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  3. Virtually everything astronomers known about objects outside the solar syste

Virtually everything astronomers known about objects outside the solar syste

游客2025-02-26  28
问题     Virtually everything astronomers known about objects outside the solar system is based on the detection of photons-quanta of electromagnetic radia- tion. Yet there is another form of radiation that permeates the universe: neutrinos. With(as its name implies)no electric charge, and negligible mass, the neutrino interacts with other particles so rarely that a neutrino can cross the entire universe, even traversing substantialaggregations of matter, without being absorbed or even deflected. Neutrinos can thus escape from regions of space where light and other kinds of electromagnetic radiation are blocked by matter. Furthermore, neutrinos carry with them information about the site and circumstances of their production: there- fore, the detection of cosmic neutrinos could provide new information about a wide variety of cosmic phenomena and about the history of the universe.
    But how can scientists detect a par- ticle that interacts so infrequently with other matter? Twenty-five years passed between Pauli’s hypothesis that the neutrino existed and its actual detection: since then virtually all research with neutrinos has been with neutrinos created artificially in large particle accelerators and studied under neutrino microscopes. But a neutrino telescope, capable of detecting cosmic neutrinos, is difficult to construct. No apparatus can detect neutrinos unless it is extremely massive, because great mass is synonymous with huge numbers of nucleons(neutrons and protons), and the more massive the detector, the greater the probability of one of its nucleon’s reacting with a neutrino. In addition, the apparatus must be sufficiently shielded from the interfering effects of other particles.
    Fortunately, a group of astrophysicists has proposed a means of detecting cosmic neutrinos by harnessing the mass of the ocean. Named DUMAND, for Deep Underwater Muon and Neutrino Detector, the project calls for placing an array of light sensors at a depth of five kilometers under the ocean surface. The detecting medium is the seawater itself: when a neutrino interacts with a particle in an atom of seawater, the result is a cascade of electrically charged particles and a flash of light that can be detected by the sensors. The five kilometers of seawater above the sensors will shield them from the interfering effects of other high-energy particles raining down through the atmosphere.
    The strongest motivation for the DUMAND project is that it will exploit an important source of information about the universe. The extension of astronomy from visible light to radio waves to x-rays and gamma rays never failed to lead to the discovery of unusual objects such as radio galaxies, quasars, and pulsars. Each of these discoveries came as a surprise. Neutrino astronomy will doubtless bring its own share of surprises. [br] Which of the following titles best summarizes the passage as a whole?
选项 A、At the Threshold of Neutrino Astronomy
B、Neutrinos and the History of the Universe
C、The Creation and Study of Neutrinos
D、The DUMAND System and How It Works
E、The Properties of the Neutrino
答案 A
解析 哪一个是描述文章内容的合适选项?(此题是主题题型的变种)A．正确。中微子天文学的开端。文章一开始就指出天体观测中中微子是一个重要工具，最后又指出对中微子的观测的原因就是它可能提供有关宇宙的重要的信息。因此，一切对中微子的考察、研究都是为天文学这一目标服务。B．中微子和宇宙历史。不够准确。C．中微子制造和研究。这是中间一大段内容，但本文作者不是以研究中微子为最终目的，研究它是为了对天文学作出贡献。D．DUMAND方式。只是文中部分内容。E．中微子性质。只是文中部分内容。
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