Radon personal dosimetry

The cause for the harmful effect of radon is the accumulation of radon daughters in the human respiratory tract. It is not the radon per se that determines the dose but the generated decay products in the air we breathe.

On principle, there are two ways to evaluate the dose. The exact determination of the exposition as the base of the dose can only be performed by means of a direct measurement of the radon daughters by its deposition on a filter and simultaneous analysis. This procedure has got disadvantages by its relatively high maintenance requirements (filter exchange in intervals, pump wear), a permanent noise emission (the instruments should be carried close to the face) as well as the required free suction (you cannot put the instrument in the pocket). So this procedure does not recommends itself for the routine operation on workplaces with varying dust loading, e.g. in mining.

Easier to handle is the assessment of the exposition by means of a radon gas measurement with adopting an equilibrium factor. The equilibrium factor depicts the relation of radon daughters and radon gas. The equilibrium factor is always between Zero and One because the activity of the daughter products cannot exceed that of the radon gas. Very clean atmospheric conditions are characterized by an equilibrium factor of less than 0.1, but atmospheres of a high particle pollution (smoke, dust, humidity) by factors that are close to One. The equilibrium factors of typical conditions for room air are within the range from 0.4 to 0.6. If so the equilibrium factor at a workplace is known and time invariant, you can determine the radon daughter concentration from the product of the radon gas concentration and the equilibrium factor. With an equilibrium factor heavily differing or varying the real value will be over- or underestimated. The equilibrium factor can be determined by means of special instruments, e.g. SARAD EQF, that measures both components simultaneously.

For both procedures SARAD offers very suitable measuring instruments. The DOSEman PRO is the smallest instrument on the market to directly determine the radon daughters. In addition to the daughter concentration the instrument also indicates the dose. Its development has been done within the framework of a project of the Federal Office for Radiation Protection.

Also suitable is the poCAMon. This instrument has a clearly higher throughput and thus a higher sensitivity but thereby it is larger and heavier.

The DOSEman and the Radon Scout Professional are available as radon personal dosimeters. Both instruments are easy to handle and robust and can be worn in the pockets of clothes. The dose will be directly indicated on the display.

The sensitivity of the Radon Scout Professional is clearly higher than that of the DOSEman. With lower concentrations and longer residence time in radon atmospheres you should give preference to this instrument. On the other hand, the DOSEman offers a very fast response time that triggers an alert immediately in case of high concentrations or an all-clear signal at low concentrations (also refer to application in water works and in mining).