Neutron Activation Analysis

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Neutron Activation Analysis

• John F. Kennedy Assignation

INORGANIC ANALYSIS
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Warren Commission Investigation

• Oswald fired three shots from behind the
  president from the Texas School Book Despository
  Building
• JFK struck by two bullets (one bullet missed the
  limousine)
• One bullet entered JFKs back, exited his throat,
  entered Connallys back, exited his chest, hit
  his wrist, lodged in thigh (bullet later fell
  onto the stretcher)
• One bullet entered JFKs skull causing the fatal
  wound

INORGANIC ANALYSIS
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Evidence

• 6.5 mm Mannlicher-Carcano rifle found in Texas
  School Book Depository Building with Oswalds
  palm print on it
• Three spent 6.5 mm Western Cartridge Co/
  Mannlicher-Carcano (WCC/MC) cartridge cases
• Bullets from victims

INORGANIC ANALYSIS
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FBI Emission Spectroscopy

• Compared the fragments from Connallys wrist to
  the bullet found on the stretcher
• technique only semiquantitative for such tiny
  fragments
• similar in composition
• no significant differences were found within the
  sensitivity of the spectrographic method
• those elements quantified had order of magnitude
  uncertainties

INORGANIC ANALYSIS
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Neutron Activation Analysis

• Analyst Dr. Vincent P. Guinn
• leading practitioner of forensic analysis of
  bullets fragments by NAA
• had examined about 165 different brands
  production lots of bullets
• Guinns studies had shown that quantities of
  anitmony, silver copper could be used to
  distinguish bullets

INORGANIC ANALYSIS
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Neutron Activation Analysis

• For chemists, nuclear chemistry provides a new
  tool for identifying and quantitating the
  elements.
• A nuclear reactor is simply a source of neutrons
  that can be used for bombarding atoms, causing
  some neutrons to be captured to produce
  radioactive isotopes.
• To identify the radioactive isotope, it is
  necessary to measure the energy of the gamma rays
  emitted as radioactivity.

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Neutron Activation Analysis

• Neutron activation analysis measures the
  gamma-ray frequencies of specimens that have been
  bombarded with neutrons.
• This method provides a highly sensitive and
  nondestructive analysis for simultaneously
  identifying and quantitating 20 to 30 trace
  elements at part per billion (ppb) levels.
• Forensic analysis has employed neutron activation
  on find trace elements in metals, drugs, paint,
  soil, gunpowder residue, and hair.
• This technique requires access to a nuclear
  reactor, it has limited value to routine forensic
  analysis.

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Neutron Activation Analysis
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Neutron Activation Analysis

• Neutron capture (n, gamma) reaction
• neutron collides non-elastically with nucleus
• compound nucleus formed in an excited state
• nucleus de-excites by emission of gamma rays

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Neutron Activation Analysis

• Rate depends on half-life of isotope
• Prompt gamma ray formation (PGNAA)
• measurement taken during irradiation
• Delayed gamma ray formation (DGNAA)
• measurements taken after irradiation
• more common operational mode
• About 70 of elements have properties suitable
  for measurement by Neutron Activation Analysis
  (NAA)

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NAA Gamma-ray Spectra
Spectra of short-lived elements in a pottery
sample
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Neutron Activation Analysis

• Antimony is most important because it varies the
  most and it is used as a hardening agent
• hardened bullets contain 0.5-4 Sb (5,000-40,000
  ppm)
• unhardened bullets contain 10-1,000 ppm Sb
• virgin lead contains lt10 ppm Sb

INORGANIC ANALYSIS
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Neutron Activation Analysis

• Compositions of most bullets of a given type are
  extremely reproducible within a box or within a
  production lot
• Mannlicher-Carcano bullet compositions vary from
  bullet to bullet
• Do not find a wide variation in composition
  within an individual bullet
• can usually be distinguished from one another

INORGANIC ANALYSIS
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The Analysis

• Guinn analyzed five types of samples
• the stretcher bullet
• two metal fragments from Connallys wrist
• a fragment from the front seat of the limosine
• two fragments from JFKs head
• three small fragments from the rear floorboard
  carpet
• These were same samples originally analyzed by
  the FBI

INORGANIC ANALYSIS
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The Results

• Antimony Data
• samples fell into two groups
• two samples with concentrations 820 ppm
• three samples with concentrations 620 ppm
• Silver analysis showed the same two groups with
  smaller differences

INORGANIC ANALYSIS
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The Results
INORGANIC ANALYSIS
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The Interpretation

• The fragments were found to be clearly
  distinguishable
• The stretcher bullet wrist fragments fall into
  group 1
• The fragments from the JFKs head, the front
  seat, rear floor fit into group 2

INORGANIC ANALYSIS
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Conclusions

• Evidence of only two bullets
• Both bullets have compositions consistent with
  WCC/MC bullet lead but other sources cannot be
  exclusively ruled out
• It is highly probable that the stretcher bullet
  also caused the wrist injury and absence of
  bullet fragments from back wounds prevents
  linking them to the stretcher bullet
• http//karws.gso.uri.edu/JFK/Scientific_topics/NAA
  /NAA.html

INORGANIC ANALYSIS