DOCSLIB.ORG

CALCULATION of BETA-DECAY RATES in HEAVY DEFORMED NUCLEI and IMPLICATIONS for the ASTROPHYSICAL R PROCESS

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
CALCULATION of BETA-DECAY RATES in HEAVY DEFORMED NUCLEI and IMPLICATIONS for the ASTROPHYSICAL R PROCESS CALCULATION OF BETA-DECAY RATES IN HEAVY DEFORMED NUCLEI AND IMPLICATIONS FOR THE ASTROPHYSICAL r PROCESS Thomas R. Shafer A dissertation submitted to the faculty at the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Physics and Astronomy. Chapel Hill 2016 Approved by: Jonathan Engel Charles Evans Carla Fröhlich Christian Iliadis John Wilkerson c 2016 Thomas R. Shafer ALL RIGHTS RESERVED ii ABSTRACT Thomas R. Shafer: Calculation of Beta-decay Rates in Heavy Deformed Nuclei and Implications for the Astrophysical r Process (Under the direction of Jonathan Engel) The rapid neutron-capture process (r process) is responsible for synthesizing approximately half of the heavy elements in the solar system, but after decades of work the astrophysical site where it occurs is unknown. Because a very large number of heavy, neutron-rich nuclei are populated during the r process, theoretical efforts to locate the r-process site require a tremendous amount of nuclear physics input. However, most nuclei populated during the r process are very neutron-rich and unstable, and many r-process nuclei cannot be studied experimentally. As a result, the basic properties of a large number of heavy, deformed, short-lived nuclei must be calculated with reliable nuclear models. β-decay half-lives are among the most important properties that affect r-process abundances. In this work we present a new, efficient method for calculating β-decay half-lives of heavy, deformed nuclei: the proton-neutron finite amplitude method (pnFAM). We apply the pnFAM to calculate half-lives of nuclei that demonstrate the strongest effects on r-process abundances in the A'80 and A'160 mass regions, including even-even, odd-A, and odd-odd nuclei. We find that our calculations result in half-lives very similar to those reported in previous studies, with correspondingly small effects on r-process abundances. iii For Martha, Mom, & Dad. iv ACKNOWLEDGEMENTS None of the work presented here would have been possible without the continuous guidance and assistance of my advisor, Jon Engel. I am tremendously grateful for the opportunity to study nuclear physics, but even more, I am grateful for his direction, insight, patience, and encouragement. I am also indebted to the postdoctoral researchers with whom I have worked during my time at UNC, particularly Mika Mustonen and Matt Braby. I believe it was Mika who first suggested attempting to build what became the pnFAM, and I greatly enjoyed working closely with him these last few years to develop this method. Many thanks are also due to my collaborators on this project, Carla Fröhlich, Gail McLaughlin, Matt Mumpower, and Rebecca Surman, who have provided astrophysical insight and r-process calculations for this work. I also gratefully acknowledge funding from the U.S. Department of Energy Topical Collaboration for Neutrinos and Nucleosynthesis in Hot and Dense Matter. I especially thank the members of my committee: Charles Evans, Carla Fröhlich, Christian Iliadis, and John Wilkerson. I greatly appreciate the time and effort you have dedicated to this project. I thank Nicolas Schunck, P. G. Reinhard, Markus Kortelainen, and Dong-Liang Fang for helpful notes, conversations, and computational programs during the course of this project. Also, my gratitude to Pedro Sarriguren for allowing me to reproduce his figures in Chapter 8 for a comparison between calculations. Thanks to Derek Vermeulen and Laurie McNeil for supervising my experimental