Chemical studies of rutherfordium at JAER

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Transcript Chemical studies of rutherfordium at JAER

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

Chemical studies of the transactinide elements at JAEA

Y. Nagame Advanced Science Research Center Japan Atomic Energy Agency (JAEA)

Periodic table of the elements

1 1

2 4

Ra Lanthanides Actinides

3 21

4 22

104

≥ 104: transactinide elements superheavy elements

5 23

105

6 24

106

7 25

107

8 26

108

9 27

109

10 28

110

11 29

111

12 30

112

112

13 5

113

113

14 6

114

114

15 7

115

115

16 8

116

116

100

101

102

103

Lr Br

17 9

35 18 2

118

118

Heavy element nuclear chemistry at JAEA 1. Chemical properties of the transactinide elements (Z



104)

- Liquid-phase chemistry of Rf and Db

2. Nuclear properties of heavy nuclei (Z

-

a-g

spectroscopy of No (

= 102) and



100)

Rf (

= 104)

3. Nuclear fission of heavy nuclei (Z

- Fission modes in heavy nuclei



100)

1. Introduction

Chemical studies of the transactinide elements  Relativistic effects in chemical properties of heavy elements  Atom-at-a-time chemistry

2. 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 Rf 3. Conclusion

1. Introduction

Chemical studies of the transactinide elements 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

Relativistic effects (1)

General: increase of the mass with increasing velocity



0 (1 (

) 2 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)

a B



2 2  2

2 1 

Direct relativistic effects

(

v c

) 2 

a B

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 chemistry

The 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 chemistry

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

1 1

We have investigated the chemical properties of

Rf together with the lighter homologues Zr and Hf

under the same on-line experiments.

2 4

88 3 21

89 4 22

104 5 23

105 6 24

106 7 25

107 8 26

108 9 27

109 10 28

110 11 29

111 12 30

112 13 5

113 14 6

114 15 7

115 16 8

116 17 9

18 2

118

Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg 112 113 114 115 116 118 Lanthanides Actinides

100

101

102

103

Schematic flow of the experiment

18 O beam He cooling gas 248 Cm target Beam stop 248 Cm( 18 O,5

) 261 Rf (

1/2 = 78 S) 248 Cm: 610 m g/cm 2 18 O 6+ : 300 pnA HAVAR window 2.0 mg/cm 2 Recoils

Chemistry Lab.

Collection Gas-jet at JAEA tandem accelerator

AIDA apparatus

Dissolution & Complex formation Miniaturized liquid chromatography Sample preparation a -particle measurement Cyclic, 80 s

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

Signal out 8 vacuum chambers 600 mm 2 PIPS detectors Preamp.

He/KCl gas-jet Pulse motors Air cylinder

ARCA

Eluent bottles Micro-columns Sampling table He gas heater Halogen lamp Ta disk reservoir Cyclic discontinuous column chromatographic separation Automated detection of a -particles

Excitation function of

248

Cm(

O, 5n)

261

Rf

10 2 Present Silva

et al

PSI Ghiorso

et al

10 1 30 25 94-MeV 18 O (2.35 x 10 16 p / 4.0 h) 261 Rf 78 s 20 10 0 15 2 57 No 26 s 10 253 Fm 3. 0 d 5 10 -1 85 90 95 100 105 110 0 7 7.5

8 8.5

9 9.5

10 10.5

a -Energy / MeV

lab / MeV Maximum production cross section : ~ 13 nb at 94-MeV 18 O Production rate ： ~ 2 atoms per minute 11 11.5

Fluoride complex formation

M 4+ +

F ⇄ MF 4+

n n

(M=Zr, Hf, and Rf) Fluoride anion (F ) strongly coordinates with metal cations.

 Formation of strong ionic bonds is expected Electrostatic interaction between M 4+ 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

120 100 80 60 4226 cycles of anion-exchange experiments  266 a events form 261 Rf and 257 No, 25 a-a correlations Column size: 1.6 mm i.d.  7.0 mm 120 (a) Column size: 1.0 mm i.d.  3.5 mm 100 80 60 26 1 Rf (Gd/Cm) 16 9 Hf (Gd/Cm) 85 Zr (Ge/Gd) 16 9 Hf (Ge/Gd) 89 m Zr (Y) 16 7 Hf (Eu) 40 40 20 0 26 1 Rf (Cm/Gd) 16 9 Hf (Cm/Gd) 85 Zr (Ge/Gd) 16 9 Hf (Ge/Gd) 10 0 [HF] ini / M 10 1 20 0 10 0 10 1 [HF] ini / M 10 2

10 3 slope = -3 [MF 7 ] 3 (M = Zr and Hf)

vs. [HF

10 2 slope = -2 [RfF 6 ] 2 ?

