Structure effects and dynamics in fusion reactions of light weakly - PowerPoint PPT Presentation

Structure effects and dynamics in fusion reactions of light weakly bound nuclei Emanuele Strano Emanuele Strano for a for a RBI Zagreb RBI Zagreb collaboration collaboration

Reaction mechanisms around the Coulomb barrier in collisions Reaction mechanisms around the Coulomb barrier in collisions induced by weakly bound nuclei induced by weakly bound nuclei Projectile: Projectile: � Low break-up threshold � Low break-up threshold � Cluster structure � Cluster structure � Diffused mass distribution � Diffused mass distribution Projectile effects on reaction mechanisms: Projectile effects on reaction mechanisms: � Direct channels (transfer, breakup) may be favored � Direct channels (transfer, breakup) may be favored � Fusion effects � Fusion effects � Static effects � Static effects Diffused mass distribution Diffused mass distribution � � � � � � � � Low coulomb barrier Low coulomb barrier � � � � � � � � fusion cross section increase fusion cross section increase � Dynamical effects on fusion and other channels � Dynamical effects on fusion and other channels Strong coupling with the break-up channel Strong coupling with the break-up channel � � � � � � � � fusion cross section reduction / enhancement? fusion cross section reduction / enhancement? � Effects on optical model potential � Effects on optical model potential

Break-up effects on fusion with weakly bound nuclei Break-up effects on fusion with weakly bound nuclei Heavy targets Heavy targets enhancement at sub barrier energies enhancement at sub barrier energies suppression above the barrier suppression above the barrier light targets light targets No effects above the barrier No effects above the barrier (no data below the barrier) (no data below the barrier) Medium targets Medium targets no effects above the barrier? no effects above the barrier? enhancement at sub barrier energies? enhancement at sub barrier energies? Universal fusion function Universal fusion function L.F. Canto et al L.F. Canto et al Nucl.Phys. A 821 (2009) 51 Nucl.Phys. A 821 (2009) 51 E → x = E − V B � ω 2 E ren σ F → F ( x ) = 2 σ F � ω R B Universal fusion function Universal fusion function �� P.R.S. Gomez et al Phys.Rev. C 79, 027606 (2009) P.R.S. Gomez et al Phys.Rev. C 79, 027606 (2009)

Goal of present experiment: study of 6,7 Li+ 64 Zn collisions Goal of present experiment: study of 6,7 Li+ 64 Zn collisions 6 Li S α α =1.4 MeV no bound excited states 6 Li S α α =1.4 MeV no bound excited states α α α α 7 Li S α α =2.5 MeV first excited state at ∼ ∼ ∼ ∼ 0.5 MeV 7 Li S α α =2.5 MeV first excited state at ∼ ∼ ∼ ∼ 0.5 MeV α α α α 6,7 Li+ 59 Co Wrong fusion cross section? Wrong fusion cross section? Effects of different structure in 6,7 Li? Effects of different structure in 6,7 Li? P.R.S. Gomez et al P.R.S. Gomez et al C.Beck et al Phys.Rev.C67,054602,(2003) C.Beck et al Phys.Rev.C67,054602,(2003) Phys.Rev. C 71, 034608 (2003) Phys.Rev. C 71, 034608 (2003)

Further information on the 6,7 Li+ 64 Zn collisions Further information on the 6,7 Li+ 64 Zn collisions � Elastic scattering angular distributions � Elastic scattering angular distributions � Optical potential energy dependance � Optical potential energy dependance � Total reaction cross section � Total reaction cross section � Total fusion excitation functions � Total fusion excitation functions Experiment status Experiment status � Analized data for 6 Li+ 64 Zn collision � Analized data for 6 Li+ 64 Zn collision � Data for 7 Li+ 64 Zn collision not yet analyzed � Data for 7 Li+ 64 Zn collision not yet analyzed

Fusion cross section: experimental method Fusion cross section: experimental method Low energies � threshold problems for E.R. detection Low energies � threshold problems for E.R. detection Target + catcher Elab Activation technique: Activation technique: [MeV] tickness [ µ g/cm2] 9 200 (Zn) + 560 (Au) 11 240 (Zn) + 560(Au) 13 250 (Zn) + 550 (Au) 17.5 620 (Zn) + 680 (Nb) 20 580 (Zn) + 700 (Nb) 24 550 (Zn) + 680 (Nb)

