itrax: description and evaluation of a new multi-function

ITRAX: description and evaluation of a new multi-function

X-ray core scanner

IAN W. CROUDACE1, ANDERS RINDBY2 & R. GUY ROTHWELL1

1National Oceanography Centre, Empress Dock, Southampton SO14 3ZH, UK2Cox Analytical Systems, Ostergardsgatan 7, SE-431 53 Molndal, Sweden

Abstract: A new automated multi-function core scanning instrument, named ITRAX, hasbeen developed that records optical, radiographic and elemental variations from sedimenthalf cores up to 1.8m long at a resolution as fine as 200mm. An intense micro-X-ray beamfocused through a flat capillary waveguide is used to irradiate samples to enable both X-radiography and X-ray fluorescence (XRF) analysis. Data are acquired incrementally byadvancing a split core, via a programmable stepped motor drive, through the flat, rectangu-lar-section X-ray beam. Traditional XRF determination of element composition in sedimentsprovides high-quality data, but it takes a considerable time and normally consumes gramquantities of material that is often only available in limited quantities. The ITRAX corescanner non-destructively collects optical and X-radiographic images, and provides high-resolution elemental profiles that are invaluable for guiding sample selection for further(destructive) detailed sampling. This paper presents a description of the construction,characteristics and capabilities of the ITRAX system. High-resolution ITRAX data obtainedfrom sediment cores are also presented and compared with results from traditionalwavelength-dispersive XRF analysis at lower resolution. Finally, some recent technicaldevelopments linked to the second-generation ITRAX are presented.

Elemental and other sediment property variationsalong core profiles can be used to infer environ-mental, sedimentological and diagenetic changes,pollution inputs and to assist in correlationstudies. Traditional methods of acquiring solid-phase geochemical data from sediment cores aretime-consuming and involve incremental samplingto obtain gram quantities of material and furtherprocessing before analysis by techniques such asX-ray fluorescence (XRF) analysis. ConventionalXRF analysis requires dried and ground sedimentand two sample preparation methods are com-monly used (Croudace & Williams-Thorpe 1988;Croudace & Gilligan 1990; Jenkins 1999). Thefusion method produces a solid solution in theform of a glass bead by dissolving about 0.5 g ofsample in a lithium borate flux for determinationof major and the more abundant trace elements.The pelletization method utilizes at least 3 g ofground sample, pressed into a briquette at 15–20tonnes, and allows major and trace elements tobe determined. Notably, material from theseXRF pellets may be re-used for other analyses ortests. In conventional XRF analysis grinding andpelletization of samples reduces mineral andparticle-size effects and density variations whilethe fusion variant circumvents particle-size andmineralogical problems and reduces inter-elementeffects by dissolving the sample and providing aconsistent matrix. The entire preparation and

analytical process for a 1m core subsampled at1 cm increments would take up to 2 weeks.

Non-destructive scanners that incorporateXRF analysis provide useful, high-resolution geo-chemical records from terrestrial and marine sedi-ment and drilled rock cores (e.g. Jansen et al. 1998;Rothwell et al. 2006;Thomson et al. 2006). Particlesize, mineralogy and density effects will exist incores, and direct analysis will lead to some degra-dation of data quality compared to the well-controlled approaches used in the conventionalXRF analysis procedures above. Some of thenew scanners do, however, allow relatively rapidand continuous analysis of split sediment coresto provide records of downcore geochemical andtextural variations. At present these instrumentsgenerally serve the valuable role of providinginitial detailed characterization of sedimentcores. Sections of interest can then be analysed athigher accuracy (although generally at poorerspatial resolution) using well-established, variablydestructive methods such as XRF analysis orinductively coupled plasma optical emissionspectroscopy.

The ITRAX core scanner

The ITRAX core scanner (Fig. 1) is uniqueamong the current generation of core scanners

From: Rothwell, R.G. 2006. New Techniques in Sediment Core Analysis. Geological Society, London,Special Publications, 267, 51–63. 0305-8719/06/$15.00 # The Geological Society of London 2006.

in being designed to gather optical and micro-radiographic images and micro-X-ray fluores-cence spectrometry (mXRF) elemental profilesfor the same sediment core section. It can operateon split cores of sediment or rock with a maxi-mum length of 1800mm and a diameter rangingfrom a few cm up to 12 cm. The instrument con-sists of a central measuring tower incorporatingan X-ray focusing unit and a range of sensors.These sensors include an optical-line camera, alaser topographic scanner, an X-ray line camerafor measuring the transmitted X-rays and ahigh count-rate XRF detection system. Furtherinformation on the technology incorporatedinto the ITRAX scanner is available from theliterature (Rindby et al. 1997; Vincze et al. 1998;Janssens et al. 2000; Streli et al. 2004; Tsuji et al.2004). On either side of the tower are two fixedprojections that are part of the motorized split-core transport bed. ‘Flat-beam’ scanning technol-ogy (Bergstrom et al. 2001) is used to providehighly resolved, two-dimensional radiographicimages and profiles of XRF spectral data overthe selected sample length. The system is fittedwith numerous safety interlocks to ensuremechanical and radiological security.

Scanning procedure and control software

The ITRAX scanner is controlled from a centralcomputer that runs on a Windows XP platform.Users control the system through a graphicaluser interface called the Core Scanner Navigatorwhere standard operation procedures can be

implemented and monitored (Table 1). Asecond program, Q-Spec, interacts with thisinterface and is activated automatically duringcertain operations. Q-Spec is primarily con-cerned with the display and on-the-fly analysisof XRF spectral data, but it can also be used torefine the X-ray spectral analysis after core scan-ning on the instrument is complete.

