Particle physics Flashcards
(72 cards)
1
Q
what are atoms made up of according to Bohr?
A
- a positively charged nucleus made up of protons + neutrons
- electrons orbiting the nucleus
2
Q
how does the size and mass of a nucleus compare to the whole atom?
A
- contains most of the mass of the atom
- diameter is 1/10000th of the atom
3
Q
what is a nucleon?
A
a proton or neutron in the nucleus
4
Q
properties of a proton
A
- charge = 1.60 * 10^-19 C
- relative charge = 1
- mass = 1.67 * 10^-27 kg
- relative mass = 1
5
Q
properties of a neutron
A
- charge = 0
- relative charge = 0
- mass = 1.67 * 10^-27 kg
- relative mass = 1
6
Q
properties of an electron
A
- charge = -1.60 * 10^-19 C
- relative charge = -1
- mass = 9.11 * 10^-31 kg
- relative mass = 0.0005
7
Q
what is the proton number?
A
aka atomic number
symbol Z
the number of protons in a nucleus - the same for all atoms of the same element
8
Q
what is the nucleon number?
A
aka mass number
symbol A
the number of protons + neutrons in the nucleus
9
Q
what is an isotope?
A
atoms with the same number of protons but different number of neutrons
10
Q
what is isotopic data and what is its uses?
A
it provides the ratios of different isotopes occuring in a material
eg. isotopic data about carbon-14 in organic matter can be used to calculate the age of archaeological finds
11
Q
what is a nuclide?
A
the different types of nuclei of the isotopes of elements
12
Q
what is specific charge?
A
the ratio of a particle’s charge to its mass:
specific charge = charge/mass
13
Q
what is a stable nucleus?
A
a nucleus where the protons and neutrons are held together strongly so that it does not disintegrate
14
Q
what is the strong nuclear force?
A
it is the force that holds stable nuclei together - it balances electrostatic repulsion between protons
15
Q
how does the effect of the strong nuclear force vary between 2 nucleons as separation increases?
A
- up to 0.5 femtometers - very short range repulsion
- 0.5-3 fm - short range attraction
- beyond 5 fm - negligible
16
Q
how do unstable nuclei become more stable?
A
they go through radioactive decay (a random process - you can’t predict how it will happen)
3 types:
- alpha decay
- beta-minus decay
- gamma radiation
17
Q
when does alpha decay happen vs beta decay?
A
- alpha radiation: large nuclei (strong nuclear force can’t keep it stable
- beta decay: when an isotope has too many neutrons (they become unstable)
18
Q
what is alpha decay?
A
(A)(Z)X -> (A-4)(Z-2)Y + (4)(2)α
- the alpha particle emitted consists of 2 protons + 2 neutrons
- has the highest ionising power
- range in air: ~5cm
- stopped by a sheet of paper
- each decay emits the same amount of energy
19
Q
what is beta decay?
A
(A)(Z)X -> (A)(Z+1)Y + (0)(-1)β + ̅νe
- neutron -> proton + electron
- electron + antineutrino is emitted
- high ionising power
- range in air = ~1m
- stopped by a few mm of aluminium
- the decays can emit a range of energies
20
Q
what is gamma radiation?
A
- the EM radiation emitted by an unstable nucleus
- emits: short wavelength, high frequency EM radiation
- nucleus loses energy
- low ionising power
- range in air = a few km
- stopped by several cm of thick lead
21
Q
how did Pauli hypothesise the existence of the neutrino/antineutrino?
A
- beta particles have a range of energies up to a max instead of just one single energy
- this meant that either energy is not conserved or there is another undetected particle being emitted that would compensate for the missing energy
- he hypothesised that this article had no charge (conserve charge) + very little mass (so its hard to detect)
- this particle is the antineutrino, the antiparticle of the neutrino
22
Q
what kind of wave is light?
A
it is an electromagnetic wave - a small part of the electromagnetic spectrum (wavelength 400-700nm)
23
Q
how fast do electromagnetic waves travel in a vacuum?
A
3.00 * 10^8 ms-1
24
Q
what is the equation linking wavelength of EM radiation, speed of light and frequency?
A
λ = c/f
where:
λ = wavelength
c = speed of light in a vacuum
f = frequency
25
what are EM waves made up of?
an electric and magnetic wave moving at right angles to each other and the direction they are travelling in and they are in phase
26
when are EM waves emitted?
when a charged particle loses energy:
- when a fast moving electron is stopped/slowed/changes direction
- an electron in the shell of an atom moves to a different lower energy shell
27
what is a photon?
