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A level Physics > Unit 3.6 - Nuclear energy > Flashcards

Unit 3.6 - Nuclear energy Flashcards

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1
Q

Binding energy

A

The energy required to completely separate the nucleus to its constituent nucleons

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2
Q

What can we know about the nucleus of an element from looking at it on the periodic table?

A

Number of protons and neutrons (top number)
Number of protons (bottom number)

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3
Q

How do we work out the number of neutrons in an element?

A

Top number - bottom number

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4
Q

How many protons and neutrons are there in a helium nucleus?

A

2 protons, 2 neutrons

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5
Q

1u

A

1 atomic mass unit

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6
Q

1 atomic mass unit (1u) definition

A

A mass equal to 1/12th of the mass of a carbon atom

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7
Q

What is it important NOT to do in this unit and why?

A

Round up or down since the numbers are so small

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8
Q

Mass defect symbol

A

Δm

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9
Q

Δm

A

Mass defect

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10
Q

Mass defect

A

The difference between the mass of the constituents and the mass of the nucleus - the energy put into the system to break it apart

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11
Q

What’s happened to the mass defect?

A

Has been turned into energy, usually kinetic

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12
Q

Equation for calculating the binding energy of a nucleus

A

E = mc^2

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13
Q

What does E = mc^2 allow us to calculate?

A

The binding energy of the nucleus

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14
Q

m in E = mc^2

A

Mass defect (u) x conversion to kg

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15
Q

c in E = mc^2

A

Speed of light

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16
Q

Converting from J to eV

A

Divide by the charge of an electron

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17
Q

1eV

A

The energy transferred when an electron travels across a p.d of 1V
Since energy transferred = charge x pd

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18
Q

MeV meaning

A

Mega electron volts

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19
Q

What’s the shortcut equation for working out binding energy in MeV?

A

Δm x 931 = E(MeV)

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20
Q

How come we can use a shortcut equation for working out binding energy?

A

Since there’s so many constants

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21
Q

What does the shortcut equation for binding energy give th answer in?

A

MeV

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22
Q

Equation for the binding energy per nucleon

A

Total binding energy/amount of nucleons

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23
Q

Nucleons

A

Things in the nucleus (protons and neutrons)

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24
Q

Protons and neutrons name

A

Nucleons

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25
Q

Why is mass that’s converted into energy huge?

A

By examining E=mc^2, we see that it’s huge since it’s multiplied by 3x10^8 squared

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26
Q

Does a nucleon have less mass in a nucleus or at rest outside the nucleus?

A

Less mass in the nucleus

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27
Q

What’s the lowest - the total mass of a nucleus or the total mass of the nucleons that make it?

A

The total mass of the nucleus is less

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28
Q

Describe the mass defect of larger atoms

A

Larger

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29
Q

What does it mean if an atom has a larger mass defect?

A

It requires more energy to pull them apart

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30
Q

How is the energy taken to bind together an atom and why?

A

The energy is taken directly from the mass of individual nucleons, since if all the nucleons were brought together from infinity, then the repulsive forces (between the protons) would be huge

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31
Q

What holds together nucleons once they’re in a very small distance of arch other?

A

The strong force

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32
Q

What are the forces acting inside the nucleus of atoms?

A

Strong force
Electromagnetic force

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33
Q

Strong force

A

Pulls protons and neutrons together

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34
Q

Electromagnetic force

A

Pulls protons and neutrons apart

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35
Q

Which force is stronger - the strong force or the electromagnetic force?

A

The strong force

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36
Q

Under which condition is the strong force stronger than the electromagnetic force?

A

At short ranges

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37
Q

Range of the strong force

A

Roughly 21/2 nucleons in diameter

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38
Q

Which force dominates at larger distances inside the nucleus of atoms?

A

The electromagnetic force

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39
Q

What happens to the nucleus of an atom as we initially add nucleons and work up the periodic table?

A

Initially, each nucleus is more tightly bound than the on before = increasing binding energy

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40
Q

Up to which element does the binding energy of the nucleus of atoms increase?

A

Iron

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41
Q

What does it mean if a nucleus is more tightly bound?

A

Higher binding energy

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42
Q

Which element has the highest binding energy of all of the elements?

A

Iron

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43
Q

Which element has the most stable nucleus and why?

A

Iron
Has the highest binding energy
Requires the greatest energy to form

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44
Q

What does a Higher binging energy mean for a nucleus?

A

More stable nucleus

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45
Q

Past which element does the electromagnetic force begin to dominate over the strong force in nuclei and why?

A

Past iron
The nucleus now has a radius more than 2 1/2 nucleons wide

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46
Q

Why does the electromagnetic force begin to dominate in nuclei past iron?

