Matter photoelectric effect

We use the X or gamma rays power penetrating to detect possible heterogeneities in inspected pieces. These rays are absorbed by the matter crossed, essentially by the photoelectrical effect, (fig. 02). 

Schrodinger s equation is widely known as a wave equation and the quantum formalism developed on the basis thereof is called wave mechanics. This terminology reflects historical developments in the theory of matter following various conjectures and experimental demonstration that matter and radiation alike, both exhibit wave-like and particle-like behaviour under appropriate conditions. The synthesis of quantum theory and a wave model was first achieved by De Broglie. By analogy with the dual character of light as revealed by the photoelectric effect and the incoherent Compton scattering... 

In 1900 Max Planck proposed a solution to the problem of black-body radiation described above. He suggested that when electromagnetic radiation interacts with matter, energy can only be absorbed or emitted in certain discrete amounts, called quanta. Planck s theory will not be described here, as it is highly technical. In any case, Planck s proposal was timid compared with the theory that followed. He supposed that quanta were only important in absorption and emission of radiation, but that otherwise the wave theory did not need to be modified. It was Einstein who took a more radical step in 1905 (the year in which he published his first paper on the theory of relativity and on several other unrelated topics). Einstein s analysis of the photoelectric effect is crucial, and has led to a complete change in the way we think of light and other radiation. 

When radiation of sufficiently short wavelength interacts with matter, ( electrons are emitted. This is the photoelectric effect. It can be observed in gases and solids, and with X-rays and y rays, as well as with ultraviolet j radiation. It was die phenomena observed with short-wavelength visible and < ultraviolet radiation on solids, however, which were known in 1905. Figure J 1.10 shows the apparatus used. Light or UV radiation falls on one electrode 4 in an evacuated tube. If electrons are emitted, some will reach the second <... 

The primary interaction of gamma rays with matter is the production of ionization or excitation. The three processes of interaction are the photoelectric effect, the Compton effect, and pair production. The predominance of each of these effects is determined by the energy of the gamma ray and the atomic number, Z, of the absorber. The photoelectric effect is favored for low energies, the Compton effect for intermediate energies, and pair production for high energies... 

The first convincing description of stationary quantum states was provided by the assumed wave nature of matter proposed by Louis de Broglie. The proposal had its roots in Einstein s explanation of the photoelectric effect and Compton s analysis of X-ray scattering. 

X-rays, gamma, and cosmic rays are similar except for the fact that gamma and cosmic rays are natural. They ionize matter by photoelectric effect, Compton effect, and pair production (electron and positron). These radiations are of very high energy and therefore more penetrating. They cause injury to the tissues of the whole body. Therefore, they are more damaging to the living tissues. 

The interaction of ionizing electromagnetic radiation with matter is different from the processes previously mentioned, and the concept of ranges and specific ionization loss cannot be applied. Only the three most important absorption processes are considered the photoelectric effect, the Compton effect, and the pair-production effect. The corpuscular description of electromagnetic radiation is the most appropriate for these effects, as one photon in a well-collimated beam of photons disappears at each interaction. The attenuation of the photon beam can be described by a simple exponential law... 

The interference phenomena demonstrated by the work of Young, Fresnel and others in the early 19th Century apparently settled the matter that light was a wave phenomenon, contrary to the views of Newton a century earlier—case closed But nearly a century later, phenomena were discovered which could not be satisfactorily accounted for by the wave theory, specifically, blackbody radiation and the photoelectric effect. 

In 1905, only five years after Planck presented his quantum theory, Albert Einstein used the theory to solve another mystery in physics, the photoelectric effect, a phenomenon in which electrons are ejected from the surface of certain metals exposed to light of at least a certain minimum frequency, called the threshold frequency (Fignre 7.5). The number of electrons ejected was proportional to the intensity (or brightness) of the light, but the energies of the ejected electrons were not. Below the threshold frequency no electrons were ejected no matter how intense the light. 

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