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) |
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. |
Nomenclature
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) |
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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. |
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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. |
Isotopes
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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