5. use of stable and radioactive isotopes soil 5813 soil-plant nutrient cycling and environmental...

Download 5. Use of Stable and Radioactive Isotopes SOIL 5813 Soil-Plant Nutrient Cycling and Environmental Quality Department of Plant and Soil Sciences Oklahoma

Post on 26-Dec-2015

213 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • Slide 1
  • 5. Use of Stable and Radioactive Isotopes SOIL 5813 Soil-Plant Nutrient Cycling and Environmental Quality Department of Plant and Soil Sciences Oklahoma State University Stillwater, OK 74078 email: wrr@mail.pss.okstate.edu Tel: (405) 744-6414 SOIL 5813 Soil-Plant Nutrient Cycling and Environmental Quality Department of Plant and Soil Sciences Oklahoma State University Stillwater, OK 74078 email: wrr@mail.pss.okstate.edu Tel: (405) 744-6414
  • Slide 2
  • Historical Einstein: Relativity theory (1905), quantum theory Roentgen: discovered x-rays Becquerel: first recognition of radioactivity Rutherford: transmutations "changing one element to another Bremsstrahlung: identified secondary x-rays Curie - Joliot: first induced artificial radioactivity (1934) Isotopes are atoms of the same element that differ in mass. They have the same number of protons and electrons but have a different mass which is due to the number of neutrons. 1. All radio isotopes have a particular kind of radiation emission 2. Energy and mass are equivalent (Einstein) higher mass, higher energy 3. All radio nuclides have a characteristic energy of radiation 4. All radio nuclides possess a characteristic rate of decayhigher mass, higher energy 1 mole of X has 6.025 x 10 23 atoms one gram of 14N has (14 g/mole) 6.025 x 10 23 atoms/mole * 1 mole/14g = 4.3 x 10 22 atoms/g Avogadros # = # of molecules in one gram molecular weight of any substance. Dealing with reactions in the outer ring that compromise and produce chemical reactions. __________________________________________ atomic mass unitscharge (amu) __________________________________________ proton1.007594+ electron0.000549- neutron1.008986none __________________________________________
  • Slide 3
  • 14 C 6 8 6 Protons- Atomic Number (determines what the element is) 8 Neutrons 14 P+N = Atomic Mass Isotope (of a given element) same atomic number, different atomic masses (different # of neutrons) 14 6 C 12 6 C 235 92 U 238 92 U Stable Isotope Non-Radioactive Isotope (not decomposing) Radioisotope or Radionuclide unstable isotope that spontaneously decays emitting radiation Radioactive decay: not affected by temperature or environmental conditions
  • Slide 4 32 16 S+ B - + e - + v(+1.71 Mev) 3. Beta "positron" (low neutron:proton ratio, comes from the nucleus which has too many protons) proton in the nucleus changes to a neutron, decreasing the atomic number by one. 30 15 P ---> 30 14 Si + B + + e + + v(+3.3 Mev)">
  • Radioactive Decay A. Particulate 1. Alpha (nucleus of the He atom, mass = 4 and charge = +2) Charge +2, mass 4 ( 4 2 He) high specific ionization, limited penetration, come only from high z (# of protons) atoms. 226 88 Ra --> 222 86 Rn + 4 2 He + energy 238 92 U --> 234 90 Th + alpha + 4.19 MeV 222 86Rn --> 218 84 Po + alpha + MeV Radionuclides which emit alpha are changed into another nuclide with a mass of 4 units less and 2 fewer protons Three sheets of paper are sufficient to stop alpha radiation. When an alpha particle loses energy it attracts electrons and becomes a neutral helium atom. Not used in plant biology and soil studies. 2. Beta "negatron" (high neutron:proton ratio, originates from the nucleus like alpha) neutron in the nucleus changes to a proton, increasing the atomic # by one. 32 15 P ---> 32 16 S+ B - + e - + v(+1.71 Mev) 3. Beta "positron" (low neutron:proton ratio, comes from the nucleus which has too many protons) proton in the nucleus changes to a neutron, decreasing the atomic number by one. 30 15 P ---> 30 14 Si + B + + e + + v(+3.3 Mev)
  • Slide 5
  • Slide 6
  • B. Photons (a quantum of radiant energy) 1. Gamma, does not have a mass (electromagnetic radiation with the speed of light) is not a mode of radioisotope decay but rather associated with particulate emission. can penetrate inches of lead 60 27 Co ---> 60 28 Ni + B - +gamma + gamma 0.31MeV1.17 MeV1.33 MeV Radio isotope decay schemes result in transmutation of elements that leave the nucleus in a suspended state of animation. Stability is reached by emitting one or more gamma photons. 2. X-ray emitting by electron capture (too many protons and not enough neutrons) emitted when cathode rays of high velocity fall directly on a metallic target (anticathode) in a vacuum tube. highly penetrating electromagnetic radiation (photons) with a short wave-length. identical to gamma rays if their energies are equal electron from K ring is pulled into the nucleus chain reaction of K ring pulling electron into K from L and so on. emission as an x-ray is external to the nucleus (come from the outer shell of the atom) 3. Cosmic radiation (radiation from outer space) mixture of particulate radiation (neutrons) and electromagnetic radiation.
