Number30

December2006

Schweizerische Gesellschaft für Neutronenstreuung Société Suisse pour la Diffusion des Neutrons Swiss Neutron Scattering Society

Editorial:

Editor: SwissNeutronScatteringSociety

BoardforthePeriodJanuary2004–January2007:

President: Dr.P.Allenspach peter.allenspach@psi.ch

BoardMembers: Prof.Dr.S.Decurtins silvio.decurtins@iac.unibe.ch

Prof.Dr.B.Schönfeld schoenfeld@iap.phys.ethz.ch

Secretary: Dr.S.Janssen stefan.janssen@psi.ch

HonoraryMembers: Prof.Dr.W.Hälg,ETHZürich

Prof.Dr.K.A.Müller,IBMRüschlikonandUniv.Zürich

Prof.Dr.A.Furrer,ETHZürichandPaulScherrerInstitut

Auditors: Dr.W.Fischer,PaulScherrerInstitut

Dr.K.Krämer,UniversityofBerne

Address: SekretariatSGN/SSDN

PaulScherrerInstitut

bldg.WLGA/002

5232VilligenPSI,Switzerland

phone: +41-(0)56-3104666

fax: +41-(0)56-3103294

www: http://sgn.web.psi.ch

BankAccount: Postfinance: 50-70723-6

BIC: POFICHBE

IBAN: CH3909000000500707236

Printing: PaulScherrerInstitut

Circulation: 2100,2numbersperyear

Copyright: SGN/SSDNandtherespectiveauthors

on thE covEr:

Historyofthefirst12hoursofMegapieneutronbeamwhennormaluser

operationhadstartedonAugust21st.

//Contents//

2 ThePresident’sPage

4 HansU.Güdelretiredinautumn2006

8 Metal-likeelasticityincolloidalcrystals

14 UpgradeofthecoldneutrondiffractometerDMCatSINQ:

Modernalgorithmsforcalibrationandintegrationof2-Ddata

24 MEGAPIEatSINQ–thefirstliquidmetaltargetdrivenbya

Megawattclassprotonbeam

32 Announcements

34 CallforHälgandLewyBertautPrize

36 5thPSISummerSchoolinZuoz2006

39 Conferences2007

//ThePresident’sPage//

2

dEar mEmbErs

TheliquidSINQ-targetMEGAPIEsuccessfully

finished itsoperation justbeforeChristmas

andwecansaythatitperformedwellbeyond

expectationwithupto80%moreneutrons

andonlyveryminortechnicalproblems.All

thepreviouspunditsIknow(andIwasone

ofthem)haveadjustedtheirviewsbythisvery

positiveexperiencetofullsupportersoffuture

liquidtargetsforSINQ.Iwouldliketocon-

gratulatePSIandallpeopleinvolvedforthis

marvelous experiment. The next target will

againbeasolidtarget,butforthefirsttime,

onewithallrodsmadeoutofZirkalloy.This

shouldresultinanincreasedfluxcompared

tothesteelrodsoftheorderof20%.With

thistargettypebuiltin,withthedevelopment

ofanewliquidtargetgoingaheadandwith

aplannedpowerupgradeoftheprotonac-

celerator,SINQcanbeexpectedtoremaina

competitiveneutronsourcefortheyearsto

come.WithMARSbeingcommissionedatthe

moment, FOCUS-SANS to be installed this

winter, EIGER entering construction phase,

DMC-IIbeingapprovedandthegradualup-

gradesonalltheotherinstruments,itisalso

assuredthattheneutronsproducedinSINQ

areusedinthemostefficientway.

In the last Swiss Neutron News issue I

informedyouaboutthisplannedworkshop

about the instrumentationon a longpulse

target station (LP-TS)ESS,which then took

placeinRencurel.Ihavetoconfessthatbased

ontheupdatedVolume3oftheESSreportI

regarded the LP-TS as a compromise espe-

ciallyinthefieldofspectroscopy.However,as

aresultoftheworkshopandthemanysimu-

lations,whichhavebeenperformedthere,I

hadtorevisemyopinion.Thecombinationof

low repetition rate, the implementation of

pulse shaping choppers and the long dis-

tancestotheinstrumentsallowforaflexible

choiceofresolutionandincreaseofintensity

bymultiplexing.Besideshighresolutionback-

scatteringandeV-spectroscopysucha5MW

3

LP-TSwilleasilybeata1MWshortpulseTS

andinadditioncompriseslesstechnicalun-

certainties.

Another positive development was the

publicationoftheESFRI-roadmapwhichin-

cludes the ILL-upgradeand the ESS-project

(5MWLP-TS).Thispublicationcausedalotof

actions,whichnowhavebeenchanneledin

awaytoobtainacommonmomentumto-

wardsarealizationofESS.There isa lotof

politicsandvestedinterestsinvolved,which

mightde-railthisprocess.Ipromiseyouthat

Iwilldowhateverpossible,asthepresident

of SGN and in my new function as ENSA

chairman,tohelptheprocesstogoaheadin

therightdirection.

//PeterAllenspach

4

Theinvitationtoparticipateinthecolloquium

for Hans U. Güdel on July 7, 2006, at the

DepartmentforChemistryandBiochemistry

oftheUniversityofBernecameasasurprise,

sincenobodyactuallyexpectedHanstoleave

hisfacultypositionbeforethenormalageof

retirement.However,Hanshasalwaysbeen

unconventional during all his life, and his

earlyretirementunderlinesagainhisattitude

todotheunexpectedratherthantofollow

thecommonrules.Thespeakersofthecol-

loquiumgaveanalmostcompleteoverview

onHans’activitiesduringthelastfourdec-

ades.Thepresenceofnumerousformerstu-

dents,collaborators,colleaguesandfriends

demonstratedthegreatimpactwhichHans

achievedduringhisactivelifeasadedicated

researcher, as a gifted teacher, and as a

highlyappreciatedadvisorinmanyscientific

committeesandcouncils.

InNovember2006,theISIwebofknowl-

edge listed 521 refereed scientific articles

whichHanspublishedsofarasauthorand

co-author,andmanymorearticlesappeared

inbooksandproceedings.Thisisanimpress-

ingscientificworkcoveringabroadrangeof

topics,andIamsomehowproudthatIhad

theopportunitytocollaboratewithHansin

somehundredoutof these521articles. In

thefollowingIwillgothroughsomeofthe

highlightsofourscientificcollaborationwhich

wasatrulyinterdisciplinaryventure,because

Hansreceivedhisuniversitydegreesininor-

ganicchemistry,whereasmyscientificback-

ground is solidstatephysics. I feel thatwe

nicelyachieved tocombineand to join the

culture of the two disciplines in common

//HansU.Güdelretiredinautumn2006//

A.Furrer

Laboratory for Neutron Scattering, Paul Scherrer Institut & ETH Zurich, CH-5232 Villigen PSI

HansU.Güdelmainlybeforetheyear2006.

�

projectswithgreatsuccess,whichwashon-

ouredthroughawardingtheWalterHälgPrize

2005 of the European Neutron Scattering

Association(ENSA).

One coherent themehasbeen running

through all our joint actvities, namely the

studyof low-dimensionalmagneticsystems

and in particular magnetic cluster systems.

The start in the mid-seventies was highly

exciting; we were the first to measure di-

rectlytheenergysplittingsofmagneticdimers

and higher multimers (so-called magnetic

clusters)byinelasticneutronscattering,see

Phys.Rev.Lett.39,657(1977).Subsequent-

lythisworkhasservedasakeyreferencein

similar measurements performed by other

groups,sinceitdidnotonlydemonstratethe

feasibilityofsuchexperiments,butprovided

thetheoreticalbasisforthedatainterpreta-

tion,asincreasinglyusedtodayinthefieldof

spin clusters including supramolecular na-

nomagnets,afieldtowhichHanshasmade

essentalcontributionsinrecentyears.

Neutronexperimentsonmagneticclusters

providedirectinformationontheexchange

interactionbetweenthemagneticions.Inthe

past,theHeisenbergmodelhasbeenwidely

used to describe exchange interactions in

magneticsystems,althoughitinherentlyrep-

resentsjustafirstapproximationofthetrue

situation. The presence of intrinsic higher-

ordertermswaspointedoutbyAndersonin

his famousarticle inMagnetism (Vol.1)al-

readyin1963.Westartedtosearchforsuch

higher-ordertermsandfoundindeeddirect

spectroscopic evidence for an appreciable

contributionofbiquadraticexchangeinneu-

tronexperimentsonMnpairsinthediluted

one-dimensionalmagnetCs(Mn,Mg)Br3,see

Phys.Rev.Lett.�2,1336(1984).Thenature

ofbiquadraticexchangedoesnotonlyinvolve

pair interactions,butalso three-body, four-

body,etc.interactionsifextendedtohigher

clusters.FurtherneutronexperimentsonMn

trimer chain segments in Cs(Mn,Mg)Br3

provedtheexistenceofatruethree-spinex-

change term similar in magnitude to the

correspondingbiquadratictwo-spinterm,see

Phys.Rev.Lett.�6,1956(1986).Thiswasa

result of fundamental importance, since n-

bodyinteractions(n>2)havesofaronlybeen

verifiedinsolid3He,nuclearmatter,anddis-

orderedbinaryalloys.

Aparticularlyinterestingsystemstudied

duringtheeightieswasthespin-dimercom-

pound Cs3Cr2Br9, because it exhibits field-

inducedmagneticorderingwhenthesinglet-

tripletenergygapcloses,thusBose-Einstein

condensationofthetripletstateswithagap-

lessGoldstonemodecouldbeexpected to

occur.However,detailedfield-dependentneu-

tronscatteringexperimentsshowedthatthe

lowestsinglet-tripletexcitationbranchdoes

notsoftencompletelyduetosomeinherent

anisotropy,seePhys.Rev.B30,6300(1984);

31,597 (1985).Nevertheless, theseexperi-

ments served as an excellent basis for the

laterobservationoftheBose-Einsteinconden-

sationinTlCuCl3.

In the lateeightiesHanswas searching

forsuitablematerialstobeusedinthedesign

ofefficientup-conversionlasers.Compounds

ofcompositionCs3R2Br9(R=rareearth)were

foundtobeparticularlywell suitedfor this

purpose. The electronicproperties of these

compoundsaregovernedbythedimersofR

ionsbuiltintothemolecularunit,thusHans

approachedmetostudythecorresponding

6

excitations. The neutron experiments per-

formed for almost the whole R series pro-

vided completely unexpected results. The

usualphenomenologicalmodels(Heisenberg,

Ising, xy) failed to reproduce the observed

energyspectra.However,anexchange-tensor

formalismwhichtakesintoaccounttheinitial

andfinalelectronicstatesoftheinteracting

ions,turnedouttoprovideanexcellentde-

scription,seePhys.Rev.Lett.64,68(1990).

