ExperimentalStudyof3α-linear-chain

StructureinHigherExcitedStatesof16C

Speaker: Liu Yang

Supervisor: Prof. Y.L. Ye

Jan. 8th , 2017 @ BUAA

School of Physics 1/18 2017/01/08

Outline

p  1. Introduction

p  2. Theoretical Predictions of 16C

Ø  Molecular-Orbit Model Calculation

Ø  AMD Calculation

p  3. Pioneering Experiments of 16C

p  4. New Experimental Proposal for 16C in RIBLL

School of Physics 2/18 2017/01/08

Introduction

K.Ikeda,PTPs(1968)E68464-475.

ClusterinstableSelf-Conjugate4NNuclei Clustertowardneutrondripline

W.vonOertzen,Phys.Rep.432(2006)43-113Clusterstructuresaremainlyfoundclosetoclusterdecaythresholds.

School of Physics 3/18 2017/01/08

HoyleState:7.65MeV

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Introduction

Richphenomenainnuclearsystems

YoshikoKanada-En’yo,PTEP2012,01A202

W.VonOerXzenetal.,Z.Phys.A357(97)355.

No Candidate IndicaFons

Developedclusterstructuresappearinexcitedstatesnearthe correspondingcluster-decaythresholdenergy.

14C 16C

(AMD calculations) 4/18 2017/01/08

Introduction ExperimentalResultsforHighLyingExcitedStates:

Z.H.Yangetal.,PRL112,162501(2014).

12Be 14C

Z.Y.Tianetal.,CPC40(2016)111001

ItispossibleforresearcherstoinvesFgatethequitehighlyingexcitedstatesofnucleifromboththetheoreFcalsideandtheexperimentalone.

School of Physics 5/18 2017/01/08

-86MeV

-77MeV

Excitation: ~15MeV Region

Excitation: ~25MeV Region

Stableagainstthebending-likemo^on.PauliBlocking

Molecular-orbitalstructureinneutron-richCisotopes.

Bending motion Breathing motion

Theexcitedstatesof16Cwithπ2σ2configuraFonforthe4fourvalenceneutronsisoneofthemostpromisingcandidatesforthelinear-chainstructure.(~25MeV)

Theoretical Predictions: Molecular-Orbit Model

N.Itagaki,PRC64(2001)014301

d dα α α

α α

α

θ

School of Physics 6/18 2017/01/08

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Theoretical Predictions: AMD

AMD:Toinves^gatethelinear-chainstatein16Cwithoutaprioriassump^onontheclustercoreandvalenceneutronorbits.

Groundband Triangular Linear-Chain

(π1/2-)2 (π3/2

-)2

(σ1/2-)2

Be10+α+2n

WeaklyBound

TightlyBound

(β,γ)=(0.44,0) (β,γ)=(0.70,41) (β,γ)=(1.10,0)

n+15C4.54

4He+12Be13.81

6He+10Be16.51

8He+8Be 22.86

Thelinear-chainconfiguraFongeneratesarotaFonalbandbuiltonthe05+stateat15.5MeVthatisclosetothe4He+12Beand6He+10BethresholdenergiesandstableagainstthebendingmoFon.

T.Baba,PRC90,064319(2014)

7/18 2017/01/08

Outline

p  1. Introduction

p  2. Theoretical Predictions of 16C

Ø  Molecular-Orbit Model Calculation

Ø  AMD Calculation

p  3. Pioneering Experiments of 16C

p  4. New Experimental Proposal for 16C in RIBLL

School of Physics 8/18 2017/01/08

Pioneering Experiments:

two-bodybreakupchannels:

16C--->12Be+4He

16C--->10Be+6He

FWHM=9MeV

≤33.2±4.3µb

≤14.9±2.9µb

threshold

threshold

Etotal＞520MeV

PJLeasket.al.,J.Phys.G27(2001)B9–B14

Thehigh16Cbeamenergy(35MeV/A)openssomanyaddiFonalreacFonchannelsthattheQ-valueisnotgoodenoughtoexcludetheinfluenceofbreakupfragmentsindifferentfinalstates.

