REVISTA MEXICANA DE FÍSICA.U SUPLEI\1ENTO 2. 77-R4 OCTUBRE 1998

The Holificld radioactive ion beams facility (HRIBF)-gctting ready to docxperiments

D. Shapira and T.A. LewisOak RidRC !\-'atimwIIÁI/)ol"utOlYOuk RiliRt:'. Téfllless('(' 3783 J. lJ5;A

Recibido el 4 tle marzo de 1995: aceptado el 25 de mayo dc 199X

Tlle convcrsinn 01"the HHIRF facility to a radioactive ion bcam facility startcd in ]994. In this ISOL type facility the cyclotron has 'heellrc-lillcd as a driver providing high intensity proton beams which react with Ihe ¡¡¡rget Irol11\••..Ilich the radioactive products are extractedalld t!len <lccelerated in the tantlem clectrostatic accclcrator to the desired encrgy ror nucle,ll' scicnce studies. Facilities for nuclear physirscxpcri IlIcnts are at di ITerent stagcs of developmcnt: A rl'coi 1mass spl'ctromcter (RMS) will1 il cOlllplellll'llt of detcctors at the focal plane amIarnund the targel is used primarily ror nuclear structurc studies. A largc re(oil separator comhining lielocity and momentum selectioll. wilhils cOlllplemcnt of focal plane detectors. will he dedicated to measuremcnts relcvalll to nuclear astrnphysics. Thc l'nge split pole spl'ctrographis hcing re-liued ror operation in a gas tilled modl', making it a more versatile tool for nuclear reaction studies. With Ihe nev.' experimenlall'quipmcl1t hring cOlllmissioned and lhe prospecls of running experimcnts with lo\\' intclIsity radioactivc beams a significant cfforl lo developequiprncnt for beam diagnostics is unclerway. SOlllCof our effons and results in developing heam diagnostic tools will he described.

Kl'nl'O/"{l.c Radioactive beams: mass spectrorneters

La conversión del equipo (i1HIRF) a un equipo de haces de iones radioactivos comenzó en 1994. En este tipo de equipo ISOL. el ciclotrónse ha ajustado a una fuente que provee haces de protones de alta intensidad los cuales rcac¡;ionan con el blanco del cual los productosr,ldio¡[ctivos son extraídos y entonces acelerados en el acelerador e1ectrost,ltico del tandem a la energía deseada para estudios de la cienciaIlUele,lr.Lus equipos para experimentos de física nuclear estan en diferentes etapas de dCS,llTOllo:Un cspectníl1letro de masas retrodispersadas(RJ\tS) l"(ln un c{lInplemento de detectores cn el plano focal y alrededor del hlanco se usa principalmcnte para estudios de estruclUra nuclear.Un .sep<lradorgrande para las masas retrodispersmlas que convina selección dc velocidades e impulsos con su complemento de detectores delpl,lIlo focal. ser:í dedicado a medidas relevantes cn astrofísica nuclear. El espectrógrafo enge split pole est:í siendo re-ajustado para operarcon gas, !l:lCiendol0 una herramienta Illas versátil para estudios de reacciones nucleares. Con el nuevo equipo experimental solicitado y lal'SpL'r~llll,adl' Cllrrcr cxperimentos con haces radioactivos de baja intcnsidad, un esfuer/.{) signi licativo para desmrollar equipo para diag:nústico(!l' 1l:ICCSest;Í l'll proceso. Dcsrrihiremos un poco de nuestro esfuerzo y resultados en el desarrollo dc la herramienta dc diagnústico de haces.

[){'ll"I"i¡I/(Jln: lIaces dc iones radioactivos: cspectrómetros de Illasas

PACS: 2.190.+w: 29.30.+h: 07.75.+h

1. lntrndllction

The possibilities and promise to nuclear scient:c rcsearch thatcan he realized w!len using radioactive ion heams has heentlw suhjct:t 01"nUlllcrous confcrences and symposia startingal the cnd of the last dccadc 111 ami \vere recenlly SUllll11a-r¡zed in a \vhile papel' follo\Ving an "all hands" meeting inCOlllIllOUS. Ooio [31. Prcscntly. HRIBr is loe only ISOL Iypcfacilily in operalion in North America eapahle of providingproton ri(.'h radioaclive hcams accclcratcd lo cncrgies in ex-ccss 01' fe\V McV/A {2]. The layout oflhe facility is shown inFig. I ami indicatcs Ihe placetllent 01"several experimenlal fa-cilities. Tllc R!"vlS-a large recoil mass speclromclcr-whichis now fully opcrational 141. The DRS-a recoil separalorhascd 011 vclocity and I110I11en1UIllselection-is in ils tlnalslages 01"commissioning 15, fil. Thc enge splil pole spectro-graph is heing rc-fillcd ror work wilh low rrcssurc gas filling..TIlL' UNISOR isotope separator f~lcilily is prescnlly lIsed rortcsting RIB produclion schcmcs and ion-sollfce dcsign us-ing proton heams from the 25 MV landclll accclcralor. The

general purposc he<lmline is in use rol' sludies 01' bcam di-agnoslic Lkviccs whicll will he discllssed laler. The first RIBexpcrilllcnl pcrl"onned al Ihe HRIBr: was also performcd inIhis hC<lllllinc [~)I.

2. Experimental facilities at HRIBF

2.1. Tlw rc(~oilmass spectrometer

The RMS-rccoil mass separator \Vas commissioned during1995-96 and is IHlW fully operational. The IUvlS comhines a1ll0lllCIHum separalor and a mass scparator and is planncd asa Iargc lilter for nuclear struclure llleasurelllcnts using holhin-hcm!l and Lkcay studies. The layout 01"the spectromcterappcars in Fig. 2 whcrc sOllle paramelers 01" Ihe dcvice arelistcd. The 1Il0111cntulll separalor refocuses Ihe products at theacllromatic forus. The momenlum acceptance is de{ennincdat lhe dispcrsion planc 01" Ihe lirsl slage ("flngcrs rcgion").The fOCllSat lhe ;:Khromat is wcak. allowing rOl' highcr accep-

7S 1) SIIAI'IRA ,\:\1) T.A, LEWIS

HOUFIELD RADIOACTlVE ION BEAM FACIUTY

nOI

..

