LUNG CANCER RISKS DUE TO THE RADON 209
210 Po
238 U decays to 222 Rn ( a gas ) and
then to 210 Pb , which settles on tobacco leaves and later decays into 210 Po
222 Rn
Fertilizer made of uraniumrich phosphate rock
210 Pb
238 U
210 Pb from the soil is absorbed through the roots
Fig . 1 . Sticky hair-like structures on both sides of tobacco leaves [ 4 ].
from use of these tobacco samples ranged from 1.67 to 3.52 mSv year – 1 . The result refers to the dual ( chemical and radioactive ) effect of smoking as a risk factor for lung cancer . Laith [ 8 ] showed that the 222 Rn concentrations in cigarette tobacco samples ranged from 228 to 778 Bq m – 3 with an average of 432 Bq m – 3 , with the radon-induced lung cancer risks varying from 103 to 353 cases per million people with an average value of 196 . Excellent correlation was observed between the radon concentration and lung cancer cases per year per million people for different brands of tobacco .
The aims of the present work were to evaluate the activity concentrations of radon and radium in tobacco and to calculate the risk parameter , namely , the number of smokers ( per million smokers per year ) who can be expected to get lung cancer as a result of smoking a particular type of cigarettes .
THEORY Activity Concentrations of Radon Gas and Radium
The activity concentration of radon ( C Rn , Bq m – 3 ) in cigarette tobacco at secular equilibrium is given by the equation [ 9 ]
C Rn = ρ /( KT ), ( 1 )
where ρ is the track density ( mm – 2 ); K , experimental calibration factor equal to 0.0022 ( mm – 2 )/( Bq day m – 3 ); and T , exposure time ( days ).
To calculate the activity concentration of 226 Ra ( C Ra , Bq kg – 1 ) in cigarette tobacco samples , we used the following equation [ 10 ]:
C Ra = ρhA /( mKT e ), ( 2 ) where ρ is the track density ( track mm – 2 ); h , distance between the detector and the top of sample ( 0.07 m ); A , surface area of the sample in the plastic cylinder ; K , calibration coefficient for CR-39 ; T e , effective exposure time ( h ); and m , sample weight [ 11 ]:
T e = T + ( 1 / λ )( e – λT – 1 ), ( 3 )
where λ is decay constant of radon gas ( 0.1814 day – 1 ), and T is the exposure time ( days ).
Radon Dose Estimation
The annual effective dose from indoor radon concentration , E Rn ( mSv year – 1 ), was calculated using the UNSCEAR model [ 12 ]:
E Rn = C Rn FHTD , ( 4 )
where F is an equilibrium factor ( 0.4 ), H is the occupancy factor ( assumed equal to 0.8 for this work ), T is the number of hours in a year ( 8760 h year – 1 ), and D is the dose conversion factor [ 9.0 × 10 – 6 mSv /( Bq m – 3 h )].
The annual effective dose for smoker lung from radon gas inhalation , E L ( mSv year – 1 ), was calculated using the following equation [ 12 ]:
E L = E Rn W R W T , ( 5 )
where W R is radiation weighting factor equal to 20 for α-particles , and W T is the tissue weighting factor equal to 0.12 for lungs .
The equivalent dose for bronchial areas of human lungs was calculated using the conversion factor of 1.0 × 10 – 5 mSv /( Bq h m – 3 ) [ 13 ]. It should be taken into
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