16Cisinelas^callyexcitedby12Ctargetfoilsandthenbreaksupintotwofragments.

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Pioneering Experiments: 16Cisinelas^callyexcitedby12Ctargetfoilsandthenbreaksupintotwofragments.

N.I.Ashwoodet.al.,PRC70,064607(2004).16C--->10Be+6He

200±190µb

16C--->10Be+6He*--->10Be+4He+2n

15±4µb

Thebeamintensityissolow(300pps)thatthestaFsFcsis

insufficienttogetpeaksinformaFonorspin-parityvalues.

Thereac^onproductsinunboundstatesmaycontribute

tothedecaychannelsonosignificantstructurewasseen

intheexcita^onenergyspectra.

School of Physics 10/18 2017/01/08

Pioneering Experiments: A18OintensestablebeamisincidentonaLi2Otarget,formingtheexcited16Cnucleibythethetwoprotontransferreac^on(18O,16C). B.J.Greenhalghet.al.,PRC66(2002)027302

16O(18O,16C)

12C(18O,16C)

7Li(18O,16C)

16O(18O,10Be*+α)

12C(18O,10Be*+α)

7Li(18O,10Be*+α)

6MeV

6MeV

6MeV

Q-valuespectrum

AferkinemaFccut

ExcitaFonenergyof16C

≤1.9±0.4µb

≤0.012±0.003µb

≤15.5±3.9µb

16O(18O,6He+6He+α)

12C(18O,6He+6He+α)

Noevidencefortheseprocessesmaybebecausetheyieldofthe(18O,16C)reacFonsaretooloworthereacFondoesn’tselecttherelevantstates.

School of Physics 2017/01/08 11/18

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16C-->6He+6He+4He

Cuts on Q-value: Qgggg ± 30MeV

Pioneering Experiments: 16Cisinelas^callyexcitedby(CH2)ntargetand(CD2)ntargetthenbreaksupintotwofragments.

16C-->10Be+6He

12Crecoil

1Hrecoil

(2004) (2001)

AMD

Apeakatabout20.6MeVisprobablyrelatedtotheexistenceofanhigh-lyingexcitedstate.

Itshowsanenhancedofthetriplecoincidenceyieldatabout34MeV.

AnewmeasurementwithbejerstaFsFcsisneededtoconfirmthepresentexperimentalfindings.

2017/01/08 12/18

Outline

p  1. Introduction

p  2. Theoretical Predictions of 16C

Ø  Molecular-Orbit Model Calculation

Ø  AMD Calculation

p  3. Pioneering Experiments of 16C

p  4. New Experimental Proposal for 16C in RIBLL

School of Physics 2017/01/08 13/18

Proposal: Main goals

Maingoals:ToInves^gatethe3alphalinear-chainstructureinthehigh-lyingexcitedstateof16C(Ex=14~25MeV)via1H(16C,4He+12Be)1Hand1H(16C,6He+10Be)1Hinelas^callybreakupreac^onat30MeV/Awithboththeinvariantmassandmissingmassmethodsininversekinema^cs.

School of Physics 2017/01/08 14/18

Observablesforclusterforma^oninaresonantstate:

1.   ExcitaFonenergyvsspinsystemaFcs:highmomentofinerFa

Ex:requiresgoodenergyresolu^on(IM);

J:requireslargesta^s^csandgoodpeaksepara^on;

2.   Largeclusterdecaywidth

Γ:requirescoincidentmeasurementofboththefragmentsand

theverylowenergyrecoiledtargetpar^cles(MM+IM).

3.   CharacterisFctransiFonstrength

M(E):requiresmeasurementoftheangulardistribu^onwith

verysmallcrosssec^ons.

Z.H.Yangetal.,PRL112,162501(2014).Sci.China57(2014)1613.

