The element formed when a radioactive element undergoes radioactive decay. The latter is called the parent. The daughter may or may not be radioactive.

An isotope that undergoes radioactive decay, its nuclei disintegrating spontaneously to form a daughter isotope (often of a different element). For example, rubidium-87 is the parent isotope of strontium-87, into which it decays with a half-life of 4.88 × 1010 years.

The unstable isotopes change over time into more stable isotopes, in a process called radioactive decay. The original unstable isotope is called the parent isotope, and the more stable form is called the daughter isotope. Isotopes decay at an exponential rate that that can be described in terms of half-life.

An unstable radioactive isotope is called a parent isotope. The stable isotope produced by radioactive decay is called the daughter isotope. Radioactive decay can occur as a single step or a series of steps. The more daughter isotope there is, the older the rock is.

Atoms of a parent radioactive isotope randomly decay into a daughter isotope. Over time the number of parent atoms decreases and the number of daughter atoms increases. Rutherford and Soddy (1902) discovered that the rate of decay of a radioactive isotope depends on the amount of the parent isotope remaining.

The pile of red atoms represents the # of atoms of the parent isotope. The blue atoms represent the # of daughter atoms produced after some time t. After a time interval based on the decay rate, 1/2 of the # of atoms of the parent = 1/2 the # of atoms of the daughter. This = the half life.

Polonium-210 is also an alpha particle emitter. Plutonium is less radioactive than polonium, so it would take some tens of milligrams ingested to kill you. Alpha particles do not readily penetrate the skin.