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一、引言对于中子水分仪在土壤介质中测量深度的确定,人们往往习惯于使用“重要云球”的概念,认为中子水分仪测得的是以中子源为中心的重要球体内的热中子平均计数。当源和探测器组合在同一中心的探头中时,这一概念无疑是适用的。但在端接源探头中,源中心与探测器中心相距一定的距离,此时采用“重要云球”概念确定测量深度,显然是不太适当的。在锂玻璃中子土壤水分仪中,源与锂玻璃之间有很长一段间隔,其中锂玻璃探测器((?)40×5)较薄。快中子与土壤介质中的氢核碰撞后,慢化扩散成为热中子,再通过锂玻璃闪烁体被仪器记录。因此,传统的“重要云球”概念已不能很好地用于确定锂玻璃中子土壤水分仪的准确深度。
I. INTRODUCTION For the determination of the depth of neutron moisture meter in the soil medium, people tend to use the concept of “important cloud ball” and think that the neutron moisture meter measures the inside of an important sphere centered on the neutron source Average number of thermal neutrons. This concept is undoubtedly applicable when the source and detector are combined in the same central probe. However, in the termination source probe, the distance between the source center and the detector center is a certain distance. In this case, it is apparently not appropriate to adopt the concept of “important cloud ball” to determine the measurement depth. In the lithium glass neutron soil moisture meter, the source and the lithium glass have a long interval, in which the lithium glass detector ((?) 40 × 5) is thinner. After colliding with hydrogen nuclei in the soil medium, the fast neutrons diffuse into thermal neutrons and are recorded by the instrument through a lithium glass scintillator. Therefore, the traditional concept of “important cloud ball” has not been well used to determine the exact depth of lithium glass neutron moisture meter.