10 20 f([f

A "ETEIlS

1011 SOIJR(l;n::sr ucnm "'"""'TII<G

ROO'

9

¡:lCilll{E l. Layout nf lhe IIIIRIF fa\.:ilily-thc Iwo major cxpl.'firnclllal arcas are Ill'W l(lllll' lüciJíty.

F1<;tlR.r' Layout 01"Ihe rccoil mass spc(:lrometcr facility.

l' l••.,..114 116 .:..

leY; •<U

W noD ,~ ,"oM Q=2G+ ;

" , ~ .•."1)

,i ;fJ

"

wU

"" ,~Dw Q=25+'M '>

"

(AjO)

MdSS Separator

Tilrget

!101:l(-lltU:n ~;('P,Hatar

(1' 'l,)l

M/M! 450

Horizontal Distance (Arb. units)

115112

Fl(iUI~E 3. i\1;ls" (A/()) .spcclrullI <lLIhe I{MS roca I pi,m\.' fol' evar-oratioll rcsidut.'s trllllllhc ,:;I'0.'"í+ ¡¡Il.\'i rC;K:tioll.

l;lIh:L' \'alul's al the l11a..•..•..•eparator stagl'. 1\ cOmplCIllL'llt 01\.k'tcctors cxists ¡¡mund Ihe I¡¡rgel stalion as well as at the 1"0-\.';t1plane 01' Ihe llIa ..•s scparator: Five clusters (clovers) amI...i, singlL' (jc high rcsolution rhotoll detectors surround IhetargL'1 chamheL Thl' focal planc is cquipped with a thin. t\I,.'O-dllll\.'llsional POSilioll s\.'llsitivc uctcclor ( J()nll x :~(JClII)I';l\.'il.ilaling AJQ idcnlilicalio!l 01' thl' rccoil products rcaching IhehIL';¡1plane. rvtass spectra ohtaincd during a tirst test run wilh210 l\1cV ,'j8i\i heam on ü()Ni target are shoWIl in Fig . .3-thL'I :4)() lllllllher <]uoled in Fig. 2 was dcrivcd from (his spcc-trul1l. The spectrllm showll in Fig . .3 is an inclusive spl'dra

lilE 1/()l.IF[EI.Il IL\I HOACTl\' E [fIN BEA\IS h\C1LITY (IIRIBFI f¡I:TTl\(¡ [{!::\I» TO DO E.\I'EI{I~lENTS 7~

< Daresbúry Recoil SéparatO'F'.., 11111l.Requircd hcalll rl'.icctioll iJl tbcsc Iypical cxpcrimcn!sis hCI\\'l'CII II)jI)-IOI:.! ¡\ L'o1l1hinalion ofposilioll alon~ thcfoc;ll p]¡Ull'. 1'11cr~y. alld l'lll'r~~ lo'S~ IIlcasurClTlcnls can pro-\'ilk addilional bal-h.grollnd I"cjl'L'tiOIl. along wilh lílllc-ol-lli)2hl (111hc ;Idlll'd Lun J.

In (lile III [11L' lir"l cUllllllissioning cxperimenls, aI\llyprllp~ IClll' largl'l \\'as hOlllhardcd with X MeV I:!C ions.The dl'\ic •..' \\a" llllll'd 1m Iranslllissioll of l:t\ recoils that\\L'rl' l"Icanl) "l'p;lr;llcd I'r011l scatlcrL'd hcam parliclcs in lhcionil.:llion dlarnhc[' al Ihc focal planc. Thc levcl of heal1l fC-jeclioll ;Idlil'\'etl hel'l' was approxilllalcly:3 x 10-11, In thcfulUl"e. plans call rol' !lew cOlllmissioning runs witll rcactiolhlhal c\hihil a higl1L'rcollllling ratc Illen thc une rcalizcd illlhistcs!. LJmkr sllch morl' laH)rahlc condiliollS. tinc 11Illing o" IheDRS l'IelllL'llts alld careful pli.lCCIllCnl of slils will rl'sllll inC\'l'll hl'lIn lll';1l1l rcjl'clilln.

FUllIre plan" call rOl" 'Surrollnding thc largcl an~a with anarr;IY ol."ilil"<lll "lrip dl'll'l'lorS. and a high cff1cil'llc)' arra)' ntphotoll dL'lcctors. Tlle ;,ddition 01' a hi!!h dCllsily ditTcrcntiallypllllllK'd gas largel ;[nd ;, gas JCI targcl will rcsult in enhanccdcapahililic" LTucial 1"01'Illcasuring processcs such a~ prolonand Ik caplurl' al lo\\' cllcrgics .

2..'. (){Ill'r l'xlll'rillll'nlal statiolls

V"lo(:llyFdlr-f

tJE\"Ion Opll(:;~

.••••••••• N E W

V' k 1I SIII Uo~~" 1-<11(1

"m

':lOO

.""l.) VU,jd~,

-v.'r.{ /I ..•.......NEW

"\ \ 'l- _'. SIII OO~\ _..- DI¡.)olf'

M;:.~n('fQu;¡rJs

ACCC¡¡I;tncesj 1 ;: ,~I\-,O

1:' 1II1,1d IG '-, n\',1¡. ¿',' ,VeIOO:I:Y

5 o ,,\/,'h)<,I!Y

~lE"',Focal P[aneAssümbly¡Y,¡le)

R3dioaclivcj.Deam

Capture Reactions in in verse Kinematlcs /': .,",,'o.H/gh-Efficiency Recoil Detection ( ~

e.g. 17F+p~ 18Ne+y -.1

2 NEW7Be+p=8S+/' T<lrgel ~

Ch<lmbefS ~J

(UNC) '.......... tJildU •.

