health physics
posted by terry .
Assuming that at the beginning of time (big bang; creation of the universe) there
were equal numbers of U235 and U238 atoms produced, estimate the age of
the Earth (using terrestrial U235 and U238 abundances).

What does this have to do with health?
Here are the numbers you need to solve the problem:
U235 half life = T235 = 7.1*10^8 y
U238 half life = T238 = 4.51*10^9 y
Present value of the U235/U238 abundance 0.072 ratio = 
i don't understand

What does this have to do with health?
Here are the numbers you need to solve the problem:
U235 half life = T235 = 7.1*10^8 y
U238 half life = T238 = 4.51*10^9 y
Present value of the U235/U238 abundance ratio = 0.0072
OK. Now solve this equation for the "age of the universe", T
(1/2)^(T/U235)/(1/2)^(T/U238) = 0.0072
(1/2)^[T*(1.41*10^9 0.22*10^9]
= (1/2)^[(1.19*10^9)T]= 0.0072
Lake logs of both sides.
[(1.19*10^9)T]*(0.301)) = 2.143
T = ____
Not a bad guess, but the actual value of the universe age is believed to be about twice as high.
Creationism notwithstanding 
My first answer was accidentally sent before completion. I hope you can understand the complete version that I just uploaded