Chemical studies of the transactinide elements at JAEA

Y. NagameAdvanced Science Research CenterJapan Atomic Energy Agency (JAEA)

6th China-Japan Joint Nuclear Physics SymposiumShanghai, China, May 17, 2006

Periodic table of the elementsPeriodic table of the elements

1 181 2

2 13 14 15 16 173 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18

3 4 5 6 7 8 9 10 11 1219 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 118

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

89 90 91 92 93 94 95 96 97 98 99 100 101 102 103

118

Al

Ni Cu Zn Ga

Si P S

H

Li

Na Mg

He

Be B NeFONC

Cl Ar

K Ca Sc Ti V Cr Mn Fe Co Ge As Se Br Kr

Rb XeITeSbSnInCd

Cs Ba La

MoNbZrY

Ta W

Sr

RnHg Tl Pb Bi AtPo

PdRhRuTc

Hf Re

Ag

116

Os Ir Pt Au

113 115

Lu

Mt

Tb Dy Ho ErEu

Rg 112 114

Lanthanides

DsHsDb Sg BhFr Ra Ac Rf

Ac ThActinides

YbLa Pr Nd Pm Sm GdCe Tm

No LrAm BkCm Cf Es FmPa U Np MdPu

Z ≥ 104: transactinide elements superheavy elements

Heavy element nuclear chemistry Heavy element nuclear chemistry at JAEAat JAEA

1. Chemical properties of the transactinide elements (Z 104) - Liquid-phase chemistry of Rf and Db2. Nuclear properties of heavy nuclei (Z 100) - spectroscopy of No (Z = 102) and Rf (Z = 104)

3. Nuclear fission of heavy nuclei (Z 100) - Fission modes in heavy nuclei

Contents

1. Introduction Chemical studies of the transactinide elements Relativistic effects in chemical properties of heavy elements Atom-at-a-time chemistry2. Chemical studies of element 104 (Rf) at JAEA Production of Rf Characteristic chemical properties of Rf based on an atom-at-a-time scale Fluoride complex formation of Rf3. Conclusion

1. Introduction

Objectives:

1. Basic chemical properties ionic charge, radius, redox potential, complex formation, volatility, etc.

2. Architecture of the Periodic table of the 　　 elements Periodicities of the chemical properties

3. Relativistic effects in chemical properties

Chemical studies of the transactinide elements

Relativistic effects (1)

General: increase of the mass with increasing velocity

At heavy elements: Increasing nuclear charge plays as the “accelerator” of the velocity of electrons.

Electrons near the nucleus are attracted closer to the nucleus and move there with high velocity. mass increase of the inner electrons and the contraction of the inner electron orbitals (Bohr radius)

Direct relativistic effects

mm0

(1 (v /c)2

aB 2

me2 2

m0e2 1 (v c)2 aB

0 1 (v c)2

Relativistic effects (2)

Electrons further away from the nucleus are better screened from the nuclear charge by the inner electrons and consequently the orbitals of the outer electrons expand. Indirect relativistic effects

It is expected that transactinide elements would show a drastic rearrangement of electrons in their atomic ground states, and as the electron configuration is responsible for the chemical behavior of elements, such relativistic effects can lead to surprising chemical properties.

Increasing deviations from the periodicity of chemical properties based on extrapolation from lighter homologues in the Periodic table are predicted.

Atom-at-a-time chemistryAtom-at-a-time chemistryThe transactinide elements must be produced at accelerators using reactions of heavy-ion beams with heavy target materials.

Because of the short half-lives and the low production rates of the transactinide nuclides, each atom produced decays before a new atom is synthesized.

Any chemistry to be performed must be done on an "atom-at-a-time" basis.

Rapid, very efficient and selective chemical procedures are indispensable to isolate desired transactinides.

