Presentation is loading. Please wait.

Presentation is loading. Please wait.

Nuclear Chemistry Part 2

Similar presentations


Presentation on theme: "Nuclear Chemistry Part 2"— Presentation transcript:

1 Nuclear Chemistry Part 2

2 Radiometric Dating in amount of radioactivity of a radionuclide is predictable & not affected by envrnmntal factors By measuring & comparing ratio of parent radioactive isotope to its stable daughter we can determine age of the object (by using t½ & previous equations) Tro: Chemistry: A Molecular Approach

3 Radiometric Dating Mineral (geological) dating
compare amount of U-238 to Pb in volcanic rocks and meteorites Pb-206 from decay has unique “signature” dates Earth: btwn 4.0 & 4.5 billion yrs. old Can also compare amount of K-40 to Ar-40 Tro: Chemistry: A Molecular Approach

4 Radiocarbon Dating All things alive (or once alive) contain carbon
3 isotopes of C exist in nature: C-12, C-13, and C–14, which is radioactive C–14 radioactive half-life = _________ yrs relatively short half-life - should have disappeared long ago Tro: Chemistry: A Molecular Approach

5 Tro: Chemistry: A Molecular Approach

6 CO2 in air source of all C in organism
While still living, C–14/C–12 is constant because organism replenishes C CO2 in air source of all C in organism Death: C–14/C–12 ratio decreases Tro: Chemistry: A Molecular Approach

7 Measure: C–14/C–12 ratio in (once living) artifact & compare to C–14/C–12 ratio in living organism  date artifact Limit ~ 50,000 years old. Why? Tro: Chemistry: A Molecular Approach

8 % C-14 (compared to living organism) Object’s Age (in years)
Radiocarbon Dating % C-14 (compared to living organism) Object’s Age (in years) 100% 90% 870 80% 1850 60% 4220 50% 5730 40% 7580 25% 11,500 10% 19,000 5% 24,800 1% 38,100 Tro: Chemistry: A Molecular Approach

9 An ancient skull gives 4.50 dis/min∙g C. If a living organism gives 15.3 dis/min∙g C, how old is the skull? Given: Find: ratet1/2 = 4.50 dis/min∙gC, ratet1/2 = 15.3 dis/min∙gC time, yr Conceptual Plan: Relationships: t1/2 k rate0, ratet t + Solve: Check: units are correct, the magnitude makes sense because it is less than 2 half-lives Tro: Chemistry: A Molecular Approach

10 Tro: Chemistry: A Molecular Approach
Clicker question: Archeologists have dated a civilization to 15,600 yrs ago. If a living sample gives 20.0 counts / min g C, what would be the # of counts per min g C for a rice grain found at the site? 3.03 counts / min g C 1.209 x 104 counts / min g C 20.2 counts / min g C A rice grain? What are you nuts? Tro: Chemistry: A Molecular Approach

11 + Given: Find: Conceptual Plan: Relationships: Solve: Check:
t = 15,600 yr, rate0 = 20.0 counts/min∙gC ratet, counts/min∙gC Conceptual Plan: Relationships: t1/2 k rate0, t ratet + Solve: Check: units are correct, the magnitude makes sense because it is between 10 and 25% of the original activity Tro: Chemistry: A Molecular Approach 11

12 Nonradioactive Nuclear Changes
A few unstable split iif hit just right by a neutron  two smaller nuclei = ____________ Small nuclei accelerated until they overcome their charge repulsion & smash together  larger nucleus = _____________ Both fission and fusion release enormous amounts of energy Lise Meitner Tro: Chemistry: A Molecular Approach

13 Tro: Chemistry: A Molecular Approach

14 Fission Chain Reaction
A chain reaction: when a reactant in the process is also a product of the process in fission  3 neutrons only need small # of on to start chain rxtn Many on’s produced in fission: ejected from U before hitting another U-235 or absorbed by surrounding U-238 Minimum amount of fissionable isotope needed to sustain chain rxtn = critical mass Tro: Chemistry: A Molecular Approach

15 Tro: Chemistry: A Molecular Approach

16 Fossil Nuclear Reaction in West Africa
Pitchblende Uranium Oxide ore

17 Natural uranium is < 1% U–235 rest mostly
Fissionable isotopes: U–235, Pu–239, & Pu–240 Natural uranium is < 1% U–235 rest mostly not enough _______ to sustain chain reaction To produce fissionable uranium, natural uranium must be enriched in U–235 to ~ ___% for “weapons grade” to ~ ___% for reactor grade Tro: Chemistry: A Molecular Approach

18 Nuclear Power Nuclear reactors use fission to generate electricity
about ____% of U.S. electricity uses fission of U–235 to produce heat Heat boils water, turning it to steam Tro: Chemistry: A Molecular Approach

19 Nuclear Power Plants vs. Coal-Burning Power Plants
Use ~ __________ kg of fuel to generate enough electricity for 1 million people Produce NO2 & SOx that add to acid rain Produce CO2 that adds to the greenhouse effect Use about ____ kg of fuel to generate enough electricity for 1 million people No air pollution Tro: Chemistry: A Molecular Approach

20 Nuclear Power Plants - Core
fissionable material stored in long tubes, called _______________, arranged in a matrix subcritical Btwn fuel rods are ___________________ made of neutron-absorbing material B and/or Cd neutrons needed to sustain chain reaction rods are placed in a material to slow down ejected neutrons = a _________________ allows chain rxtn to occur below critical mass Tro: Chemistry: A Molecular Approach

21 If the neutron flow in a reactor is carefully regulated
Nuclear Reactors If the neutron flow in a reactor is carefully regulated so that only enough heat is released to boil water, then the resulting steam can be used to produce electricity.

