Based on Polyachenko’s formulation, the complete solution of the boundary value problem for pulsed neutron logging is derived for a centralized tool model. The solution is more general than Polyachenko et al.’s earlier solution in that the unrealistic assumption of zero thermal neutron lifetime in the fluid‐filled borehole is eliminated and that, in addition to the formation signal, the borehole signal is also considered. For formations of weak absorption, the theoretical solution predicts features in the gamma‐ray die‐away curve similar to those observed in real logging cases. For formations of strong absorption, the asymptotic behavior of the gamma‐ray decay curve is influenced by the borehole size. This theoretical solution, even though not directly applicable to the complex real logging environment, offers us a means for understanding qualitatively the interrelationship among all thermal neutron parameters of the borehole and the formation.
Precise Neutron Lifetime Experiment Using Pulsed Neutron Beams At J-PARC
