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

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Sep 17, 2023 122 likes •322 views

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

SLIDE 1

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

RBI Zagreb RBI Zagreb

collaboration collaboration

SLIDE 2

Reaction mechanisms around the Coulomb barrier in collisions induced by weakly bound nuclei Reaction mechanisms around the Coulomb barrier in collisions induced by weakly bound nuclei Projectile effects on reaction mechanisms: Direct channels (transfer, breakup) may be favored Fusion effects Static effects Diffused mass distribution

Low coulomb barrier
fusion cross section increase

Dynamical effects on fusion and other channels

Strong coupling with the break-up channel

fusion cross section reduction / enhancement?

Effects on optical model potential Projectile effects on reaction mechanisms: Direct channels (transfer, breakup) may be favored Fusion effects Static effects Diffused mass distribution

Low coulomb barrier
fusion cross section increase

Dynamical effects on fusion and other channels

Strong coupling with the break-up channel

fusion cross section reduction / enhancement?

Effects on optical model potential Projectile: Low break-up threshold Cluster structure Diffused mass distribution Projectile: Low break-up threshold Cluster structure Diffused mass distribution

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Break-up effects on fusion with weakly bound nuclei Break-up effects on fusion with weakly bound nuclei

Universal fusion function P.R.S. Gomez et al Phys.Rev. C 79, 027606 (2009) Universal fusion function P.R.S. Gomez et al Phys.Rev. C 79, 027606 (2009) Heavy targets enhancement at sub barrier energies suppression above the barrier light targets No effects above the barrier (no data below the barrier) Medium targets no effects above the barrier? enhancement at sub barrier energies? Heavy targets enhancement at sub barrier energies suppression above the barrier light targets No effects above the barrier (no data below the barrier) Medium targets no effects above the barrier? enhancement at sub barrier energies?

E → x = E −VB

ω σ F → F(x) = 2E ωRB

2 σ F ren

Universal fusion function L.F. Canto et al Nucl.Phys. A 821 (2009) 51 Universal fusion function L.F. Canto et al Nucl.Phys. A 821 (2009) 51

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Goal of present experiment: study of 6,7Li+64Zn collisions Goal of present experiment: study of 6,7Li+64Zn collisions

Wrong fusion cross section? P.R.S. Gomez et al Phys.Rev. C 71, 034608 (2003) Wrong fusion cross section? P.R.S. Gomez et al Phys.Rev. C 71, 034608 (2003) Effects of different structure in 6,7 Li? C.Beck et al Phys.Rev.C67,054602,(2003) Effects of different structure in 6,7 Li? C.Beck et al Phys.Rev.C67,054602,(2003)

6,7Li+59Co 6Li Sα α α α=1.4 MeV no bound excited states 7Li Sα α α α=2.5 MeV first excited state at ∼

∼ ∼ ∼ 0.5 MeV

6Li Sα α α α=1.4 MeV no bound excited states 7Li Sα α α α=2.5 MeV first excited state at ∼

∼ ∼ ∼ 0.5 MeV

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Elastic scattering angular distributions Optical potential energy dependance Total reaction cross section Total fusion excitation functions Elastic scattering angular distributions Optical potential energy dependance Total reaction cross section Total fusion excitation functions

Further information on the 6,7Li+64Zn collisions Further information on the 6,7Li+64Zn collisions

Analized data for 6Li+64Zn collision Data for 7Li+64Zn collision not yet analyzed Analized data for 6Li+64Zn collision Data for 7Li+64Zn collision not yet analyzed

Experiment status Experiment status

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Fusion cross section: experimental method Fusion cross section: experimental method

Low energies threshold problems for E.R. detection Activation technique: Low energies threshold problems for E.R. detection Activation technique:

550 (Zn) + 680 (Nb) 24 580 (Zn) + 700 (Nb) 20 620 (Zn) + 680 (Nb) 17.5 250 (Zn) + 550 (Au) 13 240 (Zn) + 560(Au) 11 200 (Zn) + 560 (Au) 9 Target + catcher tickness [µg/cm2] Elab [MeV]

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Fusion cross section: energy spectra and activity Fusion cross section: energy spectra and activity

Zn Ga Ge Zn Ga Ge Zn Ga Ge Zn Ga Ge Zn Ga Ge Counts Counts Counts Counts Counts Ex [channels] Ex [channels] Ex [channels] Ex [channels] Ex [channels]

Z identification by X-ray energy A identification by half-life of father nucleus Z identification by X-ray energy A identification by half-life of father nucleus

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Total fusion cross section: element production yield Total fusion cross section: element production yield