Theseexperiments–togetherwiththework

onMndimersandtrimersdescribedabove

–convincinglydemonstratedtheshortcom-

ingsoftheusualphenomenologicalapproxi-

mationstodescribetheexchangeinteraction,

whosetruenaturecanonlybeunravelledif

appropriately tailored experiments are per-

formed.

IntheninetiesIwasinvolvedininvestiga-

tionsoftheinhomogeneousmaterialsproper-

ties of high-temperature superconductors.

Motivated by the fact that suitably doped

spin-ladder compounds such as Ca@Sr-

14Cu24O41 become superconducting under

pressure,Iinitiatedaco-operationwithHans

to study the novel S=1/2 spin-ladder com-

poundsACuCl3(A=K,Tl,NH4)forwhichhis

group had the necessary expertise in the

synthesisandgrowthofsinglecrystals.Ina

firststepthedispersionofthemagneticex-

citationswasestablishedforKCuCl3byinelas-

ticneutronscattering,seeEur.Phys.J.Rapid

NoteB7,519(1999).Surprisingly,themag-

neticexcitationsturnedouttobedispersive

inalldirectionsofreciprocalspace(i.e.,not

onlyalongtheladderdirectionasanticipated)

HansU.Güdelmainlyaftertheyear2006.

7

with structure factors imaging thenearest-

neighbourCupairdistance,therebyproving

thatthiscompoundserieshastheproperties

ofanS=1/2spin-dimerratherthanaspin-lad-

dercompound.Theexperimentswerethen

extended to investigate the magnetic field

dependenceof the singlet-triplet excitation

includingtheisostructuralcompoundTlCuCl3,

seePhys.Rev.B6�,132415(2002).Basedon

theseexperimentswerealisedthatthefield-

driven quantum criticality can indeed be

reached in these systems, and for the first

timethepictureoftheBose-Einsteinconden-

sationofmagnonsinTlCuCl3couldbeveri-

fied,seeNature423,62(2003).

Neutronscatteringwasakeytechnique

inmanyscientificworks inwhichHanshas

beeninvolved.However,Hanswasnotonly

amereuserandconsumerofneutrons,but

healsomadetremendouseffortstoprovide

excellentexperimentalopportunitiesforthe

Swiss neutron scattering community as a

whole.Inthemid-eighties,hewasoneofthe

initiators of the Swiss partnership with the

InstituteLaue-Langevin(ILL)inGrenoblewhich

runstheworld’smostpowerfulneutronsource

(Hans ispresently theSwissmember in the

ScientificCounciloftheILL).Hethenrealized

thatthevoiceoftheusershastobearticu-

latedinafocusedmanner,thushewaspush-

ingthisidea,andhewasthefoundingChair-

man when the Swiss Society for Neutron

Scatteringwascreatedon25October1991

inBerne.Hans strongly supported also the

ideaofaSwisshomebaseinneutronscatter-

ing, namely the spallation neutron source

SINQatPSIfromtheverybeginning,firstas

convenor of the time-of-flight instrument

groupduringtheprojectphaseandthenas

amemberoftheScientificCommitteeafter

the start of the regular SINQ operation in

1998.

Iverymuchenjoyedtheco-operationwith

Hansinthelastthirtyyears,andIwillthank-

fully remember thenumerousexperimental

campaignsandenlightningdiscussionswith

Hansandwithmanyofhisstudentswhowere

always involved as a prerequisite in almost

anyofourcommonresearchprojects.Hans,

youcanlookbacktoanextremelysuccessful

career,andyoucanbesurethatyourpurpo-

sive but yet unconventional way of doing

research will be continued by your former

studentsandcollaboratorsashonestlydem-

onstratedthroughallyourscientificlife.For-

tunately,youstillhaveyourofficeinBerne,

thus we may expect from you further sur-

prisesinresearch,yetataslightlymoderate

paceduetosomeofyouralternativeactivities

suchastennis,curling,andmountainclimbing

whichwillprobablygaininimportanceinthe

future.Hans,Icordiallythankyouforourpast

co-operation,andIwishyouallthebestfor

thebrightfutureaheadofyou.

8

in a recent study (1), the elastic properties

of single crystals consisting of charged

colloidal particles were determined from

real-space imaging experiments using

confocal microscopy. the normal modes

and the force constants of the crystal

were obtained from the fluctuations of

the particle positions around the lattice

sites using the equipartition theorem. We

show that the elasticity of the studied

crystals is largely analogous to that of

metals. like the conduction electrons in

metals, the small ions in the solvent of

the colloidal crystals give rise to non-

central forces between the big colloidal

particles and, therefore, the cauchy rela-

tion is not fulfilled.

Understanding how an elastic material de-

formsunderexternalmechanical stresses is

essentialknowledgeinmaterialscienceand

offundamentalinterest.Theelasticproperties

ofacrystalaswellastheinteractionsbetween

the particles forming a crystal lattice are

character-izedbyforceconstants(2,3).These

relatethedisplacementofoneparticlefrom

itsequilibriumpositiontotheforceactingon

aneighboringparticle.Inmetallicandother

hardcrystallinematerialsagreatdealisknown

about these microscopic forces and about

elasticity.However,insoftmaterialssuchas

colloidal suspensions the study of elasticity

currentlyreceivesalotofattentionbecause

oftheirgreatpotentialforthedevelopment

of novel materials with tailored properties.

Yet,theelasticconstantsofcolloidalcrystals

haveneverbeenmeasuredandthenatureof

theinternalforcesincolloidalcrystalsislarge-

lyunknown.

Inanalogytometals,crystalsofcharged

colloids(4)consistofmesoscopic,Brownian

macroions insuspensionthatforma lattice

and are surrounded by the much smaller

microions. Like theelectrons inmetals, the

//Metal-likeelasticityincolloidalcrystals//

U.Gasser1*,D.Reinke2,H.Stark3,H.-H.vonGrünberg4,A.B.Schofield5,G.Maret2

1 Laboratory for Neutron Scattering, ETH Zurich & Paul Scherrer Institut,

5232 Villigen PSI, Switzerland2 Physics Department, University of Konstanz, 78457 Konstanz, Germany,

3 Max-Planck-Institut für Dynamik und Selbstorganisation, Bunsenstr. 10, D-37073 Göttingen, Germany,4 Karl-Franzens-Universität, 8010 Graz, Austria,

5 School of Physics, University of Edinburgh, Edinburgh, Scotland EH9 3JZ, UK,

* To whom correspondence should be addressed; E-mail: urs.gasser@psi.ch

9

microions are much more mobile than the

large ions that form the lattice and, as a

consequence,theyalwaysarrangeinclouds

aroundthemacroionstoscreentheircharges.

Thus,inmetalsandcrystalsofchargedcolloids

therearetwospeciesthatmoveandrespond

on vastly different length and time scales.

Therefore,thequestionariseswhetherthese

similarities manifest themselves in similar

elasticpropertiesdespitethehugedifference

intherespectivemoduli.

Informationonthenatureoftheinterac-

tionsincolloidscanbeobtainedbymeasuring

the components of the tensor of elasticity.

Thesearedefinedasthesecondderivativesof

theelasticfreeenergyofacrystalwithrespect

tocomponentsofthestraintensor:Cμνρσ =

∂2F ⁄ ∂ημν ∂ηρσ(3).Thenumberofindependent

componentsofCμνρσdependson thepoint

symmetry of the crystal; a crystal with the

cubicfccsymmetryhasonlythreeindependent

elasticconstants:C11,C12,andC44,wherethe

indicesaregiveninVoigtnotation(3).In1828

A.J. Cauchy found that the assumption of

centralforcesbetweensmallvolumeelements

ofacrystalyieldsadditionalrelationsbetween

theelasticconstantsand, therefore, further

reducesthenumberofindependentcompo-

nentsinCμνρσ(2,5);e.g.foracrystalwithfcc

symmetryC12=C44forcentralforces.These

relationsarenowknownasCauchyrelations,

andtheyallowtheinterestingconclusionthat

their violation must be due to non-central

forces.Metalsareagoodexample:Because

ofnon-centralforcesduetotheconduction

electronsthatscreenthechargesoftheions

theCauchyrelationsarenotfulfilled(2).

Inarecentstudy(1)wehaveshownthat

theelasticconstantsofcolloidalcrystalsand

essentialinformationabouttheinteractions

between the colloidal particles can be ob-

tained best by real-space imaging experi-

ments.Theexperimentalmeansforthishave

recentlybecomeavailablewithfastlaserscan-

ningconfocalmicroscopes.As illustrated in

Fig.1,our3Drealspaceimagingdataallows

thedirectobservationandquantitativeanal-

ysisofthestructureanddynamicsofupto

Fig. 1: (a)Asnapshotof1909particlesinacolloidalcrystalwithfccsymmetry.Theimageisobtainedus-

ingthecoordinatesextractedfrom1002Dmicroscopyimages.

(b)Atimeaverageofthesamecrystalasshownin(A)calculatedfrom98snapshots.Thehighqualityof

thecrystalisapparent.Incomparisonwith(A)thefluctuationsoftheparticlesaroundtheirequilibrium

positionscanbevisualized.

10

104 micron-sized particles. From measure-

ments of colloidal mono-crystals with fcc

symmetryweextracttheforceconstantsof

thecrystalfromthedispersioncurvesofover-

damped normal modes and, in the q → 0

limit,allelasticconstantsofthecrystal.Our

resultsshowthattheinteractionbetweenthe

colloidal particles in the crystal cannot be

describedintermsofcentralforces,butnon-

centralforcesactingbetweenthemacroions

maketheelasticresponseofthestudiedcol-

loidal crystals similar to that of metals. In

metals,theforceconstantscanbedetermined

with scattering methods such as inelastic

neutron scattering that probe the normal

modes of the lattice. However, in colloidal

crystalsscatteringmethodssuchasdynamic

lightscattering(DLS)donotyieldthesame

information(6,7),becausethesolventofthe

suspensionstronglydampsthemotionofthe

colloidalparticlesand,therefore,preventsthe

existence of propagating lattice normal

modes.Asaconsequence,inscatteringex-

periments, the force constants are always

intertwinedwiththecomplicated,wave-vec-

tordependentfrictionalforceswiththesol-

vent.IncontrasttoDLS,hydrodynamicsdoes

notplayanyroleinthedeterminationofthe

lattice normal modes from the real-space

imaging data. Our method (8) relies exclu-

sivelyon“snapshots”oftheparticlepositions

thatareusedtocalculateensembleaverages

and,therefore,thefrictionalforcesbetween

thecolloidalparticlesandthesolventnever

enterouranalysis.

