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Discovery of X-ray emission from the eclipsing brown-dwarf binary 2MASS J05352184-0546085

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a r X i v :0809.4129v 1 [a s t r o -p h ] 24 S e p 2008Astronomy &Astrophysics manuscript no.0818text cESO 2008September 24,2008Discovery of X-ray emission from the eclipsing brown-dwarfbinary 2MASS J05352184-0546085S.Czesla,P.C.Schneider,and J.H.M.M.SchmittHamburger Sternwarte,Universit¨a t Hamburg,Gojenbergsweg 112,21029Hamburg,Germany Received .../accepted ...ABSTRACTThe eclipsing brown-dwarf binary system 2MASS J05352184-0546085is a case sui generis.For the first time,it allows a detailed analysis of the individual properties of young brown dwarfs,in particular,masses,and radii,and the temperature ratio of the system components can be determined accurately.The system shows a “temperature reversal”with the more massive component being the cooler one,and both components are found to be active.We analyze X-ray images obtained by Chandra and XMM-Newton containing 2MASS J05352184-0546085in their respective field of view.The Chandra observatory data show a clear X-ray source at the position of 2MASS J05352184-0546085,whereas the XMM-Newton data su ffer from contamination from other nearby sources,but are consistent with the Chandra detection.No indications of flaring activity are found in either of the observations (together ≈70ks),and we thus attribute the observed flux to quiescent emission.With an X-ray luminosity of 3×1028erg /s we find an L X /L bol -ratio close to the saturation limit of 10−3and an L X /L H α-ratio consistent with values obtained from low-mass stars.The X-ray detection of 2MASS J05352184-0546085reported here provides additional support for the interpretation of the temperature reversal in terms of magnetically suppressed convection,and suggests that the activity phenomena of young brown dwarfs resemble those of their more massive counterparts.Key words.Stars:low-mass,brown dwarfs —(Stars:)binaries:eclipsing —Stars:activity —X-rays:individuals:2MASS J05352184-05460851.IntroductionMagnetic activity is extremely common among late-type stars with outer convection zones (e.g.,Schmitt 1997).The cause of that activity as diagnosed by chromospheric and coronal emis-sions is ultimately thought to be a magnetic dynamo operating near the base of the convection zones of these stars.Near the spectral type ∼M3,stars are thought to become fully convec-tive,thereby preventing the emergence of a solar like dynamo in their interiors,and yet the activity properties seem to remain unchanged across this borderline (e.g.Fleming et al.1993).A saturation level of L X /L bol ∼10−3is observed also for fully convective stars,although with substantial dispersion.Ultra cool dwarfs (spectral type M7and later)show a drop in activ-ity as measured through their H αemission,and among L-type dwarfs H αemission is rarely found (Gizis et al.2000).For the majority of active M dwarfs the ratio between H αand bolomet-ric luminosity is log(L H α/L bol )∼−3.8,while for most objects of spectral class L this ratio drops below −5.Mohanty et al.(2002)argue that the high degree of neutrality in the outer at-mospheres of very low-mass stars e ffectively diminishes the activity level with e ffective temperature.X-ray detections from ultra cool dwarfs are quite sparse,and only a few objects have been identified as X-ray sources during flaring and quiescent periods.Examples comprise thebinary system GJ 569B consisting of two evolved (age ≈500Myrs)substellar objects of late-M spectral type detected by Stelzer (2004)and the latest (with respect to spectral type)object being the M9dwarf LHS 2065(e.g.,Schmitt &Liefke 2002;Robrade &Schmitt 2008).Hence,the behavior of X-ray emission is unclear as one approaches the boundary towards the substellar brown dwarfs and also the role played by the di ffer-ent stellar parameters for the activity evolution of these objects remains unclear (Stelzer &Micela 2007).It is particularly sur-prising that some of the very rapidly rotating substellar objects show little or no signs of activity.During the very early phases of their evolution,however,when the optical characteristics of brown dwarfs resemble those of stars with spectral type M6or so,they are often found to be quite active.Starting with the first X-ray detection of Cha H α1in the Chamaeleon I star forming region (Neuhauser &Comeron 1998),quite a number of brown dwarfs settled in star forming regions and (young)clusters have been detected in X-rays.The detection rate is higher for young brown dwarf compared to evolved ones,which might be related to a higher intrinsic X-ray luminosity,hotter outer atmospheres,or both.A crucial advance in the observational endeavor to un-ravel the nature of low-mass objects was the discovery of the eclipsing brown-dwarf binary (“2MASS J05352184-0546085”-in the following 2MASS 0535-0546,Stassun et al.2S.Czesla et al.:Discovery of X-ray emission from the eclipsing brown-dwarf binary2MASS J05352184-05460852006),which allowed to directly measure masses,radii,and a temperature ratio for brown dwarfs for thefirst time.The 2MASS0535-0546system is thought to be a member of the Orion Nebular Cluster(ONC)and,hence,very young(age ≈106years).It consists of two M6.5±0.5dwarfs in an ec-centric(e=0.31)9.78day orbit,such that the two eclipses are separated by a phase difference of0.67.In their analysis of2MASS0535-0546Stassun et al.(2006)determine masses of M1=56±4M Jup and M2=36±3M Jup as well as radii of R1=0.67±0.03R⊙and R2=0.49±0.02R⊙for the pri-mary and secondary component,respectively.Astonishingly, a“temperature reversal”is observed in this system,i.e.,the higher-mass primary component was found to be cooler than its lower-mass companion(T1≈2700K and T2≈2800K, Stassun et al.2007;Reiners et al.2007).From the activity point of view2MASS0535-0546is par-ticularly interesting since both components appear to be sub-stantially active,and according to Reiners et al.(2007)the Hα-emission of the primary exceeds that of the secondary by a fac-tor of7.The same authorsfind a rotational velocity of about v sin(i)=10km/s for the primary,while they give only an up-per limit of5km/s for the secondary.Assuming a magnetic ori-gin of this activity and the same scaling between Hα-emission and magneticfield strength as found for earlier type stars, Reiners et al.(2007)argue for the presence of magneticfields of B f≈4kG for the primary and B f≈2kG for the secondary.In this letter we report the discovery of X-ray emission of the eclipsing brown-dwarf binary2MASS0535-0546,which provides further support for the presence of magnetic activity in this system.2.Observations and data analysis2MASS0535-0546was serendipitously covered by observa-tions with both the Chandra and XMM-Newton observato-ries;the basic properties of these observations are provided in Table1.Table1.X-ray data of2MASS0535-0546.Instr.ID Obs.time Obs.date[ks][MJD]2.1.The Chandra dataThe“flankingfield south”of the ONC containing 2MASS0535-0546was observed with the“ACIS I”instrument onboard Chandra.In the associated im-age2MASS0535-0546is located relatively far off-axis (6.7arcmin),but is still well exposed,so that a sensitive search for X-ray emission is feasible.The Chandra image in the vicinity of2MASS0535-0546is shown in Fig.1.In an effort to suppress background and with the knowl-edge,that young brown dwarfs have X-ray spectra with me-dian energies of the order of or higher than1keV(e.g.Preibisch et al.2005),we limited the energy range of the im-age to the0.5−2.5keV band;a circle of radius5arcsec is drawn around the nominal position of2MASS0535-0546. According to our point-spread-function(PSF)modeling the en-circled region contains≈95%of the1keV photons from a point source at the respective off-axis position of the target. Within this circle wefind a total of8photons.Extrapolating the photon numbers measured in the same energy band from nearby source-free regions yields an expectation value of0.8 background counts.The Poisson probability of obtaining8or more counts with an expectation value of0.8is only2×10−7. Therefore,we attribute the recorded signal to an X-ray source with a count level of7.2±2.8photons.What about out-of-band photons?In the considered source region not a single photon with an energy below500eV was detected,while two pho-tons are contained in the2.5−10keV band.This number is, however,in good agreement with the expectation value derived from the close-by comparison region,and we,thus,attribute these photons to background.The median energy of the source photons is1.4keV,a value going well with those obtained by Preibisch et al.(2005)for 8other brown dwarf members of the ONC detected in a qui-escent state.For the depth of the absorbing column towards 2MASS0535-0546we estimated a value of n H=1021cm−2 combining the visual extinction of A V≈0.75mag given by Stassun et al.(2006)with the relationn H cm−2 =1.79×1021mag−1·A Vderived by Predehl&Schmitt(1995);a result consistent with the lower values derived from brighter,close-by X-ray sources. Assuming an absorbed one-component thermal spectrum with subsolar(0.3)abundances,a plasma temperature of≈2keV, and a distance of450pc(e.g.Stassun et al.2006)we com-pute an X-ray luminosity of(3.0±1.2)×1028erg/s in the 0.5−2.5keV band,which–again–is well covered by the range determined by Preibisch et al.