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Dual Beam Microscopy

NCJ Number
Forensic Magazine Volume: 6 Issue: 5 Dated: October - November 2009 Pages: 12,14,15,16
Hans Kruesemann
Date Published
November 2009
4 pages
This article discusses the features of dual beam microscopy, the rationale for purchasing such an expensive system for a crime laboratory, and the benefits that can be achieved, using the experience of Brasilia's Instituto Nacional de Criminalistica (INC) as an example.
INC, the central crime lab for Brazil's Federal Police Department, recently added a state of the art dual beam microscopy system to its laboratory. Dual beam instruments combine the high resolution imaging capability of scanning electron microscopes (SEM) with the cross-sectioning and sample-manipulation capabilities of a focused ion beam. In addition, the instrument purchased by the INC (Quanta 200 3D DualBeam, FEI) includes specialized environmental capabilities that assist in preserving the evidentiary integrity of the sample. Dual beam instruments add to the three-dimensional capability of SEM microscopy by allowing the investigator to use the focused ion beam to cut precisely controlled cross sections into the sample to reveal subsurface detail. Shortly after the INC's acquisition of its dual beam, it was presented with forged letters, allegedly sent from the President of Brazil, that contained a wet, green powder presumed to be a chemical or biological weapon. Twenty-five such letters were sent to embassies in Brazil. The INC analyzed samples in the dual beam microscope and determined in less than 10 minutes the granular texture and chemical composition of the material. It was a harmless chemical composition of sodium, carbon, oxygen, and silicon. The results were quickly published in the media, preventing public anxiety and possibly averting a major diplomatic incident. Other applications of the dual beam system at the INC include analysis of gunshot residue; fractures; rocks, soil, and minerals; jewels and gemstones; arts; and construction and vehicle paints and coatings. 4 figures


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