Given that it is difficult to accurately determine the uranium and thorium contents in the strata of uranium-thorium mixed deposits,this study developed a digital γ spectrum logging probe based on cerium tribromide (CeBr₃) crystals.Using CeBr₃ crystals with a diameter of 38 mm×38 mm,the logging probe improved the sensitivity to uranium and the detection efficiency of ore beds with low uranium and thorium contents.The logging probe operated as follows.First,the original signals from the CeBr₃ detector were filtered and shaped using the C8051 single-chip microcomputer as the core processor.Then,the γ spectrum data were obtained using the energy spectrum collector.After the spectrum unfolding based on the inverse matrix is performed for the γ spectrum data,precise uranium and thorium contents in the ore beds were obtained.Finally,the γ spectrum data were transmitted to the host computer for logging through the RS-485 bus.The results show that the logging probe had high measurement accuracy in the standard uranium-thorium mixed model,with indication errors of less than 6%,stability of less than 1.5%,and repeatability of less than 1%.Moreover,the 2.62 MeV energy peak drift of thorium ²⁰⁸Tl did not exceed ±0.3 channels,and the relative errors of log anomalies were less than 4%.Therefore,the digital γ spectrum logging probe proposed in this study is applicable to the exploration and logging of uranium deposits.