Discovery of the Nickel Isotopes

Transcription

1 Discovery of the Nickel Isotopes R. Robinson, M. Thoennessen National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA Abstract Thirty-one nickel isotopes have so far been observed; the discovery of these isotopes is discussed. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented. Corresponding author. address: thoennessen@nscl.msu.edu (M. Thoennessen) Preprint submitted to Atomic Data and Nuclear Data Tables April 29, 2010

2 Contents 1. Introduction Discovery of Ni Ni Ni Ni ,52 Ni Ni Ni Ni Ni Ni Ni Ni Ni ,62 Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Ni Summary References Explanation of Tables Table 1. Discovery of Nickel Isotopes. See page 12 for Explanation of Tables Introduction The discovery of the nickel isotopes is discussed as part of the series of the discovery of isotopes which began with the cerium isotopes in 2009 [1]. The purpose of this series is to document and summarize the discovery of the isotopes. Guidelines for assigning credit for discovery are (1) clear identification, either through decay-curves and relationships to other known isotopes, particle or γ-ray spectra, or unique mass and Z-identification, and (2) publication of the 2

3 discovery in a refereed journal. The authors and year of the first publication, the laboratory where the isotopes were produced as well as the production and identification methods are discussed. When appropriate, references to conference proceedings, internal reports, and theses are included. When a discovery includes a half-life measurement the measured value is compared to the currently adopted value taken from the NUBASE evaluation [2] which is based on the ENSDF database [3]. 2. Discovery of Ni Thirty-one nickel isotopes from A = have been discovered so far; these include 5 stable, 11 proton-rich and 15 neutron-rich isotopes. According to the HFB-14 model [4], 87 Ni should be the last odd-even particle stable neutron-rich nucleus while the even-even particle stable neutron-rich nuclei should continue through 94 Ni. At the proton dripline 47 Ni could still be particle stable. Thus, about 14 isotopes have yet to be discovered corresponding to about 31% of all possible nickel isotopes. Figure 1 summarizes the year of first discovery for all nickel isotopes identified by the method of discovery. The range of isotopes predicted to exist is indicated on the right side of the figure. The radioactive nickel isotopes were produced using deep-inelastic reactions (DI), heavy-ion fusion-evaporation (FE), light-particle reactions (LP), neutroninduced fission (NF), charged-particle induced fission (CPF), neutron-capture reactions (NC), heavy-ion transfer (TR), and projectile fragmentation of fission (PF). The stable isotope was identified using mass spectroscopy (MS). Heavy ions are all nuclei with an atomic mass larger than A=4 [5]. In the following, the discovery of each nickel isotope is discussed in detail Ni In the paper Discovery of Doubly Magic 48 Ni, Blank et al. reported the discovery of 48 Ni in 2000 [6]. A natural nickel target was bombarded by a 74.5 MeV/nucleon beam of 58 Ni from the GANIL cyclotrons. 48 Ni was separated and identified with the SISS/LISE3 facility. Because of the efficiency of the MCP detector part of the statistics is lost in this spectrum. Nevertheless, two events of 48 Ni are clearly observed... In this spectrum, we observe four counts which can be unambiguously attributed to 48 Ni Ni In the paper First Observation of the T z = 7/2 Nuclei 45 Fe and 49 Ni, Blank et al. reported the discovery of 49 Ni in 1996 [7]. A 600 A MeV 58 Ni beam from the SIS synchrotron bombarded a beryllium target and isotopes were separated with the projectile-fragment separator FRS. 49 Ni was identified by time-of-flight, E, and Bρ analysis. We observed ten events of 42 Cr, three events of 45 Fe, and five events of 49 Ni. These three isotopes have been identified for the first time in the present experiment Ni The 1994 paper Production cross sections and the particle stability of proton-rich nuclei from 58 Ni fragmentation reported the discovery of 50 Ni by Blank et al. [8]. A 650 MeV/nucleon beam of 58 Ni from the SIS synchrotron bombarded a beryllium target and 50 Ni was separated and identified using the FRS separator. For the yet-unobserved isotope 50 Ni, 3

