Physics
Radiation
Radiation refers to the emission of energy in the form of waves or particles. In physics, it can encompass various phenomena such as electromagnetic radiation (e.g., light, radio waves, X-rays) and nuclear radiation (e.g., alpha, beta, and gamma radiation). Radiation plays a crucial role in understanding the behavior of matter and energy at the atomic and subatomic levels.
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12 Key excerpts on "Radiation"
- Heinrich F. Beyer, Viateheslav P. Shevelko(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
Chapter 2 Radiation In the introduction we have addressed several radiative phenomena without explaining their physical foundations in detail. For a deeper physical understanding we are now going to recall electromagnetic wave phenomena. In this chapter we will recall basic definitions and discuss some Radiation physics which will prepare the stage for the later chapters. 2.1 Light and Radiation Light is a fundamental feature and has attracted philosophers since ancient times. For the Pythagoreans light was something that originated from a body and caused vision by entering the eye. Socrates and Plato reversed this idea in that the eye searches for objects by sending out light rays. In modern times, such a philosophical dispute appears strange and can only be understood by the tremendous size of the speed of light that prohibited a scientific proof in ancient times. It was at the beginning of the 19th century when it was generally agreed that light was a wave phenomenon with some similarities to water and sound waves. In 1887 Michelson and Morley established that the velocity of light was independent of the Earth’s movement. This fundamental observation was used later by Einstein to develop his theory of light. The understanding of the general properties of Radiation is central to the physics of atoms. Interaction with light is also an important tool for investigating ions and atoms. Radiation is the way in which energy is transmitted through space from one point to another without the need for any connection or medium between these two places. The terms light, Radiation, rays and waves characterize the same phenomenon and are often used as synonyms. Electromagnetic waves, i.e. periodically fluctuating electric and magnetic fields are matterless patterns, series of events that happen repeatedly.
eBook - PDF- Andreas Fuhrmann(Author)
- 2015(Publication Date)
- Thieme(Publisher)
2 Chapter 2 Radiation Physics 2.1 Types of Radiation 8 2.2 Direct and Indirect Ionization 8 2.3 Corpuscular and Photon Radiation 8 2.4 Interactions between Radiation and Matter 9 2.5 Fundamental Physical Processes Involved in the Transfer of Photon Energy to Matter 10 2.6 Interactions between X-rays and Matter 10 2.7 Radioactivity 11 2.8 Production of X-rays 12 Radiation Physics 2 8 2 Radiation Physics 2.1 Types of Radiation All life on our planet is exposed to different types of natu -rally occurring Radiation. This Radiation generally occurs in the form of electromagnetic waves that differ only by wavelength. Some Radiation can be seen or felt if it occurs at a few specific wavelengths but, in most cases, radia -tion cannot be detected by our sense organs. This applies in particular to rays with very short wavelengths beyond the ultraviolet end of the light spectrum. Radiation is defined as the emission and propagation of energy. When Radiation strikes an object, the energy generated in the Radiation field triggers interactions in the object. The body can withstand a good deal of Radiation but bio -logical damage starts when it is exposed to short-wave -length Radiation. Radiation in the infrared range is perceived as heat ra -diation that is not uncomfortable. Ultraviolet Radiation, however, starts to induce damage associated with chemi -cal reactions in the skin that can produce sunburn. Radiation at even shorter wavelengths is able to knock electrons out of an atom. This process is called ionization and such Radiation is referred to as ionizing Radiation. Note There are two basic types of Radiation: ionizing Radiation and nonionizing Radiation. 2.2 Direct and Indirect Ionization Radiation is further characterized by the manner in which its ionizing effects occur. In the case of directly ionizing Radiation, the energy from electrically charged particles is transferred directly to the irradiated structures.
