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48-502: The sensitive high-resolution ion microprobe (also sensitive high mass-resolution ion microprobe or SHRIMP ) is a large-diameter, double-focusing secondary ion mass spectrometer (SIMS) sector instrument that was produced by Australian Scientific Instruments in Canberra, Australia and now has been taken over by Chinese company Dunyi Technology Development Co. (DTDC) in Beijing. Similar to

96-488: A cryopump to trap contaminants, especially water. Typical pressures inside the SHRIMP are between ~7 x 10 mbar in the detector and ~1 x 10 mbar in the primary column (with oxygen duoplasmatron source). In normal operations, the SHRIMP achieves mass resolution of 5000 with sensitivity >20 counts/sec/ppm/nA for lead from zircon. For U-Th-Pb geochronology a beam of primary ions (O 2 ) are accelerated and collimated towards

144-404: A tungsten tip and emits ions under influence of an intense electric field. While a gallium source is able to operate with elemental gallium, recently developed sources for gold , indium and bismuth use alloys which lower their melting points . The LMIG provides a tightly focused ion beam (<50 nm) with moderate intensity and is additionally able to generate short pulsed ion beams. It

192-462: A 1000 mm radius through 72.5° to focus the secondary ions according to their mass/charge ratio according to the principles of the Lorentz force . Essentially, the path of a less massive ion will have a greater curvature through the magnetic field than the path of a more massive ion. Thus, altering the current in the electromagnet focuses a particular mass species at the detector. The ions pass through

240-494: A caesium gun during elemental depth profiling, or with a C 60 or gas cluster ion source during molecular depth profiling. Depending on the SIMS type, there are three basic analyzers available: sector, quadrupole, and time-of-flight. A sector field mass spectrometer uses a combination of an electrostatic analyzer and a magnetic analyzer to separate the secondary ions by their mass-to-charge ratio. A quadrupole mass analyzer separates

288-415: A collector slit in the focal plane of the magnetic sector and the collector assembly can be moved along an axis to optimise the focus of a given isotopic species. In typical U-Pb zircon analysis, a single secondary electron multiplier is used for ion counting. Turbomolecular pumps evacuate the entire beam path of the SHRIMP to maximise transmission and reduce contamination. The sample chamber also employs

336-408: A network of radiation damaged areas. Fission tracks and micro-cracks within the crystal will further extend this radiation damage network. These fission tracks act as conduits deep within the crystal, providing a method of transport to facilitate the leaching of lead isotopes from the zircon crystal. Under conditions where no lead loss or gain from the outside environment has occurred, the age of

384-458: A pulse of 10 electrons which is recorded directly. A microchannel plate detector is similar to an electron multiplier, with lower amplification factor but with the advantage of laterally-resolved detection. Usually it is combined with a fluorescent screen, and signals are recorded either with a CCD-camera or with a fluorescence detector. Detection limits for most trace elements are between 10 and 10 atoms per cubic centimetre , depending on

432-408: A pulsed secondary ion extraction. It is the only analyzer type able to detect all generated secondary ions simultaneously, and is the standard analyzer for static SIMS instruments. A Faraday cup measures the ion current hitting a metal cup, and is sometimes used for high current secondary ion signals. With an electron multiplier an impact of a single ion starts off an electron cascade, resulting in

480-546: A release of positive ions and neutral atoms from a solid surface induced by ion bombardment. Improved vacuum pump technology in the 1940s enabled the first prototype experiments on SIMS by Herzog and Viehböck in 1949, at the University of Vienna , Austria. In the mid-1950s Honig constructed a SIMS instrument at RCA Laboratories in Princeton, New Jersey. Then in the early 1960s two SIMS instruments were developed independently. One

528-401: A sample of the mineral can be used to reliably determine its age. The method relies on two separate decay chains , the uranium series from U to Pb, with a half-life of 4.47 billion years and the actinium series from U to Pb, with a half-life of 710 million years. Uranium decays to lead via a series of alpha and beta decays, in which U and its daughter nuclides undergo

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576-449: A series of zircon samples has lost different amounts of lead, the samples generate a discordant line. The upper intercept of the concordia and the discordia line will reflect the original age of formation, while the lower intercept will reflect the age of the event that led to open system behavior and therefore the lead loss; although there has been some disagreement regarding the meaning of the lower intercept ages. Undamaged zircon retains

624-470: A single decay scheme (usually U to Pb) leads to the U–Pb isochron dating method, analogous to the rubidium–strontium dating method. Finally, ages can also be determined from the U–Pb system by analysis of Pb isotope ratios alone. This is termed the lead–lead dating method. Clair Cameron Patterson , an American geochemist who pioneered studies of uranium–lead radiometric dating methods, used it to obtain one of

