2. Particles and Radiation

Question 1

Equation for specific charge:

Answer 1

Specific charge = charge / mass
Therefore the specific charge is the charge-mass ratio.

Question 2

What is an isotope and it’s uses?

Answer 2

Atoms with the same number of protons but different numbers of neutrons.
Carbon dating: by comparing how much carbon-14 is in the dead organism with the amount in a living one and knowing it’s half life.

Question 3

What is the strong nuclear force?

Answer 3

The force which keeps nuclei stable by countering the electrostatic force of repulsion between the protons.

Question 4

Over what range does the strong force act?

Answer 4

It’s repulsive for distances below 0.5 fm, and the attractive until about 3 fm.

Question 5

What are unstable nuclei?

Answer 5

Nuclei which contain too many protons, neutrons, or both, thereby causing the strong force to be unable to keep them stable. So they will decay.

Question 6

What decay occurs in nuclei with too many protons and neutrons?

Answer 6

Alpha decay, where 2 protons and 2 neutrons are ejected in the form of an alpha particle (α): the nucleon number decreases by 4, the proton number decreases by 2.

Question 7

What decay occurs in neutron rich nuclei?

Answer 7

Beta-minus decay, where a neutron is converted into a proton and a fast moving electron (β) and neutrino (ν^-) pair which are ejected from the nuclei: the proton number increases by 1, the nucleon number stays the same.

Question 8

How were neutrinos hypothesised?

Answer 8

Without them energy would not have been conserved during beta-minus decay.

Question 9

What is an antiparticle?

Answer 9

Something which has the same rest energy and mass as it’s particle counterpart, but the opposite of every other property.

Question 10

What is annihilation?

Answer 10

What occurs when a particle and antiparticle collide. Their masses are converted into energy. This energy combined with their kinetic energy will form two photons moving in opposite direction in order to conserve momentum.

Question 11

What’s an application of annihilation?

Answer 11

PET scanners, a positron emitting radioisotope is introduced into a patient. When the positrons are released, they will annihilate with the electrons already in the system and release gamma photons which can be easily detected allowing 3D images of inside the body to be taken.

Question 12

What is pair production?

Answer 12

Where a photon is converted into an equal amount of matter and antimatter.

Question 13

What are the fundamental forces?

Answer 13

Gravity, electromagnetic, weak nuclear, and strong nuclear.

Question 14

What causes forces between particles?

Answer 14

Exchange particles: these carry energy and momentum between particles.

Question 15

Strong force: exchange particle, range, acts on:

Answer 15

Gluon, 3x10^15, hadrons

Question 16

Weak: exchange particle, range, acts on:

Answer 16

W boson (W+ or W-), 10^-18, all particles

Question 17

Electromagnetic: exchange particle, range, acts on:

Answer 17

Virtual photon (γ), infinite, charged particles

Question 18

Gravity: (exchange particle), range, acts on:

Answer 18

(Graviton), infinite, particles with mass

Question 19

What is the weak nuclear force responsible for?

Answer 19

Beta decay, electron capture, and electron-proton collisions.

Question 20

Interaction diagrams (page 6 on PMT)

Question 21

What are leptons?

Answer 21

Fundamental particles. They do not experience the strong nuclear force.

Question 22

What are hadrons?

Answer 22

Particles made of quarks.

Question 23

What are baryons?

Answer 23

Hadrons formed from 3 quarks.

Question 24

What are mesons?

Answer 24

Hadrons formed from a quark and an anti-quark.

Question 25

What is the baryon number?

Answer 25

An indication as to whether something is: a baryon (1), an antibaryon (-1), or not a baryon (0). The baryon number is always conserved in particle interactions.

Question 26

What will happen to all baryons?

Answer 26

They will decay into the only stable baryon: the proton.

Question 27

What is the lepton number?

Answer 27

An indication as to whether something is: a lepton (1), an antilepton (-1), or not a lepton (0). The lepton number is always conserved in particle interactions.

Question 28

What are the types of lepton number?

Answer 28

Electron lepton number and muon lepton number.

Question 29

What is a muon described as?

Answer 29

A “heavy electron”, they also decay into electrons.

Question 30

What are strange particles?

Answer 30

Strangeness (s) proves that particles are always created in pairs.
Particles which are produced by the strong nuclear interaction but decay by the weak interaction (kaons decay into pions).
Strangeness is conserved in strong interactions but can change by +1, 0, or -1 in the weak.

Question 31

What’s needed to investigate particle physics?

Answer 31

Particle accelerators: scientific investigations rely on collaboration of scientists internationally.

Question 32

How do you represent antiquarks?

Answer 32

With a line above their usual symbols.

Question 33

What must be conserved in particle interactions?

Answer 33

-energy and momentum
-charge
-baryon number
-lepton number
(-strangeness during strong interactions)

Question 34

What is the photoelectric effect and what does it prove?

Answer 34

It’s where photoelectrons are emitted from the surface of a metal after light above the threshold frequency is shone at it.
It proves that EM waves travel in discrete packets called photons, which have energy that is directly proportional to frequency. Each electron can absorb a single photon. If the intensity of the light is increased and the frequency is above the threshold, more photoelectrons are emitted per second.

Question 35

What is the work function?

Answer 35

The minimum energy needed for electrons to be emitted from the surface of a metal, φ.

Question 36

What is the stopping potential?

Answer 36

The potential difference you would need to apply across a metal to stop the photoelectrons with the maximum kinetic energy.
Ek(max) = eVs (where e is the charge of an electron and Vs in the stopping potential)

Question 37

What happens if electrons gain energy?

Answer 37

Excitation where electron move up in energy level, or ionisation where electrons are removed from the atom entirely.

Question 38

How do fluorescent tubes work?

Answer 38

Fluorescent tubes are filled with mercury vapour, across which a high voltage is applied, thereby accelerating free electrons through the tube, which collide with the mercury atoms causing the electrons to become excited. When they de-excite they release UV photons, which the fluorescent (phosphorus) coating on the inside of the tube absorb causing their electrons to become excited which de-excite and release photons of visible light.

Question 39

What is an electron volt?

Answer 39

A measure of energy which is equal to the charge of an electron.

Question 40

What do line spectra show?

Answer 40

The different wavelengths of light coming from a source. This proves that electrons can only transition between discrete energy levels.
You can also get line absorption spectra which show every colour of light with black lines representing where it has been absorbed.

Question 41

What are some experiments to prove the wave-particle duality of light?

Answer 41

Wave: diffraction and interference.
Particle: photoelectric effect.

Question 42

What is an experiment to prove the wave like properties of electrons?

Answer 42

Electron diffraction, it will show an interference pattern: a large white spot in the middle with concentric circles becoming ever fainter.

Question 43

How do scientific views change?

Answer 43

Knowledge and understanding of any scientific concept changes over time in accordance to the experimental evidence gathered, which must first be peer-reviewed by the community to become validated, and eventually accepted.

Question 44

Threshold frequency; photon explanation of threshold frequency.

Question 45

Why does increasing the momentum of the particle change the amount of diffraction?

Answer 45

De Broglie wavelength…