Nuclear instability

Tlie kind of trcuisformation tliat will take place for any given radioactive element is a function of the type of nuclear instability as well as the mass/eiiergy relationship. Tlie nuclear instability is dependent on the ratio of neutrons to protons a different type of decay will occur to allow for a more stable daughter product. The mass/energy relationship stales tliat for any radioactive transformation(s) the laws of conservation of mass tuid tlie conservation of energy must be followed. 

Ruddick (1953) and Lowdermilk et al. (1958) found that flow oscillation can induce a premature boiling crisis. Moreover, in a boiling water reactor the flow oscillation may induce a nuclear instability. Thus, in designing a boiling system, it is imperative to predict and prevent those operational conditions that might create flow oscillation. 

Foltz DR, Jansen LE, Black BE, Bailey AO, Yates JR, Cleveland DW (2006) The human CENP-A centromeric nucleosome-associated complex. Nat Cell Biol 8 458 69 Foresta C, Zorzi M, Rossato M, Varotto A (1992) Sperm nuclear instability and staining with aniline blue abnormal persistence of histones in spermatozoa in infertile men. Int J Androl 15 330-337 Fukagawa T, Nogami M, Yoshikawa M, Ikeno M, Okazaki T, Takami Y, Nakayama T, Oshimura M (2004) Dicer is essential for formation of the heterochromatin structure in vertebrate cells. Nat Cell Biol 6 784-791... 

The r process can form a bridge between lead and the actinides above the nuclear instability zone. It is thus responsible for the production of long-lived actinides such as thorium-232, uranium-235, uranium-238 and plutoiuum-244 which are used to estimate the age of the Earth and the Galaxy. 

The first indications of nuclear instability came from the radiation they emit as they decay. In 1896, the French scientist Henri Becquerel happened to store a sample of uranium oxide in a drawer that contained some photographic plates (Fig. 17.2). He was astonished to find that the uranium compound darkened the plates even though they were stored in a protective covering. Becquerel realized that some kind of radiation must be given off by the uranium compound he called these rays radioactivity. Marie Sklodowska Curie (Fig. 17.3), a young Polish doctoral student, showed that the radiation was independent of the state of chemical combination of the uranium. She concluded that the source must be the uranium atoms themselves. Together with her husband Pierre, she went on to show that thorium, radium, and polonium are also radioactive. 

Radioactive decay occurs because of nuclear instability, with the end result of decay being stability. If this stability is not achieved by the first nuclear transformation, then more transformations occur. This set of transformations is called a decay series, as shown in Figure 14.4. 

Radioactive decay is a property of the atomic nucleus and is evidence of nuclear instability. The rate of decay is unaffected by temperature, pressure, concentration, or any other chemical or physical condition but is characteristic of each individual radionuclide. 

The nucleus is made up of protons, which are positively charged and neutrons, which have no charge. Neutrons and protons have about the same mass, and together account for most of the mass of the atom. Each of these particles is made up of even smaller particles, though the existence of these particles does not come into play at the energies and time spans in which most chemical reactions occur. The ratio of protons to neutrons is fairly critical, and any departure from the optimum range will lead to nuclear instability and thus radioactivity. 

In this chapter we have stressed nuclear instability to beta decay. However, in 3.4 it was learned that very heavy nuclei are unstable to fission. There is also a possibility of instability to emission of a-particles in heavy elements (circles in Figure 3.1) and to neutron and proton emission. 

This is the last chapter in Part I of the general chemistry review. In this chapter, we will discuss the different aspects of radioactivity. Radioactivity is a nuclear phenomenon. It results from natural nuclear instability or externally induced nuclear instability. We will limit our discussion of nuclear chemistry to the basic aspects of radioactivity involving radioactive emissions such as alpha emission, beta emission, gamma rays, positron emission, and electron capture. We will also review other ideas such as the half-lives of radioactive substances and the mass-energy equation. 

For some time the prevalent view in the scientific community was that the periodic system was close to its final completion. But repeated reports about syntheses of the isotopes of elements with the numbers in the second hundred gradually convinced experimenters that theoretical predictions were not that faultless. Of course, these isotopes existed for very short periods but not so short as predicted by theory. For instance, the isotope with a mass number of 261 of element 107 undergoes spontaneous fission with a half-life of 0.002 s which is very short but it is tens of billions times that predicted by theoretical calculations of increasing instability of the nuclei with increasing Z value. In fact, the growth of nuclear instability seems to be inhibited. 

Radioactivity itself was characterized by Ernest Rutherford at the beginning of the 20th century. Rutherford and others discovered that radioactivity was the result of nuclear instability many nuclei, especially the heavy ones, are unstable and decay to attain stability, releasing parts of their nucleus in the process. These emitted particles were the rays that Becquerel and the Curies detected. There are three primary types of radiation emitted by decaying nuclei alpha, beta, and garrrma radiation. 

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