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Physics > Particle physics > Flashcards

Particle physics Flashcards

1
Q

Give the composition of the proton and the neutron in terms of quarks.

A

Proton - uud quarks

Neutron - udd quarks

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2
Q

List three fundamental forces of nature and give one property of each.

A

Strong nuclear force - range of 1 x 10(-15)m
Weak nuclear force - range of 1 x 10(-18)m
Gravitational force - infinite range

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3
Q

Name the four fundamental forces of nature.

A
  • Gravitational force
  • Weak nuclear force
  • Strong nuclear force
  • Electromagnetic force
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4
Q

Which fundamental force of nature is responsible for binding the nucleus of an atom?

A

The strong nuclear force

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5
Q

Give two properties of the strong nuclear force.

A
  • a range of the orrder of 1 x 10(-15)m

- The strongest of all four forces

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6
Q

Beta decay is associated with the weak nuclear force. List two other fundamental forces of nature and give one property of each force.

A

Strong nuclear force - range of the order of 1 x 10(-15)

Gravitational force - infinite range

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7
Q

What is nuclear fission?

A

The splitting of a larger nucleus into two smaller nuclei into two smaller nuclei with the emission of neutrons and the change in mass being converted to energy.

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8
Q

What is the function of the moderator in the first nuclear reactor?

A

Slows down the emitted fast neutrons to a speed suitable for further fission.

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9
Q

How did the cadmium rods control the rate of fission (first nuclear reactor)?

A

Can absorb the neutrons and prevent them from causing further fission. This controls the rate of fission in the reactor.

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10
Q

High voltages can be used to accelerate alpha particles and protons but not neutrons. Explain why.

A

Alpha particles and protons are charged but neutrons are neutral.

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11
Q

Give an advantage of circular accelerators over linear accelerators.

A

More compact

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12
Q

Give an advantage of circular accelerators over linear accelerators.

A

More compact (occupy less space)

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13
Q

Give the quark composition of the proton.

A

uud (up, up, down) are the three quarks that make up a proton.

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14
Q

List the six flavours of quark.

A

up, down, top, bottom, charm, strange

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15
Q

What is a photon?

A

A discrete quantity of electromagnetic radiation.

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16
Q

List the fundamental forces of nature that pions experience.

A
  • Gravitational force
  • The strong nuclear force
  • Electromagnetic force
  • The weak nuclear force
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17
Q

Give the quark composition of a positive pion.

A

ud (line over d)

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18
Q

Give the quark composition of a negative pion.

A

du (line over u)

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19
Q

In Cockcroft and Walton’s experiment, how were the protons accelerated?

A

Using a very high voltage

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20
Q

In Cockcroft and Walton’s experiment, how were the alpha particles detected?

A

The alpha particles produced scintillations on the fluorescent screen.

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21
Q

In Cockcroft and Walton’s experiment, explain why new particles are formed.

A

The kinetic energy of the accelerated protons is converted into mass.

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22
Q

List three quantities that are converted in nuclear reactions.

A

Momentum, charge, mass-energy

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23
Q

In initial observations of beta-decay, not all three quantities appear to be observed. What was the solution to this contradiction?

A

Resolved by proposing the existence of the neutrino.

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24
Q

List the fundamental forces of nature in increasing order of their strength.

A
  • Gravitational
  • Weak nuclear
  • Electromagnetic
  • Strong nuclear
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25
Q

What fundamental force is involved in beta-decay?

A

Weak nuclear

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26
Q

In Cockcroft and Walton’s experiment, why were new particles produced in the collision?

A

Some of the energy of the protons is converted to mass.

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27
Q

What is a positron?

A

The antiparticle of the electron and it has a positive charge.

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28
Q

In Cockcroft and Walton’s experiment, how did they accelerate the protons?

A

Accelerated using very high voltages.

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29
Q

In Cockcroft and Walton’s experiment, how did they detect the alpha particles?

A

They caused scintillations when they hit the fluorescent screen.

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30
Q

In a circular accelerator, why is the tube evacuated?

A

So that the high speed protons do not collide with gas particles. These collisions would slow down the high speed protons.

