Outdoor Annual Effective Dose Rates Research Articles

Gamma-radiation levels along the main Karakorum thrust area of Northern Pakistan

Abstract In this contribution, the distribution of naturally occurring radionuclides in the area around Main Karakoram Thrust (MKT) in Karakoram Range, North Pakistan is documented. Three natural radionuclides (226Ra, 232Th, and 40K) and one anthropogenic radionuclide (137Cs) were studied for their specific activities in 30 samples. The measurements were made by high resolution gamma-ray spectrometry. The sampling area is located in Gilgit Baltistan province of Pakistan at an altitude of 1838 m/6030 ft above sea level. MKT separates the Karakoram plate from the Kohistan-Ladakh Terranes and Indian Plate to the south. The specific activity varied as 4.5–56.5 Bq kg−1, 18.2–61.4 Bq kg−1, 1.4–19.6 Bq kg−1 and 51–1640 Bq kg−1 for 226Ra, 232Th, 137Cs and 40K, respectively. The average radium equivalent activity was 127.8 ± 45.9 Bq kg−1. The external hazard index was <1 for all samples and representative level index was <1 for majority of the samples. The average air absorbed dose rate was 60.9 ± 23.2 nGy h−1 corresponding to the outdoor effective dose rate of 73.7 ± 28.0 μSv y−1. These values were slightly higher than the world average values for air absorbed dose rate (51 nGy h−1) and outdoor annual effective dose rate (70 μSv y−1). The data revealed significant positive correlation between 226Ra and 40K. Principal component analysis revealed distribution patterns within the samples and identified three distinct groups. Data was also evaluated for the concentrations of uranium, thorium and potassium and their ratios.

Measurement of radiological parameters in harvested sand in Bungoma county rivers, Kenya

samples of sand were collected along the course of ten selected rivers two from each river through random sampling. Activity concentration of 238U, 232Th and 40K were measured using high resolution NaI(Ti) gamma ray spectrometer. Activity concentration of the three primordial radionuclides obtained were used to calculate, absorbed dose rate, annual effective dose rate, interna and external hazard indices and radium equivalent. The average activity concentration for the three primordial radioactive nuclides were; 2±0.1Bq/kg with a range of 0± 0.03Bq/kg to 4±0.24Bq/kg for 238U, 55±2.78Bq/kg with a minimum value of 32±1.6Bq/kg and a maximum value of 87±4.38Bq/kg for 232Th and 51±2,56Bq/kg with a minimum value of 27±1.37Bq/kg and a maximum value of 76±3.8Bq/kg for 40K. The mean activity concentrations for 238U and 40K were below the world averages of 33Bq/kg and 420Bq/kg respectively.  The indoor and outdoor annual effective dose rate varied from 0±0mSv/y to 0.2±0.01mSv/y with an average of 0.1±0 mSv/y and 0±0.003mSv/y to 0.1±0.009mSv/y with a mean of 0.1±0.006 mSv/y respectively. The annual effective dose rates were below the safe limits of 1mSv/y. Therefore, use of sand from the selected rivers in Bungoma County, Kenya for construction has minimal health risks to the inhabitants.

Soil mineral analysis and environmental radioactivity in Ghizer, Eastern Hindukush, Pakistan

AbstractDistribution of natural and anthropogenic radionuclides (226Ra,232Th,137Cs and40K) was determined in 32 samples from Ghizer, an Eastern Hindukush district at an altitude of 2286 m in Pakistan using high resolution gamma-ray spectrometry. Mineralogical analysis by X-ray diffractometry identified quartz, calcite, albite and anorthite as major phases whereas actinolite, chlorite serpentine and kaolinite as minor phases. The activity concentrations for226Ra,232Th,137Cs and40K varied from 25.2 ± 1.7 to 145.3 ± 10.1 Bq kg−1, 24.9 ± 1.1 to 197 ± 9 Bq kg−1, 2.03 ± 0.21 to 16.7 ± 1.1 and 252 ± 6 to 1433 ± 35 Bq kg−1, respectively. The samples yielded average radium equivalent activity as 178.4 ± 23.3 Bq kg−1. The majority of the samples revealed external hazard index and representative level index less than one. The average air absorbed dose rate was 91.2 ± 13.6 nGy h−1corresponding to the annual effective dose rate 111.8 ± 17.4 μSv y−1. These values were higher than the world averages for air absorbed dose rate and outdoor annual effective dose rate. Principal component analysis was applied to obtain distribution pattern within the samples and among the radionuclides.

