Measurement and Assessment of Indoor and Outdoor Ambient Radiation Levels at the Take-off Site
CHAPTER ONE
Objectives of the Study
In line with the study problems stated above, the aim of this work is to measure and analyze the indoor and outdoor ambient radiation levels at the take-off campus of Federal University Dutsin-Ma, Katsina State. The specific objectives of this study are:
- To measure the ionization radiation in and outside the buildings of Federal University Dutsin-Ma take-off campus.
- To compute from the data of the field radiation measurements the annual absorbed dose in the air and the distribution of effective dose in land and buildings in milliSeviet per year (mSv/yr).
- To compare and check the safety of human beings as a result of the computed radiation distribution for the study area using the ICRP (1990) worldwide average equivalent dose rate of 2.4 mSv/yr for human being protection as basis.
CHAPTER TWO
LITERATURE REVIEW
This chapter describes some of the studies that have been carried out for the measurements of environmental radioactivity at different environments of the world using various radiation detection instruments. The biological effects of radiation, weighting factors as well as the instrumentation of the study are also described.
Radioactivity studies carried out in different parts of the world
Environmental radioactivity studies have been done in various parts of the world. Many of them have been carried out to determine the levels of natural radionuclides in soils from which the estimations of the absorbed dose were made. There have also been studies to determine the levels of radon and its exhalation rates given that radon contributes the largest percentage of natural radioactivity and radiological hazards in the environment. Other studies focused on direct measurements of environmental radiation in situ and the results integrated over certain periods of time.
Oktay et al. (2011) accessed the natural radioactivity and radiological hazards in building materials in Elazig, Turkey. They reported the specific concentrations that ranged from 3.5- 114.1 Bq kg-1(238U), 1.6-20.7 Bq kg-1 (232Th) and 201.4-4928.0 Bq kg-1 (40K). The calculated radium equivalent value was 36.5Bq kg-1 in bricks and 405.2Bq kg-1 in gas concrete with average indoor radon concentrations of 364.3 Bq m-3.
Al Mugren (2015) assessed the natural radioactivity levels and radiation dose rates in soil samples from Al-Rakkah, a historical site in Saudi Arabia. He found the mean activity concentration in surface soils to be 23 ± 1.6 Bqkg-1, 20 ± 1.4 Bqkg-1 and 233 ± 12 Bqkg-1for 226Ra, 232Th and 40K respectively. The total absorbed dose rate ranged between 17.74 – 72.24 nGyh−1 which provided a mean of 32.69 nGyh−1 which yielded an annual effective dose of 0.37 mSvy−1.
Karunakara et al., (2014) assessed the gamma dose rates within a possible uranium mining site in southern India whereby direct and integrated measurements together with soil sample analysis for 226 Ra, 232Th and 40K activity were done. The geometric mean value of outdoor and indoor gamma dose rates were found to be 97 nGy h-1and 104 nGy h-1respectively. They also did a correlation study which exhibited a better correlation of the estimated dose from soil radioactivity measurements with direct measurements by the survey meter compared to the TLD measurements. They therefore concluded that the measurements by the survey meter give a better representation of gamma dose rates especially in a region having localized mineralization.
Santawamaitre (2012) evaluated the levels of NORM in soil samples along Chao Phraya river basin, Thailand. He found the activity concentrations for 238U, 232Th and 40K to be 13.9-76.8, 12.9- 142.9 and 178.4- 810.7 Bq kg-1 respectively. He estimated the absorbed gamma dose rate in air at 1 meter above the ground to be in the range of 21.7 – 155.7 nGy h-1 which gave an annual effective dose equivalent range of 26.6- 190.9 µSv y-1 and an arithmetic mean value of 79.06µSv y-1. These activity concentration values for 238U, 232Th and 40K were comparable to the world average values of 35, 30 and 400 Bq kg-1 respectively as well as the respective worldwide effective dose of 70 µSv y-1 (UNCEAR, 2000).
Bavarnegin et al., (2012) studied the radionuclide concentration in Ramsar, northern Iran and found the average values of 16 ± 6, 25 ± 11, and 280 ± 101 Bq kg−1 for 226Ra, 232Th, and 40K levels respectively.
