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4. Atoms & Radioactivity Flashcards

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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 Democritus’ theory about the atom?

A

400BC - all matter is made of small invisible units called atoms

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4
Q

What was Dalton’s theory about the atom?

A

1803 - agreed with Democritus and said atoms of the same element are identical and indestructible

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5
Q

What was Thomson’s theory about the atom?

A

1904 - Plum Pudding Model

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6
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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7
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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8
Q

What was Chadwick’s theory about the atom?

A

1932 - discovered the neutron

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9
Q

Which scientists were involved with the history of the atom?

A
  • Democritus
  • Dalton
  • Thomson
  • Rutherford
  • Bohr
  • Chadwick
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10
Q

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

A

The electron, by Thomson

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11
Q

What was the Plum Pudding Model?

A

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

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12
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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13
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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14
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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15
Q

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

A

Rutherford

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16
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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17
Q

Why was the chamber evacuated where the scattering experiment took place?

A

So the alpha particles didn’t change direction and so no other particles would affect the results

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18
Q

Why should alpha particles be repelled by positive atomic material?

A

They both have positive charges and like charges repel

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19
Q

What happens when isotopes have unstable nuclei?

A

They break down or disintegrate

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20
Q

What happens when isotopes break down or disintegrate?

A

They give out radiation said to be radioactive

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21
Q

What is the process when isotopes with unstable nuclei disintegrate?

A

Radioactive decay

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22
Q

What may nuclear radiation be?

A
  • an alpha particle
  • a beta particle
  • a gamma ray
  • a neutron
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23
Q

What does an alpha particle consist of?

A

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

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24
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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25
Q

What is a gamma ray?

A

High energy electromagnetic radiation from the nucleus

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26
Q

What are nuclear equations used to represent?

A

Radioactive decay

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27
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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28
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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29
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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30
Q

What is an ion?

A

An atom which has lost or gained an electron

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31
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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32
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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33
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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34
Q

What is the relative charge of an alpha particle?

A

+2

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35
Q

What is the relative charge of a beta particle?

A

-1

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36
Q

Properties of gamma radiation?

A

Weakly ionising as gamma is not charged

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37
Q

What is the range of alpha in air?

A

A few cm

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38
Q

What is the range of beta in air?

A

A few metres

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39
Q

What is the range of gamma in air?

A

Infinite

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40
Q

What can alpha radiation be stopped (absorbed) by?

A

Paper, card, skin

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41
Q

What can beta radiation be stopped (absorbed) by?

A

Sheet of aluminium (5mm)

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42
Q

What can gamma radiation be stopped (absorbed) by?

A

Thick sheet of lead or metres of concrete

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43
Q

Which type of radiation is most ionising?

A

Alpha

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44
Q

Which type of radiation is least ionising?

A

Gamma

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45
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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46
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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47
Q

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

A

Alpha as it’s least penetrating

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48
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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49
Q

What is alpha used in?

A

Smoke detectors

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50
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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51
Q

Why is alpha used in smoke detectors?

A
  • Ionising
  • Charged
  • Cannot penetrate though a plastic shield
  • Can be absorbed by smoke
  • Shortest range
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52
Q

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

A

They are less ionising and have a larger range

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53
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

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54
Q

What is beta used in?

A

Beta emitters test the thickness of thin sheets of metal

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55
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

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56
Q

What is gamma used for?

A
  • Tracers in medicine
  • Leak detection in pipes
  • Radiotherapy
  • Food irradiation
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57
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

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58
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

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59
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

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60
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

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61
Q

Why is gamma used in radiotherapy?

A

Gamma kills cancer cells

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62
Q

Why is gamma used in food irradiation?

A

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

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63
Q

What happens when there are more nuclei in a sample in terms of half life?

A

When there are more nuclei, more are likely to decay in one half life, so the higher the count rate will be

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64
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

or

• The time it takes for the count rate from a sample containing the isotope to fall to half its initial level

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65
Q

What is the net decline of a radioactive sample?

A

The fraction of nuclei that have decayed in a certain time

66
Q

How is the net decline of a radioactive sample portrayed?

A

Fraction, ratio, percentage

doesn’t have a unit

67
Q

What is the half life required when sterilising medical instruments?

