Nuclear Data: A Primer

198 Pages·2021·43.915 MB·English

by  David Jenkins

Nuclear Data
A primer
IOP Series in Nuclear Spectroscopy and Nuclear Structure
Series Editors
John Wood, Georgia Institute of Technology, USA
Kristiaan Heyde, Ghent University, Belgium
David Jenkins, University of York, UK
About the Series:
TheIOPSeriesinNuclearSpectroscopyandNuclearStructureprovidesup-to-date
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(cid:129) Nuclear systematics and data
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(cid:129) Detectors employed for gamma-ray, neutron and charged-particle detection
in nuclear spectroscopy and related societal applications.
Nuclear Data
A primer
David G Jenkins
Department of Physics, University of York, Heslington, York, UK
John L Wood
School of Physics, Georgia Institute of Technology, Atlanta, Georgia, USA
IOP Publishing, Bristol, UK
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Contents
Preface viii
Acknowledgements x
Author biographies xi
1 Gross properties of nuclei 1-1
1.1 Exercises 1-17
References 1-22
2 Nuclear excitation patterns 2-1
2.1 Basic features of excited states in even–even nuclei 2-6
2.1.1 Excitation energies 2-6
2.1.2 Electromagnetic decay properties 2-10
2.2 A basic symmetry of nuclei: isospin 2-13
2.3 Nuclear data compilations and evaluations 2-14
2.4 Exercises 2-15
References 2-19
3 Nuclear deformation and rotations 3-1
3.1 The rotor model for nuclei: K = 0 bands 3-3
3.2 Odd-mass nuclei, intrinsic excitations, and rotations 3-9
3.3 Even-mass nuclei, intrinsic excitations, and rotations 3-16
3.4 Deformed nuclei and the K quantum number 3-20
3.4.1 K isomerism 3-20
3.4.2 One-nucleon transfer reactions 3-22
3.4.3 Band mixing and crossing 3-23
3.4.4 Magnetic moments 3-25
3.5 Nuclear moments of inertia 3-27
3.6 Exercises 3-29
References 3-33
4 Towards a global view of nuclear structure 4-1
4.1 Shape coexistence in nuclei 4-4
4.2 Pairing-dominated structures in single-closed shell nuclei 4-13
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4.3 Doubly closed shell nuclei 4-22
4.4 Weakly deformed nuclei 4-26
4.5 Exercises 4-29
References 4-32
5 Simple models of nuclear structure 5-1
5.1 Independent-particle models for nuclear structure 5-1
5.1.1 The shell model 5-2
5.1.2 The Nilsson model 5-8
5.2 Pairing models for nuclear structure 5-13
5.3 Rotor models for nuclear structure 5-15
5.3.1 The dumbbell rotor model 5-18
5.3.2 Simple rotor models for nuclei 5-19
5.3.3 Models of moments of inertia for nuclei 5-22
5.4 The Bohr model for nuclear structure 5-24
5.5 Exercises 5-28
References 5-30
6 Nuclear spectroscopic measurements 6-1
6.1 A quantum measurement preamble 6-1
6.2 Coulomb excitation 6-3
6.3 Radioactive decay 6-7
6.4 In-beam reaction γ-ray spectroscopy 6-9
6.5 Gamma-ray spectroscopy 6-12
6.6 Electron spectroscopy 6-17
6.7 Reaction spectroscopic studies of nuclear structure 6-19
6.8 Atomic hyperfine spectroscopy studies for nuclei 6-26
6.9 Mass measurements studies for nuclei 6-27
6.10 Isotope separation on-line (ISOL) studies for nuclear structure 6-28
6.11 Lifetime measurements by Doppler techniques 6-31
6.12 Lifetimes of states associated with radiative emission of γ-rays 6-31
6.13 Exercises 6-33
References 6-34
7 Metrology for nuclear structure study 7-1
7.1 The SI base units 7-2
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7.2 The fundamental physical constants 7-6
7.3 Exercises 7-8
References 7-9
8 Epilogue 8-1
vii
Preface
Nuclear data represent information on a fundamental level of organization of
matter, a unique manifestation of the quantum many-body problem, and a critical
base for many technological applications. As a data base, it is vast and complex.
Herein, we provide an introduction to the major features of nuclear data as an
information resource, substantially independent of the methods by which the data
were obtained or of physical and technological implications. Nevertheless, some
basic quantum mechanics is needed to organize the data, some pointers to features
important for applications are made, and essential details of the measurements
behind the data are given.
Nucleiarethecoreofatoms.Weareunawareofnucleiintheeverydayworldbecause
atomicelectrons‘shield’nuclei.Indeed,somefamiliaritywithatomicdatacomeshand-
in-hand with the process of organizing and understanding nuclear data. There is
reciprocity in this understanding in that atoms only exist by virtue of the existence of
nucleiandsoaleadingquestinsciencehasbeen:‘Wheredothechemicalelementscome
from?’ This has been answered through the realization that all but hydrogen and some
helium and traces of a few other light elements are produced in stars via nuclear
processes.Moreover,wehavelearnedthatsomeofthechemicalelementsareproduced
by the explosive coalescence of neutron stars, as recently observed in GW170817.
Thestudyofnuclearstructure(asalsoatomicstructure)isdominatedbyobserving
energy changes and is broadly termed nuclear spectroscopy (atomic spectroscopy).
Nuclearstructure andatomicstructure are twoindependent levelsoforganization of
matter.Remarkably,theyarebothquantummechanicaldomains,i.e.onemusthave
