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2 Nukleonika

2 2010

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Inversion of the Jacobi-Porstendörfer room model for the radon progeny

Thomas J., Jílek K., Brabec M.

Nukleonika

2010

Vol. 55, No. 4

433-437

The Jacobi-Porstendörfer (J-P) room model describes the behaviour of radon progeny in the atmosphere of a room. It distinguishes between free and attached radon progeny in air. It has been successfully used without substantial changes for nearly 40 years. There have been several attempts to invert the model approximately to determine the parameters describing the physical processes. Here, an exact solution is aimed at as an algebraic inversion of the system of six linear equations for the five unknown physical parameters k, X, R, qf, qa of the room model. Two strong linear dependencies in this system, unfortunately do not allow to obtain a general solution (especially not for the ventilation coefficient k), but only a parameterized one or for reduced sets of unknown parameters. More, the impossibility to eliminate one of the two linear dependencies and the departures of the measured concentrations forces to solve a set of allowed combinations of equations of the algebraic system and to accept its mean values (therefore with variances) as a result of the algebraic inversion. These results are in agreement with results of the least squares method as well as of a sophisticated modern statistical approach. The algebraic approach provides, of course, a lot of analytical relations to study the mutual dependencies between the model parameters and the measurable quantities.

First results of measurement of equilibrium factors F and unattached fractions fp of radon progeny in Czech dwellings

Jílek K., Thomas J., Tomášek L.

Nukleonika

2010

Vol. 55, No. 4

439-444

The unattached fraction of radon decay product clusters fp and equilibrium factor F are dose relevant parameters in all dosimetric approaches to dose calculation. In the past, three year continuous weekly measurements of unattached and attached activity of radon daughter product and air exchange rate were carried out during heating season in 30 occupied typical Czech family houses. The results indicated significantly different weekly averages of equilibrium factor F and fp for houses located in towns compared those in villages. Due to this fact, approximately a 10 per cent average increase of equivalent lung dose rate was estimated in the detriment in towns. Average values of equilibrium factor F and fp were 0.40 and 8.6 per cent in urban houses and 0.32 and 10.7 per cent, respectively in rural houses. Based on the measurements of mean values of fp, average effective dose conversion factors (DFC) in units of mSv per working level month (WLM) were estimated to be 15.0 mSv/WLM in urban houses and 15.9 mSv/WLM in rural houses, respectively.