Sensitive high resolution ion microprobe
The Sensitive High Resolution Ion Microprobe ( SHRIMP for short ) is an instrument based on a double focusing secondary ion mass spectrometer (SIMS) with a large diameter. Like its successors SHRIMP II and IV, the instrument is produced by the Australian company Australian Scientific Instruments (ASI) in Canberra . The SHRIMP microprobe uses an ion beam to generate secondary ions which are separated by the mass spectrometer according to their mass and energy and then collected in a counter. SHRIMP is actually not a generic term, but a product name from ASI. A similar secondary ion microprobe with a large magnetic radius is offered by the Cameca company in Paris under the name IMS1280-HR. It differs in its additional function as an ion microscope, i.e. the ability to create a direct mass-selected image of the sample; improved mass resolution and the ability to automatically measure isotopic composition in small particles.
Applications
The SHRIMP is mainly used for geological and geochemical applications. It can measure the isotope and element distributions in minerals down to a size of 5 µm . It is therefore well suited for the analysis of complex minerals, as they are often found in metamorphic rocks , in some igneous rocks and in detritic minerals in sedimentary rocks .
The most common application is radiometric dating using the uranium-thorium-lead method , whereby the SHRIMP can also be used for the analysis of other isotopes and elements.
Isotope dating
For uranium-thorium-lead dating , a beam of oxygen ions (O 2 - ) is first analyzed with regard to its mass, then guided through a collimator , and finally accelerated onto the sample in order to release secondary ions there ( sputtering ). The secondary ions are accelerated in the instrument and the amount of the various uranium , lead and thorium isotopes is measured. Together with them, a zirconium oxide (Zr 2 O + ) and a uranium oxide ion (UO + ) are measured as a reference .
Since the yield of sputtering varies depending on the type of ions and varies with the duration of the process due to the increase in the size of the microcrater generated, the influence of charge effects and other factors, the measured relative frequency of the ions does not constitute the real relative frequency in the sample from. Correction factors are therefore obtained by analyzing standards whose composition is known and comparing them with the analysis of unknown materials. These correction factors only apply to the current measurement and must be carried out again for each session.
SHRIMP instrument locations
By 2007, 14 SHRIMP instruments had been installed, most of them in Australia and Asia . Six instruments are located in Australia, three of which are at the Australian National University alone . The device closest to Germany is located in Warsaw in Państwowy Instytut Geologiczny .
Individual evidence
- ^ IS Williams: U-Th-Pb geochronology by ion microprobe. In: MA McKibben, WC Shanks III and WI Ridley (eds.): Applications of microanalytical techniques to understanding mineralizing processes. Reviews in Economic Geology, pp. 1-35, 1998
- ↑ P. Peres, F. Fernandes, E. de Chambost, M. Schuhmacher, P. Saliot and AN Davis: Towards an improved IMS 1280 model: The IMS 1280-HR In: Goldschmidt Conference Abstracts 2010, A806
- ↑ J. Claoué-Long, W. Compston, J. Roberts and CM Fanning: Two Carboniferous ages: a comparison of SHRIMP zircon dating with Conventional zircon ages and 40Ar / 39Ar analysis. In: WA Berggren, DV Kent, M.-P. Aubry and J. Hardenbol (Eds.): Geochronology, time scales and global stratigraphic correlation. Society for Sedimentary Petrology Special Publication, pp. 3-21, 1995
- ^ R. Stern: A time machine for Geoscience Australia. From Geo News, No. 81, pp. 15-17, Geoscience Australia, 2006
- ↑ List of SHRIMP operators ( Memento of the original from February 28, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
