Student Exploration: Nuclear Decay

Student Exploration: 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. The approximate mass of each particle is given in universal mass units (u). Particle Location Proton Nucleus Neutron Nucleus Electron Orbitals Charge Approximate mass 1+ 1 u 0 1 u 1- Ou 1 1. The mass number of an atom is equal to the sum of protons and neutrons in the nudeus. A helium atom has 2 protons and 2 neutrons. What is the mass number of this atom? The mass number of this atom is 4. 2. The atomic number of an element is equal to the number of protons in each atom of the element. All helium atoms have 2 protons. What is the atomic number of helium? The atomic number of helium is 2. Gizmo Warm-up While most atoms are stable, some are radioactive, which means that they have a tendency to undergo spontaneous nuclear decay. The decay of radioactive atoms generally results in the emission of particles and/or energy. Several types of nuclear decay can be explored with the Nuclear Decay Gizmo. On the Gizmo, check that Alpha decay and Uranium are selected. Key Proton Neutron Electron Positron Gamma 1. Click Play (), and then click Pause () when the alpha particle is clearly visible. What is an alpha particle made of? The alpha particle is made of two protons and two neutrons. 2. Click Play and observe. Besides the alpha particle, what else is emitted from the nucleus during alpha decay? A gamma ray is also emitted from the nuclear besides the alpha particle during alpha decay. Gamma rays are energetic electromagnetic waves; they are often emitted in nuclear decay. Get the Gizmo ready: Click Reset (2). Check that Alpha decay and Uranium are selected. 2 Question: How does alpha decay change the nucleus of a radioactive atom? 1. Predict: As you observed in the warm-up activity, an alpha particle consists of two protons and two neutrons. How will the emission of an alpha particle affect the following? A. The atomic number of the atom: The emission of an alpha particle will affect the atomic number of the atom as it will decrease the atomic number by 2, as two protons are lost during the emission. B. The mass number of the atom: The emission of an alpha particle will affect the mass number of the atom as it will decrease the mass number by four as 2 protons and 2 neutrons, in total 4, are lost during the emission. 2. Calculate: Tum on Write equation. What you see is an equation that shows the original uranium atom on the left. The boxes on the right represent the daughter product-the atom produced by radioactive decay-and the emitted alpha particle. A. In the top left box, write the mass number of the daughter product and press "Enter" on your keyboard. What is this number? This number is 234. B. In the bottom left box, write the atomic number of the daughter product and press "Enter." What is this number? This number is 90. C. 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. After filling in the boxes in the Gizmo, write the completed equation below: D. According to your equation, what isotope remains after the alpha decay of New mass number 238 234 U 92 Th + a He New atomic number uranium-238? (Note: You can look up element symbols on the periodic table.) According to my equation, the isotope that remains after the alpha dec 3. Check: Tum on Show equation, and click Play. The equation will appear at the end of the animation. Was your prediction correct? If not, modify your above. Yes, my prediction was correct. 4. Practice: Click Reset, turn off Show equation, and select Polonium. Write an equation for the alpha decay of polonium, and then use the Gizmo to check your answer. 212 84 Po 208 82 Ры He What isotope remains after the alpha decay of polonium-212? The isotope that remains after the alpha decay of polonium-212 is lead-208. 5. Practice: Click Reset, turn off Show equation, and select Radium. Write an equation for the alpha decay of radium, and then use the Gizmo to check your answer. 226 Ra- 222 88 86 Rn 4 2 He 6. What dangerous gas is produced by the decay of radium-226? The dangerous gas produced by the decay of radium-226 is radon-222, or radon. Practice: Americium-241 is a radioactive isotope used in smoke detectors. Write an equation for the alpha decay of Americium-241 below. 