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## Heavy ion transfer reactions studied with PRISMA+CLARA

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**Heavy ion transfer reactions studied with PRISMA+CLARA**L.Corradi Laboratori Nazionali di Legnaro – INFN, Italy LEA, Catania, 13-16 October, 2008**Transfer reactions (multinucleon) among heavy ions**The quasi-elastic regime is governed by - form factors < f I Vint I i > (structure) - optimum Q-values (dynamics) ‘ a’ degrees of freedom single particle states surface vibrations pair modes a A A’ couplings inelastic: collective ff transfer: single particle ff pair ff (macroscopic)**The understanding of low energy heavy ion reactions requires**a careful and consistent experimental and theoretical work • - elastic scattering (nuclear potential) • - inelastic scattering (phonon form factor) • - one particle transfer (single particle form factors) • - two particle transfer (nucleon-nucleon correlations) • - multiple particle transfer (multipair transfer, ... towards DIC) • mandatory a complete set of observables • A, Z, TKEL, dσ/dΩ, σtot**MWPPAC**IC PRISMA spectrometer – trajectory reconstruction • A physical event is composed by the parameters: • position at the entrance x, y • position at the focal plane X, Y • time of flight TOF • energy DE, E**PRISMA spectrometer – trajectory reconstruction**ΔE-E Mass A/q q**Elastic scattering – using Prisma and Clara information**elastic scattering is the first important ingredient for nuclear reaction studies. It provides information on the (outer part of) nuclear potential grazing code**Differential cross sections**forward part : mainly reflects the behaviour of the form factors backward part : mainly reflects the absorption**Total cross sections**successive transfer S.Szilner et al, Phys.Rev.C76(2007)024604**multinucleon transfer :**experiment vs. theory data : LNL theory : GRAZING code and CWKB**Evaporation processes in multinucleon transfer reactions**Evaporation processes directly identified with PRISMA+CLARA An example: 40Ca+96Zr at 152 MeV 40Ca+96Zr E=152 MeV**TKEL distributions**pure proton stripping**Pair transfer**Search for pairing vibrations Measurements at sub-barrier energies**Strong population close to the pairing vibrational region**in 40Ca+208Pb strength function (shell model calculations) S.Szilner et al, Eur.Phys.J. A21, 87(2004) S.Szilner et al, Phys.Rev.C76(2007)024604**Multineutron and multiproton transfer channels near**closed-shell nuclei 90Zr+208Pb Elab=560 MeV pure neutron pick-up channels Mass [amu] PRISMA spectrometer data GRAZING code calculations L.Corradi et al, Nucl.Phys.A787(2007)160**Population of states close to the pairing**vibrational region 2240 1874 3308 3842**Q-value window**absorptive potential form factor At energies lower than the Coulomb barrier : - few reaction channels are opened, i.e. W(r) very small - one has a much better control on the form factors F(r)inel has a decay length ~ 0.65 fm F(r)tr has a decay length ~ 1.3 fm nuclear couplings are dominated by transfer processes - Q-value distributions get much narrower than at higher energies - one can probe nucleon correlation close to the g.s. data are very scarse or almost non existing**Detection of (light) target like ions in inverse kinematics**with PRISMA SSBD (rutherford sc.) beam direction PRISMA 20o 94Zr 40Ca measurements have been performed for multinucleon transfer channels and at energies well below the barrier**GRAZING code calculations for 40Ca+94Zr transfers**differential cross sections Prisma acceptance total cross sections A.Winther, program GRAZING http://www.to.infn.it/~nanni/GRAZING**Mass vs Q-value matrix for (-1p) channels channels (El=315**MeV) background free spectra with transfer products at very low excitation energy : no evaporation effects and cleanest conditions for comparison with theory**Experimental vs Theoretical cross sections for +1n and -1p**channels very preliminary**Change of population pattern in going from neutron**poor to neutron rich nuclei (theoretical) neutron stripping and proton pick-up equal directions neutron pick-up and proton stripping C.H.Dasso, G.Pollarolo and A.Winther, Phys.Rev.Lett.73, 1907 (1994)**Multinucleon transfer reactions**with (moderately n-rich) heavy ions one can populate (nn), (pp) and (np) channels with comparable strength**Multinucleon transfer reactions with radioactive beams**One needs to learn whether and to what extent the degrees