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IB Physics HL > Topic 7: Atomic and nuclear physics > Flashcards

Topic 7: Atomic and nuclear physics Flashcards

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1
Q

Who discovered the electron and how?

A

JJ Thompson discovered the electron in 1897 by using a discharge tube.

Measurements of its charge to mass ratio showed that it was smaller than an atom.

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2
Q

How are electrons kept in orbit?

A

Electrons are kept in orbit around the nucleus as a result of the electrostatic attraction between the electrons and the nucleus.

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3
Q

Describe the Geiger-Marsden experiment

A
  1. Beam of alpha particles aimed at thin gold foil
  2. Passage through foil detected
  3. Expected that particles would pass straight through
  4. Some of the particles emerged at different angles and some reflected back
  5. It was realised that the positively charged alpha particles were being repelled and deflected by a tiny concentration of negative charge in the atom
  6. As a result, the plum pudding model was replaced by the nuclear model
  7. Rutherford concluded that the atom must have a tiny nucleus with electrons whizzing around it and that the nucleus had a positive charge to balance the negative charge of the electrons
  8. He thought that almost the whole mass of an atom was concentrated in the nucleus, so it must be incredibly dense
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4
Q

Outline one limitation of the simple model of the nuclear atom

A

Accelerating charges are known to lose energy. If the orbiting electrons were to lose energy they would spiral into the nucleus. The Rutherford model cannot explain how atoms are stable.

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5
Q

Outline evidence for the existence of atomic energy levels.

A
  1. Rutherford model was developed further by Niels Bohr who suggested that the electrons orbit the nucleus rather like a planet orbits the sun
  2. Radius of Bohr’s electrons depended on the energy they had
  3. He also suggested that they could only move in certain orbits: when the electrons moved from a high energy state to a lower energy state they emitted a photon of light and the frequency of the light depends on the difference between the energy levels
  4. As there are a fixed number of energy levels only a few wavelengths of light are given out, resulting in a line spectrum
  5. Each individual element has distinct energy levels and therefore the emission spectra can be used to identify them
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6
Q

Define: nuclide

A

An atom characterised by its proton number and atomic number:

AZX

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7
Q

Define: isotope

A

Nuclei with the same atomic number but different mass number (due to a different number of neutrons)

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8
Q

Define: nucleon

A

A proton or a neutron making up a nucleus

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9
Q

Define: nucleon/mass number, A

A

The number of nucleons in a nucleus

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10
Q

Define: proton/atomic number, Z

A

The number of protons in a nucleus.

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11
Q

Define: neutron number, N

A

The number of neutrons in a nucleus

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12
Q

Describe the interactions in a nucleus

A
  • According to our knowledge of electrostatics a nucleus should not be stable; protons are positive charges so should repel each other and so there must be another force in the nucleus that overcomes the electrostatic repulsion and hold the nucleus together
  • This force is called the strong nuclear force
  • Strong nuclear forces must be very strong to overcome the electrostatic forces and must also have a very small range as they are not observed outside of the nucleus
  • Neutrons have some involvement in strong nuclear forces: small nuclei have equal numbers of protons and neutrons, but larger nuclei, which are harder to hold together, have a greater ratio of neutrons to protons
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13
Q

Describe the phenomenon of alpha decay.

A
  • Alpha decay is one process that unstable atoms can use to become more stable. During alpha decay, an atom’s nucleus sheds two protons and two neutrons in an alpha particle.
  • Since an atom loses two protons during alpha decay, it changes from one element to another.
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14
Q

Describe the phenomenon of beta- decay.

A

Beta particles are electrons emitted from the nucleus. An electron and a proton are formed when a neutron decays. At the same time, another particle is emitted called an antineutrino.

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15
Q

Describe the phenomenon of gamma decay.

A

Gamma rays are unlike the other two radiations in that they are part of the electromagnetic spectrum. After their emission, the nucleus has less energy but its mass number and its atomic number have not changed. It is said to have changed from an excited state to a lower energy state.