Repetitive experiments

2. Chemical studies of rutherfordium

(Rf, Z = 104) at JAEA

Experimental approach to Rf chemistryExperimental approach to Rf chemistry

1 181 2

2 13 14 15 16 173 4 5 6 7 8 9 10

11 12 13 14 15 16 17 18

3 4 5 6 7 8 9 10 11 1219 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54

55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86

87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 118

57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

89 90 91 92 93 94 95 96 97 98 99 100 101 102 103

Pa U Np MdPu No LrAm BkCm Cf Es Fm

YbLa Pr Nd Pm Sm GdCe Tm

Ac ThActinides

Lanthanides

DsHsDb Sg BhFr Ra Ac Rf

Lu

Mt

Tb Dy Ho ErEu

Rg 112 114

Hf Re

Ag

116

Os Ir Pt Au

113 115

PdRhRuTc

RnHg Tl Pb Bi AtPoCs Ba La

MoNbZrY

Ta W

Sr

Br Kr

Rb XeITeSbSnInCd

Co Ge As Se

Cl Ar

K Ca Sc Ti V Cr Mn Fe

He

Be B NeFONC

H

Li

Na Mg

118

Al

Ni Cu Zn Ga

Si P S

Increasing deviations from the periodicity of the chemical properties based on extrapolations from the lighter homologues are predicted.

Experimental approach should involve detailed comparison of the chemical properties of the transactinides with those of their lighter homologues under identical conditions.

We have investigated the chemical properties of Rf together with the lighter homologues Zr and Hf under the same on-line experiments.

Schematic flow of the experiment

Collection

Dissolution &Complex formation

He cooling gas

18O beam

HAVAR window2.0 mg/cm2

248Cm target

Beam stop

Recoils Gas-jet

Miniaturizedliquid chromatography

Samplepreparation

-particlemeasurement

Cyclic, 80 s

AIDA apparatus

248Cm(18O,5n)261Rf (T1/2 = 78 S)

248Cm: 610 g/cm2

18O6+: 300 pnA

at JAEA tandem acceleratorChemistry Lab.

Eluent bottles

Ta disk reservoir

Micro-columns

He gas heaterHalogen lamp

Sampling table

Air cylinder

Pulse motorsSignal out

8 vacuum chambers

600 mm2 PIPS detectors

Preamp.

He/KCl gas-jetAIDA (Automated Ion-exchangeseparation apparatus coupled with theDetection system for Alpha-spectroscopy)

Cyclic discontinuous column chromatographic separationAutomated detection of -particles

ARCA

Excitation function of 248Cm(18O, 5n)261Rf

Maximum production cross section : ~ 13 nb at 94-MeV 18OProduction rate ： ~ 2 atoms per minute

10-1

100

101

102

85 90 95 100 105 110

PresentSilva et al.PSIGhiorso et al.

Cro

ss s

ectio

n /

nb

Elab

/ MeV

7 8 9 10 11 120

5

10

15

20

25

30

7.5 8.5 9.5 10.5 11.5

Cou

nts

per

20 k

eV

261 R

f +

257 N

o

214 A

t + 21

4mA

t

212m

Po

211m

Po

218m

Fr

215 A

t + 21

1mP

o

211m

Po

-Energy / MeV

94-MeV 18O (2.35 x 1016 p / 4.0 h)

261Rf

78 s

257No

26 s

253Fm

3.0 d

Fluoride complex formation

M4+ + nF- ⇄ MF4+nn- (M=Zr, Hf, and Rf)

Fluoride anion (F-) strongly coordinates with metal cations. Formation of strong ionic bonds is expectedElectrostatic interaction between M4+ and F- charge density, ionic radius, etc.

