Nulcear - Fission Flashcards
What hold nuclei together?
The strong force
Nuclear Fission
Where heavy elements break apart into lighter ones.
Primary fission fuel…
U235
Fission energy compared to gasoline…
U235 release 200 MeV or 1 MeV per nucleon whilst gasoline about 1/2 eV per nucleon
How does a chain reaciton in fission work?
U235 releases neutrons which can induce further fission of other uranium
How can neutrons propogate fission?
They are neutrally charged so can be absorbed without repulsion
How do neutrons INDUCE fission?
Srong interactions formed hold several MeV enough to drive further fission
Why do heavier elements have more neutrons?
Despite strong force being stronger than electrostatic, there is a limit, where neutrons are required to balance
What does increased neutron content prevent?
Alpha decay or spontaneous fission
Why are emitted neutrons unlikely to induce fission?
They are fast moving and likely to be absorbed by other nuclei
How can neutron fission be promoted?
By slowing down the solution
How are neutrons slowed down?
A moderation like water or graphite
Why are Fission reactors often enriched with U235?
U235 only accounts for small portion of uranium naturally found.
Why are control rods important?
They are made of neutron-absorbing material that capture fission-released energy.
What are control rods made of?
Cadmium, hafnium or boron
Why is boron good in control rods?
Its 5 fermion neutrons prefer being paired so B10 absorbs to B11
Alpha Decay
Process of reduction of atomic mass, being the primary source of activity
Alpha decay depends on…
Quantum tunnelling and coloumb barrier penetration
Alpha particles
Helium nuclei emitted by radioactivty with very high lifetimes
Why is tunneling important in alpha decay?
It allows the alpha particle to escape the nuclei
Where is the coloumb barrier in decay?
Between alpha particles and nuclei
When was fission discovered?
In 1930, first controlled chain reaction in 1942, electrical generation in 1951 then plants in 1955
Cross Sections
Describes collision/reaction rate of particles
Equation for flux in cross-section….
phiB = dNb/dAdt - b is incidence particle, meaning amount of particles passing a unit area per unit time