672-422: A total of eight alpha and six beta decays, whereas U and its daughters only experience seven alpha and four beta decays. The existence of two 'parallel' uranium–lead decay routes ( U to Pb and U to Pb) leads to multiple feasible dating techniques within the overall U–Pb system. The term U–Pb dating normally implies the coupled use of both decay schemes in the 'concordia diagram' (see below). However, use of

720-452: A typical U-Pb geochronology analytical mode, a beam of (O 2 ) primary ions are produced from a high-purity oxygen gas discharge in the hollow Ni cathode of a duoplasmatron . The ions are extracted from the plasma and accelerated at 10 kV. The primary column uses Köhler illumination to produce a uniform ion density across the target spot. The spot diameter can vary from ~5 μm to over 30 μm as required. Typical ion beam density on

768-500: Is easy to operate and generates roughly focused but high current ion beams. A second source type, the surface ionization source, generates Cs primary ions. Cesium atoms vaporize through a porous tungsten plug and are ionized during evaporation. Depending on the gun design, fine focus or high current can be obtained. A third source type, the liquid metal ion gun (LMIG), operates with metals or metallic alloys, which are liquid at room temperature or slightly above. The liquid metal covers

816-567: Is in uranium-thorium-lead geochronology , although the SHRIMP can be used to measure some other isotope ratio measurements (e.g., δLi or δB) and trace element abundances. The SHRIMP originated in 1973 with a proposal by Prof. Bill Compston , trying to build an ion microprobe at the Research School of Earth Sciences of the Australian National University that exceeded the sensitivity and resolution of ion probes available at

864-504: Is necessary to determine the order of usage along with other methods of analysis for fingerprints. This is because the mass of the fingerprint significantly decreases after exposure to vacuum conditions. Uranium-lead dating Uranium–lead dating , abbreviated U–Pb dating , is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routine precisions in

912-419: Is the process involved in bulk analysis, closely related to the sputtering process, using a DC primary ion beam and a magnetic sector or quadrupole mass spectrometer. Dynamic secondary ion mass spectrometry (DSIMS) is a powerful tool for characterizing surfaces, including the elemental, molecular, and isotopic composition and can be used to study the structure of thin films , the composition of polymers , and

960-644: Is therefore commonly used in static SIMS devices. The choice of the ion species and ion gun respectively depends on the required current (pulsed or continuous), the required beam dimensions of the primary ion beam and on the sample which is to be analyzed. Oxygen primary ions are often used to investigate electropositive elements due to an increase of the generation probability of positive secondary ions, while caesium primary ions often are used when electronegative elements are being investigated. For short pulsed ion beams in static SIMS, LMIGs are most often deployed for analysis; they can be combined with either an oxygen gun or

1008-419: Is used for quality assurance purposes in the semiconductor industry and for the characterization of natural samples from this planet and others. More recently, this technique is being applied to nuclear forensics, and a nanoscale version of SIMS, termed NanoSIMS, has been applied to pharmaceutical research. SIMS can be used in the forensics field to develop fingerprints. Since SIMS is a vacuum based method, it

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1056-556: The oldest terrestrial material including the Acasta Gneiss and further extending the age of zircons from the Jack Hills and the oldest impact crater on the planet. Other significant milestones include the first U/Pb ages for lunar zircon and Martian apatite dating. More recent uses include the determination of Ordovician sea surface temperature , the timing of snowball Earth events and development of stable isotope techniques. In

1104-430: The 0.1–1 percent range. The method is usually applied to zircon . This mineral incorporates uranium and thorium atoms into its crystal structure , but strongly rejects lead when forming. As a result, newly-formed zircon crystals will contain no lead, meaning that any lead found in the mineral is radiogenic . Since the exact rate at which uranium decays into lead is known, the current ratio of lead to uranium in

1152-462: The IMS 1270-1280-1300 large-geometry ion microprobes produced by CAMECA , Gennevilliers, France and like other SIMS instruments, the SHRIMP microprobe bombards a sample under vacuum with a beam of primary ions that sputters secondary ions that are focused, filtered, and measured according to their energy and mass. The SHRIMP is primarily used for geological and geochemical applications. It can measure

1200-490: The Liebl and Herzog design, and produced by Australian Scientific Instruments in Canberra, Australia . A secondary ion mass spectrometer consists of (1) a primary ion gun generating the primary ion beam , (2) a primary ion column, accelerating and focusing the beam onto the sample (and in some devices an opportunity to separate the primary ion species by Wien filter or to pulse the beam), (3) high vacuum sample chamber holding

