Sub-barrier Transfer Reaction in the Superfluid System 116Sn + 60Ni
D. Montanari1, L. Corradi2, S. Szilner3, G. Pollarolo4, E. Fioretto2, Pushpendra P. Singh2, A.M. Stefanini2, E. Farnea1,
C. Michelagnoli1, G. Montagnoli1, F. Scarlassara1, C. A. Ur1, S. Courtin5, A. Goasduff5, F. Haas5, T. Mijatović3
1
Dipartimento di Fisica e Astronomia, Università di Padova, and Istituto Nazionale di Fisica Nucleare , I-35131, Padova, Italy.
2
Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro, I-35020 Legnaro, Italy.
3
Ruđer Bošković Institute, HR-10002 Zagreb, Croatia.
4
Dipartimento di Fisica Teroica, Università di Torino, and Istituto Nazionale di Fisica Nucleare, I-10125 Torino, Italy.
5
Institut Pluridisciplinaire Hubert Curien, CNRS-IN2P3, Université de Strasbourg, F-67037, Strasbourg, France.
Transfer reactions with heavy ions give the possibility of
populating at the same time many reaction channels and
allow to understand the relative role played by the singleand pair-transfer processes [1]. Below the Coulomb barrier
and at large internuclear distances nuclei interacts only
through the tail of their wavefunctions and reaction
products are excited in a resctricted energy window. This
helps in the theoretical interpretation of data, since the
global complexity of calculation diminishes, and
allows to extract more quantitative information on pair
correlations [2,3]. Using the large solid angle magnetic
spectrometer PRISMA [4,5] we performed a reaction in
inverse kinematics for the superfluid system 116Sn+60Ni. In
the past, two other experiments concerning the sub-barrier
transfer mechanism have already been performed by our
group, for the closed shell system 96Zr+40Ca [6] and for the
same 60Ni+116Sn system [7], in direct kinematics (see [7]
also for details on the reaction described in this work).
A beam of 116Sn has been delivered by the PIAVE-ALPI
accelerator system at bombarding energies ranging from
Elab =395 - 500 MeV onto a 0.1 mg/cm2 60Ni target. The
spectrometer has been set at the angle lab=20° with respect
to the beam axis to detect the target-like reaction products.
Under these conditions we measured an excitation function
for nucleon transfer in the range of distances of closest
approach D=12.5 - 15.7 fm.
Ions have been identified in mass and atomic number on
the basis of an event-by-event reconstruction of the ion
trajectories inside the PRISMA spectrometer [5] and,
assuming a binary process, the reaction Q-values have
been reconstructed.
At energies below the barrier, where nuclei follow
almost pure Coulomb trajectories, a phenomenological
way to describe the transfer of nucleons is to plot the
transfer probabilities, Ptr, as a function of the distance of
closest approach D. At large ion-ion separation the radial
behaviour of the form factor is governed by the
exponential form of the bound-state wave function and Ptr
can be approximated by:
( )
( )
where the  parameter depends on the binding energy Eb
as follows:
(
)
Fig. 1. Transfer probabilities as a function of the distance of
closest approach D for one- and two-neutron transfer channels.
Points are experimental data (blue: +1n, red: +2n). Lines are
linear fits of data at large distances. Experimental and theoretical
values for the  parameter are reported in the figure.
Experimentally the Ptr is defined as the ratio of the
differential cross section of the transfer channel over the
one of the elastic. Figure 1 shows the Ptr for the one- and
two-neutrons transfer channels as a function of D. Data
(symbols) have been fitted in the sub-barrier region with
linear fits (dashed lines). The experimental slopes turn out
to be in good agreement with the theoretical predictions of
the binding energies. A further analysis using microscopic
theory for one- and two-particle transfers is being
performed to be able to extract more quantitative
information on the reaction mechanism.
[1] R.A. Broglia and A. Winther, "Heavy Ion Reactions"
(Addison-Wesley Pub. Co., Redwood City CA, 1991).
[2] B. F. Bayman and J. Chen, Phys. Rev. C26, 1509 (1982).
[3] G. Potel, F. Barranco, E. Vigezzi and R. A. Broglia,
Phys. Rev. Lett. 105, 172502 (2010).
[4] A.M. Stefanini et al., Nucl. Phys. A 701, 217c (2002).
[5] D. Montanari et al., Eur. Phys. J.A47, 4 (2011).
[6] L. Corradi et al., Phys Rev. C 84, 034604 (2011).
[7] D. Montanari et al., LNL Annual Report 2011, p. 29.