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HalfLife Compound Decay 
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#1
Aug2914, 03:20 PM

P: 1

A 100 mg sample of magnesium27 decays by 7% of its previous mass every minute. Determine its halflife and start the halflife 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. 


#2
Aug2914, 04:02 PM

P: 1,045

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...



#3
Aug2914, 04:09 PM

P: 680

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?



#4
Aug2914, 05:12 PM

PF Gold
P: 2,938

HalfLife 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 halflifes?



#5
Aug2914, 05:23 PM

Mentor
P: 12,081

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.



#6
Aug2914, 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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