Virtual Issue 4 ‘The Discoverers of the PGM Isotopes ... · Published by Johnson Matthey Plc Virtual Issue 4 ‘The Discoverers of the PGM Isotopes’ January 2012 E-ISSN 1471-0676

Published by Johnson Matthey Plc

Virtual Issue 4 ‘The Discoverers of

the PGM Isotopes’

January 2012

www.platinummetalsreview.com

E-ISSN 1471-0676

A quarterly journal of research on the

science and technology of the platinum

group metals and developments in their

application in industry

© 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 sixplatinum group metals produced by Anglo American Platinum Ltd, South Africa.

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E-ISSN 1471-0676 • Platinum Metals Rev., January 2012•

i © 2012 Johnson Matthey

Platinum Metals ReviewA quarterly journal of research on the platinum group metals

and developments in their application in industryhttp://www.platinummetalsreview.com/

VIRTUAL ISSUE 4 ‘THE DISCOVERERS OF THE PGM ISOTOPES’ JANUARY 2012

Contents

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, UKEmail: [email protected]

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

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

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

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The Naturally Occurring Isotopes of Iridium

Mass number Isotopic abundance, %

191Ir 37.3193Ir 62.7

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The Discoverers of the Iridium Isotopes

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

164m 100 �s p 2000 1: Kettunen et al. 22 A2: Mahmud et al. 23

165m 300 �s p, � 1995 Davids et al. 20, 21166 10.5 ms �, p 1995 Davids et al. 20, 21166m 15.1 ms �, p 1981 Hofmann et al. 25 B167 35.2 ms �, p, EC + �+ 1995 Davids et al. 20, 21167m 30.0 ms �, EC + �+?, p 1981 Hofmann et al. 25 C168 125 ms �?, EC + �+? 1978 Cabot et al. 27 D168m 161 ms � 1995 Page et al. 26169 780 ms �, EC + �+? 1999 Poli et al. 28 E169m 310 ms �, EC + �+ 1978 1: Cabot et al. 27 F

2: Schrewe et al. 29170 870 ms EC + �+, � 1995 Page et al. 26 G170m 440 ms EC + �+, IT, � 1977 1: Cabot et al. 31 H

2: Schrewe et al. 29171 3.2 s �, EC + �+, p? 2001 Rowe et al. 32171m 1.40 s �, EC + �+, p? 1966 Siivola 19 I172 4.4 s EC + �+, � 1991 Schmidt-Ott et al. 34, 35172m 2.0 s EC + �+, � 1966 Siivola 19 J173 9.0 s EC + �+, � 1991 1: Bouldjedri et al. 36

2: Schmidt-Ott et al. 34, 35173m 2.20 s EC + �+, � 1966 Siivola 19 K174 9 s EC + �+, � 1991 1: Bouldjedri et al. 36

2. Schmidt-Ott et al. 34, 35174m 4.9 s EC + �+, � 1966 Siivola 19 L175 9 s EC + �+, � 1966 Siivola 19176 8 s EC + �+, � 1966 Siivola 19177 30 s EC + �+, � 1966 Siivola 19178 12 s EC + �+ 1970 Akhmadzhanov et al. 37, 38179 1.32 min EC + �+ 1971 Nadzhakov et al. 39 M180 1.5 min EC + �+ 1970 1: Akhmadzhanov et al. 37, 38

2: Nadzhakov et al. 39181 4.90 min EC + �+ 1970 1: Akhmadzhanov et al. 37, 38

2: Nadzhakov et al. 39182 15 min EC + �+ 1961 Diamond et al. 40183 58 min EC + �+ 1960 1: Lavrukhina, Malysheva 41

and Khotin2: Diamond et al. 40

184 3.09 h EC + �+ 1960 1: Baranov et al. 422: Diamond et al. 40

185 14.4 h EC + �+ 1958 Diamond and Hollander 43186 16.64 h EC + �+ 1957 Scharff-Goldhaber et al. 44 N186m 1.92 h EC + �+, IT? 1962 Bonch-Osmolovskaya et al. 46187 10.5 h EC + �+ 1958 Diamond and Hollander 43187m 30.03 ms IT 1962 Ramaev, Gritsyna and Korda 47188 41.5 h EC + �+ 1950 Chu 48188m 4.2 ms IT, EC + �+ 1970 Goncharov et al. 49189 13.2 d EC 1955 Smith and Hollander 45189m1 13.3 ms IT 1962 Ramaev, Gritsyna and Korda 47189m2 3.7 ms IT 1974 1: André et al. 50

2: Kemnitz et al. 51

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The Discoverers of the Iridium Isotopes (cont.)


