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Virtual Issue 4 ‘The Discoverers of the PGM Isotopes’ January 2012

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VIRTUAL ISSUE 4 ‘THE DISCOVERERS OF THE PGM ISOTOPES’ JANUARY 2012 Contents Note: all page numbers are as originally published

The PGM Isotopes Discovered between 1931–2010

The Discoverers of the Platinum Isotopes By J. W. Arblaster Original publication: Platinum Metals Rev., 2000, 44, (4), 173

The Discoverers of the Iridium Isotopes By J. W. Arblaster Original publication: Platinum Metals Rev., 2003, 47, (4), 167

The Discoverers of the Osmium Isotopes By J. W. Arblaster Original publication: Platinum Metals Rev., 2004, 48, (4), 173

The Discoverers of the Palladium Isotopes By J. W. Arblaster Original publication: Platinum Metals Rev., 2006, 50, (2), 97

The Discoverers of the Rhodium Isotopes By John W. Arblaster Original publication: Platinum Metals Rev., 2011, 55, (2), 124

The Discoverers of the Ruthenium Isotopes By John W. Arblaster Original publication: Platinum Metals Rev., 2011, 55, (4), 251

Compiled by the Editorial Team: Jonathan Butler (Publications Manager); Sara Coles (Assistant Editor); Ming Chung (Editorial Assistant); Keith White (Principal Information Scientist) Platinum Metals Review, Johnson Matthey Plc, Orchard Road, Royston, Hertfordshire SG8 5HE, UK Email: [email protected]

The Discoverers of the Iridium Isotopes

THE THIRTY-SIX KNOWN IRIDIUM ISOTOPES FOUND BETWEEN 1934 AND 2001

By J. W. Arblaster Coleshill Laboratories, Gorsey Lane, Coleshill, West Midlands B46 1JU, U.K.

This paper is the second in a series of reviews of work performed that led up to the discoveries of the isotopes of the six platinum group elements. The first review, on platinum isotopes, was published in this Journal in October 2000 (1). Here, a brief history of the discovery of the thirty-six known isotopes of iridium in the sixty-seven years from the first discovery in 1934 to 2001 is considered in terms of the discoverers.

Of the thirty-six isotopes of iridium known Laboratory, University of Rome, identified a 20 today, only two occur naturally with the following hour activity (activity is generally used to indicate authorised isotopic abundances (2): the half-life of a non-specified isotope) after bombarding iridium with slow neutrons (9). In 1935, the same group (10) refined the half- The Naturally Occurring Isotopes of Iridium life to 19 hours, although Sosnowski (11) was Mass number Isotopic abundance, % unable to confirm this period but instead obtained activities of 50 minutes and three days for the half- 191 Ir 37.3 lifes. In 1936, Amaldi and Fermi (12) also discov- 193 Ir 62.7 ered an activity which they assigned to iridium, but its half-life was 60 days. In the same year Cork and Although Arthur J. Dempster (3) is credited Lawrence (13) bombarded platinum with with the discovery of these two isotopes at the deuterons (deuterium ions) and obtained activities University of Chicago, Illinois, in late 1935, using a with half-lifes of 28 minutes and 8.5 hours which new type of mass spectrograph that he had devel- they claimed were definitely associated with iridi- oped; earlier that year Venkatesachar and Sibaiya um following chemical identification. In 1937 (4) of the Department of Physics, Central College, Pool, Cork and Thornton (14) bombarded iridium Bangalore, India, had observed isotopic shifts in with neutrons and obtained a 15 hour activity the hyperfine arc spectrum of iridium which they which was very similar to that obtained by Fermi suggested were due to masses 191 and 193 in the and colleagues back in 1934. approximate ratio of 1:2. At that time, this seemed However, although in 1935 Dempster (3) had to be incorrect as it resulted in an atomic weight identified the naturally occurring isotopes, and the for iridium of 192.4 which was much lower than various radioactive discoveries could probably be the then accepted value of 193.1 (5). However, in assigned to the missing 192Ir, 194Ir or 195Ir, Livingston 1936, Sampson and Bleakney (6) carried out a pre- and Bethe (15), in a review in 1937, concluded that cision determination of the isotopic ratio using a the situation was confused and that no firm mass mass spectrograph. This confirmed the above assignments could be given at that time. However, approximate ratio and eventually, in 1953, the in the same year McMillan, Kamen and Ruben of atomic weight was lowered to 192.2 (7). the Department of Physics and Chemistry at the University of California (16) confirmed the 19 Artificial Iridium Isotopes hour activity of Fermi and colleagues (9, 10) and Almost immediately after the published discov- correctly assigned it to 194Ir while they also con- ery of artificial radioactivity by Curie and Joliot in firmed the 60 day activity of Amaldi and Fermi 1934 (8), Fermi and colleagues of the Physics (12) which they assigned to 192Ir. Actually

Platinum Metals Rev., 2003, 47, (4), 167174 167 Enrico Fermi 19011954 The physicist Enrico Fermi was born in Rome, Italy. In 1926 Fermi discovered the statistical laws governing the behaviour of particles of quantum spin one half, which are now known as fermions. A year later he became Professor of Theoretical Physics at the University of Rome where he evolved the theory of beta decay. In 1934 he set up the group which led to the discovery of numerous artificial radioactive isotopes obtained by bombarding elements with neutrons and for this he received the 1938 Nobel Prize in Physics. Immediately afterwards he moved to the United States, first to Columbia University, then to the University of Chicago to be Professor of Nuclear Studies. He was a leading member of the team that produced, on 2nd December 1942, the first controlled nuclear chain reaction. After the war he concentrated on high energy physics and cosmic rays. Element 100 is named fermium in his honour University of Chicago, courtesy of AIP Emilio Segrè Visual Archives

Philip John Woods Professor of Nuclear Physics at the University of Edinburgh. Philip Woods is a spokesman of a British- American collaboration that has performed experiments at the Argonne National Laboratory, Chicago, resulting in the discovery and measurement of a large number of proton-emitting isotopes. These include the four most unstable iridium isotopes from 164Ir to 167Ir. The object to the right of Philip Woods is the pioneering double- sided silicon strip detector (DSSD) used to identify iridium isotopes by their radioactive decays

Platinum Metals Rev., 2003, 47, (4) 168 The Discoverers of the Iridium Isotopes

Mass number Half-life Decay modes Year of Discoverers Ref. Notes discovery*

164m 100 ms p 2000 1: Kettunen et al. 22 A 2: Mahmud et al. 23 165m 300 ms p, a 1995 Davids et al. 20, 21 166 10.5 ms a, p 1995 Davids et al. 20, 21 166m 15.1 ms a, p 1981 Hofmann et al. 25 B 167 35.2 ms a, p, EC + b+ 1995 Davids et al. 20, 21 167m 30.0 ms a, EC + b+?, p 1981 Hofmann et al. 25 C 168 125 ms a?, EC + b+? 1978 Cabot et al. 27 D 168m 161 ms a 1995 Page et al. 26 169 780 ms a, EC + b+? 1999 Poli et al. 28 E 169m 310 ms a, EC + b+ 1978 1: Cabot et al. 27 F 2: Schrewe et al. 29 170 870 ms EC + b+, a 1995 Page et al. 26 G 170m 440 ms EC + b+, IT, a 1977 1: Cabot et al. 31 H 2: Schrewe et al. 29 171 3.2 s a, EC + b+, p? 2001 Rowe et al. 32 171m 1.40 s a, EC + b+, p? 1966 Siivola 19 I 172 4.4 s EC + b+, a 1991 Schmidt-Ott et al. 34, 35 172m 2.0 s EC + b+, a 1966 Siivola 19 J 173 9.0 s EC + b+, a 1991 1: Bouldjedri et al. 36 2: Schmidt-Ott et al. 34, 35 173m 2.20 s EC + b+, a 1966 Siivola 19 K 174 9 s EC + b+, a 1991 1: Bouldjedri et al. 36 2. Schmidt-Ott et al. 34, 35 174m 4.9 s EC + b+, a 1966 Siivola 19 L 175 9 s EC + b+, a 1966 Siivola 19 176 8 s EC + b+, a 1966 Siivola 19 177 30 s EC + b+, a 1966 Siivola 19 178 12 s EC + b+ 1970 Akhmadzhanov et al. 37, 38 179 1.32 min EC + b+ 1971 Nadzhakov et al. 39 M 180 1.5 min EC + b+ 1970 1: Akhmadzhanov et al. 37, 38 2: Nadzhakov et al. 39 181 4.90 min EC + b+ 1970 1: Akhmadzhanov et al. 37, 38 2: Nadzhakov et al. 39 182 15 min EC + b+ 1961 Diamond et al. 40 183 58 min EC + b+ 1960 1: Lavrukhina, Malysheva 41 and Khotin 2: Diamond et al. 40 184 3.09 h EC + b+ 1960 1: Baranov et al. 42 2: Diamond et al. 40 185 14.4 h EC + b+ 1958 Diamond and Hollander 43 186 16.64 h EC + b+ 1957 Scharff-Goldhaber et al. 44 N 186m 1.92 h EC + b+, IT? 1962 Bonch-Osmolovskaya et al. 46 187 10.5 h EC + b+ 1958 Diamond and Hollander 43 187m 30.03 ms IT 1962 Ramaev, Gritsyna and Korda 47 188 41.5 h EC + b+ 1950 Chu 48 188m 4.2 ms IT, EC + b+ 1970 Goncharov et al. 49 189 13.2 d EC 1955 Smith and Hollander 45 189m1 13.3 ms IT 1962 Ramaev, Gritsyna and Korda 47 189m2 3.7 ms IT 1974 1: André et al. 50 2: Kemnitz et al. 51

* The year of discovery is taken as available manuscript and conference dates. Where these are not available then the year of discovery is the publishing date

Platinum Metals Rev., 2003, 47, (4) 169 The Discoverers of the Iridium Isotopes (cont.)

Mass number Half-life Decay modes Year of Discoverers Ref. Notes discovery*

190 11.78 d EC + b+ 1946 Goodman and Pool 52 190m1 1.120 h IT 1964 Harmatz and Handley 53 190m2 3.087 h EC + b+, IT 1950 Chu 48 191 Stable – 1935 Dempster 3 191m 4.94 s IT 1954 1: Butement and Poë 54 2: Mihelich, McKeown 55 and Goldhaber 3: Naumann and Gerhart 56 192 78.831 d b–, EC 1937 McMillan, Kamen and Ruben 16 O 192m1 1.45 min IT, b– 1947 Goldhaber, Muehlhouse 57 P and Turkel 192m2 241 y IT 1959 Scharff-Goldhaber and McKeown 58 Q 193 Stable – 1935 Dempster 3 193m 10.53 d IT 1956 Boehm and Marmier 60 194 19.28 h b– 1937 McMillan, Kamen and Ruben 16 R 194m1 31.85 ms IT 1959 Campbell and Fettweiss 61 194m2 171 d b– 1968 Sunjar, Scharff-Goldhaber 62 S and McKeown 195 2.5 h b– 1952 Christian, Mitchell and Martin 65 195m 3.8 h b–, IT 1967 Hofstetter and Daly 66 196 52 s b– 1966 Venach, Münzer and Hille 67 T 196m 1.40 h b–, IT? 1966 Jansen and Pauw 69 U 197 5.8 min b– 1952 Christian, Mitchell and Martin 65 V 197m 8.9 min b–, IT? 1976 Petry et al. 72, 73 W 198 8 s b– 1972 Schweden and Kaffrell 74 X 199 (20 s) b– 1992 Zhao et al. 76 Y

Notes to the Table

A 164 m Ir Mahmud et al. (23) considered that the nuclide observed was an isomeric state not the +62 ground state. The half-life is a weighted average of 113 –30 μs determined by Kettunen et +46 al. (22) and 58 –18 μs determined by Mahmud et al. (23). B 166 m Ir Only the alpha energy was measured. The half-life was determined by Page et al. in 1995 (26) while the isomeric state assignment was by Davids et al. (21). C 167 m Ir Only the alpha energy was measured. The half-life was determined by Page et al. in 1995 (26) while the isomeric state assignment was by Davids et al. (21). D 168 Ir Only the alpha energy was measured. The half-life was determined by Page et al. in 1995 (26). 169 +462 E Ir The half-life was normalised from 638 –237 ms determined by Poli et al. in 1999 (28). F 169 m Ir The isomeric state assignment was by Poli et al. (28). The half-life is a weighted average of +90 308 ± 22 ms determined by Page et al. (26) and 323 –60 ms by Poli et al. (28). G 170 Ir The half-life was selected by Baglin (30). H 170 m Ir The isomeric state assignment was by Page et al. (26). The half-life was selected by Baglin (30). I 171 m Ir The half-life was selected by Baglin (33) who also assigned the activity to be an isomeric state. J 172 m Ir The isomeric state assignment was by Schmidt-Ott et al. (34).

