REVISTA f\lEXICANA DE FíSICA 045 SUPLEMENTO 2, 4()-.49

Nuclear structure physics at Yale amI Beyoud

C. \\l. lkausangWriRht Nuclear Struct/tre ["aboratO/)'. rale Unirersity, NeU' IIm'en. cr06520, USA

Recibido el 6 de enero de 19(N; :ll'eptado el 5 de mayo de 1999

OCTUBRE 1999

Sume 01'Ihe IK'W experimental equipmenr. availahle al lhe Wrighl NlKlear Slructure Lahoratory incluJing the YRAST BaH array and sornenI"ib auxiliary dClcctors are descrihcJ. Aspecls of Ihe nuclear structure physics program at Ihe WNSL are reviewed. Several new results:uc pn:~enled indwJing: the invesli!!ation of low Iying 0+ states in I.HSm and Ihe ohservalioll of:l po~sihk ncw magnetic rotational bandin ~u'jRn.

K/'l'll'Ords: Nuckar (,Ilergy levL'J.;;r ray ~peclroscopy

Se tk'~('fihl' el equipo experimental del Wright Nudcar Struclllrc L¡¡horatory: el YRAST Aall y algunos de sus detectores auxiliares. Sepresenta ulla revisiún del programa de investigaciones en la estructura Iluclear en el WNSL. Se discuten varios resultaJos nuevos. tales comola iJl\'cstigaciÍlll de los estados 0+ en 15~Sm a cnergías bajas, y la evidencia de la existenl'ia de Ulla hanJa rolacional magnética en 2osRn.

/),',lCri¡JI0l"(,S: Niveles de encrgía Iludear; especlroscopía de rayos")

/'ACS: 21.11J-k: n.71J; n.RIJ; 2~.31J.Kv

1. YRAST Ball amI ils auxiliary detcclors

lile Nuclear Slructurc program al Ihe Wrigh( Nuclear Slruc-(orc Lahoralory has recenlly heen revitalil.eo hy Ihe additionnf sC'\'C'ral llelA' researchers ami hy Ihe conslructioll and im.plemelll¡lIion 01' several ncw major experimenlal tools. TheIlCWcquiplllenl includcs Ihe YRAST Ball array amI ils suileof auxiliary dcteclors.

Th" YRi\ST Ball (Yalc Ro"hesler i\rray ror Spec-TrosL.opy) ¡II is a pO\\'erful new ,-ray spectrometcr. lhcIlh.'chanical slruclllrc supports up 10 28 COlllplOIl supprcssed(ic detccltu's. including up tol) Clover Ge detectors, around(ile tar);!ct poSilioll. Currently, thc array cOllsisls 01' four seg-11l1'1llcdChlver deteclors, cach witll approximalely 150% rel-alive cffkicm:y. one 70% coaxial Gc ami Ilinelcen 20-25(ltcoaxial Ge detectors. Thesc dcleclors givc lhe arra)' a lolalpllolopeak eniciency 01' .....,2%. making the YRAST Ball thelar);!cst university ha sed speelromeler in lhe world.

A "ariely 01' auxiliary delectors are availahlc 1'01'use wilhIhe 'YRAST Hall. Thesc include four LEJlS dctectors. a thirlytwo elemenl BCiO sum-energy Inulliplicity tiller ano an array01' 111lc.:1I1rllndctC'clors. In addilion, an array of solar ceHsror hC:l\.:'-ioll dctecLioll has becll dcvclopcd amI a slaLc 01"Iheilrt 1"C'l'llildistilllCl: plllllger devicc rOl"IireLime lllcasurcmcnlshas hecn CtlllstrtlCled ..

