Examination Of Natural Radioactivity In Building Material In Katsina State Using Gamma Ray Spectroscopy
Twenty Concrete Blocks from (20) different Local Governments in Katsina state was measured using Gamma Ray Spectroscopy with NaI (TL) detector. Three naturally Occurring Radionuclides and their activity concentrations were determined, are 40K 226Ra, and 232Th.
Their activity Concentrations ranges from 40K 46.11 ± 826.59 to 46.11± 8.55 Bq/kg, (226Ra) ranged from10.19 ± 2.43Bq/kg to 75.09 ± 4.98 Bq/kg and (232Th) ranged from 2.77 ± 9.59Bq/kg to 123.49 ± 9.35Bq/kg respectively. The highest value also determined from 40K was (826.59 ± 4.82Bq/kg), the highest value of 226Ra was 75.09 ± 4.98Bq/kg , the highest value for (232Th) is 123.49 ± 9.35 Bq/kg respectively. The Radium Equivalent mean value was obtained from the measurement ranged from (34.8 ± 1.59 to 411.26nGT/h), The absorbed dose rate in air with its mean value was obtained, ranges from (147.16 ± 3.55nGy/h). The limit set in the OECD report (370Bq/kg) and UNSCEAR, 2000 (24 to 160nGy/h). The annual effective dose obtained, ranges from 0.04 ± 0.001 to 0.20 ± 0.0001mSv/y, with mean value 0.187 ± 0.0005mSv/y. Recommended limit 0.460 mSv/y set by ICRP, 2007 for terrestrial radiation. The evident that the Results give lower value when compared with 1mSv/y for Public exposure (ICRP, 2007).
TABLE OF CONTENTS
Table of content (TC)-vi
List of tables (LT)-x
List of figure-xi
List of abbreviation-xii
CHAPTER ONE: INTRODUCTION
1.1: Background of the study-1
1.2.0: Natural Radioactivity in the Environment-4
1.2.1: Potassium-40 (40K)-4
1.2.2: Uranium Decay Series-4
1.2.3: Thorium Decay Series-5
1.3.0: NORM in Building Materials-5
1.4.0: Component of Cement Block-7
1.4.3: Gravel Aggregate-8
1.5.0: Statement of the problems-9
1.6: Aims and Objectives-10
1.7: Significant of the Study-11
1.8: Scope and Limitation of the study-11
1.10: List of local Government in Katsina State-12
CHAPTER TWO: LITERATURE REVIEW
2.0: Literature review-—-14
2.2: Sources of Natural Occurring Radioactive Materials (NORM)-16
2.2.1: Cosmic radiation-16
2.2.2: Terrestrial radiation-18
2.2.3: Man-made sources-19
2.2.4: Members of the public-19
2.2.5: Occupationally exposed individuals-20
2.3: NORMS Isotopes-20
2.4: Health Risk of Norms-21
2.4.1: Standard and regulations of radiation exposure-23
2.5: Types of Radioactive decay-25
2.5.1: Alpha particles decay-25
2.5.2: Beta decay-26
2.5.3: Gamma decay-26
2.6: Gamma-ray interaction with matter-26
2.6.1: Photo electric effects-27
2.6.2: Campton scattering-28
2.6.3: Pair Production-29
2.6.4: Biological effects of Radiation-29
2.6.5: Radium-226 (226Ra)-30
2.6.6: Potassium-40 (40K)-31
2.6.7: Thorium-232 (232Th)-32
2.6.8: Cancer Treatment-—-33
2.7.0: Review on related literature-33
CHAPTER THREE: MATERIALS AND METHOD
3.0: Materials and Method-38
3.2.0: Method of making cement blocks-38
3.2.1: Size and structure of cement blocks-39
3.3: Samples Collection-40
3.4: Samples preparation-41
3.5: Energy Calibration of Sodium Iodide Thallium--
Gamma spectroscopy system-44
CHAPTER FOUR: RESULT AND DISCUSSION
4.0: Result and Discussion-46
4.1: Experimental Result-46
4.2: Activity analysis-50
4.2.1: The radium equivalent-50
4.2.2: Absorbed dose in Air-50
4.2.3: Annual Effective Dose Rate-51
4.3: Statistical analysis of the samples-53
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
5.0: Conclusion and Recommendations-59
1.1: Background of the study
The world is naturally radioactive, and around 90% of human radiation exposure arises from natural sources such as cosmic radiation, exposure to radon gas and terrestrial radiations.