* The year of discovery is taken as available manuscript and conference dates. Where these are not available then the year of discovery is the publishing date

Platinum Metals Rev., 2003, 47, (4) 170 Notes to the Table (cont.)

K 173 m Ir The isomeric state assignment was by Schmidt-Ott et al. (34). L 174 m Ir The isomeric state assignment was by Schmidt-Ott et al. (34). M 179 Ir Half-lifes determined by Nadzhakov et al. (39) appear to be systematically in error but the discovery is otherwise accepted. N 186 Ir The isotope was actually discovered by Smith and Hollander in 1955 (45) but was wrongly assigned to 187 Ir. O 192 Ir The isotope was first observed as a non-specific activity by Amaldi and Fermi in 1936 (12). P 192 m1 Ir The isotope was actually discovered by McMillan, Kamen and Ruben in 1937 (16) but was wrongly assigned to 194 Ir. Q 192 m2 Ir Scharff-Goldhaber and McKeown only determined the half-life to be greater than five years. The accepted value was determined by Harbottle in 1969 (59). R 194 Ir The isotope was first observed as a non-specific activity by Fermi et al. in 1934 (9) and Amaldi et al. in 1935 (10). S 194 m2 Ir A 47 s activity described as being an isomer of 194 Ir by Hennies and Flammersfeld in 1959 (63) could not be found by Scharff-Goldhaber and McKeown (64). T 196 Ir The isotope was first observed by Butement and Poë in 1953 (68) but was wrongly assigned to 198 Ir. U 196 m Ir Jansen and Pauw (69) suggested that the 20 h activity originally assigned to 196 m Ir by Bishop in 1964 (70) was actually a mixture of 196 m Ir and 195 Ir. V 197 Ir The 5.8 min half-life isotope was assigned to the ground state by Petry et al. in 1978 (71). W 197 m Ir The 8.9 min half-life isotope was assigned to be the isomeric state by Petry et al. in 1978 (71). X 198 Ir Details of this isotope were first given in the open literature by Szaley and Uray in 1973 (75). Y 199 Ir Only the mass of the isotope was determined. The half-life and decay mode were estimated from nuclear systematics (24).

Decay Modes a Alpha decay is the emittance of alpha particles which are 4He nuclei. Thus the atomic number of the daughter nuclide is lower by two and the mass number is lower by four. b– Beta or electron decay for neutron-rich nuclides is the emittance of an electron (and an anti-neutrino) as a neutron decays to a proton. The mass number of the daughter nucleus remains the same but the atomic number increases by one. b+ Beta or positron decay for neutron-deficient nuclides is the emittance of a positron (and a neutrino) as a proton decays to a neutron. The mass number of the daughter nucleus 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). Positron decay is always associated with orbital electron capture (EC). EC Orbital electron capture. The nucleus captures an extranuclear (orbital) electron which reacts with a proton to form a neutron and a neutrino, so that, as with positron decay, the mass number of the daughter nucleus remains the same but the atomic number decreases by one. IT Isomeric transition, in which a high energy state of a nuclide (isomeric state or isomer) usually decays by cascade emission of g (gamma) rays (the highest energy form of electromagnetic radiation) to lower energy levels until the ground state is reached. However, certain low level states may also decay independently to other nuclides. p The emittance of protons by highly neutron-deficient nuclides. As the neutron:proton ratio decreases a point is reached where there is insufficient binding energy for the last proton which is therefore unbound and is emitted. The point at which this occurs is known as the proton drip line and such nuclides are said to be “particle unstable”.

Platinum Metals Rev., 2003, 47, (4) 171 Appendix Some of the Terms Used for this Review Atomic number the number of protons in the nucleus Mass number the combined number of protons and neutrons in the nucleus Nuclide and isotope A nuclide is an entity characterised by the number of protons and neutrons in the nucleus. For nuclides of the same element the number of protons remains the same but the number of neutrons may vary. Such nuclides are known collectively as the isotopes of the element. Although the term isotope implies plurality it is sometimes used loosely in place of nuclide. Half-life the time taken for the activity of a radioactive nuclide to fall to half its previous value Electron volt (eV) The energy acquired by any charged particle carrying a unit (electronic) charge when it falls through a potential of one volt, equivalent to 1.602 × 10–19 J. The more useful unit is the mega (million) electron volt, MeV.

McMillan, Kamen and Ruben assigned the original In the Table of the Discoverers of the Iridium identification of the 60 day activity to Fomin and Isotopes the date of discovery is a manuscript or Houtermans in 1936 (17), but these two appeared conference date, or, if unavailable, then a publish- not to have produced this activity but simply men- ing date. The half-lifes are mainly those selected in tioned its discovery by Amaldi and Fermi. the NUBASE database (24) with new or revised However Fomin and Houtermans became credited values being referenced in the Notes to the Table. with the first observation and this confusion was not resolved until 1951 (18). None of the other Acknowledgement activities reported prior to 1938 have proved to be Thanks to Mrs Linda Porter for typing the manu- correct. script. As with platinum, the most prolific decade for the discovery of iridium isotopes was the 1960s with References Antti Siivola, who was then at the Lawrence 1 J. W. Arblaster, Platinum Metals Rev., 2000, 44, (4), 173 2. K. J. R. Rosman and P. D. P. Taylor, Commission Radiation Laboratory, Berkeley, California, produc- on Atomic Weights and Isotopic Abundances, ing and identifying seven new isotopes in 1966 (19). Subcommittee for Isotopic Abundance Measurements, More recently there has been a concentration on the Pure Appl. Chem., 1998, 70, (1), 217 3 A. J. Dempster, Nature, 1935, 136, 909 proton-rich isotopes, and in 1995 a British- 4 B. Venkatesachar and L. Sibaiya, Nature, 1935, 136, American team, one of the leading members of 37 which was Philip J. Woods, announced the produc- 5 G. P. Baxter, O. Hönigschmid, P. Lebeau and R. J. tion of the three proton-emitting isotopes 165Ir, 166Ir Meyer, J. Am. Chem. Soc., 1935, 57, 787 and 167Ir and this research group was therefore the 6 M. B. Sampson and W. Bleakney, Phys. Rev., 1936, 50, 732. first to cross the proton drip line in iridium (20, 21). 7 E. Wichers, J. Am. Chem. Soc., 1954, 76, 2033 More recently two groups have independently dis- 8 I. Curie and F. Joliot, Comptes Rendu, 1934, 198, 254 covered the even lighter proton-emitting isotope 9 E. Fermi, E. Amaldi, O. DAgostino, F. Rasetti and 164Ir, the first at the Department of Physics, E. Segrè, Proc. R. Soc. Lond., 1934, A146, 483 10 E. Amaldi, O. DAgostino, E. Fermi, B. Pontecorvo, University of Jyväskylä, Finland (22), and the second F. Rasetti and E Segrè, Proc. R. Soc. Lond., 1935, by the British-American team mentioned above (23). A149, 522 The discovery of four particle-unstable isotopes (i.e. 11 L. Sosnowski, Comptes Rendu, 1935, 200, 922 proton emitters) for one element is a record. 12 E. Amaldi and E. Fermi, Ric. Sci. Riv., 1936, 7, (1), 56 Because the half-life of 164Ir is likely to be less than 13 J. M. Cork and E. O. Lawrence, Phys. Rev., 1936, 49, 788 100 ms it is likely that there may be extreme difficul- 14 M. L. Pool, J. M. Cork and R. L. Thornton, Phys. ty in producing and identifying even lighter isotopes. Rev., 1937, 52, 239

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Platinum Metals Rev., 2003, 47, (4) 173 50 S. André, J. Boutet, J. Rivier, J. Treherne, J. 68 F. D. S. Butement and A. J. Poë, Philos. Mag., 1954, Jastrzebski, J. Lukasiak, Z. Sujkowski and C. Sebille- 45, 31 Schück, Nucl. Phys., 1975, A243, 229 69 J. F. W. Jansen and H. Pauw, Nucl. Phys., 1967, A94, 235 51 P. Kemnitz, L. Funke, H. Sodan, E. Will and G. 70 W. N. Bishop, Phys. Rev., 1965, 138, 514 Winter, Nucl. Phys., 1975, A245, 221 71 R. F. Petry, H. Issaian, D. W. Anderson and J. C. 52 L. J. Goodman and M. L. Pool, Phys. Rev., 1946, 70, Hill, Bull. Am. Phys. Soc., 1978, 23, 945 112; ibid, 1947, 71, 280 72 R. F. Petry, D. G. Shirk and J. C. Hill, Bull. Am. Phys. 53 B. Harmatz and T. Handley, Nucl. Phys., 1964, 56, 1 Soc., 1976, 21, 558 54 F. D. S. Butement and A. J. Poë, Philos. Mag., 1954, 73 J. C. Hill, D. G. Shirk, R. F. Petry and K. H. Wang, 45, 1090 Proceedings of the Third International Conference 55 J. W. Mihelich, M. McKeown and M. Goldhaber, on Nuclei Far From Stability, Cargèse, Corsica, Phys. Rev., 1954, 96, 1450 France, 1926 May, 1976, CERN Rep. 7613, 1976, 56 R. A. Naumann and J. R. Gerhart, Phys. Rev., 1954, CERN, Geneva, Switzerland, p. 532 96, 1452 74 F. J. Schweden and N. Kaffrell, Bundesministerium 57 M. Goldhaber, C. O. Muehlhouse and S. H. Turkel, für Bildung und Wissenschaft, Bonn, Germany, Phys. Rev., 1947, 71, 372 Rep. BMBW-FB K72-15, 1972, p. 88 58 G. Scharff-Goldhaber and M. McKeown, Phys. Rev. 75 A. Szaley and S. Uray, Radiochem. Radioanal. Lett., Lett., 1959, 3, 47 1973, 14, 135 59 G. Harbottle, Radiochim. Acta, 1970, 13, 132 76 Zhao Kui, J. S. Lilley, P. V. Drumm, D. D. Warner, 60 F. Boehm and P. Marmier, Phys. Rev., 1957, 105, 974 R. A. Cunningham and J. N. Mo, Chin. Phys. Lett., 1993, 10, 265 and Nucl. Phys., 1995, A586, 483 61 E. C. Campbell and P. F. Fettweiss, Nucl. Phys., 1959, 13, 92 62 A. W. Sunjar, G. Scharff-Goldhaber and M. The Author McKeown, Phys. Rev. Lett., 1968, 21, 237, 506 John W. Arblaster is Chief Chemist working in metallurgical analysis at Coleshill Laboratories. He is interested in the history 63H. H. Hennies and A. Flammersfeld, of science and in the evaluation of the thermodynamic and Naturwissenschaften, 1960, 47, 11; ibid, 1961, 48, 97 crystallographic properties of the elements. 64 G. Scharff-Goldhaber and M. McKeown, Naturwissenschaften, 1961, 48, 96 The Discoverers of the Platinum Isotopes 65 D. Christian, R. F. Mitchell and D. S. Martin, Phys. In the earlier review on platinum isotopes (1), on page 174, Rev., 1952, 86, 840 the b decay mode of 202Pt was inadvertently omitted. 66 K. J. Hofstetter and P. J. Daly, Nucl. Phys., 1968, On page 177, the second and third lines on the left hand A106, 382 column should be: Table of Isotopes and the fourth line 67 H. Venach, H. Münzer and P. Hille, Z. Phys., 1966, should read In the Table of the Discoverers of the Platinum 195, 343 Isotopes, the mass number of each isotope... Recyclable Microencapsulated Osmium Tetroxide Catalyst

