Why Materials are Radioactive (1)
Radioactive Materials give out (emit) ionising radiation all the time. You cannot change the behavior of radioactive material - it emits radiation whatever its state (solid, liquid, gas) and whether or not it has taken part in a chemical reaction.
What types of Ionising Radiation is there?
Alpha - absorbed by paper Beta - penetrates paper Gamma - absorbed by only thick sheets of dense material (e.g, lead)
What's in an Atom?
3 scientists (Geiger, Marsden, and Rutherford) fired alpha particles at thin gold foil in a vacuum. Most alpha particles passed through the foil. A few of the positively charged alpha particles were reflected backward. The scientists concluded that a gold atom has a small, massive, positive region at its center - its nucleus. We now know that every atom has a tiny core or nucleus. The nucleus is surrounded by electrons. The nucleus is made up of protons and neutrons. Protons are positively charged. Neutrons have no charge. If 2 hydrogen nuclei are brought closely together, they may join to make a helium nucleus. The process releases energy, and this is called nuclear fusion.
Why Materials are Radioactive (2)
As a radioactive material decays, it contains fewer atoms with unstable nuclei. It becomes less radioactive and emits less radiation. This time taken for the radioactivity to fall to half its original value is the material's half-life.
Different radioactive materials have different half-lives.
The shorter the half-life, the greater the activity for the same amount of material.
It is possible to find out the half-life of a radioactive substance from a graph showing the count rate against time.
Safe use and Handling of Radioactive Materials (1)
Radiation is all around us. Radioactive materials do expose people to risk but they also offer benefits.
Ionising Radiation and Living Cells;
The radiations from radioactive materials - Alpha, Beta and Gamma radiation - are all ionising radiations which can damage living cells. This happens because ionising radiation can break molecules into bits called ions. These ions can then take part in other chemical reactions in the living cells. This may result in the living cells dying, or becoming cancerous.
Background radiation is all around us. It comes from radioactive substances including the ground, air, building materials and food.
Safe use and Handling of Radioactive Materials (2)
Uses of Radiation;
Ionising radiation has many uses, and one of these uses is Radiotherapy, which is used to treat cancer.
Nuclear Power Stations;
Radioactive materials release energy from changes in the nucleus. They can be used as nuclear fuels. Uranium-235 is a nuclear fuel. In a nuclear reactor, the nucleus breaks into 2 parts of similar size. This is nuclear fission. The amount of energy released during nuclear fission is much greater than that released in a chemical reaction involving the same mass of material.
Safe use and Handling of Radioactive Materials (3)
What happens to nuclear waste?
Nuclear power stations produce dangerous radioactive waste. Scientists use half-lives to work out when nuclear waste will become safe. Elements that have long half-lives remain hazardous for many thousands of years; those with short half-lives quickly become less dangerous.
There are 3 types of waste;
Low level - used protective clothing, it is packed in drums and dumped in a lined landfill site to be disposed of.
Intermediate level - materials that have been inside reactors and may remain highly reactive for many years, it is mixed with concrete and stored in stainless steel containers to be disposed of.
High level - concentrated radioactive material from spent fuel rods, decays fast and releases energy rapidly so needs cooling, in the UK, stored in a pool of water to be disposed of.