| 摘要 |
A gain stabilized natural gamma ray spectroscopy system is used to measure casing thickness in a cased well borehole. A ratio of gamma ray intensity in two selected energy ranges forms a measurement signal representative of casing thickness based on the photoelectric absorption of natural gamma rays by iron. A coincidence technique employing dual scintillation crystals (51, 57) and a stabilization source (58) of charged particles and known energy gamma rays is used for gains stabilization, the particles and gamma rays coincidentally-emitted by this source (58) being detected by the respective crystals (57, 51) and a circuit (64) testing for coincidence so that the gain stabilization can be effected in accordance with the measured value of these known energy gamma rays. |
