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Radioactivity
Contents
Atomic Structure
 Isotopes
 Background Radiation
 Alpha, Beta, Gamma
 Uses of Radiation
 Nuclear Fission
 Chain Reactions

Atomic Structure
Electron:
negative, mass
nearly nothing
Neutron:
neutral, same
mass as proton
(“1”)
Proton:
positive, same
mass as
neutron (“1”)
Isotopes
Isotopes are the same element with a different mass
number. Isotopes have different numbers of neutrons
The atomic number controls which element it is.
e.g. Oxygen must always have 8 protons
Radiation occurs when the mass number of an element changes
Background Radiation
13% are
man-made
Radon gas
Food
Cosmic rays
Gamma rays
Medical
Nuclear power
Alpha, Beta, Gamma
Alpha (α): atom decays into a new atom
& emits an alpha particle (2 protons and 2
neutrons: the nucleus of a helium atom)
Unstable
nucleus
Unstable
nucleus
Unstable
nucleus
New
nucleus
New
nucleus
New
nucleus
Alpha
particle
Beta
Beta (β): atom decays into a new atom
by changing a neutron into a proton &
electron. The fast moving, high energy
electron is called a beta particle
particle
Gamma
radiation
Gamma (γ): after α or β decay, surplus
energy is sometimes emitted. This is
called gamma radiation & has a very
high frequency with short wavelength.
The atom is not changed
Uses of Radiation
Sheet of paper Thin foil
Few cm of lead
α

γ



β passes through paper, card  γ kills microbes
etc.
 Medical instruments sterilised
β passed through sheets to a  Food keeps fresh for longer
detector
 No damage to substances
When β count slows
 Half-life short so no radiation
material is too thick
afterwards
Nuclear Fission

Nuclear fission occurs when the mass number of an element
splits. The product is a new element and released neutrons

Nuclear fission releases heat energy

This heat is harnessed in nuclear power stations to boil
water, which is used to drive turbines and machinery

The amount of energy produced by each reaction is very
small billions of reactions occur every second

The waste products from these reactions are radioactive,
which is why many people worry about nuclear power
plants
Nuclear Fission
More
neutrons
Neutron
Uranium
nucleus
Unstable
nucleus
New nuclei
(e.g. barium
and krypton)
Chain Reactions

Each fission reaction releases neutrons
that are used in further (chain) reactions
Summary
Nucleus = protons and neutrons; electrons are in shells
 Isotopes = same element with different mass number
 Background radiation = many causes, some man-made
 Alpha (highly ionising, low penetration), Beta (stopped by a
few mm of foil), Gamma (high penetration  v dangerous)
 Uses of radiation (Beta: quality assurance, Gamma: medical
instruments & food freshness)
 Nuclear fission = atom divides  releases neutrons
 Chain reactions = result of released neutrons
