| 摘要 |
A method for laboratory measurement of lithology factor L related to the photoelectric absorption properties of a rock sample for use in lighology determinations. By definition L=( sigma T- sigma C)/ sigma C where sigma C is the Compton cross section sigma T is the total photoelectric cross section of the sample which includes the binding-energy corrected Compton cross section and the Rayleigh photoelectric cross sections. A low-energy source of gamma radiation sensitive to photoelectric absorption and a high energy source of gamma radiation that has a significantly different sensitivity to photoelectric absorption are employed and the attenuation of radiation from each source is measured. With the low energy source, radiation count rates NL and NLo obtained for measuring attenuated radiation with the sample present and with the sample absent, respectively, and similar count NH and NHo are obtained for the high energy source. Lithology factor L and electron density rho e are derived by simultaneously solving a first function of the count rates NL and NLo and a second function of the count rates NH and NHo, wherein each of the functions includes the electron density rho e and thickness t of the sample. The high-energy measurements are not necessary if an elemental analysis is performed and measurements of the bulk density and sample thickness are made. Lithology factor L may be transformed into a modified photoelectric factor, Pem by a linear transform chosen such that Pem is identical to the photoelectric factor Pe in pure limestone and sandstone.
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