Solar-Cl:l1s. which opcratc \••..ithoul hias, can providc.: a~'(l'.;tdfcCli\'l' snlution rOl"the dC'tcction 01"cnergelic charged['anicles. I:(u" exalllplc. hcavy.ions following lissioll. scal-lelwl hetlm, ll-particles, amI perhaps ti-rays ll1ay he dctcctedLlsing such dcvices. ReL'cntly, \Ve have exploiled Ihis raet at'{alc hy l'Ol1strucling a protolype array consisting 01' ei);!htI cm y 1 cm solar cells [:n lile ceHs are arrangcd as clc-11l~'llts(JI a :~ x 3 malrix amI placcd al backward angles at a

Fl(jURE l. The larl!c background in Ihe top spectrum. due 10 IIS-

sion c\'ellls. has oeell removed in lhe lower panel by suhlractionnI"lhe -,-ray spcclrulll 1llcasurcJ in COillcidcllce wilh lhe prololypestll,lr-cell array.

a dislancc nI' ahout .3 cm I'rolll lhe targel, lhe heam passingIhrough lhc ('mpt)' ccnter clcl11cnl or lhe malrix, This arrayhas heen slIccesslully couplcd wilh Ihe YRAST Ball, to de-lect /lssioll fragmcnts fmm hOlh souree (lS2Cf) ami heam in-duccd ¡issioll and also lo dctccl hackscallercd hcam follow-ing Coulomb excitalion. For cxamplc, Fig. I shows the 10-tal )- ray spcclrulll rccoroctJ in YRAST Ball fo\lowing theI-IN + I!li Al! rcaclion. Tile largc.: background fmm Hssioninduccd ,-rays has hecn rcmoved in lhe bottolll spectrumhy suhtractioll (Jf Ihe ....¡-ray spcclrulll mc.:aslln:d in coinci-dencc \vilh Iission c.:vcnls rccorded in the solar-cell array. Thcgcoll1clric crticicncy of this prololype array is on Ihe oroernI" lOS}.

Encouraged by these rcsults, wc are construcling a larger;lITa)' 01"solar cel! dctectors [:n The l1ew array will consist of56 I cm x I cm solar cells arr¡¡nged in lwo hall" hoxcs (plussumc addilionalc.:nd-picccs), Thc hoxes close over Ihc largctposilion giving a lotal gcolllclric co\'crage 01"almost 1)5% oí"4i'i. Each hall" box cOllsists 01' 2X cells which will he clectri-

NUCLEAR STRUCTURE PIIYSICS AT YALE AND BEYOND 47cally COlll1ecledto produce 21 signals. Clearly, when used asa llssion veto or selector or.ly olle hJlf hox is required he-cause 01' (he kinemalics nI' lhe reaclion Illechanislll. Thc newSolar Cell ¡\Rray al Yak (SC¡\RY) will he operalional hycar!y 19tJY.

Conslnu.:tion of a new, state 01' the art recoil distanceplungcr devicc has just heen cOlllpleted. Thc New YalePlunger Device (NYPD) is now availahle rOl'use in I¡relimellICasurelllents 131. The lirst experiments are scheduled rorFehruarv 1()99.

The -design of the NYPD is bJsed on the .....ery suceessfulKii1n plunger designed by A. Dewalo. The devicc. oesignedrOl" use with large Ge deteclor arrays such as Gammasphen.~and YRAST Ball, has a minimurn 01' material ncar lhe Wr-"d chamher. A swhle mechanical guidance system moves~le tmget ami stopper foils anu ensures thal (he foils remainparallcl al all limes. In addition, a capacilallce lIleasurelllenl¡¡ud feedback Illcchanislll keeps Ihe distance helwcen Ihe foilsconslanl and compensales for lhermal expansinn caused hybe;¡m healing elTccls. The feedback Illechanislll slabilizes thediqances to helter lhan 0.1 11111. To open up Ilew frontiersin lirelime I11casurements (e.g. lo stuuy nuclei populaled hydeep-inclastic, COlllex or nssion reaclions), il is possihle tol.:ouple lhe NYPD to an array of chargeu particle deleclors,ror cxalllple lhe Rochesler Universily CHICO array 01' oursolar-l.:cll <.h:lectors.

