In April 2019, a team of researchers identified its half-life as 18 billion trillion years. Then there’s the real record-holder: xenon-124. Other isotopes may have a half-life measured in hours, days or years. Its half-life is little more than a half-second. Take the lab-made isotope lawrencium-257. By the sixth half-life, just over 1 percent remains. This simple graph shows how the amount of original material drops by one half over the course of each half-life. All of the rest have morphed into stable atoms. By the end of the fourth half-life, there are only five atoms of the original isotope. Three half-lives would leave only about 10 atoms of the original isotope. After two half-lives, just 20 atoms of the original isotope would remain. The rest will have decayed to a new isotope. If you start with 80 unstable atoms, 40 will remain at the end of the first half-life. That half-life is always the same - like an unwritten rule - that is specific to each isotope. An isotope’s half-life is defined as the amount of time it takes for one-half of the atoms of a radioactive isotope to decay. But scientists describe the process in terms of its half-life. How long it takes an isotope to decay depends on a lot of factors. Its animation also illustrates how unstable isotopes go about becoming stable. It explains the difference between stable and unstable (radioactive) atoms. But the result is the same: the unstable isotope eventually becomes a new, stable one. There are lots of ways the decay can happen. Or, it changes one or more of its neutrons into protons, also releasing energy. To do this, it gives off some of its energy and particles. This atom now strives to become balanced. Forces holding together the protons and neutrons inside an atom’s nucleus are out of balance. But it doesn’t take a tap to make an unstable atom decay. The protons and neutrons inside the nuclei of radioactive isotopes are unstable in a similar way. But sooner or later, even a small bump to the side of the bowl will make at least one of them spill out. You might be able to balance the two extra grapes on top of the pile for a while. Now let’s imagine that you try to put in 22 purple grapes instead of 20. Let’s say the bowl fits exactly 40 grapes (which would represent the nucleus of a calcium atom). Each purple grape stands in for a neutron. You can picture the decay process by imagining a bowl filled with green and purple grapes. But there are a whole host of other tiny particles that might also be shed. Often, it sheds light (a form of energy), an alpha particle (two neutrons bound to two protons) or an electron or a positron. The radiation emitted by that decay can take several forms. And decay reactions almost always involve giving off energy, radiation and more tiny particles. In radioactive decay, there are lots of ways an unstable atom’s nucleus can transform to make it more stable - and smaller.
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