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Half-Life Compound Decay

by Trustworthy
Tags: compound, decay, halflife
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Trustworthy
#1
Aug29-14, 03:20 PM
P: 1
A 100 mg sample of magnesium-27 decays by 7% of its previous mass every minute. Determine its half-life and start the half-life decay equation.

The textbook that I got this from (Nelson Physics 11) tells me the answer, but uses a long and annoying process to find it: creating a table at different points in time and then graphing. I am just wondering if there is an equation or some sort of trick to this type of question? It would save me a lot of time and trouble, thank you in advance.
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ChrisVer
#2
Aug29-14, 04:02 PM
P: 1,057
It's a series.. it tells you that at each minute it loses 7% of what it had before... So it's better to use a table and see it...
Orodruin
#3
Aug29-14, 04:09 PM
P: 681
Yes, it is very possible to derive a general expression for the amount left after a given time. If the sample loses 7% of its mass every minute, what is the ratio of mass left to original mass after 1 minute? What is the ratio after two minutes? Three minutes? Do you see a pattern? In that case, what should be the mass left after a time T?

arivero
#4
Aug29-14, 05:12 PM
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Half-Life Compound Decay

To honour the "Compound" in the title of the post... Can someone point to the general formula for a decay chain, with elements having different half-lifes?
mfb
#5
Aug29-14, 05:23 PM
Mentor
P: 12,099
The right formula depends on what you want to know, but it is possible to get everything with the right integral for the considered problem.
Meir Achuz
#6
Aug29-14, 07:26 PM
Sci Advisor
HW Helper
PF Gold
P: 2,026
The question seems too simple.
##\exp(-t/\tau)=0.93##, so ##\tau=-1/\ln(.93)## in minutes.


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