Questions+for+Introduction+to+Radiochemistry

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In this exercise you are going to make a calibration source of uranium. You will use this source to calibrate and get some experience with using a gas-filled detector. You will then use the source to investigate uncertainty in radioactive measurements. Your supervisor will demonstrate and explain the various equipment you are going to use. Never just "try it out" but ensure that you know exactly what to do and how before you do any operations with radioactive material. Before you can start in the lab you must calculate the exact amount of uranium needed for calibration source. Therefore you should answer the following questions before you arrive at the lab. Write the answers down in your laboratory journal and ask your supervisor to check before you start any work in the lab.

Question 1: Draw the disintegration schematic of the uranium series from 238 U to 230 Th. Write down the half-lives and the type of disintegration, including the energy of emitted particles.

Question 2: Assume that the sample of uranium that you have is one year old. (The uranium is chemically separated from the other elements). Why is 234 Th, 234 Pa and 234 U in equilibrium with 238 U, while 230 Th is not?

Question 3: Show that the amount of 238 U and 234 U is in agreement with the equilibrium definition λ 1 N 1 = λ 4 N 4. (Assume the abundance of the two isotopes is equal to the abundance in natural uranium.)

Question 4: math \frac{H_1}{H_4}=\frac{N_1}{N_4} math Here H 1 symbolizes the atomic abundance of a 238 U and H 4 symbolize the atomic abundance of 234 U. Compare this with math \frac{T_{{1/2}_1}}{T_{{1/2}_1}} math Does this agree with the claim that the two isotopes are in equilibrium?

Question 5: What is the mass of UO 3 that must be weighted in to get the right amount of the radioactive calibration source you are going to make?. Assume that the the counting speed **R** should be equal to 100 cps and that the counting efficiency is ε = 15%. Your counter will measure high-energy betas (the disintegration yielding low-energy betas will not be measured since we shield the source with 7 layers of tape - low-energy betas will not get through).

Background
Note down the values from the background measurement. The longer the measurement the better. Preferably it should be started the day before. Counting number: math N_{bck}=\,\,\,\,\,\,Counts math Counting Time: math t_{bck}=\,\,\,\,\,\,\, sec math Standard deviation: math \frac{\sqrt{N_{bck}}}{t_{back}}=\,\,\,\,\,\,\,\, cps math

Counting Efficiency
Do a one minute count on every shelf that is in the detector. Use these measurements to calculate the counting -efficiency of the GM-detector in %. The activity of the sample can be calculated from the amount of UO 3 used. math A=IR math where A is the true activity I is the efficiency of the detector and R is the observed counting number.


 * Shelf Number || Counts per minute || Calculated efficiency from amount of uranium ||
 * 1 ||  ||   ||
 * 2 ||  ||   ||
 * 3 ||  ||   ||
 * 4 ||  ||   ||
 * 5 ||  ||   ||

Twenty measurements with constant distance from the source
Do twenty measurements lasting for one minute. Keep the source fixed to one position. Calculate the standard deviation and complete the table
 * measurement number || N P || N P -N average || (N P -N average ) 2 ||
 * 1 ||  ||   ||   ||
 * 2 ||  ||   ||   ||
 * 3 ||  ||   ||   ||
 * 4 ||  ||   ||   ||
 * 5 ||  ||   ||   ||
 * 6 ||  ||   ||   ||
 * 7 ||  ||   ||   ||
 * 8 ||  ||   ||   ||
 * 9 ||  ||   ||   ||
 * 10 ||  ||   ||   ||
 * 11 ||  ||   ||   ||
 * 12 ||  ||   ||   ||
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 * 14 ||  ||   ||   ||
 * 15 ||  ||   ||   ||
 * 16 ||  ||   ||   ||
 * 17 ||  ||   ||   ||
 * 18 ||  ||   ||   ||
 * 19 ||  ||   ||   ||
 * 20 ||  ||   ||   ||
 * 21 ||  ||   ||   ||
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 * 23 ||  ||   ||   ||