Chemistry 28_ Nuclear Chemistry by pptfiles

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									Chemistry 28: Nuclear Chemistry
Christopher Chui

11/14/2009

Nuclear Chemistry - C. Chui

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Investigating Nuclear Structure
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A stream of charged particles from an accelerator or neutrons from a nuclear reactor can be used to bombard atomic nuclei When particles collide with a nucleus, energy from the particles may be transferred to the nucleus; the nucleus can shatter into parts; the nucleus and bombarding particle can merge Accelerators are used to increase the velocity of charged particles Accelerators make use of magnetic fields and electromagnetic waves to accelerate charged particles
Nuclear Chemistry - C. Chui 2

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Fission
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Fission is the breaking apart of a heavy nucleus into two approximately equal parts Lise Meitner (1878-1968) was able to overcome the discriminatory practices against women and Jewish people in Europe in the early 1900s to become an honored scientist. She predicted the products of a fission reaction and published the first major work on fission The fission process in a reactor consists of a chain of fission reactions. Control rods are used to break the chain and slow or stop the reaction
Nuclear Chemistry - C. Chui 3

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Nuclear Reactors
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A nuclear reactor is a device for controlling nuclear fission 235 239 92U and 94Pu are generally used as fuel in nuclear reactors Water and graphite are good moderators, which slow down neutrons through collisions, but do not absorb them In a nuclear reactor, the rate of the reaction is regulated with control rods Water is the most widely used coolant for preventing a reactor core from overheating The containment vessel encases the whole reactor system to prevent the escape of radioactive materials
Nuclear Chemistry - C. Chui 4

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Stability of Nuclides
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Rule 1: The greater the binding energy per nucleon the more stable the nucleus. Mass defect is the difference between calculated mass and actual mass. Binding energy is the energy needed to separate the nucleus into individual particles. Rule 2: Nuclei of low atomic numbers with 1:1 neutronproton ratio are very stable. For heavy elements, the larger the mass number of an element, the smaller the binding energy per nucleon. Rule 3: The most stable nuclei tend to contain an even number of both protons and neutrons
Nuclear Chemistry - C. Chui 5

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Half-Life
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Half-life is the length of time required for one-half of the atoms of a radioactive sample to decay Experimentally determined half-life figures are based on a large number of atoms A nuclear transmutation reaction occurs when an atom with a different atomic number is produced Some elements undergo natural transmutation Check the atomic number on a periodic table to determine the identity symbol of an element
Nuclear Chemistry - C. Chui 6

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Transmutations
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Rule 1: Mass number is conserved in a nuclear change Rule 2: Electric charge is conserved in a nuclear change Transuranium elements have atomic numbers greater than 92 Radon gas emits alpha particles that damage human lung tissue. 7% of US homes are at risk
Nuclear Chemistry - C. Chui 7

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Synthetic Elements
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Glenn T. Seaborg discovered several transuranium elements. He applied for and received patents for these elements and assigned patent rights to the US Government Transuranium elements have been produced by bombarding target elements with other elements

11/14/2009

Nuclear Chemistry - C. Chui

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Biological Effects of Radiation
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All radiation has an effect on living organisms The amount of radiation, called kerma, is measured in gray, Gy. 1 Gy = 1 J of energy to 1 kg of living tissue. 1 rad = 0.01 Gy The damage is measured by absorbed dose, measured in sievert, Sv. 1Sv = 1 Gy x factor of absorbed dose. 1 rem = 0.01 Sv Everybody is exposed to ~1 mSv each year
Nuclear Chemistry - C. Chui 9

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Uses of Radioactive Nuclides
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Radioactive nuclides can be used as tracers Half-life may be used to date objects Because of the low original concentration of C14, this method is sensitive only for about 4 half-lives (~20,000 years) Radioactive I-131 is used to diagnose and treat disorders of the thyroid

11/14/2009

Nuclear Chemistry - C. Chui

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Fusion
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A nuclear reaction in which 2 or more small nuclei combine to form one larger nucleus is called a fusion reaction Isotopes of hydrogen: tritium H3 and deuterium H2 Supplies of naturally occurring deuterium are estimated to be large enough to fuel fusion reactors for 1012 years Fusion reactions can be contained in “magnetic bottles”
Nuclear Chemistry - C. Chui 11

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