Hello, I have a relatively simple question. I'm just wondering, with half-life problems, how could I solve something like the following: Isotope: 226Ra Half-life: 1620 years. Initial Quantity: X (Solve for this) Amount after 1000 years: 1.5g Where I'm supposed to find the initial quantity. Wouldn't a part of the equation be something like: .5 = e^1620r, where r is the rate of decay? I'm using natural log to try to get the rate: ( ln(.5) / 1620 ) = r When I punch that in to the calculator, I get huge number and it leads me to believe that I'm messing up somewhere.