Sophie Heinz

GSI Helmholtzzentrum and

Justus-Liebig-Universität Gießen

Fusion and Transfer Reactions in

Heavy Collision Systems with

Stable and Radioactive Beams

valley of β-stability

B p = 0

discovered arGSI - SHIP

Neutron number

Pro

ton n

um

ber

X + Pb,Bi

48Ca + X

Bp = 0

valley of β-stability

discovered atGSI - SHIP

The Heaviest Known Nuclei

Binding energy of a nucleus in the liquid drop model (Weizsäcker formula):

5

2

3/123/22/

),( BA

AZaAZaAaAaAZB ACSV

Condensationenergy

Surfaceenergy ES

Coulomb-energy EC Asymmetry energy

ES EC

deformation

V fissionbarrier Bf

for Z2 / A > 50 → Z > 100

Superheavy nuclei:

Bf = 0

What is a „superheavy“ nucleus ?

268106162

298114184

Quadrupole deformation β2

LD

Pote

nti

al energ

y /

MeV

LD + shell

25098152

Superheavy Nuclei:

Bfission = Eshell + Epair

Shell correction energies in the macroscopic-microscopic model

Fission Barriers of Superheavy Nuclei

Where are the next shell closures?

Macroscopic-microscopic models

A. Sobiczewski et al., 1995

P. Möller, 1995

114

114

S. Cwiok et al., 1998

Sky

rme-

Ha

rtre

e-F

ock

114

120

120

126

126

Relativistic mean field models

184

K. Rutz, W. Greiner et al., 1997

108

„Cold“ and „Hot“ Fusion Reactions

Cold Fusion → doubly magic target nuclei: Pb, Bi; E*(CN) = 10 – 20 MeV; evaporation of 1 – 2 neutrons;

up to now successful for Z ≤ 113

Hot Fusion → actinide targets (U, Cm, …) and 48Ca projectiles; E*(CN) = 30 – 40 MeV; evaporation of 3 – 4 neutrons;

up to now successful for Z ≤ 118

Synthesis of Superheavy Nuclei in Fusion Reactions

ER cross-section:

The Fusion Process in Heavy Systems

FUSION

TRANSFER, QUASI-FISSION

Nuclear Molecule

Compound Nucleus (CN)

EvaporationResidue (ER)

FUSION-FISSION

FissionFragments

survival CN captureER P P

1 pb corresponds to 1 nucleus per week

102 104 106 108 110 112 114 116 1181E-15

1E-14

1E-13

1E-12

1E-11

1E-10

1E-9

1E-8

1E-7

1E-6

Cro

ss-s

ect

ion / b

arn

Proton Number

1 pb

Cold fusion(X + Pb, Bi)

Hot fusion(48Ca + X)

Evaporation Residue Cross-sections for Cold and Hot Fusion Reactions

Evaporation Residue Cross-sections

5 · 1012 / s

29 ms

406 ms

1

2

sf

3

49 s

6.3 s

Z=116

„stop detector"

SHIP: G. Münzenberg Detector: S. Hofmann

single isotope identificationvia alpha decays

v ~ E/B

Δv/v = 0.1

The Velocity Filter SHIP at GSI

100 / s

Separation + Single Event Identification

Synthesis of superheavy nuclei at SHIP

The reaction 48Ca + 248Cm → 296116* (2010)

9.927 MeV, 0.58 s

10.625 MeV, 13 ms

9.184 MeV, 32 s

9.818 MeV, 1.9 s

10.533 MeV, 57 ms

9.315 MeV, 0.25 s

9.707 MeV, 4.0 s

10.029 MeV, 0.28 s

TKE = 213 MeV, 20 s

4

3

2

1

3

2

1

2

1

TKE = 213 MeV, 94 ms

TKE = 210 MeV, 34 s

293 116

289114

285Cn

281Ds

277Hs

293116

289114

285Cn

281Ds

292116

288114

284Cn

4n 3n 3n

10.502 MeV, 20 ms

4 chains 1 chain 1 chain

agree well with earlier data from Dubna

SHIP

Dubna

σ(293116)/pb

0.9

1.1

+2.1- 0.7

+1.7- 0.7

σ(292116)/pb

3.4

3.3

+2.7-1.6

+2.5-1.4

S. Hofmann et al., EPJ A 48: 62

S. Heinz et al., EPJ A 48: 32

observation of an α-branch in 281Ds

Study of Transfer Reactions at SHIP

N-rich nuclei at N = 126presently produced in fragmentation reactions

N-rich superheavy nuclei not reachable in fusion reactions

126

184

114

82

► Transfer reactions as a means to proudce new neutron-rich (super-)heavy isotopes

► Transfer reactions as first step to fusion

Study of Transfer Reactions at SHIP

48Ca + 238U at 4.90 MeV/u

5000 6000 7000 8000 9000 100000

1000

2000

3000

4000

5000

At-21

7Po-

216

Rn-

220 F

r-22

1

Ra-

224

Po-

212

Po-

213

At-21

5

Fr-21

9

Po-

214

Rn-

218

Ra-

220

Ra-

221

counts

/ 10 k

eV

alpha energy / keV

Ra-

222

550 600 650 7000

100

200

300

400

coun

ts / k

eV

Gamma energy / keV

β–

XAZ

Y

AZ+1

126

82

130

134

138142

146

150

84

86

88

90

92

80

78transfer products observed at SHIP

??