of freedom and the corresponding matrix elements tested with stable beams can hold with radioactive beams. In particular whether the form factors for one and two particle transfer and their strength need to be modified neutron-proton correlations (np channel) 140Sn onset of supercurrents (neutron rich nuclei)**Summary**• Multinucleon transfer processes provide important information on the interplay between reaction mechanism and nuclear structure. The Prisma spectrometer coupled to large gamma arrays is a powerful tool to study the fine details of such processes. • The degrees of freedom involved in multiple particle transfers can be quantitatively probed only when a complete set of observables (A,Z,TKEL, dσ/dΩ, σtot) is available. This is important also for the correct description of the transition from quasi-elastic to deep-inelastic regime and other competing reaction processes (e.g. sub-barrier fusion). • Pair modes are presently being investigated looking at the decay of (possible) pair vibrational states and via extreme sub-barrier transfer of nucleons.**A.M.Stefanini, E.Fioretto, A.Gadea, B.Guiot, N.Marginean,**P.Mason, R.Silvestri, G.de Angelis, D.R.Napoli, J.J.Valiente-Dobon Laboratori Nazionali di Legnaro – INFN, Italy S.Beghini, G.Montagnoli, F.Scarlassara, E.Farnea, C.A.Ur, S.Lunardi, S.Lenzi, D.Mengoni, F.Recchia, F.della Vedova Universita’ di Padova and INFN, Sezione di Padova S.Szilner, N.Soic, D.Jelavec Ruđer Bošković Institute, Zagreb, Croatia G.Pollarolo Universita’ di Torino and INFN, Sezione di Torino, Italy F.Haas, S.Courtin, D.Lebhertz, M.-D.Salsac IReS, Strasbourg, France + CLARA collaboration**Pairing vibrations : light ion reactions**92Zr(p,t)90Zr L=0 transitions 86Sr(t,p)88Sr R.C. Ragaini et al., PRC2(1970)1020**detection of (heavy) target like ions with recoil mass**spectrometers 58Ni + xSn RMS measurements have been performed at subbarrier energies but for only one nucleon transfer and with very poor Q-value resolution R.Betts et al., PRL59(1987)978**Absolute cross sections for one and two-nucleon transfer**reactions 208Pb(16O,18Og.s.)206Pb E ~ Eb E << Eb successive successive direct direct one+two step calculations undepredict the data by a factor ~ 2 one+two step calculations undepredict the data by 25-30% B.F.Bayman and J.Chen, PRC26(1509)1982**Quasielastic barrier distributions : role of particle**transfer channels G.Pollarolo, Phys.Rev.Lett.100,252701(2008)**Sub-barrier fusion of 40Ca+94Zr**Interplay of phonon and transfer couplings sub-barrier transfer cross section measurements are important to compare with fusion cross sections in a similar energy and angular momentum range A.M.Stefanini et al., PRC76,014610(2007)**identified and known**208Pb(90Zr,92Zr)206Pb E=560 MeV identified but in overlap with other known existing ? 0+ [4283] strong in (t,p) 0+ [3992] strong in (t,p) 0+ [3589] strong in (t,p) non tab 492 934 (4000) non tab 2+ [3500] L=2 (t,p) 1225 1463 439 2+ [3058] L=2 (t,p) 0+ [2903] weak in (t,p) new (120) 1742 (n,n’) 2+ [2820] L=2 (t,p) 837 990 (1000) (n,n’) 972 2+ [2067] L=2 (t,p) 1970 2+ [1848] L=2 (t,p) 1132 (245) 912 (1100) wide peak at 893 2+ [934] L=2 (t,p) 1848 (50) 934 (4000) 0+ [g.s.]**PRISMA spectrometer – trajectory reconstruction**A/q (channels) X (channels)**Interpretation of massive transfer via diffusion models**uncorrelated N and Z diffusion linear diffusion : strong correlation between proton and neutron transfer the region with small energy loss is where nuclear structure properties play a major role K.Sapotta et al., PRC31(1985)1297**Multinucleon transfer reactions : quasi-elastic regime**pure neutron pick-up pure proton stripping N/Z equilibrization**Mass distributions for proton stripping channels channels**(El=315 MeV) K isotopes (-1p) Ar isotopes (-2p) background free spectra with transfer products at very low excitation energy : no evaporation effects and cleanest conditions for comparison with theory**Correlation between reaction channels**quasi elastic, deep inelastic quasi fission, [...] fusion In the presence of couplings the energy of relative motion is not well defined. An exchange of energy from the relative motion to the intrinsic degrees of freedom takes place**Evaporation processes directly identified with PRISMA+CLARA**an example : 40Ca+96Zr reaction at 152 MeV heavy partner -2p+2n channel light partner**PRISMA spectrometer – trajectory reconstruction**64Ni+238U ΔE E**Elastic scattering**Inelastic scattering