What is Radioactivity?

The world is changing around us all the time.
There are physical changes as matter changes from solid to liquid to gas.
When water evaporates, the water molecules stay the same but move farther apart.
There are chemical changes, too, such as iron rusting.
When iron atoms combine with oxygen atoms and water, they react together to become a different substance.
There is another way in which matter changes.
Matter can go through a nuclear change.
When a nuclear change happens, the nucleus of the atom sends out invisible rays.
Substances that contain this type of atom are called radioactive substances.
Matter contains some radioactive atoms.
They can be both harmful and useful.
Radioactive atoms have large amounts of energy, which is given out as rays.

How strong is radioactivity?

There are three main kinds of radioactive rays. 

  • A beam of alpha particles is not strong enough to pass through two pieces of strong paper. 
  • A beam of beta particles can pass through paper but can be blocked by a thin sheet of aluminum. 
  • Gamma rays can pass through a concrete wall, Only a thick layer of lead can stop the path of a gamma ray.

Using radioactivity

A gamma ray can be used to check metal pipes and machine parts for cracks. A photograph is taken as the ray passes through the metal.
A beam of beta particles can be used to check if packages are full or empty. If the package is empty, the beam will pass all the way through it.
Materials contain small amounts of radioactive atoms.
In time, these atoms gradually change into different kinds of substances and the radioactivity decays. Scientists can measure the age of rocks and fossils, bones, and even ancient cloth by measuring the amount of radioactivity left in the material.
This is called radiocarbon dating.
Although radioactivity can be very useful, it can also be very dangerous.
If people are exposed to too much radiation, they become ill or die. So radioactive substances must be handled very carefully. People who work in nuclear power stations wear special clothes to protect them from the radiation.
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