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Physics > Particle Physics > Flashcards

Particle Physics Flashcards

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1
Q

Nucleon

A

proton or neutron found in nucleus

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2
Q

Suggest what you should remember when calculating mass of an atom

A

Mass of electron is negligible

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3
Q

Isotopes

A

Atoms with the same number of protons and a different number of neutrons

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4
Q

Specific Charge

A

Charge per unit mass for a particle

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5
Q

Describe how the strong nuclear force between two nucleons varies with their separation and its role in the nucleus of an atom

A
  • strong nuclear force has a short range
  • repulsive below 0.5fm
  • attractive up to 3fm
  • overcomes electrostatic repulsion between proton and neutron
  • holds protons and neutrons together in the nucleus
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6
Q

Explain why the specific charge of an electron is approximately 2000 times that of a hydrogen nucleus

A
  • hydrogen nucleus consists of a proton
  • proton and electron have the same magnitude of charge
  • proton has a relative mass 1 and electron is 1/2000
  • specific charge of proton is approx 2000 times electron due to higher charge density
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7
Q

Suggest how charge and specific charge are different for isotopes

A
  • charge remains the same as neutrons have no charge

- specific charge is greater for the isotope with the smallest mass number

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8
Q

Nuclide Notation

A
  • A = nucleon number

- Z = proton number

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9
Q

Describe alpha decay

A
  • unstable nucleus emits an alpha particle (helium nucleus)
  • decays into a new daughter nucleus
  • mass number reduced by four and atomic number reduced by 2.
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10
Q

Suggests what happens to alpha particle from alpha decay

A

Shoots off and eventually acquires electrons to become a helium atom

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11
Q

Describe beta - decay

A
  • neutron changes into proton in nucleus
  • unstable nucleus emits a beta particle (fast moving electron)
  • antineutrino released
  • new daughter nucleus formed
  • same mass number and atomic number plus one
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12
Q

Describe beta + decay

A
  • proton changes into neutron in nucleus
  • unstable nucleus emits a beta particle (fast moving positron)
  • neutrino released
  • new daughter nucleus formed
  • same mass number and atomic number minus one
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13
Q

Describe gamma decay

A
  • excited nucleus releases gamma radiation (surplus of energy)
  • after alpha or beta decay
  • same nuclide just less energetic
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14
Q

How did beta decay lead to discovery of neutrino

A
  • realised energy was not conserved in beta decay

- existence of neutrino hypothesised to account for conservation of energy

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15
Q

Photon

A

Packet or quantum of electromagnetic waves

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16
Q

Antimatter

A

Sub-atomic particle having the same mass but opposite charge of a given particle

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17
Q

Annihilation

A
  • sub-atomic particle and its antiparticle collide
  • convert their total mass into photons
  • two photons are released to conserve momentum
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18
Q

Rest Mass/Energy

A
  • energy an object has when it is stationary
  • E=mc^2
  • hypothesised mass of an object increases with its velocity so rest mass is its minimum energy
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19
Q

Electron volt

A
  • energy transferred when an electron is moved through a potential difference of one volt
  • eV = magnitude of charge of electron
    1. 6x10-19 J
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20
Q

Pair production

A
  • photon with sufficient energy interacts with orbital electron (to conserve momentum)
  • converts its energy into a particle-antiparticle pair which separates
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21
Q

Name gauge boson and particles affected by electromagnetic force

A

Virtual photon

Charged particles only

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22
Q

Name gauge boson and particles affected by weak interaction

A

W+ and W-

All affected

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23
Q

Name gauge boson and particles affected by strong force

A

Pion (Gluon)

Hadrons only

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24
Q

Name gauge boson and particles affected by gravity

A

Graviton

Any particles with mass

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25
Q

Define gauge boson and briefly describe their role

A
  • force carriers that are exchanged when forces act

- transfer energy / momentum

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26
Q

Model for repulsion

A

Ball passed between particles moving them further apart

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27
Q

Model for attraction

A

Boomerang passed between particles moving them closer together

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28
Q

Key points to remember when drawing Feynman diagrams

A
  • incoming particles are drawn upwards in time
  • baryons and leptons must stay on their own side
  • charges must balance
  • gauge bosons represented by a wiggly line and drawn at an angle upwards
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29
Q

Compare exchange particles of electromagnetic and weak force

A
  • photon vs W boson
  • massless vs non zero rest mass
  • infinite range vs very short range
  • does not carry charge vs charged
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30
Q

Weak Force

A
  • responsible for changing the nature of particles

- for hadrons it means changing their flavour of quark e.g. in beta decay.

