杏吧原创

UNDERGROUND salt deposits could be turned into huge neutrino detectors that
might help us understand at last where high-energy 鈥渃osmic rays鈥� come from.

Ultra-high-energy neutrinos鈥攚ith energies in excess of 10¹⁶
electronvolts鈥攁re the result of interactions between photons from the
cosmic background radiation and the fast-moving particles known as cosmic rays.
The background radiation is the 鈥渁fterglow鈥� of the big bang, but where the
fastest cosmic rays come from remains a mystery.

Detecting the neutrinos is no mean feat, as they rarely interact with matter.
But inside a salt crystal, neutrinos will occasionally strike an atomic nucleus
and produce a shower of charged particles, which in turn produce an intense
burst of radio waves. To know whether they would be able to spot these bursts,
scientists had to check that the salt wouldn鈥檛 absorb the waves before they had
spread far enough to be detected.

A team led by Peter Gorham of NASA鈥檚 Jet Propulsion Laboratory in Pasadena
and David Saltzberg of the University of California at Los Angeles studied the
United Salt Corporation鈥檚 Hockley mine, in a salt dome near Houston, and the US
Waste Isolation Pilot Plant in an evaporite salt bed near Carlsbad, New
Mexico.

The physicists found that radio waves travelled several hundred metres
through the salt of the Hockley mine. 鈥淲e conclude that salt domes provide
attractive sites for the next generation of high-energy neutrino detectors,鈥�
says Gorham.