Half life can be defined as the time taken for the number of nuclei in a radioactive material to halve.It can also be defined as the time taken for the count rate of a sample of radioactive material to fall to half of its starting level.What is the activity of the radioisotope after 3 half lives?
With paper, or plastic, or aluminium foil, b rays are used, because a will not go through the paper.
We choose a source with a long half-life so that it does not need to be replaced often.
The age of the ancient organic materials can be found by measuring the amount of Carbon-14 that is left.
The most common tracer is called Technetium-99 and is very safe because it only emits gamma rays and doesn't cause much ionisation.
If smoke enters the alarm, this absorbs the a particles, the current reduces, and the alarm sounds. In paper mills, the thickness of the paper can be controlled by measuring how much beta radiation passes through the paper to a Geiger counter.
The counter controls the pressure of the rollers to give the correct thickness.This is half of the remaining 5000 radioactive nuclei.The isotope undergoes further decay and it takes 2 days for the number of radioactive nuclei to halve in number. Therefore the number of radioactive nuclei is always half the number there was 2 days ago.But it is possible to measure the time taken for half of the nuclei in a radioactive material to decay.This is called the half life of radioactive material or radioisotope.Animals and plants have a known proportion of Carbon-14 (a radioisotope of Carbon) in their tissues.