Weusedpoly-methylmethacrylatespheres

(9)withadiameterσ=1.66μmthatwere

fluorescently labeled with rhodamine and

suspendedinasolventmatchingbothden-

sityandrefractiveindexoftheparticles.The

particleswereobservedwithafastlaser-scan-

ningconfocalmicroscopeusinga100×objec-

tivelenstoobserveavolumeV≈58μm×55

μm×20μminsidethemuchlargersample

cell.Theobjectivewasmountedonapiezo

translationstageforthescanninginz-direc-

tion and, typically, 5000particleswereob-

servedinone3Dsnapshot.Ittook≈1.5sto

observe thewhole volumeV.After the ex-

periment,theparticlesaredetectedbylook-

ingforlocalintensitymaximaandtheirposi-

tionscanbedeterminedwithanaccuracyof

≈20nm(10).Sampleswithvolumefractions

0.01< φ < 0.41wereprepared inorder to

mapout thephasebehavior at room tem-

perature;allmeasurementswerecarriedout

atT=295K.Crystallizationwasobservedin

samples with volume fractions larger than

φf≈0.31.Thephasebehaviorcompareswell

withthatofhardsphereswithYukawarepul-

sion(HSY)withtheinteractionpotentialV(r)

=VHS(r)+ Bσr exp(−κ[r−σ])(11).Here,VHS(r)

isthehardspherepotential,κ−1=221±30nm

istheDebyescreeninglength,andB=kBTλBσ

(—1+Z—eff

κ—σ/—2)2≈12kBTisthecontactvaluewiththe

BjerrumlengthλBandthechargenumberZeff

=245±40.

Forφ ≥0.31largerandomhexagonalclose

packed crystals (12)with hexagonal planes

oriented parallel to the cover slip formed

withinseveraldays,andwechoseregionsof

threetotenhexagonallayerswithfcc-stack-

ing forourmeasurements.The lattice con-

stantaoftheBravaisunitcellwasmeasured,

andthestructureofthesecrystalswascom-

paredwithaperfectfcclattice.Asillustrated

by Fig. 1B, the deviations of the average

particlepositionsfromthefcc-latticepositions

11

aresmall.Forthecalculationofthedisplace-

mentui(t)=ri(t)−riofparticlei,thereference

position ri is determined by averaging its

positionoverallsnapshotstakenduringthe

measurement.Thedistributionsofthecom-

ponentsuμofthedisplacementsarefoundto

beGaussianatallvolumefractions,soweare

always in the harmonic regime of crystal

elasticity.Followingessentiallythesamepro-

cedure as in Ref. (8), the dynamical matrix

Dμν(q)(2)isdeterminedusingtheequiparti-

tiontheorem;eachq-modeoftheharmonic

approximationU=12Σq,μ,νuμ(q) Dμν(q)u*ν(q)

totheelasticenergyofthecrystalcontains

thethermalenergykBT/2.Therefore,thein-

verseofthedynamicalmatrixcanbeobtained

fromanensembleaverageofthemeasured

particledisplacements:

D−1μν(q)=

⟨uμ(q)u*ν(q)⟩

(1)

Wecalculatetheensembleaverage⟨...⟩bytakingatimeaverageoverallmeasured

configurationsandweanalyzemodeswith

wavevectorsq∝(1,1,0),(1,1,1),and(1,

0,0).Sincethesedirectionsinreciprocalspace

correspondtosymmetryaxesof2-,3-,and

4-fold rotations, the eigenmodes in these

directionsarealongitudinalmodelandtwo

transversemodest1andt2witheigenvectors

êl, êt1 , and êt2 , respectively. As shown in

Fig.2,weobtainthemodesl,t1,andswith

propagationq∝(1,1,0),t1andmforq∝

(1,0,0),andt1andmforq∝(1,1,1).Here,

sdenotesacombinationofthemodest1and

t2,andmreferstoacombinationoflongitu-

dinal and transverse modes. The full lines

representfitswithgeneralforceconstantsof

anfcclatticewithinteractionsupto3rdnear-

estneighbors.Threeforceconstants(A(1)11,A

(1)12,

A(1)33)determine the forcesbetweennearest

neighbors,whiletwo(A(2)11,A(2)22)andfour(A(3)

11,

A(3)12, A(3)

13, A(3)22 ) constants define the forces

actingonthe2ndand3rdneighbors,respec-

tively(2).Theabsolutevaluesofthe3rdorder

constantsA(3)μνarefoundtobe∼0.01| A(1)

11|;theyarenotessentialforthequalityofthe

fits.Foraradiallysymmetricinteraction,the

forceconstantsfulfilltheconditionΓ:=A(1)12

/(A(1)11−A(1)

33)=1(2).However,fromthemeas-

urementswefind Γ < 0.25at all φ. This is

clearlyincompatiblewithapairwiseadditive,

radially symmetric interaction. Furthermore

thedeterminedforceconstantsdifferstrong-

lyfromthoseexpectedforaHSY-crystal.E.g.

kBT

Fig. 2: Measureddispersion relations for (top to

bottom)φ=0.38,0.34,and0.31.The full lines

representfitstothedata.K,XandLdenotethe

edgeofthe1stBrillouinzonein(1,1,0),(1,0,0),

and(1,1,1)-direction,respectively.Foreachcol-

umn,themodesareidentifiedinthetopmostpan-

el.Forcomparison,thedispersionrelationsfora

HSYcrystalwithB=15kBTandκσ=8areshown

bythedottedlinesforφ=0.31.Seetextforde-

tails.

12

adisplacementoftheparticleat(0,0,0)in

the(1,0,0)-directionstronglyattractsthe2nd

neighborat(a,0,0);thisbehaviorisaconse-

quenceofmanybodyforcesandcannotbe

accountedforbytheHSYinteractionorany

otherradiallysymmetricpairpotential.Poten-

tialerrorsourcessuchasrandomerrorsinthe

particlecoordinates, theeffectof thefinite

scanningspeed,thelimitednumberofsnap-

shotsinameasurement,andthesizeofthe

observedvolumeVwereassessedbycompar-

ingthemeasurementswithMCsimulations.

Themeasurementswerefoundtogivereliable

results(1).

Therefore, we can determine all elastic

constantsofacolloidalcrystalfromasingle

measurement.Intheq→0limit,weobtain

the tensorBμνρσ,whichconnects stressand

strain:Tμν=Bμνρσ ερσ.Forcrystalsunderstress,

Bμνρσisnotthesameasthetensorofelastic

constantsCμνρσ,whichisdefinedviatheelas-

tic free energy (3). The studied crystals are

under stress due to the pressure p in the

samplecell;forfccsymmetrythetwotensors

areconnectedbytherelationsB11=C11−p,

B12=C12+p,andB44=C44−pwiththein-

dicesgiveninVoigtnotation(3).Forcentral

forcesandcubiclattices,theconditionΓ=1

isaconsequenceoftheCauchyrelationB12

=B44+2p. Elastic constantsBμν andelastic

moduli representative of all our results are

showninTable1alongwithvaluesforaHSY

crystal.SinceB44>B12andp>0,ourmeas-

urementsclearlycontradicttheCauchyrela-

tion,whileitholdsinHSYcrystals.Inanalogy

to metals, the non-centrality of the forces

affectsmostly thebulkmodulusK= (B11+

2B12) /3,whiletheshearmoduliG1=B11−

B12andG2=B44havesimilarvalues in the

studiedcrystalsandHSYcrystals.Thevalue

ofK obtained fromexperiment is almost a

factorof3smallerthanfortheHSYcrystal.

Theseobservationscorroboratethatthemi-

cro-ionsincrystalsofchargedcolloidsplaya

rolesimilartotheelectrongasinmetals.

Ourmainresultsarethe incompatibility

of the force constants with any effective,

radiallysymmetricpair-potentialandtheim-

portance of many-body forces. The elastic

properties and the behavior of the lattice

normalmodesinthestudiedcolloidalcrystals

arerathermetal-thanHSY-like.Moreover,we

notethatdirectobservationofcolloidalcrys-

talsyieldstheresultsthatareobtainedbye.

g.inelasticneutronscatteringinhardmateri-

als.Ourmethodsarenotlimitedtocharged

colloidsbutallowtostudytheelasticproper-

tiesofvariouscolloidalcrystals thatcanbe

treatedintheharmonicapproximation.

This work has been supported by the

Deutsche Forschungsgemeinschaft (DFG)

throughsubprojectC4oftheSFBTR6pro-

gram.

Table 1: Elastic constants Bµν with indices given in Voigt notation and elastic moduli obtainedfrom experiment and from a calculation for a HSY crystal (B = 15 kBT , κσ = 8).

kBTσ3

B11 B12 B44 = G2 G1 K

φ = 0.38 67 17 65 50 33φ = 0.34 56 13 36 43 27φ = 0.31 28 9 28 19 15

HSY, φ = 0.31 63 48 25 15 53

Figure 1: (A) A snapshot of 1909 particles in a colloidal crystal with fcc symmetry. The imageis obtained using the coordinates extracted from 100 2D microscopy images. (B) A time averageof the same crystal as shown in (A) calculated from 98 snapshots. The high quality of the crystalis apparent. In comparison with (A) the fluctuations of the particles around their equilibriumpositions can be visualized.

8

table 1: ElasticconstantsBμν with

indicesgiveninVoigtnotationand

elastic moduli obtained from ex-

perimentandfromacalculationfor

aHSYcrystal(B=15kBT,κσ=8).

13

rEFErEncEs

1. D.Reinkeet al., Phys. Rev. Lett. 98,

038301 (2007).

2. P.Brüesch,Phonons: Theory and Experiments

I, vol.34of Springer Series in Solid-State

Sciences(Springer-Verlag,NewYork1982).

3. D.C.WallaceinSolid State Physics,H.Ehren-

reich,F.Seitz,D.Turnbull,Eds.(Academic

Press,NewYork,1970),vol.25,pp.301-404.

4. P.Pieranski,Contemp. Phys. 24,25(1983).

5. A.J.Cauchy,Exerc. de Math.4,129(1828).

6. A.J.Hurd,N.A.Clark,R.C.Mockler,W.J.

O’Sullivan, Phys. Rev. A26,2869(1982).

7. Z.D.Cheng,J.X.Zhu,W.B.Russel,

P.M.Chaikin,Phys. Rev. Lett.8�,1460

(2000).

8. P.Keim,G.Maret,U.Herz,H.-H.von

Grünberg,Phys. Rev. Lett.92,215504

(2004).

9. L.Antlet al., Colloids Surf.17,67(1986).

10. J.C.Crocker,D.G.Grier,J. Colloid Interface

Sci. 179,298(1996).

11. A.-P.Hynninen,M.Dijkstra,Phys. Rev. E68,

021407(2003).

12. P.N.Puseyetal.,Phys. Rev. Lett.63,

2753-2756(1989).

