Pre-Lab 13 Assignment: Radioactive Decay

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Radioactive Decay v 0.1 Question 1.4 Compare the value you obtained in Question (1.3) with the accepted value of the half-life of 14 6C of 5730yr. Do they agree? Now that you know how to determine the half-life, the mean life, and the decay constant of a given isotope by looking at the activity of the radioactive sample as a function of time you are ready to determine the half-life of an unknown isotope by measuring its activity over a period of time. Investigation 2: Determining the Half-Life of a Radioactive Sample In this section we will determine the half-life, the mean life and the decay constant of a radioactive sample of an unknown isotope. For the activities in this investigation you will need: • computer-based laboratory system • experiment configuration files • radioactivity probe • small beaker • radioactive sample (handled by the lab technician) Precaution The level of radioactivity in the samples is very low, and will not cause any harm, provided they are not ingested or allowed to come into contact with the skin. However, care should always be exercised when handling any radioactive substance. If a spill should occur, it should be wiped up immediately and the paper towels discarded in a container provided. DO NOT EAT OR DRINK while handling radioactive material. Activity 2.1: Measuring the Activity of the Sample Step 1: Open the Lab file Lab13 A 1 Step 2: Connect the radioactivity probe to the socket named Dig.1 in the Vernier adapter. Step 3: Place the measuring window of the probe directly in front of the clean beaker. Step 4: When you are ready to start your experiment request that the lab technician put the sample in your beaker. Step 5: Immediately after your sample is poured in the beaker click the collect button in the Logger Pro software. Be patient as the total collection time is 20 minutes. Once the collect button appears again, you are ready to analyze your results. The probe will be collecting raw counts of the activity of the sample. These are the number of decays over a period of 5 seconds. PHYS-204:Physics II Laboratory 5
Radioactive Decay v 0.1 Step 6: In the axes below draw the graph you obtained in Step 5. Make sure to indicate the scale in the axes. Activity (counts) Time (s) Step 7: Using the software curve fit tools try a few different fits, for example inverse (A/t), inverse square (A/t 2 ), and natural exponent (Aexp(−Ct)+B). Question 2.1 Which of the curves best fit the data? And what are the values of the constants obtained in the fit? If the experiment went according to plan your best fit should have been the natural exponent. But, as you might have noticed that instead of the expression in Eq. (1.7) which goes to zero as times becomes very large (t → ∞) there was an extra constant (B). Question 2.2 In the expression y = Ae −Ct +B what is the value of y as t → ∞? PHYS-204:Physics II Laboratory 6
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Pre-Lab 13 Assignment: Radioactive Decay

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