1248-518: The detector must be large compared to the size of the instrument), and it also limits surface contamination by adsorption of background gas particles during measurement. Three types of ion guns are employed. In one, ions of gaseous elements are usually generated with duoplasmatrons or by electron ionization , for instance noble gases ( Ar , Xe ), oxygen ( O , O 2 , O 2 ), or even ionized molecules such as SF 5 (generated from SF 6 ) or C 60 ( fullerene ). This type of ion gun

1296-747: The earliest estimates of the age of the Earth in 1956 to be 4.550Gy ± 70My; a figure that has remained largely unchallenged since. Although zircon (ZrSiO 4 ) is most commonly used, other minerals such as monazite (see: monazite geochronology ), titanite , and baddeleyite can also be used. Where crystals such as zircon with uranium and thorium inclusions cannot be obtained, uranium–lead dating techniques have also been applied to other minerals such as calcite / aragonite and other carbonate minerals . These types of minerals often produce lower-precision ages than igneous and metamorphic minerals traditionally used for age dating, but are more commonly available in

1344-444: The geologic record. During the alpha decay steps, the zircon crystal experiences radiation damage, associated with each alpha decay. This damage is most concentrated around the parent isotope (U and Th), expelling the daughter isotope (Pb) from its original position in the zircon lattice. In areas with a high concentration of the parent isotope, damage to the crystal lattice is quite extensive, and will often interconnect to form

1392-406: The isotopic and elemental abundances in minerals at a 10 to 30 μm-diameter scale and with a depth resolution of 1–5 μm. Thus, SIMS method is well-suited for the analysis of complex minerals, as often found in metamorphic terrains, some igneous rocks , and for relatively rapid analysis of statistical valid sets of detrital minerals from sedimentary rocks. The most common application of the instrument

1440-580: The lead generated by radioactive decay of uranium and thorium up to very high temperatures (about 900 °C), though accumulated radiation damage within zones of very high uranium can lower this temperature substantially. Zircon is very chemically inert and resistant to mechanical weathering – a mixed blessing for geochronologists, as zones or even whole crystals can survive melting of their parent rock with their original uranium–lead age intact. Thus, zircon crystals with prolonged and complicated histories can contain zones of dramatically different ages (usually with

1488-417: The market by a French company years before), negative-ion stable isotope measurements and on-going work in developing a dedicated instrument for light stable isotopes. Fifteen SHRIMP instruments have now been installed around the world and SHRIMP results have been reported in more than 2000 peer reviewed scientific papers. SHRIMP is an important tool for understanding early Earth history having analysed some of

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1536-403: The masses by resonant electric fields, which allow only the selected masses to pass through. The time of flight mass analyzer separates the ions in a field-free drift path according to their velocity. Since all ions possess the same kinetic energy the velocity and therefore time of flight varies according to mass. It requires pulsed secondary ion generation using either a pulsed primary ion gun or

1584-402: The measured relative isotopic abundances do not relate to the real relative isotopic abundances in the target. Corrections are determined by analysing unknowns and reference material (matrix-matched material of known isotopic composition), and determining an analytical-session specific calibration factor. Secondary ion mass spectrometry In 1910 British physicist J. J. Thomson observed

1632-462: The notation can be ignored.) These are said to yield concordant ages ( t from each equation 1 and 2). It is these concordant ages, plotted over a series of time intervals, that result in the concordant line. Loss (leakage) of lead from the sample will result in a discrepancy in the ages determined by each decay scheme. This effect is referred to as discordance and is demonstrated in Figure ;1. If

1680-589: The project in 1989 to build a commercial version of the instrument, the SHRIMP-II, in association with ANUTECH, the Australian National University's commercial arm. Refined ion optic designs in the mid-1990s prompted development and construction of the SHRIMP-RG (Reverse Geometry) with improved mass resolution. Further advances in design have also led to multiple ion collection systems (already introduced in

1728-503: The same time, A. Benninghoven introduced the method of static SIMS , where the primary ion current density is so small that only a negligible fraction (typically 1%) of the first surface layer is necessary for surface analysis. Instruments of this type use pulsed primary ion sources and time-of-flight mass spectrometers and were developed by Benninghoven, Niehuis and Steffens at the University of Münster , Germany and also by Charles Evans & Associates. The Castaing and Slodzian design

