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SLT00196 - ASSESSMENT OF THE VARIATION OF SOIL GAS RADON CONCENTRATION WITH DEPTH WITHIN OGBOMOSO


ABSTRACT

Radon gas is one of the main contributors of the total inhalation dose in the living environment. The concentration of radon gas in soil is about a thousand times higher as compared to that of the environment. Thus, it is necessary to measure radon soil gas. Soil gas 222Rn (Radon) concentration were measured at five locations in Ogbomoso Oyo state, Nigeria (LAUTECH, SAFEJO IKOYI AREA,ODORU BAPTIST CHURCH, ALASA LAYOUT,MAYLAND OKE ANU.) by using Rad7 (Durridge Company Inc., USA).

Measurements were carried out at depths o`f 0,20,40,60,80cm. The least concentration ranged from 57±202.50 Bq/m3 at a depth of 0cm in Safejo area, Ikoyi road. While the highest was observed at a depth of 80cm in Lautech area with a reading of 26500±2047.50Bq/m3.

This result implies that the area that has granite (LAUTECH) as the underlying bedrock has the highest value of Radon gas concentration due to the presence of high content of Uranium in the underlying bedrock from which 222Rn emanates. And the area with migmatite as the underlying bedrock (SAFEJO AREA) has the lowest value of 222Rn concentration.

 

CHAPTER ONE

  • INTRODUCTION

 

1.1 Background of study

          Human beings are naturally exposed to the effects of ionizing radiation, and these exposures arising from cosmogenic and primordial radionuclide. Once dispersed into the environment, radionuclide can be incorporated by the living organism through the food chain, whose intake concentrate radioactive nuclides increases the internal exposure, and inhalation of airborne particles. Radioactive elements that contribute mostly to natural radioactivity are natural decay series radionuclide of 238U, 235U and 232Th and to a lesser extent, the 40K. Radon is a chemically inert gas from the decay of 226Ra, has a period of half-life of 3.82 days emitting alpha particles whose energy is about 5.49 MeV. Thus, the emission of ionizing radiation by rock and soil depends on its content of uranium, thorium, potassium and radium elements, since the levels of radon depend mostly on the concentration of radium.

          Radon is the second cause of lung cancer in the general population, after smoking. Epidemiological studies have provided convincing evidence of an association between indoor radon exposure and lung cancer, even at the relatively low radon levels commonly found in residential buildings. A number of approaches is used worldwide to assess the potential for elevated indoor radon concentrations across geographic areas of various dimensions. Radonprone areas can be identified directly by using indoor measurements or indirectly using radon concentration in the soil, provided there is an established correlation with the radon concentrations in homes.Thus, the emission of ionizing radiation by rock and soil depends on its content of uranium, thorium, potassium and radium elements, since the levels of radon depend mostly on the concentration of radium. It was evaluated the soil radon level on the assumption that 1 Bq.kg-1 radium is equivalent to 1.700 Bq.m-3 radon concentration in soil(K. Sun, Q. Guo, J. Cheng,)

1.2 Significance of study

          In recent years, it has being observed that there is little or no awareness when it comes to exposure to radiation, this research work has been carried out in such a way that gives a detailed report on the level of Radon gas, a radioactive element present in soil. This will go a long way in creating awareness on the need to carry out radioactive tests on food, water before consumption.

1.3 Scope of study

          This research work is limited to the investigation of the level of radon gas concentration in soil within Ogbomoso based on the five geological zones with varying depths using a rad7 detector.

1.4 Aim and Objectives

          1.4.1 Aim

The aim is to assess the variation of soil/gas radon concentration with depth within Ogbomoso, Oyo State Nigeria.

          1.4.2 Objectives

(1) The five locations were chosen based on the five bedrocks found in Ogbomoso.

(2) To measure the radon concentration in soil with depth of the five locations.

(3)To estimate the cancer risk that radon poses when inhaled in high dose rate.