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利用γ-γ土壤密度探头测量沙卵石地层密度的主要困难是不能用压打和震动的方法下进路管,为此不得不用地质勘探钢管钻孔进行测量。然而地质钻孔孔径较大,用γ-γ土壤密度探头测量时,井内散射本底远大于来自地层的康普顿散射光子,不能分辨地层密度。我们采用了图1的探头系统,用垂向屏蔽体屏蔽来自井内的康普顿散射光子,使探测器只记录来自地层的散射光子,对沙卵石地层密度进行测量。所用放射源为~(137)Cs,210mCi,源到探测器中心的距离为36cm。探头系统的提放利用了细钢丝绳、三角架和小型绞车。利
The main difficulty in measuring the density of sand-gravel stratum using γ-γ soil density probe is that it can not be routed under pressure and vibration. Therefore, geological exploration of steel pipe borehole has to be conducted for the measurement. However, when the diameter of geological boreholes is large, the in-well scattering background is far greater than the Compton-scattered photons from the formation when measured with a gamma-gamma soil density probe and the formation density can not be discerned. We use the probe system of Figure 1 to shield the Compton-scattered photons from the well with vertical shields so that the detector records only the scattered photons from the formation and measures the density of the sand-gravel formation. The radioactive source used was ~ (137) Cs, 210 mCi, with a source-detector distance of 36 cm. The probe system is populated with thin wire ropes, tripods and small winches. Lee