Monday January 29, 2018 (??)

The Daily CSI Monday, 1/30/17 In regards to forensic analysis of metals, what is meant by the term “trace elements?” Trace elements are small quantities of elements present in concentrations of less than 1 percent that provide “invisible” markers that may establish the source of a material or provide addition points for comparison.

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Trace Evidence Forensic Analysis of Metals

Opening Statements What is the usefulness of “trace elements” for forensic comparison of various types of physical evidence? What are protons, neutrons, and electrons? What is meant by the terms “atomic number” and “atomic mass?” What is an “isotope?” How can elements be made “radioactive?”

Forensic Analysis of Metals Trace elements are small quantities of elements present in concentrations of less than 1 percent. They provide “invisible” markers that may establish the source of a material or provide addition points for comparison. The three most important subatomic particles are the proton, neutron, and electron.

Forensic Analysis of Metals The proton has a positive electrical charge, the neutron has no electrical charge, and the electron has an negative electrical charge. Atomic number indicates the number of protons in the nucleus of an atom. Atomic mass refers to the total number of protons and neutrons in the nucleus.

Forensic Analysis of Metals An isotope is an atom differing from other atoms of the same element in the number of neutrons in its nucleus. Radioactivity is the emission of high-energy subatomic particles that accompanies the spontaneous disintegration of the nuclei of unstable isotopes. The three types of radiation are alpha particles, beta particles, and gamma rays.

Forensic Analysis of Metals In neutron activation analysis, a sample is bombarded with neutrons and the energy of the gamma rays emitted by the activated isotopes is measured. The gamma rays of each element are associated with characteristic energy values that help identify the specific element that produces them.

Closing Arguments Trace elements are small quantities of elements present in concentrations of less than 1 percent that provide “invisible” markers that may establish the source of a material or provide addition points for comparison. The proton has a positive electrical charge, the neutron has no electrical charge, and the electron has an negative electrical charge. Atomic number indicates the number of protons in the nucleus of an atom. Atomic mass refers to the total number of protons and neutrons in the nucleus. An isotope is an atom differing from other atoms of the same element in the number of neutrons in its nucleus. In neutron activation analysis, a sample is bombarded with neutrons and the energy of the gamma rays emitted by the activated isotopes is measured. The gamma rays of each element are associated with characteristic energy values that help identify the specific element that produces them.

Read and study section on metals as trace evidence. Forensic Textbook Read and study section on metals as trace evidence.