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Physics Y10&Y11 > Atoms & Radioactivity for EOY10 exam > Flashcards

Atoms & Radioactivity for EOY10 exam Flashcards

1
Q

Examples of nucleons?

A

Protons and neutrons

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2
Q

What is the majority of the mass of an atom?

A

The nucleus, as the mass of an electron is almost zero compared to the mass of protons and neutrons

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3
Q

What was Thomson’s theory about the atom?

A

1904 - Plum Pudding Model

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4
Q

What was Rutherford’s theory about the atom?

A

1911 - Nuclear Model; that most of the mass of the atom was concentrated in the nucleus which carries a positive charge

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5
Q

What was Bohr’s theory about the atom?

A

1913 - Bohr’s model, electrons orbit nucleus in certain energy levels

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6
Q

What was Chadwick’s theory about the atom?

A

1932 - discovered the neutron

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7
Q

Which was the first sub-atomic particles to be discovered?

A

The electron, by Thomson

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8
Q

What was the Plum Pudding Model?

A

A sphere of positive charge (dough) with electrons dotted inside (plums)

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9
Q

What did the discovery of the electron show about atoms?

A

That atoms were not the smallest thing, as the electron was smaller than the atom

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10
Q

What did the Bohr model show?

A
  • That electrons can only orbit the nucleus in certain energy levels
  • Electromagnetic energy is emitted from the atom if an electron jumps from an excited energy level to one that’s closer to the nucleus
  • If an electron absorbs energy it can jump to a higher energy state from the nucleus
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11
Q

What did later experiments suggest about the atom?

A
  • the positive charge of any nucleus could be subdivided into a whole number of smaller individual sub-atomic particles called protons
  • 1934 - Chadwick used alpha scattering experiment to provide evidence for existence of the neutron
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12
Q

Who was the first to call the nucleus of a hydrogen atom a proton?

A

Rutherford

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13
Q

In the scattering experiment, how could have the alpha particles been supplied and been moving in the right direction?

A

From radioactive matter. Surrounded by lead shielding apart from a small opening facing the way they wanted the beam

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14
Q

What happens when isotopes have unstable nuclei?

A

They break down or disintegrate

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15
Q

What happens when isotopes break down or disintegrate?

A

They give out radiation said to be radioactive

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16
Q

What is the process when isotopes with unstable nuclei disintegrate?

A

Radioactive decay

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17
Q

What may nuclear radiation be?

A
  • an alpha particle
  • a beta particle
  • a gamma ray
  • a neutron
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18
Q

What does an alpha particle consist of?

A

2 neutrons and 2 protons - the same as a helium nucleus

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19
Q

What is a beta particle?

A

When a high speed electron is ejected from the nucleus as a neutron changes into a proton

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20
Q

What is a gamma ray?

A

High energy electromagnetic radiation from the nucleus

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21
Q

What are nuclear equations used to represent?

A

Radioactive decay

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22
Q

What happens to the mass and charge of the nucleus during alpha decay?

A

Both the mass and charge of the nucleus decease

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23
Q

What happens to the mass and charge of the nucleus during beta decay?

A

The mass of the nucleus doesn’t change however the charge of the nucleus increases

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24
Q

What happens to the mass and charge of the nucleus during gamma decay?

A

The emission of a gamma ray doesn’t cause the mass or charge of the nucleus to change

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25
Q

What is an ion?

A

An atom which has lost or gained an electron

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26
Q

What happens when radioactive radiation strikes atoms in a substance?

A

They can knock an electron from one atom to another

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27
Q

Properties of alpha particles?

A
  • Relatively big, heavy and slow moving
  • Large relative charge (+2)
  • Strongly ionising - bash into lots of atoms and knock electrons off them
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28
Q

Properties of beta particles?

A
  • Quite small and move quite fast

* Moderately ionising because they have a smaller relative charge (-1)

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29
Q

What is the relative charge of an alpha particle?

A

+2

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30
Q

What is the relative charge of a beta particle?

A

-1

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31
Q

Properties of gamma radiation?

A

Weakly ionising as gamma is not charged

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32
Q

What is the range of alpha in air?

A

A few cm

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33
Q

What is the range of beta in air?

A

A few metres

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34
Q

What is the range of gamma in air?

A

Infinite

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35
Q

What can alpha radiation be stopped (absorbed) by?

A

Paper, card, skin

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36
Q

What can beta radiation be stopped (absorbed) by?

A

Sheet of aluminium (5mm)

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37
Q

What can gamma radiation be stopped (absorbed) by?

A

Thick sheet of lead or metres of concrete

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38
Q

Which type of radiation is most ionising?

A

Alpha

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39
Q

Which type of radiation is least ionising?