/'tt, £ J

HR/8F Nuclear Astrophysics Endstatlon

FI(;('Rf-'¡ L;I~OLJIorIlle DRS ;11f1RIBF.

;llld ,,!lnws very lilllc IHlIl-n:coil (01' hCillll) hackground. Fol-lu" ill~ lhi" lhin delector. OIlCL'<lllpositiun:l gas-lilk'd iOlli/a-lion dl:llllhn for Z idcnlilicatioll. or a douhlc-sidcd Si Stripd•..'lI..'l'¡UrlJ"L'd In c<llch n:coil producls ami si ud)' Iheil" prololl01";tlpha p;lnkk decays [1(J]. FUlUrc plans caH ror lile addi-[ion of BC;O shiL-Ids al"Ound Ihc (ie detcclors sUlToundill~ lhcl¡¡rgct and a cllargcd particle "hall"' surroullding lhe largcl as\\'cH a", "OIllC addilional l.:apahilitics al the rOGII planc,

2.1. Thl' Dan'shury n'(:oil sl'parator (On.S)

rhc A"lrop!Jy"ics end sl:llion is cClllcrcd aroulld lheDRS /(jl~lhL' Ihrcshury I"ccoil scparator [SI which \Va"

"i1ippcd lo ORNL in 149-1-. wllen: il \\'as I"l'inslallcd hy 1lh..'1Il-hn" (lr 11ll' RIBENS [7] (ollahoralion and IIRIBF slalT. Fig-ure"'¡ "hu\\'s Ihe "l'p;lralm which comhilll'S vL'locily and 111(1-IlIOn1l.'IlIUIllsclcclionlo sL'paratc hcam rmm reaclion pr(ldUClSIl' •..'oiling lo IL'm dcgrces. Some rcaclions which Ihc aslro~Ilh~ "il'" ~rollp plan s lo Illcasure Wilh Ihis dc\'icc arc sllowlI inthe IOP kJt (Ol"ller uf Il1al tigurc, Also shown in this ligurl' arelllc addi¡ions lo lhe targel Sl;llion and lhe rOl'al planc regioll.Tllc j"ocal pbllc assclllhly P':j, huilt al Darcshury. UK, Ctlll-"i"h 01' a po"ilioll scnsilih' loil + lllicrodwllllCI dClcclor ;1."-"•..'lllhly and ;1 .~()Clll dcep ~;ls-lilkd ioni/;ltillll charnhl'L TI1l'slwcilicaliolls rOl"Ihi", :-'PCl.trolllclcr are showll UIl lhc ri~hl-111l'spccilicd IO.Ykl rcsolution ill A/Q call he rcali/cd if IheIl(hilion I"c:-.olutioll alon~ lhe dispersivc pl;IIlC is h.l'pl hL'lo\\

TIlL' CllgL' ."plit polc "1ll'l'lrograph (SI'S) is heing rc-litlcd fOl"1l1l"tlsurcllll'nh will1 Itlw prcssurc ga:-. tilling. Tllis approach!1;¡:-.hl'l'll pionú.rL.t1 hy B. Cohen 111) and uscd more rl'-l'L'1l11yhy Rchlll ;lIId L'ollahorators 1121, The prcscllcc 01' di-IlIle ~as ;dlJllg lhl~ parlic!l"s lrajeclOry causes alllhc prodllClsdcl1L'clL'd lhrougll lhc Illagllct lo aggn~galc along Irajcclory 01'tllll~ (HlC cilargc "talc. i\)siliOIl (1IHHllentulll). tilllc-{)j".flighl(wlocil) 1;\nd l'ncr~) "ignal" for IIlL'rcaclioll produclS will hellSl'd túr idcnlitication. Positioll will he Illcasurcd \\'ilh a gas-li!lcd posilioll scnsilivl' avalanche l'ountcr !lb, 121 (PSAC)and cllcr~y wilh a plaslic scinlillalioll cOlll1lcr placcd hchindIhL' PS¡\C. Tillll'-of-flighl through Ihe magnel will hc mea-sllred lhin~ lile allndc :-.ignal uf lllL' PSAC as slan and signalsfrolll Sl'UHldary eiL'(lfOIlS cmillcd fmm ¡j lhin foil hil hy Ihcrl'al'[ioll producls will providc Ihl' slop,

TIll' lINISOI{ i"1l1opC scparator is no\\" dedicalcd lo ionSOllrl'l' lL':-.lingand lhe t1C\'CIOPIlll'llI 01"radioaclivc bealll pro-dUCliull largch. No lllili/;\lioll 01 lhc Spin Spcctromclcr isplanlled al prc'Scnl. TIll' stalionlahelcd gcncral purposc hcalll-lilll' i,,,PI"l'''l'lllly lIsed lor sludics {lf t1iagnostic cqUiplllClll alldlúr dell'l"lpr Icsts. 11has also heen uscd in lhe ti!"sl RIB cxper-iIlll' nI [!JI pL'rlúrnl'_'d al tllc facility-sllldics of coulomh cxci-lalion nI' Ij!J:\ __.

3, Ikam diagnoslks al HIUBF

Sl'\'l'r;d 1001" lor bl';UJ1 di;lgnostil"" alld profilill~ h<l\'C Ix'cnd •..'\<..'lOPL'dal HRIBI' during th\.' P;I"I 1\\'0 ycars. Irnrlclllcnla-lioll lIr IW;Ull diagllo"lil','-; al radioal'livc hl'am LlL'ililil'.s intro-dul'l':-' ""IllC !lCWdillll'llsions. Thc hl';UIl ilsclf is oncn only a",1ll;t11p;UI 01' \\'h;ll gl'IS ;ll'l'clcralcd. Isohars are 11tHeasy lo

N.('\', ,\In, I-'t\ .w S21IlJ()HI 77-x-J.

XII 1) SI{AI'II{A ANI> T.A LE\\'IS

TABLE 1.Lí~(01' lkvicc:; !,(lr Bcam Pronlin¡! .

