logbook: solar neutrinos

Logbook courtesy of Ray Davis (Click on image for larger version.)

Deep in the Homestake Gold Mine in Lead, South Dakota, during the early 1970s, Ray Davis monitored a 100,000-gallon tank of perchloroethylene, a chlorine-rich dry-cleaning chemical. The experiment was designed to detect solar neutrinos, using the theory that an incoming neutrino would produce radioactive argon by interacting with a chlorine nucleus.

Davis was successful, but detected just one-third of the expected number. This "solar neutrino puzzle" inspired a series of experiments that eventually confirmed neutrinos change flavors. For his work, Davis won the 2002 Nobel Prize in Physics.

This page from his notebook captures a piece of that work. Davis discusses the "tank cars"--500-gallon tanks mounted on rail cars--used to measure the production rate of one type of background particle, neutrons, at different depths of the mine. The tanks (he sketched one in the lower left) contained a solution of calcium nitrate, a common fertilizer. The results helped Davis determine the cosmic ray background in the 100,000-gallon tank.

Laura Mgrdichian, Brookhaven National Laboratory

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