HF ⇄ H HF + F + ⇄ + F -

HF 2 -

10 1 Rf Hf Zr 10 0 10 -1 10 0 [HF 2 ] / M R

MF 4+

 HF 2 ⇄

 R HF 2 + MF 4+

n n

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

= [R-HF 2 ]

[MF 4+

n n

– ] [R

n -

MF 4+

] [HF 2 – ]

n K

d = [M] r [M] aq = [R

n -

MF 4+

] [MF 4+

n n

– ] = [R-HF 2 ]

[HF 2 – ]

log

d = C

- n

 log[HF 2 ] slope = charge state of the metal complex

]

Conclusion

Large difference in the fluoride complex formation of Rf the lighter homologues Zr and Hf 

Fluoride complex formation: Rf < Zr ≈ Hf

and 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 Rf 4+ ion is larger than those of Zr 4+ and Hf 4+ as predicted with relativistic molecular calculations.

Zr 4+ : 0.072 nm Hf 4+ : 0.071 nm Rf 4+ : 0.079 nm (prediction)

Acknowledgement

JAERI - M. Asai, M. Hirata, S. Ichikawa, T. Ichikawa, Y. Ishii, I. Nishinaka, T. K. Sato, H. Tome, A. Toyoshima, K. Tsukada, and T. Yaita RIKEN - H. Haba Osaka Univ .

- H. Hasegawa, Y. Kitamoto, K. Matsuo, D. Saika, W. Sato, A. Shinohara, and Y. Tani Niigata Univ .

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

- H. Nakahara and Y. Oura Univ. Tsukuba - K. Akiyama and K. Sueki Kanazawa Univ .

- H. Kikunaga, N. Kinoshita, and A. Yokoyama Univ. Tokushima - M. Sakama GSI W. Brüchle, V. Pershina, and M. Schädel Univ. Mainz - J. V. Kratz

10 5 10 4 10 3

vs. [NO

]

in HF/HNO

3 Zr, Hf: slope = -2 [MF 6 ] 2 (M=Zr, Hf)

HF ⇄ H (HF + F + + F ⇄ HF 2 ) HNO 3 ⇄ H + +

NO 3 -

[F ] = 3 x 10 -3 M

Rf: slope = -2 [RfF 6 ] 2-

10 2 10 1 closed (on-line) open (off-line) 10 0 10 -2 10 -1 [NO 3 ] / M 10 0 log

d = C -

 log[NO 3 ] R

-MF 4+

 NO 3 ⇄

 R NO 3 + MF 4+

n n

= -2

10 4 10 3 10 2

0.1 M HNO 3 (CIX)

MF 5 -

vs. [F

] in HF/HNO

 MF 6 2 RfF 5  RfF 6 2-

0.01 M HNO 3 (AIX) 0.03 M HNO 3 (AIX) 0.1 M HNO 3 (AIX)

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

0.01 M HNO 3 (AIX) 0.015 M HNO 3 (AIX)

HF 2 counter ion 10 1 10 -6 10 -5 10 -4 10 -3 [F ] / M 10 -2 3x10 -3 M Formation of [MF 6 ] 2 : Zr  Hf > Rf 10 -1

Energy levels of the valence

and (

-1)

electrons

0 Ti Zr Hf Rf -0.1

-0.2

nr 4

rel 4

1/2 nr 5

rel nr rel nr 5

5/2 6

1/2 5

3/2 7

rel 6

5/2 6

3/2 -0.3

1/2 6

5/2 4

3/2 5

1/2 -0.4

5/2 3

3/2 rel: relativistic nr: non-relativistic -0.5

Radial wave functions of valence orbitals for Rf

J A E R I 0 1

Rf 5f Rf 6s Rf 6p

non-rel

Rf 6d

Contraction of orbitals

rel

spin-orbit coupling

-1 0 2 4 0 2 4

distance(a.u.)

18 O Beam

Production of

261

Rf

He Cooling Gas 248 Cm( 18 O,5

) 261 Rf (78 s) , 18 O 6+ beam: 300 pnA 248 Cm target: 610 m g/cm 2 248 Cm Target on Be Backing Gas-jet Outlet Water Cooled Beam Stop Gas-jet Inlet (He/KCl) HAVAR Window 2.0 mg/cm 2 Recoils Wheel Rotation Si PIN Photodiodes Catcher Foil 120 mg/cm 2 , 20 mm i.d.

