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)

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

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)

Diamonddetector

4

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

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

ParWcleidenWficaWon

6

•  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

Massspectra

7

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

SystemaWcerror

8

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

Two-neutronseparaWonenergyS2n

9

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

Empiricalshellgap

10

D.Lunneyetal.,Rev.Mod.Phys.75,1021(2003)

•  PeakatN=32–  indicaWngshellclosureatN=32

•  NocalculaWonsagreewithourexperimentalresult

•  EmpiricalshellgapatN=34issmallerthanN=32

Fromthiswork

Empiricalshellgap

Thiswork

•  GXPF1BR•  KB3G•  NN+3N(MBPT)

Summary

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•  Inordertostudynuclearshellevolu1onatN=32and34,directmassmeasurementofneutron-richnucleiinthevicinityof54CawasperformedatRIBF-SHARAQbyusingtheTOF-Bρmethod.

•  Massresolu1onof1/10000(σ)hasbeenachievedforZ=20nuclei.

•  Massesof55Caand56CawillbefinalizedsoonwiththeprecisionofafewhundredskeV.

•  ExperimentaldataindicatethatshellgapatN=34issmallerthanN=32intheCaisotopes,andtheore1calcalcula1onsdonotagreewellwithourdata

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

Thank you for your attention

BACKUP

Nuclearmasstoatomicmass

15

MasscalibraWon

16

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

ZcorrecWon

17

ErrorarisingfromthisfisngZ=20→ σ=3.26keV/q

ErrorsofS2nandΔ3npresentedinthistalkcontainsthiserror

Z-dependenceremains

Fisngfunc1ondoesnotcontaintheZ-term→ Z-dependenceremains

TimingresoluWonofdiamonddetector

18

•  Timedifferencebetweenbothedgesofastripinadiamonddetector

•  Correctedbyhitposi1oninthestrip

•  TimingresoluWonofthediamonddetectorisesWmatedtobeσ=12ps(cf.12Nat320AMeV→ σ=27ps)

TimedifferenceTL–TR[ps]

Preliminaryσ(Tdiff)=17ps

×BeamTL TR

cf.Timedifferencevstrackedposi1on(beforecorrec1on)

Stripwidth

σ=12ps×1/√2 

TOFresoluWon

19

•  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)

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