Physics
Neutron Number
The neutron number refers to the number of neutrons in an atomic nucleus. It is a key factor in determining the stability and properties of an atom. Neutron number varies among different isotopes of an element and can affect nuclear reactions and decay processes.
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9 Key excerpts on "Neutron Number"
eBook - ePub- Robert E. Masterson(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
11 times more than the Statue of Liberty. [Ans.]2.11How the Number of Neutrons Affects the Stability of a Nucleus
Long before anyone knew about the existence of quarks and gluons, scientists knew that atoms with larger numbers of protons seemed to need a much larger number of neutrons for their nuclei to remain stable. When they plotted the number of neutrons against the number of protons for all of the naturally occurring elements in the Periodic Table, they found an interesting relationship that we would like to present to you now. They found that the number of neutrons in the nucleus increased at a greater rate than the number of protons and that the constant of proportionality between the two of them seemed to increase as elements became heavier. In other words, the relationship between the number of protons and the number of neutrons was not at all a linear one. They ultimately concluded that the extra neutrons were needed to keep the protons from getting too close together and therefore destabilizing the nucleus as the result of the electrical forces between them.Today, we realize that this is a direct consequence of the interplay between the electromagnetic forces (which are carried by photons) and the nuclear forces (which are carried by the gluons). The relationship between the number of protons and the number of neutrons as a function of the atomic number can be seen in Figure 2.11 . If we are dealing with very heavy elements like Uranium and Plutonium, there are, on average, about 1.5 neutrons for every proton to maintain the stability of the nucleus as a whole. This seems to be a magic number that is neither too big nor too small—but just about right to hold the nucleus together. For lighter and intermediate elements, like aluminum and carbon, this ratio is much closer to 1.0. For example, Oxygen-16 has eight protons and eight neutrons. Yet it is remarkably stable and has a half-life of about 20 billion years. When the nucleus of a heavy element undergoes a fission event, some of the by-products of the nuclear chain reaction (e.g., the fission products) are “neutron rich” relative to the ideal ratios shown in Figure 2.11
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
The total number of neutrons and protons in a nucleus is called its mass number A; thus A = Z + N. (42-1) Neutrons and protons, when considered collectively as members of a nucleus, are called nucleons. We represent nuclides with symbols such as those displayed in the first col- umn of Table 42-1. Consider 197 Au, for example. The superscript 197 is the mass number A. The chemical symbol Au tells us that this element is gold, whose atomic number is 79. Sometimes the atomic number is explicitly shown as a subscript, as in 197 79 Au. From Eq. 42-1, the Neutron Number of this nuclide is the difference between the mass number and the atomic number, namely, 197 – 79, or 118. Nuclides with the same atomic number Z but different Neutron Numbers N are called isotopes of one another. The element gold has 36 isotopes, ranging from 173 Au to 204 Au. Only one of them ( 197 Au) is stable; the remaining 35 are radioactive. Such radionuclides undergo decay (or disintegration) by emitting a particle and thereby transforming to a different nuclide. Organizing the Nuclides The neutral atoms of all isotopes of an element (all with the same Z) have the same number of electrons and the same chemical properties, and they fit into the same box in the periodic table of the elements. The nuclear properties of the isotopes of a given element, however, are very different from one isotope to another. Thus, the periodic table is of limited use to the nuclear physicist, the nuclear chemist, or the nuclear engineer.