Osmium tetroxide, OsO4, is an efficient oxidation cooxidant, with (DHQD)2PHAL ligand added to PEM- catalyst, well known for olefin hydroxylation and dihy- MC OsO4 catalyst; acetone is then removed. Addition of droxylation reactions. For the catalytic asymmetric dihy- a non-ionic surfactant, Triton® X-405 (octylphenoxy- droxylation (AD) of olefins, addition of a chiral ligand, polyethoxyethanol) was found to increase yield and ee such as (DHQD)2PHAL, to the OsO4 reaction mixture, and reduce Os leaching. Issues around catalyst solubility gives access to a wide range of enantiomerically pure were resolved by adding the ligand directly to the reac- vicinal diols. The chiral ligand is based on a biscinchona tion mixture. Product diols were obtained in better yield alkaloid with a phthalazine core (1). without catalyst deactivation even after three runs. Os

However, OsO4 is highly toxic and volatile and diffi- leaching was completely suppressed by neutralising with cult to use, and to avoid hazards OsO4 has sometimes aqueous H2SO4. Other olefins behave similarly and the been bound to polymers. Replacing organic solvents by PEM-MC OsO4 can be separated by filtration, recovered water for chemical reactions is an additional interest. and reused without loss of activity. Now, a team from The University of Tokyo, Japan, References have developed a microencapsulated OsO system, 4 1 K. B. Sharpless, W. Amberg, Y. L. Bennani, G. A. Crispino, based on poly(phenoxyethoxymethylstyrene-co-styrene) J. Hartung, K.-S. Jeong, H.-L. Kwong, K. Morikawa, Z.-M. (PEM-MC OsO ) (2) which can perform AD of olefins Wang, D. Xu and X.-L. Zhang, J. Org. Chem., 1992, 57, (10), 4 2768 with water as the sole solvent without catalyst leaching. 2 T. Ishida, R. Akiyama and S. Kobayashi, Adv. Synth. Catal., The system uses a H2O-acetone solvent and K3Fe(CN)6 2003, 345, (5), 576 and references therein

Platinum Metals Rev., 2003, 47, (4) 174 DOI: 10.1595/147106704X4826 7KH'LVFRYHUHUVRIWKH2VPLXP,VRWRSHV THE THIRTY-FOUR KNOWN OSMIUM ISOTOPES FOUND BETWEEN 1931 AND 1989

By J. W. Arblaster Coleshill Laboratories, Gorsey Lane, Coleshill, West Midlands B46 1JU, U.K.; E-mail: [email protected]

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3ODWLQXP0HWDOV5HY Table II The Discoverers of the Osmium Isotopes

Mass number Half-life Decay modes Year of Discoverers Ref. Notes discovery*

162 1.87 ms α 1989 Hofmann et al. 17 163 5.5 ms α, EC + β+? 1981 Hofmann et al. 18, 19 A 164 21 ms α, EC + β+ 1981 Hofmann et al. 18, 19 165 71 ms α, EC + β+ 1978 Cabot et al.16B 166 216 ms α, EC + β+ 1977 Cabot et al.15 167 810 ms α, EC + β+ 1977 Cabot et al. 15 168 2.06 s EC + β+, α 1977 Cabot et al. 15 169 3.46 s EC + β+, α 1972 Toth et al. 21 170 7.46 s EC + β+, α 1972 Toth et al. 22 171 8.3 s EC + β+, α 1972 Toth et al. 22 172 19.2 s EC + β+, α 1970 Borgreen and Hyde 23 173 22.4 s EC + β+, α 1970 Borgreen and Hyde 23 174 44 s EC + β+, α 1970 Borgreen and Hyde 23 175 1.4 min EC + β+ 1972 Berlovich et al. 24 176 3.6 min EC + β+ 1970 1: Arlt et al.25 2: de Boer et al. 26 177 3.0 min EC + β+ 1970 Arlt 25 178 5.0 min EC + β+ 1968 Belyaev et al.27 179 6.5 min EC + β+ 1968 Belyaev et al.27 180 21.5 min EC + β+ 1965 1: Belyaev et al. 28, 29 C 2: Hofstetter and Daly 30, 31 181 1.75 h EC + β+ 1966 Hofstetter and Daly 30 D 181m 2.7 min EC + β+ 1966 Hofstetter and Daly 30 E 182 22.10 h EC 1950 Stover 37 183 13.0 h EC + β+ 1950 Stover 37 183m 9.9 h EC + β+, IT 1957 Foster, Hilborn and Yaffe 32 184 Stable – 1937 Nier 4 185 93.6 d EC 1946 Goodman and Pool 38 186 2.0 × 1015 y α 1931 Aston 3 F 187 Stable – 1931 Aston 3 G 188 Stable – 1931 Aston 3 H 189 Stable – 1931 Aston 3 189m 5.8 h IT 1958 Scharff-Goldhaber et al.43I 190 Stable – 1931 Aston 3 190m 9.9 min IT 1955 Aten et al.44 191 15.4 d β– 1940 Zingg 12 191m 13.10 h IT 1952 Swan and Hill 45 192 Stable – 1931 Aston 3 J 192m 5.9 s IT, β– 1973 Pakkenen and Heikkinen 48 K 193 30.11 h β–? 1940 Zingg 12 L 194 6.0 y β– 1951 Lindner 52 195 – β–?M 196 34.9 min β– 1976 Katcoff et al. 58, 59

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3ODWLQXP0HWDOV5HY Table III Notes to Table II

A 163Os Alpha energy only. The half-life was determined by Page et al. in 1995 (20). B 165Os Alpha energy only. The half-life was determined by Hofmann et al. (18, 19). C 180Os In 1957 Foster, Holborn and Yaffe (32) assigned a 23 min half-life activity to 181Os but according to Hofstetter and Daly (30) this now appears to have more likely been 180Os. In 1965 Bedrosyan et al. (33) identified a 23 min half-life activity but did not assign a mass number. D 181Os A 2.7 h half-life activity described by Surkov et al. in 1960 (34) and apparently associated with 181Os was not observed by Hofstetter and Daly (30). Balyaev et al. (29) observed a 2.5 h half-life activity which appeared to confirm the observations of Surkov et al. E 181mOs Hofstetter and Daly’s claim to have identified this isomeric state was only tentative but was confirmed by Goudsmit in 1967 (35). Shortly before the observations of Hofstetter and Daly, Aten and Kapteyn (36) also identified a 2.8 min half-life activity but gave no mass assignment. F 186Os The half-life was measured by Viola, Roche and Minor in 1974 (7). G 187Os Chu in 1950 (39) and Greenlees and Kuo in 1956 (40) observed activities with half-lifes of 35 h and 39 h, respectively, which they suggested could be an isomer of 187Os. However such an activity was not observed by either Newton (41) or Merz (42). H 188Os A 26 d half-life activity suggested by Greenlees and Kuo (40) as being an isomer of 188Os was not observed by Merz (42). I 189mOs A 6 h half-life activity observed by Chu in 1950 (39) and a 7.2 h half-life activity observed by Greenlees and Kuo in 1950 (40) were both likely to have been 189mOs. J 192Os Fremlin and Walters (46) suggested that the isotope, although described as being “stable”, could be radioactive with a half-life exceeding 2.3 × 1014 y. Tretyak and Zdesenko (47) reassessed the data and suggested a revised value of greater than 9.8 × 1012 y which indicates that the suggestion of radioactivity is inconclusive. K 192mOs A 6 s half-life activity assigned to 192Re by Blachot, Monnand and Moussa in 1965 (49) was reassigned to 192mOs by Pakkenen and Heikkinen (48). Hermann et al. (50) almost certainly discovered 192mOs in 1970 but could not decide as to whether it was 192Re or 192mOs. L 193Os A 40 h half-life activity described by Kurchatov et al. in 1935 (11) was assigned to 193Os by the “Table of Isotopes” (51). M 195Os In 1957 Baró and Rey (53) and Rey and Baró (54) identified a 6.5 min half-life activity which they assigned to 195Os, but in 1974 Colle et al. (55) showed that this was the rubidium isotope 81Rb, so 195Os remains undiscovered. Takahashi, Yamada and Kondoh (57) estimated the half-life to be about 9 min.

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3ODWLQXP0HWDOV5HY Table IV Some of the Terms Used for this Review

Atomic number the number of protons in the nucleus Mass number the combined number of protons and neutrons in the nucleus Nuclide and isotope A nuclide is an entity characterised by the number of protons and neutrons in the nucleus. For nuclides of the same element the number of protons remains the same but the number of neutrons may vary. Such nuclides are known collectively as the isotopes of the element. Although the term isotope implies plurality it is sometimes used loosely in place of nuclide. Half-life the time taken for the activity of a radioactive nuclide to fall to half its previous value Electron volt (eV) The energy acquired by any charged particle carrying a unit (electronic) charge when it falls through a potential of one volt, equivalent to 1.602 × 10–19 J. The more useful unit is the mega (million) electron volt, MeV.

Table V Decay Modes

α Alpha decay is the emittance of alpha particles which are 4He nuclei. Thus the atomic number of the daughter nuclide is lower by two and the mass number is lower by four. β– Beta or electron decay for neutron-rich nuclides is the emittance of an electron (and an anti-neutrino) as a neutron decays to a proton. The mass number of the daughter nucleus remains the same but the atomic number increases by one. β+ Beta or positron decay for neutron-deficient nuclides is the emittance of a positron (and a neutrino) as a proton decays to a neutron. The mass number of the daughter nucleus 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). Positron decay is always associated with orbital electron capture (EC). EC Orbital electron capture. The nucleus captures an extranuclear (orbital) electron which reacts with a proton to form a neutron and a neutrino, so that, as with positron decay, the mass number of the daughter nucleus remains the same but the atomic number decreases by one. IT Isomeric transition, in which a high energy state of a nuclide (isomeric state or isomer) usually decays by cascade emission of γ (gamma) rays (the highest energy form of electromagnetic radiation) to lower energy levels until the ground state is reached. However, certain low level states may also decay independently to other nuclides.

