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© 2003 John Wiley and Sons Publishers Chapter 5: Harnessing the Secrets of the Nucleus Courtesy Roger Ressmeyer/Corbis Images Nuclear Energy, Nuclear Medicine, and a Nuclear Calendar © 2003 John Wiley and Sons Publishers Courtesy University of Chicago/AIP Neils Bohr Library Enrico Fermi built the first atomic pile and produced the first controlled chain reaction on December 2, 1942. © 2003 John Wiley and Sons Publishers “Birth of the Atomic Age by Gary Sheahan/Chicago Historical Society. A depiction of the dawn of nuclear power as the first chain reaction begins beneath Stagg Field, Chicago. © 2003 John Wiley and Sons Publishers Figure 5.1: Schematic diagram of a nuclear power plant. © 2003 John Wiley and Sons Publishers Courtesy David Bartruff/Corbis Images Cooling towers of a nuclear power plant. © 2003 John Wiley and Sons Publishers Courtesy Sipa Press The nuclear power plant at Chernobyl, after the accident of April 16, 1986. © 2003 John Wiley and Sons Publishers Courtesy Matthew Neal McVay/Stone/Getty Images Disposal of radioactive wastes by burial in a shallow pit. © 2003 John Wiley and Sons Publishers Figure 5.2: Graphical representation of the disappearance of a radioisotope. Half-Life Half-life is the time for the radiation level to decrease (decay) to one-half of the original value. decay curve Half-Lives of Some Radioisotopes Half-Life Calculations After one half-life, 40 mg of a radioisotope will decay to 20 mg. After two half-lives, 10 mg of radioisotope remain. 40 mg x 1 x 1 = 10 mg 2 2 Initial 40 mg 1 half-life 20 mg 2 half-lives 10 mg Learning Check The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours? 1) 32 mg 2) 16 mg 3) 8 mg Solution 2) 16 mg Half life = 13 hrs Number of half lives = 2 Amount remaining = 64 mg x 1 x 1 = 16 mg 2 2 13 hrs 64 mg 13 hrs 32 mg 16 mg Medical Applications Radioisotopes with short half-lives • Are used in nuclear medicine. • Have the same chemistry in the body as the nonradioactive atoms. • In the body give off radiation that exposes a photographic plate (scan), which gives an image of an organ. Radioisotopes in Medicine • 1 out of every 3 hospital patients will undergo a nuclear medicine procedure • 24Na, • 131I, t½ = 14.8 hr, b emitter, thyroid gland activity • 123I, t½ = 13.3 hr, g-ray emitter, brain imaging • 18F, t½ = 1.8 hr, b+ emitter, positron emission tomography • 99mTc, t½ = 14.8 hr, b emitter, blood-flow tracer t½ = 6 hr, g-ray emitter, imaging agent Brain images with 123I-labeled compound 23.6 © 2003 John Wiley and Sons Publishers Courtesy Custom Medical Stock Photo An image of a thyroid gland obtained through the use of radioactive iodine. © 2003 John Wiley and Sons Publishers Courtesy CNRI/Phototake Images of human lungs obtained from a γ-ray scan. Some Radioisotopes Used in Nuclear Medicine Learning Check Which of the following radioisotopes are most likely to be used in nuclear medicine? 1) 40K half-life 1.3 x 109 years 2) 42K half-life 12 hours 3) 131I half-life 8 days Solution Which of the following radioisotopes are most likely to be used in nuclear medicine? Radioisotopes with short half-lives are used in nuclear medicine. 2) 42K half-life 12 hours 3) 131I half-life 8 days © 2003 John Wiley and Sons Publishers Courtesy Yucca Mountain Project Construction of a tunnel that will be used for burial of radioactive wastes deep within Yucca Mountain, Nevada. © 2003 John Wiley and Sons Publishers Youtube.com Courtesy Kelley Culpepper/Transparencies, Inc. A cancer patient receiving radiation therapy. © 2003 John Wiley and Sons Publishers Figure 5.4: Positron emission by fluorine-18. © 2003 John Wiley and Sons Publishers Courtesy Patrick Mesner/Liaison Agency, Inc. /Getty Images The image on the Shroud of Turin. © 2003 John Wiley and Sons Publishers Courtesy Yoav Levy/Phototake A medical worker wearing a film badge. © 2003 John Wiley and Sons Publishers Figure 5.6: The Geiger counter. 11.8 Detecting Radiation • A Geiger counter detects radioactive radiations. • Ions produced by radiation create an electrical current. 