# health physics

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Assuming that at the beginning of time (big bang; creation of the universe) there
were equal numbers of U-235 and U-238 atoms produced, estimate the age of
the Earth (using terrestrial U-235 and U-238 abundances).

• health physics -

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 =

• health physics -

i don't understand

• health physics -

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

• health physics -

My first answer was accidentally sent before completion. I hope you can understand the complete version that I just uploaded

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