Scavenger hunt: Searching for the optimal target material for low-level 210Pb accelerator mass spectrometry

Abstract

The Centre of Excellence for Dark Matter Particle Physics aims to measure 210Pb (half-life of 22.2 years) in 1 kg of NaI via accelerator mass spectrometry (AMS) for the SABRE (Sodium iodide with Active Background REjection) South dark matter experiment. The first step is to find the optimal target material (chemical compound and binder) to produce the highest and most stable negative ion output. We initially studied the outputs from Pb3O4, PbO and PbF2 mixed 1:2 with Ag. The 208PbO2− and 208PbF3− currents were 0.5–1.2 μA with the procedural PbF2 compound performing slightly better. Based on these results, we explored the performance of PbF2 mixed with fluorinating agents such as AgF, AgF2 and SbF3 at different ratios. The 1:1 mixture was the best for all additives. The possibility of using either Fe (oxide/fluoride) or NaF as bulk material for the AMS target was also studied, however, none proved suitable.