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摘要
[1] A modified three-group neutron scattering analysis in cylindrical coordinates is used to predict the neutron flux produced by an annular source of neutrons centralized in an access hole in snow or ice. The diffusion approximation to the constant cross-section neutron transport equation is used to describe neutron flux in the snow and ice. Neutron flux in the access hole is described either by the diffusion approximation or by a transient approximation depending on the magnitude of the transport mean free path for neutrons in the borehole fluid. For "dry,'' air-filled, access holes the transient solutions are most suitable. A theoretical calibration algorithm, relating snow density to the neutron count rate measured by a cylindrical detector ( also centralized in the access hole) and the access hole diameter, is derived. A good fit to experimental data is obtained using values of the physically based parameters of the algorithm within ranges determined a priori from the literature and from manufacturer's specifications. A calibration equation fitted to output from the algorithm for T = -10 degrees C is consistent with field data and shows that the accuracy and precision of density measurements made using the probe can match the accuracy and precision of field gravimetric methods, with the advantage of a continuous and unbiased sampling method.
- 出版日期2008-8-19
- 单位中国极地研究中心
