1

Transuranium elements

• Background

• Methods

• Extractions with Organic Ligands

• Search for New Isotope

2

Np synthesis

• Neptunium was the first synthetic transuranium element of the actinide series discovered

isotope 239Np was produced by McMillan and Abelson in 1940 at Berkeley, Californiabombarding uranium with cyclotron-produced neutrons 238U(n,)239U, beta decay of 239U to 239Np (t1/2=2.36 days)

Chemical properties unclear at time of discovery Actinide elements not in current location In group with W

• Chemical studies showed similar properties to U• First evidence of 5f shell• Macroscopic amounts

237Np 238U(n,2n)237U

* Beta decay of 237U 10 microgram

3

Pu synthesis• Plutonium was the second transuranium element of the actinide

series to be discoveredThe isotope 238Pu was produced in 1940 by Seaborg, McMillan, Kennedy, and Wahl deuteron bombardment of U in the 60-inch cyclotron at Berkeley, California 238U(2H, 2n)238Np

* Beta decay of 238Np to 238PuOxidation of produced Pu showed chemically different

• 239Pu produced in 1941Uranyl nitrate in paraffin block behind Be target bombarded with deuterium Separation with fluorides and extraction with diethyletherEventually showed isotope undergoes slow neutron fission

4

Am and Cm discovery• Problems with identification due to chemical

differences with lower actinidesTrivalent oxidation state

• 239Pu(4He,n)242CmChemical separation from PuIdentification of 238Pu daughter from alpha decay

• Am from 239Pu in reactorAlso formed 242Cm

• Difficulties in separating Am from Cm and from lanthanide fission products

5

Bk and Cf discovery

• Required Am and Cm as targetsNeeded to produce theses isotopes in sufficient quantities Milligrams

Am from neutron reaction with PuCm from neutron reaction with Am

• 241Am(4He,2n)243BkCation exchange separation

• 242Cm(4He,n)245CfAnion exchange

6

7

Einsteinium and Fermium

• Debris from Mike test

1st thermonuclear test

• New isotopes of Pu

244 and 246 Successive neutron capture of 238U

Correlation of log yield versus atomic mass

• Evidence for production of transcalifornium isotopes

Heavy U isotopes followed by beta decay

• Ion exchange used to demonstrate new isotopes

8

9

Md and No discovery

• 1st atom-at-a-time chemistry253Es(4H,n)256Md

• Required high degree of chemical separation• Use catcher foil

Recoil of product onto foilDissolved Au foil, then ion exchange

• No controversyExpected to have trivalent chemistry1st attempt could not be reproduced Showed divalent oxidation state

246Cm(12C,4n)254No Alpha decay from 254No Identification of 250Fm daughter using ion

exchange

10

Lr discovery

• 249, 250, 251Cf bombarded with 10,11B• New isotope with 8.6 MeV, 6 second half life

Identified at 258Lr

11

Isotopes of Rf

Mass Number Half Life Decay Mode and

Energies (MeV)

253? ­1.8­s SF,­

254? 0.5­ms SF

255 1.7­s SF

256 7­ms SF,­­(8.81)

257 4.7­s ­(8.77,­9.01,­8.95,­8.62)

258 12­ms SF

259 3.4­s ,­SF­(8.77,­8.86)

260 20­ms SF

261 65­s ­(8.29)

262 52­ms SF

12

Previous Chemistry1966 Zvara et al.242Pu(22Ne,4n)260Ku 114 Mev 12 observed eventsFormation of Ku tetrachloride in the gas phase

1970 Silva et al.248Cm(18O,5n)261Rf 92 MeV 17 observed eventsCation column extraction with Zr and Hf

1980 Hulet et al.248Cm(18O,5n)261Rf 98 MeV 6 observed eventsAl-336 Column (0.25M in o-xylene)12M HCl: removes actinides6M HCl: Zr, Hf and Rf elute

13

Why Study the Chemistry of Rf?

• Test validity of the Extrapolations of the Periodic Table

• Determine the Influence of Relativistic Effects on Chemical Properties

• Help to Predict the Chemical Properties of theHeavier Elements

• Determine Nuclear Properties of the Heaviest Elements

14

Difficulties

Chemistry of the Heaviest Elements

Low production rates

Short half-lives

Large interference from other activities

Capabilities

88-inch­cyclotron:­high­intensity­LHI­beams

Facilities­for­and­expertise­in­fabrication­and

irradiation­of­extremely­radioactive­targets

Facilities­for­and­expertise­in­fast

radiochemical­and­detection­techniques

15

261Rf Production248Cm(18O, 5n)261Rf;

5 nb

Production­Rate­­=­­1.1­min

Detection­Rate­=­1­event­/­5­exps.

