Z>92 (Heaviest Element in Nature) and upto Z=100-101
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Transcript of Z>92 (Heaviest Element in Nature) and upto Z=100-101
March, 2006 SERC Course 1
Z>92 (Heaviest Element in Nature) and upto Z=100-101 achieved by n irradiation or p, and d bombardment in Cyclotron (1940-1955) (LBL)
Z=102-106 by Light or Heavy-ion induced Fusion -evaporation using heavy element targets (1958-1974) Z=107-112 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. Z=112-116 48Ca+Pu,Am,Cm,Cf (JINR, Dubna) Identified by gas filled separators and Si strip setectors
Search for Superheavy element and Role of Fission Dynamics
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Cross-section data and extrapolated values for cold-fusionReactions (1n -evaporation channel)
Cross-section increases with increasing isospin
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48Ca+242Pu->287114+3n 48Ca+244Pu-
>288114+4n
48Ca+244Pu->289114+3n
E*~33 MeVE*~34-38 MeV
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Yury Ts. OganessianPure Appl. Chem., Vol. 76, No. 9, pp. 1715–1734, 2004.
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48Ca+244Pu
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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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Extra push energies Swiatecki
For Z1Z2>1000 to 1650 depending on the value of the charge asymmetry, Zp/ZT.
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Onset of fusion limitationDue to Extra push energies
No hindrance
Effective fissility : weighted mean of mono-nuclear and binaryWith weight for binary taken as 1/3
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Injection direction
Fusion area inside Saddle point
Difference in energyBetween touchingPoint and saddle pointSmall due to shell structureOf Ca and Pb
All trajectories reaches fusion
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Quasi-fission isdominant
Extra pocket in massSymmetric region Deep
Quasi-fission
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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.
Evgeni A. CherepanovBrazilian Journal of Physics, vol. 34, no. 3A, September, 2004
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48Ca+208PbEX=50 MeV
Aritomo and OhtaPre-print
Nuclear Physics A 744 (2004) 3–14
Mass asymm fluctuatesaround 0.5 and then relaxes quickly andTrajectory move to main pocket
March, 2006 SERC Course 2748Ca+244PuEx=50 MeV
Critical stage
Turning stage
For FF massAsymmetrieslarge
For QF neck developsand speeds up fissionkeeping mass asymm.
For deep QF mass asymmRelaxed in sub-pocketAt TS
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The smaller formation probability due to inhibition of fusion by competing mechanism:DIC,QF,FF,PEF Asymmetric channels: higher E* and unfavourable for survival
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Transition fromFF to QF
QF
Mass distribution forFF is asymmetric in shapeWith peak around 132
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Measurements at LNL,Legnaro (Italy)Measurements at LNL,Legnaro (Italy)
470-630 MeV 80Se + 208Pb
372 MeV 56Fe+232Th
288116
Measurement of fragment mass and kinetic energy and neutron correlations
80Se + 232Th 312124470-630 MeV
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Schematics of the setup for Se+Pb,Th experiment
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80Se+232Th 470 MeV80Se+208Pb 470 MeV
DIC dominates but significant events around symmetry
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Mass (amu)
50 100 150 200 25010-1
100
101
102
103470 MeV510 MeV550 MeV630 MeV
Z = 50 N = 82
Mass (amu)
50 100 150 200 250101
102
103
Z = 50 N = 82
d/d
M (a
rb. u
nits
)
80Se+232Th 470 MeV80Se+208Pb 470 MeV
Se+Pb more asymmetric compared to Se+Th
QF is expected to be more for Se+Th
March, 2006 SERC Course 35Ecm-VB (MeV)
0 20 40 60 80 100 120 140 160 180 200
cros
s se
ctio
nsX
Ecm
(arb
. un
its)
0
2000
4000
6000
8000
80Se+208Pb (gated region)80Se+232Th (gated region)Fit to Se+Pb dataFit to Se+Th data
higher extra-push energyin the case of 80Se+232Th
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80Se+208Pb 288116
ExCN (MeV)
0 50 100 150 200 250
tot
0
10
20
30
40
50
80Se+232Th 312124
ExCN (MeV)
0 50 100 150 200 250
tot
0
10
20
30
40
50
ν sf tot =10±2 for Se+Pb
12±1 for Fe+Th
=17±2 for Se+Th
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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 ΔEx 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 DubnaT. Materna et al. Nuclear Physics A734 (2004) 184-l 87
The pre-scission neutron multiplicity distribution simulated
using backtracing procedure show two components for Ca+Pu
Whereas for Ca+Pb only one component is seen
FF
QF
A/2±30
208±20
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??
Connectecd withknown species
Self-consistent
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Change fromHot fusion toCold fusionFor higher N-Z
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Survival probability Depends on fissionfission delaydelayAnd speed of coolingMainly by neutron neutron evaporationevaporation
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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
Region beyond Z= 114 needs beam intensities in excess of 1014 s-1.
Reactor based
With MAFF and spallation facility with 100μA proton of 1GeVIntensities may go up by 3 to 4 orders of magnitude
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