where t is age of the sample , D is number of atoms of the daughter isotope in the sample , D0 is number of atoms of the daughter isotope in the original composition , N is number of atoms of the parent isotope in the sample , and Î '' is the decay constant of the parent isotope , equal to the inverse of the radioactive half-life of the parent isotope times the natural logarithm of 2 . where t is age of the sample , D is number of atoms of the daughter isotope in the sample , D0 is number of atoms of the daughter isotope in the original composition , N is number of atoms of the parent isotope in the sample at time t ( the present ) , given by N = Noe - Î '' t , and Î '' is the decay constant of the parent isotope , equal to the inverse of the radioactive half-life of the parent isotope times the natural logarithm of 2 .