P1 matter + radiation

• every atom contains a positively charged nucleus composed of protons and neutrons, and electrons that surround it
• relative masses of sub-atomic particles:

  proton = 1

  neutron = 1

  electron = 1/2000
• relative charges of sub-atomic particles:

  proton = 1

  neutron = 0

  electron = -1
• every atom of an element has the same number of protons as another atom of the element
• the atomic number is the number of protons, represented by Z
• atoms of the same element with the same number of protons but a different number of neutrons are called isotopes
• a proton or neutron in the nucleus is a nucleon
• the mass number is the total number of protons and neutrons in the atom, represented by A
• each type of nucleus is called a nuclide and is labelled using isotope notation, with the symbol of the element, the mass number at the top and the atomic number at the bottom
• number of neutrons in the nucleus is mass number - atomic number
• the specific charge of a charged particle is defined as its charge divided by its mass, using actual values not relative values
• a stable nucleus does not disintegrate, so is held together by a force, called the strong nuclear force, this overcomes the electrostatic force of repulsion between the protons and holds them together with the neutrons
• the attractive range of the strong nuclear force is between 3fm and 0.5fm apart, above 3fm it has no effect, below 0.5fm it is repulsive
• an unstable nucleus has too many protons, neutrons or both for the strong nuclear force to hold it together, so it will decay until it becomes stable
• alpha decay occurs in large nuclei with too many protons and neutrons, the nucleus emits an alpha particle and forms a new nucleus
• an alpha particle has a mass number of 4 and an atomic number of 2
• beta-minus decay occurs in nuclei with too many neutrons, a neutron changes into a proton creating and emitting a beta particle
• a beta-minus particle has a mass number of 0 and an atomic number of -1
• alpha decay produces a new nucleus and an alpha particle
• beta-minus decay produces a new nucleus, a beta-minus particle, and an antineutrino
• an electromagnetic wave consists of an electric wave and a magnetic wave which travel together and vibrate at right angles to each other and in phase with each other
• electromagnetic radiation travels in packets called photons, which transfer energy and have no mass
• the energy of photons is directly proportional to the frequency of electromagnetic radiation
• the equation for energy of a photon is: E = hf

  E = energy in J

  h = plancks constant, 6.63x10^-34

  f = frequency in Hz
• for a light source emitting photons of the same frequency, use the equation: P = nhf

  P = power in W

  n = number of photons passing a point per second

  h = planck's constant, 6.63x10^-34

  f = frequency in Hz
• every particle has an antiparticle which has identical rest energy and mass, but the opposite of every other property
• the antiparticle of the electron is the positron
• the antiparticle of the proton is the antiproton
• the antiparticle of the neutron is the antineutron
• the antiparticle of the neutrino is the antineutrino
• annihilation is when a particle and its antiparticle collide, their masses are converted into energy and released in the form of two photons

  the two photons must move in opposite directions in order for momentum to be conserved
• pair production is when a photon has more energy than the total rest energy of a particle and its antiparticle, the photon can be converted into an equal amount of matter and antimatter, the excess energy is converted into kinetic energy
• there are four fundamental forces: gravity, electromagnetic, weak nuclear and strong nuclear
• forces between particles are caused by exchange particles, which carry energy and momentum between the particles experiencing the force
• each type of fundamental force has its own exchange particle
• gravity acts on all particles with mass, by attracting them towards each other

  the exchange particle of gravity is the graviton

  gravity has infinite range
• the electromagnetic force acts on charged particles, by attracting oppositely charged particles to each other and repelling same charged particles from each other

  the exchange particle is the virtual photon

  the electromagnetic force has infinite range
• the virtual photon is represented by $\gamma$
• the weak nuclear force acts on all particles, it converts protons into neutrons and neutrons into protons, it is too weak to affect stable nuclei, but is responsible for beta-decay, electron capture, and electron-proton collisions

  the exchange particle is the W+ or W- boson

  the weak nuclear force has a range of 1x10^-18 metres
• the strong nuclear force acts on hadrons, it holds the protons and neutrons in the nucleus together without pushing them into each other

  the exchange particle is the gluon

  the strong nuclear force has a range of up to 3fm