To calculate the percent of the radioactive isotope rhenium after 3 half-lives is
(1/2)^3 = 0.125 x 100 = 12.5%
We calculate that there is 12.5% percent activity of the radioactive isotope.
Radioactive isotope other called as radioisotope, radioactive nuclide or radionuclide, in any of the several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of gamma, alpha and beta rays. Rhenium is a chemical element and has an atomic number of 75. Its chemical symbol is Re. It is in the third-row transition metal in group 7 of the periodic table.