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31
Q

In a circular accelerator, what is the purpose of accelerating the particles to high velocities?

A

Allow the protons to overcome the repulsive force between them. They can join together and produce new particles.

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32
Q

In a circular accelerator, what is the purpose of the magnets?

A

The magnets contain the protons in a circular path and prevent them hitting the side walls of the tube.

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33
Q

Give an advantage of a circular accelerator over a linear accelerator.

A

They are more compact, take up less space.

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34
Q

Can an accelerator of the circular accelerator be used to accelerate neutrons? Explain your answer.

A

No. Neutrons have no charge and therefore are not affected by electric or magnetic fields.

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35
Q

Why must two positrons travel at high speeds so as to collide with each other?

A

Needed to overcome the force of repulsion between the positrons.

36
Q

How are charged particles given high speeds?

A

Particle accelerators are used to give these high speeds.

37
Q

Explain why two positrons cannot annihilate each other in collision?

A

Only a particle and an antiparticle can annihilate each other. Two positrons would both be antiparticles.

38
Q

In Cockcroft and Walton’s experiment, how were the protons produced?

A

By ionization in the hydrogen discharge tube.

39
Q

In Cockcroft and Walton’s experiment, how were the protons accelerated?

A

Using very high voltages.

40
Q

In Cockcroft and Walton’s experiment, how were the alpha-particles detected?

A

They produced scintillations when they hit the fluorescent screen.

41
Q

In Cockcroft and Walton’s experiment, how were the alpha-particles detected?

A

They produced scintillations when they hit the zinc sulphide screen.

42
Q

Explain the historical significance of Cockcroft and Walton’s experiment.

A

The first verification of Einstein’s equation, E = mc2

43
Q

Name the particle which Pauli predicted and explain how it solved the problem.

A

Neutrino - it had the missing energy and momentum.

44
Q

Why did Pauli think that the Neutrino couldn’t be detected?

A

It had a very small mas and no charge.

45
Q

Electrons are negatively charged leptons, light two other negatively charged leptons.

A
  • muon

- tau

46
Q

List three factors that muon and tau can experience, in decreasing order of strength.

A
  • Strong nuclear force
  • Electromagnetic force
  • Weak nuclear force
47
Q

List three factors that muon and tau can experience, in decreasing order of strength.

A
  • Electromagnetic force
  • Weak nuclear force
  • Gravitational force
48
Q

There are two families of hadrons, name the two families and distinguish them.

A
  • Baryons - composed of 3 quarks

- Mesons - composed of 1 quark and 1 antiquark

49
Q

The large hadron collider is a circular accelerator. How are the protons maintained in circular motion.

A

A magnetic field is used to provide the centripetal force.

50
Q

State the principle advantage of a circular accelerator over a linear accelerator.

A

More compact

51
Q

A neutral pion and two protons remain after the collision. The single pion produced must be neutral. Explain why.

A

To obey the conservation of charge.

52
Q

Give the composition of the π0.

A

uu (line over 2nd u) or dd (line over 2nd d)

53
Q

Give a use for particle accelerators.

A
  • To perform transmutations

- To make other particles as a result of collision.

54
Q

In the CERN, why are the electrons and positrons introduced in opposite directions?

A

Both the electrons and the positrons will move in circular motion in the magnetic field, one clockwise and the other anti-clockwise, as they have opposite charges. This allows a head-on collision to occur between the electrons and the positrons.

55
Q

What happens when electrons and positrons collide?

A

The particles annihilate each other (all their mass turns into energy). Two gamma rays will be produced.

56
Q

Compare the properties of an electron with that of a positron.

A
  • Electron has a negative charge while positron has a positive charge.
  • Have the same mass
  • The electron - matter, positron - anti-matter
57
Q

What happens when an electron meets a positron?

A

Annihilation happens (all mass is converted to energy).

58
Q

In beta decay it appeared that momentum was not conserved. How did Fermi’s theory of radioactive decay resolve this?

A

x

59
Q

List the four fundamental forces and state the range of each one.

A
  • Gravitational force - infinite range
  • Electromagnetic force - infinite range
  • Strong nuclear charge - 1 x 10(-15) m
  • Weak nuclear charge - 1 x 10(-18)m
60
Q

Name the three positively charged quarks.