The standard ITRAX procedure starts byloading a split sediment core onto a horizontalcradle with the core-top positioned to the right.Scanning is initiated from the software and fol-lows a logical and guided sequence involvinginputs: (i) to define the core length to be scanned;(ii) setting the excitation voltage and current tothe X-ray tube; and (iii) initiating a surface topo-graphic scan of the core. This topographic scan ismade in relation to a horizontal reference planeand is used to ensure that any subsequent posi-tioning of the XRF detector does not lead to a col-lision of the detector with the sediment surfaceand, importantly, that the detector–sample dis-tance is monitored and remains constant. Thescanning occurs by a regular left to right incre-mental movement of the core perpendicular tothe long axis of the rectangular beam (Fig. 2).This initial scan takes approximately 5 min afterwhich the core is automatically returned to itsstart position. The next procedure (iv) involvesdefining the likely elements in the sample from aperiodic table as well as adjusting and refiningthe peak-fitting parameters using one or morerepresentative parts of the core sample. This opti-mization takes place with the operator ensuring

Fig. 1. Front view of the ITRAX core scanner with open hoods. Split core sections are moved incrementallyfrom the left extension to the right extension during analysis.

52 I.W. CROUDACE ET AL.

that the best peak-fitting functions are chosen.The next step (v) is to record a reference responsefor the X-radiographic detector by automaticallydriving the core out of the path of the X-raybeam. This step calibrates and normalizes theresponse of the X-ray line camera diode arrayand takes approximately 1 min after which thecore is returned to its start position. The finalstep in the Navigator panel is (vi) to enter theBatch Analysis Mode where the user defines the

core name, reviews instrument count times,dwell times and scan limits before starting thescan process. The first operation of the ensuingautomated process is to acquire and constructthe X-radiographic image, after which the coreagain returns to the start position and thenbegins the incremental acquisition of XRF ele-mental profiles. The XRF spectral data are allstored and can, if necessary, be re-processed andrefined by the user after scanning is complete.Such re-analysis may be required if the user hasneglected to include an element for output or ifsome further refinement to the background orpeak-fitting process is deemed necessary. Astraightforward facility exists for efficiently repro-cessing a batch of spectra.

XRF spectral analysis software

The Q-Spec spectral analysis software employsstandard fitting procedures to extract the indivi-dual elemental peak areas from the spectrum.Each peak is described by a Gaussian functionwith an exponential tailing on the low-energyside with a step-like background function. Thegeneral spectral background is described with amulti-parameter function including polynomialas well as exponential terms. As previouslymentioned, the operator selects from a periodictable the elements to be extracted from the X-ray spectra. Any incorrect or unnecessary ele-mental choices or incorrect fitting parameterscan be adjusted later through a batch-controlledpost-processing of the spectra.

Table 1. Summary of typical ITRAX operator procedures

Operator task or input Result

Load split sediment core on to horizontal sample cradle Sample ready for scanning

Define kV and mA setting for 3 kW Mo X-ray tube Excitation condition set

Define core dimension to be scanned Dimensional limits set for scanning

Initiate surface scanning/photographic procedure(approximately 5min)

Surface topography profile determined and digitalphotographic image of core captured

Enter the scan increment size and the dwell time for theradiographic scan

Radiographic parameters set ready for the radiographicscan

Establish XRF parameters and select the elementslikely to be present

Elements selected and spectral-fitting parametersrefined

Set reference response for the radiographic camera byautomatically removing the core from the X-ray beam

Calibration of the X-ray line camera diode array

Enter dialogue menu where data file storage locationsare named and the XRF count time defined

Automated process commences with the acquisition ofan incremental (digital) radiographic scan. The core isthen returned to zero ready for next stage

Instrument commences XRF analysis Incremental XRF scans acquired and stored

A

B

C

D

E

FFig. 2. Schematic of the ITRAX system showing theoptical-line camera (A), laser triangulation system(B), motorized XRF Si-drift chamber detector (C),3 kW X-ray tube (D), flat-beam X-ray waveguide (E)and the X-ray line camera and slit system for theradiographic line camera (F). The horizontal arrowshows the incremental motion direction of a core andthe vertical arrows the movement directions of theXRF detector.

THE ITRAX CORE SCANNER 53

Instrumental components

Optical camera system. An optical-line camerasystem is used to generate good-quality RGBdigital images of the sediment sample surfacebefore the X-ray scan. The line camera incorpo-rates a light-sensitive 2048 pixel CMOS (comple-mentary metal oxide semiconductor) device thathas a maximum resolution of 50mm pixel�1.The optical image is available to allow the opera-tor to define the part of the sample to be analysedbefore scanning, and later serves to relate theradiographic and XRF data to visual colourfeatures of the sediments.

X-ray source and focusing. The ITRAX uses a3 kW X-ray generator and can be used with dif-ferent tube anodes to obtain excitation for arange of elements. The current system uses a3 kW molybdenum target tube that can operateup to 60 kV and 50mA, but the actual voltage–current selected can be optimized for theelements required. In practice 30 kV and 30mAare suitable for most elements. The X-raysemerging through the shutter of the tube turretare focused by means of a proprietary flat-beam optical device (not a collimator), generat-ing a 20� 0:2mm rectangular beam with itslong axis perpendicular to the sample main axis.

