nuclear structure kvi - · pdf filenuclear structure @ kvi ... broad spectrum of beams with...

Nuclear Structure@

KVI

A.M. van den Berg, M.N. Harakeh, H.J. WörtcheKernfysisch Versneller Instituut (KVI)

Groningen

Title

Nuclear Structure @ KVI

spin and isospin selective nuclear structure studies with high precission

unique combination

AGOR & Big Bite Spectrometer & EuroSuperNova detector& variety of detection systems

driven by vivid international collaborations !!!

KVI - ion accelerator AGOR

0 0.2 0.4 0.6 0.8 1.0charge / A

ener

gy /

A [M

eV] 100

10

AGORoperating diagramme

variable acceleratorbroad spectrum of beamswith high quality

proton beamsup to 190 MeVpolarized

deuteron - &alpha beams35 - 90 MeV / n

deuteronsvector- &tensor polarized

KVI - experimental facilities

TRIµP - Trapped Radioactive Isotopesµicro Laboratories forFundamental Physics

radio biology

irradiation setup

few-body physics

Big-Bite Spektrometer (BBS) &EuroSuperNova detection system(ESN detector)

KVI - BBS & ESN detector

Big-Bite Spektrometer large acceptance (momentum & angle), moderate resolution

EuroSuperNova detector light-ion detector equipped with real-time data processinghigh rate capabilities

KVI - BBS & ESN Detektor

Focal Plane Detector:(FPDS)2 VDCs

Focal Plane Polarimeter:(FPP)4 MWPCs &graphite analyzer

features a.o.:- fast readout-VDC readout by pipeline TDCs -VDC decoding using imaging technics-DSP based online analysis

BBS (mode B):

dΩ < 9.2 msrdΘ < 66 mraddΦ < 140 mradΔp/p < 19 %ΔE/E > 4 · 10-4

0o - operation

BBS - program (in part)

•(pol(p), p’) cross sections, analyzing powers Ay, polarization transfer Dnn11B, 12C, 48Ca, 58Ni, 116,124Snspectroscopy of M1, M2 strength

•(d, 2He) cross sectionsd, 6,7Li, 12C, 14N, 28,30Si, 32S, 48Ti, 50,51V, 58,61,64Ni, 56Fe, 70,72,74Ge, 116Sn spectroscopy of GT+ strength, double (0νββ) decayn-n scattering length spin entanglement

•(pol(d), 2He), (d, 2He n) cross sections, tensor analyzing powers Ayy, Azz12CJπ = 0-, 1-, 2- components spin-dipole

•(α, 2He) production rate12Cspin entanglement

•(t, 3He) cross-sections12C, 48Ca, 58Ni, 90Zr, 208Pb(no spin-flip) isovector modes

•(α, α’ γ), (α, α’ p), (α, α’ n)48Ca, 58Ni, 90Zr, 140Ce, 208Pbisospin low-lying dipole, isoscalar electric dipole (ISGDR)

BBS - selection of highlights

ISGDR + ??? in 208PbM. Hunyadi et al, PLB 576 (2003) 253, NPA 731 (2004) 49

nn - scattering lengthC. Bäumer et al., PRC 71 (2005) 044003

matrix elements 2νββRakers et al.PRC 71 (2005) 054313

BBS & ESN Detektor - 2He

d

2He

A, Z

A, Z-1

pp

target nucleusremainingnucleus

deuteron diproton (2He)

• charge exchange reaction equivalent (n,p)• close to 100% spin-flip (Gamow-Teller transition) if: protons in 1S0 state 2He detected at 0°

but enormous (!) backgrounddue to deuteron break up104 - 105 larger cross section !

(d,2He) - principle

BBS

Target

focal-plane detector:

momentum (energy), arrival time

2He protons in coincidence

BBS acceptancelimits relativekinetic energy protons < 1 MeVfor Ed < 180 MeV

2He filter

d

2He

A, Z

A, Z

pp

target nucleusremaining nucleus

internal energy [MeV]

focal-plane arrival time difference [ns]

kinetic energydeuterons: < 180 MeV 1S0

Playing with spin and isospin

14N(d,2He)14C in comparison 14N(3He, t)14O

12C((pol)d,2He)12B

(12C(d, pol(2He))12B)

2He spin-flip filter

2He spin-flip filter &ΔS, ΔL coupling

spin correlations

14C , isospin symmetrie,shell model vs cluster model

matrix elements double β-decay, parity breaking

quantum correlations in nuclear systems

(d,2He) - structure A=14 / A.L. Negret PhD, Gent 2005

14N(d,2He)14C

(d,2He) Gamow-Teller filter (time-reversed β--decay)


stability 14C againts β--decay (14C → 14N)( 14C dating, τ1/2 = 5730 years)

• ground-state transitions

• comparison with large scale shell-model calculations

• structure & strength of transitions to excited states

• nuclear-strcuture classics!

