Atomic Data and Nuclear Data Tables 98 (2012) 95–119 Contents lists available at SciVerse ScienceDirect Atomic Data and Nuclear Data Tables journal homepage: www.elsevier.com/locate/adt Discovery of yttrium, zirconium, niobium, technetium, and ruthenium isotopes A. Nystrom, M. Thoennessen ∗ National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA article info a b s t r a c t Article history: Currently, thirty-four yttrium, thirty-five zirconium, thirty-four niobium, thirty-five technetium, and Received 13 October 2010 thirty-eight ruthenium isotopes have been observed and the discovery of these isotopes is described Received in revised form here. For each isotope a brief synopsis of the first refereed publication, including the production and 19 January 2011 identification method, is presented. Accepted 8 February 2011 ' 2012 Elsevier Inc. All rights reserved. ∗ Corresponding author. Tel.: +1 517 333 6323; fax: +1 517 353 5967. E-mail address: [email protected] (M. Thoennessen). 0092-640X/$ – see front matter ' 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.adt.2011.12.002 96 A. Nystrom, M. Thoennessen / Atomic Data and Nuclear Data Tables 98 (2012) 95–119 Contents 1. Introduction........................................................................................................................................................................................................................ 96 2. Discovery of 76–109Y............................................................................................................................................................................................................ 96 3. Discovery of 78–112Zr ..........................................................................................................................................................................................................100 4. Discovery of 82–115Nb .........................................................................................................................................................................................................103 5. Discovery of 86–120Tc ..........................................................................................................................................................................................................107 6. Discovery of 87–124Ru .........................................................................................................................................................................................................110 7. Summary ............................................................................................................................................................................................................................113 Acknowledgments .............................................................................................................................................................................................................114 References...........................................................................................................................................................................................................................114 Explanation of Tables.........................................................................................................................................................................................................116 Table 1. Discovery of yttrium, zirconium, niobium, technetium, and ruthenium isotopes....................................................................................116 1. Introduction 2. Discovery of 76–109Y The discovery of yttrium, zirconium, niobium, technetium, Thirty-four yttrium isotopes from A D 76 to 109 have been and ruthenium isotopes is described as part of the series discovered so far; these include 1 stable, 13 neutron-deficient and 120 summarizing the discovery of isotopes, beginning with the cerium 20 neutron-rich isotopes. According to the HFB-14 model [17], Y should be the last odd–odd particle stable neutron-rich nucleus isotopes in 2009 [1]. Guidelines for assigning credit for discovery while the odd–even particle stable neutron-rich nuclei should are (1) clear identification, either through decay curves and continue through 131Y. The proton dripline has most likely been relationships to other known isotopes, particle or γ -ray spectra, reached at 76Y, however, 75Y and 74Y could still have half-lives or unique mass and Z-identification, and (2) publication of the longer than 10−9 s [18]. Thus, about 19 isotopes have yet to be discovery in a refereed journal. The authors and year of the first discovered corresponding to 40% of all possible yttrium isotopes. publication, the laboratory where the isotopes were produced as Fig. 1 summarizes the year of first discovery for all yttrium well as the production and identification methods are described. isotopes identified by the method of discovery. The range of When appropriate, references to conference proceedings, internal isotopes predicted to exist is indicated on the right side of the reports, and theses are included. When a discovery includes a figure. The radioactive yttrium isotopes were produced using half-life measurement the measured value is compared to the fusion–evaporation reactions, light-particle reactions, neutron currently adopted value taken from the NUBASE evaluation [2], induced fission, spallation, and projectile fragmentation or fission. which is based on the ENSDF database [3]. In cases where the The stable isotope was identified using mass spectroscopy. Light reported half-life differed significantly from the adopted half-life particles also include neutrons produced by accelerators. The (up to approximately a factor of two), we searched the subsequent discovery of each yttrium isotope is described in detail and a literature for indications that the measurement was erroneous. If summary is presented in Table 1. that was not the case we credited the authors with the discovery in spite of the inaccurate half-life. All reported half-lives inconsistent 76Y with the presently adopted half-life for the ground state were compared to isomers' half-lives and accepted as discoveries if In the 2001 article ``Synthesis and Halflives of Heavy Nuclei appropriate following the criteria described above. Relevant for the rp-Process'', Kienle et al. first reported the 76 112 The first criterion excludes measurements of half-lives of a existence of Y[19]. A 1 A · GeV Sn beam from the synchrotron 76 given element without mass identification. This affects mostly SIS at GSI, Germany, bombarded a beryllium target. Y was isotopes first observed in fission where decay curves of chemically identified with the FRS fragment separator by both magnetic separated elements were measured without the capability to deflection and by measuring the energy loss and time-of-flight determine their mass. Also the four-parameter measurements (see, of the fragments. ``The spectra show the previously unobserved D − 76 78 for example, Ref. [4]) were, in general, not considered because the T 1 nuclei Y (2 events) and Zr (one event) and demonstrate 81 mass identification was only ±1 mass unit. the absence of Nb...''. The second criterion affects especially the isotopes studied 77Y within the Manhattan Project. Although an overview of the results was published by Wiley in 1946 [5], most of the papers were only 77Y was first reported in ``Observation of the Z D N C 1 Nuclei published in the ``Plutonium Project Records of the Manhattan 77Y, 79Zr, and 83Mo'' in 1999 by Janas et al. [20]. At GANIL, France, Project Technical Series, Vol. 9A, Radiochemistry and the Fission 39 40 42 nickel targets were bombarded with a 60 MeV/nucleon 92Mo beam. Products'', in three books in 1951 [6]. We considered this first 77Y was separated with the LISE3 spectrometer and the kinetic unclassified publication to be equivalent to a refereed paper. Good energy, energy loss, and time-of-flight were measured. ``In the examples why publications in conference proceedings should not 77 118 120 region expected for 39Y, [the figure] clearly shows a peak indicating be considered are Tc and Ru, which had been reported as that the half-life of this isotope is longer than 0.5 ms, the flight time being discovered in a conference proceeding [7] but not in the through the LISE3 spectrometer''. subsequent refereed publication [8]. The initial literature search was performed using the databases 78Y ENSDF [3] and NSR [9] of the National Nuclear Data Center at Brookhaven National Laboratory. These databases are complete The discovery of 78Y is credited to Yennello et al. with the and reliable back to the early 1960's. For earlier references, several 1992 paper ``New Nuclei Along the Proton-Drip Line Near Z D editions of the Table of Isotopes [10–15] were used. A good 40'', [21]. At the National Superconducting Cyclotron Laboratory at reference for the discovery of stable isotopes was the second Michigan State University, a 70 MeV=A92Mo beam was produced edition of Aston's book ``Mass Spectra and Isotopes'' [16]. by the K1200 cyclotron and impinged on a 58Ni target. 78Y was A. Nystrom, M. Thoennessen / Atomic Data and Nuclear Data Tables 98 (2012) 95–119 97 provided beams of 75–110 MeV 24Mg and 91–110 MeV 25Mg that then bombarded enriched 58Ni targets. 80Y and 81Y were produced in the fusion–evaporation