由58Fe 和209Bi 熔合后的相关衰变过程得到的109号元素的证据

本文报导了合成109号元素的实验。用能量为4.95,5.05和5.15MeV/u 的~(58)Fe 束轰击~(209)Bi 靶,研究了全熔合产物衰变模式的特性。总辐照剂量为7×10~(17)粒子。所用的实验方法是:用静电场速度过滤器在飞行过程中分离向前方向成峰的反应产物,经过飞行时间装置后注入到位置灵敏固态探测器中,测量其动能,估算出质量、入射的时间和位置。以所有的出射粒子的能量和时间来记录很有限的反应产物发生级联α粒子和(或)自发裂变的继发衰变。在5.15 MeV/u 时的一个特别的衰变过程是:在5ms 和22ms 先分别发射两个α粒子,最后,在13s 后发生自发裂变。第一个α粒子的动能为11.10±0.04MeV。对各种可能的解释进行了详细的分析,例如纯属偶然的信号相关,转移反应产物的衰变和从能量上看允许的余核蒸发等。最后表明质量数为266的109号元素的同位素、即全熔合后的单中子蒸发道、从统计的观点看是最好的指定。本文同时也讨论了合成新元素的前景。     

现代物理教学和多媒体技术

物理教学中,怎样把物理概念、规律传授给学生,并通过生动、活泼的课内外教学使学生领略物理世界的奇景异致,激起学习物理学的兴趣,是物理教师反复思考的问题．以往的教学手段主要是老师通过演示实验、模型,配合简单的作图进行讲授．近年来随着计算机技术的飞速发展,教师利用多媒体信息显示的多样性、过程的交互性、信息的存储性、网络化、智能化等进行教学,取得更佳的教学效果．     

多重表征——建构主义物理教学的新思路

编者按:本文引用了心理学界长期使用的"结构良好领域的知识和结构不良领域的知识"的知识分类观点,实际上就科学知识而言,心理学的那种分类和解释并不很恰当,可以"通过复制与同化而获取"的知识,不能说是结构良好的,只能说是简单的确定的,"概念比较复杂,理解一个概念要涉及灵活性和变化性"的知识是多元的,开放的知识,不应该冠以"不良结构"的帽子,这一点也许正是心理学与自然科学,中、西方文化存在的差异的反映;但是我们认为对上述概念作科学的理解后,本文关于物理教学所讨论的问题仍然是有价值的.     

9-cell TESLA超导加速腔研制中Dumb-Bells的测量与调整

为了保证9-cell超导加速腔在场的平滑度、TM010的频率以及加速器的总长度达到TESLA国际标准,必须确保每个Dumb-Bell在以上各方面达到标准要求.由于冲压、机加工以及电子束焊接等过程会引起形变,因此,必须在完成iris和加强筋的电子束焊接之后对Dumb-Bells进行微波和机械测量,并根据测量的结果对其腔形和长度等作必要的调整.北京大学已经建立了一套完整的测量和调整Dumb-Bells的装置,本文深入研究了Dumb-Bells的测量与调整的方法.     

家用空调风冷冷凝器的数值分析

对单排管的家用空调风冷冷凝器进行了CFD的数值模拟,并搭建了冷凝器的实验系统对3D模型的CFD模拟进行验证.比较结果表明;两者存在一个小偏差(<9%),但是两者的趋势完全一致.CFD计算可以得到一些实验无法得到的内部流动信息,有助于我们更好地理解冷凝器的机理.本文在实验的范围以外进行了"数值实验",冷凝器的其它结构不变,翅片的间距存在一个最优值,同样管间距也存在一个最优值,为设计新的冷凝器提供了合理、可靠的方向.     

光存储技术的原理、应用和发展方向

造纸术的发明使人们可以方便的记录信息,同时也使我国数千年的历史和众多优秀的传统文化得到了较为完整的保存.随着社会的不断进步、科技的高速发展,尤其是计算机和网络技术日新月异的发展,各种信息以不可阻挡的力量涌入人们的生活,人们几乎每天都要处理和存储大量的信息,用纸张来记录信息已远不能满足人们的需求,这就需要一种更为有效的信息存储技术来存储信息,而光存储技术是信存储技术中最有效的方法.本文对光存储技术的原理、应用和发展前景做一简要介绍.     

