Topic 8: Nuclear And Particle Physics

Question 1

What are the 3 constituents an atom is formed of?

Answer 1

An atom is formed of protons, neutrons and electrons.

Question 2

What is a nucleon?

Answer 2

At the centre of the atom is a nucleus formed of protons and neutrons; these are nucleons.
Not electrons as they orbit the nucleus in shells.

Question 3

What is the proton and nucleon number?

Answer 3

The proton number is the number of protons in an atom. (Bottom number)
Nucleon number is the number of nucleons (protons and neutrons) in an atom. (Top number)

Question 4

What does the Rutherford’s gold foil experiment consist of?

Answer 4

Rutherford’s gold foil experiment consists of;
- Alpha particle source and gold foil (malleable and thinnest metal)
-in excavated chamber
-covered in fluorescent coating (to see where particles hit in the chamber)

Question 5

What were the observations and conclusion of Rutherford’s gold foil experiment?

Answer 5

1) Most alpha particles passed straight through — Atom is mainly empty space
2) Some alpha particles deflected at slight angle — centre of atom is positively charged as positive alpha was deflected from the centre.
3) Very few deflected at <90° — centre of atom was very small but very dense as very small amount of particles deflected at large angle and could deflect fast moving particles

Results showed the atom has a small, dense, positively charged nucleus in the centre.

Question 6

What is thermionic emissions?

Answer 6

Thermionic emission is when a metal is heated via a current until the free electrons gain enough energy to leave the surface.

Question 7

What are the properties that must always be conserved during particle interactions?

Answer 7

During particle interaction; following properties must be conserved
- Charge
- Momentum
- Energy

Question 8

What is a bubble chamber?

Answer 8

A bubble chamber is a t tank filled with superheated liquid hydrogen which forms bubbles around any ionised particles created as a result of movement of charged particles.

Question 9

What is the purpose of a bubble chamber?

Answer 9

Using a bubble chamber, you can observe the path taken by moving, charged particles.

Question 10

What can you tell from a track in a bubble chamber stopping, changing direction or coming from nothing?

Answer 10

Track suddenly stops - particles collided
Track changes direction - Particles have collided
Tracks come from nothing - particles created from uncharged particle (photon)

Question 11

What is de Broglie’s relation + formula?

Answer 11

de Broglie’s relation shows that a particle’s wavelength and momentum are inversely proportional
λ = h/p

λ - de Broglie’s wavelength
h - Planck constant
p - momentum of particle

Question 12

What does de Broglie’s relation tell you?

Answer 12

The smaller the de Broglie wavelength, the higher energy/momentum of the particle required.

Question 13

Why are high energies needed to investigate structure of nucleons?

Answer 13

Nucleons are incredibly small
- need to use very small wavelengths
- so particles have extremely high energies

Question 14

What did the theory of special relativity prove?

Answer 14

Mass and energy are interchangeable
ΔE = Δmc²

Question 15

What is pair production?

Answer 15

Pair production is when a photon is coverted into an equal amount of matter and antimatter.

Question 16

What are the conditions for pair production to occur?

Answer 16

For pair production to occur;
- initial photon has an energy greater than the total rest energy of both particles
- excess energy converted into kinetic energy for particles

Question 17

What is annihilation?

Answer 17

Annihilation is when a particle and its corresponding particle collide.

Question 18

What are the results of annihilation?

Answer 18

Their masses are converted to energy and released in the form of 2 photons moving in opposite directions in order to conserve momentum.

Question 19

What is an electronvolt?

Answer 19

An electron-volt (eV) is a unit of energy used to represent small energies.
It is equal to the kinetic energy of an electron accelerated across a p.d of 1V.
1.6 x 10⁻¹⁹ J

Question 20

Covert MeV/GeV to J

Answer 20

MeV = 1eV x 10⁶ = 1.6 x 10⁻¹³
GeV = 1eV x 10⁹ = 16.x10⁻¹⁰

Question 21

What are the 3 classifications of particles?

Answer 21

Hadrons, leptons or photons

Question 22

What fundamental particle?

Answer 22

Fundamental particles are particles that can’t be broken down further. Usually leptons

Question 23

What are are all hadrons formed of and what are the 2 different types?

Answer 23

Hadrons are formed of quarks and experience strong nuclear force
The 2 types are
- Baryons
- Mesons

Question 24

What are baryons and mesons made up of?

Answer 24

Baryons are formed of 3 quarks/antiquarks
Mesons are formed of a quark and anti-quark

Question 25

What are anti-particles?

Answer 25

For every type of particle it has a corresponding anti-particle.
Anti-particles have same rest energy and mass but all other properties are opposite.

Question 26

How to determine if a particle interaction is possible?

Answer 26

All the following properties must be conserved;
- Charge
- Baryon number
- Lepton number

Question 27

What are the common baryons?

Answer 27

Protons & neutrons

Question 28

What are common mesons?

Answer 28

Pion and kaon

Question 29

What are common leptons?

Answer 29

Electrons
Muon
Neutrino particles

Question 30

Explain how the cyclotron produces the high-energy proton beam

Answer 30

• There is alternating pd
• p.d accelerates protons between dees
• Magnetic field perpendicular to plane of dees
• Proton path curved by magnetic field, moving in circular motion
• As velocity increases, radius of path in dees increase
• Time for which proton is in a dee remains constant

Question 30

Explain why electrons need high energies to investigate the structure of a proton.

Answer 30

High energy electrons will have short de broglie wavelength
Wavelength needs to be comparable to proton size

Question 31

Explain how an electron is accelerated in a linac

Answer 31

• Set of metal drift tubes in a line
• Electrons accelerated by p.d
• Acceleration takes place in gaps between tubes
• Adjacent tubes connected to opposite terminals of power supply
• p.d is alternating so as electron emerges from tube, next tube is positive
• Time spent in each tube must be same so tubes get longer each time

Question 32

Explain how electrons from the source become a beam of high-energy electrons travelling through a p.d

Answer 32

• p.d creates an electric field
• Electric field does work on electrons, increasing kinetic energy