(2005).To check the uniqueness of our identification we searched for other potential emitters close(30arcsec)to 2MASS0535-0546,but neither Simbad1,NED2,nor the 2MASS-survey provided any candidates in the environment under consideration.Therefore,we attribute the detected X-ray emission to2MASS0535-0546.2.1.1.TimingDo the source photons arrive homogeneously distributed in time or not?In Fig.2we present the background-subtracted 0.5−2.5keV band light-curve of2MASS0535-0546in the upper panel and the individual photons(registered by their en-ergies)plotted against arrival time in the lower panel.While no photons arrived during thefirst quarter of the observation, the assumption of a constant arrival rate is still consistent with the observations.More importantly,the light curve(cf.,Fig.2) suggests the presence of persistent X-ray emission more or lessS.Czesla et al.:Discovery of X-ray emission from the eclipsing brown-dwarf binary 2MASS J05352184-05460853Fig.1.X-ray image (2arcsec /bin)of the surrounding of 2MASS 0535-0546.A circular (5arcsec radius)region cen-tered on the nominal target position is superimposed on the image.homogeneously distributed in arrival time and not flaring emis-sion as –for example –observed in a number of brown dwarf ONC members (Preibisch et al.2005)or the ultra cool dwarf LHS 2065(Schmitt &Liefke 2002).R a t e [p h /k s ]E n e r g y [k e V ]Time [ks] from MJD 52523.54Fig.2.Upper panel:Background-subtracted 0.5−2.5keV band light curve (13ks binning).Lower panel:Photon energy against arrival time.2.2.The XMM-Newton dataAs 2MASS 0535-0546is clearly detected in the Chandra data,we searched for further evidence in other serendipitous X-ray observations.In an XMM-Newton observation of ιOrionis 2MASS 0535-0546is located roughly 9arcmin o ff-axis and we perform a similar analysis as for the Chandra data,i.e.,we define a source-free background region in the vicinity of 2MASS 0535-0546and concentrate on the energy range 0.5−2.5keV .We calculate the excess counts in a circular re-gion with a radius of 15arcsec (to take into account the larger XMM-Newton PSF)around the nominal source position.While in the Chandra image 2MASS 0535-0546is clearly separated from all neighboring sources (see Fig.1),we can unfortunately not exclude some contamination from close-by sources in the XMM-Newton data.Furthermore,in the image constructed from the pn data (i.e.,the most sensitive instru-ment onboard XMM-Newton )the readout strip generated by the out of time events from the central bright source (ιOrionis)is located less than one arcmin from 2MASS 0535-0546pro-viding yet an additional source of possible contamination.Momentarily neglecting these problems,we find 8±4,7±4and 13±6excess photons above the background for the MOS 1,MOS 2,and pn,data respectively.Converting into count rates and fluxes using the same model as for the Chandra pho-tons (cf.Sect.2.1)and a vignetting factor of 0.6(see XMM-Newton -Users Handbook sect.3.2.2.2),we find a value of (14.0±4.0)×1028erg /s for the averaged X-ray luminosity in the MOS 1,MOS 2,and pn data using WebPIMMS 3.This is a factor of five higher than the X-ray flux from 2MASS 0535-0546observed with Chandra .If we now es-timate the contamination level of the source region by plac-ing a similarly sized region at a comparable position with respect to the neighboring,contaminating sources,the ob-served flux level decreases to values roughly consistent with the Chandra measured flux.Although the XMM-Newton data alone are insu fficient to claim a detection,we conclude that they are at least consistent with the assumption of X-ray emis-sion from 2MASS 0535-0546at the same level as observed with Chandra ,and from an inspection of the arrival times of in-dividual photons we can also exclude the presence of (stronger)flares.2.3.Phase coverage of X-ray observationsInFig.3we show the phase folded optical light curve of 2MASS 0535-0546as given by Stassun et al.(2006),where we indicate those phase intervals covered either by XMM-Newton or Chandra .The XMM-Newton observation takes place shortly after the eclipse of the secondary,but unfortu-nately,none of the eclipses is covered by the presently avail-able X-ray data.Therefore,we are unable to unambiguously attribute the detected X-ray emission to any of the individual components of 2MASS 0535-0546,which is clearly a task for follow-up observations.Fig.3.Phase folded photometric data from Stassun et al.(2006).Observation phases of Chandra and XMM-Newton are indicated by black bars at the bottom and a gray column.4S.Czesla et al.:Discovery of X-ray emission from the eclipsing brown-dwarf binary2MASS J05352184-05460852.4.Chromospheric and coronal activityThe bolometric luminosity,L bol,of the individual components can be calculated fromL bol=4πr2σT4,(1) with r denoting the radius of the brown dwarf,σthe Stefan-Boltzmann constant,and T the effective ing the values given by Stassun et al.(2007)for the radii and temper-atures of2700K and2800K,wefind bolometric luminosities of8×1031erg/s and5.1×1031erg/s for the primary and sec-ondary components.As the primary shows strong magnetic activity (Reiners et al.2007),we naturally blame it to be also re-sponsible for the X-ray paring the X-ray luminosity of3×1028erg/s to its bolometric luminosity leads to a ratio of log L X/L bol=−3.4,and similar results of−3.2and −3.6are obtained if not the primary but the secondary or both were the X-ray bright component(s).Preibisch et al.(2005)detected quiescent emission from 8young brown dwarfs in the ONC.Wefind that both the X-ray luminosity of2MASS0535-0546and the log L X/L bol-ratio (no matter whether the primary or the secondary is held responsible for the X-ray emission)point to a rather ac-tive,however,not unprecedented object.From the activ-ity point of view,it appears similar to the late M dwarf 2MASS J05350705-0525005(COUP280),which is the most active brown dwarf in the(quiescent)Preibisch et al.(2005) sample showing an log L X/L bol-ratio of−3.3;with an X-ray luminosity of5×1028erg/s it is also among the most luminous. This provides further support for our attribution of the recorded X-rayflux to the2MASS0535-0546system.What do these outcomes imply for the relation between chromospheric and coronal activity in2MASS0535-0546? Reiners et al.(2007)derive values of log(L Hα/L bol)=−3.5 for the primary and log(L Hα/L bol)=−4.3for the secondary. Substituting our results we obtain log(L X/L Hα)=0.1if the pri-mary were the X-ray bright constituent and log(L X/L Hα)=0.7 if it is the secondary.These values compare well to those given by Dahm et al. (2007)for similarly young low-mass(M<0.5M⊙)classical and weak-line T-Tauri stars in NGC2264,and are also within the range of log(L X/L Hα)-ratios obtained by Hawley et al. (1996)for active cluster andfield M-dwarfs in a more advanced evolutionary state.3.Summary and conclusionsIn summary,wefind an unambiguous X-ray detection of the eclipsing brown-dwarf binary2MASS0535-0546.An X-ray source at the nominal position of2MASS0535-0546is clearly seen with the Chandra observatory,and the results are also compatible with an XMM-Newton image observed about one year earlier.The X-ray luminosity of2MASS0535-0546is of the order of3×1028erg/s,and even though the Chandra light curve might indicate some moderate increase in luminosity,no flaring activity is seen in either of the observations.Therefore, we attribute theflux to quiescent X-ray emission.An inspection of the source photons recorded by Chandra shows that the observed plasma emits at a tempera-ture of at least1keV and probably more.The relative hard-ness of the spectrum is compatible with the results obtained by Stelzer&Micela(2007)for a wide and similarly young brown-dwarf binary system.From the bolometric luminosity of the primary component we compute a value of−3.4for the log(L X/L bol)-ratio,which is close to the saturation limit of≈−3 and within the range of values determined by Preibisch et al. (2005)for other brown dwarf members of the ONC detected in quiescence as well as compatible with values computed by Stelzer et al.(2006)for other young brown dwarfs.Invoking thefindings of Reiners et al.(2007)wefind log(L X/L Hα)val-ues well consistent with previously published results for low-mass stars.Unfortunately,none of the optical eclipses is cov-ered by the available X-ray data,so we have no way at the moment to assign the X-rayflux to the individual components of2MASS0535-0546.What can our results tell us about the origin of the tempera-ture reversal?The effect may be caused either by a non-coeval formation of the brown dwarfs or by the impact of magnetic fields,which hamper energy transport by convection.The X-ray detection of2MASS0535-0546alone supports the pres-ence of magneticfields causing the X-ray emission;further evidence is the hardness of the source photons indicating that magnetic processes are the source of the activity.Our results are,therefore,fully in line with those of Reiners et al.(2007), pointing towards the presence of strong magnetic activity in 2MASS0535-0546near the saturation limit and hence a mag-netic origin of the observed temperature reversal. Acknowledgements.This work has made use of data obtained from the Chandra and XMM-Newton data archives.S.C.acknowledges support from the DLR under grant50OR0105.P.C.S.acknowledges support from the DLR under grant50OR703.ReferencesDahm,S.E.,Simon,T.,Proszkow,E.M.,&Patten,B.M.2007,AJ, 134,999Fleming,T.A.,Giampapa,M.S.,Schmitt,J.H.M.M.,&Bookbinder, J.A.1993,ApJ,410,387Gizis,J.E.,Monet,D.G.,Reid,I.N.,et al.2000,AJ,120,1085 Hawley,S.L.,Gizis,J.E.,&Reid,I.N.1996,AJ,112,2799 Mohanty,S.,Basri,G.,Shu,F.,Allard,F.,&Chabrier,G.2002,ApJ, 571,469Neuhauser,R.&Comeron,F.1998,Science,282,83Predehl,P.&Schmitt,J.H.M.M.1995,A&A,293,889 Preibisch,T.,McCaughrean,M.J.,Grosso,N.,et al.2005,ApJS,160, 582Reiners,A.,Seifahrt,A.,Stassun,K.G.,Melo,C.,&Mathieu,R.D.2007,ApJ,671,L149Robrade,J.&Schmitt,J.H.M.M.2008,ArXiv e-prints,806 Schmitt,J.H.M.M.1997,A&A,318,215Schmitt,J.H.M.M.&Liefke,C.2002,A&A,382,L9Stassun,K.G.,Mathieu,R.D.,&Valenti,J.A.2006,Nature,440, 311Stassun,K.G.,Mathieu,R.D.,&Valenti,J.A.2007,ApJ,664,1154 Stelzer,B.2004,ApJ,615,L153Stelzer,B.&Micela,G.2007,A&A,474,129S.Czesla et al.:Discovery of X-ray emission from the eclipsing brown-dwarf binary2MASS J05352184-05460855 Stelzer, B.,Micela,G.,Flaccomio, E.,Neuh¨a user,R.,&Jayawardhana,R.2006,A&A,448,293。

