PNNL Director’s Distinguished Lecture Series Monday, 4 August , 2010 One Atom-at-a-Time Chemistry of the Transactinides (TANs) Darleane C. Hoffman Professor Emerita, Graduate School Department of Chemistry University of California, Berkeley & Faculty Sr. Scientist Nuclear Science Division Lawrence Berkeley National Laboratory
What are the Transactinides? Where are the Transactinides? Periodic Table of the Elements 2010 Periodic Table of the Elements 2010
OVERVIEW I. Introduction to TANs • II. First Atom-at-a-Time Chemistry • Chemical Separation Method • Positive Identification of Atomic Number • III. Importance, Challenges, Technical Approaches • Suitable chemistry, Isotopes, Production Rates • IV. Studies of TANS • Manual to Sophisticated Computer-Controlled Systems • Aqueous and Gas-Phase Studies • Current Status V.Relativistic Effects: Theory & Experiment • Prognosis for Future • New Isotopes, New Elements
IUPAC APPROVED HEAVY ELEMENT NAMES August 30, 1997, Geneva, Switzerland ElementNameSymbol • 101 Mendelevium Md • 102 Nobelium No • 103 Lawrencium Lr • 104 Rutherfordium Rf • 105# Dubnium (Hahnium)# Db (Ha)# • 106 Seaborgium Sg • 107 Bohrium Bh • 108 Hassium Hs • 109 Meitnerium Mt • 110 * Darmstadtium* Ds* • 111** Roentgenium** Rg** • 112*** Copernicium*** Cn*** Transactinides (TANs) • #Many publications of chemical studies before 1997 use hahnium (Ha) for 105. • *Approved by IUPAC, August 2003; **Approved by IUPAC, November 2004. • ***Approved Spring 2010. (Pure Appl. Chem., DOI: 10.1351/PAD-REC-09-08-20).
Discovery & Identification of Element 101 (Mendelevium)A Landmark Experiment First Atom-at-a-Time Chemical Identification of a New Element, Only 17 atoms in 8 experiments. Use of 253Es (~20d) target: 109 or 1010 atoms--only a few picograms! Sub-NANO Science (10-9)! Heaviest Element First discovered & identified using direct radio-chemical separation of the element itself. To date, none of the Heavier Elements have First been Identified by Chemical Methods! All Elements Beyond Md: First Identified by Nuclear Decay properties/Physical Techniques
Decay Modes and Positive Identification of Element Nuclear Fission a-a correlation to known daughters Easy to detect but difficult to identify original fissioning nucleus—ManyControversies! Gives positive i.d. of Z & A, but much more complex instrumentation & analysis needed. (n,F) (SF) 261Rf 75 s a 8.28-8.52MeV 257No 26 s a 8.22-8.27 MeV 253Fm 3 d
Chemistry of TANs CHALLENGES Must be produced & studied at suitable accelerators. Low production rates (few atoms at a time). Very short-lived (minutes to milliseconds). Rates & half-lives decrease as Z(atomic number) increases. Plethora of unwanted elements produced. UNIQUE CAPABILITIES REQUIRED Hi-Intensity beams of heavy projectiles: LBNL, Berkeley, CA, USA, 88-Inch Cyclotron; Dubna, Russia U-400 Cyclotron; Darmstadt, Germany GSI, UNILAC; JAERI, Japan; Jyvaskala, Finland; Lanzhou, China. Facilities & expertise: Preparation, handling, & irradiation of radioactive targets; Fast transport of products from accelerator to separation facility; Fast radiochemical separations & detection techniques.
Why Study??IMPORTANCE • Unique opportunity to extend knowledge of chemistry to uppermost end of periodic table. • Assess extent & magnitude of relativistic effects predicted to be especially strong in these elements due to their high nuclear charges. • Compare chemical properties with those of lighter homologues & with theoretical predictions. *Evaluate validity of extrapolation of periodic table trends. * Search for anomalous trends in oxidation states, ionic radii, complexing, and chemical bonding. * Establish chemical properties of this new 6d transition series: Compare with those of 5d(Hf, Ta, W, Re, Os) & 4d(Zr, Nb, Mo,Tc ) elements both across series & down groups 4-8 to evaluate validity of extrapolation of group trends. Elucidation of the chemical properties of the elements & their placement in the Periodic Table is one of most fundamental goals of chemistry—sometimes referred to as “Textbook Chemistry”!
