Low activity spectrometric gamma-gamma borehole logging tool for the metalliferous industry

الملخص EN

The low activity spectrometric gamma-gamma technique was applied to the quantitative determination of lead and zinc grades in boreholes well-logging.

The tool was centralized and employed a γ-ray source of very low activity (1.8 MBq).

The log tool was tested separately using (i) 133Ba and (ii) 137Cs with 37*75 mm NaI (TI) scintillation detector.

Five source-detector configurations were studied and analyzed in the present work.

The calibration equations for lead (Pb) and Zinc Metal Equivalent (ZME) prediction using Barium and Cesium sources have been quantitatively described for every studied configuration.The optimum configuration for the logging probe using a 133Ba source is determined to be 52 mm source to detector spacing.

This configuration gives the best results for both Pb and ZME grade.

The rÆm.s.

deviation for Pb and ZME are 0.33 and 2.3% respectively.

The optimum configuration for the logging probe using a 137Cs source is determined to be 64 mm source to detector spacing.

This configuration gives the best results for both Pb and ZME grade.

The rÆmÆs.

deviation for Pb and ZME are 0.36 and 2.2% respectively.

The advantage of using low activity 137Cs source is that this radioactive source does not need an extra source for spectrum gain stabilization, where the same source is used for both primary sources of radiation and gain stabilization.

In addition,137Cs source is characterized by longer half- life and greater penetration effect of its gamma radiation.

The low activity 133Ba source however necessitates an additional 137Cs microsource for gain stabilization.

The tool is sensitive to changes in Zeq number of the matrix surrounding the borehole and could find application in the metalliferous mining industry for ore body delineation.

Due to its very low γ-ray source activity and lightweight, the tool is ideal for use with portable logging systems and underground mining operations