## 3 Results
### Quantification of \({}^{211}\)At in the Presence of Bismuth  
It is apparent that bismuth can attenuate the 76.9 and 79.3 keV X-rays used to quantify \({}^{211}\)At in the target and in solution, but the extent of attenuation was not investigated until our average decay-corrected wet chemistry isolated yields became greater 100% (see Table 1: \"Optimized\" runs had an average of 104% \(\pm\) 15% decay-corrected yields). Additionally, high variability in the dose-calibrator yields for samples within a particular run suggested that attenuation in samples containing bismuth was larger than we anticipated. Therefore, two sets of experiments were conducted to understand the variability by testing the hypothesis that the dose calibrator measurements observed during the extraction process may be susceptible to bismuth attenuation and/or geometric effects due to varying sample volumes. In the first experiment, dose calibrator readings were taken for a set amount of \({}^{211}\)At, when the quantity of bismuth was increased in a constant volume of HNO\({}_{3}\). The experiment was conducted by dissolving increasing amounts of bismuth metal (0-1.5 g) in 5 mL of conc. HNO\({}_{3}\) containing \({}^{211}\)At. The data obtained is plotted in Figure 4, panel **A**. All dose calibrator readings were normalized to the measurement with no bismuth added and decay-corrected to account for the time lapsed during bismuth dissolution. It is clear that the dose calibrator readings were significantly decreased due to attenuation of bismuth. At the highest amount of bismuth added (1.5 g), where the concentration of bismuth in solution was 300 mg Bi/mL HNO\({}_{3}\), an attenuation of \(\sim\)38% was noted. Figure 4: Graphs depicting the change in dose calibrator reading of a fixed amount of \({}^{211}\)At when the concentrations of bismuth are changed. (**A**) Dependence of bismuth concentration _vs_. dose calibrator reading for a fixed (5 mL) quantity of HNO\({}_{3}\); (**B**) Dependence of sample volume _vs_. dose calibrator reading in the presence and absence of bismuth. Values in each graph have been decay corrected and normalized to; (**A**) the no added bismuth reading, or (**B**) the 5 mL reading. In the second experiment, the change in dose calibrator reading of \({}^{211}\)At was examined when the volume was increased from 5 mL to 15 mL by 1 mL additions of H\({}_{2}\)O. Although an increase in measured activity was noted with increasing volume, it was not conclusive as to whether this change was attributed to a change in geometry and/or an overall decrease in bismuth concentration. To further assess the effect of geometry, a 0.3 mL sample of isolated (_i.e._, no bismuth added) \({}^{211}\)At was similarly brought to a total volume of \(\sim\)15 mL (in 1 mL steps). The results are presented in Figure 4, panel B. That graph clearly shows that the change in reading is almost exclusively attributed to the decrease in bismuth concentration, and not to the change in sample volume. Combining the results of panel A (_i.e._, \(\sim\)38% reduction in activity when adding 1.5 mg of Bi), along with the increase of \(\sim\)21% when diluting this solution to 100 mg Bi/mL (1.5g in 15 mL), the dose calibrator reading for such a bismuth concentration and volume is expected to be \(\sim\)75% of that achieved for the case where no bismuth is added (_i.e._, underestimated by \(\sim\)33%). The simple experiments to determine the attenuation effect that bismuth has on dose calibrator readings of \({}^{211}\)At show that significant changes in readings are due to attenuation by bismuth. If an approximate attenuation value can be obtained, a more accurate estimate of the recovered yields can be made. Measurement of the amount of \({}^{211}\)At activity in an irradiated target after the HNO\({}_{3}\) dissolution has shown that \(<\)1% of the activity remains, so it is possible to say that the amount of activity in the target is essentially the same as that of the conc. HNO\({}_{3}\).