Radiation wave nature

A hundred years ago it was generally supposed that all the properties of light could be explained in terms of its wave nature. A series of investigations carried out between 1900 and 1910 by Max Planck (1858-1947) (blackbody radiation) and Albert Einstein (1879-1955) (photoelectric effect) discredited that notion. Today we consider light to be generated as a stream of particles called photons, whose energy E is given by the equation... 

The word radiant energy is the energy transmitted from one body to another in the form of radiations. This energy has wave nature and because it is associated with electric and magnetic fields, it is also called electro-magnetic radiations. The visible light, ultraviolet, infrared, X-rays, radio-waves and microwaves are all different forms of electromagnetic radiations. 

DUAL NATURE OF ELECTROMAGNETIC RADIATION WAVES AND PARTICLES... 

Figure 6.17 shows a schematic of the LEED system. The sample is bombarded through the left by a beam of electrons. Only radiation or electrons (remember the wave nature of matter ) with the same energy as the incident beam are detected. These electrons are called elastic backscattered electrons. The detection system is a fluorescent screen placed in front of the sample. Holding the screen at a large positive potential accelerates the electrons. Once they reach it, they excite the phosphorus in the screen, marking it with bright spots characteristic of the diffraction pattern. Finally, a camera in front of the screen records the diffraction pattern. 

Studies of black-body radiation led to Planck s hypothesis of the quantization of electromagnetic radiation. The photoelectric effect provided evidence of the particulate nature of electromagnetic radiation diffraction provided evidence of its wave nature. 

This section reviews the evidence for the wave nature of light and of X-rays, and then puts these two forms of radiation into the context of electromagnetic radiation in general. 

It is only for X-rays of short wave length that AX is a measurable amount in other words only for such radiation is the mass of the light quantum not too small compared with the rest mass of the electron m0. To the wave nature of the radiation a particulate nature is thus added in the complementary theory and vice versa, according to equation (4). 

Figure 24-1 Wave nature of a beam of single-frequency electromagnetic radiation. In (a), a plane-polarized wave is shown propagating along the y-axis. The electric field oscillates in a plane perpendicular to the magnetic field. If the radiation were unpolarized, a component of the electric field would be seen in all planes. In (b), only the electric field oscillations are shown. The amplitude of the wave is the length of the electric field vector at the wave maximum, while the wavelength is the distance between successive maxima.

Radiography was thus initiated without any precise understanding of the radiation used, because it was not until 1912 that the exact nature of x-rays was established. In that year the phenomenon of x-ray diffraction by crystals was discovered, and this discovery simultaneously proved the wave nature of x-rays and provided a new method for investigating the fine structure of matter. Although radiography is a very important tool in itself and has a wide field of applicability, it is ordinarily limited in the internal detail it can resolve, or disclose, to sizes of the order of 10 cm. Diffraction, on the other hand, can indirectly reveal details of internal structure of the order of 10 cm in size, and it is with this phenomenon, and its applications to metallurgical problems, that this book is concerned. The properties of x-rays and the internal structure of crystals are here described in the first two chapters as necessary preliminaries to the discussion of the diffraction of x-rays by crystals which follows. 

With reference to both their particle and their wave nature, describe the similarities and differences between visible light and ultraviolet radiation. 

The wave nature of radiation is familiarly illustrated by refraction effects in material media, diffraction, and interference phenomena. Discrete and band spectra are evidences of quantized energy states in matter and of quantized energy transfer... 

THE WAVE NATURE OF LIGHT We learn that light (radiant energy, or electromagnetic radiation) has wave-like properties and is characterized by wavelength, frequency, and speed. 

One of the most important fundamental interactions between a specimen and the imaging radiation is that of diffraction, a phenomenon that results from the wave nature of the imaging agent. Diffraction occurs whenever a wave motion encounters an object, but its effects assume particular importance in microscopy, where the dimensions of features being imaged may be close to the wavelength. The role of diffraction as the limiting factor in the performance of the microscope was first elucidated by Ernst Abbe in 1873. 

Synchrotron radiation is naturally polarized in the plane of the electron orbit. This can be used with oriented (typically single crystal) samples to make polarization-dependent measurements. In addition, it is possible to prepare circularly polarized X-ray beams, either by manipulating the properties of the electron orbit in the synchrotron or by using the X-ray analog of a quarter-wave plate. ... 

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