X-ray line camera. Adigital X-ray line camera isused for recording the intensity of X-radiationtransmitted through the sample. The camera,which consists of a linear arrangement of 1024X-ray sensitive diodes, has a pixel resolution ofapproximately 20mm and can operate with expo-sure times from 20ms up to several seconds. Theimages produced by the ITRAX are ‘radiographicpositives’, so that low-density areas appear lightand higher density areas appear darker.

The XRF detection system

Reliable XRF analysis requires that the sample–detector distance is kept constant and the ITRAXachieves this by using a laser triangulation systemto measure the topography of the sample surface.The XRF detector (Fig. 2), fitted to a verticalmotorized stage, adjusts itself according to thetopographic scan data previously acquired. TheX-ray detector used is a Si-drift detector (SDD).These are proportional solid-state devices thathave the advantage of providing high-energy reso-lution at high count rates but do not require liquidnitrogen cooling, unlike the alternative Si(Li)detectors (Lechner et al. 2001). The combinationof the SSD, the associated electronics and thedigital multi-channel analyser (MCA) allow

count rates up to 70kcps to be handled withonly minor degradation in resolution. The SDDoperates in a similar manner to a conventionaldrift chamber. Thus, the electron cloud generatedby X-ray quanta absorbed at the surface in theSDD is guided onto a specific readout site onthe device. In this way the SDD is analogous toan antenna for X-ray photons. The detector isalso fitted with a pumped acrylic nozzle with athin plastic entrance window to minimize the X-ray attenuation that would otherwise occur withabsorption in the air passage between the samplesurface and detector.

Conventional X-radiography

Until the advent of digital X-ray cameras, photo-graphic film was used to record images. If thesample is thin and the X-ray source is smallenough, each point in the recording device willcorrespond to a single point in the exposedsample (point-projection radiography). If, how-ever, the source has a finite size there is nolonger a simple point-to-point relationshipbetween the recording device and the object. Inprinciple, the structure in the exposed objectwill be affected by the source size. Structures inthe object that are much smaller than thesource size will appear blurred in the radiograph,but for structures that are much larger than thesource the finite source size will manifest itselfin a diffuse zone around the structure termed apenumbra (shadow). The penumbra phenom-enon is normally considered to set the ultimatelimit of resolution in point-projection radiogra-phy. The size of the penumbra is related to thesource size and the ratio of the distances(object–camera)/(X-ray source–object). Forthick objects, image distortions will also occurbecause of geometrical aberration generatedfrom rays penetrating the objects far from theoptical axis as these rays will penetrate theobject off the perpendicular direction. Thus, den-sity gradients that appear perpendicular to theoptical axis will only appear sharp in the radio-graph close to the optical axis, while furtheraway they will become smoothed out due tothis geometrical effect. These phenomena are sig-nificant limitations in recording radiographsfrom extended objects, particularly for objectsextending in the same direction as the densitygradient to be investigated. This might be thecase for cores from trees or sediments wherethe main interest is to investigate the density var-iation along the length axis. Another source ofdistortion for thick objects is from forward-scat-tered Compton (incoherent) radiation that is alsorecorded with the transmitted radiation. For


thinner objects the problem is less severe as for-ward Compton scattering is substantiallyreduced, but the forward Rayleigh (coherent)scattering component will still degrade spatialresolution.

Benefits of ITRAX flat-beam radiography. Oneway to avoid the problems of geometrical aberra-tions and blurring from scattered radiation is tocombine a narrow, parallel, high-flux X-raybeam with an X-ray line camera, and to recordthe radiograph by moving the object in a regularincremental manner. The use of a high-flux beamallows the line camera to record transmitted sig-nals with relatively short dwell times per incre-ment. The ideal movement direction of theobject is parallel to the axis of the density gradi-ent (e.g. perpendicular to sediment layering).Radiographic images are built up by successivelyadding the recorded radiographic information,line by line, while new areas of the samplemove through the beam. By using a narrow(adjustable) slit between the object and the linecamera the geometrical aberration and the con-tribution of scattered radiation can be reducedto practically zero, particularly in the verticaldirection. The spatial resolution in the verticaldirection is set by the width of the slit in frontof the X-ray line camera, and the resolution inthe horizontal direction is set by the size of theindividual pixels in the diode array.

ITRAX radiographic resolution. The resolutionand contrast in radiographic images is relatedto the type of X-ray source used. The 3 kW MoX-ray tube commonly used produces sufficientenergy at 55 kV for transmission through split-core samples of 10 cm diameter. For thinnercore samples lower X-ray energies from a Cu orCr tube could also be used effectively for specific

applications. During factory set-up the radio-graphic resolution and contrast are evaluatedusing a 1 cm-thick parallel slab of finely lami-nated sediment, an 11 cm-thick layered sedimentand an aluminium block with 15 sharp steps. Theresolution is estimated by comparing the sharp-ness of the intensity rise corresponding to theeach step in the aluminium block while the slitwidth was gradually reduced. When no furtherincrease in sharpness is observed when reducingthe slit width, the resolution corresponds to theactual slit size. Resolution is also recorded byestimating the minimum size of significantlayers in the radiographs from the two sedimentsamples while reducing slit width in the samemanner described above. The results show thatfor thin samples the ultimate resolution achiev-able is about 20mm, while for approximately11 cm-diameter split-sediment cores the ultimateresolution is about 100 mm. Some examples ofimage quality and resolution are shown inFigure 3 for a range of sample types.