research project. I am tremendously grateful for the support and encouragement of my family and friends, including my parents, Rick and Liz; my brother and sister-in-law, Daniel and Brenda; the Godwins; my friends in Wilmington and from The Summit Church in the Raleigh-Durham area; and my friends from Archer Lodge Middle School. Life is so much better because of these people and many others. Finally, I cannot thank my wife, Martha, enough for her ceaseless encouragement and support during this season. Only she knows how vital her wisdom and encouragement have been over these several years. I love you, Martha, and I am excited for what comes next (Romans 8:28–32)! v TABLE OF CONTENTS LIST OF TABLES . ix LIST OF FIGURES . xi LIST OF ABBREVIATIONS AND SYMBOLS . xiv 1 INTRODUCTION AND MOTIVATION . 1 1.1 The origin of the heavy elements . 1 1.2 The r process . 2 1.2.1 Abundance features . 4 1.2.2 The search for the r-process site . 4 1.3 The importance of β decay in r-process calculations . 6 1.3.1 Outline of this work . 7 2 β DECAY IN NUCLEI . 8 2.1 Allowed and forbidden β decay................................... 9 2.2 The total β-decay half-life . 11 3 NUCLEAR SHAPE DEFORMATION . 13 3.1 Deformation and angular momentum symmetry breaking . 13 3.1.1 Angular momentum projection and the collective rotor model . 14 3.2 Matrix elements and transition strengths in the collective rotor model . 15 3.3 β-decay half-lives of axially-deformed nuclei . 17 4 DENSITY FUNCTIONAL THEORY AND THE LINEAR RESPONSE OF THE NUCLEUS . 18 4.1 The Skyrme energy-density functional . 20 4.2 Time-dependent DFT . 21 4.3 Linear response theory . 22 5 THE PROTON-NEUTRON FINITE AMPLITUDE METHOD . 24 vi 5.1 Mean field theory with pairing correlations: the HFB approximation . 25 5.1.1 HFB calculations with both protons and neutrons . 27 5.1.2 The ground state solver HFBTHO . 28 5.2 Overview of the finite amplitude method . 29 5.2.1 Differences between the charge-changing and like-particle FAM . 31 5.3 Solution of the pnFAM equations in the quasiparticle basis . 32 5.3.1 Strength functions, cross-terms, and β-decay half-lives . 33 6 β DECAY OF ODD NUCLEI WITH THE PNFAM . 36 6.1 Ground states of odd nuclei and the equal filling approximation . 37 6.2 Excited states of odd nuclei . 39 6.2.1 The pnFAM equations for odd nuclei . 40 6.3 Interpretation of our results for odd nuclei . 42 7 β-DECAY HALF-LIVES OF RARE-EARTH ISOTOPES . 44 7.1 The rare-earth r-process nuclei . 44 7.2 Overview of the calculation . 45 7.3 Adjustments to and evaluation of ground state properties . 49 7.3.1 Adjustment of the pairing functional . 50 7.3.2 Calculated ground state properties . 52 7.3.3 Treatment of odd nuclei . 55 7.4 β-decay properties . 55 7.4.1 The time-odd functional . 56 7.4.2 The isoscalar proton-neutron pairing . 57 7.5 Evaluation of fits, results, and conclusions . 60 7.6 Consequences for rare-earth r-process nucleosynthesis . 66 8 β-DECAY HALF-LIVES OF ISOTOPES WITH A ' 80 ........................ 69 8.1 Ground state properties . 70 8.1.1 Adjusting the pairing strengths . 71 vii 8.1.2 Shape deformations and ground state pairing properties . 72 8.2 Excited states . 73 8.2.1 Fitting the proton-neutron isoscalar pairing . 74 8.3 Fit evaluation, results, and conclusions . 76 8.3.1 Half-lives of A ' 80 nuclei . 76 8.3.2 Consequences for the weak r process . 80 9 CONCLUSIONS AND IMPLICATIONS FOR FUTURE r-PROCESS AND β-DECAY STUDIES 83 9.1 New calculations of β-decay half-lives of deformed nuclei . 83 9.2 Consequences for the r process . 84 9.3 Future directions . 85 A DETAILED EXPRESSIONS FOR ALLOWED AND FIRST-FORBIDDEN β-DECAY RATES . 87 A.1 Overview of the β-decay rate . 87 A.2 Allowed decay . 88 A.3 First-forbidden decay . 88 B NUCLEAR SHAPE DEFORMATION . 