Abstract
The second largest cause of lung cancer is related to radon (<sup>222</sup>Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of <sup>238</sup>U from its constituents. This Radon has been recognized as one of the major contributor to the natural radiation and health hazards in the human dwellings. Even lung cancer is expected if it is present in enhanced levels beyond maximum permissible (acceptable) limit. This thesis reports the measurements of indoor radon concentration in the Lalibela dwellings of the Amhara region in Northern Ethiopia using the cellulose nitrate (LR-115 type-II) plastic track detectors. Eleven cellulose nitrate films (LR-115 SSNTD) were distributed over the study area dwellings according to the fraction of the population. The exposure time was started from February 21/2013 and lasted for 90 days. It is found that the values of radon concentration vary from 52.45 to 353.95 Bqm<sup>-3</sup> with the average value of 140.64 Bqm<sup>-3</sup>. The effective dose rates have been calculated and found to vary from 1.38 to 9.34 mSvy<sup>-1</sup> with over all mean value of 3.71 mSvy<sup>-1</sup>. It is also found that mud houses (houses use unbaked bricks) have relatively lower indoor radon as compared to the houses which are made of the baked bricks and cement.
Highlights
Radon is a naturally occurring radioactive gas generated by the decay of uranium and thorium bearing minerals in rocks and soils
Values on the higher side may be attributed to the building materials, and poor ventilation, which usually play an important role in the indoor radon concentration
Radon gas, present universally in different concentrations in air, soil and water has its harmful impacts on public health and causes lung cancer
Summary
Radon is a naturally occurring radioactive gas generated by the decay of uranium and thorium bearing minerals in rocks and soils. The half-life of thoron (radon-220), a product of the thorium halflife, thoron infiltration from the ground and subsequent migration from its production site to the immediate environment of people within a building is limited. While radon tends to be homogeneously distributed in indoor air, the thoron level varies significantly with distance from the source. One of the thoron decay product, lead-212 (212Pb), is relatively long-lived (10.64hr) allowing it time to migrate into the immediate environment of building occupants before further decaying to produce the beta (β) and gamma (γ)-emitting isotope bismuth-212 (with a half-life of 60.6 min). Unlike thoron gas, thoron decay products tend to be more homogeneously distributed in indoor air [3]
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