» Forensics

EDX – Energy-dispersive X-ray spectroscopy

Tue, 25 Aug 2009 23:35:26 +0000

Energy-dispersive X-ray spectroscopy, commonly EDX, EDS, or EDXA, refers to the analytical technique used in conjunction with a scanning electron microscope (SEM) in order to identify composition and provide chemical characterization of a specimen. An electron beam is focused onto the sample that collides with and possibly ejects some of the sample’s electrons, forcing them to give up some of their energy, causing the x-ray.

The amount of energy released is based upon the starting and ending shell of the electron. The resulting x-ray can be converted into an EDX spectrum plot. This plot shows the different peaks that correspond to the energy levels of the x-rays received. Each part of the sample can be identified by comparing the x-ray against other known atomic structures, since each element has a unique structure. These plots can be shown as a elemental map to evaluate several elements at once or as a line profile to identify a single element.

There are two major types of detectors used for EDX, Lithium drifted Silicon Detector (SiLi) or the Silicon Drift Detector (SDD). While the SiLi must be operated at liquid nitrogen temperatures, the SDD is capable of being used at relatively high temperatures. The SDD has several other advantages over the SiLi, including faster analytical capabilities and better resolution, as well as higher count rate. The larger count rates also have the added benefit of reducing the damage to the sample because smaller specimen currents can be used.

While there are some free-standing EDX machines, SEMs are the typical equipment of choice. Since SEMs have the added bonus of imaging, they can become an integrated SEM-EDX instrument. Aspex’s Personal Scanning Electron Microscope (PSEM(R)) comes standard with an EDX spectrometer and utilizes a SDD X-Ray. Capable of EDX resolution of 135 eV and a particle detection range of 100nm to 5mm, the PSEM is a reliable, easy to use instrument.

Typical uses for EDX include foreign particle analysis, corrosive evaluation, coating composition analysis, and small component material analysis. Industries such as defense, automotive, pharmaceutical and aerospace (Should we link to these industry pages) are common places EDX analysis is used. The PSEM Express is a benchtop SEM that, when combined with Aspex software such as Automated Feature Analysis (AFA) and Complex Feature Analysis (CFA), becomes a fast, fully automated, affordable desktop SEM analysis system.

Reference:

Aspex, http://www.aspexcorp.com/products/psem-express.html

EDX Analysis and WDX Analysis, http://www.siliconfareast.com/edxwdx.htm

Materials Evaluation and Engineering, Inc., http://mee-inc.com/eds.html

Wikipedia, http://en.wikipedia.org/wiki/Energy-dispersive_X-ray_spectroscopy

Particle Size Analyzer – Automated SEM EDS

Mon, 24 Aug 2009 19:42:25 +0000

The automotive industry uses particle size distribution analysis in order to control contamination both before and during the assembly process. Information about particle type, size distribution, and morphology is used to identify potential contaminates, as well as minimize the cause of contamination. In order to combat contamination, identifying and sizing particles is the first step to eliminating foreign debris.

Whether utilized in the pre-building, production, or post-production stages, eliminating contaminates from the final product is a challenge manufacturers face daily.
Since the auto industry uses various different types of materials, the foreign particles entering the product must be monitored in order to maintain the critical cleanliness instituted by the manufacturer.

From paint to oil, engines to steel content, being able to quickly and accurately analyze particle contamination that could affect the quality of the final product is a necessary step. Since contaminates in steel can alter the grain size, and debris in oils and fluids can effect product life, it is advantageous to take precautionary measures to ensure not only that the end product is up to code, but in order to prevent wasted materials that do not meet the company standards. One tool used to help identify and categorize these particles is a scanning electron microscope (SEM) with energy-dispersive X-ray (EDX) capabilities.

The Aspex Personal Scanning Electron Microscope (PSEM) comes standard with an EDX spectrometer and utilizes a silicon drift detector (SDD). EDX technology is used in various industries, such as the automotive and pharmaceutical industries, for foreign particle analysis, corrosive evaluation, and compositional analysis. With EDX resolution of 135 eV and a particle detection range of 100nm to 5mm, small particles are easily identified and sized.

Aspex also has several different software platforms to fit all your analytical needs. The Advanced Quality Control (AQC) software, part of the Perception Suite, provides manufacturers with the capability of evaluating the size, shape, and composition of all particles present in a sample. By inserting the PSEM with AQC into the product line, problem spots can be isolated and controlled, pinpointing where particles are entering the line well before the end product testing is started, thus saving the manufacturer from wasting time creating faulty products.

Whether in the lab or in the shop, the PSEM with EDX capabilities and the AQC software provides the manufacturer with reliable particle analysis techniques to help ensure that the quality of the design is maintained in each step of the manufacturing process.

