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Physics AQA AS Level > Particles and Radiation Part 2 > Flashcards

Particles and Radiation Part 2 Flashcards

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1
Q

All particles can be categorised into two groups depending on their properties - what are the categories?

A
  • Hadrons

- Leptons

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2
Q

What are hadrons?

A
  • Hadrons are particles and antiparticles that experience and interact through the strong nuclear force.
  • They are composite particles so composed of smaller ‘particles’ called quarks.
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3
Q

What other forces can hadrons feel?

A
  • Hadrons expereince the weak nuclear force because it works in the nucleus, just like the strong nuclear force.
  • Hadrons also experience the gravitational force because they have mass and so are attracted to each other.
  • Charged hadrons such as the proton also experience the electromagnetic force.

So… Hadrons can experience all four fundamental forces. Only charged Hadrons experience EM force.

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4
Q

What are leptons?

A

Leptons are particles and antiparticles which do not experience or interact through the strong nuclear force.
Leptons are fundamental particles and so are not composed of smaller particles.

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5
Q

What other force do leptons experience?

A
  • Leptons can experience the weak nuclear force. Electrons, positrons, neutrinos and antineutrinos all take part in beta decay.
  • Leptons experience the gravitational force because they have mass (whilst it may be negligible) so attract/are attracted to masses.
  • Charged Leptons will also experience the EM force.

So… Leptons can experience the weak nuclear force, the gravitational froce, the electromagnetic force (if charged) but not the strong nuclear force.

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6
Q

What is a fundamental particle?

A
  • A particles that cannot be divided into smaller particles.

- They make up other particles themselves.

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7
Q

What are the three leptons?

A

Electron, Neutrino and Muon and their corresponding anti-particles.

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8
Q

What are the antiparticles of the leptons?

A

Electron - Positron
Neutrino - Antineutrino
Muon - Antimuon

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9
Q

What is a muon and how is it created?

A

A type of lepton that is created in the Earth’s atmosphere when high energy cosmic rays (protons) collide with the nuclei of gas atoms to produce pions which decay into muons.

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10
Q

Symbol of muon?

A

μ- (negatively charged)

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11
Q

Why are muons referred to as ‘heavy electrons’?

A
  • Muons are often regarded as ‘heavy electrons’ with a rest mass 200x that of the electron.
  • They however have similar sizes, so the muon is very dense.
  • It also has a negative charge.
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12
Q
  • Muons undergo decay.

- How long is the lifetime of a muon?

A

Muons are short lived + decay within 2 μs of being formed.

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13
Q

Charge and mass of neutrino?

A

Neutrinos have no charge and have negligible mass - less than a millionth the mass of an electron.

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14
Q

Due to the low mass of neutrinos….

A

…they are able to travel at a speed closely approaching the speed of light.

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15
Q

Describe abundance of neutrinos in the universe?

A

Neutrinos are highly abundant in the unvierse.

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16
Q

Whilst neutrinos are abundant in the universe, why weren’t they discovered earlier?

A
  • Neutrinos are chargeless so do not experience the EM force.
  • Barely affected by the GM force as its mass is extremely low/negligible.
  • SO whilst being abundant, we rarely see its interaction/effect on other matter (e.g. a proton) as they just pass through it.
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17
Q

What are the two types of neutrinos?

A
  • The electron neutrino (Ve)
  • The muon neutrino (Vμ)

As well as the electron antineutrino, and the muon antineutrino (same symbol but with bar on top)

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18
Q

Hadrons are composite particles - what does this mean?

A

Hadrons are made up of quarks

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19
Q

Different hadrons have different properties e.g. charge - why?

A

Due to their differences in their quark composition.

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20
Q

What are the 3 types of quarks?

A 
up quark (u)
down quark (d)
strange quark (s)
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21
Q

What are the antiquarks?