190 11.78 d EC + �+ 1946 Goodman and Pool 52190m1 1.120 h IT 1964 Harmatz and Handley 53190m2 3.087 h EC + �+, IT 1950 Chu 48191 Stable – 1935 Dempster 3191m 4.94 s IT 1954 1: Butement and Poë 54

2: Mihelich, McKeown 55and Goldhaber3: Naumann and Gerhart 56

192 78.831 d �–, EC 1937 McMillan, Kamen and Ruben 16 O192m1 1.45 min IT, �– 1947 Goldhaber, Muehlhouse 57 P

and Turkel192m2 241 y IT 1959 Scharff-Goldhaber and McKeown 58 Q193 Stable – 1935 Dempster 3193m 10.53 d IT 1956 Boehm and Marmier 60194 19.28 h �– 1937 McMillan, Kamen and Ruben 16 R194m1 31.85 ms IT 1959 Campbell and Fettweiss 61194m2 171 d �– 1968 Sunjar, Scharff-Goldhaber 62 S

and McKeown195 2.5 h �– 1952 Christian, Mitchell and Martin 65195m 3.8 h �–, IT 1967 Hofstetter and Daly 66196 52 s �– 1966 Venach, Münzer and Hille 67 T196m 1.40 h �–, IT? 1966 Jansen and Pauw 69 U197 5.8 min �– 1952 Christian, Mitchell and Martin 65 V197m 8.9 min �–, IT? 1976 Petry et al. 72, 73 W198 8 s �– 1972 Schweden and Kaffrell 74 X199 (20 s) �– 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 ground state. The half-life is a weighted average of 113 +62 μs determined by Kettunen et –30

al. (22) and 58 +46 μs determined by Mahmud et al. (23).–18

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).

E 169 Ir The half-life was normalised from 638 +462 ms determined by Poli et al. in 1999 (28).–237

F 169 m Ir The isomeric state assignment was by Poli et al. (28). The half-life is a weighted average of308 ± 22 ms determined by Page et al. (26) and 323 +90 ms by Poli et al. (28).–60

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).

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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� 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.

�– Beta or electron decay for neutron-rich nuclides is the emittance of an electron (and an anti-neutrino) as aneutron decays to a proton. The mass number of the daughter nucleus remains the same but the atomic number increases by one.

�+ Beta or positron decay for neutron-deficient nuclides is the emittance of a positron (and a neutrino) as a protondecays to a neutron. The mass number of the daughter nucleus remains the same but the atomic numberdecreases by one. However, this decay mode cannot occur unless the decay energy exceeds 1.022 MeV (twicethe 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 daughternucleus 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 bycascade emission of ��gamma) rays (the highest energy form of electromagnetic radiation) to lowerenergy 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”.

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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 numberof 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 fallsthrough a potential of one volt, equivalent to 1.602 × 10–19 J. The more useful unit is the mega (million) electron volt, MeV.

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The AuthorJohn W. Arblaster is Chief Chemist working in metallurgical analysis at Coleshill Laboratories. He is interested in the history of science and in the evaluation of the thermodynamic and crystallographic properties of the elements.

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THE THIRTY-FOUR KNOWN OSMIUM ISOTOPES FOUND BETWEEN 1931 AND 1989

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

Table I

The Naturally Occurring Isotopes of Osmium


184Os 0.02186Os 1.59187Os 1.96188Os 13.24189Os 16.15190Os 26.26192Os 40.78

DOI: 10.1595/147106704X4826

Table II

The Discoverers of the Osmium Isotopes


162 1.87 ms α 1989 Hofmann et al. 17163 5.5 ms α, EC + β+? 1981 Hofmann et al. 18, 19 A164 21 ms α, EC + β+ 1981 Hofmann et al. 18, 19165 71 ms α, EC + β+ 1978 Cabot et al. 16 B166 216 ms α, EC + β+ 1977 Cabot et al. 15167 810 ms α, EC + β+ 1977 Cabot et al. 15168 2.06 s EC + β+, α 1977 Cabot et al. 15169 3.46 s EC + β+, α 1972 Toth et al. 21170 7.46 s EC + β+, α 1972 Toth et al. 22171 8.3 s EC + β+, α 1972 Toth et al. 22172 19.2 s EC + β+, α 1970 Borgreen and Hyde 23173 22.4 s EC + β+, α 1970 Borgreen and Hyde 23174 44 s EC + β+, α 1970 Borgreen and Hyde 23175 1.4 min EC + β+ 1972 Berlovich et al. 24176 3.6 min EC + β+ 1970 1: Arlt et al. 25

2: de Boer et al. 26177 3.0 min EC + β+ 1970 Arlt 25178 5.0 min EC + β+ 1968 Belyaev et al. 27179 6.5 min EC + β+ 1968 Belyaev et al. 27180 21.5 min EC + β+ 1965 1: Belyaev et al. 28, 29 C

2: Hofstetter and Daly 30, 31181 1.75 h EC + β+ 1966 Hofstetter and Daly 30 D181m 2.7 min EC + β+ 1966 Hofstetter and Daly 30 E182 22.10 h EC 1950 Stover 37183 13.0 h EC + β+ 1950 Stover 37183m 9.9 h EC + β+, IT 1957 Foster, Hilborn and Yaffe 32184 Stable – 1937 Nier 4185 93.6 d EC 1946 Goodman and Pool 38186 2.0 × 1015 y α 1931 Aston 3 F187 Stable – 1931 Aston 3 G188 Stable – 1931 Aston 3 H189 Stable – 1931 Aston 3189m 5.8 h IT 1958 Scharff-Goldhaber et al. 43 I190 Stable – 1931 Aston 3190m 9.9 min IT 1955 Aten et al. 44191 15.4 d β– 1940 Zingg 12191m 13.10 h IT 1952 Swan and Hill 45192 Stable – 1931 Aston 3 J192m 5.9 s IT, β– 1973 Pakkenen and Heikkinen 48 K193 30.11 h β–? 1940 Zingg 12 L194 6.0 y β– 1951 Lindner 52195 – β–? M196 34.9 min β– 1976 Katcoff et al. 58, 59

*

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 hhalf-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 35h 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.