- essentially a particle/packet/quantum of light (proven by the photoelectric effect)
- fundamental particles that make up all forms of EM radiation
- no mass but has energy + momentum
28
what is the equation for photon energy?
E = hf = hc/λ
where:
E = photon energy
h = Planck constant (6.63 * 10^-34)
29
What is rest energy of a particle?
it is equal to its rest mass (when the particle is stationary) - usually measured in MeV
the minimum energy it is possible for a particle to have
calculated using E = mc^2
30
what is an electronvolt?
the energy transferred to an electronvolt where it is accelerated through a potential difference of 1V
conversion between eV and J:
J / 1.60*10^-19 = eV
eV * 1.60*10^-19 = J
31
what is an antiparticle?
- every particle has a corresponding antiparticle
- has the same rest mass as the particle
- all other properties are opposite - eg. charge, baryon number, lepton number, magnetic moment, strangeness, etc
32
how do you denote an antiparticle?
- if the particle is written with a charge symbol, swap the charge symbol (eg. + becomes -)
- if the particle is written without a sign put a bar on top of the particle letter
33
describe the process of annihilation?
- a particle meets its corresponding antiparticle
- mass of the 2 particles is transferred entirely to electromagnetic radiation in the production of 2 photons
- the photons produced have equal amounts of energy (that sum to total original energy) and travel in equal and opposite directions (conservation of energy and momentum)
34
how to calculate minimum photon energy produced during annihilation?
E0 = h fmin
where:
E0 = rest energy of particle/antiparticle
35
give the corresponding antiparticles to:
1. electron
2. proton
3. neutron
4. neutrino
1. positron e⁺
2. antiproton
3. antineutron
4. antineutrino
36
describe the process of pair production?
- the opposite process to annihilation
- electromagnetic radiation is transferred to mass
- a photon with sufficient energy passes close to a nucleus, causing them to interact
- the photon will be converted into a particle-antiparticle pair with equal and opposite charge (to conserve charge) and travel in equal and opposite directions (to conserve momentum)
37
what is the minimum photon energy required to cause pair production?
E(photon) = 2E(rest)
38
how does pair production occur in a particle accelerator?
- through hadronic collisions eg. at CERN
- eg. 2 protons collide to produce a proton-antiproton pair
- if the particles have enough kinetic energy when they collide a particle-antiparticle pair is produced
39
how do PET scanners make use of annihilation?
- they use a positron emitting isotope and detect radiation produced by electron-positron annihilation
40
what are the 4 fundamental interactions/forces of the universe?
1. gravity - attractive force between any 2 objects due to their mass
2. electromagnetic - acts between any objects with charge - attractive w opposite charge, repulsive w same charge
3. strong nuclear - only acts on hadrons - hold protons and neutrons together in a stable nucleus
4. weak nuclear - acts on hadrons + leptons - involved in beta plus/minus decay, electron capture, electron-proton collisions
41
give the properties of gravitational force - range, relative strength, exchange particle
range: infinite
relative strength: 10^-38
exchange particle: graviton
42
give the properties of electromagnetic force - range, relative strength, exchange particle
range: infinite
relative strength: 10^-2
exchange particle: virtual photon γ
43
give the properties of weak nuclear force - range, relative strength, exchange particle
range: 10^-18m (very short range)
relative strength: 10^-5
exchange particle: W+ and W- bosons
44
give the properties of strong nuclear force - range, relative strength, exchange particle
range: 10^-15m
relative strength: 1
exchange particle: gluons for quark interactions, pions for hadrons
45
what are gauge bosons?
- aka exchange particles
- travel between 2 particles when they exert a force on (interact with) each other
- they are all virtual particles - only exist for a short period of time when the interaction takes place
46
what is beta plus decay?
- a proton in the nucleus -> neutron
- a positron + neutrino are produced
- happens with small nuclei that have too many protons
47
give the general symbol equation for beta plus decay
(A)(Z)X -> (A)(Z-1)Y + (0)(1)e⁺ + (0)(0)γ
48
what is Feynmann diagram?
used to represent interactions between particles
49
what do the different parts of a Feynmann diagram represent?