92 B.1 Nuclear matrix elements in the laboratory rest frame . 92 B.2 Reduced matrix elements, transition strengths, and cross terms . 94 C ADDITIONAL DETAILS INVOLVING THE DERIVATION OF THE PNFAM . 97 C.1 Derivation of the standard pnFAM equations . 97 C.1.1 Determination of the perturbed mean fields δH(ω) . 100 C.2 Modifications of the pnFAM equations for odd nuclei . 101 C.2.1 The perturbed mean fields δH(ω) in the pnFAM for odd nuclei . 103 REFERENCES . 104 viii LIST OF TABLES 7.1 The seventy rare-earth r-process nuclei for which we compute β-decay half-lives, including forty-five even-even nuclei and an additional twenty-five proton-odd nuclei. 45 7.2 Even-even nuclei used to fit the pairing strengths Vp and Vn. The odd-even mass indicators ∆˜ (3) are described in the text. 51 7.3 Values of the pairing strength and density dependence used in our rare-earth calculations. The value of α for SV-min, as well as all three pairing parameters for unedf1-hfb, were not changed. 51 7.4 Non-zero time-odd coupling constants used in our calculations. All couplings are in units of 5 s 3 0 0 MeV fm except C10, which has units MeV fm . The functional SkO -Nd differs from SkO s only in its value of the coupling C10................................. 58 7.5 Isotopes used to fit the proton-neutron isoscalar pairing and, later, to evaluate our complete fitting procedure. The experimental half-lives were taken from Ref. [165]. The labels a–e in the “Excluded?” column note which isotopes were excluded from our pairing fits for the functionals (a) SkO0, (b) SkO0-Nd, (c) SV-min, (d) SLy5, and (e) unedf1-hfb. Isotopes were excluded when our calculated half-lives were shorter than experimental values and the proton-neutron isoscalar pairing was disabled. 59 7.6 Fitted proton-neutron isoscalar pairing strengths describing rare-earth nuclei. We have included the dimensionless parameter gpp = V0/V1 = 2V0/(Vp + Vn), which measures the strength of the T = 0 pairing relative to its T = 1 counterpart.
Load more

Recommended publications
  • Fundamental Stellar Parameters Radiative Transfer Stellar
    Fundamental Stellar Parameters Radiative Transfer Stellar Atmospheres Equations of Stellar Structure Nuclear Reactions in Stellar Interiors Binding Energy Coulomb Barrier Penetration Hydrogen Burning Reactions Burning of Helium and Heavier Elements Element Abundances Creation of Elements Heavier than Iron Introduction Stellar evolution is determined by the reactions which take place within stars: Binding energy per nucleon determines the most stable isotopes • and therefore the most probable end products of fusion and fis- sion reactions. For fusion to occur, quantum mechanical tunneling through the • repulsive Coulomb barrier must occur so that the strong nuclear force (which is a short-range force) can take over and hold the two nuclei together. Hydrogen is converted to helium by the PP-Chain and CNO- • Cycle. In due course, helium is converted to carbon and oxygen through • the 3α-reaction. Other processes, such as neutron capture reactions, produce heav- • ier elements. Binding Energy Per Nucleon { I The general description of a nuclear reaction is I(A , Z ) + J(A , Z ) K(A , Z ) + L(A , Z ) i i j j ↔ k k ` ` where A is the baryon number, nucleon number or nuclear mass of nucleus N and • n Z is the nuclear charge of nucleus N. • n The nucleus of any element (or isotope) N is uniquely defined by the two integers An and Zn. Note also that anti-particles have the opposite charge to their corresponding particle. In any nuclear reaction, the following must be conserved: the baryon number (protons, neutrons and their anti-particles), • the lepton number (electrons, positrons, neutrinos and anti-neutrinos) and • charge.
