Seneviratne M D S, Reinhard M I, Baldock C
Institute of Medical Physics, School of Physics, University of Sydney, Sydney, Australia.
Phys Med Biol. 2007 Jul 7;52(13):3837-46. doi: 10.1088/0031-9155/52/13/012. Epub 2007 May 31.
The low energy model of the GEANT4 Monte Carlo toolkit was used to simulate the energy response of a T.P.A. Mk-II ionization chamber under a variety of different conditions. The sample position resulting in the maximum response along the axial direction of the chamber was obtained. The parameters of the simulation were chosen to account for the maximum effect of the particle backscattering and the setting of most suitable values for the production thresholds and the energy cuts in the GEANT4 Monte Carlo code. The chamber response for different compositions of detector elements was also studied. The simulated radioactive source was a glass ampoule containing 3.6 ml of the radionuclide in an aqueous solution. The energy response of the chamber at the maximum response was obtained for simulations for (60)Co, (22)Na and (59)Fe nuclides. Verification of the simulated response was obtained using experimental measurements with radioactive sources. The simulated results were in good agreement with the experimentally measured data to within 0.04-2.0%. In the energy range below 200 keV the response curve was complex due to the increase of photoelectric cross sections of the chamber materials. Effects due to backscattering occur at boundaries between chamber elements and also become significant at sites of lead shielding at photon energies above 700 keV. The chamber response for different compositions of detector elements was also studied. The response of the chamber depended highly on the energies of emitting particles, source position and materials used in electrodes and thimble wall.
使用GEANT4蒙特卡罗工具包的低能模型来模拟T.P.A. Mk-II电离室在各种不同条件下的能量响应。获得了沿电离室轴向产生最大响应的样品位置。选择模拟参数以考虑粒子背散射的最大影响，并为GEANT4蒙特卡罗代码中的产生阈值和能量截断设置最合适的值。还研究了电离室对不同探测器元件组成的响应。模拟的放射性源是一个玻璃安瓿，其中含有3.6毫升处于水溶液中的放射性核素。针对（60）Co、（22）Na和（59）Fe核素的模拟，获得了电离室在最大响应时的能量响应。使用放射性源的实验测量对模拟响应进行了验证。模拟结果与实验测量数据在0.04 - 2.0%的范围内吻合良好。在200 keV以下的能量范围内，由于电离室材料的光电截面增加，响应曲线较为复杂。背散射效应发生在电离室元件之间的边界处，并且在光子能量高于700 keV时，在铅屏蔽部位也变得显著。还研究了电离室对不同探测器元件组成的响应。电离室的响应高度依赖于发射粒子的能量、源位置以及电极和套管壁中使用的材料。
