A04_PXRF_SOW.pdf

NPS Southeast Archeological Center C/O Michael Lockman

2035 E. Paul Dirac Drive, Johnson Building, Suite 120

Tallahassee, Florida 32310

X-ray fluorescence spectroscopy (XRF) is a method of measuring materials’ elemental composition with applications that range from the evaluation of environmental contaminants to mineral prospecting. The technique has recently gained traction in archeological communities as a highly effective means of material identification, and when coupled with multivariate statistics it is a particularly effective method of geochemical sourcing. The advantages of portable XRF

(pXRF) compared to other methods of elemental analysis are its speed and accuracy, its portability, and – most importantly – its non-destructive sampling procedure.

The function of an XRF spectrometer is relatively straightforward: the instrument produces X-rays that dislodge electrons in materials’ outer atomic orbitals, sometimes resulting in a phenomenon called fluorescence wherein photons are emitted from the affected atoms. The photons’ wavelengths are unique to each element and are measured and recorded by the instrument’s onboard detector and multichannel analyzer. With proper calibration and Bayesian deconvolution, these counts can be reliably converted into quantitative data reflecting materials’ elemental composition.

The Southeast Archeological Center (SEAC) purchased a Bruker Tracer III-SD handheld XRF spectrometer nearly a decade ago – the instrument has aided numerous cultural resource studies of varying scopes and remains in high demand among staff today. This model of spectrometer, first introduced in 2008 as the third iteration in Bruker’s Tracer line, was superseded with improved fourth and fifth generations in 2011 and 2016, respectively. Technology has improved even further since that time, prompting the release of updated pXRF spectrometers across manufacturers as recently as February 2021.

To evaluate data collected by separate spectrometers, it is critical that certain parameters remain similar between instruments. To that end, some general specifications are provided below to ensure that data collected by either instrument can be interpolated within larger datasets.

• Capable of battery-powered operation using a rechargeable lithium-ion battery.

• Weighs less than 2.0 kilograms (kg) with battery.

• Operable in temperatures ranging from 0 to 40 degrees Celsius (⁰C).

• Operational with user-controlled excitation parameters (i.e. current and voltage).

• Capable of operation utilizing customized calibrations and X-ray filters.

• Features an interchangeable collimator to allow adjustment of sampling area.

• Features wired and/or wireless compatibility to communicate with Windows PCs.

• Equipped with direct-attached data storage (i.e. internal or external drives capable of being accessed by the instrument without a network connection).

• Includes an integrated screen capable of displaying instrument settings and/or spectra files with customizable data entry and the ability to adjust excitation parameters.

• Able to measure elemental concentrations in ambient atmospheric conditions (i.e. without a vacuum pump or helium flush).

• Excitation source (X-ray tube, no anode or target preference) with a range of at least 10 to 50 kilovolts (kV) and 5 to 195 microamps (µA).

• Minimally, must have the ability to accurately to measure 23 mid-Z elements from the periodic table (potassium [K; Z=19] to niobium [Nb; Z=41]).

• Able to be calibrated with standardized check sample(s) and corresponding calibration file(s), both included and/or available separately.

• Able to analyze ceramic, metal, alloy, and geologic samples accurately and reliably utilizing calibration files that are included and/or available separately.

• Utilizes a silicon drift detector with a graphene window less than or equal to 1 micrometer (µm) in thickness and a surface detection area greater than or equal to 20 square millimeters (mm2).

• Resolution greater than or equal to 140 electron-volts (eV) at greater than or equal to

200,000 counts per second.

• Includes a warranty and/or service agreement.

• Must be compatible with Windows PCs.

• Capable of reading and processing data files from the instrument’s storage.

• Able to deconvolute spectra for export as quantitative data in a format compatible with

DOI-furnished Windows PC programs (e.g. comma-separated value or Microsoft Excel).