Assessment of radiological hazards in the phosphate mining area of Kpogamé, Togo

Radioactive elements of natural origin are present everywhere in the environment as well as sediments in different concentrations depending on the local geology of soil. These elements are hazardous to the environment and to human health. This present work studied the radioactivity of a set of soil samples of phosphates tailings collected from a mining site in Kpogamé with a view to assessing the radiological hazards. Collected soil samples were analyzed at the Jožef Stefan Institute lab using high purity germanium detector, and radiological parameters such as radium equivalent, absorbed dose rate, indoor and outdoor annual effective dose rates, internal and external hazards indices, Gamma radiation representative level index and excess lifetime cancer risk for outdoor exposure were deducted. Higher values of activity concentrations were found for certain samples (values reaching 319.3 and 57.9 Bq/kg for Ra-226 and Th-232) when compared to UNSCEAR values. Higher values of these radiological parameters were also obtained when compared to the recommended limit and worldwide values (for example the maximum value of 176.10 ​nGy/h obtained for the absorbed dose rate was more than twice higher the worldwide average value of 84 ​nGy/h). Overall, five locations showed values above the norm. These locations have high values of excess lifetime cancer risk for outdoor exposure (0.3115×10-3 – 0.7525×10-3). The implication of these results is that there are locations around Kpogamé phosphate mining area with high probability of getting cancer from ionizing radiation associated to the environmental geology. Therefore, it is recommended to optimize the way to extract ores and avoid public to access the mining sites without knowing the level of radiation dose in this area.

Measurement of Natural Radionuclides and Assessment of Radiation Hazard in Coal from Parts of China.

To study the content of radionuclides in coal and to assess its associated radiological impact on the environment for potential radiological risk assessment, a total of 40 coal samples were collected from various mining areas in eight provinces of China. The specific activities of 226Ra, 232Th, 40K, 210Pb, and 238U were measured in all samples using an HPGe gamma-ray spectrometer, and results were compared with available data from other similar studies. The results reveal that the radium equivalent activity was 74.20 Bq kg-1, external hazard index was 0.20, internal hazard index was 0.27, representative gamma index was 0.52, and indoor and outdoor annual effective dose rates were 0.16 nSv y-1 and 0.04 nSv y-1, respectively. Absorbed gamma dose rate in air was 32.87 nGy h-1. In general, these values are lower than the respective threshold limits recommended by UNSCEAR, and the radiation risk to the public is extremely small.

Estimation of various radiological parameters associated with radioactive contents emanating with fly ash from Sahiwal coal-fuelled power plant, Pakistan.

The release of natural radioactive materials with the emission of fly ash as a result of coal burning in power generation plants is considered amongst the sources that elevate the technologically environmental radioactivity level. This research mainly concerns the assessment of various radiological parameters including excess lifetime cancer risk due to natural radioactive contents associated with fly ash emitted to the surrounding environment from the stack of 1320 Mw Sahiwal coal-fuelled power generation plant (CFPP). For this purpose, fifty-four soil samples were collected in a radius of 4 Km from CFPP and a highly background radiation-shielded HPGe system is used to measure radioactivity in the collected samples. The activity concentrations of radium-226, potassium-40, and thorium-232 in collected samples was found to be in the range of 20 to 138, 43 to 860, and 27 to 127 Bq/kg with average values of 66, 409, and 67 Bq/kg respectively. Activity concentrations of radium-226 and thorium-232 were observed significantly higher than UNSCEAR reported typical global average values. A significant decrease in the level of the aforementioned radionuclides in the collected soil samples was observed with increasing distance from the power plant, which is a clear indication for the elevation of radioactivity concentrations in the surrounding environment as a result of the operation of the CFPP. To assess the radiation dose delivered to the occupational workers and inhabitants living next to Sahiwal CFPP, absorbed γ-dose rate (Dγ), outdoor annual effective dose rate (EOutdoor), and excess lifetime cancer risk (ELCR) were estimated and these were found higher than the UNSCEAR recommended values of 59 nGy/h, 0.07 mSv/y, and 2.9 × 10-4 respectively. The outcome of this first systematic study is the assessment of potential radiological health risk to the occupational workers as well as the inhabitants living in the proximity of this CFPP.

