Abstract: The atmosphere of caves is a special environment where it is necessary to take
into account some particular characteristics when assessing the radon dose.
The equilibrium factor (F) between radon and its progeny, and especially its
unattached fraction ( fp), is a key parameter in radon dose evaluation. In order
to consider the specific features of the atmosphere in the Altamira Cave, the
radon and particle concentrations have been measured. The mean annual radon
concentration inside the cave over the period 2013?2019 is around
3500 Bq m?3 with a standard deviation of 1833 Bq m?3 and this exhibits
seasonal variations. This value surpasses all international (WHO, IAEA,
ICRP) upper action and reference levels (occupational and non-occupational).
Dose rate levels expressed in ?Sv h?1 were estimated for four different
equilibrium scenarios between radon and its progeny 218Po, 214Pb, 214Bi and
214Po. The most recent dose conversion factors have been used and the
contribution made to the dose by the unattached fraction of radon progeny fp
has been also assessed from the particle concentration. The results suggest that
the mean annual dose levels show variations of up to 500% due to the range of
F and the fp considered in this study. Given the high radon concentrations
usually found in show caves, the best way to reduce this variability and its associated uncertainty in dose assessment is to conduct specific studies aimed
at determining both F and fp.