A

Gamma

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40
Q

What is the safest type of radiation to have inside the body?

A

Gamma as it’s the least ionising and escapes easily

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41
Q

What is the most dangerous type of radiation to have inside the body?

A

Alpha as it’s most ionising and cannot escape

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42
Q

What is the safest type of radiation to have outside the body?

A

Alpha as it’s least penetrating

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43
Q

What is the most dangerous type of radiation to have outside the body?

A

Gamma as it’s most penetrating

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44
Q

What is alpha used in?

A

Smoke detectors

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45
Q

How do smoke detectors work?

A

Alpha ionises air particles causing a current to flow. If there is smoke in the air, the smoke binds to the ions reducing the number available to carry a current. Current falls and alarm sounds

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46
Q

Why is alpha used in smoke detectors?

A
  • Ionising
  • Charged
  • Cannot penetrate though a plastic shield
  • Can be absorbed by smoke
  • Shortest range
47
Q

Why aren’t beta or gamma used in smoke detectors?

A

They are less ionising and have a larger range

48
Q

Are smoke detectors safe given they contain alpha particles?

A

Yes as alpha has a short range and not penetrating, provided it is not pulled apart

49
Q

What is beta used in?

A

Beta emitters test the thickness of thin sheets of metal

50
Q

Why is beta used to test thickness of metal?

A

Particles are not immediately absorbed by the material like alpha, and do not penetrate as far as gamma

51
Q

What is gamma used for?

A
  • Tracers in medicine
  • Radiotherapy
  • Food irradiation
52
Q

How is gamma used for tracers in medicine?

A

Gamma radiation should be emitted from the source injected into the patient, so it can be detected outside the body

53
Q

Why isn’t alpha used for tracers in medicine?

A

Would be too dangerous as the ionisation it causes could mutate cells and cause cancer

54
Q

How is beta used for leak detection in pipes?

A

The radioactive isotope is injected into the pipe. The outside of the pipe is checked with a Geiger-Muller detector to find areas of high radioactivity - where the pipe is leaking

55
Q

Why is beta used for leak detection in pipes?

A

It has a short half life so the material doesn’t become a long term problem. It has to be detected through the metal as well as the earth

56
Q

Why is gamma used in radiotherapy?

A

Gamma kills cancer cells

57
Q

Why is gamma used in food irradiation?

A

Because gamma keeps it fresh for longer as it kills bacteria or fungi

58
Q

What is the half life of a radioactive isotope?

A

• The average time it takes for the number of nuclei of the isotope in a sample to half

59
Q

What is the net decline of a radioactive sample?

A

The fraction of nuclei that have decayed in a certain time

60
Q

How is the net decline of a radioactive sample measured?

A

Fraction, ratio, percentage

doesn’t have a unit

61
Q

What did Rutherford expect the alpha particles to do in the scattering experiment? Why?

A

He expected them to go through the thin sheet of atoms easily because they were moving at a very high speed

62
Q

What was the material of the sheet of atoms in the scattering experiment?

A

Gold

63
Q

What was Rutherford expecting to observe in the scattering experiment? Why?

A

For slight changes in the direction of the alpha particles due to them repelling from the thinly spread positive material of the atoms

64
Q

When does a nucleus become unstable?

A

When it possesses either too many or too few neutrons compared to the number of protons

65
Q

What is radiation detected with ?

A

A Geiger counter

66
Q

How is nuclear radiation used in medicine for imaging?

A
  • radioactive tracers - imaging flows

* gamma cameras - imaging internal organs

67
Q

What do radioactive tracers image?

A

Flows inside the body

68
Q

What do gamma cameras image?

A

Internal organs

69
Q

Why is imaging using radioactive radiation important?

A

To help with diagnosis

70
Q

Why is nuclear radiation used in medicine?

A

For treatment; to destroy cancer cells

71
Q

What processes using nuclear radiation help with diagnosis?

A
  • radioactive tracers

* gamma cameras

72
Q

How do radioactive tracers work?

A
  • a small amount of radioactive material is put into the patients body
  • tracer is given time to move through body
  • radioactive detector is positioned to detect radiation outside the body
  • multiple images are taken to show progress of tracer over time
73
Q

What type of radiation is used in medical tracing?

A

Gamma

74
Q

Why is gamma used in medical tracing?

A

It is the least ionising and the most penetrating, meaning it can leave the body eventually

75
Q

Why isn’t alpha used in medical tracing?

A

It can’t be detected outside the body and is very ionising so would damage cells as it moved through the bloody

76
Q

What are the properties of gamma that ensure medical tracing is not harmful to the patient?

A

Gamma is not ionising, has a short half life and is not toxic

77
Q

What does a gamma camera do?

A

Images internal organs

78
Q

How does a gamma camera work?

