Natural Radioactivity Measurements for Assessment Radiation from soils of Hadhramout Region, Yemen

Measurements of gamma-emitting radionuclides were performed on soil samples collected at various depth levels from different locations in the Hadhramout region, Yemen. The activity concentrations of 226Ra, 232Th, 40K, and 137Cs were determined by gamma spectrometry detector. The measurement concentrations of 238U, 232Th, 40K in the soil samples ranged from 9.25 to 423.84 Bq/kg, 7.85 to 667.23 Bq/kg, and from 31.54 to 373.12 Bq/kg, respectively. The concentrations of these radionuclides are compared with the recommended values. According to the present lower concentration levels of 137Cs, it does not pose any radiological complication. However, this data may provide a general background level for the area studied and may also serve as a guideline for future measurement and assessment of possible radiological risks to human health in this region.


Introduction
Natural radioactive γ emitters as 40 K, 232 Th, and 238 U are essential nuclides in the crust of the earth. The world is exposed to pollutants which are naturally radioactive. Naturally, radionuclides and almost 82% of human species absorb radiation [1]. The most common radionuclides in the crust of the Earth are Uranium-234 ( 234 U) and Uranium-238 ( 238 U). In addition, environmental isotopes are radon-222 ( 222 Rn), radium-226 ( 226 Ra), and radium-228 ( 228 Ra), and that are formed as the radioactive decay of thorium and uranium present in rock and soil is the result of [2]. These radioactive nuclides pose risks due to external exposure to emissions of γ radiation and radon and its progeny internally. Radon is called the second main cause of lung disease and is a human carcinogen [3]. For a good understanding of differences in the background of natural radiations, the starting point must be knowing the wide differing radioactivity content of naturally happing radionuclides in soils. [4,5] The most important key for detecting the radioactive natural background in the soil is measuring of radioactive concentration of the radioactive isotopes [6]. In soil, the natural radioactivity levels change according to the geological nature and geographical structure.
The natural presence of the radon gases which are radioactive and the presence of other naturally occurred radionuclides and their radioactive daughters in the soil provide exposures to humans [7]. Natural-Occurrence radioactivity depends on the type of soil; soil radioactivity sources other than