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16
Q

Effect on photographic film of alpha, beta and gamma radiation

A

Alpha - yes

Beta - yes

Gamma - yes

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17
Q

Approximate number of ion pairs produced in air for alpha, beta and gamma radiation.

A

Alpha - 104 per mm travelled

Beta - 102 per mm travelled

Gamma - 1 per mm travelled

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18
Q

Typical material needed to absorb alpha, beta and gamma radiation.

A

Alpha - 10-2 mm aluminium; piece of paper

Beta - a few mm aluminium

Gamma - 10 cm lead

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19
Q

Penetration ability of alpha, beta and gamma radiation

A

Alpha - low

Beta - medium

Gamma - high

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20
Q

Typical path length in air of alpha, beta and gamma radiation

A

Alpha - a few cm

Beta - less than one m

Gamma - infinite

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21
Q

Speed of alpha, beta and gamma radiation

A

Alpha - about 107 m s-1

Beta - about 108 m s-1, very variable

Gamma - 3 X 108 m s-1

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22
Q

Outline the biological effects of ionising radiation.

A

At the molecular level, an ionisation could cause damage directly to a biologically important molecule such as DNA or RNA. This could cause it to cease functioning. Alternatively, an ionisation in the surrounding medium is enough to interfere with the complex chemical reactions called metabolic pathways taking place.

Molecular damage can result in a disruption to the functions that are taking place within the cells that make up the organism. As well as potentially causing the cell to die, this could just prevent cells from dividing and multiplying. On top of this, it could be the cause of the transformation of the cell into a malignant form.

As all body tissues are built up of cells, damage to these can result in damage to the body systems that have been affected. The non-functioning of these systems can result in death. If malignant cells continue to grow, then this is called cancer.

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23
Q

Explain why some nuclei are stable while others are unstable.

A
  • The stability of a particular nuclide depends greatly on the numbers of neutrons present.
  • For small nuclei, the number of neutrons tends to equal the number of protons.
  • For large nuclei there are more neutrons than protons.
  • Nuclides above the band of stability have too many neutrons and will decay with either alpha or beta decay.
  • Nuclides below the band of stability have too few neutrons and will tend to emit positrons
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24
Q

Describe the process of radioactive decay

A

Radioactive decay is a random process and is not affected by external conditions. For example, increasing the temperature of a sample of radioactive material does not affect the rate of decay. This means that there is no way of knowing whether or not a particular nucleus is going to decay within a certain period of time. All we know is the chances of a decay happening in that time.

Although the process is random, the large numbers of atoms involved allows us to make some accurate predictions. If we start with a given number of atoms, then we can expect a certain number to decay within the next minute. If there were more atoms in the sample, we would expect the number decaying to be larger. On average, the rate of decay of a sample is proportional to the number of atoms in the sample. This proportionality means that radioactive decay is an exponential process. The number of atoms of a certain element, N, decreases exponentially over time.

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25
Q

Define: radioactive half life

A

The time taken for half the number of nuclides present in a sample to decay. The time taken for the rate of decay of a particular sample of nuclides to halve.

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26
Q

Define: artificial transmutation

A

The conversion of one isotope to another. This can be done through a nuclear reaction whereby a nucleus is bombarded with a nucleon, an alpha particle or another small nucleus.

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27
Q

Define: unified atomic mass unit

A

One-twelfth of the rest mass of a carbon-12 atom in its nuclear and electronic ground state.

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28
Q

Define: mass defect

A

The difference between the mass of a nucleus and the mass of its component nucleons

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29
Q

Define: binding energy

A

The amount of energy that is released when a nucleus is assembled from its component nucleons.

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30
Q

Define: binding energy per nucleon

A

Total binding energy for the nucleus divided by the total number of nucleons

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31
Q

What did JJ Thompon prove?

A
  • electrons exist and are negative
  • electrons come from atoms
  • atoms are neutral
  • atoms were not fundamental particles but must contain some sort of structure
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32
Q

What is the plum pudding model?

A

A ball of neutral mass with balls of positive or negative charge within.

or

A ball of positive charge with balls of negative charge (electrons) within.

