Mankind’s Explanation: Solar Neutrino Problem

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   “In 1968, Raymond Davis, Jr., a physicist from Brookhaven National Laboratory, began an experiment in Homestake Gold Mine in Lead, South Dakota. He constructed a 100,000-gallon tank at a depth of 4,850 feet (nearly a mile beneath the surface of the earth), and filled it with ordinary cleaning fluid. Then he set to work to see how many solar neutrinos he could detect in the tank.

   The cleaning fluid was a liquid called perchloroethylene, a compound made up of the elements carbon and chlorine; in each molecule there are two carbon and four chlorine atoms and four chlorine atoms. Davis chose this substance because, on rare occasions, a neutrino will interact with chlorine to produce an atom of argon 37. If Davis could measure the quantity of argon that was produced, he would be able to calculate how many neutrinos had entered the tank. He expected that the many trillions of neutrinos that entered his apparatus would produce argon atoms at about the rate of two per day.

   Now it so happens that argon 37 is radioactive. This fact is quite important. After all, hunting for one or two atoms of argon gas in a 100,00- gallon tank would be a hopeless task; finding the proverbial needle in a haystack would be much, much easier. But fortunately an atom of argon 37 will emit an electron when it decays, and individual electrons can be detected quite easily. All that Davis had to do was to set up an electronic apparatus that would count them. Davis was confident that his experiment would detect the neutrinos that were presumably coming from the sun, and only such neutrinos. He set up the apparatus far below the surface of the earth in order to eliminate the contaminating effects of reactions induced by cosmic rays. Neutrinos could easily penetrate to the depth at which the experiment waste up, but the particles that constituted cosmic “radiation” would not. Thus if Davis saw what looked like a neutrino-endured reaction, he could be reasonably sure that it had been induced by a neutrino from the sun.

   Davis was confident of this because, although the universe is almost certainly full of cosmic neutrinos that bombard the earth form all directions, these cosmic neutrinos (which are relics of the big bang) do not possess enough energy to convert chlorine into argon.  Finally, Davis checked his equipment to verify that he could indeed find any argon 37 atoms that were produced; and he found they could be detected with an efficiency of about 90 percent.

   Then the experiment was run. The results were not as expected. Davis found the number of neutrinos coming from the sun seemed to be only about 10 percent of the quantity that the theory predicted.”


The information contained within the quotes was obtained from: Cosmic Questions pages 55-56; published by John Wiley and Sons, Inc.; Copyright © 1993 Richard Morris

ISBN 0-471-59521-7

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