MW-RN-2020 (1)

Protocol for the Collection, Transfer and ANSI/AARST MW-RN 2020 Measurement of Radon in Water 35 12.3 Moisture and airflow The transfer system (from the bubbler to the alpha-scintillation cell) shall have an in-line column containing a desiccant (e.g., magnesium perchlorate or anhydrous calcium sulfate) to remove moisture from the air stream and a micrometer value to control the air flow (bubbling rate). A column (e.g., ascarite) to remove CO 2 from the air stream can be included, if desired. The alpha-scintillation cell and the bubbler are at opposite ends of the transfer system. With the micrometer valve closed, open the valves to the alpha-scintillation cell and the bubbler. Slightly open the micrometer valve until bubbling is observed. Adjust the micrometer valve to continue a slow bubbling of the water and transfer of the radon into the alpha-scintillation cell. To eliminate the introduction of radon into the sample, air entering the inlet of the bubbler shall come from a cylinder of aged air or, if using ambient air shall have an activate-charcoal trap so as to remove ambient radon from the inlet air stream. Adjust the micrometer valve to maintain a slow bubbling of the water until no more bubbling is observed (usually 5-10 minutes). At this point the alpha-scintillation cell is at atmospheric pressure (no remaining vacuum). Close the inlet of the alpha-scintillation cell, remove it from the transfer system. Dark-adapt the cell at least 3 hours before measurement to allow ingrowth of the short-lived decay products. Figure 12 - System to transfer radon from a bubbler (bottom) to an alpha-scintillation cell (top). - A column for moisture removal and a micrometer valve are in-line. - The gauge (left) measures vacuum and the charcoal trap (right) removes ambient radon from the air before entering the bubbler.