Monte Carlo simulation on n-γ density logging using D-T neutron generator
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摘要: 根据D-T反应中子的能谱和角分布数据，建立了中子源模型；根据石灰岩地层标准刻度井群数据，建立了井模型。采用MCNP程序模拟了井中中子和射线的输运，得到了不同地层密度、不同源距处NaI探测器中的混合能谱和非弹能谱。在混合能谱2.5~4.5 MeV能区开窗，混合射线相对计数随源距的变化曲线显示，源距应选择在20~80 cm，密度与混合射线计数之间呈现非线性关系。在非弹能谱1.0~8.0 MeV能区开窗，非弹射线相对计数随源距的变化数据显示，源距应选择在20~40 cm或80 cm附近，密度与非弹射线计数之间成近似线性关系。Abstract: D-T neutron source model is developed according to the neutron spectrum and the neutron angular distribution of D-T reaction. A standard calibration well model is built. The transports of D-T neutron and -ray in the well are simulated using MCNP code. Mixed -spectrum and inelastic -spectrum in the NaI detector are obtained for different distance and different density. The data of the mixed gamma count in the energy range of 2.5 to 4.5 MeV as a function of distance show that the detector should be located in the space of 20-80 cm. The nonlinear relationships between the density and the mixed gamma count are presented. The data of the inelastic gamma count in the energy range of 1.0 to 8.0 MeV as a function of distance show that the detector should be located in the space of 20-40 cm or in the neighborhood of 80 cm. The relationships between the density and the inelastic gamma count can be approximatively expressed as a linear function.
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Key words:
- density logging /
- D-T neutron generator /
- Monte Carlo simulation /
- limestone /
- gamma energy spectrum
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