14

//UpgradeofthecoldneutrondiffractometerDMCatSINQ:Modernalgorithmsforcalibrationandintegrationof2-Ddata//

A.CervellinoandL.Keller

Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institut, CH-5232 Villigen PSI

introduction

ThepowderdiffractometerDMChasbeenin

operationformorethan20years,firstasa

thermalneutronpowderdiffractometeratthe

reactorSaphiratPSI [1]and laterasacold

neutrondiffractometerforpowderandcrys-

talapplicationsatSINQ[2].Theinstrumentis

wellacceptedbytheusercommunity,which

isclearlydocumentedbyboththeoverload

factoroftheinstrumentaswellasthescien-

tificoutputintermsofpublications.

While monochromator and instrument

electronics have been replaced when DMC

wasmovedtoSINQ,themaininstrumentfrom

sampletabletodetector, includingdetector

electronics,isbasicallyinitsoriginalstate.With

20yearsofoperationtheguaranteedlifetime

ofthedetectorishighlyexceededandadam-

ageofessentialpartseitherofthedetectoror

itselectronicswouldleadtoatemporaryor

finalshutdownoftheinstrument.Moreover,

detectortechniquehashighlydevelopedsince

themid-eightiesandcompetitionfrommod-

erndiffractometersatotherneutroncenters

isconstantlygrowing.

Therefore,weplanamajorupgradeof

DMC,i.e.thereplacementofthesecondary

instrument.Thedesignofthenewcoldneu-

trondiffractometerwasmotivatedby clear

goals:

– highestachievableintensity,resultingina

significantincreasecomparedtothepresent

DMC

– nodecreaseofresolutionwhencompared

tocurrentDMC

– enablesignificantlyimprovedsampleenvi-

ronment conditions (e.g. high pressure,

highmagneticfields)

– versatility,applicationtopowderandsingle

crystal diffraction, including pole figure

measurementandtextureanalysis

ThecrucialpointoftheDMCupgradeisthe

largestate-of-the-artdetector.State-of-the-

artmeanshighefficiencythroughhighgas

1�

pressure, large covered angle range in the

scatteringplaneaswellasperpendiculartoit

andpseudo-2Ddetectionofscatteredneu-

tronstoresolvethecurvatureoftheDebye-

Scherrer cones. This will be fulfilled with a

large“banana-type”detector consistingof

linearly position-sensitive countingwires.A

newtoolfor instrumentdesignthatturned

outtobeveryhelpfulisMonteCarloray-trac-

ingsimulation.Withproperprogrammingof

themodulesfortheneutronsource,neutron

guide,monochromator,collimationsandde-

tector, we were able to reproduce the ex-

perimentally determined intensity relations

andresolutionfunctionsofthepresentDMC.

Tooptimizethedesignofthenewdetector,

weperformedsimilarmodelcalculationsfor

variousdimensions,numberofwires,heights

etc. anddetermined the intensitygainand

resolutionfunctions.Thefinaldesignrepre-

sentstheoptimalsolutionintermsofinten-

sity gain without loss of resolution, taking

intoaccount theavailable space foranew

instrument.UnlikethepresentDMC,which

wasinitiallybuiltforapplicationsonathermal

beamtube,theupgradedinstrumentwillbe

designed for and dedicated to the special

needs of a cold neutron diffractometer at

SINQ.Thetotalintensitygainfactorcompared

topresentDMCwillbeupto14,depending

onwavelengthandinstrumentconfiguration.

Morethanoneorderofmagnitudegain in

intensity will open up totally new fields of

research(smallsamples,smallmagneticmo-

ments,highpressure,fastprocesses, in-situ

experiments…).Moreoverthenewnon-mag-

netic constructionof detector housing and

sample table will enable the use of high

magneticfieldsupto15Tesla.

High-qualitydiffractiondatagreatlyde-

pends on the technical solutions for the

neutron detection. Similarly, it depends on

properdatatreatmenttoobtainacorrectand

aberration-freepowderpatternbyintegrating

the two-dimensional raw data. Following,

algorithms fordata integrationand correc-

tionsareoutlined.

PurPosE

The next generation 2-D neutron powder

detectorsopenawholenewsetofpossibilities

asbeingabletocollectdatamorequicklyand

efficiently.Afurtheraspectthatdeservesfull

exploitationistheverticalpositionsensitivity

(hereafter verticalwill be thedirectionper-

pendiculartotheaveragescatteringplane).

This additional information richness canbe

exploited–usingappropriatealgorithms–to

correctforsamplepositioningaberrationsand

toeliminatetheeffectoftheverticalaperture

ofthedetector,integratingthepatternalong

thecorrectconstant-diffractionanglecurves

onthedetectorsurface.Thisleads,aswewill

show,toadramaticimprovementinthedata

quality.

Thecalibrationofaneutronpowderde-

tectorentailsusuallytwophases:

(1) vanadium calibration:

Calibration of the sensitivity of each pixel,

normallyrepeatedatshorttimeintervalscom-

prisingseveralexperiments(say,monthly).

(2) standard calibration:

Calibrationofthewavelengthandthezero

ofthescatteringangle,normallyrepeatedat

short time intervals comprising several ex-

periments(say,monthly).

16

Fora2-Ddetectorathirdphaseisenvis-

aged:

(3) Geometric self-calibration:

Geometricaberrationdeterminationandself-

correction,tobeperformedoneachexperi-

mentaldataset,inthedatareductionphase.

This would replace and/or integrate the

procedureofcenteringthesamplewithrespect

tothecurvaturecenterofthedetector[3].

dEscriPtion oF a 2-d dEtEctor

ThedetectorhasheightHandangularaper-

tureζ0withcurvatureradiusR.ItcontainsNν

pixelintheverticaldirection,eachofheight

h=H/Nν. Similarly, there areNt pixels in the

tangential direction, each of width

Δr=RΔ(2θ)=Rζ0/Nt.Weshallidentifypixelsby

apairofindexesm, n, m =1…Nt, n =1…Nν.

Pixelm, ncorrespondstoin-planescattering

angle2θm=2θ0+(m−1)Δ(2θ)(withrespectto

the ideal beam direction) and at vertical

position zn = z0+(n−1)h. Note that the

ideal sample position along z is set to

zs=z0+(Nν−1)h/2.Wewillcallξtheadimen-

sionalcoordinateξ=(z−zs)/R.Afteranexpo-

suretoscatteredradiationfromanysample,

eachpixelwillhaverecordedacertainneutron

countCmntowhichweimmediatelyassociate

Fig. 1:A2-Ddetector(diffractionplaneprojection).ThedetectorsurfaceisrepresentedbyarcAB. Ois

theidealsampleposition,Stheidealpositionoftheslit,S’andO’therealsampleandslitpositions,ϕ0the

diffractionangleoffsetduetotheslitmisplacement.ζ0isthefulldetectoraperture,Oxyzisacoordinate

systemwithzorthogonaltothediffractionplane,xdirectedalongtheidealincidentbeamdirectionandy

orthogonaltoit.2θ0istheidealin-planediffractionanglecorrespondingtothefirstdetectorpixel.Pisa

detectorpixelcorrespondingtotheidealin-planediffractionangle2θandtotherealin-planediffraction

angle2θ*.Dottedlinescorrespondtotheincidentbeam.

17

the Poisson-Cauchy standard deviation

smn=[Cmn+1]1/2.Nowwewillproceedbysteps

throughthedifferentphasesofdataelabora-

tionthatwillleadustoobtainaberration-free

one-dimensional powder patterns of high

quality.

vanadium calibration oF

a 2-d dEtEctor

Here theonly difference tobe remarked is

that–evenifallpixelsareofconstantarea

–unlesstheylieonthesamez levelofthe

sample,theyarenotorthogonaltothedif-

fracted beam. The cosine of the angle be-

tweenthem,n-thpixelnormalandthedif-

fractedbeamis

Iftheneutroncountwiththevanadium

miscutcrystal(auniformsphericalscatterer)

isCmn,thesensitivitycorrectionfactorwillbe

νmn =<C/η>/[Cmn/ηmn], where <C/η> is the

weightedaverageoverallpixelsofCmn/ηmn:

scattErinG anGlE on thE

dEtEctor surFacE

With1-Ddetectorsthescatteringangle–the

angle between the incoming and the dif-

fractedbeam–isjustthein-planeangle2θ

asseeninFig.1.Ona2-Ddetector,foreach

point on the surface we have to take into

account the off-plane z shifts Δz=Rξ with

respecttothesampleposition.

Fig. 2 Simulatedintensityona2-Ddetectorsurface.Thedetectorapertureis80ºwithradiusR=1600mm

andfullheightH=400mm;2θ0=10º(2θincreasestowardstheright).ThesurfaceisdividedinNt=800and

Nν=40pixels. The simulation refers to a frequently used standardpowder (Na2Al2Ca3F14, commonly

namedNAC)atawavelengthof2.45Å,oneofthemostcommonlyusedintheDMCwavelengthrange.

BrightlinescorrespondtoBraggpeaks.Notetheprominentcurvatureatlowscatteringangles.

18

Thereforetheplanarscatteringangle2θhas

tobe replacedby the truescatteringangle

2θ∗(functionalsoofξ)givenby

wherewerecallthatη=1/ [ξ2+1]1/2.

lorEntz Factor For a 2-d dEtEctor

The Lorentz factor for powder diffraction

containsonefactorwhichweightsthepart

ofthescatteredwavethatisactuallyseenby

thedetector,andthisistheonlyonethatis

goingtobechanged.

TheclassicalpowderLorentzfactorisde-

fined–withinaproportionalityconstant–as

wherethefirstfactor(cone factor)Cdepends

on the detector geometry, the second, S,

dependsonlyonthesample.For1-Ddetectors

–whereallpixelsarecenteredinthescatter-

ing(horizontal)plane–itisclassically(within

aproportionalityfactor)

where P depends on the incoming beam

polarizationandisnormally1forunpolarized

beams.Forapixelona2-Ddetector,these

factorsbothchangeslightly.Withoutgoing

into themost complexdetails, forS it suf-

ficestosubstitutetheplanarhalfscattering

angleθbythetruehalfscatteringangleθ∗

(seetheformersection).ForCinsteaditturns

out that the sameexpression canbeused,

leaving the planar half scattering angle θ.

Formally,

wherethedependenceonξisonlythroughθ∗.

samPlE-dEPEndEnt abErrations

Weconsiderhereaberrationsdependingon

thesamplebeingnotintheidealpositionO

butinsteadin

withrespecttothexyzframe(seeFig.1).We

shall deal hereafter with the standardless

determinationofρ,β,δzandtheirusagein

order to correctly integrate the diffraction

patternalongthe(deformed)constant-true-

scattering-anglecurvesonthedetectorsur-

face.Standardlessmeansthatthedetermina-

tionofρ,β,δzcanbeperformedbasedonly

onsomeverygeneralpropertiesofthepow-

derdiffractionpatternofanaveragepowder

sample.Itisusefulifthepatternshowssev-

eralBraggpeaks,butthestructuralinforma-

tion is not used, making the computation

muchfasterandallowingittobeperformed

at thedata reduction stage (prior to struc-

turalanalysis).Nevertheless,thewavelength

hastobedeterminedusingastandardpow-

der,ascustomary.Thestandardisalsoused

for determining the zero of the scattering

angleϕ0.Afurthercorrectionduetosample

displacementsρ,βmightbenecessaryandit

needs tobeperformedon thedataduring

thestructuralanalysis,butthegeneralityof

structureanalysisprogramallowsforthis.

