Chapter 1-3

Course Introduction

• Course Title: MPHY447 Radiation Protection.
• Instructor: Prof. Zaid Ababneh.
• Primary Objectives:   - Protect the workers.   - Protect the public.   - Protect the environment.
• Core Reference Text: "An Introduction to Radiation Protection" (Seventh Edition) by Alan Martin, Sam Harbison, Karen Beach, and Peter Cole (CRC Press, Taylor & Francis Group).

The Structure of Matter

• Fundamental Definitions:   - Element: A substance that cannot be broken down by ordinary chemical processes into simpler substances.     - There are $92$ naturally occurring elements (e.g., Carbon).     - Approximately a dozen or more artificial elements have been produced, such as plutonium.   - Compound: Two or more elements chemically linked in definite proportions (e.g., water, $H_2O$).   - Atom: The basic unit of matter; each element possesses its own characteristic atom.
• Subatomic Particles:   - Proton: One unit of positive electrical charge; mass of approximately one atomic mass unit ($1\,u$).   - Electron: One unit of negative charge; mass of $\frac{1}{1840}\,u$.   - Neutron: Electrically neutral particle; mass of approximately $1\,u$.   - Atomic Mass Unit ($u$): Corresponds to a mass of about $1.7 \times 10^{-27}\,kg$.
• Atomic Model:   - Protons and neutrons form the central nucleus.   - Electrons rotate around the nucleus in orbits known as shells:     - K shell: Holds $2$ electrons.     - L shell: Holds $8$ electrons.     - M shell: Holds $18$ electrons.     - N shell: Holds $32$ electrons.   - An atom is electrically neutral when the number of protons equals the number of electrons.
• Atomic and Mass Numbers:   - Atomic Number ($Z$): The number of protons in an atom. It determines the chemical properties and defines the element (e.g., $Z=1$ is Hydrogen, $Z=2$ is Helium, $Z=3$ is Lithium, $Z=4$ is Beryllium, $Z=92$ is Uranium).   - Mass Number ($A$): The sum of protons and neutrons in the nucleus ($A = Z + \text{number of neutrons}$).   - Isotopes: Atoms of the same element (same $Z$) that have different numbers of neutrons (different $A$).     - Example (Helium isotopes):       - Helium-3 ($He-3$): $2$ protons, $1$ neutron.       - Helium-4 ($He-4$): $2$ protons, $2$ neutrons.       - Helium-5 ($He-5$): $2$ protons, $3$ neutrons.   - Nuclide: A term used to describe any specific isotope of any element.   - Chemical Identity: All isotopes of an element are chemically identical because chemical properties are determined by the atomic number ($Z$).
• Neutron-to-Proton Ratio:   - In almost all elements except the lightest, the number of neutrons exceeds the number of protons.   - This difference increases as $Z$ increases:     - ${^4}He$: $2$ protons, $2$ neutrons.     - ${^{31}}P$: $15$ protons, $16$ neutrons.     - ${^{65}}Zn$: $30$ protons, $35$ neutrons.     - ${^{238}}U$: $92$ protons, $146$ neutrons.

Radioactivity and Ionizing Radiation

• Atomic Instability: Unstable atoms undergo spontaneous transformation into more stable atoms through radioactive decay. These substances are termed radioactive.
• Historical Context: Natural radioactivity was first recognized by Henri Becquerel in $1896$.
• Types of Radiation:   - Alpha ($\alpha$): Consists of helium nuclei ($2$ protons + $2$ neutrons). Mass = $4\,u$, Charge = $+2$.   - Beta ($\beta$): High-speed electrons originating in the nucleus.     - $\beta^-$ (electron): Mass = $\frac{1}{1840}\,u$, Charge = $-1$.     - $\beta^+$ (positron): Mass = $\frac{1}{1840}\,u$, Charge = $+1$.   - Gamma ($\gamma$): Electromagnetic radiation (quanta of energy) resulting from nuclear changes. Energy is defined by $E = h\nu$.
• Decay Equations and Models:   - Alpha Decay: ${^A_Z}X \rightarrow {^{A-4}<em>{Z-2}}X' + {^4_2}\alpha$   - Beta Decay: ${^A_Z}X \rightarrow {^A</em>{Z+1}}X' + {^0_{-1}}\beta$   - Gamma Emission: ${^A_Z}X^* \rightarrow {^A_Z}X' + \gamma$ (Relaxation from excited nuclear state).
• Electromagnetic (EM) Radiation Characteristics:   - EM energy is inversely proportional to wavelength ($\lambda$). Short wavelengths correspond to higher energies.   - Radio waves (long wave): $\lambda = 1500\,m$.   - Radio waves (VHF): $\lambda = 3\,m$.   - Visible light: $\lambda = 10^{-6}$ to $10^{-7}\,m$.   - X-rays ($50\,keV$): $\lambda = 2.5 \times 10^{-11}\,m$.   - $\gamma$-rays ($1\,MeV$): $\lambda = 1.2 \times 10^{-12}\,m$.
• Radiation Energy Units:   - Electron volt ($eV$): Energy gained by an electron passing through an electrical potential of $1$ volt.   - $1\,keV = 10^3\,eV$.   - $1\,MeV = 10^6\,eV$.   - Radiation protection energy range of interest: $100\,keV$ to $10\,MeV$.   - Kinetic Energy ($E_k$): $E_k = \frac{1}{2}mv^2$.
• Radioactive Decay Mechanisms:   - Alpha emission: Occurs in heavy unstable nuclei to increase stability.   - Beta emission: A neutron changes into a proton, emitting a high-speed electron.   - Positron emission: A proton in a proton-rich nucleus ejects a positive electron ($\beta^+$) to become a neutron (e.g., $Na-22$ to $Ne-22$).   - Electron capture (EC): An alternative to positron emission where an inner orbital electron is captured by the nucleus, converting a proton to a neutron and emitting X-rays.   - Beta Spectrum: Electrons are emitted with a continuous energy distribution from zero to a maximum ($E_{max}$). The most probable energy is approximately $\frac{1}{3} E_{max}$.
• Natural Radioactive Series:   - Thorium Series: Parent $^{232}Th$ ($T_{1/2} = 1.39 \times 10^{10}\,y$), Final stable nucleus $^{208}Pb$.   - Uranium-radium Series: Parent $^{238}U$ ($T_{1/2} = 4.50 \times 10^9\,y$), Final stable nucleus $^{206}Pb$.   - Actinium Series: Parent $^{235}U$ ($T_{1/2} = 8.52 \times 10^8\,y$), Final stable nucleus $^{207}Pb$.   - Neptunium Series: Parent $^{237}Np$ ($T_{1/2} = 2.20 \times 10^6\,y$), Final stable nucleus $^{209}Bi$.