Inside a nuclear reactor unstable atoms with heavy nuclei are bombarded with neutrons. This causes the nuclei of the atoms to split into light nuclei. This is called nuclear fission.
Further neutrons are released which can hit other atoms causing further nuclear fission. This is called a chain reaction. Large amounts of energy are released during radioactive decay or nuclear fission.
This energy can be transferred into electrical energy in a nuclear power station, or used destructively as with a nuclear bomb.
Nuclear fusion is the combing of two light nuclei into a heavy nucleus. There is a slight loss of mass and a release of energy results.
Temperatures of over 100 million degrees are required so there are containment problems.
Nuclear fusion is the source of the energy produced in stars such as the sun.
Uses of Radioactivity - Thickness gauge
The thickness of paper, plastic or aluminium can be controlled by measuring how much beta radiation passes through to a gauge counter.
Uses of Radioactivity - Tracers
In Medicine - Used to check for blocked kidneys. Small amount of Iodine 123 is ijected into the patient, after 5 minutes 2 geiger counters are placed over kidneys.
In Industry - Used to detect leaking pipe, small amount of source is injectedd into pipe. It is then detected with a GM meter above ground.
Uses of Radioactivity - Radiotherapy
Gamma rays can kill living cells and are used to ill cancer cells without having to resort to difficult surgery. Cancer cells can't repair themselves when damaged by gamma rays like healthy cells can.
Its vital to get the right dose - too much and you'll damage too many healthy cells, too little and you won't stop the cancer spreading.
Uses of Radioactivity - Sterilisation
Gamma rays can be used to kill bacteria mold and insects in food. It can be used to sterilise hospital equipment, especially plastic syringes that could be damaged if heated.
Uses of Radioactivity - Archaeology
Animals and plants have a known proportion of Carbon-14 in their tissue. When they die they stop taking carbon in, then the amount of Carbon-14 goes down at a known rate. Carbon-14 has a half life of 5700 years. The age of ancient organic materials can be found by measuring the amount of Carbon-14 left.