CHEMISTRY OF SEABORGIUM (265,266Sg) ARCA: 1997 Cation Exchange Chromatography with 0.1 M HNO3/0.0005 M HF. Sg appears to behave like Group 6 element W, Forms anionic or neutral complexes that elute promptly. Unlike U(VI) that forms [UO2]2+, which sorbs on cation column as do other 2+, 3+,4+ species. (Based on detection of 3 a-a corr. from 261Rf-257No daughters of 7-s 265Sg.) 1998: New Results: Experiments repeated without any HF. 169W & 265Sg produced at same time and 169W eluted with ave. yield of 59%. 265Sg not detected although 5 a-a correlations expected. New results indicate that Sg has less tendency to hydrolyze than W and Mo and forms positively charged species such as [Sg(OH)4(H2O)2]2+ or [Sg(OH)5(H2O)2]1+ while W (Mo) reach the neutral species WO2(OH)2. This non-W like behavior is in agreement with Pershina’s earlier predictions for the group 5 elements which considered the competition between hydrolysis & halide complex formation. Hydrolysis decreases in the order Nb>Ta>105>Pa. In the presence of F- ions the formation of neutral or anionic F- complexes is favored. (DS DVM method, electronic structures, free energy change of reactions of complex formation in pure halides, followed by Born theory of metal-ion extraction shows inversion in trends between 5d and 6d elements.) RELATIVISTIC EFFECTS Primary Relativistic Effects on Atomic Orbitals# (Effects Increase as Z2) • Contraction of radius, energetic stabilization of s & p orbitals. • Spin-orbit splitting of l>0 orbitals • Resulting increase in radii, energetic de-stabilization of outer d and all f orbitals. Group 6 valence orbital eigenvalues IRs of TANs are about 0.05 Ålarger than IR of 5d elements due to orbital expansion of the 6p3/2 orbitals, but are smaller than actinide IRs due to actinide contraction (0.030 Å), mostly relativistic effect. Will influence chemistry.## #P.PyykkÖ, 1988 ##V. Pershina, 2003
CHEMISTRY OF SEABORGIUM (265,266Sg) ARCA: 1997 Cation Exchange Chromatography with 0.1 M HNO3/0.0005 M HF. Sg appears to behave like Group 6 element W, Forms anionic or neutral complexes that elute promptly. Unlike U(VI) that forms [UO2]2+, which sorbs on cation column as do other 2+, 3+,4+ species. (Based on detection of 3 a-a corr. from 261Rf-257No daughters of 7-s 265Sg.) 1998: New Results: Experiments repeated without any HF. 169W & 265Sg produced at same time and 169W eluted with ave. yield of 59%. 265Sg not detected although 5 a-a correlations expected. New results indicate that Sg has less tendency to hydrolyze than W and Mo and forms positively charged species such as [Sg(OH)4(H2O)2]2+ or [Sg(OH)5(H2O)2]1+ while W (Mo) reach the neutral species WO2(OH)2. This non-W like behavior is in agreement with Pershina’s earlier predictions for the group 5 elements which considered the competition between hydrolysis & halide complex formation. Hydrolysis decreases in the order Nb>Ta>105>Pa. In the presence of F- ions the formation of neutral or anionic F- complexes is favored. (DS DVM method, electronic structures, free energy change of reactions of complex formation in pure halides, followed by Born theory of metal-ion extraction shows inversion in trends between 5d and 6d elements.) Chemistry Valid for One Atom-at-a-Time? • Must be “FAST” enough to accomplish in times comparable to half-lives of isotopes used. • Give same results for only a few atoms as for MACRO amounts. Adloff-Guillaumont thoroughly considered validity of results obtained from very small number of atoms. CONCLUSION Results from chemical procedures with fast kinetics in which single atoms undergo many identical chemical reactions between 2-phase systems can be combined to give valid results. e.g. Ion-exchange & Gas Chromatography, Solvent Extractions Note: Results of Chemical Studies of Md & No originally conducted on one-atom basis were later confirmed with larger quantities .
