Positron A particle that has the same mass

Polymer. A compound distinguished by a high molar mass, ranging into thousands and milUons of grams, and made up of many repeating units. (25.1) Positron. A particle that has the same mass as the electron, but bears a -i-l charge. (23.1)... 

Radioactivity is the spontaneous emission of radiation from an unstable nucleus. Alpha (a) radiation consists of helium nuclei, small particles containing two protons and two neutrons (fHe). Beta (p) radiation consists of electrons ( e), and gamma (y) radiation consists of high-energy photons that have no mass. Positron emission is the conversion of a proton in the nucleus into a neutron plus an ejected positron, e or /3+, a particle that has the same mass as an electron but an opposite charge. Electron capture is the capture of an inner-shell electron by a proton in the nucleus. The process is accompanied by the emission of y rays and results in the conversion of a proton in the nucleus into a neutron. Every element in the periodic table has at least one radioactive isotope, or radioisotope. Radioactive decay is characterized kinetically by a first-order decay constant and by a half-life, h/2, the time required for the... 

Two other types of radioactive decay are positron emission and electron capture. A positron, je, is a particle that has the same mass as an electron (thus, we use the letter e and superscript 0 for the mass) but the opposite charge (represented by the -1-1 subscript). ... 

Nuchdes below the band of stability are unstable because their neutron/ proton ratio is too small. To decrease the number of protons, a proton can be converted into a neutron by emitting a positron. A positron is a particle that has the same mass as an electron, but has a positive charge and is emitted from the nucleus during some kinds of radioactive decay. 

Positron production a mode of nuclear decay in which a particle is formed that has the same mass as an electron but opposite charge. The net effect is to change a proton to a neutron. 

Since Rutherford s work, scientists have identified other types of nuclear radiation. Some consist of rapidly moving particles, such as neutrons or protons. Others consist of rapidly moving antiparticles, particles with a mass equal to that of one of the subatomic particles but with an opposite charge. For example, the positron has the same mass as an electron but a positive charge it is denoted 3 or f e. When an antiparticle encounters its corresponding particle, both particles are annihilated and completely converted into energy. Table 17.1 summarizes the properties of particles commonly found in nuclear radiation. 

The two other decay processes in Table 5.4 are less common in nature. In K-capture, any orbiting electron (usually in an inner shell) combines with a proton in the nucleus to form a neutron. This relatively rare nuclear transformation process (e + p+ —> n°) is just the opposite of that for P decay, meaning that the formed nucleus also has the same mass but is displaced one element to the left on the periodic table. Conversion of to °Ar by K-capture is an example of the chemical conversion that can attend radioactive decay, in this case leading to transformation of a non-volatile alkali metal into the inert gas Ar, the third most abundant gas in the atmosphere. Although no nuclear particle is emitted by K-capture, the attending cascade of electrons into lower orbitals leads to X-ray emission of characteristic energy that can be measured by the appropriate detectors. The last decay process (also rare) involves emission of a positron (p+), a positively charged electron. The nuclear process (p+ n° + p+) has the same net effect as K-capture and is also characterized by X-ray emission. 

The symbol ic represents an electron in or from an atomic orbital. The symbol i/3 represents an electron that, although physically identical to any other electron, comes from a nucleus (in a decay process in which a neutron is converted to a proton and an electron) and not from an atomic orbital. The positron has the same mass as the electron, but bears a +1 charge. The a particle has two protons and two neutrons, so its atomic number is 2 and its mass number is 4. 

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 ... 

Positron a particle that is similar to an electron and has the same mass but a positive charge. (20.1)... 

Note that the first product is also a hydrogen nucleus, but one that contains a neutron as well as a proton and therefore has a mass number of 2. Recall that species that have the same atomic number but different mass numbers are isotopes.The second product is a positron, sometimes referred to as a beta—plus particle. A positron has the same mass as an electron but the opposite charge. The symbol for a particle other than an element... 

In 1953 it was observed that a positron and an electron combine to form a pseudo-atom, somewhat similar to the hydrogen atom. In the hydrogen atom the electron can be described as moving around an essentially stationary nucleus, the proton. In the pseudo-atom formed by a positron and an electron, which has been given the name positronium, the two particles have the same mass, so that they carry out similar motions about their center of mass, the point midway between the two. 

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. 

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