Krypton-85 has a half-life of 10 years.

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Krypton-85 has a half-life of 10 years. What percentage of 85Kr produced from nuclear testing in 1959 still remains today?

25.0%

3.13%

12.5%

6.25%

Sep 1st, 2015

Thank you for the opportunity to help you with your question!

Note:  i did with 2 Methods

Method 1:

The half life formula: A = Ao(2^(-t/h) where
Ao = original amt
t = time
h = half life of the material
A = resulting amt

so, A=Ao(2^(-50/10))/Ao*100=3.125 % ~ 3.13 %           Answer


Method:2

Given Half life, t1/2=10yrs

t1/2=0.693/k

k=0.693/10=0.0693 yrs-1

Now let [Kr]0 be initial concentration in 1959, and [Kr] be conc today.

Time, t=2014-1959=55yrs

ln([Kr]0/[Kr])=kt

[Kr]0/[Kr]=e0.0693*55

[Kr]0/[Kr]=45.218

[Kr]=0.022[Kr]0

thus % remaining in 2014 is 2.2%

If the ques would have been solved in 2009:

Percent remaining=3.13%         Answer




Please let me know if you need any clarification. I'm always happy to answer your questions.
Sep 1st, 2015

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