Heavy water for very light particles.

Heavy water for very light particles

Astrophysicists want to know why the sun shines. The answer to that question probably involves neutrinos, some of the lightest and most elusive subatomic particles known to physics. The nuclear fusion processes that make the sun shine should produce a certain flux of neutrinos, but the one long-running experiment looking for solar neutrinos consistently records only a third as many as expected.

The explanation may be that neutrinos change their identities in flight. There are three known kinds of neutrinos, but the currently running experiment is sensitive to only one kind. If a neutrino can change from one kind to another in flight, the experiment may miss a large part of the total flux. On the premise that this happens, several experiments sensitive to all three kinds are being set up (SN:8/9/86,p.88). An experimen t planned for a mine near Sudbury. Ontario, would be unique among these in using the world's largest concentration of heavy water as a neutrino detector.

Heavy water is deuterium oxide: The hydrogen in it is the isotope deuterium, which has a neutron and a proton in its nucleus instead of the single proton of ordinary hydrogen. Deuterium oxide is thus two atomic mass units heavier than hydrogen oxide. In natural water 1 molecule in 7,000 is heavy water, and concentrating the heavy water is a laborious chemical and physical process.

In the late 1930s, Norway was the world's largest producer of heavy water, and that inspired an oft-televised film, "Heroes of Telemark," in which Allied agents try to blow up the plant. Today, Canada is the premier producer, and the 1,000 metric tons that the experiment will use is available nowhere else in the world, according to a recent announcement by the University of California at Irvine, one of the institutions involved.

Plans call for the tank of heavy water to be set up in Sudbury, 6,800 feet underground in the Creighton mine of International Nickel Co. to shield it from other kinds of radiation. When a neutrino coming into the tank interacts with a deuterium nucleus, it will produce a flash of light that will be recorded by the instrumentation. Ten trillion neturinos a second should pass through the tank; 20 per day should interact.

Once the observatory is completed, scientists will be able to observe the core of the sun in virtually real time, something no other technique has been able to do, says Herbert Chen of UC Irvine, who originated the idea for this kind of detector. Other institutions involved are: Queen's University at Kingston, Ontario, the University of Guelph (Ontario), Carleton University in Ottawa, Laurentian University of Sudbury, the National Research Council of Canada, the Chalk River (Ontario) Nuclear Laboratories, Princeton (N.J.) University and Oxford University.