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

and the AGATA demonstrator

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

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

PRISMA

beam direction

20o 96Zr 40Ca

Prisma acceptance

Reaction in inverse kinematics with PRISMA

Laboratori Nazionali di Legnaro – INFN (Italy)

g-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, 054613 (2011)

S. Szilner et al, Phys. Rev. C 76, 024604 (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)

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

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

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

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

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)

Qvalues for 96Zr+ 40Ca

The experiment – 60Ni +116SnQvalues for 116Sn + 60Ni

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

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

The end

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)

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)

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

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