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31
Q

Describe Feynman diagram for B- decay

A
  • weak force causes neutron to change into proton
  • W - boson is produced and decays into electron and antineutrino
  • conserve charge and energy
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32
Q

Describe Feynman diagram for B+ decay

A
  • weak force causes proton to change into neutron
  • W + boson is produced and decays into positron and neutrino
  • conserve charge and energy.
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33
Q

Neutron-neutrino interaction*

A
  • neutron can interact with a neutrino
  • through emission of a W- boson changing the neutron into a proton
  • neutrino turns into a B- particle
34
Q

Proton-antineutrino interaction*

A
  • proton can interact with an antineutrino
  • through the emission of a W+ boson changing the proton into a neutron
  • antineutrino turns into a B + particle
35
Q

Electron Capture

A
  • proton in proton rich nucleus interacts with inner shell electron through weak interaction
  • proton emits a W+ boson which changes electron into neutrino
  • proton turns into a neutron
36
Q

Electron-Proton collision

A
  • proton collides with a high speed electron
  • weak interaction
  • electron emits W - boson and turns into a neutrino
  • proton changes into neutron.
37
Q

Hadron

A

Particles affected by strong force

38
Q

Lepton

A

Fundamental particles not affected by strong force, e.g. electrons, muons and neutrinos

39
Q

Baryons

A

Hadrons made up to three quarks, e.g. protons and neutrons

40
Q

Mesons

A

Hadrons made up of a quark and an antiquark, e.g. pions and kaons

41
Q

Properties that must be conserved in interactions

A 
Energy 
Charge 
Baryon no.
Lepton no. 
Strangeness (only in strong interaction - may change by 0, +1 or -1 in weak interaction)
42
Q

Muon

A

Heavy electrons (decay into electrons)

43
Q

Quarks

A

Fundamental particles that make up hadrons

44
Q

Suggest what all baryons decay into

A

Proton

45
Q

Suggest what kaons decay into

A

Pion

46
Q

Strangeness

A

quantum property only conserved in strong interaction

47
Q

Strange particle interactions

A
  • produced through strong interaction

- decay through weak interaction

48
Q

Explain what happens to electrons in an atom to produce a line spectrum

A
  • electrons are excited to higher energy levels
  • electrons fall (de-excite) to lower energy levels
  • release photons with discrete frequencies/energies
  • produces discrete wavelengths of light
49
Q

Explain how a fluorescent tube works

A
  • ionisation/excitation of mercury through collisions with electrons
  • mercury atoms de-excite and emit UV photons
  • UV radiation absorbed by powder coating
  • powder atoms excited so electrons move to higher energy levels
  • de-excite and release photons with discrete frequencies
  • emitted frequencies are within he range of visible light
50
Q

Excitation

A
  • process by which atom absorbs EXACTLY the right amount of energy
  • electron moves to higher energy level from ground state
51
Q

Suggest why emitted photons have specific wavelengths

A

Electrons fall from one fixed energy level to another so emitted photons have a discrete amount of energy

52
Q

Ionisation

A

Electron is removed from the outer shell of an atom

53
Q

An atom in the ground state is given energy by electron impact. Suggest how this energy might be used.