Significantly, natural occurring radionuclides present in soil are 238U, 232Th,40K (Harb et al.,2010).
However, since these radionuclides are not uniformly distributed, the knowledge of their distribution in soils and rocks play important role in radiation protection and measurement. Some of these exposures are fairly constant and uniform for all individual persons everywhere, for examples, the dose acquire from ingestion of 40K in foods. Other exposure varies depending on location. Cosmic rays, for example, are more intense at higher altitudes and concentration of uranium and thorium in soils are elevated in localized areas.
High level of uranium and its decay products in soil and rock, and thorium in sands are the main sources of high natural background of radiations that have been identified in several areas of world (UNSCEAR, 2000).
Most building materials contain various amount of radioactivity, for example materials derived from rock and soil that contains natural radionuclides of Uranium (238U), thorium (232Th) and isotope of potassium40K series (McAulary et al., 1989).
Radiation exposure due to the building materials can be divided into external and internal exposures. The external exposure is caused by direct gamma radiation, from the nuclei in the building material whereas the internal exposure is caused by the inhalation of radioactive inert gas such as radon 222Rn, a daughter product of 238U and its short-lived secondary decay products. In order to assess the radiological hazards to human health, it is important to study the radioactivity levels emitted by the building materials (Leung et al., 1998).
Radioactivity is the spontaneous disintegration of atomic nuclei, the nuclei emits α-particles or electromagnetic rays during the process of disintegration (http://worldwide/liberary.org/1740/ext/Radiation level). The natural radioactive chain from 238U and 232Th; produce a group of radionuclides with wide range of half-life times. Most of the radio isotopes are alpha emitters, inhalation of long lived alpha emitting radionuclide and inhalation of short-live decay product of radon, this cause’s high incidence of lung cancer. There is consequently need to adopt careful radiological control measures (Abel-Ghany et al., 2007).
Naturally occurring radioactivity materials (NORMS) acknowledge as largest source of exposure to human health (UNSCAER 1993, 2000). Ionizing radiation may cause damage to human tissue and other biological system (Arafa, 2004 and Darko et al., 2005).
The Building Materials contains radionuclides of uranium and thorium series as well as 40K, the earth also contains numerous radioactive elements and also it is the origin of NORM since the formation of the world (Amrani and Tahta, 2000).NORMS also are continuously produced through nuclear reaction in the Universe (Rutherford et al.,1995).
Therefore among the former elements and the most abundant are potassium-40 (40K) and the isotopes of the natural series of Uranium, actinium, and thorium including the parent nuclei 238U, 235U and 232Th from decay products and the successive products of alpha and beta decay, 238U have its half life 4.47×109 years and235U half-life of 0.70×109 years and40K half-life =1.28×109 years (Yang et al., 2005).
Radionuclide is referring to an atom with an unstable nucleus; radionuclide is undergo radioactive decay, resulting in the emission of gamma ray(s) and or subatomic particles such as alpha or beta particle. These emissions occur naturally or artificially. Radionuclides can travel around the world on air stream. Radionuclide existing in soil can dissolved in solution or ion exchange in reaction with soil organics, they can move into water, air and food chain. It is very important to determine the activity of NORM in soils and building materials and it is important for environmental protection. The dose varies depending upon the concentration of the NORM, which can be determining from the activity concentration of 232Th, 40K and their daughter products (Sroor et al., 2001).
