The half-life of radium is 1690 years. If 90 grams are present now, how much will be present in 450 years?

Answer 1

Generally, the form of decay is S = S_oe^-kt

Where S = amount remaining, S_o = the initial amount , k = decay constant, & t = time in years

To find K, we substitute what is known

45 = 90e^-k(1690) or .5 = e^-k(1690)

Solving for k, we have k = .00041

To find how much is left after 450 years, we write S = 90e^{-(.00041)(450)} = 74.83 grams