What is this chapter about?. Trace elements and their usefulness for the forensic comparison of various types of physical evidence.Continuous and line emission spectra.Simple emission spectrograph.Simple atomic absorption spectrophotometer.Protons, neutrons, electrons, mass and charge relationship.Atomic number and atomic mass number..
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1. College Forensics: Project Advance Dr. Skolnick
Chapter 6: Inorganic Analysis
2. What is this chapter about? Trace elements and their usefulness for the forensic comparison of various types of physical evidence.
Continuous and line emission spectra.
Simple emission spectrograph.
Simple atomic absorption spectrophotometer.
Protons, neutrons, electrons, mass and charge relationship.
Atomic number and atomic mass number.
Orbital energy levels occupied by electrons.
Definite amount of energy absorbed by atoms.
Phenomenon of atoms releasing energy in the form of light.
X-ray diffraction pattern and its usefulness in chemical identification.
3. Emission: light emitted from a source and separated into its component colors or frequencies.
Continuous spectrum: a type of emission spectrum showing a continuous band of colors all blending into one another.
Line spectrum: a type of emission spectrum showing a series of lines separated by black areas.
Proton: a positively charged particle that is one of the basic structures in the nucleus of an atom.
Electron: a negatively charged particle that is one the fundamental structural units of the atom.
Neutron: a particle not having electrical charge, which along with the proton is a basic unit in the structure of the nucleus of an atom.
Nucleus: the core of an atom containing the protons and neutrons.
Atomic number: the number of protons in the nucleus of an atom. Each element has its own unique atomic number.
Electron orbital: the pathway of electrons as they move around the nuclei of atoms; each orbital is associated with a particular electronic energy level.
4. Excited state: the state in which an atom is supplied energy and an electron is moved from a lower to a higher energy level.
Atomic mass: the sum of the number of protons and neutrons in the nucleus of an atom.
Isotope: an atom differing from another atom of the same element in the number of neutrons it has in its nucleus.
Radioactivity: the particle and/or gamma ray radiation emitted by the unstable nucleus of some isotopes.
Alpha ray: a type of radiation emitted by a radioactive element. The radiation is composed of helium atoms minus their orbiting electrons.
Beta ray: a type of radiation emitted by a radioactive element. The radiation consists of electrons.
Gamma ray: a high-energy form of electromagnetic radiation emitted by a radioactive element.
X-ray diffraction: an analytical technique for identifying crystalline materials.
5. Introduction Carbon constitutes less than 0.1% of the earth’s crust. Oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium, titanium, and hydrogen make up 99% of the earth’s crust: the remaining elements may be considered impurities.
Examination of an explosive formulation containing potassium chlorate.
Examine a poisonous powder thought to be arsenic.
Does a piece of brass pipe found in the possession of a suspect compare to a broken pipe found at a crime scene?
Many manufactured products contain small quantities of elements present in concentrations of less than 1 percent.
The presence of trace elements may provide useful information.
6. Neutron Activation Analysis: Arsenic in Hair Napoleon Bonaparte – What do you know about him?
One of the most brilliant individuals in history, Napoleon Bonaparte was a masterful soldier, grand tactician, sublime statesman and exceedingly capable administrator.
After an extraordinary career, he was finally defeated and exiled to Elba. He returned from Elba to be ultimately defeated at Waterloo.
He was finally exiled to the remote tiny volcanic island of St. Helena, south of the Equator.
The nearest land is Ascension Island, 700 miles to the north.
7. Neutron Activation Analysis: Arsenic in Hair Murder or Not?
For years a controversy has raged about Napoleon being killed on St. Helena - either by French Royalists, persons in his exiled entourage or the British - and all have pointed to the high levels of arsenic in the emperor's body as being evidence of such behavior.
The emperor's body contained some 15 parts per million of the poison, where the maximum safe limit is only three parts per million.
The determination was by neutron activation analysis of his hair.
8. Who done it (if it was done at all)?
British Authorities - The Allied heads of state had no greater wish than to ensure that Napoleon was permanently “out of the way.” Strong hatred by British local commander.
Royalists - Revenge and insurance against Napoleon for declaring himself Emperor and dismantling the aristocracy.
Exiled Entourage - Jealousy (romantic triangles), intrigue, revenge.
Neutron Activation Analysis: Arsenic in Hair
9. NAA of Napoleon’s Hair
From the old tradition of keeping hair locks, many sample of Napoleon’s hair are known.
NAA showed high concentrations of As at various locations along hair shafts.
The As, however, was determined not to have been taken orally.
So how did he die and why did he have such high As concentrations?
Neutron Activation Analysis: Arsenic in Hair
10. The wallpaper in his room was dyed with Scheele's Green (Paris Green), a coloring pigment that had been used in fabrics and wallpapers from around 1770.
Named after the Swedish chemist who invented it, the dye contained copper arsenite.
It was discovered that if wallpaper containing Scheele’s Green became damp, the mold converted the copper arsenite to a poisonous vapor form of arsenic.
Breathing the arsenic on its own might not have been enough to kill Napoleon, but he was ill already with a stomach ulcer/cancer.
On the 5 May 1821, the arsenic tipped the scale against "the little corporal."
Neutron Activation Analysis: Arsenic in Hair
11. Neutron Activation Analysis NAA When atoms are bombarded with neutrons (a nuclear reactor is needed for this), some neutrons will be captured to make new isotopes.
About 70% of the elements have properties suitable for measurement by NAA.
What is an isotope?
In this state, the nuclei are said to be activated, and begin to decompose by emitting radioactivity.
