New magic numbers N = 32, 34 - University of Adelaide · New magic numbers N = 32, 34 1 Study the...
Transcript of New magic numbers N = 32, 34 - University of Adelaide · New magic numbers N = 32, 34 1 Study the...
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NewmagicnumbersN=32,34
1
Studythenuclearshellevolu1onatN=32,34bydirectmassmeasurementsofneutron-richnucleiinthevicinityof54Ca
N=32and34arecandidatesofnewmagicnumbersinCaisotopes• Wienholtzetal.Nature498,349(2013)
– Massof54CawasmeasuredbythePenningion-trapmethod– SteepdecreaseinS2nfrom52Cato54Ca– EstablishedprominentshellclosureatN=32
• Steppenbecketal.Nature502,207(2013)– Ex(2+1)in54Cawasmeasured– Ex(2+1)in54Cawasfoundtobeonly~500keVbelowthatin52Ca– SuggestedtheexistenceofanN=34shellclosurein54Ca
N>34
54Ca
Masseshavenotbeenmeasured
Thiswork
Acri1calevidenceontheshellclosureatN=34→ MassesbeyondN=34(55Ca,56Ca,...)
52Ca ?
S2n(Z=20)
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3234
Goalofthiswork
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• ObtaintheatomicmassdataofAr,K,CaandScisotopesbeyondN=32and34withtheprecisionofseveralhundredskeV
• Makeclear– MagicityofCaandScatN=34– MagicityofKandAratN=32
>1000keV
<1000keV
<500keV
<400keV
<300keV
<200keV
<100keV
Massuncertainty
☆:Es1matedbeamintensi1es>0.001cps
55Ca
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BigRIPS
High Resolution Beam Line
SHARAQ Spectrometer
Experimentalsetup
3
F3 • Timingdetector(Diamond)• Trackingdetector(LP-MWDCx2)
S0 PosiWondetector(PPAC)
S2 • Timingdetector(Diamond)
• Trackingdetector(LP-MWDCx2)• ΔEdetector(SSDx2)
Gammadetectors
Produc1ontarget(9Be)
Flightlength(F3-S2)105m(~540ns)
Primarybeam:70Zn(345MeV/u),I=150pnA
F3
S0
S2
• Momentumslit• Energydegrader
Forisomertagging(confirmPID)
@RIKENRIBeamFactory(RIBF)-SHARAQ
• TOF-Bρmethod
PrecisemeasurementofTOFandBρ
ForBρmeasurement
Dispersionmatchingmode(p/δp=14700)
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Diamonddetector
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S.Michimasa,etal.,NIMB317,710(2013)
• DevelopedbyCNS-MSUcollabora1on• PolycrystallineCVDdiamond
• Crystalsize:30×30×0.2mm3
• Paddesign– Effec1vearea:28×28mm2
– SideA:1pad(4readouts)– SideB:4strips(8readouts)
• forcorrec1onofposi1ondependence
SpecificaWon:
Fastresponse→ verygood2mingresolu2on!Diamond
(CVD:chemicalvapordeposi1on)
20ns
Pad
Strip
Strip
Rise1me:~700psDecay1me:~10ns
• Timingresolu1onwasachievedtobe27ps(σ)for320-AMeV12Nisotopes(previousexp.)
ü Inthepresentmassmeasurement,σ=11pshasbeenachievedforZ=20nuclei
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ExpectedmassresoluWon
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• MassresoluWoninthesystem
– Bρ:SHARAQoperatedindispersionmatchingtransportmode→ δBρ/Bρ=1/14700(designvalue)
– TOF:Diamonddetector(σ=30ps)→ δt/t=7.5×10-5
– Flightlength(L):correctedbyLP-MWDCs(σ=300um)→ δL/L=5.8×10-5
𝝐~1.7×10-4(1/𝝐~6000)isexpectedtobeachieved~1.7×10-4(1/𝝐~6000)isexpectedtobeachieved
• Massuncertainty
– σ(syst)=2×10-6isassumed(frompreviousTOFmeasurements)– 55Ca:σm=300keV(σ=6×10-6)→ N=3000eventsareneeded
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ParWcleidenWficaWon
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• Totalyieldof55Ca:~3000• Manyspeciesofreferencenucleioverabroad
rangeofAandZareobserved.– Thesenucleiareusedinthemasscalibra1on.