In additioll lO YRAST Ball, scvcral other programs have!leen developed at \VNSL or are under aclive consideralioll.1\ 1Il0ving I<IpCcollector has heen implcmclllcd ror hela.deca)' sludies of shorllivcd isolopes. IIcre, radioactive nucleiprodllced via hcavy-ion fusion evaporalion reacliolls are illl-planleu 011 a mylar lape. Direet healll irradialion of the tapeis prevcn(ed hy a small plug pIaced directly hehind lhe targel.Advantagc is laken 01'slllall angle straggling in the targel Inexlract IllOSt(around 70%) of the rccoils around Ihe plug. Thetape periodically Iransporls Ihe isotopcs lo a l.:Olllltingstation\\'here dee,ay ¡-rays are uClectcd llsing four Clover oelcclorsfrom YRAST Ball arranged in a close packeo gcolllelry. The10lal pholopeak eflkiency ror ,-ray detectinn in this sctup is(11\ lhe ordcr of 10%, rivaling lhe erticiency nI'Gallllllasphen:.

A progr:lIl1 lo utilizc lhe WNSL Enge Splil Pole Mag.Ilelic Spcclromcter as ti gas fillctl scparator is unoer activedevclopmcnl. The splil-polc, placel.! al zero degrees is lIsedto 1"ol.:usrccoils of inlerest onto hcavy.ion delel.:lors, ('.g. so-lar cells, while rejecling hcam and lission I"ragments. Earlylests 01"the syslcm llave heen successful and luve providcdproof nf prindplc. Translllission t:fticit:ncics for fusion evap-malinn residues 01"'""-'30c':f, have bt:en al:hievt:d. A lIew largelchamher amllllechanical supporl slruclure for st:veral Clover(ie delc<.:lorsare bcing considered.

In the ahove, I !lave described sOllle 01"lhe ncw experi-J1Iental apparallls availahle al the Wrighl Nuclear SlruclUreI .aooratory. Tn uate wc llave ulilized this appamtlls 10pursuL'él varied physics progr.llll in ooth high- amllow-spin nw,:lcarstructure physil.:s. Physics lopics whieh we have cOlKentraledon indude the invesligalioll 01'low.spilll.:ollcClive 1lI0des. lhe

sludy 01"phase lransitions or phase coexistence in nuclei, lheevnlulion of slnll.:lure in neulron rieh nuclci ano the invcsti-galion of high-spin properlies of Iight aClinide nuclei. In theremainder 01' lhis part:r I will describe sotlle of our emly re-sults fmm Yale ¡¡nd Bcyond.

2. The nature nI' excited 0+ sta tes in 154Sm

Despite years of investigation, lhe nalure 01' low Iying 0+statcs in dcformed evcn-even Iluclei remains poorly under-slood. The lradilional inlerprt:lalion of lhe firsl t:xdtcJ 0+sIates as a ¡1-vihralion ¡4J has rt:cently been the sllbjecl ofin-lense dis<':lIssiOllS[51. Indccd. rt:ccnl experimental evidenccami lheorcli<.:alslUdies are consistent wilh this stale heing aIllemher (Jf an anharmonic uouhle-1 vibralional multiplct.

Recently, lhe nature ofthc lIrsl cxciled 0+ stales in 1:i2SmIS'lS 'dhas bcen invcsligaled. lt has been shown thal - m proVI cs

a very special C:lse, since il happens lo lie in the Illiddle of avery sharp shapt: Ir:lI1sition bClwcen lhe sphcrical 150SI11andthe dcformed [!íISm [GI. Thc strong reduccd lransilion prob-ahility, LJ(E2), bclw('cn lht: (Ji and the 2t in 152Sm can hecxplained by a shape mi.xing belween deforrncd and spher-ical 0+ slates, the dcfonned slalc fonning the ground slalein 1;,.ISm. ami a sphcrical slale similar lo the grollnd slatein 1."",OSm.

