Introductory Questions and Preparation of the Sample (Introduction to Radiochemistry)
Lab Exercise and Rapports
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In this exercise you are going to make a sample of uranium, and do measurements which will show the uncertainty in measurements and decide the efficiency of the detector. Be certain that you know how the GM-detector works, before you prepare the uranium sample. You must calculate the amount of uranium needed for the sample. Therefore you should complete the following before preparing the sample.
- Draw the disintegration schematic of the uranium series from 238U to 230Th. Write down the half-lives and the type of disintegration.
- Assume that the sample of uranium that you have is one year old. (The uranium is chemically separated from the other elements). Why is 234Th, 234Pa and 234 in equilibrium with 238U, while 230Th is not.
- Show that the amount of 238U and 234U is correct with the equilibrium defenition λ1N1=λ4N4. Assume the abundance of the two isotopes will be equal to abundance in natural uranium.
compare this with
Does this agree with the claim the two isotopes are in equilibrium?
- What is the mass of UO3 that must be weighted in to get the radioactive sample. Assume that the the counting speed R should be equal to 100 cps from disintigration of 234Am and that the counting efficiency is ε = 0.15.
Preparation of the Sample
- 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.
- A sample holder card (cardboard with a punch-out hole slightly larger than the filterpaper you are going to use) is prepared for holding and sealing the uraniumoxide: Put several layers of tape on one side such that the hole is completely and securly covered. .
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.
- Weigh in the calculated amount of UO3 ca precisely in a weighing ship. Do a rough weighing first on a laboratory weight (50-150 mg).
- Transfer the weighed amount of UO3 into the filter-holder use as little as possible water the filter-holder should be filled with water. Try to get the sample as even as possible.
- The solution is vacuumed until it is dry and the filter-paper is mounted onto the counting card with seven layers of tape in a cross over the hole. The sample must be completely sealed.