A Radiological Survey in Tailings: A Case Study of Rosterman Gold Mine, Western Kenya

Thirty samples of tailing waste weighing 200 g were randomly collected from both active and inactive tunnels at the Rosterman gold mine site in western Kenya. The average activity concentration of the radionuclides (40K, 232Th and 238U) analyzed by the gamma-ray spectrometry in the tailing samples was 260 ± 14.29 Bq/Kg for 40K, 118 ± 8.25 Bq/Kg for 232Th and 81 ± 3.63 Bq/Kg for 238U. The corresponding radiological parameters for all the collected thirty tailing waste samples were determined from the specific mean activity concentrations. The average dose rate for all the samples was 54 nGy/h. The average radium equivalent value was 262 ± 12.04 Bq/Kg with a range of 154 ± 6.42 Bq/Kg to 350 ± 10.24 Bq/Kg. The average values of external and internal indices were 0.6 ± 0.03 mSv/y and 0.7 ± 0.04 mSv/y respectively. The average indoor and outdoor annual effective dose rates that were determined for this study were 0.3 ± 0.02 and 0.2 ± 0.01 respectively. Therefore, the tailing samples recorded doses and radiological indices below the world average permissible values. This implies that the radiation exposure to the miners and general public due to tailing wastes at Rosterman gold mine poses no significant health risk.

Assessment of nuclear radiation pollution in uranium mining-impacted soil

Activities associated with mining of uranium have generated significant quantities of waste materials containing uranium and other toxic metals. A qualitative and quantitative study was performed to assess the situation of nuclear pollution resulting from waste of drilling and exploration left on the surface layer of soil surrounding the abandoned uranium mine hole located in the southern of Najaf province in Iraq state. To measure the specific activity, twenty five surface soil samples were collected, prepared and analyzed by using gamma- ray spectrometer based on high counting efficiency NaI(Tl) scintillation detector. The results showed that the specific activities in Bq/kg are 37.31 to 1112.47 with mean of 268.16, 0.28 to 18.57 with mean of 6.68 and 132.25 to 678.33 with mean of 277.49 for 238U, 232Th and 40K respectively. Based on these values, radium equivalent activity in Bq/kg and absorbed dose rate one meter above the ground surface nGy/h were calculated and found to be vary 52.72 to 1189.84 and from 25.02 to 553.01. The indoor and outdoor annual effective dose rate in mSv/y ranged from 0.12 to 2.71 and from 0.03 to 0.67 respectively. To evaluate the dangerous of the study area, the external (Hex) and internal (Hin) hazard indexes are calculated and found to be ranged 0.14 to 3.21 and from 0.24 to 6.22. For the purpose of assessing the seriousness of the study area, results were compared with the world wide average. This comparison indicated that the study area is not safe from the radiological protection point view.

Naturally occurring radioactive material and risk assessment of tailings of polymetallic and Ra/U mines from legacy sites