ITRAX XRF analysis

XRF elemental detection limits are related to thetype of X-ray source used, and the 3 kWMo tubeis well suited for working on split-core samples asit produces good excitation for a range of ele-ments of environmental interest. Enhanced exci-tation for the lower Z elements may be achieved,at the cost of poorer excitation of the medium Zelements, by using a Cu or Cr tube. However, theregular changing of tubes is preferred to beavoided due to the inconvenience of dismantlingand re-instating the water-cooling circuitry. Inpractice, a single Mo tube is adequate and agood range of elements can be obtained whenoperating at 30 kV and 30mA.

A

B

C D

Fig. 3. Examples of ITRAX X-radiographic images from a variety of sediments: (A) laminated sediment core(200mm length); (B) a 25mm detail (left of centre) from (A); (C) a Moroccan laminite (3 cm in length); and(D) North Sea layered sandstone reservoir rock (5 cm in length). All images are 20mm wide.


ITRAX XRF sensitivity

The sensitivity of the XRF system was evaluatedusing various international reference samples;United States Geological Survey (USGS)marine sediment MAG-1, USGS manganesenodules NOD-A-1 and NOD-P-1, USGS GreenRiver Shale SGR-1 and US National Instituteof Standards and Testing (NIST) BorosilicateGlass 1411. Samples from these materials

(except the NIST glass) were prepared as dry,pelletized briquettes and measured on theITRAX. The detection limits were defined asthe elemental concentration corresponding to apeak area equivalent to three times the squareroot of the average background at the peakposition. For a given sample composition, thedetection limits vary substantially across the X-ray energy range according to tube anode, tubevoltage, count rate and sample composition, as

Table 2. Comparison between ITRAX and conventional WD-XRF

ITRAX Conventional WD-XRF

Services required Three-phase power, watercooling

One- or three-phase power,water cooling

Typical X-ray tube used 3 kW Mo or 2.4 kW Cu 4kW Rh

High resolution X-radiography provided Yes No

Optical image provided Yes No

X-radiographic spatial resolution(selectable)

�100mm Not possible

Potential to add other sensors to the scanner Yes Unlikely

Time to acquire optical image X-radiographdata for a 1m core at 200mm resolution

0.5 h Not possible

Sample treatment and preparationrequirement

Non-destructiveFlat exposed surface needed6mm polypropylene film used toinhibit drying during analysis

Semi-destructive (pellets) ordestructive (beads)Requires 3 g or more of sample;involves subsample removal,drying, grinding andpelletization

Vacuum system required for XRF analysis Limited option Yes

Helium system option available for volatileor powder samples

No Yes

Practicable scanning resolution �100mm 5000mm

Time to acquire data for a 1m core at 200mmscanning increments for selected elements(K, Ca, Fe, Sr)

2 h 10 working days(for 100 sample at 1 cmresolution)

Time to acquire data for a 1m core at 200mmscanning increments (e.g. Si, Al, K, Ca, Ti,Fe, Mn, Zn, Sr, Zr)

15 h 10 working days

Time to acquire data for a 1m core at 200mmscanning increments (e.g. Si, Al, S, Cl, K, Ca,Fe, As, Pb, Zn, Br, Rb, Sr, Zr)

48 h 10 working days

Elemental capability for an argillaceoussedimentElemental capability for a carbonatesediment

Si, Al, S, Cl, K, Ca, Ti, Fe, As,Pb, Zn, Br, Rb, Sr, Zr, BaCl, Ca, Ba, Fe, Zn, Br, Sr

Na–U

Na–U

Nominal detection limits (100 s); see Table 3Dependent on tube anode, excitationconditions, count-time, atomic number andsample composition

150 ppm for Ti10 ppm for Sr

10 ppm for Ti0.5 ppm for Sr

General analytical data quality for sediments Good for elements namedabove and particularly for fine-grained materials

High for most elements becauseof highly controlledpreparation approach


is well established in XRF analysis (Jenkins1999). For indicative purposes the detectionlimits were recorded with a Mo-anode X-raytube operating at two different voltages and cur-rent, optimized for medium–heavy elements andlighter elements, respectively (Table 2). It is note-worthy that wet and organic-rich sedimentmaterial may be associated with poorer detectionlimits caused by the less efficient excitation of ele-ments because of increased scattering, but grainsize and degree of compaction may also affectresponse.

Second-generation ITRAX

The prototype ITAX core scanner output all thedata as peak area integrals for elements. Furtherdevelopments allowed quantitation of the countdata, and comparison of these integrals withquantitative WD-XRF data (Figs 4 & 6, later)shows that there is a good correlation betweenthe profile shapes obtained with the two tech-niques – except in some situations where X-rayabsorption/enhancement effects become appar-ent with the ITRAX data. One clear example ofthis is shown in figure 4 of Thomson et al.(2006) where the sapropel layer (S1), which isrich in sea water and organic matter, shows alower K/Ti than the main trend. This responseis an XRF inter-element effect caused by thesea-water chlorine atoms absorbing the potas-sium K� X-rays. Had the count-rate data beenconverted to concentrations then the lower K/Ti dip shown should not occur as inter-elementcorrections would have been applied.

XRF elemental sensitivity

The second-generation ITRAX shows a signifi-cant improvement in the overall XRF elemental

sensitivity, particularly for Si and above (Table3). Al sensitivity has also been improved butremains rather imprecise at the present time.The enhancement in response has been achievedby adjusting the orientation of the X-raycapillary optic to allow greater transmission ofthe primary bremmstrahlung, thereby providingimproved excitation to the lower atomicnumber elements without detriment to theheavier elements. Additional improvementsarise from developments with the detector pre-amplifier and counting electronics that allowhigher count rates without significant loss ofenergy resolution.

