Particles and Radiation Flashcards
Specific Charge
Charge ÷ mass (Ckg⁻¹)
Isotopes
Doesn’t affect chemical properties
Affects stability of nucleus
More neutrons compared to protons, more unstable nucleus
Unstable nuclei may be radioactive and decay to make more stable`
Hydrogen isotopes examples
Protium - 1p, 0n
Deutrium - 1p, 1n
Titrium - 1p, 2n
Nuclear decay
Unstable nuclei will emit particles to become more stable
Alpha decay
Only very big atoms (>82 protons) as strong nuclear force can’t keep stable.
Emit alpha particle
Have very short range (only a few cm in air).
Use a Geiger or Spark counter to observe.
Beta-minus decay
Only in 'neutron rich' isotopes Emit electron and antineutrino Neutron changes to proton Range of several metres in air Caused by weak interaction Antineutrino carries away missing energy
Hypothesis of neutrinos
Energy of particles not conserved in beta decay Wolfgang Pauli (1930) suggested another particle with no charge and little to no mass carried away the missing energy
Forces in the nucleus
Electromagnetic
Gravitational
Strong nuclear
Electromagnetic Force
Causes protons to repel
Gravitational force
Causes all the nucleons to attract due to their masses
Not strong enough to overcome repulsion of EM
Strong Nuclear force
Other attractive force larger than EM force counteracts repulsion Very short range (up to a few fm) Repulsive up to 0.5 fm Strongest from 0.5 - 3 fm 1 fm = maximum attraction
EM radiation Spectrum
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decreasing wavelength
Photons
Max Plank suggested EM waves only be RELEASED in discrete packets (called quanta)
Einstein suggested can only EXIST in discrete packets (called photons)
E = hf = hc/λ
E is energy (J), h is Plank’s constant (6.63x10⁻³⁴ Js), f is frequence (Hz)
Pair production
Energy into mass
Equal amounts of matter and antimatter
Requires enough energy to produce particle and antiparticle
Eₘᵢₙ = 2E₀
Annnihilation
Particle meets its antiparticle
All mass of particle and antiparticle is converted to energy as 2 gamma ray photons
Min energy of particles produced by is rest energy of the pairs split between 2 gamma rays Eₘᵢₙ = E₀
Hadrons
Particles that can feel the strong force
Not fundamental particles as they are made up of 3 quarks
There are two types of hadrons - baryons and mesons
Baryons
Protons and neutrons are baryons
All baryons eventually decay to become protons
Baryon number
The baryon number is a quantum number that must be conserved
Neutron decay
When a neutron decays, it forms a proton, and electron and an antineutrino
Mesons
Pions and kaons
Can be detected in cosmic ray showers
Pions
The lightest mesons
Three variations each with different electric charges
These are the exchange particles of the strong force
Kaons
Heavier and more unstable than pions
Have a very short lifetime and decay into pions
Leptons
Fundamental particles that dont feel the strong force
only interact with other particles via the weak interaction
Muons eventually decay into electrons
Lepton numbers
Quantum numbers and must also bre conserved
Electron and muon types of lepton have to be counted separately
Strange particles
Created via the strong interaction in which strangeness is conserved
Conservation of strangeness means that strange particles can only be created in pairs
A quantum number so must be conserved except in the weak interaction
Conservation of particles
Energy, momentum are always conserved as well as the four quantum numbers
Conservation of quantum numbers
Total before must equal total after.
Except strangeness which is only conserved for strong interactions and SOME weak but not always
Quarks
Up, down and strange
The properties of particles depends on the properties of the quarks it’s made up of
Quark composition of baryons
Made up of three quarks
Charge and baryon number of a baryon is the total charge and baryon number of the particle
Quark composition of mesons
Made up of one quark and one antiquark.
Pions are variation sof up, down, antiup and antidown quarks
Kaons have strangeness so have a strange quark and one other quark
Quark confinement
It isn’t possible to get a quark by itself
Weak interaction
Beta minus decay
Beta plus decay
Beta minus decay (quarks)
A neutron changes into a proton which means that a d quark changes to a u quark
Only weak interaction can do this
Beta plus decay (quarks)
A proton changes to a neutron which means that a u quark changes to a d quark
Particle exchange
virtual particles that only exist for a short time
all forces caused by four fundamental forces each with their own exchange particle
Type of interaction, Gauge boson and particles affected
Strong - Pions - Hadrons only
EM - Virtual photons - Charged particles
Weak - W⁺, W⁻ bosons - All types
Particle interaction diagrams
Exchange particles are wiggly lines
Other particles are straight lines
Incoming start at the botton and move upwards
Baryons stay on one side, leptons on the other
W bosons carry charge from on eside to the other
