Question

The radioactive substance strontium-90 has a half-life of 28 years. In other words, it takes 28 years for half of a given quantity of strontium-90 to decay to a non-radioactive substance. The amount of radioactive strontium-90 still present after t years is modeled by the expression 8(2^-t/28) grams. Evaluate the expression for t = 0, t = 28 and t = 56. What does each value of the expression represent?

Answer 1

Strontium-90 radioactive, meaning it decays with time.
Another way to say this is the amount of Strontium-90 is a function of time.
The half life of Strontium-90 is 28 years
The half life equation for exponential decay is \[N(t)=N_02^{-t/t_{1/2}}\]
Where \(N(t\)) is the amount of substance.
\(N_0\) being the initial amount {because \(t\) is zero}
\(t\) is time, and \(t_{1/2}\) is the half-life of the substance

For Strontium-90 the half life equation is
\[^{90}_{38}\text{Sr} (t)=8\text g\times2^{-t/28}\]

Substituting a value of \(t\) {in years} and simplifying the equation will tell you how much Strontium-90 {in grams} is left un-decayed at this time .