Improved assessment of FI*(10) in the environment using two complementary active dosimetry systems

A novel method is presented for the improved assessment of the ambient dose equivalent rate, FI*(10), in the environment using two complementary active dosimetry systems having different responses towards charged component of secondary cosmic radiation (SCR). Measuring FI*(10) with a single dosemeter has the disadvantage that almost all commercially available active dosimetry systems for environmental monitoring are sensitive to both terrestrial and secondary cosmic rays (excluding neutrons), though usually with different sensitivities. Any calibration of such a detector system is therefore either appropriate for terrestrial (gamma radiation) or for secondary cosmic radiation (muons and electrons), but normally not for both. This means that a single detector either under-or overestimates one of these two components, or its calibration represents a compromise, meaning that both components are not measured correctly. Consequently, the uncertainties of FI*(10) measurements in the natural environment using a single detector only, can be considerable. The use of two complementary detector systems (complementary in the sense that their responses to various radiation fields in the environment show significant differences), however, allows the individual assessment of both contributions to FI*(10), i.e. FI*(10)TR originating from terrestrial radiation and FI*(10)SCR originating from the charged component of secondary cosmic radiation. This leads to a more accurate assessment of FI*(10) in the environment, especially at low dose rates, such as in the natural environment, and will potentially be of great importance for the modernization of radiation monitoring networks, that rely largely on stand-alone gas-based detectors. Results from systematic investigations with suitable detector pairs consisting of gas-based radiation monitors and spectrodosemeters, carried out at the reference sites for environmental dosimetry at the PTB, demonstrate the feasibility and potential of this new method.