What’s cooler than a Enzo Ferrari?

September 18, 2012

“Fall, leaves, fall; die, flowers, away;

Lengthen night and shorten day;

Every leaf speaks bliss to me

Fluttering from the autumn tree.”

As I make my way into the office now, no longer the tepid humidity of the summer embrace, instead the last death throes of the season now evident through every falling leaf on my path to work. It would have to come from the written work of Emily Brontë to capture the passing of the summer into autumnal bliss and the inexorable return of the undergraduates. The corridors of Queen’s grow larger with the heave of fresh faced, wide-eyed freshers, with palpable anticipation of the great beyond, of university life. Unfortunately for me, the face is no longer as fresh, the eyes grow dimmer by the week and anticipation has been replaced by routine, endless routine! However, there does come some moments which seem to capture the imagination in a manner as equivocal to that of the eighteen-year-old leaving home for the first time, however it does require more bells and whistles than the surprise of mid-week drinks offers and cheap pasta. It does however involve the explanation of X-ray fluorescence (XRF) and finishes with work to commence on one of the most advanced pieces of technology in Ireland!

X-ray fluorescence (XRF) is now a well-established technique for the detection and quantification for elemental analysis and for trace amounts of heavy metals. In its simplest form, a sample is irradiated by a beam of X-rays which are generated from a sealed tube with either a tungsten or molybdenum cathode. This beam of X-rays displaces orbital electrons in the atoms of the sample being irradiated, and the vacant positions along these orbitals are thus immediately filled by other electrons which jump from a higher energy level (i.e. they’re on another orbit, the see that an electron has been knocked out of a lower orbit and decide to take up that space on the lower orbit). When the electron from the outer shell moves into the lower energy shell, a quantum of energy is released, which, happens to be characteristic for each element on the periodic table (usually you’re looking at elements that are heavier than fluorine right through to lead and possibly bismuth, after that you’re into Mössbauer spectroscopy). The process of XRF is demonstrated in the figure. Quantifying elemental concentration in a sample is a lengthy and altogether precarious process as results in XRF are given as X-ray intensities in the form of counts per second (CPS). However, if properly used XRF can offer very high resolution determinations of sediment geochemical profiles, which is always a good thing!

With this in mind I’ve embarked on a mission to retrieve some of the best geochemical datasets on the new cores collected from the Sundarbans last November. Teaming up with colleagues back in Dublin, half sections of the three new cores were transported down to School of Geography, Planning and Environmental Policy, University College Dublin for ITRAX^TM core scanning. The ITRAX^TM core scanner takes high resolution radiographic and optical images at the same time as XRF measurements are retrieved. It has a flat X-ray beam with a measurement area of 100 µm x 4 mm (or 200 µm x 8 mm), rather than a spot beam system in order for the averaging of grain-to-grain variation along the horizontal core axis. Results are presented as spectral peak areas or counts per second (cps) and can be calibrated to concentration, although this may be cumbersome in some sediments due to the high variability in matrix factors (i.e. the impact of water content, organic matter content, mineral crystallinity, all have a major impact on the concentration and calibration of various elements). However, ways of calibrating the data involve expressing count data as elemental ratios or plotting XRF curves together with discrete sampling analyses carried out with destructive techniques such as inductively-coupled plasma (ICP-OES/MS) or atomic absorption spectroscopy (AAS). Given the nature of such muddy-silty sediments, structural features such as bedding planes and laminations are not always evident, thus the ITRAX^TM core scanner also provides high-resolution X-radiographs in order to photograph these ‘invisible’ sedimentary structures.

Some people will go into science for the sheer curiosity of nature, some go in for profit margins, and some go in for the opportunity to use really cool equipment… I think I’m more inclined to say that I love using cool equipment and you really can’t get cooler than operating an instrument that costs more than an Enzo Ferrari (attached image), so well-built was this model of Ferrari that they named it after the company founder! Let the undergrads keep their cheap drink and pasta!

Till next time folks!

Rory Flood, PhD Student, Queen’s University Belfast, School of Geography, Archaeology and Palaeoecology (GAP), http://www.qub.ac.uk/schools/gap/