A 
_
anti-up quark: u
                             _
anti-down quark: d
                                _
anti-strange quark: s
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22
Q

Each quark has a characteristic relative charge (a fraction of the elementary charge). What are the relative charge for:

1) up quark
2) down quark
3) strange quark
4) anti-up quark
5) anti-down quark
6) anti-strange quark

A 
up : +2/3e
down: -1/3e
strange: -1/3e
anti-up: -2/3e
anti-down: +1/3e
anti-strange: +1/3e

antiquarks - same charge magnitude but oppposite sign.

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23
Q

How can we calculate the overall charge of a hadron from its quark combination?

A

We can add the charges of the quarks that it is made up of to give its overall charge.

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24
Q

What quarks make up a proton and calculate total charge from quark composition?

A

up quark, up quark, down quark

+2/3e + 2/3e - 1/3e = +1

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25
Q

What quarks make up a neutron and calculate total charge from quark composition?

A

down quark, down quark, up quark

-1/3e - 1/3e + 2/3e = 0

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26
Q

On top of charge, some quarks have an additional property? What is this property?

A

This additional property is called strangeness

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27
Q

Which quarks possess strangeness?

A
  • Strange and anti-strange quark
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28
Q

What is the strangeness of strange and anti-strange quark?

A

Strange quark: -1 (negative strangeness)

Anti-strange quark: +1 (positive strangeness)

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29
Q

What is the strangeness of up and down quarks?

A

Up and down quarks (and their antiquarks) have no strangeness (0)

30
Q

What can hadrons be classified into?

A

Hadrons can be classified into Baryons and Mesons.

31
Q

What are Baryons?

Give two examples of baryons and their quark composition

A
  • Baryons are protons and all other hadrons that decay into a proton, directly and indirectly (as they are the most stable)
  • Baryons are hadrons made up of 3 quarks e.g. proton (uud), neutron (ddu)
32
Q

Which is the most stable Baryon?

What does this tell us about the mass of Baryons?

A
  • The most stable baryon is the proton as it is the lightest and so all baryons decay into protons directly/indirectly. This means all baryons have a mass equal to or greater than that of a proton.
33
Q

What are antibaryons made from?

A

Antibaryons e.g. antiprotons are made from the antiquarks of their corresponding baryon quark composition,
Baryons and antibaryons are made up of 3 quarks.

34
Q

What is the quark composition of an antiproton and an antineutron?

A

Antiproton: ū ū d̅
Antineutron: d̅ d̅ ū

35
Q

What are mesons?

A

Mesons are hadrons that do not include protons in their decay products
Mesons are hadrons made up of 2 quarks - specifically a quark and an antiquark

36
Q

What are antimesons made from?

A

Antimesons are made from the antiquarks of their corresponding meson quark composition.
A meson is its own antiparticle if the two quarks that its composed of are corresponding quark and antiquark.

37
Q

Examples of mesons? (The 2 that are common in interactions)

A

Kaons/ k-mesons

Pions/ π-mesons

38
Q

If mesons do not decay into a proton, directly or indirectly, what does this tell us about their mass?

A

The mass of Mesons is always less than the mass of a proton.

39
Q

What are the different types of pions?

A

Positively charged: π⁺
Negatively charged: π⁻
Neutral: π⁰

40
Q

What is the mass of pions in comparison to muons and protons?

A

Pions have a mass greater than a muon (lepton) but less than a proton (baryon)

41
Q

How can you calculate what type of pion is present?

A

By adding the charges on the quarks that it is composed of. e.g. a pion made of a down quark and an antidown quark would be..neutral = π⁰ (1/3e -1/3e)

42
Q

Estimate the number of quark compositions that are for π⁰ (netural pions) and state what they are?

A

There are 3 possible quark combinations for neutral pions:

  • u ,ū
  • d, d̅
  • s, s̅
43
Q

Quark combination for π⁺ and π⁻.

