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Powerpoint Chapter 22 Powerpoint Chapter 22 Presentation Transcript

  • New Title Page Chapter 21:Nuclear Chemistry Date start: 1-19-2010 Date Finished: Your Name Period Mr. Costein
  • Chapter 21: Nuclear Chemistry This unit looks at the nature of radiation, Types of radiation and decay products, Radiation Units and exposure precautions Nuclear fission and fusion reactions Applications of Nuclear Chemistry
  • The Geiger Counter
  • What does a Geiger Counter measure?  Radiation that can cause atoms to lose or gain electrons and become ions.  This type of radiation is called ionizing radiation.  There are two causes of background radiation:  Outer Space- Cosmic rays  Natural decay from isotopes in the earth’s crust/core
  • Daily Background Counts Date Trial 1 Trial 2 Average Final CPM
  • Historical Perspectives  1895: Wilhelm Roentgen discovers X-rays and their effects.  1896: Henri Becquerel discovers radioactive Uranium.  1898: Pierre and Marie Curie discover two new elements, polonium and radium.  1905: Albert Einstein theory of relativity and mass defect.  1908: Hans Geiger creates an instrument to measure ionizing radiation.  1934: Enrico Fermi proposes „transuranes” elements beyond uranium.  1939: Lise Meitner , Otto Hahn and Fritz Stassman explain nuclear fission.
  • Nuclear Composition  Nucleons are any particles found in the nucleus, commonly they are protons and neutrons.  We would expect, the total mass of the electrons, protons, and neutrons would be the mass of the atom, it is not, but rather it is a smaller value.  Mass defect is the difference between the mass of an atom and the sum of the masses of its protons, neutrons and electrons.  Einstein explained this loss of mass as the result of the nucleus formation. Energy is given off from the conversion of matter to energy (E=mc2 ).  This loss of mass from it‟s conversion to energy provides nuclear stability.
  • Nuclear Binding Energy  The energy released when a nucleus is formed from nucleons is called the nuclear binding energy.  This can be thought of the amount of energy to break a nucleus apart.  The higher the nuclear binding energy of a nuclide. the greater the nuclide stability.  The binding energy per nucleon is the binding energy of the nucleus divided by the number of nucleons(mass number) it contains.  Elements with intermediate atomic masses (iron through lead) have the greatest binding energies (stability).
  • Nuclear Binding Example Problem 4He 2 2 protons = 2 x 1.007276 = 2.014 552 amu 2 neutrons = 2 x 1.008665 = 2.017 330 amu 2 electrons = 2 x 0.0005486 = 0.001 097 amu Total mass combined = 4.032 979 amu Measured mass = 4.002 602 amu Mass Defect = 4.032979 – 4.002602 = 0.030377 amu
  • Nuclear Binding Page 2 Mass Defect = 4.032979 – 4.002602 = 0.030377 amu To convert amu to kg: 1 amu = 1.6605 x 10-27 kg 0.030377amu X 1.6605 x 10-27 kg = 5.0441 x 10-29 kg 1 amu Binding Energy = E = mc2
  • Nuclear Binding Page 3 Binding Energy = E = mc2 Mass = 5.0441 x 10-29 kg c = speed of light = 3.00 x 108 m/s So E = (5.0441 x 10-29 kg)(3.00 x 108 m/s)2 E = 4.54 x 10-12 J per atom E = 6.022 x 1023 atoms/mol * 4.54 x 10-12 J per atom E= 2.733988 x 1012 J/mol (4 g of helium)
  • Nuclear Stability The neutron/proton ratio can be used to predict nuclear stability. For elements with low atomic numbers (1-30) the nucleus is stable when there is a 1:1 ratio. For elements with a high atomic number (up to element 83), the nucleus is stable when the ratio is 1.5:1. Elements having an atomic number greater than 83 are unstable or radioactive. Stable nuclei tend to have even numbers of nucleons in their nucleus.