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近代物理学史(英文版)ppt课件

近代物理学史(英文版)ppt课件

近代物理学史
The Modern History of Physics
土木15-8班王康 杨程
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目录 Contents
I.经典物理学 II.现代物理学革命的序幕 III.相对论 IV.量子力学 V.原子结构理论的发展
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一、经典物理学/Classical Physics
Galileo and Newton, who founded in the 17th century classical physics. After the expansion of the various basic sectors in nineteenth Century to eighteenth Century to get a comprehensive, systematic and rapid development reached its glorious peak 由伽利略(1564—1642)和牛顿(1642—1727)等人于17世纪创立的经典 物理学。经过18世纪在各个基础部门的拓展到19世纪得到了全面、 系统和迅速的发展达到了它辉煌的顶峰。
• 本世纪20年代创立的量子力学理论为描述微观物体的 行为提供了一个全新的框架，改变了我们最基本的测 量原理，并为了解原子、分子和凝聚态物质的结构铺 平了道路。因而导致了诸如半导体、光通讯等新兴技 术的崛起，并为研制奇异材料和激光器件开辟了道路
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经典力学/Classical Mechanics
1. In l687 published "the mathematical principle of natural philosophy," Newton put forward three basic principle of dynamics and the law of universal gravitation.
X射线的发现

