Nuclear Chemistry Chapter 25 Nuclear Radiation Section 25.1.

Download Nuclear Chemistry Chapter 25 Nuclear Radiation Section 25.1.

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  • Nuclear ChemistryChapter 25

  • Nuclear RadiationSection 25.1

  • Nuclear ReactionsOccur when nuclei emit particles and/or rays.Atoms are often converted into atoms of another element.May involve protons, neutrons, and electronsAssociated with large energy changes.Reaction rate is not normally affected by temperature, pressure, or catalysts.

  • Wilhelm Roentgen1845-1923

    1895:When electrons bombarded surface of certain materials, invisible rays were emitted

  • Henri Becquerel1852-1908

    studied minerals that when exposed to sunlight, emit lightphosphorescencediscovered uranium salts (pitchblende)

  • Marie Curie1867-1934

    Marie & Pierre Curieisolated components emitting raysidentifed Po & Ra

  • MORE HISTORYRutherford (1871-1937)identified alpha, beta, and gamma radiation

  • PROPERTIES OF RADIATIONAlpha ()42He, helium nucleiBlocked by paper; 6.64 x 10-24 kgSlow moving due to mass and charge!Beta ()0-1 or 0-1e, electronsBlocked by metal foil; 9.11 x 10-28 kgFast movingEmitted from a neutron of an unstable nucleusInsignificant mass compared with mass of nucleusGreater penetrating power than alpha particlesGamma ()00 , photonsNot completely blocked by lead or concrete; 0 kgHigh energy electromagnetic radiationAlmost always accompanies alpha and beta radiation

  • Radioactive DecaySection 25.2

  • NUCLEAR STABILITYCorrelated with atoms neutron-to-proton ratio.< 20 atomic number most stable

  • BETA DECAYInstability of isotope due to too many neutrons relative to its number of protons.

  • ALPHA DECAYAll nuclei with more than 83 protons decay spontaneously

  • POSITRON EMISSIONPositron is a particle with the same mass as an electron but the opposite charge01 or 01eDuring emission, a proton in the nucleus is converted to a neutron and a positron11p --> 10n + 01

  • ELECTRON CAPTURENucleus of an atom draws in a surrounding electron (from lowest energy level)Captured electron combines with a proton to form a neutron11p + 0-1e --> 10n

  • PROBLEMWhat particle is formed when polonium-210 undergoes alpha decay?

  • PROBLEMWhat particle is formed when polonium-210 undergoes alpha decay?

    21084Po --> massatomic #Po

  • PROBLEMWhat particle is formed when polonium-210 undergoes alpha decay?

    21084Po --> 42He +

  • PROBLEMWhat particle is formed when polonium-210 undergoes alpha decay?

    21084Po --> 42He + 20682 ?

    How did I get 20682 ?

  • PROBLEMWhat particle is formed when polonium-210 undergoes alpha decay?

    21084Po --> 42He + 20682 ?

    How did I get 20682 ? The numbers must add up the same on both sides of the equation (top #s =, and bottom #s =)

  • PROBLEMWhat particle is formed when polonium-210 undergoes alpha decay?

    21084Po --> 42He + 20682 ?

    How do you determine the element? By atomic number!

  • PROBLEMWhat particle is formed when polonium-210 undergoes alpha decay?

    21084Po --> 42He + 20682 Pb

    How do you determine the element? By atomic number!

  • PROBLEMWhat would the decay process of iodine-131 into xenon-131 look like?

  • PROBLEMWhat would the decay process of iodine-131 into xenon-131 look like?

    13153I --> 13154Xe + ?

  • PROBLEMWhat would the decay process of iodine-131 into xenon-131 look like?

    13153I --> 13154Xe + 0-1?

    What type of radiation: 0-1?

  • PROBLEMWhat would the decay process of iodine-131 into xenon-131 look like?

    13153I --> 13154Xe + 0-1

    What type of radiation: 0-1? Beta!

  • RADIOACTIVE SERIESA series of nuclear reactions that begins with an unstable nucleus and results in the formation of a stable nucleus.

  • TRANSMUTATIONSection 25.3

  • TRANSMUTATIONConversion of an atom of one element to an atom of another elementIn all but gamma emission nuclear reactions

  • INDUCED TRANSMUTATIONStriking nuclei with high-velocity charged particlesMust be moving at high speeds to overcome electrostatic repulsion of target atoms nucleusUse particle accelerators (atom smashers

  • TRANSURANIUM ELEMENTSElements immediately following uranium in the periodic tableAtomic number of 93 or greaterDeveloped in the laboratory by induced transmutationRadioactive

  • PROBLEM Write a balanced nuclear equation for the induced transmutation of aluminum-27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom in the reaction.

