Why are Some Atoms Radioactive?

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Why are Some Atoms Radioactive?

Some atoms are unstable. They have too much energy or the wrong mix of particles in the nucleus. So to make themselves more stable, they breakdown (or decay) and get rid of some matter and/or some energy. This is called radioactive decay and isotopes of atoms that do this are called radioisotopes.

The process is spontaneous and random. You can't do anything to speed it up or slow it down and you can't predict when it will happen. The only reason we can do any calculations on radioisotopes is because there are huge numbers of atoms in most samples so we can use statistics to accurately predict what's most likely to happen.

A Geiger counter set up anywhere on Earth will always register a count. This is due to tiny fragments of radioactive elements present in all rocks and soil, the atmosphere and even living material. The Earth is also continuously bombarded by high-speed particles from outer space and the Sun called cosmic rays. In addition the nuclear and health industries produce small amounts of radiation each year. Collectively this radiation around us from natural and unnatural sources is called background radiation.

The chart shows the main sources of background radiation.

Why are Some Atoms Radioactive?


When carrying out practical work involving count-rates from radioactive sources, allowance should be made for this background radiation. This can usually be done effectively by measuring the background count in the laboratory for several minutes, and subtracting the appropriate amount from subsequent readings taken with the source.

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