Department of Radiation Sciences, Radiation Physics, Umeå University, SE-901 85 Umeå, Sweden.
Phys Med Biol. 2010 Aug 7;55(15):4247-60. doi: 10.1088/0031-9155/55/15/004. Epub 2010 Jul 8.
The correction for general recombination losses in liquid ionization chambers (LICs) is more complex than that in air-filled ionization chambers. The reason for this is that the saturation charge in LICs, i.e. the charge that escapes initial recombination, depends on the applied voltage. This paper presents a method, based on measurements at two different dose rates in a pulsed beam, for general recombination correction in LICs. The Boag theory for pulsed beams is used and the collection efficiency is determined by numerical methods which are equivalent to the two-voltage method used in dosimetry with air-filled ionization chambers. The method has been tested in experiments in water in a 20 MeV electron beam using two LICs filled with isooctane and tetramethylsilane. The dose per pulse in the electron beam was varied between 0.1 mGy/pulse and 8 mGy/pulse. The relative standard deviations of the collection efficiencies determined with the two-dose-rate method ranged between 0.1% and 1.5%. The dose-rate variations of the general recombination corrected charge measured with the LICs are in excellent agreement with the corresponding values obtained with an air-filled plane parallel ionization chamber.
在液体电离室（LIC）中，总复合损失的校正比在充满空气的电离室中更为复杂。原因是 LIC 中的饱和电荷，即逃脱初始复合的电荷，取决于所施加的电压。本文提出了一种基于在脉冲束中测量两个不同剂量率的方法，用于 LIC 中的总复合校正。使用脉冲束的 Boag 理论，并通过数值方法确定收集效率，该方法等效于在充满空气的电离室中进行剂量测量时使用的双电压方法。该方法已在使用两种充满异辛烷和四甲基硅烷的 LIC 的 20 MeV 电子束中的水中实验中进行了测试。电子束中的脉冲剂量在 0.1 mGy/脉冲和 8 mGy/脉冲之间变化。用双剂量率法确定的收集效率的相对标准偏差在 0.1%到 1.5%之间。用 LIC 测量的经总复合校正的电荷的剂量率变化与用充满空气的平行平板电离室获得的相应值非常吻合。