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33
Q

What fundamental property do energy levels have?

A

They are quantized. This means that they must have discrete, finite values (they cannot just take any orbit/level).

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34
Q

What is an electron that is above the ground state said to be?

A

It is said to be excited. So energy level 2 is the first excited state, energy level 3 is the second excited state etc.

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35
Q

What does quantized energy level mean?

A

Electrons cannot be anywhere between the energy levels, i.e. cannot move from an energy level to the next without completely having the threshold energy required for that level.

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36
Q

What is the light spectrum for pure white light?

A

A continuous spectrum, i.e. all wavelengths are emitted/present

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37
Q

What is the light spectrum for a hot gas?

A

A hot gas emits light, so the atomic spectrum will be a dark spectrum with thin bars/lines of bright light of discrete wavelengths.

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38
Q

What is the light spectrum for a cold gas?

A

A cold gas absorbs light, so the atomic spectrum will be a light spectrum with thin bars/lines of dark light/black of discrete wavelengths.

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39
Q

How can you find which gases are present in a gaseous nebula?

A

Compare the emission lines to emission lines of certain gases such as hydrogen and helium.

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40
Q

How can electrons move between energy levels?

A

By absorbing or emitting energy in the form of quantum such as protons (light).

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41
Q

What is a packet of light called?

A

A quantum (in this case, photon).

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42
Q

How is the energy of a photon related to its frequency?

A

Ephoton = hf

where h is Planck’s constant is Js and f is the frequency in Hz

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43
Q

How is the energy of a photon related to its wavelength?

A

Ephoton = hc/λ

where h is Planck’s constant in Js, c is the speed of light in ms-1, λ is the wavelength in m.

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44
Q

Which colour has the most energy?

A

Violet as it has the highest frequency / shortest wavelength

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45
Q

Which colour has the least energy?

A

Red as it has the lowest frequency / longest wavelength

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46
Q

Which force keeps electrons in orbit?

A

Electrostatic

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47
Q

How are emission lines formed?

A

Electrons transition from higher energy levels to lower ones, which emit photons.

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48
Q

How are absorption lines formed?

A

Electrons absorb photons with the exact energy required to transition to a higher energy level. Therefore that frequency of light is absorbed.

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49
Q

What happens if an electron absorbs enough energy to reach a hypothetical level of 0eV?

A

The electron escapes as it overcomes the electrostatic force. The atom becomes ionised.

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50
Q

In what direction to electrons move on an energy level diagram if emitting?

A

Downwards

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51
Q

In what direction to electrons move on an energy level diagram if absorbing?

A

Upwards

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52
Q

How can you calculate the emitted photon energy?

A

Ephoton = Einital level - Efinal level

Einital level should always be the energy level that is higher and where the electron drops from. It should also have a lower value that the final energy level.

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53
Q

How can you calculate the energy of an absorbed photon?

A

It is like the emitting method as the energy emitted = energy required by absorption.

So Ephoton = Efinal level - Eintial level

where Efinal level is a higher level with less energy.

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54
Q

What is radioactive decay?

A

The spontaneous disintegration of an unstable nucleus, which is accompanied by the emission of an ionising particle.

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55
Q

How is the probability of decay affected by chemical or physical conditions (e.g. state)?

A

It is unaffected. The probability will be constant in all conditions.

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56
Q

What forces are contending during decay?

A
  • electrostatic force which repels protons
  • the strong nuclear force which binds nucleons together
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57
Q

Describe the phenomenon of beta+ decay.

A

Beta+ particles are positrons emitted from the nucleus. A positron and a neutron are formed when a proton decays. At the same time, another particle is emitted called a neutrino.

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58
Q

What is the number of decays per second measured in?

A

Becquerels (Bq)

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59
Q

What is the dose received from a source measured in?

A

Sieverts (Sv) or millisievert (mSv)

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60
Q

When does alpha decay occur?

A

In unstable isotopes with too many protons and neutrons.

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61
Q

When does beta - decay occur?

A

Beta - decay occurs when a nucleus contains too many neutrons to be stable.

