Origins ANTARCTICA, Scientific Journeys from McMurdo to the Pole
Ideas Tools Place Live Field Notes
  © Per Olof Hulth
  The optical module submerged in water, nearly two miles below the surface of the ice.

A literary essay about AMANDA by Francis Halzen
page 5

Why are we looking for neutrinos that have passed through the earth? Muons generated by cosmic rays also bombard the earth constantly from every direction, and some of them can travel through miles of ice before petering out. But no muon can cross the entire planet—as much as 8,000 miles of dense iron, magma and rock. Hence by pointing its photomultipliers downward, AMANDA uses the earth itself to screen out all upward-traveling muons except the ones thought to come from high-energy neutrinos.

AS EARLY AS THE 1960s, physicists had dreamed that radio antennas, operating near gigahertz frequencies, might listen in on the electric charges sparked by neutrinos crashing into ice. Thirty-five years later, however, working through the theory behind that idea, my colleagues and I showed that the radio signal created by the neutrinos was too weak to be of any use. It was then that I hit upon the obvious alternative: Why not try to detect the flash from a neutrino collision, rather than its noise?

I suspect that others must have contemplated the same idea and given up on it. Had I not been completely ignorant of what was then known about the optical properties of natural ice, I would probably have done the same. Instead, I sent off a flurry of E-mail messages to my friend John G. Learned, then the spokesperson for the Deep Underwater Muon and Neutrino Detector (DUMAND). Like AMANDA after it, DUMAND was designed to detect high energy muons—though in ocean water off the coast of Hawai’i rather than in Antarctic ice. But though Learned’s group had already deployed a test string of photomultipliers with some success, the project was eventually abandoned. (The DUMAND concept lives on, albeit at a smaller scale, in a detector now operating in the depths of Lake Baikal in Russia.)

Learned immediately appreciated the advantages of an Antarctic neutrino telescope. For starters, sinking the photomultipliers into ice would enable investigators to walk around on top of the experiment, as well as to keep all the fragile electronics at the surface. As a result, the neutrino signals could be identified with off-the-shelf electronics. Better yet, the ice would be geologically stable (Antarctica almost never has earthquakes) and completely dark. DUMAND did not have it so easy. Although the water off the Hawaiian coast is exceptionally clear and deep, Learned’s group had to contend with waves, storms, background light from bioluminescent organisms and the radioactive decay of sea salt. Most important, NSF was already operating a research station at the geographical South Pole, with an infrastructure to rival that of a national particle physics laboratory. AMANDA, in other words, would be much cheaper and easier to build than DUMAND.

back page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 next
Origins Exploratorium ANTARCTICA


© Exploratorium