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

From mn/safe/nukwik
Jump to: navigation, search
 
(4 intermediate revisions by 2 users not shown)
Line 1: Line 1:
−
Return to [[Lab Exercise with 234Th/234Pa Radionuclide Generator|Main]]  
+
[[Lab Exercise with 234Th/234Pa Radionuclide Generator|Return]]  
  
−
<br>
+
Use a high-quality data plotting and fitting program (e.g. Origin) to analyse the data. The fitting ''must'' take the uncertainity into account (do not use Excel), otherwise you will get the wrong result.
  
−
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>
+
Notice that you always shall use the 1/3 of the time into each measuremnent as the "middle time point". This is due to decay - after 1/3 of the time you will have equally many counts before and after the 1/3 point (i.e. it is the "middle point".  
  
−
#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.
+
#For each datapoint calculate the net count (gross count - background count), the uncertainity of the net count (based on uncertainity of both the gross count and the background count). You might want to use e.g. MS Excel or similar for doing this.
−
{| cellspacing="1" cellpadding="1" border="0" style="width: 392px; height: 214px;"
+
#Enter your data in a table ("worksheet" in Origin jargong): Include measurment time (relative to start of sampling) as x-value, the net count as y-value, and the uncertainity as y-error.
−
|-
+
#Plot the data - does it look ok?
−
| [[Image:Lab_Radionuclide_generator_Counting_UO2.jpg|384x205px]]<br>
+
#Use the Origin data-fitting functionality to determine the measured half-life and associated uncertainity.  
−
|-
 
−
| ''Insertion of aluminum counting-vessel into detector.''<br>
 
−
|}
 
  
−
#Select a preset counting time of 60 s. Make a table in which you can write down your results.
+
'''Alternativ/Extra:''' Plot the gross counts instead of the net counts and ask Origin to fit both the background and the decay.  
−
#Get a stopwatch and learn how to use it.
 
−
#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!
 
−
#Write down the total number of counts in the spectrum for each measurement.
 
−
#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).
 
−
#Repeat the measurement so you get two complete disintegration curves for <sup>234m</sup>Pa.
 
  
−
<br>
+
[[Category:Half_life]] [[Category:Master]]
−
 
 
−
[[Category:Half_life]]
 

Latest revision as of 23:04, 4 October 2012

Return

Use a high-quality data plotting and fitting program (e.g. Origin) to analyse the data. The fitting must take the uncertainity into account (do not use Excel), otherwise you will get the wrong result.

Notice that you always shall use the 1/3 of the time into each measuremnent as the "middle time point". This is due to decay - after 1/3 of the time you will have equally many counts before and after the 1/3 point (i.e. it is the "middle point".

  1. For each datapoint calculate the net count (gross count - background count), the uncertainity of the net count (based on uncertainity of both the gross count and the background count). You might want to use e.g. MS Excel or similar for doing this.
  2. Enter your data in a table ("worksheet" in Origin jargong): Include measurment time (relative to start of sampling) as x-value, the net count as y-value, and the uncertainity as y-error.
  3. Plot the data - does it look ok?
  4. Use the Origin data-fitting functionality to determine the measured half-life and associated uncertainity.

Alternativ/Extra: Plot the gross counts instead of the net counts and ask Origin to fit both the background and the decay.

Retrieved from "https://wiki.uio.no/mn/safe/nukwik/index.php?title=Determining_the_Half_Life_of_234mPa&oldid=1987"