Ch 6 – Inorganic Analysis

1. Ch 6 –Inorganic Analysis • 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.

2. Orbital energy levels occupied by electrons. • Definite amount of energy absorbed by atoms. • Phenomenon of atoms releasing energy in the form of light. • Isotopes. • Radioactivity. • 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

4. Electron: a negatively charged particle that is one the fundamentals structural units of the atom • Neutron: a particle having not 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

5. Electron orbital: the pathway of electrons as they move around the nuclei of atoms; each orbital is associated with a particular electronic energy level • 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 I the nucleus of an atom

6. 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

7. 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

8. Emission Spectrum

10. Atomic Absorption (AA)

11. Neutron Activation Analysis

12. Neutron Activation Data

13. X-Ray Diffraction

14. X-Ray Diffraction Datafor a single atom

15. Ch. 6 - Inorganic Analysis

16. The Hydrogen Discharge Tube • H2 molecules are split into excited H atoms by an electric discharge • As the atoms return to lower energy states, light is emitted

19. Emission Spectroscopy • Used to detect the types of elements present in a sample • paints

20. Flame Tests

21. Atomic Absorption Spectroscopy

22. Atomic Absorption Spectroscopy • Sample heated to vaporize atoms • Vaporized atoms exposed to radiation emitted from a discharge tube • Atoms absorb radiation & become excited • The amount of radiation absorbed is recorded • The amount absorbed is determined using Beer’s Law (calibration curve)

23. Atomic Absorption Spectroscopy • Can quantitate the amount of metal ion present in a sample • gunshot residue (particularly Pb)

24. Neutron Activation Analysis • Quantitative & qualitative multi-element analysis of major, minor & trace elements • Quantitation in parts per billion • Requires a nuclear reactor

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

26. 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 NAA

27. Neutron Activation Analysis

28. Gamma-ray Spectra Spectra of short-lived elements in a pottery sample

29. Gamma-ray Spectra Shows medium- and long lived elements

30. Gamma-ray Spectra Continuation of medium- & long-lived elements

31. Applications • gunshot residues • bullet lead • glass • paint • hair

32. Neutron Activation Analysis John F. Kennedy

33. Warren Commission Conclusions • 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

34. Warren Commission Conclusions • 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

35. 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 from victims

36. FBI Emission Spectroscopy • Compared the fragments from Connally’s 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

37. 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 anitmony, silver & copper could be used to distinguish bullets

38. Neutron Activation Analysis • 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

39. 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 withing an individual bullet • can “usually be distinguished from one another”

40. 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 limosine • two fragments from JFK’s head • three small fragments from the rear floorboard carpet • The same samples originally analyzed

41. 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

42. The Interpretation • Dependent on the two groups being analytically separate • requires their difference in concentration (~30%) to be much grater than the uncertainty of each group (~1% for each of the fragments) • The fragments were found to be clearly distinguishable

43. The Interpretation • The stretcher bullet & wrist fragments fall into group #1 • The fragments from the JFK’s head, the front seat, & rear floor fit into group #2

44. 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