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
101
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.
The neutrinos are hard to detect most probably because of
选项
A、their ability to escape from different regions of space.
B、their inability to penetrate dense matter.
C、the similarity of their structure to that of nucleons.
D、the infrequency of their interaction with other matter.
答案
D
解析
推断题。原文虽然没有直接提到中微子难以探测的原因,但是第2段首句中的定语从句暗示了中微子难以探测与它极少和别的物质起反应密切相关,由此可见,选项D是最可能造成中微子难以探测的原因。
转载请注明原文地址:https://kaotiyun.com/show/53QK777K
0
专业英语四级
相关试题推荐
Everythingintheuniverseundergoes______developmentandchange.
Solidgeometryhasenabledastronomerstocalculatethepositionsoftheheavenlybodies_____tooneanother.
Primitivemonetarysystemsrequirethesamebalanceofsupplyanddemandthat_____theU.S.TreasuryandtheFederalReserveSyst
Ahighlyorganizedsystemofirrigationis______Chineseagriculture.
______,heisnotcapableofteachingallsubjects.Afterall,nobodycouldbeanexpertoneverything.
Annawasreadingapieceofsciencefiction,completely______totheoutsideworld.
Themandidn’tputhisluggageoutsidethedoorontimebecause______.
Themandidn’tputhisluggageoutsidethedoorontimebecause______.
随机试题
________、________、________三者的最初结合,就是职位。
A.经典适形放射治疗B.调强适形放射治疗C.立体定向放射治疗D.常规体外照射E.γ-刀治疗_______要求在照射方向上,照射野的形状与病变的形状一致,且靶区内及其表面的剂量处处相等的放射治疗
口腔健康调查的样本含量小就会
因继承遗产纠纷提起的诉讼,由被继承人死亡时住所地或者主要遗产所在地人民法院管辖。()
一列简谐横波沿x轴正向传播,振幅为2cm,已知在t=0时刻相距30m的两质点a、b的位移都是1cm,但运动方向相反,其中质点a沿y轴负向运动,如图11所示。则()。
赤字预算体现的是一种()的财政政策。
为各项工作提供通讯联络、档案资料以及应用电子计算机提供信息服务的工作属于()。
二阶常系数非齐次线性微分方程y"-2y’-3y=(2x+1)e-x的特解形式为().
若有以下程序typedefstructstu{charname[10],gender;intscore;}STU;voidf(char*p){strcpy(P,"Qian");}main(){STUa={"Zhao",’m’,290},b
一棵二叉树共有25个结点,其中5个是叶子结点,则度为1的结点数为
最新回复
(
0
)