0 5 10

Depth (cm)

Con

cent

ratio

n (p

pm)

0

20

40

60

80

100

120

140

15 20 25 30 35 40 45 50

Depth (cm)0 5 10 15 20 25 30 35 40 45 50

050

100

150

200

250

300

350

400

450

500

Zn160 Pb

Fig. 4. Comparison between WD-XRF and ITRAX (second generation) data for a laminated sediment fromthe Newport Deep (NPD7), Severn Estuary, UK. The dots represent contiguous samples 1 cm thick analysedusing WD-XRF and the continuous red line is the ITRAX profile obtained on the split core.

Table 3. ITRAX detection limits for ITRAXinstruments

ITRAX(Prototype)

ITRAX(Secondgeneration)

Improvementfactor

Voltage 45 kV 30 kVCurrent 40mA 40mAAl not detectable 22 000ppm –Si 33 000 ppm 9000 ppm 4�K 450 ppm 150ppm 3�Ca 200 ppm 100ppm 2�Ti 120 ppm 60ppm 2�Mn 40ppm 25ppm 2�Fe 60 ppm 25ppm 2�Rb 10 ppm 5ppm 2�Sr 10 ppm 5ppm 2�

The data are based on measurements usinginternational geochemical reference samples USGS-MAG1 and USGS-SGR1.Note that wet sediment may be less efficiently excitedowing to less compaction, higher water content andgrain-size issues.Measurement time is 100 s.


XRF analysis software

A refined ‘XRF fundamental parameters’ modelis now used in Q-Spec to compensate for inter-

element effects and to enable the conversion ofcount rates to concentration (see Table 4). Theuser is currently responsible for providing quan-tification and is able to use suitable reference

Table 4. XRF data determined for pelletized USGS reference materials using the ITRAX (second-generation) system

MAG-1Measured wt%

MAG-1Recommended wt%

SGR-1Measured wt%

SGR-1Recommended wt%

Al2O3 16.6 16.37 5.5 6.52SiO2 51.1 50.36 27.6 28.24K2O 5.6 3.55 2.7 1.66CaO 1.45 1.37 8.53 8.38TiO2 0.79 0.75 0.23 0.264MnO 0.11 0.098 0.08 0.034Fe2O3 7.23 6.8 3.09 3.03Ni 0.005 0.0053 0.004 0.0029Cu 0.004 0.0030 0.0076 0.0066Zn 0.014 0.0130 0.0071 0.0074Rb 0.017 0.0149 0.0093 0.0083Sr 0.015 0.0146 0.043 0.042

MAG-1, muddy marine sediment with low carbonate content from the Wilkinson Basin, Gulf of Maine.SGR-1, petroleum and carbonate-rich shale from the Mahogany Zone, Green River Formation.

500

Z(mm)

Ca int. Sr int. K int. Rb int. Fe int. Mn int. Zn int. Pb int. Cu int. Mo Incoh

NPD-7

Filename:- Newport - 7-1-IWCTube:- 3kW Mo

Core:- NPD - 7Radiography exposure time:- 500 ms

User:- IWCScanning increment:- 1000µm

Data produced by the SOC ItraxXRF count-time:- 100 secs/increment

5 pt smooth 5 pt smooth 5 pt smooth 5 pt smooth 5 pt smooth 5 pt smooth 5 pt smooth 5 pt smooth 5 pt smooth 5 pt smooth

250

6 cm 2 cm 10000 30000 5000 15000 2000 6000 2000 6000 100000 2000 6000 2000 6000 200 600 1000 200 600 100000 300000

opt Rad

Fig. 5. Integrated optical, radiographic and XRF data (Prototype ITRAX) for a laminated sediment coresection from the Newport Deep (NPD7), Severn Estuary, UK. Note that levels of the anthropogenic pollutantelements Zn, Pb and Cu are higher in the upper 275mm. The major elements Ca, K, Fe and Mn and traceelements Sr and Rb show much less variation throughout the core. The green line indicates a valid ITRAXmeasurement while the red broken lines are user-defined reference lines. Image generated using the programItraX-Plot.


samples to facilitate this process. This systemuses the intensity of the scattered (Comptonand Rayleigh) lines from the X-ray tube as ameans of normalization, making the quantitativeresult independent of tube ageing or any otherfactor affecting the primary beam intensity. Theratio of the Compton and Rayleigh scatteredintensities are used to estimate the variation ofthe average atomic number in the sample.

Data visualization software

The efficient visualization of the analytical dataand images from the ITRAX is an importantpart of the evaluation process, and the NationalOceanographic Centre has produced a flexiblepackage called ItraX-Plot for examining andmanipulating the core data (see, for example,Figs 5 & 6). The software opens the ITRAXfiles and allows the user to manipulate, re-sizeand optimize image files (optical and radio-graphic), as well as plotting up to 10 XRF ele-mental profiles at a time. Other options includeadjustment of scaling, data smoothing, applica-tion of elemental divisors, inclusion of regionsof interest, and the addition of horizontal and

vertical reference lines. ItraX-Plot also allowstemporary removal of suspect or meaninglessdata prior to final presentation but the originaldata are never modified. The images can beoutput or saved in high-quality formats as.PDF, .JPG or .BMP. Cox Analytical also pro-duce an in-house package called RediCore forinspecting and displaying the downcore profiles.