A

Since the nucleus now has a radius more than 2 1/2 nucleons wide

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47
Q

What happens when nucleons are added beyond iron? Why?

A

The electromagnetic force is winning and so each added nucleon is less tightly bound

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48
Q

At which element does the electromagnetic force beat the strong force?

A

Lead

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49
Q

Which elements are radioactive? why?

A

Anything past lead since the electromagnetic force and they’re now nuclei are unstable and come apart by themselves

50
Q

What does it mean that the elements past lead are unstable and come apart by themselves?

A

Are radioactive

51
Q

How can unstable nuclei become more stable?

A

Can split into other more stable nuclei —> fission

52
Q

Fission

A

When unstable nuclei splint into other more stable nuclei

53
Q

Which side of a binding energy graph shows the nuclei available for fusion?

A

LHS of iron

54
Q

Which side of a binding energy graph shows the nuclei available for fission?

A

RHS of iron

55
Q

What do both nuclear fission and fusion do?

A

Release energy

56
Q

How can we understand the differences between nuclear fission and fusion?

A

We need to look at the binding energy

57
Q

What happens during nuclear fission?

A

In order to “force” a nucleus to break up, a neutron is introduced

58
Q

How is a nucleus broken up during nuclear fission?

A

By introducing a neutron

59
Q

Are many neutrons required for nuclear fission?

A

No

60
Q

Why is a neutron used during nuclear fission?

A

Because of its electrical properties, since a proton would be repelled from any nucleus

61
Q

What would happen if a proton was used in nuclear fission instead of a neutron?

A

The proton would be repelled from the nucleus

62
Q

How can we easily explain the idea of nuclear fission?

A

The liquid drop model of the nucleus:
Large drop of water on a surface
Very small amount of water added to the drop = becomes unstable and breaks up

63
Q

Explain nuclear fission in uranium-235

A

When a neutron is added to uranium-235, it forms the very unstable uranium-236
This splits apart to produce 2 lighter atoms
Releases more neutrons than were put in
Moves up the binding energy curve —> binding energy per nucleon increases from about 7.5MeV to. Little under 8.5MeV
Since there are over 200 nucleons involved in the reaction, this represents the release of approximately 200MeV of energy per uranium-235 atom fissioned

64
Q

What happens when a nucleus is added to uranium-235?

A

It forms the very unstable uranium-236

65
Q

What does unstable uranium-236 do?

A

Splits apart to produce 2 lighter atoms

66
Q

Are more neutrons put in or taken out during nuclear fission?

A

More neutrons released than those put in

67
Q

How does nuclear fission cause a chain reaction?

A

More neutrons are released than those put in

68
Q

What happens to the binding energy per nucleon during nuclear fission?

A

Increases

69
Q

What is a good absorber do neutrons to slow down the reactions of nuclear fission?

A

Boron control rod

70
Q

Why is a boron control rod used during nuclear fission?

A

It’s a good absorber of neutrons to slow down the reaction

71
Q

What happens when a control rod fails during nuclear fission?

A

A nuclear accident occurs

72
Q

How do we calculate the energy released per nucleus during nuclear fission or fusion?

A

∆m = sum of mass on LHS - sum of mass on RHS (or the other way around, it’s just the difference between them)
Energy released (MeV) = ∆m x 931

73
Q

Why is uranium-236 not included in the calculation for the energy released during nuclear fission?

A

Very unstable and very brief so no need to include it in the calculation

74
Q

Why does nuclear fusion occur?

A

Because the sum of the mass on the left hand side is greater than that on the right hand side

75
Q

Do the products of nuclear fission have an increased or decreased binding energy per nucleon? Why?

A

Products have an increased binding energy per nucleon
Remember, binding energy is the energy given out when a nucleus is formed

76
Q

Nuclear Fusion

A

The joining of two light nuclei to form a heavier nucleus

77
Q

How does nuclear fusion produce energy?

A

Just like in nuclear fission, the production of energy results from the increase in binding energy of the products of the reaction over the reactants (the RHS having less mass than the LHS)

78
Q

Deuterium

A

Heavy hydrogen

79
Q

Heavy hydrogen

A

Deuterium

80
Q

Deuterium symbol

A

2
H
1

81
Q

When can we round up in this unit?

A

At the very end of working out the energy

82
Q

What’s highest, the energy released during the fusion of deuterium or the energy released during the fission of uranium-235?

A

The energy released during the fission of uranium-235

83
Q

What is highest - the energy released per nucleon during fission or fusion?

A

Fission

84
Q

What’s another advantage to using fission over fusion other than that it releases more energy per nucleon?

