Moti collettivi in nuclei esotici e a temperatura finita

Transcription

1 Moti collettivi in nuclei esotici e a temperatura finita F. Camera Università di Milano e INFN sezione di Milano OUTLINE Collective Modes in nuclei -Pygmy Dipole resonance (@GSI) - its connection with the radius of neutron skin in nuclei - its connection with EOS - its connection with Nucleosintesys r-process -GDR and Isospin Mixing (@LNL) - its connection with the IAS and superallowed beta decay -Dynamic Dipole (@LNL) - its connection with EOS and N-N cross section inside the nucleus - New Measurement of GQR and PDR-GDR (@LNL) - Detector Developements - AGATA, LaBr 3 :Ce, γ-imaging

2 Moti collettivi in nuclei esotici e a temperatura finita F. Camera Università di Milano e INFN sezione di Milano OUTLINE Collective Modes in nuclei -Pygmy Dipole resonance - its connection with the radius of neutron skin in nuclei - its connection with EOS - its connection with Nucleosintesys r-process -GDR and Isospin Mixing - its connection with the IAS and superallowed beta decay Skip -Dynamic Dipole - its connection with EOS and N-N cross section inside the nucleus - New Measurement of GQR and PDR-GDR - Detector Developements - AGATA, LaBr 3 :Ce, γ-imaging

3 Moti collettivi nei nuclei Isoscalar Giant Monopole Res. Isoscalar Giant Quadrupole Res. Isovector Giant Monopole Res. Isovector Giant Quadrupole Res. Isoscalar Giant Dipole Res. Isovector Giant Dipole Res. Pygmy Giant Dipole Res. They are a coherent superposition of particles-holes excitations They have high collectivity They sample the bulk properties of the nucleus They can exist on a nucleus in its ground state or in its excited state They are excitation states located at E > 10 MeV

4 Moti collettivi nei nuclei Isoscalar Giant Monopole Res. Isoscalar Giant Quadrupole Res. Isovector Giant Monopole Res. Isovector Giant Quadrupole Res. Isoscalar Giant Dipole Res. Isovector Giant Dipole Res. Pygmy Giant Dipole Res. They are a coherent superposition of particles-holes excitations They have high collectivity They sample the bulk properties of the nucleus They can exist on a nucleus in its ground state or in its excited state They are excitation states located at E > 10 MeV

5 Inelastic Scattering Reactions Inelastic Scattering 20 MeV/u Relativistic Coulomb excitation (v/c ~ 0.8) Excitation γ

6 two Phonon couplings GDR

7 High resolution γ-spectroscopy at the FRS of GSI 68 Ni beam by fragmentation of MeV/u on Be target (4g/cm 2 ): ppspill 86 Kr, Spill length 6s,period 10 s FRS provides secondary radioactive ion beams Calorimeter Telescope for beam identification CATE Position sensitive 2g/cm 2 Au

8 γ-rays spectrum of BaF 2 detectors an excess yield due to beam emission dσ/de [mb/m 1 68 Ni@600 MeV/u GDR PDR Total PDR 5% GDR E γ [MeV] O. Wieland et al., PRL102(2009) Statistical emission of γ-rays from : target nuclei ( 197 Au) beam nuclei ( 68 Ni) folded with Response Function including Doppler correction! Pygmy in 68 Ni at 11 MeV Width 2 MeV mainly due to Doppler Broadening 5 (±1.5) % of the EWSR B(E1) = 1.2 e 2 fm 2

9 Associated EOS quantities Nuclear matter EOS Symmetric matter EOS Symmetry energy S The density dependence of the symmetry energy is poorly constrained and one would like to know the key parameters L slope parameter of the Eρ 0 = saturation density sym L slope parameter K sym curvature parameter at saturation density E(ρ,δ) = E 0 (ρ,δ=0) + S(ρ)δ 2 + o(δ 2 ) δ = (ρ n - ρ p )/ (ρ n + ρ p ) S(ρ) = J +L/3 (ρ- ρ 0 )/ ρ 0 + K sym ((ρ- ρ 0 )/ ρ 0 ) 2 +. Expansion around density