To better ullderstanu Ihis shape lransition antl (o <.:heckthe consistcncy 01"Ihe interpretalion the nalure of low Iying0+ stales in 1;"'Sm was rt:cclllly invt:sligalcu at Yalt: 171 viaCoulomb excitation lllilil.ing an 1(;0 oeam at 65 MeV. Thebeam w;.¡s incidenl on a 3 mg!cm2 15.1Sm foil backed by a15 I1lg/cm:! Aulayer (o SIOPIhe rccoils.

The emiued ¡-rays wcre detected using YRAST BaHwhile back scatlcred bt:am parlicles wcre detecled usinglhe solar-ccl! array. By selccling 1'-rays in coincidence \vithhackse¡¡ttcred ht:alll particles. forward gning IS.1Sm Ilucleiwcrc identified, allowing ¡¡D()ppler Shift Allenualioll l\klhoulirelime analysis lo be performed. Lifelimes 01" 1.3 (3) psanl.! 0.61 (-4) ps were dClcrmincd ror Ihe ni and 2~ levelsin l;dSIlI. respeclively. The IHE2: oi -+ 2t) = 12 (2) \Vu,exlractcd from lhese dala. is consistenl wilh expecl:lIiolls fora ¡j-vihralioll IGJ,

3. I1i~h-spin sta tes nf nnclei in the li~ht actinidercgion

The light actinidc region, Iying lo lhe Ilorthwesl of Ihe doublyIllagic :!O.'l Pb l1udt:lJS has long been a fcrtile ground rOl"thesludy of shell model stales. As c.\pcclcd ror nuclei close lOIht: douhly magic shcll closure:tl Z = 82 anu N = 12G theirnear grounu sl:lIe exeitatinn spe<.:lraare madc IIp01'si nglc par-tiele excilalions. lIowever, al highcr cxcitalion energies :lIldspins a variety 01"colleClivc rolational hchaviors are manifesl.For example. supenlerormcd statcs (/3 '""-'0.5) are \vell estah-lislll'd in Hg, TI. Ph and Bi 18,91 nuclci :II1U an cxample hasrecelltly hecll ohservcd in 1'0 110].

N('l'. Me.\". ¡:,,,, -15S2 (199t» ..J6--49

c.w. IIEAUSA\'(j

FllilH~1. J. Spcrtra ~alcLl tlll Ihe flX9 ano 2XX kcV lrans.iliollS in2w'RI1.

FI(;UIU'.~." p;llti;J1 kvcl :-.d1L'll1C of ~O-'Rnshowing the :-.tr(ln~c.~t

di,'C1Y p;llhs

liguro;: .1

1

I "----

-t_o-,~"

~IH (~WI

2-¡-

-1-_0 _1_

-1-_0 1_-1-

_.o __ y__._¡_oo,

:-:-~~t, \\

II~I

'"

IL'Jllalive and are hasL'd 011lHlr assignmcnl 01' 1.",12+ for IhebandhL'ad 01 band 1, which is assigned lhe 1/; 1:~/2 cnnligura-lion IIG].

Band 2l'llllsisling 01" lO sln:lchcd magnetic dipo!c transi.lions wilh weak, llllobser\'ed crosso\'er Iransitions is 01' par-linllar inlLTCsl. SlIch a band appears similar In Ihe magnelicrolalional bands in Ph ;¡nd in Bi nllclci [1:2-1.t]. Band 2 isproposn\ as anolher l'xalllple 01' a magnclic rolalional hand,lhe ¡irsl in ;¡ 7. = 0(j lI11ckus.

