Description

ABSTRACT

Accidents involving industrial radiography are the most frequent cause of severe or fatal overexposure to workers and the public. The accident in industrial radiography used to come with severe overdose of non-radiation workers due to external exposure of Ir-192 and TC-99M. This paper provides a methodology for calculating doses and dose rates from the most commonly used industrial γ-sources: ¹⁹²Ir and ^99mTC. For this purpose, MCNP computer code based on Monte Carlo technique is used. The applied method helps firstly in studying and analyzing the doses from the above mentioned sources. Secondly, it provides a lead container design in a trial to reduce the dose rate within the permissible. Computer models were used to simulate the ¹⁹²Ir and ⁹⁹TC Meet Halfa accident. To verify these models, the calculated doses were compared with a well-known empirical formula to convert source activity into dose rate and then the models were applied at different distances to analyze the factors that affect the de- posited dose in the human body to find out the dose received by the victims.

 TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• AIM AND OBJECTIVE OF THE STUDY
• SCOPE OF THE STUDY
• RESEARCH QUESTION
• LIMITATION OF THE STUDY
• SIGNIFICANCE OF THE STUDY
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

• REVIEW OF RADIATION INJURY
• GAMMA RAY
• TECHNETIUM-99M
• IRIDIUM-192
• PROPOSED METHOD OF RADIATION DETECTION AND ANALYSIS
• MONTE CARLO MODELING
• MINIMUM DETECTABLE DOSE
• HISTORIC RELEASES OF RADIOACTIVE MATERIAL INTO THE ENVIRONMENT

CHAPTER THREE

3.1      MATERIALS AND METHOD

CHAPTER FOUR

• RESULT AND DISCUSSION

CHAPTER FIVE

• CONCLUSION
• RECOMMENDATION
• REFERENCES

CHAPTER TWO

1.0                                                             INTRODUCTION

1.1                                               BACKGROUND OF THE STUDY

Radioactivity is the act of emitting radiation spontaneously. This is done by an atomic nucleus that, for some reason, is unstable; it “wants” to give up some energy in order to shift to a more stable configuration. During the first half of the twentieth century, much of modern physics was devoted to exploring why this happens, with the result that nuclear decay was fairly well understood by 1960. Too many neutrons in a nucleus lead it to emit a negative beta particle, which changes one of the neutrons into a proton. Too many protons in a nucleus lead it to emit a positron (positively charged electron), changing a proton into a neutron. Too much energy leads a nucleus to emit a gamma ray, which discards great energy without changing any of the particles in the nucleus. Too much mass leads a nucleus to emit an alpha particle, discarding four heavy particles (two protons and two neutrons).

Radioactive material is any material containing unstable atoms that emit ionizing radiation as it decays. Radioactive materials are also known class of chemicals where the nucleus of the atom is unstable. They achieve stability through changes in the nucleus (spontaneous fission, emission of alpha particles, or conversion of neutrons to protons or the reverse). This process is called radioactive decay or transformation, and often is followed by the release of ionizing radiation (beta particles, neutrons, or gamma rays).