10 A. Carbone et al. In print on PRC rap. comm. Constraint on J, L and the neutron radius for 208 Pb Exp. values from O. Wieland et al., PRL 102, (2009); A. Klimkiewicz et al., PRC 76, (R) (2007). We deduce the weighted average for L then, J and finally R n -R p under that constraint MeV R n -R p = / fm for 208 Pb R n -R p = / fm for 132 Sn R n -R p = / fm for 68 Ni

11 Comparison with other ways of constraining L The L value extracted from the PDR - is consistent in 68 Ni and 132 Sn - is compatible with those extracted from analysis of heavy-ions collisions

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13 Fusion-Evaporation reactions Pre-equilibrium Emission - if E beam > MeV/u part. emission - if N/Z target N/Z projectile Dynamical Dipole γ-rays emission GDR statisticalγ-decay - Nuclear Shape and Deformation at high Temperature and Spin INFN Legnaro Laboratories PHOSWICH 16 O Sn = 132 Ce E beam (8,12,15 MeV/u) 64 Ni+ 68 Zn = 132 Ce 40 Ca + 40 Ca 80 Zr* E * = 83 MeV 37 Cl + 44 Ca 81 Rb* E * = 83 MeV Exclusive measurements - Measurement of γ-rays - Measurement of LCP - Measurement of Residues

14 Theoretically one need: -nuclei and parameters of the reaction -nuclear EOS as function of ρ (Asy-Stiff /Soft) -N-N in medium cross section (Li and Machleidt)

15 132 Sn+ 58 Ni (D=45 fm) BNV calculations V.Baran et al., PRC 79, (2009) Theoretically one need: -nuclei and parameters of the reaction -nuclear EOS as function of ρ (Asy-Stiff /Soft) -N-N in medium cross section (Li and Machleidt)

16 New Data on 16 O Sn E beam (8,12,15 MeV/u) D.Pierroutsakou et al., PRC 80, (2009) (MeV/u) (MeV/u) A. Corsi et al. PLB 679 (2009)

17 Isospin mixing induced by Coulomb interaction E* Isospin symmetry in nuclei is broken by Coulomb interaction V c which mixes states with T and T+1 (T+2,...) almost good quantum number nuclear reactions which involve low-lying states NOT Conserved Moderate excitation energy almost good quantum number fusion-evaporation reactions (E * >20 MeV) The α 2 coefficient quantifies the degree of isospin mixing The CN might decay before isospin mixes. For E* > 0 isospin-breaking Properties of proton rich nuclei (i.e. Coulomb Energy Differences) Superallowed nuclear beta decays H.L. Harney et al rev. Mod. Phys. 58(1986)607 - M.N. Harakeh et al. Phys. Lett. B 176(1986)297 - A.Behr et al. Phys. Rev. Lett. 70(1993)3201 Sagawaet al Physics Letters B Satula et al PRL 103, (2009)

18 We form a T=0 Compound Nucleus with a heavy ions fusion reaction 40 Ca + 40 Ca 80 Zr* E * = 83 MeV We form a T 0 Compound Nucleus with a heavy ions fusion reaction 37 Cl + 44 Ca 81 Rb* E * = 83 MeV We measure the γ-rays yield from the decay of the GDR built on the CN We measure the γ-rays yield from the decay of the GDR built on the CN T=0 T=0 E1 Transition are forbidden T=0 T=1 E1 Transition are allowed T=1 T=0 E1 Transition are allowed T 0 T E1 Transition are allowed Few T=1 states If α 2 > 0 Kicinska-Habior et al. NPA 731, 138 (2004) This results in a strong inhibition of the GDR γ-decay from the hot 80 Zr compound Isospin mixing, as mix T=0 states with T=1 states T 0 CN increases the GDR γ yield T=0 CN Isospin effect