11~1

~m"G ,',""

I!Wl

" ~1l1

AIHHh~r ~\t ltic ph~nOIIlCIHHl,she-ars 01' Illagnclk I'Ola(ioll,i,,, al"o 11l<ll1irc~1in th~ mass It)O-2(){) rcgion r 11-1-1]. In Ihismodcl. in a lle<lrJy'~pheril'al llucJells, Ihe si ngle--parliclc (holc),1IIgul¡¡r 1l1OlllL'IHutll\'l'(.'lors 01' high-j prolons alld ncutroll~arl' inilj;¡lI: Oril"nlcd "Itllos! pl"rpendkular lo c¿ll'h olher sollul IIlL'IOl¿lIangular lllollle-nlulll \'celor is nol aligncd alonga 11rillL'ipal ;t'\i ..•01' lhe nllcleus, OUI inslead is tihed. Higha,lnglll;¡r lllotllcnlUm sIates an: gellcraleLl hy lhe slo\\' c10sing01' 111L"Se;¡ngular 1Il01l11'1I11l11lvcelors 01' shears. 5uch a me-ch-<lni"lll gin.'s risc lo ¡,:haraclerislic h:alUrcs oflhe resulting. 'ro-lali(lllat' hands, Ilalllcly enhanced magnclic dipole lransiliollSíllld larg~ If( J/I) / /J( E'2) ralios whkh dccrcase \vilh rot¡¡~l¡(ln,ll frcqllL'IlCY.

Sllch (',\{llie sllape eoexislenc~ phCllolllella are- prct!iClcdIn pnsisl a ..•tllle IIJ0ves lo lluclei furthcr a\Vay fmm '.!Ol'lPh.HowenT, surprisingly /illle inrormalion is avai/ahle 011highspill proJl~rtics 01' Al, Rn, Fr and Ra nuclci, particular/y odd01'd~lllhIY-ildd lIul'!ei, \\'ilh Z > 8,1 ami J.Y< I'2G. Wilh lhisal Illind we han: (!L'cided lo pursllC a program al Yale (andHeyond) lo illvcs(igalc Ihis difllcult hUI sOlllelimes fasl'in~ll.in); regioll. Early expcrimellls, carrieo out al Yale and al IheUnin"rsily 01' Jy\'üskyl;i, have COIlL'eJ1lralcdon the high spinslnlclllr~ ollluc!ei inlhe vicinily or:.!o3RIl.

T\\'o L'\J1L'rilllL'lll"Wl're perforrncd 10 populate high~spin"lah:s in :.!w'Rn I llil. Thc tirsl, carded oul al lhe Uni\'l..'rsity 01'.Iyv;i"kyLí I\CL'I.~kralor Lahoralory, 1I1ilil.cd lhe .IOAr +1,111:1'reaclion al a hcalll clI~rgy of IX3 McV. The gallllll~H'ays \"-'eredClCClcd lISillg (he .Iurospherc array which consisted nf 15Llrgc Eurogalll !'hase 111'-'1 ( 'jO% relalive effkiencyl ;¡nd10 TI:SSA-lypc 11'ji ( 2;)% rl'lalivc efllciellcy) C(llllpIOll-sllllprL's"l'd (IL' dcleL'lms, lowl pholopeak eftkiency "" 1.:)\K,al 1.3 i\1cV. '1'0 discriminale againsl Ihe \'cry large lissionh;ICkgroulld CIlL'l.HIlllercd in Ihis reaclion (afllSilJll '" ,j I1lh,(J1i~si"ll "" :\()() mh) tusiOll cvaporalion residues \\'ere de-lL'cled. in COillL.idellcc willl prolllpl ')'-rays dcleeled al lhe lar-gel. U"iillg lhe RITU gas fillel! separator 118] (lransmissiollL'fliciellcy "" :UJ'X, for lhis reaelion).

