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### Topic: Calculate Decay Rate  (Read 13844 times)

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#### sweetdaisy186

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##### Calculate Decay Rate
« on: August 13, 2005, 08:20:31 PM »
The sample of RaCl2 isolated by marie Curie contained 91 mg of radium-226, with a half-life of 1600 years. What was the decay rate in s-1 of her asmple at the time it was isolated?

I know I have to use the decay rate = lambda times N. So, then I converted the 91 mg of radium to atoms so that I could find N to be 2.4245 x 1020 which seemed to be a bit high to me. So, then I took that number times the decay constant and got  3.6368 x 1015

I just wanted to make sure that I did this right. Thanks!

#### Donaldson Tan

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##### Re:Calculate Decay Rate
« Reply #1 on: August 13, 2005, 10:28:17 PM »
half-life = 1600 x 365 x 24 x 60 x 60 = 5.04576 E10
decay constant = (ln 2) / half-life = 1.373722 E-11 s-1

at time of isolation, 91mg of Ra-226 present
N = 0.091/226 = 4.0265 E-4 moles

decay rate = decay constant x N = 5.5313 E-15 moles/s = 3.318 E9 atoms/s

I think you messed up the milli- conversion twice.
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#### sweetdaisy186

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##### Re:Calculate Decay Rate
« Reply #2 on: August 14, 2005, 04:14:03 PM »
ooo, I see what I did! Thanks!