PSF in 181,182Ta and the emergence of the scissors resonance Speaker: Christiaan Brits Supervisors: Dr. M. Wiedeking Prof. P. Papka Dr. B. V. Khewsa

Introduction •  The scissors resonance (SR) is the oscillation of

the proton and neutron distribution against each other like the blades of a scissor.

•  Resonances can be observed through the photon strength function (PSF).

•  The PSF characterizes the average electromagnetic properties of excited nuclei.

•  The PSF and nuclear level density (NLD) can be simultaneously extracted using the Oslo method.

•  The Oslo method uses particle-γ coincidence data to simultaneously extract the PSF and NLD.

•  A 181Ta(d,x) and 181Ta(3He, 3He’) 181Ta reaction was used to investigate the SR of 181,182Ta.

General Motivation •  The PSF and NLD is one of the critical input parameters for

calculating reaction cross sections through reaction codes like Talys.

•  The PSF also plays a central role in elemental formation during galactic nucleosynthesis.

•  Calculations have shown that relatively small changes to the overall shape of the PSF such as pygmy resonances can have an order of magnitude effect on the rate of elemental formation [1].

•  K.L Malatji will discuss the astrophysical application in detail tomorrow afternoon.

[1] S. Goriely, Phys. Lett. B 436, 10 (1998).

Tantalum motivation

[1]M.Igashiraetal.Nucl.Phys.A,457,301–316(1986)[2]A.Wolpertetal.Phys.Rev.C,58,765(1998)

Anenhancementcanbeseenbetweenenergies1-3MeVforPr,Tb,HoandLu,butnoenhancementcanbeseeninTaorAuinthisenergyregion[1].InaNRF[2]aweakSRwasfoundinaNRFexperiment,thisbringsquesZonsontheevoluZonoftheSR.

SiRi particle telescope and CACTUS array

SiRiparZcletelescopecoversasca[eringanglebetween126°-140°.EnergyresoluZonof130keVasmeasuredfromelasZcpeak.

TheCACTUSarrayhasatotalefficiencyof14.1%andenergyresoluZonof7%FWHMfora1332keVtransiZon.

The Oslo method

By using the Oslo method the NLD and PSF can be simultaneously extracted from particle-gamma data. A detailed look at this method can be found in references [1,2]. The main steps in this method are: •  Calculate and remove the Compton background, single and

double escape peaks and effects from pair production. •  Extract the first generation γ-rays from the Compton subtracted

matrix. •  Simultaneous extraction of the NLD and PSF from the first

generation matrix. •  Normalization of the NLD and PSF.

[1]A.Schilleretal.,Nucl.Instrum.MethodsPhys.Rev.A,447,498(2000)[2]A.C.Larsenetal.,Phys.Rev.C,83,83,034315(2011)

NLD and PSF of 182Ta

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray

str

engt

h fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

Resonances of 181Ta

Thepygmyat7MeVisduetotheworkdoneby[1].Thebluelineisduetothepygmyandspin-flipresonances,theblackandpurplelinesareduetothesplitGEDRandthegreenline[2]wasaddedsothatthetotalfitmatchedexperimentalresults.

[1]A.Makinagaetal.Phys.Rev.C,90,044301(2014)[2]M.Igashiraetal.Nucl.Phys.A,457,301–316(1986)

(MeV)γ

-ray energy Eγ0 2 4 6 8 10 12 14 16

)-3

-ray

str

engt

h fu

nctio

n (M

eVγ -910

-810

-710

-610

-510 Ta, present experiment181,x), 2001 Belyaev γTa(181

'), 2014 Makinaga γ,γTa(181

Total fit

Scissors resonance

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18112.5 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

He')3He,3Ta(181

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18112.5 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

He')3He,3Ta(181

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18112.5 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

He')3He,3Ta(181

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18112.5 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

He')3He,3Ta(181

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

12.5MeV181Ta(d,d’)B(M1)=

181Ta(3He,3He’)B(M1)=

15MeV181Ta(d,d’)B(M1)=

B(M1) = 3.02±1.47µN2

B(M1) = 3.78± 0.5µN2

B(M1) = 3.17±1.75µN2

Scissors resonance

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18112.5 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

He')3He,3Ta(181

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18112.5 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

He')3He,3Ta(181

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18112.5 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

He')3He,3Ta(181

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18112.5 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

Ta(d,d')18115 MeV

1.5 2 2.5 3 3.5 4 4.5 5 5.5 6

-10

0

10

20

30

-910×

He')3He,3Ta(181

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

-ray energy (MeV)γ0 1 2 3 4 5 6

)-3

-ray s

treng

th fu

nctio

n (M

eVγ

-810

-710

upper error band observed lower error band

Ta182

FromtheSRcentroidsa13°γdeformaZoncanbecalculated[1].

