Radioactive materials

proton + neutron 0

electron -

nucleus

orbit / shellenergy level

An atom

The nucleus is positively charged so it attracts the negative electron

Animation completed

The Rutherford Scattering Experiment

Alpha particles (positive charge)

Thin gold foil

Some particles passed through, some were deflected

backwards

How do scientists know about the structure of atoms?

Particles passing through the foil indicated atoms have large amounts of space.The particles that were deflected back indicated the alpha particles had passed close to something positively charged within the atom (the nucleus)

nucleus

alpha radiation

beta radiation

gamma radiation

When an unstable nucleus changes, what can happen ?

Radioactive isotopes release radiation and the nucleus changes

The behaviour of radioactive materials (radioactive decay) cannot be changed by chemical or physical processes

IsotopesAn isotope is an atom with a different number of neutrons:

A “radioisotope” is simply an isotope that is radioactive – e.g. carbon 14, which is used in carbon dating.

1) Alpha () – an atom decays into a new atom and emits an alpha particle (2 protons and 2 neutrons – the nucleus of a helium atom)

2) Beta () – an atom decays into a new atom by changing a neutron into a proton and electron. The fast moving, high energy electron is called a beta particle.

3) Gamma – after or decay surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The atom is not changed.

Radioactive changes – some nuclei that are unstablecan become stable by emitting an alpha or beta particle

ExampleRadium-226 undergoing alpha decay forms Radon-222, an alpha particle and releases energy.

ExamplePolonium-218 undergoing beta decay forms Astatine-218, an electron and releases energy.

Alpha decay

Beta decay

RadioactivityIf a substance is capable of ALWAYS emitting radiation under any conditions we say it is radioactive. There are three types of radiation: ALPHA, BETA and GAMMA.

Sheet of paper Few mm of aluminium Few cm of lead

Background radiation

Sources of background radiation

Radiation dose measures the possible harm the radiation could do to the body. It is measures in millisieverts (mSv).The potential harm done depends on•the amount of radiation•the type of radiation

Exposure to a radiation source outside your body is called irradiationIf a radiation source enters your body, or gets on skinor clothes, it is called contamination Alpha particles are the most ionising so they are the most dangerous inside your body

Employers must ensure that radiation workers receive a Radiation dose “as low as reasonably achievable”.Precautions taken are•use protective clothing and screens•.wear gloves and aprons•wear special devices to monitor their dose

treating cancer sterilising equipment

sterilising food

Uses of gamma radiation

it can kill cancer cellsit can penetrate the outer casing and kill

microbes

it can kill microbes without harming the

food

Radon gas is harmful because it is radioactive. It produces ionising radiation that can damage cells.

Medical imaging and treatmentRadioactive materials cane be used to diagnose and cure many health problems.Radiotherapy is used to kill cancer cells

Half lifeThe HALF-LIFE of an atom is the time taken for HALF of the radioisotopes in a sample to decay…

At start there are 16 radioisotopes

After 1 half life half have

decayed (that’s 8)

After 3 half lives another 2 have

decayed (14 altogether)

After 2 half lives another half

have decayed (12 altogether)

= radioisotope = new atom formed

A radioactive decay graph

Time

Count

1 half life

A substance is considered safe once its activity drops to the same level as background radiation.

Nuclear fission

neutron

U-235nucleus

ENERGY

Smaller nucleus

neutrons

The energy released can be calculated from Einstein’sequation : E = mc²

The fission of one atom can set off several more causing a chain reaction

Nuclear reactor

Nuclear wasteHigh level waste – this is “spent” fuel rodsIntermediate level waste – HLW decays to become ILWLow level waste – protective clothing and medical equipment

Nuclear fusion – the nuclei of two hydrogen atoms jointogether and energy is released.

Protons and neutrons in a nucleus are held together by astrong nuclear force, which acts against the electrical repulsive force between protons