Sensitive high-resolution ion microprobe

A sensitive high resolution ion microprobe (SHRIMP, with a maximum mass resolution of m/Am of 30 000) was designed on the basis of the double-focusing sector field Matsuda type instrument190 as discussed by Compston in 1996.191 The first SHRIMP and a modified version for precise isotope ratio measurements were constructed in the 1980s and later produced commercially.192 The main application of this instrument so far has been in situ U-Pb dating of zircon.192,193... 

LA-ICP-MS using a multi-collector instrument for Pb-Pb dating via ° Pb/ °" Pb and ° Pb/ ° Pb isotope ratio measurements of natural rutile crystals has been utilized to study geological temperature-time histories. The significance of Devonian-Carboniferous igneous activity in Tasmania on the basis of U-Pb dating has been measured by sensitive high resolution ion microprobe (SHRIMP). ... 

Stem R. (1997) The GSG sensitive high resolution ion microprobe (SHRIMP) analytical techniques of zircon U—Th—Pb age determinations and performance evaluation in radiogenic age and isotopic studies. Geol. Surv. Can. Current Res. 1997-F(Report 10), 1-31. 

These techniques fall into two categories those considered as routine (e.g. atomic absorption and emission spectroscopy, X-ray fluorescence) and a growing number of microanalytical surface techniques (e.g. laser microprobe mass analysis [LAMMA] and sensitive high-resolution ion microprobe [SHRIMP]). Each analytical technique requires specific sample preparation prior to analysis, as summarised in Table 13.1. 

XRD, X-ray diffraction XRF, X-ray fluorescence AAS, atomic absorption spectrometry ICP-AES, inductively coupled plasma-atomic emission spectrometry ICP-MS, Inductively coupled plasma/mass spectroscopy IC, ion chromatography EPMA, electron probe microanalysis SEM, scanning electron microscope ESEM, environmental scanning electron microscope HRTEM, high-resolution transmission electron microscopy LAMMA, laser microprobe mass analysis XPS, X-ray photo-electron spectroscopy RLMP, Raman laser microprobe analysis SHRIMP, sensitive high resolution ion microprobe. PIXE, proton-induced X-ray emission FTIR, Fourier transform infrared. 

Sato, T., Yanase, N., Williams, I.S., Compston, W., Zaw, M., Payne, T.E. Airey, P.L. (1998) Uranium micro-isotopic analysis of weathered rock by sensitive high resolution ion microprobe (SHRIMP). Radiochimica Acta 82, 335-340. 

Equipped with an array of Faraday cups, the multiple collector-ICP-MS achieves comparable or better quality of measurements than TIMS without double spiking [58-60]. However, as for TIMS, a chemical separation before measurement is required to obtain such precision. Micro-beam techniques such as the sensitive high resolution ion microprobe (SHRIMP) [39,61] and LA-ICP-MS [58] are also useful for obtaining high resolution sampling of solid samples and simultaneous measurements of isotopic composition. 

Since the middle of the 1980s, the traditional method of zircon geochronology was complemented by the use of the sensitive high-resolution ion microprobe (SHRIMP) [17], with which 15 pm diameter spots on zircons can be dated, and metamict or mixed-age domains avoided. Since minimal amounts of material are used, this method is still preferred in cases where the material to be analyzed is scarce, such as zircons from extraterrestrial samples, or the early Archean ( 4.4 Ga) [18]. Unfortunately, the number of SHRIMP instmments is limited, and in cases where scarcity of material is not a problem, and a precision on the level of a few million years is acceptable, SHRIMP and TIMS techniques for zircon dating have been largely replaced by LA-ICP-MS analyses, pioneered in the early 1990s [19,20]. Here a laser beam is used to excavate a small (15-90 pm diameter) pit in the mineral, from which the ablated material is transferred to the plasma of an ICP-MS instrument, where ionization and analysis take place (see also Chapters 2 and 4). 

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