PAMELA合作组的测量数据挑战宇宙射线理论

欧洲PAMELA合作组的科学家声称,PAMELA合作组所获得的测量数据对宇宙射线在宇宙中如何加速的理论提出了挑战.根据他们的说法,通过宇宙的质子和氦核的能谱不仅彼此不同,而且不符合宇宙射线理论中用于描述这些粒子的能谱(通量与能量之间的关系)的简单幂律.这种不一致可能意味着物理学家不得不寻找对宇宙射线加速的新的解释.     

降低了对称程度的狭义相对论

作为爱因斯坦狭义相对论基础的两个假设是:相对性原理和光速不变原理.相对性原理说的是不论对于一个固定不动的观测者,还是对于一个匀速运动的观测者,各种物理现象的规律应该是相同的 光速不变原理认为不论光源如何运动,光速总是恒定的.欲使这两个假设成立,时-空必须具有一定的对称性.将以上这些合并考虑便形成了与旋转及速度之变化有关的所谓Lorentz对称群(以下简称"L对称"):如果在你进行一项物理实验时,实验室上下倒置了或开始以不同的速度移动,但由于L对称,自然界的基本规律是不会改变的.     

高能粒子辐照二氧化硅玻璃E''色心形成机理研究

考虑高能粒子辐照二氧化硅玻璃形成E'色心的情况.建立了E'色心形成的动力学模型,得到了E'色心浓度与辐照剂量的关系式.结果表明,在高能粒子辐照情况下,E'色心的形成包括两个过程,即色心的创造过程和色心的激活过程.色心的创造过程主要由二氧化硅网格中疲劳键的断裂形成或网格中氧移位形成,E'色心浓度随剂量的变化呈线性增长.色心的激活过程主要由二氧化硅玻璃中固有点缺陷形成,E'色心浓度随剂量的变化呈饱和趋势.理论结果和实验结果符合很好,说明建立的模型是有效的.     

欢迎作者将被他刊拒绝的佳作再投本刊

在物理学的科技成就中,激光可算是仅次于核能的1项重大发明创造。第1台激光器是1960年由美国物理学家梅曼(见本刊《邮票上的科学家——佼佼者之路》一书中之M4)发明的。然而《物理评论快报》却拒绝刊登梅曼的论文,理由是:这是微波激射物理方面的文章,对快速出版物不再有价值。这真是令人啼笑皆非!     

Meeting Reports

From the Introductory Course in Saclay to ECNS 2005 in Montpellier, by Joel Mesot Magnetism and Progress in Superconductors, by Stephane Raymond Chemical Structure and Dynamics, by Don Kearley Industrial and Medical Applications, by P. Allenspach Section Instruments and Methods, by Helmut Schober Soft Matter, by Arantxa Arbe Fundamental Physics with Neutrons, by Tyno Abdul-Redah and C. Aris Chatzidimitriou-Dreismann Disordered and Frustrated Systems, by Reiner Zorn Neutrons and Life Science, by Stephane Longeville Mecasens 2003 Comes to Manchester, by Sue Edwards Oxford Summer School Takes Place in September 2003, by Gerry Lander KEK and JAERI Host IPN2003, by Masatoshi Arai UKJ2003 Held in Japan, by Uschi Steigenberger     

Photo-induced ESR and optical absorption edge shift in amorphous Ge-S films

Reversible shift of the optical absorption edge by the cycle of band-gap illumination and annealing has been observed for Ge-S films for the first time. Photo-induced ESR has been observed, and it is explained by two processes: (1)Increase in randomness of the structure by illumination, and (2)Trapping of free carriers excited by illumination by charged dangling bonds. The ESR signal caused by the former process does not disappear either by warming the film up to room temperature or by illuminating it with the mid-gap light, while that by the latter process disappears.     

