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Discovery of the

R. Robinson, M. Thoennessen∗ National Superconducting Cyclotron Laboratory and Department of Physics and , 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 a brief summary of the first refereed publication, including the production and identification method, is presented.

∗Corresponding author. Email address: [email protected] (M. Thoennessen)

Preprint submitted to Atomic Data and Tables April 29, 2010 Contents 1. Introduction ...... 2 2. Discovery of 48−78Ni...... 3 2.1. 48Ni...... 3 2.2. 49Ni...... 3 2.3. 50Ni...... 3 2.4. 51,52Ni...... 5 2.5. 53Ni...... 5 2.6. 54Ni...... 5 2.7. 55Ni...... 5 2.8. 56Ni...... 5 2.9. 57Ni...... 6 2.10. 58Ni...... 6 2.11. 59Ni...... 6 2.12. 60Ni...... 6 2.13. 61,62Ni...... 6 2.14. 63Ni...... 7 2.15. 64Ni...... 7 2.16. 65Ni...... 7 2.17. 66Ni...... 7 2.18. 67Ni...... 7 2.19. 68Ni...... 8 2.20. 69Ni...... 8 2.21. 70−74Ni...... 8 2.22. 75Ni...... 8 2.23. 76−78Ni...... 9 3. Summary ...... 9 References ...... 9 Explanation of Tables ...... 12 Table 1. Discovery of Nickel Isotopes. See page 12 for Explanation of Tables ...... 13

1. Introduction

The discovery of the nickel isotopes is discussed as part of the series of the discovery of isotopes which began with the 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 and Z-identification, and (2) publication of the 2 discovery in a refereed journal. The authors and 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 48−78Ni

Thirty-one nickel isotopes from A = 48−78 have been discovered so far; these include 5 stable, 11 -rich and 15 -rich isotopes. According to the HFB-14 model [4], 87Ni should be the last odd-even particle stable neutron-rich nucleus while the even-even particle stable neutron-rich nuclei should continue through 94Ni. At the proton dripline 47Ni 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), neutron- induced 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 (MS). Heavy ions are all nuclei with an larger than A=4 [5]. In the following, the discovery of each nickel isotope is discussed in detail.

2.1. 48Ni

In the paper “Discovery of Doubly Magic 48Ni”, Blank et al. reported the discovery of 48Ni in 2000 [6]. A natural nickel target was bombarded by a 74.5 MeV/ beam of 58Ni from the GANIL cyclotrons. 48Ni 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 48Ni are clearly observed... In this spectrum, we observe four counts which can be unambiguously attributed to 48Ni.”

2.2. 49Ni

45 49 In the paper “First Observation of the Tz = −7/2 Nuclei Fe and Ni,” Blank et al. reported the discovery of 49Ni in 1996 [7]. A 600 A·MeV 58Ni beam from the SIS synchrotron bombarded a target and isotopes were separated with the projectile-fragment separator FRS. 49Ni was identified by time-of-flight, ∆E, and Bρ analysis. “We observed ten events of 42Cr, three events of 45Fe, and five events of 49Ni. These three isotopes have been identified for the first time in the present experiment.”

2.3. 50Ni

The 1994 paper “Production cross sections and the particle stability of proton-rich nuclei from 58Ni fragmentation” reported the discovery of 50Ni by Blank et al. [8]. A 650 MeV/nucleon beam of 58Ni from the SIS synchrotron bombarded a beryllium target and 50Ni was separated and identified using the FRS separator. “For the yet-unobserved isotope 50Ni,

3 qae ntergthn ieo h ltaeiooe rdce ob on yteHB1 model. HFB-14 the by bound be to predicted isotopes are plot the of side hand right the on squares 1 Fig. ikliooe safnto ftm hnte eedsoee.Tedffrn rdcinmtosaeidctd h oi black solid The indicated. are methods production different The discovered. were they when time of function a as isotopes Nickel :

Mass Number (A) 100 40 50 60 70 80 90 1910 1920 Fusion EvaporationReactions(FE) Undiscovered, predictedtobebound Char Projectile FissionorFragmentati Deep Inelastic(DI) Heavy-Ion (NC) Neutron Fission(NF) Mass Spectroscopy(MS) Light ParticleReactions(LP) 1930 ged ParticleFission(CPF) 1940 T ransfer Reactions(TR) 1950 Y ear Discovered 4 1960 1970 on (PF) 1980 1990 2000 2010 2020 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.”