Quantification issues in micro-XRF analysis

The ITRAX geochemical data are normallyoutput as counts and can be considered semi-quantitative in nature, and as such need to beinterpreted with caution. Errors may arise dueto poor peak discrimination in the X-ray spectra,porosity changes, compaction or grain-size/shape-related artefacts (recorded for K and Sr)and low count rates. Invalid data may berecorded when the X-ray detector is not in thecorrect position, particularly when the cut coresurface is uneven or shows sudden variabilityfrom crack-related effects. Careful study of varia-tion in the element integral profiles, the Comptonscatter integral and the detector–sediment dis-tance (validity) index can aid in identifying

0

200

400

600

800

zmm

0 0 4000 0 3000

0 30000

Fe µg/g0 50

CaCO3 wt.%0 120

Br µg/g0 400

Ti µg/gWDXRF

ITRAX scanner XRF Fe integral Ca integral Br integral Ti integral

Sapro

pel S

1

LC21 S#11A

Sapro

pel S

1

1000020000

Fig. 6. Comparison between WD-XRF data (red bars at 1 cm resolution; scale at bottom) and ITRAX scanelemental integral profiles (Prototype ITRAX; continuous black lines; 200mm resolution; scale at top) forMediterranean sediment core (LC21 S#11A) containing the sapropel S1.


such invalid data. The ItraX-Plot data visualiza-tion software allows for ready examination of thedata at various scales to consider whether theyare spurious.

Quantitative ITRAX X-ray microanalysis ofnatural samples can be successfully carried out,but usually involves a post-processing refinementsession followed by a full batch re-analysis.Quantification uses ‘XRF fundamental param-eters’ calculations and assumes compositionaland physical homogeneity for the measuredsamples, and any deviation from this ideal statewill introduce errors. The effectiveness of thequantitation will be impaired for some sampletypes where the small excitation volume,medium–coarse grain sizes and mineral effectscombine. The analysis of natural samples con-taining discrete medium–coarse fragments (e.g.quartz, feldspar, rutile, ilmenite, zircon, biogeniccarbonate clasts) may lead to analytical inaccura-cies and will be most significant when measuringlow Z elements or low energy X-ray energies.Where the unknown and reference sampleshave similar granular structures and elementaland mineral compositions then these problemscan be reduced. Another effect requiring con-sideration is where pore-water solutes can dryout on a sediment surface, which will lead tospurious count rates. Frequently, this effect canbe remedied by careful removal of a thin surfacelayer (using a glass slide, for example) prior toanalysis. In spite of the potential problemsnoted above, the elemental profiles obtainedusing the ITRAX show that useful semi-quanti-tative and quantitative data can be obtained fora good range of elements.

ITRAX measurement accuracy and

precison

The analytical data shown in Figure 4 and Table4 demonstrate that reasonable accuracy can beachieved. The poorer K2O data (Table 4) foundwhen quantifying XRF data for the USGS refer-ence samples may reflect unresolved inter-element or particle-size effects. The next stagein the development of the ITRAX system is todevelop and refine the conversion of count datato concentration data.

The measurement precision of the ITRAXcan be simply determined by calculating thesquare root of the count integral. Anothermeans of estimating precision is from the generalsmoothness or spikiness of the XRF elementalprofiles (e.g. Figs 4–6). Some variations reflectstatistical noise or changes caused by composi-tional boundaries or cracks.

Examples of ITRAX applications

The capability of the ITRAX core scanner hasbeen evaluated by investigating diverse sedimenttypes from wet, unconsolidated materials suchas cores from the eastern Mediterranean Seacontaining sapropels (Thomson et al. 2006) toheavy metal-polluted estuarine sediment. Othersample types such as peat, organic-rich lake sedi-ment and mineralized rocks have also beenexamined. Some of the compositional param-eters that can aid in routine sedimentological orlithostratigraphic analysis of marine sedimentcores are summarized in Table 5. Further detailsof such information can be found in Rothwellet al. (2006) and Thomson et al. (2006). Twospecific examples of ITRAX applications aregiven here.

Polluted Severn Estuary sediment

A subtidal sediment core collected from theNewport Deep, Severn Estuary (Fig. 5) wasinvestigated to examine records of metal pollu-tion from different industrial sources. Earlierstudies by Allen & Rae (1986) and Allen (1988)had defined chemozones in sediment cores fromthe Severn Estuary. A recent study by the firstauthor examined sedimentological, radiometricand geochemical data from the Newport Deepto determine the record of anthropogenicinputs in several sediment cores. The ITRAXwas used to compare elemental profiles withthose obtained using a Philips MAGIX-ProWD-XRF spectrometer, also based at theNational Oceanography Centre, Southampton.The latter method, though delivering high-quality quantitative data, involved subsamplecollection and took approximately 8–10 daysoverall to acquire the final data. By contrast,ITRAX analysis only involves halving the corefollowed by measurement, which may takeapproximately 2 days if trace-element data arerequired (1m core scanned at 200 mm resolutionwith an XRF measurement time of 100 s perincrement).

The ITRAX radiographs acquired for New-port Deep sediment cores NPD7 (Fig. 5) showdistinctive mm-scale layering caused throughvariations in carbonate, clay and sand. Some ele-mental profiles show steps, very similar to thosepreviously seen using the Philips WD-XRF.These steps are clearly evident for Cu, Zn andPb in the ITRAX profiles (but are also evidentfor a wider set of elements with the WD-XRF,i.e. P, Cr, As, Sn, I and S) and are caused byanthropogenic inputs of heavy metals to the estu-ary over the last 50 years or more. Additional


cores examined from the Severn Estuary confirmthe findings seen in NPD7.