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62
Q

When does beta + decay occur?

A

When a nucleus contains too many protons to be stable.

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63
Q

When does gamma decay occur?

A

When an excited nucleus recombines into a lower energy level, gamma radiation is emitted to conserve energy. Usually after alpha or beta decay.

64
Q

Why are isotopes with low numbers of protons usually very stable?

A

Less electrostatic repulsion

65
Q

For isotopes with low proton numbers, when are they most stable?

A

When the number of protons = the number of neutrons.

66
Q

For isotopes with high proton numbers, when are they most stable?

A

The neutron number is greater than the proton number

67
Q

What is the first pattern of stability?

A

Isotopes with low numbers of protons are usually very stable due to having less electrostatic repulsion.

68
Q

What is the second pattern of stability?

A

If the number of protons and neutrons are both even, the isotope tends to be far more stable.

(There are only 5 stable nuclides with odd numbers of both protons and neutrons.)

69
Q

What is the third pattern of stability?

A

Nuclides tend to be stable if either the number of protons or neutrons is equal to 2, 8, 20, 28, 50, 82 or 126.

If both are these numbers then they are very stable.

70
Q

What does the band of stability look like?

A

A graph of neutron number vs proton number.

The band of stability is constant with N = Z up to 20 (ish) then the band leans more to neutrons (becomes more vertical).

71
Q

What decay is on the left side of the band of stability?

A

Beta - decy

72
Q

What decay is on the right side of the band of stability?

A

Beta + decay (or electron capture)

73
Q

What decay is on the top corner of the band of stability?

A

Alpha decay

74
Q

What decay is on the band of stability?

A

No decay (stable)

75
Q

What is the range of the strong nuclear force?

A

≈ 10-15 m or 1 fm

76
Q

What has more energy:

  • a bonded nucleus
  • a separated nucleus
A

a separated nucleus

(it has “greater mass”)

77
Q

What is the mass-energy relationship?

A

E = mc2

Where E is the energy, m is the equivalent mass and c is the speed of light in a vacuum.

78
Q

What is needed to separate a nucleus?

A

Nucleus + binding energy = separated nucleus

79
Q

How can you find the binding energy?

A

The masses of a bonded and separated nucleus will differ.

Using E = mc2, Δm = ΔE/c2

where E is the binding energy

80
Q

What does the binding energy look like for a nucleus that is bonding?

A
  • Δm = -ΔE/c2

Just put minus signs as the work is done by the system not against it.

81
Q

How is the stability of a nucleus determined?

A

The binding energy per nucleon,

A high binding energy per nucleon is a stable nucleus.

82
Q

What is an example of a stable element (one with high binding energy per nucleon)

A

Iron (Fe)

Nickel (Ni)

83
Q

What does the binding energy per nucleon vs nucleon number graph look like?

A

A very steep upward curve with occasional dips, which flattens out at a peak of 60 nucleons and 9 MeV per nucleon, which the steadily decreases at a smooth curve.

84
Q

Where do you find fusion and fission on the binding energy per nucleon vs nucleon number graph?

A

Fusion on the upward slope, fission on the downward slope.

Stability on the peak

85
Q

Where does nuclear fusion naturally occur?

A

The core of a star

86
Q

What are the conditions required for nuclear fusion?

A

The nuclei must have enough kinetic energy to overcome the electrostatic repulsion and get near enough to be in the range of the strong nuclear force (to fuse them).

87
Q

How does fusion occur?

A

Through collisions.

88
Q

What is the relationship between the mass before and after fusion?

A

Masses before fusion: m1 and m2

Masses after fusion: m3 and m4

(m1 + m2) > (m3 + m4)

89
Q

What is the fusion equation?

A

ΔE = [(m1 + m2) - (m3 + m4)] c2

is ΔE is positive, energy has been released (exothermic), this is equivalent to increased binding energy, which is the kinetic energy of the released particles.

90
Q

When does fission occur?

A

When a very heavy and unstable nucleus splits into two small nuclei.

