Nuclear Chemistry

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Nuclear Chemistry
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Radioactivity

• Emission of subatomic particles or high-energy
  electromagnetic radiation by nuclei
• Such atoms/isotopes said to be radioactive

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Its discovery

• Discovered in 1896 by Becquerel
• Called strange, new emission uranic rays
• Cuz emitted from uranium
• Marie Curie hubby discovered two new elements,
  both of which emitted uranic rays
• Polonium Radium
• Uranic rays became radioactivity

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Types of radioactivity

• Rutherford and Curie found that emissions
  produced by nuclei
• Different types
• Alpha decay
• Beta decay
• Gamma ray emission

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Isotopic symbolism

• Lets briefly go over it
• Proton 11p
• Neutron 10n
• Electron 0-1e

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Types of decay alpha decay

• Alpha (?) particle helium-4 bereft of 2e-
• 42He
• Parent nuclide ? daughter nuclide He-4
• 23892U ? 23490Th 42He
• Daughter nuclide parent nuclide atomic minus
  2
• Sum of atomic s mass s must be on both
  sides of nuclear equation!

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Alpha decay

• Has largest ionizing power
• ability to ionize molecules atoms due to
  largeness of ?-particle
• But has lowest penetrating power
• ability to penetrate matter
• Skin, even air, protect against ?-particle
  radiation

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Beta decay

• Beta (?) particle e-
• How does nucleus emit an e-?
• ? neutron changes into proton emits e-
• ? 10n ? 11p 0-1e
• Daughter nuclide parent nuclide atomic number
  plus 1
• 13755Cs ? 13756Ba 0-1e-

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Beta decay

• Lower ionizing power than alpha particle
• But higher penetration power
• Requires sheet of metal or thick piece of wood to
  arrest penetration
• ? more damage outside of body, but less in (alpha
  particle is opposite)

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Gamma ray emission

• Electromagnetic radiation
• High-energy photons
• 00?
• No charge, no mass
• Usually emitted in conjunction with other
  radiation types
• Lowest ionizing power, highest penetrating power
  ? requires several inches lead shielding

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Problems

• Write a nuclear equation for each of the
  following
• 1. beta decay in Bk-249
• 2. alpha decay of Ra-224

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Cont.

• In determining nuclear stability, ratio of
  neutrons to protons (N/Z) important
• Notice lower part of valley (N/Z 1)
• Bi last stable (non-radioactive) isotopes
• N/Z too high above valley, too many n, convert n
  to p, beta-decay
• N/Z too low below valley, too many p, convert p
  to n

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Magic numbers

• Actual of n p affects nuclear stability
• Even s of both n p give stability
• Similar to noble gas electron configurations 2,
  10, 18, 36, etc.
• Since nucleons ( np) occupy energy levels
  within nucleus
• N or Z 2, 8, 20, 28, 50, 82, and N 126
• Magic numbers

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Radioactive decay series
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Detecting radioactivity

• Particles detected through interactions w/atoms
  or molecules
• Simplest ? film-badge dosimeter
• Photographic film in small case, pinned to
  clothing
• Monitors exposure
• Greater exposure of film ? greater exposure to
  radioactivity

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Geiger counter

• Emitted particles pass through Ar-filled chamber
• Create trail of ionized Ar atoms
• Induced electric signal detected on meter and
  then clicks
• Each click particle passing through gas chamber

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Radioactive decay kinetics

• Half-life time taken for ½ of parent nuclides
  to decay to daughter nuclides

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Radiometric dating radiocarbon dating

• Devised in 1949 by Libby at U of Chicago
• Age of artifacts, etc., revealed by presence of
  C-14
• C-14 formed in upper atmosphere via
• 147N 10n ? 146C 11H
• C-14 then decays back to N by ?-emission
• 146C ? 147N 0-1e t1/2 5730 years

• Approximately constant supply of C-14
• Taken up by plants via 14CO2 later incorporated
  in animals
• Living organisms have same ratio of C-14C-12
• Once dead, no longer incorporating C-14 ? ratio
  decreases
• 5 deviation due to variance of atmospheric C-14
• Bristlecone pine used to calibrate data
• Carbon-dating good for 50,000 years

