DOCSLIB.ORG

Plonic Radioactivity Versus Spontaneous Fission in Decay of Superheavy Nuclei

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Plonic Radioactivity Versus Spontaneous Fission in Decay of Superheavy Nuclei CENTRAL INSTITUTE OF PHYSICS INSTITUTE FOR PHYSICS AND NUCLEAR ENGINEERING Bucharest, P.O.Box MG-6, ROMANIA BUCHAREST UNIVERSITY, FACULTY OF PHYSICS Bucharest, P.O.Box MG-6, ROMANIA ^\tf ~ FT-350-*fta9 March Plonic radioactivity versus spontaneous fission in decay of superheavy nuclei D.B.ION*. R.ION-MIHAI** M. IVASCU* \* ^^ Ab4.f./iac-t» In this paper ,th3 pionic radioactivity as dominant decay mode of superheavy elements (SHE) is investigated. The dynamical thresholds as well as the competition between the ground state pionic radioactivity and the spontaneous fission are discussed. It is shown that the usual island of stability around the double magic nucleus 29 8[114 ] is destroied via a deep instability due to the spontaneous -,ion emission. An is­ land of relative stability against the pionic dominant decay mode is predicted to be around the magic nucleus [120],The pionic radioactivity dominance in the SHE region can be con­ sidered as one of the possible reasons why SHE nuclei have not been synthesized and/or identified using heavy ion reac­ tions. 1. INTRODUCTION In some recent papers [1-13J we have initiated the investi­ gation of the spontaneous pion emission from the ground state of a nucleus as a new possible natural radioactivity called pionic nuclear radioactivity. Then, the Q^ - systematics, the definitions of the "width" (T^) and the Lorentz invariant statistical factors of the pionic nuc>ear radioactivity are presented [1-3]. It was shown that this new type of nuclear radioactivity is energetically possible via two (or many)-body fragmentation of the parent nucleus and that the most statistically favoured pionic emitters are those with Z > 92. Experimental detection of the neutral and charqed pions as well as some possible two step mechanisms for the spon­ taneous pion emission are also discussed in ref. [1-6]. An Optical Theorem for the inclusive pionic radioactivity was- proved [6]. Ex­ tensions of these results to other possible natural radioactivi­ ties, such as muonic nuclear radioactivity, lantbdonic (\°) nuclear radioactivity, hyperfission, etc., are also presented in refs. [2, 7, 13]. The dynamical predictions for the pionic nuclear radioac­ tivity were obtained in refs. [ 8-12 ]. The credibility of these predictions is verified by applying the same fission-like model [ see e.g. refs. [ 11-13 ]] to the light-charged-particle (LCP) emis­ sion data. Moreover, the absolute predictions for the yieldr /rs are in agreement with the experimental upper limits obtained at Bucharest [14-16] for charged pions and also with those measured at: CEN - Saclay [17], ORNL [18], and TRIUMF-Vancouver [19]for neutral pions. Also, it is important to note that, recently [21], the unusual background observed experimentally by Wild et al El ] in the (AE, E) - energy region below that characteristic of LRA's - 2 - 257 emission from Fm is interpreted by us as being produced by 257 negative pions emitted spontaneously by Fm. If this interpreta­ tion is correct then the inferred value of the negative pionic 257 -3 yield of Fm is r /rCc = 1° • This result is with ten orders II or of magnitude higher than that predicted by us in ref. [10]. Now, we remember that in refs. [5,12] we pointed ^ut that: the discovery of the pionic radioactivity will contribute to a much deeper understanding of the nuclear instabilities in the region of the superheavy elements where the ground state jnowic ra­ dioactivity is expected to be one of the dominant nuclear decay m ode. Consequently a detailed investigation of this last conjec­ ture is needed. So, in this paper, the fission-like model [ 12] is applied for the calculation of the pionic yields (^-„/^cc) for the superheavy elements in terms of their spontaneous fission half-lives. The Q -systematic for the superheavy elements (SHE) is presented in Section 2, wm'le the dynamical thresholds for the ground state pionic radioactivity are discussed in Section 3. The competition between tK« pionic radioactivity ind spontaneous fission in decay of the superheavy element' is investigated in Section 4 while the conclusions are sutmarized in Section 5. 