Materials and Methods
Soil samples have been taken randomly among selected locations of the Hadhramout region (As sufale site) in Yemen at varying depths as, surface (0-5), (5-50), (50-60), and (60-70) cm. The strange material like plant roots, stones were taken away from the mix. The samples were handled as they dried in the sun, one-hole day drying inside an oven of one hundred °C, crushed, ground to a soft powder, and homogenized by blending before the test [10]. Then a combined sample of about 500 gm was sealed and kept for about four weeks duration to let the equilibrium of radioactive [11]. The activity concentrations were measured for the 40 K, 232 Th , 226 Ra The γ -spectrometer used for analyzing all samples is High purity Germanium (HPGe) detector with a 25% of relative efficiency, coaxial-type. The resolution (FWHM) is from 3 to 3.5 keV for 1332.5 keV γ -ray peak of 60 Co, and Compton peak ratio is 41:1. In our study, the background was estimated each week under the same circumstances as a measurement of the sample. The elapsed time of measurement was 82800 s. The specific activity of 226 Ra was estimated from γ-ray lines of 214 Bi at 609.3, 1120.3 & 1764.49 keV, and 214 Pb at 351 keV, while the specific activity of 232 Th was decided from γ-ray lines of 228 Ac at 911. 16 & 968.9 keV, 212 Pb at 238.58 Kev and 212 Bi at 727. 25. 40 K was defined by measuring its single peak at 1460.8 Kev. The reference decay for detecting 137 Cs is the decay of 137 Ba. Activity calculations in each sample were estimated utilizing the next equation [12,13].
Ac (Bq/kg) =Nc/εβM (1) Where: Nc represents counting rate of gamma, ε represents the efficiency of detector, β represents the absolute transition probability of γ-decay, M represents the sample's mass in kilograms. The radioactivity of 226 Ra was from 9.25 Bq/kg for sample S5 (no.18) at depth (5-50) cm to 423.84 Bq/kg for sample S1 (no.2) at depth (5-50) cm. Comparing these values with the reported world range of 226 Ra activity concentrations which varies from 10 to 50 Bq/kg as reported by UNSCEAR2000, it can be seen that the upper value in the current work is 7 times more than the reported upper-value concentration of 60 Bq/kg. The activity concentration for 232 Th ranges from 7.85 Bq/kg for sample S5 (no.20) at a depth (60-70) cm to 667.23 Bq/kg in sample S1 (no.2) at a depth (5-50) cm. The reported world values of 232 Th range from 16 to 110 Bq/kg (UNSCEAR2000). So, the measured upper value in the current research is ten times as much as the upper limit world values. The 40 K activity concentration was determined are within the range from 31.54 Bq/kg in sample S2 (no.8) at a depth (60-70) cm to 373.12 Bq/kg in sample S5 (no. 18) at a depth (5-50) cm. The scope of activity concentration values of 40 K is beneath the world range in soil (140 to 850 Bq/kg) UNSCEAR2000.
Also from Table 1, it can be seen that the samples S1, S2, S3, and S4 at depths (0-5) cm and ( 5-50) cm have much lower values of 40 K activity concentrations and greater values for 226 Ra and 232 Th in comparison with the other present soil samples and the reported range values [7]. The higher values of 226 Ra and 232 Th for these samples may be attributed to their graphical locations under investigation from which the samples were collected, where, these samples were located in the vicinity of the sea and exposed to rapidly spreading water due to the crack of wavefronts at the shore. Consequently, radionuclides are deposited from those transports with seawater during high tide and then pass downward through the porous sandy soil surface. According to the findings of this research, exceptional samples (S1, S2, S3and S4) at depths (0-5) and (5-50) cm denote the U enrichment in this area needs a very good uranium prospect with economic potential is high.
The of the soil samples lies away from the sea and may be due to the absence of igneous rocks. The difference in the soil radioactivity content may be recognized from one location to the other depending on the soil type, soil formation, soil transport method.
The man-made radionuclide concentrations of 137 Cs in the samples of the Hadhramout region have been observed only in samples S1 (no. 1, no. 2, no. 4), S2 (no 5, no 6), S3 (no. 9), S4 (no. 13) and S5 (no. 17) as presented in the table (1) and varies from 0.64 Bq/kg in sample S5 (no 17) at a depth (0-5) cm to 5.80 Bq/kg in sample S1 (no 2) at depth (5-50) cm. These values of measurements are usual measurements of fallout in the global atmospheric and comparable to the information summarized in different places, 5.4 Bq/kg in Turkey [14], 2.5 Bq/kg in Belgrade [15], and 0.9 Bq/kg in Sudan [16]. However, the lower concentration levels of 137 Cs determined in the present study for soil samples in table 1 are not posing any radiological complication.

Hazard indices 3.2.1 Radium equivalent activity (Raeq)
This index was determined through the next relation [17]: The last equation is based on the presumption 481 Bq/kg of 40 K, 370 Bq/kg of 226 Ra, 259 Bq/kg of 232 Th gives the same γ-ray dose rate [18].
As presented in table 2, radium equivalent Raeq for all soil samples vary from 39.08 Bq/kg in sample S1 (no.3) at a depth (50-60) cm to 1384.23 Bq/kg in sample S1 (no.2) at a depth (5-50) cm. Radium equivalent values for the samples S1 (no. 1 & no.2) at depths (0-5) & (5-50) cm and sample S2 (no.6) at a depth (5-50) cm are 1068.27, 1384.23, and 1151.61 Bq/kg, where these values are more than three times the limit value 370 Bq/kg. Fig. 2. Represents a comparison between the measured radium equivalent for samples S1, S2, S3, S4 & S5 at different depths and the reported value in (UNSCEAR, 2000). Where: AK, ARa, and ATh are the activity concentrations (Bq/kg) of the specific radiation. The highest value of Hex to be less than unity agrees to the top limit of Raeq (370 Bq/kg).
As presented in table 2, the highest values of the outdoor radiation hazard index (Hex) are present in the sample S1 (no. 1& no. 2) as 2.89 & 3.74 and in the sample S2 (no. 6) As 3.11, where these values are more than three times the critical limit reported by UNSCEAR 2000. External index values for the other samples are smaller than the unity of critical value.