Fast reaction kinetics of the fluoride complex formation

Ion-exchange chromatographic behavior of Rf, Zr, and Hf in hydrofluoric acid (HF) solution

Anion-exchange behavior of Rf, Zr, and Hf in HF

Column size: 1.0 mm i.d. 3.5 mmColumn size: 1.6 mm i.d. 7.0 mm

4226 cycles of anion-exchange experiments 266 events form 261Rf and 257No, 25 correlations

0

20

40

60

80

100

120

261Rf (Cm/Gd) 169Hf (Cm/Gd)85Zr (Ge/Gd)169Hf (Ge/Gd)

100 101

Ads

orpt

ion

prob

abili

ty

[HF]ini / M

(a)

100 101 102

261Rf (Gd/Cm)169Hf (Gd/Cm) 85Zr (Ge/Gd)169Hf (Ge/Gd)89mZr (Y)167Hf (Eu)

0

20

40

60

80

100

120

[HF]ini / M

(b)

[HF]ini / M

(b)

Rn-MF4+n + nHF2- ⇄ nR-HF2 + MF4+n

n- (M=Rf, Hf and Zr), R: resin

Kd vs. [HF2-]

100

101

102

103

10-1 100

Rf

Zr

Hf

Kd /

mL

g-1

[HF2-] / M

slope = -3

[MF7]3- (M = Zr and Hf)

slope = -2

[RfF6]2- ?

HF ⇄ H+ + F-

HF + F- ⇄ HF2-

HF ⇄ H+ + F-

HF + F- ⇄ HF2-

log Kd = C - nlog[HF2-]

[R-HF2 ]n [MF4+n n–]

[Rn-MF4+n ] [HF2–]n

K =[M]r

[M]aq

[Rn-MF4+n ]

[MF4+n n–]

[R-HF2 ]n

[HF2–]n

= =Kd =

slope = charge state of the metal complex

Conclusion

Large difference in the fluoride complex formation of Rffluoride complex formation of Rf and the lighter homologues Zr and Hf Fluoride complex formation: Rf < Zr ≈ Hf

According to the HSAB (Hard and Soft Acids and Bases) concept, the fluoride anion is a hard anion and interacts stronger with (hard) small cations. Thus, a weaker fluoride complex formation of Rf as compared to those of Zr and Hf would be reasonable if the size of the Rf4+ ion is larger than those of Zr4+ and Hf4+ as predicted with relativistic molecular calculations.

Zr4+ : 0.072 nmHf4+ : 0.071 nmRf4+ : 0.079 nm (prediction)

AcknowledgementAcknowledgement

JAERIJAERI - M. Asai, M. Hirata, S. Ichikawa, T. Ichikawa, Y. Ishii, - M. Asai, M. Hirata, S. Ichikawa, T. Ichikawa, Y. Ishii,

I. Nishinaka, T. K. Sato, H. Tome, A. Toyoshima, K. Tsukada, and I. Nishinaka, T. K. Sato, H. Tome, A. Toyoshima, K. Tsukada, and

T. YaitaT. Yaita

RIKENRIKEN - H. Haba - H. Haba

Osaka UnivOsaka Univ.. - H. Hasegawa, Y. Kitamoto, K. Matsuo, D. Saika, - H. Hasegawa, Y. Kitamoto, K. Matsuo, D. Saika,

W. Sato, A. Shinohara, and Y. TaniW. Sato, A. Shinohara, and Y. Tani

Niigata UnivNiigata Univ.. - S. Goto, T. Hirai, H. Kudo, M. Ito, S. Ono, and J. Saito - S. Goto, T. Hirai, H. Kudo, M. Ito, S. Ono, and J. Saito

Tokyo Metropolitan UnivTokyo Metropolitan Univ.. - H. Nakahara and Y. Oura - H. Nakahara and Y. Oura

Univ. TsukubaUniv. Tsukuba - K. Akiyama and K. Sueki - K. Akiyama and K. Sueki

Kanazawa UnivKanazawa Univ.. - H. Kikunaga, N. Kinoshita, and A. Yokoyama - H. Kikunaga, N. Kinoshita, and A. Yokoyama