Fusion cross section: energy spectra and activity Fusion cross section: energy spectra and activity Counts Counts Counts Counts Zn Ga Ge Zn Ga Ge Zn Ga Ge Zn Ga Ge Ex [channels] Ex [channels] Ex [channels] Ex [channels] Counts Zn Ga Ge Z identification by X-ray energy Z identification by X-ray energy A identification by half-life of father nucleus A identification by half-life of father nucleus Ex [channels]

Total fusion cross section: element production yield Total fusion cross section: element production yield � Beam current profile � Beam current profile Example � Intrinsic and geometric � Intrinsic and geometric X-ray Si(Li) detector X-ray Si(Li) detector Elab = 24 MeV � Activity analisys � Activity analisys � Target thickness � Target thickness � K α fluorescence � K α fluorescence Probability Probability � � Single element Single element � production cross section � production cross section

Fusion and total reaction cross sections Fusion and total reaction cross sections Measured Fusion cross sections larger than existing data Measured Fusion cross sections larger than existing data ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ Detection threshold problem in existing data Detection threshold problem in existing data

Effects on Threshold anomaly Effects on Threshold anomaly ‘ ‘Normal Normal’ ’ well bound Nuclei: well bound Nuclei: ‘Normal’ well bound Nuclei: Weakly bound Nuclei: is “ “usual usual” ” Weakly bound Nuclei: is “usual” “usual “ usual” ” threshold anomaly threshold anomaly “usual” threshold anomaly threshold anomaly still present? threshold anomaly still present? threshold anomaly still present? 6 Li+ 27 Al Example from: J. M. Figueira Example from: J. M. Figueira Example from: G.R.Satchler Example from: G.R.Satchler Phys.Rev. C73,054603,(2006) Phys.Rev. C73,054603,(2006) Phys.Rep. 199(1991)147 Phys.Rep. 199(1991)147 break-up threshold anomaly ? break-up threshold anomaly ?

Elastic scattering angular distributions Elastic scattering angular distributions Low bombarding energy: difficult task Low bombarding energy: difficult task � Need to measure at very backward angles � Need to measure at very backward angles � high statistics � high statistics � Particular attention to normalization � Particular attention to normalization � Avoid sistematic and alignment errors � average between left and right � Avoid sistematic and alignment errors � average between left and right � Target: 400 � g/cm 2 thick 64 Zn foil tilted 45° � Target: 400 � g/cm 2 thick 64 Zn foil tilted 45° � 5 Telescopes: 10- µ � 5 Telescopes: 10- µ µ m-thick ∆ µ µ ∆ E detector followed by a 200- µ ∆ ∆ µ m-thick E detector µ µ µ m-thick ∆ µ µ ∆ ∆ E detector followed by a 200- µ ∆ µ m-thick E detector µ µ � E lab = 12 ÷ 22 MeV � E lab = 12 ÷ 22 MeV � 25° ≤ θ θ lab ≤ 170° � 25° ≤ θ θ lab ≤ 170° θ θ θ θ

Elastic scattering angular distributions: analysis and results Elastic scattering angular distributions: analysis and results Optical model fits assuming: Optical model fits assuming: � Double folding potential for both real and � Double folding potential for both real and imaginary part imaginary part � Double folding real potential and � Double folding real potential and Woods-Saxon imaginary potential Woods-Saxon imaginary potential Angular distributions Angular distributions Optical Model fits with different potentials performed on elastic scattering Optical Model fits with different potentials performed on elastic scattering angular distributions around the Coulomb Barrier (VC ∼ ∼ ∼ 13 MeV) ∼ angular distributions around the Coulomb Barrier (VC ∼ ∼ ∼ 13 MeV) ∼ Result: absence of usual threshold anomaly Result: absence of usual threshold anomaly M.Zadro et al., Phys. Rev. C80,064610,(2009) M.Zadro et al., Phys. Rev. C80,064610,(2009)

Fusion and total reaction cross sections Fusion and total reaction cross sections Measured Total Reaction cross sections in agreement with existing data Measured Total Reaction cross sections in agreement with existing data

Fusion and total reaction cross sections Fusion and total reaction cross sections Differences between measured Fusion cross sections and Differences between measured Fusion cross sections and measured Total Reaction cross sections measured Total Reaction cross sections Measured Total Reaction cross sections in agreement with existing data Measured Total Reaction cross sections in agreement with existing data ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ Larger break-up contribution at energies below the coulomb barrier Larger break-up contribution at energies below the coulomb barrier Lower break-up cross section with respect to existing data Lower break-up cross section with respect to existing data