Effect of accelerating voltage on beam damage of asbestos fibers in the transmission electron microscope (TEM)

Our plain-English summary of Effect of accelerating voltage on beam damage of asbestos fibers in the transmission electron microscope (TEM), by J. Martin, M. Beauparlant, S. Sauvé, et al (Micron, 2017).

The study

• Authors: J. Martin, M. Beauparlant, S. Sauvé, G. L'Espérance
• Journal: Micron
• Published: 2017;96:1-8
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Transmission electron microscopy (TEM) is a powerful and efficient tool for the analysis of asbestos fibers. Although this analysis technique is common and several standard methods exist for asbestos analysis, questions remain about the optimal conditions to be used. Because asbestos fibers are relatively sensitive to the electron beam, it is important to better understand the phenomena of damage in order to avoid them. This study specifically investigates the effect of the acceleration voltage on damage to four different types of asbestos fibers: chrysotile, amosite, crocidolite and anthophyllite. The results support the conclusion that, contrary to what is usually recommended, it is best to use an acceleration voltage of 200kV rather than 100kV in order to avoid damage. The findings shed light on possible damage mechanisms, the most predominant of which seems to be caused by an induced electric field.

Copyright © 2017 Elsevier Ltd. All rights reserved.

In plain English

This laboratory study tested how the voltage of a transmission electron microscope (TEM) affects beam damage to asbestos fibers during analysis. It did not study people or health effects. The authors examined 34 fibers from standard reference samples: 10 amosite, 9 anthophyllite, 7 crocidolite and 8 chrysotile. Along each fiber they used X-ray analysis (EDS) to measure the intensity ratio of magnesium to silicon, plus sodium to silicon for crocidolite, at 100 kV and at 200 kV. At beam intensities that did not cause damage, voltage did not appear to affect these ratios. At a damaging current density of 200 A/cm2, the ratios dropped considerably less at 200 kV for 28 of the 34 fibers. Measured ratios were 23%, 27% and 30% higher at 200 kV for amosite, anthophyllite and crocidolite. For chrysotile the gain was 7%, or 22% at a lower current density of 100 A/cm2. No correlation was observed between fiber diameter and the amount of damage in the fibers tested, and the authors said more precise testing was needed. The authors concluded that, contrary to usual recommendations, 200 kV is better than 100 kV for avoiding damage.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment using transmission electron microscopy on asbestos reference samples (published as a tutorial); no human subjects
• Who was studied: 34 individual asbestos fibers from Union for International Cancer Control (UICC) standard reference samples: 10 amosite (Penge mine, South Africa), 9 anthophyllite (Paakkila mine, Finland), 7 crocidolite (Koegas mine, South Africa) and 8 chrysotile (Chrysotile B, from eight Canadian mines)
• Exposure: Electron beam irradiation in the microscope at accelerating voltages of 100 kV and 200 kV, at increasing current densities. The four fiber types were amosite, anthophyllite, crocidolite and chrysotile. Damage was tracked using EDS X-ray intensity ratios (Mg/Si, and Na/Si for crocidolite).
• Main results:
  • At current densities that did not cause damage, the accelerating voltage did not appear to affect the measured intensity ratios
  • At a current density of 200 A/cm2, for 28 of 34 fibers the Mg/Si and Na/Si intensity ratios dropped considerably less at 200 kV than at 100 kV
  • Using 200 kV instead of 100 kV increased the measured intensity ratios by 23% for amosite, 27% for anthophyllite and 30% for crocidolite
  • For chrysotile, the Mg/Si ratio improved by 7% at 200 A/cm2 and by 22% at a lower current density of 100 A/cm2
  • Five of the eight chrysotile fibers were less damaged at 200 kV than at 100 kV
  • In the fibers tested, using the Mg/Si intensity ratio as the damage indicator, no correlation was observed between the degree of damage and fiber diameter. The authors said more precise testing was needed.
  • In a chrysotile fiber profile taken at 200 kV, magnesium appeared to be expelled from the beam-damaged area and found in larger amounts at its edge
• The authors' conclusion: The authors concluded that, contrary to what is usually recommended, it is best to use 200 kV rather than 100 kV to avoid beam damage to asbestos fibers. They also concluded that the predominant damage mechanism results from ionization processes.
• Limitations the authors state:
  • Amphibole fibers are not always cylindrical, so the diameter used as a stand-in for thickness is not always precise
  • The intensity ratio is only one possible indicator of damage, so some structural changes may have gone unnoticed
  • The possibility that damage is independent of sample thickness, within the range of thicknesses observed, needs more precise testing
  • For very fine chrysotile fibers, damage may already have been under way when the fibers were first measured
  • Further experiments are needed to confirm the atomic processes involved

Topics

Medical terms in this study, explained in our Lexicon: Transmission Electron Microscopy (TEM), Chrysotile, Amosite, Crocidolite, Anthophyllite.

Related studies

• Effect of temperature on beam damage of asbestos fibers in the transmission electron microscope (TEM) at 100kV — J. Martin, M. Beauparlant, et al. (2017)
• On the threshold conditions for electron beam damage of asbestos amosite fibers in the transmission electron microscope (TEM) — J. Martin, M. Beauparlant, et al. (2016)
• Quantitative assessment of inorganic fibrous particulates in dust samples with an analytical transmission electron microscope — F.D. Pooley, N.J. Clark (1979)
• Preparation of extrapulmonary tissues and body fluids for quantitative transmission electron microscope analysis of asbestos and other mineral particle concentrations — P.M. Cook (1979)
• The interactions between asbestos fibers and metaphase chromosomes of rat pleural mesothelial cells in culture. A scanning and transmission electron microscopic study — N.S. Wang, M.C. Jaurand, et al. (1987)
• Assessment of occupational exposure to asbestos fibers: Contribution of analytical transmission electron microscopy analysis and comparison with phase-contrast microscopy — C. Eypert-Blaison, A. Romero-Hariot, et al. (2018)

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