Bleaching of Emissions From Xenon Trapped Barium

When light is shined on barium atoms trapped in a solid xenon matrix, the light they emit only lasts for a finite time. This process is called bleaching, and is not well understood. We are investigating emissions produced by single barium atoms in solid xenon as a posible future means of discriminating background events from those of interest for nEXO's neutrinoless double beta decay search1. Bleaching limits the duration of fluorescence from a single barium atom, and thus the strength of single atom signals in a scanned image. Thus, it is important to understand the properties of bleaching to overcome it. In recent experiments we have found that annealing in the dark shows consistent recovery of lost signal from bleached barium samples in xenon cavities. In some cases, after annealing, we see an increase in signal from Ba atoms in a 7-vacancy site, and a decrease in signal from Ba atoms in a 4-vacancy site. Changes like this indicate barium atom transitions between vacancy sites.