27 Geiger counter 28 • A Geiger counter determines the amount of ionization by detecting an electric current. • A thin window is penetrated by the radiation and causes the ionization of Ar gas. • The ionized gas carried a charge and so current is produced. • The current pulse generated when the radiation enters is amplified and counted. 29 Chapter 22 Slide 29 Biological Effects of Radiation • The penetrating power of radiation is a function of its mass: g-rays > b-particles >> -particles. • When ionizing radiation passes through tissue it removes an electron from water to form H2O+ ions. • The H2O+ ions react with another water molecule to produce H3O+ and a highly reactive •OH radical. • Free radicals generally undergo chain reactions, producing many radicals in the biomolecules. 30 Chapter 22 Slide 30 Radiation Measurement • The Curie measures the number of atoms that decay in one second. Curie: 1 Ci = 3.7 x 1010 disintegrations • The rad (radiation absorbed dose) measures the radiation absorbed by the tissues of the body. • The rem (Roentgen equivalent for man (rem) ) measures the biological damage. 31 © 2003 John Wiley and Sons Publishers Courtesy AP/Wide World Photos Girl being scanned with a Geiger counter after a nuclear accident. © 2003 John Wiley and Sons Publishers Courtesy PhotoDisc, Inc./Getty Images Receiving radiation from a dental X-ray. Background Radiation • A person is exposed to radiation from naturally occurring radioisotopes and medical X rays. 34 Effects of Radiation 35 QUESTION © 2003 John Wiley and Sons Publishers (a) What percentage of the world’s nuclear power plants are located in the United States? (b) Rank the countries of Table 5.1 in terms of the percentage of electric power produced from nuclear plants. Where in this ranking does the United States stand? QUESTION © 2003 John Wiley and Sons Publishers What is the most serious form of damage that could occur if a natural disaster such as a hurricane, a tornado, or an earthquake struck a nuclear power plant? Explain. QUESTION © 2003 John Wiley and Sons Publishers Describe one advantage of a breeder reactor over a conventional nuclear reactor. Describe one disadvantage. QUESTION © 2003 John Wiley and Sons Publishers What is the ultimate fate of every radioactive atom now in existence? QUESTION © 2003 John Wiley and Sons Publishers If each of the radioisotopes of Table 5.3 were stored at the Yucca Mountain site, which would still be present after 10,000 years at a level of 10% or more of the original amount? QUESTION © 2003 John Wiley and Sons Publishers (a) What is one cost of electric power production by nuclear power that is not a factor in the use of coal, petroleum, or natural gas? (b) What is one cost of electric power production by these fuels that is not a factor in the use of nuclear power? QUESTION © 2003 John Wiley and Sons Publishers Name and describe two types of biological damage caused by ionizing radiation. QUESTION © 2003 John Wiley and Sons Publishers How is each of the following used in medical diagnosis and/or therapy? (a) I-131; (b) Tc99m; (c) Co-60. QUESTION © 2003 John Wiley and Sons Publishers Into what element is an atom of nitrogen-13 transformed when it emits a positron? QUESTION © 2003 John Wiley and Sons Publishers What would the ratio of Pb-206 to U-238 atoms be if the sample of meteorite in the exercise were 18.0 x 109 years old? QUESTION © 2003 John Wiley and Sons Publishers Which of the following can be dated by radiocarbon techniques: (a) a rock; (b) a leather slipper; (c) a wooden boat; (d) a mummified body; (e) a silver spoon. Describe your reasoning. QUESTION © 2003 John Wiley and Sons Publishers Which one or more of the detection devices described in this Section would you use if you wished to determine immediately whether the residue left by a spilled chemical is radioactive? Which would you use if you wanted to determine the total, cumulative amount of radiation you might be exposed to in the course of an entire month? QUESTION © 2003 John Wiley and Sons Publishers Assign the data of each of the sources of Table 5.6 into one of two categories: (a) originates in human activities; (b) natural, not dependent on human activities. What total percentage of exposure is associated with each of the two categories?