The hazardous elements found in NORM are 226 Ra, 228Th and 222Rn and also daughter products from these radionuclides. The elements are referred to as “bone seekers” which when inside the body migrate to the bone tissue and concentrate. This exposure can cause bone cancers and other bone abnormalities (http://en.wikipedia.org/w/index.php?title=Naturally occurring radioactive material & oldid=549075774″).
And the objective of this study is to determine the activity concentration in soil samples and building materials.
Another source of NORM which is consider as non-series have long half-life and low specific activity which leads to difficulty in identification and detection of the emitted radiation. An example of non-series radionuclides 113Cd, 114Ce and40K. 40K is the richest element on the earth crust which is 0.0118% of 40K on earth. It has a half-life (𝑡1⁄2) = 1.28 × 109 years, decay by β-emission to40Ar with energy 1.312 MeV and by electron capture 40Ca with energy 1.461 MeV which is strong gamma emitter and both isotopes are stable. This radionuclide transfer in to the metabolic pathways and enter the human body through drinking water, eating or even breathing air. The body control the level of40K and that’s mean the food that we eat will not increase the amount of 40Kin the body (Alphen, E.L. 2006).
1.2: Natural Radioactivity in the Environment
Uranium and thorium occurs naturally in variable, but minute quantities throughout the earth’s crust, but there are certain areas where the concentrations are enhanced. The naturally occurring 238U and 232Th are present members of two radioactive decay series. The decay products emits α-, β-and γ-rays. Potassium is also radioactive and is distributed in the Earth’s crust in variable amount of which 0.0118% is the radioactive isotope of 40K. The distribution of radionuclide is as follows:
1.2.1: Potassium-40 (40K)
Among the naturally occurring potassium isotopes, 40K is unstable. It has a half-life of 1.227 x109years. The relative abundance of Potassium is 1.18×10-4. Potassium-40 (40K) is the largest source of natural radioactivity in animal and humans. An adult human body contains about 160 grams of potassium, hence about 0.000117 x 160 = 0.0187 grams of 40K; which undergoes 4,400 disintegrations per second (Becquerel) continuously throughout the life of the
body (Muhammed, 1992).
1.2.2: Uranium Decay series
Uranium occurs naturally in the form of 234U, 235U and238U. The relative abundance of 238U is 99.27% and the equilibrium concentration of 234U is 0.0054%. The relative abundance of 235U is 0.7205% on the average.238U and 235U is the parent of two radioactive decay series. The contribution of 235U in natural pollution is negligible because of its relatively low abundance; therefore, I would be concentrating on 238U and its decay products.
1.2.3: Thorium Decay Series
Natural thorium consists almost entirely of 232Th, 1.35 x 10-8 % of 228Th and extremely small amount of 234Th, 230Th, 231Th. All the daughter products are short lived when compared with 232Th. The range of concentration on232Th on the Earth’s crust varies from zero to several hundreds of parts per million (ppm).
One of the decay products of the uranium and thorium decay series is an inert gas. This radioactive gas, now called “Radon” was discover in 1900 by Ernst Dorn, who named it “Radium Emanation Gas”. It was later named it “nitron”. It was named “radon” in early 1920s.
The atomic number of radon is 82 and like any other noble gas, radon is colourless and odourless. It consists of three isotopes 219Rn, 220Rn and 222Rn which belong to235U, 232Th and 238U series respectively.
Radon emanates from the materials carrying uranium. Initially, it fills the space in the host materials (soil, sand, rocks, gravels, etc.). Being relatively long lived, it may succeed in escaping out of materials and get mixed with air. If it escapes to a confined space such as a basement of a building or room with limited ventilation, the concentration of radon may become fairly high.
