Published by Johnson Matthey Plc A quarterly journal of research on the science and technology of the platinum group metals and developments in their application in industry Virtual Issue 4 ‘The Discoverers of the PGM Isotopes’ January 2012 www.platinummetalsreview.com E-ISSN 1471-0676 © Copyright 2012 Johnson Matthey http://www.platinummetalsreview.com/ Platinum Metals Review is published by Johnson Matthey Plc, refi ner and fabricator of the precious metals and sole marketing agent for the six platinum group metals produced by Anglo American Platinum Ltd, South Africa. All rights are reserved. Material from this publication may be reproduced for personal use only but may not be offered for re-sale or incorporated into, reproduced on, or stored in any website, electronic retrieval system, or in any other publication, whether in hard copy or electronic form, without the prior written permission of Johnson Matthey. Any such copy shall retain all copyrights and other proprietary notices, and any disclaimer contained thereon, and must acknowledge Platinum Metals Review and Johnson Matthey as the source. No warranties, representations or undertakings of any kind are made in relation to any of the content of this publication including the accuracy, quality or fi tness for any purpose by any person or organisation. E-ISSN 1471-0676 • Platinum Metals Rev., January 2012• Platinum Metals Review A quarterly journal of research on the platinum group metals and developments in their application in industry http://www.platinummetalsreview.com/ 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] i © 2012 Johnson Matthey 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 bom- barding 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.