What is radioactive half-life?
radioactive half-life Being unstable does not lead an atomic nucleus to emit radiation immediately. Instead, the probability of an atom disintegrating is constant, as if unstable nuclei continuously participate in a sort of lottery, with random drawings to decide which atom will next emit radiation and disintegrate to a more stable state.
The time it takes for half of the atoms in a given mass to “win the lottery”–that is, emit radiation and change to a more stable state–is called the half-life. Half-lives vary greatly among types of atoms, from less than a second to billions of years. For example, it will take about 4.5 billion years for half of the atoms in a mass of uranium 238 to spontaneously disintegrate, but only 24,000 years for half of the atoms in a mass of plutonium 239 to spontaneously disintegrate. Iodine 131, commonly used in medicine, has a half-life of only eight days.