91
Q

What is the relationship between the mass before and after fission?

A

ΔE = [m1 - (m2 + m3)] c2

where ΔE is the difference between the two binding energies.

92
Q

What are nuclear fission reactions usually?

A

They are usually chain reactions.

i.e. one of the particles on the left side e.g. neutron, which caused the fission reaction, is also a product, which would then continue the reaction.

93
Q

What is a fundamental particle?

A

A particle that is not composed of smaller particles.

94
Q

What is the effect of the strong nuclear force?

A

Binds quarks and hadrons

95
Q

What is the effect of the electromagnetic force?

A

A force experienced by charged particles i.e. attraction between opposite charges, repulsion between equal charges

96
Q

What is the effect of the weak nuclear force?

A

Mediates beta decay

97
Q

What is the effect of gravity?

A

Masses attract eachother

98
Q

What is the relative strength of the strong nuclear force?

A

1037

99
Q

What is the relative strength of the electromagnetic force?

A

1035

100
Q

What is the relative strength of the weak nuclear force?

A

1024

101
Q

What is the relative strength of gravity?

A

1

102
Q

What is the range of the strong nuclear force?

A

≈ 10-15 m

103
Q

What is the range of the weak nuclear force?

A

≈ 10-18 m

104
Q

What is the range of the electromagnetic force?

A

∞

(infinite)

105
Q

What is the range of gravity?

A

∞

(infinite)

106
Q

What is the boson associated with the strong nuclear force?

A

Gluon

“glues nucleons together”

107
Q

What is the boson associated with the electromagnetic force?

A

Photon

108
Q

What is the boson associated with the weak nuclear force?

A

W+, W- and Z0

109
Q

What is the boson associated with gravity?

A

Graviton (hypothetical)

110
Q

What is the boson responsible for the existence of mass?

A

Higgs boson

111
Q

What is a boson?

A

The particle that mediates forces.

(Strong nuclear, weak nuclear, electromagnetic, and it is hypothetical for gravity)

112
Q

What are the three groups that particles can fall into?

A
  • Bosons
  • Hadrons
  • Leptons
113
Q

What are hadrons?

Examples?

A

Particles which can experience the strong nuclear force as well as the weak nuclear force.

Examples: protons, neutrons

114
Q

What are all hadrons composed of?

A

Quarks

115
Q

What are leptons?

Examples?

A

Particles that do not experience the strong nuclear force but do experience the weak nuclear force.

Examples: electrons, neutrinos

116
Q

What are all leptons composed of?

A

All leptons are fundamental particles (i.e. are not composed of other particles)

117
Q

What do all leptons have?

A

They all have an antiparticle.

e.g. electrons and positrons

118
Q

What happens if a particle meets its antiparticle?

A

The two will annihilate, their combined mass will be converted into photons.

119
Q

What happens after annihilation and why?

A

The combined masses will be converted into photons due to conservation of energy/mass.

120
Q

What does each lepton have linked to it?

A

Another lepton called a neutrino.

121
Q

What do all neutrinos have?

A

An antiparticle equivalent called an antineutrino.

122
Q

What is the charge of neutrinos and antineutrinos?

A

0

123
Q

What is the lepton number of leptons and anti leptons?

A

All leptons and neutrinos have a lepton number of +1

All antileptons and antineutrinos have a lepton number of -1

124
Q

What is the symbol of an antiparticle version of a lepton?

A

A horizon line above the symbol

125
Q

What is the charge of leptons and anti leptons?

A

Leptons such as electrons have a charge of -1 (e)

Antileptons such as positrons have a charge of +1 (e)

Note: neutrinos and antineutrinos do not have charge!

126
Q

What are quarks?

A

Quarks are fundamental particles that make up hadrons.

127
Q

Can quarks exist on their own?

A

NO, it is impossible.

128
Q

What do all quarks have?

A

An antiquark equivalent.

e.g. up and antiup

129
Q

What must quarks combine to form?

A

They must combine to form hadrons of integral charge. e.g. a charge of +1 not +1/3

130
Q

What are the 6 types of quarks?

