# PHYA1 - Particle Physics

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• 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

Rutherford

• 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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## Antiparticles

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

Anihilation

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

Baryons

• 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

• 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

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