LLNL-PRES-725106This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

Fabrication of Radioactive Targets for Laser ExperimentsTargetFabricationMeeting2017

LLNLTargetFabricationTeam

March 12, 2017

LLNL-PRES-7251062

§ ChallengesofworkingwithPuandDU— Radioactiveandtoxic

• Puworkisdoneinaninertatmosphereglovebox• DUworkisdoneinafumehood

— Reactive(oxidizereadily)— Limitedmetrologyandmachiningtools

• Oftenrequiresspecializedencapsulation— Targetmassesareassmallaspossible— Multiplephasetransformationslimitabilitytoheatthematerial

§ PupartscontainPu-242,whichiswonfrommetaloxidepowder

§ DUpartsarecutfromthicksheetandhand-polishedtothickness

Weproducehigh-precisionplutonium(Pu)anddepleteduranium(DU)componentsforavarietyoftargets

2 mmMechanically polished Pu

Oxide coating on Pu metal

Part after 1 year in glovebox

LLNL-PRES-7251063

Were-createdthecapabilitytowinsub-gramquantitiesofplutoniummetal

Am-241 is chemically removed from the Pu oxide, and Pu is precipitated

as an oxalate (Pu(C2O4)2)

The oxalate is calcined to oxide and converted to fluoride

PuO2 + 4HF è PuF4 + 2H2O

Thisprocesshadnotbeendonefor70years

LLNL-PRES-7251064

Themetalisformedviaametallothermicreactioninaninductionfurnace,insideaglovebox

As cast material, with cruciblePu metal after combining 2 batches

and re-melting with CaCl2

2 mm

Ca + I2

Ca + I2

Ca + I2 + PuF4

General reaction:PuF4 + 2Ca è Pu + 2CaF2

Iodine is added to add heat, to encourage the Pu metal to coalesce, and to lower the melting point of the slag

PuF4 + 4Ca +I2 è Pu + 2CaF2 + 2CaICa + I2 è CaI2

LLNL-PRES-7251065

50 µm

Improvementsinthemetal-makingprocessresultedinasingle-phasea-Pumicrostructure

Precipitate a grains (light contrast)Eutectoid (dark contrast) Note: Images are at the same magnification

First metalTwo-phase mixture: a-Pu + a-Pu/PuNi eutectoid

50 µm

New metala-Pu with grain boundary impurities

a grains (light contrast)Grain-boundary impurities (dark contrast)

LLNL-PRES-7251066

ThefirstPutargetswere2mmdiameterdiscs,6µmthick(mass~0.5mg)

NOT TO SCALE

(110) oriented diamond* window150 ± 5 µm thickSputter-deposited Al “washer”

9 µm thick (to be ablated/polished to match sample)

Sputtered Au heat shield2 ± 1 µm thick (110) oriented diamond*

40 ± 2 µm thick

(110) oriented diamond*40 ± 2 µm thick

Pu Sample6 ± 1 µm thick

2 mm diameter

Stycast 1266 GlueMax 1.5 µm thick

Stycast 1266 GlueMax 1.5 µm thick

Stycast 1266 GlueMax 1.5 µm thick

*Single-crystal, natural diamond; polished to thickness

3 mm

LLNL-PRES-7251067

ThePuingotwassectionedandeachpiecewasnear-netshapedintheb-phase

Eachpiecewasmeltedandre-solidifiedinUHVtoform~175µmthickdiscsDiscswerepressedat~140°C(b-phase)tonear-netshape

2 mm

2 mm

Ingotwascutinto4pieces

LLNL-PRES-7251068

Thesamplewashandpolishedtothickness;surfacefinish(RA)was27nm,<0.5µmround-off/1mmradius

PolishedPusample,with2mmdiametersamplelocationshowninred

Finalthickness:9.6µm,including~1µmglueLargescratchestypically<0.25µmdeep

2 mm

Pusample,afterlasercuttingtofinaldimensions

LLNL-PRES-7251069

Thepolishedsamplewaslasercutintoa2mmdiameterdisc

2 mm

Side 1 Side 2

LLNL-PRES-72510610

Thephysicspackagewasassembledwithamini-manipulatorintheglovebox

3 mm

Pu sample(2 mm diameter)

