Question:easy
What is the physical half-life of Iodine-131?
What is the physical half-life of Iodine-131?
Show Hint
Recall the short therapeutic radioiodine used for thyroid ablation.
Updated On: Jun 24, 2026
- 8 hours
- 8 days
- 8 weeks
- 8 months
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: The question asks for the decay half-life of I-131, the workhorse radioiodine in thyroid imaging and ablation therapy.
Step 2: By definition the half-life is the interval over which the radioactivity of a sample drops to one half of its starting value. For Iodine-131 this period is close to 8 days, short enough that the isotope clears in weeks yet long enough to deliver an effective therapeutic dose.
Step 3: Distinguishing it from its relatives helps confirm the answer: I-123 decays in roughly 13 hours and I-132 in about 2.3 hours, so an 8-hour answer would suit neither. Values of 8 weeks or 8 months grossly overstate the persistence of any clinically used iodine isotope.
Step 4: So the half-life of Iodine-131 is 8 days.
\[\boxed{\text{8 days}}\]
Step 2: By definition the half-life is the interval over which the radioactivity of a sample drops to one half of its starting value. For Iodine-131 this period is close to 8 days, short enough that the isotope clears in weeks yet long enough to deliver an effective therapeutic dose.
Step 3: Distinguishing it from its relatives helps confirm the answer: I-123 decays in roughly 13 hours and I-132 in about 2.3 hours, so an 8-hour answer would suit neither. Values of 8 weeks or 8 months grossly overstate the persistence of any clinically used iodine isotope.
Step 4: So the half-life of Iodine-131 is 8 days.
\[\boxed{\text{8 days}}\]
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