Defining Half-Life
Half-life is the time required for half of the radioactive atoms in a sample to decay. During this period, the activity of a radioactive substance decreases by 50%. It is a statistical measure, meaning that while we can predict when half of a large sample will decay, we cannot predict when an individual atom will decay.
The Exponential Nature of Decay
Radioactive decay follows an exponential pattern. After one half-life, 50% of the original substance remains. After two half-lives, 25% remains (half of the remaining 50%), and so on. This consistent rate allows scientists to predict how much of a radioactive isotope will be present after a certain amount of time.
Practical Applications
Half-life has crucial applications across various fields. In archaeology and geology, it's used for radiometric dating (e.g., carbon-14 dating to determine the age of ancient artifacts or uranium-lead dating for rocks). In medicine, isotopes with short half-lives are used in diagnostic imaging and cancer therapy, minimizing patient exposure to radiation.
Factors Not Affecting Half-Life
It's important to note that the half-life of a radioactive isotope is a fundamental property of that isotope and is not affected by external factors such as temperature, pressure, chemical state, or magnetic fields. This constancy makes it a reliable clock for measuring vast spans of time or precise medical dosages.