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3ODWLQXP0HWDOV5HY The Author John W. Arblaster is Chief Chemist working in metallurgical analysis at Coleshill Laboratories, in the West Midlands of England. He is interested in the history of science and in the evaluation of the thermodynamic and crystallographic properties of the elements.

3ODWLQXP0HWDOV5HY DOI: 10.1595/147106706X110817 The Discoverers of the Palladium Isotopes THE THIRTY-FOUR KNOWN PALLADIUM ISOTOPES FOUND BETWEEN 1935 AND 1997

By J. W. Arblaster Coleshill Laboratories, Gorsey Lane, Coleshill, West Midlands B46 1JU, U.K.; E-mail: [email protected]

This is the fourth in a series of reviews of circumstances surrounding the discoveries of the isotopes of the six platinum group elements. The first review, on platinum isotopes, was published in this Journal in October 2000, the second, on iridium isotopes, was published here in October 2003 and the third, on osmium isotopes, was published in October 2004 (1). The current review looks at the discovery and the discoverers of the thirty-four isotopes of palladium.

Of the thirty-four known isotopes of palladium, ment activities found for palladium, such as a half- six occur naturally with the following authorised life of six hours discovered by Fermi et al. in 1934 isotopic abundances (2): (9) and half-lifes of 3 minutes and 60 hours discovered by Kurchatov et al. (10) in 1935 do not appear to have been confirmed. The Naturally Occurring Isotopes of Palladium In 1940, Nishima et al. (11) obtained an unspec- Mass number Isotopic abundance, % ified activity with a half-life of 26 minutes which is also likely to have been 111Pd. The actual half-life of 102Pd 1.02 111 104Pd 11.14 Pd is now known to be 23 minutes, so the differ- 105Pd 22.33 ent values obtained above are probably indicative 106 Pd 27.33 of calibration problems. 108Pd 26.46 These unspecified activities raise problems con- 110Pd 11.72 cerning the precedence for treating each discovery in this paper. Once the properties of an isotope are These naturally occurring isotopes were discov- established and it is obvious that an unspecified ered by Arthur J. Dempster in 1935 (3) at the activity must have been due to this particular iso- University of Chicago, Illinois, using a new mass tope, then the activity is assigned to that isotope spectrograph made to his design, although only the and can be regarded as being “the discovery”. mass numbers were observed. The actual isotopic However, using the definition that the primary cri- abundances were determined for the first time in terion for discovery is the determination of both the following year by Sampson and Bleakney (4). the atomic number and the mass number, these unspecified activities are included here only in the Artificial Palladium Isotopes Notes to the Table that accompanies the Table of In 1935, using slow neutron bombardment, The Discoverers of the Palladium Isotopes. Amaldi et al. (5) identified two palladium activities Literature manuscript dates and conference with half-lifes of 15 minutes and 12 hours. The lat- report dates can be either the actual year of discov- ter value appeared to confirm a half-life of 14 ery or close to it, so when they are placed in the hours that had been obtained earlier that year by public domain these dates can be considered as McLennan, Grimmett and Reid (6). In 1937, Pool, being the “year of discovery”. However, complica- Cook and Thornton (7) obtained similar half-lifes tions arise with internal reports, especially if they of 18 minutes and 12.5 hours, and Kraus and Cork represent the actual discovery, since they may not (8) were able to show experimentally, in that year, become publicly known until several years later. In that these two activities belonged to 111Pd and these cases the historical date must obviously take 109Pd, respectively. Other slow neutron bombard- precedence over the public domain date. As an

Platinum Metals Rev., 2006, 50, (2), 97–103 97 Irène Joliot-Curie 1900–1958

Frédéric Joliot-Curie 1897–1956 AIP Emilio Segrè Visual Archives Photo by Studio France Presse, courtesy AIP Emilio Segrè Visual Archives Born in Paris, Irène Curie was the daughter of sci- positron radiation. They concluded that they had pro- entists Pierre and Marie Curie, and therefore it was duced a new isotope of phosphorus of mass 30, hardly surprising that she was academically brilliant. compared to mass 31 found in natural phosphorus, and She became her mother’s assistant at the Radium that the positron emission represented the decay of this Institute, Paris, when only 21 years old and showed isotope. This is the first example of the production of an excellent aptitude in the use of the laboratory’s instru- artificial radioactive isotope. The discovery was mentation. announced in January 1934, and for this work they Frédéric Joliot was also born in Paris and in his were awarded the 1935 Nobel Prize in Chemistry. Now, twenties studied at the major Paris industrial engineer- more than seventy years later, there are over 2700 arti- ing school, the École Supérieure de Physique et de ficial radioactive isotopes. Chimie Industrielle, under the tutelage of the physicist Like many physicists in the late 1930s the Joliot- Paul Langevin, a friend of Marie Curie. Langevin sug- Curies carried out research on nuclear fission that gested that Joliot should be considered for a post at the eventually led to both the atom bomb and nuclear power. Radium Institute. Here Joliot met Irène Curie, who he After the war Frédéric convinced the French government married in 1926, adopting the surname Joliot-Curie. to set up its own Atomic Energy Commission and he After Frédéric had carried out major work to became its first High Commissioner. Irène succeeded her improve the sensitivity of the Wilson cloud chamber for mother in becoming the Director of the Radium Institute. detecting charged atomic particles, the Joliot-Curies However, this was the time of the Cold War and became interested in the work of the German physicists Frédéric had strong left-wing political views. In 1950 Walther Bothe and Hans Becker who had noted that Frédéric was dismissed from his post. Undaunted, both strong radiations were emitted when light elements put great effort into helping to set up a large particle were bombarded with alpha particles. The Joliot- accelerator and laboratory complex at Orsay, south of Curies owned the major source of alpha particles Paris (Institut de Physique Nucléaire d’Orsay). This is available at that time – polonium which had accumu- now considered to be one of the major physics institutes lated over many years at the Radium Institute. They in the world. used this source to bombard aluminium foil, and found Irène died in 1956 and Frédéric in 1958, both from first neutron emission, followed by a long period of diseases related to prolonged exposure to radiation.

example, Brosi’s discovery of 103Pd (12, 13) was inclusion in the 1948 “Table of Isotopes” (14). given in an unpublished internal report dated July Therefore the discovery was not placed in the pub- 1946 and was not mentioned publicly until its lic domain until 1948, although 1946 is obviously

Platinum Metals Rev., 2006, 50, (2) 98 The Discoverers of the Palladium Isotopes

Mass Half-life Decay Year of Discoverers References Notes number modes discovery

91 ps EC + E+ ? 1994 Rykaczewski et al. 17, 18 92 1.1 s EC + E+ 1994 Hencheck et al.19A 93 1.07 s EC + E+ 1994 Hencheck et al.19B 94 9.0 s EC + E+ 1982 Kurcewicz et al.24 95 – EC + E+ ?– – –C 95m 13.3 s EC + E+, IT 1980 Nolte and Hick 26 96 2.03 m EC + E+ 1980 Aras, Gallagher and Walters 27 97 3.10 m EC + E+ 1969 Aten and Kapteyn 28 98 17.7 m EC + E+ 1955 Aten and De Vries-Hamerling 29 D 99 21.4 m EC + E+ 1955 Aten and De Vries-Hamerling 29 E 100 3.63 d EC 1948 Lindner and Perlman 32 101 8.47 h EC + E+ 1948 Lindner and Perlman 32 102 Stable – 1935 Dempster 3 103 16.991 d EC 1946 1. Brosi 12, 13 F 2. Matthews and Pool 33 104 Stable – 1935 Dempster 3 105 Stable – 1935 Dempster 3 106 Stable – 1935 Dempster 3 107 6.5 x 106 y E– 1949 Parker et al.34G 107m 21.3 s IT 1957 Schindewolf 35 H 108 Stable – 1935 Dempster 3 109 13.7012 h E– 1937 Kraus and Cork 8 109m 4.696 m IT 1951 Kahn 38 I 110 Stable – 1935 Dempster 3 111 23.4 m E– 1937 Kraus and Cork 8 J 111m 5.5 h IT, E– 1952 McGinnis 40 112 21.03 h E– 1940 Nishina et al.11 113 1.55 m E– 1953 Hicks and Gilbert 41 113m 300 ms IT 1993 Penttilä et al.42K 114 2.42 m E– 1958 Alexander, Schindewolf and 46 Coryell 115 25 s E– 1987 Fogelberg et al. 44, 45 115m 50 s E–, IT 1958 Alexander, Schindewolf and 46 L Coryell 116 11.8 s E– 1970 Aronsson, Ehn and Rydberg 47 117 4.3 s E– 1968 Weiss, Elzie and Fresco 48 117m 19.1 ms IT 1989 Penttilä et al. 49, 50 118 1.9 s E– 1969 Weiss et al.51 119 920 ms E– 1990 Penttilä et al.50 120 492 ms E– 1992 Janas et al. 52, 53 121 285 ms E– ? 1994 Bernas et al.54 122 175 ms E– ? 1994 Bernas et al.54 123 174 ms E– ? 1994 Bernas et al.55 124 38 ms E– ? 1997 Bernas et al.55

ps = particle stable; IT = isomeric transition

Platinum Metals Rev., 2006, 50, (2) 99 Notes to the Table

A 92Pd Hencheck et al. (19) only determined the isotope to be particle stable. The half-life was first determined by Wefers et al. in 1999 (20). B 93Pd Hencheck et al. (19) only determined the isotope to be particle stable. The half-life was first accurately determined by Schmidt et al. (21) and Wefers et al. (22, 23) in 2000. A preliminary half-life of 9.3 s, determined by Wefers et al. in 1999 (20), was later withdrawn (22). C 95Pd The ground state has not been discovered, but Schmidt et al. (25) have suggested that the half-life is probably between 1.7 and 7.5 s from a consideration of the decay characteristics of 95Rh. D 98Pd Aten and De Vries-Hamerling (30) first suggested the existence of this isotope in 1953. The discovery was independently confirmed by Katcoff and Abrash in 1956 (31). E 99Pd The discovery by Aten and De Vries-Hamerling (29) in 1955 was independently confirmed by Katcoff and Abrash in 1956 (31). F 103Pd The unpublished 1946 internal report of Brosi (12, 13) was not made public knowledge until included in the 1948 “Table of Isotopes” (14). Thus, Matthews and Pool appeared to be unaware of it in 1947 and their discovery can be considered to be independent. G 107Pd The unpublished 1949 internal report of Parkes et al. (34) was not made public until its inclusion in the 1953 “Table of Isotopes” (15). H 107mPd Both Flammersfeld in 1952 (36) and Stribel in 1957 (37) observed this isotope but both ascribed it to 105mPd for which Schindewolf (35) could find no evidence. I 109mPd The discovery by Kahn (38) was given in an unpublished 1951 report and was not made public until its inclusion in the 1953 “Table of Isotopes” (15). Flammersfeld (36) observed this isotope in 1952 but could not decide whether or not it was 107mPd or 109mPd. J 111Pd Segrè and Seaborg (39) appeared to dispute the discovery by Kraus and Cook (8) since their half-life of 26 m differed significantly from that of 17 m determined by the latter. However Kraus and Cook appear to have definitely identified the 180 h (7.45 d) half-life daughter isotope 111Ag. K 113mPd Meikrantz et al. (43) suggested the existence of an isomer of 113Pd with a half-life exceeding 100 s; such an isomer should have been observed by Fogelberg et al. (44) but was not found. L 115mPd According to Fogelberg et al. (45), Alexander, Schindewolf and Coryell (46), as with later obserrvations of this isotope, may only have been observing a mixture of the ground state and isomeric state. Therefore the discovery of the pure isomeric state should probably be credited to Fogelberg et al. (44) in 1987.

