# Determining the Half Life of 234mPa

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Before you plot the data subtract the background counts from each measurement and calculate the uncertainty for each point.

- Plot your measured data on a A3-sized semi-logarithmic paper. Your data should lie on a straight line (why?). Fit the best possible line through your data. Remember to plot the uncertainty also.
- Select a point on your fitted line from the left side (e.g. 1000 counts), note the corresponding time, t1.
- Now, divide the number of counts for t1 by 2 three times (for 1000 counts you get 125) and find the time, t2, your fitted line passed through this number of counts.
- The difference between t1 and t2 corresponds to three half lives (why?).
- Estimate the uncertainty in your fit by drawing two worst-case lines through your data, one with the steepest possible slope and one with the least possible slope. Analyse these lines in the same way as the main line - the respective half lives indicate your lower and upper uncertainty limits.