Table V

Decay Modes

α Alpha decay is the emittance of alpha particles which are 4He nuclei. Thus the atomic number of the daughternuclide 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 aneutron 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 protondecays to a neutron. The mass number of the daughter nucleus remains the same but the atomic numberdecreases by one. However, this decay mode cannot occur unless the decay energy exceeds 1.022 MeV (twicethe electron mass in energy units). Positron decay is always associated with orbital electron capture (EC).


IT Isomeric transition, in which a high energy state of a nuclide (isomeric state or isomer) usually decays bycascade emission of γ (gamma) rays (the highest energy form of electromagnetic radiation) to lowerenergy levels until the ground state is reached. However, certain low level states may also decay independently to other nuclides.

Table IV




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.


Electron volt (eV) The energy acquired by any charged particle carrying a unit (electronic) charge when it fallsthrough a potential of one volt, equivalent to 1.602 × 10–19 J. The more useful unit is the mega(million) electron volt, MeV.

The AuthorJohn W. Arblaster is Chief Chemist working in metallurgicalanalysis at Coleshill Laboratories, in the West Midlands ofEngland. He is interested in the history of science and in theevaluation of the thermodynamic and crystallographicproperties of the elements.

Platinum Metals Rev., 2006, 50, (2), 97–103 97

Of the thirty-four known isotopes of palladium,six occur naturally with the following authorisedisotopic abundances (2):

These naturally occurring isotopes were discov-ered by Arthur J. Dempster in 1935 (3) at theUniversity of Chicago, Illinois, using a new massspectrograph made to his design, although only themass numbers were observed. The actual isotopicabundances were determined for the first time inthe following year by Sampson and Bleakney (4).

Artificial Palladium IsotopesIn 1935, using slow neutron bombardment,

Amaldi et al. (5) identified two palladium activitieswith half-lifes of 15 minutes and 12 hours. The lat-ter value appeared to confirm a half-life of 14hours that had been obtained earlier that year byMcLennan, Grimmett and Reid (6). In 1937, Pool,Cook and Thornton (7) obtained similar half-lifesof 18 minutes and 12.5 hours, and Kraus and Cork(8) were able to show experimentally, in that year,that these two activities belonged to 111Pd and109Pd, respectively. Other slow neutron bombard-

ment activities found for palladium, such as a half-life of six hours discovered by Fermi et al. in 1934(9) and half-lifes of 3 minutes and 60 hours discov-ered by Kurchatov et al. (10) in 1935 do not appearto have been confirmed.

In 1940, Nishima et al. (11) obtained an unspec-ified activity with a half-life of 26 minutes which isalso likely to have been 111Pd. The actual half-life of111Pd is now known to be 23 minutes, so the differ-ent values obtained above are probably indicativeof calibration problems.

These unspecified activities raise problems con-cerning the precedence for treating each discoveryin this paper. Once the properties of an isotope areestablished and it is obvious that an unspecifiedactivity must have been due to this particular iso-tope, then the activity is assigned to that isotopeand can be regarded as being “the discovery”.However, using the definition that the primary cri-terion for discovery is the determination of boththe atomic number and the mass number, theseunspecified activities are included here only in theNotes to the Table that accompanies the Table ofThe Discoverers of the Palladium Isotopes.

Literature manuscript dates and conferencereport dates can be either the actual year of discov-ery or close to it, so when they are placed in thepublic domain these dates can be considered asbeing the “year of discovery”. However, complica-tions arise with internal reports, especially if theyrepresent the actual discovery, since they may notbecome publicly known until several years later. Inthese cases the historical date must obviously take precedence over the public domain date. As an

DOI: 10.1595/147106706X110817

The Discoverers of the Palladium IsotopesTHE 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 theisotopes of the six platinum group elements. The first review, on platinum isotopes, was publishedin this Journal in October 2000, the second, on iridium isotopes, was published here in October2003 and the third, on osmium isotopes, was published in October 2004 (1). The current reviewlooks at the discovery and the discoverers of the thirty-four isotopes of palladium.

The Naturally Occurring Isotopes of Palladium


102Pd 1.02104Pd 11.14105Pd 22.33106Pd 27.33108Pd 26.46110Pd 11.72

Platinum Metals Rev., 2006, 50, (2) 98

Born in Paris, Irène Curie was the daughter of sci-entists Pierre and Marie Curie, and therefore it washardly surprising that she was academically brilliant.She became her mother’s assistant at the RadiumInstitute, Paris, when only 21 years old and showedexcellent aptitude in the use of the laboratory’s instru-mentation.

Frédéric Joliot was also born in Paris and in histwenties studied at the major Paris industrial engineer-ing school, the École Supérieure de Physique et deChimie Industrielle, under the tutelage of the physicistPaul Langevin, a friend of Marie Curie. Langevin sug-gested that Joliot should be considered for a post at theRadium Institute. Here Joliot met Irène Curie, who hemarried in 1926, adopting the surname Joliot-Curie.