Univ. TokushimaUniv. Tokushima - M. Sakama - M. Sakama

GSIGSI - W. Brüchle, V. Pershina, and M. Schädel - W. Brüchle, V. Pershina, and M. Schädel

Univ. MainzUniv. Mainz - J. V. Kratz - J. V. Kratz

Kd vs. [NO3]- in HF/HNO3

Rn-MF4+n + nNO3- ⇄ nR-NO3 + MF4+n

n- : n = -2

100

101

102

103

104

105

10-2 10-1 100

Kd /

mL

g-1

[NO3-] / M

Rf: slope = -2 [RfF6]2-

Zr, Hf: slope = -2 [MF6]2- (M=Zr, Hf)

closed (on-line)open (off-line)

[F-] = 3 x 10-3 M

HF ⇄ H+ + F-

(HF + F- ⇄ HF2-)

HNO3 ⇄ H+ + NO3-

HF ⇄ H+ + F-

(HF + F- ⇄ HF2-)

HNO3 ⇄ H+ + NO3-

log Kd = C - nlog[NO3-]

Kd vs. [F-] in HF/HNO3

MF5- MF6

2- RfF5- RfF6

2-

HF2-

counter ion

3x10-3 M

101

102

103

104

10-6 10-5 10-4 10-3 10-2 10-1

Kd /

mL

g-1

[F-] / M

0.01 M HNO3

(AIX)

0.03 M HNO3

(AIX)

0.01 M HNO3

(AIX)

0.015 M HNO3

(AIX)

0.1 M HNO3

(AIX)

0.1 M HNO3

(CIX)

Rf (on-line)Zr (off-line)Hf (off-line)

Rf (on-line)Zr (off-line)Hf (off-line)

Formation of [MF6]2-: Zr Hf > Rf

Energy levels of the valence ns and (n-1)d electrons

-0.5

-0.4

-0.3

-0.2

-0.1

0

Orb

ital E

nerg

y /

a.u.

Ti Zr Hf Rf

nr nr nr nrrel rel rel rel

5s 6s 7s4s 4s1/2

5s1/2

6s1/2

7s1/2

3d 3d3/2

3d5/2

4d 4d3/2

4d5/2

5d

5d5/2

5d3/2

6d3/2

6d5/2

6d

rel: relativisticnr: non-relativistic

non-rel rel

distance(a.u.)

rad

ial

den

sity

r

R(r

)

J A E R I

0 2 4 0 2 4

0

1

-1

spin-orbit coupling

Rf 5fRf 6s

Rf 6d

Contraction of orbitals

Rf 6p

Radial wave functions of valence orbitals for Rf

18O Beam

248Cm Target on Be Backing

HAVAR Window2.0 mg/cm2

Gas-jet Outlet

Gas-jet Inlet(He/KCl)

Water CooledBeam Stop

He Cooling Gas

Recoils

248Cm(18O,5n)261Rf (78 s), 18O6+ beam: 300 pnA

248Cm target: 610 g/cm2

MANON: Measurement system for Alpha-particle and spontaneous fissioN events ON-line

Si PIN Photodiodes Catcher Foil120 mg/cm2, 20 mm i.d.

Wheel Rotation

Production of 261Rf

Production rates of transactinide nuclides used for chemistry study

Z Nuclide T1/2 (s) Reaction (nb) Production

rate*

104 261Rf 78 248Cm(18O,5n) 13 4 min-1

105 262Db 34 248Cm(19F,5n) 1.5 0.5 min-1

106 265Sg 7.4 248Cm(22Ne,5n) 0.24 5 h-1

107 267Bh 17 249Bk(22Ne,4n) 0.06 1 h-1

108 269Hs 14 248Cm(26Mg,5n) 0.006 3 d-1

* Assuming typical values of 0.8 mg/cm2 for the target thickness and beam intensities

of 3x1012 particles per second.