2. Q - SYSTEMATICS FOR SUPERHEAVY ELEMENTS IT Superheavy elements (SHE) have been postulated in 1955 by Wheeler [22] and in 1967 by Scharf Goldhaber [231. But the inter­ national interest in detection and synthesizatlon of these elements began in the latter part of 1960's as a result of the theoretical predictions [23] for their localization around the doubly magic nucleus 292[H4]. So predictions given by Myers and Swiateckl [24], Strutlnsky [25], Meldner *.26], Nilsson [27], N1x [28] and their - 3 - co-workers, have given the naif-lives we can expect for the nuclei from the island of stability arcund element 114. They rar.qe in 9 294 this island as high as 10 years e.g. for 110 . Another .-.land of stability has been predicted 1291 to exist around element V21164 1. The continuing progress "n synthesis and study of the pro­ perties of the heaviest nuclei 130-33: demands further improvements in the theoretical predictions of these r;UCiiJes. Various methods of calculations of the ground state o.t:-rqy and fission barriers and various models for description of the internal structure of these nuclei have been used, leading to many different estimates of their lifetime [see e.g. reviews |36-39)| . Most searches for SHE's in nature and at heavy ion accelerators have used spontaneous fission as detection methods Isee e .q . ref. [35]] . This is because of extreme sensitivity ana iow b-trkground offered by this method and the expectation that superheavy nuclei will either decay by spontaneous fission themselves or at least r!<-cay by another nuclide which will decay by spontaneous fission. 1,'nfor tunatel y to date no superheavy elements have been discovered. Several possible reasons why SHE's have not been synthesized and/or identified using heavy ion reactioni are analysed in ref. 140]. Here, we analyse in more detail the possibility of the competition between the spontaneous pion emission and the sponta­ neous fission in the decay of superheavy elements suggested in refs. [5,12], As we can see in Section 4, this new hypothesis can explain why the efforts to synthesize and identify superheavy elements using heavy-.on reactions have been unsuccessful up to present time. - 4 - The ground state pion radioactivity is energetically pos­ sible only accompanied by the spontaneous fission of the parent nucleus. Hence, we start our discussion with the following nuclear reaction: (A,Z) > •: • (Aj. Zj) + (A2, Z2) (2.1a) with A = AL + A2, Z = Z^ + Z, + Z2 (2.1b) where A, A,, A- and Z, Z., Z2 are the usual mass numbers and charge numbers of the involved nuclei, while Z« denotes the pion charge. If the nuclear masses: H(A,Z) - M, M(A.,Z.) = n., i = 1,2, and also the pion rest mass m , are given in units of energy, then the total energy liberated in the reaction (2.1a,b) is given by Q = M - m, - m0 - m = Q0 - m = LW - m, - m0 - m (2.2) v XTI 1 2 ^ 2 ^ 1 2 TI ' where .'-M , Am-, i = 1,2,are the nuclear mass decrements. Here, usinq the nuclear masses from ref. 1411 we calculate the Q , when the .i° emission is accompanied by symmetric fission rr (A1 = A2 = A/2, Zj = Z2 = Z/2) for the heavy nuclei with even Z = 106 T 108 and A = 251 r ?10. The results for Q are given in Table 1. 