| 摘要 |
Methods and apparatus are provided for determining the thermal neutron lifetime of earth formations in the vicinity of a well borehole. The borehole environs are irradiated with pulses of fast neutrons. Between neutron pulses capture gamma rays are detected in at least six, non-overlapping, sequential time intervals and count rate signals representative thereof are generated. Comparisons of the six count rate signals are made to determine which ones have been affected by a borehole component. Only those count rate signals not affected by the borehole component are used to determine the thermal neutron lifetime by a least-squares fitting technique.
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