The mineral-PET rock sorter : a study of the ( y,n) activation process

Abstract

Positron Emission Tonwgraphy is a technique used for imaging in diagnostic medicine. In this technique a nutrient is labeled with a positron emitter and imaging of the metabolic uptake rates is performed. Mineral-PET uses an analogous process where a diamond inside a kimberlite rock can be imaged in an on-line mining situation. The diamond is PET-inactive and therefore a minute fraction of carbon atoms need to be temporarily activated as a positron radiation source. Gamma radiation is used to convert the dominant carbon-12 isotope to the positron emitter isotope carbon-11, via the gammaneutron (y,n) nuclear reaction. The emitted positron thermalizes and annihilates with an electron resulting in two back-to-bad<: gamma photons, each at 511 keV energy, which is then detected by the matrix of position sensitive fast timing BGO (bismuth germanate- Bi₁₂Ge₄O₄) detectors. This study investigate the activation process where gamma photons in the energy range of around 25 lVIe V are produced by bremsstrahlung from an electron beam, where a high atomic number material is used as a target. The study then concludes on the parameters of accelerator design (i.e. converter type and thickness and electron beam energy) based on the feasibility study of the new technology.