Some of the Terms Used for this Review

Platinum Metals Rev., 2006, 50, (2) 100 Decay Modes

D Alpha decay is the emittance of alpha particles, which are 4He nuclei. Thus the atomic number of the daughter nuclide is lower by two and the mass number is lower by four. E– Beta or electron decay for neutron-rich nuclides is the emittance of an electron (and an anti-neutrino) as a neutron decays to a proton. The mass number of the daughter nucleus remains the same but the atomic number increases by one. E+ Beta or positron decay for neutron-deficient nuclides is the emittance of a positron (and a neutrino) as a proton decays to a neutron. The mass number of the daughter nucleus 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). Positron decay is always associated with orbital electron capture (EC). EC Orbital electron capture. The nucleus captures an extranuclear (orbital) electron which reacts with a proton to form a neutron and a neutrino, so that, as with positron decay, the mass number of the daughter nucleus remains the same but the atomic number decreases by one. IT Isomeric transition, in which a high energy state of a nuclide (isomeric state or isomer) usually decays by cascade emission of J gamma) rays (the highest energy form of electromagnetic radiation) to lower energy levels until the ground state is reached. However, certain low-level states may also decay independently to other nuclides.

the proper historic year and must be treated as the and neutron drip lines have not yet been reached actual “year of discovery”. for this element. A technique is used for light and medium-heavy Selected half-lifes in the Table of ‘The nuclides in which the nuclide fragments from a Discoverers of the Palladium Isotopes’ are from nuclear reaction are guided into a time-of-flight the revised NUBASE database (16), except for mass spectrometer. those of masses 120 to 124 which are from the The atomic numbers and the mass numbers of later measurements of Montes et al. (56). The crite- the detected nuclides can be determined by mea- ria for discovery are generally those adopted in the suring: the total kinetic energy of the beam, the review on platinum (1). loss in energy when the beam is injected into an ionisation chamber and the actual time of flight. References The determination of these numbers satisfies the 1 J. W. Arblaster, Platinum Metals Rev., 2000, 44, (4), criteria of discovery. 173; Platinum Metals Rev., 2003, 47, (4), 167; Platinum 48, For detection in the mass spectrometer, the life- Metals Rev., 2004, (4), 173 2 J. R. de Laeter, J. K. Böhlke, P. de Bièvre, H. Hidaka, times of the nuclides must exceed 500 H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor, nanoseconds and must therefore be particle stable. Pure. Appl. Chem., 2003, 75, 683 It is expected that particle unstable nuclides, that is 3 A. J. Dempster, Nature, 1935, 136, 65 those that emit protons for the lighter isotopes of 4 M. B. Sampson and W. Bleakney, Phys. Rev., 1936, 50, 732 an element and those which emit neutrons for the 5 E. Amaldi, O. D’Agostino, E. Fermi, B. Pontecorvo, heavier isotopes, are likely to have extremely short F. Rasetti and E. Sègre, Proc. Roy. Soc. Lond., 1935, A149 half-lifes in this mass region. If, statistically, a , 522 6 J. C. McLennan, L. G. Grimmett and J. Read, Nature, nuclide should have been detected by the sensitiv- 1935, 135, 147 ity of the technique, but was not, then it is likely to 7 M. L. Pool, J. M. Cork and R. L.Thornton, Phys. Rev., be particle unstable and thus can also satisfy the 1937, 52, 239 criteria of discovery, especially if it confirms theo- 8 J. D. Kraus and J. M. Cork, Phys. Rev., 1937, 52, 763 retical predictions. None of the lighter and heavier 9 E. Fermi, E. Amaldi, O. D’Agostino, F. Rasetti and E. Sègre, Proc. Roy. Soc. Lond., 1934, A146, 483 palladium isotopes discovered by this technique 10 L. V. Kurchatov, G. D. Latyshev, L. M. Nemenov have proved to be particle unstable, so the proton and I. P. Selinov, Phys. Z. Sowjet Union, 1935, 8, 589

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Platinum Metals Rev., 2006, 50, (2) 102 50 H. Penttilä, J. Äystö, K. Eskola, Z. Janas, P. P. 55 M. Bernas, C. Engelmann, P. Armbruster, S. Jauho, A. Jokinen, M. E. Leino, J. M. Parmonen and Czajkowski, F. Amiel, C. Böckstiegel, Ph. Dessagne, P. Taskinen, Z. Phys. A, 1991, 338, 291 C. Donzaud, H. Geissel, A. Heinz, Z. Janas, C. Kozhuharov, Ch. Miehé, G. Münzenberg, M. 51 H. V. Weiss, N. E. Ballou, J. L. Elzie and J. M. Pfützner, W. Schwab, C. Stéphan, K. Sümmerer, L. Fresco, Phys. Rev., 1969, 188, 1893 Tassan-Got and B. Voss, Phys. Lett. B, 1997, 415, 111 52 Z. Janas, J. Äystö, K. Eskola, P. P. Jauho, A. Jokinen, 56 F. Montes, A. Estrade, P. T. Hosmer, S. N. Liddick, J. Kownacki, M. Leino, J. M. Parmonen, H. Penttilä, P. F. Mantica, A. C. Morton, W. F. Mueller, M. 552 J. Szerypo and J. Zylicz, Nucl. Phys. A, 1993, , 340 Ouellette, E. Pellegrini, P. Santi, H. Schatz, A. Stolz, 53 A. Jokinen, J. Äystö, K. Eskola, T. Enqvist, Z. Janas, B. E. Tomlin, O. Arndt, K. L. Kratz, B. Pfeiffer, P. P. P. Jauho, M. Leino, J. M. Parmonen, H. Penttilä Reeder, W. B. Walters, A. Aprahamian and A. Wöhr, and J. Zylicz, “Sixth Int. Conf. on Nuclei Far From Phys. Rev. C, 2006, 73, 035801-1 Stability and Ninth Int. Conf. on Atomic Masses and Fundamental Constants”, ed. R. Neugart and A. The Author Wohr, Bernkastel-Kues, Germany, 19–24 July 1992, John W. Arblaster is Chief Chemist, Inst. of Phys. Conf. Series No. 132, IOP Publishing, working in metallurgical analysis on a Bristol and Philadelphia, 1993, p. 563 wide range of ferrous and non-ferrous 54 M. Bernas, S. Czajkowski, P. Armbruster, H. alloys for standards in chemical analysis, at Coleshill Laboratories in Geíssel, Ph. Dessagne, C. Donzaud, H. R. Faust, E. the West Midlands of England. He is Hanelt, A. Heinz, M. Hesse, C. Kozhuharov, Ch. interested in the history of science and Miehe, G. Münzenberg, M. Pfützner, C. Röhl, K. H. in the evaluation of the Schmidt, W. Schwab, C. Stéphan, K. Sümmerer, L. thermodynamic and crystallographic Tassan-Got and B. Voss, Phys. Lett. B, 1994, 331, 19 properties of the elements.

Nitrous Oxide Greenhouse Gas Abatement Catalyst Among the naturally occurring greenhouse gases, Johnson Matthey, as a catalyst gauze supplier, will nitrous oxide (N2O) is estimated to absorb 310 times market the catalyst to ‘clean development mechanism’ (1, 2) more heat per molecule than carbon dioxide, (CDM) and ‘joint implementation’ (JI) countries as thus contributing substantially to global warming (3). defined by the Kyoto Protocol. N2O emission reduc-

Atmospheric N2O is estimated to have increased by tions can thus be brought into line with requirements ~ 16% since the Industrial Revolution, and has con- sought by the Kyoto Protocol (7). T. KOPPERUD tributed 6 to 11% to enhancing the greenhouse effect. References Up to 40% of total atmospheric N2O is estimated to 1 “Global Warming Potentials”, Greenhouse Gas be man-made – equivalent to ~ 15 million tonnes per Inventory Data, http://ghg.unfccc.int/gwp.html year (4). N2O is gradually accumulating in the atmos- 2 “Data by gas – N2O without LULUCF”, phere (2), despite slow breakdown by sunlight. http://ghg.unfccc.int/tables/a2n2owo_lulucf.html

To reduce the production/emission of N2O as a 3 “Greenhouse Gas Emissions”, Atmos., Climate & Environ. Info. Programme, Manchester Metro. Univ., waste product from nitric acid plants, the Norwegian http://www.ace.mmu.ac.uk/eae/Global_Warming/ nitrogen fertiliser manufacturer Yara International Older/Emissions.html

ASA (5) has developed a N2O abatement catalyst 4 U.S. EPA, “Nitrous oxide”, based on the reaction: http://www.epa.gov/nitrousoxide/scientific.html 5 Yara, http://www.yara.com/ 2N O o 2N + O 2 2 2 6 (a) B. T. Horner, Platinum Metals Rev., 1993, 37, (2), 76; The de-N2O catalyst, which can cope with the high (b) B. T. Horner, Platinum Metals Rev., 1991, 35, (2), temperatures and corrosive environment of a nitric 58; (c) K. G. Gough and B. L. Wibberley, Platinum 30 acid plant, is placed under the rhodium-platinum Metals Rev., 1986, , (4), 168; (d) A. E. Heywood, Platinum Metals Rev., 1982, 26, (1), 28 gauze pack and the catchment gauzes (6). It enables 7 UN Framework Convention on Climate Change, “The the N2O output in most plants to be reduced by 80% Mechanisms under the Kyoto Protocol: Joint Implemen., or more. The catalyst is of pelleted configuration, and the Clean Dev. Mechan. and Emissions Trading”, http://unfccc.int/kyoto_mechanisms/items/1673.php when used with the Pt-Rh catalyst system gives an environmentally enhanced process with highly effi- The Author Trine Kopperud is Head of the Catalyst Department at Yara International cient N2O abatement. The catalyst is installed in in Porsgrunn, Norway. She looks after global catalyst supply strategies several nitric acid plants, and more are planned. for nitric acid and ammonia plants. E-mail: [email protected]

DOI: 10.1595/147106706X113878

Platinum Metals Rev., 2006, 50, (2) 103 •Platinum Metals Rev., 2011, 55, (2), 124–134•

The Discoverers of the Rhodium Isotopes The thirty-eight known rhodium isotopes found between 1934 and 2010

doi:10.1595/147106711X555656 http://www.platinummetalsreview.com/

By John W. Arblaster This is the fifth in a series of reviews on the circumstances surrounding the discoveries of the isotopes Wombourne, West Midlands, UK; of the six platinum group elements. The first review E-mmail: [email protected] on platinum isotopes was published in this Journal in October 2000 (1), the second on iridium isotopes in October 2003 (2), the third on osmium isotopes in October 2004 (3) and the fourth on palladium isotopes in April 2006 (4).