Production Reactions for TAN Chemistry Hot Fusion—Elements 104 through 108 4,5 n Fission Products • ___________________________________________________________________________ • 18O + 248Cm 261Rf78ss ~ 5nb • 18O + 249Bk 262Db(Ha)34ss ~ 6nb • 22Ne + 248Cm 266,265Sg21s, 7s s ~ 0.3nb • 22Ne + 249Bk 267,266Bh17s, ~1s s ~ 0.07nb 26Mg + 248Cm 270,269Hs ~4s, 14s s ~ 0.005nb ______________________________________________________________ **For s ~5 nb, ~2 atoms/min produced. After transport efficiency (50%), chemical yield (80%),detection efficiency(35%), & decay (50%), only detect 0.1/min~144/d. For Hs, only 0.14/d or ~1/week!
Investigations of chemical and nuclear properties are complementary and should proceed “Hand-in-Hand” Nuclear Nuclear Chemical Chemical Nuclear properties, production methods, and detection techniques must be known in order to study chemical properties on an Atom-at-a-Time basis. Knowledge of chemical properties permits separation and positive identification of atomic number. Can provide pure samples for study of nuclear properties and discovery of new isotopes.
2003 Chart of Nuclides Elements beyond 111 not confirmed. Ds No isotopes with N>161 confirmed
Technical Approaches CHEMICAL SEPARATION THEN-MANUAL 1987 Repeated “SRAFP” collections of recoil products transported via He-jet followed by rapid liquid-liquid extractions or column chromatography. NOW & FUTURE-AUTOMATED ARCA & SISAK for Solution Chemistry HEVI & OLGA for Volatility Studies BGS as Pre-Separator/Recoil Transfer Chamber (RCT) In-situ Volatilization On-line (IVO) & Cryo-On-Line Detector (COLD) for rapid cyrogenic gas-phase separations. DETECTION Passivated, ion-implanted planar silicon detectors (PIPS)/ Pin Diodes for alpha & SF detection & kinetic-energy measurements. Multiple detector systems for aqueous chemistry. Rotating wheel system (MGA) for collection & detection. Flowing Liquid Scintillation Systems. Record time, energy, position via computer.
First Chemistry on Element 105 (1987-1988) Manual 50-s “glass chemistry” on 34-s 262Ha. • "Glass chemistry" suggested by Prof. Herrmann (Mainz) based on their experience with homologs Nb & Pa(V) which sorb on glass while actinides and Zr, Hf do not. • Picked up activity laden aerosol deposited on glass discs on rotating wheel in hood outside radiation area. Washed to remove actinides, and counted. Stopwatch Chem. (50 s) • Grad students performed 801 such separations. Zr,Hf,actinides didn’t sorb. Showed it was Ha(V) not (III) as some had suggested. • Produced at LBNL 88-Inch Cyclotron via (249Bk,18O, 5n) reaction. • Positive ID via known decay of 34-s 262Ha to 4.3-s 248Lr. Ken Gregorich, Darleane Hoffman demonstrate simple setup for first ever studies of 105 solution chemistry using "glass chemistry".
Technical Approaches: THEN: 1987—Manual Chemistry “Glass” chemistry: ~50 s from collection to detectors for a & SF First aqueous chemistry of 34-s hahnium shows it sorbs on glass like group 5 elements not like group 4 elements and trivalent actinides.
