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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  51
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] In the last paragraph, the author describes the development of astronomy in order to
选项 A、suggest that the potential findings of neutrino astronomy can be seen as part of a series of astronomical successes.
B、illustrate the role of surprise in scientific discovery.
C、demonstrate the effectiveness of the DUMAND apparatus in detecting neutrinos.
D、name some cosmic phenomena that neutrino astronomy will illuminate.
E、contrast the motivation of earlier astronomers with that of the astrophysicists working on the DUMAND project.
答案 A
解析 最后一段，作者描写天文学的发展是为了：A．指出中微子天文学将来的发现可被看作天文学一系列成果之一。正确(见原文L72—75)。B．描述“surprise”在科学发现中的地位。无。C．表现DUMAND在探测中微子上的有效性。不是最后一段内容。D．列举几个中微子天文学能发现的现象。文中未给出具体例证。E．早期天文学家和进行DUMAND计划的天体物理学家动机的不同。无。
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