- #1
soopo
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Homework Statement
The initial activity of I_131 is 0.74MBq.
The half time of I_131 is 8 days.
How large is the activity after two days?
Homework Equations
[tex] A = A_0 e^{-\lambda t} [/tex]
The Attempt at a Solution
We know
t = 2 days
A_0 = 0.74 MBq
T_0.5 = 8 days
1. Solve the activity constant
[tex] \lambda = ln2 / T_0.5 [/tex]
2. Plug it to the equation
[tex] A = A_0 e^{(-ln2 / T_0.5) * t} [/tex]
I standardise the units to SI and then omit/cancel them
[tex] A = 0.74E6 * e^{-ln2 / 4} [/tex]
[tex] = 6.22E5 Bq [/tex]
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The right answer is 0.4 times what I get
[tex] A = 0.4 * 6.22E5 Bq [/tex]
[tex] = 250 kBq[/tex]
I am not sure where the 0.4 is got.