[1]E.LippariniandS.Stringari,Phys.Rep.175,103(1989)

Discussion Theresultsaresurprising.182TadoesnothaveavisibleSR,181TahowevermayhaveaweakSR.ThisissupportedbyNRFexperimentfindingsinRef[1].181,182TashouldalsohaveastrongSRconsideringonlyδ≈0.265for181Taandδ≈0.255for182Ta[2].TheacZnideshaveaSRstrengthof10[3-6]andtherare-earthshaveSRstrengthsof6-9[7,8].ThesumrulepredicZon[9]predictedaSRstrengthof8.3for181Ta. [1]C.T.Angell,R.HajimaandT.Shizuma,Phys.Rev.Le[117142501(2016)[2]S.HilaireandM.Girod,AIPconferenceproceedings1012,359(2008)

[3]M.Gu[ormsenetal.,Phys.Rev.Le[.109,162503(2012).[4]M.Gu[ormsenetal.,Phys.Rev.C89,014302(2014).[5]T.G.Tornyietal.,Phys.Rev.C89,044323(2014).[6]T.Laplaceetal.,Phys.Rev.C93,014323(2016).[7]A.Schilleretal.,Phys.Le[.B633,225(2006).[8]H.T.Nyhusetal.,Phys.Rev.C81,024325(2010).[9]E.LippariniandS.Stringari,Phys.Rep.175,103(1989)

Discussion TheSRweaknesscanbeexplainedbya13°γdeformaZon[1].PotenZalenergysurfacecalculaZonsusingthecrankingNilssonmodel[2]plusshellcorrecZoncalculatedatheoreZcalγdeformaZon.TheresultssupportnucleartriaxialityasthelikelymechanismofSRsplimngin181Ta.AnotherpossibleexplanaZonfortheSRsplimngwasproposedfrommicroscopiccalculaZons[3].InthesecalculaZonstheSRmodeofprotonsoscillaZngagainstneutronsisaccompaniedbylower-energynuclearspinscissorsmodewherespin-upnucleonsoscillateagainstspin-downnucleons.[1]E.LippariniandS.Stringari,Phys.Rep.175,103(1989)[2]S.Frauendorn,Nucl.Phys.A667,115(2000)[3]E.BalbutsevandI.Molodtsova,Phys.Rev.C88,014306(2013).

The PSF and NLD of 181,182Ta was extracted using the Oslo method. In 181Ta the average SR strength is 3.2±0.78 , only 40% of the expected SR strength. This is similar to the latest NRF result where only 30% of the expected strength was found. No observable SR was found in 182Ta, possibly due the extra unpaired nucleon spreading the strength apart. The SR weakness could be due to the 13° γ deformation of Ta. More work needs to be done on γ-soft, odd-even, and odd-odd nuclei. In light of the proposed nuclear spin scissors mode [1], theoretical guidance on possible observables and specific experimental signatures for this mode are highly desirable.

Conclusion

Wiedeking M., 2 Kheswa B.V., 2 Bello Garrote F.L., 4 Bleuel D.L, 3 Giacoppo F., 4 Guttormsen M., 4 Gőrgen A., 4 Hadynska-Klek K., 4 Hagen T.W., 4 Klintefjord M., 4 Larsen A.C., 4 Nyhus H.T., 4 Papka P., 1,2 Renstrøm T., 4 Rose S., 4 Sahin E., 4 Siem S., 4 Tveten G.M., 4 Zeiser F., 4 Ingeberg V.W. 4 1.  Department of Physics, University of Stellenbosch 2.  Department of Nuclear Physics, iThemba LABS 3.  Lawrence Livermore National Laboratory 4.  University of Oslo, Norway

Collaborators

Dankie Thank you Enkosi

NLD and PSF

[1]A.Schilleretal.,Nucl.Instrum.MethodsPhys.Res.A447,498(2000).

•  NLDistheamountoflevelsaccessibleatagivenexcitaZonenergy,spinandparity.

