV for fields of equivalent area from 5 X 5 cm2 to 25 X 25 cm2. By eliminating the inverse square effect, the presence of contaminants from the head and the effect of build-up in air are clearly seen and well separated. Comparison between the curves at different energies indicates an increasing effect of contamination from the head with energy and a decreasing effect of electron production in air with increasing energy.
通过使用薄窗电离室测量表面电荷，研究了钴 - 60以及4兆伏、8兆伏、10兆伏、15兆伏和25兆伏X射线光子束中二次电子的存在情况。对于从4×4平方厘米到35×35平方厘米的方形射野，在从准直器头部到距靶4米的位置进行了测量。此外，对于10兆伏和25兆伏的矩形射野，在等效面积从5×5平方厘米到25×25平方厘米的范围内进行了测量。通过消除平方反比效应，可以清楚地看到头部污染物的存在以及空气中积累的影响，并且它们得到了很好的区分。不同能量下曲线之间的比较表明，随着能量增加，头部污染的影响增大，而空气中电子产生的影响减小。
