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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2024-01-13  65
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] According to the passage, one advantage that neutrinos have for studies in astronomy is that they
选项 A、have been detected for the last twenty-five years.
B、possess a variable electric charge.
C、are usually extremely massive.
D、carry information about their history with them.
E、are very similar to other electromagnetic particles.
答案 D
解析 中微子用于天文学研究的一个优点是：A．在最近25年间被观测。文中未提这是优点。B．拥有大量电荷。原文L7—8。中微子根本不带电荷。C．通常很大。原文L8。“其质量小到可以忽略”。D．携带了一些其自身历史信息。正确。见原文L17—19。E．和其他电磁粒子很像。第一段指出它和其他粒子相比，可以穿越宇宙，从一些天体中逃逸出来，这都是指中微子和其他粒子的不同之处。
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