Lab Exercise - Basic Laboratory Procedures for Radiochemistry
Developed By
Section of Radiochemistry
Institute of Chemistry
Faculty of Mathematics and Natural sciences
University of Oslo
Learning Goals
- Basic laboratory safety rules and procedures.
- Basic procedures for working with modest amounts of radioactivity.
- How to use a radiation monitor.
Explanation and Exercise Guide
Radiation Protection
- Safety rules in Radiochemistry (read)
Experimental Procedure
In this 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 comparison, 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 Bq/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.
In this 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.
Questions for the Students
Before students start the laboratory exercise they should answer the following questions and write the answers in your laboratory journal. Your lab suppervisor will check the answers and you are not allowed to start before she/he has signed the page in your journal.
Q1: What does the symbol that marks radioactivity look like?
Q2: Why is it strictly forbidden to work in such a way that there is danger of internal contamination (the radioactive source enters the body), while it is legal to a certain degree to expose oneself to external radiation (for instance working close to a radioactive source)?
Q3: The exposure should always be as little as possible ( the ALARA principle). For an external radiation source there is three main ways to do this. Which?
Other
How to do calculations or other important aspects for the theory that is not directly related to exercise.
Safety Aspects
Safety Rules in Radiochemistry