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

Production rates of transactinide nuclides used for chemistry study

Z 104 105 Nuclide T 1/2 (s) 261 262 265 Rf Db Sg 78 34 7.4 248 Reaction 248 Cm( 18 O,5n) Cm( 19 F,5n)  (nb) Production rate * 13 1.5 248 Cm( 22 Ne,5n) 0.24 4 min -1 0.5 min -1 5 h -1 106 107 267 Bh 17 249 Bk( 22 Ne,4n) 0.06 1 h -1 108 269 Hs 14 248 Cm( 26 Mg,5n) 0.006 3 d -1 * Assuming typical values of 0.8 mg/cm 2 for the target thickness and beam intensities of 3x10 12 particles per second.

“Classical” Phase1 Activity 1

Atom-at-a-time-chemistry

“Single atom” >> Phase 2 Activity 2 Times ：： 8 1 2 3 4 5 6 7 Phase 1 ：： Phase 2 Probability 1 >> Probability 2

Anion-exchange procedure in HF with AIDA

1. Collection of 261 Rf and 169 Hf for 125 s 2. Dissolution with 240 m L of 1.9 M - 13.9 M HF and feed onto the column at 740 m L/min 3. 210 m L of 4.0 M HCl at 1.0 mL/min AIX column: MCI GEL CA08Y resin (20 m m) 1.6 mm i.d.  7.0 mm (1.0 mm i.d.  3.5 mm)

Fraction 1 (A 1 ) Fraction 2 (A 2 ) Adsorption probability = 100 A 2 / (A 1 + A 2 )

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

Anion-exchange in HF

R 2 RfF 6 + 2HF 2 ⇔ 2R-HF 2 + RfF 6 2-

Anion-exchange resin

r Adsorption on resin r r r r N + N + RfF 6 2-

HF solution

HF 2 HF 2 HF  HF + F H +  + F -

HF 2 -

exchanger Anion-exchange between RfF 6 2 and HF 2 r r r r r N + N + HF 2 HF 2 RfF 6 2-

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

Front view

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

Side view

He/KCl Jet in Collection site Eluent in 240 –260 μL 4 M HCl 200 –210 μL Gas out Slider Magazine 2 nd fraction Sample 1 st fraction

α/γ-spectroscopy

Magazine 20 micro-columns, MCI GEL CA08Y, 22 m m 1.6 mm Φ x 7.0 mm or 1.0 mmΦ x 3.5 mm Ta disk 5 cm Schädel

et al.

RCA

(1989)171.

Ionic radii of the group-4 elements (M

)

Element Ti Zr Hf Rf

22 40 72 104 Ionic radius ( ) 0.605

0.72

0.71

0. 79 (prediction) Remarks Lanthanide contraction Actinide contraction + Relativis tic effect Actinide contraction : The radii of the actinide ions (An 3+ ) 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

electron shell, so that the imperfect screening of the increasing nuclear charge by the additional

electron results in a contraction of the outer or valence orbital.

Charge state n of an anion MF

4+n

–

(M

= Rf, Zr and Hf)

Assuming that the adsorption equilibrium of an ion MF 4+

n n

– equation, can be represented by the R

n -

MF 4+

 HF 2 – ⇔

 R-HF 2 + MF 4+

n n

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

K =

[R-HF 2 ]

[MF 4+

n n

– ] [R

n -

MF 4+

] [HF 2 – ]

The distribution coefficient

d is expressed as

d = [M] [M] r aq = [R

n -

MF 4+

] [MF 4+

n n

– ] = 1

[R-HF 2 ]

[HF 2 – ]

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

[R-HF 2 ]

c .

Thus, the following equation is deduced log

d = log [R-HF 2 ]

K -

 log [HF 2 – ] ≈ c -

 log [HF 2 – ] .

Simultaneous production of Rf, Zr and Hf

 Chemical experiments on Rf should be conducted together with the homologues under strictly identical conditions.