4 Fusion Evaporation Reactions (FE) Light Particle Reactions (LP) Mass Spectroscopy (MS) Neutron Fission (NF) Neutron Capture (NC) Heavy-Ion Transfer Reactions (TR) Deep Inelastic (DI) Projectile Fission or Fragmentation (PF) Charged Particle Fission (CPF) Undiscovered, predicted to be bound Mass Number (A) Year Discovered Fig. 1: Nickel isotopes as a function of time when they were discovered. The different production methods are indicated. The solid black squares on the right hand side of the plot are isotopes predicted to be bound by the HFB-14 model. 4

5 we find three counts which fulfill the conditions we impose on the TOF, on the energy loss, and on the position at the final focus ,52 Ni The 1987 paper Direct Observation of New Proton Rich Nuclei in the Region 23 Z 29 Using A 55A MeV 58 Ni Beam, reported the first observation of 51 Ni and 52 Ni by Pougheon et al. [9]. The fragmentation of a 55 A MeV 58 Ni beam at GANIL on nickel and aluminum targets were used to produce proton-rich isotopes which were separated with the LISE spectrometer. Energy loss, time of flight, and magnetic rigidity measurements were made. Here, 52 Ni (T z = 2) and 51 Ni (T z = 5/2) are identified with respectively 68 and 7 counts Ni Vieira et al. reported the observation of excited states of 53 Ni in 1976 in the paper Extension of the T z = 3/2 Beta-Delayed Proton Precursor Series to 57 Zn [10]. The Berkeley 88-in. cyclotron accelerated 16 O beams to 60 and 65 MeV which then bombarded calcium targets and 53 Ni was produced in the fusion-evaporation reaction 40 Ca( 16 O,3n). Beta-delayed protons were measured with a semiconducting counter telescope. The most reasonable source of the 1.94 MeV activity is βdelayed proton emission following the decay of 53 Ni produced via the 40 Ca( 16 O,3n) reaction. The measured half-life of 45(15) ms corresponds to the currently accepted value Ni In the paper Mass measurements of the proton-rich nuclei 50 Fe and 54 Ni, Tribble et al. reported the discovery of 54 Ni in 1977 [11]. Alpha particles accelerated to 110 MeV with the Texas A&M University 88-inch Cyclotron were used to produce the reaction 58 Ni( 4 He, 8 He) and the ejectiles were observed at the focal plane of an Enge split-pole magnetic spectrograph. The experiments provide the first observation and subsequent mass measurement of the proton-rich nuclei 50 Fe and 54 Ni. The measured β-decay energy was 7.77(5) MeV which was used to estimate a half-life of 140 ms; this is close to the adapted value of 104(7) ms Ni In the paper entitled New Proton-Rich Nuclei in the f 7/2 Shell, Proctor et al. described the discovery of 55 Ni in 1972 [12]. The Michigan State University sector-focused cyclotron accelerated 3 He to MeV and the reaction 58 Ni( 3 He, 6 He) was used to produce 55 Ni. The outgoing 6 He particles were detected in the focal plane of an Enge split-pole magnetic spectrograph. The present measurements represent the first observation of 47 Cr, 51 Fe, and 55 Ni Ni In his 1952 paper Nickel 56, Worthington reported on the discovery of 56 Ni [13]. At Berkeley, a 340 MeV proton beam irradiated zinc foils and 56 Ni was identified by measuring the decay with a Geiger counter following chemical separation. From this work it may be deduced that (1) the half-life of Ni 56 should be 6.0±0.5 days; (2) there are at least four gamma-rays associated with the disintegration, with energies of approximately 0.16, 0.5, 0.8, and >1.4 Mev; (3) the decay is mainly by electron capture rather than positron emission. The measured half-life agrees with the presently adopted value of 6.075(10) d. An independent observation [14] of 56 Ni was submitted only three weeks after 5

