AJ asked in Science & MathematicsPhysics · 8 months ago

# One of the decay products of 238U 238 U is 226Ra . A rock originally contained 238U , which has a half-life of 4.5×10^ 9 yr........?

One of the decay products of 238U

238 U is 226Ra . A rock originally contained 238U , which has a half-life of 4.5×10^ 9 yr, and 226Ra, which has a half-life of 1,600 yr. After 5×10^9 yr, which isotopes would you expect to be present in significant amounts in the rock?

Now choose from one of the following optionsWhy?

a 226Ra but not 238U

b Neither 238U nor 226Ra

c 238U but not 226Ra

dBoth 238U and 226Ra

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• 8 months ago

D is the correct answer. Both of them will be present significantly in the rock.

• 8 months ago

As the time is about one half life of Uranium about half of the original amount is present.

As the half life of Ra is very low then as soon as it is made it decays.  Meaning very little Ra would be present.

• D g
Lv 7
8 months ago

5.9x 10^9/1.6x 10^2

3.5x10^7 times means almost all Ra is gone

238 u has a half life 4.5 x10^9 means it has a bit lless than  half