Indoor radon-222 concentration measurements during the summer season of year 2000 in some houses in the Western Part of Yatta City

Abstract EN

Radon, as a natural noble gas, has three main natural isotopes; namely, radon-222 (222Rn), a decay product of 238U, radon-220 (220Rn, known as thoron), produced in the decay series of thorium-232 (232Th), and radon-219 (219Rn), a decay product from the chain originating with 235U [1].

Both 238U and 232Th occur naturally in soil and rocks at variable concentrations of about 1 pCi/g and also 226Ra, the parent of 222Rn [2].

The 222Rn isotope has a half-life of 3.82 days; while 220Rn isotope has a half-life of 55 seconds and 219Rn isotope has a half-life of about 3.96 seconds.

222Rn decays into polonium-218 (218Po), which in turn decays within minutes to lead-214 (214Pb), bismuth-214 (214Bi), and polonium-214 (214Po) [3].

In particular, 222Rn poses a major concern in regard to radiation pollution and human health hazard [4,5].

The radon gas can diffuse easily out of the soil surface into air or houses; it can be trapped in poorly ventilated houses and so its concentration can build up to higher levels.

Although soil is considered to be the main source of indoor radon concentration, raw building materials (especially quartz, cement, etc.) can make a significant contribution to the level of natural radioactivity in closed spaces such as stores and badly-ventilated dwellings [6].

Moreover, the production rate of radon in dwellings depends on the concentration of radium content in the subsoil, building materials, and porosity as well as the density of the wall material [7,8].

The emission of radon from building materials is found to be a function of ventilation as well as of the radium content in building materials.

The nongaseous 222Rn decay products are partially suspended in air as a mixture of attached and unattached fractions and partially deposited on walls and furniture [9].

Over the past four decades, natural radiation exposure due to 222Rn and its progeny inside houses has been recognized as a worldwide problem and a cause of significant lung cancer risk to the population [10,12].

Therefore, it is of great importance to assess the exposure to 222Rn and its progeny in houses and areas of high 222Rn levels for the purposes of quality control, radioactivity monitoring for building materials, and for correction measures recommendations.

During the past two decades, a tremendous number of investigations have been conducted in different countries all over the world in order to monitor radon level before action can be taken.

The recommended indoor action level for the population ranges between 200 and 600 Bq/m3 [13].

An indoor concentration of 200 Bq/m3 has been assigned as a reference for radon level in most European countries [10].

A radon level of 150 Bq/m3 and an average effective dose of 7.5 mSv/y have been also adopted in the USA as a reference level for 222Rn concentration and as an acceptable dose before taking any action [6].