Iridium-192 is one radioisotope used in brachytherapy, in which a radioactive so
ID: 801017 • Letter: I
Question
Iridium-192 is one radioisotope used in 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 dose 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.
The point of the graph at 150 days is 24.46%, sorry I can't seem to upload the graph
a) If the initial sample is 2.25 g, what mass of the original iridium-192 remains after 150 days?
b) Estimate the half-life of the radioisotope.
c) How many days would it take for three-fourths of the sample to decay?
Explanation / Answer
% of reaction left after n t1/2 = a/2^n
2^n= 100/24.46 = 4.08
n= no of t1/2= 2
half life time = 150/2 = 75 days
a) mass of the original iridium-192 remains after 150 days
2.25------> 1.125------------>0.5625
= 0.5625 grams
b)half life time = 75 days
c) no days takes for three-fourths of the sample to decay= 150 days
(3/4th decay means 1/4th sample left in 150 days)
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