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Part I – Nuclear Decay Vocabulary: alpha particle, atomic number, beta particle, daughter product, gamma ray, isotope, mass number, nuclear decay, positron, radioactive, subatomic particle Prior Knowledge Questions (Do these BEFORE using the Gizmo.) The chart below gives the locations, charges, and approximate masses of three subatomic particles. Gizmo Warm-up While most atoms are stable, some are radioactive, which means that they have a tendency to undergo spontaneous nuclear decay.
The approximate mass of each particle is given in universal mass units (u). The atomic number of an element is equal to the number of protons in each atom of the element. The decay of radioactive atoms generally results in the emission of particles and/or energy. Besides the alpha particle, what else is emitted from the nucleus during alpha decay? What you see is an equation that shows the original uranium atom on the left. In the bottom left box, write the atomic number of the daughter product and press “Enter.” What is this number? In the next set of boxes, enter the mass number and atomic number of the alpha particle, which has the same composition as the nucleus of a helium (He) atom. What happened to the proton after absorbing an electron? What is the mass number and charge of the absorbed electron? Predict: During electron capture, an electron is absorbed into the nucleus, causing a proton to transform into a neutron. Think and discuss: What do electron capture and positron emission have in common? Is the rate of decay fastest at the beginning, middle, or end of the process?
Because this assignment is linked with your work in Assignment 3, you will have "If Scientists Think. Before scientists had modern technology to assist them in their research, they had to use their power of observation to infer the relative ages of the rocks they were studying.
The process of Relative Dating was established by Nicholaus Steno in the 1600's.
How will the emission of an alpha particle affect the following? (Note: You can look up element symbols on the periodic table.)3. The equation will appear at the end of the animation. Write an equation for the alpha decay of polonium, and then use the Gizmo to check your answer.
What isotope remains after the alpha decay of polonium-212? Practice: Click Reset, turn off Show equation, and select Radium.
Some isotopes have very long half-lives, measured in billions or even trillions of years.
Activity B: Measuring half-life Get the Gizmo ready: • Click Reset. Apply: Suppose you found a material in which 12.5% of the original radioactive atoms were present. Paste the images into a blank document, and label each image with the half-life.Steno developed a set of Laws (Steno's Laws) to help explain his method of inferring the ages of geological structures.These laws are a set of hypotheses that the scientific community accepts as a starting basis without absolute proof.How will the emission of an alpha particle affect the following? (Note: You can look up element symbols on the periodic table.) 3. The equation will appear at the end of the animation. What isotope remains after the alpha decay of polonium-212? Practice: Click Reset, turn off Show equation, and select Radium. Gamma rays are often emitted during beta decay as well. Fill in the first set of boxes with the mass number and atomic number of the daughter product and the next set of boxes with the mass number and atomic number of the beta particle. Fill in the equations for the beta decay of iodine-131 and sodium-24 in the spaces below. Activity C: Protons into neutrons Get the Gizmo ready: • Click Reset, and turn off Show equation. If a positron and an electron meet, they will annihilate one another in a burst of gamma rays. The positron will fly through space until it encounters an electron. Fill in the first set of boxes with the mass number and atomic number of the daughter product and the next set of boxes with the mass number and atomic number of the positron. Fill in the equations for the positron emission of xenon-118 and manganese-50 in the spaces below. Fill in the last set of boxes with the mass number and atomic number of the daughter product. This process, called decay, causes the radioactive atom to change into a stable daughter atom. • Check that the Half-life is 20 seconds and the Number of atoms is 128. Run a simulation with the Half-life set to 5 seconds, and then run another simulation with the Half-life set to 35 seconds. Trial 0 s 10 s 20 s 30 s 40 s 50 s 1 2 3 4 5 Averages: 15.Write an equation for the alpha decay of radium, and then use the Gizmo to check your answer. Think and discuss: Helium is the second most abundant element in the universe, but it is rare in Earth’s atmosphere. Question: How does beta decay change the nucleus of a radioactive atom? How will beta decay affect the atomic number and mass number of the atom? (Note: The atomic number of an electron is -1.) Check your answer by turning on Show equation and clicking Play. What isotope is produced by the beta decay of carbon-14? Question: How do positron emission and electron capture change an atom? How will positron emission affect the atomic number and mass number of the atom? (Note: The atomic number of a positron is 1.) Check your answer by turning on Show equation and clicking Play. What isotope is produced when carbon-11 emits a positron? The Half-life Gizmo™ allows you to observe and measure the decay of a radioactive substance. Question: How do we measure the rate of radioactive decay? Observe: Select the BAR CHART on the right side of the Gizmo and click Play. What happens to the numbers of radioactive and daughter atoms as the simulation proceeds? Do the numbers of radioactive and daughter atoms change at the same rate throughout the simulation? Take a screen shot of each of the graphs (5 seconds and 35 seconds) and insert them into your lab. Interpret: How does the Half-life setting affect how quickly the simulated substance decays? Analyze: A half-life is defined as the amount of time it takes for half of the radioactive particles to decay. Collect data: In the first row of the table below, write how many seconds represent one half-life, two half-lives, and so forth.