Coulomb barrier distributions:

puzzles and recent experiments

Eryk Piasecki

and

The Barrier CollaborationSeptember 2006

B

VN + V

C

VN

VC

V(R)

R

V(R)

R

58Ni + 60Ni

A.M.Stefanini et al., Phys.Rev.Lett. 74(1995)864

Determination of importance of various couplings (vibrational, rotational, single-particle ones) in different reaction and systems.

What is the influence of the Q of reaction?

What is the influence of formfactors?

Determination of the nuclei deformation parameters (2, 3, 4 and perhaps even 6), including their sign, what is pretty difficult using the standard Coulomb excitation methods.

Reliable calculation of the nucleus-nucleus cross-sections in sub-barrier region.

Optimization of superheavy elements production.

Investigation of the influence of exotic nuclear structures (e.g. “halo”) on the reaction mechanisms.

Motivation (hopes)

Two experimental methods:

fusfus EdE

dED

2

2

Ruth

qeqe dE

dED

42 44 46 48 50 52 54 56 58 600.1

1

10

100

1000

fus

[mb]

Ecms

[MeV]

42 44 46 48 50 52 54 56 58 600.0

0.2

0.4

0.6

0.8

1.0

qe/

Rut

h

Eeff

[MeV]

H.Timmers et al., NP A 633(1998)421

Are the methods equivalent?

H.Timmers et al., NP. A584(1995)195

16O + 144Sm

Shape of 20Ne

Cluster

model

Predictions of Coupled Channels Theory

for 20Ne + 118Sn(CCFULL code)

No couplings

With couplings

Suspicion: perhaps the „weak” channels (transfers,

s.p. excitations) are not that weak as it is assumed

in the CC calculations?

What we miss in the calcs???

20Ne + 116Sn

p - stripping

- stripping

0,92 0,96 1,00 1,04 1,08 1,12 1,161E-4

1E-3

0,01

0,1

22Ne

20Ne

16-12-2005 00:45:32

Transfer in 20,22Ne + 118Sn

-

tran

sfer

/ to

tal b

acks

catte

ring

Eeff

/B [MeV]

20Ne; Tel1+3+4 (160o)

20Ne; Tel2 (120o)

22Ne; Tel1+3+4 (160o)

22Ne; Tel2 (120o)

~Z1*Z2*

50 55 60 65 70

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

50 55 60 65 70

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

30 35 40 45

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

30 35 40 45

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

exp. data inert

CC: 4(20Ne)=0.27

Ne(0+,2+,4+,6+) x Sn(0+,2+,2ph);

2(Ne) = 0.46,

2(Sn) = 0.13

20Ne + 118Sn

Dqe

[MeV

-1 ]

CC: 4(22Ne)=0.10

20-09-2006 21:24:10

22Ne + 118Sn

Dqe

[MeV

-1 ]

Eeff

[MeV]

22Ne + natNi

20Ne + natNi

Eeff

[MeV]

20Ne+58Ni 20Ne+118Sn 22Ne+118Sn0

50

100

150

200

250

300

-1n -2n +1n +2n -1p +1p -1

Ca

lc. t

ran

sfe

r cr

oss

se

ctio

ns

[mb

]

Projectile + Target

Estimated from systematics

20Ne+58Ni 20Ne+90Zr 20Ne+92Zr 20Ne+118Sn 20Ne+208Pb0

50

100

150

200

250

300

Near-barrier energy25-12-2005 19:21:18

-1n -2n +1n +2n -1p +1p -1

Ca

lc. t

rans

fer

cros

s se

ctio

ns [m

b]

Projectile + Target

Estimated from systematics

40 42 44 46 48 50 52 54 56 58 60 620.00

0.05

0.10

0.15

0.20

90Zr

Dqe

40 42 44 46 48 50 52 54 56 58 60 620.00

0.05

0.10

0.15

0.20

90Zr

Dqe

40 42 44 46 48 50 52 54 56 58 60 620.00

0.05

0.10

0.15

0.20

92Zr

Dqe

Eeff

[MeV]

Expectations & experimental results:20Ne + 90Zr:

weak neutron

transfer

barrier structure

20Ne + 92Zr:

stronger neutron

transfer

no structure

wider barrier distribution

Open questions:

Transfers and/or s.p. exciations?

Quantitative relation between the strength of „weak” channels and barrier smoothing

Why the barrier structure has been observed in many experiments?

Is Dfus as sensitive for smoothing as Dqe?

CC treatment of these problems

Is the puzzle solved??

84 88 92 96 100 1041E-3

0.01

0.1

1

10

100

1000

84 88 92 96 100 104

0.0

0.2

0.4

0.6

0.8

1.0

84 88 92 96 100 1040.00

0.05

0.10

0.15

0.20

2005-09-01 08:40:1920Ne + 208Pb (CC calculations)

fus [

mb

]

q

e/R

uth

fusion qe

Dqe; D

fus

[Me

V-1]

Ecms

[MeV]

JYUAug/Sept. 2006

Simultaneous measurements of Dfus & Dqe

E

MCP START

beam

20Ne

Target

natNi90,92Zr

118Sn

206,208Pb

(E,ToF) A

LToF = 55cm

FWHMToF ≈ 200ps

Measurements of weak channels strengths

(transfers & s.p. excitations)

SD array

MCP

Targets

Energy

20Ne

22Ne

19Fe

16O

20Ne + 118Sn

Conclusions:

•The weak channels can have quite considerable influence on the barrier height distributions

•There are still some (interesting) open questions

Transfers and/or s.p. exciations?

Quantitative relation between the strngth of „weak” chanels and barrier smoothing

Why the barrier structure has been observed in many experiments?

Is Dfus as sensitive for smoothing as Dqe?

Some of the answers are probably already in our hands and will be presented soon.

CC treatment of these problems is badly needed

September 2006

The BARRIER Collaboration:Warsaw University (Inst. Exp. Phys. & Heavy Ion Lab):

Ł.Świderski, P. & T. Czosnyka, J.Jastrzębski, A.Kordyasz, M.Kowalczyk, M.Kisieliński, K.Piasecki, E.Piasecki

Białystok University: T.Krogulski

Technische Universitat (Darmstadt): M.Mutterer

Radium Institute (St. Petersburg): S.Kchlebnikov, G.Turin

University of Jyvaskyla: W.Trzaska, M. Sillanpää

Tohoku University: K.Hagino

IReS (Strasbourg): N.Rowley

Inst. Nucl. Studies (Warsaw): K.Rusek

LNL (Legnaro): A.Stefanini

LNS (Catania): P.Russotto

JINR (Dubna): E.Kozulin, S.Smirnov

Kurchatov Inst. (Moscow): A.Ogloblin, S.Dmitriev