ridium-192 is one radioisotope used in brachytherapy, in which a radioactive sou
ID: 1060225 • Letter: R
Question
ridium-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 92 click to edit Answer the following three questions (a, b, and c) based on the radioactive decay curve of iridium shown below. Click on the graphand move the mouse over a point to get values for that point olo) Sample remaining 100 90 80 70 60 50 40 30 20 10 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 Time (days)Explanation / Answer
a/ At 35 days there is 38% of the sample
m(105 days) = 38% x 8.75 = 3.325 g of 192-Iridium
b
m(t) = m(to) x e(- x t)
. . . with : = ln(2) / T½
m(t) / m(to) = e(- x t)
ln(m(t) / m(to)) = - x t
= - ln(m(t) / m(to)) / t
= - ln(3.325 / 8.75) / 105
= 9.21•10^-3 day^-1
. . . finally :
T½ = ln(2) /
T½ = ln(2) / 9.21•10^-3
T½ = 75.26 days
c)
m(t) / m(to) = 0.67
ln(m(t) / m(to)) = - x t
t = - ln(m(t) / m(to)) /
t = - ln(0.67) / 9.21•10^-3
t = 43.48 days
The half-life of 14C is 5730 years.
(1/2)^(x/5730) = 0.95
Take the log of both sides:
(x/5730) log (1/2) = log (0.95)
Divide by log (1/2):
x/5730 = log (0.95) / log (1/2)
Multiply by 5730:
x = 5730 log (0.95) / log (1/2) 424 years
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