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Introduction
Published in Armen S. Casparian, Gergely Sirokman, Ann O. Omollo, Rapid Review of Chemistry for the Life Sciences and Engineering, 2021
Armen S. Casparian, Gergely Sirokman, Ann O. Omollo
The mass number, A, of an element is the sum of the number of protons and the number of neutrons in the nucleus, collectively known as the number of nucleons. Protons and neutrons are assigned a mass number of one atomic mass unit (amu) each, based on the carbon-12 atom as the standard. Although an element can have only one atomic number, it may have more than one mass number. This fact gives rise to the phenomenon of isotopes. Isotopes are atoms of the same element with the same atomic number but with a different number of neutrons. An element may have several isotopes, one or more of which may be radioactive and hence unstable. For example, oxygen has three naturally occurring isotopes, all of which are stable, while carbon also has three, one of which is radioactive. The mathematical average of all isotopic mass numbers of an element, weighted by the percent abundance in nature of these isotopes, constitutes the element’s atomic mass. It is impossible to predict theoretically how many isotopes an element may have or how many may be radioactive. The isotopes of a given element have almost identical chemical properties (i.e., reactivity) but different physical properties (i.e., density, melting point, etc.). The mass number is expressed as a left-hand superscript to the element symbol, for example, 12C.
Nuclear Energy Security
Published in Maria G. Burns, Managing Energy Security, 2019
Every atom comprises a nucleus, which in turn is made up of protons and neutrons. To generate nuclear energy a nuclear reaction is induced to change the number of protons and/or neutrons, and consequently change the nucleus of an atom. The energy launched by atomic nuclei reactions (also called radioactive processes) derives from nuclear fission or fusion. In nuclear fission a reaction or a radioactive decay process is induced in which an atomic nucleus is split in two to produce smaller nuclei. This process generates energy.In nuclear fusion a reaction is induced in which two atomic nuclei are united (fused) to produce a larger nucleus. Again, this process generates energy.
Nuclear energy and the management of radioactive waste
Published in Gianluca Ferraro, The Politics of Radioactive Waste Management, 2018
Nuclear science is a relatively recent discipline that has developed over the last century. Its origin can be traced back to the late 1800s when the phenomenon of radioactivity was discovered (U.S. Department of Energy 2011; Weingart 2007). Radioactivity consists of a process by which the nucleus of an unstable atom loses energy by emitting electromagnetic waves or sub-atomic particles. This energy is called radiation (NEA 2012d). We know, now, that a specific type of radiation, i.e. ionising radiation, is capable of causing damage to living cells. In particular, the radiation generated during the production of nuclear energy has the potential to harm people and the environment if it is released accidentally (NEA 2012d). Exposure to high doses of radiation increases the chance of developing cancer; very high doses can cause immediate death (Weingart 2007). For this reason, high levels of safety are considered essential for the use of nuclear energy (NEA 2012d).
Effect of 14.7-MeV Protons and 3.6-MeV Alpha Particles on Fusion Structural Materials
Published in Fusion Science and Technology, 2020
S. I. Radwan, S. Abdel Samad, H. El-Khabeary
Fusion power is a power generation in which energy is generated by using nuclear fusion reactions to produce heat for electricity generation through a device named the thermonuclear reactor.1 Fusion reactions occur when two or more light atomic nuclei come close enough at a distance of 10−15 m to form a heavier atomic nucleus, then the nuclear force pulling them together exceeds the electrostatic force pushing them apart, fusing them into heavier nuclei.2 The strong force becomes effective at this distance and the two nuclei unite into one nucleus. Since the atomic nuclei have positive charges, they must overcome the Coulomb potential in order to approach each other within 10−15 m. The light nuclei must be moving at high speed in their collision. Thus, the nuclei are either accelerated or heated to a high temperature. Fusion processes require fuel and a highly confined environment with a high temperature and pressure to create a plasma in which fusion can occur. Fusion reactors generally use hydrogen isotopes, such as deuterium and tritium, that react more easily and create a confined plasma of millions of degrees using inertial methods (laser)3–6 or magnetic methods (tokamak and similar),7,8 although many other concepts have been attempted. Fusion reactions are of two basic types: (1) those that preserve the number of protons and neutrons and (2) those converted between protons and neutrons. Reactions of the first type are the most important for practical fusion energy production, whereas those of the second type are crucial to the initiation of star burning.