Recent Developments in Handheld X-ray Fluorescence (XRF) Instrumentation

RECENT DEVELOPMENTS IN HANDHELD X-RAY FLUORESENCE INSTRUMENTATION The introduction of new large area silicon drift detectors to handheld XRF technology expands technique capabilities with greater analytical range and lower detection limits James Pasmore, Director, Business Development [email protected] Thermo Niton Analyzers LLC Thermo Fisher Scientific 900 Middlesex Turnpike, Building 8 Billerica, MA 01821 USA Tel: 978-670-7460 Fax: 978-670-7430 Handheld x-ray fluorescence (HHXRF) analyzers have become the standard for non-destructive quality control testing of finished titanium alloy products. These systems are routinely utilized for rapid quality control inspection and analysis to ensure product chemistry specifications are met. Like most scientific technologies, XRF instruments have evolved dramatically over the last forty years to harness miniaturization and computer advancements and to meet increasing demands from the industry. Most recently, the introduction of new proprietary large area silicon drift detectors (SDD) into HHXRF instruments has produced significant performance improvements over traditional XRF capabilities. Known as GOLDD (Geometrically Optimized Large area Drift Detector) technology, these systems process much higher count rates, with excellent resolution and shaping time, to produce, in general, three times better limits of detection than traditional SDD systems, and 10 times better sensitivities over conventional silicon PIN detector instruments. As a result, a handheld XRF can now be used for the analysis of tramp elements in production facilities and ultralow residual element detection in specialized inspection work. Coupled with a high output, 50kV, miniaturized x-ray tube, the GOLDD system can also perform light element analysis work without vacuum or helium purge, something considered impossible with a handheld instrument as recently as one year ago. Aluminum, sulfur, magnesium, phosphorous, silicon and other light elements can be measured in titanium alloy materials directly, with little if any sample preparation necessary. When optimal sensitivities are necessary, the GOLDD system can be combined with a portable helium purging mechanism to produce two times better limits of detection for light elements than without the purge. This paper will offer an explanation of the XRF technique and the evolution of HHXRF systems. It will also offer an in-depth discussion of new silicon drift detector technology. Performance considerations and specific applications will be explored. Introduction: Portable XRF Instrumentation Using portable XRF for the analysis of alloy chemistry and identification of alloy grade assures users that the composition of the metal they purchase, fabricate, verify, install, or recycle is the grade that they specified. Since the late 1960s, portable XRF technology has evolved through seven generations of increasingly sophisticated alloy analyzers, which are commercially available to perform this crucial task. Each succeeding generation has added new capabilities, such as smaller size, increased speed, better performance, and greater ease of use. Today, nearly all alloys can be tested and identified for correct alloying content with these powerful handheld tools. Evolution of Portable XRF to Handheld XRF 1970s to Present The earliest portable XRF alloy analyzers were large and bulky two-piece devices, with only an 11 element-sequential measurement capability and limited alloy analysis performance (see Figure 1). They weighed over 20 lbs. (10 kg) and required up to a few minutes of testing per sample to determine the grade and chemistry of the alloy. They were effective for primarily high alloyed content grades that contained significant differences in alloy chemistry specifications from all other grades (no close or nearly twin alloy specs please). Fixed energy (in keV) and fixed excitation intensity (in millicuries) isotope sources limited the ability to optimize measurement conditions. Further, battery use lasted only a few hours between recharge, while temperature as well as other environmental conditions dramatically affected performance and reliability. Figure 1 First generation alloy analyzer, the TN 9266, circa 1970s Recent Developments Unlike the bulky, two-piece, slow and low performance portable analyzers of decades past, today’s one-piece handheld XRF analyzers are miniaturized and designed for ultra high speed with lab-quality performance (see Figures 2 and 3). Figure 2 Seventh generation alloy analyzer, the Thermo Scientific Niton XL3t-S with Geometrically Optimized Large Area Drift Detector (GOLDDTM) technology, circa 2009