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and the Transactinides

Dr Clint Sharrad Centre for Radiochemistry Research School of Chemical Engineering and Analytical Research Centre for Radwaste and Decommissioning Nuclear Institute The University of Manchester

[email protected]

Marie

No involvement in the discovery of curium or the transactinides. Who first discovered Cm?

Glenn T. Albert Ralph A. Seaborg Ghiorso James

for 1951 • Discovered 10 elements

• Discovered 12 elements • Expert in developing detection 1912 - 1999 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. entitled “Nuclear and Chemical Properties of and Curium” in 1948 Why Curium?

G. T. Seaborg, R. A. James and A. Ghiorso, National Nuclear Energy Series , 1949, 14B , 1554-71. Vasili Samarsky- Johan Why Bykhovets Gadolin Curium?

Lanthanides

Actinides

Marie & Pierre Enrico Dmitri Alfred Ernest Transactinides Curie Fermi Mendelev Noble Lawrence

Cn Copernicium (285)

Ernest Glenn T. Lise Wilhelm Nicolaus Rutherford Seaborg Meitner Copernicus 1850 Timeline 1859 – 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 (with ) 1906– Death of Pierre Curie 1911 – awarded Nobel prize for chemistry 1912 – Glenn Seaborg born 1915– born

1934– Death of Marie Curie; Seaborg awarded B.Sc. 1937– Seaborg awarded PhD; Ghiorso awarded B.Sc. 1939– Start of WWII 1940– Discovery of (Seaborg et al. ) 1942– established 1944– Discovery of curium and americium 1950 1949– Discovery of ; 1950 – Discovery of 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 at Berkeley

•Pu(NO 3)4 solutions allowed to evaporate onto a grooved Pt plate. •“Mild ignition ” formed

PuO 2. •Predicted properties of Cm were exploited to separate from Pu. •Proof of the presence of 239 Pu + He 2+ → 242 Cm + n Cm by analysing α particle energies.

239 Pu + He 2+ → 240 Cm + 3n •Also made by irradiation of Am samples. Where is Cm found? Curium facts

• Curium from 238 Cm to 251 Cm. • Most common isotopes are 244 Cm, 246 Cm and 248 Cm. • Typically formed by .

• Most Cm isotopes have a higher specific activity than 239 Pu. • Predominantly α emitters. • Chemical properties are similar to the . Redox properties Curium vs

D. L. Clark, The Chemical Complexities of Plutonium, Los Alamos Science, 2000, 26. Curium redox properties • Cm(III) is very stable. - as predicted by Seaborg. - due to half-filled (5f 7) configuration. • Redox potentials for the Cm(IV/III) couple are not known but oxidation to Cm 4+ 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 separations are by - exchange or solvent extraction processes.

How was Cm separated from Pu when it was first made?

1) Bombarded PuO 2 dissolved in H 2SO 4 and heated to dryness.

2) Residue dissolved in HNO 3 with any remaining insoluble dissolved by heating with a small amount of HF. 2- 3) Pu oxidised to Pu(VI) in HNO 3 (or Cr 2O7 ). 4) Addition of fluoride precipitates insoluble CmF 3 (and LnF 3 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 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 : - Americium – used in smoke detectors. - Lanthanides – potential worldwide shortages. How is curium separated from lanthanides? • With great difficulty!! • General process: - transfer of a charged complex (or ion) from a polar aqueous 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/ 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 . 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 244 Cm.

W. E. Prout, H. E. , H. P. Holcomb, W. J. Jenkins, DP-1302 , 1972. O OH O OH N OH O Lactic acid Lactic N exes it forms forms it exes DTPA e. OH HDEHP N O O H H O O HO O ORNL- Trivalent Actinide-Lanthanide Actinide-Lanthanide Separation by Trivalent , , 1964. B. Weaver and F. Kappelmann, F., F., Kappelmann, F. and Weaver B. 3559 Phosporous Reagent Extraction from Aqueous Aqueous Complexes Phosporous Reagent Extraction from with Cm and Am stay in the aqueous phase. theinaqueous stay Amand Cm with phas organic the into extracted are lanthanides The TALSPEAK TALSPEAK thecompl as reagent back” “hold a as known is DTPA • • 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 What is the role of lactate? OH OHO O HO N N N 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. - 242 Cm produces 3 W/g of heat energy. • Used to characterise lunar soil. Transactinides

Cn Copernicium (285)

• Most of the transactinides can be formed using 248 Cm. • Obtained by hot fusion reactions with 18 O, 19 F, 22 Ne, 26 Mg, 34 S and 48 Ca projectiles. • Need particle accelerators that provide heavy ion beam currents of ~3 × 10 12 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 at a time. • Providing proof of existence is extremely difficult and has, at times, been controversial. Single atom chemistry • Initial characterisation usually by measuring . - 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 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.”