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•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
Wombourne, West Midlands, UK;
E-mail: jwarblaster@yahoo.co.uk
This is the fifth in a series of reviews on the 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 (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 ( 103 Rh). 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 ( 101 Rh) 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 101 Rh 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 101 Rh had
been discovered (see Table I) and although shown to
be radioactive, no evidence was obtained for a longlived
isomer. This demonstrated conclusively that
rhodium does in fact exist in nature as a single
nuclide: 103 Rh.
Artificial Rhodium Isotopes
In 1934, using slow neutron bombardment, Fermi
et al. (9) identified two rhodium activities with halflives
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