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Measurement of the Natural Radioactivity and Radiological Hazard of Soil, Sand and Sediment Samples Collected from Coastal Area, Cox’s Bazar, Bangladesh.

Sariful
Department of Physics, Jagannath University, Dhaka-1100, Bangladesh.

Suranjan Kumar Das
Department of Physics, Jagannath University, Dhaka-1100, Bangladesh.

Md. Murad Ahmed
Department of Physics, Jagannath University, Dhaka-1100, Bangladesh.

Selina Yeasmin
Health Physics Division, Atomic Energy Centre, Dhaka, Bangladesh.

Abstract/ Executive Summary:

The radioactivity concentrations of 24 samples of soil and sand sediments from Cox’s Bazar were determined using high purity germanium detector. The results of ²²⁶ Ra, ²³² Th and ⁴⁰ K in the soil samples were found to vary from 15.34 ± 1.66 to 33.70 ± 2.08 Bq/kg, 30.09 ± 3.62 to 58.06 ± 4.23 Bq/kg and 379.99 ± 33.43 to 755.26 ± 38.03 Bq/kg, respectively. For sand samples the activity concentrations were between 8.98 ± 1.49 to 31.33±2.04 Bq/kg, 16.82 ± 3.24 to 63.28 ± 4.37 Bq/kg and 252.42 ± 31.72 to 565.72 ± 35.78 Bq/kg, respectively, for sediment samples values were 13.90 ± 1.64 to 38.41 ± 2.19 Bq/kg, 37.94 ± 3.82 to 51.92 ± 4.11 Bq/kg and 367.70 ± 33.28 to 665.05 ± 36.97B q/kg, 367.70 ± 33.28 to 665.05 ± 36.97 Bq/kg, respectively. The absorbed dose rate of soil, sand and sediment samples were found as 79.98, 77.17, and 57.86 nGy/h, respectively. Outdoor annual effective doses were 0.49, 0.47 and 0.36 mSv/y.

Keywords: Natural radioactivity, Radiological hazard, Sediment samples, Coastal area, Cox’s bazar

Location: Himchori beach to Inani beach within Ukhia Thana, 35 km to the south of Cox's Bazar.

Start Date: 00-00-2014

End Date: 00-00-2014

Program Area: Crop-Soil-Water Management

Commodity: Contamination of soil

Objectives:

To determine the conc. of ⁴⁰K, ²³²Th, ²²⁶Ra in soil, beach sand and sediment samples collected from Cox’s Bazar.

Methodology:

Coastal area of Cox’s Bazar sea beach was the study area of the present study. The study area included Himchori beach to Inani beach within Ukhia Thana, 35 km to the south of Cox's Bazar. The sand, soil and sediment samples were collected from the beach of the interested coastal region during the month of February, 2014. The coordinates of the sampling area is in between 21°14'15" to 21°17'7"N and 92°2'3" to 92°2'56"E. Twenty four samples of three kinds (soil, sand and sediment) were carefully collected at 5-10 cm depth from the soil-surface by using shovel and each of the samples weighing approximately 1 to 1.2kg and were transferred into polyethylene bags and labeled accordingly. The samples were then transported, stored and processed at the sample preparation laboratory of Bangladesh Atomic Energy Center (AEC), Dhaka. The samples were cleaned for stones, gravels, grass-roots, vegetation etc. and then dried in the sun for several days. The samples were then crushed and ground to fine grains using a grinding machine. The samples were mixed homogeneously and passed through a sieve of 200 µm mesh size. The samples were dried again in a temperature controlled oven at 104℃ for 24 hrs in order to eliminate any traces of water. Upon drying, the samples were transferred to sealable cylindrical plastic containers of 7 cm height and 5.5 cm in diameter and the weights of the samples were recorded using an electrical balance. The sample-filled plastic containers were sealed tightly with cap and wrapped with thick vinyl tape around their necks; marked individually with identification number, sample location, date of preparation and net weight and then stored for about 30 days to reach secular equilibrium between ²³⁸U and ²³² Th series and their daughter progenies. The detection and measurement of radionuclides in the samples were carried out by gamma spectrometry system using a p-type co-axial HPGe detector of 93 cm 3 active volume and 20% relative efficiency. The co-axial geometry with electrical contacts in the form of concentric cylinders closed at the end makes it possible to produce very large volume detector elements with excellent efficiencies for high-energy photons. The HPGe had a resolution of 2 keV at 1332 keV of cobalt-60 gamma-ray line. The detector was coupled to a 16 K- channel analyzer. The spectra of all samples were perfectly analyzed using Genie-2000 spectra analysis software (which matched various gamma energy peaks to a library of all possible radionuclides) to calculate the concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K. The detector was enclosed in a cylindrical shielding container made up of lead and iron and having a moving cover to reduce the external gamma-ray background. All the samples were counted for 5 Ks. Prior to the measurement of the samples, the environmental gamma background at the laboratory site was determined with an identical empty plastic container using in the sample measurement. The energy regions selected for the corresponding radionuclides were 295 and 352 keV of ²¹⁴Pb and 609, 1120 and 1764 keV of ²¹⁴Bi and ²²⁶Ra, 583 and 2614 keV of ²⁰⁸Tl, 911 and 969 keV of ²²⁸Ac and ²³²Th and 1460 keV of ⁴⁰K. The efficiency calibration of the detector was carried out by standard source of solid matrix prepared using ²²⁶Ra standard solution. The standard source was prepared using identical container for the measurement of the samples. The preparation process of standard sources had been reported elsewhere. The energy calibration of the detector was performed by ¹³⁷Cs and ⁶⁰Co point sources. After adjustment of necessary parameters such as resolution, peak to compton ratio, minimum detectable activity of the detectors, the prepared samples were analyzed by keeping then within the shielding arrangement and counted for above 5000 seconds. The specific activity, in terms of the activity concentration, is defined as the activity per unit mass of the sample. The term net count rate associated with the activity measurement is the difference between the gross count rate of the sample (which is the summation of background count rate and sample count rate) and the background count rate.

Source of Information: J. Bangladesh Acad. Sci., Vol.39, No.2, 233-240, 2015

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The activity concentrations and radiological impact of the soil, sand and sediment samples collected from Himchori beach to Inani beach (Cox’s Bazar district) of Bangladesh and its adjacent areas were investigated in the present study. In fact these values were found smaller (average value 122.75 Bq/kg) than the world average value (370 Bq/kg) in some cases, specially in the case if radium equivalent activity. The results indicated that no artificial radionuclide was present, only the natural radionuclide was present in the samples. It can be concluded that the probability of the radiological impact on the inhabitants living in this area will be insignificant.

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