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ID: 1036606 • Letter: N
Question
nglearning.com/ibiscms/mod/ibis/view.php?id 4656106 ning Jump to... ore 4/1/2018 11:55 PM 51/100 4/1/2018 03:50 AM Gradebook 15 of 21 Sapling Learning 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. Sample remaining (%) 0 0 10 20 30 40 so ? 70 80 90 100 110 130 130 140 150 160 170 180 190 Time (days) a) If the initial sample is 5.00 g, what mass of the original iridium-192 remains after 80 days?Explanation / Answer
a)
From graph, after 80 days 53% of origininal sample is dacayed
remaining % of original sample = 47%
mass of original iridium-192 sample remain after 80 days = (5.00/100)×47 = 2.35g
b)
Half life is time required to decay 50% of original sample
From graph, time required to decay 50% of original sample = 74 days
Therefore,
Half life of iridium - 192 = 74days
c)
From graph, time required to dacay 1/4th (25%) original sample = 30days
by calculation
rate constant, k = 0.693/t1/2 = 0.693/74days = 9.36×103days-1
t = (2.303/k) log ([A]0 /[A]t)
t = (2.303/9.36×10-3days-1)log(100/75)
t = 30.74days
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