Old mine tailings from Northern and Central Portugal were studied in order to perform a radiological and chemical characterization. The evaluation of massic activity of natural radionuclides and concentrations in tailings of polymetallic and Ra/U mines was performed by gamma spectrometry and neutron activation analysis. Iron speciation was carried out by Mössbauer spectroscopy. In polymetallic tailings with physical ore processing (Cumieira and Verdes - exploited for Sn, Nb-Ta) higher contents of Th, 228Ra and 226Ra in the coarser materials occur, probably due to their presence in host rock and ore fragments. In finer tailings, washing may explain the lower 226Ra and 210Pb massic activity. In tailings with physical/chemical ore processing (Covas - exploited for W and Sn) high U contents and a tendency for higher 226Ra and 210Pb massic activity in the fine materials is observed, probably due to their incorporation in nano-sized particles of iron oxides. A high variation of the 210Pb/226Ra ratio occurs in polymetallic tailings; a deficit of 210Pb can be observed particularly in deposits of settling tanks drained from dumps of chemically treated ore. In Ervideira-Mestras tailings (Ra/U exploitation) where no ore process in situ was performed, a near equilibrium between 210Pb and 226Ra occurs. Dose risk assessment was carried out by calculating external outdoor Annual Effective Dose Rate; the dose rates in air due to terrestrial gamma radiation are low for the polymetallic tailings (<47 nGy/h), and higher for tailings of Ra/U (up to 4130 nGy/h), in the worst scenario.

Assessment of Radiological Hazard Indices from Exposures to Background Ionizing Radiation Measurements in South-South Nigeria

Radioactivity in the environment from sources of natural and human activities resulting in planned, emergency and existing exposure to human population, environment and other biota has led to growing apprehensions in Nigeria and the world. The existing exposure situations mainly from natural radionuclides, present in the earth crust from creation emits background ionizing radiation leading to gamma dose exposures. The objective of this study was to assess the background ionizing radiation and associated radiological hazard indices in Itu, Nigeria located at 5010’0” N 7059’0” E, and establish an eco-radiological baseline data prior to the construction of any nuclear fission reaction facility in the area. A systematic random method of measurement was employed within demarcated monitoring zones of entire geological map of Itu, Nigeria. The global positioning system finder (GARMIN Etrex 10) was used for data point location, while RDS-31S/R Multi-purpose survey meter was used for dose rate measurement. The background ionizing radiation measurement obtained ranged from 0.041 ± 0.002 - 0.045 ± 0.002 µSv/hr with overall mean of 0.042 ± 002 µSv/hr, which was lower than the world mean of 0.2 µSv/hr. Radiological hazard indices arising from the background ionizing radiation measurement were also evaluated. The mean estimated Gamma Dose Rate was 9.312 nGy/hr, the terrestrial outdoor Annual Effective Dose Rate arising from gamma was 6.83 mSv/yr, that of indoor was 21.85 mSv/yr and Excess Life Cancer Risk was 0.05 × 10-3. The mean evaluated radiological hazard indices were found to be below admissible limits, and thus poses no significant radiological health threat to the populace. Therefore, the assessment demonstrates that there is no elevated level of dose rate, which is makes it safe for human habitation, but care should be taken to avoid increase radiation level from human activities. It is recommended that constant radiological monitoring be encourage, and the data considered as radiological baseline in Itu, Nigeria.

Comparison of Gamma Dose Levels in Assessed by Various Methods

Abstract Indoor and outdoor gamma dose rates were evaluated along the coastal regions of Thangasherry, Kollam district, Kerala through direct measurements using a GM based gamma dose survey meter, time integrated measurement using CaSO4:Dy based thermo luminescent dosimeters (TLDs) and theoretically gamma spectrometry of soil samples. The mean values of indoor and outdoor Annual Effective dose rates observed were 1.26±1 mSv/yr and 0.378±0.08 mSv/yr, respectively with an indoor to outdoor dose ratio of 0.86. The radioactivity content in the soil samples, the absorbed dose rate, annual effective dose equivalent, radium equivalent activity, internal and external hazard indices , the representative gamma index and alpha index (Igamma and Ialpha), the annual gonad dose equivalent (AGDE) and the excess lifetime cancer risk (ELCR) were determined and compared with recommended values. Correlation study showed that the dose estimated from the TLDs is better correlated with that measured directly using the portable survey meter. The results of natural radioactivity levels in the soil samples has been compared with the levels reported in other Indian cities as well as other parts of the world.