核酸碱基的付立叶变换红外拉曼光谱特征

本文给出了核酸碱基付立叶变换红外（ＦＴ—ＩＲ）激光拉曼光谱特征，并与可见光激光拉曼光谱进行了比较。结果表明，付立叶变换红外激光拉曼获得较可见光激光拉曼光谱波数范围更宽（低波数）的谱带范围，所获谱图荧光干扰小，谱图质量明显高于普通激光拉曼光谱谱图。     

反应离子镀光学薄膜的微观结构分析

用反应离子镀方法制备了ＴｉＯ２单层膜及ＴｉＯ２／ＳｉＯ２多层膜，用透射电子显微镜分别观察了由反应离子镀方法及传统蒸镀法二种不同工艺制得的ＴｉＯ２单层膜及ＴｉＯ２／ＳｉＯ２多层膜的断面结构，并对ＴｉＯ２单层膜进行了喇曼分析和卢瑟福背散射分析。     

A theory of the diffraction of an electromagnetic wave by a plane screen

The problem of the diffraction of an arbitrarily polarized electromagnetic plane wave by a perfectly conducting plane screen of infinitesimal thickness is reduced to scalar problems by the method known from earlier papers. The wave field diffracted either by a screen of infinite extent which is perforated by an aperture of arbitrary size and shape or by a complementary screen is then described by means of the bra-vectors, ket-vectors and linear operators introduced by the present author in one of his preceding papers.     

Scholte Wave at Air-Metal Interface Generated by a Pulsed Disc-Like Source

The normal displacement and pressure of Scholte and Leaky Rayleigh waves at air-metal interface generated by a pulsed disc-like source are simulated theoretically by the Cagniard-de Hoop method and studied by laser ultrasound technique experimentally. It is found that the Scholte wave detected by a photorefractive interferometer is mainly contributed by the surface pressure and the Leaky Rayleigh wave is dominated by the surface displacement. It is also proven that the pulse width of these interface waves is mainly determined by the acoustic time delay on the generating source size under our experimental conditions.     

General theory for the ferroelectric polarization induced by spin-spiral order

The ferroelectric polarization of triangular-lattice antiferromagnets induced by helical spin-spiral order is not explained by any existing model of magnetic-order-driven ferroelectricity. We resolve this problem by developing a general theory for the ferroelectric polarization induced by spin-spiral order and then by evaluating the coefficients needed to specify the general theory on the basis of density functional calculations. Our theory correctly describes the ferroelectricity of triangular-lattice antiferromagnets driven by helical spin-spiral order and incorporates known models of magnetic-order-driven ferroelectricity as special cases.     

Meeting Reports

African Neutron Diffraction Meeting Held in South Africa, by Andrew Venter Faraday Prize Awarded at BIW04, by Myra Fultz, Tom Shea, Coles Sibeley, and Charlie Horak American Conference on Neutron Scattering Deemed a Success, by C. F. Majkrzak and R. Cappelletti Third Sample Environment Workshop Reviewed, by Ian Bailey New Perspectives in Neutron and Muon Science Meets in Warwick, by Mark Telling Neutron and Muon Meeting Provides a Forum for Users, by Mark Telling Gen Shirane and the Frontiers of Neutron Scattering, by Steve Shapiro     

Specification of spectral line shape and multiplex dispersion by self-imaging and moiré technique

Due to finite width of a spectral line, the visibility of the moiré fringes formed by a grating and the self-image of another similar grating reduces by the increase of the self-image order. This effect is exploited to specify the spectral line shape by evaluating the Fourier transform of a function related to the visibility. Even, by using in-expensive optics, the technique can provide the spectral line shapes of rather broad widths—of the order of nanometer and more—by precisions that are comparable by those obtained by expensive Fourier transform spectrometers.Besides, it is shown that by comparing the line shapes obtained with and without a dispersive medium between the gratings, one can specify the dispersion function of the medium in the wavelength range covered by the spectrum.     

Improved first Rayleigh-sommerfeld method for analysis of cylindrical microlenses with small f-numbers

An improved first Rayleigh-Sommerfeld method (IRSM1) is proposed and applied to the analysis of cylindrical microlenses with small f-numbers. Numerical results obtained by both the IRSM1 and the original Rayleigh-Sommerfeld method (ORSM1) are compared with those obtained by the rigorous boundary element method (BEM). For both refractive and diffractive lenses, the results obtained by the IRSM1 are close to those obtained by the BEM even for small f-numbers; by contrast, the results by the ORSM1 differ significantly from those obtained by the BEM. Moreover, the IRSM1 uses much less time and computer memory in the computations than the BEM.