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ST 2.1 –
Radiación natural, NORM y TENORM
DOSES FROM THE USE OF ORNAMENTAL ROCKS AS
BUILDING MATERIAL
Carmo Leal, André Luiz
1
; da Costa Lauria, Dejanira
2
*
1
Instituto Federal do Rio de Janeiro – IFRJ. Brasil.
2
Instituto de Radioproteção e Dosimetria – IRD/CNEN. Brasil.
* Responsible author, email:
dejanira@ird.gov.br
The ornamental rocks are part of those materials for which above-normal levels of natural
radionuclides have been found. The dose due to its use do not only depend on the concentrations
of natural radionuclides in the building material, but also on the intrinsic proprieties of the material
and the characteristics of environment in which this material is used. From the radionuclide
concentrations in 180 samples, the radon concentration indoor and the external and radon
inhalation doses arriving from the use of Brazilian rocks as floor covering in residential buildings
were assessed. The radionuclide concentrations reached a wide range of values: Ra-228
concentrations ranged from <2 to 530 Bq.kg
-1
, Ra-226 concentrations varied between <5 and
600 Bq.kg
-1
, while the K-40 ones varied between 190 and 2797 Bq.kg
-1
. The contribution of
rocks for indoor Rn-222 concentration falls far of the recommend investigation level of 300 Bq m
-3
,
or even the one that has been adopted by some countries of 200 Bq.m
-3
, since the estimated
concentrations of Rn-222 ranged from 0.07 to 8.6 Bq m
-3
, (mean value of 0.77±1.04 and median
of 0.45 Bq m
-3
). The mean radon inhalation dose of 0.006±0.009 mSv.year
-1
(range between
0.001 and 0.07 mSv.year
-1
and median value of 0.0004 mSv.year
-1
) was far lower than the
recommended level (10 mSv.year
-1
). The value of the external dose due to use of ornamental
rocks as floor covering in the residential scenario ranged between 0.01 and 0.61 mSv.year
-1
,
value of mean of 0.19±0.10 and median of 0.16 mSv.year
-1
. The sensitivity analysis highlighted
the importance of the ventilation rate and the emanation rate to the Rn dose, whereas for
external dose the only parameters that affect the value of dose are the density of the material
and the location of the receptor.