A
  • a radioactive isotope (gamma emitting) is objected into the patient
  • the isotope concentrates in the organ
  • a gamma camera is positioned over the area emitting gamma
79
Q

What does ionising mean?

A

When atoms are turned into ions by losing or gaining electrons

80
Q

What can ionising radiation do to cells?

A

Low doses - damage cells

High doses - destroy cells

This can lead to cancer

81
Q

How are cancer cells destroyed in a tumour?

A

Gamma radiation in narrow beams

82
Q

What is irradiation?

A

When the radiation stops as soon as the source of radiation has been removed

83
Q

Example of irradiation?

A

When a light is turned on the room is filled with electromagnetic radiation (visible light). When the light is turns off the electromagnetic radiation is gone

84
Q

What is contamination?

A

When the source of ionising radiation is transferred

85
Q

Example of contamination?

A

When radioactive isotopes in solids, liquids or gases are introduced into the environment

86
Q

What is nuclear fission?

A

The splitting of a large nucleus into two smaller nuclei (‘daughters’) while releasing energy

87
Q

Which nuclei are split in fission reactions?

A

Usually uranium-235 but also plutonium-239

88
Q

What is induced fission?

A

When a reaction occurs due to a neutron being fired at a uranium nucleus

89
Q

What do fission reactions release?

A
  • two or three neutrons at high speeds (these are used in further reactions)
  • energy in the form of radiation and kinetic energy of the fission neutrons
90
Q

What form of energy is released in fission?

A
  • radiation

* kinetic - of the neutrons and the fragment nuclei

91
Q

How is the output of a nuclear fission power station made stable?

A

The energy released must be constant and not grow rapidly like in an uncontrolled chain reaction

92
Q

In a nuclear reactor, what is the function of the control rods?

A

To absorb surplus neutrons to keep chain reaction under control

93
Q

In a nuclear reactor, what is the function of the moderator?

A

To slow the fission neutrons down

94
Q

Why is water used as a moderator in a nuclear reactor?

A

Fission neutrons are slowed down by collisions with the atoms in the water molecules

95
Q

What is a fission neutron?

A

A neutron released when a nucleus undergoes nuclear fission

96
Q

In a nuclear reactor, what is the function of the coolant?

A

Water - transfers heat so radioactive water is not turned to steam

97
Q

In a nuclear reactor, why is the reactor core in a thick steel vessel surrounded by concrete walls?

A

To withstand high temperature and pressure. Walls absorb gamma radiation that escapes steel vessel

98
Q

In a nuclear reactor, why does the coolant circulate through sealed pipes to and from a heat exchanger?

A

So contaminated water is not turned to steam and enters the atmosphere

99
Q

In a nuclear reactor, why may the control rods need to be inserted completely into the reactor core?

A

So there isn’t too much energy being released from uncontrolled fission

100
Q

What is nuclear fusion?

A

When two small nuclei collide and fuse to form a larger nucleus, releasing energy

101
Q

What process powers the sun and the stars?

A

Nuclear fusion

102
Q

What happens when the gas in a fusion reactor gets very hot?

A

It forms a plasma of small nuclei

103
Q

How is the plasma contained in a fusion reactor?

A

Using a magnetic field to prevent it from touching the container walls

104
Q

What is one of the products when hydrogen nuclei fuse?

A

Helium

105
Q

What happens in a fusion reactor if the plasma touches the sides of the container?

A

The plasma would cool down, and fusion would stop

106
Q

In fusion, what do nuclei need to fuse?

A

Enough kinetic energy

107
Q

In fusion, what happens if nuclei do not have enough kinetic energy to fuse?

A

They will repel each other and not fuse

108
Q

Advantages of nuclear fission?

A
  • concentrated source of energy
  • no polluting gases - energy is released from nuclear reactions not combustion
  • supply of uranium for many years
  • reliable - 24/7 (doesn’t depend on weather like renewables)
109
Q

Disadvantages of nuclear fission?

A
  • produces radioactive waste
  • chain reaction must be controlled
  • non-renewable
110
Q

Advantages of nuclear fusion?

A
  • produces very little radioactive waste - safer
  • no chain reaction to control - safer
  • even more concentrated energy
  • fuel readily available (hydrogen in water)
  • renewable
  • hydrogen is cheap
111
Q

Disadvantages of nuclear fusion?

A

• not yet viable - fusion on earth needs more energy input than output (need 5 million amp current!)

112
Q

Which is a more concentrated source of energy: fission or fusion?

A

Fusion

113
Q

Which type of nuclei fuse in the sun?

A

Hydrogen

114
Q

Which type of nuclei are formed in the sun?

A

Helium

Physics Y10&Y11 (17 decks)

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