19 Statistical Model Analysis The set of parameters giving the best fit has been determined with χ 2 test: 1) Fit of GDR parameters on 81 Rb γ-ray spectrum using Γ =0 S=90%, E GDR =16.2 MeV, Γ=10.6 MeV 2) Using GDR parameters of 1), fit of Γ on 80 Zr spectrum Γ =0.012±0.04 MeV corresponding to α <2 = 5±1.5% 37 Cl + 44 Ca 81 Rb* E * = 83 MeV 40 Ca + 40 Ca 80 Zr* E * = 83 MeV

20 Isospin mixing dependence on Z and Temperature Satula et al., PRL 103, (2009) Γ =0.012±0.04 MeV corresponding to α <2 = 5±1.5% Sagawa et al., PLB 444, 1 (1998)

21 Inelastic Scattering at 20 MeV/u beam energy (Legnaro Laboratories) AGATA Demonstrator Scintillator array Large volume LaBr 3 :Ce E- E Telescopes from the TRACE project Scintillator array Large volume BaF 2

22 Inelastic Scattering at 20 MeV/n beam energy (Legnaro Laboratories) AGATA Demonstrator Scintillator array Large volume LaBr 3 :Ce E- E Telescopes from the TRACE project Scintillator array Large volume BaF 2

23 Pygmy Dipole Resonance Giant Quadrupole Resonance Branching ratios Different population with (γ,γ ), (α,α γ) Fine structure g.s Zr Pb 3 - D. Savran et al., PRL97(2006) Shevchenko PRL93(2004) J. Beene et al PRC39(1989)

24 Detectors Arrays Measurement of high Energy γ-rays 5-20 MeV the γ-decay from collective states The source of radiation moves at v/c Huge Doppler Broadening effect Huge background We are using radioactive beams they have intensity of 10 5 pps High Full Energy Peak Efficiency Good Peak to Background ratio Good Energy Resolution Good Time Resolution Position Sensitivity (γ-imaging) - Doppler Broadening Correction Detector 10 cm D = 20 cm 1 MeV γ-rays source v/c = 0.1 FWHM (60 ) 30 kev 1 MeV γ-rays source v/c = 0.5 FWHM (60 ) = 160 kev

25 Detectors Arrays HPGe detectors AGATA (Eu), GRETA (Usa) Array of Segmented HPGe Detectors Segmentation and PSA provide Tracking/Imaging Position resolution 5 mm

26 A. Gadea et al in print on NIMA E. Farnea et al in print on NIMA Now in Legnaro

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29 Detectors Arrays New Generation Scintillators i.e. LaBr3:Ce HECTOR+ (It), SHOGUN (Jp), PARIS (Fr) Large volume LaBr 3 :Ce Good Energy Resolution High efficiency Excellent time resolution R&D on imaging properties and PSA Guillot-Noël, O. (1999). et al. J. Lumin., 85, 21. Van Loef, E. V. D. (2001). et al. Appl. Phys. Lett., 79, 1574.

30 LaBr 3 :Ce Scintillators L.Y. 63 ph/kev Decay Time 16 ns λ 380 nm N 1.9 ρ = 5.3 g/cm 3 RL (661 kev) 1.9 cm Co NaI BaF 2 LaBr Energy (kev) FWHM 540 ps R. Nicolini et al NIMA 582 (2007) F. C.L.Crespi et al NIMA 602 (2009)

31 Blasi, N. et al (2009). IEEE Nucl. Sci. Sym. Conference Record N F. Qurati et al submitted to NIM A 3.5 x 8 LaBr 3 :Ce Response to High Energy γ-rays Normal Phototubes Segmented Phototubes Position Sensitive light Sensor SiPMT or d-sipmt Silicon Drift Detectors

32 662 kev collimated beam 1 x 1 LaBr3:Ce crystal + H8500C-100 Mod 8 phototube PSF Image - 3 x 3 LaBr3:Ce crystal PSF Charge Simulations - Birocchi, F. et al. (2009). IEEE Nucl. Sci. Sym. Conference Record, N Marone, A. et al.(2009) IEEE Nucl. Sci. Sym. Conference Record, N