19

scattErinG anGlE on thE

dEtEctor surFacE in thE PrEsEncE

oF samPlE disPlacEmEnts

Thegeneralexpressionofthetruescattering

angle ismorecomplexthantheoneabove

reported,validintheidealcase.Weshallsplit

thetaskintwophases,becausethecoupling

between the vertical and the in-plane dis-

placements is negligible. Therefore we will

consider first the case when only vertical

aberrationispresent(ρ=0,δz≠0).Thenwe

will present the case of planar aberration

only(ρ≠0,δz=0).Finallyweshallpresentthe

proceduresabletodetermineandcorrectthe

verticalaberrationandtheplanarone(sepa-

rately),sothatthegeneralcasecanbene-

glected.

vErtical abErration

Theexpressionofthetruescatteringanglein

thepresenceofaverticalsampledisplacement

δz=Rδzistrivial.Infact,thez-dependence

ofthetruescatteringangleisallthroughthe

relativedistancefromtheplaneofthesample.

Thereforeitsufficestoreplaceξbyξ’=ξ−

δzandηby η’⋅ =1/ [(ξ’)2+1]1/2 .Onceδz is

known,achangeoforiginisenoughtocor-

rectforit.Thetruediffractionanglewillbe

then

Invertingwithrespecttotheplanardiffraction

angle,weobtain

Thisisimportantbecauseitallowsusto

drawtheconstant-true-scattering-anglecurves

onthedetectorsurface.Drawingthecurves

isimportantbecauseitallowsustointegrate

thepatternalongtheconstant-true-scatter-

ing-angle lines. For integrating the discrete

intensitydistributiononthedetectorsurface

weneedtointerpolatetheobservedintensity

(alreadycorrectedforpixelsensitivity–accord-

ingtothevanadiumcalibration–andforthe

Lorentz factor) between data points. The

simplestwaytodothisisbilinearinterpolation

(see[4]).Morecomplexinterpolationmethods

(e.g.bicubic)givebetterresultsbuttheyare

alsomoretime-consuming.Thedetailedeval-

uationofthisandotheradvancedaspectswill

be the argument of a forthcoming paper.

Hereafterweshallpresentresultsobtainedby

bilinearinterpolation.Notethattheresulting

integrated intensities – corresponding to a

selected2θ∗grid–willalwaysbecalculated

aslinearcombinationsofacertainnumberof

pixel intensities. Therefore the standardde-

viationswillalsobeeasilydeterminedusing

thewell-knownweighted-averagemethod.

At thispointwehave thepossibility to

calculateanintegrated1-DpatternIn,n=1…

Nobs,andtherelevantstandarddeviationsσn,

foreveryarbitrarilychosenvalueofδz.Now

wecandefine(seealso[5])twofunctionsof

thepattern,thesharpness

orthesymmetry

20

whereI+andI−(aswellastherelatedσ)are

obtainedbypartiallyintegratingforξ’>0or

<0,respectively.Asshandsyarefunctions

ofδzonly,onecanproceedassumingthatthe

actualvalueofδzwillbettheonethatmaxi-

mizessh –orminimizessy.Ourfirst tests

demonstrate (a bit surprisingly) that sh is

superiorinperformanceandaccuracy.Thisis

goodnewsbecausethesharpnessisfasterto

computeanditissupposedtobemorerobust

withrespecttospecialsamplefeatures(tex-

ture).Aplotofthebehaviourofsharound

thetruevalueisshowninFig.3.

Planar abErration

Theexpressionofthetruescatteringanglein

thepresenceofaplanarsampledisplacement

isabitmoreinvolved.Firstly,inordertosim-

plifythetreatment,weshallneglecthereafter

theeffectsofthezeroofthescatteringangle

ϕ0.Inotherwords,weshallassumethatthe

incidentbeamonthesample isdirectedto

2θ=0.Infact,bothϕ0andρ(themagnitude

ofthehorizontalsampleoff-centershiftdi-

vided by the sample-detector distance) are

quite small and it can be shown that the

distortioneffectdue toϕ0≠ 0 isof second

orderinϕ0andρandthereforenegligible.On

the other side, as mentioned, all available

dataanalysissoftwarecancopewithasmall

scatteringanglebias.

Assuming then that thebeam is in the

idealdirectionbutthesampleisshiftedby(ρ

cosβ,ρsinβ,0)inthexyplaneweobtainthe

followingexpression for the truescattering

angleasafunctionoftheidealplanarscat-

Fig. 3 Sharpnessfunctionplot(a.u.)aroundthetrueposition.Abscissaistheverticalsampledisplacement

(mm)with respect to the truevalue.The sample-detectordistance isR=1600mm, soadisplacement

of10mmcorrespondstoξ=0.00625andη=0.9999805.Asimple1-Dscancanfindamaximum<1sec-

ond.Kinksareduetothesimple(bilinear)interpolationalgorithmused.

21

tering angle 2θ, of the vertical coordinate

(hereencodedintoη)andofρ,β:

Inrealitywewouldneedtheinverseexpres-

sion–yielding2θasafunctionof2θ∗,ρ,β,

η.Thereisananalyticalexpressionthatcan

befoundbysubstituting

intotheformerandsolvingwithrespecttot

theresulting4thdegreeequation.However,

because the resulting expressions are quite

involvedandfurthermorenumericalsolution

iscompetitivewithanalyticalsolutionforthis

inversion,weshallsimplydenotetheinverse

as

Now,givenanytrialvaluefortheρ,βpair,we

can construct the constant-true-scattering-

anglecurvesonthedetectorsurfaceandin-

tegratethesignalalongthem.Againwecan

follow theprincipleofmaximum sharpness

– already introduced in the former sections

–andacceptastruetheρ,βpairthatmaxi-

mizesthesharpnessfunctionsh.Anexample

oftheshsurfacearoundthetruevalueofthe

samplepositionisgiveninFig.4.

Fig. 4 Sharpnessfunctionplot(a.u.)aroundthetruesamplepositioninthehorizontalplane.Theplane

coordinatesarex-ρcosβandy-ρsinβ,orthecartesiandisplacementcomponents(mm)fromtheideal

samplepositioninthehorizontalplane.Notethesharpmaximuminthecenter.Asimplegrid-scanalgo-

rithmcanbeusedtofindthemaximum,withaCPU-timerequirementintheorderoffewseconds.Again,

thesurfaceroughnessisduetothelow-level(bilinear)interpolationhereused.Roughnessisjustanaes-

tethicnuisanceasitdoesnotprejudicetheeffectiveness.

22

Final data rEduction

Thefinaldatareductionstepistheintegration

ina1-Dpowderpattern.Thistaskhasbeen

previously described. At this point sample

displacement parameters have been deter-

minedandaberration-compensatedconstant-

true-diffraction-angle curves can be drawn

onthedetectorsurface,inordertoobtainthe

mostfaithfulintegrationofthepattern,with-

outdetectoraberrations.TheLorentzfactor

isproperlytakenintoaccountduringthein-

tegration process, and depending on the

dataanalysisprogramrequirements,output

datacaneitherbeLorentzfactor-freeorin-

cludeaproperlycalculatedLorentzfactorfor

a1-Dpattern.

Theadvantagesofintegratingalongthe

curvedconstant-true-diffraction-anglepaths

onthedetectorsurfacewithrespecttocrude-

ly integrating along the vertical direction

(summingpixelcolumns)areevidentinFig.

5,where the samepattern (see Fig.2)has

beenintegratedwiththetwomethods.Peak

profile asymmetric broadening and aniso-

tropicshifts–artifactsoftheverticalintegra-

tion–arevisiblycorrectedfor.

Fig. �Exemplificationoftheadvantagesofintegratinga2-Dpattern(seeFig.2)alongthecorrectcurved

constant-true-diffraction-anglepathsoralongverticalpixelcolumns(asinaclassical1-Ddetector).The

differenceplot(below)isonthesamescale.Apartfromthesharperpeakshape,thecurved-integrationis

abletocorrectadisturbingeffectofanisotropicpeakshiftpresentinthevericallyintegratedpattern.

23

summary and conclusions

TheforthcomingupdgradeoftheDMCneu-

tron powder diffractometer has been illus-

trated.Thenew2-Ddetectorprojectwillopen

a whole new set of possibilities for more

advancedexperiments.Inordertofullyexploit

thenewdetector’scapabilities,thedatacol-

lectionandreductionsoftwareshallbealso

innovatedinthewaytoa)self-correctgeo-

metricaberrationsduetosamplemisplace-

ment,b)integratethepatternto1-Dinthe

mostfaithfulpossibleway.

In this way, we plan to keep the DMC

diffractometer at the cutting edge of the

scientificresearchandtosatisfytherequests

ofitsbroadSwissandinternationalusercom-

munity.

rEFErEncEs

[1] J.Schefer,P.Fischer,H.Heer,A.Isacson,

M.KochandR.Thut,Nuclear Instruments

and Methods in Physics Research A288,

477-485(1990)

[2] P.Fischer,L.Keller,J.ScheferandJ.Kohlbre-

cher,Neutron News11,No.3,19-21(2000)

[3] L.Cranswick,Oralcontribution,EPDIC10

conference(Geneva,Sept.2006)

http://www.sgk-sscr.ch/EPDIC10/Abstracts/

Instrumentation/Oral/CranswickNo76.doc

[4] W.H.Press,B.P.Flannery,S.A.Teukolsky,

W.T.Vetterling,Numerical Recipes in Fortran

77, 2nd Ed.,CambridgeUniversityPress:

Cambridge,chap.3(1992)

[5] A.Cervellino,C.Giannini,A.Guagliardiand

M.Ladisa,J. Appl. Cryst.39,745-748(2006)

24

the lead-bismuth liquid metal target

mEGaPiE (mEGawatt Pilot Experiment)

was operated at the swiss spallation

neutron source sinQ starting mid-august

2006, for a scheduled irradiation period

until december 2006. the continuous (�1

mhz) �90 mev proton beam hitting the

target reaches routinely an average cur-

rent of ∼1300 μa, corresponding to a

beam power 0.77 mW. this article illus-

trates the main features of the target and

the ancillary systems specially needed for

the liquid metal target operation. Further,

the operational experiences made with

this target during start-up and routine

operation are summarized, besides the

general performance highlighting the

performance of new beam and target

safety devices, and last but not least the

neutronic performance in relation to the

previously operated solid lead target.

introduction

SINQ,theSwissspallationneutronsource,is

drivenbyPSI´s590MeVprotonaccelerator.