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Radiometric dating uranium/lead dating

• Relies on ratio of U-238Pb-206 w/in igneous
  rocks (rocks of volcanic origin)
• Measures time that has passed since rock
  solidified
• t1/2 4.5 x 109 years
• For ex, if rock contains equal amts of isotopes
  above, it would be 4.5 billion years old

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Fission

• Meitner, Strassmann, and Hahn discovered fission
  splitting of uranium-235
• Instead of making heavier elements, created a Ba
  and Kr isotope plus 3 neutrons and a lot of
  energy
• Sample rich in U-235 could create a chain rxn
• To make a bomb, however, need critical mass
  enough mass of U-235 to produce a self-sustaining
  rxn

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Nuclear power

• In America, about 20 electricity generated by
  nuclear fission
• Imagine
• Nuclear-powered car
• Fuel pencil-sized U-cylinder
• Energy 1000 20-gallon tanks of gasoline
• Refuel every 1000 weeks (about 20 years)

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Nuclear power plant

• Controlled fission through U fuel rods (3.5
  U-235)
• Rods absorb neutrons
• Retractable
• Heat boils water, making steam, turning turbine
  on generator to make electricity

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Comparing

• Typical nuclear power plant makes enough E for
  city of 1,000,000 ppl and uses about 50 kg of
  fuel/day
• No air pollution/greenhouses gases
• But, nuclear meltdown (overheating of nuclear
  core)
• Also, waste disposal location, containment
  problems?

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Comparing

• OTOH, coal-burning power plant uses about
  2,000,000 kg of fuel to make same amt of E
• But, releases huge amts of SO2, NO2, CO2

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Fusion

• H-bonds utilize fusion (but needs high-temps to
  react cuz both positively charged)
• As does the sun 21H 31H ? 42He 10n
• 10 x more energy/gram than fission

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Transmutation

• Transforming one element into another
• In 1919, Rutherford bombarded N-17 to make O-17
• The Joliot-Curies bombarded Al-27 to form P-30
• In 30s, devices needed that could accelerate
  particles to high velocities
• 1. linear accelerator
• 2. cyclotron

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Linear accelerator

• Charged-particle accelerated in evacuated tube
• Alternating current causes particle to be pulled
  into next tube
• Continues, allowing velocity 90 speed of
  light!
• 2 miles long ???

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Cyclotron

• Similar alternating voltage used
• But applied btwn two semicircular halves of
  cyclotron
• Particle spirals due to magnets
• Hits target

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Radiation on life

• 3 divisions
• 1. acute radiation
• 2. Increased cancer risk
• 3. genetic effects

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The first

• Quickly dividing cell at greatest risk
• Intestinal lining
• Immune response cells
• Likelihood of death
• Depends on dose/
• duration

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2nd

• Cancer uncontrolled cell growth leading to
  tumors
• Dose? Unknown
• Cancer is a murky illness

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3rd

• Causes genetic defects ? teratogenic

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Average American 360 mrem/yr
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Good site

• http//www.deq.idaho.gov/inl_oversight/radiation/r
  adiation_guide.cfm

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Lets try the handout
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More facts

• 20 rem ? decreased white blood cell count after
  instantaneous exposure
• 100-400 rem ? vomiting, diarrhea, lesions,
  cancer-risk increase
• 500-1000 ? death w/in 2 months
• 1000-2000 ? death w/in 2 weeks
• Above 2000 ? death w/in hours

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Diagnostic and therapeutic radiation

• Radiotracer radioactive nuclide in brew to
  track movement of brew in body
• Tc-99 ? bones
• I-131 ? thyroid
• Tl-201 ? heart
• F-18 ? heart, brain
• P-31 ? tumors

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PET

• Positron emission tomography
• Shows both rate of glucose metabolism and
  structural features of imaged organ
• F-18 emits positrons
• Positron and e- produce two gamma rays
• Rays detected
• Imaged

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Radiotherapy

• Using radiation to treat cancer
• Develop symptoms of radiation sickness vomiting,
  diarrhea, skin burns, hair loss

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Other applications

• Irradiating foods
• Nuking bugs like fruit flies and screw-worm flies