Target recoil chamber + gas-jet transport system 248 Cm( 18 O,5

) 261 Rf (78 s) + Gd( 18 O,

) 169 Hf (3.24 min) nat Ge( 18 O,

) 85 Zr (7.86 min) + Gd( 18 O,

) 169 Hf (3.24 min) He Cooling Gas 248 Cm target: 610 m g/cm 2 18 O 6+ beam: 300 pnA 248 Cm Target on Be Backing Gas-jet Outlet 18 O Beam Water Cooled Beam Stop Gas-jet Inlet (He/KCl) HAVAR Window 2.0 mg/cm 2 Recoils Rapid Chemical Separation Apparatus AIDA

1 1

2 4

3 21

4 22

104

5 23

105

Anion-exchange behavior

6 24

106

of Rf, Zr and Hf in HCl

100 80 60 Hf (Cm/Gd) Rf (Cm/Gd) Zr (Ge/Gd) Hf (Ge/Gd)

7 25

107

Bh 40 20 0 3 5 7 9 HCl concentration / M Adsorption of Rf is similar to those of Zr and Hf.

typical behavior of the group-4 element

Upper part of the chart of nuclides

117 118 118 294 1.8 ms 116 116 290 15 ms 116 291 6.3 ms 115 115 287 32 ms 115 288 87 ms 114 114 286 0.29 s 114 287 1.1 s 114 288 0.63 s 114 289 2.7 s 113 283 100 ms 113 284 0.48 s 113 113 344 278 m s 112 Ds Mt Ds 267 3.1μs ?

Mt 266 1.7 ms Rg Rg 272 1.6 ms Ds 269 170μs Ds 270 100 6 μs ms Ds 271 1.1 56 ms ms Mt 268 42 ms Mt 270 7.16 ms Rg 274 9.26 ms Ds 273 0.15 ms Sg Db Rf Sg 258 2.9 ms Db 257 0.8 1.5

s s Rf 256 6.2 ms 152 Bh Sg 259 0.48 s Db 258 4.4 s Db 259 0.5 s Db Hs Bh 261 11.8 ms Bh 262 102 8.0

ms ms Sg 260 3.6 ms Sg 261 0.23 s 260 1.5 s Hs 264 0.26 ms Hs 265 0.8 1.7

ms ms Bh 264 1.0 s Sg Db 262 6.9 ms 261 1.8 s Sg 263 0.3 0.9

s s Db 262 34 s Hs 266 2.3 ms Bh 265 0.94 s Db 263 27 s Rf 257 4.7 s 153 Rf 258 13 ms Rf 259 3.1 s Rf 260 20 ms 155 Rf 261 78 4.2

s s 157 Rf 262 47 2.1

ms s Hs 267 59 ms Bh 266 2.47 s Bh 267 17 s Sg 265 7.9 s Rf 263 ~15 m 159 Sg 266 21 s Hs 269 14 s 161 Hs 270 2.4 s Db 267 73 m Db 268 16 h 162 163 112 277 0.6 ms Bh 271 ?

Bh 272 9.8 s 165 Mt 275 9.7 ms Mt 276 0.72 s 167 Rg 279 170 ms Rg 280 3.6 s Ds 279 0.29 s Hs 277 11 m 169 112 282 1.0 ms 112 283 6.1 s 112 284 98 ms 112 285 34 s Ds 281 9.6 s 171 173 175 116 293 53 ms

Chemical studies of rutherfordium at JAER

Transcript Chemical studies of rutherfordium at JAER

Chemical studies of the transactinide elements at JAEA

Periodic table of the elements

≥ 104: transactinide elements superheavy elements

Heavy element nuclear chemistry at JAEA 1. Chemical properties of the transactinide elements (Z

104)

- Liquid-phase chemistry of Rf and Db

-

spectroscopy of No (

= 102) and

Rf (

= 104)

- Fission modes in heavy nuclei

Contents

1.

Introduction

Chemical studies of the transactinide elements Objectives:

Relativistic effects (1)

Relativistic effects (2)

Atom-at-a-time chemistry

2. Chemical studies of rutherfordium (Rf, Z = 104) at JAEA

Experimental approach to Rf chemistry

Schematic flow of the experiment

Excitation function of

Cm(

O, 5n)

Rf

Fluoride complex formation

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

vs. [HF

]

Conclusion

Acknowledgement

vs. [NO

]

in HF/HNO

vs. [F

] in HF/HNO

Energy levels of the valence

and (

-1)

electrons

Radial wave functions of valence orbitals for Rf

Production of

Rf

Production rates of transactinide nuclides used for chemistry study

Atom-at-a-time-chemistry

Anion-exchange procedure in HF with AIDA

Ionic radii of the group-4 elements (M

)

Charge state n of an anion MF

(M

= Rf, Zr and Hf)

Simultaneous production of Rf, Zr and Hf

Anion-exchange behavior

of Rf, Zr and Hf in HCl

Upper part of the chart of nuclides

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