3. DYNAMICAL THRESHOLDS FOR GROUND STATE PION RADIOACTIVITY OF THE SUPERHEAVY NUCLEI A nuclear theory based on an exact Hatniltonian (which includes a complete knowledge of the nuclear constituents and the interconstituents forces) could in principle provide us a complete explanation of all nuclear phenomena i r,c 1 ud 1 ng : fission, alpha emission, etc., and also the ground state pion radioactivity. - 5 - But we do not know all these ingredients in sufficient detail and then it is necessary to replace the exact Hamiltonian with a simpler oae which we can solve. Hence, recently [8-12] assuming that the pionic nuclear radioactivicy is a fission-like process in which EJ|(nF) i E° - ran , E°(*F) " E° (3.1) we introduced the pionic f.ssility parameter E (irF) C x m 2E o Xwc = "^ = r " ,r/ £ (3-2) 2ES(TTF) where E° , =* yZ2/A1/3, E^ = 6A2/3 are the usual Coulomb e**<$H . and the nuclearfctCwjiA, respectively, for the spherical shape corresponding to the parent nucleus. In th€. case r ; ' that the pion rest mass is considered as originated froâ both energies, the electromagnetic and the nuclear one, then we can write •% = mţj + m^ = otm^ + (1 - a)m^ , a ~ m^/m^ , (3.3a) and F F E"C (0) = E£ - an, , E* (0) - E| - (1 - a)*, (3.3b) c s where n, 3 am , m* = (1 -<*)"% are the contributions of the Conlomb energy and the nuclear energy to the pion rest mass. Consequently we obtain the following general definition of the w- fissilUy parameter F Ej (0) E° - «m, (3#4) X* F * r»Fr 2E* (0) 2lE|-(l-a)m1tl - 6 - This is the essential parameter for the discussion of the nuclear stability with the respect to the * - fission just as in case of usu:al fission. Indeed, assuming that we si ightly deform a spherical parent nucleus into an elipsoidal one with the aid of a small symmetrical distortion of eP2(cos 8) type, then it can be shown that F F 2 Ec (c) = E£ (0) II - I E + hioher powers of e] (3.5») ESF(G) = ESF(°* ll + I e2 * ni1ner powers of e] (3.5b) and therefore the total change of energy is qiven by F F AE^ = AEJ • AEj = F 2 F - Y- C<(0) - Ej (0)] - | e E; (0) 11 - Xj»>] (3.6) IT F T[ F The AEC and AE$ arr the differences between the Coulomb a'nd the surface energies for the elipsoidal and for the spherical configurations, while x|p' is the n - fissility parameter defined by eq.
Load more

Recommended publications
  • Spontaneous Fission of U234, Pu236, Cm240, and Cm244
    Lawrence Berkeley National Laboratory Lawrence Berkeley National Laboratory Title Spontaneous Fission of U234, Pu236, Cm240, and Cm244 Permalink https://escholarship.org/uc/item/0df1j1qm Authors Ghiorso, A. Higgins, G.H. Larsh, A.E. et al. Publication Date 1952-04-21 eScholarship.org Powered by the California Digital Library University of California TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Division, Ext. 5545 UCRL-1772 Unclassified-Chemistry Distribution UNIVEBSITY OF CALIFCEiNIil Radiation Laboratory Contract No, ti-7405-eng-4.8 24.4 SPONTANEOUS FISSION OF' I'Zu6, ~m~~~~ AND Gm A, Ghiorso, G. H, Higgins, A. E. Larsh, Go To Seaborg, and So G, Thompson April 21, 1752 Berkeley, California A. Ghiorso, G. H. Higgins, A. E. Larsh, G. T. Seaborg, and S. Go Thompson Radiation Laboratory and Department of Chemistry Uni versity of California, Berkeley, Californf a April 21, 1952 In a recent communication commenting on the mechanism of fission we called attention to the simple exponential dependence of spontaneous fission rate on Z~/Aand to the effect of an odd nucleon in slowing the fission process.1 Since it is of interest to test further the simple correlation of the spontaneous fission rate for even-even nuclides wfth z~/A~a further number of such rates have been determined, The spontaneous fission rates were measured by pladng the chemically purified samples on one electrode of a parallel plate ionization chamber, filled with a mixture of argon and carbon dioxide, which was connected with an amplifier f ollawed by a register and a stylus recorder.
