Radioactive Aerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 392

deposition, clearance, and decay of radon progeny within the respiratory airways. We must discuss
this statement because of its great importance to the dosimetry of radon decay products.
In the irst step of this consideration, that is, the correlation of the concentration in the breath-
ing zone and that in the place of sampling, it is very dificult to predict how some of the param-
eters of the irst and second group will interact. It is dificult, or even impossible, to model the
concentration in the breathing zone, especially for hard-working miners. Even the sparse data
available showed that the ratio between the breathing zone concentration and that measured at
some distance varies within very broad limits. This is especially true for aerosol particle size
distribution and activity particle size distribution, which are responsible for the deposition in dif-
ferent parts of the lungs.
The second step of the distortion of particle size distribution spectra is the change of particle size
distribution inside the lung pathways due to change in humidity and temperature. The modeling of
this step can lead to very high uncertainty in the calculation of particle activity deposition.
It is true that the physical effect of alpha-radiation of the lung tissue cannot be measured directly.
But very often, when the direct measurements of the physical factors are not possible, a different
approach is used. In such cases, we often try to ind other measurable physical parameters, and
at the same time use a correlation (analytically or in another way) between this measurable and
nonmeasurable physical value. One method is external gamma-ray counting of the lung.
Such analytical correlation of the gamma-activity of radon progeny (a measurable factor) and the
alpha-dose to the lung tissue (nonmeasurable factor) was derived in (Ruzer, 1958, 1964). The pos-
sibilities of practical application of this “direct method,” including an introduction of the necessary
corrections and assessment of the accuracy of measurement, were presented in Ruzer (1962), Vasin
et al. (1975), Ruzer and Urusov (1969), and Urusov (1972).
The practical applications of the direct measurement of the activity in the lungs of miners were
carried out in uranium and nonuranium mines of the republics of Kazakhstan, Uzbekistan, and
Tadjikistan on more than 500 miners. The results of these studies were published in three disserta-
tions (Urusov, 1972; Alterman, 1974) (in Russian) and in my topic Radioactive Aerosols published
in Russia in 2001.
The radon decay products of gamma-radiation of 214 Pb and 214 Bi are natural markers, and the rela-
tively high historic radon progeny concentration in mines makes it possible to obtain information from
direct measurements of the gamma-activity of radon decay products deposited in the lungs of miners.
In principle, using more sophisticated gamma-detectors together with collimators, it is possible to
measure the distribution of radon progeny in different parts of the lungs under real mining conditions.
A detailed analysis of all corrections in such measurements suggested that the accuracy in the
activity assessment is satisfactory from the point of view of practical dosimetry.
In all calculations of the dose to the lung tissue provided in NRC Report (1998), it is assumed that
activity of the radon decay products in the lung or in part of it is known, without taking into account
uncertainties in the activity assessment.
However, here lies the main problem. There are no real data on the activity in the lung. From a
practical point of view, it makes no sense to use data concerning the activity of radon progeny with-
out mention of the errors of the calculation of the dose distribution through lung tissue, especially
because the errors in the activity assessment are so large.
The purpose of practical dosimetry is to present a set of rules (algorithm) for determining the
quantity responsible for a biological effect (in this case, the absorbed dose due to alpha-radiation of
radon progeny) using the value—in the case of miners—measured by the standard procedure radon
progeny concentration. This should be done with the assessment of associated errors.
The method of direct measurement of activity in the lungs of miners allowed the study of the
transition coeficient between activity in the air and in the lungs. It was demonstrated in Ruzer
and Urusov (1969), Urusov (1972), Alterman (1974), and Ruzer et al. (1995) that this coeficient—
FAL—is different for different physical activities, which resulted in different doses (intake) in dif-
ferent groups of miners.