Isotope ID via α- or gamma decays

→ population of n-rich isotopes

Study of Transfer Reactions at SHIP

64Ni + 207Pb → Study of the capture process

survival CN captureER P P

Transfer

Transfer

Fusion

excitation functions of cold fusion reactions with Pb targets

Study of quasi-fission and fusion-fission

survival CN captureER P P

U(r

,Z,N

,L)

/ M

eVr / fm

232Th + 250Cf

A 1–A 2

/(A 1+A 2

)R

VNN

RDNS

nucleus-nucleus potential potential energy surface

→ potential energy landscape determines the preferred evolution paths of the nuclear system

Study of quasi-fission and fusion-fissionT

KE

/ M

eVyi

eld

/ re

l. un

its

mass number

E* = 35 MeV E* = 40 MeV E* = 46 MeV E* = 56 MeV

courtesy: Y. Itkis et al.

36S + 238U → 274Hs (Z = 108)

survival CN captureER P P

→ experiments in Dubna, JYFL, … (E. Kozulin et al.)

→ since 2012 also at GSI (E. Kozulin, S. Heinz et al.) CORSET setup

The CORSET Spectrometer

rotatable

Si stop detectorTOF(MCP detectors)

0.5 – 1 m

▪ time resolution: < 150 ps (ΔTOF/TOF ≈ 2 %)

▪ atomic mass from TOF and E (≥ 3 units for very heavy nuclei)

ΔΩ ≈ 50 msr

Si detector

TOF detector

The CORSET Spectrometer

CORSET setup at GSI

1 m

Penningtrap• mass selective• T1/2 > 100 ms

• m/Δm > 106 - 107

Time-of-Flight spectrometer• broad-band• T1/2 > 10 ms

• m/Δm > 105

stopping cell

(T. Dickel, W. Plaß et al., JLU Gießen)

Isobaric Identification through precision mass measurements

Study of other Techniques for Isotope ID

The MR-TOF-MS

DifferentialPumpingSection

Injection Trap System

Time-of-FlightAnalyzer

Ion GateIsochronous

SEM

Post-AnalyzerReflector

Gate Detectors

10-8 mbar

10-4 mbar

10-2 mbar

10-6 mbar

Kinetic Energy750 eV

W. Plass, T. Dickel et al., Univ. Gießen and GSI

ion catcher(cryogenic)

mass filterbuncher

MR-TOF-MS

Fusion Reactions with RIBs

actinide targets

Pb, Bi targets

radioactive beams

→ access to neutron-rich superheavy nucleibut: present beam intensities are too low

106 107 108 109 1010 1011 1012

100 b

10 b

100 pb

10 nb

100 nb

1 b

beam particles per second

1 nb

Required Beam Intensities

Required beam intensities to obtain 10 events per day at the given cross-section

500 μg / cm2 targets

fusion

Z ≥ 102

transfer, quasi-fission, fusion-fission

requires separator

Possible Experiments with RIBs

Study of transfer, quasi-fission and fusion-fission

in very heavy systems

Production of new n-richisotopes in deep inelastic

transfer reactions

Study of reactioncross-sections as function of the

projectile neutron number

Required beam intensities: > 107 / s

Required beam energies: ≥ 4 MeV / u

Summary

► We perform experiments in the region of the heaviest nuclei: ● Synthesis of superheavy nuclei in fusion reactions ● Study of related processes like capture, quasi-fisison, fusion-fission etc. ● Investigation of different reactions to produce new heavy isotopes

► Experimental setups: ● Separators for reactions with very low cross-sections: σ < 1 μb ● TOF–E–spectrometer for reactions with σ > 1 μb ● Multiple reflection TOF spectrometer plus injection system for separation and isotope ID

► Present RIB intensities do not allow for synthesis of SHN in fusion but allow for the study and application of quasifission, fusion-fission etc.

Collaborating Institutes

– GSI Helmholtzzentrum, Darmstadt

– Justus-Liebig-Universität Gießen

– Joint Institute for Nuclear Reactions, Dubna, Russia

– RIKEN Nishina Center for Accelerator-based Science, Japan

– Japan Atomic Energy Agency