Devicc Effcct 011 BC<lnl Sensitivity Usagl'

Phosphor + CCD camera S\oPS lt)-1_111'¡ 'l:llldclll. Beamlinl'

2-D PSAC Transrnits 10°_JO'" Bearnlincs

I'lale + Chanllcltron Stops 1O:~-10" Talll.lem. Bcamlinc

Foil + MCP Transmits 10°_101• Beamlincs

R.es. Gas Sampling Transparcllt 101_10") Beamlincs

separate. cxccpt in very few lo\\' mass cases, hencc lhe Ileedto idcntify lhe presencc 01' particular spccics in Ihe hcam. Asccond requirclIlcnt is lhe nccd lo he able lo localil.c (protilc)hl'<Ims over ti largc rangc of intcnsitics (Iow inLcnsitics in par-ticular) ami lO do so wilh rninimull1 contamination illlpancJlO lhe apparatus.

Tu Jctcct lhe prescl1cc of a ccrtain raJioaclivc spccics isonen lhe purvicw of a careful experimenler. lIowever, at lhefacility, a 1Il0ving tape is lIsed (o sillllple Ihe healll at severalcritical stations helwecn Ihe ion sourcc and the tandelll. Thehcam is illlplanled on a Illoving tape \vhich is Iransferred lo anIIll-linc higl1-resolulion galllll1a-ray detector. The gamma-rayl'llergies from the daughter nucleus following Ihe decay (lf thehcam are lIscd lo identify Ihe radioactivc products. One suchdevice is inslalled at lhe exil oí" lhe RIB injector, and anolherolle \vill he inslalled pasl Ihe isohar scparator magnet and amihcfore lhe YO degree hcnd into Ihe tandelll. Such a dcvicc in-lerferes wilh Ihe heam dclivery huI is a nccessary 1001 in sucha facilily. Physical scparalion of isohars is a daunling laskhccause so me are loo c10se in mass lo separale, even \vilh Ihelarge isohar separator magnet.

\Vc are presenlly working on Ihe devclopmenl of a varielynI' devices ror heam diagnostics. SOIllC are dcsigned lo aid lheoperator in steering the heam inside Ihe tanuem accelcralOl".Other deviccs are designcd lo mensure hcam protilc and canhe used hy the operalor or the experimenter for localing andsleering lhe heam. A IiSI summarizing Ihe different dcvicesilnd thcir range of applicahility is shown in Tahle 1.

J.t. Phosphor and scnsitiye CCD camera

The ¡¡rst device hsted is an old standard in heam diagnos-¡ies excepl for Ihe fael Ihal a phosphor (JI' high hrighlncssand good durahility was uscd (a 5% er dopcd AlulIlina-AI;l(h:Cr) in conjunetioll w¡lh a sensitive CCO camcra.t The(omhinalion 01"Ihis CCD camera and lhe Cr doped AlulIIinapbosphor providcs an eXlended sensilivc range as quoledin Tabk I (sce <lIso Re!". 14). The tesIs 01' lhe ahove lIIen-ti(}[lcJ ullllhination wcrc pcrformcd w¡th a 120 tv1cV :~"2S

heam¡ L:>l.

.\.2. ()ual position sensili,'c ayalallclu.' l'fHlI1ter-llSAC

The second device listed in Table I is also a newer ami illl-pmvcd vcrsion of a dcvice used heforc 116]. The PSAC is a

Beam

HV power5UPPIyBer1an 36S

F](;[JI{L 5. [31.';l1llillll'llsity llHlnitOf hased on secundary clectron

L'rnlssion l'rom a solid pi ate.

position sensili\'c avalanchc delcclor in which aplane made01' individual sen s\..'wires hookcd lo a delay line is useu 101lH,.'asure lile posilioll tlf ¡he discllarge in Ihe counler. In [hisversion, 111\.'call1odl' and lhe anodc planes were dl'lineJ byclusely spaced thin win.'s [17]. ThL' deteclor has one calhodeplan\..' and IWO anode planes with Iw() position scnsing \vireplanes placed helweell lhe calhmk: and anode planes. Thescl\Vo posilion sensing planes record posilions in two perpen-dicular directiolls. This arr~lIlgeJllenl resulls in de<.:reased en-ergy loss sulfcred hy Ihe particles passing Ihrough lhe de-leelOr al Ihe eosl of somc translllissioll losses (usually a fewpen.:enl).

3,J, IlCtl'ctioll ('1' sl't:ondary dedrnll Cl11lSSHlI1~eneratedhy thl'lll'al1l hiltin~ a lIll'tal plate

The Ihird devicc on lhc lisl was inlro{\uced lo aid Ihe landem01lL'raIOrSin tunin~ low-inlcnsily heams Ihrou!!h Ihe accelera-hlr [ I.~l. This de"il"l' and schelllalics ()f lhe signal processingfmm il are ShOWll in ¡:ig. ). In Ihis de\'ice. sc(onuary elec-lrons emitled fmm lhe plale. which is placed in Ihe heam'spath. tire counlcd in ;¡ channellmn (:1Il eleclmn lIlultiplier).tvleasurcmcnls wilh 12 MeV :~!"JCI ha\'c showll Ihe oUIPUllOhe proportional lo Ihe hc:un current (sce Fig. 6).

R('I'. ,\,/('\. Fú. -t4 S2 (1 ()9X) 77-X4

TitE IIOLlFIELJ) RAI)I()ACT1VE ION BEAMS FACll.ITY (ltRIBF)-(jETT1NCi REAI>Y TO I>() EXPERIt\lENTS XI

I3cam Monitor Calihralioll

/

Bealll CIllTl'nl (pA)

/

21KI-IlHI U

Emi~,i"l1 I'lale \'"Ila~l'(\'ulh)

-31KI

lU'

-,nn25021111150

/

lOO

•

511

•••I

••H,'+UH

"

;3 f ••,+U:;

2;;

:5

FIl¡URL (l. Calihration curve ror heam inlcnsity haseJ 011 scc-ond;¡ry dCL:lron cmission-fuJJ rangc,

F\(¡UI<E X. :'-.ka.'oured yields fmm the <:tlanncllron as a function 01"voll:lgl' appliL'd lo the l'lTlissioll plate, Thc hcarn in(emily was keptI!lC samc lhroll~holll lhe test.

l3cam i\lonilOr Calihration

FUj1.IRE 7. Calihration curve for heam integrator hased 011 scc-ondary e1Cl'lron cmission-Iow intcnsily rcgion.