Mediterranean sediment with sapropel

A well-characterized subcore held in the BOS-CORF archive (Section 11A of core LC21),previously examined by Mercone et al. (2000,

2001), was scanned (Fig. 6). This core containsan example of the organic-rich sedimentaryunits (sapropels) that form periodically in theeastern Mediterranean basin. Sapropels arevisually distinct because of their dark colour,but the ITRAX X-radiograph also revealscoincident physical property changes that resultmainly from the lower sediment density and

Table 5. Examples of ITRAX output parameters that aid in sedimentological or lithostratigraphic analysis

Property measuredITRAX detectionefficiency Comment on property

Compton scatteringMoKinc

High . Relates inversely to the mean atomic number. Will vary with mineralogical composition, water and organiccarbon content

. Inflections may occur at bed boundaries

. Will vary with sediment packing density

Ca/Fe High . Indicative of biogenic carbonate :detrital clay ratio. May show strong correlation with sedimentary units. Ca/Fe profile is a good proxy for sediment grading and forassessing source relationships

. Can distinguish foraminifer- or shell-rich layers

Sr/Ca High . Enhanced Sr may indicate the presence of high-Sr aragonite whichrequires a shallow-water source

. Affected by sediment packing/porosity and grain-size/shapevariations

K/Rb Moderate . K is commonly associated with detrital clay and may be enhancedin turbidite muds

. Potentially unreliable parameter as sea-water Cl atoms will absorbpotassium X-rays, so apparent high K may reflect increasedporosity

Zr/RbTi/Rb

Moderate . Zr and Ti are high in heavy resistate minerals and may be enhancedin turbidite bases

. Useful as sediment-source/provenance indicators

Si Moderate–low . Important terrigenous or productivity indicator. Normalization using detrital divisor can distinguish terrigenous orproductivity origin

. May be useful as a sediment-source and provenance indicator

Fe/RbFe/Ti

Good . Commonly shows grain-size-related fractionation effects. Fe mobilized during redox-related diagenesis and elevated Fecommonly seen in oxic, or formerly oxic, parts of sediment

. Rb is an element commonly associated with detrital clay and maybe enhanced in turbidite muds

Cu/RbCu/Ti

Moderate . Sharp Cu peaks are largely of diagenetic origin

As Moderate . Commonly an indicator of pyrite which may be detrital orauthigenic in origin

Mn/Ti Good . Good indicator of redox-related diagenesis

Ba/Ti Low–moderate . Important productivity indicator

Br/ClS/Cl

Moderate–low . For marine sediments a constant ratio implies sea-water ratios.High ratios may indicate organic-rich layers as Br and S are high inorganic-rich sediments

The property refers to an element ratio or peak area integral.See Rothwell et al. (2006) and Thomson et al. (2006) for more specific discussion of the above parameters.


high pore-water content in sapropels. ITRAXelemental profiles were compared with wave-length dispersive XRF data from discrete 1 cmsamples taken through the most recent sapropel(S1). While recognizing that the measured XRFelement integrals from the ITRAX do not havean exact constant relationship with elementconcentration over changing sediment types,the data show a good comparison (Fig. 6).There are plans to quantify the ITRAX dataroutinely. The ITRAX data (discussed in detailby Thomson et al. 2006) show that higher Ba/Ti and Br/Cl ratios correspond with the highCorg content in the visual and oxidized sapropel.The thinning of the original sapropel thicknessby post-depositional oxidation is revealed fromMn/Ti and Cu/Ti ratios, pyrite authigenesis inthe residual visual sapropel from Fe/Ti and S/Cl ratios and the As integral, and aragoniteformation in and around the sapropel from theSr/Ca ratio.

Conclusions

The ITRAX multi-function core scanner has thecapability to rapidly and conveniently acquiredata for three important physical and chemicalproperties from split-sediment cores. A scannerrun will provide a high-quality optical imagefile, a 16-bit X-radiography image file andmultiple X-ray spectral files, and an immediateend-of-run analytical summary. Further post-run re-processing of X-ray is straightforward.This combined acquisition of physical andchemical data is of considerable attractionwhere initial non-destructive characterization oflake and marine sediment and rock cores isrequired. The ITRAX may be an acceptable sub-stitute for traditional analytical methods in somecases and for some elements, but more generallyit will be useful in acquiring indicative data forcores held in repositories before destructive sam-pling for further detailed investigations. XRFscanner systems cannot be expected to deliver aquality of data comparable to that of systemssuch as WD-XRFs because of the small excita-tion volume used, the air path, and the effectsof mineralogy, particle size, porosity and watercontent variations. Their high-resolution cap-ability, however, considerably exceeds thatachievable by conventional sampling methodsand may lead to specific new applications (e.g.ombrotrophic peat analysis, examination ofmineralized rock sections). The ITRAX instru-ment also provides a convenient platform foradding other sensors (e.g. Fourier TransformInfra Red spectroscopy, spectrophotometry)

that may provide helpful data such as havebeen used to extract palaeoenvironmental infor-mation from cores (Giosan et al. 2002a,b; Berg& Jarrard 2003).

