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Uranium Dating

  • #1

Homework Statement


The isostopc abundances of a sample is U-235 and U-238 are 0.72 and 99.27 respectively; what is the age of the sample? (assume isotope abundance was equal when sample was formed)

Homework Equations


[itex]\lambda=\frac{ln2}{ t_{\frac{1}{2}}}[/itex]

The Attempt at a Solution


for U-238 [itex]N_{238}(T)=N_{238}(t)e^{\lambda _{238}t}[/itex]
U-235 [itex]N_{235}(T)=N_{235}(t)e^{\lambda _{235}t}[/itex]
T is time at present and t is time of sample formation.

diving the two equations gives
[itex] \frac{N_{238}(T)}{N_{235}(T)}=\frac{N_{238}(t)}{N_{235}(t)}e^{(\lambda _{238}- \lambda _{235})t}[/itex]

From the assumption, one can say [itex]\frac{N_{238}(t)}{N_{235}(t)}=1[/itex]
It's here where i'm not sure; do i just say that [itex]\frac{N_{238}(T)}{N_{235}(T)}=\frac{99.27}{0.72}[/itex] and solve for t or am I missing something? Thanks

EDIT: Sorry, I can't get my latex to work, I can't seem to fix it
 
Last edited:

Answers and Replies

  • #2
34,037
9,871
I fixed the two broken equations, but the first one looks odd.
Yes, just do that and solve for t.
 
  • #3
Thanks for that, I fixed the first equation.
 

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