23.1:
Radioactivity all
around us
Ways at which radioactive substances can
cause problems:
If a radioactive substance
gets inside us, its
radiation can harm us. We
say that we have been
contaminated.
If the radiation a
radioactive substance
produces hits our bodies,
we receive a dose of
radiation. We have been
irradiated.
background
radiation
The radiation from the
environment to which
we are exposed all
the time.
Different sources of radiation
Sources of natural background radiation
1- The air is radioactive. It contains a radioactive gas called radon, which
seeps up to the Earth's surface from radioactive uranium rocks underground.
Because we breathe in air all the time, we are exposed to radiation from this
substance. This contributes about half of our annual exposure.
2- The ground contains radioactive substances. We use materials from the ground
to build our houses, so we are exposed to radiation from these.
3- Our food and drink is also slightly radioactive. Living things grow by taking in
materials from the air and the ground. Some of these materials are radioactive so
the plants which feed into our food chains will also be slightly radioactive.
4- Radiation reaches us from space in the form of cosmic rays. Some of this
radiation comes from the Sun, some from further out in space. Most cosmic rays
are stopped by the Earth's atmosphere. If you live up a mountain, you will be
exposed to more radiation from this source.
Sources of artificial background radiation:
1- Most radiation from artificial sources comes from medical
sources. This includes the:
❑use of X-rays and gamma rays for seeing inside the body.
❑the use of radiation for destroying cancer cells.
There is always a danger that exposure to such radiation may trigger
cancer. Medical physicists are always working to reduce the levels of
radiation used in medical procedures.
2- Today, most nuclear weapons testing is done underground. In the
past, bombs were detonated on land or in the air, and this contributed
much more to the radiation dose received by people around the world.
3- When you fly in an aircraft (air travel) , you are high in the atmosphere.
You are exposed to more cosmic rays.
4- small amounts of radioactive substances escape from the nuclear
industry (nuclear power stations), which processes uranium for use as
the fuel in nuclear power stations
Detecting radiation:
Radiation can be measured using a Geiger
counter.
This consists of:
1.A detector called a Geiger-Müller tube which
detects radiation.
2.A counter.
The counter records the rate at which radiation is
detected. This is known as the count rate and it
is measured in counts per second (count/s) or
counts per minute (count/min).
Questions Page 431:
1- The radiation which we are exposed to all the time from radioactive
sources.
2- Natural, any three from: materials in the ground, building materials,
cosmic rays, food and drink, gases in the atmosphere.
Artificial, any three from: medical uses, weapons testing, air travel,
nuclear power stations.
3- cosmic rays