Radon exhalation

In Table I results of Rn-226 activity measurements cn geological samples are shewn together with measurements cn Rn exhalation rates from the sanples. The exhalation rates varies considerably with the moisture content of material. The exhalation rate is lew for dry samples and when the moisture content increases, the exhalation rate increases until it reaches a plateau. When the moisture content increases further, a rapid increase in radon exhalation occur. When the saturation level of moisture is reached, the exhalation rate drops dramatically. The exhalation rates given in Table I are obtained by assuming that the most probable moisture content is whithin the plateau of exhalation rate/moisture curve. (Stranden et al, 1984, Stranden et al, 1984a). 

Stranden E., Kolstad A.K. and Lind B., 1984, Radon Exhalation Moisture and Temperature Dependence, Health Phys, 47, 480-484. 

Stranden E., Ulbak K., Edhwall H. and Jcnassen N., 1985, Measurement of Radon Exhalation from the Ground A Usuable Tool for Classification of the Radon Risk of Building Ground, Radiation Portecticn Dosimetry, 12, 33-38. 

SAMUELSSON Critical Assessment of Radon Exhalation Measurements... 

Figure 5. The areal exhalation rate from the porous sample in Figure 2, enclosed in three different exhalation cans. Two of them ( a1 and 0 ) are completely radon-tight and the third Cb1) has a radon leak rate constant v, numerically equal to the radon decay rate constant (v=A= 2.1 10" s" ). The cans are closed at time zero. The radon exhalation evolution as a function of time is discussed in the text (theory).

In order to experimentally check the validity of the time-dependent diffusion theory as applied to the closed-can method, extensive systematic investigations of radon exhalation, with carefully controlled parameters, are needed. To the author s knowledge no such investigations have yet been performed. 

Jonassen N., The Determination of Radon Exhalation Rates, Health Physics 45 369-376 (1983). 

Lamm I-L, C. Samuelsson, and H. Pettersson, Solution of the One-Dimensional Time-Dependent Diffusion Equation with Boundary Conditions Applicable to Radon Exhalation from Porous Materials, Coden Report LUNFD6(NFRA3042), Lund University, Lund (1983). 

The radon emanation and the ventilation rate of a room can be derived from the increase of the radon concentration by the radon exhalation and from the steady state condition between exhalation and air exchange with the free atmosphere. In Fig. 2 the variation of the radon concentration as function of time is shown measured in two houses with different radon emanations and ventilation rates. 

Standen, E., Kilstad, A.K. Lind, B. (1984) The influence of moisture and temperature on radon exhalation. Radiation Protection Dosimetry, 7, 55-8. 

Radon exhalation is the flux of Rn from surfaces of U-containing materials. In many instances, it is necessary to measure this flux to determine the source term of radon represented by the material (e.g. radon exhaled from tailings dams as a radiological impact on the public or from building materials used for houses, to determine the potential radiation hazard). There are various ways to measure this parameter. 

The accumulation method was one of the earliest procedures and consists, basically, of placing the open end of a vessel on the surface being measured. This method requires the use of a suitable sized container, ranging in volume from a few liters up to as much as 2201. The radon concentration inside the vessel is then measured, either at some selected time or serially over a period of several hours. The requirements for the accumulation method are that the accumulation time is short compared with the 3.82 day half-life of Rn, that the concentration in the vessel is lower (perhaps 10% or less) than that in the solid material, and that the measuring device does not significantly affect the radon exhalation. 

The radon exhalation rate from soil was determined using a model proposed by UNSCEAR for the evaluation of the flux density of Rn at a surface of dry soil. The UNSCEAR model used is represented by the following equation ... 

All the results obtained for radon exhalation rate, radiiun equivalent activity and external and internal hazard indices indicate that the exposure around IPEN facilities due to the radioactive discharges is negligible. 

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