Novel methods in ²¹⁹Rn generation and detection from ²²³Ra Sources in dry and liquid samples.

Introduction: Among the most common alpha emitting radio-isotopes is ²²³Ra which emits a potentially dangerous alpha emitting gas, ²¹⁹Rn. Methods of measuring ²¹⁹Rn outgassing from a variety of ²²³Ra sources were developed to understand and quantify the extent of ²¹⁹Rn contamination in a pre-clinical bio-distribution lab setting. Materials and Methods: Using aspiration techniques, two different aspiration holders were designed and 3D printed, one for a dry and one for a liquid ²²³Ra sample. The holders were then placed at the inlet of a vacuum tube with 5 carbon filters in series which absorbed the ²¹⁹Rn emission from the ²²³Ra source. The dry source was created by placing a few microliters of a ²²³Ra solution, in the 37kBq range of activity, on a piece of glass fiber filter paper and allowed to dry. The filter paper was then placed in a cone holder which held the filter paper between two grid plates allowing air to flow through the ²²³Ra laced filter paper collecting the ²¹⁹Rn emissions onto the carbon filters in the vacuum tube. The ²¹⁹Rn gas decays through various decay chains to ²¹¹Pb which is then collected by the pellets of the carbon filters. ²¹¹Pb activity levels were measured with specifically designed and developed micro-dose calibrator which allowed for accurate radio-assaying of the carbon filters. ²¹¹Pb activity levels were then extrapolated back to ²¹⁹Rn levels to measure the ²¹⁹Rn outgassing levels. A second cone was designed to be placed over an open vial containing a liquid sample of ²²³Ra which would collect the ²¹⁹Rn emissions. A nozzle which hovered a few millimeters above the surface of the ²²³Ra solution was designed into the cone to ensure proper collection of the emissions.

Results: The dry and liquid sampling holders were able to collect ²²³Rn outgassing from their respective ²²³Ra sources in a safe and reproducible way. The ²¹⁹Rn outgassing collection holders and the methods for quantifying the outgassing revealed a stark difference in outgassing magnitudes between dry and liquid ²²³Ra sources. Dry ²²³Ra outgasses ²¹⁹Rn at an average rate of 51%±21% with rates up to 81%, while emissions from a liquid ²²³Ra source was so small that only an upper limit of 0.9%±0.3% was measured.