Environmental radioactivity levels in agricultural soil and wheat grains collected from wheat-farming lands of Koya district, Kurdistan region-Iraq

The purpose of this study is to determine the activity concentration levels of radionuclides of226Ra,232Th,40K, and137Cs in soil and wheat grain samples. A total of 72 samples of soil and wheat grains were collected in the study area. Measurements were performed using a gamma-ray spectroscopic system based on high purity germanium detector. The average activity concentrations of226Ra,232Th, and40K in soil samples were found to be 14.7 ± 0.2 Bq/kg, 19.9 ± 0.5 Bq/kg, and 329 ± 5.4 Bq/kg, respectively, and for the measured wheat grain samples their values were found to be 0.4 ± 0.09 Bq/kg for226Ra, 0.36 ± 0.1 Bq/kg for228Ra, and 109.2 ± 2.2 Bq/kg for40K. The calculated mean values of radium equivalent activity Raeq, outdoor absorbed dose rate Dout, and outdoor annual effective dose rate of the soil samples were found to be 68.55 Bq/kg, 32.5 nGy/h, and 0.039 mSv/year, respectively. Moreover, the radionuclide transfer factor from soil-to-wheat grains of naturally occurring radionuclides were found in this order40K > 226Ra > 228Ra.

Measurement of Radioactivity And Assessment of Radiological Hazard of Tea Samples Collected From Local Market In Bangladesh

The activity concentrations of natural radionuclides and radiological hazard indices in eleven tea samples collected from local market in Bangladesh have been analyzed by using High Purity Germanium (HPGe) Detector. The average activity concentrations of 226Ra, 232Th and 40K in tea samples have been found to be 21.21±14.04, 32.43±7.48 and 93.47 ± 43.94 Bqkg-1 respectively. The calculated absorbed dose rates due to these radioactive nuclides in tea samples have been found to vary from 26.24 nGyh-1 to 37.95 nGyh-1 and average value was 33.28 nGyh-1. The estimated outdoor annual effective dose rates varied from 38.64 µSvy-1 to 55.89 µSvy-1 with the mean value of 49.02 µSvy-1 which is less than the world average value of 1000 µSvy-1. The values of radium equivalent activity in all samples are less than the permissible maximum value of the radium equivalent activity which is 370 Bqkg-1 according to UNSCEAR 2000 report. The values of external and internal hazard indices for different samples varied from 0.16 to 0.23 with the average value of 0.20 and from 0.21 to 0.29 with an average of 0.26. The value of this index must be less than unity in order to keep the radiation hazard insignificant. It was also found that there is no artificial radionuclide (for example 137Cs) in any of the samples. The data generated in this study will provide baseline radiometric values for natural and artificial radioactivity in tea samples in Bangladesh.&#x0D; Journal of Bangladesh Academy of Sciences, Vol. 42, No. 2, 171-176, 2018

Measurement of the radioactivity in raw materials used in the ceramic industry in AL-Ramadi ceramic factory using (HPGe) detector

In this research, we have measured specific activity concentrations in five samples for raw materials used in ceramic industry in AL-Ramadi ceramic factory by using (HPGe) detector. The results have shown that, the average specific activity, for 238 U, 232 Th and 40 K are equal to (18.300�6.4 Bq/kg), (17.988�6.1 Bq/kg), (167.952�63.5 Bq/kg), respectively. In order to assess the radiological hazards of the radioactivity in samples, radium equivalent activity, absorbed gamma dose rate, indoor and outdoor annual effective dose rates, gamma Index and both (external and internal) hazard effects have been calculated. All results were found to be less than the allowed global limit given by (UNSCEAR, 2000).

NORM Analysis of the Reservoir Sand Section in the Dorado Natural Gas Discovery, Mannar Basin Offshore Sri Lanka