­­­­­­­­­­­­­­­­­­­­­­­=­1­event/­7­minutes

Transport to chemistry hood via gas-jet

Target: 0.5 mg/cm2; Beam: 0.5 pA

16

Target System

17

261Rf Decay

261Rf

65 s

257No

8.29 MeV

8.22 MeV8.27 MeV8.32 MeV

26 s

18

261Rf Spectra

19

Rf Chemical Separation Liquid-Liquid­Extraction­System­Requirements:

Rapid­Phase­Separation

Quick­kinetics­(<­10­seconds)

Clean­separation­from­actinides

­­•Actinides­are­formed­by­transfer­reactions

Organic­phase­must­­evaporate­quickly­and­cleanly

­­•Required­for­good­alpha­spectroscopy

Pick­up­activity­with­10­µL­aqueous­phase

Add­to­20­µL­organic­phase­in­a­1­mL­centrifuge­tube

Mix­for­5­seconds

Centrifuge­for­5­seconds

Remove­and­evaporate­organic­phase­on­a­

counting­plate

Place­plate­on­a­PIPS­detector­for­­and­SF­counting

Time­of­chemistry­is­about­1­minute

Repeat­every­90­seconds

Up­to­1000­extractions­per­day

20

Fast Chemical Extraction ProcedurePick­up­activity­with­10­µL­aqueous­phase

Add­to­20­µL­organic­phase­in­a­1­mL­centrifuge­tube

Mix­for­5­seconds

Centrifuge­for­5­seconds

Remove­and­evaporate­organic­phase­on­a­

counting­plate

Place­plate­on­a­PIPS­detector­for­­and­SF­counting

Time­of­chemistry­is­about­1­minute

Repeat­every­90­seconds

Up­to­1000­extractions­per­day

21

IsotopesHomolog tracer Study

0.1­to­0.5­mL­Aqueous­and­Organic­phases

Mix­phase­in­a­5­mL­centrifuge­tube­for­1­minute

Centrifuge­for­30­seconds

Separate­Phases­and­count

­•Alpha­or­Gamma­Spectroscopy­to­determine­

%­Extracted

Isotopes

On­line­at­88-inch­cyclotron

- 261Rf,­162,169Hf

Tracers238Pu,­228Th,­95Zr,­172Hf,­152Eu

22

Organic Extractants

Triisooctylamine­­­(C8H17)3­N Anionic­Species

(TIOA)

Tributyl­Phophate­ Neutral­Species

(TBP)

Thenoyltrifluoroactone­ Chelation

(TTA)

(CH3(CH2)3O)3PO

Organic Soluble

Low Boiling Point

Chemically Specific

23

Experimental ConditionsOrganic­Phase:­­Ligand­­in­Benzene

0.1,­1.0­M­for­TIOA

0.25­M­for­TBP

0.5­M­for­TTA

Aqueous­Phase:

For­TIOA­:­12­M­HCl

For­TBP:­­­ HCl­:­­­8­to­12­M

­­ Cl­­:­­­­8­to­12­M­with­[H­­]­=­8­M

­­­ H­­:­­­­8­to­12­M­with­[Cl­­]=12­M

For­TTA 0.24,­0.10,­and­0.05­M­HCl

+

+-

-

24

261Rf TIOA Extraction Data

[TIOA]M Extraction #­Events #­Experiments

(%)

1.0 29.1­+­6.5 20 343

0.1 117­+­22.0 28 120

Extraction Similar to Group 4

Anionic Species Formation

Results Similar to Anion Exchange

Loss Due to Evaporation

25

0

20

40

60

80

100

7 8 9 10 11 12 13

261Rf

169Hf228Th238Pu

95Zr

% E

xtr

ac

tio

n

HCl [M]

Effect­of­HCl­on­Extraction

26

0

20

40

60

80

100

7 8 9 10 11 12 13

261Rf

169Hf228Th238Pu

95Zr

% E

xtr

ac

tio

n

Cl - [M]

Effect­of­Cl -­on­Extraction

27

TBP ResultsSimilar­to­Pu­Extraction

Anionic­Species­Formation­

Deviation­from­Group­4­Elements

Trends­Towards­Actinides

log Keq for Rutherfordium with TTASolution log Kd log Keq

0.24 M HCl 0.78 + 0.16 3.58 + 0.76

0.10 M HCl 1.6 + 0.3 2.77 + 0.54

Ave 3.18 + 0.90

Values between Th and Pu

28

0

20

40

60

80

100

0 0.05 0.1 0.15 0.2 0.25

% E

xtr

ac

tio

n

[HCl] M

95Zr172Hf

238Pu

261Rf

228Th

TTA Extraction

29

Rutherfordium Hydrolysis ConstantsXY log­Kxy

11 -2.6­+­0.7

12 -5.9­+­1.7

13 -10.2­+­2.9

14 -14.5­+­4.1

Values between Th and Pu/Hf

30

Ionic Radius for Tetravalent RutherfordiumCoordination­Number Ionic­Radius­

(pm)

