Difference between revisions of "Exercise: Working With Radioactive Material"

From mn/safe/nukwik
Jump to: navigation, search
m
 
(9 intermediate revisions by 2 users not shown)
Line 1: Line 1:
Return to [[Basic Laboratory Procedures for Radio-Chemistry|main]]  
+
[[Basic Laboratory Procedures for Radio-Chemistry|Return]]  
  
In the first exercise you shall learn how to use a contamination detector to find contaminated equipment or areas. The monitor is a simple radioactive detector that uses a handheld gass filled probe (Geiger-müller detector) to find active areas. Your counsellor will show you hove to use the detector.  
+
In the first exercise you are going to learn how to use a contamination detector ("monitor") to identify contaminated equipment or areas. The monitor ("Automess") contains a simple gas-filled chamber in which the ionizing radiation is detected (proportional or Geiger-Müller detector). Your supervisor will instruct you on how to use the detector.  
  
The student must write a short description of the things that are important to remember when using the detector:
+
In your journal, you are required to write down the important things to remember when using the monitor.
  
<br>  
+
'''Task 1: Measurements with the external probe'''<br>Perform the following measurements with the probe connected to the hand-held monitor, in each case measure five times with ~30 s intervals:
  
<br>
+
The count rate (counts per second – cps) at the following places: Close to the laboratory bench. Inside the fume hood. Outside of the laboratory.
  
<br>
+
Was there any significant difference for the three places?
  
<br>  
+
'''Task 2: Measurements with the internal probe'''<br>Remove the probe (unplug the cable from the instrument - be careful so that you destroy the cable¸ ask for help if unsure).
  
<br>
+
The "Automess" hand-held monitor has a built in probe which is constructed in such a way that it will accurately measure external radiation dose (for γ radiation) for an extensive range of energies and intensities. Dose rate is a measurement of how much “strain” the radiation gives the body. It is measured in Sievert (Sv) per unit time. Sievert is a large unit and dose rate is therefore presented in μSv per hour (the instrument switches to mSv in high radiation field, but this should not happen in low-level training labs!). For comparision, the natural background radiation (in Norway) will give you a yearly dose of about 3-4 mSv (~0.5 μSv per hour).
  
Do the following measurements with the probe connected to the hand held detector:
+
Measure the dose rate at the same places as you measured the count rate!
  
The count rate (counts per second – cps ) on the following places:<br> The laboratory bench …................ cps<br> Inside of the fume hood …............... cps<br> outside of the laboratory …................ cps<br>
+
'''Task 3: Measure a strong γ-source'''<br>Reconnect the probe. There is a source placed on one of the benches in the laboratory (the place is clearly labeled). The source is well shielded, but there is an opening where you can insert the probe so that it will "see" the source.  
  
was there any significant difference in the counting in the three places?  
+
Write down the source strength and nucleus. What is the count rate of the source?  
  
<br>  
+
'''Task 4: Calibration of the external probe'''<br>In the lab you will find a <sup>90</sup>Y/<sup>90</sup>Sr calibration probe with a disintegration rate of 30 Bq/cm<sup>2</sup>.
  
<br> Remove the probe - ''be careful so that you don’t pull the cable ''([[Ask the lab-assistant]]). The handheld detector is calibrated to measure dose rate. Dose rate is a measurement of how much “strain” the radiation gives the body. It is measured in sievert (Sv) per unit time. Sievert is a large unit and dose rate is therefore often given in <span class="texhtml">μ</span>Sv per hour. In comparision the natural background radiation will give you a yearly dose of about 4 mSv (0.46<span class="texhtml">μ</span>Sv per hour)<br> measure the dose the same places you measured the count rate. The laboratory bench …................ <span class="texhtml">μ</span>Sv/h<br> Inside of the fume hood …............... <span class="texhtml">μ</span>Sv/h<br> outside of the laboratory …................ <span class="texhtml">μ</span>Sv/h<br>
+
Measure the count rate about 0.5 cm and 5 cm from the surface. What is the relationship between disintegration rate and measured count rate? (I.e. what is the efficiency of the detector).  
  
Reconnect the probe. There is a source placed on one of the benches in the laboratory ( the place should be clearly marked). The source is well shielded, but you can insert the probe past it, so that you can see what happens when the probe finds activity.<br>
+
A surface is regarded as contaminated if the disintegration rate is above 4 Bg/cm<sup>2</sup> (for γ and β radiation). For the monitor you are using, will you be able to measure such a disintegration rate? What is the detection limit of your monitor?
  
