1. 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

2. 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

3. 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)

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

5. Light charged particle multiplicities in the ternary fission

6. Initial TNS configuration is defined using the sudden approximation

8. 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)

11. 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 →
At EKr = 460, 500 and 600 MeV
Z2/A = (BfLDM = 0); αent = 0,415; (Z2/A)eff= 43.67

12. 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 =
Capture barrier : Bcupt = 295 MeV, Qfus = MeV
ELAB Ecm Ecomp Eex.p. Eex.ex.p σ fus ΘLABgraz
< mb
< mb mb

13. 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. ?

14. V = Vnucl + VCoul

15. Experimental setup to study 86Kr + Pb reaction

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

18. FLNR

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

20. 86Kr + 208Pb , E(86Kr) = 460, 500, 600 MeV

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

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

24. Post-scission neutron multiplicities

25. 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

32. 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

33. 86Kr + 208Pb →
at EKr=(500 – 600) MeV

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

35. 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 Legnaro, Italy
V.A. Rubchenya, D.N. Vakhtin
V.G.Khlopin Radium Institute, , St.Petersburg, Russia
A.A. Alexandrov, Yu.E. Penionzhkevich, Yu.G. Sobolev
FLNR, Joint Institute for Nuclear Research, , Dubna, Russia