(1) A mathematical relationship between two values, where one value is divided by the other, commonly expressed as a fraction.
(2) In Thermal Decay Time Logging. A measurement recorded with the Dual-Spacing Thermal Decay Time tool which is derived from the counting rates of the two detectors. The ratio measurement has characteristics similar to those of a neutron log and for specific cases can be calibrated to serve as such. Used with the measurement of the Thermal Decay Time tool, it provides an apparent porosity and an apparent formation water salinity, useful for cased-hole formation evaluation.
(3) With other dual-spaced radiation detector systems, it is the count-rate ratio (of near to far detector) sometimes recorded with two-detector tools such as the compensated neutron log.