PRC91(2015)024324

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Proposal: Main goals

Emissionanglesoftheclusterbreakupfragments:

0.0 0.5 1.0 1.5 2.0 2.5 3.00123456789

10E x= 14MeVE x= 23MeV

angleof4 Η

e(deg

ree)

a ng le of12B e(deg ree)

0 1 2 3 4 5 6 70

3

6

9E x= 16.58E x= 25

angleof6 H

e(Deg

ree)

a ng le of10B e(deg ree)

0 5 10 15 20 25 30 35 400

5

10

15

20

25

30

35

40E x= 14MeVE x= 15MeVE x= 23MeV

Ep/M

eV

θlab(deg ree)

T0:64×64mm2DSSD,260mmfromtarget,coverangle:±7

TL:64×64mm2DSSD,80mmfromT0,coverangle:10.5~23.3

TR:64×64mm2DSSD,80mmfromT0,coverangle:-10.5~-23.3

3PPACsbeforesecondarytarget(CH2)n

T0mainlyfocusesonthebreakupfragments(IM).

TL&TRdetecttherecoilnucleusinsupplementary(MM).

invariantmass

missingmass

missingmass

2017/01/08 15/18

Proposal: Beam Intensity

PrimaryBeam: 18O; (70MeV/A,200enA)

PrimaryTarget: 9Be; (4600um)

SecondaryBeam: 16C; (1.19×104pps,Purity=92%)

SecondaryTarget:(CH2)n ;

Energyof16Cbeforesecondarytarget:30MeV/A

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OpFmumbeamenergyforinelasFcexcitaFonoftheclusterdegreeoffreedom:20~30MeV/A

H.Takemoto,PRC63(2001)034615

Improvementsofthefutureexperiments:

1.  30MeV/A16Ctoincreasethecrosssec^onsofclusterbreakupreac^ons.

2.  Thickertargetstoincreasesta^s^cssothatspin-parityanalysisbecomespossible.

3.  Zero-degreemeasurementstoincreasecoincidenceefficiencyoftwofragmentsandto

studyexcitedstatesin16Cwithlowrela^veenergy.(bandhead)

4.  Invariantmassmethodtogetpeaksinforma^onandspin-parityvalues.

Year Beam Intensity(pps)

E(MeV)

Ecm(MeV)

Target Thickness(μm)

Zero-Degree

Efficiency(10Be+6He)

StaFsFcs(20.8MeV)

2001 16C 2×104 560 240 12C 88.8 Yes 63% 5

2002 18O stable 130 36(Li)61(O)

Li2O 1.2 No 15% >22MeV

2004 16C 300 736 315 12C 1221 Yes --- 2

2016 16C 105 792 47(H)88(D)

(CH2)n(CD2)n

5028

No 28% 18

Future 16C 2×104 480 28(H)206(C)

(CH2)n 100 Yes ~60% =18/5*2*2*10=144

Proposal: Setups

School of Physics 2017/01/08 17/18

Proposal: Beam Request

Supposingthat:BeamIntensity: 1×104pps(consideringtransmissionefficiency)PPACDetec^onEfficiency: ~65%(thedetec^onefficiencyforoneplateis~60%)TargetThickness: (CH2)n~100μm(massthickness~8mg/cm2)Breakupcrosssec^ons: 16C--->12Be+4He(~400μb),16C--->10Be+6He(~200μb)Zero-degreeDetec^onEfficiency: ~50%(FromZ.H.Yang’sPhDthesis)ExcitedstateswithEx=14~25MeV: 10(FromBaba-san’sAMDcalcula^on2014)ThenthetotalcoincidencecountsforbreakupproductseveryhourcanbewriXenas:N=Intensity×3600×PPAC.eff×Target.Atoms×CrossSec^on×DSSD.eff=1×104×3600×0.65×8/14×10-3×6.022×1023×2×600×10-6×10-24×0.50=4.831/hourIfthebeam^meis200hours,thetotalcoincidencecountsamountto966witheachpeak97countsandthesta^s^cerrorof~10%.40hoursforbackgroundmeasurement.20hoursforelectronicsetupcheckanddetectorscalibra^on.

So260hoursbeamarenecessarytoinves^gatethelinear-chainclusterstructureof16C.

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Thanks for your attention! PKUExperimentalGroupIMPRIBLL1Cooperators