Environmental Radioactivity and Emergency Preparedness

Mats Isaksson, Christopher L. Raaf

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781315355559
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Nuclear Physics

Radioactive sources such as nuclear power installations can pose a great threat to both humans and our environment. How do we measure, model and regulate such threats? Environmental Radioactivity and Emergency Preparedness addresses these topical questions and aims to plug the gap in the lack of comprehensive literature in this field.

The book explores how to deal with the threats posed by different radiological sources, including those that are lost or hidden, and the issues posed by the use of such sources. It presents measurement methods and approaches to model and quantify the extent of threat, and also presents strategies for emergency preparedness, such as strategies for first-responders and radiological triage in case an accident should happen.

Containing the latest recommendations and procedures from bodies such as the IAEA, this book is an essential reference for both students and academicians studying radiation safety, as well as for radiation protection experts in public bodies or in the industry.

Chapter 1 Sources of Radiation

Contents

1.1 Naturally Occurring Radiation

1.1.1 Cosmic Radiation

1.1.2 Cosmogenic Radionuclides

1.1.2.1 Tritium

1.1.2.2 Beryllium-7

1.1.2.3 Carbon-14

1.1.2.4 Sodium-22

1.1.3 Primordial Radionuclides

1.1.3.1 Potassium

1.1.3.2 Uranium

1.1.3.3 Thorium

1.1.3.4 Radium

1.1.3.5 Radon

1.1.4 Series Decay and Equilibria

1.2 Technologically Enhanced Naturally Occurring Radioactive Material (NORM and TENORM)

1.2.1 Radon and Radon Exposure Enhanced by Man

1.2.1.1 Potential Alpha Energy

1.2.1.2 Radon in the Indoor Environment

1.2.2 Sources Generated by Industrial and Technological Processes

1.2.2.1 Radioactivity Associated with Fossil Fuels

1.2.2.2 Radioactivity Associated with the Production and Use of Minerals

1.2.2.3 Phosphate Ore and Phosphate Fertilizers

1.2.2.4 Manufacturing of Equipment and Household Goods

1.2.2.5 Water Treatment and the Provision of Running Water

1.2.2.6 Exemption and Clearance

1.3 Anthropogenic Radiation

1.3.1 The Nuclear Industry

1.3.1.1 The Nuclear Fission Process

1.3.1.2 Controlled Nuclear Fission

1.3.1.3 Nuclear Reactors

1.3.1.4 Production of Radionuclides in a Reactor

1.3.2 Nuclear Weapons

1.3.2.1 Nuclear Weapons Tests

1.3.2.2 Effects of Nuclear Weapons

1.3.2.3 Nuclear Fission Bombs

1.3.2.4 Thermonuclear Weapons

1.3.3 Radioisotopes Used in Medicine

1.3.4 Radiation Sources in Industry and Research

1.4 References

IN THIS CHAPTER, we give an overview of the sources of radionuclides found in our environment. Some, such as²³⁸U and ⁴⁰K occur naturally, while others, such as ¹³⁷Cs and ⁶⁰Co are man-made, and result from industrial or military activities.

The first artificial nuclear reaction was performed by Ernest Rutherford in 1917, when he bombarded stable ¹⁴N with α-particles, each reaction creating an ¹⁷O nucleus and a proton. However, no radionuclides were produced because ¹⁷O is stable. With the discovery of the neutron by James Chadwick in 1932, a number of radionuclides of non-natural origin began to be created. Using neutrons, Enrico Fermi and others attempted to produce elements heavier than uranium using nuclear reactions, but in many of the experiments the radionuclides produced were lighter than uranium, for example, barium. This was explained by Lise Meitner and Otto Frisch in 1938, who showed that bombarding uranium with neutrons caused the uranium nucleus to split into two parts. This process, called nuclear fission, was found to release large amounts of energy, and attempts were made to construct a device for controlled nuclear fission on a larger scale. These attempts proved successful in 1942, when Fermi was able to produce a self-sustaining chain reaction, heralding the start of the nuclear era.

1.1 Naturally Occurring Radiation

The naturally occurring radionuclides can be divided into two groups, depending on their origin. Cosmogenic radionuclides are produced in nuclear reactions between cosmic radiation and either the constituents of the atmosphere or the surface of the earth, while primordial radionuclides have existed since the earth was formed, approximately 4.6 billion (4.6·10⁹) years ago.