6 the submission of Worthington. It should be mentioned that Aston had reported tentative evidence that 56 Ni would be stable [15] Ni The discovery of 57 Ni was reported in the 1938 paper Radio Isotopes of Nickel by Livingood and Seaborg [16]. 57 Ni was observed at the University of California, Berkeley, by irradiating iron with 12.6 and 16 MeV α-particles. Positrons and γ-rays were measured following chemical separation. We wish to report a new radioactive isotope of nickel, formed as the result of the exposure of iron to several microampere hours of bombardment with helium ions at 12.6 Mev and also at 16 Mev... We have not been able to detect this activity after strong irradiation of nickel with deuterons or slow neutrons, so we feel justified in ascribing the activity to Ni 57 through Fe 54 (α,n)ni 57. The reported 36(2) h half-life agrees with the currently accepted value of 35.60(6) h Ni In the paper The Constitution of Nickel, Aston described the discovery of 58 Ni in 1921 [17]. At the Cavendish Laboratory in Cambridge, England a discharge tube with a mixture of nickel carbonyl vapor and carbon dioxide was used to obtain mass spectra. The spectrum consists of two lines, the stronger at 58 and the weaker at Nickel therefore consists of at least two isotopes Ni In 1959, Brosi et al. identified 59 Ni in 1951 as reported in the paper Characteristics of Ni 59 and Ni 63 [18]. Enriched 58 Ni targets were irradiated at the Oak Ridge reactor and activities were measured with Geiger-Müller counters following chemical separation. The data used in the calculation are given in [the table] along with estimated probable errors. These data give 7.5± yrs for the K electron capture half-life of Ni 59. This half-life agrees with the currently accepted value of y Ni In the paper The Constitution of Nickel, Aston described the discovery of 58 Ni in 1921 [17]. At the Cavendish Laboratory in Cambridge, England a discharge tube with a mixture of nickel carbonyl vapor and carbon dioxide was used to obtain mass spectra. The spectrum consists of two lines, the stronger at 58 and the weaker at Nickel therefore consists of at least two isotopes ,62 Ni The discovery of the stable isotopes 61 Ni and 62 Ni was published in the 1934 paper Constitution of Carbon, Nickel, and Cadmium by Aston [15]. The isotopes were identified with the Cavendish Laboratory mass spectrograph. The analysis of nickel by means of its carbonyl has been repeated, and the more intense mass-spectra obtained reveal two new isotopes 62 and 61. Lines at 56 and 64 present to less than 1 per cent are probably due to isotopes, but this is not yet certain. 6