/

.\t'+U~r---------------/-=_-::--,.~.------ The device JIlenlioneu in Ihe previous paragraph operates unlhe principie 01"detecting secondary electrons emitled follow-ing illteraclioll of lhe heam wilh a thin foil. The thick plalehas hL'en rcplaceu by a Ihin foil which allows for transmis.sioll 01' Ihe incident beam. TlJe channeltron has oecll replacedhy;¡ Illicrochallncl platc detector. providing Ihe added ahililylo read OUI (he POSilioll nI" the heam"s incidcnce on ¡he foilas \vell as giving a fasl and accurale time rcadout. Thc de.teetor is madI.' 01" individual multipliers each a few tens ofmicrolls in sil.e and is thcrcfore capahle nI' resolving hits Ollils fronl facc with detail nI' that oruer of magnitude_ The ul-limale rcsolulion 01' Ihe wholc ucvicc. however, depends alsoon the Iranspt)rt of Ihe electrons frollllhc collisioll sitc (wherelhe heam hil Ihe foil) lo the de lector. The type of device lhalcOllld provide good lillling ami Iwo-dimensional profiles ofIhe passing hcam is sho\\'1l in Pig,lJ (sec Ref. 19).

The main impedilllcnt to accurale transpon of secondaryelectrolls frolll Ihe eollisioll sitc to the microchannel plate isIhe lnltls\"erSl' velocilY componenl 01"the secondary eleclmnshci ng emiued from Ihe foi 1, Fig. t) shows two schemes of min-imil.ing Ihe slllear in posilion signals, as recorded al the faccof IhL' lIlicrodwllllel platc tille lO the Iransvcrse motion of theeleclrons exiling Ihe foil. Bolh mClhods have sOlTle limita.lions. 111lhe case 01' elcclrostatic acccleralion. we face Iheprohlem 01"spolltaneolls emission of electrons fmm lhe foilin lhe presence of a slrong clretrie ficld gradient perpendicu-lar (o Ihe foil !leal' ils surfacc. The magnetic confinement rc-qLlire~ a strong hOlllogencolls magnelic fleld which is not triv-ial lo supply. Sludies are undcrway now lO determine whichrnclhod \vould serve liS hes!. The micmchanncl plate provides

JA, Beam lu-otile ami liming mcasurcmenl by recordingsl'(ondaQ' dl'clrnn cmissinn from fnils lIsing a mi-lTflchannd plale delt.'('lor .

Jo10 20Ik~lll Current (pA)

•

As shO\vn in Fig. X, Ihe lTleasured rate also dependssll"Ongly Oll lhe din:clioll nI" Ihe voltagc graLlicnl hClwccn thel'lllission plale ami Ihc channeltron cntrancc. Thcrc are Iwo"kvcls'\hown in Fig. X: Thc '"normal" molle in whieh elec-¡mns arc aL'celcraleLl off the plales illto the channcllron <lnLltlll' so-calkd '"ion molle" in which eleclron elllission is hin-dcred hy lile opposing hias. These levels diffcr hy allllosllWoonlers 01"lIlagniluLle gi\'ing lhe tlcvicc an enhanced dYllamicrange. The dcviee is used in "ion l11ode" for more illlenseheilms (lIp lo fe\\! pA) where il can he calihraled amI thenswilched to "normalmodc" for very low intensily heams, Asol id plate ralher 1hcn ¡¡ foil is lIsed here becallse it is ilion;rohllst ami can he repcalcdly insertcu (hy remole rnechanism)inlt) Ihe heam palh,

NI'I'. ,Hex. ¡:/.~.+1 S2 (1~~X) 77-X-t

" ,". 1>.SIIAI'IRA :\:'\1) T.o\ 1.E\\ [S

I'MT •• _

muk

PMT + Scinllliator

l,~'

tolCP,m..

"

PSOT

•Source

MCP delO'Clo,4o:c_.''''ga,id_, -)l)O(l~

'M. "OO. "

-".~ ". ~:~,- "" ~ R_\llon

SlolO.-/Mt¡Jion

~:-':f:~:V ~~,~ > "oo. ".::. ~.

~EA'" -.. "',> :::~n'M'Ace"...•-

1"lliL IH 9. TW(Jsllllllílll1 t'or cO[l(,lining Ihe I,lteral spread illl'lCl'-111111Irajcl"l(lries ;1:-' llw)' ll1(lV(' frol1l ¡he foil lo ¡!ll' micrOl"llalllll'lI'l:ill' (ai I'rolllpl cieclroslalic :ln.'c!crali(lll and (h) COnlllll'1l1CI1\ [o

'1111,tl 11,ljec!(lriL" 111 a Illa~rh:!il' ti\?ld.ToQoe lo QOC lo aoe lo QDC lo QOC

(d)

lb) ~

'I

E

- '" -•. -•••

.1.f'f-(,

"

¡'I

'e'

¡<,

"".. .,

"

Ft(;¡ Id ltl Tl....( ...,'tup tlf a I'SDT h:l"l'd 1II1rWlllpl ,leee!l'ratjoll \1111!l'cil'l'lnlll". :\Ilh' Ihe di'>lOltioll ,,1 lile m:lsk al [11l'!oil :-'llIlacc.

