Question

A thyroid cancer patient is given a dosage of ¹³¹I (half-life = 8.1 d). What fraction of the dosage of ¹³¹I will still be in the patient's thyroid after 56.7 days?

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Answer 1

Solution:-

If the total time is 56.7 days and the half life is 8.1 days, then no. of half lives n = 56.7 / 8.1 = 7.

So 8 is the number of times that the 131l undergoes a half-life during the 56.7 day period, in other words the number of times it divides itself into half of what it used to be.

Ending amount = Beginning amount / 2ⁿ

Ending amount = Beginning amount / (2)^7 = Beginning amount / 128

Therefore 1/128 th fraction of the dosage will still be in the patient's thyroid after 56.7 days.