Question 569108
The Radioactive isotope technetium 99m (99mTc) is used in imaging the brain. the isotope has a half life of 6 hours. If 12 milligrams are used how much will be present after three hours and 24 hours?
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The radioactive decay formula can be written {{{N(t) = N0(1/2)^(t/T)}}} 
where T = the half-life, N0 = the amount at t=0, and N(t) = the amount at time t
Given: N0 = 12 mg, T = 6 h
So the formula can be written {{{N(t) = 12(1/2)^(t/6)}}}
The amount after 3 hrs is {{{N(3) = 12(1/2)^(1/2) = 8.49}}} mg
The amount after 24 hrs is {{{N(24) = 12(1/2)^(24/6) = 12(1/2)^4 = 0.75}}} mg