Nuclear Physics Part 2 Flashcards
What is mass defect or mass difference?
The difference in mass between a nucleus and the mass of its constituent nucleons.
What is binding energy?
The energy needed to separate all of the nucleons in a nucleus.
How do you work out the average binding energy per nucleon?
Binding energy divided by nucleon number.
Describe the graph of Average Binding Energy Per Nucleon against Nucleon Number.
- 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
What is the most stable nucleus?
Iron.
What is Fission?
When large nuclei are unstable and split into two smaller nuclei.
Why is energy released in Fission?
Because the new, smaller nuclei have a higher average binding energy per nucleon.
How can Fission be induced?
By making a neutron enter a Uranium-235 nucleus, causing it to become very unstable.
What is a low energy neutron called?
A thermal neutron.
What is Fusion?
When two light nuclei combine to create a larger nucleus.
Why is a lot of energy released in Fusion?
Because the new, heavier nuclei have a much higher average binding energy per nucleon.
Why is it so hard to fuse nuclei together and about how much kinetic energy is needed?
- 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
How can you tell if it is energetically favourable for an element to undergo fission or fusion?
- 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
How can you work out the energy released through fusion or fission?
The change in binding energy gives the energy released.
What is another way of finding the energy released during fission or fusion other than using the graph?
Using E = Δmc ^ 2, where Δm is the total difference in mass between the initial and final nuclei (including neutrons).
What are the 5 things included in a Nuclear Fission Reactor?
- Control rods
- Concrete case
- Fuel rods
- Moderator
- Coolant
What do fuel rods contain and what are they used for?
Fuel rods contain Uranium-235 (sometimes Plutonium-239) which are used as fuel.
How are chain reactions used in Nuclear Fission Reactors?
- Fission reactions produce more neutrons which then induce other nuclei to fission
- Neutrons will only cause a chain reaction if they’re slowed down
What is an example of a moderator and what is it used for?
- A good moderator is water
- It is used to slow down and/or absorb neutrons
How does a moderator slow down neutrons?
Through elastic collisions (kinetic energy is conserved) - all kinetic energy and momentum is transferred from neutron to moderator particle.
What is the critical mass in a fission reactor?
The right amount of fuel which allows for fission to continue on it’s own at a steady rate, where one fission follows another.
What are control rods used for?
To control the rate of fission.
How do control rods control the rate of fission and what are they made of?
They absorb neutrons so the rate of fission is controlled (normally made of Boron).
What is coolant used for in a fission reactor?
To remove heat produced by the fission (coolant usually the same water which is used as moderator).
What are the three main safety points to keep a Nuclear fission reactor safe?
- Reactor shielding
- Emergency shut-down
- Handling and storing fission waste products
What is reactor shielding?
Reactor surrounded by a thick concrete case, which acts as shielding and prevents radiation escaping.
How can reactors be shut down in an emergency?
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.
What is the problem with spent fuel rods?
They can release beta and gamma radiation which is highly penetrating.
How can spent fuel rods be stored?
initially placed in cooling ponds to cool down, then stored in sealed containers until its activity has fallen sufficiently.
What are the two main benefits of nuclear power?
- Doesn’t produce greenhouse gases
- Generates a lot more energy than fossil fuels
What are the problems with nuclear power?
- Risk of nuclear disaster
- Waste products and how they’re dealt with safely