Naturally Occurring Rhodium In 1934, at the University of Cambridge’s Cavendish Laboratory,Aston (5) showed by using a mass spectrograph that rhodium appeared to consist of a single nuclide of mass 103 (103Rh). Two years later Sampson and Bleakney (6) at Princeton University,New Jersey, using a similar instrument, suggested the presence of a further isotope of mass 101 (101Rh) with an abundance of 0.08%. Since this isotope had not been discovered at that time, its existence in nature could not be discounted. Then in 1943 Cohen (7) at the University of Minnesota used an improved mass spectrograph to show that the abundance of 101Rh must be less than 0.001%. Finally in 1963 Leipziger (8) at the Sperry Rand Research Center, Sudbury, Massachusetts, used an extremely sensitive double-focusing mass spectrograph to reduce any possible abundance to less than 0.0001%. However by that time 101Rh had been discovered (see Table I) and although shown to be radioactive, no evidence was obtained for a long- lived isomer. This demonstrated conclusively that rhodium does in fact exist in nature as a single nuclide: 103Rh.

Artificial Rhodium Isotopes In 1934, using slow neutron bombardment, Fermi et al. (9) identified two rhodium activities with half- lives of 50 seconds and 5 minutes. A year later the same group (10) refined these half-lives to 44 seconds and 3.9 minutes. These discoveries were said to be ‘non-specific’ since the mass numbers were not

determined, although later measurements identified were identified are considered as satisfying the dis- these activities to be the ground state and isomeric covery criteria. state of 104Rh, respectively. In 1940 Nishina et al. (11, 12), using fast neutron bombardment, identified Discovery Dates a 34 hour non-specific activity which was later identi- The actual year of discovery is generally considered fied as 105Rh. In 1949 Eggen and Pool (13) confirmed to be that when the details of the discovery were the already known nuclide 101Pd and identified the placed in the public domain, such as manuscript existence of a 4.7 day half-life rhodium daughter dates or conference report dates. However, complica- product. They did not comment on its mass although tions arise with internal reports which may not be the half-life is consistent with the isomeric state of placed in the public domain until several years after 101Rh. Eggen and Pool also identified a 5 hour half-life the discovery,and in these cases it is considered that activity which was never subsequently confirmed. the historical date takes precedence over the public Activities with half-lives of 4 minutes and 1.1 hours, domain date. Certain rhodium isotopes were discov- obtained by fast neutron bombardment, were identi- ered during the highly secretive Plutonium Project of fied by Pool, Cork and Thornton (14) in 1937 but the Second World War, the results of which were not these also were never confirmed. actually published until 1951 (16) although much of Although some of these measured activities repre- the information was made available in 1946 by Siegel sent the first observations of specific nuclides, the (17, 18) and in the 1948 “Table of Isotopes”(19). exact nuclide mass numbers were not determined and therefore they are not considered to represent Half-Lives actual discoveries. They are however included in Selected half-lives used in Table I are generally those the notes to Table I. The first unambiguous identifi- accepted in the revised NUBASE evaluation of cation of a radioactive rhodium isotope was by nuclear and decay properties in 2003 (20) although Crittenden in 1939 (15) who correctly identified literature values are used when the NUBASE data are both 104Rh and its principal isomer. Nuclides where not available or where they have been superseded by only the atomic number and atomic mass number later determinations.

Table I The Discoverers of the Rhodium Isotopes

Mass numbera Half-llife Decay Year of Discoverers References Notes modes discovery

89 psb EC + β+ ? 1994 Rykaczewski et al. 21, 22 90 15 ms EC + β+ 1994 Hencheck et al.23A 90m 1.1 s EC + β+ 2000 Stolz et al.24A 91 1.5 s EC + β+ 1994 Hencheck et al.23B 91m 1.5 s IT 2004 Dean et al.25B 92 4.7 s EC + β+ 1994 Hencheck et al.23C 92m 0.5 s IT? 2004 Dean et al.25C 93 11.9 s EC + β+ 1994 Hencheck et al.23D 94 70.6 s EC + β+ 1973 Weiffenbach, Gujrathi and Lee 26 94m 25.8 s EC + β+ 1973 Weiffenbach, Gujrathi and Lee 26 95 5.02 min EC + β+ 1966 Aten and Kapteyn 27 95m 1.96 min IT, EC + β+ 1974 Weiffenbach, Gujrathi and Lee 28 Continued

Table I The Discoverers of the Rhodium Isotopes (Continued)

Mass numbera Half-llife Decay Year of Discoverers References Notes modes discovery

96 9.90 min EC + β+ 1966 Aten and Kapteyn 27 96m 1.51 min IT, EC + β+ 1966 Aten and Kapteyn 27 97 30.7 min EC + β+ 1955 Aten and de Vries-Hamerling 29 97m 46.2 min EC + β+, IT 1971 Lopez, Prestwich and Arad 30 98 8.7 min EC + β+ 1955 Aten and de Vries-Hamerling 29 E 98m 3.6 min EC + β+ 1966 Aten and Kapteyn 31 99 16.1 d EC + β+ 1956 Hisatake, Jones and Kurbatov 32 F 99m 4.7 h EC + β+ 1952 Scoville, Fultz and Pool 33 100 20.8 h EC + β+ 1944 Sullivan, Sleight and Gladrow 34, 35 G 100m 4.6 min IT, EC + β+ 1973 Sieniawski 36 101 3.3 y EC 1956 Hisatake, Jones and Kurbatov 32 F 101m 4.34 d EC, IT 1944 Sullivan, Sleight and Gladrow 34, 37 G 102 207.0 d EC + β+, β− 1941 Minakawa 38 102m 3.742 y EC + β+, IT 1962 Born et al.39 103 Stable – 1934 Aston 5 103m 56.114 min IT 1943 (a) Glendenin and Steinberg (a) 40, 41 H (b) Flammersfeld (b) 42 104 42.3 s β− 1939 Crittenden 15 I 104m 4.34 min IT, β− 1939 Crittenden 15 I 105 35.36 h β− 1944 (a) Sullivan, Sleight and Gladrow (a) 34, 43 J (b) Bohr and Hole (b) 44 105m 42.9 s IT 1950 Duffield and Langer 45 106 30.1 s β− 1943 (a) Glendenin and Steinberg (a) 40, 41 K (b) Grummitt and Wilkinson (b) 46 (c) Seelmann-Eggebert (c) 47 106m 2.18 h β− 1955 Baró, Seelmann-Eggebert 48 L and Zabala 107 21.7 min β− 1954 (a) Nervik and Seaborg (a) 49 M (b) Baró, Rey and (b) 50 Seelmann-Eggebert 108 16.8 s β− 1955 Baró, Rey and 50 N Seelmann-Eggebert 108m 6.0 min β− 1969 Pinston, Schussler and Moussa 51

Continued

Table I The Discoverers of the Rhodium Isotopes (Continued)

Mass numbera Half-llife Decay Year of Discoverers References Notes modes discovery

109 1.33 min β− 1969 Wilhelmy et al. 52, 53 110 28.5 s β− 1969 (a) Pinston and Schussler (a) 54 (b) Ward et al. (b) 55 110m 3.2 s β− 1963 Karras and Kantele 56 111 11 s β− 1975 Franz and Herrmann 57 112 3.4 s β− 1969 Wilhelmy et al. 52, 53 112m 6.73 s β− 1987 Äystö et al.58 113 2.80 s β− 1988 Penttilä et al.59 114 1.85 s β− 1969 Wilhelmy et al. 52, 53 114m 1.85 s β− 1987 Äystö et al.58 115 990 ms β− 1987 Äystö et al. 60, 61 116 680 ms β− 1987 Äystö et al. 58, 60, 61 116m 570 ms β− 1987 Äystö et al. 58, 60, 61 117 394 ms β− 1991 Penttilä et al.62 118 266 ms β− 1994 Bernas et al.63O 119 171 ms β− 1994 Bernas et al.63P 120 136 ms β− 1994 Bernas et al.63Q 121 151 ms β− 1994 Bernas et al.63P 122 psb β− ? 1997 Bernas et al.64 123 psb β− ? 2010 Ohnishi et al. 65 See Figures 1 and 2 124 psb β− ? 2010 Ohnishi et al. 65 See Figures 1 and 2 125 psb β− ? 2010 Ohnishi et al. 65 See Figures 1 and 2 126 psb β− ? 2010 Ohnishi et al. 65 See Figures 1 and 2 am = isomeric state bps = particle stable (resistant to proton and neutron decay)

Fig. 1. The superconducting ring cyclotron (SRC) in the Radioactive Isotope Beam Factory (RIBF) at the RIKEN Nishina Center for Accelerator-Based Science where the newest isotopes of palladium, rhodium and ruthenium were discovered (65) (Copyright 2010 RIKEN)

Dr Toshiyuki Kubo Toshiyuki Kubo is the team leader of the Research Group at RIKEN. He was born in Tochigi, Japan, in 1956. He received his BS degree in Physics from The University of Tokyo in 1978, and his PhD degree from the Tokyo Institute of Technology in 1985. He joined RIKEN as an Assistant Research Scientist in 1980, and was promoted to Research Scientist in 1985 and to Senior Research Scientist in 1992. He spent time at the National Superconducting Cyclotron Laboratory of Michigan State University in the USA as a visiting physicist from 1992 to 1994. In 2001, he became the team leader for the in-flight separator, dubbed ‘BigRIPS’, which analyses the fragments produced in the RIBF.He was promoted to Group Director of the Research Instruments Group at the RIKEN Nishina Center in 2007. He is in charge of the design, construction, development and operation of major research instruments, as well as related infra- structure and equipment, at the RIKEN Nishina Center. His current Fig. 2. Dr Toshiyuki Kubo research focuses on the production of rare isotope beams, in-flight (Copyright 2010 RIKEN) separator issues, and the structure and reactions of exotic nuclei.

Notes to Table I

A 90Rh and 90mRh Hencheck et al. (23) only proved that the isotope was particle stable. Stolz et al. (24) in 2000 identified both the ground state and an isomer. The half-life determined by Wefers et al. in 1999 (66) appears to be consistent with the ground state. The discovery by Hencheck et al. is nominally assigned to the ground state. B 91Rh and 91mRh Hencheck et al. (23) only proved that the isotope was particle stable. Wefers et al. (66) first determined a half-life in 1999 but Dean et al. (25) remeasured the half- life in 2004 and identified both a ground state and an isomer having identical half-lives within experimental limits. The discovery by Hencheck et al. is nominally assigned to the ground state. C 92Rh and 92mRh Hencheck et al. (23) only proved that the isotope was particle stable. Wefers et al. (66) incorrectly determined the half-life in 1999 with more accurate values being determined by both Górska et al. (67) and Stolz et al. (24) in 2000. Dean et al. (25) showed that these determinations were for the ground state and not for the isomeric state which they also identified. The discovery by Hencheck et al. is nominally assigned to the ground state. D 93Rh Hencheck et al. (23) only proved that the isotope was particle stable. Wefers et al. in (66) incorrectly measured the half-life in 1999 with more accurate values being obtained by both Górska et al. (67) and Stolz et al. (24) in 2000. E 98Rh Aten et al. (68) observed this isotope in 1952 but could not decide if it was 96Rh or 98Rh. F 99Rh and 101Rh Farmer (69) identified both of these isotopes in 1955 but could not assign mass numbers. G 100Rh and 101mRh For these isotopes the 1944 discovery by Sullivan, Sleight and Gladrow (34) was not made public until its inclusion in the 1948 “Table of Isotopes” (19). H 103mRh Although both Glendenin and Steinberg (40) and Flammersfeld (42) discovered the isomer in 1943 the results of Glendenin and Steinberg were not made public until their inclusion in the 1946 table compiled by Siegel (17, 18). I 104Rh and 104mRh Both the ground state and isomer were first observed by Fermi et al. (9) in 1934 and by Amaldi et al. (10) in 1935 as non-specific activities. Pontecorvo (70, 71) discussed these activities in detail but assigned them to 105Rh. EC + β+ was also detected as a rare decay mode (0.45% of all decays) in 104Rh by Frevert, Schöneberg and Flammersfeld (72) in 1965. J 105Rh For this isotope the 1944 discovery by Sullivan, Sleight and Gladrow (34) was not made public until its inclusion in the 1946 table of Siegel (17, 18). The isotope was first identified by Nishina et al. (11, 12) in 1940 as a non-specific activity. K 106Rh The discovery by Glendenin and Steinberg (40) in 1943 was not made public until