    [Show full text]
  • Spontaneous Fission Half-Lives of Heavy and Superheavy Nuclei Within a Generalized Liquid Drop Model
    Spontaneous fission half-lives of heavy and superheavy nuclei within a generalized liquid drop model Xiaojun Bao1, Hongfei Zhang1,∗ G. Royer2, Junqing Li1,3 June 4, 2018 1. School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China 2. Laboratoire Subatech, UMR: IN2P3/CNRS-Universit´e-Ecole des Mines, 4 rue A. Kastler, 44 Nantes, France 3. Institute of Modern Physics, Chinese Academy of Science, Lanzhou 730000, China Abstract We systematically calculate the spontaneous fission half-lives for heavy and superheavy arXiv:1302.7117v1 [nucl-th] 28 Feb 2013 nuclei between U and Fl isotopes. The spontaneous fission process is studied within the semi-empirical WKB approximation. The potential barrier is obtained using a generalized liquid drop model, taking into account the nuclear proximity, the mass asymmetry, the phenomenological pairing correction, and the microscopic shell cor- rection. Macroscopic inertial-mass function has been employed for the calculation of the fission half-life. The results reproduce rather well the experimental data. Rela- tively long half-lives are predicted for many unknown nuclei, sufficient to detect them if synthesized in a laboratory. Keywords: heavy and superheavy nuclei; half-lives; spontaneous fission ∗Corresponding author. Tel.: +86 931 8622306. E-mail address: [email protected] 1 1 Introduction Spontaneous fission of heavy nuclei was first predicted by Bohr and Wheeler in 1939 [1]. Their fission theory was based on the liquid drop model. Interestingly, their work also con- tained an estimate of a lifetime for fission from the ground state. Soon afterwards, Flerov and Petrzak [2] presented the first experimental evidence for spontaneous fission.
    [Show full text]
  • Photofission Cross Sections of 238U and 235U from 5.0 Mev to 8.0 Mev Robert Andrew Anderl Iowa State University
    Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1972 Photofission cross sections of 238U and 235U from 5.0 MeV to 8.0 MeV Robert Andrew Anderl Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Nuclear Commons, and the Oil, Gas, and Energy Commons Recommended Citation Anderl, Robert Andrew, "Photofission cross sections of 238U and 235U from 5.0 MeV to 8.0 MeV " (1972). Retrospective Theses and Dissertations. 4715. https://lib.dr.iastate.edu/rtd/4715 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.
    [Show full text]
  • Spontaneous Fission
    13) Nuclear fission (1) Remind! Nuclear binding energy Nuclear binding energy per nucleon V - Sum of the masses of nucleons is bigger than the e M / nucleus of an atom n o e l - Difference: nuclear binding energy c u n r e p - Energy can be gained by fusion of light elements y g r e or fission of heavy elements n e g n i d n i B Mass number 157 13) Nuclear fission (2) Spontaneous fission - heavy nuclei are instable for spontaneous fission - according to calculations this should be valid for all nuclei with A > 46 (Pd !!!!) - practically, a high energy barrier prevents the lighter elements from fission - spontaneous fission is observed for elements heavier than actinium - partial half-lifes for 238U: 4,47 x 109 a (α-decay) 9 x 1015 a (spontaneous fission) - Sponatenous fission of uranium is practically the only natural source for technetium - contribution increases with very heavy elements (99% with 254Cf) 158 1 13) Nuclear fission (3) Potential energy of a nucleus as function of the deformation (A, B = energy barriers which represent fission barriers Saddle point - transition state of a nucleus is determined by its deformation - almost no deformation in the ground state - fission barrier is higher by 6 MeV Ground state Point of - tunneling of the barrier at spontaneous fission fission y g r e n e l a i t n e t o P 159 13) Nuclear fission (4) Artificially initiated fission - initiated by the bombardment with slow (thermal neutrons) - as chain reaction discovered in 1938 by Hahn, Meitner and Strassmann - intermediate is a strongly deformed
    [Show full text]
  • Production and Properties Towards the Island of Stability
    This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail. Author(s): Leino, Matti Title: Production and properties towards the island of stability Year: 2016 Version: Please cite the original version: Leino, M. (2016). Production and properties towards the island of stability. In D. Rudolph (Ed.), Nobel Symposium NS 160 - Chemistry and Physics of Heavy and Superheavy Elements (Article 01002). EDP Sciences. EPJ Web of Conferences, 131. https://doi.org/10.1051/epjconf/201613101002 All material supplied via JYX is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. EPJ Web of Conferences 131, 01002 (2016) DOI: 10.1051/epjconf/201613101002 Nobel Symposium NS160 – Chemistry and Physics of Heavy and Superheavy Elements Production and properties towards the island of stability Matti Leino Department of Physics, University of Jyväskylä, PO Box 35, 40014 University of Jyväskylä, Finland Abstract. The structure of the nuclei of the heaviest elements is discussed with emphasis on single-particle properties as determined by decay and in- beam spectroscopy. The basic features of production of these nuclei using fusion evaporation reactions will also be discussed. 1. Introduction In this short review, some examples of nuclear structure physics and experimental methods relevant for the study of the heaviest elements will be presented.