1.3: NORM in Building Materials
Most building materials of natural origin contain small amounts of Naturally Occurring Radioactive Materials (NORM), mainly radionuclides from 226Ra and 232Th decay chains and 40K. Building materials of natural origin reflect the geology of their site of origin. The average 226Ra 232Th and 40K activity concentration in the Earth’s crust is 35, 30 and400Bq/kg. Industrial waste or by-products containing high concentrations of NORM, e.g. fly ash, coal slag, phosphogypsum, are extensively used in building materials. Several surveys were conducted at different locations worldwide to characterize the activity concentration of NORM and the random exhalation rate from raw material and building materials. The external radiation exposure, caused by gamma emitting radionuclides, is assessed either by direct measurement or by mathematical calculations. The evaluation of internal radiation exposure, due to 222Rn exhaled from building materials into the room air, is more complicated and may strongly depend on environmental parameters. e.g. the ventilation rate. The correlation between the radon exhalation rate measured under laboratory conditions and the in-situ wall exhalation rate is not fully understood. Regulation on the radioactivity in building materials is based on dose criteria for controls and on exemption levels. Setting a low reference radon concentration from other sources without exceeding the level (Rosabianca et al., 2001). However, elevated levels of natural radionuclides causing annual doses of several mSv were identified in some regions around the world, e.g. in Brazil, France, India, Nigeria, Iran. Recycle industrial by-products containing Technologically Enhanced Natural Occurring Radioactive Materials. (TENORM) are extensively used in the construction industry. Coal ash, produced as waste in the combustion of coal, issued as an additive to cement, in concrete and in some countries bricks are made from fly ash. Coal slag is used in floor structures as insulating filling material.
Phosphogypsum, a by-product in the production of phosphorous fertilizer is used as building materials, and red mud , a waste from primary aluminum production, is used in bricks, ceramics and tiles.
1.4: Component of cement Block
Sand is a composed mainly of quartz grains (more than 90%) along with aluminum minerals and silicates. The size of grains ranges from 0.06 to 2 mm. Sand is used for making concrete and sand-cement mixture needed for plastering the wall make of bricks or concrete.
In mixtures, by volume sand is three to four times the volume of cement and in concrete; it is two times of cement by volume. The compositions and densities of sand vary somewhat from location to location depending on the source of the sand. Sand is basically rock that has been degraded through various physical/ chemical processes; as such, it has a mineral composition with the most common constituent of sand in general use being quartz, SiO2.
The density of sand, even if pure silica may vary depending on grain size and the degree of packing of the sand and whether it is wet. The density of pure crystalline quartz (single crystal) is about 2.65 g cm3; the densities of sand can range from about 1.4 to somewhat greater than 2.g cm3.
Any substance that acts as a bonding agent is called cement. More commonly the word “cement” implies the binding material used in building and civil engineering construction. The cements used for construction purposes are called hydraulic cements because; when they mixed with water, have property of setting and hardening under water. The most important of these is the Portland cement. This name was introduced by Joseph Aspdin of England because the cement patented by them had the hardening properties of the Portland stone found in England. The Portland cement is powdered calcium aluminosilicate, which is made by pulverizing a mixture of limestone and clay and heating it to about 8130C.
The lumps of minerals are ground with some gypsum to form a fine powder-cement.
The construction of houses and shelters is one of the basic and essential needs of human beings. The modern trend to build durable and fancy houses cannot be achieved without the use of such material. Cement is used for making block and concrete, and for plastering the houses made of bricks. The essential constitutes of most of the cements are lime, silica, magnesia, iron oxide and gypsum. The variations in the composition of these constituents result in different brands of cements. Most of these constituents are materials obtained from the mines which contain clay. The clay in the limestone may be as high as 25% by weight. The clay is also present in variable amounts in other materials used to manufacture cement. The silica, alumina and iron oxide present in clay combine to some extent with the limestone to form silicate and aluminates which impart the hydraulic properties to the product. The cement industries in Pakistan are located in various parts of the country and use as raw materials available at the nearby places which have different geological formations. Therefore, the natural y-ray activity in cement is also expected to vary according to location of the factory.