After Frédéric had carried out major work toimprove the sensitivity of the Wilson cloud chamber fordetecting charged atomic particles, the Joliot-Curiesbecame interested in the work of the German physicistsWalther Bothe and Hans Becker who had noted thatstrong radiations were emitted when light elementswere bombarded with alpha particles. The Joliot-Curies owned the major source of alpha particlesavailable at that time – polonium which had accumu-lated over many years at the Radium Institute. Theyused this source to bombard aluminium foil, and foundfirst neutron emission, followed by a long period of

positron radiation. They concluded that they had pro-duced a new isotope of phosphorus of mass 30,compared to mass 31 found in natural phosphorus, andthat the positron emission represented the decay of thisisotope. This is the first example of the production of anartificial radioactive isotope. The discovery wasannounced in January 1934, and for this work theywere awarded the 1935 Nobel Prize in Chemistry. Now,more than seventy years later, there are over 2700 arti-ficial radioactive isotopes.

Like many physicists in the late 1930s the Joliot-Curies carried out research on nuclear fission thateventually led to both the atom bomb and nuclear power.After the war Frédéric convinced the French governmentto set up its own Atomic Energy Commission and hebecame its first High Commissioner. Irène succeeded hermother in becoming the Director of the Radium Institute.However, this was the time of the Cold War andFrédéric had strong left-wing political views. In 1950Frédéric was dismissed from his post. Undaunted, bothput great effort into helping to set up a large particleaccelerator and laboratory complex at Orsay, south ofParis (Institut de Physique Nucléaire d’Orsay). This isnow considered to be one of the major physics institutesin the world.

Irène died in 1956 and Frédéric in 1958, both fromdiseases related to prolonged exposure to radiation.

Frédéric Joliot-Curie1897–1956

Irène Joliot-Curie1900–1958

example, Brosi’s discovery of 103Pd (12, 13) wasgiven in an unpublished internal report dated July1946 and was not mentioned publicly until its

inclusion in the 1948 “Table of Isotopes” (14).Therefore the discovery was not placed in the pub-lic domain until 1948, although 1946 is obviously

AIP Emilio Segrè Visual Archives Photo by Studio France Presse, courtesy AIP Emilio Segrè Visual Archives

The Discoverers of the Palladium Isotopes

Mass Half-life Decay Year of Discoverers References Notesnumber modes discovery

91 ps EC + + ? 1994 Rykaczewski et al. 17, 1892 1.1 s EC + + 1994 Hencheck et al. 19 A93 1.07 s EC + + 1994 Hencheck et al. 19 B94 9.0 s EC + + 1982 Kurcewicz et al. 2495 – EC + + ? – – – C95m 13.3 s EC + +, IT 1980 Nolte and Hick 2696 2.03 m EC + + 1980 Aras, Gallagher and Walters 2797 3.10 m EC + + 1969 Aten and Kapteyn 2898 17.7 m EC + + 1955 Aten and De Vries-Hamerling 29 D99 21.4 m EC + + 1955 Aten and De Vries-Hamerling 29 E

100 3.63 d EC 1948 Lindner and Perlman 32101 8.47 h EC + + 1948 Lindner and Perlman 32102 Stable – 1935 Dempster 3

103 16.991 d EC 1946 1. Brosi 12, 132. Matthews and Pool 33

F

104 Stable – 1935 Dempster 3105 Stable – 1935 Dempster 3106 Stable – 1935 Dempster 3107 6.5 x 106 y – 1949 Parker et al. 34 G107m 21.3 s IT 1957 Schindewolf 35 H108 Stable – 1935 Dempster 3109 13.7012 h – 1937 Kraus and Cork 8109m 4.696 m IT 1951 Kahn 38 I110 Stable – 1935 Dempster 3111 23.4 m – 1937 Kraus and Cork 8 J111m 5.5 h IT, – 1952 McGinnis 40112 21.03 h – 1940 Nishina et al. 11113 1.55 m – 1953 Hicks and Gilbert 41113m 300 ms IT 1993 Penttilä et al. 42 K114 2.42 m – 1958 Alexander, Schindewolf and 46

Coryell115 25 s – 1987 Fogelberg et al. 44, 45115m 50 s –, IT 1958 Alexander, Schindewolf and 46 L

Coryell116 11.8 s – 1970 Aronsson, Ehn and Rydberg 47117 4.3 s – 1968 Weiss, Elzie and Fresco 48117m 19.1 ms IT 1989 Penttilä et al. 49, 50118 1.9 s – 1969 Weiss et al. 51119 920 ms – 1990 Penttilä et al. 50120 492 ms – 1992 Janas et al. 52, 53121 285 ms – ? 1994 Bernas et al. 54122 175 ms – ? 1994 Bernas et al. 54123 174 ms – ? 1994 Bernas et al. 55124 38 ms – ? 1997 Bernas et al. 55


ps = particle stable; IT = isomeric transition


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 thehalf-life is probably between 1.7 and 7.5 s from a consideration of the decay characteristics of95Rh.

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 unawareof 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 ascribedit 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 publicuntil 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 Krausand 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 andisomeric state. Therefore the discovery of the pure isomeric state should probably be credited to Fogelberg et al. (44) in 1987.




