A  Study of Natural Radiation Levels and Distribution of Dose Rates Within the Younger Granite Province of Nigeria

A  Study of Natural Radiation Levels and Distribution of Dose Rates Within the Younger Granite Province of Nigeria.

ABSTRACT

A study of natural radiation levels and distribution of dose rates in parts of the Younger Granite Province of Nigeria constitutes this work. It has established the extent and distribution of various parameters of ionizing radiation across the area.

By using a combined solid scintillation and gas filled radiation detection techniques, gross gamma as well as gross alpha/beta radiations were detected and measured within the different rock units, the result of which show that radiation levels are high within the younger granites and in parts of the basement areas but low within the basalts.

Radiation maps prepared for this area show a good correlation with existing geological maps of the area signifying that natural terrestrial radiation signatures can be used as a tool for regional geological mappings especially in poorly exposed plains.

The maps indicate that absorbed dose rates in air range from 0.030-0.431 μGyh-1 , while dose equivalents and effective dose rates are well in excess of 1mSv/yr maximum permissible limits in some areas, suggesting a reasonably good chance of radiation hazards in those places.

Highest values were found within the Ririwai Sheet 126, attributable to high concentration of radionuclides within both the peralkaline and non-peralkaline granites that constitute the complex.

People living in areas identified with high background radiation levels in this study should therefore be made aware of the potential radiation related health problems, while government should also do more to stop the common practice of using mine wastes for foundation fillings and block construction because of the radiological implications.

TABLE OF CONTENTS

PAGES
TITLE i
DECLARATION ii
CERTIFICATION iii
ACKNOWLEDGEMENT iv
DEDICATION v
TABLE OF CONTENTS vi
LIST OF TABLES ix
LIST OF FIGURES x
LIST OF PLATES xix
LIST OF APPENDICES xxi
ABSTRACT xxiv

CHAPTER ONE GENERAL INTRODUCTION

1.1 Introduction 1
1.2 The Study Problem 5
1.3 Objectives of the Study 7
1.4 Usefulness of the Study 7
1.5 Location, Extent and Accessibility 8
1.6 Climate and Vegetation 10
1.7 Relief and Drainage 11
1.8 Settlement and Land Use 21
1.9 Radioactivity 27
1.9.1 Alpha particles 30
1.9.2 Beta particles 31
1.9.3 Gamma radiation 32
1.10 Sources of radiation 33
1.10.1 Natural sources of radiation 35
1.10.2 Man made sources 39
-vii1.11 Radioactivity Pathways 40
1.12 Radiation Surveys 41
1.12.1 Ionization chambers 42
1.12.2 Proportional counters 42
1.12.3 Geiger-Mueller (GM) counters 43
1.12.4 Scintillation detectors 44
1.13 Units and Standards 45
1.13.1 Count rates 46
1.13.2 Exposure (The roentgen) 46
1.13.3 Absorbed dose (The rad) 47
1.13.4 Dose equivalent (The rem or sievert) 47
1.13.5 Unit conversion 51
1.14 Maximum Permissible Dose 51

CHAPTER TWO GEOLOGY

2.1 General Geological Setting 53
2.2 The Basement Complex 55
2.2.1 Gneisses 56
2.2.2 Migmatites 63
2.2.3 Older granites 79
2.2.4 Intermediate rocks, calc-silicates and amphibolites 84
2.3 The Younger Granite 86
2.3.1 Lithological summary 88
2.4 Basaltic Rocks 97

CHAPTER THREE LITERATURE REVIEW

3.1 Natural Radioactivity 102

CHAPTER FOUR METHOD OF INVESTIGATION

4.1 Introduction 110
-viii4.2 Gross Gamma Radiation Measurement 111
4.3 Gross Alpha/Beta Radiation Measurement 117
4.4 Statistical Analysis 119
4.4.1 Coefficient of determination 120
4.4.2 The t-test 120
4.4.3 The z-test 121
4.4.4 The f-test 121
4.4.5 The z-score histogram for distribution of dose rates 123
4.5 Map of distribution of radiation dose rates 124