33 Conclusions: Collective Modes in exotic nuclei and at high temperature Tool for the study of Nuclear Structure and Dinamics Tool for the extract informations on EOS, N-N cross sections inside the nucleus Neutron Capture rate for Stellar Nucleosyntesis Radius of neutron skin in nuclei - Detector Developements for high energy γ-rays AGATA Demonstrator LaBr 3 :Ce γ-imaging

34 Many Thanks to: HECTOR Collaboration GARFIELD Collaboration AGATA Collaboration RISING/PRESPEC Collaboration

35 Moti collettivi in nuclei esotici e a temperatura finita F. Camera Università di Milano e INFN sezione di Milano The study of the collective properties of the nucleus are a powerful tool > to understand the structure which lays inside the nucleus. > A successful technique which has been used in this field is the > measurement of the gamma decay of highly collective state like the Giant > Dipole Resonance (GDR) and Giant Quadrupole Resonance (GQR). Depending on > the used experimental technique, GDR and GQR states con be excited either > on the nuclear ground state or on an excited state (both p-h state or > compound nucleus) and, because of the extremely high collectivity, the > energy of gamma-rays emitted ranges between 5 to 30 MeV. > Using GDR and GQR it was possible to measure nuclear properties along the > three different degrees of freedom, namely excitation energy, angular > momentum and Isospin. > In the first two cases fusion-evaporation reactions have been used. The > measurement of the isospin dependence of the nuclear properties is now > possible through the use of radioactive beams and a new generation of HPGe > and scintillators detector arrays. >>From the analysis of these data it was shown that it is possible to > extract fundamental observables like the thickness of neutron skin in > neutron rich nuclei and the slope parameter L of the symmetry energy. > A review of experimental results and of the newly developed experimental > arrays used in this research field will be presented.

36 Why the Pygmy Resonance is important? There is an extrapolation of 18 orders of magnitude from the neutron radius of a nucleus (from 5-6 fm to 10 km radius) of a neutron star. Yet both radii depend on the knowledge of equation of state of neutron rich matter exp Relative Abundance pygmy Theory A Pygmy Resonance has an important impact on the r-process nucleosynthesis

37 Features of this mode There is a trend of the strength to increase with the proton-toneutron asymmetry 40 Ca 0.025% EWSR 48 Ca 0.29% EWSR Stable nuclei photon scattering,photoabsorption (γ,γ ),(γ,n) T. Hartmann PRL85(2000) Sn 132 Sn 4% EWSR Exotic nuclei Virtual photon breakup LAND experiment Adrich et al. PRL 95(2005)132501

38 Search for pygmy strength in 68 Ni Different approaches give similar predictions in terms of collectivity, strength and line-shape of the pygmy resonance n excess vs inert core : oscillation of the neutron skin Theoretical predictions RMF ~10 MeV 7% 68 Ni mb ~10 MeV 3-8% 68 Ni RPA D. Vretnar et al. NPA 692(2001)496 G. Colo private communications Energy (MeV) + J. Liang et al., PRC75(2007) frpa: 7-8%:

39 Virtual photon scattering technique Peripheral heavy-ion collision on a high Z target at relativistic energies Virtual photon excitation and decay 197 Au( 68 Ni, 68 Ni*+γ) 197 Au Relativistic Coulomb excitation (v/c ~ 0.8%) θ < θ max 200 Virtual Photon spectrum E1 Virtual photon γ emission a.u b > b min 50 dσ C de * 1 πλ = N ( E*) E * πλ γ σ γ πλ ( E*) E 0 max = βγ c b min E* (kev) E max