•  Theamountofavailablequasi-parZclesandavailablesingle-parZcleorbitalsinthevicinityoftheFermi-levelisthebasicblocksthatdeterminestheNLD

•  ThePSFisadistribuZonofaveragereducedwidthsfortransiZonsofacertainmulZpoletypeXLbetweentwodifferentstatesofenergies.

•  ThePSFisgivenintermsoftransiZonwidthsandresonancespacingby[1]:

Discussion

Only33-50%M1strengthfortheodd-massnucleicouldbedetectedintheenergyrange2.5-3.7MeVinsomeexperiments,duetolargefragmentaZon.Groundstatewidthdecaysfor163Dyfromtwoexperimentsareshownhere.

Discussion

ThesensiZvityofthelatestexperimentwasgreatlyimprovedandanumberofpreviouslyundetectabletransiZonswerefound.TheM1strengthofthelatestexperimentcomparesbe[ertocloselyingeven-massM1strengthandaccountsforthelostM1strengthinodd-massnuclei[1].

[1]P.vonNeumann-Cosel,K.Heyde,andA.Richter.Rev.Mod.Phys.,82,2365(2010)

CACTUS array calibration BypumngagateonindividualparZclepeaksintheexcitaZonenergyspectrumthe𝛾-rayscanbecalibrated.TheexcitaZonenergyspectrumof29SiwasUsed.

1273keV

2028keV

3067keV

3623keV

4079keV

4895,4933keV

3623keV1595keV

2028keV

2028keV

Data analysis

TheparZcle-𝛾coincidencematricesof182Taand181Taareshownhere.Thereissome12CcontaminantwhichundergoesthereacZon12C(d,p)13C.Theresultant13Cemits𝛾 -raysofenergies3854keVand3089keV.

182Ta 181Ta

Statistical and systematic errors

AtheoreZcalfit(line)totheexperimentaldatafortheχ2minimizaZoniscomparedtotheexperimentaldata(points)

Motivation ObservedsolarabundancedistribuZon.SolarabundancecalculaZonwithoutthepygmyresonance,theA=90-110nucleiareproducedmoreaccurately.SolarabundancecalculaZonwiththeinclusionofthepygmyresonance,theA=130nucleiareproducedmoreaccurately.

M.ThoennessenadoptedfromS.Goriely,Phys.Le[.B436,10(1998).

The First Generation method

A.C.Larsen,PhDthesis,UniversityofOslo,2008.

ThedistribuZonofprimary𝛾-rayscontainsinformaZonontheNLDandPSF.Highlyexcitednucleiprimarilydecaythroughacascadeof𝛾-rays.

𝐸↓𝛾 

𝐸↓𝑥 

Discussion

Recently,datafromOslohaveshownthatthescissorsresonanceisstronglyobservableintheacZnideregion.Unlikeintherare-earthregion,thescissorsresonanceisnotfragmentedforodd-odd[1],even-odd[2]oreven-even[2]nucleiintheacZnideregion,butareconsistentlylocalized,althoughsomeexhibitanunexplaineddouble-humpedstructure[2].

[1]M.Gu[ormsenetal.Phys.Rev.Le[.,109,162503(2012)[2]T.G.Tornyietal.Phys.Rev.C,89,044323(2014)

Comparing strength functions

SimilarPSFfromdifferentexcitaZonregionsvalidatesBrink’shypothesis.

CurrentPSFcomparedto181Ta(3He,3He’)181Ta[1]data.

[1]K.L.Malatji.Master’sthesis,UniversityoftheWesternCape,2016.

Giant dipole resonances

The Giant magnetic dipole resonance is induced by spin oscillation of the proton and neutron distributions

Extraction cuts

TheupperexcitaZonenergyboundissetattheSn-energyresoluZonwhichis5.9MeVfor182Taand3.8MeVfor181Ta.

Extraction cuts

Below2.5MeVexcitaZonenergysomediscretestatescansZllbeobserved.ThelowerbandissetatEx=2.5MeVforboth182Taand181Tatoensurethatonlyeventsfromthequasi-conZnuumregionareusedsothatBrink’shypothesisisvalid.

Extraction cuts

DuetothesystemaZcssomeoverandundersubtracZonareobservedasverZcallinesatlowenergies.Thelowerboundforthe𝛾-energyissetat950keVfor182Taand800keVfor181Ta.