Section 1: Particles And Radiation

Question 1

What is Alpha Decay?

Answer 1

Nuclei of very big atoms (more than 82 protons) are too big for the strong nuclear force to keep them stable. To make themselves more stable they emit an alpha particle ⁴α₂ from their nucleus.

Question 2

How can strange particles change?

Answer 2

Strange particles decay throughout the weak interaction, where strangeness can change by -1, 0 or +1.

Question 3

What is annihilation?

Answer 3

When a particle meets its antiparticle and all the mass of the particle and antiparticle gets converted into energy in the form of two gamma ray photons.

Question 4

How can isotopic data be used?

Answer 4

All living things contain isotopes of carbon. After they die, the amount of carbon-14 inside them decreases. Scientists can calculate the approximate age of archaeological finds made from dead organic matter by using isotopic data to see how much carbon-14 is left in the object.

Question 5

What are the exchange particles for the weak interaction?

Answer 5

W⁺ and W^- bosons.

Question 6

Draw the particle interaction diagram for electron capture.

Answer 6

Proton-rich nuclei can ‘capture’ an electron from inside the atom and change into a neutron.

p + e^- → n + v_e

The proton is ‘acting’ on the electron as it captures it, so the W boson comes from the proton.

Question 7

Define specific charge and how do you calculate it?

Answer 7

The specific charge of a particle is the ratio of its charge to its mass.

Question 8

What are baryons and what do they decay into?

Answer 8

3 quarks. All baryons will eventually decay into a proton.

Question 9

What are the exchange particles for the electromagnetic force?

Answer 9

Virtual Photons.

Question 10

What is the proton number?

Answer 10

Z - the number of protons in an atoms nucleus.

Question 11

What are the constituents of an atom?

Answer 11

Proton, Electron and Neutron.

Question 12

What are antiparticles?

Answer 12

Each particle has a corresponding antiparticle with the same mass and rest energy but with opposite quantum numbers

Question 13

Draw the particle interaction diagram for beta-minus and beta-plus decay.

Answer 13

Question 14

What are hadrons?

Answer 14

Particles that feel the strong force. They aren’t fundamental particles, they’re made up of smaller particles called quarks, and there is two different types of hadrons : Baryons and Mesons.

Question 15

What are leptons?

Answer 15

Leptons are fundamental particles that don’t feel the strong force. They only really interact via the weak interaction.

Question 16

Name the three main types of leptons.

Answer 16

1) Electron
2) Muon (decays into the electron)
3) Neutrino

Question 17

What are mesons?

Answer 17

A Quark - Antiquark pair. All mesons are unstable.

Question 18

Explain the minimum energy needed for pair production.

Answer 18

The minimum energy needed = the total rest energy of the partcles that are produced.

Question 19

What is the change of quark character in beta-plus decay?

Answer 19

In ß⁺ decay a proton is changed into a neutron - in other words uud changes into udd turning a u quark into a d quark. Only the weak interaction can do this.

p → n + e⁺ + v_e

Question 20

How do PET scans work?

Answer 20

A positron-emitting isotope is placed into the bloodstream, and the gamma rays produced by electron-positron annihilation are detected, The two rays are moving in opposite directions, so they’re easy to distinguish from other gamma rays. The radiation is detected by a scintillator.

Question 21

Draw the particle interaction diagram for electromagnetic replusion.

Answer 21

Question 22

What are the two main mesons?

Answer 22

Pion) The lightest mesons. There are three versions, all with different electric charges - π⁺,π⁰,π^-.

Kaon) Are heavier and more unstable than pions. Kaons have a very short lifetime and decay into pions.

Question 23

What is the nucleon number?

Answer 23

A - the total number of neutrons and protons in an atoms nucleus. (Mass Number)

Question 24

What led to the hypothesis of the neutrino?

Answer 24

Observations showed that the energy of the particles after the beta decay was less than it was before, which didn’t fit with the principle of conservation of energy. It was suggested that another particle was being emitted and it carried away the missing energy. This particle had to be neutral (or charge wouldnt be conserved) and had to have zero or almost zero mass (as it had never been detected)

Question 25

How are strange particles produced?

Answer 25

Through the strong interaction. Strangeness is always conserved in the strong interaction, so they must be made in quark-antiquark pairs to conserve strangeness

Question 26

Why does the strong nuclear force vary with nucleon separation?

Answer 26

It’s initially needed to be attractive to keep the nucleus together. At very small distances, the strong nuclear force must be repulsive - otherwise there would be nothing to stop it crushing the nucleus to a point.

Question 27

What are the possible quark combnations for the mesons?

Answer 27

Question 28

How does the strong nuclear force and the electromagnetic force vary with nucleon seperation?

Answer 28

1) The Strong Nuclear Force is repulsive for separations of nucleons less than about 0.5 fm

2) As nucleon separation increases past 0.5 fm, the strong nuclear force becomes attractive. It reaches a maximum attractive value, and then rapidly falls towards 0 after about 3 fm.

3) The electromagnetic repulsive force extends over a much larger range (infinitely)

Question 29

How does the neutron decay?

Answer 29

(Also known as Beta Minus Decay), It decays into a proton, and electron and an electron antineutrino. A down quark in the neutron turns into an up quark.

Question 30

What is the photon model of Electromagnetic radiation? What are the equations related to it?

Answer 30

EM waves can only be released in discrete packets, or quanta. These wave-packets are called photons.

Question 31

What is an isotope?

Answer 31

Isotopes are atoms of the same element with the same number of protons but different number of neutrons.

Question 32

Give two examples of pair production.

Answer 32

1) Fire two protons with a large amount of kinetic energy at each other. The large amount of energy at impact creates a proton anti-proton pair.

2) If a photon has enough energy, it can pass near a nucleus and create a electron-positron pair, they curve away from each other since they’re oppositely charged.

Question 33

What are the 4 fundamental interactions?

Answer 33

1) Gravity

2) Electromagnetic

3) Weak Nuclear

4) Strong Nuclear

Question 34

What is the strong nuclear force?

Answer 34

In a nucleus, electromagnetic forces cause the protons to be repelled, whilst the gravitational force causes all nucleons to be attracted, however the electrostatic repulsion is much larger than the gravitational attraction. So there is another strong attractive force holding the nucleus together - the strong nuclear force.

Question 35

What is Beta Minus Decay?

Answer 35

The emission of an electron and an antineutrino. When a beta particle is emitted, one of the neutrons in the nucleus is changed into a proton. The antineutrino released carries away some energy and momentum.

Question 36

How do you work out the minimum energy of a photon produced in annihilation?

Answer 36

Since two photons are produced, 2E_min = 2E₀ therefore E_min = E₀

Question 37

What is the change of quark character in beta-minus decay?

Answer 37

In ß^- decay a neutron is changed into a proton - in other words udd changes into uud turning a d quark into a u quark. Only the weak interaction can do this.

Question 38

Draw the particle interaction diagram for an electron-proton collision.

Answer 38

In an electron-proton collision, the electron is the particle that’s acting because it’s being fired at the proton, so the W boson comes from the electron.

Question 39

What is pair production?

Answer 39

When energy is converted into mass and you get equal amounts of matter and antimatter.

Question 40

What is an exchange particle?

Answer 40

Exchange particles are how forces act between two particles. They are virtual particles meaning they only exist for a very short time - long enough to transfer energy, momentum and other properties betweeen particles.

Question 41

What is the exchange particle for the strong interaction?

Answer 41

Pions.