Abstract
AREVA Mines and the Nuclear Measurement Laboratory of CEA Cadarache are collaborating to improve the sensitivity and precision of uranium concentration evaluation by means of gamma measurements. This paper reports gamma-ray spectra, recorded with a high-purity coaxial germanium detector, on standard cement blocks with increasing uranium content, and the corresponding MCNP simulations. The detailed MCNP model of the detector and experimental setup has been validated by calculation vs. experiment comparisons. An optimization of the detector MCNP model is presented in this paper, as well as a comparison of different nuclear data libraries to explain missing or exceeding peaks in the simulation. Energy shifts observed between the fluorescence X-rays produced by MCNP and atomic data are also investigated. The qualified numerical model will be used in further studies to develop new gamma spectroscopy approaches aiming at reducing acquisition times, especially for ore samples with low uranium content.
Highlights
Gamma logging for uranium exploration is currently based on total counting with Geiger Müller gas detectors or NaI(Tl) scintillators
The total count rate interpretation in terms of uranium concentration may be impaired in case of roll fronts, when the radioactive equilibrium of the natural 238U radioactive chain is modified by differential leaching of uranium and its daughter elements (Th, Ra, Rn, etc.)
In the case of secular equilibrium, more than 95% of gamma rays emitted by uranium ores come from 214Pb and 214Bi isotopes, which are in the back-end of 238U chain
Summary
Gamma logging for uranium exploration is currently based on total counting with Geiger Müller gas detectors or NaI(Tl) scintillators. In order to study the potential of these new approaches and to establish a numerical simulation model, a measurement campaign was carried out in the radiometric calibration station of AREVA Mines in Bessines, France [1], with a coaxial HPGe detector. This station holds seven cement blocks with increasing uranium contents, up to 1% weight fraction (i.e. 10,000 ppm). Energy biases between the fluorescence X-rays produced by MCNP and atomic data will be investigated
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