Scientists dream of shining an atomic 'flashlight' into the Earth
San Francisco — Using neutrinos - the ''ghost particles of the universe'' - to explore for oil, gas, and minerals must be one of the most science-fictionlike ideas to come out of the intellectual ferment touched off by the energy crisis.
Yet for several years, four prominent physicists have been studying just such a possibility in their spare time. The results are being published in the periodical Physics Reports.
The initiator of this work, particle theorist Alvaro De Rujula of the European scientific center CERN, calls it ''our mad project'' in acknowledgment of the fact that the idea seems so far-fetched. For the scientists involved it was more a stimulating intellectual exercise than a serious proposal. Still, members of the group seem to have convinced themselves that sometime in the future, when energy and minerals shortages are severe enough, such a project may be undertaken.
Neutrinos were christened ghost particles because they travel through solid objects almost as if they are not there. A high-energy beam of neutrinos could pass through the center of the Earth and emerge only slightly dimmed. Despite their elusive nature, physicists studying the nature of the particles that make up the atom have developed methods to detect them. So, if it were possible to generate a strong beam of high-energy neutrinos and shine it through various portions of the Earth, it should reveal the geological structure of the planet much the way X-rays reveal a person's skeleton.
At least that was the idea that came to Dr. De Rujula in the heyday of the energy crisis. His idea elicited the interest and collaboration of CERN co-worker Georges Charpak, Sheldon Glashow of Harvard, and Robert R. Wilson of Cornell.
The first big problem in the plan is a source for a strong beam of neutrinos. They envision this as a large, underwater particle accelerator, or atom smasher. This would have roughly a 10-mile diameter. The accelerator, properly called a proton synchrotron, would produce a beam of protons traveling at a good fraction of the speed of light. These would bombard a special target, generating a beam of subatomic particles that rapidly decay into neutrinos.
The accelerator would require a somewhat innovative design; but Dr. Wilson, an experienced accelerator experimenter, is convinced it can be done. Mostly, the problem is one of scale, as such a machine would be extremely large. The group estimates the accelerator, called the Geotron, would cost about $1 billion and take three years to build.
Once you have a neutrino beam, the next problem is using it. The scientists are fairly sure that beaming it down through the Earth to an array of special detectors would let them study the planet's internal structure. ''Personally, this is what interests me the most, and I'm quite convinced you could do it,'' Dr. Wilson comments.
To prospect for oil, gas, and minerals closer to the surface, however, the physicists had to be more creative.
They suggest that if the beam were aimed at a shallow angle, individual neutrinos that collide with atoms would give off sonic bursts that might be detectable from the surface. The nature of the bursts would be different, given the different densities of rock, liquid, and gas. Thus it might be possible to detect heavy minerals, oil, and natural-gas deposits. The nature of the acoustic signals that would be produced in such a fashion needs further study to verify the possibility of this approach to exploration, the scientists acknowledge.