Plzz help Iridium-192 is one radioisotope used in brachytherapy, in which a radi
ID: 880838 • Letter: P
Question
Plzz help Iridium-192 is one radioisotope used in brachytherapy, in which a radioactive source is placed inside a tient'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 (%) 901 so 70 60 s0 40 10 20 10 0 10 20 30 40 0 60 0 80 90 100 110 120 130 140 110 160 170 180 190 200 Time (days) a) If the initial sample is 6.50 g, what mass of the original iridium-192 remains after 85 days? Number continued below. b) Estimate the half-life of the radioisotope. Number days continued below c) How many days would it take for one-third of the sample to decay? Number days
Explanation / Answer
a) From the plot, time required for 50% of material to decay = 70 days (t1/2)
So,
Calculate rate constant k,
k = 0.693/t1/2
= 0.693/70 = 9.9 x 10^-3
Now we know that,
ln(No/N) = kt
given,
No = 6.5 g
N = amount left after t time
t = 85 days
Feed values,
ln(6.5/N) = 9.9 x 10^-3 x 85
N = 2.80 g of 192Ir left after 85 days
b) approximate half life t1/2 = 250/2 = 125 days
c) Days required for 1/3 of sample to decay.
After 1/3 decay, the remaining sample left N = 1-0.33 = 0.67
t = unknown
Feed values,
ln(No/N) = kt
ln(1/0.67) = 9.9 x 10^-3 x t
t = 41 days would be needed for the deacy of 1/3 sample
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