1.7 Particles and Nuclear Structure

Question 1

What are the main constituents of an atom?

Answer 1

● Proton
● Neutron
● Electron

Question 2

What is the letter associated with a proton number?

Answer 2

Z

Question 3

What is a nucleon?

Answer 3

A constituent of the nucleus: a proton or a neutron.

Question 4

What letter represents nucleon number?

Answer 4

A

Question 5

What is the strong nuclear force?

Answer 5

The fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons.

Question 6

Describe the range of the strong force.

Answer 6

Repulsive up to 0.5fm
Attractive from 0.5-3fm
Negligible past 3fm

Question 7

What makes a nucleus unstable?

Answer 7

● Nuclei which have too many protons, neutrons, or both.
●Too many protons means the electrostatic force is too strong and pushes them apart.
●Too many neutrons or both will make the nucleus larger than the range of the strong force, so it will no longer be held together.

Question 8

What is an antiparticle?

Answer 8

For each particle there is an antiparticle which has the same rest energy and mass, the opposite charge, and will annihilate with the particle if they ever come into contact.

Question 9

True or false?
‘Every fundamental particle has a antiparticle’.

Answer 9

True.

Question 10

What is the name of the antiparticle of an electron?

Answer 10

Positron.

Question 11

What is the antiparticle of π0 (pion with neutral charge)?

Answer 11

π0, its antiparticle is itself

Question 12

Explain the process of annihilation.

Answer 12

● When a particle and its corresponding antiparticle come into contact with each other, they will annihilate
● The mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which are released in opposite directions in order to conserve momentum.

Question 13

What is pair production?

Answer 13

When a gamma photon has sufficient energy, it can be converted into a corresponding particle-antiparticle pair.

Question 14

Name the 4 fundamental forces.

Answer 14

● Gravity
● Electromagnetic/electrostatic
● Weak nuclear
● Strong nuclear

Question 15

The virtual photon is the exchange particle of which force?

Answer 15

The electromagnetic force.

Question 16

What type of particles are affected by the strong nuclear force?

Answer 16

Hadrons

Question 17

What is the exchange particle of the weak nuclear force?

Answer 17

The W boson (W+ or W-).

Question 18

What does the electromagnetic force act on?

Answer 18

It acts on all charged objects.
For example: when a positively charged ball repels another positively charged ball.

Question 19

When does the weak nuclear interaction occur?

Answer 19

When quark character changes (a quark changes into another quark). It affects all types of particles.

Question 20

Which properties must be conserved in particle interactions?

Answer 20

● Energy
● Charge
● Baryon number
●Lepton number (treat electrons and muons separately)
● Momentum
●Strangeness (only in strong interactions - it can change by ±1 in weak interactions.)

Question 21

What is a lepton?

Answer 21

A fundamental particle that is not made of quarks and does not experience the strong nuclear force (electrons, neutrinos and muons).

Question 22

What is a hadron?

Answer 22

A particle made of quarks that are held together by the strong force. Mesons and baryons are hadrons.

Question 23

What are the classes of hadrons?

Answer 23

● Baryons (three quarks)
● Mesons (1 quark, 1 antiquark)

Question 24

The pion and kaon are both examples of which class of particle?

Answer 24

Mesons

Question 25

The pion can be an exchange particle for which force?

Answer 25

The strong nuclear force.

Question 26

What does a kaon decay into?

Answer 26

Pions.

Question 27

Give some examples of baryons.

Answer 27

Proton - uud quark composition
Neutron - udd quark composition

Question 28

What is significant about a proton?

Answer 28

● It is the only stable baryon.
● All baryons will eventually decay into
protons.

Question 29

Give some example of leptons.

Answer 29

● Electron
● Muon
● Neutrino
● (the antiparticles of the above)

Question 30

What does a muon decay into?

Answer 30

An electron, muon neutrino and electron antineutrino.

Lepton number for electrons is zero before and after, and the lepton number for muons is 1 before and after.

Question 31

What is the strangeness value of a strange quark?

Answer 31

-1

Question 32

True or false? ‘Strangeness is always conserved in a weak interaction.

Answer 32

False.
Strangeness is only conserved in the strong interaction. In weak interactions it can change by 0, -1 or +1

Question 33

Complete the sentence: Strange particles are produced through the
____ interaction and decay through the ____ interaction.

Answer 33

Strange particles are particles that are produced through the strong interaction and decay through the weak interaction.

Question 34

State the relative charge for an electron, electron neutrino, an up quark and a down quark.

Answer 34

Electron: -1 Electron neutrino: 0 Up quark: +2⁄3 Down quark: -1⁄3

Question 35

What is the symbol for a positron?

Answer 35

e+ (or sometimes β+ in the context of beta decay)

Question 36

What is the symbol for an anti-up quark?

Answer 36

u (with bar)

Question 37

What is the quark composition of a proton and neutron?

Answer 37

Proton: uud Neutron: udd (or ddu)