2.4. 51,52Ni

The 1987 paper “Direct Observation of New Proton Rich Nuclei in the Region 23≤Z≤29 Using A 55A·MeV 58Ni Beam,” reported the first observation of 51Ni and 52Ni by Pougheon et al. [9]. The fragmentation of a 55 A·MeV 58Ni 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, 52Ni 51 (Tz = −2) and Ni (Tz = −5/2) are identified with respectively 68 and 7 counts.”

2.5. 53Ni

53 Vieira et al. reported the observation of excited states of Ni in 1976 in the paper “Extension of the Tz = −3/2 -Delayed Proton Precursor Series to 57Zn” [10]. The Berkeley 88-in. cyclotron accelerated 16O beams to 60 and 65 MeV which then bombarded targets and 53Ni was produced in the fusion-evaporation reaction 40Ca(16O,3n). Beta-delayed were measured with a semiconducting counter telescope. “The most reasonable source of the 1.94 MeV activity is βdelayed following the decay of 53Ni produced via the 40Ca(16O,3n) reaction.” The measured half-life of 45(15) ms corresponds to the currently accepted value.

2.6. 54Ni

In the paper “Mass measurements of the proton-rich nuclei 50Fe and 54Ni,” Tribble et al. reported the discovery of 54Ni in 1977 [11]. Alpha particles accelerated to 110 MeV with the Texas A&M University 88-inch Cyclotron were used to produce the reaction 58Ni(4He,8He) 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 50Fe and 54Ni.” The measured β- 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.

2.7. 55Ni

55 In the paper entitled “New Proton-Rich Nuclei in the f7/2 Shell,” Proctor et al. described the discovery of Ni in 1972 [12]. The Michigan State University sector-focused cyclotron accelerated 3He to 65−75 MeV and the reaction 58Ni(3He,6He) was used to produce 55Ni. The outgoing 6He particles were detected in the focal plane of an Enge split-pole magnetic spectrograph. “The present measurements represent the first observation of 47Cr, 51Fe, and 55Ni.”

2.8. 56Ni

In his 1952 paper “Nickel 56,” Worthington reported on the discovery of 56Ni [13]. At Berkeley, a 340 MeV proton beam irradiated foils and 56Ni 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 Ni56 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 capture rather than .” The measured half-life agrees with the presently adopted value of 6.075(10) d. An independent observation [14] of 56Ni was submitted only three weeks after

5 the submission of Worthington. It should be mentioned that Aston had reported tentative evidence that 56Ni would be stable [15].

2.9. 57Ni

The discovery of 57Ni was reported in the 1938 paper “Radio ” by Livingood and Seaborg [16]. 57Ni was observed at the University of California, Berkeley, by irradiating 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 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 , so we feel justified in ascribing the activity to Ni57 through Fe54(α,n)Ni57.” The reported 36(2) h half-life agrees with the currently accepted value of 35.60(6) h.

2.10. 58Ni

In the paper “The Constitution of Nickel,” Aston described the discovery of 58Ni in 1921 [17]. At the Cavendish Laboratory in Cambridge, England a discharge tube with a mixture of nickel carbonyl vapor and dioxide was used to obtain mass spectra. “The spectrum consists of two lines, the stronger at 58 and the weaker at 60... Nickel therefore consists of at least two isotopes.”

2.11. 59Ni

In 1959, Brosi et al. identified 59Ni in 1951 as reported in the paper “Characteristics of Ni59 and Ni63” [18]. Enriched 58Ni targets were irradiated at the Oak Ridge reactor and activities were measured with Geiger-M¨ullercounters following chemical separation. “The data used in the calculation are given in [the table] along with estimated probable errors. These data give 7.5±1.3×104 yrs for the K half-life of Ni59.” This half-life agrees with the currently accepted value of 7.6×104 y.

2.12. 60Ni

In the paper “The Constitution of Nickel,” Aston described the discovery of 58Ni 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 60... Nickel therefore consists of at least two isotopes.”

