PHYA1 - Particle Physics

  • Created by: Franklin
  • Created on: 19-04-14 13:21

Constituents of an atom and radiation products

  • Atomic no. - no. of protons in the nucleus
  • Mass number - total number of nucleons (protons and neutrons)
  • isotopes - atoms with the same amount of protons but different number of neutons
  • Alpha radiation - nucleus emits alpha particle which consists of 2 protons and 2 neutrons (equivalent to a helium nucleus)
  • Beta minus radiation - neutron turns into proton, beta- particle (electron) is emitted


  • when alpha particles were fired at a thin sheet of gold foil most when through indicated the atom was mostly empty space
  • Some deflected indicating a positive center 
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Strong force and specific charge

The protons and neutrons in a nucleus are held togther by the strong force. This counters the electromagnetic proton-proton repulsion.

The strong force:

  • Has a short range of about 3 fm
  • At distances of about 0.5 fm the strong force is repulsive otherwise the nucleus would crush to a point

Specific Charge

Specific charge (Ckg-1) = charge (C)/ mass (kg)

  • Electron has highest specific charge
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Alpha and beta-minus decay

In alpha decay the nucleus emits an alpha particle: 2 protons and 2 neutrons (helium nucleus)


In beta minus decay a neutron turns into a proton and an electron and antielectron neutrino are emitted


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Electromagnetic Radiation

Electromagnetic Spectrum is the complete range of possible frequencies of electromagnetic radiation.

Radiowaves - Microwaves - Infra-red - visible light- UV - X-rays - Gamma Radiation 

             Increasing Frequency ------->      

  • EM radiation only exist in discrete packets called quanta
  • E= hf
  • h = Planck's constant: 6.63 x 10-34
  • energy in J = (6.63 x 10-34) * frequency of light in Hz
  • f=c/wavelength therefore E = hc/wavelength (c = speed of light in a vacuum: 3*10**-8)                                       
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Each particle has a corresponding antiparticle with the same mass and rest energy, but opposite charge

Pair Production

  • When energy is converted into mass, you get equal amounts of matter and antimatter
  • It only takes place if there is enough energy to create both particles

If a photon has enough energy it can produce a positron-electron pair. The minimum energy required for pair production is the total rest energy of the particles produced

Emin = 2E0


When a particle and antiparticle meet they anhilate and their mass is converted into energy in the form of gamma radiation. Emin of photon = E

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Classification of Particles - Hadrons

  • Hadrons can feel the nulear strong force
  • They are not fundamental particles; they can be split into baryons and mesons
  • Hadrons decay through the weak interaction


  • Have a quark composition of qqq 
  • Neutrons and protons are baryons
  • All baryons except protons are unstable, meaning that all baryons decay into protons
  • Baryon number is always conserved in a particle reaction
  • Baryons have a baryon no. =1
  • Antibaryons have a baryon no = -1
  • Other particles have baryon no. = 0
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Classification of Particles - Hadrons - Mesons


  • Mesons interact with baryons via the strong force
  • All mesons are unstable and have Baryon no. 0
  • Pions are the lightest mesons and can have +,- or no charge
  • Pions can interact with protons and turn them into neutrons and vice-versa


  • Kaons are heavier and more unstable than pions
  • Kaons decay into pions
  • The can have +, - or no charge
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Table of pions and kaons

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Quarks and Antiquarks


  • Baryons are made up of 3 quarks. Quarks are fundamental particles
  •  Proton = uud
  • Neutron = udd
  • Mesons are made up of a quark and antiquark

    • Pions only involve up and/or down quarks (and their antiparticle counterparts)
    • Kaons involve up, down or strange quarks (and their antiparticle equivalents)
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Classification of Particles - Leptons

Leptons are fundamental particles which interact through the weak nuclear force.

  • Electrons are stable leptons and have a Lepton electron number of +1 and lepton muon no. of zero
  • Muons are heavier than electrons and are unstable
  • Muons have a lepton muon no. of +1 and lepton electron no. of 0
  • Both lepton muon and lepton electron numbers have to be conserved in order for an interaction to take place (as well as charge). That is why an anti-electron neutrino must be released in neutron decay
  • positrons have lepton electron no.: -1
  • electron neutrino has a lepton electron no. of +1
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