ON THE AGE VS DEPTH AND OPTICAL CLARITY OF DEEP ICE AT THE SOUTH-POLE

The first four strings of phototubes for the AMANDA high-energy neutri no observatory are now frozen in place at a depth of 800-1000 m in ice at the South Pole. During the 1995-96 season, as many as six more str ings will be deployed at greater depths. Provided absorption, scatteri ng and refraction of visible light are sufficiently small, the traject ory of a muon into which a neutrino converts can be determined by usin g the array of phototubes to measure the arrival times of Cherenkov li ght emitted by the muon. To help in deciding on the depth for implanta tion of the six new strings, we discuss models of age vs depth for Sou th Pole ice, we estimate mean free paths for scattering from bubbles a nd dust as a function of depth and we assess distortion of light paths due to refraction at crystal boundaries and interfaces between air-hy drate inclusions and normal ice. We conclude that the interval 1600-21 00 m will be suitably transparent for a future 1 km(3) observatory exc ept possibly in a region a few tens of meters thick at a depth corresp onding to a peak in the dust concentration at 60 k year BP.