Fundamental particles Positron Proton

The series of Radioactive disintegrations the uranium-radium series, the uranium-actinium series, the thorium series, and the neptunium series. The age of the earth. The fundamental particles electron, proton, positron, neutron, positive, negative, and neutral mesons, neutrino. The photon (light quantum) the energy of a photon, hv. Planck s constant. The wave-particle duality of light and of matter. The wavelengths of electrons. 

For the purposes of this chapter, the discussion of the fundamental particles occurring in nuclear reactions will be limited to the nucleons (the proton and neutron), the (negative) electron, and the positive electron (or positron). In Table 21-1 the masses of these particles are given in atomic mass units (Chapter 2) and their charges are expressed as multiples of the elementary charge e = 1.602 x 10 C. 

Positron emission involves the emission of a positron from the nucleus. A key idea of modern physics is that every fundamental particle has a corresponding antiparticle with the same mass but opposite charge. The positron (symbolized note the positive Z) is the antiparticle of the electron. Positron emission occurs through a process in which a proton in the nucleus is converted into a neutron, and a positron is expelled. Positron emission has the opposite effect of P decay, resulting in a daughter nuclide with the same A but with Z one lower one fewer proton) than the parent thus, an atom of the element with the next lower atomic number forms. Carbon-11, a synthetic radioisotope, decays to a stable boron isotope through emission of a positron ... 

The investigation of cosmic radiation has had a profound influence on nuclear science. When Chadwick in 1932 discovered the neutron, the picture of matter seemed complete all matter appeared to be composed of four fundamental particles protons, neutrons, electrons, and photons. However, through studies of the cosmic radiation Anderson discovered the positron (the first antiparticle) in the same year. Five years later Anderson and Neddermeyer discovered another new particle with a mass about one-tenth of a proton or about 200 times heavier than the electron. This particle is the muon, designated by p. Since that time a large number of subatomic particles have been discovered. 

Most of the fundamental particles decompose spontaneously. The exceptions, the stable particles, comprise the proton, and antiproton, the electron, the positron, and the particles that move with the speed of light. 

The process, which leads to the liberation of a target electron, following the impact of a charged particle on an atom or a molecule, is one of the most important and fundamental phenomena studied in the field of atomic collisions. The interest in the ionization process goes back many decades, and it has been studied intensively since then. The largest volume of experimental data has been obtained for impact of electrons and protons, but a great deal of information has also been collected for impact of heavier ions. Recently, the electron data have been surveyed by for example Tawara et al. [4.1] and the proton data by Rudd et al. [4.2]. Since then, it has become possible to measure ionization cross sections for antiproton and positron impact. Some of the experimental measurements of positron-impact ionization were reviewed by Charlton and Laricchia [2.12]. From comparisons between data obtained with equivelocity p", p , e", and e , a substantial amount of new information on the ionization process has become available. In this section, we will review the new results obtained for the single-ionization cross section,... 

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