1. Particles And Radiation

Question 1

What is the charge of a proton, neutron and electron?

Answer 1

Proton: +1.6x10^-19

Neutron: 0

Electron: -1.6x10^-19

Question 2

What are the masses of protons, neutrons and electrons?

Answer 2

Proton: 1.673x10^-27

Neutron: 1.675x10^-27

Electron: 9.11x10^-31

Question 3

What is the formula for specific charge?

Answer 3

Specific charge = charge / mass

Question 4

What is an isotope?

Answer 4

An isotope is an atom of the same proton number but a different neutron number

Question 5

What are the four fundamental forces?

Answer 5

• S.N.F
• W.N.F
• EM
• Graviatational

Question 6

At what ranges is the strong nuclear force attractive and repulsive?

Answer 6

Repulsion at <0.5fm
Strong attraction until 3fm - 4fm, where it begins to taper off.

Question 7

What is alpha decay, why does it happen and how can it be observed?

Answer 7

Alpha decay is when large atoms (82+ protons) emit an alpha particle (2 protons + 2 neutrons) in order to make the nucleus more stable.
It has a range of a few cm in air. It can be observed with a cloud chamber, spark counter or Geiger counter.

Question 8

What is beta minus decay and why does it happen?

Answer 8

Beta minus decay is the emission of an electron from the nucleus along with an antineutrino particle. It happens in isotopes that are neutron rich. When a beta minus particle is ejected, a neutron changes to a proton in the nucleus. The antineutrino carries away energy and momentum. They can travel several meters through air.

Question 9

How did beta decay lead to the hypothesis about neutrinos?

Answer 9

During beta minus decay, there had to be another particle that carried energy away or it would not follow the laws of the conservation of energy, so the neutrino was theorised as having zero or little mass.

Question 10

What are the equations for the energy of a photon?

Answer 10

E = hf
E = hc / λ

Question 11

What is an antiparticle?

Answer 11

Each particle has a corresponding antiparticle with the same rest energy and mass but with an opposite charge.

Question 12

What is pair production?

Answer 12

• Energy is converted into mass resulting in equal amounts of matter and antimatter being produced.
• When two photons or two protons collide with high kinetic energy, as long as there is enough energy to produce a particle an its antiparticle, pair production will occur.
• Tends to happen when a photon passes near the nucleus.
• E(min) =2 E(0)
• Usually an electron positron is produced because of their low rest energy.

Question 13

What is annihilation?

Answer 13

• It happens when a particle meets its antiparticle.
• All mass is converted to energy in the form of two gamma ray photons.
• E(min) = E(0)

Question 14

What is a hadron?

Answer 14

• Particles that can feel the strong nuclear force.
• Not fundamental particles as they are made up of quarks.
• There are two kinds, baryons and mesons.

Question 15

What is a baryon?

Answer 15

• A baryon is a type of hadron.
• All baryons other than free protons are unstable, and will decay into a proton.
• Each baryon has a baryon number of one, and this is a quantum number which must be conserved in interactions.
• The antiparticles of baryons are called antibaryons, and have a baryon number of -1.

Question 16

What force does the beta minus decay interact with?

Answer 16

The weak interaction.

Question 17

What is a meson?

Answer 17

• A meson is a kind of hadron.
• All are unstable and B=0.
• Interact with baryons via the strong force.

Question 18

What is a pion?

Answer 18

• Pions (π mesons) are the lightest mesons, and have a range of charges from -1 to 1
• Each 0 meson is the antiparticle of itself.
• Pions are the exchange particle of the strong nuclear force.

Question 19

What are kaons?

Answer 19

• Kaons (K-mesons) are heavier and more unstable than pions. They decay into pions.

Question 20

How can mesons be detected?

Answer 20

Mesons can be detected in a cloud chamber of by placing Geiger counters above each other separated by lead. If they detect something at the same time, it is likely that this is cosmic radiation.

Question 21

What are leptons?

Answer 21

• Fundamental particles that don’t feel the strong nuclear force.
• They only interact via the weak interaction (other than gravitational and EM if they’re charged).

Question 22

What are muons?

Answer 22

Muons are unstable leptons that decay into electrons.

Question 23

What is a neutrino?

Answer 23

• You can get muon neutrinos and electron neutrinos.
• They have very little mass and no electric charge.
• They are leptons.

Question 24

What is a lepton number?

Answer 24

• A lepton number is a quantum number that must be conserved.
• There are two different kinds, L(e) and L(μ)

Question 25

What are strange particles?

Answer 25

- Strange particles have a property called strangeness. - They are created via the strong interaction, in which strangeness is conserved. - They can only be created in pairs. - Strangeness is a quantum number. Leptons have 0 strangeness. - They decay through the weak interaction.

Question 26

What quantities are conserved in interactions?

Answer 26

- Charge. - Baryon number. - L(e) - L(μ) - Strangeness is only conserved in strong interactions, as the only way to change the type of quark is with the weak interaction.

Question 27

What is the quark composition of baryons?

Answer 27

Three quarks.

Question 28

What is the quark composition of mesons?

Answer 28

- Made of one quark and one antiquark.

Question 29

What is the general quark composition of a pion?

Answer 29

Combinations of up, down, anti up and anti down quarks.

Question 30

What is the general quark composition of a kaon?

Answer 30

Combinations of up, down, anti up, anti down quark and strange quarks.

Question 31

What is quark confinement, and what happens if you blast a photon with a lot of energy?

Answer 31

- It is not possible to get a quark by itself. - The energy would be turned to matter in the form of pair production (e.g. up + anti up).

Question 32

What is the reason for beta minus decay only being able to interact with the weak interaction?

Answer 32

- In beta minus decay, the character of a quark is change from d into a u inside a neutron. Only the weak interaction can do this.

Question 33

What is beta plus decay?

Answer 33

p —> n + e(+) + v(e) - The quark character of a proton changes such that it becomes a neutron (u to d)

Question 34

What is a exchange particle?

Answer 34

An exchange particle is the idea that when two particles exert a force on each other, something must go between them to let the other know that they are there. They are virtual particles. Virtual particles only exist for a short time, just long enough to transfer energy, momentum and other properties.

Question 35

What are the gauge bosons for each interaction, and which particles do they each affect?

Answer 35

Strong: pions Affects: hadrons only EM: virtual photon Affects: charged particles only Weak: W+ and W- bosons. Affects: all types

Question 36

What determines the range of a force?

Answer 36

The size of the exchange particle (heavier have shorter range).

Question 37

What are the rules when drawing a Feynman diagram (4)?

Answer 37

- Incoming particles start at the bottom and move upwards. - Baryons stay on one side, and leptons on the other. - W bosons carry charge from one side to the other, to make sure that they balance. - A W- particle going left has the same effect as a W+ particle going right. **NOTE: you only have to draw diagrams for weak and EM interactions.**

Question 38

What is electron capture?

Answer 38

When proton rich nuclei can capture an electron from inside the atom and change it into a neutron.

Question 39

Although the symbol equation is the same for electron capture and electron - proton collision, how do their diagrams differ?

Answer 39

The W boson is positive in electron capture because the proton is acting on the neutron, however it is negative in electron - proton collisions because the electron is acting on the proton. Note that the W+ boson is left to right and the W- boson is right to left.

Question 40

What happens when two particles of equal charge get close to each other?

Answer 40

They repel due to the EM force, and the exchange particle is a virtual photon.