X射线的发现

The Discovery of X-rays X-射线的发现One hundred years ago this month, Wilhelm Conrad Rontgen cast thefirst x-ray images by chance 一百年前的这一个月,威廉.康德拉.伦琴意外地得到了第一张X-射线的图象by Graham FarmeloThe maid had to be dispatched several times to call him from his laboratory. 必须几次差遣侍女才能将他从实验室中叫出来When Wilhelm Conrad Rontgen, the head of the physics department at the University of Wurzburg, finally joined his wife at the dinner table, he was distracted, eating little and saying less.威廉.康德拉. 伦琴是伍尔兹伯格大学物理系系主任,当他终于和他的妻子一起坐在吃正餐的卓子旁时,他是心烦意乱的,吃得很少,说得更少.No sooner had they finished their meal than he returned to his work.他们一起吃完饭,他就回去工作了.It was November 8,1895. For several months, Rontgen had been investigating the behavior of cathode rays, later identified by other scientists as electrons.时间是1895年11月8日.几个月来,伦琴一直在研究后来由其他科学家确定为电子的阴极射线的特性.He knew that these rays, copiously produced in a special evacuated tube charged with high-voltage elctricity, penetrated only a few centimetersof air.他知道,在一个充有高压电的特制的真空管内大量产生的这些射线, 只能渗入几厘米的空气.And so he was astonished on that Friday evening before dinner to see flickering image so far away from the tube that it could not have been caused by the cathode rays, but it appeared only when they were present. 所以他对星期五晚餐前的傍晚,看到一个闪烁的图象离真空管这样远感到十分惊异,因为它不可能是由阴极射线引起的,但是只有当阴极射线存在的时候,它才出现.Rontgen pursued the matter intensively that night, failing to hear an elderly laboratory assistant knock at the door enter and leave. For days after, he ate and slept in his laboratory.(So preoccupied was he with this puzzle that he ignored a cardinal rule of experimentation he did not begin to take notes until nearly a week later. ) 那天晚上,伦琴全神贯注地考虑这一问题,以致连一个老的实验助手敲门和进出的声音都没有听到.以后几天,他吃住都在实验室.(他是这样全神贯注地思考这一难题,以致他忽略了实验室的一项基本规则-直到将近一个星期以后才开始记笔记).Only by repeating the experiment many times did Rontgen come to believe that a new type of ray had cast the image he saw. Because he did not know the nature of these rays, he called them x-ray--"X" for unknown. 只有通过重复这一实验许多次以后, 伦琴才开始相信一种新型的射线造成了他所看到的这幅图象.因为他不知道这些射线的性质,他就将其称为X-射线--"X"表示未知的.He told no one but his closest friend, Wthzburg zoologist Theodor H. Boveri, about the rays."I have discovered something interesting. " he said,"but I do not know whether or not my observations are correct. "关于这些射线,除了他的最亲密的朋友,伍尔兹伯格大学的动物学家 Theodor H.Boveri之外,他没有告诉任何人."我发现了一些有趣的东西,"他说," 但是我不知道我的观察是否正确."First to witness his experiments was his wife, Bertha whom he invitedinto his laboratory on the Sunday before Christmas. There he made aportrait exposing the bones in her left hand-the first permanent x-ray photograph of a part of the human body.首先亲眼看到他的实验的是他的妻子Bertha,是他在圣诞节前的星期天请她到他的实验室来的.他在那里拍摄了一幅展示她的左手骨骼的照片-第一张永久性的部分人体X-射线照片.The week after Christmas, Rontgen published a short paper, and by thefirst week of the new year, newspapers all over the world began reporting his discovery. Never before had a scientific breakthrough caused such excitement in the popular press. Any number of truly remarkable inventions emerged during the late 19th century, but the public was particularly fascinated by Rontgen`s find; it provide a wayto probe the human body without cutting it open.圣诞节后一个星期,伦琴发表了一篇简短的论文,到了新年的第一个星期,全世界的报纸都开始报导他的发现.在大众化的出版物中,以前没有哪一个科学上的突破引起这样大的激动.在十九世纪后期出现了许多真正很著名的发明,但是公众特别被伦琴的发现所迷住了,它提供了一种检查人体的方法,而不需要切开人体.The diagnostic potential of x-ray was grasped almost immediately. Within a month, surgeons in Europe and the U.S. were using them in a variety of ways. Perhaps the most bizarre early application was an attempt,described by the College of Physicians and Surgeons in New York City, "to reflect anatomic diagrams diagrams directly into the brainsof their students, making a much more enduring impression than the ordinary methods of learning anatomic details. " Some 20 years would pass before scientists determined the true nature of x- rays. All the same, Rontgen`s initial announcement proved to be one of the most celebrated in the history of physics-despite the several scientists atthe time who argued that it owed more to luck than to skill. 人们几乎立刻就抓住了用X-射线进行诊断的可能性.在一个月内,欧洲与美国的外科医生就以各种各样的方式应用它们. 也许最奇异的早期应用是纽约市内科与外科医生学院所描述的一种尝试,即"直接将解剖图反射到他们的学生的大脑中, 产生比学习解剖细节的普通方法更为持久的印象."大约过了20年,科学家们才确定了X- 射线的真正的性质.然而,伦琴最先宣布他的发现被证明在物理学的历史中是最有名的一个发现--尽管当时有几个科学家争辨说,这项发明更多的应归功于侥幸,而不是特殊的技巧.Cathode Rays 阴极射线Although he eventually attained celebrity as a physicist, Rontgen had originally planned to become an engineer. He was born in 1845 into a well-to-do(富有的)mercantile family(商人家庭)in the small town of Lennepin northwestern Germany and spent most of his childhood in the Netherlands. At age 20, he moved to Zurich(苏黎士)and three years later graduated witha bachelor`s degree in engineering from the Federal Institute of Technology. (三年后毕业于联邦理工学院,并且获的了工程学士的学位)Although Rontgen had not taken any experimental physics courses as an undergraduate, he decided to pursue graduate work in the field, persuadedin part by his mentor, August E.E. Kundt, professor of physics at the institute.虽然伦琴作为一个大学生没有学习过任何实验物理的课程,但是部分是在该学院的物理学教授,他的导师 August E. E. Kundt 的劝说下,他决定选择在该领域的研究生课程.After receiving his Ph.D. in 1869, Rontgen held a series of teaching positions at sundry(各式各样的)German universities. In collaboration with Kundt,he made careful studies of the behavior of matter and was, for example, the first to demonstrate(using a homemade thermometer) that it is easierto heat humid air than dry air. Other aspects of his work lent strongsupport to the unified theory of electricity and magnetism put forward inthe 1870s by Scottish mathematical physicist James Clerk Maxwell.