So food treated with this radiation have a longer shelf life.
Surgical instruments and syringes are also treated with gamma rays, in order, to prevent infections been transferred from patient to patient.
This means it is the radiation responsible for ionising molecules. Small doses of radiation over a long period of time can cause the cells to multiply. Background radiation comes from the soil, rocks, the air, water, plants, building materials and food.
If this happens in our body, the cells may die or they may undergo a change called a mutation. Some radiation is due to cosmic rays from outer space.
Radioactive substances will give out radiation all the time, regardless of what happens to them physically or chemically.
The half-life of a substance can be found by measuring the count-rate of the substance with a Geiger-Muller tube over a period of time.
By plotting a graph of count-rate against time the half-life can be seen on the graph.
They can even use this idea to detect when toothpaste tubes are full of toothpaste! Photographic radiation detectors - these make use of the fact that radiation can change the colour of photographic film.
The more radiation that is absorbed by the film the darker the colour it will go when it is developed. As the half-life is very long for Carbon-14, objects that are thousands of years old can be compared to new substances and the change in the amount of Carbon-14 can date the object.