    [Show full text]
  • Alpha Decay and Spontaneous Fission Laboratory Exercise in Nuclear Physics
    Alpha Decay and Spontaneous Fission Laboratory Exercise in Nuclear Physics Note: Before attending the laboratory exercise, make sure you read the radiation safety information! This laboratory exercise consists of three parts: • Spectroscopy of an unknown alpha source. • A measurement of the fragment energies from spontaneous fission of 252Cf. • A measurement of the energy loss of alpha particles in air as a function of air pressure. Preparation: Read K.S. Krane, chapter 8 (alpha decay), chapter 13 (fis- sion), and paragraphs 7.1 (Interactions of radiation with matter, the section about heavy charged particles) and 7.4 (semiconductor detectors). In the lab- oration a triple α-source containing the radioactive isotopes 244Cm, 241Am and 239Pu will be used for energy calibration of the instrumentation. Calcu- late the Q−values of the alpha decays for these isotopes using e.g. the table of nuclear properties found at the Brookhaven National Laboratory web- site: http://www2.bnl.gov/ton/. Deduce the kinetic energies of the emitted α-particles from the Q−values. Alpha Decay Alpha decay involves the spontaneous emission of an alpha particle from an atomic nucleus. The alpha particle consists of two protons and two neutrons 1 and is the same species as the nucleus of a helium (4He) atom. These four nucleons have their origin in the nucleus X before the decay (the mother nucleus) and the nucleus is therefore transformed into a nucleus X0 (the daughter nucleus) of another basic element according to the relation: A A−4 0 Z XN !Z−2 XN−2 + α; (1) where α is the alpha particle, N is the number of neutrons, Z is the number of protons, and A = N + Z is the mass number.
    [Show full text]
  • Binding Energy of the Mother Nucleus Is Lower Than That of the Daughter Nucleus
    Chapter 1 Learning Objectives • Historical Recap • Understand the different length scales of nuclear physics • Know the nomenclature for isotopes and nuclear reactions • Know the different types of neutron nuclear collisions and their relationship to each other • Basic principles of nuclear reactor Learning Objectives • Neutron Sources • Basic Principles of Nuclear Reactor • Bindinggg energyy curve • Liquid drop model • Fission Reaction • ODE Review • Radioactive Decay • Decay Chains • Chart of Nuclides Historical Recap • Driscoll handout • New programs – GNEP/AFCI – Gen-IV – Nuclear Power 2010 Why nuclear? • Power density – 1000 MW electric • 10 000 tons o f coal per DAY!! • 20 tons of uranium per YEAR (of which only 1 ton is U -235) A typical pellet of uranium weighs about 7 grams (0.24ounces). It can generate as much energy as…… 3.5 barrels of oil or…… 17,000 cubic feet of natural gas, or….. 1,780 pounds of coal. Why nuclear? • Why still use coal – Capital cost – Politics – Public perception of nuclear, nuclear waster issue What do you think is the biggest barrier to constructing the next U.S. nuclear power plant? 50% 40% 30% 20% 44% 10% 16% 15% 14% 0% 10% - 2008 survey of Political Nuclear Waste Cost of Fear of Other Resistance to Disposal Nuclear Nuclear energy professionals Nuclear Energy Issues Power Plant Accident Construction Image by MIT OpenCourseWare. “Eighty-two percent of Americans living in close proximity to nuclear power plants favor nuclear energy, and 71 percent are willing to see a new reactor built near them, according to a new public opinion survey of more than 1,100 adults nationwide.”– NEI, September 2007 Basic Principles ofof Nuclear Reactor • Simple device – Fissioning fuel releases energy in the “core” – Heat isis transported away by a coolant which couples the heat source to a Rankine steam cycle – Very similar to a coal plant, with the exception of the combustion process – Main complication arises from the spent fuel, a mix of over 300 fission products Public domain image from wikipedia.
