12/27/16 Creative Commons License Ch. 21: Nuclear Chemistry ! Images and tables in this file have been used from the following sources: ! OpenStax: Creative Commons Attribution License 4.0. ! ChemWiki (CC BY-NC-SA 3.0): Unless otherwise noted, the StatWiki is licensed under a The image Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Permissions beyond the scope of this license may be available at [email protected]. Nuclear chemistry provides the basis for many useful diagnostic and therapeutic methods in medicine, such as these positron emission tomography (PET) scans. The PET/computed tomography scan on the left shows muscle activity. The brain scans in the center show chemical differences in dopamine signaling in the brains of addicts and nonaddicts. The images on the right show an oncological application of PET scans to identify lymph node metastasis. Chemistry: OpenStax ! Nuclear (NOT Nucular) chemistry involves changes in the nuclear composition (protons and neutrons) of atoms that are radioactive. X ! Nuclear chemistry can be used: Atomic number (Z) = number of protons Mass number (A) = number of protons and neutrons in a specific isotope (or nuclide) of an element ! for radiocarbon dating (e.g., determining the age of a mummy or a meteorite) ! for medical diagnosis and treatment ! for medical imaging (PET scans, brain scans, x-rays) ! in nuclear power plants ! to create new elements Protons and neutrons are collectively called nucleons. How many neutrons are in each isotope? C 13 6 C 14 6 C 2 Nuclear Reactions Spontaneous emission of particles or electromagnetic radiation is known as radioactivity. 12 6 http://2012books.lardbucket.org/pdfs/principles-of-generalchemistry-v1.0.pdf 1 Nuclei and Nuclear Reactions A Atomic notation and terms: Z ! Principles of General Chemistry (CC BY-NC-SA 3.0): 4 3 21.1 Nuclear Structure and Stability How do we know whether an isotope is stable? Which radioisotopes will spontaneously decay? 1) Nuclei containing a magic number of protons and/or neutrons are stable. ! The numbers 2, 8, 20, 50, 82, and 126 are called magic numbers. 2) Even numbers of protons and neutrons tend to be stable. 3) All isotopes of the elements with atomic numbers > 83 are radioactive. 4) All isotopes of technetium (Tc, Z = 43) and promethium (Pm, Z = 61) are radioactive. CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_ for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_ 5 Components_of_the_Nucleus Band of Stability CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_ for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_ 6 Components_of_the_Nucleus 1 12/27/16 Predicting Types of Decay The three general classes of radioactive nuclei are characterized by a different decay process or set of processes: Neutron-rich nuclei. The nuclei on the upper left side of the band of stable nuclei in Figure 18.1.2 have a neutron-to-proton ratio that is too high to give a stable nucleus. These nuclei decay by a beta decay – converting a neutron to a proton, thereby decreasing the neutron-to-proton ratio. Predicting Types of Decay Neutron-poor nuclei. Nuclei on the lower right side of the band of stable nuclei have a neutron-to-proton ratio that is too low to give a stable nucleus. These nuclei decay by positron emission or electron capture - converting a proton to a neutron, thereby increasing the neutron-to-proton ratio. Heavy nuclei. With very few exceptions, heavy nuclei (those with A ≥ 200) are intrinsically unstable regardless of the neutron-to-proton ratio, and all nuclei with Z > 83 are unstable. Such nuclei tend to decay by emitting an α particle which decreases the number of protons and neutrons in the original nucleus by 2. The net result of alpha emission is an increase in the neutron-to-proton ratio. https://en.wikipedia.org/wiki/Radioactive_decay#Types_of_decay Penetrating Ability of Particles 21.2 Nuclear Equations Figure 21.4: Symbols for subatomic particles Figure 21.33 9 Types of Nuclear Reactions Figure 21.7: Types of Nuclear Decay • Radioactive decay/emission: an unstable nuclide emits a particle or energy. • Parent nuclide ! daughter nuclide + radiation 212 208 + 42 He 84 Po 82 Pb • Fission: bombarding an isotope with a neutron to break it apart into lighter isotopes. Fusion: light isotopes collide to form heavier isotopes (only up to Fe can be done naturally in the universe) Transmutation: atoms are bombarded by high energy particles to create new elements/isotopes. 