Speaker
Description
One puzzling observation in the $^7$Li recoil spectra of the BeEST data is the fact that the peaks widths were significantly larger than the ∼2eV width of the laser peaks set by the energy resolution of the STJ's. This isn't currently understood, thus is a limitation to the progression of the BeEST experimentation through the sensitivity, which is crucial for the observation of small SN masses which are especially interesting for WDM candidates. A possible investigation to provide clarity in where this broadening could have come from, involves looking deeper into the material properties of STJ's themselves, especially in the low temperature range. While Ta has been used for a long time in the fabrication of STJ's, its material behaviours in this environment remain unresearched. With this in consideration, $\beta$NMR was utilised to analyse the material effects of a sputtered thin foil of Ta. This experiment consisted of the film being implanted with a $^8$Li probe, used for its similar properties to the recoil daughter nucleus from the BeEST experiment. This technique allows the ability to infer the probes landing site in the Ta lattice after implantation at 25keV. The preliminary results showed a single resonance curve at all temperatures, with no observable quadrupolar splitting, unlike what is seen in similar materials. This indicates that the probe must land in a highly symmetrical location in the lattice indicating only a few options. An interesting observable in the data which also emerged was the change in features from analysis like the 'Knight' shift at low temperatures. The reasoning behind this is theorised but is currently under further investigation. In my presentation, I will present the experimental method and discuss preliminary results of the ongoing data analysis.
