GMAT阅读练习及答案(10)
2011-09-15 14:03:00   来源：作文地带整理    双击单词自动翻译

　　Virtually everything astronomers known about objects

　　outside the solar system is based on the detection of

　　photons-quanta of electromagnetic radiation. Yet there

　　is another form of radiation that permeates the universe：

　　(5) 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 substantial ag美国GREgations of

　　matter， without being absorbed or even deflected. Neu-

　　(10) trinos 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： therefore， the detection of cosmic neutrinos

　　(15) could provide new information about a wide variety of

　　cosmic phenomena and about the history of the uni-

　　verse.

　　But how can scientists detect a particle that interacts

　　so infrequently with other matter? Twenty-five years

　　(20) 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，

　　(25) capable of detecting cosmic neutrinos， is difficult to co-

　　nstruct. No apparatus can detect neutrinos unless it is

　　extremely massive， because 美国GREat mass is synonymous

　　with huge numbers of nucleons (neutrons and protons)，

　　and the more massive the detector， the 美国GREater the pro-

　　(30) bability 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

　　(35) mass of the ocean. Named DUMAND， for Deep Under-

　　water Muon and Neutrino Detector， the project calls for

　　placing an array of light sensors at a depth of five kilo-

　　meters under the ocean surface. The detecting medium is

　　the seawater itself： when a neutrino interacts with a

　　(40) 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 sea-

　　water above the sensors will shield them from the interf-

　　ering effects of other high-energy particles raining down

　　(45) through the atmosphere.

　　The strongest motivation for the DUMAND project

　　is that it will exploit an important source of information