2.13. 61,62Ni

The discovery of the stable isotopes 61Ni and 62Ni was published in the 1934 paper “Constitution of Carbon, Nickel, and ” 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 2.14. 63Ni

In 1959, Brosi et al. identified 63Ni in 1951 as reported in the paper “Characteristics of Ni59 and Ni63” [18]. Enriched 62Ni targets were irradiated at the Oak Ridge reactor and activities were measured with Geiger-M¨ullercounters following chemical separation. “The half-life of 85 yrs for Ni63 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 63Ni or 65Ni [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 63Ni. Livingood and Seaborg even stated: “The identification with this previously known seems to be complete” [16].

2.15. 64Ni

The discovery of the stable isotopes 64Ni was published in the 1934 paper “Constitution of Carbon, Nickel, and Cadmium” by Aston [15]. 64Ni 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.”

2.16. 65Ni

Swartout et al. reported the discovery of 65Ni in the 1946 paper “Mass Assignment of 2.6 h Ni65” [23]. Enriched 63Cu and 65Cu were irradiated with neutrons from the Oak Ridge pile. 65Ni was formed in the (n,p) charge-exchange reaction and β- and γ-rays were measured following chemical separation. “The availability of enriched isotopes in the has now made possible a positive assignment of the 2.6 h Ni isotope to a of 65.” This half-life agrees with the currently accepted value of 2.5172(3) h. Previously, an activity of 160(10) min. was assigned to either 63Ni or 65Ni [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 63Ni. Livingood and Seaborg even stated: “The identification with this previously known period seems to be complete” [16].

2.17. 66Ni

The discovery of 66Ni was reported by Goeckermann and Perlman in the 1948 publication “Characteristics of 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): Ca45, Fe59, Ni66, Cu67...” The half-life of 67Cu is given in a footnote: “A 56-hr. β−-emitter which proved to be the parent of 5-min. Cu66.” This half-life agrees with the presently accepted value of 54.6(3) h.

2.18. 67Ni

Runte et al. identified 67Ni in the 1983 paper “Decay Studies of Neutron-Rich Products from 76Ge Induced Multinu- cleon Transfer Reactions Including the New Isotopes 62Mn, 63Fe, and 71,72,73Cu” [25]. A 9 MeV/u 76Ge beam from the GSI UNILAC accelerator was used to bombard a natural W target. Deep inelastic reaction were produced in a catcher inside a FEBIAD-E ion source and 67Ni was identified with an on-line mass separator. “In our experiment no 7 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 T1/2 = 21(1) s... We have tentatively assigned this activity to 67Ni.” 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 70Cu.

2.19. 68Ni

In their paper “Masses of 62Fe and the New Isotope 68Ni from (18O,20Ne) Reactions,” Bhatia et al. presented the first observation of 68Ni in 1977 [29]. At the Heidelberg MP tandem beams of 18O with energies 81-84 MeV were incident on enriched 70Zn targets. Reaction products were detected by a ∆E-E counter and analyzed by a Q3D Spectrograph. “The utility of the (18O,20Ne) reaction at small angles for the mass determination of highly neutron rich nuclei is demonstrated by a determination of the mass excess of 62Fe as (−58.946±0.022) MeV and of 68Ni as (−63.466±0.028) MeV.”

2.20. 69Ni

Dessagne et al. observed 69Ni for the first time in 1984 as reported in their paper “The Complex Transfer Reaction (14C,15O) on Ni, Zn, and Ge Targets: Existence and Mass of 69Ni” [30]. A 72 MeV beam of 14C provided by the Orsay MP tandem was incident on an enriched 70Zn target. 69Ni was identified by measuring the 15O ejectiles in the double-focussing n=1/2 magnetic spectrometer BACCHUS. “In the case of the 68Zn and 70Zn targets, the (14C,15O) reactions clearly populate the ground states of 67Ni and 69Ni... The 69Ni nucleus is observed and its mass measured here for the first time.”

2.21. 70−74Ni

In the 1987 paper “Identification of the New-Neutron Rich Isotopes 70−74Ni and 74−77Cu in Thermal Neutron Fission of 235U” Armbruster et al. described the discovery of 70Ni, 71Ni, 72Ni, 73Ni, and 74Ni [31]. At the Institut Laue-Langevin in Grenoble, France, fragments from thermal neutron induced fission of 235U were analyzed in the LOHENGRIN recoil separator. “Events associated with different elements are well enough separated to show unambiguously the occurrence of the isotopes 70−74Ni and 74−77Cu among other isotopes already known.”

