Iridium-192 is one radioisotope used in brachytherapy, in which a radioactive so

Question

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 (%) 100 80 70 60 50 40 30 20 10 0 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) According to the curve after 5 days the sample remaining (%) in Y axis is 95%. So we have to calculate 95% of 9.00g:

Sample remaining after 5 days = (9.00g)(95/100) = 0.81g

b)Estimating the half life of the radio isotope (50% decay or 50% remain) : In the graphic you have to locate in the Y axis (sample remaining)   50 % value and then see what time corresponds, it is 70 days. Half-life: 70 days.

c) Three fourths represents 75% decay, as you can see:

3/4 = 0.75 = 75%

75% decay represents : 100-75% = 25% remaining...

Then you locate in Y axis (sample remaining ) the 25% and relates what vaklue of X axis corresponds, It is 150 days.

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