Geological Society of America

6 Getting a Better Handle on the “Dirt” Covering the Bedrock—Mapping and Dating of Surficial Deposits

Monday, 11 May 2009
1:00 PM - 5:00 PM

LASER-INDUCED BREAKDOWN SPECTROSCOPY: A NEW PARADIGM IN GEOCHEMICAL ANALYSIS

Paper number: 6-8
Program: Theme Sessions
Time: 3:00 PM – 3:20 PM

Authors

Nancy McMillan Presenting Author
New Mexico State University, Las Cruces, NM
Brittani McNamee
University of North Carolina - Asheville, Asheville, NC
Emerlene Aragon
New Mexico State University, Las Cruces, NM
Matthew Dawkins
New Mexico State University, Las Crcuces, NM
Austin Hanson
New Mexico State University, Las Cruces, NM
Mary Hernandez
New Mexico State University, Las Crcuces, NM
Tristan Likes
New Mexico State University, Las Cruces, NM
Carlos Montoya
New Mexico State University, Las Cruces, NM
Patrick Montoya
New Mexico State University, Las Crcuces, NM
T.J. Sadler
New Mexico State University, Las Crcuces, NM

Abstract

Laser-Induced Breakdown Spectroscopy (LIBS) is a relatively new, instantaneous, minimally-destructive laser ablation geochemical analysis technique that has potential to add new dimensions to geochemical investigation. In LIBS, a pulsed laser is focused on a sample surface (solid or liquid, but gases can also be analyzed). The energy ablates a small amount of material, which forms a short-lived plasma. As the plasma cools, excited atoms emit photons in the UV-VIS-IR range (200 – 1000 nm) as electrons decay to lower-energy orbitals. The light is collected by an optic fiber, diffracted, and displayed as a spectrum. LIBS' advantages are that analyses : 1) are minimally destructive (similar to laser ablation ICP-MS, with spot sizes as small as 10 microns); 2) are instantaneous (the analysis requires no sample preparation and is complete in less than a second); 3) can be performed by a portable or remote unit; and 4) each potentially contain information from every element. Because of these characteristics, LIBS can be employed in field mapping situations, in analysis of tiny and valuable materials, and in situations where geochemistry is a part of the real-time decision-making process.

Immediate analysis with no sample preparation has its drawbacks. Precision is only fair. However, LIBS excels at distinguishing the chemical differences between two materials because concentrations of essentially all elements present in the sample are recorded. To overcome the precision issue, many spot analyses are averaged (>100) to create a single spectrum, and data are interpreted through Principal Component Analysis (PCA).

The NMSU LIBS lab is exploring LIBS applications in geology, including whole-rock analysis, correlation of ash flow tuffs, quantitative analysis of Li, analysis of S in coal, analysis of crude oil, the stoichiometry of ablation, rapid analysis of highway aggregate to control the amount of unwanted material, and gem analysis. Both nano-second and pico-second lasers are being used.