| 摘要 |
A well tool (14) is positioned in a borehole at a depth to be investigated. The tool houses a neutron source (36) which irradiates the borehole environs with neutrons of sufficient energy to cause the nuclear reaction O<1><6> (n,p) N<1><6> . Three gamma ray detectors (34,35,39) are spaced longitudinally from the source and from one another and detect gamma rays resulting from the decay of the unstable isotope N <1><6>. A pulse height analyser (85) makes individual counts of the three sets of detected gamma rays, and the count signals are utilized in predetermined relationships to provide a signal representative of the linear flow rate of an undesired water flow outside said casing in a direction from said source towards the detectors. The provision of three detectors enables the linear flow rate signal to be obtained without the necessity of obtaining counts of background gamma radiation. |
