Download Curium and the trans

Curium and the
Transactinides
Dr Clint Sharrad
Centre for Radiochemistry Research
School of Chemical Engineering and Analytical Science
Research Centre for Radwaste and Decommissioning
Dalton Nuclear Institute
The University of Manchester
[email protected]
Marie Curie
No involvement in the discovery of curium
or the transactinides.
Who first discovered Cm?
Glenn T.
Seaborg
Albert
Ghiorso
Ralph A.
James
• Nobel prize for Chemistry 1951
• Discovered 10 elements
1912 - 1999
• Discovered 12 elements
• Expert in developing
radiation detection
instrumentation
1915 - 2010
G. T. Seaborg, R. A.
James and A. Ghiorso,
National Nuclear
Energy Series, 1949,
14B, 1554-71.
Was anyone else involved in
the discovery of curium???
Stanley G. Thompson
Submitted Ph.D. thesis entitled “Nuclear and
Chemical Properties of Americium and
Curium” in 1948
Why Curium?
G. T. Seaborg, R. A. James and A.
Ghiorso, National Nuclear Energy
Series, 1949, 14B, 1554-71.
Why
Curium?
Vasili SamarskyBykhovets
Johan
Gadolin
Lanthanides
Actinides
Marie & Pierre
Curie
Transactinides
Albert Einstein
Cn
Copernicium
(285)
Ernest
Rutherford
Glenn T.
Seaborg
Niels Bohr
Lise
Meitner
Wilhelm
Roentgen
Nicolaus
Copernicus
Enrico
Fermi
Dmitri
Mendelev
Alfred
Noble
Ernest
Lawrence
1850
Timeline
1859 – Pierre Curie born
1867 – Maria Skłodowska born
1891 – Maria Skłodowska moves to Paris to study chemistry at the
Sarbonne
1895– Maria Skłodowska marries Pierre Curie
1898– Curie’s publish discovery of Po and Ra
1903– Curie’s awarded Nobel prize for physics (with Becquerel)
1906– Death of Pierre Curie
1911– Marie Curie awarded Nobel prize for chemistry
1912– Glenn Seaborg born
1915– Albert Ghiorso born
1950
1934– Death of Marie Curie; Seaborg awarded B.Sc.
1937– Seaborg awarded PhD; Ghiorso awarded B.Sc.
1939– Start of WWII 1940– Discovery of plutonium (Seaborg et al.)
1942– Manhattan project established
1944– Discovery of curium and americium
1949– Discovery of berkelium; 1950 – Discovery of californium
1951– Seaborg awarded Nobel prize for chemistry (with McMillan)
Any link between Marie Curie and
Seaborg et al.?
How was Cm first made?
60 inch cyclotron
at Berkeley
•Pu(NO3)4 solutions
239Pu
239Pu
+ He2+ → 242Cm + n
+ He2+ → 240Cm + 3n
allowed to evaporate
onto a grooved Pt plate.
•“Mild ignition” formed
PuO2.
•Predicted redox
properties of Cm were
exploited to separate
from Pu.
•Proof of the presence of
Cm by analysing α
particle energies.
•Also made by neutron irradiation
of Am samples.
Where is Cm found?
Curium facts
• Curium isotopes from 238Cm to 251Cm.
• Most common isotopes are 244Cm, 246Cm and 248Cm.
• Typically formed by neutron capture.
• Most Cm isotopes have a higher specific activity than 239Pu.
• Predominantly α emitters.
• Chemical properties are similar to the lanthanides.
Redox properties
Curium vs Light actinides
D. L. Clark, The Chemical
Complexities of Plutonium,
Los Alamos Science, 2000,
26.
Curium redox properties
• Cm(III) oxidation state is very stable.
- as predicted by Seaborg.
- due to half-filled (5f7) configuration.
• Redox potentials for the Cm(IV/III) couple are not known but
oxidation to Cm4+ only occurs with the strongest oxidising
agents and conditions.
Curium spectroscopy
• Solutions of Cm(III) are normally colourless
but concentrated solutions can have a green
appearance.
• Weak f-f transitions observed.
• Strong flourescence at ~600 nm after
appropriate excitation.
- Used to probe Cm solution speciation.
W. T. Carnall, P. R. Fields, D. C. Stewart and T. K.
Keenan, J. Inorg. Nucl.Chem., 1958, 6, 213.
Curium separations
• Most common methods for actinide separations are by ionexchange or solvent extraction processes.
How was Cm separated from Pu when it was first made?
1) Bombarded PuO2 dissolved in H2SO4 and heated to
dryness.
2) Residue dissolved in HNO3 with any remaining
insoluble oxide dissolved by heating with a small
amount of HF.