- F I Woodward, J E Sheehy(Authors)
- 2017(Publication Date)
- Butterworth-Heinemann(Publisher)
Commonly, two alternative theories may be used to describe radiant energy. In one theory Radiation is des-cribed in terms of waves, and in the other it is described in terms of discrete packets of energy known as quanta. Table 2.1 Names of different wavelength regions in the electromagnetic spectrum Wavelength region Type of Radiation 0 to 0.1 nm 0.1 to 10 nm 10 to 400 nm 400 to 700 nm* 0.70 to 1000 μπι 1 mm to 100 m Gamma X-rays Ultra-violet Visible light Infra-red Microwave and short-wave radio It should be noted that the division between the wavebands is not precise * Sometimes known as photosynthetically active Radiation (PAR) The relationship between the two theories does not concern us, although it should be noted that a single unifying theory known as quantum electrodynamics has been developed. An understanding of many optical instru-ments can be obtained using the wave theory, but instruments utilizing the absorption or release of radia-tion from atoms or molecules require an additional understanding of the quantum theory. Thus, to under-stand interactions between Radiation and matter it is necessary to understand a little of the two physical theories of Radiation. We shall begin by discussing the wave theory. Electromagnetic or wave theory of Radiation Electromagnetic Radiation is energy in the form of com-bined electric and magnetic disturbances transmitted as waves (Figure 2.1). The oscillating magnetic and electro-static fields are generated by the movement of electrons or other charged particles. Radiation is often character-ized as shown in Figure 2.2. For simplicity the magnetic component has been excluded from the simple wave diagram, which is a cross-sectional view. Another view is obtained by visualizing the waves as moving out from their source in all directions as shown in Figure 2.3. 23
eBook - PDF- Barbara Ryden, Bradley M. Peterson(Authors)
- 2020(Publication Date)
- Cambridge University Press(Publisher)
5 Interaction of Radiation and Matter Much of what we know about the universe comes from collecting and analyzing electro- magnetic Radiation, otherwise known as “light.” Thanks to wave–particle duality, light can be thought of either as electromagnetic waves or as a stream of massless particles, called photons. Electromagnetic waves are characterized by their wavelength λ, or fre- quency ν = c/λ, where c is the speed of light. Photons are characterized by their energy E = hν , where h is the Planck constant, h = 6.626 × 10 −34 J s. In studying atomic struc- ture, a handy unit of energy is the electron volt (eV), defined as the change in energy of an electron when the electrical potential drops by one volt. When expressed in terms of joules, the electron volt is seen to be a small amount of energy: 1 eV = 1 .602 × 10 −19 J. Using electron volts as our unit of energy, the Planck constant is h = 4.135 × 10 −15 eV s. Early astronomers could detect only visible light, that is, light that stimulates a response in the retina of the human eye. Visible light lies in the wavelength range 4 × 10 −7 m < λ < 7 × 10 −7 m, corresponding to photons in the energy range 1 .8 eV < E < 3.1 eV. Modern astronomers, as we see in Chapter 6, have instruments that enable them to detect photons over a much broader range of energies. It has proved convenient for scientists to subdivide the continuous electromagnetic spectrum into different wave- length ranges, from radio waves, which have the longest wavelength and smallest photon energy, to gamma rays, which have the shortest wavelength and highest photon energy. A summary of the main subdivisions of the full spectrum, with approximate ranges in wavelength and photon energy, is given in Table 5.1. In this chapter, we will study how light and matter interact at the level of individual particles. To begin, we’ll explore the nature of atomic structure by examining Niels Bohr’s model of the hydrogen atom.
eBook - PDF- Kenneth S. Krane(Author)
- 2020(Publication Date)
- Wiley(Publisher)
Chapter 3 THE PARTICLE-LIKE PROPERTIES OF ELECTROMAGNETIC Radiation Thermal emission, the Radiation emitted by all objects due to their temperatures, laid the groundwork for the development of quantum mechanics around the beginning of the 20th century. Today we use thermography for many applications, including the study of heat loss by buildings, medical diagnostics, night vision and other surveillance, and monitoring potential volcanoes. Ted Kinsman / Getty Images 72 Chapter 3 The Particle-like Properties of Electromagnetic Radiation We now turn to a discussion of wave mechanics, the second theory on which modern physics is based. One consequence of wave mechanics is the break- down of the classical distinction between particles and waves. In this chapter, we consider the three early experiments that provided evidence that light, which we usually regard as a wave phenomenon, has properties that we nor- mally associate with particles. Instead of spreading its energy smoothly over a wave front, the energy is delivered in concentrated bundles like particles; a discrete bundle (quantum) of electromagnetic energy is known as a photon. Before we begin to discuss the experimental evidence that supports the exis- tence of the photon and the particle-like properties of light, we first review some of the properties of electromagnetic waves. 3.1 REVIEW OF ELECTROMAGNETIC WAVES A distribution of electric charges sets up an electric field E, and current- carrying wires set up a magnetic field B. If the charges do not move and the currents do not change, then E and B are static fields that vary with location but not with time. However, if the charges are accelerated and the currents vary with time, an electromagnetic wave is produced in which the E and B fields of the wave vary both with location and time.
