10 of 14 Map Sapling Learning in which a radioactive source is placed inside a I

Question

10 of 14 Map Sapling Learning in which a radioactive source is placed inside a Iridium-192 is one radioisotope used in patient's body to treat cancen he tunor while lowering the risk of allows the use of a higher than normal dose to be placed near 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. Clck on the graph and move the mouse over a point to get values for that point Sample remaining (%) 100 80 70 80 50 30 20 10 0 10 20 30 40 50 60 70 80 90 100 11D 120 130 140 150 180 170 180 190 Time (days) a) If the initial sample is 7.00 g, what mass of the original iridium- 192 remains after 35 days? continued below

Explanation / Answer

a) From the graph after 35 days the sample remaining is 72%

thus if we start from 7.00g of sample

the remaining amount is 7.00g x 72/100 = 5.04g

b) From the observation of graph

505 reaction is completed in 75 days

Thus half life of the sample = 75days

c) Radioactive decay is first order kinetics

k = [2.303/t ] log a/a-x

and k = 0.693/half life

Thus k = 0.693/75 /days

and a = 1 and a-x= 3/4

Thus

[0.693/75] = [2.303/t] log 1/(3/4)

hence t = 31.14 days

Thus time taken for 1/4 of the sample to disintegrate is 31.14 days

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