# Help With Half Life

by Chris Smith
Tags: life
 P: 2 Hi, I'm new to the forum and came here because I could use some help. At the moment I am really confused because I know that A = DecayConstant * N, where A is activity and N is the number of atoms before decay. Isn't the Activity is how many atoms decay after 1 second with a specific value of N? So if the DecayConstant = 0.5, N will half each second. So I figured if the DecayConstant is 0.5 then the half life (T1/2) is 1 second. But then I realized that contradicts the following equation: DecayConstant = ln(2) / T1/2, if T1/2 = 1 then DecayConstant = ln(2) =/= 0.5 What have I done wrong and why isn't any of this making sense? Did I make a basic error or do I have poor understanding? Thank you for reading and helping.
 P: 2 Ok I understand now, Activity decreases over the course of the second as well. I assumed it to be the average number of atoms decaying over a second, but it isn't. It is the activity from one point in time and as the atoms decay over the second the Activity decreases. /resolved

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