• Nucleiwhosemasseshavenotbeenmeasured:
Z Nuclei(Yield>1000)
17 47Cl,48Cl
18 50Ar
19 --
20 55Ca
21 58Sc,59Sc
22 58Ti,59Ti,60Ti
23 62V,63V
MassesofthesenucleiwillbedeterminedwiththeprecisionofseveralhundredskeV
PIDspectrumaoerroughmasscalibra1on
A/Q2.5 2.55 2.6 2.65 2.7 2.75 2.8 2.85 2.9
Z
10
12
14
16
18
20
22
24
58Sc 59Sc
61Ti60Ti59Ti58Ti
63V62V
50Ar
47Cl 48Cl
Newmasses
55Ca56Ca
Preliminary
54K
51Ar
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Massspectra
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Preliminary Preliminary
• MassresoluWonof1/10000(σ)hasbeenachievedforZ=20nuclei– 55Ca:σm(stat)=90keV(3000events)– 56Ca:σm(stat)=200keV(400events)
NoZgate(allnuclei)
2.694 2.704A/Q0.001
54Ca
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SystemaWcerror
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σm/q(syst)=6.1keV/q
• Referencenuclei– 52-54Ca,49,51-52K,46-48Ar,43-46Cl,41-42S,38-42P,36-40Si
• Massuncertain1es<300keV• Noknownisomericstates• MassvaluesaretakenfromAME2012except
53,54Caand52K• 53,54Ca:F.Wienholtzetal.,Nature498,349(2013)• 52K:M.Rosenbuschetal.,PRL114,202501(2015)
• Systema1cerror– evaluatedfromthestandarddevia1onof
them/qdifferencesforthereferencenuclei
(Z=20→ σm(syst)=122keV)
Preliminary
• Massesof55Caand56CaaredeterminedwithprecisionsofafewhundredskeV– σm=150keV(55Ca),σm=230keV(56Ca)(Preliminary)
• Wewillfixsoonthefinalvalues(especiallyerrors)ofthemasses
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Two-neutronseparaWonenergyS2n
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Thiswork
• GXPF1BR(pf-shell):Nature502,207(2013)• KB3G(pf-shell)• NN+3N(MBPT,pf+g9/2):PRC90,024312(2014)
Theore1calcalcula1ons
Enlarge
N=35:KB3GandNN+3NlookgoodN=36:NocalculaWonsreproducethenewvalueswell
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Empiricalshellgap
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D.Lunneyetal.,Rev.Mod.Phys.75,1021(2003)
• PeakatN=32– indicaWngshellclosureatN=32
• NocalculaWonsagreewithourexperimentalresult
• EmpiricalshellgapatN=34issmallerthanN=32
Fromthiswork
Empiricalshellgap
Thiswork
• GXPF1BR• KB3G• NN+3N(MBPT)
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Summary
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• Inordertostudynuclearshellevolu1onatN=32and34,directmassmeasurementofneutron-richnucleiinthevicinityof54CawasperformedatRIBF-SHARAQbyusingtheTOF-Bρmethod.
• Massresolu1onof1/10000(σ)hasbeenachievedforZ=20nuclei.
• Massesof55Caand56CawillbefinalizedsoonwiththeprecisionofafewhundredskeV.
