Transuranium elements

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, California
• bombarding uranium with cyclotron-produced
  neutrons
• 238U(n,g)239U, beta decay of 239U to 239Np
  (t1/22.36 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 discovered
• The 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 238Pu
• Oxidation of produced Pu showed chemically
  different
• 239Pu produced in 1941
• Uranyl nitrate in paraffin block behind Be target
  bombarded with deuterium
• Separation with fluorides and extraction with
  diethylether
• Eventually showed isotope undergoes slow neutron
  fission

4
Am and Cm discovery

• Problems with identification due to chemical
  differences with lower actinides
• Trivalent oxidation state
• 239Pu(4He,n)242Cm
• Chemical separation from Pu
• Identification of 238Pu daughter from alpha decay
• Am from 239Pu in reactor
• Also formed 242Cm
• Difficulties in separating Am from Cm and from
  lanthanide fission products

5
Bk and Cf discovery

• Required Am and Cm as targets
• Needed to produce theses isotopes in sufficient
  quantities
• Milligrams
• Am from neutron reaction with Pu
• Cm from neutron reaction with Am
• 241Am(4He,2n)243Bk
• Cation exchange separation
• 242Cm(4He,n)245Cf
• Anion exchange

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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

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Md and No discovery

• 1st atom-at-a-time chemistry
• 253Es(4H,n)256Md
• Required high degree of chemical separation
• Use catcher foil
• Recoil of product onto foil
• Dissolved Au foil, then ion exchange
• No controversy
• Expected to have trivalent chemistry
• 1st 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
• a Energies (MeV)
• 253? 1.8 s SF, a
• 254? 0.5 ms SF
• 255 1.7 s SF
• 256 7 ms SF, a (8.81)
• 257 4.7 s a (8.77, 9.01, 8.95, 8.62)
• 258 12 ms SF
• 259 3.4 s a, SF (8.77, 8.86)
• 260 20 ms SF
• 261 65 s a (8.29)
• 262 52 ms SF

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Previous Chemistry
1966 Zvara et al. 242Pu(22Ne,4n)260Ku 114 Mev
12 observed events Formation of Ku tetrachloride
in the gas phase 1970 Silva et
al. 248Cm(18O,5n)261Rf 92 MeV 17 observed
events Cation column extraction with Zr and Hf
1980 Hulet et al. 248Cm(18O,5n)261Rf 98
MeV 6 observed events Al-336 Column (0.25M in
o-xylene) 12M HCl removes actinides 6M HCl
Zr, Hf and Rf elute
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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

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Difficulties
Chemistry of the Heaviest Elements

Low production rates Short half-lives Large
interference from other activities
Capabilities

• 88-inch cyclotron high intensity LHI beams
• Facilities for and expertise in fabrication and
• irradiation of extremely radioactive targets
• Facilities for and expertise in fast
• radiochemical and detection techniques

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261Rf Production
s 5 nb
248Cm(18O, 5n)261Rf

• Production Rate 1.1 min
• Detection Rate 1 event / 5 exps.
• 1 event/ 7 minutes

Target 0.5 mg/cm2 Beam 0.5 pmA
Transport to chemistry hood via gas-jet
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Target System
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261Rf Decay

261
Rf
8.29 MeV
65 s
a
8.22 MeV 8.27 MeV 8.32 MeV
257
No
26 s
a
18
261Rf Spectra
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Rf Chemical Separation

• Liquid-Liquid Extraction System Requirements
• Rapid Phase Separation
• Quick kinetics (lt 10 seconds)
• Clean separation from actinides
• Actinides are formed by transfer reactions
• Organic phase must evaporate quickly and cleanly
• Required for good alpha spectroscopy
• Pick up activity with 10 µL aqueous phase
• Add to 20 µL organic phase in a 1 mL centrifuge
  tube
• Mix for 5 seconds
• Centrifuge for 5 seconds
• Remove and evaporate organic phase on a
• counting plate
• Place plate on a PIPS detector for a and SF
  counting
• Time of chemistry is about 1 minute
• Repeat every 90 seconds
• Up to 1000 extractions per day

