A total of twenty soil sample at depths (0 - 5, 5 - 50, 50 - 60 and 60 - 70 cm) underground and 6 granite rock samples were collected from different locations in Shabwah and Hadramout regions, Yemen, respectively. The sampling locations were chosen mostly in a wide area that we believe that it’s representative of the important region. All soil samples collected from undisturbed sites located away from buildings, trees and roads to ensure that there was no influence of man- made structures and anthropogenic activities.The collected samples (soil and

granite) were first sundried and then oven dried at 110˚C to constant weight. The samples were pulverized, homogenized and sieved through 1-mm mesh [4] . 500 gm of each meshed sample was replaced in Marinelli beaker and then was stored for four weeks to reach the equilibrium state between radium and its decay products [5] . Radioactivity measurements were performed by using High purity Germanium (HPGe) detector (25% relative efficiency). The measurement time of activity or background was 82800 seconds. The radioactivity concentration of ²²⁶Ra was determined from the photopeaks of 295.09, 351.87 Kev (²¹⁴Pb), 609.31 Kev & 1120.27 keV & 1764.49 keV (²¹⁴Bi). ²³²Th radioactivity was determined from 238.58 Kev (²¹²Pb), 727.25 Kev (²¹²Bi) and 911.16 keV & 968.97 Kev (²²⁸Ac) while the ⁴⁰K radioactivity was determined from 1460.8 Kev and finally, ¹³⁷Cs was determined from the decay of ⁴⁰Ar and ¹³⁷Ba [4] .

The activity concentrations (Bq/kg) for the natural radionuclides in the measured samples were calculated after decay correction using the equation:

where A_c is the activity concentration (Bq/kg) in the sample, Nc is the net area under the corresponding peak/second, m the dry weight sample mass (kg), β the branching ratio, and ε_abs is the detection absolute efficiency of a specific energy.

The radium equivalent activity is a very useful guideline in organization the safety standards in radiation protection for humans. The index calculated by the following relation [6] .

Ra_eq = A_Ra + (A_Th × 1.43) + (A_K × 0.077) (2)

where A_Ra, A_Th and A_K are the activities of ²²⁶Ra, ²³²Th and ⁴⁰K, respectively, in Bq/kg, The formula is based on the assumption that 370 Bq/kg of ²²⁶Ra, 259 Bq/kg of ²³²Th and 481 Bq/kg of ⁴⁰K produce the same gamma-ray dose rate [7] .

The representative level index, I_γ is used to estimate gamma radiation associated with the natural radionuclides in soil and calculated by the following equation [1] :

where A_Ra, A_Th and A_K are the activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K, respectively in Bq/kg.

The external hazard index Hex can be calculated by the following equation [8] :

where A_Ra, A_Th and A_K are the activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K, respectively. The maximum value of H_ex to be less than unity [8] .

The absorbed gamma dose rates D(nGy/h) in air at 1m above the Earth’s surface for the uniform distribution of radionuclides were calculated based on guidelines given by [8] :

where, A_Ra, A_Th and A_K are the activity concentrations (Bq/kg) of ²²⁶Ra, ²³²Th and ⁴⁰K, respectively.

The annual effective dose rate was calculated from the absorbed dose through the application of dose conversion factor of 0.7 Sv/Gy with occupancy in the outdoor factor 0.2. [8]

where 8,760 h is the number of hours in 1 year. 10⁻⁶ is a conversion factor of nano and Milli.

The results of the measured values of activity concentrations for ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs obtained from the samples are presented in Table 1. From this table, the average values, concentrations of ²²⁶Ra, ²³²Th, in soil and are less than the world average values [8] . ⁴⁰K activity concentrations are in the range between 510.92 in the sample (S3) to 600.75 Bq/kg in sample (S5) with an average value is

higher than the world average value [8] . Higher concentration values of ⁴⁰K were obtained from the soil of Shabwah region, probably because the use of inorganic fertilizer in some locations and could also be attributed to the wearing away from the weathered surfaces of the potassium rich, igneous rocks which dominate a part of the geology of this region. The artificial radionuclide of ¹³⁷Cs concentrations in the soil samples are within the global atmospheric fallout and lower than the reported data for other countries. For granite samples, ²²⁶Ra, ²³²Th and ⁴⁰K average concentrations are 45, 106, and 1235 Bq/kg respectively. The average values of ²²⁶Ra fall within the worldwide average values. While, ²³²Th and ⁴⁰K average values are twice the worldwide average values (50, 50 and 500 Bq/kg) respectively [8] . The content of ⁴⁰K in granite samples is the highest in all the sampling areas. So, it is the most abundant radionuclide of the total (²³⁸U + ²³²Th + ⁴⁰K), it is abundant about 89% followed by ²³²Th 7.7%. And finally ²²⁶Ra is 3.3%. ¹³⁷Cs is detected in all granite samples under investigation. The mean concentration of ¹³⁷Cs is 0.67 Bq/kg. These values are not radiologically important. Table 2 shows the comparison between the activity concentrations of soil samples with that of other countries of the World. The variations in the activity concentrations in the soil of the various locations of the world, depend upon the geological and geographical conditions of the area and the extent of fertilizer applied to the agricultural lands [8] . Table 3, shows that, for granite samples results obtained in the present work are consistent with previous results and all results being within the range given in the report [8] . In general, the radioactivity in granite samples varied from one country to another [8] . Figure 2 shows a comparison between the obtained average values activity concentrations in soil and granite and the recommended values by UNSCEAR2000.

The computed results of the radiological hazard indices were listed in Table 4.

The values of Ra_eq Bq/kg for soil and granite rock samples are lower than the allowed value of 370 Bq/kg [8] . Representative level index (I_ɣ) average value is less than one, this means that the external radiation dose within the soil samples is less than the recommended dose of 1 Bq/kg [8] . The I_ɣ average values for granite rock is higher than 1 Bq/kg. External hazard index (Hex) for soil and granite samples are less than the limit value of unity. As can be seen in Table 4. The total absorbed dose rate calculated for Shabowah’s soil, it less than the world average value of 57 nGy/h. The presence of ⁴⁰K in Shabwah’s soil contributes a maximum of 52% to the total absorbed dose rate, followed by ²³²Th of 35% and ²²⁶Ra of 13%, these contributions were illustrated in Figure 3.

The average value of annual effective dose equivalent of the study soil less than the world average value effective dose of 0.07 mSv/y [8] . According to these results of radiogecal hazard indices, one can indicate that the soil samples are safe and can be used as a construction material without posing any significant radiological threat to the population. As shown in Table 4, the average value of the absorbed dose rate of Hadramout region’s granite samples is almost twice the world average value. So, the local people must avoid using these granite samples in the building construction, especially in the interior decorative materials of dwelling without radioactivity control. The average total effective dose rates (D_eff) for granite samples is far lower than the 1.0 mSv/y recommended by [8] . This value is According to these results of radiogecal hazard indices, one can indicate that the soil samples are safe and can be used as a construction material without posing any significant radiological threat to the population. As shown in Table 4, the average value of the absorbed dose rate of Hadramout region’s granite samples is almost twice the world average value. So, the local people must avoid using these granite samples in the building construction, especially in the interior decorative materials of dwelling without radioactivity control. The average total effective dose rates (D_eff) for granite samples is far lower than the 1.0 mSv/y recommended by [8] .