CHAPTER FIVE RESULTS

5.1 Introduction 129
5.2 Line Graphs 130
5.2.1 Rock radiation parameters & regression characteristics 141
5.3 Maps of Distribution of Radiation Dose Rates 166
5.3.1 Dutsen Wai Sheet 125 167
5.3.2 Ririwai Sheet 126 181
5.3.3 Lere Sheet 147 191
5.3.4 Toro Sheet 148 196
5.3.5 Naraguta Sheet 168 210
5.3.6 Maijuju Sheet 169 220
5.4 Radiation Hazard Maps 228

CHAPTER SIX DISCUSSION, CONCLUSION AND RECOMMENDATIONS

6.1 Research Summary 236
6.2 Discussion 237
6.3 Conclusion and Recommendations 241
6.4 Contribution to Knowledge 243
REFERENCES 245
APPENDIX 258

INTRODUCTION

Beyond the ultraviolet are higher energy radiations which we all get in low doses from space, air, and from the earth.

Collectively, these radiations are referred to as ionizing radiation. Ionizing radiation is that class of radiation which is able to produce ions that is capable of disrupting life processes.

Non ionizing radiations are not able to create ions, although they may adversely affect human health in other ways.

At the formation of the earth about four billion years ago, the materials with which it was made contained many radioactive isotopes some with short and others with very long half-life. Natural radioactive materials are found in rocks, soil, air, food and drinking water.

The natural environment therefore is a major source of radiation, to which man is exposed. Ionizing radiation from natural sources that we are all exposed to at all times is called natural background radiation.

According to United Nations Scientific Committee on Effect of Atomic Radiation (1988), each inhabitant of the earth is exposed to an average of about 2.4 mSv radiation dose per year both from cosmic sources and earth’s crust.

Other sources of radiation are artificial, resulting from medical applications, nuclear industry and nuclear bomb explosion. Radiation can be defined as the emission and propagation of energy in the form of rays or waves from the atoms and molecules of a radioactive substance as a result of nuclear decay. It can be classified into two main types namely ionizing and non-ionizing.

Ionizing radiation is the type of radiation capable of ionizing an atom, and ionization usually occurs when one of the orbital electrons of an atom has been completely removed from it.

The resultant effect of this is that the residual atom becomes positively charged (positive ion or cation), and the freed electron becomes negatively charged (negative ion or anion).

To be able to do this, the energy propagated must be sufficient to overcome the binding force of the atom as explained by the quantum theory:

REFERENCES

Abe, S. K., Fujiataka, L and Fujimoto, K. (1980). Natural radiation in Japan. In: Natural Radiation Environment III. (vol. 2) pp1030 – 1048.

AcAulay, I. R. and Colgan, P. A. (1980). Gamma ray background radiation measurement in Ireland. Health Physics 39, pp. 821 – 826.

Adiukwu-Brown, M. E. and Ogezi A. E. (2001). Radiation levels of cassiterite tailings in Jos, Plateau State. Journal of Environmental Sciences 4(1), 2001, pp. 8-12.

Advisory Committee on the Biological Effects of Ionizing Radiation (1977). Consideration of health benefit-cost analysis for activities involving ionizing radiation exposure and alternative. BEIR II Report, EPA-520/4-77-003.

Ajayi, I. R. and Ajayi, O. S. (1999). Estimation of absorbed dose rate and collective effective dose equivalent due to gamma radiation from selected radionuclides in soil in Ondo and Ekiti State, south-western Nigeria. Radiation Protection Dosimetry. 86(3), pp221-224.

Ajayi, O. S. (2002). Evaluation of absorbed dose rate and annual effective dose due to terrestrial gamma radiation in rocks in a part of southwestern Nigeria. Radiation Protection Dosimetry. 98(4), pp441-444.