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.


Electron volt (eV) The energy acquired by any charged particle carrying a unit (electronic) charge when it fallsthrough a potential of one volt, equivalent to 1.602 × 10–19 J. The more useful unit is themega (million) electron volt, MeV.


Decay Modes

Alpha decay is the emittance of alpha particles, which are 4He nuclei. Thus the atomic number of the daughternuclide is lower by two and the mass number is lower by four.

– Beta or electron decay for neutron-rich nuclides is the emittance of an electron (and an anti-neutrino) as aneutron decays to a proton. The mass number of the daughter nucleus remains the same but the atomic number increases by one.

+ Beta or positron decay for neutron-deficient nuclides is the emittance of a positron (and a neutrino) as a protondecays to a neutron. The mass number of the daughter nucleus remains the same but the atomic numberdecreases by one. However, this decay mode cannot occur unless the decay energy exceeds 1.022 MeV (twicethe electron mass in energy units). Positron decay is always associated with orbital electron capture (EC).


IT Isomeric transition, in which a high energy state of a nuclide (isomeric state or isomer) usually decays bycascade emission of gamma) rays (the highest energy form of electromagnetic radiation) to lowerenergy 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 theactual “year of discovery”.

A technique is used for light and medium-heavynuclides in which the nuclide fragments from anuclear reaction are guided into a time-of-flightmass spectrometer.

The atomic numbers and the mass numbers ofthe detected nuclides can be determined by mea-suring: the total kinetic energy of the beam, theloss in energy when the beam is injected into anionisation chamber and the actual time of flight.The determination of these numbers satisfies thecriteria of discovery.

For detection in the mass spectrometer, the life-times of the nuclides must exceed 500nanoseconds and must therefore be particle stable.It is expected that particle unstable nuclides, that isthose that emit protons for the lighter isotopes ofan element and those which emit neutrons for theheavier isotopes, are likely to have extremely shorthalf-lifes in this mass region. If, statistically, anuclide should have been detected by the sensitiv-ity of the technique, but was not, then it is likely tobe particle unstable and thus can also satisfy thecriteria of discovery, especially if it confirms theo-retical predictions. None of the lighter and heavierpalladium isotopes discovered by this techniquehave proved to be particle unstable, so the proton

and neutron drip lines have not yet been reachedfor this element.

Selected half-lifes in the Table of ‘TheDiscoverers of the Palladium Isotopes’ are fromthe revised NUBASE database (16), except forthose of masses 120 to 124 which are from thelater measurements of Montes et al. (56). The crite-ria for discovery are generally those adopted in thereview on platinum (1).

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54 M. Bernas, S. Czajkowski, P. Armbruster, H.Geíssel, Ph. Dessagne, C. Donzaud, H. R. Faust, E.Hanelt, A. Heinz, M. Hesse, C. Kozhuharov, Ch.Miehe, G. Münzenberg, M. Pfützner, C. Röhl, K. H.Schmidt, W. Schwab, C. Stéphan, K. Sümmerer, L.Tassan-Got and B. Voss, Phys. Lett. B, 1994, 331, 19

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56 F. Montes, A. Estrade, P. T. Hosmer, S. N. Liddick,P. F. Mantica, A. C. Morton, W. F. Mueller, M.Ouellette, E. Pellegrini, P. Santi, H. Schatz, A. Stolz,B. E. Tomlin, O. Arndt, K. L. Kratz, B. Pfeiffer, P.Reeder, W. B. Walters, A. Aprahamian and A. Wöhr,Phys. Rev. C, 2006, 73, 035801-1

The AuthorJohn W. Arblaster is Chief Chemist,working in metallurgical analysis on awide range of ferrous and non-ferrousalloys for standards in chemicalanalysis, at Coleshill Laboratories inthe West Midlands of England. He isinterested in the history of science andin the evaluation of thethermodynamic and crystallographicproperties of the elements.

Nitrous Oxide Greenhouse Gas Abatement CatalystAmong the naturally occurring greenhouse gases,

nitrous oxide (N2O) is estimated to absorb 310 times(1, 2) more heat per molecule than carbon dioxide,thus contributing substantially to global warming (3).Atmospheric N2O is estimated to have increased by ~ 16% since the Industrial Revolution, and has con-tributed 6 to 11% to enhancing the greenhouse effect.Up to 40% of total atmospheric N2O is estimated tobe man-made – equivalent to ~ 15 million tonnes peryear (4). N2O is gradually accumulating in the atmos-phere (2), despite slow breakdown by sunlight.

To reduce the production/emission of N2O as awaste product from nitric acid plants, the Norwegiannitrogen fertiliser manufacturer Yara InternationalASA (5) has developed a N2O abatement catalystbased on the reaction:

2N2O 2N2 + O2

The de-N2O catalyst, which can cope with the hightemperatures and corrosive environment of a nitricacid plant, is placed under the rhodium-platinumgauze pack and the catchment gauzes (6). It enablesthe N2O output in most plants to be reduced by 80%or more. The catalyst is of pelleted configuration, andwhen used with the Pt-Rh catalyst system gives anenvironmentally enhanced process with highly effi-cient N2O abatement. The catalyst is installed inseveral nitric acid plants, and more are planned.