Receivingastableprotoncurrentof∼1.3mA,

SINQisthepresentlymostpowerfulaccelera-

tor driven facility worldwide. Besides the

primarydesignationofSINQtoserveasuser

facility for neutron scattering and neutron

imaging,PSIseekstoplaya leadingrole in

thedevelopmentofthefacility,focusingto

spallationtargetsandmaterialsresearchfor

high-dose radiation environments. Serving

theseactivities,SINQhasestablishedseveral

projects,themostprominentonebeingMEG-

APIE (Megawatt Pilot Experiment), a joint

initiativebysixEuropeanresearchinstitutions,

plusEU,JEAE(Japan),DOE(USA),andKAERI

(Korea)todesign,built,operateandexplore

aliquidlead-bismuthspallationtargetfor1

MW of beam power [1]. Such a target is

underconsiderationforvariousconceptsof

acceleratordrivensystems(ADS)tobeused

//MEGAPIEatSINQ–theFirstLiquidMetalTargetDrivenbyaMegawattClassProtonBeam//

W.Wagner,F.Gröschel,K.ThomsenandH.Heyck

Paul Scherrer Institut, 5232 Villigen PSI, Switzerland

2�

intransmutationofnuclearwasteandother

applicationsworldwide.Thegoalofthisex-

perimentistoexploretheconditionsunder

whichsuchatargetsystemcanbelicensed,

toaccruerelevantmaterialsdataforadesign

data base for liquid metal targets, to gain

experienceinoperatingsuchasystemunder

realisticbeamconditions,andtoascertainthe

neutronicperformanceofsuchatargetfor

theuseinSINQandother(future)accelerator

drivenneutronsources.

thE mEGaPiE tarGEt

Inshapeandexternaldimensions,theMEG-

APIEtargethastomatchthegivenopening

in the target block shielding, demanding a

slim,about5mhighstructure[2].Initsinte-

rior,itiscompletelydifferentascomparedto

thenormal solid ‘lead-cannelloni’ target of

SINQ:TheMEGAPIE targethousesabout1

tonofliquidleadbismutheutectic(LBE,melt-

ing point at 125 ºC) in a steel container,

closed-endbyahemisphericalbeamwindow

atthebottom.Themainfeaturesinsideare

twoelectromagneticpumpsforforcedcircu-

lationoftheLBE,aflowguidetubeinserted

intothelowerliquidmetalcontainertosepa-

rate the annular LBE down-flow from the

centralup-flow,andtwelveheatexchanger

pins for removing the energydepositedby

thebeamand/orkeepingthetargetattem-

peraturewhenthebeamisoff.Further,the

target is equippedwith a variety of instru-

mentation,mostlythermocouples,foropera-

tional control, or serving safety features or

experimentalobservation.Figure1showstwo

ofthemajortargetcomponents,i.e.the12-

pin heat exchanger (lower right) and the

centralflowguidetube.Figure2showsthe

fullyassembledMEGAPIEtargetliftedbefore

insertingitintotheSINQoperationposition.

ancillary systEms

TheMEGAPIEancillarysystemsdirectlyneces-

sary for the target operation are the heat

removalsystem(HRS),thecovergassystem

(CGS),theinsulationgassystem(IGS)andthe

fillanddrainsystem(F&D).

Fig. 1:Twomajortargetcomponentspriortointegration:the12-pinheatexchanger(left)andthecentral

flowguidetube.

26

TheHRS[3]consistsoftwosubsystems:

anintermediatecoolingloopwithoilDiphyl

THT as cooling medium, connected to the

heatexchangerpinsinthetarget,andaback-

coolingwaterloop(WCL).Theoilloop,op-

eratingbetween160ºCand230ºC,ispri-

marily necessary to remove the about 0.6

MegawattofheatloaddepositedintheLBE

bytheprotonbeam.Asasecondfunctionit

mustalsobecapabletomanageacontrolled

hot-standby operation after beam trips or

scheduled beam interruptions to prevent

freezingofthetarget.

TheCGS[4]musthandlethevolatilera-

dioactive inventory of spallation products

releasedfromtheLBEinthetarget.Handling

of radioactive gases and volatiles imposes

stringent requirementson safeand remote

operation,onretentionofradioactivity, like

second containmentand tightness, andon

shielding.

TheIGS[5]fillsthevolumebetweenthe

innerhotpartofthetargetandtheoutercold

hullbyaninsulatinggas.Besidesitsfunction

asthermalbarrieritmustsafelycopewiththe

potentialincidentofcoolingwaterentering

the insulationgapandgetting intocontact

withthehotinteriorofthetarget.

TheF&Dsystemisneededtoallowfilling

anddrainingofliquidLBEintooroutofthe

target, respectively. Figure 3 shows a view

from top into the target head enclosure

chamberTKE (situationofApril2006).The

targetheadisinthecentre,stillwithoutthe

cablesconnectedwhichareinpreparationin

therear,theoilloopoftheHRSisattheright,

theCGSintheleftrearcorner,andtheF&D

systemattheleft.

The initial baseline for the F&D system

requireddrainingofactivatedLBEfromthe

targetaftertheoperationperiod.Adetailed

designforthatwaselaborated;however,the

drainingoptionwasrecognisedtobearcon-

siderablerisks,immediateonesforaccessing

theTKEandmoregeneralonesrelatedtoli-

censing.Aswell,ithadrequiredconsiderable

extraexpenditureinthetechnicalrealization.

Viewing these difficulties the decision was

takentoabandontheinitialconceptinfavour

ofonlyinactivedrainingandfinalfreezingof

theLBEinthetargetaftercompletionofthe

irradiationexperiment[6].

mEGaPiE irradiation start-uP

ThefirstbeamonMegapiewasreceivedon

Aug.14,2006,closelywatchedbytheop-

erationalteamandprominentguestsinthe

SINQcontrolroom,anddocumentedinFigure

Fig. 2:

Thefullyassembled

MEGAPIEtargetbe-

foreinsertingitinto

theSINQoperation

position.

27

4.Ata relativelystableandconstantbeam

currentof40μA,whichcorrespondstoabout

25kWofbeampower,thetargetaccumu-

lated a total charge of 60 μAh in this first

phase. The second phase of the start-up

procedurewassuccessfullyaccomplishedthe

followingday,wherethepowerwasstepwise

increasedto150kW(250μAprotoncurrent).

Thecorrespondingbeamhistoryisshownin

Figure5.Thegoalofthisphasewastocheck

andverifytheresponseoftheheatremoval

system at power conditions comparable to

thoseusedwhenoperatedoutofbeamat

the test stand in theautumnof2005.The

thirdandfinalphaseofthestart-upprocedure

wassuccessfullyaccomplishedonthe17thof

Fig. 3: ViewintothetargetheadenclosurechamberTKEwhichislocatedontopoftheSINQmainshield-

ingblock(situationofApril2006).Thetargetheadisinthecentre,stillwithoutthecablesconnected

whichareinpreparationintherear,theoilloopoftheHRSisattheright,theF&Dsystemattheleft,and

theCGSintheleftrearcorner(partlyhiddenbehindtheconnectorboxoftheF&D).

Fig. 4: FirstbeamonMegapie,closelywatchedby

theoperational teamandprominentguests (not

allshown)intheSINQcontrolroom:fromleft,a

French colleague from CEA observing fission

chamber reactions, Stefan Joray pointing to the

screen,SergejDementjev,KurtClausenandKnud

Thomsen.

28

August, when the power was stepwise in-

creasedto700kW(1200μAprotoncurrent).

ThesecondgraphofFigure5showsthebeam

historyduring the ramp-upphase.Ateach

powerlevelthebeamwasinterruptedafter

some10minuteswithastableprotonbeam,

toverifythepredictedtemperaturetransients

inthetarget.Mostoftheerraticbeambe-

haviourwasthusintentional.

mEGaPiE in usEr oPEration

WithMEGAPIE,normaluseroperationwas

startedonAugust21staround8:30a.m.,and

wascontinueduntilthenormalannualwinter

shut-downstartingonDecember21st,2006.

Thefirst12hoursofprotonbeamisseenin

Figure6.SincethenSINQwiththeMEGAPIE

targetwasoperating routinely and reliably.

Meanwhilethegoalcurrentof1350μAhas

beenreached.Thestatisticsofweeklyaccu-

mulatedprotonchargeonSINQisillustrated

inFigure7,distinguishingchargedeliveredby

theacceleratorandchargeacceptedbySINQ.

The ratioofbothdefines theavailabilityof

SINQwhich,exceptforthestartingweek,was

atsatisfactory∼95%.Thetotalprotoncharge

accumulatedattheendofweek49was2.54

Ah.

Fig. �: Beamhistoryduringthesecondphaseofthestart-upprocedure(Aug.15)wherethepowerwas

stepwiseincreasedto150kW,andthethirdphase(Aug.17)wherethebeamwasramped-uptofull

power.Mostoftheerraticbeambehaviourwasintentional.

Fig. 6: Thefirst12hoursofprotonbeamwhen

normaluseroperationhadstartedonAugust21st

29

Fig. 7: StatisticsofweeklyaccumulatedprotonchargeonSINQduringMEGAPIEoperation.Theavailabil-

ityofSINQ,evenwiththecomplexMEGAPIEsystemsandvariousadditionalbeaminterruptchannels,

wasatthesatisfactorylevelof∼95%.

During the entire MEGAPIE irradiation

experimentthetargetbehaviourwasfound

excellent,bothduringstableoperationand

duringtransientsduetobeamtripsandmore

extendedbeaminterrupts.Thetemperature

distributionsand-transientswereasexpected,

very close to predictions. The electromag-

netic pumps operated stable and reliably,

without any indication of degradation. For

themainMEGAPIEancillarysystemsdirectly

connected to the target, i.e. heat removal

system(HRS),thecovergassystem(CGS),and

theinsulationgassystem(IGS),theexperience

isverypositive,aswell.Allinall,theMEGA-

PIE systems worked reliably according to

specifications,exceedingourrathercautious

expectations.

nEW Proton bEam saFEty dEvicEs

For its safe operation a sufficiently broad

footprintoftheincidentprotonbeamonthe

SINQtarget ismandatory. If forany reason

theprotonswerenotscatteredsufficientlyin

anupstreamtarget(TargetE)theirfootprint

ontheSINQtargetcouldshrinkleadingtoa

riseinthemaximumdensityofthebeamby

afactorof25.Attheresultinghighcurrent

densityitwouldtakeonly170msuntilahole

isburnedthroughboththeliquidmetalcon-

tainerinsidethetargetandthelowertarget

enclosure.The liquidmetalwouldspill into

thebeamlineandintothecatchervertically

belowtheSINQtarget.Suchafailurewould

result inanextendedshutdownperiodfor

SINQ.

