Hanging steel to catch neutrinos

6 October 1999

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This huge steel plate is a prototype layer for a detector to trap the elusive particles known as neutrinos.The MINOS (Main Injector Neutrino Oscillation Search) experiment aims to detect neutrinos produced at the Fermi National Accelerator Laboratory in Illinois after they have travelled 730 km beneath the Earth's surface to the Soudan Underground Laboratory in Minnesota. The plan will be to compare neutrino interactions in a detector close to the source at Fermilab with interactions in the distant Soudan Laboratory, in order to see if the neutrinos "oscillate", that is, change from one type to another.

The distant detector will be a 5400-tonne sandwich of steel (to make the neutrinos interact) and scintillator (to reveal products of the interactions). Each steel sheet in the sandwich will be only 2.5 cm thick, but 8 m wide and 8 m tall. With a weight of 11.25 tonnes each, the sheets must be carefully supported to prevent them from crinkling. The prototype steel sheet seen here was attached to a backing frame (in the foreground) while it was being raised. Once vertical, the sheet was hung from "ears" at the side, and the backing frame removed. (The person on the balcony to the right gives a sense of scale.) This demonstrated the support system that will be used in the final detector. One other problem is that the actual detector will be assembled underground at the site of an historic mine. The steel will have to pass down a mine shaft only 1 m by 2m, so the final 8-m plate must be welded from eight 2-m panels - you can see the seams in the larger view.

Credit: Email Jeff Nelson, University of Minnesota

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