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Search for Superheavy element and Role of Fission Dynamics. Z>92 (Heaviest Element in Nature) and upto Z=100-101 achieved by n irradiation or p, a, and d bombardment in Cyclotron (1940-1955) (LBL) Z=102-106 by Light or Heavy-ion induced Fusion

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Presentation Transcript
slide1

Search for Superheavy element and

Role of Fission Dynamics

  • Z>92 (Heaviest Element in Nature) and upto Z=100-101

achieved by n irradiation or p, a, 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

SERC Course

slide6

Cross-section data and extrapolated values for cold-fusion

Reactions (1n -evaporation channel)

Cross-section increases with increasing isospin

SERC Course

slide8

E*~33 MeV

E*~34-38 MeV

48Ca+244Pu->289114+3n

48Ca+244Pu->288114+4n

48Ca+242Pu->287114+3n

SERC Course

slide11

48Ca+244Pu

SERC Course

slide16

∙ 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,

SERC Course

slide17

BLDf gradually disappears

Spherical

Deformed

SERC Course

slide18

Fission barrier calculations of Smolanzuk et al.

106Sg has highest barrier with half life of 3 hrs

SERC Course

slide20

For Z1Z2>1000 to 1650 depending

on the value of the charge

asymmetry, Zp/ZT.

Extra push energies

Swiatecki

SERC Course

slide21

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

SERC Course

slide23

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

SERC Course

slide24

Quasi-fission is

dominant

Extra pocket in mass

Symmetric region

Deep

Quasi-

fission

SERC Course

slide25

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.

SERC Course

slide26

Mass asymm fluctuates

around 0.5 and then

relaxes quickly and

Trajectory move to main

pocket

48Ca+208Pb

EX=50 MeV

Aritomo and Ohta

Pre-print

Nuclear Physics A 744 (2004) 3–14

SERC Course

slide27

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

48Ca+244Pu

Ex=50 MeV

SERC Course

slide29
The smaller formation probability due to inhibition of fusion by competing mechanism:DIC,QF,FF,PEFAsymmetric channels: higher E*

and unfavourable for survival

SERC Course

slide30

Transition from

FF to QF

Mass distribution for

FF is asymmetric in shape

With peak around 132

QF

SERC Course

measurements at lnl legnaro italy
Measurements at LNL,Legnaro (Italy)

470-630 MeV 80Se + 208Pb

372 MeV 56Fe+232Th

288116

470-630 MeV

312124

80Se + 232Th

Measurement of fragment mass and kinetic energy

and neutron correlations

SERC Course

slide33

80Se+208Pb

470 MeV

80Se+232Th

470 MeV

DIC dominates but significant events around symmetry

SERC Course

slide34

Se+Pb more asymmetric compared to Se+Th

QF is expected to be more for Se+Th

80Se+208Pb

470 MeV

80Se+232Th

470 MeV

SERC Course

slide35

higher extra-push energy

in the case of 80Se+232Th

SERC Course

slide36

80Se+208Pb

288116

80Se+232Th

312124

ν sftot=10±2 for Se+Pb

12±1 for Fe+Th

=17±2 for Se+Th

SERC Course

slide38

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.

SERC Course

slide39

JINR,Dubna

SERC Course

slide40

41 detectors of DEMON at Dubna

T. Materna et al. Nuclear Physics A734

(2004) 184-l 87

208±20

QF

FF

A/2±30

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

SERC Course

slide41

??

Self-consistent

Connectecd with

known species

SERC Course

slide42

Change from

Hot fusion to

Cold fusion

For higher N-Z

SERC Course

slide43

Survival probability

Depends on fissiondelay

And speed of cooling

Mainly by neutron

evaporation

SERC Course

slide46

Expected intensities s-1for neutron-rich radioactive beams

SPIRAL 24Ne 7 x 107

HI based 44Ar 5 x107

PIAFE 78Zn 108

84Ge 2 x108

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

SERC Course

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