SECTION 1 - PARTICLES

Question 1

What is the atomic number?

Answer 1

The atomic (proton) number is the number of protons in the nucleus.

Number of electrons = number of protons

Question 2

What is the mass number?

Answer 2

Mass (nucleon) number is the number of protons and neutrons in the nucleus. This is also the atom’s relative mass.

Question 3

What is an isotope?

Answer 3

An atom of the same element with the same number of protons but different number of neutrons.

(Same atomic number, different mass number)

Question 4

What is specific charge?
Equation?

Answer 4

Specific charge of a particle is the ratio of charge to mass.

Specific charge = charge / mass

Question 5

What does the strong nuclear force do?
What is its range?
Is it attractive or repulsive? Why?

Answer 5

SNF holds the nucleus together with an attractive force stronger than the electrostatic force.

It has a very short range of a few femtometers (fm).

Attractive between around 0.5 - 3 fm, and repulsive below 0.5fm to stop nucleons colliding and crushing the nucleus.

Question 6

What are the four forces that act on atoms?

Answer 6

Strong nuclear force, weak nuclear force, electrostatic, and gravitational

Question 7

What is the range of electrostatic force?

Answer 7

Infinite

Question 8

Explain alpha emission.

Answer 8

Happens in large nuclei as SNF cannot keep the nuclei stable. When an alpha particle is emitted, proton number decreases by 2, and nucleon number decreases by 4.

There is a count rate for any nuclei undergoing alpha emission which can be measured with a Geiger counter.

Question 9

What is the range of alpha particles, and how can this be seen?

Answer 9

Very short range of a few cm in air, and can be seen by observing alpha radiation in a cloud chamber.

Question 10

Explain Beta-minus decay.
What particles are emitted?

Answer 10

Beta-minus decay is the emission of an electron from the nucleus with an antineutrino.

It happens in neutron-rich isotopes, and when a Beta-minus particle is emitted, a neutron turns into a proton. Proton number increases by one, nucleon number stays the same.

Question 11

What are photons?

Answer 11

Photons are packets of EM radiation, or bundles of energy.

Question 12

What is pair production?

What is the minimum energy required of a photon?

Answer 12

Pair production is when a photon of sufficient energy produces a particle-antiparticle pair.

Energy of the photon is converted into mass of the pair (and kinetic energy).

Minimum energy required is equal to the rest energy of both the particle and antiparticle that are produced.

Question 13

What is annihilation?

What is the minimum energy of a photon produced?

Answer 13

Annihilation is when a particle collides with its antiparticle, producing two photons which are sent in opposite directions.

Minimum energy of one photon produced equals rest energy of one of the particle-antiparticle pair.

Question 14

What are exchange particles?

Answer 14

Exchange particles are called gauge bosons. These cause forces between particles, and explain repulsion and attraction.

Gauge bosons are virtual particles that only exist for a very short time.

Question 15

Ignoring gravity, what are the gauge bosons for the fundamental forces, and what particles do they affect?

Answer 15

Electromagnetic - virtual photon, only affects charged particles.

Weak nuclear force - W+ or - bosons, affects all types of particles.

SNF - pions (+, -, or 0), only affect hadrons.

Question 16

How does mass relate to range of gauge bosons?

Answer 16

Greater mass = shorter range.

Photons have 0 mass, so EM force has infinite range, while W bosons have very large mass, so WNF has a very short range.

Question 17

What is electromagnetic repulsion?

Answer 17

When two particles of equal charge get close to each other, they repel.

Question 18

How do electron capture and electron-proton collisions work? (Show the interaction/feynman diagram)

Answer 18

Electron capture: Proton + electron —> neutron + electron neutrino
W+ boson acts from proton-neutron side to electron-neutrino side on Feynman diagram

Electron-proton collisions are the same as electron capture, but a W- boson goes from electron to proton instead.

Question 19

What are Beta-minus and Beta-plus decay equations?

Answer 19

Beta-minus decay: neutron decays into proton, electron, and electron antinuetrino. W- boson from neutron to electron

Beta-plus decay: proton decays into neutron, positron, and electron neutrino. W+ boson goes from proton to electron.

Question 20

What are hadrons?

Answer 20

Hadrons are particles that fell the strong nuclear force. They can be baryons or mesons.

Hadrons are made up of smaller particles called quarks (they aren’t fundamental particles).

Question 21

What are baryons?

Answer 21

Protons and neutrons are baryons.
All baryons are unstable except the proton, so all baryons except protons decay to a proton.

Question 22

What is baryon number?

Answer 22

The number of baryons in an interaction. Baryon number never changes and must be conserved in any interaction.

Question 23

What are mesons?

Answer 23

Pions and Kaons are mesons. All mesons are unstable and can be positive, negative, or neutral.

Mesons feel the SNF.

Question 24

What are leptons?

Answer 24

Leptons are fundamental particles that don’t feel the SNF, and only interact via the weak interaction (but may interact via gravitational or EM if charged)

Electrons are stable leptons.
Muons are unstable leptons and eventually decay into electrons.
Neutrinos have almost zero mass, and zero charge, and only take part in weak interactions.

Question 25

What is lepton number?

Answer 25

The lepton number is the number of leptons on either side of an interaction.

Lepton number must be conserved, however, it is counted separately for electrons and electron neutrinos, and muons and muon neutrinos.

Question 26

What are quarks and antiquarks?

Answer 26

Quarks and antiquarks are fundamental particles that make up hadrons.

You must know quark compositions for protons, neutrons, kaons, and pions.

Question 27

Strangeness is not always conserved. Strange particles, like kaons, are created via the strong interaction but decay via the weak interaction.

When is strangeness conserved?

Answer 27

Strangeness is conserved in the strong interaction, but not the weak interaction.

In the weak interaction, it can change by +1, -1, or 0.

Question 28

The weak interaction changes quark type.

Answer 28

The weak interaction changes quark type.

Question 29

What is conserved in particle interactions?

Answer 29

Momentum
Charge
Baryon number
Lepton number (muon and electron separately)
Strangeness (in strong interactions)