SHRIMP History

Ion microprobes have been around in various forms for many years. It was not until the mid 70's that the ion probe was viewed as having the potential to be the geologist's ultimate weapon. The ion probe uses a focused beam of primary ions to sputter away the sample surface. A small fraction of the sputtered material is ionized and can then be accelerated into a mass spectrometer. A characteristic of secondary ion mass spectrometry (SIMS) is a plethora of atomic and molecular species which often cause isobaric interferences. The first ion microprobes relied on low mass resolution mass spectrometers and tried to strip away interferences by monitoring other peaks containing the interfering elements. This method is fraught with difficulty because it relies on the correct identification of all potential interferences. The first SIMS instrument capable of high mass resolution was the Cameca ims-3f. This instrument works as an ion microscope, that is, a direct image of the spatial distribution of the isotopes in the target can be obtained. High mass resolving power could only be achieved on this instrument at the expense of beam transmission - entrance and exit slits had to be very narrow thereby reducing the amount of beam transmission.


Professor William Compston, Dr. Kentaro Terada, Professor Hisashi Matsuda
Hiroshima University SHRIMP Workshop, November 11, 2004

The first SHRIMP (SHRIMP I) was conceived by Professor William Compston of the Australian National University, Canberra, as a response to the lack of a commercially available ion microprobe capable of isotopic analyses of geological materials. Steve Clement was called on to produce a blueprint for the ion microprobe and he chose the ion optical design of Professor H Matsuda as the best for the purpose.

The beam transport theory indicated that the mass analyzer needed to made as large as possible so as to maintain sensitivity at the high mass resolving powers required to discriminate against molecular isobaric interferences. The magnet turning radius was set at 1000 mm with the other lens elements scaled accordingly from Matsuda (1974). Construction began in 1977 and by 1981 the first isotopic analyses were made. SHRIMP I was the first ion microprobe capable of accurate U-Pb analyses on a microscale (ca. 30 microns). The fundamentals for the U-Pb calibration were published by Compston et al. (1984) and the capability for rapid analysis led to the discovery of Earth's oldest zircons (Froude et al. 1983). SHRIMP was also turned to the study of S isotopic distributions in ore minerals (Eldridge et al. 1987) and also to studies of extraterrestrial minerals with large isotopic anomalies (Ireland et al. 1985).


SHRIMP II at the Research School of Earth Sciences, ANU, Canberra, Australia


SHRIMP II at the All-Russian Research Geological Institute, St. Petersburg, Russia

SHRIMP II was the commercial prototype that was completed in 1990. It uses the same ion optical design as SHRIMP II but with a modified secondary extraction geometry that gives a three fold increase in the extracted secondary ion yield.

SHRIMP RG uses the same source chamber and primary column as SHRIMP II but it is a reverse geometry mass spectrometer capable of higher mass resolution for a given sensitivity.

References
Compston et al. (1984)
Eldridge et al
Froude et al. 1983
Ireland et al. 1985
Matsuda (1974)
Matsuda (1990)