I.W. Croudace and R.G. Rothwell, and other col-leagues and former colleagues at NOC, particularlyProfessors C. German, J. Thomson and P. Weaver,are grateful to the UK Office of Science and Technol-ogy via the Natural Environment Research Councilfor providing funds to purchase X-ray analytical instru-ments that included the ITRAX. The realization of theITRAX core scanner is due to a co-operative venturebetween COX Analytical (A. Rindby, B. Stocklasser,P. Engstrom, S. Norder and J. Rudolfsson) and NOC(I.W. Croudace and R.G. Rothwell). We thank NOCcolleagues R. Pearce for the loan of laminated sedimentblocks and K. Davis for improvements to the technicalartwork.

References

Allen, J.R.L. 1988. Modern-period muddy sedimentsin the Severn Estuary (southwestern UK): a pollu-tant-based model for dating and correlation. Sedi-mentary Geology, 58, 1–21.

Allen, J.R.L. & Rae, J.E. 1986. Time sequence ofmetal pollution, Severn estuary, southwesternUK. Marine Pollution Bulletin, 17, 427–431.

Berg, M.D.V. & Jarrard, R.D. 2004. Cenozoic massaccumulation rates in the equatorial Pacific basedon high-resolution mineralogy of Ocean DrillingProgram Leg 199. Paleoceanography, 19, 1–12.PA2021, doi: 10.1029/2003PA000928.

Bergstrom, U., Lindeberg, J. & Rindby, A. 2001.Batch measurements of wood density on intact orprepared drill cores using X-ray microdensitometry.Wood Science and Technology, 35, 435–452.

Croudace, I.W. & Williams-Thorpe, O. 1988. A lowdilution, wavelength-dispersive X-ray fluorescenceprocedure for the analysis of archaeological rockartefacts. Archaeometry, 30, 227–236.

Croudace, I.W. & Gilligan, J. 1990. Versatile andaccurate trace element determinations in iron-richand other geological samples using X-ray fluores-cence analysis. X-ray Spectrometry, 19, 117–123.

Giosan, L., Flood, R.D. & Aller, R.C. 2002a. Paleo-ceanographic significance of sediment color on wes-tern North Atlantic drifts: I. Origin of color.MarineGeology, 189, 25–41.

Giosan, L., Flood, R.D., Grutzner, J. & Mudie, P.2002b. Paleoceanographic significance of sedimentcolor on western North Atlantic Drifts: II. LatePliocene-Pleistocene sedimentation. Marine Geol-ogy, 189, 43–61.

Jansen, J.H.F., Van der Gaast, S.J., Koster, B. &

Vaars, A.J. 1998. CORTEX, a shipboard XRF-scanner for element analyses in split sedimentcores. Marine Geology, 151, 143–153.

Janssens, K., Adams, F. & Rindby, A. (eds). 2000.Microscopic X-Ray Fluorescence Analysis. Wiley,Chichester.


Jenkins, R. 1999. X-Ray Fluorescence Spectrometry,2nd edn. Wiley, Chichester.

Lechner, P., Fiorini, C. ET AL. 2001. Silicon driftdetectors for high count rate X-ray spectroscopyat room temperature. Nuclear Instruments andMethods, 458A, 281–287.

Mercone, D., Thomson, J., Abu-Zied, R.H., Crou-

dace, I.W. & Rohling, E. 2001. High-resolutiongeochemical and micropalaeontological profilingof the most recent eastern Mediterranean sapropel.Marine Geology, 177, 25–44.

Mercone, D., Thomson, J., Croudace, I.W., Siani, G.,

Paterne, M. & Troelstra, S.R. 2000. Duration ofS1, the most recent eastern Mediterranean sapropelas indicated by AMS radiocarbon and geochemicalevidence. Palaeoceanography, 15, 336–347.

Rindby, A., Engstrom, P. & Janssens, K. 1997. Theuse of a scanning X-ray microprobe for simulta-neous XRF/XRD studies of fly-ash particles.Journal of Synchrotron Radiation, 4, 228–235.

Rothwell, R.G., Hoogakker, B., Thomson, J., Crou-

dace, I.W. & Frenz, M. 2006. Turbidite emplace-ment on the southern Balearic Abyssal Plain(western Mediterranean Sea) during Marine IsotopeStages 1–3: an application of ITRAXXRF scanningof sediment cores in lithostratigraphic analysis. In:

Rothwell, R.G. (ed.) New Techniques in SedimentCore Analysis. Geological Society, London, SpecialPublications, 267, 79–98.

Streli, C., Wobrauschek, P., Pepponi, G. & Zoeger,

N. 2004. A new total reflection X-ray fluorescencevacuum chamber with sample changer analysisusing a silicon drift detector for chemical analysis.Spectrochimica Acta, B59, 199–203.

Thomson, J., Croudace, I.W. & Rothwell, R.G.2006. A geochemical application of the ITRAXscanner to a sediment core containing easternMediterranean sapropel units. In: Rothwell,

R.G. (ed.) New Techniques in Sediment Core Analy-sis. Geological Society, London, Special Publica-tions, 267, 65–77.

Tsuji, K., Injuk, J. & Van Grieken, R. (eds). 2004. X-ray Spectrometry: Recent Technological Advances.Wiley, Chichester.

Vincze, L., Janssens, K., Adams, F., Rindby, A. &

Engstrom, P. 1998. Interpretation of capillarygenerated spatial and angular distributions of X-rays: theoretical modelling and experimental verifi-cation using the European Synchrotron RadiationFacility Optical beam line. Review of ScientificInstruments, 69, 3494–3503.


itrax: description and evaluation of a new multi-function

Documents