Environmental Engineering Reference
In-Depth Information
Finally, the very concept of the “work place” and “concentration at the work place” are indeinite
since miners are at several work places during their work shift, each with different possible concen-
trations of radon decay products and physical work loads.
For a correct evaluation of the exposure under actual working conditions, we have also taken
into account that in some cases miners used respirators for protection of the lung from the aerosol
conditions in the mine. All these factors are important for the assessment of the irradiation of the
lungs and we will call them “the exposure scenario ” or “the working itinerary.”
Since practically all measurements of the air concentration of radon progeny at work sites in
mines are performed only once or twice a month, there cannot be a precise correspondence between
the actual and measured individual (or for group of miners) breathing zone concentrations.
No systematic studies have been made for the assessment of the breathing rate and deposition in
lungs for individual or group of miners in real underground conditions. Therefore, it is impossible
to calculate the individual exposures correctly.
We present here a method for making direct measurements of the radioactivity in miners' lungs,
including the experimental development, the assessment of error, the necessary corrections and
the results of direct measurements of the activity (dose) of miners using portable instruments. The
research studies, that is, the model and phantom measurements, were performed in Moscow (in
the former Soviet Union) in the All-Union Institute of Physico-Technical and Radio-Technical
Measurements (VNIIFTRI) and Institute of Biophysics (Ministry of Health). The practical applica-
tion took place in uranium and non-uranium mines in Uzbekistan and Tadjikistan (former USSR).
Some aspects of the work have been published, for example Ruzer et al. (1995). The complete
experimental and theoretical details of the method along with the compilation of the results and
observed health effects in these mines have not been published before.
15.10.2.1
Theory of the Method
The basic equations in the most generalized form for the radon series were derived in Ruzer (1958,
1960a,b). The derivations of the equations are based on the equations described in Bateman (1910)
with some appropriate transformations. Bateman's equations for the decay chain transformations
were used for the determination of the correlation between the measured air concentration and
activity of each decay product on the ilter (or lungs).
In order to use these equations for the buildup of activity in the lungs due to iltration, that is,
breathing, we assumed that each member of this chain of decay products supplies the decay prod-
ucts to the lungs at a constant rate
Q
i
=
q
i
vk
/λ
i
. From a mathematical point of view, the constant
rate of supply is equal to the equilibrium between the irst and the second member of the chain of
radioactive transformation. In this case, the number of atoms
N
of each decay product in the lungs
can be found according to
−
λ
1
t
−
λ
2
t
−
λ
it
N
=
c
e
+
c
e
+
+
c
e
i
1
2
i
where
c
i
=
N
1,0
λ
1
λ
2
… λ
i
−1
/(λ
1
− λ
i
) (λ
2
− λ
i
) … (λ
i
−1
− λ
i
)
λ
i
is the decay constant of the “
i
” progeny
The idea in Ruzer (1958) was to ind a correlation between the dose from the alpha-radiation of
218
Po and
214
Po, which cannot be measured directly in the lung, and the gamma-radiation from
214
Pb
and
214
Bi, which at least theoretically can be measured by external counting. The carcinogenic dose
is delivered by the alpha-radiation due to its high-energy transfer to the irradiated cells.
Due to the gamma-emission from the decay products
214
Pb and
214
Bi and also the relatively high
maximum permissible air concentration in comparison with other radioactive aerosols, radon decay
products present a unique opportunity for the direct measurement of activity in the lungs.
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