    [Show full text]
  • Redalyc.Projected Shell Model Description for Nuclear Isomers
    Revista Mexicana de Física ISSN: 0035-001X [email protected] Sociedad Mexicana de Física A.C. México Sun, Yang Projected shell model description for nuclear isomers Revista Mexicana de Física, vol. 54, núm. 3, diciembre, 2008, pp. 122-128 Sociedad Mexicana de Física A.C. Distrito Federal, México Available in: http://www.redalyc.org/articulo.oa?id=57016055020 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative REVISTA MEXICANA DE FISICA´ S 54 (3) 122–128 DICIEMBRE 2008 Projected shell model description for nuclear isomers Yang Sun Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, P.R. China, Joint Institute for Nuclear Astrophysics, University of Notre Dame, Notre Dame, Indiana 46545, USA. Recibido el 10 de marzo de 2008; aceptado el 7 de mayo de 2008 The study of nuclear isomer properties is a current research focus. To describe isomers, we present a method based on the Projected Shell Model. Two kinds of isomers, K-isomers and shape isomers, are discussed. For the K-isomer treatment, K-mixing is properly implemented in the model. It is found however that in order to describe the strong K-violation more efficiently, it may be necessary to further introduce triaxiality into the shell model basis. To treat shape isomers, a scheme is outlined which allows mixing those configurations belonging to different shapes. Keywords: Shell model; nuclear energy levels. Se estudian las propiedades de isomeros´ nucleares a traves´ del modelo de capas proyectadas.
    [Show full text]
  • The FRIB Decay Station
    The FRIB Decay Station WHITEPAPER The FRIB Decay Station This document was prepared with input from the FRIB Decay Station Working Group, Low-Energy Community Meetings, and associated community workshops. The first workshop was held at JINPA, Oak Ridge National Laboratory (January 2016) and the second at the National Superconducting Cyclotron Laboratory (January 2018). Additional focused workshops were held on γ-ray detection for fast beams at Argonne National Laboratory (November 2017) and stopped beams at Lawrence Livermore National Laboratory (June 2018). Contributors and Workshop Participants (24 institutions, 66 individuals) Mitch Allmond Miguel Madurga Kwame Appiah Scott Marley Greg Bollen Zach Meisel Nathan Brewer Santiago MunoZ VeleZ Mike Carpenter Oscar Naviliat-Cuncic Katherine Childers Neerajan Nepal Partha Chowdhury Shumpei Noji Heather Crawford Thomas Papenbrock Ben Crider Stan Paulauskas AleX Dombos David Radford Darryl Dowling Mustafa Rajabali Alfredo Estrade Charlie Rasco Aleksandra Fijalkowska Andrea Richard Alejandro Garcia Andrew Rogers Adam Garnsworthy KrZysZtof RykacZewski Jacklyn Gates Guy Savard Shintaro Go Hendrik SchatZ Ken Gregorich Nicholas Scielzo Carl Gross DariusZ Seweryniak Robert GrzywacZ Karl Smith Daryl Harley Mallory Smith Morten Hjorth-Jensen Artemis Spyrou Robert Janssens Dan Stracener Marek Karny Rebecca Surman Thomas King Sam Tabor Kay Kolos Vandana Tripathi Filip Kondev Robert Varner Kyle Leach Kailong Wang Rebecca Lewis Jeff Winger Sean Liddick John Wood Yuan Liu Chris Wrede Zhong Liu Rin Yokoyama Stephanie Lyons Ed Zganjar “Close collaborations between universities and national laboratories allow nuclear science to reap the benefits of large investments while training the next generation of nuclear scientists to meet societal needs.” – [NSAC15] 2 Table of Contents EXECUTIVE SUMMARY ........................................................................................................................................................................................