eBook - PDFFundamentals of Radio Astronomy
Observational Methods
- Jonathan M. Marr, Ronald L. Snell, Stanley E. Kurtz(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
31 C H A P T E R 2 Introduction to Radiation Physics A radio astronomer must analyze and interpret the Radiation detected in order to learn about the physics of the object being studied. Therefore, a solid understanding of the basic physics of Radiation is critically important. In this chapter, we discuss some introductory Radiation physics essential to the rest of the book. 2.1 MEASURES OF THE AMOUNT OF Radiation One quantitative measure that astronomers can make when they observe a light source is the amount of Radiation that was received. How this amount is to be quantified is not as obvious as you might think. In addition to the Radiation that is received, we also want to quantify the amount of Radiation an astronomical source emits. As you will see, the amount of Radiation we receive and the amount of Radiation emitted by the source are quite different, but they are related. With these ideas in mind, we will start this chapter by discussing the various ways in which the amount of Radiation can be described. First, at radio wavelengths (as well as with almost all bands of the EM spectrum except perhaps for X-rays and γ -rays), we generally measure the amount of Radiation by its energy, rather than by the number of photons. Our first quantity to consider, then, is the total light energy emitted by a source. 2.1.1 Total Energy Emitted One can describe a source’s light output in terms of the total amount of energy emitted over a source’s lifetime, at all frequencies, and in all directions. This, however, is clearly not the kind of measurement that we can readily make. Since one can make measurements only over a finite time period, one can only describe the amount of energy detected in that time period. We wish to make a measurement that is independent of the time interval observed, and so a more useful quantity is luminosity or power, which is energy normal-ized by the time period.
- C.V. Heer(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Radiation 2.1 Introduction Planck's introduction of the concept of the quantization of electro-magnetic Radiation to provide a satisfactory explanation of thermal or blackbody Radiation has led to the description of thermal Radiation as a gas composed of photons. The linear form of Maxwell's equations for electromagnetic phenomena indicates that photons do not interact with each other and the photon gas is an ideal gas. In many respects, the dis-cussion given for particles in Chapter I applies to photons. In Chapter I, the particles were treated in a classical manner, and quantum mechanics is needed to explain binary encounters and molecular forces. For photons, a quantum mechanical explanation is required at the beginning of the de-velopment. Although the historical approach to problems of radiant energy are of considerable interest, the study is greatly facilitated by the use of more recent developments. This latter approach is used here; therefore the elegant deductions made from experimental studies prior to 1900 will often appear as almost trivial. This is indeed not the case; the author does not wish to retrace this tortuous path of discovery, but wishes to devote the present chapter to problems to which this work is applicable. An excellent review is given in Planck's Wärmestrahlung [7]. The next section discusses some aspects of electromagnetic Radiation that follow directly from Maxwell's equations. Measurable aspects of radia-tion from independent sources and the concept of the modes of the radia-36 II 2.2 ELECTROMAGNETIC Radiation 37 tion field are introduced. This is then combined with the basic postulate of Planck to form the basis for a consideration of thermal Radiation. Section 2.4 starts the discussion of the transfer of radiant energy and includes most of the simple and useful concepts in the transfer of thermal Radiation. The next two sections can be omitted for the reader primarily interested in the transfer of radiant energy.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
Thermal Radiation is generated when thermal energy from the movement of charges in the material (electrons and protons in common forms of matter) is converted to electromagnetic Radiation. Sun-shine, or solar Radiation, is thermal Radiation from the extremely hot plasma of the Sun, and this Radiation heats the Earth. The Earth also emits thermal Radiation, but at a much lower intensity because it is cooler. The balance between heating by incoming solar Radiation and cooling by the Earth's outgoing Radiation is the primary process that determines the Earth's overall temperature. If the object is a black body in thermodynamic equilibrium, the Radiation is termed black-body Radiation . The emitted wave frequency of the black body thermal Radiation is ________________________ WORLD TECHNOLOGIES ________________________ described by a probability distribution depending only on temperature, and for a genuine black body in thermodynamic equilibrium is given by Planck’s law of Radiation. Wien's law gives the most likely frequency of the emitted Radiation, and the Stefan–Boltzmann law gives the radiant intensity. Overview Thermal Radiation is the transfer of energy by electromagnetic waves. All objects with a temperature above absolute zero radiate energy at a rate equal to their emissivity multi-plied by the rate at which energy would radiate from them if they were a black body. Thermal Radiation does not require the presence of a medium. For instance, the energy from the Sun travels through the vacuum of space before warming the Earth. Electro-magnetic Radiation is the only form of energy transfer that can occur in the absence of any form of matter. Thermal energy is a direct result of the movements of atoms and molecules in a material. Since these atoms and molecules are composed of charged particles, i.e. protons and elec-trons, their movements result in the emission of electromagnetic Radiation, which carries energy away from the material.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