A

The products are more stable and aren’t radioactive

85
Q

What do we move up during fission?

A

The binding energy curve

86
Q

Is a lot of energy released during nuclear fusion? Explain

A

Although it’s less than that released per nucleon during nuclear fission, the mass is several times less than the energy released, so a lot of energy can be obtained from very little fuel

87
Q

How has nuclear fusion been achieved so far?

A

In an uncontrolled way in thermonuclear explosions (the hydrogen bomb)

88
Q

Why is it difficult to harness nuclear fusion for more peaceful purposes?

A

The difficulty comes in providing the energy to enable two positively charged nuclei to overcome huge repulsion caused by the electric force between protons in the nuclei so that they can come close enough for the strong nuclear force to cause them to fuse

89
Q

Why do we need energy for nuclear fusion to occur?

A

We need energy to enable two positively charged nuclei to overcome the huge repulsion caused by the electric force (between protons in the nuclei) so that they can come close enough for the strong nuclear force to cause them to fuse

90
Q

How are nuclei given kinetic energy for nuclear fusion?

A

Through the use of extremely high temperatures, between 10^8k and 10^10k

91
Q

What’s plotted on a binding energy per nucleon curve?

A

Negative binding energy per nucleon

92
Q

By plotting negative binding entry per nucleon on the binding energy curves, what does it mean?

A

The more either process moves the resulting nucleus up the curve, the more energy is released

93
Q

What fact shows why fusion releases much more energy per unit mass?

A

The fact that it is energy released per nucleon

94
Q

Assumption made in nuclear fusion/fission calculations

A

That the energy just about causes the reaction with no leftover energy (conservation of energy)

95
Q

Isotopes

A

Nuclei with the same atomic number (proton number) but different nucleon number (due to different neutron numbers)

96
Q

What happens on a binding energy per nucleon curve at a helium nucleus?

A

There’s a spike

97
Q

Why is there a spike at the helium nucleus on a binging energy per nucleon curve?

A

Very high binding energy

98
Q

What does a high binding energy mean for a nucleus?

A

Stable nucleus

99
Q

How do we know if an element has a stable nucleus?

A

High binding energy

100
Q

Why is alpha decay likely?

A

As the helium nucleus is a very stable nucleus (high binding energy) and alpha decay emits helium nuclei

101
Q

Explain why nuclear fission is possible in the case of some elements and nuclear fusion in others

A

Nucleons to the left of iron-56 with a lower nucleon number will move up the binding energy per nucleus curve if they fuse together. Those to the right of the iron-56 with a higher nucleon number will move up the curve by fissioning.
The higher up the curve, the more stable the nucleus.

102
Q

What happens to the nucleus the higher up the binding energy per nucleon curve we are?

A

The more stable

103
Q

How do we know if a nucleus is more stable?

A

Higher binding energy per nucleon

104
Q

What does a positive energy output imply in a nuclear equation?

A

Getting more stable

105
Q

What is higher - the binding energy of the products or reactants when energy is released during the reaction? Why?

A

The total binding energy of the products is greater as if energy is released, they’re getting more stable so the binding energy is higher

106
Q

Which conservation laws do nuclear reactions have to follow?

A

Conservation of momentum
Conservation of energy

107
Q

Conservation of momentum

A

Momentum before = momentum after

108
Q

What is the binding energy of n and p? Why?

A

Zero
They are the constituents

109
Q

How come energy is released during fusion and fission?

A

When a reduction in mass occurs, energy is released (mass converted into energy)

110
Q

What do we do in a question where we’re asked to “determine a value” and we’re given a graph?

A

Calculate the gradient

111
Q

What do we do in a question where we’re asked to “justify” a claim?

A

Do calculations

112
Q

When would we have to use the E=mc^2 method to calculate the binding energy of a nucleus or the energy released in a reaction?

A

If given masses in kg instead of u

113
Q

How do both fusion and fission release energy?

A

Mass is converted into energy

114
Q

u to kg

A

MULTIPLY by conversion factor in data book

115
Q

MeV to J

A

x e
x 10^6

116
Q

How do we know when energy has been released?

A

BE per nucleon/stability increases

117
Q

What happens when BE per nucleon or stability Increases?

A

Energy is released

118
Q

What happens per revolution in a synchrotron?

A

Two energy kicks

119
Q

What’s m in F = mv x no of electrons per second when working out the force an electron beam exerts on a target?

A

The mass of one electron

120
Q

What do we need to mention about fusion and fission every time?

A

Energy released = binding energy per nucleon increases = stability increases, lower mass

A level Physics (29 decks)

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