    [Show full text]
  • STUDY of the NEUTRON and PROTON CAPTURE REACTIONS 10,11B(N, ), 11B(P, ), 14C(P, ), and 15N(P, ) at THERMAL and ASTROPHYSICAL ENERGIES
    STUDY OF THE NEUTRON AND PROTON CAPTURE REACTIONS 10,11B(n, ), 11B(p, ), 14C(p, ), AND 15N(p, ) AT THERMAL AND ASTROPHYSICAL ENERGIES SERGEY DUBOVICHENKO*,†, ALBERT DZHAZAIROV-KAKHRAMANOV*,† *V. G. Fessenkov Astrophysical Institute “NCSRT” NSA RK, 050020, Observatory 23, Kamenskoe plato, Almaty, Kazakhstan †Institute of Nuclear Physics CAE MINT RK, 050032, str. Ibragimova 1, Almaty, Kazakhstan *[email protected] †[email protected] We have studied the neutron-capture reactions 10,11B(n, ) and the role of the 11B(n, ) reaction in seeding r-process nucleosynthesis. The possibility of the description of the available experimental data for cross sections of the neutron capture reaction on 10B at thermal and astrophysical energies, taking into account the resonance at 475 keV, was considered within the framework of the modified potential cluster model (MPCM) with forbidden states and accounting for the resonance behavior of the scattering phase shifts. In the framework of the same model the possibility of describing the available experimental data for the total cross sections of the neutron radiative capture on 11B at thermal and astrophysical energies were considered with taking into account the 21 and 430 keV resonances. Description of the available experimental data on the total cross sections and astrophysical S-factor of the radiative proton capture on 11B to the ground state of 12C was treated at astrophysical energies. The possibility of description of the experimental data for the astrophysical S-factor of the radiative proton capture on 14C to the ground state of 15N at astrophysical energies, and the radiative proton capture on 15N at the energies from 50 to 1500 keV was considered in the framework of the MPCM with the classification of the orbital states according to Young tableaux.
    [Show full text]
  • Photofission Cross Sections of 232Th and 236U from Threshold to 8
    Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1972 Photofission cross sections of 232Th nda 236U from threshold to 8 MeV Michael Vincent Yester Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Nuclear Commons Recommended Citation Yester, Michael Vincent, "Photofission cross sections of 232Th nda 236U from threshold to 8 MeV " (1972). Retrospective Theses and Dissertations. 6137. https://lib.dr.iastate.edu/rtd/6137 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This dissertation was produced from a microfilm copy of the original document. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the original submitted. The following explanation of techniques is provided to help you understand markings or patterns which may appear on this reproduction. 1. The sign or "target" for pages apparently lacking from the document photographed is "Missing Page(s)". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting thru an image and duplicating adjacent pages to insure you complete continuity. 2. When an image on the film is obliterated with a large round black mark, it is an indication that the photographer suspected that the copy may have moved during exposure and thus cause a blurred image.
    [Show full text]
  • Nucleosynthesis •Light Element Processes •Neutron Capture Processes •LEPP and P Nuclei •Explosive C-Burning •Explosive H-Burning •Degenerate Environments
    Lecture 21: Nucleosynthesis •Light element processes •Neutron capture processes •LEPP and P nuclei •Explosive C-burning •Explosive H-burning •Degenerate environments Lecture 21: Ohio University PHYS7501, Fall 2017, Z. Meisel ([email protected]) Nuclear Astrophysics: Nuclear physics from dripline to dripline •The diverse sets of conditions in astrophysical environments leads to a variety of nuclear reaction sequences •The goal of nuclear astrophysics is to identify, reduce, and/or remove the nuclear physics uncertainties to which models of astrophysical environments are most sensitive A.Arcones et al. Prog.Theor.Part.Phys. (2017) 2 In the beginning: Big Bang Nucleosynthesis • From the expansion of the early universe and the cosmic microwave background (CMB), we know the initial universe was cool enough to form nuclei but hot enough to have nuclear reactions from the first several seconds to the first several minutes • Starting with neutrons and protons, the resulting reaction S. Weinberg, The First Three Minutes (1977) sequence is the Big Bang Nucleosynthesis (BBN) reaction network • Reactions primarily involve neutrons, isotopes of H, He, Li, and Be, but some reaction flow extends up to C • For the most part (we’ll elaborate in a moment), the predicted abundances agree with observations of low-metallicity stars and primordial gas clouds • The agreement between BBN, the CMB, and the universe expansion rate is known as the Concordance Cosmology Coc & Vangioni, IJMPE (2017) 3 BBN open questions & Predictions • Notable discrepancies exist between BBN predictions (using constraints on the astrophysical conditions provided by the CMB) and observations of primordial abundances • The famous “lithium problem” is the several-sigma discrepancy in the 7Li abundance.