e.\pl'riIllL'IlI. 111Il1i" de\'ice. bl'dlll poSílioll is salllpll.'d hy:tlolllic collisiolls hL'I\VL'I'IIIIlC hL'<lm:t11l11heresidual 10\\/ prcs-

sure gas intllL' dL'IL'CIOr"S\'olullIc. It opcratl's hy n:conling Ihe

pt)"i [illll (11alTival (11'lile rccoil íng i{U1Sfrom Ihis a!<lInic ('olli-..•ion. TIlL' Jlo •..•ilIOIl 01 thc ion lhal drillt.'d Itl\\'anllhl.' L'IL'L'lrodl.'pl'tlvilk ..•inl(lrlll,lIillll (lllly IHl (11lL'dilltL'n"í{)[llranS\'L'rsL' 10 Ihl'

Iw;tm [IAjl'(I(lf~ [:'>l'l' I:! 11 amI Icll'leIKL'''i lhercill j. In ()lit. dc-

ViLT, 11lL'"l'l'Ollll díll1l'lhioll is pfovidcd hy rL'l:oldin,!! <lIso Ihe

l'1L'L'[roll llITi\'allillll'. The ekl'll'tllh drilt inlhc opposill' direc-

[ioll. huI [1lL'YIIlO\l' vL'r~ Id"'- Tl1nl'!(lfL' lhe liml' dillcrL'nl:c

3.5. Rl'sidllal gas Ill'am prnfilt, sampll'r

\l'I~ fa..,1si~llal tlUIPlIl anJ \\'l' han: hL'¡;n ah le ((l t!L'1 .••uh-l1itrltl-Sl'l"Olld lillljll~ lrolll Ihis dL'lL'l"IOr in lwo dilfcrclll L'.\-

pnilllL'n¡..; L'\'l'll 111lhe pn.'sL'llcL' of hi~h r;llc ..••nf incidelll p,II'-

lll'k'.., l in L'\CL'SSnI I{)¡¡p/s). The posilioll rL'adout can be <l bitll10re Cl1Illplic;lICd. ¡\ rl'sisli\'c layer is placcd al Ihe ('xiI or

[Ill' J1licrochalllll'l ami the charge prodlH:ed al Ihe microdl,1I1-

1!l'1pbtL. alludl' i ....1.:o!lL'L'ledon Ihe resislivc layer and read oul

!IIIIll 10m nlfcllll' C{lrnL'r~ (JI' IhL' resislivc la~cr. By cOlllpar-

ill~ lile Charf!L's ;IITi\'ill~ al Ihe four exlreme posilions on lherl'~isl¡Vl' layer. a pnsili(lll signal is derived. Figurc lO shO\vs

(iJe "l'lllP ll"L'd in Illl' jirsl lLsts nI' Ihis (k'viL'c. This ligurL';t1"tl show" tlll' ....i~n;d procC'ssing schL'lIle lllal was li"l'd [o

dc(ode POSílioll in lhe prC'scllce (Ir high ratcs of inci<1cllL'l',

()nl~ lhc ,ignals for whieh :111intcresling cvenl occurrcd are

l011\ l'r!l'd ;111<1....[Ofl.tl. \Ve lISC'chargl' inlegraling ¡-'\(JCs wilh

d )() IlS ",ide gall', supplil'd hy a coineil!L'nec hCI\\'l'CIl lile

llli(l'(lcllanllel ;¡nOdl' signal (delayed) and lhc linal detector

(1.1' Ihc L'X[K'rilllelll). Figurc 11 shows rcsulls 01' Ihe al pila

panick t('''1 with Ihe ....L'IUp showll in Fig. lO, The hOllolll dis-

pl;¡y" are (he I\\'o-dimensional POSilioll SPL'Clf<l\\'ilh seleclcdIl'gil1lh (ngatc,,") dra\\'n in. The Sl'COlld ro\\' sho\\'s po"i,lion

SpL'l"tra projl'L"ll'd wilh II1L'segales (." is Ihe dirC'clioll ;lIong

\\'hídl [hc foillilh.-i.e, [hc !lucc Ill'aks rcpresenl díllerel1l

dl"[;1I1(L'~ IlL'tWl'L'Jl slar[ :Ind Slop deleClor"i). OhvíOll"ily. tlle

pn"ilioll rl'''iolulioll ¡)-(llIllll f'\VflM) i" lllcdiocre hUI tilllingrl...•lllutítln i" "hOlIl n.) Il"i F\VHi\1. NOle that Ihe I\\n spel'lra

111llar! l' C(lITl'''llOllll tn lilllL' rrojl'ctions ror Ihe t\\"o region ...

,:';I[ed in Fig. Ila. Tlw Iwo peaks in Ilw rtl~ilioll SllL'ClrUIll

"hown in Fig. 11h l'orrespond lo lhl' )' positions projl'l'll'd110111(lile orthe ga[L's shO\vn in Fig. Ila.

1'Ih..' Ia"l dniL'c IIIl'llliollCd in Tahle 1 i~ pmhably lllo,,1 ~lIill'dhll' ....ludie" \\ill1 radío;(clin.' hL'<lIII.... 11 i ... a "all1plill~ dL'-

\ I,'l' 1:![JI. ¡,l'. il d{h:'" no[ lü:ord L'\'l'ry hL';Im partiL'k. onlya Idlldtllll s;¡l1Iplíl1~ olllwlIl. II is. IHW...'l~VL'r,non illvasi\'l', ,l1ld

l'ould bl' u"L'd [o 11I0ni[or [he hcalll ]lo"i[ioll during ,1Il elllirL'

I<l'I'. ,\!t'.\. ¡,,'.\ -t-l S.:! Illjl)X¡ 77-X'¡

n lE IHJlJFIELD RAI)IO:\CTI\'E 10:\ HEA~ISFACll.lll" IIIRIBFI-(j¡. rTl:\li REA!))' T() D<)E.\I'EKIMENTS X3('¡Ilihratinll 01'Dril"!Time Spel'lnllll