ABSTRACT Oil and Gas production always ties with drawing out of naturally-occurring radionuclides deposited beneath the earth, which are referred to as “NORM”. Understanding the prevailing background levels of these elements in the sub-surface reservoir rock formations will be beneficial to all stakeholders, more importantly to regulatory authorities of the country. The drill cutting samples from 5 m sampling intervals of natural gas reservoir sand section in the depth range 3025m to 3095m from deep water exploratory well “CLPL-Dorado 91 H/1z” drilled in the Mannar basin offshore Sri Lanka were tested in the laboratory using high-resolution Gamma-ray detectors. Test results revealed that the activity concentration of 40K, 210Pb,226Ra and 232Th levels and the calculated outdoor annual effective dose rate varies between considerably lower range when compared with the global standard limits. NORM concentration ranges of the sedimentary rocks within the tested section were recorded on the lower side, when the test results compared with the International Atomic Energy Agency published data on NORM concentration ranges of the sedimentary rocks found elsewhere in the world. Study results proved that there is no harmful public exposure of NORM by disposing these drill cuttings to environment or storing at any site location as it is. Also, it can be predicted that there will be very low level of NORM contaminations occur, if Dorado reservoir taken in to the production stage and well operations conducted with proper solid control mechanisms in future.

Analysis of natural radioactivity in Yatağan coal – fired power plant in Turkey

Use of the coal in order to generate electricity increases the exposure of people to radiation. In this paper, the activity concentrations of nuclides 226 Ra, 232 Th and 40 K in samples of coal and bottom ash from the Yatagan Coal–Fired thermal power plant determined using gamma ray spectrometer with a NaI(Tl) scintillation detector. The mean activity concentrations of 226 Ra, 232 Th, and 40 K in the coal were found to be 37.2±2.8 Bqkg -1 , 51.8±3.4 Bqkg -1 and 166.7±11.1 Bqkg -1 , respectively. Whereas in the bottom ashes, the concentrations of the corresponding radionuclides were found to be 62.2±5.6 Bqkg -1 , 87.4±5.9 Bqkg -1 and 221.0 ±12.5 Bqkg -1 , respectively. The findings show that bottom ashes show higher activity concentrations of related radionuclide to coal samples. The absorbed gamma dose rate in outdoor air DR OUT and annual effective dose rate (AED) from coal were calculated to define radiological risk. The average findings of annual effective doses were detected as 68.6±5.1 μSvy -1 and 110.3±11.2 μSvy -1 , respectively.

Ground radiometric investigation of natural radiation levels and their radiological effects in Akpabuyo, Nigeria

Ground investigations of the activity concentrations from primordial radionuclides (238U, 232Th and 40K) were conducted in Akpabuyo, southeastern Nigeria. These investigations were aimed at assessing the magnitude and spatial distribution of activity concentrations from primordial radionuclides. Also, radiological hazard assessment and their associated risk to both human environmental healths and suitability of soils in the area for constructing dwellings places will be made. Instrument used for the investigations, which were conducted both randomly and along 6 profiles with inter-profile distance of 100 m, was a potable GRS-2 model of a Pico Envirotec spectrometer. Activity concentrations in the area, which vary with spatial distribution of soil texture, lithology, land use and topography, range between 2.22 and 116.09 Bq kg−1 (mean of 34.67 Bq kg−1) for 238U, 3.65–87.41 Bq kg−1 (mean of 38.59 Bq kg−1) for 232Th and 6.26–384.99 Bq kg−1 (mean of 114.66 Bq kg−1) for 40K. The mean activity concentrations of 238U and 232Th are marginally higher than world averages of 30 and 39 Bq kg−1 respectively. However, the activity concentration of 40K, which is the most abundant radionuclide (60.02%), is less than the world average of 400 Bq kg−1. Results obtained from skew and kurtosis analyses of the activity concentration data show that the distribution of 238U and 232Th radionuclides in the soils is nearly symmetrical. The radiological hazard indicators computed from the activity concentrations of the radionuclides are all below maximum permissible limits. For instance, values of radium equivalent, which vary from 41.72 to 171.02 Bq kg−1 (average of 98.68 Bq kg−1), are below the permissible limit of 370 Bq kg−1. External and internal hazard indices vary between 0.11 and 0.46 Bq kg−1 (mean of 0.27 Bq kg−1) and 0.14–0.72 Bq kg−1 (mean of 0.36 Bq kg−1) respectively. These results are below the 1 Bq kg−1 benchmark required for materials to be safe for use in constructing residential buildings. Absorbed dose, indoor and outdoor annual effective dose rates vary from 19.37 to 76.72 nGy h−1 (mean of 44.11 nGy h−1), 0.10–0.38 mSv yr−1 (mean of 0.22 mSv yr−1) and 0.02–0.09 (mean of 0.05 mSv yr−1) respectively. The mean absorbed dose rate is almost equal to the world average of 44 nGy hr−1, but the means of the indoor and outdoor annual effective doses are below the 0.50 mSv yr−1 limit set for materials to be safe. Thus, the soils in Akpabuyo are safe for use in constructing dwelling places for the population. However, periodical monitoring of the radionuclides and radioisotopes should be performed.

