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Platinum Metals Rev., 2014, 58, (1), 38


The Discoverers of the Isotopes of the Platinum Group of Elements: Update 2014

A resolution of the discovery circumstances of 1950s plus new isotopes found for Ru

    • John W. Arblaster
    • Wombourne, West Midlands, UK



Further to a previous update (1), a new investigation of the discovery circumstances of 195Os by Juan Flegen (2) has shown that Baró and Rey almost certainly discovered this isotope in 1957 (3, 4). A previous suggestion that they had only observed the isotope 81Rb was due to a misunderstanding which was only resolved by a critical assessment of the papers of Rey and Baró by Birch et al. (5). In addition Reed et al. (6) have identified an isomer of 195Os by determining the half-life on the bare nucleus, Os76+. They obtained 32+154–16 m for the half-life which NUBASE 2012 (7) normalised to a value of 2 ± 1.7 h. The details surrounding the discoveries of 195Os isotopes are summarised in Table I. In addition the new isotopes 85Ru and 86Ru have been discovered at the RIKEN Nishina Center in Japan (8) with the discovery circumstances summarised in Table II. Table III shows the total number of isotopes to date for each platinum group element.

Table I

The Discoverers of the 195Os Isotopes

Mass numberHalf-lifeDecay modesYear of discoveryDiscoverersReferences
195 6.5 min β? 1957 Baró and Rey 3, 4
195m 2 h β?, IT? 2012 Reed et al. 6
Table II

New Isotopes of Ruthenium

Mass numberHalf-lifeDecay modesYear of discoveryDiscoverersReferences
85 ps EC + β+? 2013 Suzuki et al. 8
86 ps EC + β+? 2013 Suzuki et al. 8

[i] ps: Particle stable (resistant to proton and neutron decay)

[ii] EC: Orbital electron capture in which the nucleus captures an extranuclear (orbital) electron which reacts with a proton to form a neutron and a neutrino, so that the mass number of the daughter nucleus remains the same but the atomic number decreases by one

[iii] β+: Beta or proton decay for nuclear deficient nuclides is the emission of a positron (and a neutrino) as a proton in the nucleus decays to a neutron. As with EC the mass number of the daughter nuclide remains the same but the atomic number decreases by one. However this decay mode cannot occur unless the decay energy exceeds 1.022 MeV (twice the electron mass in energy units)

Table III

Total Number of Isotopes and Mass Ranges Known for Each Platinum Group Element to 2014

ElementNumber of known isotopesKnown mass number ranges
Ru 40 85–124
Rh 38 89–126
Pd 38 91–128
Os 43 161–203
Ir 42 164–205
Pt 44 166–209



  1. J. W. Arblaster, Platinum Metals Rev., 2012, 56, (4), 271 LINK
  2. J. Flegen private communication to J. W. Arblaster, June 2013
  3. G. Baró and P. Rey, Z. Naturforsch., 1957, 129, (6), 520
  4. P. Rey and G. Baró, Publs. Com. Nucl. Energia Atòmica (Buenos Aires) Ser. Quim., 1957, 1, (10), 115
  5. M. Birch, J. Flegenheimer, Z. Schaedig, B. Singh and M. Thoennessen, Preprint arXiv: 1312.3985v1 [nucl-ex], 14th December, 2013 LINK
  6. M. W. Reed, P. M. Walker, I. J. Cullen, Yu. A. Litvinov, S. Shubina, G. D. Dracoulis, K. Blaum, F. Bosch, C. Brandau, J. J. Carroll, D. M. Cullen, A. Y. Deo, B. Detwiler, C. Dimopoulou, G. X. Dong, F. Farinon, H. Geissel, E. Haettner, M. Heil, R. S. Kempley, R. Knöbel, C. Kozhuharov, J. Kurcewicz, N. Kuzminchuk, S. Litvinov, Z. Liu, R. Mao, C. Nociforo, F. Nolden, W. R. Plaβ, Zs. Podolyak, A. Prochazka, C. Scheidenberger, M. Steck, Th. Stöhlker, B. Sun, T. P. D. Swan, G. Trees, H. Weick, N. Winckler, M. Winkler, P. J. Woods, F. R. Xu and T. Yamaguchi, Phys. Rev. C, 2012, 86, (5), 054321 LINK
  7. G. Audi, F. G. Kondev, M. Wang, B. Pfeiffer, X. Sun, J. Blachot and M. MacCormick, Chinese Phys. C, 2012, 36, (12), 1157 LINK
  8. H. Suzuki, T. Kubo, N. Fukuda, N. Inabe, D. Kameda, H. Takeda, K. Yoshida, K. Kusaka, Y. Yanagisawa, M. Ohtake, H. Sato, Y. Shimizu, H. Baba, M. Kurokawa, T. Ohnishi, K. Tanaka, O. B. Tarasov, D. Bazin, D. J. Morrissey, B. M. Sherrill, K. Ieki, D. Murai, N. Iwasa, A. Chiba, Y. Ohkoda, E. Ideguchi, S. Go, R. Yokoyama, T. Fujii, D. Nishimura, H. Nishibata, S. Momota, M. Lewitowicz, G. DeFrance, I. Celikovic and K. Steiger, Preprint arXiv:1310.5945v1 [nucl-ex], 22nd October, 2013 LINK

The Author

John W. Arblaster is interested in the history of science and the evaluation of the thermodynamic and crystallographic properties of the elements. Now retired, he previously worked as a metallurgical chemist in a number of commercial laboratories and was involved in the analysis of a wide range of ferrous and non-ferrous alloys.

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