Nuclei at large distance t unneling effects
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Transcript of Nuclei at large distance t unneling effects
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Neutron transfer reactions at large internuclear distances studied with the PRISMA spectrometer
and the AGATA demonstrator
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Nuclei at large distancetunneling effects
Relative role of one- and multi-nucleon transfer channels
Overlap between transfer and fusion reactions
successive
direct
Sub-barrier transfer reactions
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Sub-barrier transfer reactions
Angular distributions are backward peaked
Cross sections are very small (need for high efficiency)
Difficult identification of reactionproducts in A, Z and Q-values
Experimental difficulties
in direct kinematics projectile-like particles have low kinetic energy
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PRISMA
beam direction
20o 96Zr 40Ca
Prisma acceptance
Reaction in inverse kinematics with PRISMA
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Laboratori Nazionali di Legnaro – INFN (Italy)
g-array
PRISMA
The PRISMA magnetic spectrometer
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Optics:• quadrupole magnet• dipole magnet
Detectors:• entrance detector (MCP)• focal plane detector (MWPPAC)• ionization chamber (IC)
The PRISMA magnetic spectrometer
D. Montanari et al., Eur. Phys. J. A (2011) 47
D. Montanari et al., Phys. Rev. C 84, 054613 (2011)
S. Szilner et al, Phys. Rev. C 76, 024604 (2007)
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Enhancement needed for two particle transfer
probabilities R. Künkel et al., Z. Phys. 336(1990)336
Sub-barrier transfer reactions
Neglecting correlations (successive transfer):
P(2) = P(1)*P(1)
P(3) = P(1)*P(1)*P(1)
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P2n ~ 3 (P1n)2
P3n ~ P2n P1n
P4n ~ (P2n)2
L. Corradi, FUSION11, St. Malo – France
P1n
slopes in nice agreement with those expected from the binding energies
Previous experiment - 96Zr+40Ca
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Previous experiment - 96Zr+40Ca
+1n well reproduced by theory in slope and absolute value
Same slope of +2n between theory and experiment
L. Corradi et al., Phys. Rev. C 84, 034603 (2011)
Experiment vs
microscopic calculation
+2n enhancement due to the presence of other excited
states?
Absorption reproduced by theory
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The experiment – 60Ni +116Sn
+1n +2n +3n +4n
96Zr + 40Ca + 0.51 + 5.53 + 5.24 + 9.64
116Sn + 60Ni - 1.74 + 1.31 - 2.15 - 0.24
Ground state Q-values
Closed-shell
Superfluid
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Direct kinematics
Angular distributionsqlab = 50° and 70°
(D ≈ 14.5 fm and 16.7 fm)
The experiment – 60Ni +116Sn
Inverse kinematics
Excitation functionEbeam = 410 – 500 MeV (qlab
= 20°)(D ≈ 12.3 to 15.0 fm)
+1n +2n +3n +4n
96Zr + 40Ca + 0.51 + 5.53 + 5.24 + 9.64
116Sn + 60Ni - 1.74 + 1.31 - 2.15 - 0.24
Ground state Q-values
PRISMA + AGATA PRISMA only
Gamma-rays used to estimate the population of
excited states
Closed-shell
Superfluid
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Direct kinematics Inverse kinematics
The experiment – 60Ni +116SnPRISMA + AGATA PRISMA only
RV [a. u.]
Energy [a.u.]
A/q [a.u.
]
X-ppac [a.u.]
Angular distributionsqlab = 50° and 70°
(D ≈ 14.5 fm and 16.7 fm)
Excitation functionEbeam = 410 – 500 MeV (qlab
= 20°)(D ≈ 12.3 to 15.0 fm)
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Qvalues for 96Zr+ 40Ca
The experiment – 60Ni +116SnQvalues for 116Sn + 60Ni
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Slopes for 116Sn + 60Ni
The experiment – 116Sn + 60Ni
PRELIMINARY
+1n and +2n slopes are in agreement with those expected from binding
energies
Preliminary dataData under analysis
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Conclusions•We performed sub-barrier transfer reactions in direct and inverse
kinematics for a superfluid system (previously with closed-shell system)
•Possibility offered by the g-array to estimate the population of excited
states in reaction products
Analysis for both direct and inverse kinematics is in progress
Future goals
- More systematics, e.g. nuclei of different structure- Studying n-p correlations
[experiment proposed and approved at the LNL – INFN (Italy)]
Next steps
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The end
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Grazing code calculations
Probing nucleon-nucleon correlations via transfer of (nn), (pp) and (np) pairs at sub-barrier energies in 92Mo+54Fe PRISMA
S.Szilner, L.Corradi, G.Pollarolo et al, May 2012 LNL PAC Proposal (approved)
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Two particle transfer (semiclassical theory, microscopic calculations)
only the successive term contributes to the transfer amplitude
3 terms : simultaneous, orthogonal and successive
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One particle transfer (semiclassical theory)
to obtain the total transfer probability we summed over all possible transitions that can be constructed from the single particle states in projectile and target
the set of single particle states covers a full shell below the Fermi level for 96Zr and a full shell above for 40Ca
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Light ions (Q3D) Heavy ions spectrometers Tracking spectrometers
single particle levels (shell model)nucleon-nucleon correlations (pair transfer)
A,Z yieldscross sectionsQ-value distributions
Reaction mechanismGamma spectroscopy
3-5 msr 5-10 msr 80-100 msr
70’s 80’s - 90’s recent years
Magnetic spectrometers for transfer reaction studies
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