Hi:

I am struggling with a laboratory exercise. Our book has not arrived at the shop yet, and the Professor is away.

We measured a radio isotope with a GM-counter for 12 minutes (automatic instrument) at 15 seconds intervals. There half-life is supposedly relatively short, and I can see the number of counts dropping with time.

What I have to do, is to find the half life. We have some example graphs with time t on the x-axis and number of nuclides N on the y-axis. However, I am not quite sure how to manage my data set to get these values.

The solution of the first order diff. equation -dN/dt = λN is the following:

N = N_{0}e^{-λt}, where λ is the disintegration rate, N_{0} is the number of nuclides at t_{0}.

So how do I get from counts or counts-per-minute to N? That is what I do not understand. The lab instructions do not explain how to do it very well. I do not ask you to do my work for me, I am merely asking for suggestions or new ways of thinking.

I hope someone can help me out! In addition of drowning in reports, I decided to write them all in LaTeX and this takes three times as long (because I am still new to LaTeX).

I have imported my data to R-Commander, and subtracted the background to each measurement. That is as far as I have come. Again, I would appreciate any *delete me*

Sincerely,

Anders