|Year : 2013 | Volume
| Issue : 2 | Page : 52-56
Study on radiological contamination of ship scraps and environmental materials in ship breaking area of Chittagong, Bangladesh
Bijoy Sonker Barua1, Md. Shuza Uddin2, Md. Asad Shariff2, A. K. M. Saiful Islam Bhuian3, Masud Kamal3, MA Rashid4
1 Department of Physics, Chittagong University of Engineering and Technology, Chittagong; Tandem Accelerator Facility Division, INST, Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh
2 Tandem Accelerator Facility Division, INST, Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh
3 Radioactivity Testing and Monitoring Laboratory, Bangladesh Atomic Energy Commission, Chittagong, Bangladesh
4 Department of Physics, Chittagong University of Engineering and Technology, Chittagong, Bangladesh
|Date of Web Publication||14-Mar-2014|
Bijoy Sonker Barua
Department of Physics, Chittagong University of Engineering and Technology, Chittagong - 4349
Source of Support: 1. National Science and Technology Fellow, 2. Chittaogng University of Engineering and Technology authority, 3. Bangladesh Atomic Energy Commission., Conflict of Interest: None
The environmental radioactivity levels, both natural and anthropogenic, in the ship scrapped materials such as metal, rubber and foam and tree bark of ship breaking area of Bhatiari, Chittagong in the southern part of Bangladesh were analyzed by using a high purity germanium γ-ray spectrometry. The specific radioactivities of Radium (226 Ra), Thorium (232 Th) and Potassium (40 K) were measured in the above samples. From the measured specific radioactivities of the above three natural radionuclides, the radium equivalent activity (Ra eq) and the external hazard index (H ex) were calculated. The natural radioactivity in scrapped metal collected from the engine of a ship is found to be a bit higher. In other samples, the Ra eq values were in the range of 21 → 145 Bq/kg and the H ex varied from 0.06 to 0.39, which indicates that the working environment of the ship breaking area of Chittagong is radiologically safe.
Keywords: High purity germanium γ-ray spectroscopy, natural radioactivity, radiological parameter, ship breaking activity
|How to cite this article:|
Barua BS, Uddin M, Shariff M, Bhuian AS, Kamal M, Rashid M A. Study on radiological contamination of ship scraps and environmental materials in ship breaking area of Chittagong, Bangladesh. Radiat Prot Environ 2013;36:52-6
|How to cite this URL:|
Barua BS, Uddin M, Shariff M, Bhuian AS, Kamal M, Rashid M A. Study on radiological contamination of ship scraps and environmental materials in ship breaking area of Chittagong, Bangladesh. Radiat Prot Environ [serial online] 2013 [cited 2019 Nov 11];36:52-6. Available from: http://www.rpe.org.in/text.asp?2013/36/2/52/128867
| Introduction|| |
Ship used for scrapping may contain radioactive materials from transportation of radioactive materials, natural and man-made. Moreover, there is a possibility of sea water getting contaminated by man-made radionuclides through nuclear accident like Fukushima nuclear power plant damage, so the scrap products may get contaminated with the radionuclides and become a source of radiation. The scrap products such as iron, steel, asbestos, foam, rubber etc., and environmental materials of ship breaking area are randomly used by people. If these are contaminated by radioactive materials, it may pose radiological hazard. Natural radioactivity arises mainly from the primordial radionuclides, such as 40 K and the radionuclides from 238 U and 232 Th series and their decay products.  Gamma radiation emitted from the decay of naturally occurring radioisotopes represents the main external source of irradiation of the human body.
The environmental radioactivity and the associated external exposure due to gamma radiation depend primarily on the geological and geographical conditions. ,, A significant part of the total dose contribution in the form of natural sources comes from terrestrial gamma radionuclides. 
Therefore, it is necessary to measure the concentrations of radionuclides, namely 40 K, 238 U, 232 Th and 137 Cs in ship scraps as well as in environmental samples, which is essential for the estimation of the radiation exposures of human being and in monitoring of environmental radioactivity at ship breaking area.
