THE PHILIPS PW 2400 SEQUENTIAL WAVELENGTH X-RAY SPECTROMETER

ARCHAEOLOGICAL XRF LABORATORY

The Philips PW2400 Sequential WXRF Spectrometer

The new Philips PW 2400 spectrometer  in the Department of Geology/Geophysics, is a state-of-the-art instrument that allows us to acquire more precise data on smaller samples.  This means that we can now analyze smaller samples (>5 <10mm) with greater precision non-destructively.   The instrument is equipped with a 30 sample changer.  Thirty samples can be analyzed in under 3.5 hours.

Non-destructive analysis is facilitated by the SuperQ software designed by Philips allowing for ratioing to the Compton scatter similar to EDXRF analysis.  We are currently accepting samples for analysis with the new instrument at the same cost as before.  Routine analyses of obsidian include measurement of Rb, Sr, Y, Zr, Nb, and Ba.   Many other elements can be acquired if necessary, destructively however.

Description of the major components (from Philips)

End-window x-ray tube - source of high power x-rays for sample excitation.
Primary collimator - closely spaced parallel metal plates reduce beam divergence.
Sample - a flat-surfaced solid (e.g. metal, glass), compressed powder, or liquid supported on a plastic membrane (plus whole samples analyzed by ratioing to the Compton scatter). When bombarded with x-rays, it emits secondary radiation (fluorescence) at wavelengths characteristic of each element present.
Analyzing crystal - a natural or synthetic material with regular d-spacing, which diffracts x-rays of differing wavelength, depending upon the angle at which the incident beam strikes it.

Secondary collimator.
Interchangeable detector - converts x-ray photon energy into electrical current pulses that provide a measure of element concentration.

Illustration of a sequential WXRF system

Features

Total application versatility.
Optimal measurement conditions programmable for each element.
Very high sensitivity, measures down to parts-per-million concentrations.

A sequential spectrometer enables any number and combination of elements - from Be (atomic number 4) to U (atomic number 92) and beyond - to be measured one after another. It employs an optical assembly called a 'goniometer', which is equipped with two concentric, rotatable shafts. These enable the analyzing crystal to
turn through angular increments (theta degrees), while the detector rotates through 2-theta degrees to intercept the diffracted beam.
Spectral peaks are detected at various wavelengths, according to the conditions described by Bragg's Law.

The results of continuous scanning over an angular range can be plotted as a spectral pattern, from which the elements present in a
sample may be identified. Individual peak intensities are measured to determine element concentrations.

Measurement times as short as 2 seconds suffice for many elements - although longer times are required for the lightest elements, which
produce relatively small numbers of characteristic fluorescent photons.

Unlike the ThermoScientific Quant'X EDXRF, however, the sample cups only allow for samples less than 42mm in diameter.

The PW2400 and the PW2510 sample changer allowing for unattended analyses of up to 30 samples.

Philips WXRF concentrations for obsidian archaeological samples submitted by Mooney & Associates, analyzed 10 September 1999 and measurement of RGM-1, USGS obsidian standard. All measurements in parts per million (ppm).  Sample 113 was less than 7mm in maximum length; all others over 10mm. Further calibration will increase precision within the next week.

Raw elemental concentrations for Obsidian Butte source standards measured on the Spectrace EDXRF. All measurements in parts per million (ppm).

Last updated: Saturday, 21 March 2015 04:53:15 AM -0800

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