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Text 3. Cosmic SNUs
(CLOSING IN ON THE «SOLAR NEUTRINO PROBLEM»)
For a tiny, chargeless and (maybe) massless subatomic particle, the neutrino carries a lot of scientific weight. The fusion reactions that cause the sun to shine produce neutrinos. The number of neutrinos produced is about one third less than theory predicts. Clearly, something is seriously amiss - either astronomers do not understand the internal structure of the sun, or else physicists do not understand how subatomic particles behave. Two ingenious new experiments strengthen the case for a revised physics.
The deficit first came to light around 1970, soon after Raymond Davis, Jr., now at the University of Pennsylvania, set up an underground detector, a giant tank of perchloroethylene in the Homestake gold mine in South Dakota. Subsequent observations by Kamiokande, a complementary neutrino detector located in Japan, seemed to confirm the result.
In 1990 another, quite different kind of neutrino detector - the Soviet-American Gallium Experiment, or SAGE - began operation in the Russian Caucasus. SAGE incorporates a 60-ton tank of liquid gallium; on rare occasions, a neutrino will hit an atom of gallium 71, transforming it into an atom of germanium 71. The number of germanium 71 atoms collected in the tank indicates the flux of solar neutrinos passing through SAGE. In 1991 a second, similar experiment - GALLEX (short for Gallium Experiment) - started operating in the Apennine Mountains of Italy.
SAGE and GALLEX offer significant insight into solar physics because they are sensitive to neutrinos produced by the collision of two protons, the most fundamental energy-producing reaction in the sun. Theoretical calculations indicate that the gallium detectors should pick up a flux of about 130 solar neutrino units, or SNUs. In September a group of researchers affiliated with SAGE reported detecting about 70 SNUs. The GALLEX collaboration recently wrote that their instrument is picking up about 87 SNUs.
So, where have all the solar neutrinos gone? In a theory originated by Lincoln Wolfenstein of Carnegie Mellon University and elaborated by Russian physicists Stanislaw P.Mikheyev and Aleksei Y.Smirnov, neutrinos “oscillate” between different types. According to their theory, known as the MSW effect, the electron neutrino, which shows up in existing detectors, could transform into other forms of electrons that the detectors cannot collect.
One of the corollaries of the MSW effect is that the neutrino, long thought to be a massless particle, must possess a tiny mass. For years, some cosmologists have wondered if mass-bearing neutrinos could make up part or all of the cosmic “dark matter” - an unseen component of the universe whose gravity may strongly influence the evolution and dynamics of galaxies.
“It is still a bit of a crap-shoot at this point”, Hahn says, “but at the conferences, people are talking more and more about oscillations”. Several upcoming neutrino detectors may finally sort out this mess. The most important may be the Sudbury Neutrino Observatory in Canada, which will be able to detect all forms of neutrinos and so should finally clarify whether the MSW theory is correct.
Richard L.Hahn. Scientific American, 1993
Vocabulary and Comprehension Exercises
I. Translate these into your own language:
• a chargeless and massless particle
• to carry a lot of scientific weight
• the fusion reactions
• something is amiss
• the internal structure of the sun
• to come to light
• to confirm the result
• a 60-ton tank of liquid gallium
• the flux of solar neutrinos
• to offer significant insight into solar physics
• the collision of two protons
• to pick up a flux of about 130 solar neutrino units, or SNUs
II. Give the situations from the text in which the following words and expressions are used:
• to carry a lot of scientific weight
• to produce neutrinos
• to predict
• to come to light
• to begin operating
• to offer significant insight into solar physics
• to pick up a flux
• to “oscillate” between different types
• the electron neutrino
• to possess a tiny mass
III. Comment on the structure of the following sentences:
• The fusion reactions that cause the sun to shine produce neutrinos.
• In a theory originated by Lincoln Wolfenstein of Carnegie Mellon University and elaborated by Russian physicists Stanislav P.Mikheyev and Aleksei Y.Smirnov, neutrinos “oscillate” between different types.
• According to their theory, known as the MSW effect, the electron neutrino, which shows up in existing detectors, could transform into other forms of electrons that the detectors cannot collect.
IV. Ask questions to which the following statements might be the answer:
• The neutrino carries a lot of scientific weight.
• The fusion reactions that cause the sun to shine produce neutrinos.
• The number of neutrinos produced is about one third less than theory predicts.
• The deficit first came to light around 1970.
• In 1990 a new kind of neutrino detector - SAGE - began operating in the Russian Caucasus.
• In 1991 a second similar experiment - GALLEX - started operating in Italy.
• Theoretical calculations indicate that the gallium detectors should pick up a flux of about 130 SNUs.
• One of the corollaries of the MSW effect is that the neutrino must possess a tiny mass.
V Arrange the items of the plan in a logical order according to the text.
• In the years 1990-1991 two neutrino detectors started operating in Russia and in Italy.
• The fusion reactions that cause the sun to shine produce neutrinos.
• The number of neutrinos produced is about one third less than theory predicts.
• The researchers reported detecting about 70-90 SNUs.
• The electron neutrino which shows up in existing detectors, could transform into other forms of electrons that the detectors cannot collect.
• Theoretical calculations indicate that the gallium detectors should pick up a flux of about 130 SNUs.
• The deficit first came to light around 1970.
• According to the theory, known as the MSW effect, neutrinos “oscillate” between different types.
VI. Agree or disagree with the following statements:
• As a tiny, chargeless subatomic particle the neutrino carries no scientific weight.
• The fusion reactions that cause the sun to shine produce neutrinos.
• The number of neutrinos produced is about one third more than theory predicts.
• The deficit first came to light around 1950.
• In the years 1990-1991 five neutrino detectors started operating in France and in Germany.
• Theoretical calculations indicate that the gallium detectors should pick up a flux of about 130 SNUs.
• The researches reported detecting about 90-100 SNUs.
• According to the theory, known as the MSW effect, neutrinos “oscillate” between different types.
VII. Answer the questions:
• What is a neutrino?
• What produces neutrinos?
• What are the reasons for the fact that the number of neutrinos produced is about one third less than theory predicts?
• When did the deficit first come to light?
• What neutrino detector began to operate in the Caucasus?
• What neutrino detector began to operate in the Apennine Mountains ?
• Why do SAGE and GALLEX offer significant insight into solar physics?
• Are the numbers from SAGE and GALLEX exact?
• Why do the solar neutrinos disappear?
• What is the MSW effect?
• What is one of the corollaries of the MSW effect?
• What can clarify whether the MSW theory is correct?
VIII. Write a summary in English (or in your own language).
• Give each paragraph a suitable title in English (or in your own language).
• Develop the titles of the paragraphs into topic sentences. Join the topic sentences together.
• Re-read your summary and make sure that the sentences are presented in a logical order.