The synthesis of Ba1 and Ra1 were carried out in open-front fume hoods with no attempt to exclude moisture or oxygen. All reagents were used as received from the manufacturer without any further purification. Ba(NO3)2 (Fisher Scientific), D2O (Sigma), deionized water (≥18 MΩ･cm), MeCN (VWR), Bu4NBPh4 (Sigma), DB30C10 (Parish Chemicals), and immersion oil (Type NVH, Electron Microscopy Services) were used for the syntheses and preparations of Ba1 and Ra1. Ra (97.1% purity by mass; < 0.1% Ba) was purchased as a dried down nitrate salt from the National Isotope Development Center and used without further purification. It was delivered in a vial equipped with a septum cap. To minimize the risk of a contamination event, the solid was reconstituted with D2O via syringe to a concentration of ~50 mM (11.3 mCi/mL) prior to uncapping the vial.