Question

1-Explain the transformation (decay) scheme of Iodine 131

4. ThB is transformed to ThC at a rate of 0.065 hr , and ThC is transformed at a rate of 0.0115 min . How long will it take for the two isotopes to reach

their equilibrium state?

Answer 1

1)

Iodine-131 decays into xenon-131 by a first order process using beta negative decay process with different energy releases.

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2)

(ThB) = 0.065

( ThC) = 0.0115 / min = 0.69 / hr

now, to find the time when ThC activity reaches maximum,

t = ln ( ( ThC) / (ThB)) / ( ( ThC) -   (ThB)

t = ln ( 0.69 / 0065) / ( 0.69 - 0.065)

t = 3.78 hr

however, the equilibrium will be reached after around 6 to 7 half lives.

so, it will take around 423 minutes