In the present study, the 40 K, 238 U, 232 Th and 137 Cs activities in ship scraps (e.g., metal, rubber and foam) and bark of trees grown in the ship breaking area of Bhatiari, Chittagong, Bangladesh were measured by high purity germanium (HPGe) γ-ray spectroscopy.
| Materials and Methods|| |
Sample collection and preparation
Several samples of ship scraps and bark of trees were collected from the bank of Bay of Bengal is located in Bhatiari, Chittagong, Bangladesh. The sampling locations are shown in [Figure 1]. All investigated samples were dried under the direct sunlight for several days to evaporate the water. The bark of trees was dried at 60-110°C in an electric oven until constant weight was attained. Metal samples, rubber and foam samples were cut into small pieces and placed in a cylindrical plastic container of 7 cm diameter and 8 cm height for γ-activity counting, where the samples were pressed to obtain compact packing and the geometry similar to standard reference materials. The size of sample in the container was about 154 cm 3 (7 cm diameter × ~4 cm height). Tree bark samples were dried and ground with agate mortar and then transferred to a container. These samples were stored for 1 month before the measurement of radioactivity to allow for the attainment of secular equilibrium between 226 Ra and 232 Th and their progeny. ,
|Figure 1: The map showing sampling locations (red balloons) in Bhatiari, Chittagong, Bangladesh|
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The sampling locations lie between the longitudes of 91°43.895/−91°44.746/and the latitudes of 22°25.473/−22°26.293/.
The radioactivities of the investigated samples and International Atomic Energy Agency (IAEA) reference samples of the same geometry were measured for 10,000 s by using closed-end coaxial HPGe detector of relative efficiency 20%, resolution 1.8 keV (full-width at half maximum) at 1332 keV of 60 Co. The HPGe γ-ray detector (GC2018, CANBERRA, USA) coupled with digital spectrum analyzer, DSA-1000. To reduce the γ-ray background the detector was shielded by a cylindrical 5.08 cm thick lead. After adjustment of the necessary parameters such as resolution, peak to Compton ratio, etc., and measurement of minimum detectable activity of the detector, the sample was placed on the top of the detector within the shielding arrangement.  The γ-ray spectra of the samples were taken and analyzed by using the program GENIE 2000. The entire γ-ray counts of investigated samples were subtracted from the background count. The background count was also measured for 10,000 s.
HPGe γ-ray detector efficiency
Radioactivity measurements for volume samples play an indispensable role to the radiation protection works. The γ-ray spectrometry method using a germanium semiconductor detector is generally used for this purpose. The detector efficiency is dependent on volume as well as distance of the sample. Therefore, efficiency is an important factor for the measurement of bulk material. The γ-ray peak efficiency versus energy curve corresponding to each objective volume sample must be given in advance of the measurements. The detection efficiency curve depends on detection system, sample shape and sample matrix. At present the reliable efficiency versus energy curve for the HPGe γ-ray detector was determined by measuring the known activity of the volume samples prepared using IAEA reference samples RGU-1, RGTh-1 and RGK-1. The 10.0140 g, 10.0072 g and 10.0053 g of ore of IAEA reference samples namely RGU-1, RGTh-1 and RGK-1, respectively, were individually mixed homogeneously with 100 g milk powder to make three separate standards γ-ray source materials and it was done by IAEA. These three standard sources of same volume were used to generate efficiency versus energy curve for the HPGe γ-ray spectrometer. We have strictly followed volume same for all the investigated samples. It should be mentioned that despite same volume, the weight is much different due to various unknown constituents of the samples. The obtained efficiency versus energy curve is shown in [Figure 2].
|Figure 2: Efficiency versus energy curve for high purity germanium γ-ray detector|
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A typical γ-ray spectrum of a soft rubber sample is shown in [Figure 3]. A background spectrum is also shown in [Figure 4]. The 226 Ra ( 238 U) activity was determined individually from the net area of peak at energies of 351.9 keV ( 214 Pb), 1120 keV ( 214 Bi) and 1764 keV ( 214 Bi). 214 Pb and 214 Bi are the decay products of 238 U series. Similarly, the 232 Th activity was determined from the counts at peak energies of 238.6 keV ( 212 Pb), 727 keV ( 212 Bi), 911 keV ( 228 Ac) and 583 keV ( 208 Tl). Finally, we took average of the values obtained from different peak energies. The activity of 40 K was determined from its 1460.83 keV γ-line. No peak at energy of 661 keV due to 137 Cs was appeared in the spectrum, because its radioactivity in the investigated samples was below the detection limit. In this experiment the lower limit of detection for 137 Cs was measured by equation 3 as given in Appendix and the obtained value is 0.043679 Bq.
