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Assessment of Natural Radioactivity and Radiation Hazard in Soil Samples of Rajbari District of Bangladesh

R. Khatun
AFD, Atomic Energy Centre, 4 Kazi Nazrul Islam Avenue, Dhaka, Bangladesh

A. H. M. Saadat
Department of Environmental Sciences, Jahangirnagar University

M. M. Ahasan
AFD, Atomic Energy Centre, 4 Kazi Nazrul Islam Avenue, Dhaka, Bangladesh

S. Akter
AFD, Atomic Energy Centre, 4 Kazi Nazrul Islam Avenue, Dhaka, Bangladesh

Abstract/ Executive Summary:

Rajbari district of Bangladesh, have been studied and possible health effect were estimated. The experiment has been done by using gamma ray spectrometry system consisting of a HPGe detector coupled with MCA and associate electronics. The average natural radioactivities of 238U, 232Th and 40K have been measured as 29.03±5.67 Bq/kg, 50.91±10.17 Bq/kg and 535.32±89.19 Bq/kg respectively. To estimate health effect due to the activity of those radionuclides, the radium equivalent activity (Raeq), external hazard index (Hex), absorbed dose rate (D) and effective dose have been calculated and compared to the world average values. The results are also compared with the literature values reported for other regions of the world and found that the soil of the study area are not hazards by the radiation and does not pose any harmful effect to the environment. The outcome of this study may provide valuable information about radiation hazard and also may take part in the monitoring of environmental radioactivity.

Keywords: Radionuclide; Absorbed dose; External hazard index; Radium equivalent activity; Annual effective dose

Location: Different locations of Rajbari district.

Start Date: 00-00-2009

End Date: 00-00-2010

Program Area: Risk Management in Agriculture

Commodity: Radiation

Objectives:

Measurements of natural radioactivity in soils and the radiation doses are of great interest to the researchers which have led the nationwide surveys throughout the world

Methodology:

Sample Collection and Preparation: Soil samples (0-15 cm depth) were collected during 2009 to 2010 from twelve different locations of Rajbari district. After removing the stones and vegetation, all soil samples were oven dried at 105⁰C for 24 h. Then they were grinded homogeneously and each sample of 400g was kept in the plastic container of 7.2 cm diameter and 8.3 cm in height labeled with appropriate identifications and left for four weeks to reach radioactive equilibrium. Blank plastic container of same geometry was used for background counts. Method of Analysis Radioactivity of soil samples were measured using a low level gamma counting system, a HPGe detector with a relative efficiency of 19.6% and energy resolution of the 1.33 MeV for the 1332 keV 60Co peak. The corresponding background counts for each sample have been measured for 5000s and it was subtracted from the sample activity counting. The radioactivities of 238U and 232Th were estimated on the assumption that they are in secular equilibrium with their respective daughter products within four weeks. The measurement was based on the recording natural radioactivity quantities of three natural long-lived elements: 238U, 232Th and 40K which are considered the photopeaks at 1760, 2610 and 1460 keV respectively. The concentration of 212Pb, 208Tl, 214Pb and 214Bi occur in the samples due to disintegration of 238U and 232Th respectively. Therefore, the activities of 212Pb, 208Tl, 214Pb and 214Bi in the samples indicate the presence of 238U and 232Th respectively.

Source of Information: Jahangirnagar University Environmental Bulletin, Vol.2, 1-8, 2013

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The study showed that the radioactivity levels of 238U, 232Th and 40K were 29.03±10.17 Bq/kg, 50.91±10.17 Bq/kg and 535.32±89.19 Bq/kg respectively and were comparable with the other regions. However, slight variation in the radioactivity content in soil observed with different locations worldwide mainly due to soil type, formation and transport process involved. This may be the reason for the variation observed results. The mean absorbed dose rate obtained in the present study (66.64±6.81 nGy/h) is comparable to the world average (55 nGy/h). The calculated annual effective dose with average value of 0.082 mSv is lower than the world average value (0.480 mSv). All values obtained for radium equivalent activity are less than 370 Bq/kg, which are acceptable for safe use as recommended by the IAEA [UNSCEAR, 1988]. The measured values of external hazard index found in this study range from 0.33 to 0.47 (all are lower than unity), which means that it does not cause any health hazard to the population living in the investigated area.

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