The decay of atoms depends on the specific radioactive isotope involved. Each radioactive isotope has its own decay rate, expressed by its half-life, which is the time it takes for half of the atoms in a sample to decay.
Some isotopes have extremely short half-lives, measured in fractions of a second, while others can have half-lives measured in billions of years. It is important to note that the decay of individual atoms is a probabilistic process, meaning that while we can predict the average behavior of a large group of atoms, we cannot predict the exact time at which a particular atom will decay.
As for the possibility of an atom stopping decay and becoming stable forever, it depends on the specific isotope and its stability. Stable isotopes do not undergo radioactive decay, meaning they do not spontaneously decay over time. These isotopes are considered to be indefinitely stable unless they undergo a nuclear reaction or are affected by external factors.
On the other hand, radioactive isotopes are inherently unstable, and they will eventually decay into other elements or isotopes. Once an isotope decays and transforms into a stable daughter isotope, that particular atom will no longer decay. However, other atoms of the original radioactive isotope will continue to undergo decay until they all eventually decay or reach a stable state.
In summary, the time it takes for atoms to decay varies depending on the specific isotope involved, and while individual atoms cannot be predicted, the behavior of a large group of atoms can be estimated. Stable isotopes do not decay, but radioactive isotopes will continue to decay until they reach a stable state.