1.4.3: Gravel Aggregate
Gravel aggregate or crush is used in concrete for making concrete blocks for walls, lying down the foundations, floors and ceiling, and making beams in dwellings. In concrete, gravel aggregate and cement are mixed in ratio of 2:1 by volume. The sources of the gravel aggregate or crush for our work are the suppliers and the under construction sites. The predominant rock type in gravels being limestone provides excellent parent material yield good quality gravel which cannot be transported by natural agencies is dumped in the steam beds and piedmonts. Purple sandstone, magnesian sandstone and other sedimentary rocks are found in various parts of the salt Range and are quite suitable for use as building or engineering stones. Sandstones are mainly composed of SIO2 (up to 90%) and the
remaining is CaO, MgO, Al2O3, Fc2O3 and silicates in variable concentrations.
Concrete as a building material is used for manufacturing of blocks, as a structural material and lying down floors, etc. in the dwellings. Normally it is prepared by mixing cement, sand and aggregate or crush in 1:2:4 ratios by volume. The water to cement ratio by weight is 2:1 All the materials used in preparing the concrete contain naturally occurring radionuclide and the activity levels in these materials depend upon the site from where the raw materials are collected. Therefore, it is essential to determine the activity concentration in the raw materials used in the concrete.
1.5: Statement of the Problems
Man is continuously exposed to ionizing radiation from naturally Occurring Radioactive material (NORM) present in the Earth’s crust. Radiation is all around us; it is naturally present in our environment and has been since the birth of this planet. Consequently, life has evolved in an environment which has significant level of ionizing radiation. Radiation comes from outer space (cosmic radiation), the ground (terrestrial), and even our own bodies. It is present in the air we breathe, food we eat, the water we drink, and in the construction materials used to build our homes. Brick and stone homes have higher natural radiation levels than homes made of other building materials such as wood.
Exposure to natural sources of radiation has become an important issue in terms of radiological protection. Exposure to ionization radiation is generally regarded as undesirable at all levels, although no harmful effects are known to follow very low exposures (UNSCEAR, 2000). Recently considerable attention has been given to low level exposure arising from naturally occurring radionuclides, particularly 238U, 232Th and 40K. Building materials which are used in our homes derived from rock and soil are also contributed to environmental radioactivity in two ways;
i. By gamma radiation mainly226Ra, 232Th and40K. And their progenies to a whole body dose and in some cases by beta radiation to skin dose.
ii. By releasing the noble gas radon, its radioactive daughter nuclei have effect in lung tissue (Quindos et al., 1998).
1.6: Aims and Objectives
1. The purpose of this research work is to determine the concentration of natural radioactivity of some building materials. Several environmental problems are currently affecting this part of the world and these problems have not received serious attention. The main interest of this work is to measure the activity concentration of the natural radioactivity in concrete blocks made in Katsina state using a Gamma spectroscopy with sodium iodide thallium [NaI (TL)] detector which under gone standard calibration and quality assurance programmes and
2. To investigate the effects of the measured activity concentration on the populace of Katsina state of Nigeria.
1.7: Significant of the study
The significant of this research work could be empirically admitted to the naturally occurring radioactivity in building materials, because the materials that are used in building houses contains some amount of Radioactive elements which are very dangerous to human health. It is therefore important to undertake this research in order to proffer some basic solution for people living around the study area.
1.8: Scope and limitation of the study
The scope of this research work involves sample collection from 20 different locations in Katsina state. Katsina State is located in the North-Western region of Nigerian, bordering with Niger Republic, Zamfara, Kano and Jigawa State. The state has a land area of approximately 24,000 square Kilometers. These samples collected will be taken for analysis in CERT; A.B.U Zaria (Ahmadu Bello University) .The result obtained will be critically examined and further interpreted which will be reported in my chapter four. Finally the dissertation is concluded with summary and recommendation.
The limitations of this study are:
1. one samples collected in each area so that to minimize the cost of transportation and time taken during the samples collections,
2. and also to reduce the cost implication for the analysis
3. the nature of the availability of the machine used in this measurement
Fig. 1.1 Map of Katsina State showing all local governments were the samples collected
1.10: List of local government in Katsina state