Determination of 222Radon (222Rn) from the hot and acidic fumaroles gases to the atmosphere of the highly populated Campi Flegrei caldera (Naples, Southern Italy) by using a RAD7 detector: a procedure overcoming instrumental limits

Fumaroles spread out several elements to the atmosphere and may include radon that contributes to environmental radioactivity. The long-lasting vigorous gaseous emissions of the Campi Flegrei volcanic caldera, i.e., Solfatara and Pisciarelli, occur in densely inhabited areas of Naples where the population may be exposed to ionizing radiation from 222-radon. In 2021, we started a study on radon levels from the Solfatara and Pisciarelli fumaroles by using the RAD7 commercial detector, one of the most widely used instruments for measuring 222Rn, either dissolved in water or in soil gas. However, the local high H2S levels and hot temperatures did not allow direct measurements of Rn, resulting in the instrumentation (RAD7) damage. Thus, we developed a proper technique for sampling and measuring radon gas from fumarolic gases in such a “critical” areas to overcome the instrumental issue. At fumarole sites i.e., Bocca Nuova and Bocca Grande within the Solfatara crater, and Pisciarelli, the gas was periodically sampled in Tedlar® bag of 1 or 3 liters in order to have the possibility to repeat the measurements two or three times to verify the accuracy of the data. In laboratory, at first, H2S traps were prepared by filling silicone tubes with lead acetate powder, bordered, at both ends, by hydrophilic cotton and closed. Then the fumarole gas was transferred from the Tedlar® bag into a glass tube. Finally, radon gas was measured via a closed loop by using the RAD7. Rn printouts obtained from RAD7 were corrected for the time lag between sampling and measurement. RAD7 and charcoal canister measurements were compared to check the obtained results. Preliminary results, published in Iovine et al. (2023), demonstrate that the methodology utilized enables the analysis of Rn concentrations even in H2S-bearing gases, discharged from the fumaroles of the Campi Flegrei volcano and, most importantly, without instrumental issues. Fumaroles sampled and analyzed over time according to the methodology adopted, may be suitable for environmental radioactivity assessment and volcanic monitoring purposes as well.   Iovine RS, Avino R, Minopoli C, Cuoco E, Caliro S, Galli G, Piochi M. (2023). A procedure to use the RAD7 detector for measuring 222Rn in soil gases exceeding instrumental limits: an application to chemically aggressive fumaroles of the Campi Flegrei area. Rapp. Tec. INGV, 473: 1­18, https://doi.org/10.13127/rpt/473.