nature of mixed-symmetry 2 + states in 94 mo from high-resolution electron and proton scattering
DESCRIPTION
Nature of Mixed-Symmetry 2 + States in 94 Mo from High-Resolution Electron and Proton Scattering and Line Shape of the First Excited 1/2 + State in 9 Be. Oleksiy Burda , 19.11.2007. Motivation. Experiments. Results and microscopic interpretations. Summary. - PowerPoint PPT PresentationTRANSCRIPT
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Nature of Mixed-Symmetry 2+ States in 94Mofrom High-Resolution Electron and Proton Scattering
and Line Shape of the First Excited 1/2+ State in 9Be
Oleksiy Burda, 19.11.2007
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Motivation
Experiments
Results and microscopic interpretations
Summary
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Interacting Boson Model - 2
F-spin: boson: Fz = 1/2 boson: Fz = -1/2
Pairing of nucleons to s- / d- bosons
N, N: Fmax =N + N
2 ≥ F ≥|N – N|
2
F = Fmax: fully symmetric states (FSS) isoscalar
F < Fmax: mixed-symmetry states (MSS) isovector
Q-phonon scheme: Qs = Q + Q |21 Qs | 01 + +
N NQms = |2ms Qms| 01 2 N
Q – 2 NQ
+ +
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N. Pietralla et al., Phys. Rev. Lett. 83, 1303 (1999); Phys. Rev. Lett. 84, 3775 (2000) C. Fransen et al., Phys. Lett. B 508, 219 (2001); Phys. Rev. C 67, 024307 (2003)
Test case 94Mo
Qs
QsQs
Qms
QsQms
F = Fmax – 1(MSS)
F = Fmax
(FSS)
01
+
21
+
02,22,41
+++2ms
+
0ms,…,4ms
+ +
Strong E2 transitionsfor decay of symmetric Q-phonon
Weak E2 transitionsfor decay of ms Q-phonon
Strong M1 transitionsfor decay of ms statesto symmetric states
Signatures of MSS
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Why (e,e´) and (p,p´)?
sensitive to one-phonon components of the wave functions
Study of one- and two-phonon 2+ FSS and MSS with (e,e´) and (p,p´)
test of fundamental phonon character
isoscalar / isovector decomposition
purity of two-phonon states
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Experiments
High resolution required to resolve all 2+ states below 4 MeV
Lateral dispersion matching technique
(e,e´): S-DALINAC, TU Darmstadt
Ee = 70 MeVe = 93° – 165°E = 30 keV (FWHM)
(p,p´):iThemba LABS
Ep = 200 MeVp = 4.5° – 26°E = 35 keV (FWHM)
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Data: Strong Transitions
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Data: Weak Transitions
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Theoretical Calculation
Quasiparticle Phonon Model (QPM) full (up to 3 phonons) pure one- or two-phonon states
Shell Model (SM) 88Sr core / Vlow-k
IBM-2 transition densities from SM U(5) limit to describe dominant transitions
Cross Section DWBA / Love-Franey effective projectile-target interaction for (p,p´)
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One-Phonon FSS and MSS
one-phonon character confirmed
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Wave Functions of One-Phonon FSS and MSS
FSS isoscalar
MSS isovector
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Two-Phonon FSS and MSS
pure two-phonon state ~10% one-phonon
admixtures in MSS two-step contributions ?
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admixture to two-phonon MSS confirmed
pure two-phonon FSS confirmed
Coupled-Channel Analysis
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Summary
two-phonon FSS quite pure
Combined analysis with microscopic models reveals:
dominant one-phonon character of 21 and 23 states+ +
isovector character of one-phonon MSS within the valence shell
quantitatively consistent conclusions after inclusion of two-step processes in (p,p´) cross sections
Study of one- and two-phonon FSS and MSS 2 states in 94Mo with high-resolution (e,e´) and (p,p´) experiments
+
dominant two-phonon character of two-phonon MSS
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Mo94: Theoretical Predictions
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Mo94: Radial Transition Charge Densities
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In n-rich environment (core-collapse supernovae) this reaction path may provide an alternative route for building up the heavy elements and triggering the r process
Possible Role of 9Be in the Production of 12C
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J = 1/2+ State at Threshold
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Lintott Spectrometer
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Si microstrip detector system: 4 modules, each 96 strips with pitch of 650 m
Count rate up to 100 kHz
Energy resolution 1.5x10-4
10 cm
Focal Plane Detector System
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Data
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Final values: Ex = 1.748(6) MeV and = 274(8) keV of J = 1/2+ resonance
– For T9 = 0.1 – 3 K this resonance determines exclusively 4He(,)8Be(n,)9Be chain
– Determined reaction rate differs up to 20% from adopted values
Comparison: 9Be(,n) and 9Be(e,e´)
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NCSM: correct q dependence but difference in magnitude compared to the data (C. Forssén)
B(C1) ≠ B(E1) at photon point k = q violation of Siegert theorem ?
Form Factor of the J = 1/2+ State
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