Nuclear Physics Flashcards
What happens if a nucleus is too neutron-rich?
Beta-minus decay.
What happens if a nucleus is too heavy?
It decays by releasing an alpha particle
What happens if a nucleus is too proton-rich?
Beta plus decay
What happens if a nucleus is too energetic?
Gamma radiation emitted
When are the two situations where gamma decay takes place?
1) after beta or alpha decay- excess energy
2) electron capture- nucleus captures one of it’s own electrons. Proton changes to neutron. Unstable atom.
What is not conserved in a nuclear reaction?
Mass!
Due to E= mc2
Define the mass defect.
The mass of a nucleus is less than the sum of the individual masses of it’s nucleons. The difference in mass is the mass defect.
Define the binding energy.
The energy required to separate all of the nucleons in a nucleus.
The more binding energy per nucleon, the more energy is needed to remove the nucleons (so more stable)
Which element is the most stable in terms of binding energy?
Iron (56 nucleons)
The closer you get to iron the more stable the atom (think in terms of graph- the higher the line, the more stable)
What limits the amount of nucleons a nucleus can contain?
Spontaneous fission. (More likely as size increases)
What are fuel rods made from?
Uranium-235 (also contain 238)
What is a thermal neutron and why are some neutrons scattered by the fuel rods?
Scattered because they are too energetic. Only thermal neutrons (low energy neutrons) can induce fission as reduced speed allows them to be captured by the uranium nuclei.
Why does a moderator need to be able to absorb more neutrons the higher the temperature ?
Decreases the chance of a meltdown if the reactor overheats
What is the critical mass?
The mass required for reaction to continue at it’s own steady rate
What is the significance of the supercritical mass of a nuclear reactor?
Several new fissions follow each fission. Rate of fission controlled by control rods
What are control rods and how are they used to control nuclear reactor?
They limit the number of neutrons in the reactor by absorbing some. Inserted to varying amounts. Fully inserted shuts down reactor.
What is the coolant and why is it used?
Sent around the reactor to remove heat that can be then used to make steam for powering turbines.
Often same water as the moderator.
What is the concrete case?
Shielding to prevent escape of radiation.
Why are waste products of nuclear reactors radioactive?
Usually have a higher proportion of neutrons than nuclei of similar atomic number, so unstable.
Why are spent fuel rods more radioactive than unspent fuel rods?
Spent emit gamma, unspent emit alpha which has far less range.
How is low level waste disposed of practically?
Medical tracers
How is high level radioactive waste disposed of ?
Cooling ponds and when safe temperature stored underground until radioactivity has fallen sufficiently.
Why does fusion require a lot of energy?
Nuclei can only fuse together when they have enough energy to overcome the electrostatic force of repulsion and get close enough for the strong nuclear force to hold them together. (About 1MeV required)
