Nuclear Energy Revision Questions

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  • Created by: Lizzy Day
  • Created on: 25-06-16 16:47
How can a nucleus be unstable?
A nucleus will be unstable if it has too many neutrons, too few neutrons, too many nucleons all together or too much energy.
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What happens to nuclei above the line of stability in the graph?
Nuclei have so many neutrons, they undergo B- decay.
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What happens to nuclei below the line of stability in the graph?
Nuclei have too many protons, so they undergo B+ decay.
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What happens to very heavy nuclei in the graph?
Very heavy nuclei have too many nucleons all together, so they undergo a decay.
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How is the line of stability found?
The line of stability is found by plotting N against Z for stable nuclei.
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What is alpha emission?
In very heavy atoms (e.g. uranium and radium). The nuclei of these atoms are too massive to be stable. When an alpha particle is emitted, the proton number decreases by two, and the nucleon number decreases by four.
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What is beta emission?
B- decay is the emission of an electron from the atom along with an anti neutrino. This happens in isotopes that are neutron rich. When a nucleus ejects a B- particle, one of the neutrons in the nucleus is changed into a proton.
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What are the two ways in which gamma radiation is produced?
A nucleus losing excess energy through gamma emission, and electron capture.
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What happens in gamma emission?
After a or B- decay, the nucleus often has excess energy - it is in an excited state. This energy is lost by emitting a gamma ray. The nucleus loses energy.
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What happens in electron capture?
A nucelus captures and absorbs one of its own orbiting electrons, this causes a proton to change to a neutron. A neutrino is also released.
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What are the conservation rules in nuclear reactions?
In every nuclear reaction: energy, momentum, charge, nucleon number and lepton number must be conserved.
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What is Einstein's equation for energy?
E= mc^2
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What is mass defect?
The difference between the mass of a nucleus, and the sum of individual masses of the nucleons. Equivalent to the binding energy of the nucleus.
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What is binding energy?
The energy released when a nucleus forms, as well as the energy required to separate all the nucleons in that nucleus. Equivalent to the mass defect of the nucleus.
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What is the binding energy per unit of mass defect?
1u = 931.5 MeV
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What is the binding energy per nucleon?
= Binding energy (B) / Nucleon number (A)
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What is nuclear fission?
The spontaneous or induced splitting of a larger nucleus into two smaller nuclei.
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What happens during nuclear fission?
Energy is released as the new, smaller nuclei have a higher binding energy per nucleon. The larger the nucleus, the more unstable it will be - more likely to spontaneously fission. This limits the no. of nucleons that a nucleus can contain.
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What is nuclear fusion?
The fusing of two smaller nuclei to form one larger nucleus. A lot of energy is released during fusion because the new, heavier nuclei have a much higher binding energy per nucleon.
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How do the nuclei fuse?
All nuclei are positively charged. This means that there will be an electrostatic force of repulsion between them. Nuclei can only fuse if they overcome this and get close enough for the strong interaction (attractive force) to hold them together.
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What is a nuclear fission reactor?
Nuclear reactors harness the energy released during nuclear fission reactions.
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What is a chain reaction in a nuclear reactor?
When the neutrons released during fission cause other nuclei to fission and release more neutrons - and so on. The neutrons will only cause a chain reaction if they are slowed down, which allows them to be captured by the nuclei.
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What are thermal neutrons?
Neutrons that have been slowed down.
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What 'fuel' is used for fission reactions?
Nuclear reactors use roads of uranium that are rich in Uranium 235 as fuel for fission reactions.
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What is a moderator used for?
Fuel rods are placed in a moderator to slow down neutrons. The moderator will slow down the neutrons enough to cause further fission, keeping the reaction going at a steady state.
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What are the features of a good moderator?
The best moderator will absorb more neutrons as the temperature gets higher. This will decrease the chance of meltdown if the reactor overheats.
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What are control rods used for?
Control rods control the chain reaction by limiting the number of neutrons in the reactor. They absorb neutrons so that the rate of fission is controlled. Control rods are made up of a material that absorbs neutrons.
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How can control rods change the reaction rate?
The rods can be inserted by varying amounts, absorbing more or less neutrons, to control the reaction rate.
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What is initial mass in a nuclear reactor?
The amount of fuel needed for a fission chain reaction to continue at a steady rate on its own.
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What is the coolant used for?
Coolant is sent around the reactor to remove heat produced by fission. The material used should be a liquid or gas at room temperature, and be efficient at transferring heat.
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Where does the heat from the reactor go?
The heat from the reactor can be used to make steam for powering electricity generating turbines.
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What are the safety features of the reactor?
Reactor shielding, emergency shut-down and fuel and disposal of fission waste products.
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What is reactor shielding?
The nuclear reactor is surrounded by a thick concrete case, which acts as shielding. This prevents radiation escaping and reaching the workers in the power station.
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What is emergency shut-down?
In an emergency, the reactor can be shut down automatically by the release of control rods in the reactor. Control rods are lowered fully into the reactor, which slows down the reaction as quickly as possible.
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What is fuel and disposal of fission waste products?
Unused uranium fuel rods emit only alpha radiation, which is weakly penetrating and so is easily contained. Spent fuel rods are more dangerous fission waste products have a large proportion of neutrons they are unstable and radioactive.
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Other cards in this set

Card 2

Front

What happens to nuclei above the line of stability in the graph?

Back

Nuclei have so many neutrons, they undergo B- decay.

Card 3

Front

What happens to nuclei below the line of stability in the graph?

Back

Preview of the front of card 3

Card 4

Front

What happens to very heavy nuclei in the graph?

Back

Preview of the front of card 4

Card 5

Front

How is the line of stability found?

Back

Preview of the front of card 5
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