    [Show full text]
  • (Α,N) Reactions with FISPIN
    Nexia Solutions 8088 Issue 2 (DRAFT 2) UKNSF(2007)P221 JEF/DOC-1194 Page 1 of 11 Technical note on using JEFF-3.1 and JEFF-3.1.1 data to calculate neutron emission from spontaneous fission and (α,n) reactions with FISPIN. Nexia Solutions Ltd Dr. Robert W. Mills and Dr. Craig Shearer, 20 November 2007 EXECUTIVE SUMMARY This paper describes the production of new heavy element decay data files for FISPIN using the JEFF-3.1 and JEFF-3.1.1 data (released by the JEFF project for testing) with revised spontaneous fission and (α, n) reaction terms. In addition to the heavy element decay data files for metal and uranium dioxide fuel a new file of data for the FISPIN Graphical User Interface (FISGUI) was produced to allow (α, n) neutron emission to be calculated for arbitrary compounds. The new data was then compared to neutron emission measurements showing good agreement. Finally, it is shown that the new data increases the neutron emission for typical PWR fuel by ~3%. In addition, a review was carried out for the nuclides which most changed between JEF-2.2 and JEFF-3.1, U232, U235, U236, Pu239 and Am241. This showed that the U232 and Pu236 differ significantly from the values currently in ENDSF and probably require a review by an evaluator. Nexia Solutions 8088 Issue 2 (DRAFT 2) UKNSF(2007)P221 JEF/DOC-1194 Page 2 of 11 CONTENTS 1 Introduction ............................................................................................3 2 FISPIN neutron emission calculation methodology .................................4 2.1 Spontaneous fission............................................................................... 4 2.2 (α,n) reactions ....................................................................................
    [Show full text]
  • 16. Fission and Fusion Particle and Nuclear Physics
    16. Fission and Fusion Particle and Nuclear Physics Dr. Tina Potter Dr. Tina Potter 16. Fission and Fusion 1 In this section... Fission Reactors Fusion Nucleosynthesis Solar neutrinos Dr. Tina Potter 16. Fission and Fusion 2 Fission and Fusion Most stable form of matter at A~60 Fission occurs because the total Fusion occurs because the two Fission low A nuclei have too large a Coulomb repulsion energy of p's in a surface area for their volume. nucleus is reduced if the nucleus The surface area decreases Fusion splits into two smaller nuclei. when they amalgamate. The nuclear surface The Coulomb energy increases, energy increases but its influence in the process, is smaller. but its effect is smaller. Expect a large amount of energy released in the fission of a heavy nucleus into two medium-sized nuclei or in the fusion of two light nuclei into a single medium nucleus. a Z 2 (N − Z)2 SEMF B(A; Z) = a A − a A2=3 − c − a + δ(A) V S A1=3 A A Dr. Tina Potter 16. Fission and Fusion 3 Spontaneous Fission Expect spontaneous fission to occur if energy released E0 = B(A1; Z1) + B(A2; Z2) − B(A; Z) > 0 Assume nucleus divides as A , Z A1 Z1 A2 Z2 1 1 where = = y and = = 1 − y A, Z A Z A Z A2, Z2 2 2=3 2=3 2=3 Z 5=3 5=3 from SEMF E0 = aSA (1 − y − (1 − y) ) + aC (1 − y − (1 − y) ) A1=3 @E0 maximum energy released when @y = 0 @E 2 2 Z 2 5 5 0 = a A2=3(− y −1=3 + (1 − y)−1=3) + a (− y 2=3 + (1 − y)2=3) = 0 @y S 3 3 C A1=3 3 3 solution y = 1=2 ) Symmetric fission Z 2 2=3 max.
