NECK FRAGMENTATION IN FISSION AND QUASIFISSION OF HEAVY AND SUPERHEAVY NUCLEI V.A. Rubchenya Department of Physics, University of Jyväskylä, Finland.

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NECK FRAGMENTATION IN FISSION AND QUASIFISSION OF HEAVY AND SUPERHEAVY NUCLEI V.A. Rubchenya Department of Physics, University of Jyväskylä, Finland V.G. Khlopin Radium Institute, St. Petersburg, Russia September 25, 2008, Kazimerz Dolni

Fission (ternary fission) Near scission emission of LCP (or IMF) - NSE LCP Fission (ternary fission) HI fusion-fission (165Ho+56Fe(465): PRL 51 (1983) 99) neck F2 F1 Quasifission DNS Deep inelalastic collision τ

Possible mechamisms of NSE: Double random neck rupture model of NF - LCP evaporation from neck region (hot spot) Neck Fragmentation (NF) due to the dynamical instability of nuclear matter in the neck region. Double random neck rupture model of NF (V. Rubchenya, Sov. J. Nucl. Phys. 35 (1982) 334)

Estimate of the neck rupture time: Ternary fission probability: Coefficients are different for the specific fission modes: m = SY, SI, SII, SAS

Light charged particle multiplicities in the ternary fission

Initial TNS configuration is defined using the sudden approximation

The final mass and charge LCP distribution is mainly formed in the result of nucleon exchange process in DNS (LF + LCP) (V.Rubchenya, S. Yavshits, ZfP A 329 (1988) 217)

86Kr + 208Pb → 294118 Dynamics of superheavy composite systems Interplay between fusion and quasifission Instability toward the neck fragmentation Nuclear friction in superheavy composite systems 86Kr + 208Pb → 294118 At EKr = 460, 500 and 600 MeV Z2/A = 47.36 (BfLDM = 0); αent = 0,415; (Z2/A)eff= 43.67

86Kr + 208Pb Reaction parameters Fissility parameter = Coulomb energy /2 Surface energy = (Z2 / A)/(Z2/A)cr Z2/A =47.36 Effective fissility parameter = Coulomb force / proximity force = (Z1Z2e2/(R1 + R2)2)/4πγRav.c = (Z2/A)eff /(Z2/A)cr (Z2/A)eff = 43.67 Mass asymmetry parameter : α = (AT - AP) / (AT + AP) , α = 0.415 Capture barrier : Bcupt = 295 MeV, Qfus = 296.9 MeV ELAB Ecm Ecomp Eex.p. Eex.ex.p. σ fus ΘLABgraz 318.4 21.8 66 111 < mb 84.5 353.7 56.8 -- -- < mb 66.9 600 424.5 127.5 -- -- 31 mb 45.9

L α Z2/A (Z2/A)eff Vpot entrance Vpot exit < 47 all < LB=0 Fusion-fission <0.7 < 40 ≥ LB=0 Fast fission ≥ 40 ≥ 47 Quasi-fission Fus.-fis. ?

V = Vnucl + VCoul

Experimental setup to study 86Kr + Pb reaction

TOP VIEW T3 T7 SIDE VIEW T7 T0; T1;T2; T3 beam PSAC

FLNR

Mass yields (normalised to 100% at 97 < M < 197)

86Kr + 208Pb , E(86Kr) = 460, 500, 600 MeV

TKE and fragment excitation energy at EKr= 600 MeV (Fu-Fi model: V.R. et al. PRC 58(1998)1587)

The difference between experimental TKE and theoretical values (Fu-Fi model)

Post-scission neutron multiplicities

Multiple-source particle emission model Here ΘRF is a direction of the fragmentation axis CN stands for the composite nucleus NF stands for the neck source FR stands for the fragment sources WCN(ε) and WFR(ε) are evaporation spectra X Z VLCP

Light charged particle emission characteristics ELAB MeV MpCN Mpneck Mppost error MαCN Mαneck Mαpost 460 0.00 -- 500 0.040 0.005 0.026 0.054 600 0.210 0.004 0.060 0.006 0.170 Mnpre = 0.0 ± 0.9

86Kr + 208Pb → 294118 at EKr=(500 – 600) MeV

Next experiment in October, 2008: 238U + 64Ni -> 302120, Z2/A= 47.68

V.A. Rubchenya, W.H. Trzaska Department of Physics, University of Jyväskylä, FIN-40351, Jyväskylä E. Vardaci INFN and Dipartimento di Fisika dell’Università di Napoli, Italy G. Prete INFN Laboratory di Legnaro, I-35020 Legnaro, Italy V.A. Rubchenya, D.N. Vakhtin V.G.Khlopin Radium Institute, 194021, St.Petersburg, Russia A.A. Alexandrov, Yu.E. Penionzhkevich, Yu.G. Sobolev FLNR, Joint Institute for Nuclear Research, 149980, Dubna, Russia