(This observation led to Albert Einstein's development of the theory of special relativity.) In a medium (other than vacuum), velocity factor or refractive index are considered, depending on frequency and application. Both of these are ratios of the speed in a medium to speed in a vacuum. Thermal Radiation and electromagnetic Radiation as a form of heat The basic structure of matter involves charged particles bound together in many different ways. When electromagnetic Radiation is incident on matter, it causes the charged particles to oscillate and gain energy. The ultimate fate of this energy depends on the situation. It could be immediately re-radiated and appear as scattered, reflected, or transmitted Radiation. It may also get dissipated into other microscopic motions within the matter, coming to thermal equilibrium and manifesting itself as thermal energy in the material. With a few exceptions such as fluorescence, harmonic generation, photo-chemical reactions and the photovoltaic effect, absorbed electromagnetic Radiation simply deposits its energy by heating the material. This happens both for infrared and non-infrared Radiation. Intense radio waves can thermally burn living tissue and can cook food. In addition to infrared lasers, sufficiently intense visible and ultraviolet lasers can ____________________ WORLD TECHNOLOGIES ____________________ also easily set paper afire. Ionizing electromagnetic Radiation can create high-speed electrons in a material and break chemical bonds, but after these electrons collide many times with other atoms in the material eventually most of the energy gets downgraded to thermal energy, this whole process happening in a tiny fraction of a second. That infrared Radiation is a form of heat and other electromagnetic Radiation is not, is a widespread misconception in physics. Any electromagnetic Radiation can heat a material when it is absorbed.
eBook - PDF- Liou(Author)
- 1981(Publication Date)
- Academic Press(Publisher)
Chapter 1 FUNDAMENTALS OF Radiation 1.1 CONCEPTS, DEFINITIONS, AND UNITS 1.1.1 Electromagnetic Spectrum The most important of the processes responsible for energy transfer in the atmosphere is electromagnetic Radiation. Electromagnetic Radiation travels in the wave form, and all electromagnetic waves travel at the same speed, which is the speed of light. This is 2.99793 ± 1 x 10 8 m sec-1 in a vacuum and at very nearly this speed in air. Visible light together with gamma rays, x rays, ultraviolet light, infrared Radiation, microwaves, television signals, and radio waves form the electromagnetic spectrum. The retina of the human eye is sensitive to electromagnetic waves with frequencies between 4.3 x 10 14 vibrations per second (usually written as cycles per second and abbreviated cps) and 7.5 x 10 14 cps. Hence, this band of frequencies is called the visible region of the electromagnetic spectrum. The eye, however, does not respond to frequencies of the electromagnetic waves higher than 7.5 x 10 1 4 cps. Such waves, lying beyond the violet edge of the spectrum, are called ultraviolet light. Moreover, if the waves have frequencies lower than 4.3 x 10 14 cps, the eye again does not respond to them. These waves, having frequencies lower than the lowest frequency of visible light at the red end of the spectrum and higher than about 3 x 10 1 2 cps, are called infrared light or infrared Radiation. Just beyond the infrared portion of the spectrum are the microwaves, which cover the frequency from about 3 x 10 10 to 3 X 10 12 cps. The most significant spectral regions associated 1 2 Name of region 1 Fundamentalsof Radiation Wavelength Frequency (em) (cps) 3X10-' 10 Violet Purple Blue Green Yellow Orange Red 10' 10' 3X 1 0 3X 1 0 '• 3X10 3X 10'0 3X10· 3X 10' 3X 10· 3X 10' Fig. 1.1 The electromagnetic spectrum. 1.1 Concepts, Definitions, and Units 3 with the radiative energy transfer in planetary atmospheres lie between the ultraviolet light and microwaves.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 5 Electromagnetic Radiation Electromagnetic Radiation (often abbreviated E-M Radiation or EMR ) is a pheno-menon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic Radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared Radiation, visible light, ultraviolet Radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic Radiation and is also the force carrier for the electromagnetic force. EM Radiation carries energy and momentum that may be imparted to matter with which it interacts. ________________________ WORLD TECHNOLOGIES ________________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 6 Electromagnetic Radiation Electromagnetic Radiation (often abbreviated E-M Radiation or EMR ) is a phenol-menon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic Radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared Radiation, visible light, ultraviolet Radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic Radiation and is also the force carrier for the electromagnetic force. EM Radiation carries energy and momentum that may be imparted to matter with which it interacts. ________________________ WORLD TECHNOLOGIES ________________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
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