他的另一方面的工作对十九世纪七十年代苏格兰的数学物理学家J.C.马克斯韦尔的一元化电磁理论提供了强有力的支持.Rontgen was 43 years old when he became professor of physics and director of the physical institute at the university in Wurzburg, a small, prosperous Bavarian city. On the second floor of the institute, heand his wife shared ample accommodations, including a study connectedto one of two private laboratories. This appointment must have givenhim considerable pleasure; 18 years earlier the university had not allowed him to pursue a position as a professor there, because he couldnot produce an Abitur, a certificate testifying that he had commpletedhigh school.当伦琴成为Wurzburg市这所大学的物理学教授和物理研究所的主任时,他才43岁.Wurzburg是一座较小的,但是繁荣兴旺的巴伐利亚城市.在研究所二楼,他和他的妻子分到了宽敞的宿舍,包括与两个专用实验室之一相连结的一个书房.这项任命使他非常高兴,18年前这所大学没有让他在这里担任教授职位,因为他不能出示证明他曾经完成了高中学业的毕业证书.Rontgen devoted a good deal of time to winning laboratory space, additional staff and other resources for the fledgling physics department at Wurzburg. By dint of his efforts, he sought to make it among the best in Geermany. His colleagues knew him to be a particularlyambitious, meticulous worker, who was extraordinarily knowledgeable about the latest developments in all areas of physics. Although he was sociable, during his entire working life he hardly exchanged a professional word with another physicist. 伦琴将大部分时间花在为Wurzburg大学初创的物理系争取实验室有更大的场所, 更多的职员与其他资源上.他企图凭借自己的努力,使Wurzburg大学物理系跻身德国最好的物理系之列.他的同事都知道他是一个特别有抱负的,细心的人,他对物理学所有领域中的最新进展都有非常透彻的了解.虽然他是爱交际的,但是在他的整个研究生涯中, 他几乎没有和另一个物理学家交换过专业上的只言片语.In June 1894 he began studying cathode rays, then an extrimely popular research topic. German physicist Eugen Goldstein of the University of Berlin had named these rays 18 years earlier. Goldsteinand several others established that cathode rays were negatively charged and that they traveled considerably slower than the speed of light. But one central puzzle remained:whereas most British physicists believed that these rays were particles, their German counterparts thought them to be disturbances in some all-pervasive ether.在1894年6月, 他开始研究阴极射线,当时那是一个极为普通的研究课题.18年前, 柏林大学的德国物理学家Eugen Goldstein 给这些射线命了名.Goldstein与其他几个人确定, 阴极射线带负电荷并且它们传播速度比光的速度慢得多. 但是仍有一个重要的难题没有解决:大部分英国物理学家认为这些射线是粒子,而他们的德国同行则认为它们是一些全弥漫性以太中的扰动.We shall probably never hnow Rontger`s motivation in turning his attention to cathode rays. His notebooks indicate that he was checking results obtained by two experimenters at the University of Bonn- the recently deceased Heinrich R. Hertz, the discoverer of radio waves, and his assistant, Philipp E. A. Lenard. Rontgen`s work was interrupted in the jall, when he was elected rector of the university, its highest office. Some scientists become addicted to the manifold pleasures of administration, but not Rontgen. By the autumn of the following year, he had returned to his laboratory.我们大概将永远不会知道伦琴将其注意力转向阴极射线的动机是什么.他的笔记本表明,他在检验无线电波的发现者--刚去世的赫兹与他的助手Philip E.A.Lenard在柏林大学进行的两项实验所获得的结果.在这一年的秋季,当伦琴被选为这个大学的校长这一最高职务的时候,他的研究被中断了. 一些科学家耽溺于行政管理的各种各样的乐趣,但是伦琴却不是这样.到了下一年秋天,他又回到了实验室去了.Discovery Day(发现日)Today a visitor to room 119A of the Technical College in Wurzburg can quickly tell that it is a special part of the buiding. It was in this high-ceilinged space, six meters square, overlooking the botanical gardens and leafy Pleicher Ring road(now called the Rontgen Ring) , that Rontgen made the discovery that was to astonish the world. Although this one-room museum does not contain the actual apparatus he used, it breathes history. It is no wonder that the college staff reverentially lower their voices when they usher visitors into the shrine. 今天凡是到伍尔兹伯格理工学院119A室的参观者都能够很快说出哪里是这栋建筑物的特别之处.就是在这个有高天花板,可俯瞰植物园与树叶覆盖的Pleicher环行路( 现称为伦琴环行路)的六平方米空间,伦琴做出了震惊世界的发现. 虽然这个仅有一室的博物馆没有陈列他实际用过的仪器,但是它散发出历史的气息.当这所学院的职员带领参观者走进这块圣地时,难怪他们都虔诚地把说话的声音压得很低.The night of Novenber 8, 1895, together with its seven-week aftermath of secrecy, is a rich source of fascination and speculation. Rontgen himself did much to fuel this interest, no doubt unintentionally, by his characteristic reticence and inscrutability, and also because he never gave a definitive account of what actually happened. The description here is, therefore, a version of the events, compiled fromRontgen`s reported comments and scant writings.1895年11月8日的晚上,加之该发现被保密七个星期的后果是吸引力与推测的丰富源泉. 由于伦琴特有的沉默寡言与不可思议,还因为他从不对实际发生了什么给予一个明确的说明,伦琴本人不是故意地给这种兴趣火上加油.所以,这里所描述的只是根据伦琴的已报导过的评论与与有限的文件而编辑的对这一事件的看法.The equipment he used to investigate cathode rays at that time among the best available. He preferred to build his own apparatus whenever possible, but most of the equipment for these experiments had been suppplied and designed by leading instrument makers. 他用来研究阴极射线的设备是当时可以得到的最好的设备.只要可能,他就宁可自己制造仪器, 但是用于这些实验的大部分设备则是由第一流仪器制造厂家提供和设计的.To prepare his cathode ray tube. Rontgen removed gas and vapor from it using a vacuum pump. In this standard procedure, the tube was pumped for three or four days to reduce the pressure to below about a thousandth of the usual atmospheric pressure. This low pressure enabled the cathode rays to pass as freely as possible through the tube , colliding only rarely with gas molecules.为了制备阴极射线管, 伦琴用真空泵从管子中除去气体与蒸气.在这一标准工艺过程中,管子被抽吸了3,4 天以便将压力减到大约通常大气压力的千分之一以下. 