• ExperimentaldataindicatethatshellgapatN=34issmallerthanN=32intheCaisotopes,andtheore1calcalcula1onsdonotagreewellwithourdata
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Collaborators
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CNS,UniversityofTokyoM.Kobayashi,S.Michimasa,Y.Kiyokawa,M.Dozono,S.Kawase,K.Kisamori,Y.Kubota,C.S.Lee,M.Matsushita,H.Miya,S.Ota,S.Shimoura,M.Takaki,H.Tokieda,K.Yako,R.Yokoyama
RIKENNishinaCenterH.Baba,N.Fukuda,N.Inabe,T.Kubo,H.Sakai,H.Suzuki,H.Takeda,S.Takeuchi,T.Uesaka,Y.Yanagisawa,K.Yoshida
MSUNSCLA.Stolz
Univ.ofNotreDameG.P.A.Berg
KyotoUniversityT.Furuno,T.Kawabata
RCNP,OsakaUniv.E.Ideguchi
RikkyoUniversityK.Kobayashi,H.Nagakura,Y.Yamaguchi
TokyoUniversityofScienceA.Mizukami,D.Nishimura,H.Oikawa
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Thank you for your attention
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BACKUP
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Nuclearmasstoatomicmass
15
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MasscalibraWon
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σm/q(syst)=6.1keV/q
• Referencenuclei– 52-54Ca,49,51-52K,46-48Ar,43-46Cl,41-42S,38-42P,36-40Si
• Massuncertain1es<300keV• Noknownisomericstates• MassvaluesaretakenfromAME2012except
53-54Caand52K• 53-54Ca:F.Wienholtzetal.,Nature498,349
(2013)• 52K:M.Rosenbuschetal.,PRL114,202501(2015)
• Fisngfunc1on
– uptothe4thorderaberra1onsareconsidered
• t:TOF(betweenF3andS2)• x,y:beamposi1on(atF3,S0orS2)• a,b:beamangle(atF3orS2)
• Systema1cerror– evaluatedfromthestandarddevia1onof
them/qdifferencesforthereferencenuclei
(Z=20→ σm/q(syst)=122keV)
Preliminary
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ZcorrecWon
17
ErrorarisingfromthisfisngZ=20→ σ=3.26keV/q
ErrorsofS2nandΔ3npresentedinthistalkcontainsthiserror
Z-dependenceremains
Fisngfunc1ondoesnotcontaintheZ-term→ Z-dependenceremains
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TimingresoluWonofdiamonddetector
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• Timedifferencebetweenbothedgesofastripinadiamonddetector
• Correctedbyhitposi1oninthestrip
• TimingresoluWonofthediamonddetectorisesWmatedtobeσ=12ps(cf.12Nat320AMeV→ σ=27ps)
TimedifferenceTL–TR[ps]
Preliminaryσ(Tdiff)=17ps
×BeamTL TR
cf.Timedifferencevstrackedposi1on(beforecorrec1on)
Stripwidth
σ=12ps×1/√2
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TOFresoluWon
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• Correc1onofaberra1onsupto4thorderofxF3,aF3,yF3,bF3,andxS0
– Coefficients(fisngparameters)c0,c1,c2,…aredeterminedbyleastsquaremethod
• TOF:about540ns(57Sc,Bρ~7Tm)
• ΔTOF/TOF=7.8×10-5(σ)hasbeenachieved
Preliminary
beforecorrec1on
aoercorrec1onσ(TOF)=42ps
57Sc
TOFbetweenF3andS2[ns](Timingoffsetisnotadded)
1st
2nd
>3rd
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beforecorrec1on(measurementvalue)
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Δ3value
20
W.Satulaetal.,PRL81,3599(1998)
M(N):Massexcess
32 34
Meanfieldpart(shellgap)atN=34isnotsolargeasN=32
Fromthiswork
Δ3(N=even):pairing+mean-fieldΔ3(N=odd):pairing
• Significantpeaksappearatconven1onalmagicnumbers(e.g.N=28)
• PeakatN=32– indicaWngshellclosureatN=32
Δ3value:indicatorofnuclearshellevolu1on
Thiswork