Alpha rays (+ charged helium nucleus)
Beta rays (- charged electrons)
Gamma rays (powerful EM radiation)
12. Neutron Activation Analysis To identify the activated isotope, it is necessary to measure the gamma ray energy emitted as radioactivity.
The gamma rays of each element can be associated with a characteristic energy value.
Concentration of an element can be measured by the intensity of its gamma ray radiation.
Highly sensitive for identifying and quantitating trace elements: can work with one nanogram.
Can simultaneously analyze 20-30 elements. Drawback: expensive (need access to a nuclear reactor).
Used in detecting trace elements in metals, drugs, paint, soil, gunpowder residues, and hair.
13. Neutron Activation Analysis John F. Kennedy Assassination
What do you know?
Warren Commission Conclusions:
Oswald fired three shots from behind the president from the Texas School Book Depository Building.
JFK struck by two bullets (one bullet missed the limousine).
One bullet entered JFK’s back, exited his throat, entered Connally’s back, exited his chest, hit his wrist, lodged in thigh (bullet later fell onto the stretcher).
One bullet entered JFK’s skull causing the fatal wound.
14. Evidence 6.5 mm Mannlicher-Carcano rifle found in Texas School Book Depository Building.
Oswald’s palm print
Three spent 6.5 mm Western Cartridge Co/ Mannlicher-Carcano (WCC/MC) cartridge cases.
Bullets/fragments from victims.
15. 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
Guinn’s studies had shown that quantities of antimony, silver & copper could be used to distinguish bullets.
Antimony is most important because it varies the most.
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 <10 ppm Sb
*one part per million equals 0.0001 percent.
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”
16. The Analysis Guinn analyzed five types of samples.
the stretcher bullet
two metal fragments from Connally’s wrist
a fragment from the front seat of the limousine
two fragments from JFK’s head
three small fragments from the rear floorboard carpet
The same samples originally analyzed.
samples fell into two groups
two samples with concentrations ~820 ppm
three samples with concentrations ~620 ppm
The stretcher bullet & wrist fragments fall into group #1.
The fragments from JFK’s head, the front seat, & rear floor fit into group #2.
17. Conclusions Evidence of only two bullets.
Both bullets have compositions consistent with WCC/MC bullet lead.
other sources cannot be exclusively ruled out
It is highly probable that the stretcher bullet also caused the wrist injury.
absence of bullet fragments from back wounds prevents linking them to the stretcher bullet
18. The Emission Spectrum of Elements When sunlight is passed through a prism, a range of rainbow colors is produced, called a Continuous Spectrum.
Not all light sources produce such a spectrum.
19. Emission Spectrograph An emission spectrograph vaporizes and heats samples to a high temperature so that the atoms present in the material achieve an “excited” state. The excited atoms emit light.
If the light is separated into its components, one observes a Line Spectrum. Each element in the spectrum can be identified by its characteristic line frequencies.
Each line represents a definite wavelength or frequency of light.
In this way, the elemental composition of a substance may be determined.
Bullets, fibers, hair, paint, etc.
20. Atomic Absorption Spectrophotometry When an atom is vaporized, it absorbs many of the same frequencies of light that it emits in an excited state.
In this process, a specimen is heated to a temperature that is hot enough to vaporize its atoms, which are exposed to radiation emitted from a light source specific for a particular element.
If the element is present in the material under investigation, a portion of the light is absorbed by the substance.
The higher the concentration of the element, the more light is absorbed.
21. Atomic Absorption Spectrophotometry (AAS) Typical Problem:
A child becomes quite ill and is taken to the hospital.
It is found that the child is suffering from lead poisoning.
A forensic laboratory is contacted and asked if it can determine the source of the lead which the child has ingested.
No crime has been committed, but the source must be eliminated to prevent future danger to the child.
Paint samples from a number of objects with which the child has had repeated contact are collected. Paint on the child's crib, paint from his toys, and paint from the child's swing, to name a few, are sent to the laboratory.
AAS is the best method for these analyses.
22. If atoms are exposed to intense heat, electrons are pushed into unoccupied higher-energy orbitals (excited state).
The electrons quickly fall back to their original energy levels, and release energy in the form of light.
Because each element has its own characteristic set of energy levels, each emits a unique set of frequency values.
Atomic Absorption Spectrophotometry measures the value and amount of light energy going into an atom.
Emission Spectroscopy measures the amount given off.
23. (a) The absorption of light by an atom, causing an electron to jump into a higher orbital. (b) The emission of light by an atom, caused by an electron falling back to a lower orbital.
24. X-Ray Diffraction Emission spectroscopy, atomic absorption, and neutron activation analysis tell us what elements are present in a particular substance, but not how they are arranged into compounds.
X-Ray diffraction can help with this: aim a beam of X-Rays at a crystal and study how they interact with the atoms that compose a substance.
Can only be applied to solid, crystalline materials. Many substances, including 95% of all inorganic compounds, are crystalline.
25. X-Ray Diffraction The atoms in a crystal can be thought of as being composed of a series of parallel planes.
As X-rays penetrate the crystal, a portion of the beam is reflected by each of the atomic planes.
As the reflected beams leave the crystal’s planes, they combine with one another to form a series of light and dark bands known as a diffraction pattern. Every compound produces a unique pattern.
26. A beam of X-rays being reflected off the atomic planes of a crystal. The diffraction patterns that form are recorded on photographic film. These patterns are unique for each crystalline substance. Drawback: lack of sensitivity. Cannot detect the presence of substances comprising less than 5% of a mixture.
27. Comparison of Techniques