Neutron transfer reactions at large internuclear distances studied with the PRISMA spectrometer and the AGATA demonstrator

Nuclei at large distance tunneling effects Relative role of one- and multi-nucleon transfer channels Overlap between transfer and fusion reactions successive direct Sub-barrier transfer reactions

Angular distributions are backward peaked Cross sections are very small (need for high efficiency) Difficult identification of reaction products in A, Z and Q-values Experimental difficulties in direct kinematics projectile-like particles have low kinetic energy

PRISMA beam direction 20 o 96 Zr 40 Ca Prisma acceptance Reaction in inverse kinematics with PRISMA

Laboratori Nazionali di Legnaro – INFN (Italy)  -array PRISMA The PRISMA magnetic spectrometer

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, (2011) S. Szilner et al, Phys. Rev. C 76, (2007)

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)

P 2n ~ 3 (P 1n ) 2 P 3n ~ P 2n P 1n P 4n ~ (P 2n ) 2 L. Corradi, FUSION11, St. Malo – France P 1n slopes in nice agreement with those expected from the binding energies Previous experiment - 96 Zr+ 40 Ca

+1n well reproduced by theory in slope and absolute value Same slope of +2n between theory and experiment +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, (2011) Experiment vs microscopic calculation Experiment vs microscopic calculation +2n enhancement due to the presence of other excited states? Absorption reproduced by theory

The experiment – 60 Ni Sn +1n +2n +3n +4n 96 Zr + 40 Ca Sn + 60 Ni Ground state Q-values Closed-shell Superfluid

Direct kinematics Angular distributions  lab = 50° and 70° (D ≈ 14.5 fm and 16.7 fm) The experiment – 60 Ni Sn Inverse kinematics Excitation function E beam = 410 – 500 MeV (  lab = 20°) (D ≈ 12.3 to 15.0 fm) +1n +2n +3n +4n 96 Zr + 40 Ca Sn + 60 Ni Ground state Q-values PRISMA + AGATAPRISMA only Gamma-rays used to estimate the population of excited states Closed-shell Superfluid

Direct kinematics Inverse kinematics The experiment – 60 Ni Sn PRISMA + AGATAPRISMA only RV [a. u.] Energy [a.u.] A/q [a.u.] X-ppac [a.u.] Angular distributions  lab = 50° and 70° (D ≈ 14.5 fm and 16.7 fm) Excitation function E beam = 410 – 500 MeV (  lab = 20°) (D ≈ 12.3 to 15.0 fm)

Qvalues for 96 Zr+ 40 Ca The experiment – 60 Ni Sn Qvalues for 116 Sn + 60 Ni

Slopes for 116 Sn + 60 Ni The experiment – 116 Sn + 60 Ni PRELIMINARY +1n and +2n slopes are in agreement with those expected from binding energies Preliminary data Data under analysis Preliminary data Data under analysis

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  -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

The end

Grazing code calculations Probing nucleon-nucleon correlations via transfer of (nn), (pp) and Probing nucleon-nucleon correlations via transfer of (nn), (pp) and (np) pairs at sub-barrier energies in 92 Mo+ 54 Fe (np) pairs at sub-barrier energies in 92 Mo+ 54 Fe PRISMA PRISMA Probing nucleon-nucleon correlations via transfer of (nn), (pp) and Probing nucleon-nucleon correlations via transfer of (nn), (pp) and (np) pairs at sub-barrier energies in 92 Mo+ 54 Fe (np) pairs at sub-barrier energies in 92 Mo+ 54 Fe PRISMA PRISMA S.Szilner, L.Corradi, G.Pollarolo et al, May 2012 LNL PAC Proposal (approved)

Two particle transfer (semiclassical theory, microscopic calculations) Two particle transfer (semiclassical theory, microscopic calculations) only the successive term contributes to the transfer amplitude 3 terms : simultaneous, orthogonal and successive

One particle transfer (semiclassical theory) 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 96 Zr and a full shell above for 40 Ca

Light ions (Q3D)Heavy ions spectrometersTracking spectrometers single particle levels (shell model) nucleon-nucleon correlations (pair transfer) A,Z yields cross sections Q-value distributions Reaction mechanism Gamma spectroscopy 3-5 msr5-10 msr msr 70’s80’s - 90’srecent years Magnetic spectrometers for transfer reaction studies