首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Virtually everything astronomers known about objects outside the solar system is based on the detection of photons-quanta of ele
Virtually everything astronomers known about objects outside the solar system is based on the detection of photons-quanta of ele
admin
2013-06-03
30
问题
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: neutrinos (中微子). 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 aggregations 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: therefore, 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 particle 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 wilt 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 (类星体), and pulsars (脉冲星). Each of these discoveries came as a surprise. Neutrino astronomy will doubtless bring its own share of surprises.
One advantage that neutrinos have for studies in astronomy is that they
选项
A、have been detected for 25 years.
B、possess a variable electric charge.
C、are usually extremely massive.
D、record information about their own origin.
答案
D
解析
细节题。选项D是对首段末句中的第一个原因分句的近义改写,因此选项D为本题答案。
转载请注明原文地址:https://kaotiyun.com/show/w3QK777K
0
专业英语四级
相关试题推荐
Truepatriotism______puttingtheinterestsofonecountryaboveeverything,______one’slife.
Primitivemonetarysystemsrequirethesamebalanceofsupplyanddemandthat_____theU.S.TreasuryandtheFederalReserveSyst
Themanstopstotakehisdogoutsidetodoexercisebecause
______,heisnotcapableofteachingallsubjects.Afterall,nobodycouldbeanexpertoneverything.
Wecanuseoureyesandfacialexpressionstocommunicatevirtuallyevery______nuanceofemotion.
Themandidn’tputhisluggageoutsidethedoorontimebecause______.
随机试题
下列关于冷冻干燥的正确表述
关于缺铁性贫血患者的表现,下列哪项不正确
患者,男性,80岁。因右腹股沟斜疝6小时来诊。既往有可复性腹股沟肿物史30年。检查:右侧腹股沟至阴囊10cm×6cm,嵌顿疝,皮肤无红肿。首选的治疗方法是()
可出现嗜酸性粒细胞减少的疾病是()
甲某与深圳某经纪公司签订了一份期货经纪合同,开立账户炒作美国S&P500指数期货。甲某直接操作,前后共亏损30万元。该案正确的处理方式有()。
没有人能够否认A在这次事件中所起到的不容忽视的作用。如果上述论断为真,则下列各项说法中正确的是:
公共信息资源指社会公共领域中由特定管理机构依法管理,面向全体社会公众提供信息服务的各种数据系统,具有公共性、广泛性、基础性和公益性等特点。根据上述定义,下列属于公共信息资源的是:
文法G=({E),{+,*,(,),a),P,E),其中P由下列产生式组成E->E+E|E*E|(E)|A它生成由a,+,*,(,)组成的算术表达式,该文法在乔姆斯基分层中属于(66)型文法,其对应的自动机是(67),如产生句子a*a+a,它的派生树是(6
关于电子商务,以下哪种说法是不正确的?
有以下程序:#includemain(){intn,*p=NULL:*p=&n:prinff(“Inputn:”);8eanf(“%d”,&p);prinff(“outputn:”);prinff(“
最新回复
(
0
)