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Unformatted text preview: 12/12/05 1 Activity 10 Solutions: Ionizing Radiation I 10.1 What is Ionizing Radiation? 1) Stable and Unstable Nuclei a) Watch the demonstration of isotopes placed near a Geiger counter. Geiger counter clicks indicate unstable nuclei. Record the results of the experiment. Isotope Geiger counter clicks? Stable or Unstable? U 238 92 (uranium-238) __yes__ __unstable__ Pb 207 82 (lead-207) __no__ __stable__ Al 26 13 (aluminum-26) __no__ __stable__ Ra 226 88 (radium-226) __yes__ __unstable__ b) The Geiger counter clicks when it detects ionizing radiation. Which of these isotopes are radioactive? ___ Uranium and radium___ c) Why are unstable nuclei radioactive? Materials containing atoms with unstable nuclei are radioactive. As the nuclei decay, they give off some combination of types of ionizing radiation depending on the nuclear reaction. 2) Ionizing radiation a) What is an alpha particle ( )? What is the electric charge of an alpha particle? An alpha particle is made up of a helium nuclei 2 protons and 2 neutrons ( He 4 2 ). Since an alpha particle has two protons, it has a charge of +2. b) What are the two types of beta particles ( )? What is the electric charge of each type of beta particle? A beta particle can be an electron ( ) and have an electric charge of 1. A beta particle can also be an antielectron ( + ), which is also called a positron. An antielectron has a charge of +1. c) What is a gamma particle ( )? Do gamma particles have an electric charge? Gamma particles are photons of high energy electromagnetic radiation. Gamma particles have no electric charge. 12/12/05 2 d) Which type of ionizing radiation has the most ionizing ability? Why? Alpha particles have the most ionizing ability. Because an alpha particle is much heavier than an electron (a beta particle), it moves more slowly. Also, each alpha particle has two electric charges. For both reasons, an alpha particle is more ionizing than a beta particle. e) Which type of ionizing radiation has the least ionizing ability? Why? Gamma particles have the least ionizing ability because they have no electric charge. 3) Summary of Ionizing Radiation Fill in the table below, which summarizes the properties of the types of ionizing radiation. Radiation Particle emitted A = # of nucleons Z = # of protons Electric Charge alpha ( ) helium nuclei ( He 4 2 ) 4 2 +2 beta ( ) electron (e ) 0 0 -1 beta ( + ) antielectron (e + ) 0 0 +1 gamma ( ) high energy photon 0 0 0 4) Radioactive decay of large unstable nuclei a) Why are large nuclei with more than 83 protons unstable? The strong nuclear force that binds the nucleus operates over a very short distance. In large nuclei, the strong force cannot bind the nucleons tightly enough to overcome the long-range repulsive electromagnetic force between the positively charged protons....
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