E

~~~~c:= =_~ +V

/ •• 11 ~------------------,

•~.I1

•.!,U

•-- J.IIo •

~.II

• .SSd •.I'.!,"'l"1.11 • ss d•.I'J d"l:I

u.uU.U IIHI.U ~(HUI JUU.O .!UU.U 5H1l.U

llrift Tilll.,(l<daliH'1

1:11;1'RF 12. Principies 111'Detector. Residual gas ion ;lmll'lcctronpairs fornlt'd in coJ1isiol1s \Virh heam partícles are ,,\Vcr! vcrli<:allyrn lhe dircclion ol;ln ;lpplil'o decirle lil'ld. \1inochanne] dCl.:lrOll

tlllJltipJiers alllplify lile signals amI provioc !illling ano PO\itiOll sig-1\a"- rOl' Ihe posilive i01l hits tlmilirning only rOl" clectron hih.

r-[(jLJf{t~14. i\ caJibr;ltion Cllrw showing drin lime ".\'. Ihe squarcroOl of tl1l' lIlass (It" Ihe accekraled iOIl.The ions idelllilicd wcrc 11.;\i(douhly l:har~cdl. N(singly l:harged), IhO and ~:!

I~'"'~----------- .,

1011 Drift T¡tIIlo Sl'l'l'lra IOlllm

11""'

'"

",\tI

HM' !UU .JIMI

"L ~..LIL --lH ~I'J .1"1 •• KI 1"01 11!Kl 14<11

I',,,(i,,,, 'l~n,,1

111 ,"un (,!U ;\ill"lll.:l'lI Ll'a"

I;I(¡¡I]<E 13. SPCCll'<1 shmo,'ing ion drifllilllL'S rOl' two cases: in '1);1

Il:;() k¡ll.; ami in 11)a N~ leak \Vere introduccd.

helw(,Cll lhe ch,'ctron anJ ion arrival tilllcs is prop0rlionalltl

llit' i(lns" drift lime ami therefore to ils l11ass lo charge ratio;1" \Vell as lo IllL' distancc which il had to drino Thc devicei" "I1O\V11i11Fig, 12. In it Ihe elel'trons antl Ihe posilive ion"pnll.luL'cd in iOlli/.ing L'ollisions hetwccll Ihc heam particles<llld Ihe residual gas ll10leculcs in Ihc e\'acuatctl heam pipeare s\\'epl lO\Vanl Ihe orrositc clcctrodcs. The ion drift tilllet1epends 011 ils pnsilion 01" formal ion and ils mass lo charger;llio. To rclain Illaximum scnsi!ivily lo posilioll. il is impor-tanl lo know ¡¡nd L'\"L'1lregulale the residual gas conlenls. Thiscan he accolllplished with a comhinalion 01"gOOlI jllllllping;lI1d cOlllrolled injeclioll nI" knowll gas. if I1cetlctl. Figure l.'

'",

IIMI 2UU .'IMI

(-Imlllld Ji ¡!)rin Ti"It'1

41HI

FI(j[IRI: 1:) ll(ll"ilolllal projl'clioll nI' hC:lm SPO!tlhlailK'd \'o'itll4partick Pt\ oll(¡(l :\1eV II'Ti twalll.

~ho\\'s drill tillles l11easuretl after pumping dowl1 the sys-lem and inlrodllcillg two dilTcrell1 componcnts tOlhe residualgas mixturc. \Vater vapor (whieh would reslllt in ionil.ationintn 11+ ¡¡nd 11011+) and nilrogen gas (resulting in ions of)Jj, .\'-1 , alld:'-J-I-+) \Vcre injccletl in Ihese tdals. Figure 1...J.~IH)\\.'SlIle depclldellce of Ihe J"ccort!cd drirt times on mass lOd1argL' ralio (JI' Ihe ions. Thcsc data also serve as gond c,lIi.nralion hClldllllarks. It is (kal" that ir we maintain a nearlypure .\" "atJllosJlhen.~" \Ve could salllple pusilions over a rangce\cecding [\V¡) illL'hcs-m{)rL' than cllough for ¡HII'purposes,

This hL';UIl profile sampler has heen (csted wilh slahleheams and lIsed in conjullclion wilh a Coulomb excitalion cx-pcrilllcllI donc ",ilh (;!J A."i heams al lile HRIBr- facilil)' [D, 221,

Figure 15 shO\'is Ihe hori/onlal position signal obtaincdwith...J. pA (ahollt 107p/s) Il"Ti he:ull. Thc slructurc sccn intl1L' ]ll,.'ak Shd]lC rL'lkcls granularily associalcd wilh Ihe dis-crcle c1l'JIIL'IlISllscd rOl' positioll del'oding in this case (chargcpiCKUP "ilrips-I I11Illpitch). Note the pallcity ofhackgroundin lhi" SIWClrtlJlI.

() SIlr\I'IKA ANIJ T.A LEWJS

.\ mm

"

'".IU

4111111

Al'kIHlwled~l11ents

FI(ilIRI: 17. Ilmi/onul ;Illd \'cniral pnl.irclion nf hcalll spOI oh-lained wilh a heam (Ir lO" ¡¡'I:\s iml" per Sl'(Il[Ki

111MI

y -Il,•.•ili""

I.\IIU 51MIU

71MI

,u

1U

Thl' ;lulhors lhank (,..1, (,I"OSS ami ~1.S, Smirh for provid-ing Ihl' infmmalioll prescllll'd hcrein on [he RMS and lhef)RS l.kvices. Oak Ridgc Nalional Lanoralory is Illanagedhy Lockhced tvlarlin Encrgy Resl'arch Corro for Ihe U,S.Dep;lrlllll'lll (}f Elll'rgy lInder C(lnlracl llllllloer DE-AC05-%OR22~(1~.