¡\ "¡,:L'ond c.\pL'rimclll. carricd oul al Yale ulilil.cd lll~1,1N + 1'1,Au l'¡,"aclillll al hCilm energies ranging fmm t)() lo110 i\kV For lhis l'\perilllenllhe rceoils were slopped in Ihelhiek ( 2(1 lllg/clll:.!) Au largel. Thc galTlllla-rays were dc-[L'l.IL'dllsing \'I<AST Hall. Tu generalc elcaner gill11l1la-ray"¡Welra. ti ..•..•ion producl.s \vere detecled using our prolOt)'pe"01<11'cdl alTay, "ice Fig. l.

Plipr 10 IhL"SL"C\pcrilllcnls no galllllla-ray lransilions \\'L'rekllO\\'1l in .w"'l<n. ,\ pania[ Ien.'l s<.:hellle showing lhe mainL1ecay palhways is prescnled in Fig. 2. The transilions \\'erea ..•..•igllL.d lo 1<11ha sed (lJl X-ray coincid~nces anJ lo 2o:JRnha"ed 011thL' 1'l""UItS01' om e.\eilation funclion IllCaSUrelllentsll"lll~ YRAST Hall \.•'hik lb!.: lc:vcl scheme has heen deducedII1OSII)'lIsing IhL' Jurosphere dala,

Two c;lscades, lahell'd bands I and 2 in Fig. 2, dOlllinalcIhe high-spin portioll (Jf lile d~cay. To illuslrale lhe qualily nI'Ihe dala, SpL:L'tragaled hy lile úXI) keV ami 288 keV lrallsi-lioll\ are prcsL'1I1ed in Fig, 3. Spin amI parily assignmcnls an:

NUCLEAR STRUCTURE I'HYSICS AT YALE AND HEYOND

Tl1I:rc are (wo Iikcly candiJatcs ror the conliguration ufhand 2.lhc Ilcgativc parity lIi¡:il'l 0 ¡r(lI!J/'lil:~/'l) or lhe pos-¡t¡ve parity /Ji 1:1/2 v) rr(i13j'lf.! contiguration. Bolh are caku-lalcd lo !lave a small obl¡ltc dcformation 01' (2 < 0.1. UsingIhis dcform<llion ami lhe proton anu neutron pairing cncrgics.~1' aud ~II obtaincd from lhe TRS calculations. TAe calcu-iatiolls \\'crc pcrformcd. Tile rcsults indicare lhal hoth ofthcscconligurations indccd corrcspolld lo tillcu nI' shcars hands\\ ilh large lJ(.\/1 JI D(E2) ral;os. Furthcr. Ihe calculationsindicalc tha! hoth positivc alH.lncgativc paríl)' configuralionsJic al a comparahlt: c.xdtatioll cllcrgy al ahout I.S ~lcV rcla.tive 10 (he yrast ui l:l/:!' in cXt.:CIlClll agrccl11cnl ''''¡Ih Ihe cxpcr-im~n1al data. Sillcc Ihe angular dislrioution ami correlationdata favor a qlladrllpole eharacter, Jllost likcly E'2. ror lhe 977ami 11RO keV transitions linking oands I :lIld 2. Ihe positivcparit)' /11 ni:.! ) rrif;i/:.! conllguratioll is lentativcly assigncd.I.ifclimc Illcasun.'lllenls. lo cxlraet the ahsolutc 1J(J/I) val-ues rol' Ihe transiliolls in hand 2 arc neecssary lo conl1nn Ihesh~ars char:lcter 01' this hand. In addilion cOl1version clec-(ron ami gaJllllla-ray poli.lri/,alioll llleaSUrClllents are plannedto conlirlll ()llf cOllliguration assignlllenl ror hand 2.

