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Monte Carlo Simulation of Dose-distribution Nearby Au-CuPc and γ-Ray Shield for Neutron Element Analysis

Author: ZhangHui
Tutor: ZhaoGuangYi
School: Jilin University
Course: Particle Physics and Nuclear Physics
Keywords: Monte Carlo method X-ray Dose enhancement factor Organic semiconductor gamma-ray shielding
CLC: O571.5
Type: Master's thesis
Year: 2009
Downloads: 53
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Abstract


Semiconductor device with the structure of“Metallizing-semiconductor”would be damaged by X-rays or gamma rays, the reason is that the cross-section of photoelectric effect in high-Z (atomic number) material is much larger than in low-Z material for low-energy rays, and accordingly when the metallizing is made of high-Z materials, there will be nonequilibrium fluxion of photon-electron between the high-Z region and low-Z region because of the different consistencies of two regions. Therefore, the Dose Enhancement Effect appears in the silicon with the additional photoelectrons diffusing from the high-Z material via the interface,and the dose enhancement factor, called DEF for short, is a important parameter in Dose Enhancement Effect, and which is defined as follows. DEF=dose of sensitive region/equilibrium doseSince the semiconductor device is very small and easily damaged, it is difficult to measure the dose distribution and the dose enhancement in sensitive region of semiconductor-metal interface irradiating with X-rays in experiment. Therefore, the dose enhancement effect of the semiconductor-metal interface in different metallizing layer is usually obtained by theoretical calculations.This paper describes the interface dose enhancement effects in different thickness of metal materials, as well as the development history of organic semiconductors and the researching actuality of organic semiconductors at home and abroad. We have used the Monte Carlo photon-electron coupling transporting method simulated the dose enhancement in Au-Si interface. We compared and analyzed the dose enhancement factor (DEF) we have gained with foreign papers, and the result is consistent with foreign data both in DEF and the energy range of X-rays caused dose enhancement, so Monte Carlo method is feasible to calculate the dose enhancement effect of the semiconductor-metal interface. Then the semiconductor-metal interface model of“Metallizing- copper phthalocyanine”is established, according to the model, dose distribution and dose enhancement factor (DEF) nearby the interface of “Metallizing- copper phthalocyanine”are calculated by MCNP program, and gained the dose enhancement effect nearby Au- copper phthalocyanine interface irradiating with X-rays with different thicknesses of Au.Through the Monte Carlo simulation, this paper gives out the curves of dose enhancement factor (DEF) to X-rays’ energy and direction when the thickness of Au at 0.5,1,2,4,8,10,12,16,30μm separately, these curves have much technical guidance function towards the organic semiconductor device’s anti-radiation reinforcement.In addition, this paper also calculated by MCNP program through keeping the distance between the neutron generator and gamma rays detector unchanged, increasing the thickness of lead between neutron generator and gamma-rays detector to reduce background interference and optimize the shield design ,improving the detection efficiency and having a good guide for hydrocarbon material containing of neutron element analysis.

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CLC: > Mathematical sciences and chemical > Physics > Nuclear physics,high energy physics > Nuclear physics > Neutron physics
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