ridium-192 is one radioisotope used in brachytherapy, in which a radioactive sou
ID: 882623 • Letter: R
Question
ridium-192 is one radioisotope used in brachytherapy, in which a radioactive source is placed inside a rearing hea ridium-192 is often used in to be ead or breas placed near the normal dose questions (a, b, and c) based on the radioactive decay curve of inidium-192 Answer the following three shown below. Click on the graph and move the mouse over a point to get values for that point Sample remaining 20 30 40 30 60 70 30 0 120 30 140 30 160 170 30 190 200 Time (days) the initial sample is 825g, what mass of the original indium-192 renains after 80 days? Nuriber continued bebw. b) Estimate the half-life of the radialsotope Number continued below days c) How many days would it take for two-thirds ofthe sample todeeay Number daysExplanation / Answer
initial mass = A = 8.25 g
mass after time t = At
time (t) = 80 days
from the graph half-life = 70 days
dissociation constant (K) = 0.693 / half -life
= 0.693 / 70
= 9.9 x 10^-3 day-1
radio active decay follows first order kinetics
t = (2.303 / K) (log A/At)
80 = (2.303 / 9.9 x 10^-3 ) log (8.25 /At)
log (8.25 /At) = 0.343
8.25 /At = 10^0.343 = 2.202
At = 8.25 / 2.202
At = 3.745
after 80 days sample remaining = 3.745 g
for 50 % consumption 70 days are required from the above graph
(b) for 8.25 g total consumption ----------------> 200 days required
4.125 g consumption(half the sample) --------------------> howmany days required
half -life = 4.125 x 200 / 8.25
= 100 days
(c)
A = 8.25 g
decay =x 2/3 of initial means = 8.25 x 2/3 = 5.5
remaining = At = 8.25 - 5.5 = 2.75 g
t = (2.303 / K) (log A/At)
t = (2.303 / 9.9 x 10^-3 ) log (8.25 /2.75)
t = 111 days
t = 111 days
111 days required to decay of 2/3 of orginal sample--------------(answer)
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