Automated Chemistry to Berkeley, 1988 No Faster than Manual, but More Reproducible, Much Less Tedious, & Saves Grad Students! ARCA (Aqueous Chemistry) OLGA (Gas-phase Chemistry) GSI/Mainz PSI/Switzerland Participated in Investigations of Chemistry of Element 105 (then Hahnium, now Dubnium)
Isothermal Gas-Phase Studies of Element 104 (Rf) Heavy Element Volatility Instrument Merry-Go-Around (MG) (HEVI) 1992 1993 18O 248Cm 261Rf
GAS-PHASE CHEMISTRY BEYOND 104 and 105 1988-1996 • Comparisons of volatilities of halides of Rf &Db (Ha) with lighter homologs inGroups 4 & 5showed unexpected differences. • Indicated gas-phase properties of TANs could not be predicted by simple extrapolation from properties of lighter group 4 & 5 homologs. • Created much interest in studying heavier TANs. • Plans initiatedto study gas-phase properties of still heavier elements: • Seaborgium (Sg,106) • Bohrium (Bh107) • Hassium Hs (108)
Volatility of Rf, Hf, Zr chlorides & bromides (1996,2000) a a 261Rf 75 s 257No 26 s 253Fm 3 d 8.28-8.52 MeV 8.22-8.27 MeV Br<Cl (predicted) Hf <HfOCl2?
Confirmation & Naming of Element 106 • 1993:Our group decided it was important to confirm discovery of element 106 so discoverers# could propose a name. • Used same 249Cf(18O,4n) reaction as discoverers. • Used the 88-Inch Cyclotron rather than the HILAC. • Different horizontal rotating wheel system in special parent-daughter mode. • Positively identified 263106 via α-decay to its known 3.1-s 259Rf daughter. • Half-life and cross section consistent with that of 0.9 s and 0.3 nb reported in the original discovery. [Reported by Gregorich for our group at ACS meeting (1993); Phys. Rev. Lett. 72, 1423 (1994). ] • After much deliberation, Albert Ghiorso & Discovery Group proposed Seaborgium to IUPAC. First rejected as Seaborg was still alive—finally found there was no rule against it and was officially approved in 1997!! • #Original discovery published in Phys. Rev. Lett. 33, 1490 (1974) by LBL/LLNL collaboration: LBL: A. Ghiorso, J. M. Nitschke, J. R. Alonso, C. T. Alonso, M. Nurmia, G. T. Seaborg, LLNL: E. K. Hulet and R. W. Lougheed.Same year Yu. Ts. Oganessian et al. published a claim to 106—later retracted by a new group of Soviet scientists.
249Cf + 18O ~0.6 nb263106 + 4n 263 106 0.9 s ~50% a ~50% SF 9.25, 9.06 MeV 259 Rf 3 s >97% a <3% SF 8.77, 8.86 MeV 255 No 3.1 m 62% a 38% EC 8.12, 7.93, 8.08 MeV
Discovery of longer-lived isotopes of Sg (1996-97), Bh (2000), & Hs (2002) made Chemical Studies possible. 248Cm + 22Ne -5n -4n 116 MeV 121 MeV 265Sg (8 s) 266Sg (21 s) 8.71-8.91 MeV a 8.54-8.74 MeV a 261Rf (75 s) 262Rf m (2 s) SF 8.28 MeV a
Gas-Phase Experiments with Sg (106) International Collaboration at UNILAC at GSI, 1997 Volatility: Mo>W>Sg (as predicted) ΔHads=-90 kj/mol (59 s) ΔHads=-96 kj/mol (51 s) ΔHads= -98 kj/mol (8 s) Temperature [oC]
First Chemical Studies of Bh (107), 2001-2 International Collaboration Discovery of ~17-s 267Bh LBNL, 2000 Gas-phase studies at PSI/GSI Tc>Re>Bh (as predicted)
Chemical Studies of Hs (108), 2002 International Collaboration: PSI, GSI, LBNL HsO4 In-situVolatilization Chamber (IVO) &CryoOn-LineDetector (COLD) OsO4 Hs<Os (Ru)<Os≤Hs (Theory) COLD IVO Ch.E. Düllmann et al. Nature 418 (2002) 859
BGS as Pre-Separator for Chemical/Nuclear Studies • Provides decontamination from plethora of unwanted products. • Uniquely suited for use at high beam intensity accelerators. • BGS-SISAK studies of Rf show feasibility for studying solution chemistry of other short-lived transactinides. • Demonstrated with Cyrogenic Thermo-Chromatographic Separator to study volatilities of Group 8 tetroxides, Os, Hs. Recoil Transfer Chamber Important for pre-separation prior to other chemical studies
SISAK (Short-lived Isotopes Studied by the AKufve technique) Continuous liquid-liquid extractions & detection 208Pb(50Ti,n)257Rf (T1/2= 4.3 s) Led by J.P. Omtvedt, U. of Oslo First successful transactinide chemistry experiment with SISAK. Detected 24 257Rf (4s half-life) a-decays in 17 hours. Proved flowing liquid scintillator system can be used for TANs. Demonstrated advantage of using BGS as a pre-separator.