Glue drop diameter: ~ 250 µm

LLNL-PRES-72510611

Finalassemblyandmetrologyiscompletedinacleanroom,constructedspecificallyforthiswork

AssemblyofthePuphysicspackageontotheU6Nbpinhole

Physicspackage7.6µmthickPusurroundedbyanAlwasher,encapsulatedbetween

diamonds

3 mm

LLNL-PRES-72510612

Asecondtargettypeincludesmicron-scale2Dsine-waveripples

Pusampleis1mmdiameter(~0.5mg)

Pu sample(30 µm thick)

Au washerMg alloy washer

Depleted uranium (10 µm thick)

Stycast 1266 epoxy (1 – 3 µm thick)PVDF (40 µm thick)

HDC [Diamond] (500 µm thick)

Stycast 1266 epoxy

NOT TO SCALE

Au Au (100 µm thick)

Gold (~0.25 µm thick)

Molybdenum (40 µm thick)

LLNL-PRES-72510613

§ 1mmdiameterPupartissurroundedby2rings— Physicsoftheexperimentsnecessitates2materials— Allmaterialsmustpolishsimilarly— Allmaterialsmustcoinsimilarly— Annulargapsmustbe<50µm— PumustbondtoMowithnoglue

§ Fabricationplan— Eachofthe3partspolishedtonear-thicknessandlasercut— Mechanicalassemblywithamicroscope— Compressincoiningpress— Polishentireassemblytothickness— CointoformripplesandbondtoMo— Lasercut— Gluetodiamond— GlueonPVDFlayer

FabricationofthePulayerpresentedmanyscientificandtechnicalchallenges

5 mm

LLNL-PRES-72510614

ThePusampleismechanicallypressedintoa3-partassembly,whichispolishedtothickness

Pu samples are laser cut from a pressed “sheet”

Pu is mechanically fit into a gold ring

Au/Pu is fit into a Mg alloy disc

Samples mounted for lapping

1 mm

1 mm

12 mm

LLNL-PRES-72510615

Ripplesareformedwithacustomcoiningpress,andwearestilloptimizingparametersforfullyformedfeatures

Pu1.5µmAu1.5µm Au0.4µmPu0.4µm

Die amplitude = 1.5 µmAmplitude formed = 0.758 µm

LLNL-PRES-72510616

Ripplesareformedwithacustomcoiningpress,andwearestilloptimizingparametersforfullyformedfeatures

Au1.5µm Au0.4µmPu0.4µmPu0.4µmPu1.5µm

Die amplitude = 0.4 µmAmplitude formed = 0.194 µm

Die amplitude = 1.5 µmAmplitude formed = 0.758 µm

LLNL-PRES-72510617

§ Athinlayerofgold(0.125µm)issputteredontothePuandtheMo

§ Whentheripplesareformedviacoining,themetal-metalbondisformedsimultaneously

§ Whilewehavehadinitialsuccessonnon-Pusystems,sputteringequipmentfailureprecludeduseofthisbondoncompletephysicspackages

A“glueless”bondbetweenthePuandMolayersposestechnicalchallenges

Final bonded assembly (no glue)

12 mm

Alignment of coated components in coining press

12 mm

LLNL-PRES-72510618

Cross-sectionalmetallographyshowsanintact“glueless”bondinatestassembly(Mo/Mg)

Mo

Mg

Au-AuMo

Mg

18.5 µm

Post-lapping oxide/corrosion in Mg

LLNL-PRES-72510619

Thefinalassemblyislasercutandgluedtoadiamondwithadditionalfeaturesonthebackside

5 mm

Rippled sample assembly

LLNL-PRES-72510620

Thefinalassemblyislasercutandgluedtoadiamondwithadditionalfeaturesonthebackside

5 mm

Rippled sample assembly

Pu

Au

Mg alloy

HDC

LLNL-PRES-72510621

§ Capabilitiesarebeingexpandedinanewlabwithlargergloveboxes

§ Areasforcontinuedwork— Gluelessbonding— Designingcoiningdiestoproducedesiredripplepatterns— Oxidationprevention— Densitymeasurementonverysmallsamples— High-precisionPumachining

Developmentandproductionofradioactivetargetswillcontinueinthefuture