Scientists from UH pursue key particles
By Jan TenBruggencate
Physicists hope within a few years to sink a 60-foot sphere filled with mineral oil into the deep ocean off the Hawaiian Islands to serve as a detector of some of science's most enigmatic particles: neutrinos and anti-neutrinos.
The study of neutrino physics is in its infancy. University of Hawai'i scientists are part of a team that announced in the journal Nature the first positive identification of anti-neutrinos from the decay of radioactive matter in the Earth.
"This is the first piece of evidence regarding how radioactivity is distributed within the Earth and the first time neutrinos have played a role in the study of geophysics," UH physicist Eugene Guillian said.
Fellow physicist John Learned said scientists hope to use the detected particles to map the deep structure of our planet by measuring the decay of the radioactive elements uranium and thorium, which gives off anti-neutrinos. That information could lead to a better understanding of the Earth's magnetic field and how energy moves within the planet.
"This measurement opens a new era in neutrino applications, and one in which, for the first time, humans will be able to peer into the planet upon which we live," said Learned, who leads a team of UH scientists that includes Guillian, Jelena Maricic, Shigenobu Matsuno, Sandip Pakvasa, Stephen Olsen and Michael W. Peters.
Learned and members of his team have been working in a zinc mine more than half a mile below the surface in the Japanese Alps on the island of Honshu. They are operating the Kamioka Liquid Scintillator Anti-Neutrino Detector, or KamLAND, a 1,000-ton container of mineral oil and dye. The Hawai'i team is part of a collaboration of roughly 100 scientists on the project.
Normally, anti-neutrinos pass through matter without leaving any evidence, but sometimes one will crash into a proton, and in KamLAND the resulting reaction releases two flashes of light occurring 200 millionths of a second apart. The detector is deep under the rock to shield it from solar radiation and radioactive products from nuclear plants.
Learned said anti-neutrino impacts in the detector occur only about once every 20 days. Three out of four of the collisions involve anti-neutrinos from the surrounding rock, but about a quarter of them come from deep in the Earth. Learned said the team hopes to install an anti-neutrino detector in the deep sea off Hawai'i because the location will produce a clearer picture.
"We have a special opportunity in Hawai'i, due to our location in the mid-ocean, away from all power reactors and above only the relatively thin ocean crust. ... " he said. "We are planning an experiment which can make the first definitive measurements of neutrinos from the Earth's mantle and core, and make a definitive search for neutrino radiation from a hypothetical reactor at the core of the Earth."
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WHAT'S A NEUTRINO?Neutrinos are among the tiniest building blocks of matter — smaller than atoms, weighing less than an electron, and with a neutral electrical charge. They are produced naturally in the fusion reactions that power the sun and stars. Anti-neutrinos, which are very similar to neutrinos, are produced through the decay of radioactive materials, such as uranium and thorium.
There are three "flavors" of particles: electron, muon and tau neutrinos. All three come in both regular and anti-neutrino forms. Neutrinos are unaffected by electromagnetic forces and can pass through apparently solid matter without leaving a trace. However, occasionally, they will collide with another particle, and in a neutrino detector, physicists can record the impact as a double flash of light in an anti-neutrino detector.
For more information go to www.phys.hawaii.edu/~jgl/kamland_news_7-28-05.html. 
