Nuclear Physics

Half-Life

The time it takes for half of the radioisotopes in a sample of a given radioisotope to undergo decay.
Mass does not disappear - if the question asks how much sample is left, it is the same
3 ways to measure
- Number of nuclei - however, the decayed nuclides are now nuclides of a different isotope
- Mass - but actual mass of entire sample will not change significantly since little actual mass is lost because of the existence of other isotopes
- Actually measured disintegrations per second ($DPS$ measured in becquerels - $Bq$)

The fact that the mass of any given nuclide is less than the sum of the individual masses of its protons and neutrons of which it is composed
- i.e. there is a mass defect
- This was converted to energy when the nuclide was formed, related by the equation $E=mc^2$
**Nuclear binding energy is not the energy holding the nucleus together
- Instead, it is the energy that was lost in forming the nucleus
- It is the same amount of energy that is required to break the nucleus apart.
One AMU (Atomic Mass Unit) is $1/12$ the mass of a carbon-12 atom

Bombard large nuclei with neutrons, then they have a tendency to become unstable and can split into $2+$ fragments.

Fuel - $U^{235}$
Fuel rods
Moderator - slows down neutrons longer to be captured by nuclides - water, heavy water, graphite
Control Rods - absorb excess neutrons - boron and cadmium
Coolant - water, heavy water

Low Level
- Clothing, wrappings, containers, tools
- Incineration - i.e. putting it into the atmosphere, the isotope isn't actually destroyed
- Burying - fine, don't go digging
Medium Level
High Level