30

Inordertopreventaninsufficientlyscat-

tered beam from reaching the SINQ target

threeindependentsafetysystemshavebeen

installed: a dedicated current monitoring

system,abeamcollimatingslitandanovel

beam diagnostic device named VIMOS [7].

Thelattermonitorsthecorrectglowingofa

tungstenmeshclosely infrontoftheliquid

metaltarget.Allthesesystemshavetomeet

thebasicrequirementtoswitchoffthebeam

within100mswhen10%of theprotons

by-passTargetE(correspondingtoanincrease

inpeak intensitybya factorof two). Inan

extensive collaboration amongst different

groups at PSI the new safety devices have

beeninstalled.Earlyintheramp-upphaseas

wellasduringroutineoperationtheirproper

functioninghasbeenverified.

nEutronic PErFormancE oF

mEGaPiE

Duringthestart-upphases,severalneutronic

measurementswereperformed,i.e.measure-

mentsofdelayedneutronsinthetargethead

area,Bonnerspheresandchoppermeasure-

ments for spectral resolution at the ICON

beamport, fission chamber measurements

frominsidethetargetandneutronfluxmeas-

urements inside theD2OModeratorandat

selected instruments and beam ports. The

neutronfluxesofMEGAPIEinrelationtothe

previouslyoperatedsolidleadtargetwereof

particular interest. Based on earlier Monte

Carlosimulationstheliquidmetaltargetwas

expectedtoprovidea40%increaseinneu-

tronflux(atidenticalcurrent).Initialmeasure-

mentsatselectedinstrumentsconfirmedan

increaseinneutronfluxwhichatfirstglance

was met with some scepticism: While the

powderdiffractometerHRPTatthethermal

beamportreported41%,veryclosetothe

prediction,theSANS-Iinstrumentatthecold

guidequotedafluxincreaseashighas70to

Fig. 8: NeutronfluxincreasebyMEGAPIEinrela-

tiontothestandardsteel-leadcannellonitarget,

measuredduringthestart-upphaseofMEGAPIE:

the powder diffractometer HRPT at the thermal

beamport reportedaflux increaseof41%, the

SANS1instrumentatthecoldguidearound70%.

Meanwhilegoldfoilactivationmeasurementshave

confirmedfluxincreasesbetween80and85%at

both,athermalbeamport (NEUTRA)andacold

beamport(ICON),and70%atsector80(thermal

waterscatterer).

31

80 % (see Figure 8). Meanwhile gold foil

activationmeasurementshaveconfirmedflux

increasesbetween80 and85%at both, a

thermalbeamport(NEUTRA)andacoldbeam

port(ICON),and70%atsector80(thermal

water scatterer). Revised calculations with

moredetailedtargetandmoderatorgeom-

etryreproducetheseresults.

rEFErEncEs

[1] G.S.Bauer,M.Salvatores,G.Heusener,

J.Nucl.Mater.296(2001)17

[2] F.Gröschel,A.Cadiou,S.Dementjev,

M.Dubs,C.Fazio,T.Kirchner,Ch.Latge,

P.Ming,K.ThomsenandW.Wagner,

TheMEGAPIEProjectStatusUpdate–High

PowerLiquidMetalSpallationTarget,Proc.

ICANS-XVII,InternationalCollaborationon

AdvancedNeutronSources,SantaFe,NM,

LA-UR-06-3904(2006)590

[3] G.Corsini,M.Dubs,B.Sigg,W.Wagner,

HeatRemovalSystem:FinalUpdateofCon-

ceptandDetailDesign,Dimensionaland

FunctionalIssues,Proc.4thMEGAPIETechni-

calReviewMeeting,FZKA6876(2003)34

[4] W.Wagner,F.Groeschel,G.Corsini,

CoverGasSystem:UpdatedBoundaryC

onditionsandCurrentConcept,Proc.4th

MEGAPIETechnicalReviewMeeting,

FZKA6876(2003)40

[5] W.Wagner,J.Welte,S.Joray,B.Sigg,Insula-

tionGasSystemofMEGAPIE:AConcept

Update,Proc.4thMEGAPIETechnicalReview

Meeting,FZKA6876(2003)52

[6] W.Wagner,P.Turroni,P.Agostini,K.Thom-

sen,E.Wagner,J.Welte,FillandDrainand

Freezing:SystemModificationsforMerely

non-activeDraining,Proc.4thMEGAPIETech-

nicalReviewMeeting,FZKA6876(2003)46

[7] K.Thomsen,VIMOS,aNovelVisualDevice

forNear-TargetBeamDiagnostics,Proc.

ICANS-XVII,InternationalCollaborationon

AdvancedNeutronSources,SantaFe,NM,

LA-UR-06-3904(2006)374

32

//Announcements//

sGn/ssdn mEmbErs

The Swiss Neutron Scattering Society wel-

comesthefollowingnewmembers:

– JustinHoppler,UniversityofFribourg,

Switzerland

– SureshChathot,UniversityofGöttingen,

Germany

– RajashekharaShabadi,UniversityofLille,

France

PresentlytheSGNhas200members.Online

registrationfornewmembersofoursociety

isavailablefromtheSGNwebsite:http://sgn.

web.psi.ch

PEtEr allEnsPach nEW

Ensa chairman

Ontheoccasionoftherecentmeetingofthe

‘European Neutron Scattering Association

ENSA’inOctober2006thePresidentofthe

‘SwissNeutronScatteringSociety’PeterAl-

lenspach(PaulScherrerInstitut,NUMdepart-

ment)waselectedasnewENSAchairman.

Thetermofofficeistwoyears.

oPEn Positions at ill

TochecktheopenpositionsatILLpleasehave

a look at the ILL-website: http://www.ill.fr/

jobs.html.

nEWs From Psi usEr oFFicE

2006wasaveryencouragingyearregarding

thesubmissionofnewSINQproposals:Thanks

totheveryactiveusercommunitytotally328

new proposals were submitted at the two

deadlinesinMayandNovember.Thatnumber

exceedsthepreviousrecordof213intheyear

2004bymorethan50%!

AsbeforetheSINQusercommunityisvery

international: The proposals for cycle I/07

originate from 22 different countries, one

thirdwassubmittedbyauthorswithaSwiss

affiliation(seefiguresbelow).

SubmittedProposalssince1999,(*):in2005only

onecallforproposalswasopenedinsteadoftwo

(extendedMEGAPIEshutdown).

33

GeographicaldistributionofnewSINQproposals

(cycleI/07).

sinQ usErs’ mEEtinG 2007

The2007-SINQusers‘meetingwillbeorgan-

ized as a special session during the ECNS

conferencetotakeplaceinLund,June25-29,

2007:

http://www.ecns2007.org

The users‘ meeting will consist of one

session(halfaday)withoralpresentations,

which will NOT overlap with plenary ECNS

sessions.InconjunctionwiththeECNSpro-

gramcommitteesomeabstractssubmittedto

ECNS and containing SINQ results will be

selected for oral presentations at the SINQ

users‘meeting.

Therefore, in order to facilitate the or-

ganization,andifyourworkinvolvesSINQ,

weaskyoutosendacopy(MSwordorpdf)

ofyoursubmittedabstracttosinq@psi.chwith

the mention „SINQ users meeting“ in the

headline.

TheECNSdeadlineforabstractsubmis-

sionisFebruary5,2007.

Limited funds covering the registration

feeandtravel(economyclass)willbeavail-

able for the selected speakers of the SINQ

users‘meeting.

in addition, the annual meeting of the

swiss neutron scattering society sGn

(http://sgn.web.psi.ch) will be organized

in connection with the sinQ users‘ meet-

ing.

10th annivErsary oF sinQ

In summer 1997 the first user experiments

wereperformedatSINQ.Tenyearsandap-

proximately2000experimentslatertheSwiss

neutronsourcehasbecomearealsuccess.The

10thanniversaryofSINQwillbecelebratedin

aspecialoccasionatPSIonseptember 21,

2007.Moreinformationwillbepublishedon

theSINQwebpage:http://sinq.web.psi.ch

34

//The2007WalterHälgPrizeoftheEuropeanNeutronScatteringAssociation//

thE WaltEr hälG PrizE

The prize was made available to the Euro-

peanNeutronScatteringAssociation(ENSA)

byadonationfromProfessorWalterHälgwho

isthefounderofneutronscatteringinSwit-

zerland.ThePrizeisawardedbienniallytoa

Europeanscientistforoutstanding,coherent

work in neutron scattering with long-term

impactonscientificand/ortechnicalneutron

scattering applications. The previous Prize

winnerswereF.Mezei(1999),J.Brown(2001),

R.Cowley(2003),A.FurrerandH.U.Güdel

(2005).ThefifthawardofthePrize(10’000

CHF)istobemadeataspecialceremonyand

sessionat the4th EuropeanConferenceon

NeutronScattering(ECNS2007),25–29June

2007,Lund,Sweden.Informationonprevious

laureatesareavailableontheENSAweb-site

(http://neutron.neutron-eu.net/n_ensa).

sElEction committEE

Nominationsfortheprizewillbeconsidered

byaSelectionCommitteewhichconsistsof

authorities representing the major scientific

disciplines.Itincludesacknowledgedexperts

bothinneutronscatteringandfromoutside

theneutronscatteringcommunity.Member-

shipintheSelectionCommitteeisobtainedby

invitationextendedbytheENSACommittee.

call For nominations

Nominationsforthe2007WalterHälgPrizeof

theEuropeanNeutronScatteringAssociation

(ENSA)maybesubmittedbyEuropeanscien-

tistsasindividualsoronbehalfofaDivision,

SectionorGroup.Toestablishahighstandard

it is necessary that the Committee receive

3�

proposals which represent the breadth and

strengthofEuropeanneutronscattering.

Nominationsshouldincludethemotivation

fortheaward,abriefcurriculumvitaeofthe

nomineeandashortlistofmajorpublications.

Lettersofsupportfromauthoritiesinthefield

which outline the importance of the work

would also be helpful. Nominations for the

Prizewillbetreatedinconfidenceandalthough

theywillbeacknowledged therewillbeno

furthercommunication.Previousnominations

havetobeup-datedandresubmitted.

dEadlinE

Nominationsshouldbesentbefore2 march

2007totheChairmanoftheSelectionCom-

mittee, preferably by electronic mail in pdf

format:

Dr.PeterAllenspach,ENSAChairman

PaulScherrerInstitut

CH-5232VilligenPSI,Switzerland

Phone: +41563102527

Fax: +41563102939

E-mail: peter.allenspach@psi.ch

The European Crystallographic Association

(ECA)andtheEuropeanNeutronScattering

Association(ENSA)announcethecreationof

aprizeinhonourofthelateErwinFelixLewy

Bertaut,inmemoryofhisscientificachieve-

ments,cornerstonesincrystallographyand

inneutronscattering.