6 91­+­4

8 102­+­4

For 6 Coordinate

Previous Experimental Data89 pm

Theoretical Calculations80-82 pm

31

Search for Rf263

Previous­Work

­­­Cm(­­­Ne,­,­3n)­­­Rf

No­events­detected

Half-life­upper­limit­of­20­­minutes

248 26322

Cm( O, 3n) Rf

92 MeV on target

Cross Section Estimate = 300 pb

248 18 263

Production Reaction

32

Alpha Half-Life RangeFrom Masses

Assumes Ground State to Ground State TransitionMass­Model E­(MeV) t

(sec.)

Satpathy 8.139 222

Möller­and­Nix 7.736 6920

1/2

33

Log =6ft

Satpathy Möller­and­Nix

­­­­Rf 104.61 104.64

­­­­Lr 103.31 103.01

1.301.63

EC­Half-life 4000 3600

SecondsEC

263

263

EC Half-life estimate

34

Fission Half-Life Estimate

For 159th neutron Fm

Hinderance Factor 4000

SF t for Rf= 52 ms

Estimate for Rf 206 s1/2

262

263

259

35

Results7­SF­and­no­alpha­events­in­Rf­chemical­fraction­in­300­

experiments

Cross­Section

140­+­50­pb­­(300­pb­Estimate)

Half-life

500­+­­­­­­­­­seconds­(200­s­Estimate­from­SF)300200

Conclusions

SF Dominate Decay Mode

Möller and Nix Masses

36

Ceramic Plutonium Target Development for the MASHA Separator for the

Synthesis of Element 114• A Pu ceramic target is being developed for the MASHA

mass separatorRange of energies as particle travels through target

• Ceramic must be capable ofTolerating temperatures up to 2000 ºCReaction products must diffuse out of the target into an ion Low vapor pressure

• Experiments on MASHA will allow measurements that verify the identification of element 114 and provide data for future experiments on chemical properties of the heaviest elements.

37

Project Goals

• Develop Pu containing ceramic for target.

• (Sm,Zr)O2-x ceramics are produced and evaluated

Production of Pb (homolog of element 114) by the reaction of Ca on Sm

• Analysis on the feasibility of using a ZrO2-PuO2 as a target for the production of element 114

• Phases of the resulting Sm, Zr oxide ceramics are evaluated using XRD and subsequent data analysis along with microscopy and thermal analysis

38

MASHA Separator

• Mass Analyzer of Super Heavy Atoms

• on-line mass separator under development at the Flerov Laboratory of Nuclear Reactions at JINR

Reaction products diffuse out of the heated, porous target and drift to an ion source

ionized and injected into the separator

• The products impinge on a position-sensitive focal-plane detector array for mass measurement

• Initial tests will use surrogate products

• Element 114 experiments will be performed using ceramics containing 244Pu to be irradiated by 48Ca ions

39

MASHA Separator

40

Ceramic Target

• Range of particle energies in interaction with ceramics

Different cross sections evaluated

Sample entire excitation range

Permits production of different isotopes of element 114

41

Candidate ceramics

• PuN, Pu2C3, PuP, PuS, PuB, PuO2

• Oxide best candidatePu solid solutions can be synthesizedVarious zirconia containing ceramics have been examined, including ZrO2-PuO2

Properties of ZrO2-PuO2 have been examined by experiment and by models

(Pu,Zr)O2 based targets should have suitable properties for the production of element 114 Ease of synthesis Single phase over a large range Ability to design porous ceramic Low Pu volatility

• Start with Sm oxides to produce Pb (homolog of element 114)

42

Ceramic Composition

# SmO1.5­ ZrO2­ Zn­Stearate­ PEG­

1 65 35 3 3

2 65 35 3 6

3 80 20 3 3

4 80 20 3 6

5 50 50 3 3

6 50 50 3 6

Mol % Oxides Wt. % additive

43

XRD Analysis

0.0

20.0

40.0

60.0

80.0

100.0

1 2 3 4 5 6

Sm2Zr

2O

7 (cubic, pyrochlore-type)

(Sm,Zr)O2-x

solid solution (cubic)

Sm2O

3 (monoclinic)

ZrO2 (monoclinic)

Ph

as

e W

t. %

Sample #

44

Element 114 Conclusions

• Candidates for the MASHA target are currently being prepared and characterized.

• On-line tests with MASHA will begin with surrogate Sm targets, but subsequent irradiations with 242Pu and ultimately 244Pu will be performed.

• Once the target is prepared and tested, experiments designed to measure the mass of element 114 will begin.