# Lab Exercise - Uranium-oxide Calibration Standard for     GM-tubes

### Developed By

Institute of Chemistry

Faculty of Mathematics and Natural sciences

University of Oslo

### Learning Goals

• To understand the relationship between amount of radioactive material and decay rate.
• To understand the relationship between count rate and decay rate.
• To understand the uncertainty in measured number of counts and be able to calculate the uncertainty in numbers derived from such numbers.
• Be able to use a radioactivity detector.
• To know and understand the basic principles for work with open radioactive sources.
• Be able to conduct contamination checks.

### Explanation and Exercise Guide

Theory

• Geiger-Müller Counter and Counting Efficiency (read)

Experimental Procedure

Preparation of an Uraniumoxide Sample:

1. A filter-holder with vacuum suction will be used to make the uranium calibration source. The setup will be demonstrated by your supervisor. Before you start with the uranium, test the setup thoroughly for leaks and other problems (with water). All equipment and radioactive material should be in a tray with absorbing paper at the bottom. Non-active equipment and materials should be kept separately. Keep your workspace tidy.
2. On the high-precision scale (demonstrated by your supervisor) measure the exact weight of your weighing ship.
3. Transfer the calculated amount of uranimoxide to your weighing ship using the laboratory scale (low precision) to control the amount.
4. When you transport your UO3 (or any other radioactive material) from one place to another (e.g. from the scale to your work space) always use a tray, preferentially with a lid, such that any spills/contamination will be in the tray and not on the floor.
5. Measure the exact amount of uraniumoxide you have on the high-precission scale by weighing the ship with the oxide. Calculate the exact amount of uraniumoxide you have.
6. Transfer the UO3 into the filter-holder setup by flushing out the ship with water. Make sure everything is transferred and try to do it in such a way that the oxide is evenly distributed on the filter.
7. Apply vacuum to remove the water and leave it on until the uraniumoxide on the filter is reasonably dry.
8. A sample holder card (cardboard with a punch-out hole slightly larger than the filter paper you are going to use) is prepared for holding and sealing the uraniumoxide: Put seven layers of tape on one side such that the hole is completely and securely covered.The seven layers of tape will ensure that low-energy betas will not pass through (why is this important?).
9. Disconnect the vacuum suction and "catch" the filter with the tape on the sample holder card. Remove it very carefully, turn it and securely seal the filter/uraniumoxide with tape.
10. Write your initials, date, and amount of UO3 on the sample card.
11. Check the sample card holder for surface contamination by using a swipe (your supervisor will explain/demonstrate).
12. Clean up your workplace and make sure that all radioactive waste is disposed of properly in appropriate waste containers. Update the waste accumulation logs.

Figure 1. On the left side is a prepared counting paper with a filter with uraniumoxide taped on. On the right side there is a unprepared filter.

Questions for the Students

### Equipment

• Geiger-müller counter and associated equipment
• Uranium oxide or similar source
• A filter holder that can be coupled to a vacuum suction
• A high precision scale
• A low precision scale
• Insoluble filters
• Thin tape
• Cardboard card with a hole punched through which fits your filter