Strontium-86 is a stable element that does not undergo radioactive change.
In addition, it is not formed as the result of a radioactive decay process.
An atom with the same number of protons in the nucleus but a different number of neutrons is called an isotope.
For example, uranium-238 is an isotope of uranium-235, because it has 3 more neutrons in the nucleus.
It has the same number of protons, otherwise it wouldn't be uranium.
The number of protons in the nucleus of an atom is called its atomic number.
Because of radioactivity, the fraction of rubidium-87 decreases from an initial value of 100% at the time of formation of the mineral, and approaches zero with increasing number of half lives.
F, the fraction of K40 remaining, is equal to the amount of potassium-40 in the sample, divided by the sum of potassium-40 in the sample plus the calculated amount of potassium required to produce the amount of argon found. In spite of the fact that it is a gas, the argon is trapped in the mineral and can't escape.Potassium-Argon dating: The element potassium (symbol K) has three nuclides, K39, K40, and K41. K40 can decay in two different ways: it can break down into either calcium or argon.The ratio of calcium formed to argon formed is fixed and known.Therefore the amount of argon formed provides a direct measurement of the amount of potassium-40 present in the specimen when it was originally formed.Because argon is an inert gas, it is not possible that it might have been in the mineral when it was first formed from molten magma.