14N + 4He " 17O + 1H • " " " • • " " 11 12 2 12/27/16 21.3 Radioactive Decay Alpha Decay (or Emission) In balancing a nuclear reaction, we balance the total of all atomic numbers and total of all mass numbers for the products and reactants (conservation of protons and neutrons). Mass number: 212 212 84 Atomic number: Po ! Alpha decay - heavy radioisotopes tend to emit alpha particles (A dec. by 4, Z dec by 2) ! 238U " 4He + 234Th 208 + 4 = 212 208 82 84 Pb + 4 2 He ! Predict products: 82 + 2 = 84 Example 21.4 13 226Ra " 4He + X 244Pu " 4He + X 14 http://underground.physics.berkeley.edu/SNO+.html Beta Decay (or Emission) Gamma Decay (or Emission) ! Beta decay - neutron is converted to a proton and an ! Gamma – γ: energy with no mass or charge; the most electron (A is same, Z inc. by 1) penetrating radiation (A and Z remain the same) ! 14C " 14N + e- ! This often occurs in conjunction with alpha or beta decay. ! 60*Co " 60Ni + e- + γ ! Predict products: ! 239U " X + ehttp://www.ck12.org/user:chjpdgnoyxjkx3naagnkzs5vcmc./book/Chemical-Equations-and-Balancing-TheEquations/section/24.2/ 15 Positron Decay (or Emission) http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24nuclear-chemistry.html Electron Capture ! Electron Capture – electron combines with a ! Positron decay – proton is converted to a neutron and an electron (A is same, Z dec. by 1) proton to form a neutron (A is same, Z dec by 1) 23 11 Same result as Positron Emission; Opposite of Beta Emission 81 Kr + 0 e → 81 Br + 0γ 23 11 Mg → Na + 0 +1 0 0 e+ γ 36 -1 35 0 ! Predict products: ! 197Hg + e- " X ! Predict products: ! 207Po " X + +10 e http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24nuclear-chemistry.html 16 17 http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24nuclear-chemistry.html 18 3 12/27/16 Group Work - Practice ! Write balanced equations for the following: ! Alpha decay of curium-242 (238Pu) ! Beta decay of magnesium-28 Determining Products of Reactions Nuclear Transmutation: 249 98 48 Cf + 20 Ca → X + 3 01 n Natural radioactive decay: (28Al) 238 92 ! Positron emission from xenon-118 U → X + 8 24α + 6 -10 β Nuclear fission: (118I) ! Electron capture by polonium-204 235 92 (204Bi) U + 1 0 n → X + 143 54 Xe + 3 01 n 19 https://en.wikipedia.org/wiki/Full_body_scanner 20 Radioactive Decay Series Uranium Series of Decay The disintegration of a radioactive nucleus often is the beginning of a radioactive decay series, which is a sequence of nuclear reactions that ultimately result in the formation of a stable isotope. 232Th " 208Tl Decay calculations help us determine how long radioactive waste has to be stored. Typically 10 half-lives: 2-10 = 0.000977 (so 99.9023% has decayed) http://commons.wikimedia.org/wiki/User:BatesIsBack - http://commons.wikimedia.org/ wiki/File:Decay_Chain_of_Thorium.svg, CC BY-SA 3.0, https://commons.wikimedia.org/ 21 w/index.php?curid=16983885 CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_ 162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity Four New Elements! https://www.sciencenews.org/article/four-elements-earnpermanent-seats-periodic-table 22 Uses of Radioactive Isotopes ! ! ! ! ! ! ! ! ! ! Prostate Cancer: yttrium-90 Bones: calcium-47 (also phosphorus) Positron-emission tomography (PET scans): carbon-11 Leukemia: actinium-225 Spleens: iron-59 Arteries: rhenium-188 Arthritis: erbium-169 Liver: cobalt Thyroid: iodine Technetium-99: tumors and imaging brain, lungs, liver, skeleton, and blood 4 12/27/16 Annual Radiation Exposure Symptoms of Exposure Dose (rem) Symptoms/Effects <5 No observable effect 5-20 Possible chromosomal damage 20-100 Temporary reduction in white blood cell count 50-100 Temporary sterility in men (up to a year) 100-200 Mild radiation sickness, vomiting, diarrhea, fatigue; immune system suppressed; bone growth in children retarded Figure 21.37: The total annual radiation exposure for a person in the US is about 620 mrem. The various sources and their relative amounts are shown in this bar graph. (source: U.S. Nuclear Regulatory Commission) 25 Nuclear Decay – Half-Lives > 300 Permanent sterility in women > 500 Fatal to 50% within 30 days; destruction of bone marro and intestine > 3000 Fatal within hours http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24nuclear-chemistry.html First Order Decay ! The rate of decay, as well as the type and energy of the radiation, determines the damage caused by radiation. ! Nuclear decay follows first-order kinetics, which gives a constant t1/2 over the course of the decay. ! Typically we are given half-life (t1/2) values. We can use these to calculate rate constants (or decay constants) for radioactive nuclides. 