A 
π⁺ = ud̅  = 2/3e + 1/3e = +1
π⁻ = dū = -1/3e -2/3e = -1
44
Q

What is the antiparticle of π⁺ and π⁰?

A

The antiparticle of π⁺ is π⁻

The antiparticle of π⁰ is itself.

45
Q

What are the different types of kaons?

A

Positively charged: K⁺
Negatively charged: K⁻
Neutral: K⁰
Neutral Antikaon: K⁰ with overbar

46
Q

Compare the mass of a kaon to that of a pion and a proton?

A

Mass is greater than a pion (a different meson) but less than a proton (a baryon)

47
Q

How can you calculate what type of kaon is present?

A

By adding the charges on the quarks that it is composed of. e.g. a kaon made from a strange quark and an anti-down quark would be…neutral = K⁰ (-1/3e + 1/3e)

48
Q

What is the quark composition for the K⁰?
What is the quark composition for the K⁰ overbar?
What is the quark composition for the K⁺?
What is the quark composition for the K⁻?
Describe the relationships.

A

K⁰ : ds̅
K⁰ overbar : d̅s
K⁺ : s̅u
K⁻ : sū

The antiparticle of K⁺ is K⁻
The antiparticle of K⁰ is K⁰ overbar (the neutral antikaon)

49
Q

We have seen that cosmic rays collide with gas particles to produce short-lived particles. What exactly are cosmic rays?

A

Cosmic rays are actually fast-moving protons or small nuclei.

50
Q

What particles (an antiparticles) are made when cosmic rays collide with gas particles and how can this be observed?

A

When cosmic rays collide with gas particles in the atmosphere, they create muons, pions and kaons.
This can be observed using cloud chambers - certain particles have characteristic paths.

51
Q

What was the first strange particle to be discovered?

A

The first strange particle to be discovered was the kaon.
It was found using a cloud chamber due to its distinctive ‘V’ shaped tracks (this is the decay path of strange particles)
Scientists had never seen this track before which suggested the existence of another particle

52
Q

How are kaons produced?

A

When high-speed protons collide with the nucleus pg gas atoms ily removing a particle (neutron or proton) from that nucleus.
If the cosmic ray proton and nuclear proton/neutron then decay some distance from the nucleus, kaons may be formed through the strong interaction (along with other particles for conservation)

53
Q

Kaons undergo decay.

How long is the lifetime of a kaon, compared to muons and pions and why?

A

Whilst, short-lived (in general), they have an unusually long time before they decay in comparison to muons and pions.
This is due to the fact that kaons decay via the weak interaction.

54
Q

What does each of the following decay into?

K⁰, K⁺, K⁻

A

K⁰ → π⁺ + π⁻ (decays into two pions
_
K⁻ → μ⁻ + Vμ (decays into a muon and a muon antineutrino)

K⁺ → μ⁺ + Vμ (decays into antimon and a muon neutrino)

55
Q

Pions decay.

How long is the lifetime of a pion?

A

Short lived + quickly decay after formation

56
Q

What does each of the following decay into?

π⁰, π⁺, π⁻

A

_
π⁻ → μ⁻ + Vμ (muon and and an muon antineutrino)

π⁺ → μ⁺ + Vμ (antimuon and an muon neutrino)

π⁰ → γ + γ (high energy photons)

57
Q

Muons are short lived and quickly decay after formation what do they decay into? What do the folowing decay into?
μ⁻, μ⁺

A

_
μ⁻ → e⁻ + Ve + Vμ ( electron, electron antineutrino, muon neutrino)
_
μ⁺ → e⁺ + Ve + Vμ (positron, electron neutrino, muon antineutrino)

58
Q

Observations of their decay , showed that kaons had longer lifetimes than expected for their mass and size. What was this due to?

A

Their long lifetime was due to the fact that they decay through the weak interaction, whilst being made through the strong interaction

59
Q

What is the definition of strange particles?

A

Strange particles are particles created through the strong interaction but decay through the weak interaction.

