Gamma versus alpha sensors for Rn-222 long-term monitoring in geological environments

The behavior of alpha silicon diodes, gamma crystal scintillators and ionization chamber detectors employed for long-term radon monitoring in geological media was studied and a comparison of the efficiency and sensitivity, the capability to resolve signal to noise, background, stability, and reliability of their long-term measurements is presented. An understanding of the qualities of monitoring techniques is necessary for determining suitability to the characteristics of the individual monitoring site and what exactly they will measure: radon in an air cavity, in porous media or in water. The experimental layout was located inside the Amram Mountain research tunnel near Elat (Gulf of Aqaba), within a closed room in the tunnel core. This enabled monitoring natural temporal radon variations under fairly stable internal conditions, at a high-resolution sampling rate of once every several minutes. In an interval of several days, all the sensors responded simultaneously to the same eventual radon variations. An ionization chamber device, the AlphaGUARD designed with a long-time stable calibration factor and an inherent QA-System, was used as reference calibration of the different radon detectors. The results indicate that the higher sensitivity of 2–4 orders of magnitude exhibited by gamma sensors even with narrow dimensions (1" × 3" BGO detector) are preferred for long-term radon monitoring in comparison to the solid-state alpha detectors and ionization chambers. ► A performance comparison of radon gamma and alpha detectors is presented. ► These systems are employed adequate for radon monitoring in natural subsurface media. ► The experiment is based on the analysis of natural multi-day radon signals. ► The tests were in a confined subsurface tunnel at stable environmental conditions. ► Gamma sensors are preferred due to higher sensitivity of 2–4 orders and reliability.