A comparison between the activity concentrations of soil samples from different locations in the world is illustrated in Table (4).Table.4: Comparison of average activity concentrations values in (Bq/kg) for Ra-226,Th-232 and K-40 in soil samples for different countries .
Referance 40K 232Th 226Ra Country No 66.1 5.95 8.
26 Northeast Libya Present studyBaeza et al.,1992 653 41 38.8 Spain 1Yu et al.,1992 352 146 119 Hong Kong 2Mc-Aulay et al.
,1988 350 26 37 Ireland 3Ibrahiem et al.,1993 316 19 17 Egypt, Nile Delta 4Alberto et al.,1996 704 47.8 29.2 Brazil 5Elmabrouk et., 2008 al.
,2008 27.5 4.2 7.5 Northwest Libya 6Travidon et al.
,1996 1130 43 212 Greece 7Lambrechts et al.,1992 599 38 38 France 8El Mamoney and Ashraf ,2004 427.5 31.4 24.
6 Red Sea, Egypt 9Higgy ,2000 46 2.1 5.0 Mediterranean sea 10Saad and Al-Azmi,2002 227 6 36 Kuwait 11UNSCEAR .,2000 420 45 32 World average 12DISCUSSIONThe samples were ordered so that they follow the location along the coast from west to east. From the figs. (1), (2) and (3) and Tables (1-1) and (1-2) it is clear that the activity concentrations of 226Ra , in samples taken at depth (5-10 cm) ranged from 1.2 Bq/kg to 14.
1Bq/kg with an average value 8.26 Bq/kg, 232Th ranged from 0.76 Bq/kg to 10.6 Bq/kg with an average value 5.95 Bq/kg, 40K ranged from 21.1 Bq/kg to 100.4 Bq/kg with an average value 66.
1 Bq/kg.The corresponding results at depth (50 – 70 cm) are within the range from 1.17Bq/kg to 11.7 Bq/kg with an average value 7.5 Bq/kg for 226Ra, from 0.8 Bq/kg to 11 Bq/kg with an average value 5.
1 Bq/kg for 232Th, from 13.5Bq/kg to 100 Bq/kg with an average value 68.6 Bq/kg for 40K.Two different depths (5-10 and 50-70 cm) are considered is the present work to estimate the dependence of the radioactivity values on the depth also to look for climatotherapy places as those already utilized in our neigbouring countery (Egypt). The radioactivity concentration of 226Ra, 232Th and 40K at Al bayda beach are to a great extent identical to the results of (Meijer et al., 2001) concerning North sea studies at the western Australia coast and those of (Saad and Al Azmi, 2002) concerning the southern areas of Kuwait, as well as the results of (El Mamoney and Khater, 2004) concerning the Red Sea coast and those of (El Kameesy, 2007) concerning the Gulf coast northeast of KSA.
Additionally, the activity concentration of 226Ra(8.26 Bq/kg) and 232Th (5.95 Bq/kg ) in our study are comparable to those of (El Mabrouk, 2008) concerning the northwest beach of Libya (7.5 Bq/kg for 226Ra and 4.2 Bq/kg for 232Th). In contrast to these results, the activity concentration of 40K in the northwest beaches of Libya (27.5 Bq/kg) is less than those in northeast beaches of Libya (66.1 Bq/kg).
A comparison between the activity concentrations of soil samples from different locations in the world is illustrated in Table (4).responding result of 210Pb in eight soil samples and which the values are given in Bq/kg on a dry weight basis and the activity ratio of 210Pb/226Ra are presented in Table (2). The samples were ordered so that they follow the location along the coast from west to east. It is clear that the activity concentrations of 210Pb , in samples taken at depth (5-10 cm) ranged from 3.8 Bq/kg to 19.
4 Bq/kg with an average value 12.39 Bq/kg. The corresponding results at depth (50-70 cm) are within the range from 3.1 Bq/kg to 13.1 Bq/kg with an average value 9.
64 Bq/kg for 210Pb.From Table (2), it is clear that, the average activity ratio of 210Pb/226Ra is 1.48 for depths at 5 – 10 cm and 1.27 for depths at 50 – 70cm. The variation in these ratios could be due to the presence of varying degrees of disequilibrium between the members of 238U decay series in the coastal marine sediments or some amounts of different pollutants in the sea water. In addition, the 210Pb (222Rn decay products) fallout flux from the atmosphere and/or geochemical behavior of both Pb and Ra in the environment could explain uranium series (U, Ra, Pb) disequilibrium in the environment. Radium forms a complex with chloride and in this form is quite mobile. Conversely, even moderate amounts of sulfate ion inhibits transport because of the co-precipitation of radium sulfate along with barium sulfate.
The radium equivalent values for soil samples are shown in Table (3). The Raeq ranged from 3.912 to 36.99 Bq kg-1, with an average of 21.9 Bq kg-1 at depth 5-10 cm and ranged from 3.
354 to 28.474 Bq kg-1, with an average of 20.073 Bq kg-1 at depth 50-70 cm as shown the range of the absorbed dose rate that obtained for the soil samples in the studied area is from 1.906 nGy/h to 17.283 nGy/h with an average 10.3 nGy/h at 5-10 cm and is from 1.
6 nGy/h to 13.426 nGy/h with an average 9.492 nGy/h at 50-70 cm. While the external hazard indices ranged from 0.0106 to 0.
09990, with an average of 0.059 at depth 5-10 cm and ranged from 0.009 to 0.0769, with an average of 0.054 at depth 50-70 cm, and representative level index (Ir) ranging between 0.0297 to 0.
2669 with an average 0.1586 at depth 5 -10 cm and ranged from 0.0248 to 0.207, with an average 0.1467 at depth 50 – 70 cm, and the annual dose equivalent in the studied area was ranging between 0.0023 mSv y-1 to 0.
0212 mSv y-1, with an average 0.0126 mSv y-1 at depth 5-10 cm and ranged from 0.002 mSv y-1 to 0.0165 mSv y-1, with an average 0.012 mSv y-1 at depth 50 – 70 cm.A comparison between the activity concentrations of soil samples from different locations in the world is illustrated in Table (4). The obtained results of the present work show that, the activity concentration of naturally occurring radionuclides in soil samples in the study area were within the world average range.CONCLUSIONIn the present work, the radioactivity concentrations of the two main radioactive 238U and 232Th series along with 40K have been experimentally evaluated using advanced techniques such as gamma ray spectrometer based on HPGe detectors and alpha spectrometer based on NSST detectors.
In general, the study can be radioactivity concentration in the soil samples were measured in 24 soil samples from the northwest Libyan coast in Al Bayda, region using different nuclear techniques.1) It was observed that the activity concentrations of 226Ra, 232Th, 40K, and 210Pb in soil samples taken at depth 5-10 cm have an average 8.26 ± 1.
6 Bq/kg, 5.95 ± 1.3Bq/kg, 66.1 ± 15.
2 Bq/kg and 12.4 ± 2.4Bq/kg respectively. While, the activity concentrations at depth 50-70 cm have an average 7.5 ± 0.
99 Bq/kg for 226Ra, 5.1 ± 1.54 Bq/kg for 232Th, 68.
6 ± 8.33 Bq/Kg for 40K, and 9.6±1.9Bq/kg for 210Pb.2) The average activity ratio 210Pb/226Ra is 1.48 for depths at 5-10cm and 1.
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