Radioactive elements have a half-life. Half-life occurs naturally in some of the radioactive elements while it could be artificially stimulated in some other elements.
For example: If you have 10 grams of a radioactive element to start with….. after one half-life there will be 5 grams of the radioactive element left.
After another half-life, there will be 2.5 g of the original element left, after another half-life, 1.25 g will be left.
Each and every radioactive element has its own half-life. For instance, 238U has a half-life of 4.5billion years.
A radioactive substance has a half-life of 20 minutes. If we begin with a 500 g sample, how much of the original sample remains after two hours?
Two hours is 120 minutes -> six half-lives. At the end of the stated time period, 7.8 g remains.
500 g -> 250 g -> 125 g -> 62.5 g -> 31.25 g -> 15.625 g -> 7.8125 g
7.8 g remains
Another interesting fact is half-life of 14C is 5730 years and this is very helpful in geological dating of any archaeological material. (CARBON DATING)
The ratio of normal carbon (carbon-12) to carbon-14 in the air and in all living things at any given time is nearly constant. At this moment, your body has a certain percentage of carbon-14 atoms in it, and all living plants and animals have the same percentage.
As soon as a living organism dies, it stops taking in new carbon. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely.
Three types of natural radioactive decay include alpha radiation, beta radiation and gamma radiation.