A

Long - years

68
Q

What is the half life required when using medical tracers?

A

Short - days

69
Q

What is the half life required when using a thickness monitor?

A

Long - years

70
Q

What is the half life required when using industrial tracers?

A

Short - days

71
Q

What is the half life required when using a smoke alarm?

A

Long - years

72
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

73
Q

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

A

Gold

74
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

75
Q

Why should alpha particles be repelled by positive atomic material?

A

They’re both positively charged

76
Q

Why did Rutherford not expect the electrons to have any noticeable effect on the movement of the alpha particles?

A

Alpha particles are much larger and have momentum and so need force for them to deflect their direction

77
Q

What was the set-up that allowed Geiger and Marsden to observe what happened to the alpha particles in the scattering experiment?

A

A fluorescent screen that when hit by alpha gives off spots of light - looked at using a microscope

78
Q

During the scattering experiment, which path of the alpha particles agreed with the plum pudding model?

A

The path which was slightly deflected

79
Q

During the scattering experiment, which path of the alpha particles disagrees most strongly with the prediction of the plum pudding model?

A

The path which was reflected over 90 degrees -because alpha have a positive charge and repelled the positive protons in the nucleus of the gold atoms. The nucleus was so dense that it caused the alpha particles to bounce back

80
Q

During the scattering experiment, only 1 in 10,000 alpha particles were deflected over 90 degrees. What does this suggest about the nucleus of an atom?

A

It is very small so have very few collisions with alpha particles

81
Q

When does a nucleus become unstable?

A

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

82
Q

What is radiation detected with ?

A

A Geiger counter

83
Q

Define half life using the idea of activity

A

The time it takes for activity to half from its original value

84
Q

Define half life using the idea of count rate

A

The time it takes for count rate to half from its original value

85
Q

Define half life using the idea of undecayed atoms left in the source

A

The time it take for half of the nuclei present to decay

86
Q

How is nuclear radiation used in medicine for imaging?

A
  • radioactive tracers - imaging flows

* gamma cameras - imaging internal organs

87
Q

What do radioactive tracers image?

A

Flows inside the body

88
Q

What do gamma cameras image?

A

Internal organs

89
Q

Why is imaging using radioactive radiation important?

A

To help with diagnosis

90
Q

Why is nuclear radiation used in medicine?

A

For treatment; to destroy cancer cells

91
Q

What processes using nuclear radiation help with diagnosis?

A
  • radioactive tracers

* gamma cameras

92
Q

What processes using nuclear radiation help with treatment?

A
  • gamma radiotherapy

* radioactive implants

93
Q

What are radioactive tracers used for?

A

To trace the flow of a substance through an organ

94
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
95
Q

How is radioactive material put into a patients body to be used as a tracer?

A

By ingestion or injection

96
Q

What type of radiation is used in medical tracing?

A

Gamma

97
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

98
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

99
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

100
Q

What does a gamma camera do?

A

Images internal organs

101
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
102
Q

What are gamma cameras made from?

A

A crystal scintillator (sodium iodide)

103
Q

What happens when gamma hits a crystal scintillator?

A

It produces a burst of light

104
Q

What do photo multiplier tubes do?

A

Convert energy in electrical signals - which are fed to a computer to produce an image

105
Q

What does the lead grid do in a gamma camera?

A

Acts as a collinator - only allows gamma aligned with the holes to hit the crystal, making image sharper

106
Q

What is a collinator used for in a gamma camera?

A

To make the image sharper, less blurred

107
Q

What is the process happening inside a gamma camera to produce an image?

A
  • gamma rays hit a crystal scintillator and crystal produces a burst of light
  • bursts of light are picked up by a photo multiplier which convert energy to electrical signals
  • the electrical signals are sent to a computer to produce an image
108
Q

What does ionising mean?

A

When atoms are turned into ions by losing or gaining electrons

109
Q

What can ionising radiation do to cells?

A

Low doses - damage cells

High doses - destroy cells

This can lead to cancer

110
Q

How are cancer cells destroyed in a tumour?

A

Gamma radiation in narrow beams

111
Q

Where is radiation emitted from in radiotherapy?

