New scintillators and method for spectral gamma logging in slim boreholes

Abstract

Wide-spread application of spectral gamma ray logging system in mineral exploration has not really developed in the geotechnical, environmental-groundwater, and mining industries, but. A new approach to borehole logging by the Deep Exploration and Technologies Commonwealth Research Centre (DET CRC) has created a Logging-While-Drilling tool, the shuttle, to measure natural gamma ray activity during the drilling process. The Shuttle allows the collection of high quality natural gamma spectra by placing a sensor on the core-barrel and logging whilst drilling; a much slower process than wireline logging. To make good the time advantage that the shuttle approach provides we need to use better scintillators than the commonly used materials of NaI, CsI and BGO, which perform poorly in slim-hole applications. Newer materials: SrI, GAGG and CWO scintillators were tested to evaluate their use in future slim-line logging-while–drilling. All of the newer scintillators outperform the older generation in either resolution or stopping power. However, for small-size detectors the heavier scintillators perform far better in measuring the natural radioactive isotopes and gamma interactions with the rock mass. For future shuttle sensors GAGG and CWO scintillators are our preferred scintillators as they perform well in capturing a reasonable natural gamma spectrum even in sizes as small as 25mm in diameter.