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Topic 1 - Fundamentals by

Basic Radiation Units

SI units

Energy: joule (J) (kilog­ram­-metre2 per second2)
we use an energy unit based on a single (positive) electron charge when experi­encing a voltage of 1 V, and this is referred to as the electron volt (eV).
Radiation Exposure: coulomb per kilogram (C/kg) (Previ­ously roentgen (r))
Absorbed Dose: Gray (Gy) (one joule per kilogram) (Previ­ously rad, 1 Gy =100 rads)
Radioa­cti­vity: rate of decay of a radioa­ctive material, becquerel (Bq) (one decay per second)

Expone­ntial Function

Decay of a radioa­ctive material

A0 is the initial activity (at time t = 0) and At is the activity after time t. λ is a constant that is specific to the radioa­ctive material under consid­era­tion.



Z is the atomic number (i.e. the number of protons, determines the element)
N is the number of neutrons
A is the mass number (Z + N)

Inverse Square Law

The intensity of a point source of radiation decreases as the distance from the source is increased. The amount of decrease is inversely propor­tional to the square of the distance.

Fundam­ental Particles

Quarks: points of matter that exist with other quarks as a pair or triplet.
Bound together by gluons
Collec­tions of quarks are hadrons. A triplet of quarks is known as a baryon.
A Meson is one quark, and one anti-q­uark. The most commonly encoun­tered meson is the pion, formed by anti-m­atter, extremely unstable.
Six quarks - up, down, top, bottom, strange and charm; there are also six anti-q­uarks.
Leptons: point particles that can exist in isolation
Much lower mass than a quark
May carry a negative unit charge (-1) or have no charge (0).
Six leptons. The three charged leptons are electrons, muons and tau. The three uncharged leptons are neutrinos.
The special antimatter anti-l­epton is the positron.
All known matter in the universe is made up of: The up and down quark; The electron lepton; The three uncharged neutrinos and the three uncharged anti-n­eut­rinos
All intera­ctions are made up of forces between these particles. Four forces: 1. The strong force or nuclear force, mediated by gluons; 2. The electr­oma­gnetic force, mediated by photons; 3.The weak force, mediated by the W-bosons and the Z-boson; 4. Gravity, for which the force carrier particle still eludes detection

The Atom

Smallest unit in the compos­ition of matter
Composed of a central nucleus surrounded by one or more orbiting electrons
The nucleus consists of two types of hadrons: Protons positively charged (+1), Neutrons neutrally charged
Nucleons: protons and neutrons
The nucleus is held together by the residual strong force, which occurs between quarks of neighb­ouring nuclei.
Nucleons are about 2000 times heavier than electrons
Atoms combine to form molecules and chemical compounds
The size of the atom (its diameter) is about 10-10 m, whereas the nucleus has a diameter of 10-14 m, a factor of 10,000 smaller.
The atom is largely unoccupied space which has an enormous bearing on intera­ctions of radiation with matter, including human tissue.

The Electron Position

Heisen­berg's Uncert­ainty Principle: the exact momentum (energy) and the exact position can't be known simult­ane­ously
Observing something alters it

Wave-P­article Duality

We can consider the atomic entity as either a: 1. particle (the localised ‘billiard ball’ approach) with particle diameter (d) and mass (m) 2. wave (an extended and vibrating phenom­enon) with energy (E), wavelength (λ), and frequency (f).
E = mc2
Energy here is in J and must be converted into MeV.

Atomic Mass Unit (u)

One atomic mass unit is 1/12 of the mass of the carbon-12 atom.


Elements exist with different numbers of neutrons than the neutral atom
'Isotope’ does not necess­arily imply a radioa­ctive material.

Electronic Structure of the Atom

Bohr model: electrons rotate around the nucleus in discrete energy shells that are stationary and arranged in increasing order of energy.
A maximum number of electrons allowable in each shell
K shell can hold 2 electrons, the L shell 8 electrons, the M shell 18 electrons, etc.
Orbital electrons don't actually exist in precise circular orbits, but rather in imprec­isely defined regions of space around the nucleus
The electron’s position is defined by probab­ility, with decreasing probab­ility for locations outside of the ‘most likely’ regions

Electron Binding Energy

Electrons have different binding energies, depending on the electron shell
In the most stable config­ura­tions, electrons occupy the innermost shells where they are most tightly bound to the nucleus.
Excita­tion: an electron is raised from a lower energy shell to an upper energy shell (releasing energy)
Ionisa­tion: an electron is removed completely from an atom
Binding energy of an electron is the energy required to remove it completely from a shell
Binding energy is higher for orbitals nearer the nucleus (KB>LB­>MB).
Binding energy increases with the charge (equal to the atomic number Z) of the nucleus
Removing an electr­on/­going from an inner to an outer shell, requires energy input
An electron moving from an outer to an inner shell results in energy emission


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