Nuclear 2 Flashcards
What type of nuclei undergo alpha decay?
large nuclei
What type of nuclei undergo beta minus decay?
neutron-rich nuclei
What type of nuclei undergo beta plus decay?
proton-rich nuclei
What type of nuclei undergo electron capture?
proton-rich nuclei
Where does the electron come from for electron capture?
the electron from one of the inner orbitals
For the plot of number of neutrons against number of protons, for what region does Z = N?
for Z (or N) is less than 20
What is the N value when Z = 80 on a plot of number of neutrons against number of protons?
A = 120
Define binding energy
the energy required to separate a nucleus into its component parts
Define mass defect
the difference between the mass of the component parts and the nuclear mass
Explain why a nucleus has a lower mass per nucleon compared to free nucleons
- more stable when in a nucleus
- due to being in a lower energy state (less PE) (SNF)
- energy is proportional to mass (ΔE = Δmc²)
- therefore it has a lower mass per nucleon
What does ΔE/A measure?
measures stability, the greater ΔE/A, the more stable
What is ΔE/A for Iron-56?
≈9 MeV
What is ΔE/A for U-235?
≈7
What is ΔE/A for He-4?
≈7.5
Define nuclear fission?
the splitting of a large nucleus into two smaller, daughter nuclei (plus several neutrons and a release of energy)
Why are 2/3/4 neutrons released during nuclear fission?
as the ratio of neutrons to protons is greater for heavier nuclei
What is meant by a controlled chain reaction?
only one neutron from each fission causes another fission, on average
What do the control rods do, and what is their function?
- control rods absorb neutrons
- so they control the chain reaction by limiting the number of neutrons in the reactor
What type of material are control rods made out of, and why?
- a material that can absorb a neutron to create a stable product
- e.g. boron steel
What are fuel rods?
contain enriched uranium as fuel
What does the moderator do, and why?
- scatters neutrons through a series of elastic collisions, in order to slow neutrons down to thermal speeds
- it does this so that there is a greater period of time for the SNF to act
What type of materials are used for a moderator, and why?
- a material with relatively light nuclei so they can exchange energy effectively with the neutrons
- e.g. graphite or water
What is the optimal mass for the moderator?
a moderator with similar mass to the neutrons is more efficient as slowing the neutrons down
What does the coolant do?
is sent around the reactor to remove the heat produced by fission
What type of material should be used as a coolant?
the material should be a liquid or gas at room temperature, and should be efficient at transferring heat
What is meant by enriched uranium?
- the ratio or U-235 to U-238 is high (higher than natural uranium)
- (as U-235 is needed for fission)
Why do both nuclear fission and nuclear fusion result in a release of energy?
BOTH increase ΔE/A, increase stability, reduce PE, work out / energy released
Why is nuclear fusion considered ‘clean’?
- no long half lives
- very little radiation
What conditions are required for fusion?
- very hot
- very high pressure
List and explain 3 things that increase the likelihood of further fission occurring?
- spherical shape, lowest SA to volume ratio so fewer neutrons escape
- a critical mass (enough U-235)
- high level of enrichment (high ratio of U-235 to U-238)