这样低的压力可以使阴极射线尽可能自由地通过管子,很少和气体分子碰撞.An induction coil, similar in principle to the transformer that generates the high-voltage sparks in a car`s engine, supplied the electric current. Rontgen`s transformer took a 20- volt suppplly from batteeries housed in the basement of the institute and converted it into individual pulses of about 35000 volts apiece. Every second about eight pulses were generated, catch one audibly accompanied by a loud crack coming from the electrical discharge between the ends of the secondary coil.一个原理上类似于汽车发动机中产生高压火花的变压器的感应线圈提供电流.伦琴的变压器从放在研究所的地下室内的电池中获得20伏电流,并将其转换为大约各35000伏的单个脉冲.每秒大约产生8次脉冲,每次脉冲都可以听到伴有来自次级线圈端部之间放电的响亮的噼啪喀啦声.Rontgen was working alone, as he normally did. He knew well that cathode rays caused a barium platinocyanide-coated screen to fluoresce with a characteristic green color. But he probably found this glow difficult to discern because he was partially color blind. so he darkened the room and blocked all light coming from the gaslit street outside. He also covered the cathode- ray tube with pieces of black cardboard, pasted together so that no visible light could escape from the tube.伦琴就像平常那样单独在进行研究.他很清楚,阴极射线能够使氰亚铂酸钡涂覆的屏幕产生具有特有绿色的荧光.但是他大概发现这种辉光很难辨识,因为他是部分色盲.于是他将房间遮起来,挡住来自外边街道上煤气灯的所有光线. 他也用粘贴在一起的黑卡片将阴极射线管盖上,以便使可见光不致从管中逸散出来.In the pitch black of the laboratory, hearing the coil snapping in the background, Rontgen happened to notice on his worktable a smallpiece of paper sparkling as though a single ray of light had fallen on it. This light, he realized, came from the letter "A" that a student had written on the sheet in platinocyanide solution. He must have been astonished: cathode rays could not have traveled the distance from his tube to the paper to reveal its markings. Further experiments indicated that indeed the flickering light was caused by something emitted from the tube more penetrating than cathode rays.在漆黑的实验室中,伦琴听到线圈在背景中劈拍作响,他偶然注意到在他的实验桌上有一小块纸在发火花,仿佛一道光线照在它上面. 他认为这道光线来自一个学生用氰亚铂酸盐溶液写在纸上的字母"A".他一定大吃一惊:阴极射线不能传播从真空管到纸这样远的距离来显示其痕迹. 进一步的实验表明,闪烁的光的确是由真空管内发射出来的东西引起的,它的穿透性比阴极射线更强."By accident,"Rontgen said, he discovered that this emanation went unhindered through a piece of black paper. He then demonstrated that it passed though a playing card. A thick book, he noted, cast a sharp shadow on the screen, giving a clear indication that he was observing rays of some kind, moving in straight lines. When he examined the exlent to which the rays penetrated metals, he had perhaps the biggest surprise of all. As he put a small piece of lead in the path of the rays , he saw not only the object`s dark shadow, but a fainter shadow in the shape of his thumb and finger as well. That shadow in turn enclosed another set outlining the bones of his hand."无意中"伦琴说,他发现这种发射出来的东西不受阻碍地穿过一张黑纸.他接着证明它穿过了一张扑克牌.他注意到, 一本厚书在屏幕上投下一个轮廓清晰的阴影,清楚地表明,他正在观察某种以直线移动的射线.当他检查这些射线穿透金属的程度时,他也许对这一切感到非常吃惊. 因为他放置了一小块铅在射线的通路上,他不仅看到了铅的较深的阴影,而且也看见了呈现他的大姆指与其他几个手指形状的模糊阴影. 那片阴影本身又包含勾画出他的手指骨骼的另一组阴影.Rontgen elucidated the properties of x-rays in a classic piece of experimentation. Using a magnet to deflect a beam of cathode rays so that it struck the side of the vacuum tube in different areas, he convinced himsellf--in a matter of minutes- - that the x- rays were emitted from the point at which the cathode rays hit the interior wall of the tube and not from any other point in the circuit. He also showed that magnetic forces did not affect x-rays, confirming that they had no electrical charge.伦琴用一个经典的实验阐明了X-射线的性质.用一块磁铁使一束阴极射线偏转,以致它照射在真空管侧面的不同区域以后,他确信, 在大约几分钟内--X-射线是阴极射线照在真空管的内壁那一点, 而不是电路上的任何其它点发出来的.他还指出,磁力不影响X-射线,证明它们不带电.Rontgen nixt determined that x-rays, like cathode rays, could darken a photographic plate. By placing objects between the source of the rays and the plate, he took permanent x-ray photographs, exploiting the deffering abilities of materials to transmit the rays. In taking these photographs, he pioneered three key areas of x-ray imaging. First, aphotograph of his closed wooden box of weights clearly revealed its contents, thus presaging the security application found at every airport check-in.(伦琴下一步测定了X-射线,它像阴极射线一样,能够使照相底板变黑.通过将物体放在射线源与底板之间,利用材料传送射线的不同能力, 他摄取了持久性的X-射线照片.在摄取这些照片中,他开发X-射线成像的三个关键性的领域. 首先,他的一幅装有重物的关闭了的木箱的图象,清楚地显露出它的内容物, 从而预示了在每个机场安全检查时的应用.)Second, an x-ray image of his hunting rifle revealed a flaw inside the metal of the gun:it was the first time a hidden structural fllaw had been exposed without destroying the object. Finally, and most startling of all, he took a permanent x-ray photograph of his wife`s left hand, revealing the bones and the rings that she was wearing. To produce this image, Bertha held her hand still against the plate for about 15 minuted, which gave her a dose of x- rays that dangerously exceeded the limits set in modern health and safety standards. Such are the hazards that pioneers unwittingly face.(第二,一幅他的猎枪的X- 射线图象揭示在枪的材料内部有一条裂缝: 一条隐藏在结构中的裂缝被揭露出来而没有毁坏物体这还是第一次.最后,并且也是所有三个领域中最使人吃惊的是, 他拍摄了一张他的妻子左手的永久性X-射线照片,显露出她的骨骼与她戴着的戒指.为了产生这幅图象,Bertha的手对着板保持静止不动约15分钟,她接受的X-射线的剂量危险地超过现代保健与安全标准所设定的极限.这是开拓者们不知不觉地面对的危险.)Rontgen carefully compared the properties of x- rays with those of visible light. Although both are electrically neutral and can cast sharp shadows, he found that in other ways, the x- ray appeared to deffer from light. He was unable to reflect them, nor could he refract them( he could not change their direction by making them traverse from one medium to another, for example, by passing them through a glass prism). In addition, he found no evidence that they could be diffracted (the rays did not bend around obstacles in their path).(伦琴仔细地比较了X-射线与可见光的特性. 虽然两者在电学上都是中性的而且能够投射边缘清楚的阴影,他发现在其他方面,X-射线似乎不同于光线.