page 3-1
Ionising radiations

the scale of the nucleus
Picture 1. The nucleus of an atom is a tiny speck in the middle.

What are ionising radiations?
What's in an atom?
An atom is a tiny neutral particle. It has negative electrons on the outside and a positive nucleus in the middle. The nucleus is miniscule compared with the atom - it is equivalent to a pin head in the middle of an athletics stadium.

The positive and negative charges balance each other so that the atom has no overall charge. It is neutral.

An atom
Picture 2. A helium atom. An electron can be knocked off to make a positively charged ion.

What is ionisation?
It is possible to remove one or more electrons from the outside of an atom, leaving it with an excess of positive charge. It has then become a positive ion. One way that electrons can be removed is if the atom is struck by ionising radiation from a radioactive material.
What is ionising radiation?
Some natural materials give out an invisible radiation that can ionise the surroundings. We say that they are radioactive. The ionising radiation can be hazardous but also has many uses in science and medicine. These materials are part of our lives and it’s important to understand what they are and how they behave. In this resource, we will look at the basic properties of ionising radiations and how some of them are used and monitored in the metals industry.
Using ionising radiation
Some types of ionising radiation can get through even quite thick materials. They are therefore a useful way to find out the level of something within a container. They are used for this purpose within the metals industry (see page 3-3) as well as other packaging industries. Radioactive sources are also used in hospitals and nuclear power plants. Sometimes, the scrap metal from these environments can be contaminated with old sources of ionising radiation. Scientists at Corus have developed methods to detect these sources and to prevent them being recycled with, for example, scrap steel (see page 3-5).

Question 3-1.

Fill in the gaps in the paragraph below. Choose the best answer in each case.

The is the positive core of an atom; it is surrounded by particles called . An atom that loses one of these becomes a .
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