Continued

Notes to Table I (Continued)

its inclusion in the 1946 table of Siegel (17, 18) and therefore the discovery of this isotope by both Grummitt and Wilkinson (46) and Seelmann-Eggebert (47) in 1946 are considered to be independent. L 106mRh Nervik and Seaborg (49) also observed this isotope in 1955 but tentatively assigned it to 107Rh. M 107Rh First observed by Born and Seelmann-Eggebert (73) in 1943 as a non-specific activity and also tentatively identified by Glendenin (74, 75) in 1944. N 108Rh Although credited with the discovery, the claim by Baró, Rey and Seelmann- Eggebert (50) is considered to be tentative and a more definite claim to the discovery was made by Baumgärtner, Plata Bedmar and Kindermann (76) in 1957. O 118Rh Bernas et al. (63) only confirmed that the isotope was particle stable. The half-life was first determined by Jokinen et al. (77) in 2000. P 119Rh and 121Rh Bernas et al. (63) only confirmed that the isotopes were particle stable. The half- lives were first determined by Montes et al. (78) in 2005. Q 120Rh Bernas et al. (63) only confirmed that the isotope was particle stable. The half-life was first determined by Walters et al. (79) in 2004.

Some of the Terms Used for This Review

Atomic number The number of protons in the nucleus. Mass number The combined number of protons and neutrons in the nucleus. Nuclide and isotope A nuclide is an entity containing a unique number of protons and neutrons in the nucleus. For nuclides of the same element the number of protons remains the same but the number of neutrons may vary. Such nuclides are known collectively as the isotopes of the element. Although the term isotope implies plurality it is sometimes used loosely in place of nuclide. Isomer/isomeric state An isomer or isomeric state is a high energy state of a nuclide which may decay by isomeric transition (IT) as described in the list of decay modes below, although certain low-lying states may decay independently to other nuclides rather than the ground state. Half-life The time taken for the activity of a radioactive nuclide to fall to half of its previous value. Electron volt (eV) The energy acquired by any charged particle carrying a unit (electronic) charge when it falls through a potential of one volt, equivalent to 1.602 × 10–19 J. The more useful unit is the mega (million) electron volt (MeV).

Decay Modes

α Alpha decay is the emission of alpha particles which are 4He nuclei. Thus the atomic number of the daughter nuclide is two lower and the mass number is four lower. β– Beta or electron decay for neutron-rich nuclides is the emission of an electron (and an anti-neutrino) as a neutron in the nucleus decays to a proton. The mass number of the daughter nuclide remains the same but the atomic number increases by one. β+ Beta or positron decay for neutron-deficient nuclides is the emission of a positron (and a neutrino) as a proton in the nucleus decays to a neutron. 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). Positron decay is always associated with orbital electron capture (EC). 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, as with positron decay, the mass number of the daughter nuclide remains the same but the atomic number decreases by one. IT Isomeric transition in which a high energy state of a nuclide (isomeric state or isomer) usually decays by cascade emission of γ (gamma) rays (the highest energy form of electromagnetic radiation) to lower energy levels until the ground state is reached. p Proton decay in which a proton is emitted from the nucleus so both the atomic number and mass number decrease by one. Such a nuclide is said to be ‘particle unstable’. n Neutron decay in which a neutron is emitted from the nucleus so the atomic number remains the same but the atomic mass is decreased by one. Such a nuclide is said to be ‘particle unstable’.

Erratum: In the previous reviews (1–4) the alpha and beta decay modes were described in terms of ‘emittance’. This should read ‘emission’.

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77 A. Jokinen, J. C. Wang, J. Äystö, P. Dendooven, The Author S. Nummela, J. Huikari, V. Kolhinen, A. Nieminen, John W. Arblaster is interested in K. Peräjärvi and S. Rinta-Antila, Eur. Phys. J. A, 2000, the history of science and the 9, (1), 9 evaluation of the thermodynamic and crystallographic properties of the 78 F. Montes, A. Estrade, P. T. Hosmer, S. N. Liddick, P. F. elements. Now retired, he previously Mantica, A. C. Morton, W. F. Mueller, M. Ouellette, worked as a metallurgical chemist in a E. Pellegrini, P. Santi, H. Schatz, A. Stolz, B. E. Tomlin, number of commercial laboratories O. Arndt, K.-L. Kratz, B. Pfeiffer, P. Reeder, W. B. Walters, and was involved in the analysis of a wide range of ferrous and non-fer- A. Aprahamian and A. Wöhr, Phys. Rev. C, 2006, 73, (3), rous alloys. 035801 79 W. B. Walters, B. E. Tomlin, P. F. Mantica, B. A. Brown, J. Rikovska Stone, A. D. Davies, A. Estrade, P. T. Hosmer, N. Hoteling, S. N. Liddick, T. J. Mertzimekis, F. Montes, A. C. Morton, W. F. Mueller, M. Ouellette, E. Pellegrini, P. Santi, D. Seweryniak, H. Schatz, J. Shergur and A. Stolz, Phys. Rev. C, 2004, 70, (3), 034314

The Discoverers of the Ruthenium Isotopes

Updated information on the discoveries of the six platinum group metals to 2010

http://dx.doi.org/10.1595/147106711X592448 http://www.platinummetalsreview.com/

By John W. Arblaster This review looks at the discovery and the discoverers Wombourne, West Midlands, UK of the thirty-eight known ruthenium isotopes with mass numbers from 87 to 124 found between 1931 and 2010. Email: [email protected] This is the sixth and fi nal review on the circumstances surrounding the discoveries of the isotopes of the six platinum group elements. The fi rst review on platinum isotopes was published in this Journal in October 2000 (1), the second on iridium isotopes in October 2003 (2), the third on osmium isotopes in October 2004 (3), the fourth on palladium isotopes in April 2006 (4) and the fi fth on rhodium isotopes in April 2011 (5). An update on the new isotopes of palladium, osmium, iridium and platinum discovered since the previous reviews in this series is also included.

Naturally Occurring Ruthenium Of the thirty-eight known isotopes of ruthenium, seven occur naturally with the authorised isotopic abundances (6) shown in Table I. The isotopes were fi rst detected in 1931 by Aston (7, 8) using a mass spectrograph at the Cavendish Laboratory, Cambridge University, UK. Because of diffi cult experimental conditions due to the use of poor quality samples, Aston actually only detected six of the isotopes and obtained very approximate

Table I The Naturally Occurring Isotopes of Ruthenium

Mass number Isotopic Abundance, % 96Ru 5.54 98Ru 1.87 99Ru 12.76 100Ru 12.60 101Ru 17.06 102Ru 31.55 104Ru 18.62

percentage abundances. However, he did specu- or conference report dates. However, once again late on the existence of a seventh isotope with mass complications arise with the case of internal reports number 98. In 1943 Ewald (9) of the Aus dem Kaiser which may not be placed in the public domain until Wilhelm-Institut für Chemie, Berlin-Dahlem, Germany, several years later. As with rhodium (5), several ruthe- carried out a more refi ned spectrographic analysis and nium isotopes were fi rst identifi ed during the highly obtained precision values for the isotopic abundances, secretive Plutonium Project of the Second World War including confi rming the isotope of mass number 98. which was not actually published until 1951 (17), although much of the information had become avail- Artiﬁ cial Ruthenium Isotopes able in 1946 in the tables of Siegel (18, 19) or in the Early investigations of activities associated with 1948 edition of the “Table of Isotopes” (20). ruthenium tended to lead to half-life values which initially did not appear to be connected to each Discovery Acceptance other. For example, in 1935 Kurchatov, Nemenov The discovery criteria used in this series of papers and Selinov (10) used slow neutron bombardment to relate to the identifi cation of the ground state and obtain half-lives of 40 seconds, 100 seconds, 11 hours those isomers in which the half-life exceeds one and 75 hours, and in 1936 Livingood (11) used deu- millisecond, except in the very special circumstances teron bombardment to obtain different half-lives of where the ground state half-life is itself very short and 4 hours, 39 hours, 11 days and 46 days. In 1937, Pool, the half-lives of corresponding isomers are of a similar Cork and Thornton (12) used fast neutron bombard- order. This procedure was adopted to keep the tables ment and obtained activities with half-lives of 24 min- succinct by avoiding the inclusion of the exceedingly utes and 3.6 hours and in 1940 Nishina et al. (13) also large number of isomers with half-lives of less than used fast neutron bombardment to obtain ruthenium one millisecond which are known for the isotopes of activities of 4 hours and 60 hours and a rhodium activ- the platinum group elements and which would have ity of 34 hours. However, Nishina et al. (14) later spec- greatly complicated the text. ulated that the 60 hour activity was in reality a mixture of the 4 hour ruthenium and 34 hour rhodium activi- Half-Lives ties plus a further long lived ruthenium activity which Selected half-lives used in Table II were generally had not been identifi ed. They also pointed out that in those accepted in the revised NUBASE database (21) 1940 Segrè and Seaborg (15) had found a 4 hour half- although literature values were used when either life ruthenium activity in fi ssion products. In 1938, De these were not available or had been superseded by Vries and Veldkamp (16) used the different technique later determinations. of slow neutron bombardment and had identifi ed three activities: a 4 hour activity which they suggested An Update on the Discovery and Discoverers was 103Ru, a 20 hour activity which they suggested of the Platinum Group of Elements was 105Ru and a 45 day half-life activity which they Since the publication of the fi rst four reviews in this suggested was 105Rh. All of these suggestions were series (1–4) a number of new isotopes have been dis- incorrect but it would appear that all of the activities covered for palladium, osmium, iridium and platinum observed with an approximate 4 hour half-life were and the discovery circumstances for these isotopes probably 105Ru and the 46 day activity identifi ed by are listed in Table III. The total number of isotopes for Livingood and the equal 45 day activity identifi ed by each element and their mass number ranges are now De Vries and Veldkamp were probably 103Ru. None as shown in Table IV. of these observations could be seriously considered In addition the half-life of 199Ir was unknown until as being contenders to the discovery of any isotopes determined to be 6 seconds by Kurtukian-Nieto (77). since the discovery criterion of an accurate determination of the atomic mass number had not been met. The Number of Nuclides If a nuclide is defi ned as being a unique combina- Discovery Date tion of protons and neutrons, then the platinum group As discussed in previous articles in the present series elements currently include 235 known nuclides out (1–5), the actual year of discovery is generally consid- of a total for all elements of about 3200. Of these, ered to be that when the details of the discovery were 286 are primordial, that is they were present when placed in the public domain such as manuscript dates the Earth was formed and are still present now. The

