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Physics > Nuclear Physics Part 2 > Flashcards

Nuclear Physics Part 2 Flashcards

1
Q

What is mass defect or mass difference?

A

The difference in mass between a nucleus and the mass of its constituent nucleons.

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2
Q

What is binding energy?

A

The energy needed to separate all of the nucleons in a nucleus.

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3
Q

How do you work out the average binding energy per nucleon?

A

Binding energy divided by nucleon number.

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4
Q

Describe the graph of Average Binding Energy Per Nucleon against Nucleon Number.

A
  • Steep gradient starting at about 1 MeV/2 nucleons and peaking at 8.8 MeV/56 nucleon number
  • Steady decrease after peak down to about 7.2 MeV/250 nucleons
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5
Q

What is the most stable nucleus?

A

Iron.

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6
Q

What is Fission?

A

When large nuclei are unstable and split into two smaller nuclei.

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7
Q

Why is energy released in Fission?

A

Because the new, smaller nuclei have a higher average binding energy per nucleon.

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8
Q

How can Fission be induced?

A

By making a neutron enter a Uranium-235 nucleus, causing it to become very unstable.

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9
Q

What is a low energy neutron called?

A

A thermal neutron.

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10
Q

What is Fusion?

A

When two light nuclei combine to create a larger nucleus.

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11
Q

Why is a lot of energy released in Fusion?

A

Because the new, heavier nuclei have a much higher average binding energy per nucleon.

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12
Q

Why is it so hard to fuse nuclei together and about how much kinetic energy is needed?

A
  • Because all nuclei are positively charged therefore there will be an electrostatic force of repulsion between them
  • About 1 MeV of kinetic energy needed to fuse nuclei together
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13
Q

How can you tell if it is energetically favourable for an element to undergo fission or fusion?

A
  • By looking at the graph of average binding energy per nucleon against nucleon number
  • Elements to the right of Iron can release energy through nuclear fission, and elements to the left of Iron can release energy through nuclear fusion
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14
Q

How can you work out the energy released through fusion or fission?

A

The change in binding energy gives the energy released.

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15
Q

What is another way of finding the energy released during fission or fusion other than using the graph?

A

Using E = Δmc ^ 2, where Δm is the total difference in mass between the initial and final nuclei (including neutrons).

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16
Q

What are the 5 things included in a Nuclear Fission Reactor?

A
  • Control rods
  • Concrete case
  • Fuel rods
  • Moderator
  • Coolant
17
Q

What do fuel rods contain and what are they used for?

A

Fuel rods contain Uranium-235 (sometimes Plutonium-239) which are used as fuel.

18
Q

How are chain reactions used in Nuclear Fission Reactors?

A
  • Fission reactions produce more neutrons which then induce other nuclei to fission
  • Neutrons will only cause a chain reaction if they’re slowed down
19
Q

What is an example of a moderator and what is it used for?

A
  • A good moderator is water

- It is used to slow down and/or absorb neutrons

20
Q

How does a moderator slow down neutrons?

A

Through elastic collisions (kinetic energy is conserved) - all kinetic energy and momentum is transferred from neutron to moderator particle.

21
Q

What is the critical mass in a fission reactor?

A

The right amount of fuel which allows for fission to continue on it’s own at a steady rate, where one fission follows another.

22
Q

What are control rods used for?

A

To control the rate of fission.

23
Q

How do control rods control the rate of fission and what are they made of?

A

They absorb neutrons so the rate of fission is controlled (normally made of Boron).

24
Q

What is coolant used for in a fission reactor?

A

To remove heat produced by the fission (coolant usually the same water which is used as moderator).

25
Q

What are the three main safety points to keep a Nuclear fission reactor safe?

A
  • Reactor shielding
  • Emergency shut-down
  • Handling and storing fission waste products
26
Q

What is reactor shielding?

A

Reactor surrounded by a thick concrete case, which acts as shielding and prevents radiation escaping.

27
Q

How can reactors be shut down in an emergency?

A

Through the release of control rods into the reactor - they are lowered fully into the reactor which slows the reaction down as quickly as possible.

28
Q

What is the problem with spent fuel rods?

A

They can release beta and gamma radiation which is highly penetrating.

29
Q

How can spent fuel rods be stored?

A

initially placed in cooling ponds to cool down, then stored in sealed containers until its activity has fallen sufficiently.

30
Q

What are the two main benefits of nuclear power?

A
  • Doesn’t produce greenhouse gases

- Generates a lot more energy than fossil fuels

31
Q

What are the problems with nuclear power?

A
  • Risk of nuclear disaster

- Waste products and how they’re dealt with safely

Physics (8 decks)

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