7 Ni In 1959, Brosi et al. identified 63 Ni in 1951 as reported in the paper Characteristics of Ni 59 and Ni 63 [18]. Enriched 62 Ni targets were irradiated at the Oak Ridge reactor and activities were measured with Geiger-Müller counters following chemical separation. The half-life of 85 yrs for Ni 63 calculated from the data in [the table] is considerably shorter than values previously estimated from activation data. The measured half-life of 85(20) y is consistent with the presently adopted value of 101.2(15) y. Previously, an activity of 160(10) min. was assigned to either 63 Ni or 65 Ni [19], and subsequently activities of a few hours [20], 2.5 h [21], 2.60(3) h [16] and 2.6 h [22] were incorrectly assigned to 63 Ni. Livingood and Seaborg even stated: The identification with this previously known period seems to be complete [16] Ni The discovery of the stable isotopes 64 Ni was published in the 1934 paper Constitution of Carbon, Nickel, and Cadmium by Aston [15]. 64 Ni was tentatively identified with the Cavendish Laboratory mass spectrograph. The analysis of nickel by means of its carbonyl has been repeated, and the more intense mass-spectra obtained reveal two new isotopes 62 and 61. Lines at 56 and 64 present to less than 1 per cent are probably due to isotopes, but this is not yet certain Ni Swartout et al. reported the discovery of 65 Ni in the 1946 paper Mass Assignment of 2.6 h Ni 65 [23]. Enriched 63 Cu and 65 Cu were irradiated with neutrons from the Oak Ridge uranium pile. 65 Ni was formed in the (n,p) charge-exchange reaction and β- and γ-rays were measured following chemical separation. The availability of enriched copper isotopes in the Manhattan Project has now made possible a positive assignment of the 2.6 h Ni isotope to a mass number of 65. This half-life agrees with the currently accepted value of (3) h. Previously, an activity of 160(10) min. was assigned to either 63 Ni or 65 Ni [19], and subsequently activities of a few hours [20], 2.5 h [21], 2.60(3) h [16] and 2.6 h [22] were incorrectly assigned to 63 Ni. Livingood and Seaborg even stated: The identification with this previously known period seems to be complete [16] Ni The discovery of 66 Ni was reported by Goeckermann and Perlman in the 1948 publication Characteristics of Bismuth Fission with High Energy Particles [24]. 200 MeV deuterons from the 184-in Berkeley cyclotron were used to produced fragments from the fission of bismuth. The following is a list of bismuth fission products which were identified in the present studies (references are given for isotopes which only recently appeared in the literature or which have been hitherto unreported): Ca 45, Fe 59, Ni 66, Cu The half-life of 67 Cu is given in a footnote: A 56-hr. β -emitter which proved to be the parent of 5-min. Cu 66. This half-life agrees with the presently accepted value of 54.6(3) h Ni Runte et al. identified 67 Ni in the 1983 paper Decay Studies of Neutron-Rich Products from 76 Ge Induced Multinucleon Transfer Reactions Including the New Isotopes 62 Mn, 63 Fe, and 71,72,73 Cu [25]. A 9 MeV/u 76 Ge beam from the GSI UNILAC accelerator was used to bombard a natural W target. Deep inelastic reaction were produced in a graphite catcher inside a FEBIAD-E ion source and 67 Ni was identified with an on-line mass separator. In our experiment no 7

8 γ-ray activity was observe at A = 67 using a 49 s collection and counting time during a total measurement of 22 min. However, we have measured a short-lived β-activity with a half-life of T 1/2 = 21(1) s... We have tentatively assigned this activity to 67 Ni. This half-life corresponds to the currently accepted value. Previous observation of half-lives of 50(3) s [26], 18(4) s [27], and 16(4) s [28] could not be confirmed. The latter two assignments were based on γ-ray measurements which were reassigned by Runte et al. to 70 Cu Ni In their paper Masses of 62 Fe and the New Isotope 68 Ni from ( 18 O, 20 Ne) Reactions, Bhatia et al. presented the first observation of 68 Ni in 1977 [29]. At the Heidelberg MP tandem beams of 18 O with energies MeV were incident on enriched 70 Zn targets. Reaction products were detected by a E-E counter and analyzed by a Q3D Spectrograph. The utility of the ( 18 O, 20 Ne) reaction at small angles for the mass determination of highly neutron rich nuclei is demonstrated by a determination of the mass excess of 62 Fe as ( ±0.022) MeV and of 68 Ni as ( ±0.028) MeV Ni Dessagne et al. observed 69 Ni for the first time in 1984 as reported in their paper The Complex Transfer Reaction ( 14 C, 15 O) on Ni, Zn, and Ge Targets: Existence and Mass of 69 Ni [30]. A 72 MeV beam of 14 C provided by the Orsay MP tandem was incident on an enriched 70 Zn target. 69 Ni was identified by measuring the 15 O ejectiles in the double-focussing n=1/2 magnetic spectrometer BACCHUS. In the case of the 68 Zn and 70 Zn targets, the ( 14 C, 15 O) reactions clearly populate the ground states of 67 Ni and 69 Ni... The 69 Ni nucleus is observed and its mass measured here for the first time Ni In the 1987 paper Identification of the New-Neutron Rich Isotopes Ni and Cu in Thermal Neutron Fission of 235 U Armbruster et al. described the discovery of 70 Ni, 71 Ni, 72 Ni, 73 Ni, and 74 Ni [31]. At the Institut Laue-Langevin in Grenoble, France, fragments from thermal neutron induced fission of 235 U were analyzed in the LOHENGRIN recoil separator. Events associated with different elements are well enough separated to show unambiguously the occurrence of the isotopes Ni and Cu among other isotopes already known Ni In their paper New neutron-rich isotopes in the scandium-to-nickel region, produced by fragmentation of a 500 MeV/u 86 Kr beam, Weber et al. presented the first observation of 75 Ni in 1992 [32]. 75 Ni was produced in the fragmentation reaction of a 500 A MeV 86 Kr beam from the heavy-ion synchroton SIS on a beryllium target and separated with the zero-degree spectrometer FRS at GSI. The results...represent unambiguous evidence for the production of the very neutron-rich isotopes 58 Ti, 61 V, 63 Cr, 66 Mn, 69 Fe, and 71 Co, and yield indicative evidence for the production of 64 Cr, 72 Co, and 75 Ni. Two counts of 75 Ni were observed. 8