Atom-at-a-time-chemistryAtom-at-a-time-chemistry

Times

1

2

3

4

5

6

7

8

：　　　　　　　　　　　 　：：　　　　　　　　　　 　　：

“Classical”

“Single atom”

Phase 2Phase1

Activity 1　　 >>　　 Activity 2

Phase 1 Phase 2

Probability 1　 >>　 Probability 2

Anion-exchange procedure in HF with AIDAAnion-exchange procedure in HF with AIDA1. Collection of 261Rf and 169Hf for 125 s2. Dissolution with 240 L of 1.9 M - 13.9 M HF and feed onto the column at 740 L/min

AIX column: MCI GEL CA08Y resin (20 m)1.6 mm i.d. 7.0 mm (1.0 mm i.d. 3.5 mm)

3. 210 L of 4.0 M HCl at 1.0 mL/min

Fraction 1 (A1) Fraction 2 (A2)

Adsorption probability = 100 A2 / (A1 + A2)

169Hf : elution behavior and chemical yields (~ 60%)85Zr and 169Hf from Ge/Gd target

N

+

+

HF2-

HF2-

RfF62-

HF2-

R2-RfF6 + 2HF2- ⇔ 2R-HF2 + RfF6

2-

HF solutionAnion-exchange resin

RfF62-

r

N

HF2-

Anion-exchange between RfF62- and HF2

-

rrr

rrrrr

Adsorption on resin

exchanger

N

+

+

N

r

HF H+ + F-

HF + F- HF2-

HF H+ + F-

HF + F- HF2-

Anion-exchangein HF

Automated Ion exchange separation apparatus coupled with the Detection system for Alpha spectroscopy (AIDA)

AIDAHe/KCl Jet in

Slider

Eluent inCollection site

Sample

5 cm

Magazine20 micro-columns, MCI GEL CA08Y, 22 m1.6 mmΦ x 7.0 mm or 1.0 mmΦ x 3.5 mm

Anion-exchange procedures for Rf andAnion-exchange procedures for Rf and the homologues, Zr and Hf in HFthe homologues, Zr and Hf in HF

4 M HCl200–210 μL Gas out

Magazine

1.9–13.9 M HF240–260 μL

α/γ-spectroscopy

1st fraction

2nd fraction

Front view Side view

Ta disk

Schädel et al. RCA 48(1989)171.

Actinide contraction: The radii of the actinide ions (An3+) are observed to decrease with increasing positive charge of the nucleus. This contraction is a consequence of the addition of successive electrons to an inner f electron shell, so that the imperfect screening of the increasing nuclear charge by the additional f electron results in a contraction of the outer or valence orbital.

Element Z Ionic radius () Remarks

Ti

Zr

22

40

0.605

0.72

Hf 72 0.71 Lanthanide contraction

Rf 104 0. 79

(prediction)

Actinide contraction

+ Relativistic effect

Ionic radii of the group-4 elements (M4+)

Assuming that the adsorption equilibrium of an ion MF4+n n– can be represented by the

equation,

Rn-MF4+n + nHF2– ⇔ nR-HF2 + MF4+n

n–

(where R represents the resin), one obtains the mass action constant

The distribution coefficient Kd is expressed as

Thus, the following equation is deduced

For tracer solutions, the following simplification will be assumed using the constant c

[R-HF2]n = c .

[R-HF2 ]n [MF4+n n–]

[Rn-MF4+n ] [HF2–]n

K =

[M]r

[M]aq

Kd =[Rn-MF4+n ]

[MF4+n n–]

= =1

K

[R-HF2 ]n

[HF2–]n

log Kd = log [R-HF2 ]n

K- nlog [HF2

–]

≈ c - nlog [HF2–].

.

.

