Sensitive High Resolution Ion Microprobe

The sensitive high resolution ion Microprobe ( SHRIMP short ) is an instrument based on a double focusing secondary ion mass spectrometer (SIMS) with a large diameter. The instrument is as well as his successor SHRIMP II and IV produced by the Australian company Australian Scientific Instruments (ASI ) in Canberra. The SHRIMP microprobe uses an ion beam to generate secondary ions that are separated by the mass spectrometer according to their mass and energy and collected in a counter. SHRIMP is strictly speaking not generic, but a product name of ASI. A similar secondary ion microprobe with a large magnetic radius is offered by the company Cameca in Paris under the name IMS1280 -HR. It differs in its additional function as an ion microscope, which is the ability to create a direct mass-selected image of the sample; an improved mass resolution and the ability to measure the isotopic composition automatically in small particles.

Applications

The SHRIMP is mainly used for geological and geochemical applications. It can measure the isotopic and elemental distributions in minerals down to a size of 5 microns. It is therefore well suited for the analysis of complex construction minerals, as they are encountered often in metamorphic rocks and in some igneous rocks and detrital minerals in sedimentary rocks.

The most common application is the radiometric dating using the thorium uranium -lead method, where the shrimp can also be used for the analysis of other elements and isotopes.

Isotopic dating

For thorium uranium -lead dating a beam of oxygen ions (O2 - ) is analyzed with respect to its mass, then through a collimator, and then accelerated to the sample to strike there secondary ions ( sputtering). The secondary ions are accelerated in the instrument, and in each case measured, the amount of the various uranium, lead and thorium isotopes. Along with them is measured as a reference per zirconia ( Zr2O ) and a uranium oxide ion ( UO ).

Since the yield of Sputterings differs with each type of ion, and varied by increasing the size of micro- crater produced, the influence of charge effects and other factors with the duration of the operation, the measured relative frequency of the ion is not the real relative frequency in the sample from. Correction factors are, therefore, obtained by the analysis of standards, the composition of which is known, and by comparison with the analysis of unknown materials. These correction factors apply only to the current measurement and must be repeated at every meeting ..

Locations of SHRIMP instruments

By 2007, 14 SHRIMP-I were installed nstruments, most of them in Australia and Asia. Six instruments are located in Australia, three of them alone at the Australian National University. The closest of Germany unit is located in Warsaw at the National Research Geologiczny.