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IB Physics > Nuclear Physics > Flashcards

Nuclear Physics Flashcards

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1
Q

emission spectrum

A
  • expose a container of gas at low pressure to a strong electric field
  • light emitted from gas
  • light analysed by passing it through a prism or diffraction grating
  • definition: set of possible wavelengths that can be emitted by a gas
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2
Q

discrete energy

A

energy can have one of a specific set of values

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3
Q

energy level diagram

A

each horizontal value represents a possible energy of the atom

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4
Q

how to explain the emission spectrum?

A
  • atom can make a transition from a state of higher energy to a state of lower energy by emitting a photon
  • the energy of the emitted photon is the difference in energy between the two levels
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5
Q

ground state

A

lowest energy state

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6
Q

excited state

A
  • if energy is supplied to the atom, the electron may move to a higher energy level by absorbing the right amount of energy exactly to move up
  • electron immediately makes transition down to lower energy (relaxation)
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7
Q

hydrogen energy level diagrams for all possible transitions from n=3

A

whether the electron will make a direct or indirect transition is just probability

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8
Q

how is the absorption spectrum produced?

A
  • beam of white light through gas
  • majority of atoms in ground state
  • electrons may absorb photons in beam and become excited
  • only happens if photon that is absorbed has the exact right energy that corresponds to difference in levels
  • light that is transmitted through gas will be missing photons - corresponds to dark lines
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9
Q

why are the photons in an absorption spectrum missing?

A

photons emitted in all directions, not necessarily along the direction of the observer

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10
Q

nucleon

A

proton or neutron

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11
Q

nuclide

A

nucleus with specific number of protons and neutrons

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12
Q

isotopes

A

nuclei that have the same number of protons but a different number of neutrons

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13
Q

unstable nucleus

A

nucleus that randomly and spontaneously emits particles that carry energy away from nucleus

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14
Q

radioactivity

A

emission of particles and energy from a nucleus

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15
Q

alpha decay

A

alpha particle is emitted from the nucleus and the decaying nucleus turns into a different nucleus

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16
Q

beta minus decay

A

neutron in the decaying nucleus turns into a proton, emitting an electron and an anti-neutrino

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17
Q

alpha particle

A

helium nucleus

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18
Q

beta minus particle

A

electron

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19
Q

beta plus decay

A

nucleus emits positron and neutrino

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20
Q

gamma decay

A

nucleus emits a gamma ray

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21
Q

gamma particle

A

photon of high-frequency electromagnetic radiation

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22
Q

penetrative power of alpha, beta minus, gamma particles

A
  • alpha is least penetrating
  • beta minus has less charge and travels faster so interacts less with environment so more penetrative
  • gamma has no ionising power bc no charge so most penetrative
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23
Q

ionising power of alpha, beta minus and gamma

A
  • alpha has a lot of momentum and double charge so a lot of interaction
  • beta minus has less momentum and less charge so less interaction
  • gamma is not very ionising - depends on intensity
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24
Q

decay series

A

set of decays that takes place until a given nucleus ends up as a stable nucleus

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25
Q

random

A

cannot predict which unstable nucleus in a sample will decay or when there will be a decay

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26
Q

spontaneous

A

cannot affect the rate of decay of a given sample in any way

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27
Q

law of radioactive decay

A

rate of decay is proportional to the number of nuclei that have not yet decayed

28
Q

what is a consequence of the law of radiactive decay?

A

number of radioactive nuclei decreases exponentially

29
Q

half-life

A

time after which the number of radioactive nuclei is reduced by a factor of 2

30
Q

activity

A

number of decays per second

31
Q

becquerel

A
  • unit of activity
  • 1Bq = one decay per second
32
Q

does activity obey the exponential decay law?