  • Slide 7
  • 1.When is an Isotope Stable, or Why are Some Isotopes Radioactive? Radioactive isotope Stable Isotope RULES A.All nuclei > 84 protons are unstable (the nucleus gets too big, too many protons) B.Very Stable: Atomic Number 2, 8, 20, 50, 82 or 126 C.Isotopes with Proton=Neutrons are more stable than unequal number of nucleons # of neutrons # of protons unstable Belt of stability 80 0
  • Slide 8
  • Where do Radionuclides/Stable Isotopes Come From? Fission: Splitting the Nucleus to Release Energy and Sub Atomic Particles Decay Series: Series of Reactions That Ends With a Stable Isotope U, Th, Pa, U, Th, Ra, Rn, Po, Pb, Bi, Po, Pb, Bi, Po, Pb Fission Reaction Used for Radio Dating 238 U Geologic Time (106 years) t 1/2 = 4.5x109 yr 14C Up to 20,000 B.P. (before present) t 1/2 =5700 yr
  • Slide 9
  • 14 7 N + 1 0 n 14 6 C + 1 1 H ( 14 C being produced all the time in the upper atmosphere) 14 6 C 14 7 N + 0 -1 e (beta particle) Living Tissue 14 C/ 12 C, Tissue ratio same as atmospheric ratio Dead Tissue 14 C/ 12 C< 14 C/ 12 C tissueatmosphere Clock starts when you die
  • Slide 10 97 36 Kr + 138 56 Ba + 1 0 n + energy 235 92 U + 1 0 n ---> 90 38 Sr + 144 54 Xe + 2 1 0 n + energy 138 56 Ba is a fission fragment Strictly chance of actually knowing what we will have as products from the bombardment of 235 92 U with neutrons. 235 92 U "controlled reaction that is a chain reaction" using uranium rods 238 U accounts for 99.3 percent of the uranium found on earth 235 92 U is used for fission, because it splits easier. neutrons emitted in fission can produce a chain reaction Nuclear fission taps about 1/1000 of the total possible energy of the atom">
  • Fusion: Making hydrogen atoms combine resulting in released energy -no remnant radioactivity -no atmospheric contamination 2 1 H+ 3 1 H ---> 4 2 He + 1 0 n deuteriumtritium (alpha) 2 gallons of tritium would provide the U.S. with energy for 1 year if fusion were feasible. Sustained fusion requires 40,00,000K Our Sun: = 73%H, 26%He Fission: "Splitting atoms -results in the production of radioactive materials 235 92 U + 1 0 n ---> 97 36 Kr + 138 56 Ba + 1 0 n + energy 235 92 U + 1 0 n ---> 90 38 Sr + 144 54 Xe + 2 1 0 n + energy 138 56 Ba is a fission fragment Strictly chance of actually knowing what we will have as products from the bombardment of 235 92 U with neutrons. 235 92 U "controlled reaction that is a chain reaction" using uranium rods 238 U accounts for 99.3 percent of the uranium found on earth 235 92 U is used for fission, because it splits easier. neutrons emitted in fission can produce a chain reaction Nuclear fission taps about 1/1000 of the total possible energy of the atom
  • Slide 11
  • Slide 12
  • Nuclear Binding Energies- Energy needed to decompose a nucleus (totally) 4 2 He + energy 2 1 1 p + 2 1 0 n Highest energy most stable nucleus Fusion 56 Fission iron Preferential accumulation of Fe earth, older stars Consider Star: H He Li Fe (most stable, stops) Low High 0250 Atomic mass number
  • Slide 13
  • Where did elements with an atomic mass > 56 come from? How ere they made? Why isnt Fe the heaviest element of the periodic table? Star Fe cool down death Star Fe SUPERNOVA! Huge # of neutrons/energy Produce elements with Atomic Number > 26 (above Fe) So much energy that it overcomes the binding energy and can make elements bigger than Fe http://ie.lbl.gov/education/isotopes.htm http://user88.lbl.gov/NSD_docs/abc/home.html
  • Slide 14
  • U.S. Department of Energy Berkeley Lab Isotope Project
  • Slide 15
  • m Z E 1 1 H 4 2 He E- element m mass z - atomic number (# of protons in the nucleus) All hydrogen atoms have one proton __________________________________________ 1 1 H 2 1 H 3 1 H __________________________________________ stablestableradioactive deuteriumtritium mass = 1 mass=2mass=3 no neutron1 neutron2 neutrons 1 proton1 proton1 proton 1 electron1 electron1 electron __________________________________________ 12 6 C 13 6 C 14 6 C __________________________________________ stablestableradioactive mass=12mass=13mass=14 6 neutrons7 neutrons8 neutrons 6 protons6 protons6 protons 6 electrons6 electrons6 electrons __________________________________________
  • Slide 16
  • Chemical versus Nuclear Reactions: 1. 2Na + + H 2 O ----> 2NaOH + 2H + 3-5 eV in this reaction 2. 4 2 He + 9 4 Be ----> 12 6 C + 1 0 n 10 million eV in this reaction In a nuclear reaction, we have to balance both mass and proton number. Transmutation: changing one element into another 35 17 Cl + 1 0 n ------> 32 15 P + 4 2 He 32 16 S + 1 0 n ------> 32 15 P + 1 1 p Chemical reactions involve changes in the outer electronic structure of the atom whereas nuclear reactions involve changes in the nucleus
  • Slide 17

Recommended

View more >