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Physics Paper 2 > Mass and Energy > Flashcards

Mass and Energy Flashcards

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1
Q

What is the Mass and Energy Equation

A

E = mc2

Energy = Mass x Speed of Light2

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2
Q

What is the Mass Defect / Mass Difference

A

The difference between the total mass of all the nucleons sperately compared to the mass of the nucleus

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3
Q

Why is there a Mass Defect

A
  • Because energy is needed to bring the constituent parts of a nucleus together
  • The mass that is “lost” is converted into energy and released when the nucleons fuse to form a nucleus
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4
Q

What is Binding Energy

A

The energy required to separate the nucleus into its indivdual neutrons and protons

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5
Q

What is the Binding Energy per Nucleon

A

The binding energy per nucleon is the binding energy of a nucleus divided by the number of nucleons in the nucleus

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6
Q

Describe the graph of binding energy per nucleon against nucleon number

A
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7
Q

Which element has the highest binding energy per nucleon

A
  • Iron has the highest binding energy per nucleon
  • Nuclei smaller than iron can undergo fusion
  • Muclei larger than iron can undergo fission
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8
Q

What is the one Atomic Mass Unit

A

1u is defined as 1/12th of the mass of a carbon-12 atom, which is 1 × 1 .661 x 10-27 kg

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9
Q

What is Nuclear Fission

A
  • Nuclear fission is the splitting of a large nucleus into two daughter nuclei with the release of lots of energy
  • It occurs in very large nuclei, which are unstable (such as uranium), and occurs completely randomly, howevever it can also be induced
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10
Q

Why is Energy released during Nuclear Fisson

A

The smaller daughter nuclei have a higher binding energy per nucleon

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11
Q

What is Nuclear Fusion

A
  • Nuclear fusion is where two smaller nuclei join together to form one larger nucleus
  • It only occurs in fairly small nuclei
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12
Q

Explain why energy is released during Nuclear Fussion

A

The larger nucleus has a much higher binding energy per nucleon

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13
Q

State two nuclei that are most likely to be used to form the plasma of a fusion reactor

A

Deuterium and tritium

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14
Q

Does Fusion or Fission release more energy

A

Fussion releases far more energy than fission however fusion can only occur at extremely high temperatures (for example in stars) because a massive amount of energy is required to overcome the electrostatic force of repulsion between nuclei

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15
Q

Describe how fission can be induced

A

Fission can be induced by firing a thermal neutron into the uranium nucleus causing it to become extremely unstable

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16
Q

What are the Advantages and Disadvantages of using Nuclear Fisson to generate electrcity

A

Advantages -

  • No greenhouse gases are emitted reducing global warming
  • The quanity of waste is small compared to other methods of generating electricty because far less fuel is used
  • It is quite a reliable way of generating electricty as supplies of uranium are set to last thousands of years (not completely reliable though) and the output can be controlled to match demands

Disadvantages -

  • The waste products need to be stored securely for many decades (though only small waste and some can be recycled)
  • New nuclear power stations are extremely expensive
  • Decommissioning nuclear power stations is very expensive as the safe disposal of intermediate-level waste adds to the cost
  • Risk of nuclear meltdown could have catastrophic consequences
17
Q

Why are thermal neutrons used to induce fisson

A

Thermal neutrons have a low energy meaning they can induce fission whereas neutrons with a higher energy rebound away from the uranium-235 after a collision and do not cause a fission reaction.