  • N/P Ratio
  • Nuclear Shell Model  Stable nuclei tend to have even numbers of nucleons in their nucleus. (protons, neutrons or total nucleons)  The most stable atoms have 2, 8, 20, 28, 50, 82 or 126 protons, neutrons, or total nucleons.  The nuclear shell theory states that nucleons exists in different energy levels, or shells, in the nucleus. Completed nuclear energy levels are those with 2, 8, 20, 28, 50, 82 and 126 nucleons.  These numbers are sometimes called the “magic numbers” for nuclear stability.  If both the protons and neutrons are equal to the magic numbers, these are called the “double magic numbers” and have the greatest stability.
  • Nuclear Shell Model Examples The most stable atoms have 2, 8, 20, 28, 50, 82 or 126 protons, neutrons, or total nucleons. Examples of stable nuclides 40 Ca 20 16 O 8 28 Si 14
  • Nuclear Reactions and terms: 4 types of Nuclear Reactions: Radioactive decay refers to the emission of an alpha particle, a beta particle, or gamma ray and the formation of a slightly lighter and more stable nucleus. Nuclear disintegration is when an unstable nuclei from nuclear bombardment emits a proton or neutron and becomes more stable. Fission refers to the process in which a very heavy nucleus splits to form two or more medium- mass nuclei. Fusion refers to the process in which lightweight nuclei combine to form heavier more stable nuclei.
  • Other Nuclear Terms: Transmutation is the change in the identity of a nucleus as a result of a change in the number of protons. Radioactive decay is spontaneous disintegration of a nucleus into slightly lighter and more stable nucleus, accompanied by the emission of particles, electromagnetic radiation or both. Radiation- the process of emitting or releasing waves of energy, such as light, x-rays, or other types of electromagnetic waves. Radioactivity is the property of some elements to spontaneously emit alpha or beta particles with gamma rays by the disintegration of the nuclei.
  • Properties of Radioactive Nuclides:  They expose light sensitive emulsions. (Roentgen, 1895)  They fluoresce or glow with certain compounds. (Curie, 1898)  They produce “charged” or ionized gas particles. (Geiger, 1908)  Exposure to radio-nuclides can cause harmful physiological effects leading to death.  They undergo radioactive decay and have a half- life.
  • Half-Life of a Radioisotope Half-life is the time it required for half the atoms of a radioactive nuclide to decay. It can be measured in seconds, minutes, days, or years. decay curve initial 1 half-life 2 3 8 mg 4 mg 2 mg 1 mg
  • Examples of Half-Life Isotope Half life C-15 2.4 sec K-42 12.36 hours Na-24 15 hours Ra-224 3.6 days Ra-223 12 days I-125 60 days C-14 5700 years U-235 710 000 000 years
  • Half-Life Problem Ra-223 has a half-life of 12 days. If today, you had 100 grams of this isotope, how much would remain after 36 days? 1. How many half-life periods has it undergone in 36 days? 36 days = 3 half life periods 12 days/half-life 100 g 50g 25g 12.5 g
  • Types of Radioactive Decay Alpha Emission Beta Emission Positron Emission Electron Capture Gamma Emission
  • Comparing Nuclide Emissions
  • Decay Models Graphic shows U-238 with an alpha and one beta decays. Protactinium atomic number 91 is formed.
  • Alpha and Beta Decay Alpha decay Beta Decay
  • Key points in Balancing Nuclear Equations 1. Most decay products reduce the decaying atom’s atomic mass or atomic number or both. 2. The beta particle is the exception, when it is a decay product, the atomic number of the decaying atom increases by one. 3. Gamma ray emission by a decaying atom does NOT change the atomic mass or atomic number of the atom.
