Background: γ spectrometry logging is one method for accurately computing uranium content in uranium-thorium mixed type deposit for slim borehole application. Purpose: The aim is to design slim borehole γ spectrometry logger N451 with ?30 mm×100 mm high detection efficiency Bi4Ge3O12 (BGO) scintillation detector

whose diameter and length are 45 mm and 1300 mm

respectively. Methods: By applying the configuration of dual-microprocessor plus dual port RAM to improving the data throughput rate

the aim of reducing dead time was achieved. As to auto-stabilization

by means of 4-window algorithm with 133Ba reference source

plus temperature-based coarse set while power on and fine tune Photomultiplier Tube (PMT) high voltage while logging

the auto-stabilization accuracy was considerably improved. Using Pb-Sn mask method

N451 overcomes the interference on auto-stabilization system from the high level uranium deposit low energy γ-ray. Results: After multiple saturated modules and 226Ra point source calibration and Fe as well as H2O coefficient correction

field logging was surveyed. Conclusion: The uranium content relative error was less than 10%. The slim borehole γ spectrometry logger is up to the specification. Abstract