some familiarity with quantum mechanics to understand data pertaining to either
domain. This reach of quantum mechanics extends into molecular structure. Indeed,
the manifestation of quantization at all three levels (nuclear, atomic, molecular)
provides a ‘cross-fertilization’ of paradigmsofquantumphenomena, e.g. both nuclei
and molecules exhibit quantized rotations (but atoms do not).
The study of levels of organization of matter also extends more deeply to
subnuclear structure, i.e. the description of nucleon structure: the protons and
neutrons of nuclei are made up of quarks. Yet again, quantum mechanics provides
the description of matter at the subnucleon level of organization. Quarks (q) form
baryon (qqq), antibaryon (qqq), and meson (qq) combinations. At present, this
forms the deepest level of matter for which we have established a microstructure.
Independently of the quarks, leptons also play a fundamental role in the manifes-
tations of matter. Electrons are present in our every-day world; muons and tauons
have fleeting existence in high-energy processes. Their partner neutrinos are every-
where,butveryhardtodetect.Atthelevelofnuclearspectroscopy,someknowledge
of this particle zoo is essential.
Inallofthemanifestationsofmatterintheforegoing,theentitiesareorganizedinto
finite numbers of particle ‘building blocks’. As such, they obey the laws of quantum
mechanics for finite systems. This dictates conservation of angular momentum.
Thus, familiarity with the quantization of angular momentum and the concept of
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spin is essential almost at the outset for pursuing the study of any of these systems.
Perhaps,mostdramatically,quantizationofangularmomentuminatomsunderliesall
of chemistry at the level of the Periodic Table. The building up (aufbau) of
configurations in many-electron atoms is understood via the Pauli principle applied
touniquelylabeled orbitalsusingangularmomentumandspin quantumnumbers of
independent-particlebehavioroftheelectrons.Afewsimpleaddedrulesprovideafar-
reaching qualitative basis for a near-complete understanding of the Periodic Table:
Hund’srule(whichfavorsmaximallyalignedspinsinanangularmomentumsubshell
due to magnetic effects) and screening effects of inner shell electrons (due to the
Coulomb repulsion between electrons) are key concepts in this process.
The structure of many-nucleon nuclei can be approached via an aufbau process.
However, this is an extremely limited approach in that while nucleons in many-
nucleon systems exhibit some organization as independent-particles they do not
exhibita‘Hund’srule’andtheydonotrepeleachother.Theseissuesthatdistinguish
many-nucleon systems from (finite) many-electron systems provides the starting
point for assembling and interpreting nuclear data.
Nuclear data are substantially organized by ‘mass-chains’ or ‘A-chains’. This
approach compiles and evaluates data for nuclear isobars (isobar = same mass
number, A = Z + N, Z = proton number, N = neutron number), and is carried out
undertheauspicesoftheNuclearDataGroupwhoproducetheEvaluatedNuclear
Structure Data File (ENSDF). This is supported by unevaluated data compilations
through the Unevaluated Nuclear Data List (XUNDL). A-chain evaluations are
published intermittently in Nuclear Data Sheets. This resourceis critical totheentire
taskofmaintainingausableandaccessiblebasefornuclearscience.Unlessotherwise
stated, all data shown in the figures and tables are taken from these sources.
While compilation and evaluation of nuclear data are ordered by A chain
(sometimes just an individual isotope), ‘horizontal’ compilations and evaluations
are limited or rare. By horizontal is meant a specific nuclear property across the
entire range of A, Z, and N, sometimes referred to as the ‘mass surface’. A leading
example is that of nuclear masses, maintained by the Atomic Mass Evaluation
network. The present endeavor is horizontal and it aspires to a global perspective.
Toencourageourreaderstoengageintheprocessofaccessingandmanipulating
nucleardata,weembedanumberofshortvideotutorialsintheelectronicversionof
this book (see exercises 1-23, 1-24, 2-11, 3-6 and 4-11). These are designed to
demonstratehowtheprocessofworkingwithnucleardataiscarriedoutinpractice.
The goal is to familiarize the reader with concepts and quantities that are ‘derived’
fromthedatasources,i.e.theconceptsandquantitiescannotbeseendirectlybyjust
lookingatthedata.Thesetutorialsrangefrombasicextrapolationoftheperspective
available from established data bases to nuclei not yet studied, to the use of the
equations for deduction of properties such as electromagnetic moments (which
cannot be observed directly in nuclei). The examples chosen and the level of detail
presented are aimed at providing the reader with the sense that they can exercise
controlofthehandlingofnucleardataandtheequationsandbasictheoryconcepts
involved.Ultimately,ourgoalistoimpartasenseoftheengagementinexploration
that can be reached by becoming familiar with nuclear data.
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