Patent Document ID: 4409481
Application ID: 06383680
Patent Flag: 1

Claim One:
1. A method for simultaneously determining the borehole component and the formation component of thermal neutron decay time of a borehole and earth formations in the vicinity of the borehole, comprising the steps of: repetitively emitting, in a well borehole, relatively short duration pulses of fast neutrons which are rapidly moderated by interaction with nuclei of materials in the borehole and surrounding earth formations and slowed down to thermal energy, creating repetitive bursts of thermal neutron population in the borehole and surrounding earth formations; detecting, in the borehole during a time interval between said repetitive pulses of fast neutrons, radiations representative of the thermal neutron population in the borehole and surrounding earth formations, in at least four time subintervals subsequent to a pulse of fast neutrons and generating at least four count rate signals representative of said thermal neutron populations during said at least four time subintervals; detecting, during a separate time interval between said repetitive bursts of fast neutrons, radiations attributable to a background radiation component of radiation and generating a background count signal representative thereof; correcting said at least four count rate signals for the presence of said background radiation component to provide at least four background corrected count rate signals; combining said at least four background corrected count rate signals according to an iterative fitting technique in which exponential relationships are assumed to exist for a borehole and a formation component of thermal neutron decay time to simultaneously obtain two measurement signals representative of the borehole component and the formation component of thermal neutron decay times; and recording said measurement signals as a function of borehole depth.