If radioisotopes are injected into the blood stream of someone seeking treatment . To find out the activity of the radioisotope , the nurse would probably draw lets say 10 ml of blood and measure the activity. After a few days the process is repeated to measure the activity again. It is obvious the the same 10 ml of blood should be drawn to measure its activity.If for some reason only 5 ml is drawn than the activity must be multiplied by 2 . The activity must be taken from the same amount of sample so that it can be compared correctly.
The same goes with carbon dating. 1C14 to 2000000 (fresh wood) and 1 C14 to 4000000 (old wood)would actually mean initial N (fresh wood) = 2 and old wood to be N=1 . Hence the age of the old wood is one half life.
This principle must be employed at all times in dealing with any kind of application.
