# Question #705ba

All radio-isotope decay is 1st order kinetics and follows the classic 1st order decay trend described by ${A}_{\text{(final)" = A_"(initial)"e^-"kt}}$ ; A = Activity, k = decay constant, t = time. The half-life equation can be used to calculate decay constant => $k = \left(\frac{0.693}{t} _ \text{1/2}\right)$ The initial activity = 100%, t = 75-yrs.