Method and apparatus for nuclear well logging with optimized timing for simultaneous measurement of thermal neutron decay time and gamma ray pulse height spectra
The invention relates to a novel method and apparatus for the cyclical timing of the neutron bursts, spectral gates, tau determination gates, and background measurement periods in a capture spectroscopy measurement. Each measurement cycle period is divided in time into 62 tau units, where tau is the thermal decay time constant determined from the immediately preceding cycle period. The neutron accelerator bursts eight times, each burst lasting for one tau unit and beginning at 0, 6, 12, . . . 42 taus. The capture spectral gates, two units long, follow ea neutron burst after a one tau unit long delay. Spectral background due to activation is measured in a long background window until tau equals 61, following a two tau delay from the eighth spectral gate and, properly normalized, is subtracted on a channel-by-channel basis from the spectrum accumulated from the capture spectral gates. Tau determination gates I and ii follow each neutron burst after a two tau delay. Each gate I is one tau long; each gate ii immediately follows gate I and is two tau long. After the eighth gate ii, a long gate iii (49 tau to 61 tau) is provided for correcting background counts in the tau determination gates I and ii.
- Assignee:
- Schlumberger Technology Corp
- Patent Number(s):
- US 4327290
- Application Number:
- TRN: 82-018170
- OSTI ID:
- 5239342
- Resource Relation:
- Patent File Date: Filed date 2 Nov 1979; Other Information: PAT-APPL-090800
- Country of Publication:
- United States
- Language:
- English
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NUCLEAR MAGNETIC LOGGING
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