Atomic structure

excitation

an electron absorbs electromagnetic radiation and moves to a higher energy level (orbital)

deexcitation

the electron emits electromagnetic radiation and moves to a lower energy level (orbital)

Background radiation

• nuclear radiation that exists all around us

• natural – rocks, radon(carbon based organisms), food and air

• man-made – nuclear weapons, medical uses and nuclear power plants

alpha decay

• nucleus is too heavy (unstable)

• too many protons and neutrons in nucleus

• emits (drops) 2 protons and 2 neutrons

properties of alpha decay

• can’t travel far ~ 2cm in air

• can be blocked (absorbed) by paper/skin

• extremely ionising - can knock electrons out of atoms

beta decay

• an electron from a nucleus

• nucleus isn’t balanced

• a neutron turns into a proton and an electron

• this electron shoots out of the nucleus

properties of beta decay

• can travel a few m in air

• absorbed by a few mm of aluminium

• e.g Sr90 - beta emitter

Gamma decay

• after emitting an alpha/beta particle, the nucleus will often still be ‘excited’ and will need to lose energy.

• emits high energy electromagnetic wave from unstable nuclei to release energy

Gamma decay properties

• 0 protons and neutrons are lost

• element doesn’t change

Examples of radioactive tracers

• geiger counter

• medical uses

• traces radioactive fertiliser

• most common tracer Technetium-99

Radioactive tracers

• emits gamma rays that easily pass through the body to a detector outside the body,

• isotope can be followed as it flows through a particular organ in the body

• have very short half-lives

• not be poisonous.

Sterilising

• kills bacteria, mould and insects in food

• prolongs shelf life of food

• gamma rays

• cancer cells can be killed

smoke detection

• weak source of Americium-241

• emits alpha particles

• alpha particles pass between charged metal plates

• electrical currents sound alarm

Thickness control

• radioactive isotopes act as emitter

• placed on either side of a sheet

• beta source used as it can penetrate paper

• amount of penetration varies on thickness

detecting faulty pipe welds

build up of gamma emission can be found using a geiger muller tube

Half life (of a radioactive source)

time taken for its activity to fall to half of the original activity

nuclear fission

the splitting of a nucleus into smaller fragments by the release of neutrons and lots on energy

fission releases which hits other fissionable atoms producing more neutrons which can react with even more fissionable atoms

chain reaction

How is nuclear fission controlled?

• control rod made of boron

• pushed into reaction to absorb energy

• pulled out and slows reaction down

nuclear fusion

two or more nuclei combine to create a nucleus of greater mass

What condition does it have to be for nuclear fusion to occur?

• high pressure & high temperature

• naturally in the core of stars (mainly the sun)