3.2 Particles and radiation

Question 1

What is ionisation?

Answer 1

The removal (or addition) of electrons from (or to) an atom or molecule

Question 2

2 reasons why smoke detectors (that use radioactive material) are safe

Answer 2

• Smoke detectors only emit alpha particles, which do not travel more than 4cm in air, so would be stoped before reaching outside of detector
• Only a small quantity of material is needed

Question 3

Unloading line on a F/e graph where plastic deformation has occurred:
- Why is the intercept non-zero?
- Why is the gradient unchanged?

Answer 3

• Plastic deformation has caused permanent extension, hence non-zero intercept
• Gradient unchanged because the forces between the bonds is identical before and after extension

Question 4

3 ways to spot a weak interaction

Answer 4

• If there is a change of quark character
• If the interaction involves both hadrons and leptons
• (If strangeness changes)

Question 5

What is the work function?

Answer 5

The minimum energy an electron needs to overcome the metallic bond holding it in the metal, and be released from the surface of the metal

Question 6

How can emission and absorption spectra be used as evidence for discrete energy levels in atoms?

Answer 6

Lines appear at discrete points which show where a light photon of specific frequency and wavelength has been absorbed (or emitted)

Question 7

One application of annihilation?

Answer 7

PET scanners

Question 8

Name 3 weak interactions

Answer 8

Beta plus decay
Beta minus decay
Electron capture

Question 9

Name a source of high energy particles

Answer 9

Pions and kaons come from cosmic rays

Question 10

Describe the role of exchange particles in the creation of forces

Answer 10

The force arises when the exchange particle moves between the other particles

Question 11

Why is it important to test by experiment the prediction of a scientific theory?

Answer 11

• If a reliable experiment supports a theory, the theory can be accepted, and extended on
• If a reliable experiment does not support a theory, the theory must be changed

Question 12

4 reason why it is necessary for many teams of scientists and engineers to collaborate in order for advancements to be made in particle physics

Answer 12

• results of experiments must be independently peer reviewed before they are accepted
• particle accelerators are very expensive and collaboration helps to spread the cost of building them
• many skills and disciplines are required (which one team are unlikely to have)
• lots of data to process (so more teams needed)

Question 13

What is ionisation energy?

Answer 13

Energy needed to remove an electron from an atom from its ground state

Question 14

How is an absorption spectrum created?

Answer 14

• Passing white light through a cooled gas
• Black lines represent the possible difference in discrete energy levels as the atoms in the gas only absorb photons of exact energies equal to exact differences

Question 15

How is an emission spectrum created?

Answer 15

• Passing the light emitted from a hot gas through a prism or diffraction grating
• Coloured lines represent the possible difference in discrete energy levels as the atoms in the gas only emit photons of an exact energies equal to exact differences, as electrons move down to lower energy levels

Question 16

What will kaons eventually decay into?

Answer 16

Pions

Question 17

What is the strong nuclear force?

Answer 17

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

Question 18

State the names of the particles that are produced when a muon decays

Answer 18

electron + electron antineutrino + muon neutrino

Question 19

Name a way to detect if an electron has been released from an experiment

Answer 19

Observing tracks in a cloud chamber

Question 20

What is an isotope?

Answer 20

atoms/nuclei with same number of protons but different numbers of neutrons

Question 21

What happens when a particle and antiparticle meet?

Answer 21

• They annihilate each other
• Their mass is converted back into the energy of two gamma ray photons, which travel off in different directions in order to conserve momentum

Question 22

Quark composition of K0

Answer 22

down quark, strange antiquark

Question 23

Quark composition of K0bar

Answer 23

down antiquark, strange quark

Question 24

Range of strong nuclear force

Answer 24

• repulsive up to 0.5fm
• attractive from 0.5-3fm
• zero past 3fm

Question 25

What are hadrons

Answer 25

Particles consisting of 2 or more quarks held together by the strong nuclear force

Question 26

What is the exchange particle for the strong nuclear force?

Answer 26

pion

Question 27

Strange particles are produced through the ___________________ and decay through the ___________________.

Answer 27

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

Question 28

Describe the photoelectric effect

Answer 28

• When electromagnetic radiation above a particular frequency is shone on the surface of a metal, photons transfer their energy to electrons in one-to-one interactions, and these electrons are released from the surface of the metal
• These released electrons are called “photoelectrons”

Question 29

Define electron volt

Answer 29

The kinetic energy of an electron that has been accelerated from rest through a potential difference of 1V

Question 30

How does a fluorescent tube work?

Answer 30

• A high voltage is applied across mercury vapour, which accelerates free electrons
• These fast moving free electrons collide with mercury atoms, exciting and ionising them
• When the electrons in mercury atoms fall back down to ground state, they release energy in form of a ultraviolet photon
• Phosphor atoms in the coating of the tube absorb these UV photos and their electrons become excited to higher energy levels
• As the de-excite, the electrons cascade down to the ground state, emitting visible light photons with a range of wavelengths

Question 31

What is wave-particle duality?

Answer 31

• Every particle or quantum entity may be described as either a particle or as a wave
• All particles have wave properties - all waves have particle properties

Question 31

What is wave-particle duality?

Answer 31

• Every particle or quantum entity may be described as either a particle as wave
• All particles have wave properties - all waves have particle properties

Question 32

Exchange particle for: 1. Electron capture 2. Electron-proton collision

Answer 32

1. W+
2. W-