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 Map 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 90 80 70 e0 50 40 30 20 10 0 10 20 30 40 50 0 70 80 90 100 110 120 130 140 15O 180 170 180 190 200 Time (days) a) If the initial sample is 7.75 g, what mass of the original iridium-192 remains after 5 days? Number continued below... 7.36

Explanation / Answer

1. half life :  Afinal= Ainitial - (Ainitial)= Ainitial 2

when the final concentration of sample is half the initial concentration of sample

i.e concentration of sample is 50% of initial concenttration ; i.e concentration of sample left = 50%

which corresponds to 70 days from graph, therefore half life is 70 days.

2. for decay of one fourth of sample: Afinal= Ainitial - (Ainitial)= 3 Ainitial 

final concentration of sample is three fourth the initial concentration of sample;

therefore, final concentration of sample is 75% , i.e according to graph corresponds to 30 days.

thus 30 days are required in the decay of one fourth of the sample

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