Elab = 24 MeV

Beam current profile Intrinsic and geometric X-ray Si(Li) detector Activity analisys Target thickness Kα fluorescence Probability

Single element

production cross section Beam current profile Intrinsic and geometric X-ray Si(Li) detector Activity analisys Target thickness Kα fluorescence Probability

Single element

production cross section

Example

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

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Effects on Threshold anomaly Effects on Threshold anomaly

Example from: G.R.Satchler Phys.Rep. 199(1991)147 Example from: G.R.Satchler Phys.Rep. 199(1991)147 Example from: J. M. Figueira Phys.Rev. C73,054603,(2006) Example from: J. M. Figueira Phys.Rev. C73,054603,(2006)

6Li+27Al

‘Normal’ well bound Nuclei: “usual” threshold anomaly ‘ ‘Normal Normal’ ’ well bound Nuclei: well bound Nuclei: “ “usual usual” ” threshold anomaly threshold anomaly Weakly bound Nuclei: is “usual” threshold anomaly still present? Weakly bound Nuclei: is “ “usual usual” ” threshold anomaly still present? threshold anomaly still present? break-up threshold anomaly ? break-up threshold anomaly ?

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Elastic scattering angular distributions Elastic scattering angular distributions Low bombarding energy: difficult task Need to measure at very backward angles high statistics Particular attention to normalization Avoid sistematic and alignment errors average between left and right Low bombarding energy: difficult task Need to measure at very backward angles high statistics Particular attention to normalization Avoid sistematic and alignment errors average between left and right Target: 400 g/cm2 thick 64Zn foil tilted 45° 5 Telescopes: 10-µ µ µ µm-thick ∆ ∆ ∆ ∆E detector followed by a 200-µ µ µ µm-thick E detector Elab = 12 ÷ 22 MeV 25° ≤ θ θ θ θlab ≤ 170° Target: 400 g/cm2 thick 64Zn foil tilted 45° 5 Telescopes: 10-µ µ µ µm-thick ∆ ∆ ∆ ∆E detector followed by a 200-µ µ µ µm-thick E detector Elab = 12 ÷ 22 MeV 25° ≤ θ θ θ θlab ≤ 170°

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

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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

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

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Summary and conclusions Summary and conclusions Total fusion

Measured the activity of the products in the collision 6Li+64Zn
Extracted the total fusion cross section
Confirmed the problem in previous data
Increasing EBU contribution at energies below the coulomb barrier

Elastic scattering

Measured the elastic scattering angular distribution
Optical model fit on angular distribution
Observed no usual threshold anomaly, break-up threshold anomaly

Future projects

Theoretical calculation on measured data
Analisys of the elastic scattering angular distribution for 7Li+64Zn collision
Analysis of the total fusion cross section for 7Li+64Zn collision
Compare the results with 6Li data

Total fusion

Measured the activity of the products in the collision 6Li+64Zn
Extracted the total fusion cross section
Confirmed the problem in previous data
Increasing EBU contribution at energies below the coulomb barrier

Elastic scattering

Measured the elastic scattering angular distribution
Optical model fit on angular distribution
Observed no usual threshold anomaly, break-up threshold anomaly

Future projects

Theoretical calculation on measured data
Analisys of the elastic scattering angular distribution for 7Li+64Zn collision
Analysis of the total fusion cross section for 7Li+64Zn collision
Compare the results with 6Li data

SLIDE 16

Collaboration Collaboration

RBI Zagreb RBI Zagreb

Thanks for your attention! Thanks for your attention!

E.Strano, A.DiPietro, P.Figuer, M.Fisichella, M.Lattuada, C.Maiolino, A.Musumarra, M.G.Pellegriti, D. Santonocito, V.Scuderi, D.Torresi, M.Zadro INFN Laboratori Nazionali del Sud, Catania, Italy Università degli studi di Catania, Catania, Italy Ruñer Boškovic Institute, Zagreb, Croatia

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Elastic scattering angular distributions: ∆ ∆ ∆ ∆E-E matrix Elastic scattering angular distributions: ∆ ∆ ∆ ∆E-E matrix

E [channels] ∆E [channels]

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E → x = E −VB

ω σ F → F(x) = 2E ωRB

2 σ F ren

σ F

ren = σ F

F0(x) F

CC(x)

F0(x) = ln 1+ exp(2π ⋅ x)

[ ]

Barrier Height Barrier Height Barrier Curvature Barrier Curvature Barrier Radius Barrier Radius Wong’s cross section Wong’s cross section Coupling to other “not break-up” channels Coupling to other “not break-up” channels