27 Nuclear Radioactivity Nuclear Decay - Kinetics ! Can use kinetics equations, just like in Chapter 12, All radioactive decays obey first-order kinetics. N ln t = - kt N0 Half-life is the time it takes for the amount of a substance to decrease by 50%. The corresponding half-life of the reaction is given by: t1 = 2 CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_ 162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity 0.693 k 29 to perform calculations: ! How much nuclide (mass or %) is left after ___ time? ! How long does it take for ___% to decay (or remain)? ! The half-life for sodium-24, a radioisotope used medically in blood studies, is 906 minutes. What is the rate constant for 24Na (in hr-1)? ! 4.59 x 10-2 hr-1 30 5 12/27/16 Informative/Interesting Links Group Work Video about fallout from Chernobyl(46 min.): http://www.youtube.com/watch?v=GezeZlu70oI ! If you ingest a 75.0 mg sample of 131I with a rate constant of 0.0861 d-1, how long would it take to decay to 12.5 mg? ! 20.8 days ! Gold-128 undergoes beta decay to give mercury-128 Fermi and the “Atomic Pile”: http://www.fi.edu/learn/case-files/fermi/pile.html with a half-life of 2.7 days. If you start with 5.6 mg of 128Au, what mass of gold-128 is left after 9.5 days? ! 0.49 mg Distribution and history of energy sources: http://www.world-nuclear.org/info/Current-and-Future-Generation/ Nuclear-Power-in-the-World-Today/#.Uebm_ZyETLc ! 226Ra has a half-life of 1620 years. Calculate the rate constant and what percent of a sample would remain after 100 years. ! 4.28 x 10-4 yr-1; 95.8% remains ! Examples 21.5 – 21.7 10 Interesting Facts about Chernobyl: http://imgur.com/gallery/AfbNLQ9 31 Global Energy Sources How geological dating on rocks is done: http://www.youtube.com/watch?v=1920gi3swe4 32 World Energy Consumption http://www.world-nuclear.org/info/inf01.html http://www.nucleartourist.com/basics/why.htm ! List of advantages/disadvantages of each energy source. https://en.wikipedia.org/wiki/Renewable_energy#/media/File:Total_World_Energy_ Consumption_by_Source_2013.png Nuclear Energy 21.4 Nuclear Transmutation Schematic of a cyclotron particle accelerator. ! Energy released from 200 g U = 2x1013 J ! Energy released from 1 ton coal = 5x107 J ! It would take 1 million tons of coal to create the same amount of energy. ! Nuclear power plants don’t explode (like TNT) unless an uncontrolled nuclear chain reaction occurs. When nuclear power plants have meltdowns, the threat is from leakage of radioactive material (water, airborne, soil contamination, etc.) 35 http://www.physbot.co.uk/magnetic-fields-and-induction.html 36 6 12/27/16 Transmutation Transmutation Nuclear transmutation differs from radioactive decay in that transmutation is brought about by the collision of two particles. 1 14 4 17 p 7 N + 2α 8O + 1 Particle accelerators made it possible to synthesize the socalled transuranium elements, elements with atomic numbers greater than 92. 37 A Linear Particle Accelerator. (a) An aerial view of the SLAC, the longest linear particle accelerator in the world; the overall length of the tunnel is 2 miles. (b) Rapidly reversing the polarity of the electrodes in the tube causes the charged particles to be alternately attracted as they enter one section of the tube and repelled as they leave that section. As a result, the particles are continuously accelerated along the length of the tube. 38 CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_ 162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity Nuclear Fission Nuclear Fission Nuclear fission: heavy nuclei (mass number > 200) are bombarded by neutrons to form smaller nuclei and one or more neutrons. Used in nuclear power plants. 