Nuclear Physics

Activity

The rate of decay of the radioactive sample which is proportional to the total number of nuclei in the sample (unit: Bq)

Atomic mass unit

It is equal to 1/12 of the mass of a carbon atom

Background radiation

The radiation found in small quantities around us originates from natural sources like rock and man made sources like medical sources

Binding energy

Amount of energy required to split a nucleus into its separate constituent nucleons

Chain reaction 

The process of the neutrons released by a fission reaction including further fissile nuclei to undergo fission

Contamination 

Introduction of radioactive material to another object which cause it to be radioactive as well

Irradiation

The exposure of an object to radiation which does NOT cause it to become radioactive 

Function of control rods

Absorbs neutrons and control the rate of reactions and amount of energy produced

Usually made of boron or cadmium

Function of moderator

Slows down the neutrons released during fission via elastic collisions with its nuclei

Slow neutrons are less damaging to the structure of the reactor and are more likely to be absorbed by Uranium-235 

Usually water or graphite because their molecules are not fissionable and are able to absorb a lot of energy 

Function of coolant

Absorbs the heat released during fission in the core and delivers it to the boiler via heat exchange which also maintains a safe working temperature within the core

Usually water, molten salt or gas (eg. Helium) because they have high specific heat capacity and low viscosity

Fission

The splitting of a nucleus to form two smaller daughter nuclei, neutrons and energy

Critical mass

Minimum mass of material required in a fission reactor for a chain reaction to be sustained

Fusion

Joining of two smaller nuclei o form a larger nucleus and to release energy

Half-life

The average time it takes for the number of radioactive nuclei in a sample to halve

Alpha radiation properties 

Helium nucleus (+2 charge) hard to produce

Highly ionising

Around 2 - 10 cm range in air (least penetrating)

Can be absorbed by paper

Beta radiation properties 

Electron (-1 charge) easier to produce

Weakly ionising

Around 1m range in air

Can be absorbed by 3mm aluminium foil

Gamma radiation properties

Energy in forms of photons (no charge) randomly produced

Very weakly ionising 

Infinite range in air (most penetrating)

Can be absorbed by several metres of concrete or several inches of lead

Low-level radioactive waste

Short-lived radioactivity (eg. Tools and gloves)

High-level radioactive waste

The fission fragments and the spent fuel rods

How is it treated:

1. Removed and handles remotely as it is highly radioactive 

2. It is very hot so it is placed in cooling ponds close to the reactor first 

3. Uranium or plutonium is separated to be recycled 

4. Vitrified (encased in glass) to prevent leaking when it is liquid 

5. Placed in steel or concrete containers and stored deep underground as it will be radioactive for hundreds/ thousands of years