A

yes

33
Q

background radiation

A
  • activity does not approach zero, it approaches the activity due to all other sources of radiation
  • cosmic rays from Sun, radioactive material in rocks and ground, radiation from nuclear weapons testing
34
Q

electromagnetic interaction

A
  • acts on any particle that has electric charge
  • force given by Coulomb’s law
  • infinite range
35
Q

weak nuclear interaction

A
  • acts on protons, neutrons, electrons and neutrinos in order to bring about beta decay
  • very short range
36
Q

strong nuclear interaction

A
  • mainly attractive force acts on protons and neutrons to keep them bound to each other inside the nucleus
  • short range
37
Q

gravitational interaction

A
  • force of attraction between masses
  • small mass on atomic particles makes this force irrelevant for atomic and nuclear physics
  • infinite range
38
Q

electroweak interaction

A

electromagnetic interaction and weak interaction are two sides of the same force

39
Q

how does strong force explain why stable large nuclei have more neutrons than protons

A
  • as more protons are added to a nucleus the tendency for the nucleus to break apart increases because all protons repel each other through electromagnetic force
  • strong force has short range so any one proton only attracts its immediate neighbours
  • to keep nucleus together we need more neutrons that will contribute to nuclear binding through strong force but will not add to repulsive force
40
Q

atomic mass unit

A

1/12 of the mass of an atom of carbon-12

41
Q

mass defect

A

difference between the mass of the protons plus the mass of the neutrons and the mass of the nucleus

42
Q

binding energy

A
  • energy required to completely separate the nucleons of that nucleus
  • 1u=931.5MeVc-2
43
Q

binding energy curve and its features

A
  • binding energy per nucleon for hydrogen is zero because there is only one particle in the nucleus
  • curve rises sharply for low values of A
  • curve has a maximum for A=62 (nickel) which makes this nucleus particularly stable
  • peaks at position of nuclei He, C and O makes these nuclei unusually stable compared to immediate neighbours
  • curve drops gently from peak onwards
44
Q

why is the binding energy per nucleon roughly constant above a certain value of A?

A
  • short range of force implies that any given nucleon can interact with its immediate neighbours
  • for large nuclei any one nucleon is surrounded by the same number immediate neighbours so energy needed to remove that nucleon from the nucleus is the same
45
Q

nuclear fission

A

process in which a heavy nucleus splits up into lighter nuclei

46
Q

nuclear fusion

A

joining of two light nuclei into a heavier one with the associated production of energy

47
Q

thomson model

A

atom is a sphere of positive charge with the electrons moving inside the sphere

48
Q

Rutherford experiment

A
  • alpha particles were directed at a thin gold foil in an evacuated changer
  • number of particles deflected by different angles were recorded
  • great majority of alpha particles went straight through foil with little deviation
  • occasionally alpha particles were detected at very large scattering angles
49
Q

elementary particles

A

particles which are not made out of any smaller component particles

50
Q

what are the three classes of elementary particles

A

quarks, leptons, exchange particles

51
Q

what are the six flavors of quarks?

A
  • up, charm, top
  • down, strange, bottom
52
Q

anti-particles

A
  • have the same mass as quarks but all other properties are opposite
  • denoted with a bar on top of symbol
53
Q

hadron

A

particle made out of quarks

54
Q

baryon

A

combination of three quarks

55
Q

quark + anti-quark

A

meson

56
Q

three anti-particles combine

A

anti-baryon

57
Q

baryon number

A
  • quarks assigned +1/3
  • antiquarks assigned -1/3
58
Q

what is conserved in all reactions?

A

baryon number and electric charge

59
Q

lepton types

A
  • electron and its neutrino
  • muon and its neutrino
  • tau and its neutrino
60
Q

Feynman diagrams

a) photon absorption by an electron
b) photon absorption by a positron
c) electron emitting a proton
d) photon materialises into an electron and a positron - pair production
e) electron-positron annihilation

A
61
Q

quark confinement

A

not possible to observe isolated quarks

62
Q

what causes quark confinement?

A
  • force between quark and anti-quark is constant no matter the separation
  • total energy needed to separate the quark from the anti-quark gets larger as separation increases
  • free the quark completely would require an infinite amount of energy and so is impossible
  • all that would happen would be the production of a meson-anti-meson pair
63
Q

higgs particle

A

responsible, through its interactions, for the mass of the particles of the standard model, in particular the masses of the W and the Z

64
Q

antiparticle

A

same mass as its particle but all the quantum numbers are opposite

65
Q

lepton family number

A

conserved in all reactions

66
Q

color interaction

A

interaction between objects with color

67
Q

gluon

A
  • force-carrying particle
  • eight types each with zero mass
  • carries a combination of color and anti-color
  • emission and absorption by different quarks causes the color force

IB Physics (14 decks)

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