Yoritaka Iwata 1, Naoyuki Itagaki 2, Takaharu Otsuka 1,2,3 1 Department of Physics, University of Tokyo. 2 CNS, University of Tokyo. 3 RIKEN. Competitive Reaction Mechanisms in Exotic Nuclear Reactions J. A Maruhn (University of Frankfurt) K. Yabana & T. Nakatsukasa (Univ. Tsukuba) C. Simenel (Saclay) Thanks to …

ii) Spin excitation mechanism Reaction mechanism with exotic nuclei i) Different effect of Pauli Principle Based on quantum numbers (equivalence & difference ) For spin difference iii) Isospin dependent motion For isospin difference The competition between these i), ii), iii)

Reaction mechanisms I  Spin dependence of the force (~ spin-orbit force) causes “spin-excitation” On the reaction plane J.A. Maruhn, P.-G.Reinhard et al, PRC74 (2006)

  Neutron-richProton-rich Stronger attraction or Reaction mechanisms II  Isospin dependence of the force causes “isospin-excitation” probe Target or Effective interaction Target nucleus Nucleon (as a probe)

4 He + 40 Ca → 44 Ti “Isovector”“Isospin dependent” “Isovector” expectation value <= “Isospin dependent” motion of each nucleon The isovector GDR is experimentally observed in  -scatterings Validity of isospin dependent motion Contact time ~ 225fm/c Non-trivial oscillation exists ! TDHF calc. Exp.

For isospin difference For spin difference Spin excitation Isospin excitation Pauli Principle → Independent motion NeutronProton time space Trajectory Spin-upSpin-down time space Trajectory The competition & Specific dynamics Isospin … p or n Spin … + or -

For a bounded  -particle, internal interactions (blue arrows in the figure) are equilibrated. For an isolated  -particle (before the collision), external interactions (red arrows in the figure) are turned off. initial alpha-particle For the initial  -particle, the center-of-mass positions and the center-of-mass velocities are taken to be exactly the same. Domain limit of attraction due to the nuclear force from the target nuclei Dynamically fluctuating alpha-particle Alpha-particle in collision Interaction between the target (External interaction)

We would like to see the competition of these fundamental dynamics  -particle Dynamically fluctuating  -particle casting an  -particle for Ca-isotopes For a bounded  -particle, internal interactions are equilibrated. We would like to turn on the interaction channel from outside though the dynamical reaction process Nice probe for the competition

4 He + 40 Ca → 44 Ti b = 0 total neutron proton Spin excitation is relatively dominant Initial spin-excitation 1.8fm0.2fm Large spin-excitation 0.2fm 4.0fm TDHF3 d

b = 0 A = 34 A = 46 The spin excitation is mainly observed in the collision with total isospin symmetric case; i.e. A=40, Z=20 (in this case). A = 40 4 He + A Ca → A+4 Ti Time hindrance of spin-excitation in exotic reactions High mountain Low land Small mountain Hindrance of spin excitation

Theoretical framework for competitive reaction mechanism nonlinear  amplitude of excitation linear Iwata-Itagaki et. al.

competition Non-central collision exhibiting the competition total neutron proton b = 2.5 TDHF Center-of-mass trajectory (200 fm/c to 1125 fm/c) neutron v.s. proton spin-up v.s. spin-down On the reaction plane > “alpha + 40 Ca” Deuteron-like cluster Dineutron, diproton-like cluster TDHF3 d

ii) Spin excitation mechanism i) Pauli Principle iii) Isospin dependent motion The competition between these i), ii), iii), iv) + iv) Coulomb force For fusion reactions with heavy nuclei, it should be prominent ! Advice from Prof. Dr. K. Yabana & Prof. Dr. T. Nakatsukasa (Univ. Tsukuba) Fusion reaction with heavy nuclei by TDHF3d The attention are especially paid to the Coulomb int. Now in progress Exotic reaction mechanism+

Fusion reactions with heavy nuclei R1R1 Z1Z1 A1A1 Z2Z2 A2A2 [1] Swiatecki, 82. [2] Wada and Abe [3] Washiyama, Yilmaz, Ayik and Takigawa (Quantum diffusion theory) Head-on collision contact RcRc Fusion process the Coulomb Barrier Is it possible to get over the Coulomb Barrier ? Ref.) R i = r 0 A 1/3 R C = R 1 + R 2 Fusion Hindrance in reaction with heavy nuclei O 16 +O 16 Sn 132 +Sn 132 For barrier-top fusions, what can we see in 3d-TDHF frame ? For example: For example: 16MeV for 16 O+ 16 O, and 310MeV for 132 Sn Sn Interest the fusion hindrance There is the fusion hindrance for Z 1 Z 2 > 1800 (1800) 1/2 ~ 42 TheoryExp. (spherical nuclei)

157.5 fm/c112.5 fm/c fm/c fm/c fm/c Keep oscillating Box: 96fm*80fm*80fm 16 O + 16 O fm/c fm/c fm/c427.5 fm/c fm/c Keep oscillating Barrier top fusion Fusion occurs Contact (1 st Barrier) Total density plot

67.5 fm/c/c157.5 fm/c/c247.5 fm/c/c fm/c/c427.5 fm/c/c 132 Sn Sn Box: 96fm*80fm*80fm Barrier top fusion Contact (1 st Barrier)The 2 nd internal Barrier* (Extra-push) *Hindrance by two steps: T.Abe, T.Wada et al. Repulsion Central peak density distribution can never achieved in this case. Fusion never occurs Total density plot

Boundary of the hindrance 40 Ca + 40 Ca 56 Ni + 56 Ni 100 Sn Sn 132 Sn Sn 80 Zr + 80 Zr Barrier-top fusion (TDHF3D)

Summary Note  Two principal reaction dynamics in heavy-ion collisions a competition  There is a competition between these two reactions including the Pauli effect. Spin excitationthe spin-orbit force Spin excitation: originated from the spin-orbit force >>> dynamical LS-splitting due to time-odd part J.A. Maruhn, P.-G.Reinhard et al., PRC74 (2006) Iso-spin-excitationisospin dependence of the force”. Iso-spin-excitation: originatedfrom isospin dependence of the force”. >>> It is also the origin for isovector-GDR.

ii) Spin excitation mechanism i) Pauli Principle iii) Isospin dependent motion The competition between these i), ii), iii), iv) + iv) Coulomb force For fusion reactions with heavy nuclei, it should be prominent ! Summary Reaction mechanism in the frontier of heavy nuclei