Register to reply

Half-Life Compound Decay

by Trustworthy
Tags: compound, decay, halflife
Share this thread:
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.
Phys.Org News Partner Physics news on
New complex oxides could advance memory devices
Nature's designs inspire research into new light-based technologies
UCI team is first to capture motion of single molecule in real time
Aug29-14, 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...
Aug29-14, 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?

Aug29-14, 05:12 PM
PF Gold
arivero's Avatar
P: 2,938
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?
Aug29-14, 05:23 PM
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.
Meir Achuz
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.

Register to reply

Related Discussions
Half-Life decay question High Energy, Nuclear, Particle Physics 2
How to find the mass of a compound given the half life and activity? Biology, Chemistry & Other Homework 1
Nuclear decay and half-life Biology, Chemistry & Other Homework 3
Half life and nuclear decay. High Energy, Nuclear, Particle Physics 8
Half-life and decay Calculus & Beyond Homework 5