18
Q

How is fission used in nuclear reactors

A
  • Rods of uranium-235 absorb neutrons and become unstable and then split into two daughter nuclei
  • They also then release 2/3 more neutrons
  • The neutrons released during fission then have the possibility to go on to cause more fission reactions forming a chain reaction, where each fission goes on to cause at least one more fission
19
Q

What is Critical Mass

A
  • The critical mass is the minimum mass of fuel required to maintain a steady chain reaction
  • Using exactly the critical mass of fuel will mean that a single fission reaction follows the last, while using less than the critical mass would lead the reaction to eventually stop
20
Q

What are the key features inside a thermal nuclear reactor

A
  • Moderator
  • Control rods
  • Coolant
21
Q

What is the function of a Moderator

A
  • To slow down the neutrons so they travel slow enough to be absorbed by the uranium
  • They do this through elastic collisons between the moderator and the nucleus
22
Q

Describe the best choice of material for the moderator

A
  • The closer the moderator atoms are in size to a neutron, the larger the proportion of momentum which is transferred, therefore the lower the number of collisions required to get the neutrons to thermal speeds
  • Because of this, water is often used as a moderator as it contains hydrogen, also it’s inexpensive and not very reactive
  • Graphite is also used as a moderator
23
Q

What is the function of the control rods in a thermal nuclear reactor

A
  • They absorb neutrons so that only 1 of the neutrons released in each reaction can go on to be absorbed by another uranium
  • This stops the chain reaction from being out of control and the reactor from overheating from too many reactions happening at once
24
Q

Describe the best choice of material for the control rods

A

They are made of materials which absorb neutrons without undergoing fission such as boron and cadmium

25
Q

What is the function of the coolant in a thermal nuclear reactor

A
  • The colleant absorbs the heat released during fission reactions in the core of the reactor, this stops the reactor from overheating
  • This heat is then used to make steam which powers electricity-generating turbines
26
Q

Describe the best choice of material for the coolant

A
  • Water is used as it has a high specific heat capacity meaning it can transfer large amounts of thermal energy
  • Otherwise molten salt or gas (e.g helium) can be used as a coolant
27
Q

What fuel is used in a nuclear reactor

A
  • The fuel used in nuclear reactors is called enriched uranium, which is formed through the enrichment of mined uranium which consists of around 99% U-238
  • U-238 does not experience fission
  • The U-238 absorbs fission neutrons and so helps to control the rate of fission reactions
28
Q

Why are fuel rods are added remotely

A

The fuel rods are inserted into the reactor remotely to limit the worker’s exposure to radiation

29
Q

Describe some of the safety aspects used in a nuclear reactor

A
  • Fuel used - the fuel used in nuclear reactors is called enriched uranium, which is formed through the enrichment of mined uranium which consists of around 99% U-238, U-238 does not experience fission and asorbs fission neutrons and so helps to control the rate of fission reactions
  • Remote handling of Fuel - the fuel rods are inserted into the reactor remotely to limit the worker’s exposure to radiation
  • Shielding - around the nuclear reactor is a very thick concrete shielding, which blocks radiation from escaping from the reactor and affecting the workers in the power station
  • Emergency shut-down - in an emergency, the control rods are dropped into the reactor core entirely in order to stop fission reactions from occuring as soon as possible by absorbing all the free neutrons in the core
30
Q

Why are spent fuel rods the most dangerous product from a nuclear reaction

A

Spent fuel rods are the two daughter nuclei that are produced, these nuclei are usually extremely unstable and have a very high activity because of this spent fuel rods are some of the most dangerous types of nuclear waste

31
Q

What is an example of High Level Waste

A

Spent fuel rods

32
Q

Describe how High Level Waste is disposed off

A
  1. The waste is removed and handled remotely, so that exposure is limited
  2. Any material removed from the reactor will be extremely hot due to fission reactions occurring within the reactor, so they must be placed in cooling ponds for up to a year while they may still be producing heat due to radioactive emissions
  3. At this point any plutonium or usable uranium is removed from spent fuel rods in order to be recycled
  4. The waste is then vitrified (encased in glass) and placed in thick steel casks and stored in deep caverns in geologically stable locations, so that there is no chance of the waste coming free of its casing.
33
Q

What are some examples of Low Level Waste

A
  • Shielding used to protect workers
  • Clothes and gloves used by workers
  • Tools used
    *
34
Q

How is Low Level Waste disposed off

A

Low-level waste can be disposed of close to the surface as it will not take very long to stop being radioactive

Physics Paper 2 (9 decks)

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