- wavy lines= exchange particles
- straight lines = all other particles
- arrows on straight lines = direction of travel in time
- sequence of time = up the page
- angles between line != paths of particles
50
what are the 3 main types of particles?
1. Hadrons - not fundamental (made of quarks), affected by strong nuclear force
2. leptons - fundamental, not affected by strong nuclear force, can change into other leptons through weak nuclear force
3. gauge bosons - mediate fundamental interactions eg. photons
51
what can hadrons be divided into?
- baryons - made of 3 quarks or 3 antiquarks, will eventually decay into protons
- mesons - made up of 1 quark + 1 antiquark, unstable - dont include protons in decay products
52
what is the baryon number, charge and strangeness of up quarks? (it will be the opposite for antiquarks)
baryon number: 1/3
charge: 2/3
strangeness: 0
53
what is the baryon number, charge and strangeness of down quarks? (it will be the opposite for antiquarks)
baryon number: 1/3
charge: -1/3
strangeness: 0
54
what is the baryon number, charge and strangeness of strange quarks? (it will be the opposite for antiquarks)
baryon number: 1/3
charge: -1/3
strangeness: -1
55
what is the only stable baryon?
a proton - all baryons eventually decay into protons
56
what is the quark composition of a proton and antiproton?
proton: uud
antiproton: u̅u̅d̅
57
what is the quark composition of a neutron and antineutron?
neutron: udd
antineutron: u̅d̅d̅
58
what is the quark composition of a sigma particle?
any combo of 3 quarks - must have a strange quark
59
what is the difference between pions and kaons?
pions are made up of only up and down quarks/antiquarks
kaons contain one strange/antistrange quark
60
what is the quark composition of the different π particles?
π⁺: ud̅
π⁰: dd̅ or uu̅
π⁻: du̅
61
what is the quark composition of different kaons?
K⁰: ds̅
K⁺: us̅
K⁻: su̅
K̅⁰: sd̅
62
what are some key facts to remember about quark composition of mesons?
- π⁰ is any up/down quark and its antiquark
- kaons always have a stange quark
- the uncharged kaons are antiparticles
- the charged kaons are antiparticles
- pions only have up and down quarks
63
what is the relative charge and lepton number of leptons in the electron generation?
- electron: lepton number = +1, relative charge = -1
- positron: lepton number = -1, relative charge = +1
- electron neutrino: lepton number = +1, relative charge = 0
- electron antineutrino: lepton number = -1, relative charge = 0
64
what is the relative charge and lepton number of leptons in the muon generation?
- muon: lepton number = +1, relative charge = -1
- anti-muon: lepton number = -1, relative charge = +1
- muon neutrino: lepton number = +1, relative charge = 0
- muon anti-neutrino: lepton number = -1, relative charge = 0
65
what is a lepton?
- a family of particles that is much lighter than baryons and mesons
- fundamental particles
- not subject to the fundamental interaction
- the muon generation is much more massive than the electron generation - about 200x more massive
66
what are the conserved quantities?
- energy
- momentum
- charge
- baryon number
- lepton number
67
outline the conservation laws
1. charge is conserved in all particle reactions
2. lepton number is conserved separately for each generation in all particle reactions
3. baryon number is conserved in all particle reactions
4. momentum and energy are always conserved
68
what is the weak interaction?
- a fundamental force that acts between all particles (hadrons + leptons) over a very short range
- responsible for electron capture, beta decay, interactions between leptons
- the only interaction to cause quarks to change flavour (eg. an up quark becomes a down quark)
69
what is the strong interaction?
- acts between quarks so only experienced by hadrons
- exchange particle with quarks is gluons
- exchange particle with particles is pions
- the signature: production or annihilation of quark antiquark pairs
70
what are the 3 types of interactions?
- production interactions - excess kinetic energy during particle collision creates quark-antiquark pairs
- annihilation interactions - mass of a quark-antiquark pair is converted into kinetic energy
- combination reactions - quarks are rearranged or one pair is annihilated and another pair produced with excess energy becoming kinetic energy
71
how does conservation of strangeness work?
- in the strong interaction, strangeness is conserved
- in the weak interaction strangeness is not conserved - it changes by +/-1
72
key facts about W⁺/W⁻ bosons
- since they are charge, particles must change flavour when receiving/emitting one
- can also decay into a particle and antiparticle of different flavours