CHAPTER THREE
MATERIALS AND METHODS
Equipment used
The main equipment used in this research include the Digital Radiation Meter (Radiation Inspector Alert) and Geographical Positioning System (GPS). A personal computer and Excel software were also used for statistical analysis. Plates 1(a.) and 1(b.) shows the radiation inspector alert and the GPS used in the work.
based on the ionization of gases caused by radiation. It consists of a cylindrical metal tube filled with a gas and an opening called a ‘window’ made of a material (e.g. paper) that can be easily penetrated by alpha, beta, or gamma rays. At the center of the cylindrical tube is a wire which is connected to one terminal of a source of direct current, and the metal cylinder is attached to the other terminal. The ions and electrons produced by the ionizing radiation permit conduction of an electrical current. This current flows between the wire and metal cylinder whenever ions are produced by incoming radiation. The current pulse created when radiation enters the cylindrical tube is amplified and each current pulse is counted and displayed on a digital screen as a measure of the amount of background radiation measured (wps.prenhall.com, 2015).
The Study Area and Sampled Points
Dutsin-Ma is a Local Government Area in Katsina State, North-Western Nigeria. Dutsin-Ma LGA lies on latitude 12°26’N and longitude 07°29’E. It is bounded by Kurfi and Charanchi LGAs to the north, Kankia LGA to the East, Safana and Dan-Musa LGAs to the West, and Matazu LGA to the Southeast (Abaje et al., 2014). The Federal University Dutsin-Ma was established on 7th February, 2011 along with eight other Federal Universities to tackle the challenges of inadequate enrolment space for eligible University applicants in some educationally less privileged states who don’t have Federal Universities. With the support of the State Government, the permanent as well as the take-off site were identified; with the take-off site located at Kilometer Sixty Katsina-Kankara road in Dutsin-Ma Local Government Area of Katsina State (FUDMA, 2015). Table 1 shows the key to the coding of the sampled points in this research while Plate 2 shows a satellite view of the sampled points in FUDMA.
CHAPTER FOUR
RESULTS AND DISCUSSION
The summary of the results obtained from the measurement of the ambient radiation levels in the different lecture venues and laboratories at the take-off site of FUDMA are displayed
Table 2 presents the results of indoor and outdoor annual equivalent dose rate from lecture venues. The mean annual equivalent dose rate from indoor ranges from 0.85±0.22 to 2.27±0.33 with an average of 1.41±0.29 as presented in table 1. In figure 1, the chart presented showed that, AC6 (Old Biology laboratory) and AC7 (Biochemistry laboratory) have the highest value of annual equivalent dose rate 2.27±0.29 and 2.27±0.33 respectively all for indoor. The possible reasons for the high values in Biochemistry laboratory could be either as a result of high concentration of Radon gas in air within the laboratory or higher activity levels in the radio – nuclides in the building materials (e.g. soil, blocks and tiles) used in the construction of the laboratory (UNSCEAR, 1998). Also, the present of UVSpectrophotometer in this laboratory can emit ionizing radiation at high energy. This could also be a reason for high values. The high value recorded in the old Biology laboratory might be due to foundation rocks beneath the laboratory which could contain some active radio – nuclides and some radio – nuclides in the building materials.
CHAPTER FIVE
Conclusion
In this work the results of the indoor and outdoor annual equivalent dose rates from lecture venues, block of offices and also the outdoor annual equivalent dose rates from open structures of Federal University Dutsin-Ma take off Campus were measured. The overall mean Indoor Annual Effective Dose Rate (IAEDR) of 1.41±0.31 (0.212±0.04) was recorded (i.e. for indoor facilities such as lecture halls, laboratories, office) while the overall mean Outdoor Annual Effective Dose Rate (IAEDR) of 0.33±0.08 (0.227±0.03) was also recorded (i.e. for outside buildings, road pavements and outdoor sports facilities). It is worthy to note that all the ambient radiation recorded for all the outdoor facilities fall way below the recommended limit of 1.0 set by the International Commission on Radiation Protection (ICRP) in 1990 while the background radiation for the indoor facilities falls below the worldwide value of 2.4 average equivalent dose limit set for ionizing radiation by the United Nation Scientific Committee on the Effects of Atomic Radiations (UNSCEAR) in 2000. Thus, the ambient radiation levels in the take-off campus of Federal University Dutsin-Ma are within the safety limit and hence, there are no health risks from harmful radiation exposure in the location.
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