22 Tro: Chemistry: A Molecular Approach

23 PLWR - Core control rods made of n absorbing material.
Allows rate of n flow thru reactor to be controlled. Because n’s are required to continue chain rxtn, control rods control the rate of nuclear fission Hot Water Control Rods Fuel Rods Cold Water Tro: Chemistry: A Molecular Approach

24 Nuclear Reactors Light-water reactors: Used to produce electricity Fuel rods containing fissile isotope in stabilized form (uranium oxide pellets encased in a corrosion- resistant zirconium alloy) suspended in a cooling bath - transfers heat generated by fission rxtn to a 2dary cooling system.

25 Nuclear Reactors Light-water reactors: Heat generates steam for production of electricity. Control rods absorb n’s & control rate of nuclear chain rxtn. Pulling control rods out increases n flow, allowing reactor to generate more heat. inserting rods completely stops the rxtn.

26 ~800 oC water under pressure Control rod storage

27 Heavy-water reactors:
Nuclear Reactors Heavy-water reactors: Deuterium (2H) absorbs n’s less effectively than (1H), but is ~ 2x as effective at scattering neutrons. A nuclear reactor using D2O instead of H2O as the moderator is so efficient it can use un-enriched uranium as fuel, which reduces operating costs & eliminates need for plants that produce enriched uranium

28 A nuclear fission reactor that produces
Nuclear Reactors Breeder reactors: A nuclear fission reactor that produces more fissionable fuel than it consumes. Fuel produced is not the same as the fuel consumed. Overall rxtn is conversion of _______________________________ which can be isolated chemically and used to fuel a new reactor.

29 Concerns about Nuclear Power
Core melt-down Waste disposal Transporting waste How do we deal with nuclear power plants that are no longer safe to operate? Tro: Chemistry: A Molecular Approach

30 Three Mile Island 28 March thru early April of 1979 Chernobyl Reactor 1986

31 Japan in 2011 In what condition are American Nuclear Reactors?

32 Where Does Energy from Fission Come from?
During nuclear fission, some of the mass of the nucleus is converted into energy E = mc2 Each mole of U–235 that fissions produces about _________________ J of energy a very exothermic chemical reaction produces _______________ J / mole Tro: Chemistry: A Molecular Approach

33 Mass Defect & Binding Energy
When nucleus forms, some mass of separate nucleons is converted into E Diff in mass btwn separate nucleons & combined nucleus = the mass defect E that is released when nucleus forms = the binding energy Tro: Chemistry: A Molecular Approach

34 Tro: Chemistry: A Molecular Approach

35 Calculate mass defect & nuke binding E per nucleon (in MeV) for C–16, radioactive isotope of carbon with a mass of amu Given: Find: mass C-16 = amu, mass p+ = amu, mass n0 = amu mass defect in amu, binding energy per nucleon in MeV Conceptual Plan: Relationships: mp+, mn0, mC-16 mass defect binding energy Solve: Tro: Chemistry: A Molecular Approach 35

36

37 Calculate the binding E per nucleon in Fe–56 (mass 55.93494 amu)
Tro: Chemistry: A Molecular Approach

38 Calculate the binding E per nucleon in Fe–56 (mass 55.93494 amu)
Tro: Chemistry: A Molecular Approach

39 Nuclear Fusion Fusion is combining light nuclei to make heavier, more stable nuclide Sun uses fusion of H isotopes to make helium as a power source Tro: Chemistry: A Molecular Approach

40 Requires high input of E to initiate process
need to overcome repulsion of pos nuclei Produces 10x energy per gram as fission No radioactive byproducts Unfortunately, only currently working application is the H-bomb Tro: Chemistry: A Molecular Approach

41 Fusion Tro: Chemistry: A Molecular Approach

42 Tokamak Fusion Reactor
Tro: Chemistry: A Molecular Approach

43 Making New Elements: Artificial Transmutation
High E particles can be smashed into target nuclei, resulting in production of new nuclei Tro: Chemistry: A Molecular Approach

44 Rutherford made O–17 bombarding N–14 with alpha rays from radium
Particles may be radiation from other radionuclide, or charged particles that are accelerated Rutherford made O–17 bombarding N–14 with alpha rays from radium Cf–244 is made by bombarding U–238 with C–12 in a particle accelerator Tro: Chemistry: A Molecular Approach

45 Artificial Transmutation
Bombardment of one nucleus with another causing new atoms to be made can also bombard with neutrons Reaction done in a particle accelerator Tc-97 is made by bombarding Mo-96 with deuterium, releasing a neutron Tro: Chemistry: A Molecular Approach

46

47

48

49 Cyclotron target source Tro: Chemistry: A Molecular Approach

50 Practice – Predict the other daughter nuclide and write a nuclear equation for each of the following
bombarding Ni–60 with a proton to make Co–57 bombarding N–14 with a neutron to make C–12 bombarding Cf–250 with B–11 producing 4 neutrons Tro: Chemistry: A Molecular Approach


Download ppt "Nuclear Chemistry Part 2"

Similar presentations


Ads by Google