Lukasik et al, INDRA collaboration PRC55, 1906 (1997)

1. Pioneering work on neck fragmentation: C.P. Montoya et al., PRL 73, 3070 (1994) J. Toke et al.,PRL 75, 2920 (1995) Y.Larochelle et al. PRC55, 1869 (1997) Increasing centrality Centrality selected by transverse energy of light charged particles For peripheral and mid-central collisions: • Galilean invariant diagrams show protons and alphas arise mostly from sequential decay of PLF and TLF (with forward/backward peaking). • In contrast: d,t, and IMFS mainly originate from neck/mid-velocity. All this work deduced theexcess emission above statistical emission from spherical binary reaction partners (PLF and TLF) Lukasik et al, INDRA collaboration PRC55, 1906 (1997)

2. 114,106Cd + 92,98 Mo at E/A=50 MeV LASSA: 9 Telescope Si Strip array 7º lab58º; Z,A,E, lab Isotope identification for Z  8 BEAM Miniball/wall Fast plastic/CsI(Tl) 2º lab170º Global event characterization Nc,Zsum,Etrans, etc. Si-CsI(PD) Ring Counter (16 sector) 2º lab4.5º Z,E, lab for Z>2 Zbeam=48 <Nc>=15 Yield Yield Charged Particle Multiplicity Z*10 Romualdo de Souza

3. Neck Double Rupture Model3 Previous work on dynamical decay of a cylinder (Brosa and Grossman1) and cylindrical neck (Carjan, Sierk, and Nix2) • Three assumptions: • During descent from saddle to scission, neck thickness does not decrease below a critical value. • Rupture is fast compared to collective motion (sc single particle period). • Ternary fission occurs when two statistically independent neck ruptures occur during a time interval t  sc. 1 Brosa and Grossman, Z. Phys. A310, 177 (1983) 2 Carjan, Sierk, and Nix, Nucl. Phys. A452, 381 (1986) 3 Rubchenya and Yavshits, Z. Phys. A329, 217 (1988) Able to explain the increase of ternary to binary probability with increasing fissility. Romualdo de Souza

4. Ecost = B + V + K Where does the necessary energy come from? Deformation (Halpern) Temperature (Fong) • system remains in statistical thermodynamic equilibrium throughout the fission process (adiabatic). • Y(Z,A)  exp(-Ecost/T) • Ecost 20 MeV for  particles • Ternary fission would be immeasurably small. Y/Yn  3 x 10-7. In reality it is ***. • T  1 MeV implies alpha emission rates orders of magnitude smaller than observed. • Rapid transfer of deformation energy into release energy of ternary particle as a sudden snap of the neck stub after scission (non-adiabatic) • Y middle particle exp(-const*Ecost) • only able to explain relative yields • for large middle fragments Ecost becomes large implying large middle fragments come from extremely deformed (and cold) systems. Ternary Fission in Spontaneous Fission and low energy induced fission is a dynamical process. Romualdo de Souza

5. Ecost = B + V + K Where does the necessary energy come from? Deformation (Halpern) Temperature (Fong) • system remains in statistical thermodynamic equilibrium throughout the fission process (adiabatic). • Y(Z,A)  exp(-Ecost/T) • Ecost 20 MeV for  particles • Ternary fission would be immeasurably small. Y/Yn  3 x 10-7. In reality it is ***. • T  1 MeV implies alpha emission rates orders of magnitude smaller than observed. • Rapid transfer of deformation energy into release energy of ternary particle as a sudden snap of the neck stub after scission (non-adiabatic) • Y middle particle exp[(Qmax-V)/T] • -- Qmax = total energy release in TF • -- V = Coulomb energy of ternary config. Ternary Fission in Spontaneous Fission and low energy induced fission is a dynamical process. Romualdo de Souza