SISAK Collaboration Group, Norway, Sweden, Germany, USA Berkeley, November 2000
Chemical Periodic Table of the Elements 1 18 1 2 He 2 14 15 16 17 13 H Bh, Hs Gas- phase 3 4 114- 112 Cryo 5 6 7 8 9 10 Rf, Ha, Sg Solution & Gas-phase Mt, Ds ? ? Li Be B C N O F Ne 11 12 13 14 15 16 17 18 4 5 6 7 8 9 10 11 12 3 Na Mg Al Si P S Cl Ar 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 111 87 88 89 104 105 106 107 108 109 110 112 115 114 117 118 116 116 Ha (Db) Fr Ra Ac Rf Sg Bh Hs Mt Rg Cn Ds 113 58 59 60 61 62 63 64 65 66 67 68 69 70 71 Lanthanides Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Actinides Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Role of Chemical Theory “Atom-at-a-time chemistry” has furnished much new data on TANs through Hs (108) and some preliminary info on Cn (112), and E-114. Collaboration at TASCA/GSI just reported (June 2010) observation of 13 atoms of E-114 in month-long experiment! Analysis of chemical behavior is in progress. Studies are extremely challenging for theorists as Schrödinger equation is no longer applicable; fully relativistic calculations must be performed. As early as 1975 (Pitzer) reported (based on Hartree-Fock relativistic calculations) that 112, 114, and 118 might be volatile, relatively inert gases due to relativistic effects. These effects increase as Z2. Therehas been a recent “new wave” of theoretical relativistic investigations summarized in several reviews by V. Pershina. These results help experimentalists design experiments to answer important theoretical questions. (Predictions for solution chemistry are especially difficult.) Theoretical predictions for elements up to 118 are now available. In turn, experimental results help improve theoretical models. Such “synergistic” interactions lead to enhanced understanding of the role & magnitude of relativistic effects.
Global CAST: Heavy Element Nuclear & Radiochemistry Group, U. of Cal. Berkeley/Lawrence Berkeley Natl. Lab. & Groups from around the world:Mainz U., GSI-Darmstadt, TU Munich, Germany; Bern U., Paul Scherrer Inst., Switzerland; Oslo U., Norway; Chalmers U., Gothenborg, Sweden; Tokyo Metropolitan U, JAERI, Japan; Dubna, Russia & FSU. (2003)
Chart of TAN Isotopes, July 2010 (Courtesy of C. Duellmann)
Element 114 Studies Summary 285114 0.12 s 286114 0.12 s 287114 0.45 s 288114 0.80 s 289114 2.70 s 281Cn 97 ms 282Cn 1 ms 283Cn 3.83 s 284Cn 0.10 s 285Cn 33.5 s 277Ds 5.7 ms 279Ds 0.20 s 281Ds 9.6 s 273Hs 0.25 s 275Hs 0.19 s 277Hs 3 ms 269Sg 130 s 271Sg 114 s 265Rf 105 s 267Rf 77 m H. Nitsche Group, LBNL, UCB • First independent verification of element 114 from 48Ca(242Pu,3-4n)287-286114 using BGS 114 • Actively participated in further investigations of element 114 from 48Ca(242Pu,3, 4n)287-286114 reactions using new separator TASCA at GSI. 112 • Production & ID at LBNL with BGS: 6 new isotopes from 48Ca(242Pu,5n)285114 110 108 106 • 17 total element-114 chains observed from Berkeley/GSI • 43 total element-114 chains observed from DUBNA 104
Advantages of Pre-SeparationOpportunities for Chemistry Chemistry without pre-separation System needs to separate out all interfering nuclides Chemistry with pre-separation System can favor selectivity between homologues over removal of interfering nuclides. Opens way to classes of chemical systems previously deemed unsuitable. Accelerator “Cocktail” Beam Target Beam trajectory BGS or TASCA Separation Sites SISAK HEVI/OLGA IVO-COLD CTS L/L extractions RTC > Product trajectory Mylar window
Status of "One-Atom-At-A-Time" Chemistry of TANS • Experimental techniques have evolved from simple "manual" chemistry to sophisticated computer-controlled automated systems. • The LBNL Gas-filled Separator (BGS) at LBNL has been used successfully as a pre-separator prior to studies of chemical properties which has many advantages. (BGS is also used for many other experimental programs.) • The TransActinide Separator and Chemistry Apparatus (TASCA), recently completed at the GSI accelerator in Germany, is used to study chemical, atomic, and nuclear properties of the TANs. • Experimenters must go to one of these large installations (more in the mode of high energy physics programs) to apply for access to the facilities and/or participate in large collaborations. Currently, there are very few such installations with similar facilities. • Synergistic interactions between experimenters and chemical theorists and experimenters have proven to be extremely fruitful.
