Catching ghostly messengers from inner earth

By Robert Shikina

Scientists at the University of Hawai'i at Manoa are proposing to build a steel capsule 65 feet in diameter, fill it with mineral oil and submerge it four kilometers into the Pacific Ocean, in an effort to discover the contents of the Earth's core.

This capsule will be a self-contained science experiment to count geoneutrinos flying from within the earth, which could reveal a giant natural reactor within the core of the earth.

A natural reactor may be the lifeblood of Earth, explaining the formation of its crust, magnetic fields and life-sustaining atmosphere. Imaginably, a core natural reactor could be an essential element in the search for life on other planets.

Before scientists are able to X-ray the core of the earth, they must catch more of the elusive neutrinos. But that's not so easy. These sub-atomic particles, with no charge and very little mass, are so small they can pass through the entire earth without interacting with it.

Moreover, neutrinos often oscillate or change type among three kinds - electron, muon and tau.

That's why neutrino detectors are so large. Buried beneath a mountain in Japan, the Kamioka Liquid-scintillator Anti-Neutrino Detector, or KamLAND, is 42 feet in diameter and filled with 1,000 tons of mineral oil and dye. In Canada, the Sudbury Neutrino Observatory fills a cavern 45 feet high, 50 feet wide and over 270 feet long. In Japan, Super-Kamiokande is filled with 12.5 million gallons of purified water. In Antarctica, the Ice Cube project will turn a cubic kilometer of ice into a neutrino detector.

These experiments may one day explain the morphing of neutrinos among the three types.

John Learned, a physics professor at UHM, said this project "will lead to a grand unified theory of elementary particle physics, the holy grail of particle physics."

Learned has studied neutrinos for 30 years. Now, he leads the proposal for a UH detector, the Hawaii Anti-Neutrino Observatory, or HANOHANO, the Hawaiian word for 'excellent.' The detector is a $40 million collaboration between the University of Hawai'i and Makai Ocean Engineering.

HANOHANO will use a process similar to KamLAND's to detect a handful of the millions of neutrinos flying from the Earth. Inside the KamLAND, anti-neutrinos occasionally collide with protons, creating a neutron and a flash of light. Within 200 millionths of a second, the neutron combines with a proton, causing a second flash of light. Scientists call this double flash reaction 'inverse beta decay.'

Lining the inner walls of the detector, thousands of photomultipliers record the flashes of light as electrical signals, which tell scientists a neutrino was present. The inverse beta decay of anti-neutrinos creates a unique signature that scientists can distinguish from other pollutants in the detector.

HANOHANO will detect anti-neutrinos produced in the decay of uranium and thorium deposits within the earth. Locating the deposits will help scientists understand the earth's heat flows that make life possible on the surface.

HANOHANO will search for clues of a natural reactor, probably comprised of uranium and thorium, below. Marvin Herndon, a geophysicist, theorizes that a natural reactor four billion years old burns at the core.

Learned said that the earth's magnetic field, possibly a precursor to the atmosphere, could be generated by an internal natural reactor.

The cause of Earth's magnetic field is still unknown, but most likely, it is not a permanent magnet because of the earth's heat.

"If you take a magnet, any kind of magnet, and you heat it up very much at all, the magnet will go away," Learned said. "Hot stuff can't sustain a magnetic field. It has to be driven by (something) like an electromagnet."

For an earthly electromagnet, there would need to be a source of heat, such as a reactor, to drive the flow that creates a magnetic field.

"I started out thinking that it's nonsense, and now, based on all that I've read, I think there's some reasonable chance it's there," Learned said. "If it's there, this is one of the discoveries that will go down in the textbooks."

Learned estimated that it will take two years to build HANOHANO and two years to collect data. After the detector is built and data collected, scientists should be able to get to the bottom of this within a year, Learned said.

Earth scientists will gather in Hawai'i to discuss geoneutrinos at the end of the year. For more information on the conference visit www.phys.hawaii.edu/~sdye/hnsc.html.

Neutrinos Defined:

Neutrinos are the smallest particles that make up the universe - smaller than atoms, quarks and leptons. They have no electrical charge and a very small mass.

There are three types of neutrinos: electron, muon and tau. Anti-neutrinos are the anti-matter of neutrinos and also come in three types. Neutrinos can pass through large amounts of solid matter without being affected by it. Neutrinos are produced during fusion reactions, the process that burns the Sun.

Electron anti-neutrinos are produced during atomic fission, the reaction that powers nuclear power plants and the radioactive decay of uranium and thorium. Inside neutrino detectors, a neutrino will occasionally collide with a proton, setting off a flash of light and signifying their presence.

Some scientists speculate about the importance of neutrinos during the big bang. Professor John Learned, a physicist at UHM, said, "Without neutrinos, there may have been equal parts matter and anti-matter, which would have annihilated down, and the universe would be nothing but radiation light. At this point, there'd be a dim glow and that would be it."