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Particles & Radiation (Particle Interactions
To explain the forces…
Particles & Radiation
Constituents of the Atom
The constituents of the atom are protons, neutrons and electrons. The protons and neutrons (nucleons) are found in the nucleus of atoms. The nucleus of an atom is surrounded by empty space in which there are electrons.
Proton
- Mass = 1 (1.67 x 10⁻²⁷)
- Charge = - 1 (+1.6 x 10^-19)
Neutrons
- Mass = 1 (1.67 x 10⁻²⁷)
- Charge = Neutral ( 0 )
Electrons
- Mass = 0.0005 (9.11 x 10^-31)
- Charge = -1 (-1.6 x 10^19)
Atoms and Isotopes
Atoms
- Described by proton number (Z) and nucleon number (A)
Isotopes
- atoms which have the same number of protons but different neutrons
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Particles, Antiparticles & Photons
Every particle has a corresponding antiparticle of opposite charge and or quarks
- the positron is the antiparticle of the electron
- the antiproton is the antiparticle of the proton
- the antineutron is the antiparticle of the neutron
the antineutrino is the antiparticle of the neutrino
Pair production and annihilation
- When a particle and its antiparticle meet each other they annihilate each other. Their mass is converted into energy in the form of 2 photons in opposing direction.
- This is an example of mass being converted into energy but it can also work the other way around with energy being converted into mass.
- High energy photons can produce a particle and its antiparticle, this is called pair production.
Photons
- Electromagnetic radiation (like gamma rays, x-rays and visible light etc.) have wave properties and they can also behave as particles, these particles are called photons.
- The energy (E) of a photon depends on its frequency (f). (E = hf = hc/λ)
Particle Interactions
To explain the forces between particles we use the concept of exchange particles or bosons.
Gravity – gravitons
All particles with mass attract each other with the force of gravity, the mechanism by which particles attract each other is through the exchange of particles called gravitons (as yet undetected).
Electromagnetic force – virtual photons
The virtual photon is the exchange particle (or boson) which carries the electromagnetic force between charged particles. Particles with electric charges can either attract or repel each other by exchanging particles called virtual photons.
Strong Nuclear - Gluons
Gluons are the exchange particles involved in the strong nuclear force interaction.
Weak nuclear force – W+, W- bosons
W bosons are the exchange particles involved in the weak nuclear force interaction.
The weak force acts within the nucleus, quarks and leptons excerpt forces on each other by exchanging bosons. The weak nuclear force is very weak and acts over a very small distance.
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Conservation laws for particle interactions
- During particle interactions the following are conserved (the number before the interaction must equal the number after the interaction).
- Charge
- Baryon number
- Lepton
- Strangness