Reference:
Aspex, http://www.aspexcorp.com/industries/industrial-automation.html

Forensic Trace Evidence Analysis – Microscopic CSI

Sat, 22 Aug 2009 00:28:14 +0000

Trace evidence encompasses the multitude of materials left at or taken from a crime scene, such as blood droplets, clothing fragments, or gunshot residue. In order for these substances to be useful, they must carefully be preserved and collected at the crime scene, minimizing and controlling the further contact with them as not to expose them to additional contaminates. The trace evidence is placed into individual sterilized containers or paper bags, labeled, and taken to the forensic lab for analysis.

The first step in the forensic trace evidence analysis process is the visual examination. Each piece of evidence is visually inspected, with the notes written down. Detailed information must be kept about each inspection done on the sample, so that peers may be able to draw logical conclusions from the records. Once the visual information is recorded, the analyst can begin the microscopic analysis. This type of analysis can show details unavailable to the naked eye, such as composition and morphology of the sample. In the case of gunshot residue, it can lead to the vital information needed in solving a case.

Since the late 60’s, scanning electron microscopes have been used for gunshot residue analysis. Typically, these SEMs are equipped with an energy dispersive spectroscope, used for elemental analysis, and a software program capable of automated detection. Using the SEM to detect the components and morphology of the residue helps determine what type of material was left behind, which can lead to the reconstruction of the bullets and ultimately the crime scene.

The Aspex Personal Scanning Electron Microscope (PSEM), when coupled with the Aspex GSR™ reporter software, becomes an all-in-one GSR analysis machine. This fully integrated SEM-EDS system that can detect, relocate, and confirm the presence of gunshot residue is typically employed throughout modern-day forensic laboratories. Templates are available that comply with American Society for Testing and Materials (ASTM) E1588, or templates can be created for more precise information gathering in the forensic lab and customized for your specific lab. Since the PSEM is fully automated, the chance of false positives or contamination by handling remains low.

Reference:

Aspex, http://www.aspexcorp.com/products/gsr.html,http://www.aspexcorp.com/industries/forensics.html

ASTM, http://www.astm.org/JOURNALS/FORENSIC/PAGES/3938.htm

Wikipedia, http://en.wikipedia.org/wiki/Trace_evidence

GSR Trace Evidence System Using SEM

tricia — Fri, 05 Jun 2009 14:24:00 +0000

Gun Shot Residue (GSR) consists of particles from the explosive primer, both burnt and unburnt, as well as the propellant, bullet fragments, the casing and the firearm used. When the gun is fired, the pressure from the bullet leaving the muzzle forces the debris out of the barrel at a high velocity, and scatters the debris in a cone-shaped pattern. Since it is a mix of all parts involved, it is a highly-specific tool in aiding forensic laboratories piece together a crime. These fragments and debris can be analyzed, providing information such as bullet and gun type, distance to target, or shooter conformation by comparing to known evidence samples.

Modern forensic laboratories rely on Scanning Electron Microscopes (SEM) with Energy Dispersive X-ray Spectrometry (EDS) technology to analyze GSR. Most GSR contains lead, antimony and barium, though some newer primers are lead-free. Thus, the best way to assess if the debris was GSR remains is to be analyzing the elemental composition and comparing it to known GSR characteristics as well as other evidence found at the scene. SEMs are able to analyze these particles for morphology and elemental composition without destroying the sample, unlike some other methods of GSR analysis previously used, allowing the analyst to evaluate the same sample multiple times if necessary.

In order to present the forensic community with a fast, accurate, non-invasive method to analyze GSR, Aspex has created a GSR software package for its Personal Scanning Electron Microscope (PSEM), making it a complete SEM/EDS system with a software suite designed specifically for high throughput GSR™ analysis. The GSR software has templates compliant with the American Society for Testing and Materials (ASTM) E1588 – Standard Guide for Gunshot Residue Analysis by Scanning Electron Microscopy/ Energy Dispersive X-ray Spectrometry, or the analyst can create templates for specific analytical needs.

The GSR Reporter software works with the Automated Feature Analysis (AFA) platform to assess the chemical and morphological makeup of the given sample. Since the PSEM is a fully-automated SEM/EDS system, contamination during the analysis is virtually nonexistent, as long as proper attention is paid when collecting and transferring the sample prior to and after the analysis.

Today, GSR analysis is a vital tool for crime units, allowing them to literally place the gun in the shooter’s hand in some cases. By analyzing particles for morphology and elemental composition, and comparing with other evidence found at the crime scene, analysts can recreate the scene and present solid evidence in court. The Aspex PSEM with GSR Reporter software is a complete GSR trace evidence system, providing forensic analysts with accurate results with minimal sample handling.

Reference:
Aspex, http://www.aspexcorp.com/industries/forensics.html
Wikipedia, http://en.wikipedia.org/wiki/Gunshot_residue
ASTM, http://www.astm.org/Standards/E1588.htm
FirearmsID, http://www.firearmsid.com/A_distanceGSR.htm