Different Materials Interface Dose Enhancement Of Theoretical Research

When low-energy gamma-ray enters the interface constructed with two different materials, the dose would be enhanced on the low-Z material side. The reason is that the cross section of photoelectric effect in high-Z material is much larger than in low-Z material for low-energy gamma-ray ,and there is more photoelectron entering the low-Z material from high-Z material through the interface than from low-Z material to high-Z material. Therefore, the dose would be enhanced by the additional photoelectron in the low-Z material near interface. The dose would be corrected when there exist interface constructed with two different materials. The Dose-enhancement-factor is a important parameter in dose enhancement effect. It is very difficult to measure this parameter by experiment. Usually it is obtained by theoretic calculation. Laws of interaction between low-energy gamma ray and matter are introduced in this paper. The cause of dose enhancement effect is found from these laws. The dose enhancement effects of various devices are introduced also. We selected coupled photon-electron transport model to calculate the dose-enhancement-factor(DEF). The mathematic description of photon and electron is given in the Monte-Carlo method. Two interface models were established, one is material interface, another is CMOS interface. According to these models, we designed intake programs for MCNP at each case. Then we obtained dose-enhancement-factor of each interface. We drew the variation curve of dose-enhancement-factor with X-ray energy. It is showed from these curves that they are similar. The range of dose enhancement is I OKeV?5OKeV. The largest dose-enhancement-factor of W/Si interface is 13. And it is 19 to W/Si02 interface, 15 to Ta/Si interface and 17 to TalSiO2 interface.