Johnson Matthey, as a catalyst gauze supplier, willmarket the catalyst to ‘clean development mechanism’(CDM) and ‘joint implementation’ (JI) countries asdefined by the Kyoto Protocol. N2O emission reduc-tions can thus be brought into line with requirementssought by the Kyoto Protocol (7). T. KOPPERUD

References1 “Global Warming Potentials”, Greenhouse Gas

Inventory Data, http://ghg.unfccc.int/gwp.html2 “Data by gas – N2O without LULUCF”,

http://ghg.unfccc.int/tables/a2n2owo_lulucf.html3 “Greenhouse Gas Emissions”, Atmos., Climate &

Environ. Info. Programme, Manchester Metro. Univ.,http://www.ace.mmu.ac.uk/eae/Global_Warming/Older/Emissions.html

4 U.S. EPA, “Nitrous oxide”,http://www.epa.gov/nitrousoxide/scientific.html

5 Yara, http://www.yara.com/6 (a) B. T. Horner, Platinum Metals Rev., 1993, 37, (2), 76;

(b) B. T. Horner, Platinum Metals Rev., 1991, 35, (2),58; (c) K. G. Gough and B. L. Wibberley, PlatinumMetals Rev., 1986, 30, (4), 168; (d) A. E. Heywood,Platinum Metals Rev., 1982, 26, (1), 28

7 UN Framework Convention on Climate Change, “TheMechanisms under the Kyoto Protocol: Joint Implemen.,the Clean Dev. Mechan. and Emissions Trading”,http://unfccc.int/kyoto_mechanisms/items/1673.php

The AuthorTrine Kopperud is Head of the Catalyst Department at Yara Internationalin Porsgrunn, Norway. She looks after global catalyst supply strategiesfor nitric acid and ammonia plants. E-mail: [email protected]

DOI: 10.1595/147106706X113878

By John W. Arblaster

Wombourne, West Midlands, UK;

E-mmail: [email protected]

This is the fifth in a series of reviews on the circum-

stances 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 (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 RhodiumIn 1934, at the University of Cambridge’s Cavendish

Laboratory, Aston (5) showed by using a mass spec-

trograph 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 abun-

dance of 0.08%. Since this isotope had not been dis-

covered 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 spec-

trograph 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 IsotopesIn 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

124 © 2011 Johnson Matthey

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

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

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

determined, although later measurements identified

these activities to be the ground state and isomeric

state of 104Rh, respectively. In 1940 Nishina et al.

(11, 12), using fast neutron bombardment, identified

a 34 hour non-specific activity which was later identi-

fied as 105Rh. In 1949 Eggen and Pool (13) confirmed

the already known nuclide 101Pd and identified the

existence of a 4.7 day half-life rhodium daughter

product. They did not comment on its mass although

the half-life is consistent with the isomeric state of101

Rh. Eggen and Pool also identified a 5 hour half-life

activity which was never subsequently confirmed.

Activities with half-lives of 4 minutes and 1.1 hours,

obtained by fast neutron bombardment, were identi-

fied by Pool, Cork and Thornton (14) in 1937 but

these also were never confirmed.

Although some of these measured activities repre-

sent the first observations of specific nuclides, the

exact nuclide mass numbers were not determined

and therefore they are not considered to represent

actual discoveries. They are however included in

the notes to Table I. The first unambiguous identifi-

cation of a radioactive rhodium isotope was by

Crittenden in 1939 (15) who correctly identified

both 104Rh and its principal isomer. Nuclides where

only the atomic number and atomic mass number

were identified are considered as satisfying the dis-

covery criteria.

Discovery DatesThe actual year of discovery is generally considered

to be that when the details of the discovery were

placed in the public domain, such as manuscript

dates or conference report dates. However, complica-

tions arise with internal reports which may not be

placed in the public domain until several years after

the discovery, and in these cases it is considered that

the historical date takes precedence over the public

domain date. Certain rhodium isotopes were discov-

ered during the highly secretive Plutonium Project of

the Second World War, the results of which were not

actually published until 1951 (16) although much of

the information was made available in 1946 by Siegel

(17, 18) and in the 1948 “Table of Isotopes”(19).

Half-LivesSelected half-lives used in Table I are generally those

accepted in the revised NUBASE evaluation of

nuclear and decay properties in 2003 (20) although

literature values are used when the NUBASE data are

not available or where they have been superseded by

later determinations.


doi:10.1595/147106711X555656 •Platinum Metals Rev., 2011, 55, (2)•

Table I

The Discoverers of the Rhodium Isotopes

Mass numberaa Half-llife Decay Year of Discoverers References Notesmodes discovery

89 psb EC + β+ ? 1994 Rykaczewski et al. 21, 22

90 15 ms EC + β+ 1994 Hencheck et al. 23 A

90m 1.1 s EC + β+ 2000 Stolz et al. 24 A

91 1.5 s EC + β+ 1994 Hencheck et al. 23 B

91m 1.5 s IT 2004 Dean et al. 25 B

92 4.7 s EC + β+ 1994 Hencheck et al. 23 C

92m 0.5 s IT? 2004 Dean et al. 25 C

93 11.9 s EC + β+ 1994 Hencheck et al. 23 D

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)


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)


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. 63 O

119 171 ms β− 1994 Bernas et al. 63 P

120 136 ms β− 1994 Bernas et al. 63 Q

121 151 ms β− 1994 Bernas et al. 63 P

122 psb β− ? 1997 Bernas et al. 64

123 psb β− ? 2010 Ohnishi et al. 65 See Figures 1

and 2


and 2


and 2


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 theRIKEN Nishina Center for Accelerator-Based Science where the newest isotopes of palladium, rhodiumand 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 promot-

ed 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 frag-

ments 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

research focuses on the production of rare isotope beams, in-flight

separator issues, and the structure and reactions of exotic nuclei.

