Radiochemistry Techniques in Research

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Radiochemistry Techniques in Research

• Unique Aspects of Radiochemistry Research
• Availability of Radioactive Material
• Targetry
• Measuring Beam Intensity and Fluxes
• Recoils
• Radiochemical Separation and Measurement

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Aspects of Radiochemistry

• Chemical study of radioactive substances
• nuclear analytical methods
• application of radionuclides
• chemistry of the radioelements
• physics and chemistry of high activity level
  matter
• radiotracer studies
• Features of radioisotope research
• Large activity range
• pCi to MCi
• Chemical ionization at high concentrations
• Oxidation in solution
• Redox change of radionuclides
• Range of concentrations
• Molar to atom-at-a-time
• 2nd order kinetics impacted
• Sorption to surfaces ignored in normal chemistry
• Nuclear Transmutation

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Reaction with water

• Radicals are formed by the interaction of
  radiation with water
• Radicals drive reactions
• Solvated electrons, peroxide

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Radicals

• G values
• moles of molecules or species formed or
  decomposed per Joule of energy absorbed

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Hot Atom Chemistry

• Chemical reactions produced by nuclear
  transformation
• Neutron irradiation of ethyl iodide
• Iodine extracted into aqueous phase
• 127I(n,g)128I
• Possible to produce specific isotope
• Conditions needed
• Bond of produced atom must be broken
• Should not recombine with fragments
• Should not exchange with target molecule
• Slow kinetics
• Separation of new species
• Bonds are broken due to reaction energy
• Bond energies on the order of eV
• In neutron capture the emitted photon provides
  recoil
• Halogens produced in this method

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Hot Atom Chemistry

• Beta reactions
• TeO32-?IO3- e-
• Recoil is not quantized
• Kinetic energy shared
• E is maximum beta energy (MeV)
• Rmax(eV)573E(E1.02)/M
• 0.5 MeV in 100 amu is about 4 MeV
• Energy is distributed
• Translational, rotational, vibrational
• Bond usually not broken
• Internal conversion set atom in excited state
• Rearrangement of electrons

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Hot Atom Chemistry

• Conservation of momentum imparts recoil
• Solve based on momentum
• For M in amu and E photon energy in MeV
• Er(eV)537E2/M
• Photon on the order of 7 MeV

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Availability of radionuclides

• Source
• Natural or synthesized
• Reactions with neutrons or charged particles

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Targetry

• Targets for nuclear reactions
• Stable during reaction
• Heat transfer
• Limitation of other products
• Limit interactions with neutrons
• Boron containing samples
• Ease of production
• Evaporation
• Electrospray
• Electroplating
• the direct deposit of a metal on a cathodic
  surface by reduction
• precipitation of a cationic species in an
  insoluble form on an electrode
• Vacuum deposition
• Limited contaminants

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Electroplating
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Electroplating
Vacuum Deposition
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Target thickness

• Thickness of targets can be measured using a
  variety of techniques
• Weighing
• Mass of known area of target material and
  computes its density.
• ?-particle thickness gauges
• collimated beam of low energy ?-particles passes
  through the foil whose thickness is to be
  measured
• X-ray fluorescence or neutron activation
• Radiochemical methods if target is active or
  tracer added
• Mono-energetic ions through material

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Beam Intensity

• Measurement of charged particle beam intensities
  performed with physical methods
• measure the intensity of a charged particle beam
  with a Faraday cup
• beam is stopped in electrically isolated section
  of beam pipe
• collected charge is measured with an electrometer
  
• beam intensity is just the current divided by the
  charge on each ion
• Faraday cup is long cylinder to inhibit electron
  escape geometrically
• magnetic field applied to the cup along with a
  suppressing voltage to prevent electron escape
• Also can use secondary ionization chamber or foil
• Foil can monitor reactions and determine beam
  from products and cross section

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Separation methods

• Ion Exchange
• Chromatographic Methods
• paper chromatography
• thin-layer chromatography
• electrochromatography
• extraction chromatography
• Solvent Extraction
• Volatilization
• exploitation of differences in vapor pressure for
  radiochemical separations
• removal of radioactive rare gases from aqueous
  solutions or melts by sweeping with inert gas
• often gives clean separations
• Electrochemical Methods