Radiological hazard in the sediment of the Xining section of the Huangshui River, China

Natural radioactivity was determined in sediment samples collected from the Xining section of the Huangshui River in northwest China. The activity concentrations of 226 Ra, 232 Th and 40 K in the sediment samples range from 15.8 to 65.3, 24.3 to 86.0 and 432.6 to 702.4 Bq.kg-1 with an average of 32.4, 43.0 and 527.5 Bq.kg-1 , respectively. All investigated sediment samples have radium equivalent activity lower than the limit of 370 Bq.kg-1 and an external hazard index less than unity. The mean outdoor air absorbed dose rate is 63.5 nGy.h-1 and the corresponding outdoor annual effective dose rate is 0.078 mSv.y-1 . The radiation level of the studied location is safe, and the sediment can be safely used in construction according to the current norms.

Terrestrial Radiation Doses from Selected Towns of Southwestern Nigeria

The activity concentrations of natural gamma-emitting radionuclides 238U, 232Th and 40K in soils from 7 sampling sites each in Ondo and Lagos States, southwestern Nigeria have been measured by using a well calibrated Hyper Pure Germanium Detector (HPGe). The mean activity concentration values of 39.24±1.12, 52.86±1.40 and 445.02±12.24 Bq kg-1 for 238U, 232Th and 40K respectively were obtained for . Activity concentration values of 23.21±0.92, 22.84 ± 0.78 and 204.02±7.00 Bq kg-1 were recorded for 238U, 232Th and 40K respectively for . The results obtained were used to estimate the absorbed dose rates in outdoor air which was found to be in the range of 12.35±179.59 nGy h-1 for Ondo State and 5.91±83.29 nGy h-1 for Lagos State with an overall mean values of 67.50±1.86 nGy h-1 and 33.83±1.17 nGy h-1 respectively for the two States. The corresponding outdoor annual effective dose rates were estimated to be between 22.7 and 330.6 μSv y-1 for and between 7.3 and 102.2 μSv y-1 for assuming 30% and 20% occupancy factors for the two states respectively. The average outdoor annual effective dose rate for towns in Ondo State is 64.85 μSv y-1 representing 92.64% of the world average value (70 μSv y-1) given by UNSCEAR. However, the cities in have an average outdoor effective dose of 41.52 μSv y-1 which is less than 60% of the world average value. The values of the collective effective dose as calculated from the outdoor annual effective dose rates were found to be 540858 and 273296 person-Sv for Ondo and Lagos States respectively.

Natural Radioactivity Measurements of Basalt Rocks in Aden governorate, South of Yemen on Gulf of Aden

The amounts of radioactivity in the igneous rocks have been investigated; 63 basalt rock samples were collected from Aden governorate, South of Yemen. The activity concentration of 226 Ra, 232 Th and 40 K were measured using NaI (TI) detector. Along the study area the radium equivalent activities Raeq in Bq/Kg of samples under investigation were found in the range of 51.60to 809.26Bq/Kg with an average value of 237.01Bq/Kg, this value is below the internationally accepted value of 370 Bq/Kg. To estimate the health effects of this natural radioactive composition, the average values of absorbed gamma dose rate D (55 nGyh -1 ), Indoor and outdoor annual effective dose rates Eied (0.11 mSvy -1 ), and Eoed (0.03 mSvy -1 ), External hazard index Hex(0.138) and internal hazard index Hin (0.154), and representative level index Iγr(0.386) have been calculated and found to be higher than the worldwide average values.