Final answer:
The half-life of iodine-131 is approximately 1.25 days.
Step-by-step explanation:
The question asks about the half-life of iodine-131. The half-life of a radioactive substance is the time it takes for half of the substance to decay or break down. In this case, if a 160 mg sample of iodine-131 became 5 mg after 40 days, we can use the concept of half-life to determine the half-life of iodine-131.
Let's use the given example to understand how to calculate the half-life of iodine-131. In Example 8.3.1, it is mentioned that the half-life of iodine-131 is 8.1 days. This means that every 8.1 days, half of the original amount of iodine-131 will decay. Using this information, we can set up a proportion:
(160 mg) / (5 mg) = (1 half-life) / (40 days)
Cross-multiplying and solving for the unknown, we find:
(1 half-life) = (40 days) * (5 mg) / (160 mg) = 1.25 days
Therefore, the half-life of iodine-131 is approximately 1.25 days.