A
  • Up
  • Down
  • Charm
  • Strange
  • Top
  • Bottom
131
Q

What are the 6 types of antiquarks?

A
  • Antiup
  • Antidown
  • Anticharm
  • Antistrange
  • Antitop
  • Antibottom
132
Q

What are the charges for all the quarks?

A

Up, charm, top: + 2/3 (e)

Down, strange, bottom: - 1/3 (e)

[given in data booklet]

133
Q

What are the charges for all the antiquarks?

A

Antiup, anticharm, antitop: - 2/3 (e)

Antidown, antistrange, antibottom: + 1/3 (e)

[these are not given in the data booklet, but you should just be able to invert the sign in front of the regular quark values]

134
Q

What are the two types of hadrons and what do each of them have?

A
  • Baryon (3 quarks)
  • Meson (quark & antiquark pair)
135
Q

Is it possible to have a baryon with a mix of quarks and antiquarks? Why?

A

No, as the charge would not be an integer.

136
Q

What baryon number baryons and antibaryons have?

A

Baryons: +1

Antibaryons: -1

137
Q

What is strangeness?

A

Strange quarks have a property called strangeness.

For every strange quark, the strangeness is +1

For every antistrange quark, the strangeness is -1

138
Q

What is the standard model of particle physics?

A

A table with all the fundamental particles.

139
Q

What are the four conservation laws in all particle interactions?

A
  • Charge must be conserved
  • Lepton number is conserved
  • Baryon number is conserved
  • Strangeness is conserved
140
Q

When is strangeness not conserved?

A

When strange particles decay through the weak interaction. E.g. when a strange quark decays into an up quark.

141
Q

What are the symbols for electrons, muons and tau?

A

Electrons: e

Muons: μ

Taus: 𝜏

142
Q

What are Feynmann diagrams? What are its axes?

A

Diagrams that are used to represent possible particle interactions. They are used to calculate the overall probability of an interaction taking place.

Position on the x-axis, time on the y-axis (although this can be switched).

143
Q

Rules for Feynmann diagrams

(6)

A
  • Each junction in the diagram (vertex) has an arrow going in and one going out. These will represent a lepton–lepton transition or a quark-quark transition.
  • Quarks or leptons are solid straight lines.
  • Exchange particles are either wavy or broken (photons, W± or Z°) or curly (gluons).
  • Time flows from bottom to top. Arrows from bottom to top represent particles travelling forward in time. Arrows from top to bottom represent antiparticles travelling backwards in time.
  • The labels for the different particles are shown at the end of the line.
  • The junctions will be linked by a line representing the exchange particle involved.
144
Q

Feynmann diagram for:

An electron emits a photon.

A
145
Q

Feynmann diagram for:

An electron absorbs a photon.

A
146
Q

Feynmann diagram for:

A positron emits a photon.

A
147
Q

Feynmann diagram for:

A positron absorbs a photon.

A
148
Q

Feynmann diagram for:

A photon produces an electron and a positron (an electron-positron pair)

A
149
Q

Feynmann diagram for:

An electron and a positron meet and annihilate (disappear), producing a photon.

A
150
Q

Feynmann diagram for:

Beta decay.

A

A down quark changes into an up quark with the emission of a W particle. This decays into an electron and an antineutrino. The top vertex involves quarks, the bottom vertex involves leptons.

151
Q

Feynmann diagram for:

Pion decay.

A

The quark and antiquark annihilate to produce a W+ particle. This decays into an antimuon and a muon neutrino.

152
Q

Feynmann diagram for:

An electron and positron annihilate to produce two photons.

A
153
Q

Feynmann diagram for:

An up quark (in a proton) emits a gluon which in turn transforms into a down/antidown quark pair.

A

This reaction could take place as a result of a proton-proton collision: p + p → p + n + π+

154
Q

Feynmann diagram for:

Beta decay (hadron version)

A
155
Q

Feynmann diagram for:

A π° mediates the strong nuclear force between a proton and a neutron in a nucleus.

A

IB Physics HL (13 decks)

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