Physics
Protons
Protons are subatomic particles found in the nucleus of an atom, carrying a positive electric charge. They are fundamental components of matter and play a crucial role in determining the chemical and physical properties of elements. With a mass approximately 1,836 times that of an electron, protons are essential for the stability and structure of atoms.
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10 Key excerpts on "Protons"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Research World(Publisher)
The constituent particles of an atom are the electron, the proton and the neutron. However, the hydrogen-1 atom has no neutrons and a positive hydrogen ion has no electrons. The electron is by far the least massive of these particles at 9.11×10 −31 kg, with a negative electrical charge and a size that is too small to be measured using available techniques. Protons have a positive charge and a mass 1,836 times that of the electron, at 1.6726×10 −27 kg, although this can be reduced by changes to the energy binding the proton into an atom. Neutrons have no electrical charge and have a free mass of 1,839 times the mass of electrons, or 1.6929×10 −27 kg. Neutrons and Protons have comparable dimensions—on the order of 2.5×10 −15 m—although the 'surface' of these particles is not sharply defined. In the Standard Model of physics, both Protons and neutrons are composed of elementary particles called quarks. The quark belongs to the fermion group of particles, and is one of the two basic constituents of matter—the other being the lepton, of which the electron is an example. There are six types of quarks, each having a fractional electric charge of either + 2 ⁄ 3 or − 1 ⁄ 3 . Protons are composed of two up quarks and one down quark, while a neutron consists of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles. The quarks are held together by the strong nuclear force, which is mediated by gluons. The gluon is a member of the family of gauge bosons, which are elementary particles that mediate physical forces. ________________________ WORLD TECHNOLOGIES ________________________ Nucleus The binding energy needed for a nucleon to escape the nucleus, for various isotopes. All the bound Protons and neutrons in an atom make up a tiny atomic nucleus, and are collectively called nucleons. The radius of a nucleus is approximately equal to , where A is the total number of nucleons.
eBook - ePubFrom Atoms to Higgs Bosons
Voyages in Quasi-Spacetime
- Chary Rangacharyulu, Christopher J. A. Polachic, Chary Rangacharyulu, Christopher J. A. Polachic(Authors)
- 2019(Publication Date)
- Jenny Stanford Publishing(Publisher)
At this point, there was an additional problem with the way chemical atoms were conceived: The Protons, alone, could not account for the total observed mass of atomic nuclei. A heavy, electrically neutral particle was required to contribute the additional mass while keeping the overall electric charge of atoms neutral. The neutron was discovered in 1932, satisfying this demand.Thus, Protons and neutrons are now known to give mass to the nucleus of a chemical atom. Protons fix the rank of an atom in the Mendeleevian periodic table of elements, while electrons guarantee zero overall electric charge and are responsible for all chemical reactions and thus the complex biological phenomena of life. It would be reasonable to think that having identified three basic constituents that suffice for the formation of chemical atoms, we might have found the true physical entities of Democritus’ philosophy. The proton, neutron, and electron certainly appear to be a complete set of particles necessary to build matter and explain the world as it is around us. However, almost immediately, the status of the proton and neutron as “fundamental particles” came under scrutiny.7.3 Protons and Neutrons Are Particles, but Are They Fundamental?
Physicists of the twentieth century had several concerns with identifying Protons and neutrons as fundamental: the finite size of the nucleons, the instability of free neutrons, and the presence of excitations similar to those seen in composite bodies such as atoms.The first difficulty is a philosophical one: Protons and neutrons are not point objects, which is another way of saying that they appear to have definite size. Indeed, the electromagnetic properties of Protons and neutrons do not conform to the theoretical predictions of point-like entities, but it should be said that even in recent years, there has been intense discussion among particle physicists about discrepancies in the size of the proton as measured by different experimental techniques.
- Andrei D. Polyanin, Alexei Chernoutsan(Authors)
- 2010(Publication Date)
- CRC Press(Publisher)
Chapter P8 Elements of Nuclear Physics The idea that practically the entire mass of an atom is concentrated in its positively charged nucleus of infinitesimally small dimensions is due to Rutherford’s experiments (see Chap-ter P6). Since the dimensions of nuclei turned out to be by five orders less than those of atoms, it can be assumed, in the framework of atomic physics, that the nucleus is a point Coulomb center. Actually, the nucleus is a complex structure formed by strongly interacting particles (several ones or hundreds) obeying the laws of quantum mechanics and quantum statistics. The nuclei can undergo radioactive transformations, participate in nuclear reac-tions, disintegrate, and merge with other nuclei. The characteristic energies in that nuclear world are measured in millions of electron-volts, which explains why nuclei appear as stable objects in atomic processes with energies up to several hundred electron-volts. P8.1. Basic Properties of Nuclei P8.1.1. Characteristics of Nuclei ◮ Nuclear Composition. The atomic nucleus consists of Protons and neutrons—particles collectively named nucleons . The proton is a subatomic particle with positive charge e and mass m p = 1836 . 15 m e , where m e is the electron mass. The neutron is an electrically neutral particle whose mass is slightly greater than that of the proton: m n = 1838 . 68 m e . In its free state, the neutron is unstable in the sense that within 15.5 minutes, on the average, it turns into a proton after emitting an electron and an antineutrino: n → p + e + tildewide ν . 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 ).
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
______________________________ WORLD TECHNOLOGIES ______________________________ Components Subatomic particles Though the word atom originally denoted a particle that cannot be cut into smaller particles, in modern scientific usage the atom is composed of various subatomic particles. The constituent particles of an atom are the electron, the proton and the neutron. However, the hydrogen-1 atom has no neutrons and a positive hydrogen ion has no electrons. The electron is by far the least massive of these particles at 9.11×10 −31 kg, with a negative electrical charge and a size that is too small to be measured using available techniques. Protons have a positive charge and a mass 1,836 times that of the electron, at 1.6726×10 −27 kg, although this can be reduced by changes to the energy binding the proton into an atom. Neutrons have no electrical charge and have a free mass of 1,839 times the mass of electrons, or 1.6929×10 −27 kg. Neutrons and Protons have comparable dimensions—on the order of 2.5×10 −15 m—although the 'surface' of these particles is not sharply defined. In the Standard Model of physics, both Protons and neutrons are composed of elementary particles called quarks. The quark belongs to the fermion group of particles, and is one of the two basic constituents of matter—the other being the lepton, of which the electron is an example. There are six types of quarks, each having a fractional electric charge of either + 2 ⁄ 3 or − 1 ⁄ 3 . Protons are composed of two up quarks and one down quark, while a neutron consists of one up quark and two down quarks. This distinction accounts for the difference in mass and charge between the two particles. The quarks are held together by the strong nuclear force, which is mediated by gluons. The gluon is a member of the family of gauge bosons, which are elementary particles that mediate physical forces.
eBook - PDFFoundations of Chemistry
An Introductory Course for Science Students
- Philippa B. Cranwell, Elizabeth M. Page(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
This will be dis-cussed in Section 1.2.4. Protons and neutrons have the same mass and are much larger and heavier than electrons. Protons have a positive charge, and neutrons have no charge and so are neutral. Both Protons and neutrons are found in the nucleus of the atom (Figure 1.1). Electrons have a much smaller mass than Protons and neutrons and have a negative charge. Electrons are found in the region of space surrounding the nucleus. Table 1.1 gives the properties of the three main subatomic particles. 1.1.2 Mass number ( A ) and atomic number ( Z ) Each element is described by the number of Protons, neutrons, and electrons it possesses. These are represented by two quantities: the mass number ( A ) and the atomic number ( Z ) The mass number indicates the total number of Protons and neutrons in the nucleus of the atom (p + n). The atomic number gives the number of Protons in a neutral atom of the element (p). A neutral atom must have the same number of Protons as electrons, so Z also indicates the number of electrons (e). For any element X, we can represent the information about the mass number, A , and atomic number, Z , as shown in Figure 1.2a. As you can see, the mass number is written as a superscript and the atomic number as a subscript in front of the symbol for the element. Information about the element beryllium is shown in Figure 1.2b using this convention. Beryllium (Be) has an atomic number, Z , of 4; therefore, in a neutral mole-cule, there are 4 Protons and 4 electrons. Beryllium has a mass number, A , of 9; therefore it has 5 neutrons (because the mass number is 9 and we already know that it has 4 Protons from the atomic number, so 9 -4 = 5 neutrons). The mass Nucleus: contains Protons and neutrons Electron: moves around the nucleus Figure 1.1 Simplified structure of the atom (not to scale).
eBook - PDFQuestioning the Universe
Concepts in Physics
- Ahren Sadoff(Author)
- 2008(Publication Date)
- Chapman and Hall/CRC(Publisher)
87 10 The Nucleus As we have seen, the atom is the key to understanding all the forces, except for grav-ity, that affect us in our everyday life. For these atomic interactions, the nucleus plays a dual role. It holds the atom together by the electric attraction between the positive constituents in the nucleus and the negatively charged electrons. It also attracts the electrons in other atoms to cause these atoms to stay together to form the matter that we come in contact with, including ourselves. We have seen earlier that, in fact, there is a delicate attractive-repulsive balance causing atoms to attract each other in some cases, and in others causing repulsion, as in the case, for example, when a knife cuts through butter. In addition, except for the lonely proton in hydrogen, the nucleus has a rich and complex life of its own. 10.1 NUCLEAR PROPERTIES The nucleus is made up of Protons and neutrons. Protons have a positive electrical charge, while neutrons, as the name implies, are neutral. As we noted at the end of the last chapter, the proton and neutron masses are almost identical, being approxi-mately 2,000 times the mass of the electron but differing by only about 0.1%. A typi-cal nuclear size is about 10 − 14 m, about 1/10,000 (10 − 4 ) the size of the atom. A question? These facts should suggest a question in your mind. As usual, try to think of it before reading further. The question: What holds the nucleus together? A first guess might be the gravitational force. After all, it is always attractive, and over such minute distances perhaps it is strong enough to bind the nuclear particles together. But unfortunately, gravity cannot do it. In Chapter 5, we showed that the ratio of the electric force to the gravitational force is 10 42 . In other words, the Protons are repelling each other with an electric force tremendously larger than the attractive gravitational force. Thus, there must exist an attractive force greater than the electri-cal repulsive force.
eBook - PDF- Young, William Vining, Roberta Day, Beatrice Botch(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
Fluorescent screen Undeflected alpha particles Radioactive source of fast moving alpha particles Gold foil Deflected particles Interactive Figure 2.2.4 Explore the Rutherford gold foil experiment. A diagram showing the Rutherford (Geiger-Marsden) gold foil experiment Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 Unit 2 Atoms and Elements 39 Two of the subatomic particles, Protons and neutrons, are found in the atomic nucleus, a very small region of high density at the center of the atom. Electrons are found in the region around the nucleus. As you will see when we study atomic structure in more detail in Electromagnetic Radiation and the Electronic Structure of the Atom (Unit 3), the pre-cise location of electrons is not determined. Instead, we visualize an electron cloud sur-rounding the nucleus that represents the most probable location of electrons (Interactive Figure 2.2.5). The atom represented in Interactive Figure 2.2.5 is not drawn to scale. In reality, elec-trons account for most of the volume of an atom, and the nucleus of an atom is about 1 > 10,000 the diameter of a typical atom. For example, if an atom had a diameter the same size as a football field, 100 yards, or about 90 meters, the nucleus of the atom would have a diameter of only about 1 cm! Mass and Charge of an Atom The mass and charge of an atom affect the physical and chemical properties of the element and the compounds it forms. As shown in Table 2.2.1, the three subatomic particles are easily differentiated by both charge and mass. The mass of an atom is almost entirely accounted for by its dense nucleus of Protons and neutrons. The actual mass of Protons and neutrons is very small, so it is more convenient to define the mass of these particles using a different unit. The atomic mass unit (u) is defined as 1 > 12 the mass of a carbon atom that contains six Protons and six neutrons.
eBook - PDF- Palash B. Pal(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
In a paper published in 1911, Rutherford demonstrated that the results of that experiment implied the existence of an atomic nucleus that is positively charged. It was then naturally concluded that the positively charged building blocks of atoms reside in the nucleus. The presence of some electrically neutral particles in the nucleus was antic-ipated by the existence of nuclear isotopes. In 1932, Irene Curie and Frederic Joliot showed that some neutral radiation coming out of nuclei in certain pro-cesses cannot be gamma rays, i.e., electromagnetic radiation. Because the radiation was neutral, one could not determine the mass of the particle from its charge and its q/m ratio, as was done for the electron. In the same year, James Chadwick determined the mass of the particles emitted by these pro-cesses and found that the mass was very close to that of the proton. With this, the existence of the neutron was established. Although this happened in 1932, the idea of the neutron was around for more than a decade by that time. Scientists started to believe that the elec-tron, proton and the neutron are the only fundamental fermions in the uni-verse. The proton and the neutron make the atomic nucleus, and the elec-trons move around the nuclei. Electromagnetic interactions are mediated by the photon. That is all there is to it! But this worldview was shattered al-most as soon as it was born, with the advent of experiments with high energy particles. 230 Chapter 9. Discovering particles 9.2 New particles in cosmic rays In § 1.5, we explained why an exploration into smaller and smaller objects required the control of higher and higher energies. In the early part of the twentieth century, the kind of energy that could be produced in a laboratory was not enough to produce any of the unstable particles in a collision process.
- Martinus J G Veltman(Author)
- 2003(Publication Date)
- World Scientific(Publisher)
The way these quarks are bound in a proton or neutron is quite complicated, and not fully under-stood. Statements about the quark content of proton and neutron must be taken with a grain of salt, because in addition there are particles called gluons which cause the binding and which are u u u d d d u d u u d d P N 13 P R E L I M I N A R I E S much more dominantly present than for example photons in an atom (the atomic binding is due to electromagnetic forces, thus photons do the job of binding the electrons to the nucleus). In fact, much of the mass of a proton or a neutron resides in the form of energy of the gluons, while the energy residing in the electric field of an atom is very small. For all we know electrons and quarks are elementary particles, which means that in no experiment has there anything like a structure of these particles been seen. They appear point-like, unlike the proton, neutron, nucleus and atom that have sizes that can be measured. It is of course entirely possible that particles that are called elementary today shall turn out to be composite; let it be said though that they have been probed quite extensively. This book is about elementary particles. The aim is to know all about them, their properties and their interactions. The idea is that from this nuclear physics, atomic physics, chemistry, in fact the whole physical world derives. Thus particles and their interactions are the very fundamentals of nature. That is the view now. An elementary particle physicist studies primarily these elementary particles and not the larger structures such as Protons, nuclei or atoms. The main laboratory for elementary particle research in Europe has been named CERN (Conseil Européen pour la Recherche Nucléaire), now officially called European Organization for Nuclear Research and that is a misnomer. In principle no nuclear physics is being done there.
eBook - PDFRadioisotope and Radiation Physics
An Introduction
- M Miladjenovic(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
We have seen that gravitational forces can be neglected in considering processes that occur in the passage of radia-tion through matter. Thus, the behavior of the electron is described only by the electromagnetic forces. 2.5. Nucleons Nuclear processes can be described by assuming that atomic nuclei are made up of Protons and neutrons. These are called by the common name nucleons, not only because they are the only constituent particles of nuclei, but also because they have many properties in common. Their masses and radii are similar, they can transform into each other, and, apart from the proton charge effect, they behave in the same way in the nucleus. They formally differ from each other by the fact that the proton is charged, whereas the neutron is not. Also, a proton in the free state is a stable particle, whereas the neutron is radioactive and transforms by beta decay into a proton, emitting an electron and an antineutrino. Nuclear Forces. Although modern physics has not yet arrived at an accurate mathematical formulation of the forces between nucleons, a large amount of information is available. A model for their description makes use of the forces between electrons. In analogy with electrons, which exchange virtual photons, nucleons are considered to exchange virtual mesons. There are several kinds of mesons, π, κ, and η, but we shall mainly be concerned with π mesons (pions), which have the smallest mass and are the most abundantly produced. Since three types of pions, the positive, the negative, and the neutral, have been found experimentally, the following modes of emission and 2.5. Nucleons 25 subsequent absorption of a virtual meson by a nucleon are possible: η —» ρ + π —» η; / ? —> ΑΖ + 7 Γ + —> / ? ; ΑΖ —> Λ + π 0 —> η; The neutron transforms in a very short time into a proton and a nega-tive pion. The duration of this virtual process is limited by the Heisen-berg uncertainty principle.
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