241 237 95 Am 93 Np 4 2 7. Analyze: In each equation, how is the mass number on the left side of the arrow related to the sum of mass numbers on the right side of the arrow? Is this true for atomic numbers? The mass of the left side of the arrow is related to the sum of mass numbers on the right side of the arrow because the mass number on the left side (reactant side) is equal to the mass number on the right side (product side). This means that the mass number on the left side is the same as the sum of the mass numbers on the right side as the law of conservation of mass states that in a chemical reaction, the total mass of reactants is equal to the total mass of products. This is also true for atomic numbers as the atomic number on the left side is equal to the atomic number on the right side. 8. Summarize: In general, how can you determine the mass number of the daughter product after alpha decay has taken place? How can you determine the atomic number? You can determine the mass number of the daughter product after alpha decay has taken place by subtracting the mass number from the left side (reactant side) with the mass number of the helium on the right side (product side). This would give you a-4 (a = mass number of left side). You can determine the atomic number of the daughter product by subtracting the atomic number from the left side with the atomic number from the helium on the right side. This would give you z-2 (z = atomic mass from left side). If you put this together, you would get: This is what would help you to get both the atomic number and the mass number of a daughter product after alpha decay has taken place. 9. Think and discuss: Helium is the second most abundant element in the universe, but it is rare in Earth's atmosphere. Most of the helium used to fill balloons and blimps must be extracted from Earth's crust. How do you think this helium formed? This helium is formed from the radioactive decay of elements under the earth's crust. Due to radioactive decay naturally occurring to keep atoms' nuclei stable underground, alpha decay also occurs to break these unstable nuclei to daughter products with more stable nuclei. Because of this alpha decay that occurs underground, alpha particles, composed of a helium nucleus, are emitted. For this reason, helium forms from the alpha decay happening under the earth's surface, allowing helium to be rare, but form abundantly as well. Get the Gizmo ready: Activity B: Beta decay Click Reset, and turn off Show equation. Select Beta decay from the Type of decay menu. Check that Carbon is selected. Question: How does beta decay change the nucleus of a radioactive atom? 1. Observe: Click Play and watch the animation. A. What happens to the decaying neutron during beta decay? During beta decay, the decaying neutron decays or turns into a proton. (It also turns into a electron, but this electron is emitted as it cannot stay in the nucleus.) B. What is emitted from the nucleus during beta decay? A gamma ray and an electron is emitted from the nucleus during beta decay. C. What is the mass number and charge of the emitted particle? Mass number: 0 u e Charge: 1- (negative charge (-)) 2. Predict: During beta decay, a neutron is transformed into a proton and an electron (the beta particle), which is emitted. Gamma rays are often emitted during beta decay as well. How will beta decay affect the atomic number and mass number of the atom? Since during beta decay the nucleus turns into a proton, the new proton created will affect the atomic number of the atom as it will increase by 1. Also, since during beta decay an electron with the charge of 1- and mass number of 0 is emitted, the mass number of the atom will remain the same because the mass number of the electron is 0. 3. Calculate: Tum on Write equation. 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. (Note: The atomic number of an electron is -1.) Check your answer by turning on Show equation and clicking Play. Modify your equation if necessary. What isotope is produced by the beta decay of carbon-14? The isotope produced by the beta decay of carbon-14 is nitrogen-14. Practice: Tum off Show equation. Fill in the equations for the beta decay of iodine-131 and sodium-24 in the spaces below. Use the Gizmo to check your answers. 131 131 53 54 Xe + 0 -1 24 Na- 24 11 12 Mg + Activity C: Get the Gizmo ready: 이 Protons into neutrons • Select Positron emission. Click Reset, and turn off Show equation. Check that Carbon is selected. e Introduction: A positron is a type of antimatter that is equivalent to an electron. If a positron and an electron meet, they will annihilate one another in a burst of gamma rays. Question: How do positron emission and electron capture change an atom? 1. Observe: Click Play and watch the animation. A. What happens to the decaying proton during positron emission? During positron emission, the decaying proton turns or decays into a neutron. (It also turns into a positron which gets emitted afterwards). B. What is the mass number and charge of the emitted positron? Mass number: 0u +0 Charge: +1 (positive charge (+)) et 2. Predict: During positron emission, a proton is transformed into a neutron and a positron, which is emitted. The positron will fly through space until it encounters an electron. How will positron emission affect the atomic number and mass number of the atom? Since during positron emission, a proton turns into a neutron and a positron, the atomic number of the atom will decrease by one as it will lose one proton. Also, since a position with the charge of +1 and mass number of 0 will be emitted, the atomic mass of the atom will remain the same during positron emission as the mass number of the positron is 0.