Radioactive Aerosols - Aerosols: Measurement, Dosimetry, and Health Effects - page 404

It should be pointed out that the measurement of the gamma-activity in the lungs of miners was
provided in the environment with a relatively high gamma-background, especially when the mea-
surements took place near the working sites. In such cases, the parameter “quality of measurement”
q = n 2 / n b ( n , count rate above the background; n b , background count rate) was chosen to achieve the
best measurement conditions.

15.10.2.3 Accounting for Parametric Variations: Variations of Concentrations,
Breathing Rate, and Deposition Coeficients in Real Working Conditions
All dosimetric parameters under actual working conditions are not uniform. This is important both
in the case of the estimated or indirect calculation of the dose (lung activity) and in the case of direct
measurement.
Let us denote Q (the activity in the lung) as a combination of all parameters (air concentration,
breathing rate, lung deposition, respirator eficiency):

( )

Q qvk = 1 − f

where
f is the coeficient of effectiveness of a respirator
Q is the rate of the intake

To take into account the variation of intake, two options were used:

1. Experimental, by placing a portable gamma-counter near the work site and, for parts of the
shift, with special attention to the situation when Q is high.

2. Theoretical, by calculation of corresponding corrections on the inequality of Q during the
time of exposure for different types of working itinerary (scenario of exposure).

To perform such a calculation, the whole working shift time, θ, should be divided by n periods in
which every dosimetric parameter will be constant. Different typical scenarios of exposure (work
itinerary) in terms of the rate of intake, Q , changing during the shift were calculated.
Variants present situations during the work shift:

1. Ventilation turned off (on) resulting in increasing (decreasing) q

2. Change in physico-chemical properties of aerosols resulting in an increase (decrease) of
the coeficient k

3. Change in the work load resulting in changed breathing rate and deposition coeficient

4. Miners use of respirators resulting in a change of the factor 1 − f

For the introduction of a correction factor for Q we have to obtain additional information on each
concrete working situation (variation of Q during the shift). The degree of the error in determining
the correction factor depends on the proximity of the chosen variant of the function Q to the variant
under actual conditions.
According to the calculations (Urusov 1972), even if the magnitude of Q max / Q min is close to 30 the
total error in the measurement of activity in the lungs of miners by the direct method will not exceed
40%, which is acceptable for the purposes of individual dosimetry.

15.10.2.4 Model Measurements
Experiments to determine the detection limit of the gamma-activity measurement of radon prog-
eny in the lungs of miners were provided using a Human Body Spectrometer at the Biophysics
Institute in Moscow. It consisted of a measurement chamber protected by a 20 cm layer of iron.