2.22. 75Ni

In their paper “New neutron-rich isotopes in the -to-nickel region, produced by fragmentation of a 500 MeV/u 86Kr beam,” Weber et al. presented the first observation of 75Ni in 1992 [32]. 75Ni was produced in the fragmentation reaction of a 500 A·MeV 86Kr 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 58Ti, 61V, 63Cr, 66Mn, 69Fe, and 71Co, and yield indicative evidence for the production of 64Cr, 72Co, and 75Ni.” Two counts of 75Ni were observed.

8 2.23. 76−78Ni

In 1995 Engelmann et al. reported the discovery of 76Ni, 77Ni, and 78Ni, in “Production and Identification of Heavy 78 238 Ni Isotopes: Evidence for the Doubly Magic Nucleus 28Ni” [33]. 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 1013 U ions delivered in 132 h on the target three events can be assigned to the isotope 78Ni. Other new nuclei, 77Ni, 73,74,75Co and 80Cu can be identified, the low count rate requires a background-free measurement.” One hundred thirty two, 13, and 3 counts were observed for 76Ni, 77Ni and 78Ni, respectively. 76Ni 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 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 56Ni was stable, and an incorrect half-life measurement for 67Ni which was corrected only 18 years later. Also, the half-life of 65Ni was initially assigned to 63Ni.

Acknowledgments

This work was supported by the National Science Foundation under grant No. PHY06-06007 (NSCL).

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11 Explanation of Tables

Table 1. Discovery of nickel isotopes

Isotope Nickel isotope Author First author of refereed publication Journal Journal of publication Ref. Reference Method 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 Laboratory where the experiment was performed Country Country of laboratory Year Year of discovery

12 Table 1 Discovery of Nickel Isotopes. See page 12 for Explanation of Tables Isotope Author Journal Ref. Method Laboratory Country Year

48Ni B. Blank Phys. Rev. Lett. [6] PF GANIL France 2000 49Ni B. Blank Phys. Rev. Lett. [7] PF Darmstadt Germany 1996 50Ni B. Blank Phys. Rev. C [8] PF Darmstadt Germany 1994 51Ni F. Pougheon Z. Phys. A [9] PF GANIL France 1987 52Ni F. Pougheon Z. Phys. A [9] PF GANIL France 1987 53Ni D.J. Vieira Phys. Lett. B [10] FE Berkeley USA 1976 54Ni R.E. Tribble Phys. Rev. C [11] LP Texas A&M USA 1977 55Ni I.D. Proctor Phys. Rev. Lett. [12] LP Michigan State USA 1972 56Ni W.J. Worthington Phys. Rev. [13] LP Berkeley USA 1952 57Ni J.J. Livingood Phys. Rev. [16] LP Berkeley USA 1938 58Ni F.W. Aston Nature [17] MS Cambridge UK 1921 59Ni A.R. Brosi Phys. Rev. [18] NC Oak Ridge USA 1951 60Ni F.W. Aston Nature [17] MS Cambridge UK 1921 61Ni F.W. Aston Nature [15] MS Cambridge UK 1934 62Ni F.W. Aston Nature [15] MS Cambridge UK 1934 63Ni A.R. Brosi Phys. Rev. [18] NC Oak Ridge USA 1951 64Ni F.W. Aston Nature [15] MS Cambridge UK 1934 65Ni J.A. Swartout Phys. Rev. [23] LP Oak Ridge USA 1946 66Ni R.H. Goeckermann Phys. Rev. [24] CPF Berkeley USA 1948 67Ni E. Runte Nucl. Phys. A [25] DI Darmstadt Germany 1983 68Ni T.S. Bhatia Z. Phys. A [29] TR Heidelberg Germany 1977 69Ni Ph. Dessagne Nucl. Phys. A [30] TR Orsay France 1984 70Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France 1987 71Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France 1987 72Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France 1987 73Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France 1987 74Ni P. Armbruster Europhys. Lett. [31] NF Grenoble France 1987 75Ni M. Weber Z. Phys. A [32] PF Darmstadt Germany 1992 76Ni Ch. Engelmann Z. Phys. A [33] PF Darmstadt Germany 1995 77Ni Ch. Engelmann Z. Phys. A [33] PF Darmstadt Germany 1995 78Ni Ch. Engelmann Z. Phys. A [33] PF Darmstadt Germany 1995

13