EllC()l1faged hy our results for :.!o"RIl. several otherA....., 2(J{) aClinide lluclei have reccntly oeclI sludied al Yaleand Beyond, \Vc have extended our sean.:h for lIIagnelic ro-tation to the .v = 1HI isoloncs. :'W:lpO and 2041\) using IheGarel array at lhe ¡ReS Slrashourg anu the YRAST Ball ar-ray al Yak. respectively. Prior 10 these expl~rilllenls no infor.mation was avai1ahlc on excited slales in :.lO.1Al. These dalaare currenlly lInder analysis. A heginning has ocen made loeXI~lld our illvcsligations lo hcavicr Z Iluclei. The rcactioll1(¡()+1~17Al! at heam energics nI' 90-100 t\1eV was uscd lopopulalc high-spin states in :.lo•. :w .••..:.1O!IFrfor Ihe !irst timc.The gamma.rays \••:crc detcctcd using YRAST Ball while thesolar cells \\'cre used lo discrilllinale againsl f1ssion evenls. ¡\

1. CW. Reatl~al1~('1al.. (lo he puhlishcJl.

'2 R Krücken ('1 01.. (lo he puhlishcJ).

:J R Kriickcn (,{ al .. (lO tx' puhlished).

A. Bohr and B, ~lottt'1son.l''''lIcleo,. 511'l1C1Urt'. (Bcnjamin. NcwYork. 19(19. 1975) anJ (\Vorh..l Scicnlilk. Ncw York. 199X)Vol.l!.

::i. SCl..' forcxample. RE Castcn and P. von Brenlano.l'hy,\'. R('I'. esu (199-1.) R 12XO. and I'!lv.\'. Rl'I', e 51 (1995) 1525.

G F. lachello. N.V. Zamfir. ami R.E Castcn. I'hy.\'. R('\'. /.el/. XI(PNX) 1191.

l. R.. Krlickcn (,( (//.. 1'11.".\'. Lell. H 454 (1999) 15,

S. R..VF Jansscns <tlld T.L K1100. AmI. Re\'. NI/el. Hm. Sci. "1(i'!'!I) 321.

FIGURE -1..Preliminary level scheme ror :!()/lpr. As~ig.nmcnt to Fr is

hased un X-ray coinciJcnccs. hov.'cver the assignmcnt 10 A = 20Sis lenlalivc.

preliminary level schelllc for 211~Fr is showll in Fig. 4. Thispapel' reprcscnls (he work 01' many individuals. In particu-lar, Ihe work 01' John Novak who has heen responsihle lhedata analysis on :.!w'Rn is acknowledged. Reiner Krlicken isresponsihle 1'01'Ihe I""Sm analysis and ror the NYPD. Dis-cussions with Slcfan Frauendorf and Jing-ye Zhang are gratc-fully aeknowledgcd. The entire Yale Nuclear Slructure Gmupis rcsponsihlc rOl' the YRAST Hall and ils suile 01' detectors.

Acknowlcdgmcnts

This \Vork is suppoftcd hy the U.S, D.O.E. undel' grant IlUIl1-her, DE-FG02-91 ER--10609.

9. R. Pircstone amI B. Singh. Nuel. Data. 511('('1.\' 7X (1996) 1.

10. n.p. ~1c!\ahh el al .. PII\'.\'. Nl'I'. e S3 (1996) R541.

11. S. PrauendorfNl/cI. Phn. A557 (1993) 259.

12. (j. Baldsicfcn el al., I'hy,\'. Re\'. e 50l (1996) 1106.

13. R.M. Clark el al., Pln'.\ R(.\., Lel1. 7X (1997) I X6R.

¡.1. P.J. Dagnalll'fa/. . .I.l'hr.\'. G20(1994) 1591.

1[). P.J. i':olan. NI/d. Phy.\'. A A520 (1<)90) 657c.

lG. lR. Novak £'1(//.. Plly.\'. Re!'. C59 (1999) R29~9.

17. P.J. No!an, D. Gifford. and P.l Twin. Nuel. 111.1'(.a1/(1 Aft>th. h

23(, (I'!X5) '!5.

18. 1\1.Leino et al., NI/el. hl.\'l. (/1/(1M(,tli. IJ 99 (1995) 653.

Rel: /1.-1l'X.Fú. -lS S2 (1999) 46--49