Coulomb barrier distributions: puzzles and recent experiments Eryk Piasecki and The Barrier Collaboration September 2006

58 Ni + 60 Ni A.M.Stefanini et al., Phys.Rev.Lett. 74(1995)864

 Determination of importance of various couplings (vibrational, rotational, single-particle ones) in different reaction and systems.  What is the influence of the Q of reaction?  What is the influence of formfactors?  Determination of the nuclei deformation parameters (  2,  3,  4 and perhaps even  6 ), including their sign, what is pretty difficult using the standard Coulomb excitation methods.  Reliable calculation of the nucleus-nucleus cross-sections in sub-barrier region.  Optimization of superheavy elements production.  Investigation of the influence of exotic nuclear structures (e.g. “halo”) on the reaction mechanisms. Motivation (hopes)

Two experimental methods:

H.Timmers et al., NP A 633(1998)421 Are the methods equivalent?

H.Timmers et al., NP. A584(1995) O Sm

Shape of 20 Ne          Cluster model Predictions of Coupled Channels Theory for 20 Ne Sn (CCFULL code) No couplings With couplings

Suspicion: perhaps the „weak” channels (transfers, s.p. excitations) are not that weak as it is assumed in the CC calculations? What we miss in the calcs???

20 Ne Sn p - stripping  - stripping

~Z 1 *Z 2 * 

Estimated from systematics

Expectations & experimental results: 20 Ne + 90 Zr: weak neutron transfer barrier structure 20 Ne + 92 Zr: stronger neutron transfer no structure wider barrier distribution

Open questions:  Transfers and/or s.p. exciations?  Quantitative relation between the strength of „weak” channels and barrier smoothing  Why the barrier structure has been observed in many experiments?  Is D fus as sensitive for smoothing as D qe ?  CC treatment of these problems Is the puzzle solved??

JYU Aug/Sept Simultaneous measurements of D fus & D qe

E MCP START beam 20 Ne Target nat Ni 90,92 Zr 118 Sn 206,208 Pb (E,ToF)  A L ToF = 55cm FWHM ToF ≈ 200ps Measurements of weak channels strengths (transfers & s.p. excitations)

SD array MCP Targets

Energy 20 Ne 22 Ne 19 Fe 16 O 20 Ne Sn

Conclusions: The weak channels can have quite considerable influence on the barrier height distributions There are still some (interesting) open questions  Transfers and/or s.p. exciations?  Quantitative relation between the strngth of „weak” chanels and barrier smoothing  Why the barrier structure has been observed in many experiments?  Is D fus as sensitive for smoothing as D qe ? Some of the answers are probably already in our hands and will be presented soon.  CC treatment of these problems is badly needed September 2006

The BARRIER Collaboration: Warsaw University (Inst. Exp. Phys. & Heavy Ion Lab): Ł.Świderski, P. & T. Czosnyka, J.Jastrzębski, A.Kordyasz, M.Kowalczyk, M.Kisieliński, K.Piasecki, E.Piasecki Białystok University: T.Krogulski Technische Universitat (Darmstadt): M.Mutterer Radium Institute (St. Petersburg): S.Kchlebnikov, G.Turin University of Jyvaskyla : W.Trzaska, M. Sillanpää Tohoku University: K.Hagino IReS (Strasbourg): N.Rowley Inst. Nucl. Studies (Warsaw): K.Rusek LNL (Legnaro): A.Stefanini LNS (Catania): P.Russotto JINR (Dubna): E.Kozulin, S.Smirnov Kurchatov Inst. (Moscow): A.Ogloblin, S.Dmitriev