1;J[jlIRE 1(, T\\I,-dimensional hcam prohlc nhtaincd w¡lh a heam(111{)~' w :\~ iOI!"Jlcr secolld.

x - position

Figure lh shu\\: a lwo-dimensional plOI of the oealll pm-lile nOlainL'l1 'vilh (¡HAs neam al irHensilies Ilcar 10::' particlespl'I sClond. \\'e uscd a nilrogcll leJk ami ran with amoiCll1prL'SSlIre IlL':tr I x 10-;' Tmr lllainlained throughout lhe ex.[ll'liIllCIlt. The data showll were ¡¡ccumul¡¡led in Icss then ulleminute. TIlL' Y POSiliol1 \\las dcrived from lhe N1 drift linlL'.;llld a hiascd TAe was uscd In amplify lhe fegion afOlInd thatPl';¡~, A ..•can Ol' seen fmm lhe 1\".0 orthogona! projecliolls of111l'hL',ltll proli1L' in Fig, 17, lhe rcsolulions in X ami ). arel'n:nparahk :tnd lhe hcalll spol in Ihis experilllenl was aooul2 3 lllm in diall'('ter,

1:!. K.E. Rchllll'l (J/., NI/d. 111.1(1"11I11 (~, ¡\/l'Iluuis A J-U (\lJlJ4) 614.

11. HI.. ('ohen ami eH Fulmcr. Nl/d. PII\'l. (, (\lJ5X) 547 .

n. H II{ldladcl el ell., ,V/td }I/.\/I"IIIII. l~ Akrlwd\ A J.B ( I()l)4) 401

R. (';lSIl'Il. "( )ppol'1l111ieswilh Radio,ll.live Nudcdl' Bcams"1'lIl("("nlmgs (Ir /lIi.\ nmll'I"I'IIU'

10 J Ibll"hddcr ('II/f, lo ;'ppcar in }'II\',I NI'l'. e NI/II/e! Comlll ..

I {)I);';

l.!. R.e. Rugcrs e/ 01., Texas A&~l Univcrsily Cyc!olroll InslilulCSingle Evcnt Ellcd FaeililY.

};j. ;-.:.(;:111 and D. Shapira, ORNL.()C)j(,j'h\'lin /)il'. I'm~rl's,\'Rt'-11(11"{ l. I()

lG D Shapira ('/1/1., ,Vlle!. jl/\'fI"IIIlI. ,\jf'fl/lldl' 111 1'111"\. NI',I. ,\ -,ni(I{NI) 7h

17. T.A. Ll'\\i~ ;ll1dD Shapir;l. ()NN'--(,()}(J I'hysin /Jil'. Pmgl"l'j"J

Ul'flor! 1, I ~

18. 1\1.,\tei~s. D. Ilayncs. C. JOllCSami C. Lceroy, ,,¡\ Ncw Bcam('lllTl'll1 ivfoniloring Sy,slClllwilh \V:'Jc Dynamil..' Rangc for lhcIlolilicld Radio;lclive Ion l1eam FacililY". Poste!" prcscnted allhe }'arl. Aeed ,\lITlmg in /)(/lIw. T.\:, .\lay 1-5. 1995.

19. O.JI. Odland 1'/ (/1.. NI/tI ItH/rtllII. ¡~ Melh(}d.~ A .\7X (1996)I..j.t),

'J')

:!o. D Sh;lpira, T.A. Lcwis, ;LndJ. \111shef. Sud. Itn/mm ~( A1('lh-od, A -HlIl (It)l)X) IX).

The ClIllCI;11:-':1CCI) B/W cunera Modcl SE~(J()S fmm ELr-.l0.\lr~.COlP, I!JIkwIiOl/C/ll'¡' ,Vuclt'lll"lkl/f1l.\-} s( bll. cOfljén'fI(,{'. cdiled hy \V ().\I~e~r. .1.~1. i\il~('hkc, amI E.B. A'onnan. (World ~ci('ntilic19lJ() )

.¡ .l.D. (jarrell, 'Tlle Holilicld KadioaClivc 1011Beam Facilily ¡tIOak Rid~c N;llional Lahoralory". Proc. (!l (j/(' CO/!/á1:f1Cl' 0/1

,\'"di'ar :'úmi'tl/n' al lllt' ¡,i",i(.\", Argnnnc Nalional Lahoralory.July ::!::!~::!(¡. 19lJ6.

., R. Ca"lL'n ¡'l al., Scif'l/(i/ic O¡¡¡'Orlltllitit's lI'i/h mI Adl'/ll/{'l'(j

I,\'()L Fal'Ífilr. Nov. 1()97.

e Grms 1'1 l// .• "[nilial Rcsults of lhe Cotllmissionin~ 01 lheHRIBF I~l'l.(\il ~1:lss Spl'l.:lrollleler".l'ro('. O/COII{. 011AI'I,lim.ri(l/l,1 /Jj •.\("¡"¡'II'J"Il!Ol".\ /" !\l'.\'I'arch (l//(f b/(1I1.\"In., cditcd hy J.1..nll~aJl ;¡nd 11.. r-.torgall, (AIP Prcss. Ncw York. 1(97),

., .\1.S, SlllillJ. NI/d 1".I"trlllll. & M{'lIlOds U l)t) (1995) ~49.jo .\ 1.S Slllill1, j'm,'. l?!"COIlt: I!!"O,.i~itIS l~!"M(/I/l'r llIul E('o/lItio/l

0/(;1//11.1/1',1 '(JI, ¡"';O\'.5-7. 11)97,Tokyo (\Vorld Scienlilic II)()X)111prcs:-.The RIBENS (Radioaelivc ion hcams for cxplosivc llllclcosyn-l!lcsi" \Il1die,,) coll,lhoralioll includcs scicnlisls fmm: ORNI ..)'a!L-. 1111ivl'rsity 01' North Carolina Chapel ¡Iill, Tennessl'l'Tecl1nologlcal Univ., Ruhr.Univ. Bochum, Ulli\'crsily 01"Liv.Crl'llOI. ('ni\". pf Edinhurgh, Colorado School of \fines, Uni\'.pf B\1mh;I~',ami Louisiana Slalc Univ,

~ A.:\. bllIC" ('1 (JI., NI/el. !II.Hmlll. & /\41'(11011.\' A 2<.7 (\()H5) 144.

~)c. Bartoll ('1 111 .• eOlllribulcd ahslrae! lo AI'S/AAPT Illl.'L'¡ing..\¡xil 1(1);';

Rt'I'. Me.\'. j'/I, -U S2 (1l)()X) 77-X4