A
  • energy could be used to liberate electron in ground state (ionise atom)
  • extra energy would be converted into kinetic energy of electron
54
Q

Explain the difference between an electron and photon of the same energy colliding with an electron in an atom at ground state

A
  • for electron impact
  • electron would be excited to a higher energy level
  • even if the energy does not correspond with a particular energy level
  • extra energy is converted into kinetic energy
  • photons are only absorbed if they have EXACT energies allowing electron to be excited to a higher energy level
55
Q

Properties of electrons and electromagnetic waves that suggest they could be particles or waves

A

Waves
- electrons diffract
Particles
- photoelectric effect for waves
- electrons can be accelerated by electric field so carry momentum/KE
- electrons can be deflected by magnetic fields so carry charge

56
Q

Suggest a suitable material to observe diffraction pattern of electrons and explain your choice

A
  • crystals
  • spacing between atoms is small enough to behave like an aperture
  • gaps similar in size to the de Broglie wavelength of an electron
57
Q

Photoelectric effect

A
  • emission of electrons from a metal surface
  • when it is illuminated by light
  • of frequency greater than threshold frequency
58
Q

Suggest issues with wave theory shown by photoelectric effect

A
  • lack of time delay with electron emission (should take time for electrons to gain energy)
  • threshold frequency (electrons should gain some energy from wave regardless of frequency)
59
Q

Suggest what impact intensity of radiation has on electrons in the photoelectric effect and explain why it does not affect their kinetic energy

A
  • intensity affects rate of electron emission as more photons can liberate more photoelectrons
  • kinetic energy is unaffected since energy gained by a photoelectron is due to one photon only
60
Q

Work Function

A
  • minimum amount of energy

- required to release an electron from a metal surface

61
Q

State which factor affects kinetic energy of photoelectrons

A

Frequency

62
Q

Stopping Potential

A
  • minimum potential applied to metal plate

- to attract all photoelectrons emitted from surface back to surface of metal

63
Q

De Broglie Hypothesis

A

All matter has wavelike nature characterised by its de Broglie wavelength

64
Q

Suggest what can alter de Broglie wavelength of a particle

A

Its velocity since de Broglie wavelength is calculated based on momentum of the particle

65
Q

Explain the reason we often do not experience the wavelike nature of particles

A

Wavelike behaviour is only evident when the aperture the particle passes through is almost equal to the size of its de Broglie wavelength which is rarely the case

66
Q

Explain why alpha particle is no longer affected by the strong nuclear force once outside nucleus

A
  • short range

- no effect for distances larger than 3fm

67
Q

Antiparticle for photon

A

Photon since it does not carry charge

68
Q

Properties of strange particles that make them different from those that are not strange

A
  • strange quark
  • longer half life than expected
  • decays by weak interaction
69
Q

Explain why kinetic energy of photoelectrons emitted has a range of values up to certain maximum

A
  • energy of all photons is the same since E=hf
  • more energy required to remove deeper electrons
  • Ek cannot exceed hf - Φ
69
Q

Explain what is meant by validated evidence

A
  • predictions have been tested through experiments
  • peer reviewed
  • results are repeatable/reproducible
69
Q

Ground state

A

Electrons in lowest energy state

70
Q

Suggest why photoelectron emission does not take place below threshold frequency

A

E=hf so photon does not have enough energy to release electrons

72
Q

Suggest why a high voltage is needed in a fluorescent tube

A

Needed to start the flow of current as it gives electrons enough kinetic energy to ionise mercury atoms

73
Q

Threshold Frequency

A
  • minimum frequency of photons (light) to overcome work function
  • below which no photoelectrons are emitted
74
Q

Suggest why low pressure is needed in a fluorescent tube

A

Too many atoms means electrons cannot reach the anode

75
Q

Explain why electrons used to diffract around atomic nuclei would require larger kinetic energy if they are to show a diffraction pattern compared to when diffracted through a thin specimen of graphite

A
  • atomic nucleus is smaller than atom
  • wavelength of electron must be smaller for noticeable diffraction
  • smaller wavelength requires larger momentum according to de Broglie’s equation
  • larger momentum requires larger kinetic energy
76
Q

Explain how the diffraction pattern observed changes when electrons travel through crystal with smaller velocity

A
  • electrons have smaller momentum
  • associated de Broglie wavelength larger
  • more diffraction observed with larger wavelength
  • spacing of fringes would increase and pattern covers larger area
77
Q

Evidence for weak interaction

A
  • strangeness not conserved

- decay in quark flavour

78
Q

Suggest difference between hadrons and leptons

A
  • hadrons are not fundamental but leptons are

- hadrons are affected by the strong force but leptons are not

79
Q

Suggest what happens to a positron created from pair production

A
  • collides with another electron and annihilates

- releases two photons

Physics (5 decks)

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