Daniel Giannotti, MSc

D. Giannotti¹, D. Gregory¹, C. Charles¹

¹Earth Sciences, University of Toronto, Toronto, Ontario, Canada

Analytical tools are crucial for advancing our understanding of the geological processes that govern the transport and enrichment of metals in the Earth's crust. One such tool fundamental for the formation of genetic models for mineral deposits is geochronology. Many deposit medals fall within age ranges best suited for U-Pb and Pb-Pb systems, which require precise measurement of small quantities of lead isotopes present in the rocks using isotope dilution thermal ionization mass spectrometry (ID-TIMS). For the correction of internal fractionation within the TIMS instrument, a reference solution known as a double spike is added. The ²⁰²Pb-²⁰⁵Pb double spike solution comprised of synthetic isotopes of lead. This system has been shown to produce the most accurate and reproducible age data. As well, in the U-Pb system, other mixed spikes containing ²⁰⁵Pb, such as those produced by the EARTHTIME initiative, have been shown to produce data at a similarly high standard. The caveat to using synthetic ²⁰²Pb or ²⁰⁵Pb is that they are not naturally occurring and cannot be mined or extracted; they must be produced via particle accelerators or from nuclear reactor waste. Current stockpiles that were produced in the late 80s are being depleted and are at the end of their lifetimes. If the geologic community wishes to continue producing high-level geochronologic data with the U-Pb and Pb-Pb systems, a new stockpile will need to be produced. The large cyclotron at the TRI-University Meson Facility (TRIUMF) was used for the production of the initial ²⁰⁵Pb stockpile and will be utilized again for this production run. The process begins with numerical modelling of the production process. Utilizing both the FLUKA and GEANT4 software to model beam particle interactions that produce ²⁰⁵Pb will serve as a method to further optimize production. By varying target thickness and geometry, as well as beam parameters such as energy and duration, the goal of this project is to produce experimental parameters that would lead to efficient production that could produce a new stockpile larger than what was previously created.