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Some isotopes of atoms can be unstable.

They may have:

a) Too much energy


b) The wrong number of particles in the nucleus.

We call these radioisotopes.

To make themselves more stable, they throw out particles and/or energy from the nucleus. We call this process 'radioactive decay'. The atom is also said to disintegrate.

The atom left behind (the daughter) is different from the original atom (the parent). It is an atom of a new element. For example uranium breaks down to radon which in turn breaks down into other elements.

The particles and energy given out are what we call 'radiation' or 'radioactive emissions'.

There is a certain amount of radiation around us (and even inside us) all the time. There always has been - since the beginning of the Earth. It is called Background radiation.

Background radiation comes from a huge number of sources.

The list below gives some of these sources:

See if you can number the sources listed here by the amount of background radiation they produce (1 = highest level of radiation):

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In most areas, Background radiation is safe. It is at such a low level that it doesn't harm you. You need to be exposed to many times the normal background level before you notice any symptoms.

However, some areas of the country have a higher level of background radiation than others because the rocks near the surface contain more radioactive isotopes (for example, Cornwall).

Look at this example:

You use a radiation detector to record that a sample of rock produces 100 decays per minute. You then remove the rock and record the background radiation in the room. It is 7 decays per minute.

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The radiation emitted by radioactive substances has a huge amount of energy, which is why it is so dangerous. The energetic radiation causes ionisation.

When radiation hits a neutral atom, some of the energy from the radiation is passed to the atom. This energy can cause an electron from the atom to escape, leaving the atom with a positive charge. This positively charged atom is called an ion, so the process is called ionisation.

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As the radiation travels along it ionises atoms that are close enough. The more atoms the radiation ionises the more energy the radiation gives away, until eventually there is no energy left. The radiation is then said to have been absorbed.

You will see in the following quick learn that there is more than one type of radiation, but each sort causes ionisation. This is how we are able to detect radiation.

It is hard to detect the actual particles or waves emitted by radioactive substances, but it is easy to detect the positive and negative ions produced by the ionisation they cause. A device called a Geiger-Muller tube collects the charged ions and can measure the amount of ionisation that is taking place in a certain time. The greater the amount of ionisation the more radiation there must be.

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It is this process of ionisation that makes radioactive substances so dangerous. Living cells can be fatally damaged if molecules in the cell are ionised. This damage can kill cells or cause cancers to form. The greater the dose of radiation the more likely it is that cancer will occur.