Table II The Discoverers of the Ruthenium Isotopes

Mass Half-life Decay modes Year of Discoverers References Notes numbera discovery

87 psb EC   ? 1994 Rykaczewski et al. 22, 23 88 1.3 s EC   1994 Hencheck et al.24A 89 1.38 s EC   1992 Mohar et al. 25, 26 B 90 12 s EC   1991 Zhou et al. 27, 28 C 91 7.9 s EC   1983 Komninos, Nolte and Blasi 29 91m 7.6 s EC  , IT ? 1982 Hagberg et al.30 92 3.65 min EC   1971 (a) Arl’t et al. (a) 31, 32 (b) De Jesus and Neirinckx (b) 33 93 59.7 s EC   1955 Aten Jr. and De Vries- 34 D Hamerling 93m 10.8 s EC  , IT 1976 De Lange et al.35E 94 51.8 min EC   1952 Van Der Wiel and Aten Jr. 36 95 1.643 h EC   1948 Eggen and Pool 37 F 96 Stable – 1931 Aston 7, 8 97 2.9 d EC   1944 Sullivan, Sleight and Gladrow 38, 39 G 98 Stable – 1943 Ewald 9 99 Stable – 1931 Aston 7, 8 100 Stable – 1931 Aston 7, 8 101 Stable – 1931 Aston 7, 8 102 Stable – 1931 Aston 7, 8 103 39.25 d  1944 (a) Sullivan, Sleight and (a) 38, 40 H Gladrow (b) Bohr and Hole (b) 41 103m 1.69 ms IT 1964 Brandi et al. 42 104 Stable – 1931 Aston 7, 8 105 4.44 h  1944 (a) Sullivan, Sleight and (a) 38, 43 H Gladrow (b) Bohr and Hole (b) 41 106 371.8 d  1946 (a) Glendenin (a) 44, 45 I (b) Grummitt and Wilkinson (b) 46 107 3.75 min  1962 Pierson, Grifﬁ n and Coryell 47 J

(Continued)

Table II (Continued)

Mass Half-life Decay modes Year of Discoverers References Notes numbera discovery

108 4.55 min  1955 Baró, Rey and Seelmann- 48 Eggebert 109 34.5 s  1966 Grifﬁ ths and Fritze 49, 50 K 110 11.6 s  1969 Wilhelmy et al. 51, 52 111 2.12 s  1975 Fettweis and del Marmol 53 L 112 1.7 s  1969 Wilhelmy et al. 51, 52 113 800 ms  1988 Penttilä et al.54M 113m 510 ms IT ?,  ? 1998 Kurpeta et al. 55 114 540 ms  1991 Leino et al. 56 115 318 ms  1992 Äystö et al. 57, 58 115m 76 ms IT 2010 Kurpeta et al. 59 116 204 ms  1994 Bernas et al. 60 N 117 142 ms  1994 Bernas et al. 60 N 118 123 ms  1994 Bernas et al. 60 N 119 psb  ? 1995 Czajkowski et al. 61, 62 120 psb  ? 2010 Ohnishi et al. 63 P 121 psb  ? 2010 Ohnishi et al. 63 122 psb  ? 2010 Ohnishi et al. 63 123 psb  ? 2010 Ohnishi et al. 63 124 psb  ? 2010 Ohnishi et al. 63 am  isomeric state bps  particle stable (resistant to proton and neutron decay)

Notes to Table II

A 88Ru Hencheck et al. (24) only proved that the isotope was particle stable. The half-life was ﬁ rst determined by Wefers et al. in 1999 (64). B 89Ru Mohar et al. (25, 26) only proved that the isotope was particle stable. The half-life was ﬁ rst determined by Li Zhankui et al. in 1999 (65). C 90Ru Mohar et al. (25, 26) also claimed the discovery of this isotope in 1992 and appeared to be unaware of the prior discovery by Zhou et al. (27, 28). However they only determined that the isotope was particle stable whereas Zhou et al. had already determined the half-life.

(Continued)

Notes to Table II (Continued)

D 93Ru The discovery by Aten Jr. and De Vries-Hamerling (34) is considered to be tentative but was confi rmed by Doron and Lanford (66) in 1971. E 93mRu Doron and Lanford (66) also claimed to have discovered this isomer in 1971 but de Lange et al. (35) could not confi rm their half-life of 45 s. F 95Ru Mock et al. (67) appeared to independently claim the discovery even though their manuscript date was October 1948; the discovery claim by Eggen and Pool (37) had already been published in July 1948. G 97Ru The 1944 discovery by Sullivan, Sleight and Gladrow (38) was not made public for this isotope until included in the 1946 public report (39). H 103Ru and 105Ru The 1944 discovery for these isotopes by Sullivan, Sleight and Gladrow (38) was not made public until included in the 1946 table of Siegel (18, 19). I 106Ru Although produced in 1946, the results of Glendenin (44) were only made public at this time by including in the 1946 table of Siegel (18, 19). J 107Ru A preliminary identifi cation of this isotope by Glendenin (68, 69) in 1944 was made public in the 1946 table of Siegel (18, 19). K 109Ru Franz and Herrmann (70) proposed the existence of a 12.9 s half-life isomer but this could not be found by Kaffrell et al. (71). L 111Ru Franz and Herrmann (70) also tentatively identifi ed this isotope in 1975. M 113Ru Franz and Herrmann (70) tentatively claimed to have discovered this isotope in 1975 but Penttilä et al. (54) consider that the isotope observed was probably 113Rh. N 116Ru to 118Ru Bernas et al. (60) only determined that these isotopes were particle stable. The half-lives were fi rst measured by Montes et al. (72) in 2005. P 120Ru A 1995 claim by Czajkowski et al. (61) to have discovered this isotope was highly preliminary and was not included in the later 1997 report by Bernas et al. (62). Ohnishi et al. (63) detected this isotope in 2010 but did not claim the discovery possibly under the impression that the isotope had already been found but they can be considered to be the actual discoverers.

Table III New Discoveries

Element Mass Half-life Decay Year of Discoverers References Notes numbera mode discovery

Pd 125 psb – ? 2008 Ohnishi et al. 73 126 psb – ? 2008 Ohnishi et al. 73 127 psb – ? 2010 Ohnishi et al. 63 128 psb – ? 2010 Ohnishi et al. 63

(Continued)

Table III (Continued)

Element Mass Half-life Decay Year of Discoverers References Notes numbera mode discovery

Os 161 570 s  2008 Page et al. 74 195m 26 ns IT 2002 Podolyák et al. 75 A1 197 2.8 min – 2003 Xu et al. 76 198 psb – ? 2006 Kurtukian-Nieto et al. 77, 78 B1 199 5 s – 2005 Kurtukian-Nieto et al. 79 200 6 s – 2005 Kurtukian-Nieto et al. 79 201 psb – ? 2007 Kurtukian-Nieto 78 Ir 200 psb – ? 2006 Kurtukian-Nieto et al. 77, 78 B1 201 psb – ? 2006 Kurtukian-Nieto et al. 77, 78 B1 202 11 s – 2006 Kurtukian-Nieto et al. 77, 78 B1 203 psb – ? 2006 Kurtukian-Nieto et al. 77, 78 B1 Pt 203 10.1 s – 2005 Kurtukian-Nieto et al. 79 204 10.3 s – 2006 Kurtukian-Nieto et al. 77, 78 B1, C1 205 psb – ? 2010 Alvarez-Pol et al. 80 D1 am  isomeric state bps  particle stable (resistant to proton and neutron decay)

Notes to Table III

A1 Although the ground state of 195Os has not been discovered information on the very high level isomer is included to indicate that the isotope has been observed. B1 Kurtukian-Nieto et al. (77) only showed results in the form of a chart with actual mass numbers being given by Kurtukian-Nieto (78) in 2007. C1 Kurtukian-Nieto et al. (77) only determined the isotope to be particle stable. The half-life was ﬁ rst determined by Morales et al. (81) in 2008. D1 Evidence for this isotope was also given by Benlliure et al. (82).

Table IV Total Number of Isotopes and Mass Ranges Known for Each Platinum Group Element to 2010

Element Number of known isotopes Known mass number ranges

Ru 38 87–124 Rh 38 89–126 Pd 38 91–128 Os 41 161–201 Ir 40 164–203 Pt 40 166–205

Some of the Terms Used for This Review

Atomic number The number of protons in the nucleus. Mass number The combined number of protons and neutrons in the nucleus. Nuclide and isotope A nuclide is an entity containing a unique number of protons and neutrons in the nucleus. For nuclides of the same element the number of protons remains the same but the number of neutrons may vary. Such nuclides are known collectively as the isotopes of the element. Although the term isotope implies plurality it is sometimes used loosely in place of nuclide. Isomer/isomeric state An isomer or isomeric state is a high energy state of a nuclide which may decay by isomeric transition (IT) as described in the table below, although certain low-lying states may decay independently to other nuclides rather than the ground state. Half-life The time taken for the activity of a radioactive nuclide to fall to half of its previous value. Electron volt (eV) The energy acquired by any charged particle carrying a unit (electronic) charge when it falls through a potential of one volt, equivalent to 1.602  1019 J. The more useful unit is the mega (million) electron volt (MeV).

Decay Modes

 Alpha decay is the emission of alpha particles which are 4He nuclei. Thus the atomic number of the daughter nuclide is two lower and the mass number is four lower. – Beta or electron decay for neutron-rich nuclides is the emission of an electron (and an anti-neutrino) as a neutron in the nucleus decays to a proton. The mass number of the daughter nuclide remains the same but the atomic number increases by one. + Beta or positron decay for neutron-deﬁ cient nuclides is the emission of a positron (and a neutrino) as a proton in the nucleus decays to a neutron. 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). Positron decay is always associated with orbital electron capture (EC). 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, as with positron decay, the mass number of the daughter nuclide remains the same but the atomic number decreases by one. IT Isomeric transition in which a high energy state of a nuclide (isomeric state or isomer) usually decays by cascade emissions of  (gamma) rays (the highest energy form of electromagnetic radiation) to lower energy levels until the ground state is reached. p Proton decay in which a proton is emitted from the nucleus so both the atomic number and mass number decrease by one. Such a nuclide is said to be ‘particle unstable’. n Neutron decay in which a neutron is emitted from the nucleus so the atomic number remains the same but the atomic mass is decreased by one. Such a nuclide is said to be ‘particle unstable’.

Professor Michael Thoennessen Michael Thoennessen (Figure 1) is a Professor in the Department of Physics & Astronomy at Michigan State University (MSU), USA, and Associate Director at the National Superconducting Cyclotron Laboratory (NSCL) located on the campus of MSU. His main research interest is the study of exotic nuclei far from stability, concentrating on neutron- unbound nuclei beyond the neutron dripline. He performs most of his experiments at NSCL with the Modular Neutron Array (MoNA) -- a large- area high effi ciency neutron detector (Figure 2). He recently initiated a project to document the discovery of all isotopes. These reviews are currently being published in the journal Atomic Data and Nuclear Data Tables. The detailed description for each isotope has been carried out for about 70% and will be fi nished next year. Whilst some of the discovery criteria differ from these adopted here, there is generally good agreement as to assigning credit to the discoverers. Fig. 1. Professor Michael Thoennessen

Fig. 2. The Modular Neutron Array (MoNA) at the National Superconducting Cyclotron Laboratory (NSCL) located on the campus of Michigan State University (MSU), USA (Courtesy of T. Baumann)

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