  • PROBLEMWrite a balanced nuclear equation for the induced transmutation of aluminum-27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom in the reaction.

    Write all symbols on proper sides of the equation. Make certain numbers add up!

  • PROBLEMWrite a balanced nuclear equation for the induced transmutation of aluminum-27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom in the reaction.

    Write all symbols on proper sides of the equation. Make certain numbers add up!

    2713Al + 42He ---> 10n + 3015P

  • PROBLEMWrite a balanced nuclear equation for the induced transmutation of aluminum-27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom in the reaction.

    2713Al + 42He ---> 10n + 3015P

    How did I know the symbol for a neutron?A neutron has mass but no nuclear charge!

  • HALF-LIFETime required for one-half of a radioisotopes nuclei to decay into its products.Exponential decay!

    Strontium-90 has a half-life of 29 years.

    So, if you had 10 g of this, in 29 years you would have 5 grams left.

  • HALF-LIFEAmount remaining = (initial amount)(1/2)n

    n is equal to the number of half lives that has passedOR

    Amount remaining = (initial amount)(1/2)T/t 1/2

    T is equal to the elapsed time and t 1/2 is the duration of the half-life

  • PROBLEMIron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days?

  • PROBLEMIron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days?

    Amount remaining = (initial amount)(1/2)n

    X = 2.000 (1/2)133.5/44.5

  • PROBLEMIron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2,000 mg sample will remain after 133.5 days?

    Amount remaining = (initial amount)(1/2)n

    X = 2.000 (1/2)133.5/44.5

    Amount remaining = 0.2500 mg

  • RADIOCHEMICAL DATINGProcess of determining an age of an object by measuring the amount of a certain radioisotope remaining in that objectUraniumHalf-life of 4.5 c 109 yearsMeteorites; have estimated age of solar system at 4.6 x 109 yearsCarbon dating146C ---> 147N + 0-1Half-life of 5730 yearsLimited to accurately dating objects up to 24,000 years of age

  • Fission and Fusion of Atomic NucleiSection 25.4

  • E = mc2I lied! (kind of) For most practical situations, mass is conserved, butEnergy and mass can be converted into each other!It has been determined that the mass of the nucleus is always less than the sum of the masses of the individual protons and neutrons that comprise it. (CALLED MASS DEFECT)The missing mass provides tremendous energy required to bind the nucleus together.

  • NUCLEAR FISSIONHeavier atoms (mass # > 60) tend to fragment into smaller atoms to increase their stabilityThis is accompanied by a very large release of energy

  • NUCLEAR POWER PLANTSUse fission to generate powerUO2 encased in corrosion-resistant fuel rodsEnriched to contain 3% uranium-235 (meets critical mass to sustain the chain reaction)Control rods of cadmium or boron absorb neutrons released during the reaction, controlling the fission processWater circulates throughout the core to carry off the heat generatedThis is used to power stream driven turbines which produce electrical powerDense concrete structure encloses the reactor

  • NUCLEAR POWER PLANTSDrawbacksHazardous radioactive fuels and fission productsLimited supply of uranium-235Where to store spent fuel rods?Require 20 half-lives to decay to safe levelsAmount of spent fuel for a lifetime/person would equal the size of a basketball

  • NUCLEAR FUSIONBinding together two light (mass # < 60) and less stable nucleiCapable of releasing very large amounts of energyThe sun!Requires temperatures of 40,000,000 K!Can achieve this by atomic explosion (not safe!)Dont have materials capable of withstanding these high temperatures

  • ATOMIC BOMBUtilizes principles of fission (uncontrolled!)Equal to effect of 20,000 tons of TNT

  • HYDROGEN BOMBNever used in warfareExplosive force 1000 X greater than atomic bombFission reaction triggers a fusion reaction of hydrogen isotopes (deuterium and tritium)Equal to 15 million tons of TNT

  • IONIZING RADIATIONRadiation energetic enough to ionize matter with which it collidesDetected by:Geiger counterMetal tube filled with a gas; gets ionized; creates an electrical currentScintillation counterRadiation energizes a phosphorcoated surface that releases bright flashes

  • USES OF RADIATIONNeutron activation analysisDetermine quality of silicon wafers used in computersRadiotracersTrace biological pathwaysPETImagery used in medical diagnosesRadiation to kill cancer cellsIrradiation of meats, fruits

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