Week 1-5

Question 1

What is spin?

Answer 1

Intrinsic angular momentum (this is restricted to certain values)

Question 2

When will a particle be a boson (force particles) ?

Answer 2

When it has an integer spin

Question 3

When will a particle be a fermion (matter particles) ?

Answer 3

When it has a half integer spin

Question 4

What is the EM force mediated by?

Answer 4

By photons

Question 5

What is charge?

Answer 5

It is a value which parametrises the amount of interaction

Question 6

What does the strong force do?

Answer 6

Binds particles (quarks)

Question 7

What does feel the strong force?

Answer 7

Leptons

Question 8

If something something is coloured, what does it interact with?

Answer 8

The strong force

Question 9

Which colours cancel each other out?

Answer 9

Mesons, quarks and anti quarks

Question 10

What are gauge bosons?

Answer 10

Force carrying particles: photons, weak bosons and gluons

Question 11

Which properties are conserved?

Answer 11

Electric charge, lepton number, baryon number, colour, quark flavour, energy, momentum and angular momentum

Question 12

What violates flavour and strangeness?

Answer 12

Weak force

Question 13

What is not conserved?

Answer 13

Spin and mass

Question 14

What is an antiparticle?

Answer 14

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)

Question 15

Why can’t the photon be detected?

Answer 15

It is virtual (exchange particle)

Question 16

What is conserved at each interaction vertex?

Answer 16

Energy and momentum

Question 17

What can charged particles do?

Answer 17

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)

Question 18

What is the strong nuclear force?

Answer 18

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

Question 19

What is the range of the strong force?

Answer 19

It has a short range (found using change in x equation)

Question 20

What is pion exchange?

Answer 20

Quark exchange

Question 21

What are the characteristics of photons?

Answer 21

They must be off shell
They must be virtual
Give off the same pair as a result

Question 22

What does Pauli Exclusion require?

Answer 22

An extra degree of freedom

Question 23

What are the three distinct colours of each quark flavour?

Answer 23

Red, Blue, green

Colours are an extra way of labelling quarks that we have

Question 24

What do gluons couple to?

Answer 24

Colour and they carry colour (colour and anti colour)

Question 25

In EM why do charges form their field lines shape?

Answer 25

Due to photons which give rise to the field lines, they don't interact with each other

Question 26

How is the strong force confined?

Answer 26

All field lines from one particle reach the other particle unlike EM

Question 27

What happens as a red and anti red are pulled apart?

Answer 27

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

Question 28

When is the strong force weak?

Answer 28

When short distances are reached (inside a hadron)

Question 29

What is different about hadrons?

Answer 29

They are colourless (white) and they weigh more than their constituent quarks

Question 30

What does the weak force not conserve and why?

Answer 30

Do not conserve flavour as weak interactions are allowed between generations

Question 31

How is the W force worked out on a Feynman diagram?

Answer 31

Charge has to be conserved at each vertex to find which type is needed

Question 32

Why does the weak force not conserved strangeness?

Answer 32

Due to the cross generational types of interactions being allowed

Question 33

What impact parameter is expected to give the largest deflection in the alpha particle scattering?

Answer 33

When it is of order of the nucleus radius itself and will lead to a hyperbola path of electron

Question 34

When does the coulomb repulsion act?

Answer 34

When reasonably close to nucleus (small impact parameter b)

Question 35

How was the radius of the nucleus found?

Answer 35

Plotting the log of events against the scattering angle and the max angle found is the only non-rare event

Question 36

What does high energy scattering show?

Answer 36

Uniform charge density

Question 37

What does the nucleus consist of?

Answer 37

Protons and neutrons but behaves more like an incompressible fluid of nuclear material

Question 38

What are isobar nuclides?

Answer 38

Nuclides with the same mass/nucleon number (A)

Question 39

What are isotope nuclides?

Answer 39

Nuclides with the same number of protons (Z)

Question 40

What are isotone nuclides?

Answer 40

Nuclides with the same number of neutrons (N)

Question 41

What is the Valley of Stability?

Answer 41

Nuclides further from valley are less stable

Question 42

How much does binding energy account for in regards to mass?

Answer 42

Around 1 % of the mass

Question 43

Why are there "magic number" in regards to the more stable nuclei?

Answer 43

They have a higher binding energy than neighbours and lower mass than neighbours

Question 44

What kind of binding energy do most nuclides have?

Answer 44

Eb/A is around 8Mev

Question 45

What does the Liquid Drop Model dictate?

Answer 45

It gives three contributions to binding energy Treats nucleus as drop of charged incompressible fluid Nearest neighbour interactions only (plus Coulomb)

Question 46

What are the contributions of the Liquid drop model?

Answer 46

Volume term and surface term | Indicates that there are more interactions at the centre

Question 47

What is the Fermi Gas Model

Answer 47

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

Question 48

What has a deep potential well?

Answer 48

Neutrons as there are typically more neutrons than protons even though they have the same fermi energy

Question 49

When is the binding energy per nucleon roughly constant?

Answer 49

When A is large

Question 50

What is fermi energy independent of?

Answer 50

The number of nucleons

Question 51

What can be assumed about heavy nuclei?

Answer 51

They don't travel fast so no need to to use relativistic energy

Question 52

What does asymmetry mean?

Answer 52

Higher energy states (lower binding energy)