Borehole logging using LaBr3 scintillation detector and digital spectrometer which rejects pile-up pulses

摘要

A gamma ray detector assembly 10 for a borehole logging system requires the measurement of gamma radiation with optimized gamma ray energy resolution and with fast emission times required to obtain meaningful measurements in high radiation fields. The detector assembly 11 comprises a lanthanum bromide (LaBr3) scintillation crystal and a digital spectrometer that cooperates with the crystal to maximize pulse processing throughput by digital filtering and digital pile-up inspection of the pulses. The assembly 10 also includes a pulsed neutron source 12. The detector assembly is capable of digital pulse measurement and digital pile-up inspection with dead-time less than 600 nanoseconds per event. Pulse height can be accurately measured (corrected for pile-up effects) for two pulses separated by as little as 150 nanoseconds. Although the invention is applicable to virtually any borehole logging methodology that uses the measure of gamma radiation in harsh borehole conditions, the invention is particularly applicable to carbon/oxygen logging.