Final answer:
To find the remaining mass of Radium-226 after a certain number of years, use the half-life decay formula with the initial mass of 120 grams and the half-life of 1620 years, adjusting 't' for the time elapsed.
Step-by-step explanation:
To calculate the amount of a radioactive sample remaining after a given time has passed, you can use the half-life decay formula:
N(t) = N_0 × (1/2)^(t/T)
Where N(t) is the amount remaining after time t, N_0 is the initial amount, T is the half-life of the substance, and t is the elapsed time.
For a 120-gram sample of Radium-226 which has a half-life of 1,620 years, the amount remaining after t years is:
N(t) = 120 grams × (1/2)^(t/1620)
To use the formula, simply replace t with the number of years that have passed.