3) Pu oxidised to Pu(VI) in HNO3 (or Cr2O72-).
4) Addition of fluoride precipitates insoluble CmF3 (and
LnF3 present as fission products) while the Pu
remains soluble.
5) The fluoride precipitate redissolved and procedure
repeated until all Pu removed.
• Higher FP concentration in Cm fraction accepted, as the α activity
from Cm could still be examined.
• Methods for the extraction of U
and Pu from spent nuclear fuel
have been established (e.g.
PUREX).
• Separation usually achieved by
exploiting the different chemical
properties of light actinides vs
FPs.
Why separate curium?
• Research interests.
• Waste management – timeframes for storage/disposal.
• Separate other nuclides:
- Americium – used in smoke detectors.
- Lanthanides – potential worldwide shortages.
How is curium separated from
lanthanides?
• With great difficulty!!
• General process:
- transfer of a charged metal complex (or ion) from a polar
aqueous phase to an immiscible phase (different solvation
properties).
• Dictated by:
- phase transfer properties of the species present.
- the relative affinity of the counterphase for the species to
be separated.
• For curium/lanthanide separations need to exploit the subtle
differences in ionic radii/covalency/polarisability.
• Main difference between ion-exchange and solvent extraction
methods:
- Solvation of a hydrophobic complex in solvent extraction.
- Resin acts as a second aqueous phase in ion exchange.
Example separation processes
• Most processes attempt to separate both Am and Cm
from lanthanides.
TRAMEX
Tertiary Amine Extraction
n-octyl and n-decyl
tertiary amines in
diethylbenzene
• Various mixtures used in all 3 extraction
steps.
• Separation of Cm from Am achieved by
exploiting accessible higher oxidation states
of Am.
• Developed at Oak Ridge National Lab (1961).
• Pilot plant purified ~1.5 kg of 244Cm.
W. E. Prout, H. E. Henry, H. P. Holcomb, W. J. Jenkins, DP-1302, 1972.
TALSPEAK Trivalent Actinide-Lanthanide Separation by
Phosporous Reagent Extraction from Aqueous Complexes
O
O
O
OH
OHO
O HO
N
N
N
DTPA
OH
O
OH
Lactic acid
HO
B. Weaver and F. Kappelmann, F., ORNL3559, 1964.
HDEHP
• DTPA is known as a “hold back” reagent as the complexes it forms
with Cm and Am stay in the aqueous phase.
• The lanthanides are extracted into the organic phase.
OH
Where to from here for curium/lanthanide
separations?
•Better understanding of the chemistry that underpins separations
processes is required.
•Molecular speciation, binding affinities, mass transfer kinetics, role of
phase transfer catalysts, solubilities, pH dependency, ionic strength etc.
TALSPEAK
O
O
O
O
OH
OHO
O HO
N
N
N
OH
What is the role of lactate?
Buffer, Complexant or both?
HO
OH
OH
•Using “soft” donor ligands for preferential binding of trivalent
actinides over lanthanides
• exploits the slightly greater
covalency exhibited in actinide
binding vs lanthanides.
• continuing development of
novel extractants.
Uses for Curium
• Space batteries in satellites or crewless
space probes.
- 242Cm produces 3 W/g of heat energy.
• Used to characterise lunar soil.
Transactinides
Cn
Copernicium
(285)
• Most of the transactinides can be formed using 248Cm.
• Obtained by hot fusion reactions with 18O, 19F, 22Ne, 26Mg, 34S
and 48Ca projectiles.
• Need particle accelerators that provide heavy ion beam
currents of ~3 × 1012 particles per second.
Particle accelerator at Dubna laboratories.
Properties of the Transactinides
• All transactinide isotopes are radioactive.
• Half-lives less than 3 min; typically between 30 s and 0.5 ms.
• Some isotopes can only be formed a single atom at a time.
• Providing proof of existence is extremely difficult and has, at
times, been controversial.
Single atom chemistry
• Initial characterisation usually by measuring radioactive decay.
- many transactinides confirmed by detecting α emission
to known α-decaying daughters and granddaughters.
• Single atom experiments need to be repeated many times to get
statistically valid results.
• Development of chemical procedures with fast process times and
reproducible (usually automated) methods.
• Gas phase - thermochromatographic separations.
- Aqueous chemistry – rapid HPLC and liquid-liquid extractions.
Why?
“We must not forget that when radium was discovered no
one knew that it would prove useful in hospitals. The work
was one of pure science. And this is a proof that scientific
work must not be considered from the point of view of the
direct usefulness of it. It must be done for itself, for the
beauty of science, and then there is always the chance that
a scientific discovery may become, like radium, a benefit for
humanity.”