Monday, November 23, 2009

Why we are going to Antarctica

This blog will be an account of my trip to Moore’s Bay, on the Ross Ice Shelf in Antarctica. Thorsten Stezelberger (an LBNL Engineer) and I are going there to study the site conditions and test prototype electronics for ARIANNA, a proposed experiment to look for radio pulses produced by neutrino interactions in the Antarctic ice. I will try to capture the adventure of traveling to Antarctica and camping out on the ice, while also giving you and idea of why this crazy trip is worthwhile, scientifically.

We plan to leave Berkeley on November 28th, and fly via Christchurch, New Zealand to McMurdo Station, in Antarctica. There, we will attend “Snow School,” (aka survival training) and gather our equipment, before being deposited by helicopter on an empty patch of ice in Moore’s Bay, about 70 miles from McMurdo, where we will camp on the 650 m thick Ross Ice Shelf. We plan to spend 10 days in Moore’s Bay, characterizing the ice (e.g. measuring the radio wave reflections from the ice-water interface, etc.) and setting up a prototype radio detector which will be left in place for a year. Of course, plans sometimes change quickly in Antarctica.

The prototype is one step toward ARIANNA, a proposed array of about 10,000 stations, covering roughly 900 square kilometers. Each station will consist of 8 TV-like antennae embedded in the ice, connected to an electronics box containing trigger electronic and waveform digitizers. The whole thing will be powered by solar panels in the summer (when the sun is continuously above the horizon). For the winter, we are testing a wind generator, but this will place stringent limits on station power consumption.

The ARIANNA detectors search for radio waves produced by neutrino interactions in the ice. The radio pulses come from the particle showers produced when occur when the neutrino converts it’s energy into matter, creating a shower containing up to a trillion particles. The showers contain more electrons than positrons (because some of the photons Compton scatter from atomic electrons in the ice). The moving charges emit Cherenkov radiation. For radio wavelengths longer than the shower diameter, the radiation is coherent, producing large signals in the 50 MHz to 1 GHz frequency range. The signal size rises as the square of the neutrino energy; ARIANNA should detect neutrinos with energies above 10^17 eV.

We use these neutrinos to probe the high energy cosmos, to find the origin of the high energy cosmic rays that have been observed by surface air shower arrays like Auger. ARIANNA will complement smaller neutrino detectors like the 1 cubic-kilometer IceCube array which is optimized for lower energy (10^11 to 10^17 eV) neutrinos.

1 comment:

  1. Spencer, et al.,
    Have a safe, productive trip. We look forward to your postings. Happy hunting!!

    The Bennett's