Rubidium strontium age dating
(Do not confuse with the highly radioactive isotope, strontium-90.) Strontium occurs naturally as a mixture of several nuclides, including the stable isotope strontium-86.
If three different strontium-containing minerals form at the same time in the same magma, each strontium containing mineral will have the same ratios of the different strontium nuclides, since all strontium nuclides behave the same chemically.
The amount of strontium-86 in a given mineral sample will not change.
Therefore the relative amounts of rubidium-87 and strontium-87 can be determined by expressing their ratios to strontium-86: Rb-87/Sr-86 and Sr87/Sr-86 We measure the amounts of rubidium-87 and strontium-87 as ratios to an unchanging content of strontium-86.
Strontium-87 is a stable element; it does not undergo further radioactive decay.
The two curves cross each other at half life = 1.00.
At this point the fraction of Rb87 = Sr87 = 0.500; at half life = 2.00, Rb87 = 25% and Sr87 = 75%, and so on. 131, Strahler, Science and Earth History: Points are taken from these curves and a plot of fraction Sr-87/Sr-86 (as ordinate) vs. It turns out to be a straight line with a slope of -1.00.
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.