9 Ni In 1995 Engelmann et al. reported the discovery of 76 Ni, 77 Ni, and 78 Ni, in Production and Identification of Heavy Ni Isotopes: Evidence for the Doubly Magic Nucleus 78 28Ni [33]. 238 U ions were accelerated in the UNILAC and the heavy-ion synchrotron SIS at GSI to an energy of 750 A-MeV. The nickel isotopes were produced by projectile fission, separated in-flight by the FRS and identified event-by-event by measuring magnetic rigidity, energy loss and time of flight. For a total dose of U ions delivered in 132 h on the target three events can be assigned to the isotope 78 Ni. Other new nuclei, 77 Ni, 73,74,75 Co and 80 Cu can be identified, the low count rate requires a background-free measurement. One hundred thirty two, 13, and 3 counts were observed for 76 Ni, 77 Ni and 78 Ni, respectively. 76 Ni was not considered a new nucleus quoting an internal report [34]. The results of this report were subsequently published in a conference proceedings [35], however, publication in a refereed journal occurred only three years later [36]. 3. Summary The discoveries of the known nickel isotopes have been compiled and the methods of their production discussed. The identification for most isotopes was non-controversial. The few exceptions included the tentative claim that 56 Ni was stable, and an incorrect half-life measurement for 67 Ni which was corrected only 18 years later. Also, the half-life of 65 Ni was initially assigned to 63 Ni. Acknowledgments This work was supported by the National Science Foundation under grant No. PHY (NSCL). References [1] G. Q. Ginepro, J. Snyder, M. Thoennessen, At. Data. Nucl. Data. Tables 95 (2009) 805. [2] G. Audi, O. Bersillon, J. Blachot, A. H. Wapstra, Nucl. Phys. A 729 (2003) 3. [3] ENSDF, Evaluated Nuclear Structure Data File, maintained by the National Nuclear Data Center at Brookhaven National Laboratory, published in Nuclear Data Sheets (Academic Press, Elsevier Science). [4] S. Goriely, M. Samyn, J. M. Pearson, Phys. Rev. C 75 (2007) [5] H. A. Grunder, F. Selph, Annu. Rev. Nucl. Sci. 27 (1977) 353. [6] B. Blank, M. Chartier, S. Czajkowski, J. Giovinazzo, M. S. Pravikoff, J.-C. Thomas, G. de France, F. de Oliveira Santos, M. Lewitowicz, C. Borcea, R. Grzywacz, Z. Janas, M. Pfützner, Phys. Rev. Lett. 84 (2000) [7] B. Blank, S. Czajkowski, F. Davi, R. D. Moral, J. P. Dufour, A. Fleury, C. M. M. S. Pravikoff, J. Benlliure, F. Boué, R. Collatz, A. Heinz, M. Hellström, Z. Hu, E. Roeckl, M. Shibata, K. Sümmerer, Z. Janas, M. Karny, M. Pfützner, M. Lewitowicz, Phys. Rev. Lett. 77 (1996) [8] B. Blank, S. Andriamonje, R. D. Moral, J. P. Dufour, A. Fleury, T. Josso, M. S. Pravikoff, S. Czajkowski, Z. Janas, A. Piechaczek, E. Roeckl, K.-H. Schmidt, K. Sümmerer, W. Trinder, M. Weber, T. Brohm, A. Grewe, E. Hanelt, A. Heinz, A. Jonghans, C. Röhl, S. Steinhäuser, B. Voss, M. Pfützner, Phys. Rev. C 50 (1994)