The use of radioactive materials continues to offer a wide range of benefits throughout the world in medicine, research and industry. Exposure to large amounts of radioactivity can cause nausea, vomiting, hair loss, diarrhea, hemorrhage, destruction of the intestinal lining, central nervous system damage, and death. It also causes Deoxyribonucleic acid (DNA) damage and raises the risk of cancer, particularly in young children and fetuses according to Delacroix et al (2012). Precautions are, however necessary in order to protect people from the detrimental effects of the radiations. Where the amount of radioactive material is substantial with sources used in radiography, extreme care is necessary to prevent accidents that may have severe consequences for the individuals affected. Many methods have been developed and widely implemented, the unique details of data obtained by radiography, and this has caused radiography to be more appreciated according to [1]. Simplicity in application and accepted results of radiography using radiation sources are the major reason to consider these sources most predominant. Typical γ-ray sources which are used in in this work are ¹⁹²Ir, and ⁹⁹Tc (Turai et al., 2011). About one third of radiation accidents occur in industry, roughly each eighth of them in connection with the medical application of sources of ionizing radiation, while close to one third of them have nuclear origin. Radiation accidents are the rarest in the transport and waste management or military application of radioactive materials or devices. A radiation accident is different from accidents in other fields as the effects of radiation are not immediately felt. Because of this insidious nature, a radiation accident can lead to very serious consequences. The likelihood of occurrence of an accident in industrial radiography is fairly high (Briesmeister et al., 2016), because majority of the radiography work is carried out in public domain, such as construction sites, workshop areas and inaccessible locations. The source activities used in industrial radiography are quiet high, hence in the event of an accident; there is the possibility of very high doses, even up to lethal doses in certain cases. Accidents and consequent radiation exposure/injury during use happen mainly because of the following reasons:

1. handling of sources by untrained persons,
2. use of defective equipment and/or its failure,

• failure to use radiation

In this study, MCNP computer code based on Monte Carlo techniques was used to design a computer model which studies and analyzes the doses from γ-sources and design a lead container which reduces the dose rate from these sources to less than 1 μSv/h. Also, exposure from ¹⁹²Ir and ⁹⁹Tc source is studied to simulate accident. This is to analyze and simulate the dose received by the infected persons. Several scenarios are assumed and the dose rate from each scenario is compared with the documented accident dose.

1.2                                                  PROBLEM STATEMENT

Ionizing radiation has sufficient energy to affect the atoms in living cells and thereby damage their genetic material (DNA). Fortunately, the cells in our bodies are extremely efficient at repairing this damage. However, if the damage is not repaired correctly, a cell may die or eventually become cancerous (Cobb et al., 2019).

Exposure to very high levels of radiation, such as being close to an atomic blast, can cause acute health effects such as skin burns and acute radiation syndrome (“radiation sickness”). It can also result in long-term health effects such as cancer and cardiovascular disease.

A very high level of radiation exposure delivered over a short period of time can cause symptoms such as nausea and vomiting within hours and can sometimes result in death over the following days or weeks (National Cancer Institute, 2020). This is known as acute radiation syndrome, commonly known as “radiation sickness.”

It takes a very high radiation exposure to cause acute radiation syndrome—more than 0.75 gray (75 rad) in a short time span (minutes to hours). This level of radiation would be like getting the radiation from 18,000 chest x-rays distributed over your entire body in this short period.

There are studies that keep track of groups of people who have been exposed to radiation, including atomic bomb survivors and radiation industry workers. These studies show that radiation exposure increases the chance of getting cancer, and the risk increases as the dose increases: the higher the dose, the greater the risk. Conversely, cancer risk from radiation exposure declines as the dose falls: the lower the dose, the lower the risk (Hendee et al., 2015; Mettler et al., 2020).

For anyone working in industrial radiography, there is high level of radiation exposure. But many experts are concerned about an explosion in the use of higher (excess) radiation–dose tests, such as industrial (NCRP, 2018). The study was carried out to enlighten the reader about the effects of excess dose of beta-ray radiation.

1.3                                     AIM AND OBJECTIVE OF THE STUDY

The main aim of this work is to provide methodologies for calculating doses and dose rates from the most commonly used industrial γ-sources: ¹⁹²Ir and ^99mTC. The objectives are:

1. To provide information about dose rates of ¹⁹²Ir and ^99mTC
2. To simulate an estimate of the radiation dose received by the human body using MCNP5b radiation code

1.5                                                      SIGNIFICANCE OF THE STUDY

This research work will provide an insight into the magnitude of the radiation received when exposed to γ-ray sources.

1.6                                     PROJECT ORGANISATION

The work is organized as follows: chapter one discuss the introductory part of the work,   chapter two presents the literature review of the study, chapter three describes the methodology applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations