DOCSLIB.ORG

Shell Model Spectroscopy Far from Stability

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Shell Model Spectroscopy Far from Stability Home Search Collections Journals About Contact us My IOPscience Shell model spectroscopy far from stability This content has been downloaded from IOPscience. Please scroll down to see the full text. 2017 J. Phys. G: Nucl. Part. Phys. 44 084002 (http://iopscience.iop.org/0954-3899/44/8/084002) View the table of contents for this issue, or go to the journal homepage for more Download details: IP Address: 188.184.3.52 This content was downloaded on 05/09/2017 at 18:21 Please note that terms and conditions apply. You may also be interested in: The nuclear shell model toward the drip lines A Poves, E Caurier, F Nowacki et al. Shape coexistence: the shell model view A Poves Shape coexistence in neutron-rich nuclei A Gade and S N Liddick Shape coexistence in the N = 19 and N = 21 isotones Gerda Neyens Spectroscopy in and around the Island of Inversion Heiko Scheit Nuclear-structure studies of exotic nuclei with MINIBALL P A Butler, J Cederkall and P Reiter A new view of nuclear shells Rituparna Kanungo Exotic nuclei and nuclear forces Takaharu Otsuka Three-body forces and shell structure in calcium isotopes Jason D Holt, Takaharu Otsuka, Achim Schwenk et al. Made open access 7 August 2017 Journal of Physics G: Nuclear and Particle Physics J. Phys. G: Nucl. Part. Phys. 44 (2017) 084002 (8pp) https://doi.org/10.1088/1361-6471/aa7789 * Shell model spectroscopy far from stability A Poves Departamento de Física Teórica and IFT, UAM-CSIC, Universidad Autónoma de Madrid, Spain E-mail: [email protected] Received 24 November 2016, revised 1 June 2017 Accepted for publication 6 June 2017 Published 29 June 2017 Abstract I will discuss the impact of the research on exotic nuclei carried out at ISO- LDE and later on, following its impulse, in many laboratories worldwide, in our present knowledge of the nuclear dynamics. I will put particular emphasis on the occurrence of islands of inversion (IoI) at several magic numbers for the neutrons, far from stability. I will also discuss the appearance of new local shell closures in the calcium and silicon isotopic chains, and qualify their status as new doubly magic nuclei. Keywords: nuclear structure, shell model calculations, neutron rich nuclei, new magic numbers, islands of inversion (Some figures may appear in colour only in the online journal) 1. Introduction Not so long ago, experimental nuclear spectroscopy was dominated by heavy ion collisions and high spin physics. Mean field methods thrived in the theoretical arena, later joined by the interacting boson model. The shell model realm seemed dormant. Nevertheless, studies of very neutron rich radioactive isotopes were pursued at the ISOLDE facility under the CERN umbrella. And one can safely say that this activity paved the way for the present explosion of new results on nuclei far from stability, which have radically modified our understanding of nuclear dynamics. In this contribution, I will deal with the medium–light neutron rich nuclei from oxygen to calcium with special emphasis on the contributions from ISOLDE. 2. The discovery of the N=20 ‘island of inversion’ The story starts with the mass measurements made at CERN by what would later be the Orsay group of the ISOLDE Collaboration [1]. They found an excess of binding in 31Na and 32Na which could not be explained by the available theoretical models. Simultaneously, a group of * This article belongs to the Focus on Exotic Beams at ISOLDE: A Laboratory Portrait special issue. 0954-3899/17/084002+08$33.00 © 2017 IOP Publishing Ltd Printed in the UK 1 Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. J. Phys. G: Nucl. Part. Phys. 44 (2017) 084002 A Poves theorists at Orsay tried to reproduce this effect with projected Hartree–Fock (PHF) calcula- tions using density dependent interactions [2]. They got a normal, spherical, solution for 31Na with a small shoulder in the prolate side of the energy versus deformation curve. Never- theless, they argued that by applying a rotational correction, this shoulder might become a minimum, and explained that the anomaly was due to the gain in energy due to deformation. Even with this proviso, their model was unable to explain the 31Na data. Three decades and huge developments in beyond mean field (BMF) techniques were necessary to produce this minimum in the easier to treat nucleus 32Mg. All in all, their idea was correct even if the calculations were not conclusive. Already in Thibault’s paper [1], the possibility of having a new region of deformation was contemplated. Further work by the same group [3–5] extended the mass measurements to magnesium isotopes finding the same kind of anomaly in 32Mg. In addition, studying the beta decay of 32Na, they populated the first 2+ state in 32Mg at 881keV. Indeed this is a very low excitation energy compared with the corresponding one in 30Mg (1.48 MeV). Much more so, common sense would predict that the 2+ excitation energy should increase at the magic neutron number N=20 and not decrease almost by a factor two. The idea of the existence of an unexpected new region of deformation, precisely where the current models would have predicted enhanced sphericity, was reinforced. New shell model studies of these nuclei were triggered by a paper by Wildenthal and Chung [6] in 1980 with the provocative title ‘Collapse of the conventional shell-model ordering in the very-neutron-rich isotopes of Na and Mg’. In it, the authors, using their newly fitted high quality interaction for the upper part of the sd-shell, concluded that it was impossible to explain the behaviour of the neutron rich N=20 isotones in this valence space. The question that remains unanswered, and which has continued to produce a lot of confusion until now, is the meaning of the sentence ‘Collapse of the conventional shell-model ordering’. For many, this had to be interpreted as if, at the mean field level, some single particle orbits of the pf-shell would lay below the upper orbits of the sd-shell. Work in this direction was carried out by the Glasgow group [7, 8] by including the 0f7/2 orbit in the valence space, essentially degenerated with the 0d3/2. With this prescription they indeed got an increase in the binding energy of the N=20 isotones, but the proposed solution was far from being physically sound, and did not address at all the issue about deformation risen by the PHF calculations on [2]. Our work in [9] interpreted the collapse of the shell model ordering in a different way: they were not the spherical single particle orbits of the two adjacent major harmonic oscillator shells which collapsed far from stability, instead, what happened was that the intruder con- figurations of (neutron) 2p–2h nature, somehow became more bound than the normal, 0p–0h, ones. Therefore, the collapse must be due to the nuclear correlations. This interpretation makes a natural link with the surmise of [2], provided the correlations are of quadrupole– quadrupole type and the intruder configurations become deformed. The problem was how to get this behaviour out of a realistic shell model calculation. The solution was to include the 1p3/2 orbit—the quadrupole partner of the 0f7/2—in the valence space. This calculation produced deformed solutions for 32Mg, 31Na and 30Ne, keeping a substantial single particle gap between the sd and the pf-shells. Shortly after, Warburton, Becker and Brown [10] made extensive shell model calculations in the same model space reaching the same conclusions. And they coined the term ‘island of inversion’ (IoI) which has enjoyed immense success since then (I would have favoured the alternative ‘Island of Deformation’ though). Further work in the same context was carried out in [11, 12]. Since then, there has been a plethora of new experimental results, including mass measurements, radii isotope shifts, magnetic and quadrupole moments, spectroscopic factors 2 J. Phys. G: Nucl. Part. Phys. 44 (2017) 084002 A Poves etc, many of them performed at ISOLDE [13, 14]. The existence of an IoI at N=20 is now well established, even if its boundaries are not fully delineated yet. A very important mile- stone was the measurement during a coulex experiment at RIKEN of the B(E2) connecting the 2+ with the ground state of 32Mg, which confirmed its well deformed nature corresp- onding to β=0.45 [15]. Other coulex experiments followed soon [16]. Indeed, the activity in the theory sector continued, both in the shell model framework [17] and with BMF methods [18]. The latter only got quantitative agreement with experiment after including the triaxial degrees of freedom, breaking time reversal invariance and allowing configuration mixing via the generator coordinate approximation [19]. A more detailed description of the mechanism producing the IoI can be found in [20]. 3. The heaviest potassium and calcium isotopes We have seen how the availability of very heavy sodium isotopes at ISOLDE made it possible to discover the N=20 IoI. But many other elements were abundantly produced as well, and put to good use. This is the case for potassium, studied mainly by the Strasbourg members of the ISOLDE collaboration. 52K was produced for the first time (hence discovered) at ISO- LDE. Its decay produced and discovered 52Ca as well [21], whose spectroscopy was very interesting, with a first 2+ excited state at 2.56MeV, a rather high energy.
Load more

Recommended publications
  • Arxiv:Nucl-Th/0402046V1 13 Feb 2004
    The Shell Model as Unified View of Nuclear Structure E. Caurier,1, ∗ G. Mart´ınez-Pinedo,2,3, † F. Nowacki,1, ‡ A. Poves,4, § and A. P. Zuker1, ¶ 1Institut de Recherches Subatomiques, IN2P3-CNRS, Universit´eLouis Pasteur, F-67037 Strasbourg, France 2Institut d’Estudis Espacials de Catalunya, Edifici Nexus, Gran Capit`a2, E-08034 Barcelona, Spain 3Instituci´oCatalana de Recerca i Estudis Avan¸cats, Llu´ıs Companys 23, E-08010 Barcelona, Spain 4Departamento de F´ısica Te´orica, Universidad Aut´onoma, Cantoblanco, 28049, Madrid, Spain (Dated: October 23, 2018) The last decade has witnessed both quantitative and qualitative progresses in Shell Model stud- ies, which have resulted in remarkable gains in our understanding of the structure of the nucleus. Indeed, it is now possible to diagonalize matrices in determinantal spaces of dimensionality up to 109 using the Lanczos tridiagonal construction, whose formal and numerical aspects we will analyze. Besides, many new approximation methods have been developed in order to overcome the dimensionality limitations. Furthermore, new effective nucleon-nucleon interactions have been constructed that contain both two and three-body contributions. The former are derived from realistic potentials (i.e., consistent with two nucleon data). The latter incorporate the pure monopole terms necessary to correct the bad saturation and shell-formation properties of the real- istic two-body forces. This combination appears to solve a number of hitherto puzzling problems. In the present review we will concentrate on those results which illustrate the global features of the approach: the universality of the effective interaction and the capacity of the Shell Model to describe simultaneously all the manifestations of the nuclear dynamics either of single particle or collective nature.
    [Show full text]
  • 14. Structure of Nuclei Particle and Nuclear Physics
    14. Structure of Nuclei Particle and Nuclear Physics Dr. Tina Potter Dr. Tina Potter 14. Structure of Nuclei 1 In this section... Magic Numbers The Nuclear Shell Model Excited States Dr. Tina Potter 14. Structure of Nuclei 2 Magic Numbers Magic Numbers = 2; 8; 20; 28; 50; 82; 126... Nuclei with a magic number of Z and/or N are particularly stable, e.g. Binding energy per nucleon is large for magic numbers Doubly magic nuclei are especially stable. Dr. Tina Potter 14. Structure of Nuclei 3 Magic Numbers Other notable behaviour includes Greater abundance of isotopes and isotones for magic numbers e.g. Z = 20 has6 stable isotopes (average=2) Z = 50 has 10 stable isotopes (average=4) Odd A nuclei have small quadrupole moments when magic First excited states for magic nuclei higher than neighbours Large energy release in α, β decay when the daughter nucleus is magic Spontaneous neutron emitters have N = magic + 1 Nuclear radius shows only small change with Z, N at magic numbers. etc... etc... Dr. Tina Potter 14. Structure of Nuclei 4 Magic Numbers Analogy with atomic behaviour as electron shells fill. Atomic case - reminder Electrons move independently in central potential V (r) ∼ 1=r (Coulomb field of nucleus). Shells filled progressively according to Pauli exclusion principle. Chemical properties of an atom defined by valence (unpaired) electrons. Energy levels can be obtained (to first order) by solving Schr¨odinger equation for central potential. 1 E = n = principle quantum number n n2 Shell closure gives noble gas atoms. Are magic nuclei analogous to the noble gas atoms? Dr.
    [Show full text]
  • Low-Energy Nuclear Physics Part 2: Low-Energy Nuclear Physics
    BNL-113453-2017-JA White paper on nuclear astrophysics and low-energy nuclear physics Part 2: Low-energy nuclear physics Mark A. Riley, Charlotte Elster, Joe Carlson, Michael P. Carpenter, Richard Casten, Paul Fallon, Alexandra Gade, Carl Gross, Gaute Hagen, Anna C. Hayes, Douglas W. Higinbotham, Calvin R. Howell, Charles J. Horowitz, Kate L. Jones, Filip G. Kondev, Suzanne Lapi, Augusto Macchiavelli, Elizabeth A. McCutchen, Joe Natowitz, Witold Nazarewicz, Thomas Papenbrock, Sanjay Reddy, Martin J. Savage, Guy Savard, Bradley M. Sherrill, Lee G. Sobotka, Mark A. Stoyer, M. Betty Tsang, Kai Vetter, Ingo Wiedenhoever, Alan H. Wuosmaa, Sherry Yennello Submitted to Progress in Particle and Nuclear Physics January 13, 2017 National Nuclear Data Center Brookhaven National Laboratory U.S. Department of Energy USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26) Notice: This manuscript has been authored by employees of Brookhaven Science Associates, LLC under Contract No.DE-SC0012704 with the U.S. Department of Energy. The publisher by accepting the manuscript for publication acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use or the results of such use of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.
    [Show full text]
  • Nuclear Physics
    Massachusetts Institute of Technology 22.02 INTRODUCTION to APPLIED NUCLEAR PHYSICS Spring 2012 Prof. Paola Cappellaro Nuclear Science and Engineering Department [This page intentionally blank.] 2 Contents 1 Introduction to Nuclear Physics 5 1.1 Basic Concepts ..................................................... 5 1.1.1 Terminology .................................................. 5 1.1.2 Units, dimensions and physical constants .................................. 6 1.1.3 Nuclear Radius ................................................ 6 1.2 Binding energy and Semi-empirical mass formula .................................. 6 1.2.1 Binding energy ................................................. 6 1.2.2 Semi-empirical mass formula ......................................... 7 1.2.3 Line of Stability in the Chart of nuclides ................................... 9 1.3 Radioactive decay ................................................... 11 1.3.1 Alpha decay ................................................... 11 1.3.2 Beta decay ................................................... 13 1.3.3 Gamma decay ................................................. 15 1.3.4 Spontaneous fission ............................................... 15 1.3.5 Branching Ratios ................................................ 15 2 Introduction to Quantum Mechanics 17 2.1 Laws of Quantum Mechanics ............................................. 17 2.2 States, observables and eigenvalues ......................................... 18 2.2.1 Properties of eigenfunctions .........................................
    [Show full text]
  • Father of the Shell Model
    CENTENARY Father of the shell model Heidelberg University held a symposium on fundamental physics and the shell model this summer to celebrate the 100th anniversary of the birth of Hans Jensen, the German who created the nuclear shell model with Maria Goeppert-Mayer of Argonne. Hans Jensen (1907–1973) is the only theorist among the three winners from Heidelberg University of the Nobel Prize for Physics. He shared the award with Maria Goeppert-Mayer in 1963 for the development of the nuclear shell model, which they published independently in 1949. The model offered the first coherent expla- nation for the variety of properties and structures of atomic nuclei. In particular, the “magic numbers” of protons and neutrons, which had been determined experimentally from the stability properties and observed abundances of chemical elements, found a natural explanation in terms of the spin-orbit coupling of the nucleons. These numbers play a decisive role in the synthesis of the ele- ments in stars, as well as in the artificial synthesis of the heaviest elements at the borderline of the periodic table of elements. Hans Jensen was born in Hamburg on 25 June 1907. He studied physics, mathematics, chemistry and philosophy in Hamburg and Freiburg, obtaining his PhD in 1932. After a short period in the Hans Jensen in his study at 16 Philosophenweg, Heidelberg German army’s weather service, he became professor of theo- in 1963. (Courtesy Bettmann/UPI/Corbis.) retical physics in Hannover in 1940. Jensen then accepted a new chair for theoretical physics in Heidelberg in 1949 on the initiative Mayer 1949).
    [Show full text]
  • PHYS 4134, Fall 2016, Homework #3 1. Semi Empirical Mass Formula And
    PHYS 4134, Fall 2016, Homework #3 Due Wednesday, September 15 2016, at 1:00 pm 1. Semi empirical mass formula and nuclear radii Derive an expression for the Coulomb energy of a uniformly charged sphere, total charge Q and radius R. [Hint: refer to any E&M book for help here. This problem is very similar to problem 2.1 in your text.] If the binding energies of the mirror nuclei 39K and 39Ca are 333.724 and 326.409 MeV, respectively, estimate the radii of the two nuclei by using the semi-empirical mass formula (SEMF). Discuss the contribution of each term individually to this difference in binding energy. 2. Semi empirical mass formula Use the SEMF to obtain an expression for the Z value of the isobar which will have the lowest mass for a given A. Hence, determine which isobar with A = 86 is predicted to be the most stable. [Hint: this is a lot like problem 2.3 in the text. Take A and Z to be independent, and vary N to keep A constant. Re-write any terms which go like N, using N=A-Z. Hint: this is a lot like problem 2.3 in the text.] 3. Nuclear Shell Model Find the spin and parity of for the ground state and first excited state of 7Li and 33S and 99Tc (a good source for this might be the National Nuclear Data Center; http://www.nndc.bnl.gov , then click on “Structure and Decay” and “Chart of the Nuclides”). Using Fig. 1, determine the single particle shell model configuration for these states and compare them to the observed values.
    [Show full text]
  • Chapter 2 the Atomic Nucleus
    Nuclear Science—A Guide to the Nuclear Science Wall Chart ©2018 Contemporary Physics Education Project (CPEP) Chapter 2 The Atomic Nucleus Searching for the ultimate building blocks of the physical world has always been a central theme in the history of scientific research. Many acclaimed ancient philosophers from very different cultures have pondered the consequences of subdividing regular, tangible objects into their smaller and smaller, invisible constituents. Many of them believed that eventually there would exist a final, inseparable fundamental entity of matter, as emphasized by the use of the ancient Greek word, atoos (atom), which means “not divisible.” Were these atoms really the long sought-after, indivisible, structureless building blocks of the physical world? The Atom By the early 20th century, there was rather compelling evidence that matter could be described by an atomic theory. That is, matter is composed of relatively few building blocks that we refer to as atoms. This theory provided a consistent and unified picture for all known chemical processes at that time. However, some mysteries could not be explained by this atomic theory. In 1896, A.H. Becquerel discovered penetrating radiation. In 1897, J.J. Thomson showed that electrons have negative electric charge and come from ordinary matter. For matter to be electrically neutral, there must also be positive charges lurking somewhere. Where are and what carries these positive charges? A monumental breakthrough came in 1911 when Ernest Rutherford and his coworkers conducted an experiment intended to determine the angles through which a beam of alpha particles (helium nuclei) would scatter after passing through a thin foil of gold.
    [Show full text]
  • Particle and Nuclear Physics
    Particle and Nuclear Physics Handout #3 Nuclear Physics Lent/Easter Terms 2021 Dr. Tina Potter 13. Basic Nuclear Properties Particle and Nuclear Physics Dr. Tina Potter Dr. Tina Potter 13. Basic Nuclear Properties 1 In this section... Motivation for study The strong nuclear force Stable nuclei Binding energy & nuclear mass (SEMF) Spin & parity Nuclear size (scattering, muonic atoms, mirror nuclei) Nuclear moments (electric, magnetic) Dr. Tina Potter 13. Basic Nuclear Properties 2 Introduction Nuclear processes play a fundamental role in the physical world: Origin of the universe Creation of chemical elements Energy of stars Constituents of matter; influence properties of atoms Nuclear processes also have many practical applications: Uses of radioactivity in research, health and industry, e.g. NMR, radioactive dating. Various tools for the study of materials, e.g. M¨ossbauer,NMR. Nuclear power and weapons. Dr. Tina Potter 13. Basic Nuclear Properties 3 The Nuclear Force Consider the pp interaction, Range ~/mπc 1fm p p ∼ ∼ π0 ≡ p p Hadron level Quark-gluon level Pion vs. gluon exchange is similar to the Coulomb potential vs. van der Waals’ force in QED. The treatment of the strong nuclear force between nucleons is a many-body problem in which quarks do not behave as if they were completely independent. nor do they behave as if they were completely bound. The nuclear force is not yet calculable in detail at the quark level and can only be deduced empirically from nuclear data. Dr. Tina Potter 13. Basic Nuclear Properties 4 Stable Nuclei Stable nuclei do not decay by the strong interaction. They may transform by β and α emission (weak or electromagnetic) with long lifetimes.
    [Show full text]
  • The Oxygen Isotopes
    2nd Reading February 13, 2017 10:18 WSPC/S0218-3013 143-IJMPE 1740003 International Journal of Modern Physics E Vol. 26, Nos. 1 & 2 (2017) 1740003 (12 pages) c World Scientific Publishing Company DOI: 10.1142/S0218301317400031 The oxygen isotopes B. Alex Brown Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory Michigan State University, East Lansing, Michigan 48824-1321, USA Published 26 January 2017 The properties of the oxygen isotopes provide diverse examples of progress made in experiments and theory. This chain of isotopes has been studied from beyond the proton drip line in 12O to beyond the neutron drip line in 25,26O. This short survey starts with the microscopic G matrix approach for 18O of Kuo and Brown in the 1960’s and shows how theory has evolved. The nuclear structure around the doubly-magic nucleus 24Ois particularly simple in terms of the nuclear shell model. The nuclear structure around the doubly-magic nucleus 16O exhibits the coexistence of single-particle and collective structure. Keywords: Shell model; oxygen isostopes. PACS Number(s): 21.10.−k, 21.60.Cs, 27.10.+n, 27.30.+t, 29.30.Hs 1. Introduction The properties of the oxygen isotopes provide diverse examples of progress made in experiment and theory. The known isotopes are shown in Fig. 1. There are three 16,17,18 Int. J. Mod. Phys. E 2017.26. Downloaded from www.worldscientific.com by MICHIGAN STATE UNIVERSITY on 03/28/17. For personal use only. stable isotopes O. Due to the temperature-dependent effect of the mass differ- ence on evaporation and condensation, measurement of the changes in the isotopic ratio 18O/16O in ice cores provides information on historic climate changes.1 With the advent of radioactive beams, there is now a nearly complete set of data known for all of the oxygen isotopes.2 12O lies beyond the proton drip line and is observed to decay by emission of two protons 25O lies beyond the neutron drip line and is observed to decay by the emission of one neutron.
    [Show full text]
  • Nuclear Shell Model & Alpha Decay
    Nuclear Shell Model & Alpha Decay Stanley Yen TRIUMF Nuclear Shell Model Electrons in atoms occupy well-defined shells of discrete, well-separated energy. Do nucleons inside a nucleus do the same, or not? Evidence for electron shells in atoms: sudden jumps in atomic properties as a shell gets filled up, e.g. atomic radius, ionization energy, chemical properties. atomic from Krane, radius Introductory Nuclear Physics atomic ionization energy chemical reactivity Not evident a priori that nuclei should show shell structure. Why not? 1. Success of liquid drop model in predicting nuclear binding energies. Liquid drops have smooth behaviour with increasing size, and do not exhibit jumps. 2. No obvious center for nucleons to orbit around, unlike electrons in an atom. 3rd objection to a shell model Strong repulsive core in the nucleon-nucleon potential should scatter the nucleons far out of their orbits -- nucleons should not have a well-defined energy, but should behave more like molecules in a gas, colliding and exchanging energy with each other. before overlap of one pion after 3-quark bags; two pion exchange complicated and short-range heavy meson behaviour exchange Many theoretical reasons were given why nuclei should not show any shell structure .... but experiment says otherwise! 2-neutron separation energy in nuclei -- analogous to ionization energy in atoms Note jumps at nucleon numbers 8, 20, 28, 50, 82, 126 from Krane, Introductory Nuclear Physics abundances of even-even nuclides local maxima at 50, 82, 126 neutron capture cross section
    [Show full text]
  • Natural Superheavy Nuclei in Astrophysical Data
    Prepared for submission to JCAP Natural superheavy nuclei in astrophysical data A. Alexandrov,a;b;c;e V. Alexeev,d A. Bagulya,a A. Dashkina,e M. Chernyavsky,a A. Gippius,a L. Goncharova,a S. Gorbunov,a V. Grachev,f G. Kalinina,d N. Konovalova,a;e N. Okateva,a;e T. Pavlova,d N. Polukhina,a;e;f;1 R. Rymzhanov,h N. Starkov,a;e T. N. Soe,a;e T. Shchedrina,a;e and A. Volkova;g;h aLebedev Physical Institute, Russian Academy of Sciences, 53 Leninsky Prosp., Moscow 119991, Russia bINFN sezione di Napoli, I-80126, Napoli, Italy cUniversita’ degli Studi di Napoli Federico II, I-80126, Napoli, Italy dVernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sci- arXiv:1908.02931v1 [nucl-ex] 8 Aug 2019 ences, 19 Kosygin Str., Moscow 119991, Russia eNational University of Science and Technology MISIS, 4 Leninsky Prosp., Moscow 119049, Russia f National Research Nuclear University MEPhI, 31 Kashirskoe Shosse, Moscow 115409, Russia gNational Research Centre “Kurchatov Institute”, 1 Kurchatov Sq., Moscow 123182, Russia hFlerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, 6 Joliot-Curie Street, Dubna 141980, Russia 1Corresponding author. E-mail: [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] Abstract.
    [Show full text]
  • 2. Nuclear Models and Stability
    2. Nuclear models and stability The aim of this chapter is to understand how certain combinations of N neu- trons and Z protons form bound states and to understand the masses, spins and parities of those states. The known (N,Z) combinations are shown in Fig. 2.1. The great majority of nuclear species contain excess neutrons or protons and are therefore β-unstable. Many heavy nuclei decay by α-particle emis- sion or by other forms of spontaneous fission into lighter elements. Another aim of this chapter is to understand why certain nuclei are stable against these decays and what determines the dominant decay modes of unstable nu- clei. Finally, forbidden combinations of (N,Z) are those outside the lines in Fig. 2.1 marked “last proton/neutron unbound.” Such nuclei rapidly (within ∼ 10−20s) shed neutrons or protons until they reach a bound configuration. The problem of calculating the energies, spins and parities of nuclei is one of the most difficult problems of theoretical physics. To the extent that nuclei can be considered as bound states of nucleons (rather than of quarks and glu- ons), one can start with empirically established two-nucleon potentials (Fig. 1.12) and then, in principle, calculate the eigenstates and energies of many nucleon systems. In practice, the problem is intractable because the number of nucleons in a nucleus with A>3ismuchtoolargetoperformadirect calculation but is too small to use the techniques of statistical mechanics. We also note that it is sometimes suggested that intrinsic three-body forces are necessary to explain the details of nuclear binding.
    [Show full text]