    [Show full text]
  • 570 Possibilities to Investigate Astrophysical
    POSSIBILITIES TO INVESTIGATE ASTROPHYSICAL PHOTONUCLEAR REACTIONS IN UKRAINE Ye. Skakun1, I. Semisalov1, V. Kasilov1, V. Popov1, S. Kochetov1, N. Avramenko1, V. Maslyuk2, V. Mazur2, O. Parlag2, D. Simochko2, I. Gajnish2 1NSC KIPT, Institute of High Energy and Nuclear Physics, Kharkiv, Ukraine 2 Institute of Electron Physics, National Academy of Sciences of Ukraine, Uzhgorod, Ukraine Reactions of proton capture (rp-process) and sequences of photodisintegrations of the (γ,n), (γ,α) and (γ,p) types (γ-process) play the key role in stellar nucleosynthesis of the so-called p-nuclei − a group of stable proton rich nuclides which could be created by none of slow (s) and rapid (r) radiative neutron capture reactions. There is need of knowledge of thousands of reaction rates to simulate natural abundances of the p-nuclei. Using bremsstrahlung beams from thin tantalum converters of the electron linear accelerator of NSC KIPT (Kharkiv) and the microtron of IEP (Uzhgorod) and conventional activation technique applying high resolution gamma-spectrometry we measured the integral cross sections of the (γ,n)-reactions on the nuclei of the 96Ru, 98Ru, 104Ru, 102Pd, and 110Pd isotopes the first two of which and palladium-102 are p-nuclei, and determined the reaction rates by a procedure of superposition of several bremsstrahlung spectra with different endpoints in the range from the thresholds to 14 MeV. The experimental reaction cross sections were compared to available data in overlapping energy range and the derived reaction rates to the predictions of the Hauser - Feshbach statistical model of nuclear reactions. In most cases theory underestimates the observed reaction rates in not great extent.
    [Show full text]
  • Evidence of a Sudden Increase in the Nuclear Size of Proton-Rich Silver-96 ✉ M
    ARTICLE https://doi.org/10.1038/s41467-021-24888-x OPEN Evidence of a sudden increase in the nuclear size of proton-rich silver-96 ✉ M. Reponen 1 , R. P. de Groote1, L. Al Ayoubi 1,2, O. Beliuskina1, M. L. Bissell3, P. Campbell 3, L. Cañete4, B. Cheal 5, K. Chrysalidis 6, C. Delafosse1,2, A. de Roubin 1,7, C. S. Devlin 5, T. Eronen 1, R. F. Garcia Ruiz 8, S. Geldhof 1,9, W. Gins1, M. Hukkanen1,7, P. Imgram 10, A. Kankainen 1, M. Kortelainen 1, Á. Koszorús5, S. Kujanpää 1, R. Mathieson 5, D. A. Nesterenko 1, I. Pohjalainen1,11, M. Vilén 1,6, A. Zadvornaya1 & I. D. Moore 1 1234567890():,; Understanding the evolution of the nuclear charge radius is one of the long-standing chal- lenges for nuclear theory. Recently, density functional theory calculations utilizing Fayans functionals have successfully reproduced the charge radii of a variety of exotic isotopes. However, difficulties in the isotope production have hindered testing these models in the immediate region of the nuclear chart below the heaviest self-conjugate doubly-magic nucleus 100Sn, where the near-equal number of protons (Z) and neutrons (N) lead to enhanced neutron-proton pairing. Here, we present an optical excursion into this region by crossing the N = 50 magic neutron number in the silver isotopic chain with the measurement of the charge radius of 96Ag (N = 49). The results provide a challenge for nuclear theory: calculations are unable to reproduce the pronounced discontinuity in the charge radii as one moves below N = 50.