235 92 141 U + 01 n → 236 92 U → 56 Ba + 92 36 Kr + 3 01 n CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_ 162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity Nuclear Fission 39 235U is capable of a self-sustaining sequence of nuclear fission known as a nuclear chain reaction. The minimum mass of material required to generate a self-sustaining chain reaction is the critical mass. CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_ for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_ 40 Components_of_the_Nucleus youtube video 21.5 Archeological Dating C -14 Dating: http://www.youtube.com/watch?v=81dWTeregEA&feature=related ! The decay of radioactive isotopes allows for the relative age of once-living things to be calculated. ! Radiocarbon dating uses 14C ! Living things have a dynamic equilibrium of 14C in their system (ex: inhaling/exhaling) (a) The Diablo Canyon Nuclear Power Plant near San Luis Obispo is the only nuclear power plant currently in operation in California. The domes are the containment structures for the nuclear reactors, and the brown building houses the turbine where electricity is generated. Ocean water is used for cooling. (b) The Diablo Canyon uses a pressurized water reactor, one of a few different fission reactor designs in use around the world, to produce electricity. Energy from the nuclear fission reactions in the core heats water in a closed, pressurized system. Heat from this system produces steam that drives a turbine, which in turn produces electricity. (credit a: modification of work by “Mike” Michael L. Baird; credit b: modification CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_ 41 of work by the Nuclear Regulatory Commission) 162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity ! When a plant or animal dies, it no longer incorporates new 14C, and the 14C begins to decay, causing the 14C content to become less than that in the atmosphere. ! 14 6C " 147N + 0-1e- 42 7 12/27/16 Geological Dating Radiometric Dating: Well-Known Incidents http://www.youtube.com/watch?v=1920gi3swe4 ! Three-Mile Island (Pennsylvania, 1979): Caused by mechanical failures; small radiation leak (not linked to a cancer fatality, no observable long term health effects). ! Geological dating is similar to archeological dating, but uses longer-lived nuclides ! Measure ratio of 40K to 40Ar in rocks ! 4019K + 0-1e " 4018Ar ! Chernobyl (Ukraine, 1986): No containment, 31 deaths attributed to accident, radiation leak caused health issues (50,000 excess cancer cases). ! 4019K " 4020Ca + 0-1e ! 40K has a half-life of 1.28x109 years ! Rocks are crushed, 40Ar escapes, and the ratio of 40K to 40Ar is measured. ! This allowed the age of the earth to be calculated to be 4.5 billion years. 43 ! Fukushima, Japan (March 2011): Not caused by earthquake – low-lying generators flooded from tsunami; seawater to cool down reactors used too late. Singlereplacement reaction produced hydrogen gas causing several chemical explosions. Radioactivity release about 1/10 of Chernobyl. 44 Nuclear Fusion Nuclear Fusion Nuclear fusion is the process of combining small nuclei into larger ones (up to 59Fe). Because fusion reactions take place at very high temperatures, they are often called thermonuclear reactions. ITER: France – building the Tokamak, a device that uses magnetic fields to contain and control hot plasma needed for fusion. 2 3 4 1 1 D + 1T → 2 He + 0 n + 17.6 MeV Due to the high temperature requirements, containment is an issue. CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_ for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_ 45 Components_of_the_Nucleus 21.5 Uses of Isotopes https://en.wikipedia.org/wiki/Tokamak_Fusion_Test_Reactor 46 21.6 Biological Effects of Radiation The fundamental unit of radioactivity is the curie (Ci) Radioactive and stable isotopes have applications in science and medicine. 1 Ci = 3.70 x 1010 disintegrations per second. Radioactive isotopes are used as tracers. Use of tracers for diagnosis include: ! Sodium-24 – blood flow ! Iodine-131 – thyroid conditions ! Iodine-123 – brain imaging https://en.wikipedia.org/wiki/Brain_positron_emission_tomography 47 https://en.wikipedia.org/wiki/Geiger_counter 48 8 12/27/16 Biological Effects of Radiation A common unit for the absorbed dose of radiation is the rad (radiation absorbed dose). 1 rad = 1 x 10-5 J/g of tissue irradiated The rem (roentgen equivalent for man) is determined from the number of rads: Number of rems = number of rads x 1 RBE RBE = the relative biological effectivness. 49 9
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