The prize is awarded to a young Euro-

peanscientist,withacareerextendingto5

to8yearsafterthesisdefence,inrecognition

ofnotableexperimental,theoreticalormeth-

odologicalcontributionsinthefieldofanal-

ysisofmatterusingcrystallographicorneu-

tronscatteringmethods.

Theamountof theprize is2000euros

andthelaunchoftheprizeissponsoredby

NMI3,theNeutronandMuonIntegratedIn-

frastructureInitiative(http://neutron.neutron-

eu.net).InthelongtermECAandENSAaim

tomakeequalcontributionstothefinancing

oftheprizethroughdonations,sponsorsetc..

TomaintaintheprizeECAandENSAwilles-

tablishadedicatedfund.

The first call for nominations is open

untilFebruary28th2007.Detailsforthepro-

cedure and guidelines for application are

available on the web-sites of ECA (http://

www.ecanews.org/) and ENSA (http://neu-

tron.neutron-eu.net/n_ensa/).Thefirstprize

willbedistributedattheEuropeanconference

forNeutronScatteringinLund,Sweden,June

25-29,2007(http://www.ecns2007.org).

ErwinFelixLewyBertautprizeofEuropeanCrystallographicAssociationandEuropeanNeutronScatteringAssociation(ECA-ENSA)

36

OnceayearthePaulScherrerInstitutorgan-

izes its tradional summer schools on con-

densedmatterresearchatthe‘LyceumAlpi-

num’ in Zuoz, Engadin valley. While the

experimentalmethodsprovidedbyPSItothe

scientificcommunity,thatisneutrons,muons

andsynchrotronlightplayacrucialbutnot

exclusiverole,theemphasisoftheschoolis

onaparticulartopic,tobedefinedeveryyear.

Thetopicofthefifthschool(2006)was‘Neu-

tron,X-rayandMuonStudiesofNanoScale

Structures’withaspecialemphasison‘Soft

Condensed Matter Systems’. As usual the

schoolwasmainlyaddressedtotheeducation

of PhD and postdoctoral students without

priorknowledgeofneutron,X-rayandmuon

techniques.

The program started with introductory

coursesonX-rayandneutronsourcesbyL.

RivkinandK.Clausen,respectively,followed

by two lectures on ‘Elementary Scattering’

givenbyJ.Mesot(neutronpart)andJ.F.van

derVeen(X-raypart).

Thesecondpartoftheschoolwasthen

devoted to the various neutron, X-ray and

muontechniques,whicharerelevantforthe

field.T.ProkschaandR.Scheuermannshared

theintroductionto‘muonspinrotation’and

presentedvariousrelevantscientificexamples.

T. Gutberlet and P. Müller-Buschbaum (TU

München)gavepresentationson‘Reflectom-

etry’ and ‘Grazing Incidence Small Angle

Scattering’, respectively, before J. Kohlbre-

chertalkedaboutthegeneralaspectsof‘Small

AngleScattering’.Allthoseintroductorylec-

turesonthe techniqueswereaccomplished

bypracticalsessions,wherethestudentscould

eitherdeepenthecontentofthelecturesor

wheretheyreceivedimportantadditionalin-

formationaboutthepracticalaspectsofre-

latedexperimentsanddataanalysis.

The remaining part of the school con-

tainedscientificpresentationson‘hottopics’

fromthefieldof‘NanoScaleStructuresand

SoftCondensedMatter’:

• ProteinCrystallography(E.Pohl,PSIVilligen)

//5thPSISummerSchoolonCondensedMatterResearch,Zuoz,Switzerland//

S.Janssen,K.Clausen

NUM Department, Paul Scherrer Institut, CH-5232 Villigen PSI

37

• SmallAngleScatteringfromBiological

Macromolecules

(D.Svergun,EMBL/DESY,Hamburg)

• Proteins:FromModelColloidstoCataract

Formation

(A.Stradner,UniversityofFribourg)

• Bio-Membranes

(H.Wacklin,UniversityofOxford)

• Membranes(K.Mortensen,

DanishPolymerCentre,Risø)

• X-rayandNeutronScatteringStudiesof

Polymers

(I.W.Hamley,UniversityofReading)

• PolymerDynamicsStudiedbyInelastic

NeutronScattering

(R.Zorn,ForschungszentrumJülich)

• DynamicsofMacromolecularSystems

StudiedbyμSR

(I.McKenzie,UniversityofStuttgart)

• FibreDiffractionUsingX-raysandNeu-

trons(T.Forsyth,ILLGrenoble)

• Colloids

(S.Egelhaaf,UniversityofDüsseldorf)

• TheoryofColloids

(M.Fuchs,UniversityofKonstanz)

The evening sessions in Zuoz traditionally

containpresentationsonveryinterestingtop-

ics and tend to have the character to be

highlightsoftheschools.Alsoin2006those

presentations were very stimulating: Two

eveningswerededicated to the fascinating

andevolvingfieldofimagingtechniques.E.

Lehmanntalkedabout‘Options,Performance

andLimitationsofNeutronImagingSystems’

andM.Stampanonipresenteda‘Fascinating

TripfromMacrotoNanobyX-rayImaging’.

Thethirdeveningpresentationwasgivenby

F.Pfeifferonthepossibilitiesofferedbythe

techniqueof‘CoherentX-rayScattering’.

TheschoolendedwithaBiologist’spoint

ofviewonthephysicaltechniquespresented

duringtheschool:K.Ballmergaveapresenta-

tionentitled ‘NewTricks toSolveBiological

Problems:WhatBiologistsExpectfromPhys-

ics’.

Theparticipantsofthe5thsummerschoolinZuozinfrontoftheLyceumAlpinum.

38

The students did not only listen to the

presentations but could also present their

scientificactivitiesinadedicatedposterses-

sionwith35postersintotal.Thatsessiongave

alsotheopportunitytodiscusswiththespeak-

ersandtocreatenewcontacts.

The school was attended by totally 87

participants,whichiswellinagreementwith

theaverageparticipantnumbersoftheprevi-

ousyears.Those87participantsconsistedof

11 master students, 34 Ph.D. students, 10

PostDocs,29seniorscientistsincludingthe

invited lecturers and 3 participants with a

status different from the categories men-

tionedbefore.Naturallymostofthepartici-

pants were affiliated to Swiss institutions

(44%) followed by Germany (22%), Italy

(7%),UnitedKingdom(6%)andRussia(5%).

Intotalparticipantsfrom15differentcoun-

triesattendedtheschool.

The completeprogramof the school is

onlineavailabletogetherwithpdf-versionsof

allgivenpresentationsfrom:http://num.web.

psi.ch/zuoz2006/

FromtheverybeginningofthePSIsummer

schoolsitwasalwaysaimedbytheorganizers

tostimulatenotonlythescientificexchange

butalsotoofferaninterestingsocialprogram

withmainlysportingactivitiesinthefascinating

environmentof theAlpesaroundZuoz. The

traditionofthefreeafternoonswaskeptalso

in 2006 and the participants could choose

betweenvariousactivitiessuchasexcursions

tothenearby‘NationalPark’,amountainhik-

ing tour to the ‘Piz Languard’ guided by H.

Grimmeror toplay tennisonthe traditional

courtsof the Lyceum.Thosewhowerepar-

ticularly courageous could even show their

abilityinthedisciplineof‘RiverRafting’.

WethanktheschoolsecretaryMrsRenate

Bercherfortheperfectorganizationandsup-

port before, during and after the school.

Furthermore financial support by the Euro-

peanCommissionunderthe6thFramework

ProgrammethroughtheKeyAction:Strength-

eningtheEuropeanResearchArea,Research

Infrastructures, Contract n°: RII3-CT-2003-

505925‘(NMI3)isgratefullyacknowledged.

Done!Thehikingtourgrouponthesummitof

‘PizLanguard’.

Someof the ‘non-hydrophobic’participantsdur-

ingtheir‘RiverRafting’adventure.

39

//ConferencesandWorkshops2007//

January

InternationalWorkshoponCurrent

ChallengesinLiquidandGlassScience

January 10-12, 2007, The Coseners House,

Abingdon, England

InternationalWorkshoponAdvancedLaue

DiffractioninFrontierScience

January 23-27, 2007, Grenoble, France

FirstEuropeanXFELUsersMeeting

January 24-25, 2007, Hamburg, Germany

DMM2007:DynamicsofMoleculesand

Materials

January 31 - February 2, 2007, Grenoble,

France

FEbruary

AnnualMeetingoftheSwissPhysicalSociety

February 20-21, 2007, University of Zurich,

Switzerland

28thHMISchoolonNeutronScattering

February 26 - March 2, 2007, HMI Berlin,

Germany

march

NOP07:EuropeanWorkshoponNeutron

Optics

March 5-7, 2007, PSI Villigen, Switzerland

may

GISAXS–anadvancedscatteringmethod

May 9-11, 2007, Hamburg, Germany

SCES07–InternationalConferenceon

StronglyCorrelatedElectronSystems

May 13-18, 2007, Houston, USA

BENSCUsersMeeting2007

May 23-25, 2007, HMI Berlin, Germany

ICCS2007:InternationalConferenceon

ComputationalScience

May 27-30, 2007, Beijing, China

JunE

EngineeringofCrystallineMaterials

Properties:State-of-the-ArtinModeling,

Design,andApplications

June 7-17, 2007, Erice, Italy

(anupdatedlistwithonlinelinkscanbefoundhere:http://sinq.web.psi.ch/sinq/links.html)

40

1stSchoolandWorkshoponX-rayMicro

andNanoprobes:Instruments,Methodolo-

giesandApplications

June 11-17, 2007, Erice, Italy

ECNS2007:4thEuropeanConference

onNeutronScattering

June 25-29, 2007, Lund, Sweden

9thSINQUsers‘Meeting,SatelliteMeeting

ofECNS2007

Between June 25-29, 2007, Lund, Sweden

ICNM-2007:4thInternationalConference

onNanoscaledMagnetism

June 25-29, 2007, Istanbul, Turkey

July

NIB2007:NeutronsinBiology

July 11-13, 2007, Rutherford Appleton Lab-

oratory, Oxfordshire, UK

auGust

6thPSISummerSchoolonCondensedMat-

terResearch

August 18-25, 2007, Zuoz, Switzerland

ECM24:24thEuropeanCrystallographic

Meeting

August 22-27, 2007, Marrakech, Morocco

DiffusionFundamentalsII

August 26-29, 2007, L‘Aquila, Italy

sEPtEmbEr

AnnualMeetingoftheSwissSocietyfor

Crystallography

September 10-11, 2007, PSI Villigen, Swit-

zerland

8thSLSUsers‘Meeting

September 11-12, 2007, PSI Villigen, Swit-

zerland

DyProSoXXXI:31stInternationalSymposium

onDynamicPropertiesofSolids

September 25-29, 2007, Porto, Portugal

swiss neutron scattering society

SekretariatSGN/SSDN

PaulScherrerInstitut

bldg.WLGA/002

5232VilligenPSI,Switzerland