Radon continuous monitoring in Altamira Cave (northern Spain) to assess userʹs annual effective dose

In this work, we present the values of radon concentration, measured by continuous monitoring during a complete annual cycle in the Polychromes Hall of Altamira Cave in order to undertake more precise calculations of annual effective dose for guides and visitors in tourist caves. The 222Rn levels monitored inside the cave ranges from 186 Bq m−3 to 7120 Bq m−3, with an annual average of 3562 Bq m−3. In order to more accurately estimate effective dose we use three scenarios with different equilibrium factors (F=0.5, 0.7 and 1.0) together with different dose conversion factors proposed in the literature. Neither effective dose exceeds international recommendations. Moreover, with an automatic radon monitoring system the time remaining to reach the maximum annual dose recommended could be automatically updated.