FUTURE: "One-Atom-At-A-Time" Chemistry of TANS • Continue use of BGS and TASCA as pre-separators for chemical studies. • More detailed studies of solution chemistry of Rf through Sg and study solution chemistry of Bh, Hs, & Mt. • New chemical investigations with 242Pu and 244Pu targets to produce more neutron-rich, longer-lived TAN isotopes. • If longer-lived TANs are identified, devise methods for increasing yields, and “stockpiling” them. • Investigate chemistry of Mt, Ds,Rg,Cn. Produce sufficient quantities for chemical studies using reported longer-lived isotopes such as 9-s Mt, 10-s Ds, 6-s Rg,34-s Cn. Chemistry should be rather interesting & exhibit wide range of oxidation states. • Attempt to make separators smaller and even portable, e.g., a new super-conducting compact gas-filled separator with near 100% transmission has been proposed. • Reconsider production of E-119 using 254Es (275 d) microgram targets with 48Ca beams or other suitable projectiles.
TAN PRODUCTION REACTIONS Hot Fusion—Elements 104 through 106 4,5 n 263Sg 249Cf 18O Fission Products Cold Fusion—Elements 107 through 112,113? 1 n 54Cr 209Bi 262Bh Fission Products Hot (warm) Fusion-reported elements 114,115,116,117,118 3,4,5 n? 48Ca 244,242Pu 289-286114 Fission Products
Contour Plot 2003 (6) (6) 254Es + 48Ca <0.1 s (+) 0.1 s to 0.5 min (o) >0.5 min (•)
CURRENT & FUTURE SHORTAGE OF NUCLEAR SCIENTISTS Exotic, frontier studies attract many undergraduate & graduate students to nuclear & radiochemistry. Excellent education & training for future careers & contributions to basic research & teaching as well as a variety of applied areas including national security & energy missions. • Ultrasensitive & radioanalytical analyses. • Stockpile stewardship & validation. • Surveillance of clandestine nuclear activities (nuclear forensics). • Automated, computer-controlled remote processing systems. • Environmental studies: prediction & monitoring of behavior • of actinides & other species in the environment. • Nuclear medicine, isotope production, radiopharmaceutical preparation; diagnostics & therapy. • Nuclear power: reactor design & performance; mitigation of “Greenhouse” effects. • Treatment, processing, & minimization of nuclear waste. • Nuclear waste isolation & site remediation.
QUOTES “We cannot very often predict the practical applications of basic science--but we can predict that these applications will occur--to the positive benefit of mankind.” Glenn T. Seaborg “There is a beauty in discovery. There is mathematics in music, a kinship of science and poetry in the description of nature, and exquisite form in a molecule. Attempts to place different disciplines in different camps are revealed as artificial in the face of the unity of knowledge. All literate men are sustained by the philosopher, the historian, the political analyst, the economist, the scientist, the poet, the artisan and the musician.” Glenn T. Seaborg, Acceptance Speech Chancellorship at Berkeley, 1958