NUCLEAR CHEMISTRY

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NUCLEAR CHEMISTRY

• BY
• MARUTHUPANDI M
• MSC CHEMISTRY

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NEUTRON ACTIVATION ANALYSIS (NAA)
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• Frank (1908-1990)
• The Nobel Prize winner in Physics 1956
• Neutron activation analysis (NAA) is a nuclear
  process used for determining the concentrations
  of elements in a vast amount of materials.
• THIS techniques used for quantitative
  multi-element analysis of major, minor, trace,
  and rare elements
• A particular advantage of this technique used for
  analysis of works of art and historical
  artifacts.

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Principle OF Neutron Activation Analysis

• The method is based on neutron activation and
  therefore requires a source of neutrons.
• The sample is bombarded with neutrons, causing
  the elements to form radioactive isotopes.
• The radioactive emissions(gamma rays) and
  radioactive decay paths for each element are well
  known.
• Using this information, it is possible to study
  spectra of the emissions of the radioactive
  sample, and determine the concentrations of the
  elements within it.

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Neutron Activation Analysis REACTION
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Advantages of NAA

• The advantages of NAA over other analytical
  techniques were quickly recognized, including
• (1) ease of sample preparation
• (2) high precision
• (3) simultaneous measurement of multiple
  elements
• (4) outstanding replicability and
• (5) excellent inter-laboratory comparability

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Method for NAA

• (Radiochemical), the elements of the resulting
  radioactive sample undergoes decomposition and
  chemical separation process.
• (Instrumental), chemical separation is not
  performed, and therefore the resulting
  radioactive sample is not decomposed to
  elemental fragments.

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Applications of NAA

• NAA can be used for a large variety of
  applications the following represent some
  examples for scientific uses in different
  disciplines
• Archeology -  Sourcing of clays and old matter
•   Biology-  Toxins in Fish and agricultural
  products,-  Trace elements in oil ,
• Chemistry-  Contaminants in salts, pure crystals
  and metals 
• Forensics-  Analysis of bullets,and other scene
  materials (paint, glass, metals) 
• Medicine-  Toxins and trace elements in hair,
  skin and nail samples

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Isotope dilution 
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• Isotope dilution analysis is a method of
  determining the quantity of chemical substances.
• In its most simple conception, the method
  of isotope dilutioncomprises the addition of
  known amounts of isotopically-enriched substance
  to the analyzed sample.
• ISOTOPE DILUTION technique is part of Sample
  Analysis Design (activation analysis)

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TYPES OF ISOTOPE DILUTION

• Single dilution method
• natural analyte rich in isotope AND
  enriched in isotope SPIKE
• Double dilution method
• TWO AMOUNT OF enriched in isotope SPIKE
• Triple dilution method
• THREE  isotopically-enriched spike

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CONDITION

• Most accurate and precise calibration method
  available
• Requires analyte with two stable isotopes
• ? Monoisotopic elements cannot be determined via
  isotope dilution
• ? Spike natural sample with enriched isotope
  spike of analyte

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Applications

• Isotope dilution is almost exclusively employed
  with mass spectrometry in applications where
  high-accuracy is demanded.
• For example, all National Metrology Institutes
  rely significantly on isotope dilution when
  producing certified reference materials.
• In addition to the use of stable isotopes,
  radioactive isotopes can be employed in isotope
  dilution which is often encountered in biomedical
  applications, for example, in estimating
  the volume of blood.

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Advantages

• ?Most accurate and precise method for
  quantitative elemental concentrations
• ?Partial loss of analyte during preparation is
  compensated for since physical and chemical
  interferences are not an issue -- will cancel out
  as they will affect each isotope identically
• ?Ideal form of internal standardization since
  another isotope of the same element is used in
  this capacity

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Disadvantages

• ?Generally only applicable to multiple-isotopic
  elements
• ?Need an enriched isotope spike for the analyte
  of interest - not always available or sometimes
  at very high cost
• ?Need two interference free isotopes ?
• VERY time consuming

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Radiometric Titrations
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• radiometry
• The measurement of quantities associated
  with radiant energy.
• The energy with respect to other
  variables such as wavelength, time,
  
  position,
  direction (solid angle).
• radiometric titration
• A titration in which a radioactive indicator is
  used to monitor the end-point of the titration.

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Radiometric Titrations

• Radiometric titration is a volumetric titration
  method with a special opportunity for the
  indication of the end-point. It can be used when
  the titrant gives an insoluble precipitate.
• EX,
• Use of radioactive indicator to track the transfer
   of material between two liquid phases in equilibr
  ium, such as titration of110AgNO3(silver nitrate, 
  with the silver atom having mass number 110) again
  st potassium chloride

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Procedure

• 110AgNO3                NaCl-  ?       110AgCl
  (ppt) NaNO3
• A typical example of radiometric titration is for
  the determination of halides using 110Ag (t1/2 
  252 d) as tracer where corresponding silver
  halide is precipitated. 10 mL of 1mM NaCl
  solution containing Cl- with 1 mM solution
  of 110AgNO3 to follow the reaction
• . Initially solution containing NaCl has no
  activity. With the addition of increasing amount
  of 110AgNO3, supernatant will have very little or
  insignificant activity because all the activity
  would have gone to the precipitate of 110AgCl.
• After the end point, however, activity
  of 110AgNO3 will come into the solution and keep
  increasing with every additional drop. Titration
  data are plotted as shown in Figure from where
  equivalence point is the intercept of the two
  straight lines of the curve.

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Advantages and Limitations

• This method has an advantage that the detection
  of end point does not depend on the chemical
  reaction.
• Unlike the normal titration where indicator such
  as phenolphthalein, methyl orange, ferroin, etc
  participate in the reaction.
• A major limitation of radiometric titration is
  the requirement of phase separation method which
  of course is automatic in precipitation
  titrations.
• For other types of titrations, special phase
  separation methods will have to be employed.

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