exotic nuclei structure and reaction noyaux exotiques ... - IPN - IN2P3

esults by reference to various experimental studies,
all leading to the same compound nucleus
220 Th, but covering a large spread of mass asymmetries
(ranging from 16 O + 204 Pb to 96 Zr + 124 Sn).
The entrance-channel effects are best expressed
in terms of the s-wave transmission coefficient
rather than through the total capture cross section
(though this does not imply that higher partial
waves do not play a role). We show that the data
on the above systems require a distribution of entrance-channel
Coulomb barriers [2,3], and are all
consistent with a quasi-fission probability which
depends only on the barrier in question; a result
consistent with the philosophy of the di-nuclearsystem
(DNS) model [4].
For the compound nucleus under consideration,
the maximum theoretical reduced cross section
(that is, with all relevant partial waves saturated
and with no quasi-fission) is a relatively smooth
function of the excitation energy. It may be extracted
directly from the set of experiments under
consideration and allows a direct inference of the
role of quasi-fission. This can be seen in Fig. 1
where we compare the experimental barrier distribution
for fusion (compound-nucleus creation) in
the 96 Zr + 124 Sn reaction [5] with the theoretical
capture distribution calculated with the coupledchannels
program CCFULL [6]. This calculation
includes multi-phonon excitations in both the target
and the projectile, and gives a good agreement
with the capture data of Ref. [7] (the data themselves
are not sufficiently complete to derive an
experimental capture barrier distribution directly).
For this reaction, the results show clearly the dominant
role of quasi-fission which completely suppresses
the contribution to compound nucleus formation
from all but the very highest entrancechannel
barriers.
References:
[1] A.C. Berriman et al., Nature Vol. 413,144 (2001).
[2] N. Rowley, G.R. Satchler and P.H. Stelson, Phys.
Lett. B254, 25 (1991).
[3] M. Dasgupta, D.J. Hinde, N. Rowley, and A.M.
Stefanini, Ann. Rev. Nucl. Part. Sci. 48, 401
(1998).
[4] G.G. Adamian, N.V. Antonenko and W. Scheid,
Nucl. Phys. A 678, 24 (2000); G.G. Adamian,
N.V. Antonenko, W. Scheid and V.V. Volkov,
Nucl. Phys. A 627, 361 (1997).
[5] C.-C. Sahm et al., Nucl. Phys. A 441, 316 (1985).
[6] K. Hagino, N. Rowley and A.T. Kruppa, Comp.
Phys. Comm. 123, 143 (1999).
[7] A.M. Vinodkumar et al., Phys. Rev. C 74, 064612
(2006).
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