Plants and animals also absorb radioactive material that is present in the atmosphere.
These plants and animals are part of the food chain. We constantly receive cosmic
radiation from space. Exposure to low levels of radioactivity is part of everyday living.
A dose of radiation that exceeds normal levels can be dangerous. Radiation can affect
the way in which the cells in bodies operate and can cause them to become cancerous.
Radiation, however, when used in a careful controlled way can be beneficial. Radiation
can be used in medicine. It can be used to kill cancerous body cells.
Radioactive sources can also be used to find out if different organs in our bodies are
working properly. The radioactive substance is carried by the blood to the organ. The
radiation coming from the organ is measured. The measurements can be processed so
that an image of the organ is displayed. This helps to diagnose what is wrong with the
Types of radiation
An atom is made up of a small nucleus surrounded by orbiting
electrons. The nucleus of the atom contains particles called
protons and neutrons.
The nuclei of the atoms in some elements are unstable and emit
radiation. The radiation can be of three types - alpha radiation,
beta radiation and gamma radiation.
Alpha α radiation is slow moving helium nuclei
Beta β radiation is fast moving electrons
Gamma γ radiation is high-energy electromagnetic waves.
The three radiations transfer energy from the nucleus when they are emitted.
Absorption of radiation
Type of Radiation Alpha particle Beta particle Gamma ray
or or or
Mass (atomic mass units) 4 1/2000 0
Charge +2 -1 0
Speed slow fast very fast (speed of light)
Ionising ability high medium 0
Penetrating power low medium high
Stopped by: paper aluminium lead
The radiation on passing through the material causes electrons to be stripped from some
of the atoms in the absorbing material. The process is called ionisation. As a result the
atoms become positiveions.
Energy is transferred to the absorber during the ionisation process.
Negative ions occur when electrons are added to atoms which doesn’t happen in
Activity of a radioactive source
The activity of a radioactive source is the number of ionising radiations it emits per
second. Activity is measured in becquerels. The symbol forbecquerel is Bq. One
becquerel is one ionising radiation emitted per second. The activity of a radioactive
source decreases with time.
Safety and radiation dose
Safety precautions are necessary when working with radioactive sources. Radioactive
sources should be kept away from the body and never brought close to the eyes.
The radiation dose received by body tissue depends on the type of radiation absorbed by
the tissue. The radiation dose received also depends on the energy of the radiation.
A way of expressing the radiation dose received from different sources is in terms of a
quantity called equivalent dose. Equivalent dose is measured insieverts (Sv). A dose of
one sievert from an alpha radiation source, for example, is equivalent to a dose of one
sievert from a beta radiation source or any other source of radiation.
Nuclear power stations
Nuclear power stations use fuel containing uranium or plutonium.
These are the steps by which electricity is generated by nuclear power:
1. Uranium atoms split releasing energy so fuel becomes hot. This heats the water
turning it into steam.
2. The steam turns the turbine.
3. The turbine turns a generator and electricity is produced.
4. The electricity goes to the transformers to produce the correct voltage.
The fuel used eventually becomes solid nuclear waste. This waste is radioactive and emits
Nuclear power is created from the release of energy from nuclear reactions. These
reactions usually use uranium or plutonium.
Advantages of nuclear power:
1. Only small amounts of fuel needed to produce lots of energy compared to fossil fuels
2. Low carbon emissions
3. Tends to be supported by large companies and governments
4. Once up and running it is cheap to produce electricity
5. There has been a lot of investment in making sure it is as safe as possible
Disadvantages of nuclear power:
1. Nuclear waste is highly radioactive
2. Accidents and leaks can be deadly and last for a long time
3. Storing nuclear waste is very expensive
4. Decommissioning nuclear power stations is very expensive
5. Uranium and plutonium are not renewable so will run out
Nuclear reactors use a type of nuclear reaction called nuclear fission.
Another type of nuclear reaction - nuclear fusion - happens in the Sun and
Nuclear power reactors use a reaction called nuclear fission. Two isotopes in
common use as nuclear fuels are uranium-235 and plutonium-239.
Fission is another word for splitting of a nucleus. Uranium or plutonium isotopes
are normally used as the fuel in nuclear reactors, because their atoms have
relatively large nuclei that are easy to split, especially when hit by neutrons.
When a uranium-235 or plutonium-239 nucleus is hit by a neutron, the following
1. The nucleus splits into two smaller nuclei, which are radioactive
2. Two or three more neutrons are released
3. Energy is released
The additional neutrons released may also hit other uranium or plutonium nuclei
and cause them to split. Even more neutrons are then released, which in turn can
split more nuclei. This is called a chain reaction. The chain reaction in nuclear
reactors is controlled to stop it going too fast.
Nuclear fusion involves two atomic nuclei
joining to make a large nucleus. Energy is
released when this happens.
The Sun and other stars use nuclear fusion
to release energy. The sequence of nuclear
fusion reactions in a star is complex, but
overall hydrogen nuclei join to form helium
nuclei. Here is one nuclear fusion reaction that takes place:
Hydrogen-1 nuclei fuse with Hydrogen-2 nuclei to make Helium-3 nuclei
Marie became fascinated by rays that were discovered by scientists. She began to
doexperiments and examined pitchblende. She expected there to be few rays
from uranium, but instead found a lot of rays. She realized that there must be an
undiscovered element in pitchblende.
Marie spent hours in their lab investigating it. She had discovered two new
Marie named the elements polonium and other radium. The Curies came up with
the term "radioactivity" to describe elements that emitted strong rays.
In 1903, the Nobel Prize in Physics was awarded to Marie and Pierre Curie as
well as Henri Becquerel for their work in radiation.
In 1911 Marie won the Nobel Prize in Chemistry for discovering two elements.
Scientists came from around the world to study radioactivity with Marie.