Student Exploration: Half-life Vocabulary: daughter atom, decay, Geiger counter, half-life, isotope, neutron, radiation, radioactive, radiometric dating Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. Have you ever made microwave popcorn? If so, what do you hear while the popcorn is in the microwave? Yes, I hear the kernels popping in the bag. 2. If you turn the microwave on for two minutes, is the rate of popping always the same, or does it change? Explain. The rate of popping is not always the same because when you first put the bag of popcorn in and start the microwave, there is not a lot of popping, but when the contents of the bag begin to heat up, the popping increases. By the end of the cooking session, all of the kernels should be popped so there is no more popping. Gizmo Warm-up Like an unpopped kernel in the microwave, a radioactive atom can change at any time. Radioactive atoms change by emitting radiation in the form of tiny particles and/or energy. This process, called decay, causes the radioactive atom to change into a stable daughter atom. The Half-life Gizmo™ allows you to observe and measure the decay of a radioactive substance. Be sure the sound is turned on and click Play ( ). 1. What do you see and hear? There is a static sort of popping sound as the atoms turn from red to blueish gray. Note: The clicking sound you hear comes from a Geiger counter, an instrument that detects the particles and energy emitted by decaying radioactive atoms. 2. What remains at the end of the decay process? Daughter Atoms 3. Is the rate of decay fastest at the beginning, middle, or end of the process? The rate of decay is fastest near the beginning. Activity A: Decay curves Get the Gizmo ready: Click Reset ( ). Be sure that User chooses half-life and Random decay are selected. Check that the Half-life is 20 seconds and the Number of atoms is 128. Question: How do we measure the rate of radioactive decay? 1. Observe: Select the BAR CHART on the right side of the Gizmo and click Play. A. What happens to the numbers of radioactive and daughter atoms as the simulation proceeds? The number of radioactive atoms decreases until they reach zero and the number of daughter atoms increases. B. Do the numbers of radioactive and daughter atoms change at the same rate throughout the simulation? Explain. No, the numbers of daughter atoms increase steadily while towards the end of the reaction, the radioactive atoms take longer to disappear. 2. Experiment: Click Reset, and select the GRAPH tab. Run a simulation with the Half-life set to 5 seconds, and then run another simulation with the Half-life set to 35 seconds. Sketch each resulting decay curve graph in the spaces below. Half-life = 5 seconds Half-life = 35 seconds 3. Interpret: How does the Half-life setting affect how quickly the simulated substance decays? The shorter the Half-life, the less time it takes for the substance to decay.