Difference between revisions of "Determining the Half Life of 234mPa"

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Return to [[Lab Exercise with 234Th/234Pa Radionuclide Generator|Main]]
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Return to [[Lab Exercise with 234Th/234Pa Radionuclide Generator|Main]]  
  
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<br>
  
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Before you get your sample, make sure you know exactly what to do. Test the counting<br>procedure without a sample to ensure that this is the case.<br>
  
Before you plot the data subtract the background counts from each measurement and calculate the uncertainty for each point.  
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#Make a god background measurement, i.e.&nbsp;use a long&nbsp;counting time&nbsp;(at least 30 min). It would be smart to start the background measurement before you prepare the radionuclide generator, as this will take at least one hour. Then you can start directly with the <sup>234m</sup>Pa measurements once the generator is ready.
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#Select a preset counting time of 60 s. Make a table in which you can write down your results.
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#Get a stopwatch and learn how to use it.
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#You will count your sample repeatedly in 60 s intervals in order to get the disintegration curve for <sup>234m</sup>Pa. Between each interval a break of 30 s is recommended for writing down the result, clearing the spectrum/counter and prepare for the next measurement. Make sure you write down the exact time you start each counting - do not cheat to fit your planned schedule, write down the actual time!
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#Write down the total number of counts in the spectrum for each measurement.
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#Repeat the 60 s countings until there is no more <sup>234m</sup>Pa left, then do a 600 s background measurement (remember to change the preset counting time).
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#Repeat the measurement so you get two complete disintegration curves for <sup>234m</sup>Pa.
  
#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.
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#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.
 
  
 
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[[Category:Half_life]]
 
 
[[Category:Laboratory_exercise]] [[Category:Half_life]] [[Category:Detection]]
 

Revision as of 10:52, 2 July 2012

Return to Main


Before you get your sample, make sure you know exactly what to do. Test the counting
procedure without a sample to ensure that this is the case.

  1. Make a god background measurement, i.e. use a long counting time (at least 30 min). It would be smart to start the background measurement before you prepare the radionuclide generator, as this will take at least one hour. Then you can start directly with the 234mPa measurements once the generator is ready.
  2. Select a preset counting time of 60 s. Make a table in which you can write down your results.
  3. Get a stopwatch and learn how to use it.
  4. You will count your sample repeatedly in 60 s intervals in order to get the disintegration curve for 234mPa. Between each interval a break of 30 s is recommended for writing down the result, clearing the spectrum/counter and prepare for the next measurement. Make sure you write down the exact time you start each counting - do not cheat to fit your planned schedule, write down the actual time!
  5. Write down the total number of counts in the spectrum for each measurement.
  6. Repeat the 60 s countings until there is no more 234mPa left, then do a 600 s background measurement (remember to change the preset counting time).
  7. Repeat the measurement so you get two complete disintegration curves for 234mPa.