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12 Explanation of Tables Table 1. Discovery of nickel isotopes Isotope Author Journal Ref. Method Laboratory Country Year Nickel isotope First author of refereed publication Journal of publication Reference Production method used in the discovery: FE: Fusion Evaporation LP: Light-Particle Reactions (including neutrons) MS: Mass Spectroscopy TR: Heavy-Ion Transfer NC: Neutron Capture Reactions PF: Projectile Fission or Fragmentation NF: Neutron Induced Fission DI: Deep Inelastic Reactions CPF: Charged-Particle Induced Fission Laboratory where the experiment was performed Country of laboratory Year of discovery 12

13 Table 1 Discovery of Nickel Isotopes. See page 12 for Explanation of Tables Isotope Author Journal Ref. Method Laboratory Country Year 48 Ni B. Blank Phys. Rev. Lett. [6] PF GANIL France Ni B. Blank Phys. Rev. Lett. [7] PF Darmstadt Germany Ni B. Blank Phys. Rev. C [8] PF Darmstadt Germany Ni F. Pougheon Z. Phys. A [9] PF GANIL France Ni F. Pougheon Z. Phys. A [9] PF GANIL France Ni D.J. Vieira Phys. Lett. B [10] FE Berkeley USA Ni R.E. Tribble Phys. Rev. C [11] LP Texas A&M USA Ni I.D. Proctor Phys. Rev. Lett. [12] LP Michigan State USA Ni W.J. Worthington Phys. Rev. [13] LP Berkeley USA Ni J.J. Livingood Phys. Rev. [16] LP Berkeley USA Ni F.W. Aston Nature [17] MS Cambridge UK Ni A.R. Brosi Phys. Rev. [18] NC Oak Ridge USA Ni F.W. Aston Nature [17] MS Cambridge UK Ni F.W. Aston Nature [15] MS Cambridge UK Ni F.W. Aston Nature [15] MS Cambridge UK Ni A.R. Brosi Phys. Rev. [18] NC Oak Ridge USA Ni F.W. Aston Nature [15] MS Cambridge UK Ni J.A. Swartout Phys. Rev. [23] LP Oak Ridge USA Ni R.H. Goeckermann Phys. Rev. [24] CPF Berkeley USA Ni E. Runte Nucl. Phys. A [25] DI Darmstadt Germany Ni T.S. Bhatia Z. Phys. A [29] TR Heidelberg Germany Ni Ph. Dessagne Nucl. Phys. A [30] TR Orsay France Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France Ni M. Weber Z. Phys. A [32] PF Darmstadt Germany Ni Ch. Engelmann Z. Phys. A [33] PF Darmstadt Germany Ni Ch. Engelmann Z. Phys. A [33] PF Darmstadt Germany Ni Ch. Engelmann Z. Phys. A [33] PF Darmstadt Germany