| 摘要 |
Porosity measurements are carried out by employing a pulsed source of high energy neutrons actuated to irradiate a medium; some of the neutrons returning from the medium are detected by a specially filtered epithermal neutron detector. Control states are generated to define each of an ordered series of successively longer time intervals, the first of which is a few microseconds in length. Counters connected to the detector count representative numbers of the epithermal neutrons during each of the control states. Ratio functions are generated representative of the ratios of the epithermal neutrons counted during successively later equal length combinations of the time intervals. The ratio functions are compared with a predetermined threshold level and a porosity function is established in dependence upon the ratio function which earliest in time with reference to one of the irradiating pulses bears a predetermined relation to the threshold level.
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