Week 1-5 Flashcards
What is spin?
Intrinsic angular momentum (this is restricted to certain values)
When will a particle be a boson (force particles) ?
When it has an integer spin
When will a particle be a fermion (matter particles) ?
When it has a half integer spin
What is the EM force mediated by?
By photons
What is charge?
It is a value which parametrises the amount of interaction
What does the strong force do?
Binds particles (quarks)
What does feel the strong force?
Leptons
If something something is coloured, what does it interact with?
The strong force
Which colours cancel each other out?
Mesons, quarks and anti quarks
What are gauge bosons?
Force carrying particles: photons, weak bosons and gluons
Which properties are conserved?
Electric charge, lepton number, baryon number, colour, quark flavour, energy, momentum and angular momentum
What violates flavour and strangeness?
Weak force
What is not conserved?
Spin and mass
What is an antiparticle?
A corresponding particle which has same mass and all other properties have same magnitude but OPPOSITE SIGN
They travel backwards in time (wrong way through time)
Why can’t the photon be detected?
It is virtual (exchange particle)
What is conserved at each interaction vertex?
Energy and momentum
What can charged particles do?
Emit a photon and reabsorb it, leading to a cloud of virtual photons around any charged particle.
This cloud’s density shows Coulomb’s law (inverse square law)
What is the strong nuclear force?
A strong attractive force which overcomes repulsion and it is felt in the nuclear radius (10^-14m) which is positively charged
it interacts between quarks
What is the range of the strong force?
It has a short range (found using change in x equation)
What is pion exchange?
Quark exchange
What are the characteristics of photons?
They must be off shell
They must be virtual
Give off the same pair as a result
What does Pauli Exclusion require?
An extra degree of freedom
What are the three distinct colours of each quark flavour?
Red, Blue, green
Colours are an extra way of labelling quarks that we have
What do gluons couple to?
Colour and they carry colour (colour and anti colour)
In EM why do charges form their field lines shape?
Due to photons which give rise to the field lines, they don’t interact with each other
How is the strong force confined?
All field lines from one particle reach the other particle unlike EM
What happens as a red and anti red are pulled apart?
Potential energy in system increases linearly due to the constant force and if they are pulled enough apart this will give them enough energy to create a new red and anti red particle which will be closer together
When is the strong force weak?
When short distances are reached (inside a hadron)
What is different about hadrons?
They are colourless (white) and they weigh more than their constituent quarks
What does the weak force not conserve and why?
Do not conserve flavour as weak interactions are allowed between generations
How is the W force worked out on a Feynman diagram?
Charge has to be conserved at each vertex to find which type is needed
Why does the weak force not conserved strangeness?
Due to the cross generational types of interactions being allowed
What impact parameter is expected to give the largest deflection in the alpha particle scattering?
When it is of order of the nucleus radius itself and will lead to a hyperbola path of electron
When does the coulomb repulsion act?
When reasonably close to nucleus (small impact parameter b)
How was the radius of the nucleus found?
Plotting the log of events against the scattering angle and the max angle found is the only non-rare event
What does high energy scattering show?
Uniform charge density
What does the nucleus consist of?
Protons and neutrons but behaves more like an incompressible fluid of nuclear material
What are isobar nuclides?
Nuclides with the same mass/nucleon number (A)
What are isotope nuclides?
Nuclides with the same number of protons (Z)
What are isotone nuclides?
Nuclides with the same number of neutrons (N)
What is the Valley of Stability?
Nuclides further from valley are less stable
How much does binding energy account for in regards to mass?
Around 1 % of the mass
Why are there “magic number” in regards to the more stable nuclei?
They have a higher binding energy than neighbours and lower mass than neighbours
What kind of binding energy do most nuclides have?
Eb/A is around 8Mev
What does the Liquid Drop Model dictate?
It gives three contributions to binding energy
Treats nucleus as drop of charged incompressible fluid
Nearest neighbour interactions only (plus Coulomb)
What are the contributions of the Liquid drop model?
Volume term and surface term
Indicates that there are more interactions at the centre
What is the Fermi Gas Model
It treats nucleons as independent non-interacting Fermi gases
They are free to move in spherically symmetric potential well
Discrete energy levels
Build up from ground state to Fermi energy
What has a deep potential well?
Neutrons as there are typically more neutrons than protons even though they have the same fermi energy
When is the binding energy per nucleon roughly constant?
When A is large
What is fermi energy independent of?
The number of nucleons
What can be assumed about heavy nuclei?
They don’t travel fast so no need to to use relativistic energy
What does asymmetry mean?
Higher energy states (lower binding energy)