他既不能够反射X-射线,也不能使它们折射(他不能使4它们从一种介质穿向另一种介质,例如, 使它们通过玻璃棱镜而改变方向.)此外,他没有发现它们能够衍射的证据(这些射线在它们的通道中不会在障碍物周围弯曲).The similarifies between x-rays and light nonetheless led Rontgen to propose that they were in some way related. According to the theory put forward by Maxwell in 1873, light is an electromagnetic wave propagating in the ether, having electrical and magnetic signals vibrating perpendivular to the wave`s direction of motion. Rontgen tentatively suggested that the x-rays were vibrations in the ether in the same direction in which the rays were traveling. This speculation- -which turned out to be wrong--concluded his paper, On a New Kind of Rays, a Preliminary Communication, a masterpiece of experimental pphysics and concise reporting for which the University of Wurzburgreceives requests to this day.(然而,X-射线与光线间的类似性导致伦琴提出, 它们在某些方面是相近的.按照Maxwell在1873年提出的理论, 光是一种在以太中传播的电磁波,具有垂直于波运动方向振动的电磁信号.伦琴试探性地提出,X- 射线是在以太中的振荡,其方向与射线的传播方向相同.这一推测--被证明是错误的--是他的论文"关于一种新射线,初步信息"得出的结论.这是实验物理学的一篇杰作, 同时Wurzburg大学直至今天都接到获得这篇简报的要求.)Three days after Christmas in 1895, he gave the 10-page, handwritten manuscript to the secretary of the Wurzburger Physical Medical Society with the unusual requesst that it be published quickly. On New Year`s Day, after postingcoopies of his manuscript and photographs to several leading European physcists, he remarked to his wife:"Now there will be the devil to pay."(在1895年圣诞节后三天,他将一份十页的手稿交给伍尔兹伯格物理医学学会的秘书并提出一个异乎寻常的申请,要求早点出版它.将它的手稿副本与照片邮寄给欧洲的几个第一流的物理学家后的新年这一天,他对他的妻子说:" 现在将有无穷的后患了.")The Immediate Aftermath直接的后果In a few days Iwas disgusted with the business. I could not recognize my own work in the reports any more," Rontgen wrote to former assistant about a month after the news of his discovery broke. He was angry and upset by the initial newspaper stories, which seized on his remarkable photographs as though they represented by far the most immportant aspect of his experiments. Rontgen himself was for more interested in discovering both the true nature and the properties of x-ray."有几天我讨厌工作.我再也不能在报告中承认自己的工作," 他的发现这一新闻透露出去以后大约一个月,他写信告诉他以前的助手说.他生气了, 并且被报纸上最初的描述搞得心烦意乱,这些描述把重点放在他的著名的照片上,好像它们代表他的试验的最为重要的方面.伦琴自己更为感兴趣的是发现了X- 射线的真正的性质和特性.The first newspapeer account appeared on Sunday, January 5, in the Vienna Presse, and by January 16, word had reached the New York Times. Most scientists resd these reports before translations of the original paper became available, so it is not surprising that several experts did not initially believe them. Among these skeptics was Lord Kelvin of the University of Glasgow, regarded by many at the time as the greatest living scientist. Kelvin at first thought that the announcement was a hoax(he soon changed his mind).第一篇新闻报导出现在1月5日星期天的<维也纳新闻报导>中,到了1月16日,<纽约时报>也刊载了这一消息.在获得原文的译文之前, 大多数的科学家已经看过了这些报告, 因此有几个专家开始不相信这些报告是不足为奇的.在这些怀疑的人中有一个是格拉斯哥大学的Kelvin爵士,当时被许多人认为是活着的最伟大的科学家.Kelvin最初认为这一宣告是一个骗局(他很快改变了这一想法).The astonishing ability of x-rays to penerate matter gave rise to many cartoons that betrayed popular misunderstandings about the new rays. In addition the discovery stimulated a good deal of quackery( 庸医的医术). A London firm advertised its "x-ray-proof underclothing." and French enthusiasts(热心人)made attempts at "photographing the soul." In Iowa, a farmer reported that he had used the new rays to transform a 13-cent piece of metal into gold worth $153.X-射线穿透物质的惊人的能力引起起许多显示大众对这种新射线的误解的漫画.此外,这一发现激发了许多欺骗行为.一家伦敦的公司打广告宣传它的"防X-射线内衣",法国的热心人企图"拍摄灵魂的照片".在衣阿华州,一个农民报告,他已经用这种新射线将一块13厘米厚的金属变成了价值153美元的黄金.Engineers and photographers were on the whole even quicker than doctors to grasp the potential of x- ray devices. As the American journal Electrical Engineer commented in March 1896, "It is safe to say that there is probably no one possessed of a vacuum tube and an induction coil, who has not undertaken to repeat Professor Rontgen`s experiments." By the end of the year hundreds of crude x- ray machines were in operation. The first attempts at radiography were haphazard because its practitioners could only guess at the exposures needed to produce clear photographs. From 1899, doctors began to test the rays tor remedying cancer tuberculosis and various inflammations. Their success was unever and some patients and doctors suffered severe radiation burns.工程师与摄影者总的来说甚至比医生更快地了解了X-射线装置的潜在用处.正如美国的杂志<电气工程师>1896年3月号上所评论的,"可以说, 没有那一个拥有真空管与感应线圈的人,不会重复伦琴教授的实验."到了那一年的年底,已有数百个原始的X-射线机在运行之中.第一个辐射摄影的试验是偶然的事,因为它的专业人员仅仅能够推测产生清楚的照片所需的曝光时间.从1899年起,医生们开始试验性地将射线用于治疗癌症,肺结核病与各种炎症.他们的成功是参差不齐的, 并且有一些病人与医生遭受了严重的辐射灼伤.All the while, Rontgen tried to continue his research in an unaccustomed role--as an international celebrity. He did not answer most of the letters he received and refused all but two lecture invitations. One acceptance came in response to a summons from the Imperial Court in Berlin. He was asked to demonstrate his discovery on January 13 to the emperor, Wilhelm ll, whom Rontgen addmired for his politics and interest in science. After the successful demonstration, the emperor awarded Rontgen the Prussian Ordeer of the Crown and promptly commissioned three other scientists to investigate the military potential of the discovery. Rontgen knew of this work but neither helped nor hindered it.伦琴始终试图继续他的研究,他不习惯作为一个国际著名人士的角色.他对收到的信大部分都没有覆信,并且除了两次演讲外, 他谢绝了所有这样的邀请.有一次接受邀请,是为了响应来自柏林帝国宫廷的召唤. 他在1月13日向皇帝威廉二世表演他的发现,伦琴因为他的政策和对科学的兴趣而佩服他. 成功地表演以后, 皇帝授予伦琴普鲁士皇冠勋章并且迅速地委托其他的三个科学家来调查研究这一发现在军事上的潜力.伦琴知道这项工作,但是既不帮助他, 也不阻扰他.He gave a second lecture for the faculty and students at Wurzburg,。

