.
3. A sample of a radioactive isotope was found to be 40 mg 18 days ago and 5 mg today.
a) What is the half-life of the substance?
b) How many milligrams of the substance will be left 12 days from today?
~~~~~~~~~~~~~~~~~
(a) The ratio of the current mass to the initial mass is = = .
It means that 3 (three) half-lives passed from the beginning to the current moment.
It means that 18 days comprize 3 half-lives. Hence, one half-life is = 6 days. ANSWER
(b) 12 days from today comprise 12/6 = 2 half-lives;
So, in 12 days after today, the remaining mass will be = = 1.25 milligrams. ANSWER
Solved. // All questions are answered.
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On radioactive decay, see the lesson
- Radioactive decay problems
in this site.
You will find many similar (and different) solved problems there.
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Learn the subject from there once and for all.
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lesson is the part of this online textbook under the topic "Logarithms".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
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to your archive and use it when it is needed.