    [Show full text]
  • THE R-, S-, and P-PROCESSES in NUCLEOSYNTHESIS
    NASA-CR-204924 ,'.';.t"i.--' '" Annu. Rev. Axtron. Asttr_phys. 1994 32:153-90 Copyright (_ 1994 by Annual Reviews Inc. All rights reserved THE r-, s-, AND p-PROCESSES IN NUCLEOSYNTHESIS Bradley S. Meyer Department of Physics and Astronomy, Clemson University, Clemson, South Carolina 29634-1911 KEY WORDS: heavy elements, supernovae, AGB stars, abundances 1. INTRODUCTION Burbidge et al (1957) and Cameron (1957) laid out the framework for our understanding of the formation of the heavy nuclei (those nuclei with mass number A > 70). From systematics in the solar system abundance distribution, Burbidge et al determined that the heavy nuclei were formed in three distinct nucleosynthetic processes, which they termed the r-, s-, and p-processes. That we still use these terms today is a credit to the soundness of this work done 37 years ago. We may understand how Burbidge et al and Cameron arrived at their con- clusions from Figure 1. One population of nuclei, the s-nuclei, shows an abundance distribution with peaks near mass numbers 87, 138, and 208. These nuclei are made in a slow neutron-capture process, the s-process. A rapid neutron-capture process, the r-process, is responsible for the r-nuclei, whose abundance distribution shows peaks at mass numbers 80, 130, and 195. The p-process is responsible for production of the rarer, more proton-rich heavy isotopes (the p-nuclei) that cannot be made by neutron capture. The first quantitive evaluations of the ideas of Burbidge et a] and Cameron came to light in the early 1960s with work on the s-process (Clayton et al 1961, Seeger et al 1965) and the r-process (Seeger et al 1965).
    [Show full text]
  • Gamow-Teller Strength Distribution in Proton-Rich Nucleus $^{57} $ Zn And
    Gamow-Teller strength distribution in proton-rich nucleus 57Zn and its implications in astrophysics Jameel-Un Nabi 1 • Muneeb-Ur Rahman Abstract Gamow-Teller (GT) transitions play a pre- on 57Zn are compared to the seminal work of Fuller, eminent role in the collapse of stellar core in the stages Fowler and Newman (FFN). The pn-QRPA calculated leading to a Type-II supernova. The microscopically β+-decay rates are generally in good agreement with calculated GT strength distributions from ground and the FFN calculation. However at high stellar tempera- excited states are used for the calculation of weak decay tures the calculated β+-decay rates are almost half of rates for the core-collapse supernova dynamics and for FFN rates. On the other hand, for rp-process condi- probing the concomitant nucleosynthesis problem. The tions, the calculated electron capture (β+-decay) rates B(GT) strength for 57Zn is calculated in the domain of are bigger than FFN rates by more than a factor 2 (1.5) proton-neutron Quasiparticle Random Phase Approxi- and may have interesting astrophysical consequences. mation (pn-QRPA) theory. No experimental insertions were made (as usually made in other pn-QRPA calcula- Keywords weak-interaction rates; electron capture tions of B(GT) strength function) to check the perfor- and beta decay, pn-QRPA theory; GT strength distri- mance of the model for proton-rich nuclei. The calcu- bution, rp-process. lated B(GT) strength distribution is in good agreement with measurements and shows differences with the ear- lier reported shell model calculation. The pn-QRPA 1 Introduction model reproduced the measured low-lying strength for 57 Zn better in comparison to the KB3G interaction The weak interactions and gravity are the guru that used in the large-scale shell model calculation.
