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Half-life of tritium

Question: The half-life of tritium (hydrogen-3) is 12.3 yr. If 46.9 mg of tritium is released from a nuclear power plant during the course of an accident, what mass of this nuclide will remain after 24.6 yr? (Significant figures are important)

My answer: 11.7 mg. I came to this answer by recognizing that 24.6 yr is the duration of 2 half lives. Thus, 1/4 of the original amount will be present. Dividing 46.9 by 4 yields 11.725; however, I must use the correct number of significant figures (3, I believe), so my final answer is 11.7 mg.

Please tell me what I am doing wrong, because my answer has been marked wrong and I cannot figure out why.
 

Answers and Replies

Gokul43201
Staff Emeritus
Science Advisor
Gold Member
6,987
14
Your answer is correct. I would also try 11.65mg - just in case they weren't being careful with sig figs.
 
berkeman
Mentor
56,086
6,136
Moved to homework forum.
 

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