  • Nuclear Equation Problem
  • Example Nuclear Reactions 226 Ra 226 Ac + ________ 88 89 226 Pu 4 He + ________ 94 2 235 U 235 Pa + ________ 92 91
  • Alpha Emission  consists of a Helium nucleus with no electrons.  has 2 protons and 2 neutrons.  has a +2 charge  has an atomic mass of 4  has a speed that is 1/10 the speed of light.  can be stopped by a piece of paper, cloth, or skin.  The symbol is the Greek letter alpha a particle or 4 He 2
  • Beta Emission  is a stream of negatively charged electrons.  has a very light mass of an electron  has a -1 charge  can be stopped by a piece of aluminum  has a speed that is 90% of the speed of light.  can ionize air and other particles.  The symbol is the Greek letter, beta b - particle or 0 -1 e
  • Positron Emission  is a stream of positively charged electrons.  has a very light mass of an electron  has a +1 charge (change this in notes)  can be stopped by a piece of aluminum  has a speed that is 90% of the speed of light.  can ionize air and other particles.  The symbol is the Greek letter, beta b + particle or o +1 e
  • Electron Capture is a capture of an inner orbital electron by the nucleus. has a very light mass of an electron. has a -1 charge. results in a combination of an electron and a proton to form a neutron. The symbol on the reaction side of a nuclear reaction is o -1 e
  • Gamma Emission  is form of energy or electromagnetic radiation.  has an extremely short wavelength.  has no mass since it is energy.  travel at the speed of light.  can cause air and most materials to become ionized or charged.  can only be stopped by using 2 to 4 inches of lead or many feet of concrete.  does not change the identity of the radionuclide. g  The symbol is the Greek letter, gamma
  • Decay Series A decay series is a series of radioactive nuclides produced by successive radioactive decay until a stable nuclide is reached. The heaviest nuclide in a decay series is called the parent nuclide. The particles in a decay series that are produced from parent nuclides are called daughter nuclides. U-238 the parent nuclide decays to Pb-206, which is stable and non-radioactive.
  • U-238 Decay Series
  • Units of Radioactivity: Roentgen: the amount of gamma or x- rays required to produce one unit of electrical charge per cubic centimeter from ionization of air. (1 roentgen = 86 ergs per gram) REP: (roentgen equivalent units) the amount of radiation to produce an harmful effect on living tissue. REM: (roentgen equivalent man) the amount of radiation that produces the same biological damage in man resulting from the absorption of 1 REP of radiation.
  • Additional Units of Radioactivity Curie: the number of nuclear disintegrations that occur in one second. Commonly used in medical laboratory diagnostic procedures. One cure is 3.7 x 1010 nuclear disintegrations. RAD: (radiation absorbed dose) similar to a REM, and is used in monitoring dosimeter measurements for X-ray personnel. Sievert(Sv)- SI derived unit of dose and reflects the biological effects of radiation that is absorbed (in gray units). REMS, and RADS are the two most common units for measuring radiation exposure.
  • Exposure Limits: Average citizen: No more than 500 millirems per year. X-rays can cause exposures of 100 millirem per procedure. Radiation or Nuclear medicine workers: No more than 5 rems per year. Physiological effects: Acute Radiation sickness: 100-400 rems LD-50 (lethal dose 50%): 400 rems LD-100 Death: over 1000 rems Hyperlink to Radiation poisoning
  • Protection from Radiation  Three factors to protect radiation workers are S-Shielding; the use of lead and or concrete in high radiation areas. T-Time; limit the amount of time in high radiation areas. D-Distance; the farther away from a high radiation area the lower the exposure.
  • Shielding Graphic
  • Nuclear Fission  When a nucleus fissions, it splits into several smaller fragments or atoms.  These fragments, or fission products, are about equal to half the original mass.  Two or three neutrons can also be emitted.  The sum of the masses of these fragments is less than the original mass. This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's equation.  Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen spontaneously
  • Fission Reactors The heat from a fission reactor is used to heat water to steam, which turns turbines to generate electricity. Fuels rods made of aluminum hold the Uranium-235 or U-238 which is the most common nuclide used in fission reactors. Control rods made of neutron-absorbing steel are used to limit the number of free neutrons. Graphite(carbon) is used to slow down fast neutrons produced from fission. Control rods allow for a limited self-sustaining reaction.
  • Oak Ridge Fission Reactor
  • Production of Electricity
  • Nuclear Fusion  Nuclear energy can also be released by fusion of two light elements (elements with low atomic numbers).  The power that fuels the sun and the stars is nuclear fusion.  In a hydrogen bomb, two isotopes of hydrogen, deuterium and tritium are fused to form a nucleus of helium and a neutron.  Unlike nuclear fission, there is no limit on the amount of the fusion that can occur.
  • Applications of Nuclear Chemistry Radioactive Dating using C-14 Treatment of Cancer (Phosphorous and Cobalt) NMR and CAT scans in Radiology Sterilization of foods Radioactive tracers (cardiology) Fission reactors for Electrical Power Medical Laboratory procedures Defensive and Offensive Weapons