Iridium-192 is one radioisotope used brachytherapy, in which a radioactive sourc
ID: 520599 • Letter: I
Question
Iridium-192 is one radioisotope used brachytherapy, in which a radioactive source is placed inside a patient's body to treat cancer. Brachytherapy allows the use of a higher than normal does to be placed near the tumor while lowering the risk of damage to healthy tissue. Iridium-192 is often used in the head or breast. Answer the following three questions (a, b, and c) based on the radioactive decay curve of iridium-192 shown below. Click on the graph and move the mouse over a point to get values for that point. a) If the initial sample is 3.50 g, what mass of the original iridium-192 remains after 55 days? a) If the initial sample is 3.50 g, what mass of the original iridium-192 remains after 55 days? b) Estimate the half-life of the radioisotope. c) How many days would it take for one-fourth of the sample to decay?Explanation / Answer
From the graph, after ~55 days 60 % of the sample is remaining. So, if the initial sample is 3.5 g, then mass of original iridium-192 that remains is (0.6 x 3.5 g = ) 2.1 g
The half-life is the amount of time taken by the sample to decay to half of its initial value. From, the graph, initially we are at 100 %, so for the half-life, we should have 50 % sample remaining as 50 % would have decayed. Thus, from the graph, we have 50 % sample remaining after ~72 days. So the half-life of the radioisotope is ~72 days.
As one-fourth of the sample decays, it means three-fourth of the sample is remaining. So ((3 / 4) x 100 % = ) 75 % of the sample is remaining. And from the graph, ~75 % of the sample is remaining after 30 days.
[P.S. Since I cannot move the mouse over a point, I am unable to put the exact numbers on certain quantities but they will be close to what I estimate.]
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