scanning exercises

scanning exercises

Reading skills for academic study: Scanning forspecific information.Exercise 1Read the following text quickly and fill in the table. What do the numbers given in the table refer to?Spoon-fed feel lost at the cutting edgeBefore arriving at university students will have been powerfully influenced by their school’s approach to learning particular subjects. Yet this is only rarely taken into account by teachers in higher education, according to new research carried out at Nottingham University, which could explain why so many students experience problems making the transition.Historian Alan Booth says there is a growing feeling on both sides of the Atlantic that the shift from school to university-style learning could be vastly improved. But little consensus exists about who or what is at fault when the students cannot cope. “School teachers commonly blame the poor quality of university teaching, citing factors such as large first-year lectures, the widespread use of inexperienced postgraduate tutors and the general lack of concern for students in an environment where research is dominant in career progression,” Dr Booth said.Many university tutors on the other hand claim that the school system is failing to prepare students for what will be expected of them at university. A-level history in particular is seen to be teacher-dominated, creating a passive dependency culture.But while both sides are bent on attacking each other, little is heard during such exchanges from the students themselves, according to Dr Booth, who has devised a questionnaire to test the views of more than 200 first-year history students at Nottingham over a three-year period. The students were asked about their experience of how history is taught at the outset of their degree programme. It quickly became clear that teaching methods in school were pretty staid.About 30 per cent of respondents claimed to have made significant use of primary sources (few felt very confident in handling them) and this had mostly been in connection with project work. Only 16 per cent had used video/audio; 2 per cent had experienced field trips and less than 1 per cent had engaged in role-play.Dr Booth found students and teachers were frequently restricted by the assessment style which remains dominated by exams. These put obstacles in the way of more adventurous teaching and active learning, he said. Of the students in the survey just 13 per cent felt their A-level course had prepared them very well for work at university. Three-quarters felt it had prepared them fairly well.One typical comment sums up the contrasting approach: “At A-level we tended to be spoon-fed with dictated notes and if we were told to do any background reading (which was rare) we were told exactly which pages to read out of the book”.To test this further the students were asked how well they were prepared in specific skills central to degree level history study. The answers reveal that the students felt most confident at taking notes from lectures and organising their notes. They were least able to give an oral presentation and there was no great confidence in contributing to seminars, knowing how much to read, using primary sources and searching for texts. Even reading and taking notes from a book were often problematic. Just 6 per cent of the sample said they felt competent at writing essays, the staple A level assessment activity.The personal influence of the teacher was paramount. In fact individual teachers were the cent re of students’ learning at A level with some 86 per cent of respondents reporting that their teachers had been more influential in their development as historians than the students’ own reading and thinking.The ideal teacher turned out to be someone who was enthusiastic about the subject; a good clear communicator who encouraged discussion. The ideal teacher was able to develop students involvement and independence. He or she was approachable and willing to help. The bad teacher, according to the survey, dictates notes and allows no room for discussion. He or she makes students learn strings of facts; appears uninterested in the subject and fails to listen to other points of view.No matter how poor the students judged their preparedness for degree-level study, however, there was a fairly widespread optimism that the experiencewould change them significantly, particularly in terms of their open mindedness and ability to cope with people.But it was clear, Dr Booth said, that the importance attached by many departments to third-year teaching could be misplaced. “Very often tutors regard the third year as the crucial time, allowing postgraduates to do a lot of the earlier teaching. But I am coming to the conclusion that the first year at university is the critical point of intervention”.Alison Utley, Times Higher Education Supplement. February 6th, 1998.Reading skills for academic study: Scanning forspecific information.Exercise 1 - AnswersRead the following text quickly and fill in the table. What do the numbers given in the table refer to?Reading skills for academic study: Scanning forspecific information.Exercise 2Read the following text quickly and answer the questions.1. W hen were X-rays discovered?2. W ho discovered them?3. W hat are the four characteristics of X-rays?The Discovery of X-raysExcept for a brief description of the Compton effect, and a few other remarks, we have postponed the discussion of X-rays until the present chapter because it is particularly convenient to treat X-ray spectra after treating optical spectra. Although this ordering may have given the reader a distorted impression of the historical importance of X-rays, this impression will be corrected shortly as we describe the crucial role played by X-rays in the development of modern physics.X-rays were discovered in 1895 by Roentgen while studying the phenomena of gaseous discharge. Using a cathode ray tube with a high voltage of several tens of kilovolts, he noticed that salts of barium would fluoresce when brought near the tube, although nothing visible was emitted by the tube. This effect persisted when the tube was wrapped with a layer of black cardboard. Roentgen soon established that the agency responsible for the fluorescence originated at the point at which the stream of energetic electrons struck the glass wall of the tube. Because of its unknown nature, he gave this agency the name X-rays. He found that X-rays could manifest themselves by darkening wrapped photographic plates, discharging charged electroscopes, as well as by causing fluorescence in a number of different substances. He also found that X-rays can penetrate considerable thicknesses of materials of low atomic number, whereas substances of high atomic number are relatively opaque. Roentgen took thefirst steps in identifying the nature of X-rays by using a system of slits to show that (1) they travel in straight lines, and that (2) they are uncharged, because they are not deflected by electric or magnetic fields.The discovery of X-rays aroused the interest of all physicists, and many joined in the investigation of their properties. In 1899 Haga and Wind performed a single slit diffraction experiment with X-rays which showed that (3) X-rays are a wave motion phenomenon, and, from the size of the diffraction pattern, their wavelength could be estimated to be 10-8 cm. In 1906 Barkla proved that (4) the waves are transverse by showing that they can be polarized by scattering from many materials.There is, of course, no longer anything unknown about the nature of X-rays. They are electromagnetic radiation of exactly the same nature as visible light, except that their wavelength is several orders of magnitude shorter. This conclusion follows from comparing properties 1 through 4 with the similarproperties of visible light, but it was actually postulated by Thomson several years before all these properties were known. Thomson argued that X-rays are electromagnetic radiation because such radiation would be expected to be emitted from the point at which the electrons strike the wall of a cathode ray tube. At this point, the electrons suffer very violent accelerations in coming to a stop and, according to classical electromagnetic theory, all accelerated charged particles emit electromagnetic radiations. We shall see later that this explanation of the production of X-rays is at least partially correct.In common with other electromagnetic radiations, X-rays exhibit particle-like aspects as well as wave-like aspects. The reader will recall that the Compton effect, which is one of the most convincing demonstrations of the existence of quanta, was originally observed with electromagnetic radiation in the X-ray region of wavelengths.Reading skills for academic study: Scanning forspecific information.Exercise 2 - AnswersRead the following text quickly and answer the questions.1. W hen were X-rays discovered?2. W ho discovered them?3. W hat are the four characteristics of X-rays?1. 18952. R oentgen3. 1. they travel in straight lines2. they are uncharged3. they are a wave motion phenomenon4. the waves are transverse。

塞曼效应测量电子荷质比

塞曼效应测量电子荷质比

毕业设计(论文)题目塞曼效应测量电子荷质比学院名称核科学技术学院指导教师谢安平职称副教授班级核技065 学号 20064530511 学生姓名韩楷2010年5月29日南华大学毕业设计（论文）任务书学院：核科学技术学院题目：塞曼效应测量电子荷质比起止时间： 2009.12至 2010.5学生姓名：韩楷专业班级：核技065指导教师：谢安平教研室主任：院长：肖德涛2009年11月25日设计（论文）内容及要求：内容：1、塞曼效应有关知识；2、国内外塞曼效应实验测量技术应用现状；3、反常塞曼效应分析；4、塞曼效应测量电子荷质比实验。

要求：1、调研并做出设计进度安排，写出开题报告；2、收集查找足够多的资料；3、翻译一篇英文资料；4、完成实验的测量计算，整理和分析实验数据5、按格式、字数等要求撰写论文；6、将答辩论文制作成PPT文件。

主要参考：1、原子及原子核相关书籍、论文；2、塞曼效应实验讲义及相关书籍、论文；3、数据处理的相关书籍、论文。

指导教师：谢安平2009年 11 月 25 日摘要：1896年发现的塞曼效应被誉为是物理学上继X射线之后的一大发现，科学家塞曼也因关于这一现象的研究而荣获1902年度的诺贝尔物理学奖，塞曼效应分为正常塞曼效应和反常塞曼效应，我们利用塞曼效应的原理测量电子荷质比，在现实中，塞曼效应主要应用于光谱背景的校正。

本文回顾了塞曼效应的发现背景，介绍了正常塞曼效应和反常塞曼效应的实验现象和理论解释，并对二者进行了深入的比较，调查了塞曼效应在光谱背景校正领域的应用。

最后，本文着重记录了利用塞曼效应测量电子荷质比的实验的全过程关键词：正常塞曼效应反常塞曼效应荷质比光谱校正Summary：the Zeeman effect found in 1896 is known as another big discovery after the discovery of X-ray , scientist Zeeman who researches on this phenomenon won the 1902 Nobel Prize in Physics, Zeeman effect include normal Zeeman effect and the anomalous Zeeman effect, we use the Zeeman effect in the measurement of electronic charge to mass ratio, in reality, the Zeeman effect mainly used in background correction.This paper reviews the discovery background of the Zeeman effect , describes the normal Zeeman effect and the anomalous Zeeman effect of the experimental results and theoretical interpretation, and show the comparison of the two in-depth 。