1776-406: The sample and the secondary ion extraction lens, (4) a mass analyser separating the ions according to their mass-to-charge ratio, and (5) a detector. SIMS requires a high vacuum with pressures below 10 Pa (roughly 10 mbar or torr ). This is needed to ensure that secondary ions do not collide with background gases on their way to the detector (i.e. the mean free path of gas molecules within

1824-411: The sample during analysis. The secondary ions are filtered and focussed according to their kinetic energy by a 1272 mm radius 90° electrostatic sector . A mechanically-operated slit provides fine-tuning of the energy spectrum transmitted into the magnetic sector and an electrostatic quadrupole lens is used to reduce aberrations in transmitting the ions to the magnetic sector. The electromagnet has

1872-512: The sample is ~10 pA/μm and an analysis of 15–20 minutes creates an ablation pit of less than 1 μm. The primary beam is 45° incident to the plane of the sample surface with secondary ions extracted at 90° and accelerated at 10 kV. Three quadrupole lenses focus the secondary ions onto a source slit and the design aims to maximise transmission of ions rather than preserving an ion image unlike other ion probe designs. A Schwarzschild objective lens provides reflected-light direct microscopic viewing of

1920-453: The sputtering process are used to analyze the chemical composition of the material, these represent a small fraction of the particles emitted from the sample. In the field of surface analysis, it is usual to distinguish static SIMS and dynamic SIMS . Static SIMS is the process involved in surface atomic monolayer analysis, or surface molecular analysis, usually with a pulsed ion beam and a time of flight mass spectrometer, while dynamic SIMS

1968-424: The surface chemistry of catalysts . DSIMS was developed by John B. Fenn and Koichi Tanaka in the early 1980s. DSIMS is mainly used by the semiconductor industry . The COSIMA instrument onboard Rosetta was the first instrument to determine the composition of cometary dust in situ with secondary ion mass spectrometry during the spacecraft's 2014–2016 close approaches to comet 67P/Churyumov–Gerasimenko . SIMS

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2016-479: The target where it sputters "secondary" ions from the sample. These secondary ions are accelerated along the instrument where the various isotopes of uranium , lead and thorium are measured successively, along with reference peaks for Zr 2 O, ThO and UO. Since the sputtering yield differs between ion species and relative sputtering yield increases or decreases with time depending on the ion species (due to increasing crater depth, charging effects and other factors),

2064-433: The time in order to analyse individual mineral grains. Optic designer Steve Clement based the prototype instrument (now referred to as 'SHRIMP-I') on a design by Matsuda which minimised aberrations in transmitting ions through the various sectors. The instrument was built from 1975 and 1977 with testing and redesigning from 1978. The first successful geological applications occurred in 1980. The first major scientific impact

2112-422: The type of instrumentation used, the primary ion beam used and the analytical area, and other factors. Samples as small as individual pollen grains and microfossils can yield results by this technique. The amount of surface cratering created by the process depends on the current (pulsed or continuous) and dimensions of the primary ion beam. While only charged secondary ions emitted from the material surface through

2160-451: The zircon can be calculated by assuming exponential decay of uranium. That is where This gives which can be written as The more commonly used decay chains of Uranium and Lead gives the following equations: (The notation Pb ∗ {\displaystyle {\text{Pb}}^{*}} , sometimes used in this context, refers to radiogenic lead. For zircon, the original lead content can be assumed to be zero, and

2208-596: Was an American project, led by Liebel and Herzog, which was sponsored by NASA at GCA Corp, Massachusetts, for analyzing Moon rocks , the other at the University of Paris-Sud in Orsay by R. Castaing for the PhD thesis of G. Slodzian. These first instruments were based on a magnetic double focusing sector field mass spectrometer and used argon for the primary beam ions. In the 1970s, K. Wittmaack and C. Magee developed SIMS instruments equipped with quadrupole mass analyzers . Around

2256-470: Was developed in the 1960s by the French company CAMECA S.A.S. and used in materials science and surface science . Recent developments are focusing on novel primary ion species like C 60 , ionized clusters of gold and bismuth , or large gas cluster ion beams (e.g., Ar 700 ). The sensitive high-resolution ion microprobe (SHRIMP) is a large-diameter, double-focusing SIMS sector instrument based on

2304-681: Was the discovery of Hadean (>4000 million year old) zircon grains at Mt. Narryer in Western Australia and then later at the nearby Jack Hills . These results and the SHRIMP analytical method itself were initially questioned but subsequent conventional analysis were partially confirmed. SHRIMP-I also pioneered ion microprobe studies of titanium , hafnium and sulfur isotopic systems. Growing interest from commercial companies and other academic research groups, notably Prof. John de Laeter of Curtin University (Perth, Western Australia), led to

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