Beta-particle production A decay process

Beta-particle production a decay process for radioactive nuclides in which the mass number remains constant and the atomic number changes. The net effect is to change a neutron to a proton. (21.1)... 

Te 5.10 alpha particles and 5 beta particles 7. Refer to Table 21.2 for potential radioactive decay processes. 17F and, 8F contain too many protons or too few neutrons. Electron capture or positron production are both possible decay mechanisms that increase the neu-tron-to-proton ratio. Alpha-particle production also increases the neu-tron-to-proton ratio, but it is not likely for these light nuclei. 21F contains too many neutrons or too few protons. Beta-particle production lowers the neutron-to-proton ratio, so we expect 21F to be a /3-emitter. 9. a. 2gCf + gO - fcIJSg + 4jn b. Rf 11. 6.35 X 1011 13. a. 

Beta-particle production is another common decay process. For example, the thorium-234 nuclide produces a p particle as it changes to protactinium-234. 

Beta particles A beta particle is a very fast-moving electron that is emitted when a neutron in an unstable nucleus converts into a proton. Beta particles are represented by the symbol (3 or e. They have a 1 — charge. Their mass is so small compared with the mass of nuclei involved in nuclear reactions that it can be approximated to zero. Beta radiation consists of a stream of fast-moving electrons. An example of the beta decay process is the decay of iodine-131 into xenon-131 by beta-particle emission, as shown in Figure 24.4. Note that the mass number of the product nucleus is the same as that of the original nucleus (they are both 131), but its atomic number has increased by 1 (54 instead of 53). This change in atomic number occurs because a neutron is converted into a proton, as shown by the following equation. 

Each of the following nuclides is known to undergo radioactive decay by production of a beta particle. Write a balanced nuclear equation for each process. 

The numerical combination of protons and neutrons in most nuclides is such that the nucleus is quantum mechanically stable and the atom is said to be stable, i.e., not radioactive however, if there are too few or too many neutrons, the nucleus is unstable and the atom is said to be radioactive. Unstable nuclides undergo radioactive transformation, a process in which a neutron or proton converts into the other and a beta particle is emitted, or else an alpha particle is emitted. Each type of decay is typically accompanied by the emission of gamma rays. These unstable atoms are called radionuclides their emissions are called ionizing radiation and the whole property is called radioactivity. Transformation or decay results in the formation of new nuclides some of which may themselves be radionuclides, while others are stable nuclides. This series of transformations is called the decay chain of the radionuclide. The first radionuclide in the chain is called the parent the subsequent products of the transformation are called progeny, daughters, or decay products. 

In contrast to alpha emission, beta emission is characterized by production of particles with a continuous spectrum of energies ranging from nearly zero to some maximum that is characteristic of each decay process. The jS particle is not nearly as effective as the alpha particle in producing ion pairs in matte r because of its small mass (about /7(XK) that of an alpha particle), At the same time, its penetrating power is substantially greater than that of the alpha particle. Beta-particle energies are frequently related to the thickness of an absorber, ordinarily aluminum, required to stop the particle. 

FIGURE 32-6 Overview of the neutron activation process. The incident neutron is captured by the target nucleus to produce an excited compound nucleus, which de-excites with emission of a prompt gamma ray. The radioactive nucleus formed decays by emitting a beta particle. If an excited product nucleus is formed, a delayed gamma ray can be emitted. If decay is directly to the ground state of the product nucleus, no gamma ray is emitted. 

Positron emission occurs only when the energy difference between the parent radionuclide and the products exceeds 1.02 MeV (the energy equivalent of the sum of the masses of an electron and a positron). The atom s recoil, as for beta-particle emission, is a few electron volts. At lesser energy differences, a proton in the nucleus can be converted to a neutron by electron capture, i.e., the capture by the nucleus of an atomic electron from, most probably, an inner electron shell (see discussion below of CEs). The process of electron capture parallels positron emission and may occur in the same isotope. It is accompanied by emission of a neutrino and characteristic X rays due to the rearrangement of atomic electrons. Electron capture may also be signaled by the subsequent emission of gamma rays. Examples of these decays are given in Sections 9.3.4 and 9.3.6. 

Radioactivity is measured by detecting the products of radioactive decay processes. The most well-known instrument used for this purpose is the Geiger counter. A Geiger counter is sensitive to the products of nuclear decay, including alpha and beta particles and gamma rays. The units used to quantify radiation are the Curie or the Bec-querel, which describe the number of nuclear decays a substance undergoes per unit of time. 

In 1913 the British scientist A. Cranston worked with the radioelement MsTh-II (an isotope of actinium-228). This isotope emits beta particles and converts into thorium-228. But Cranston thought that he detected a very weak alpha decay, too. If that was true the product of the decay had to be the long-expected eka-cesium. Indeed, the process is described by... 

A beta particle, (3 , is an electron in all respects it is identical to any other electron. Following on from Section 1.1, the sum of the masses of the "Ni plus the mass of the (3 , and i>, the anti-neutrino, are less than the mass of "Co. That mass difference drives the decay and appears as energy of the decay products. What happens during the decay process is that a neutron is converted to a proton within the nucleus. In that way the atomic number increases by one and the nuclide drops down the side of the valley to a more stable condition. A fact not often realized is that the neutron itself is radioactive when it is not bound within a nucleus. A free neutron has a half-life of only 10.2 min and decays by beta emission ... 

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