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13 old > Particle Physics > Flashcards

Particle Physics Flashcards

To revise particle physics

1
Q

Describe the nuclear model of the atom

A

A positive nucleus containing protons and neutrons with electrons found in shells orbiting the nucleus

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2
Q

State the relative charge of all sub atomic particles

A

Proton +1

Neutron 0

Electron -1

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3
Q

State the relative masses of all sub atomic particles

A

Proton 1

Neutron 1

Electron almost 0 (1/1840)

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4
Q

How can you calculate the specific charge? Giving all units

A

Specific charge (C/kg) = charge (C) / mass (kg)

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5
Q

Define atomic (proton number)

A

The number of protons in a nucleus = the number of electrons for an uncharged atom

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6
Q

Define nucleon number

A

The number of nucleons (protons + neutrons)

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7
Q

Define an isotope

A

An isotope is the same element with the same number of protons but different number of neutrons

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8
Q

Why is the strong nuclear force important?

A

It keeps nucleus stable

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9
Q

Sketch a graph of force against seperation for the strong nucear force.

A

Must be attractive and repulsive at different distance.

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10
Q

When is the strong nuclear force attractive

A

up to approximately 3 fm

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11
Q

When is the strong nuclear force repulsive

A

A distances closer than 0.5 fm

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12
Q

Describe some properties of the strong nuclear force

A
  1. Very strong - overcomes repulsion between positive protons
  2. Very short range - only acts between adjacent nucleons
  3. Acts on any nucleon (proton or neutron) and is independent of charge
  4. Can be attractive or repulsive Is repulsive if nucleons gets too close - stops nuclei collapsing
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13
Q

How does the strong nuclear force cause particles to be in equilibrium?

A

Increase in nucleon separation leads to an attractive force Decrease in nucleon separation leads to a repulsive force In both situations, force will return nucleons back to equilibrium position.

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14
Q

What are the three types of radioactive decay?

A
  1. Alpha
  2. Beta
  3. Gamma
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15
Q

Describe an alpha particle

A
  1. 2 protons and 2 neutrons or aHelium nucleus
  2. Relative mass of 4
  3. Relative charge of +2
  4. highly ionising
  5. Stopped by skin, paper, 5 - 10 cm of air
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16
Q

Describe a beta particle

A
  1. fast moving electron ejected from the nucleus
  2. Relative mass of almost 0
  3. Relative charge of -1
  4. moderately
  5. ionising Stopped by mm’s aluminium or 1 meter of air
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17
Q

Describe a gamma wave

A
  1. Electromagnetic wave that moves at the speed of light through a vacuum
  2. Relative mass of 0
  3. Relative charge of 0
  4. very weakly ionising
  5. Reduced by cm’s lead or m’s of concrete
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18
Q

Describe the changes that take place in beta decay

A

A neutron decays into a proton creating the beta particle and an electron antineutrino.

For a neutron to decay into a proton a down quark decays into a up quark

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19
Q

Describe the evidence that neutrinos exist

A
  1. Experimental data shows that as a beta particle is emitted in beta decay it will have a range of energies from nearly zero up to a maximum.
  2. All decays must have the same energy (conservation of energy)
  3. The total energy and momentum of the beta particle and recoiling nucleus was not constant.
  4. Energy has to be conserved Wolfgang pauli (1930) predicted a particle that could carry away the extra energy/momentum so they would be conserved. This particle was discovered and named the antineutrino
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20
Q

Describe the changes that take place in positron emission

A

A proton decays into a neutron creating the positron and an electron neutrino.

For a proton to decay into a neutron a up quark decays into a down quark.

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21
Q

Why does an antineutrino need to be released during beta decay

A

To conserve, energy, momentum and lepton number

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22
Q

Define a fundamental particle

A

Fundamental particles cannot be divided into other particles. They have no internal structure.

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23
Q

Give some examples of fundamental particles

A

Electron, neutrino, all quarks

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24
Q

What are the 6 types of quark

A
  1. Up
  2. down
  3. top
  4. bottom
  5. strange
  6. charm
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25
Q

What is the quark structure of a proton?

A

u u d

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26
Q

What is the quark structure of a neutron?

A

u d d

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27
Q

What is an antiparticle

A

particles with the same mass but opposite charge

28
Q

State the name of the anti electron

A

Positron

29
Q

Define a hadron

A

Hadrons are any particle made up of quarks.

Hadrons are not fundamental.

Hadrons can be either Baryons or mesons.

30
Q

What force are hadrons subject to?

A

Strong nuclear force

31
Q

Define a baryon

A

Baryons are made up of three quarks.

Common baryons are protons and neutrons and have a baryon number of 1

32
Q

Which is the most stable baryon?

A

Proton

33
Q

Define a meson

A

Mesons are classified as hadrons as they are made of quarks. Mesons contain a quark and an antiquark have a baryon number of 0

34
Q

Name some typical mesons

A

Pions and Kaons

35
Q

Name some leptons

A

Electrons, neutrinos, Tau, muon

36
Q

What force controls leptons?