Which source is placed out?.....................<br> What is the count rate of the source?......................cps<br>  
+
'''Task 5: Find a contamination on a surface'''<br>One of the laboratory benches shall be checked for contamination. For this particular exercise, we have covered and sealed the contamination (not normally the case). Thus, there is no need to worry that you by accident will become contamination. However, for the purpose of training you should observe the same precautions as if it had been a real (unprotected) contamination.<br>
  
One of the laboratory benches shall be controlled for contamination. For this part of the exercise the contamination is covered and sealed. There is no need to worry that you will receive any contamination on yourself or your clothes. Therefore the exercise can be done outside of the fume hoods. You shall still take the same precautions you would as if it had been a unprotected contamination.  
+
It is very important that you manage these exercises since in exercise [[Measurement of 99mTc gamma-spectrum]] and [[Yield of Tc in Liquid-Liquid Extraction]] you will work with activety that is not sealed and then you must be able to identify eventual contaminations.  
  
''It is very important that you manage these exercises since in exercise [[Measurement of 99mTc gamma-spectrum]] and [[Yield of Tc in Liquid-Liquid Extraction]] you will work with activety that is not sealed and then you must be able to identify eventual contaminations ''
+
[[Category:Radiation_protection]] [[Category:Laboratory_exercise]] [[Category:Radio_chemistry]]
 
 
<br> Find the contamination(s) on the benches. Draw in the approximate position and give the count rate for each contaminated are on the drawing.
 
 
 
[[Category:Radiation_protection]][[Category:Laboratory_exercise]][[Category:Radio_chemistry]]
 

Latest revision as of 06:19, 23 September 2012

Return

In the first exercise you are going to learn how to use a contamination detector ("monitor") to identify contaminated equipment or areas. The monitor ("Automess") contains a simple gas-filled chamber in which the ionizing radiation is detected (proportional or Geiger-Müller detector). Your supervisor will instruct you on how to use the detector.

In your journal, you are required to write down the important things to remember when using the monitor.

Task 1: Measurements with the external probe
Perform the following measurements with the probe connected to the hand-held monitor, in each case measure five times with ~30 s intervals:

The count rate (counts per second – cps) at the following places: Close to the laboratory bench. Inside the fume hood. Outside of the laboratory.

Was there any significant difference for the three places?

Task 2: Measurements with the internal probe
Remove the probe (unplug the cable from the instrument - be careful so that you destroy the cable¸ ask for help if unsure).

The "Automess" hand-held monitor has a built in probe which is constructed in such a way that it will accurately measure external radiation dose (for γ radiation) for an extensive range of energies and intensities. Dose rate is a measurement of how much “strain” the radiation gives the body. It is measured in Sievert (Sv) per unit time. Sievert is a large unit and dose rate is therefore presented in μSv per hour (the instrument switches to mSv in high radiation field, but this should not happen in low-level training labs!). For comparision, the natural background radiation (in Norway) will give you a yearly dose of about 3-4 mSv (~0.5 μSv per hour).

Measure the dose rate at the same places as you measured the count rate!

Task 3: Measure a strong γ-source
Reconnect the probe. There is a source placed on one of the benches in the laboratory (the place is clearly labeled). The source is well shielded, but there is an opening where you can insert the probe so that it will "see" the source.

Write down the source strength and nucleus. What is the count rate of the source?

Task 4: Calibration of the external probe
In the lab you will find a 90Y/90Sr calibration probe with a disintegration rate of 30 Bq/cm2.

Measure the count rate about 0.5 cm and 5 cm from the surface. What is the relationship between disintegration rate and measured count rate? (I.e. what is the efficiency of the detector).

A surface is regarded as contaminated if the disintegration rate is above 4 Bg/cm2 (for γ and β radiation). For the monitor you are using, will you be able to measure such a disintegration rate? What is the detection limit of your monitor?

Task 5: Find a contamination on a surface
One of the laboratory benches shall be checked for contamination. For this particular exercise, we have covered and sealed the contamination (not normally the case). Thus, there is no need to worry that you by accident will become contamination. However, for the purpose of training you should observe the same precautions as if it had been a real (unprotected) contamination.

It is very important that you manage these exercises since in exercise Measurement of 99mTc gamma-spectrum and Yield of Tc in Liquid-Liquid Extraction you will work with activety that is not sealed and then you must be able to identify eventual contaminations.