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The radioisotope rubidium-84 has been used to measure cardiac output. if Rb-84 has a half life of 33 days , how many milligrams of a 77.9 mg sample remains after 99 days
Accepted Answer
After 99 days, three half-lives of rubidium-84 have passed (99 days / 33 days/half-life = 3 half-lives).
Each half-life reduces the amount of the isotope by half.
After the first half-life, 77.9 mg / 2 = 38.95 mg remains.
After the second half-life, 38.95 mg / 2 = 19.48 mg remains.
After the third half-life, 19.48 mg / 2 = 9.74 mg remains.
Therefore, 9.74 mg of the original 77.9 mg sample of rubidium-84 would remain after 99 days.
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