A

Leptons are subject to the weak nuclear force

37
Q

In a nuclear event what must be conserved?

A
  1. Charge
  2. Baryon number
  3. Lepton number
  4. Energy
  5. Momentum
38
Q

What force of nature creates strange particles?

A

Strange particles are made through the strong interaction

39
Q

What force allows strange particles to decay?

A

Strange particles decay through the weak interaction (e.g. Kaons)

40
Q

Why must strange particles be created in pairs?

A

To conserve strangness

41
Q

When must strangeness be conserved?

A

When strange particles are made in pairs. Strangeness is conserved with the strong interaction (only the weak interaction can change the type of quark, so there must be the same number of strange particles before and after)

42
Q

When can strangeness change?

A

Strangeness can change by +1, 0 or -1 in the weak interaction when a strange particles decay

43
Q

Define annihilation

A

If a particle and anti-particle meet they will annihilate each other and their entire mass is converted into energy into the form of two identical gamma photons (e.g PET scanners)

44
Q

During annihilation what is the minimum energy of one the gamma photons equal to?

A

The rest mass of one of the original particles

Minimum energy of each photon = Eo

45
Q

Define pair production

A

In pair production a single photon vanishes and its energy is converted into mass in the form of a particle and its anti-particle.

46
Q

What is the condition required for pair production?

A

This can only happen if the energy of the photon is enough to produce the (rest) mass of the particle and anti particle.

Min energy of photon = 2Eo

This normally happens near a nucleus to conserve momentum.

47
Q

In pair productin what happens if the initial photon has an energy greater than the rest mass of the particels and anti particle?

A

The particle and anti particle take the extra energy away as kinetic energy

48
Q

What is quark confinement?

A

The energy required to produce a separation of two quarks far exceeds the pair production energy of a quark-antiquark pair, so instead of pulling out an isolated quark, you produce mesons as the produced quark-antiquark pairs combine.

49
Q

Define an exchange particle

A

Exchange particles are how forces act between two particles.

They are virtual particles and only exist for a very short amount of time.

They can transfer energy, charge force and momentum

50
Q

For the strong nuclear force state:

the particles affected

the name of the exchange particle

its range

A

Nucleons (all hadrons)

Gluons and Pions

Range up to 3 fm

51
Q

For the electromagnetic force state:

the particles affected

the name of the exchange particle

Range

A

Charged particles

Virtual photons

infinite range

52
Q

For the weak nuclear force state:

the particles affected

the name of the exchange particle

Range

A

Responsible for beta decay and changing quarks e.g u to d

W+, W- bosons

10-18 m

53
Q

For the gravitational force state:

the particles affected

the name of the exchange particle

Range

A

all particles with mass

Gravitron

Infinite

54
Q

What are the rules for drawing particle interaction diagrams

A

Rules for drawing particle interaction diagrams:

  1. Exchange particles are represented by wiggly lines
  2. Other particles are represented by straight lines
  3. Incoming particles start at the bottom of the diagram and move upwards
  4. Baryons stay on one side of the diagram and leptons on the other
  5. The W boson carries charge from one side to the other (make sure charges balance)
  6. A W- particle going to the left has the same effect as a W+ moving to the right
55
Q

What is electron capture?

A

Electron capture is a process in which the proton-rich nucleus absorbs an electron. This process thereby changes a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino

56
Q

What is an electron-proton collision?

A

An electron collides at high speed with a proton. The proton decays into a neutron and an electron neutrino.

57
Q

What are the similarities and differences between electron capture and electron-proton collisions?

A

Similarities - both change a nuclear proton to a neutron and simultaneously causes the emission of an electron neutrino

Differences - In electron-proton collision the electron is the particle thats acting because its being fired at a proton so the W boson comes from the elctron. It must be the W- (moving to the left) to conserve charge. With electron capture the exchange particel is the W+(moving to the right)

58
Q

Sketch and label a Feyman diagram for electron repulsion.

A

See diagram

59
Q

Sketch and label a Feyman diagram for beta decay (in terms of protons and neutrons)

A

See diagram

60
Q

Sketch and label a Feyman diagram for beta decay (in terms of quarks)

A

See diagram

61
Q

Sketch and label a Feyman diagram for positron emmision (in terms of protons and neutrons)

A

see diagram

62
Q

Sketch and label a Feyman diagram for beta decay (in terms of quarks)

A

See diagram

63
Q

Sketch and label a Feyman diagram for electron capture

A

see diagram

64
Q

Sketch and label a Feyman diagram for electron - proton collision

A

see diagram

65
Q

Sketch and label a feyman diagram for a neutrino and neutron interaction where a beta particle and proton are created

A

See diagram

66
Q

Sketch and label a feyman diagram for a antineutrino and proton interaction where a positron and neutron are created

A

see diagram

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