bluedicius Posts: 20, Reputation: 1 New Member #1 Mar 13, 2005, 08:06 AM
exponential decay
The radioactive decay formula is A = A0(1/2)^t/n, where A is the current amoutn of the radioactive sample, A0 is the original amount, t is the elapsed time and n is the length of the half life.

The half life of Sodium-24 is 14.9h. A researcher begins with 100mg of sodium-24. What is the exponential decay equation for this sample of sodium-24?
How much of the sample will be remaining in 48hours?
How long will it take until the sample decays to only 1mg of sodium-24?
 reinsuranc Posts: 92, Reputation: 6 Junior Member #2 Mar 14, 2005, 07:17 AM
Exponential decay
A = (Ao) * (.5 ^ (t/n))
A = (100) * (.5 ^ (t/14.9))

1. (100) * (.5 ^ (48/14.9)) = 10.72

2. 1 = (100) * (.5 ^ (t/14.9))
LN(1) = LN[ (100) * (.5 ^ (t/14.9)) ]
LN(1) = LN(100) + LN[ (.5 ^ (t/14.9)) ]
LN(1) = LN(100) + (t/14.9) * LN(.5)
14.9 * [ LN(1) - LN(100) ] / LN(.5) = t
14.9 * [ 0 - 4.60517 ] / -.69315 = t
t = 98.99

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