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2018(Publication Date)
- Wiley(Publisher)
(42-1) Neutrons and protons, when considered collectively as members of a nucleus, are called nucleons. We represent nuclides with symbols such as those displayed in the first col- umn of Table 42-1. Consider 197 Au, for example. The superscript 197 is the mass number A. The chemical symbol Au tells us that this element is gold, whose atomic number is 79. Sometimes the atomic number is explicitly shown as a subscript, as in 197 79 Au. From Eq. 42-1, the Neutron Number of this nuclide is the difference between the mass number and the atomic number, namely, 197 – 79, or 118. Nuclides with the same atomic number Z but different Neutron Numbers N are called isotopes of one another. The element gold has 36 isotopes, ranging from 173 Au to 204 Au. Only one of them ( 197 Au) is stable; the remaining 35 are radioactive. Such radionuclides undergo decay (or disintegration) by emitting a particle and thereby transforming to a different nuclide. Organizing the Nuclides The neutral atoms of all isotopes of an element (all with the same Z) have the same number of electrons and the same chemical properties, and they fit into the same box in the periodic table of the elements. The nuclear properties of the isotopes of a given element, however, are very different from one isotope to another. Thus, the periodic table is of limited use to the nuclear physicist, the nuclear chemist, or the nuclear engineer.
eBook - PDF- Stephen Thornton, Andrew Rex, Carol Hood, , Stephen Thornton, Stephen Thornton, Andrew Rex, Carol Hood(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
Bettmann/Getty Images Copyright 2021 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 438 Chapter 12 The Atomic Nucleus produced in the a 1 Be reaction, the neutrons could then collide elastically with the protons in paraffin, thereby accounting for the 5.7-MeV protons. In his pub- lished results* Chadwick used his experimental data to estimate the neutron’s mass as somewhere between 1.005 u and 1.008 u, not far from the modern value of 1.0087 u. For this careful experimental work and theoretical analysis, Chadwick is recognized for having confirmed the neutron’s existence. 12.2 Nuclear Properties The primary constituents of nuclei are the proton and neutron, and the nuclear mass is roughly the sum of its constituent proton and neutron masses (the slight difference being the binding energy of the nucleus). The nuclear charge is 1e times the number (Z) of protons (e 5 1.6 3 10 219 C). Helium has Z 5 2, oxygen has Z 5 8, and uranium has Z 5 92. The simplest form of hydrogen has a single proton for a nucleus. However, we know that multiple forms of hydrogen exist. Deuterium—sometimes called “heavy hydrogen”—has a neutron as well as a proton in its nucleus. Another form of hydrogen is called tritium—it has two neutrons and one proton. The nuclei of the deuterium and tritium atoms are called deuterons and tritons, respectively. The atomic (and nuclear) mass number A is the total integral number of protons and neutrons in a nucleus. Atoms with the same Z , but different A, are called isotopes.
eBook - PDF- Gary N. Felder, Kenny M. Felder(Authors)
- 2022(Publication Date)
- Cambridge University Press(Publisher)
Each “nucleon” (proton or neutron) has about 2000 times the mass of an electron. But they’re not identical; a neutron is about 0.1% heavier than a proton. A nucleus is described by three (related) numbers: Z Atomic number The number of protons N Neutron Number The number of neutrons A = Z + N Mass number The total number of nucleons Because Z and A are the most commonly discussed quantities, we often write formulas with A − Z instead of explicitly using the letter N. We can summarize a number of the key facts that describe a nucleus. • The total charge of a nucleus is eZ, where e is the charge of one proton. • The total mass of a nucleus is roughly m p A, where m p is the proton mass. (The actual mass is somewhat smaller than this, because the binding energy – the negative potential energy that holds the nucleus together – reduces the total mass. Section 12.3 will present a more accurate mass estimate called the “semiempirical mass formula.”) • A typical nuclear radius is 1–10 “femtometers” (1 fm = 10 −15 m), about 10,000 times smaller than the radius of a typical atom. • The density of a typical nucleus is on the order of 10 17 kg/m 3 . (A quart of nuclear-density milk would weigh more than Mount Everest.) Different nuclei generally have similar densities, so their radii are proportional to A 1/3 (Problem 8). Early twentieth-century physicists saw that the charge of any nucleus is an integer (Z) times the charge of a hydrogen nucleus, and that the mass of any nucleus is approximately an integer (A) times the mass of a hydrogen nucleus. This “whole number rule” suggested the existence of protons, indivisible particles that make up every nucleus. 558 12 The Atomic Nucleus But if protons were the whole story, then A and Z would always be the same as each other. How to explain the fact that, for almost all nuclei, A > Z? The obvious answer was that the nucleus contained A protons and A − Z electrons.
- Andrei D. Polyanin, Alexei Chernoutsan(Authors)
- 2010(Publication Date)
- CRC Press(Publisher)
The spin* of both the proton and neutron is equal to 1 / 2 , which means that they belong to the class of fermions. Both the proton and the neutron possess nonzero magnetic moments: μ p = 2 . 793 μ N and μ n = – 1 . 91 μ N , where μ N = e planckover2pi1 / 2 m p is the so-called nuclear magneton ( μ N = μ B / 1836 . 15 ). The nonzero magnetic moment of the neutron suggests that nucleons must have an internal structure involving more elementary charged particles. The nuclear composition is described by two integers: the atomic number Z , equal to the number of protons in the nucleus (and so identical to the charge number of the nucleus), and the mass number A , equal to the total number of nucleons in the nucleus. The number of neutrons (the Neutron Number ) is N = A – Z . The charge number of an element coincides with its ordinal number in Mendeleev’s table (see Chapter S7) and determines its physical-chemical properties, since these depend on the charge of the nucleus and are almost independent of its mass. The charge and the mass numbers of an element X are specified as indices to the left of its symbol: A Z X; for example, 3 2 He, 13 6 C. Since the element symbol uniquely determines its number in the periodic table, which coincides with the charge number Z , the left lower index is sometimes dropped ( 3 He, 13 C). Particular atoms with A nucleons in their nucleus and Z protons, together with their electronic shell containing Z electrons, are called nuclides . All nuclides with the same Z * Here and henceforth, we often use the word “spin” for short to mean the “spin quantum number.” 617 618 E LEMENTS OF N UCLEAR P HYSICS are called isotopes of a given element. The isotopes of hydrogen 1 H, 2 H, and 3 H, whose nuclei are essentially distinct, are respectively called the common hydrogen (sometimes the term protium is used), deuterium (D), and tritium (T), and the nuclei of deuterium and tritium are called deuteron (d) and triton (t).
eBook - PDFElements of Slow-Neutron Scattering
Basics, Techniques, and Applications
- J. M. Carpenter, C.-K. Loong(Authors)
- 2015(Publication Date)
- Cambridge University Press(Publisher)
1 About neutrons The neutron and its quark structure (udd), wave packet, wave vector, spin, and magnetic dipole and electric dipole moments. 1.1 The neutron as an elementary particle As a fundamental particle, the neutron is one of the basic building blocks of material at the nuclear scale – the other is the proton, the nucleus of a hydrogen atom. James Chadwick, in 1932, first recognized the neutron as a product of irradiating beryl- lium with alpha particles in the reaction that we now denote 9 Be(α, n) 12 C. Chad- wick’s discovery resolved numerous questions about the nature of atomic nuclei and for the first time allowed scientists to organize the atomic nuclei as consist- ing of neutrons and protons, which we now call the nucleons. As a member of the family of isotopes and elements, stable and radioactive, the neutron fills the “zero charge” slot, completing the list of nuclides on the low-mass side. Neutrons do not exist for long in free space – free neutrons have a mean lifetime of only about 881 seconds, 15 minutes, (half-life 611 s, 10.2 min) and decay into a proton, an 1.1 The neutron as an elementary particle 11 Table 1.1 Properties of the quarks (Nakamura et al. 2010) Generation Flavor Symbol Charge, e units Rest Mass, MeV First down D −1/3 ≈5 First up U 2/3 ≈10 Second strange S −1/3 ≈200 Second charm C 2/3 ≈1500 Third bottom B −1/3 ≈5000 Third top T 2/3 ≈173 000 electron, and an electron antineutrino. The fundamental properties of the neutron underlie the technology of producing neutrons and the application of slow-neutron scattering in materials science, as described in the Introduction. At the energies of interest in neutron technology, nuclei must be considered as modifiable, loosely bound clusters of nucleons (protons and neutrons), while the nucleons themselves are immutable structured entities that consist of quark constituents.
- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
Instructional video is available at the website www.wiley.com After reading this module, you should be able to . . . 42.2.1 Identify nuclides, atomic number (or proton number), Neutron Number, mass number, nucleon, isotope, disintegration, neutron excess, isobar, zone of stable nuclei, and island of stability, and explain the symbols used for nuclei (such as 197 Au). 42.2.2 Sketch a graph of proton number versus Neutron Number and identify the approximate location of the stable nuclei, the proton-rich nuclei, and the neutron-rich nuclei. 42.2.3 For spherical nuclei, apply the relationship between radius and mass number and calculate the nuclear density. 42.2.4 Work with masses in atomic mass units, relate the mass number and the approximate nuclear mass, and convert between mass units and energy. 42.2 SOME NUCLEAR PROPERTIES KEY IDEAS 1. Different types of nuclei are called nuclides. Each is characterized by an atomic number Z (the number of protons), a Neutron Number N, and a mass number A (the total number of nucleons—protons and neutrons). Thus, A = Z + N. A nuclide is represented with a symbol such as 197 Au or 197 79 Au, where the chemical symbol carries a superscript with the value of A and (possibly) a subscript with the value of Z. 2. Nuclides with the same atomic number but different Neutron Numbers are isotopes of one another. 3. Nuclei have a mean radius r given by r = r 0 A 1/3 where r 0 ≈ 1.2 fm. 4. Atomic masses are often reported in terms of mass excess Δ = M − A, where M is the actual mass of an atom in atomic mass units and A is the mass number for that atom’s nucleus. 5. The binding energy of a nucleus is the difference ΔE be = ∑( mc 2 ) − Mc 2 , where ∑ (mc 2 ) is the total mass energy of the individual protons and neutrons. The binding energy of a nucleus is the amount of energy needed to break the nucleus into its constituent parts (and is not an energy that resides in the nucleus).
eBook - PDF- Hans Rudolf Wenk(Author)
- 2018(Publication Date)
- De Gruyter(Publisher)
and Diamond/ISIS at Chilton, United Kingdom. This chapter provides some of the important properties of the neutron and an introduction the mathematical basis for neutron scattering. More detailed explanations of the applications are provided in subsequent chapters. The applications and instruments to carry them out depend on how neutrons are produced, at either reactor or spallation sources and these aspects are cov-ered explicitly in Vogel and Priesmeyer (2006, this volume). For other details see the neutron portal http://neutron.neutron-eu.net/n_links for links to new and existing facilities for neutron research. PROPERTIES OF THE NEUTRON It is important to understand those properties that make the neutron such a unique probe for condensed matter research. A neutron is an elementary particle found in the nucleus of atoms. As all particles of this length scale (protons, electrons, photons etc.), it has both particle (e.g., mass) and wave properties (e.g., wavelength). Some of the more important of the properties of the neutron are summarized in Table 1. Four properties are of particular note. Charge The neutron has zero net charge and so interacts very weakly with matter, penetrating deeply into a sample. This allows the use of large, geologically relevant, rock samples for absorption studies (Winkler 2006, this volume). The neutron also easily penetrates sample enclosures such as low temperatures cryostats and pressure cells. Further, there is no Coulomb interaction with the electronic charge cloud and neutrons interact directly with the nuclei of atoms. Although for most elements the absorption cross section is small, there are important exceptions and these are discussed below along with the nuclear scattering process. Magnetic moment Although the neutron carries no net charge, and so does not interact with the charge of the electron, it does have a magnetic moment, a spin, that interacts with the unpaired electron spins.
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