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Fast Chemical Extraction Procedure

• Pick up activity with 10 µL aqueous phase
• Add to 20 µL organic phase in a 1 mL centrifuge
  tube
• Mix for 5 seconds
• Centrifuge for 5 seconds
• Remove and evaporate organic phase on a
• counting plate
• Place plate on a PIPS detector for a and SF
  counting
• Time of chemistry is about 1 minute
• Repeat every 90 seconds
• Up to 1000 extractions per day

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Isotopes

• Homolog tracer Study
• 0.1 to 0.5 mL Aqueous and Organic phases
• Mix phase in a 5 mL centrifuge tube for 1 minute
• Centrifuge for 30 seconds
• Separate Phases and count
• Alpha or Gamma Spectroscopy to determine
• Extracted
• Isotopes
• On line at 88-inch cyclotron
• 261Rf, 162,169Hf
• Tracers
• 238Pu, 228Th, 95Zr, 172Hf, 152Eu

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Organic Extractants

• Triisooctylamine (C8H17)3 N Anionic Species
• (TIOA)
• Tributyl Phophate Neutral Species
• (TBP)
• Thenoyltrifluoroactone Chelation
• (TTA)

(CH3(CH2)3O)3PO
Organic Soluble Low Boiling Point Chemically
Specific
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Experimental Conditions

• Organic Phase Ligand in Benzene
• 0.1, 1.0 M for TIOA
• 0.25 M for TBP
• 0.5 M for TTA
• Aqueous Phase
• For TIOA 12 M HCl
• For TBP HCl 8 to 12 M
• Cl 8 to 12 M with H 8 M
• H 8 to 12 M with Cl 12 M
• For TTA 0.24, 0.10, and 0.05 M HCl

-


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261Rf TIOA Extraction Data

• TIOAM 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
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TBP Results

• Similar to Pu Extraction
• Anionic Species Formation
• Deviation from Group 4 Elements
• Trends Towards Actinides

log Keq for Rutherfordium with TTA
Solution 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
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TTA Extraction
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Rutherfordium Hydrolysis Constants

• XY log Kxy
• 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
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Ionic Radius for Tetravalent Rutherfordium

• Coordination Number Ionic Radius (pm)
• 91 4
• 102 4

For 6 Coordinate Previous Experimental
Data 89 pm Theoretical Calculations 80-82 pm
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Search for Rf
263

• Previous Work
• Cm( Ne, a, 3n) Rf
• No events detected
• Half-life upper limit of 20 minutes

263
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248
Production Reaction
18
263
248
Cm( O, 3n) Rf 92 MeV on target Cross
Section Estimate 300 pb
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Alpha Half-Life Range
From Masses Assumes Ground State to Ground State
Transition

• Mass Model Ea (MeV) t
• (sec.)
• Satpathy 8.139 222
• Möller and Nix 7.736 6920

1/2
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EC Half-life estimate

• Satpathy Möller and Nix
• Rf 104.61 104.64
• Lr 103.31 103.01
• 1.30 1.63
• EC Half-life 4000 3600
• Seconds

Log 6
ft
263
263
EC
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Fission Half-Life Estimate
259
For 159th neutron Fm Hinderance Factor 4000
SF t for Rf 52 ms Estimate for Rf
206 s
262
1/2
263
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Results

• 7 SF and no alpha events in Rf chemical fraction
  in 300 experiments
• Cross Section
• 140 50 pb (300 pb Estimate)
• Half-life
• 500 seconds (200 s Estimate from SF)

300 200
Conclusions
SF Dominate Decay Mode Möller and Nix Masses
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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 separator
• Range of energies as particle travels through
  target
• Ceramic must be capable of
• Tolerating temperatures up to 2000 ºC
• Reaction 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.

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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

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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

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MASHA Separator
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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

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Candidate ceramics

• PuN, Pu2C3, PuP, PuS, PuB, PuO2
• Oxide best candidate
• Pu solid solutions can be synthesized
• Various 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)

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Ceramic Composition
Mol Oxides Wt. additive
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XRD Analysis
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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.