Representative level index
The equation is as follows used to estimate Iγr for soil samples under investigation.

Absorbed γ dose rates D "
The absorbed γ dose rates" in the air at 1m over the ground were measured using UNSCEAR 2000 guidelines: D (nG per hour) =.427ARa + .623ATh +.043AK (5) Where: AK, ARa, and ATh are radioactivities (Bq/kg) of 40 K, 226 Ra, and 232 Th, respectively. As present in table 2, the total absorbed dose rate range between the lowest value 17.22 nGy//h in the sample S1 (no. 3) at a depth (50-60) cm to the highest value 600.16 nGy/h in the sample S1 (no. 2) at a depth (5-50) cm. The absorbed dose can be seen in the group samples S1 (no.1 & no.

Annual effective dose equivalent (AEDoutdoor)
It was determined from the absorbed dose by using the dose conversion factor of 0.7 Sv/Gy with an outdoor occupancy factor of 0.2 [7]: Deff (mSv/Y) = D (nGy/h) ×8,766 h/y × 0.7(Sv/Gy) × 0.2 ×10 -6 (6) Table 2 shows the effective dose equivalent per year, from 0.021 mSv/Y in sample S1 (no.3) to 0.736 ms/Y in sample S1 (no.2). The annual effective dose for samples S1 (no.1 & no.2), S2 (no.5) is higher than the global average value of 0. 48 mSv/Y for outdoor terrestrial radiation for the region of normal radiation background UNSCEAR (2000). Whereas, the effective dose of the other samples at different depths is less than the global average value reported in UNSCEAR2000.
According to the analysis of the soil samples S1, S2, S3, S4 at depths (0-50) cm, we can say that the housing construction of the housing in these regions is not safe for human habitation. Whereas, analysis of the soil sample S5 at all depths showed that no health hazards. And so, we can say that samples from S1 to S4 at depths greater than 50 cm and samples from S5 for all depths are secure and can be utilized as frame materials, with no major radiological hazards to on population.

Excess lifetime cancer risk outdoors (CR)
It was measured as follows [13]: Where: T is the life duration (70 years) and RF is a risk factor (Sv -1 ), fatal cancer risk per Sever. To calculate the damage-adjusted cancer risk of 5.52 × 10 -2 Sv -1 for the entire people. The excess lifetime cancer risk ranges from 0.88 ×10 -4 to 29.51×10 -4 . The present average is significantly higher than the global average (0.29x10 -3 ) [7]. As shown in Table 2 all the samples have a risk value higher than the recommended value.

Conclusion
We used γ -spectrometry to calculate radioactivity per kg at different depths of 20 samples of soil were taken from the Hadhramout area, Yemen. The findings reveal that the radioactivity per unit mass for 40 K, 226 Ra, and 232 Th range (31.54 to 373.12 Bq/kg), (9.25 to 423.84 Bq/kg), and (7.85 to 667.23 Bq/kg) respectively. Also, the average value of the whole absorbed dose rate is 463.12 nGy/h, and it is significantly higher than the identical global average value which is 57 nGy/h. Because of the high values of Hazard indices of the samples S1, S2, S3, and S4 at the surface and at depth (5-50) cm, we can conclude that the use of these soil samples for the construction of the housing is not secure for people occupancy. Whereas, it says there isn't a health risk of Hadhramout region from the soil samples of S5 at all depths and the samples S1, S2, S3, and S4 at depths greater than 50 cm underground. However, these results may give a public knowledge level for the region studied and