Radiometric Dating: Finding the Age of the Earth
Question 1. What is the value of the decay constant for rubidium-strontium? |
Solution: Use the basic decay equation P(t) = P0e- λ t. When
t = half-life for Rb-Sr = 4.88 x 104 million years,
then the initial number of atoms is reduced by half (from
to
) , so denoting half-life by h, set t = h and solve
for λ
,
So now we solve 
for λ, with h = 4.88 x 104.
Cancel P0 from each side, then take the natural logarithm of both sides,
But
so
.
We have found the decay constant λ = 1.42 x10-5 for the Rb-Sr system.