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 over the mouse over a point to get values for a point.

Explanation / Answer

A)

initial sample m = 8.25 g

find mass after

t = 80 days...

the % remain after t = 80 days = 48 % approx

therefore

0.48*8.25 = 3.96 g approx

If you need an specific vlaue

from the graph, half life = 70 days

so

Afinal = Ainitial * (1/2)^(t/HL)

Afinal = 8.25*(0.5)^(80/70)

Afinal = 3.7361 g left

b)

the half life... from previous data

HAlf life = 50% has decayed

from the graph, at 50% --> t = 71 days (approx, hard to read)

c)

find time required for 2/3 of sample to decay

that is:

Afinal / Ainitial = (3-2)/(3) = 1/3

Afinal = Ainitial * (1/2)^(t/HL)

Ainitial /Afinal = (1/2)^(t/HL)

1/3 = (1/2)^(t/HL)

ln(1/3) / ln(1/2) = t/(71)

1.584 = t/71

t = 1.584*71

t = 112.464 days required aprox

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