1.1.1 Cosmic Radiation

There are many kinds of radiation in outer space, including the microwave background radiation originating from the Big Bang, γ-rays and x-rays. However, there are three main sources of radiation which affect living beings on earth: galactic cosmic radiation, solar cosmic radiation and radiation from the Van Allen belts which surround the earth (UNSCEAR 2008). Radiation from these sources is usually referred to as primary cosmic radiation, while their interaction with the atmosphere gives rise to secondary cosmic radiation.

The origin of galactic cosmic radiation is still not fully understood, but it has been suggested that supernovas could impart sufficient energy to the particles making up the galactic radiation field. These include protons (85.5%), α-particles (~12%), and electrons (2%) (UNSCEAR 2008). The nuclei of various elements, even those as heavy as uranium, are also found in the galactic cosmic radiation (~1%). The energy of these cosmic particles ranges from 100 MeV to over 10¹⁷ MeV! Most of this radiation emanates from within our own galaxy, the Milky Way. The energy spectrum of the galactic cosmic radiation is described by two different power functions, depending on the energy of the particles. For energies below 10¹² MeV, the particles have an energy distribution that is described by

ΦE∝E−2.7,(1.1)

where Φ_E is the spectral energy fluence (number of particles per unit area per unit energy) and E is given in eV. For higher energies the relation is instead given by

ΦE∝E−3.(1.2)

The cosmic radiation arising from the sun (solar cosmic radiation) consists mainly of protons (~ 99%) with energies below 100 MeV, which are emitted by solar flares. The fluence varies with solar activity, which follows roughly an 11-year cycle. The intensity of the galactic cosmic radiation is affected by the highly ionized plasma of the solar wind, and thus it also varies with solar activity, being at a maximum when solar activity is at its minimum. To a large extent, the earth is shielded from cosmic radiation by its magnetic field, and also by the atmosphere. The dose rate resulting from galactic cosmic radiation can thus be quite high at high altitudes, but only the particles with the highest energies contribute to the dose rate at the surface of the earth.

The Van Allen belts consist of charged particles, mainly protons but also electrons, captured by the earth’s magnetic field. The energies of the protons can reach several hundred MeV, while the electrons have much lower energies, on the order of a few MeV. There is an internal Van Allen belt whose mid-point is about 3000 km from the earth’s surface, while the external belt is at an altitude of about 22 000 km.

When high-energy particles in the primary cosmic radiation enter the atmosphere, they interact with atoms and molecules to produce several kinds of charged and uncharged particles. This secondary cosmic radiation consists of particles such as protons, neutrons and pions. However, at lower altitudes, neutrons dominate the particle fluence due to their longer range.

FIGURE 1.1 Protons (p) from the primary cosmic radiation enter the atmosphere and collide with nuclei, such as nitrogen (N), producing secondary particles including pions (π), neutrons (n), antineutrons (n¯) and antiprotons (p¯). These secondary particles may then decay into muons (μ), neutrinos (ν) and electrons (e), and cause nuclear reactions in other atoms in the atmosphere. The interaction between electrons from the secondary cosmic radiation and molecules in the atmosphere causes the Northern and Southern Lights (Aurora Borealis and Aurora Australis).

The unstable particles, for example, positively charged pions, decay into muons, electrons, neutrinos and photons. The muons, which have a low probability of interacting with the atoms in the atmosphere, reach the earth with energies between 1 and 20 GeV, before they decay. Muons are thus the largest source of the absorbed dose at the surface of the earth (UNSCEAR 2008). Uncharged pions produce a cascade of photons and electrons since they decay into photons with high energies. These photons form electrons and positrons through pair production, which then produce new photons by annihilation, and the cycle repeats. Figure 1.1 depicts a simplified series of events resulting from the interaction of high-energy protons with nitrogen nuclei in the upper atmosphere. In this way, a proton with a very high energy can produce a so-called cosmic ray shower consisting of photons, muons and electrons, which covers an area on the earth’s surface of several square kilometres.

Another effect of the earth’s magnetic...

Table of contents

• Cover
• Half-Title Page
• Series Page
• Title Page
• Copyright Page
• Dedication Page
• Table of Contents
• List of Figures
• List of Tables
• Foreword
• Preface
• Authors
• Author Bios
• Chapter 1 ▪ Sources of Radiation
• Chapter 2 ▪ Radiation Biology and Radiation Dosimetry
• Chapter 3 ▪ Environmental Exposure Pathways and Models
• Chapter 4 ▪ Radiometry
• Chapter 5 ▪ Sampling and Sample Preparation for Radiometry
• Chapter 6 ▪ Nuclear and Radiological Safety
• Chapter 7 ▪ Emergency Preparedness
• Index