Date post: | 28-Dec-2015 |
Category: |
Documents |
Upload: | berenice-dawson |
View: | 217 times |
Download: | 1 times |
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
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
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
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
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.