A

Up, top, charm.

61
Q

What is the difference in the quark composition of a baryon and a meson?

A

Baryon - three quarks

Meson - 1 quark and 1 antiquark

62
Q

What is the quark composition of the proton?

A

up, up, down

63
Q

What is the net charge of the three pions?

A

Zero - conservation of charge

64
Q

What is anti-matter?

A

A particle with the same mass as another particle but with the opposite charge. Both particles have the same magnitude of charge.

65
Q

An anti-matter particle was first discovered during the study of cosmic rays in 1932. Name the anti-particle and give its symbol.

A

Positron

symbol - e(+)

66
Q

What happens when a particle meets its anti-particle?

A

They annihilate each other and the total mass of both is converted to energy.

67
Q

What is meant by pair production?

A

Occurs when the energy of a y-ray is converted to a particle and its corresponding anti-particle.

68
Q

What famous Irish writer first thought up the name ‘quark’?

A

James Joyce

69
Q

A member of a meson family consists of two particles. Each particle is composed of up and down quarks and their anti-particles. Construct the possible combinations Deduce the charge of each combination and identify each combination.

A
  • Pi-plus π(+), charge of +1, composed of u + d (line over d)
  • Pi-minus π(-), charge of -1, composed of u + d (line over u)
  • Pi-zero π(0), no charge, composed of u + u (line over 2nd u)
  • Pi-zero, no charge, composed of d + d (line over 2nd d)
70
Q

A member of a meson family consists of two particles. Each particle is composed of up and down quarks and their anti-particles. Construct the possible combinations Deduce the charge of each combination and identify each combination.

A
  • Pi-plus π(+), charge of +1, composed of u + d (line over d)
  • Pi-minus π(-), charge of -1, composed of u + d (line over u)
  • Pi-zero π(0), no charge, composed of u + u (line over 2nd u)
  • Pi-zero, π(0) no charge, composed of d + d (line over 2nd d)
71
Q

When a positron and an electron meet two photons are produced. Write an equation to represent this interaction.

A

e(+) + e(-) → y + y

72
Q

Why are protons produced in the interaction between a positron and an electron meeting two photons?

A

As mass is converted to energy.

73
Q

Explain why are two protons are produced in the interaction between a positron and an electron meeting two photons?

A

To conserve the momentum.

74
Q

Explain why the photons produced usually have a greater frequency than your calculated minimum frequency value.

A

The electron and positron would have kinetic energy before the collision. Some of this kinetic energy is given to the photons which increase the frequency.

75
Q

Electrons are leptons. List the three fundamental forces that electrons experience in increasing order of strength.

A
  • Gravitational force
  • Weak nuclear force
  • Electromagnetic force
76
Q

Why do the photons produced in pair annihilation travel in opposite directions?

A

So that momentum could be conserved.

77
Q

Write a nuclear equation to represent the decay of carbon-11.

A

11C6 → 11B5 + 0e-1 (+v(small e)

78
Q

Electrons are members of the lepton family. Name two other leptons.

A

tau, muon (pg 48)

79
Q

Name one fundamental particle that is subject to the strong nuclear force.

A

The quark

80
Q

Are protons and neutrons fundamental particles?

A

NO

81
Q

What is the principle force that neutrinos experience?

A

Weak nuclear force.

82
Q

Pauli proposed that a neutrino is emitted during beta-decay. Why did he make this proposal?

A

Because without the neutrino it would appear that during beta-decay, momentum is not conserved and energy is not conserved.

83
Q

An electron can be detected in a cloud chamber. However it is much more difficult to detect a neutrino. Explain why.

A

Neutrino has no charge and very small mass.

84
Q

Describe the path of a neutrino in the same magnetic field.

A

The neutrino passes straight through the magnetic field. There is no deviation in its direction of travel as it is neutral.

85
Q

What is a positron?

A

A positively charged electron. The antiparticle of the electron.

86
Q

Why are protons always produced in pairs during pair annihilation?

A

To obey the law of the conservation of momentum.

Physics (12 decks)

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