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.
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.
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
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
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