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Physics > Particles > Flashcards

Particles Flashcards

1
Q

What are the forces in the nucleus and why do they exist

A

There are electrostatic forces between the protons due to their electric charge and gravitational forces due to their mass.

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2
Q

Why is electrostatic repulsion between protons stronger than their gravitational attraction

A

Gravity is a very weak force

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3
Q

What is the force which holds the nucleus together

A

The strong nuclear force

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4
Q

How does the strong nuclear force hold the nucleus together

A

It keeps the nucleus stable by holding the quarks together

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5
Q

How far is the short range attraction of the strong nuclear force approximately

A

3 fm

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6
Q

How far is the very-short range repulsion of the strong nuclear force

A

approximately closer than 0.5 fm

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7
Q

1 fm = how many metres

A

1x10^-15m

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8
Q

What happens to the strong force/strong interaction after 3fm

A

It becomes zero or has no effect

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9
Q

Where does alpha decay occur

A

Commonly in large, UNSTABLE NUCLEI with too many protons

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10
Q

What happens in alpha decay

A

A nucleus emits an alpha particle and decays into different nucleus

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11
Q

What does an alpha particle consist of

A

2 protons and 2 neutrons (same as the nucleus of a helium atom)

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12
Q

What happens to the protons and nucleon number when an alpha particle is emitted from the nucleus

A

proton number - decreases by 2
nucleon number - decreases by 4

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13
Q

What is a beta minus particle

A

High energy electron emitted from the nucleus

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14
Q

What is beta minus decay

A

When a neutron turns into a proton emitting an electron and an anti-electron neutrino

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15
Q

What happens to the proton number and nucleon number when a beta minus particle is emitted from a nucleus

A

Proton number - increases by 1
Nucleon number - stays the same

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16
Q

What is a beta plus particle

A

A high energy positron emitted from the nucleus

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17
Q

What is beta plus decay

A

When a proton turns into a neutron emitting a positron and an electron neutrino

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18
Q

What happens to proton and nucleon numbers when a beta plus particle is emitted from a nucleus

A

Proton number - decreases by 1
Nucleon number - stays the same

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19
Q

What is an electron neutrino

A

A subatomic particle with no charge and negligible mass which is also emitted from the nucleus

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20
Q

What other subatomic particle is produced in beta minus decay

A

Electron anti-neutrinos

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21
Q

What other subatomic particle is produced in beta plus decay

A

Electron neutrinos

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22
Q

Why was the existence of the neutrino hypothesised

A

To account for the conservation of energy in beta decay

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23
Q

For every particle there is …..

A

A corresponding antiparticle

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24
Q

Properties of antiparticles

A

Opposite charges to their matter counterparts
Identical mass and rest mass-energy

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25
Q

What happens when a particle meets its antiparticle pair

A

The two will annihilate and a photon is produced

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26
Q

Annihilation

A

When a particle meets its equivalent anti-particle they both are destroyed and their mass is converted into energy in the form of 2 gamma ray photons

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27
Q

Energy after annihilation =

A

h x minimum frequency of one photon produced = rest mass energy of one of the particles

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28
Q

Pair production

A

When a photon interacts with a nucleus or atom and the energy of the photon is used to create a particle-antiparticle pair

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29
Q

Application of annihilation

A

PET scanner

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30
Q

Minimum energy for photon to undergo pair production =

A

h x minimum frequency of the photon = 2 x rest mass energy of one of the particles

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31
Q

Hadrons

A

Group of subatomic particles that are made up of quarks and so can feel the strong interaction force

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32
Q

What are the 2 classes of hadrons

A

Baryons ( protons, neutrons) and antibaryons (antiproton and antineutron) - have 3 quarks

Mesons (pion, kaon) - have a quark and antiquark pair

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33
Q

What is the rule for combination of quarks in baryons

A

they are all either quarks or all antiquarks AND there must be 3

34
Q

Baryon numbers of baryons, anti-baryons and particles which are not baryons

A

Baryons = +1
Anti-baryons = -1
Non-baryons = 0

35
Q

What is baryon number

A

A quantum number which is conserved in all interactions

36
Q

What is a proton in terms of baryons

A

The most stable baryon therefore has the longest half life of any baryon and so it is the particle which other baryons eventually decay to

