Activity standardisation of 32Si at IRA-METAS

This work explores the primary activity standardisation of Si-32 as part of the SINCHRON project that aims at filling the geochronological dating gap by making a new precise measurement of the half-life of this nuclide. The stability of some of the radioactive test solutions, providing Si-32 as hexafluorosilicic acid (H2(32)SiF(6)), was monitored over long periods, pointing to the adequate sample composition and vial type to ensure stability. These solutions were standardised using liquid scintillation counting with the triple to double coincidence ratio (TDCR) technique and the CIEMAT-NIST efficiency tracing (CNET) method. Complementary backup measurements, using 4 pi beta-gamma coincidence counting with Co-60 as a tracer, were performed with both liquid and plastic scintillation for beta detection. While Co-60 coincidence tracing with a liquid scintillator predicted activities in agreement with the TDCR and CNET determinations, using plastic scintillation turned out to be unfeasible as the addition of lanthanum nitrate and ammonia to fix the silicon during the drying process generated large crystals that compromised the linearity of the efficiency function.