Lab: Half-Life Simulation Lab
Purpose: The purpose of this lab is to simulate the decay of a radioactive isotope.
Introduction:
In this lab pennies will be used to simulate the decay and half-life of a radioactive isotope. Radioactive decay occurs for several reasons; the nucleus is too large; neutron to proton ratio in the unstable nucleus is incorrect, either too high or too low; or the nucleus is left with too much energy. In order for a new element to form, the number of protons in the nucleus must change. Radioactive decay, which forms a new element, is called transmutation. Among the types of radioactive decay, which form new elements, are alpha decay, beta decay, and positron (emission) decay. After undergoing alpha, beta or positron decay, the nucleus can still contain excess energy. To remove this energy, the nucleus will give off high-energy electromagnetic radiation called gamma radiation. This is called gamma decay. Since the atomic number does not change, NO new element is formed during gamma decay.
Radioactive decay is a random process. It is not possible to predict when a particular nucleus will decay, but we can make fairly accurate predictions regarding how many nuclei in a large number will decay in a given period of time. The half-life is the length of time it takes for half the nuclei in a radioactive sample to undergo radioactive decay. After one half-life, 50 % of the original amount of the sample will have undergone radioactive decay. After another half-life, half of the remaining 50 % will undergo radioactive decay. Only 25 % of the original sample of radioactive substance will be left. Each time that a half-life occurs, half the remaining sample will undergo decay. Eventually, the quantity of a radioactive substance will approach zero given enough time or, in other words, half-lives. The length of the half-life will depend on the radioactive substance and is unaffected by any factor, such as temperature or pressure. Some radioactive substances have a very short half-life, such as nitrogen-16, N-16, with a half-life of 7 seconds. Other substances have a very long half-life, such as uranium-238, U-238, with a half-life of 4.51 x 10 9 years (4.5 billion years.) The length of the half-life will determine how to dispose of a radioactive substance or how long to store this radioactive substance until the level of radioactivity reaches a safe level. On reference table N, the length of the half-life and the mode of decay for selected radioisotopes are listed. Reference table O lists selected symbols used in nuclear chemistry.
Materials: Shoe box
80 pennies
Procedure:
Note: Each lab group will be assigned a number.
1. Place 80 pennies heads up in the shoe box. This will represent the radioactive isotope, headsium. Close the box and shake vigorously once.
2. Open the box, remove and count the number of pennies, which are now tails up. These pennies represent the atoms of headsium , which have undergone decay. Headsium's decay product is called tailsium. Record the number of headsium and tailsium atoms on Data Table #1. After the first half-life the number of changed pennies for half-life will be the same as the total number of tailsium. This represents one half-life. Set the removed pennies aside.
3. Close the box and repeat the steps 1 and 2 three (3) more times. After each half-life, record the number of headsium left, the number of changed for halflife (the new tailsium atoms). To determine the total number of tailsium, add the number of changed for half-life to the previous total number of tailsium. Your sample will have undergone 4 half lives.
4. When you are done, place all pennies back in the shoebox and return to the teacher.
5. Place your group's data on the overhead for the class data. Record the class data in Data Table # 2and # 3.
Name: / Group #: / Minutes: / Grade:Lab: Half-Life Simulation Lab
Objective: ______
______
Data Table #1 (Individual Group)
Data Table #2: # Headsium after each half-life (Parent) (Class Data)
Data Table #3: Total # Tailsium after each half-life (Daughter) (Class Data)
Analysis:
Prepare a line graph of the class data. Plot the number of half-lives on the x-axis and the total number of headsium (Parent) on the y-axis. Use circles around the headsium data points. Then plot the Tailsium (Daughter) data on the SAME graph using triangles around the data points. Make a key for the two different lines. Remember to label the axes and give the graph a title.
QUESTIONS- Short answers BUT Work must be shown for math problems.
1. Explain the type of relationship, direct or indirect, that exists between the parent nuclide, headsium, and time.
______
2. Explain the type of relationship, direct or indirect, that exists between the daughter nuclide, tailsium, and time.
______
3. Write the nuclear equation for HEADSIUM (Hs) if it decays to TAILSIUM (Ts) by alpha decay. Use the symbol Ts for the daughter nuclide.
280
Hs -> ______+ ______
120
4. Write the nuclear equation for HEADSIUM (Hs) if it decays to TAILSIUM (Ts) by beta decay. Use the symbol Ts for the daughter nuclide.
280
Hs -> ______+ ______
120
5 . Write the nuclear equation for HEADSIUM (Hs) if it decays to TAILSIUM (Ts) by positron decay. Use the symbol Ts for the daughter nuclide.
280
Hs -> ______+ ______
120
6. Why does a new element NOT form if headsium only decays by giving off gamma radiation?
______
7) For the parent nuclide, headsium-280, complete the chart below:
Number of ProtonsNumber of Neutrons
Number of Electrons
Nuclear Charge
Number of Nucleons
8) Scientists found two isotopes of headsium, Hs-280 and Hs-284. The following data was collected. Determine the weighted atomic mass that should be placed on the Periodic Table.
Isotope / Percent Abundance / Atomic MassHs-280 / 83.4 % / 279.8
Hs-284 / 16.6 % / 284.2
9. a) What is the mode of decay and the length of the half life of cobalt-60?
Mode of decay: ______Length of Half-life: ______
b) If you had a 200. mg sample of cobalt-60, how many milligrams would be left after 15.9 years ? MUST SHOW WORK.
11. A doctor needs 5.0 mg of I-131 to treat his patients. The doctor orders 10.0 mg from the supplier to account for the decay of some of the sample during shipping. The package with I-131 gets sent elsewhere initially but finally arrives 16 days after shipping. Will the doctor have enough of the I-131 left to treat his patients? Explain your answer. (You MUST SHOW MATH WORK to help explain your may help explain your answer.)
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