40 Virtual photon scattering technique High selectivity for dipole excitation!! 600 MeV/u 68 Ni Au (high statistics) 400 MeV/u 68 Ni Au (small statistics) Virtual photon excitation and decay of GDR - PYGMY σ ( GDR) σ ( GQR) 16 O+ 208 Pb 20 Coulex maximum excitation energy (adiabatic cut off) ca. E*max=18.5 MeV γ GDR Ground state decay branching ratio ~ 2% measured on 208 Pb T.Aumann et al EPJ 26(2005)441 At relativistic energies σ for GR Coul-ex > nuclear geometrical σ! [Beene et al PRC 41(1990)920]

41 Dynamical Dipole angular distribution 1 W ( θ ) = 1 4 with x = cos ( ϑ + ϑ ) f + i 3 4 x sin( θ ϑ ) i i 3 2 θ ϑ cos( ϑ) a 2 f f O 116 Sn θ Z 16 O(@ 8 MeV/u) Sn, b=4 fm/c with BNV simulation and asy stiff EOS: angular distributions Z DD integratedemission probability Rotation (θ) of DD axis DD angulardistribution A.Corsi PHD thesis

42 How we measure Isospin mixing We form a T=0 Compound Nucleus with a heavy ions fusion reaction 40 Ca + 40 Ca 80 Zr* E * = 83 MeV We measure the γ-ray yield from the decay of the GDR built on the CN T = 0 to T = 0 E1 Transition are forbidden T = 0 to T = 1 E1 transition are allowed but there are much less T=1 state available to be populated by GDR decay in respect to T = 0 states ρ(t=1,e * ) = ρ(t=0,(e* - E IAS ) ) This results in a strong inhibition of the GDR γ-decay from the hot 80 Zr compound Isospin mixing, as mix T=0 states with T=1 states,will increase the GDR γ yield Two extreme scenarios No Mixing a 2 < = 0 strong inhibition of the gamma decay channel Full Mixing a 2 < = 1/2 No inhibition of the gamma decay channel

43 Isospin mixing induced by Coulomb interaction Fermi superallowed β-decay provides constraints to the properties of electroweak interaction once correction to Fermi matrix elements are taken into account M F 2 = M F0 2 (1-δ c -δ r ) δ c takes into account isospin symmetry breaking between parent and daughter states Finustar3, Rhodes, August 2010 Anna Corsi, Universita degli Studi & INFN Milano 43/18

44 Isospin mixing induced by Coulomb interaction neutron decay and spreading width of IAS T 1/ 2, T0 0 3/ 2 IAS = T T 0, 0 1 T0 3/ 2, T0 3/ 2 T0 1/ 2, T0 1/ 2 IAS acquires a T=T 0-1 component (from which n decay is allowed) and a spreading width through Coulomb interaction Finustar3, Rhodes, August 2010 Anna Corsi, Universita degli Studi & INFN Milano 44/18

45 Moti collettivi nei nuclei Some of them decay through the emission of high energy gamma rays They sample the bulk properties of the nucleus They provide information on the structure of the inital and final state - Isospin Mixing - Isoscalar Giant Quadrupole Res. Isovector Giant Quadrupole Res. Isovector Giant Dipole Res. Pygmy Giant Dipole Res.

46 Isospin mixing induced by Coulomb interaction Isospin symmetry in nuclei is broken by Coulomb interaction V c which mixes states with T and T+1 (T+2,...) H.L. Harney et al rev. Mod. Phys. 58(1986)607 - M.N. Harakeh et al. Phys. Lett. B 176(1986)297 - A.Behr et al. Phys. Rev. Lett. 70 Sagawaet al Physics Letters B Satula et al PRL 103, (2009) almost good quantum number nuclear reactions which involve low-lying states. NOT Conserved moderate excitation energy almost good quantum number fusion-evaporation reactions (E * >20 MeV) The α 2 coefficient quantifies the degree of isospin mixing No Mixing a 2 < = 0 Full Mixing a 2 < = 1/2 the CN might decay before isospin mixes the degree of isospin mixing of CN state is an interplay between the compound nucleus Decay Width Γ and the Coulomb or IAS Spreading Width Γ