## 3 Results  
### Wet Chemistry Isolation of \({}^{211}\)At  
The steps involved in the wet chemistry \({}^{211}\)At isolation approach are outlined in Figure 1. The first step in the isolation process is to remove the bismuth and \({}^{211}\)At from the aluminum target backing by dissolution in concentrated HNO\({}_{3}\). This is a very efficient process, where \(>\)99% of the \({}^{211}\)At activity is transferred to the round bottom flask used in the next (distillation) step. Pictures of the target (bismuth face down) placed in the modified 1 L bottle are provided in the Supplemental Material (Figure S4). In this step it can be noted that reddish-brown gas (NO\({}_{\text{x}}\) fumes) is released upon dissolution of the bismuth. It was somewhat surprising to find that this process does not release significant quantities of volatile \({}^{211}\)At. The release of the NO\({}_{\text{x}}\) gas, however, is damaging to the stainless steel interior of the glovebox, requiring covering the surface with adhesive PTFE sheet (Bytac, Sigma-Aldrich, St. Louis, MO, USA). Studies were conducted to replace the open dissolution chamber with a closed chamber system in which a stream of air (or N\({}_{2}\)) was used to sweep the NO\({}_{\text{x}}\) fumes through a scrubbing bubbler system. The HNO\({}_{3}\) distillation was part of the system, as NOx fumes are also released during distillation. A picture and scheme for the scrubber system is shown in the Supplemental Material (Figure S5). Ultimately, this approach was not used since it would occupy too much space in the glove box. The second and third steps in the isolation process involve removal of the conc. HNO\({}_{3}\) and dissolution of the residue in 8M HCl. Although it had been shown that having some HNO\({}_{3}\) present did not cause problems in the subsequent DIPE extraction step, the fact that HNO\({}_{3}\) is efficiently extracted into DIPE [35] caused problems with loss of At so all of the HNO\({}_{3}\) was removed by distillation to give a colorless residue. To obtain an efficient HNO\({}_{3}\) distillation, a heat block temperature of \(\sim\)300 \({}^{\circ}\)C is required and the distilling flask needs to be covered with aluminum foil. Once the HNO\({}_{3}\) is removed the white residue was readily dissolved in 8 M HCl. This process is also very efficient with 93%-98% of the activity transferred into the 8 M HCl. The glassware setup is shown in the Supplemental Material (Figure S6). The fourth step in the isolation process is extraction of \({}^{211}\)At from 8 M HCl into diisopropyl ether (DIPE). In this step the bismuth remains in the 8 M HCl allowing a separation of the bulk quantities of bismuth from the \({}^{211}\)At. To further decrease the levels of bismuth, several washes with 8 M HCl are required. When carrying out the separations, there were difficulties with removing specified amounts of DIPE after mixing due to volume changes, as the DIPE and 8 M HCl are somewhat miscible  
Figure 1: Steps involved in the “wet chemistry” isolation and purification of \({}^{211}\)At from a \({}^{209}\)Bi target. Note that the isolation process is usually stopped at step 5, but an additional distillation under reductive conditions can be conducted to obtain \({}^{211}\)At solutions without bismuth and other chemical contaminants from the wet chemistry process. making it difficult to quantitatively isolate either reagent. Therefore, as with many of the earlier investigators, the DIPE and 8 M HCl were mixed prior to their use to minimize the loss of reagent due to miscibility. The miscibility is problematic as some \({}^{211}\)At is present in each wash (probably in the miscible DIPE). The number of washes required to obtain low levels of Bi was investigated. It was found that four washes were required to obtain a low level of bismuth in the isolated \({}^{211}\)At solutions. The fifth step in the isolation process is back-extraction of the \({}^{211}\)At from DIPE into 4 M NaOH.