37
Q

Exchange particle of the strong nuclear force/strong interaction

A

Pion

38
Q

How are kaons produced

A

By the strong interaction between pions and protons

39
Q

What do kaons decay into

A

Pions

40
Q

Why do kaons have long lifetimes

A

They contain a strange quark

41
Q

How do kaons decay

A

Through the weak interaction

42
Q

Leptons

A

Fundamental particles (not made up of any other particle therefore have no quarks)

43
Q

How do leptons interact with other particles

A

Via weak, gravitational or electromagnetic interactions ONLY.

NOT STRONG INTERACTIONS

44
Q

Most common leptons

A

Electron
muon
neutrino (electron and muon neutrino only)
Their antiparticles

45
Q

Lepton number

A

Quantum number, similar to baryon number, and is conserved in all interactions

46
Q

Lepton number of : lepton, anti-leptons and non-leptons

A

Leptons = +1
Anti-lepton = -1
Non-lepton = 0

47
Q

What do muons normally decay into

A

Electrons

48
Q

What do anti-muons usually decay into

A

positrons

49
Q

3 main flavours of quarks

A

up, down and strange

50
Q

Quark combination in protons

A

UUD

51
Q

Quark combination in neutrons

A

UDD

52
Q

Quark combination in pi +

A

Up quark and anti-down quark

53
Q

Quark combination in pi -

A

Anti up quark and down quark

54
Q

Quark combination in pi 0

A

up and anti-up or down and anti-down

55
Q

Quark combination in K+

A

Up and anti-strange

56
Q

Quark combination in K-

A

anti-up and strange

57
Q

Quark combination in K0

A

down and anti-strange
OR
anti-down and strange

58
Q

How are strange particles produced

A

Through the strong interaction

59
Q

How do strange particles decay

A

Through the weak interaction

60
Q

Examples of strange particles

A

kaons

61
Q

Strangeness

A

Quantum number. This reflects the fact that strange particles are always created in pairs

62
Q

Strangeness in particles with : an anti-strange quark, strange quark and no strange quark

A

Anti-strange quark - +1
Strange quark = -1
No strange quark = 0

63
Q

What can strangeness change by in weak interactions

A

0, +1 or -1

64
Q

What happens to strangeness number in strong interactions

A

It is conserved. (In interactions where strangeness changes by 0,-1 or +1 it is a weak interaction)

65
Q

What does particle physics rely on

A

Collaborative efforts of large teams of scientists and engineers to validate new knowledge

66
Q

What are the 4 fundamental interactions

A

Gravity
Electromagnetism
Strong nuclear / interaction
Weak nuclear / interaction

67
Q

What particles does gravitational interaction affect

A

Particles with mass

68
Q

What particles does electromagnetic interaction affect

A

Affects only particles with charge

69
Q

What particles does weak interaction affect

A

All particles

70
Q

What particles does strong interaction affect

A

Only hadrons - particles made up of quarks

71
Q

What explains forces between elementary particles

A

Concept of exchange particles

72
Q

Exchange particle in stron interaction

A

Pion

73
Q

Exchange particle in weak interaction

A

W+, W-

74
Q

Exchange particle in electromagnetic interaction

A

Photon

75
Q

Properties of a photon

A

No mass or charge and it is its own antiparticle

76
Q

What reactions have weak interaction

A

Beta plus and minus decay, electron capture and electron-proton collisions

77
Q

Equation for electron capture and electron-protons collisions

A

p + e- = n + ve

78
Q

Rules for Feynman diagrams

A

Y axis = time
X axis = space
particles must be labelled and shows as straight lines
Arrows must always be forward in time

79
Q

What happens to quark character in beta minus decay

A

down quark turns into an up quark since a neutron turns into a proton

80
Q

What happens to quark character in beta plus decay

A

Proton turns into neutron.
Up quark turns into a down quark

81
Q

What must be conserved in all particle interactions

A

Charge
Baryon number
Lepton number
Strangeness (except in weak interactions)
Energy
Momentum

Physics (10 decks)

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