Z92 Heaviest Element in Nature and upto Z100101

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Search for Superheavy element and Role of
Fission Dynamics

• Zgt92 (Heaviest Element in Nature) and upto
  Z100-101
• achieved by n irradiation or p, a, and d
  bombardment in
• Cyclotron (1940-1955) (LBL)
• Z102-106 by Light or Heavy-ion induced Fusion
• -evaporation using heavy element targets
  (1958-1974)
• Z107-112 Heavy ion inuced fusion 208Pb,209Bi
  targets
• (GSI)
• Identified by recoil separation technique
  and connecting
• to known daughter decay after implanting into
  Si strip
• detectors.
• Z112-116 48CaPu,Am,Cm,Cf (JINR, Dubna)
• Identified by gas filled separators and Si
  strip setectors

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Cross-section data and extrapolated values for
cold-fusion Reactions (1n -evaporation channel)
Cross-section increases with increasing isospin
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E33 MeV
E34-38 MeV
48Ca244Pu-gt2891143n
48Ca244Pu-gt2881144n
48Ca242Pu-gt2871143n
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Yury Ts. OganessianPure Appl. Chem., Vol. 76, No.
9, pp. 17151734, 2004.
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48Ca244Pu
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The flight time of the reaction products through
SHIP is 2 ms.
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Cold Fusion 208Pb and 209Bi targets
bombarded by the following projectiles 48Ca,
50Ti, 54Cr,58Fe, 62Ni, 64Ni, 70Zn, 76Ge, 82Se,
and 86Kr. ? Hot Fusion 48Ca projectiles
bombarded targets of 238U, 244Pu, 243Am, 245Cm,
248Cm, and 249Cf,
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BLDf gradually disappears
Spherical
Deformed
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Fission barrier calculations of Smolanzuk et al.
106Sg has highest barrier with half life of 3 hrs
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For Z1Z2gt1000 to 1650 depending on the value of
the charge asymmetry, Zp/ZT.
Extra push energies
Swiatecki
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No hindrance
Onset of fusion limitation Due to Extra push
energies
Effective fissility weighted mean of
mono-nuclear and binary With weight for binary
taken as 1/3
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Injection direction
Difference in energy Between touching Point and
saddle point Small due to shell structure Of Ca
and Pb
Fusion area inside Saddle point
All trajectories reaches fusion
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Quasi-fission is dominant
Extra pocket in mass Symmetric region
Deep Quasi- fission
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Evgeni A. Cherepanov Brazilian Journal of
Physics, vol. 34, no. 3A, September, 2004
The curve V (Z,L 0) (for the value of R
corresponding to the pocket) has a few local
minima, which reflect the shell structure in the
interacting nuclei.
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Mass asymm fluctuates around 0.5 and then
relaxes quickly and Trajectory move to main
pocket
48Ca208Pb EX50 MeV
Aritomo and Ohta Pre-print
Nuclear Physics A 744 (2004) 314
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Critical stage
For FF mass Asymmetries large
Turning stage
For QF neck develops and speeds up
fission keeping mass asymm.
For deep QF mass asymm Relaxed in sub-pocket At TS
48Ca244Pu Ex50 MeV
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The smaller formation probability due to
inhibition of fusion by competing
mechanismDIC,QF,FF,PEF Asymmetric channels
higher E
and unfavourable for survival
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Transition from FF to QF
Mass distribution for FF is asymmetric in
shape With peak around 132
QF
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Measurements at LNL,Legnaro (Italy)
470-630 MeV 80Se 208Pb 372 MeV
56Fe232Th

288116
80Se 232Th
312124
470-630 MeV
Measurement of fragment mass and kinetic energy
and neutron correlations
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Schematics of the setup for SePb,Th experiment
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80Se232Th
470 MeV
80Se208Pb
470 MeV
DIC dominates but significant events around
symmetry
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SePb more asymmetric compared to SeTh
QF is expected to be more for SeTh
80Se232Th
470 MeV
80Se208Pb
470 MeV
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higher extra-push energy in the case of
80Se232Th
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80Se208Pb
288116
80Se232Th
312124
? sf tot 102 for SePb 121
for FeTh 172 for SeTh
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on average of about 0.6 neutron per unit Z
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an increase of about 0.54 neutron per unit Z
excitation energy gained by the system in its
transition from the saddle to the scission point
(the term ?Ex by Hilscher) that is known to show
a strong mass and Z dependence.
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JINR,Dubna
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41 detectors of DEMON at Dubna T. Materna et al.
Nuclear Physics A734 (2004) 184-l 87
20820
QF
FF
A/230
The pre-scission neutron multiplicity
distribution simulated using backtracing
procedure show two components for CaPu Whereas
for CaPb only one component is seen
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??
Self-consistent
Connectecd with known species
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Change from Hot fusion to Cold fusion For higher
N-Z
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Survival probability Depends on fission
delay And speed of cooling Mainly by neutron
evaporation
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Expected intensities s-1 for neutron-rich
radioactive beams SPIRAL 24Ne 7 x
107 HI based 44Ar 5 x 107
PIAFE 78Zn 108
84Ge 2 x 108 94Kr 2
x 109
Reactor based
Region beyond Z 114 needs beam intensities in
excess of 1014 s-1.
With MAFF and spallation facility with 100µA
proton of 1GeV Intensities may go up by 3 to 4
orders of magnitude
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