60
Q

Why are strange particles always created in pairs?

A

To conserve strangeness.

61
Q

The strangeness of a kaon is determined by its quark composition. What is the strangeness of?
K⁰, K⁰ overbar, K⁺, K⁻

A

K⁰ : ds̅ → +1 strangeness
K⁰ overbar : d̅s → -1 strangeness
K⁺ : s̅u → +1 strangeness
K⁻ : sū → -1 strangenss

up and down quarks have no strangeness, so fully dependant on if it contains an ‘s’ or ‘s̅’

62
Q

What shape tracks do all strange particle show in a cloud chamber?

A

All strange particles produce a V-shaped track in a cloud chamber because they decay via the weak interaction.

63
Q

What is another example of a strange particle and what does it decay into?

A

An example of another strange particle is the Sigma particle (Σ) which de cays into pions(π⁻) and protons.

64
Q

Are sigma particles baryons or mesons?

A

Sigma particles are baryons, this is because it can decay into a proton.

65
Q

Describe the rest mass of a sigma particle compared to a proton?

A

Sigma particles decay into protons and so their rest mass must be greater than that of a proton.

66
Q

What can occur when a pion collides with a proton?

A

When a pion, collides with a proton, the proton, through the strong interaction, can create a kaon and a sigma particle.
The kaon and sigma particles, produced by the storng interaction, then can decay again, via the weak interaction (as they are strange particles).
The sigma particle decays into a negatively charged pion (π⁻) and the proton.
The kaon decays into two pions (π⁺ + π⁻)

67
Q

State the conservation rules:

A
  • Conservation of energy and charge - conserved in all changes in science
  • Conservation of lepton number and baryon number - conserved only in particle and antiparticle interactions/decays
  • Conservation of strangeness - conserved only in particle and antiparticle interactions/decays HOWEVER whilst its always conserved in the strong interaction, in the weak interaction it can be unchanged or unchanged by ±1
68
Q

What is the quark composition of Σ⁺ Σ⁻ Σ⁰?

A 
Σ⁺ = uus
Σ⁻ = dds
Σ⁰ = uds
69
Q

What are quark flavour changes?

A

Quark flavour changes are exclusive to the weak interaction, A quark flavour change is when a quark in a hadron before the interaction changes to a different quark at the end of the interaction.
_
e.g. n → p + e⁻ + Ve
udd (in neutron) becomes uud (in proton) so an down quark changes to an up quark.

70
Q

What is the baryon number for a:
baryon (e.g. n, p, Σ⁺, Σ⁻, Σ⁰)
antibaryon (n overbar, p overbar, Σ⁺overbar, Σ⁻overbar, Σ⁰ overbar)
lepton (e.g. e⁻, μ⁻ Ve, Vμ)
antilepton (e⁺, μ⁺, Ve overbar, Vμ overbar)
quarks
antiquarks

A 
baryon = +1
antibaryon = -1
lepton = 0
antilepton = 0
quarks (all quark) = +1/3
antiquarks (all antiquarks) = -1/3
71
Q 
What is the lepton number for a:
baryon
antibaryon
lepton
antilepton
quarks
antiquarks
A 
baryon = 0
antibaryon = 0
lepton = +1
antilepton = -1
quarks (all quark) = 0
antiquarks (all antiquarks) = 0
72
Q

JUST SOME THINGS TO REMEMBER:

A
  • K⁺ is the PARTICLE and K⁻ is the ANTIPARTICLE
  • K⁰ is the PARTICLE and K⁰ overbar is the ANTIPARTICLE
  • π⁺ is the PARTICLE and π⁻ is the ANTIPARTICLE
  • π⁰ is its own ANTIPARTICLE as quark composition does not change.

Pions and Kaons (the only mesons we needs to know about) have a baryon number of 0 and a lepton number of 0 (as they are not baryons or leptons).

Physics AQA AS Level (16 decks)

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