Particle physics

Question 1

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

Answer 1

Proton - uud quarks

Neutron - udd quarks

Question 2

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

Answer 2

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

Question 3

Name the four fundamental forces of nature.

Answer 3

• Gravitational force
• Weak nuclear force
• Strong nuclear force
• Electromagnetic force

Question 4

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

Answer 4

The strong nuclear force

Question 5

Give two properties of the strong nuclear force.

Answer 5

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

- The strongest of all four forces

Question 6

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

Answer 6

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

Gravitational force - infinite range

Question 7

What is nuclear fission?

Answer 7

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.

Question 8

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

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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

Answer 10

Alpha particles and protons are charged but neutrons are neutral.

Question 11

Give an advantage of circular accelerators over linear accelerators.

Answer 11

More compact

Question 12

Give an advantage of circular accelerators over linear accelerators.

Answer 12

More compact (occupy less space)

Question 13

Give the quark composition of the proton.

Answer 13

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

Question 14

List the six flavours of quark.

Answer 14

up, down, top, bottom, charm, strange

Question 15

What is a photon?

Answer 15

A discrete quantity of electromagnetic radiation.

Question 16

List the fundamental forces of nature that pions experience.

Answer 16

• Gravitational force
• The strong nuclear force
• Electromagnetic force
• The weak nuclear force

Question 17

Give the quark composition of a positive pion.

Answer 17

ud (line over d)

Question 18

Give the quark composition of a negative pion.

Answer 18

du (line over u)

Question 19

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

Answer 19

Using a very high voltage

Question 20

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

Answer 20

The alpha particles produced scintillations on the fluorescent screen.

Question 21

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

Answer 21

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

Question 22

List three quantities that are converted in nuclear reactions.

Answer 22

Momentum, charge, mass-energy

Question 23

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

Answer 23

Resolved by proposing the existence of the neutrino.

Question 24

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

Answer 24

• Gravitational
• Weak nuclear
• Electromagnetic
• Strong nuclear

Question 25

What fundamental force is involved in beta-decay?

Answer 25

Weak nuclear

Question 26

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

Answer 26

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

Question 27

What is a positron?

Answer 27

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

Question 28

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

Answer 28

Accelerated using very high voltages.

Question 29

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

Answer 29

They caused scintillations when they hit the fluorescent screen.

Question 30

In a circular accelerator, why is the tube evacuated?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

They are more compact, take up less space.

Question 34

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

Answer 34

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

Question 35

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

Answer 35

Needed to overcome the force of repulsion between the positrons.

Question 36

How are charged particles given high speeds?

Answer 36

Particle accelerators are used to give these high speeds.

Question 37

Explain why two positrons cannot annihilate each other in collision?

Answer 37

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

Question 38

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

Answer 38

By ionization in the hydrogen discharge tube.

Question 39

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

Answer 39

Using very high voltages.

Question 40

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

Answer 40

They produced scintillations when they hit the fluorescent screen.

Question 41

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

Answer 41

They produced scintillations when they hit the zinc sulphide screen.

Question 42

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

Answer 42

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

Question 43

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

Answer 43

Neutrino - it had the missing energy and momentum.

Question 44

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

Answer 44

It had a very small mas and no charge.

Question 45

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

Answer 45

- muon | - tau

Question 46

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

Answer 46

- Strong nuclear force - Electromagnetic force - Weak nuclear force

Question 47

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

Answer 47

- Electromagnetic force - Weak nuclear force - Gravitational force

Question 48

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

Answer 48

- Baryons - composed of 3 quarks | - Mesons - composed of 1 quark and 1 antiquark

Question 49

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

Answer 49

A magnetic field is used to provide the centripetal force.

Question 50

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

Answer 50

More compact

Question 51

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

Answer 51

To obey the conservation of charge.

Question 52

Give the composition of the π0.

Answer 52

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

Question 53

Give a use for particle accelerators.

Answer 53

- To perform transmutations | - To make other particles as a result of collision.

Question 54

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

Answer 54

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.

Question 55

What happens when electrons and positrons collide?

Answer 55

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

Question 56

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

Answer 56

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

Question 57

What happens when an electron meets a positron?

Answer 57

Annihilation happens (all mass is converted to energy).

Question 58

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

Answer 58

x

Question 59

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

Answer 59

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

Question 60

Name the three positively charged quarks.

Answer 60

Up, top, charm.

Question 61

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

Answer 61

Baryon - three quarks | Meson - 1 quark and 1 antiquark

Question 62

What is the quark composition of the proton?

Answer 62

up, up, down

Question 63

What is the net charge of the three pions?

Answer 63

Zero - conservation of charge

Question 64

What is anti-matter?

Answer 64

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

Question 65

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

Answer 65

Positron | symbol - e(+)

Question 66

What happens when a particle meets its anti-particle?

Answer 66

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

Question 67

What is meant by pair production?

Answer 67

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

Question 68

What famous Irish writer first thought up the name 'quark'?

Answer 68

James Joyce

Question 69

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.

Answer 69

- 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)

Question 70

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.

Answer 70

- 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)

Question 71

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

Answer 71

e(+) + e(-) → y + y

Question 72

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

Answer 72

As mass is converted to energy.

Question 73

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

Answer 73

To conserve the momentum.

Question 74

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

Answer 74

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.

Question 75

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

Answer 75

- Gravitational force - Weak nuclear force - Electromagnetic force

Question 76

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

Answer 76

So that momentum could be conserved.

Question 77

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

Answer 77

11C6 → 11B5 + 0e-1 (+v(small e)

Question 78

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

Answer 78

tau, muon (pg 48)

Question 79

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

Answer 79

The quark

Question 80

Are protons and neutrons fundamental particles?

Answer 80

NO

Question 81

What is the principle force that neutrinos experience?

Answer 81

Weak nuclear force.

Question 82

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

Answer 82

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

Question 83

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

Answer 83

Neutrino has no charge and very small mass.

Question 84

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

Answer 84

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

Question 85

What is a positron?

Answer 85

A positively charged electron. The antiparticle of the electron.

Question 86

Why are protons always produced in pairs during pair annihilation?

Answer 86

To obey the law of the conservation of momentum.