Fig. 2. Dr Toshiyuki Kubo(Copyright 2010 RIKEN)



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 deter-

mined 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 nomi-

nally 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 was96Rh 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



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).

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.



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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The Author John W. Arblaster is interested inthe history of science and theevaluation of the thermodynamic andcrystallographic properties of theelements. Now retired, he previouslyworked as a metallurgical chemist in anumber of commercial laboratoriesand was involved in the analysis of awide range of ferrous and non-fer-rous alloys.



•Platinum Metals Rev., 2011, 55, (4), 251–262•


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

By John W. Arblaster

Wombourne, West Midlands, UK

Email: [email protected]

This review looks at the discovery and the discoverers

of the thirty-eight known ruthenium isotopes with mass

numbers from 87 to 124 found between 1931 and 2010.

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 RutheniumOf the thirty-eight known isotopes of ruthenium, seven

occur naturally with the authorised isotopic abun-

dances (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

The Discoverers of the Ruthenium IsotopesUpdated information on the discoveries of the six platinum group metals to 2010

Table I

The Naturally Occurring Isotopes of Ruthenium

Mass number Isotopic Abundance, %

96Ru 5.54 98Ru 1.87 99Ru 12.76100Ru 12.60101Ru 17.06102Ru 31.55104Ru 18.62

http://dx.doi.org/10.1595/147106711X592448 •Platinum Metals Rev., 2011, 55, (4)•


percentage abundances. However, he did specu-

late on the existence of a seventh isotope with mass

number 98. In 1943 Ewald (9) of the Aus dem Kaiser

Wilhelm- Institut für Chemie, Berlin-Dahlem, Germany,

carried out a more refi ned spectrographic analysis and

obtained precision values for the isotopic abundances,

including confi rming the isotope of mass number 98.

Artifi cial Ruthenium IsotopesEarly investigations of activities associated with

ruthenium tended to lead to half-life values which

initially did not appear to be connected to each

other. For example, in 1935 Kurchatov, Nemenov

and Selinov (10) used slow neutron bombardment to

obtain half-lives of 40 seconds, 100 seconds, 11 hours

and 75 hours, and in 1936 Livingood (11) used deu-

teron bombardment to obtain different half-lives of

4 hours, 39 hours, 11 days and 46 days. In 1937, Pool,

Cork and Thornton (12) used fast neutron bombard-

ment and obtained activities with half-lives of 24 min-

utes and 3.6 hours and in 1940 Nishina et al. (13) also

used fast neutron bombardment to obtain ruthenium

activities of 4 hours and 60 hours and a rhodium activ-

ity of 34 hours. However, Nishina et al. (14) later spec-

ulated that the 60 hour activity was in reality a mixture

of the 4 hour ruthenium and 34 hour rhodium activi-

ties plus a further long lived ruthenium activity which

had not been identifi ed. They also pointed out that in

1940 Segrè and Seaborg (15) had found a 4 hour half-

life ruthenium activity in fi ssion products. In 1938, De

Vries and Veldkamp (16) used the different technique

of slow neutron bombardment and had identifi ed

three activities: a 4 hour activity which they suggested

was 103Ru, a 20 hour activity which they suggested

was 105Ru and a 45 day half-life activity which they

suggested was 105Rh. All of these suggestions were

incorrect but it would appear that all of the activities

observed with an approximate 4 hour half-life were

probably 105Ru and the 46 day activity identifi ed by

Livingood and the equal 45 day activity identifi ed by

De Vries and Veldkamp were probably 103Ru. None

of these observations could be seriously considered

as being contenders to the discovery of any isotopes

since the discovery criterion of an accurate determi-

nation of the atomic mass number had not been met.

Discovery DateAs discussed in previous articles in the present series

(1–5), the actual year of discovery is generally consid-

ered to be that when the details of the discovery were

placed in the public domain such as manuscript dates

or conference report dates. However, once again

complications arise with the case of internal reports

which may not be placed in the public domain until

several years later. As with rhodium (5), several ruthe-

nium isotopes were fi rst identifi ed during the highly

secretive Plutonium Project of the Second World War

which was not actually published until 1951 (17),

although much of the information had become avail-

able in 1946 in the tables of Siegel (18, 19) or in the

1948 edition of the “Table of Isotopes” (20).

Discovery AcceptanceThe discovery criteria used in this series of papers

relate to the identifi cation of the ground state and

those isomers in which the half-life exceeds one

millisecond, except in the very special circumstances

where the ground state half-life is itself very short and

the half-lives of corresponding isomers are of a similar

order. This procedure was adopted to keep the tables

succinct by avoiding the inclusion of the exceedingly

large number of isomers with half-lives of less than

one millisecond which are known for the isotopes of

the platinum group elements and which would have

greatly complicated the text.