    [Show full text]
  • Simulation of Neutron and Gamma Ray Emission from Fission
    UCRL-AR-228518 Simulation of Neutron and Gamma Ray Emission from Fission J. Verbeke, C. Hagmann, D. M. Wright March 1, 2007 Disclaimer This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. UCRL-AR-228518 Simulation of Neutron and Gamma Ray Emission from Fission and Photofission Jerome M. Verbeke, Chris Hagmann, Doug Wright∗ Lawrence Livermore National Laboratory May 11, 2010 Contents 1 Introduction 2 1.1 Copyright notice . 3 2 Spontaneous fission and neutron-induced fission 4 2.1 Neutron number distribution . 4 2.2 Neutron energy distribution . 7 2.3 Gamma-ray number distribution . 11 2.4 Gamma-ray energy distribution .
    [Show full text]
  • Arxiv:2102.03686V1 [Nucl-Th] 6 Feb 2021
    Fission fragment distributions and their impact on the r-process nucleosynthesis in neutron star mergers J.-F. Lema^ıtre∗ Institut d'Astronomie et d'Astrophysique, Universit´eLibre de Bruxelles, Campus de la Plaine CP 226, BE-1050 Brussels, Belgium and CEA, DAM, DIF, F-91297 Arpajon, France S. Goriely Institut d'Astronomie et d'Astrophysique, Universit´eLibre de Bruxelles, Campus de la Plaine CP 226, BE-1050 Brussels, Belgium A. Bauswein GSI Helmholtzzentrum f¨urSchwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany and Helmholtz Forschungsakademie Hessen f¨urFAIR (HFHF), GSI Helmholtzzentrum f¨urSchwerionenforschung, Campus Darmstadt, Germany H.-T. Janka Max-Planck-Institut f¨urAstrophysik, Postfach 1317, D-85741 Garching, Germany Neutron star (NS) merger ejecta offer a viable site for the production of heavy r-process elements with nuclear mass numbers A & 140. The crucial role of fission recycling is responsible for the robustness of this site against many astrophysical uncertainties. Here, we introduce new improve- ments to our scission-point model, called SPY, to derive the fission fragment distribution for all neutron-rich fissioning nuclei of relevance in r-process calculations. These improvements include a phenomenological modification of the scission distance and a smoothing procedure of the distribu- tion. Such corrections lead to a much better agreement with experimental fission yields. Those yields are also used to estimate the number of neutrons emitted by the excited fragments on the basis of different neutron evaporation models. Our new fission yields are extensively compared to those predicted by the so-called GEF model. The impact of fission on the r-process nucleosynthesis in binary neutron mergers is also re- analyzed.
    [Show full text]
  • 17Th, 2003 Half-Lives of Long-Lived A-Decay, P-Decay
    Prepared for the 42nd IUPAC General Assembly in Ottawa, Canada August 8th - 17th, 2003 Half-lives of Long-lived a-decay, P-decay, electron capture decay, PP-decay, proton decay and Spontaneous Fission decay Nuclides* Norman E. Holden' Brookhaven National Laboratory Upton, New York 11973-5000 1. Introduction In his review of radionuclides for dating purposes, Roth noted that there were a large number of nuclides, normally considered "stable" but which are radioactive with a very long half-life. Roth suggested' that I review the data on the half-life values of these long-lived nuclides for the 2001 Atomic Weights Commission meeting in Brisbane. I provided a report, BNL-NCS-68377, to fulfill Roth's request. Peiser has now made a similar suggestion that I review these data for our next Commission meeting in Ottawa for their possible inclusion in our Tables. These half-life values for long-lived nuclides include those due to various decay modes, a-decay, P-decay, electron capture decay, PP-decay, proton decay and spontaneous fission decay. This data review (post Brisbane) provides an update to the recommendation of the 2001 review. 2. Discussion There is some vagueness in the definition of what constitutes a long-lived nuclide. A definition used for this report will be a nuclide with a half-life that exceeds the age of the universe, which is greater than approximately 12.5 billion years or 1.25 f 0.30 x (10)" years (a recent measurement of stellar age2). There are a number of nuclides which are normally considered stable but which can decay via normal modes such as electron capture, negative and positive beta emission, alpha emission and exotic decay modes of double beta decay, proton decay or spontaneous fission.
    [Show full text]