Charge state n of an anion MF4+nn–

(M4+ = Rf, Zr and Hf)

Simultaneous production of Rf, Zr and HfSimultaneous production of Rf, Zr and Hf

248Cm target: 610 g/cm2

18O6+ beam: 300 pnA

18O Beam

248Cm Target on Be Backing

HAVAR Window2.0 mg/cm2

Gas-jet Outlet

Gas-jet Inlet(He/KCl)

Water CooledBeam Stop

He Cooling Gas

Recoils Rapid Chemical Separation Apparatus AIDA

Target recoil chamber + gas-jet transport systemTarget recoil chamber + gas-jet transport system

248248Cm(Cm(1818O,5O,5nn))261261Rf (78 s) + Gd(Rf (78 s) + Gd(1818O,O,xnxn))169169Hf (3.24 min)Hf (3.24 min)

natnatGe(Ge(1818O,O,5n5n))8585Zr (7.86 min) + Gd(Zr (7.86 min) + Gd(1818O,O,xnxn))169169Hf (3.24 min) Hf (3.24 min)

Chemical experiments on Rf should be conducted togetherwith the homologues under strictly identical conditions.

Anion-exchange behavior

of Rf, Zr and Hf in HCl 11

23 4

11 12

3 4 5 6 719 20 21 22 23 24 25

37 38 39 40 41 42 43

55 56 57 72 73 74 75

87 88 89 104 105 106 107

H

Li

Na Mg

Be

K Ca Sc Ti V Cr Mn

Rb

Cs Ba La

MoNbZrY

Ta W

Sr Tc

Hf Re

Db Sg BhFr Ra Ac Rf

Adsorption of Rf is similar to those of Zr and Hf.- typical behavior of the group-4 element

0

20

40

60

80

100

Hf (Cm/Gd)Rf (Cm/Gd) Zr (Ge/Gd)Hf (Ge/Gd)

3 5 7 9 11

Ads

orpt

ion

/ %

HCl concentration / M

Upper part of the chart of nuclides 118

117

116

115

114

113

112

Rg

Ds

Mt

Hs

Bh

Sg

Db

Rf

152 153 155 157 159 161 162 163 165 167 169 171 173 175

114 2860.29 s

Rf 26178 4.2 s s

Sg 2582.9 ms

Rf 2566.2 ms

Db 2570.8 1.5s s

Rf 25813 ms

Db 2584.4 s

Rf 2593.1 s

Db 2611.8 s

Db 26234 s

Db 26327 s

Sg 2603.6 ms

Hs 2662.3 ms

Rf 263~15 m

Rf 26020 ms

Rf 262 47 2.1 ms s

Db 2590.5 s

Db 2601.5 s

Db 26773 m

Db 26816 h

Sg 2590.48 s

Sg 2610.23 s

Sg 2626.9 ms

Sg 263 0.3 0.9 s s

Sg 2657.9 s

Sg 26621 s

Bh 26111.8 ms

Bh 262102 8.0 ms ms

Bh 2641.0 s

Bh 2662.47 s

Bh 26717 s

Bh 271 ?

Bh 2729.8 s

Hs 265 0.8 1.7 ms ms

Hs 26759 ms

Hs 26914 s

Hs 2702.4 s

Hs 27711 m

Hs 2640.26 ms

Mt 2661.7 ms

Mt 26842 ms

Mt 2759.7 ms

Mt 2760.72 s

Ds 2673.1μs

?

Ds 269170μs

Ds 270100 6 μs ms

Ds 2711.1 56ms ms

Ds 2730.15 ms

Ds 2819.6 s

Rg 2721.6 ms

Rg 279170 ms

Rg 2803.6 s

112 2770.6 ms

112 2836.1 s

112 28498 ms

112 28534 s

113 283100 ms

113 2840.48 s

114 2871.1 s

114 2880.63 s

114 2892.7 s

115 28732 ms

115 28887 ms

116 29015 ms

116 2916.3 ms

118 2941.8 ms

Rf 257 4.7 s

116 29353 ms

Ds 2790.29 s

112 2821.0 ms

Bh 2650.94 s

113 278344 s

Rg 2749.26 ms

Mt 2707.16 ms