The count rate of each radionuclide measured was converted to activity per kilogram of dry sample (Bq/kg) by applying the usual corrections, like the intensity of the emitted γ-ray, the efficiency of the detector and the weight of sample. The uncertainty in the specific radioactivities of the individual samples was determined by considering the uncertainties in counting statistic (1-7%), peak area analysis (2%), detector efficiency (5%), gamma emission probability (<0.2%) and sample weight (0.01%) respectively. The overall uncertainties were in the range of 5-9%. However, we have also calculated the standard deviation from the several values and their average for a radionuclide and the results are also given in [Table 1] and [Table 2]. From the measured specific radioactivities of the 226 Ra ( 238 U), 232 Th and 40 K radionuclides, the radium equivalent activity (Ra eq ) and the external hazard index (H ex ) were calculated using the well-known formulae. ,,
|Table 1: Measured specific activities of the investigated ship scrapped metal samples, radium equivalent activity (Ra eq) and external hazard index (H ex)|
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|Table 2: Measured specific activities of the investigated rubber, foam and tree barks, radium equivalent activity (Ra eq) and external hazard index (H ex)|
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| Results and Discussion|| |
The measured specific radionuclide concentrations of 226 Ra ( 238 U), 232 Th and 40 K in various ship scrapped metal samples are given in [Table 1]. The uncertainties in the measured radioactivities are also mentioned as a foot note of [Table 1]. In most of the samples, the 226 Ra ( 238 U) radioactivities are very low except two samples and those varied in the range of 6.89 ± 0.84-15.27 ± 1.14 Bq/kg. The radioactivity in the scrapped metal sample collected from ship engine is rather high and amounted to 415 ± 22.25 Bq/kg, which is not comparable to others and the reason is unknown. The variation of the 232 Th and 40 K radioactivities in those samples was found in the range of 6.78 ± 1.06-238 ± 8.98 and 7.40 ± 0.67-67.32 ± 7.41 Bq/kg, respectively.
A variation of 7.78 ± 0.66-25.57 ± 1.53, 8.62 ± 0.41-31.05 ± 1.55 and 12.57 ± 0.88-312 ± 34.26 Bq/kg in the levels of the three radionuclides respectively were observed in the mixture of rubber and foam samples. The detailed results are given in [Table 2].
The radioactivities in barks of only two plants namely Eucalyptus tree and Jackfruit tree were measured and the results are given in [Table 2]. The plant is rare in the area of ship breaking, we could get only two. The outer layer of tree bark, in particular, is to be an effective passive accumulator of airborne particles that are settled on the outer bark by wet and dry deposition, remaining there until the tree sheds its bark, or are leached or washed away by rain, or a combination of the two. Therefore, the activity in bark may help for understanding the effect of ship breaking on environmental radioactivity.
Ra eq , H ex
The Ra eq and H ex were calculated using the measured radioactivities of 238 U, 232 Th and 40 K and the results are given in [Table 1] and [Table 2]. Only one scrapped metal from engine having Ra eq = 760 Bq/kg, the corresponding H ex = 2.05 is rather high and is of radiological concern. Except this one, all other samples having the Ra eq in the range of 21-145 Bq/kg and these values are less than 370 Bq/kg, and are acceptable for safe use.  Similarly the H ex varied from 0.06 to 0.39. Since these values are lower than unity, the external radiation hazard in the ship breaking area is low.
However, the results of analysis of ship scrapped metal, foam, rubber and tree bark could help to find the level of environmental radioactivity prevailing in the ship breaking area.
| Conclusion|| |
We have made a careful analysis to determine the concentrations of 238 U, 232 Th and 40 K radioactivities in ship scraps metal, foam and rubber and tree bark of the ship breaking area of Bhatiari, Chittagong, Bangladesh. The higher values of radiation parameters of only one sample (metal from engine) indicated the presence of radioactive contamination, the reason for which is not known. However, the results in general, reflect that the investigated ship breaking area seems to be radiologically safe for working. Attempts were made to detect and measure artificially produced radionuclide 137 Cs, the activity of which was found to be below detection limit. As a radioactive indicator the use of tree barks is a good option. The results obtained by the study would be useful to monitor environmental radioactivity in that area.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2]