(d, 2He) - structure A=14 / A.L. Negret PhD, Gent 2005

Coulomb

KVI, 14N(d,2He)14CEd = 170 MeV (n,p) - equivalent

RCNP, Osaka, 14(3He,t)14OEHe = 420 MeV(p,n) - equivalent


complexity

Gamow-Tellertransition strength in 14C

shell-model calculationsS. Aroua et al.,Nucl. Phys. A720, 71 (2003)


GT strength distribution experiment vs theory

strength 2+ states notreproduced by shell-model!

triple α-cluster +2 nucleon structure /molecular states ?

(d,2He) - spin dipole in 12B / M.A. de Huu PhD, KVI 2003

12C((pol)d,2He)12B

(pol(d),2He) filtering Jπ components spin dipole (time reversed first forbidden β--decay)a testcase !


spin dipole: ΔS = 1 (spin flip), ΔL = 1 (momentum transfer)time reversed, first forbidden β--decay

• starting from 0+ ground state: Jπ = 0-, 1-, 2- final states

• angular separation of transitions not possible, identical for Jπ = 1-, 2-

• predicted differences in cross-section depending on tensor polarisation - but: subtile effect !!! • relevant for analysis 0ν2β-decay

• high lying, collective 0- states relevant parity mixing of ground state (for 0+ ground state)


• vector polarisedpZ = N+ - N-

• tensor polarisedpZZ = N+ + N- - 2N0

withN+ + N_ + N0 = 1

extrema:pZZ = 1 , N+ = N_ = 1/2pZZ = -2, N0 = 1

• KVI deuteron beam, E0 = 171 MeVpZZ = 0.57 ± 0.03, pZ = 0.06 ± 0.01pZZ = -1.24 ± 0.05, pZ = -0.01 ± 0.01

N- N+

N0

z


Separation of 0-,1-,2- spin-dipole strengthfor scattering close 0°

z

q (ΔL)

ΔS

q

ΔS

PZZ = -2transversal orientationfavours natural parityπ = (-1)J

i.e. Jπ = 1-

PZZ = 1longitudinal orientationfavours non-natural parityπ = (-1)J+1

i.e. Jπ = 0- , 2-

tensor analysing powers: Ayy = 1, Azz = -2 for 0-

Ayy = -1/2, Azz = 1 for 1- (natural parity)

(ΔL)


1+

2+2-

1-

2-

1+

3+

1-1-

0-, 1-, 2- ?

12C(d, 2He)12B E0 = 171 MeV, θ = 0° - 4° ∆E ≈ 130 keV

first time verificationof predictions Ayy, Azz !


PZZ = -1.24

PZZ = 0.57

12C((pol)d,2He)12Bθlab = 0° - 1.7°Ed = 172 MeV

n-threshold quasi-free backgroundsubtracted

background verificationthrough n-decay data

differences forpolarisation modes


Low Lying Transitions

2-

1.67 MeV

1-

2.62 MeV

2- + ?4.4 MeV

angular dependencyof cross-sectiondoesn’t allow 1-, 2- separation

1- transition nicely fit Ayy , Azz close 0°(also 2+ at 0.96 MeV)unique fingerprint !

2- exhibit indifferent asymmetries


(PZZ = 0.57) - (PZZ = -1.24)

AZZ

naturalparity

naturalparity

indicationslocalized 0- strengthat 9.5 MeV(H. Okamura et al., Phys. Rev. C66 054602 (2003))


first time verificiation of Ayy , Azz predictions

selection of 0-, 1-, (2-) excitations possible

extension to heavier nuclei i.e. range relevant for 0νββ, A > 48

extraction transition strength ?

(α, α’ γ) structure Pigmy/ D. Savran PhD, TuD

(α, α’ γ) 48Ca, 58Ni, 140Ce

isospin structure of the electrical dipole (E1) strengthjust below the particle threshold-Pigmy resonance -

combining hadronic probeswithhigh resolution γ - spectroscopy


48Ca, 58Ni, 140Ce (α,α’γ)

2 years of experimentalstudies

Ge-setup extremelysensitive to backgrounds

change up to factor 10hadron / γ trigger rateany AGOR fine tune

• unique way of linking hadronic/electromagnetic probes• (p,p’ γ) under investigation

58Ni E = 136 MeV θ = 3 - 8 deg


Pigmy resonance

140Ceconcentration of E1below particle threshold-Pigmy resonance - :

a new collective mode ?

correlated to neutron/proton excess ?

αscattering indicatessplitting of strength inisoscalar - isovector component

nuclear structure program at BBS ends 2005

but there is a high need on precision datawhich can only be obtained with stable beamfacilities

to early to make them history !

Conclusion

nuclear structure kvi - · pdf filenuclear structure @ kvi ... broad spectrum of beams with...

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