Half-LivesSelected half-lives used in Table II were generally

those accepted in the revised NUBASE database (21)

although literature values were used when either

these were not available or had been superseded by

later determinations.

An Update on the Discovery and Discoverers of the Platinum Group of ElementsSince the publication of the fi rst four reviews in this

series (1–4) a number of new isotopes have been dis-

covered for palladium, osmium, iridium and platinum

and the discovery circumstances for these isotopes

are listed in Table III. The total number of isotopes for

each element and their mass number ranges are now

as shown in Table IV.

In addition the half-life of 199Ir was unknown until

determined to be 6 seconds by Kurtukian-Nieto (77).

The Number of Nuclides If a nuclide is defi ned as being a unique combina-

tion of protons and neutrons, then the platinum group

elements currently include 235 known nuclides out

of a total for all elements of about 3200. Of these,

286 are primordial, that is they were present when

the Earth was formed and are still present now. The



Table II

The Discoverers of the Ruthenium Isotopes

Mass

numbera

Half-life Decay modes Year of

discovery

Discoverers References Notes

87 psb EC ? 1994 Rykaczewski et al. 22, 23

88 1.3 s EC 1994 Hencheck et al. 24 A

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.

(b) De Jesus and Neirinckx

(a) 31, 32

(b) 33

93 59.7 s EC 1955 Aten Jr. and De Vries-

Hamerling

34 D

93m 10.8 s EC , IT 1976 De Lange et al. 35 E

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

Gladrow

(b) Bohr and Hole

(a) 38, 40

(b) 41

H

103m

104

1.69 ms

Stable

IT

–

1964

1931

Brandi et al.

Aston

42

7, 8

105 4.44 h 1944 (a) Sullivan, Sleight and

Gladrow

(b) Bohr and Hole

(a) 38, 43

(b) 41

H

106 371.8 d 1946 (a) Glendenin

(b) Grummitt and Wilkinson

(a) 44, 45

(b) 46

I

107 3.75 min 1962 Pierson, Griffi n and Coryell 47 J

(Continued)



Table II (Continued)

Mass

numbera

Half-life Decay modes Year of

discovery


108 4.55 min 1955 Baró, Rey and Seelmann-

Eggebert

48

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. 54 M

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




am isomeric statebps 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

numbera

Half-life Decay

mode

Year of

discovery


Pd 125

126

127

128

psb

psb

psb

psb

– ?

– ?

– ?

– ?

2008

2008

2010

2010

Ohnishi et al.

Ohnishi et al.

Ohnishi et al.

Ohnishi et al.

73

73

63

63

(Continued)



Table III (Continued)

Element Mass

numbera

Half-life Decay

mode

Year of

discovery


Os 161

195m

197

198

199

200

201

570 s

26 ns

2.8 min

psb

5 s

6 s

psb

IT

–

– ?

–

–

– ?

2008

2002

2003

2006

2005

2005

2007

Page et al.

Podolyák et al.

Xu et al.

Kurtukian-Nieto et al.



Kurtukian-Nieto

74

75

76

77, 78

79

79

78

A1

B1

Ir 200

201

202

203

psb

psb

11 s

psb

– ?

– ?

–

– ?

2006

2006

2006

2006





77, 78

77, 78

77, 78

77, 78

B1

B1

B1

B1

Pt 203

204

205

10.1 s

10.3 s

psb

–

–

– ?

2005

2006

2010



Alvarez-Pol et al.

79

77, 78

80

B1, C1

D1

am isomeric statebps 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 1019 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)



remaining ~2900 are described for these purposes as

being ‘artifi cial’ radioactive nuclides, since a num-

ber of the primordial nuclides are also radioactive

but with very long half-lives. There exist in nature a

signifi cant number of nuclides other than those of

primordial origin due to various radioactive decay

modes of naturally occurring thorium and uranium

isotopes. The limits on the stability of the nuclides are

defi ned by the proton and neutron drip lines beyond

which the nuclides lose particle stability, become

unbound and emit protons in the case of the proton

drip line and neutrons in the case of the neutron drip

line. Nuclides do exist beyond the drip lines but in

the case of the light elements the half-lives immedi-

ately plunge to very short values. Thoennessen (83)

has discussed the diffi culties in producing nuclides

close to the edges of the drip lines, and whilst for the

lighter elements both the proton and neutron drip

lines have been reached, only the proton drip line

has been approached throughout the Periodic Table.

For the medium to heavy elements, a large number

of nuclides remain to be discovered before the neu-

tron drip line is reached. Thoennessen and Sherrill

(84) predict that up to the presently known limits of

the Periodic Table the number of nuclides remaining

to be discovered is likely to be at least equal to the

number already known. There is optimism that at least

1000 of these will be discovered in the next ten years.

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

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Virtual Issue 4 ‘The Discoverers of the PGM Isotopes ... · Published by Johnson Matthey Plc Virtual Issue 4 ‘The Discoverers of the PGM Isotopes’ January 2012 E-ISSN 1471-0676