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3 Abstract The SIMS technique provides an ideal tool for measuring hydrogen (H) profiles for use in obsidian hydration dating (OHD). The measurement of a natural obsidian fracture surface by SIMS is not straightforward, however, and subject to several factors. Measurements have been collected using both magnetic-sector and quadrupole-based SIMS instruments, with comparable results. The quadrupole-based instrument may provide a somewhat simpler analysis in terms of charge compensation and requiring less sample preparation. Although early measurements were made using negatively charged oxygen (O- ) bombardment with positive ion detection, modern instruments using cesium (Cs) bombardment with negative ion detection should provide superior backgrounds for H analysis. Analysis of natural obsidian surfaces may be subject to problems due to surface roughness, cracking, or the presence of natural inclusions or vesicles. Measurements by atomic force microscopy (AFM) indicate root mean square (RMS) roughness values as low as 5 nanometers (nm) for conchoidal fracture surfaces. Rippling that develops within the SIMS craters due to ion bombardment causes RMS roughness of about 40–50 nm. These values are similar to the rate of fall of the H profile for deep profiles. Sputtering rates measured for a suite of obsidians from archaeological sites show a variation of less than 4%, indicating that an external obsidian standard can be used to calibrate the sputtering rate within the typical measurement error. For the hydration layer thickness measurement, the important parameter is the thickness of the hydration layer, as measured at the ½ fall of the H profile. Repeat measurements indicate this thickness can be measured to within ±1% on some samples. Excellent correlation between SIMS and IR measurements indicate the ability of SIMS to provide highly quantitative measurement of H in obsidian. 1. Introduction Over five decades ago Friedman and Smith (1960) noted that freshly exposed surfaces of obsidian artifacts begin to absorb water immediately, eventually forming a water-rich hydrated layer in the range of 1–10 micrometers (μm). If the ground temperature, soil relative humidity, and rate of water diffusion in obsidian are accurately known, an age may be calculated for the creation of the artifact from a measurement of the hydrated layer thickness (Friedman and Long 1976). The measurement of obsidian hydration rims for the purpose of dating has been undertaken for many years now. Initial efforts used physical cross-sections and optical measurement, but more recently a number of advanced analytical methods have been used including nuclear reaction analysis, sputter-induced optical emission, and secondary ion mass spectrometry (SIMS). Among these techniques, SIMS should provide the most accurate and detailed measurement of the diffusion profile shape, due to the nature of the profiling technique. In this chapter we will summarize work done to date on SIMS profiling of archaeological obsidian samples, discuss some aspects of the technique that may affect the accuracy of the measured profiles, and present some new data Chapter 1 Aspects of Secondary Ion Mass Spectrometry (SIMS) Depth Profiling for Obsidian Hydration Dating Steven W. Novak and Christopher M. Stevenson 4 | OBSIDIAN HYDRATION DATING on sputtering rates of obsidian and the roughness of fracture surfaces by atomic force microscopy (AFM) (see also Liritzis and Laskaris 2011; Liritzis et al. 2008a, 2008b). We hope to give readers a means to understand what is required for a SIMS analysis of a sample and the parameters that affect the accuracy of the measurements. In addition to the measurement of artifacts, we have performed a number of laboratory hydration experiments on obsidian to better define three parameters: (1) What is the effect of glass density and composition on the calibration used to estimate crater depth? (2) What is the effect of surface roughness on the precision of SIMS measurements ? and (3) Can the calibration between infrared photoacoustic spectroscopy (IR-PAS) absorbance measurements and depth be improved? 2. Previous work Initial development of the obsidian hydration dating method used cross-sectional polishing of the glass and optical width measurement of the hydrated rim. For relatively thick hydration layers present on very old artifacts, this method at times produced good linear correlation between layer thickness and hydration age (e.g., Meighan et al. 1968; Hull 2001). The first modern surface analysis technique applied to measuring hydration rim thickness was by Lee et al. (1974) and Lanford (1977), who measured the hydrogen profiles using nuclear reaction analysis. This method showed good correlation between hydration layer thickness and hydration temperature and provided quantitative H values. Curiously, this high-quality technique was not widely applied to the measurement...

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