Origins ANTARCTICA, Scientific Journeys from McMurdo to the Pole
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  © Per Olof Hulth
  At 240 meters, a single lamp from the module illuminates the hole.

A literary essay about AMANDA by Francis Halzen
page 8

At 10:30 P.M. on December 24, 1993, when the first of four strings of photomultipliers was deployed and ready for testing, I was at my family’s house in Tienen, Belgium, sitting down to a late Christmas Eve dinner. As usual in a Belgian home, the spread was magnificent, but I hardly paid attention. When the news finally arrived, dessert was being served and my laptop was propped on my knees. "First string deployed," the E-mail message read. The sender was too tired to write anything more.

IT WOULD HAVE BEEN EASY to build a more conventional neutrino telescope than AMANDA. We would have covered a square kilometer with spark chambers, shielding them from cosmic radiation with lead plates a few inches thick. The end result would have detected neutrinos beautifully and cost about $10 billion—a thousand times as much as we could afford. Instead, we resigned ourselves to using the simplest instruments possible to detect neutrinos across the greatest possible volume of water at the least possible cost. We would build a telescope that barely works.

Unfortunately, such a design depends, to some extent, on nature’s cooperation. So it was that our initial euphoria, on Christmas Eve, turned quickly to perplexity. We knew that some downward-traveling muons, created by cosmic-ray events at the surface, would reach our photomultipliers—even 800 to 1,000 meters beneath the surface. But we detected a hundred times as many as we expected. And though we had expected that bubbles, at that depth, would scatter the Cherenkov light to some degree, what we saw instead was a nearly meaningless blur.

Everything glaciologists had told us about Antarctic ice, it seemed, was wrong. To begin with, the ice down there was far more transparent than anyone had expected. Condensed from snow that fell 10,000 years ago, at the end of the last ice age, it could transmit a streak of blue light as far as one hundred meters, not just the eight meters that had been predicted. (The discrepancy seemed to arise from the fact that glaciologists carried out their tests with distilled water, which was much less pure than Antarctic ice.) In fact, because our photomultipliers operate at wavelengths where neither atomic nor molecular excitations absorb photons, the ice was almost infinitely transparent. That implied we could detect a few more upward-traveling muons than we had hoped, but it also explained the excess downward-traveling muons.

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