    [Show full text]
  • Arxiv:Nucl-Th/0203071V2 16 Sep 2002
    Nuclear weak-interaction processes in stars K. Langanke∗ Institut for Fysik og Astronomi, Arhus˚ Universitet, DK-8000 Arhus,˚ Denmark G. Mart´ınez-Pinedo† Department f¨ur Physik und Astronomie, Universit¨at Basel, CH-4056 Basel, Switzerland‡ (Dated: October 22, 2018) Recent experimental data and progress in nuclear structure modeling have lead to improved de- scriptions of astrophysically important weak-interaction processes. The review discusses these advances and their applications to hydrostatic solar and stellar burning, to the slow and rapid neutron-capture processes, to neutrino nucleosynthesis, and to explosive hydrogen burning. Spe- cial emphasis is given to the weak-interaction processes associated with core-collapse supernovae. Despite some significant progress, important improvements are still warranted. Such improve- ments are expected to come from future radioactive ion-beam facilities. Contents I. INTRODUCTION I. Introduction 1 The weak interaction is one the four fundamental II. Theoretical description 2 forces in nature. Like the other three – strong, elec- A. Weak interactions in nuclei 2 tromagnetic and gravitation – it plays a keyrole in many B. Nuclear models 4 astrophysical processes. This can be nicely illustrated by the observation that new insights into the nature of III. Hydrogen burning and solar neutrinos 6 the weak interaction usually were closely followed by the recognition of their importance in some astrophys- IV. Late-stage stellar evolution 10 A. General remarks 10 ical context. Shortly after Pauli postulated the exis- B. Shell-model electron capture and β decay rates 10 tence of the neutrino and Fermi developed the first theory C. Consequences of the shell model rates in stellar of weak interaction (Fermi, 1934), Gamow and Schoen- models 13 berg speculated about the possible role of neutrinos in stellar evolution and proposed their production in the V.
    [Show full text]
  • Proton Drip-Line Calculations and the Rp Process
    PHYSICAL REVIEW C, VOLUME 65, 045802 Proton drip-line calculations and the rp process B. A. Brown, R. R. C. Clement, H. Schatz, and A. Volya Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824-1321 W. A. Richter Department of Physics, University of Stellenbosch, Stellenbosch 7600, South Africa ͑Received 23 July 2001; revised manuscript received 19 December 2001; published 19 March 2002͒ One-proton and two-proton separation energies are calculated for proton-rich nuclei in the region A ϭ41–75. The method is based on Skyrme Hartree-Fock calculations of Coulomb displacement energies of mirror nuclei in combination with the experimental masses of the neutron-rich nuclei. The implications for the proton drip line and the astrophysical rp process are discussed. This is done within the framework of a detailed analysis of the sensitivity of rp process calculations in type I x-ray burst models on nuclear masses. We find that the remaining mass uncertainties, in particular for some nuclei with NϭZ, still lead to large uncertainties in calculations of x-ray burst light curves. Further experimental or theoretical improvements of nuclear mass data are necessary before observed x-ray burst light curves can be used to obtain quantitative constraints on ignition conditions and neutron star properties. We identify a list of nuclei for which improved mass data would be most important. DOI: 10.1103/PhysRevC.65.045802 PACS number͑s͒: 21.10.Dr, 26.50.ϩx, 97.60.Jd I. INTRODUCTION AWE͒. Thus we combine the experimental binding energy Ͼ for the neutron-rich nucleus BE(A,Tz )exp together with the ϭ The masses for the proton-rich nuclei above A 60 have Hartree-Fock value for D(A,T)HF to provide an extrapola- not yet been measured.
    [Show full text]