A

A radioactive isotope of cobalt

112
Q

What is the half live of the radioactive isotope of cobalt?

A

Five years

113
Q

Why are narrow beams used in radiotherapy?

A

So that no tissue before the area that is being treated becomes damaged

114
Q

How do narrow beams of gamma destroy a tumour?

A

Lots of beams are shone from different angles to overlap on the problem area

115
Q

Why is gamma used in radiotherapy?

A

It can damage deep inside the body - it is very penetrating - and can escape the body easily

116
Q

Why is a half life of five years suitable for gamma radiotherapy?

A

It lasts for long enough so it doesn’t need to be replaced and the dose each patient receives doesn’t decrease

117
Q

What are gamma knives used for?

A

To accurately focus many beams of gamma radiation on one or more brain tumours

118
Q

What are the beams of radiation in gamma knives life?

A
  • very low intensity

* approximately 200 beams - concentrated on a small volume very accurately

119
Q

What are radioactive implants used for?

A

To attack the tumour from inside the body

120
Q

How do radioactive implants work?

A

The sources of radiation are placed directly inside the tumour or nearly tissue

121
Q

How long can radioactive implants stay in for?

A

Hours or days due to low dose rate sources

122
Q

What type of radiation can radioactive implants emit?

A

Beta because they are more local to the tumour and are more ionising than gamma

123
Q

What is a suitable half life for a radioactive implant?

A

A few weeks:

  • enough time for radiation dose to be low for an extended period
  • not long enough to stay active in patient after it’s needed
124
Q

Advantages of radioactive implants?

A
  • therapy over longer period compared to external beam therapy
  • radiation more localised - especially with beta
  • patient can spend less time in hospital
125
Q

Disadvantages of radioactive implants?

A
  • small risk of exposure of radiation to family and friends

* only early stage diseases and small tumours can be treated

126
Q

What is irradiation?

A

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

127
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

128
Q

What is contamination?

A

When the source of ionising radiation is transferred

129
Q

Example of contamination?

A

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

130
Q

Why is a patient more likely to get cancer through contamination than through irradiation?

A

In contamination the source of radiation is transferred and will stay in the body for longer. It is inside the body so is closer and therefore more intense.

131
Q

What is nuclear fission?

A

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

132
Q

Which nuclei are split in fission reactions?

A

Usually uranium-235 but also plutonium-239

133
Q

What is induced fission?

A

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

134
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
135
Q

What form of energy is released in fission?

A
  • radiation

* kinetic - of the neutrons and the fragment nuclei

136
Q

What happens in a chain reaction?

A

Each reaction causes more reactions which cause more reactions etc.

137
Q

What is the energy produced in fission used for?

A

Heats water and turns it into steam -> turns turbine -> turns generator transforms kinetic to electrical energy

138
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

139
Q

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

A

To absorb surplus neutrons to keep chain reaction under control

140
Q

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

A

To slow the fission neutrons down

141
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

142
Q

What is a fission neutron?

A

A neutron released when a nucleus undergoes nuclear fission

143
Q

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

A

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

144
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

145
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

146
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

147
Q

What is nuclear fusion?

A

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

148
Q

What process powers the sun and the stars?

A

Nuclear fusion

149
Q

How is the gas in a fusion reactor heated?

A

By passing an electric current through it

150
Q

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

A

It forms a plasma of small nuclei

151
Q

How is the plasma contained in a fusion reactor?

A

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

152
Q

What is one of the products when hydrogen nuclei fuse?

A

Helium

153
Q

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

A

The plasma would cool down, and fusion would stop

154
Q

In fusion, what do nuclei need to fuse?

A

Enough kinetic energy

155
Q

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

A

They will repel each other and not fuse

156
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)
157
Q

Disadvantages of nuclear fission?

A
  • produces radioactive waste
  • chain reaction must be controlled
  • non-renewable
158
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
159
Q

Disadvantages of nuclear fusion?

A

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

160
Q

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

A

Fusion

161
Q

Which type of nuclei fuse in the sun?

A

Hydrogen

162
Q

Which type of nuclei are formed in the sun?

A

Helium

Physics (11 decks)

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