Cluster structure of 6Li from anomalous large angle scattering of d, 3He and α-particles

CLUSTER STRUCTURE OF

CLUSTER STRUCTURE OF

66

Li

_Li

FROM ANOMALOUS LARGE ANGLE

FROM ANOMALOUS LARGE ANGLE

SCATTERING OF d,

SCATTERING OF d,

33

He AND

_{He AND}

α

α

-

-

PARTICLES

PARTICLES

N. Burtebaev

N. Burtebaev

11

, A. Duisebaev

_{, A. Duisebaev}

11

, S.B. Sakuta

_{, S.B. Sakuta}

22

,

_,

S

S

.

.

V

V

.

.

Artemov

Artemov

33

and R. Yarmukhamedov

_{and R. Yarmukhamedov}

33

1

1Institute of Nuclear Physics NNC, Kazakhstan,_{Institute of Nuclear Physics NNC, Kazakhstan,}

2

2Russian Research Center “Kurchatov Institute”, Russia_{Russian Research Center “Kurchatov Institute”, Russia}

3

Introduction

Introduction

• Problems in description of particle scattering on light nuclei. 1. The level density of compound nuclei is very low.

2. The number of particles is not so much. The role of cluster effects grows. The uniform nuclear matter approximation does not work longer.

3. Projectile is not point particle here and nonlocal effects must be more essential.

• As consequence, the Global optical model description does not include the А<12 region.

• Main objectives

1. Applicability of optical model to the description of d, 3He and

α-scattering on 6Li nuclei.

2. Taking into account channels coupling effects and clusters exchange mechanisms.

3. Obtaining the unified description the scattering data in wide energy range. Study evolution the scattering mechanism at large angles versus energy of ingoing particles.

Experimental data

Experimental data

Eα,MeV References

18.54 H.G.Bingham ea. 1971 36.6 V.I. Chuev et al. 1971 45.0 M. Bernas et al. 1975 50.5 Н. Буртебаев 1996 59.0 F. Foroughi et al. 1979 104 G. Hauser et al. 1969 166 D. Bachelier et al.1972 Ed MeV References 10 H.G.Bingham ea. 1971 12 H.G.Bingham ea. 1971 14.7 S.Matsuki ea 1969 19.6 V.I. Chuev ea 1971 50.0 A.T. Rudchik 1996 E3He MeV References 50 N. Burtebaev 1995 60 N. Burtebaev 1995 72 N. Burtebaev 1995

ANALYSIS

ANALYSIS

• Failure of standard ОМ in describing of scattering on

6Li stimulates to use other

approaches.

• Analysis was carried out using couple channels

method with collective form factor of rotation model.

The reorientation effects were also included.

• Cross sections for the one- and two-step cluster

exchange were obtained by DWBA in the framework of CRC method. Spectroscopic amplitudes α+d=6Li S A= 1.06 3He+t=6Li S A= 0.707

Deuterons scattering

Deuterons scattering

• Calculation were done in the framework of

Coupled Reaction Channel with code FRESCO

• The coupling with the first 3+ - state and the

exchange mechanism of α-particle cluster were taken into account

Blue line – coupled channel calculation

Green – exchange mechanism Red line - coherent sum

Deuterons scattering

Deuterons scattering

Optical potentials

Optical potentials

E_d, MeV V, MeV a_V, fm I_V/2A, MeVfm3 W, MeV a_W, fm I_W/2A, MeV 10 59 0.82 479 5.0 1.0 105 12 58 0.85 493 6.0 1.0 126 14.7 60 0.72 418 8.0 1.0 168 19.6 58 0.72 404 8.0 1.2 207 50 52 0.60 301 6.0 1.3 172

Optical model parameters for 6Li+d

The r_V=1.15 fm, r_W=1.7 fm, δ₂=2.0 fm parameters were fixed

3

He scattering

E, MeV V, MeV r_V, fm a_V, fm W_s MeV r_V, fm a_V, fm 50 105.4 1.15 0.755 26.5 1.7 0.93 60 111.6 1.15 0.755 24.4 1.7 0.93 72 112.5 1.15 0.782 40.4 1.46 0.83 Woods-Saxon OM potentials for scattering of 3_{He by} 6_Li

α

α

-particles scattering

-particles scattering

Coupled channels calculations + one-step deuteron exchange

Two-step deuteron exchange

α

α

-particles scattering

-particles scattering

Coupled channels calculations + one-step deuteron exchange

Two-step deuteron exchange

• Coupling of the elastic and inelastic

scattering improves the agreement but discrepancies still remain at large

angles.

• Taking into account one-step deuteron

exchange allows to describe cross sections at large angles with

spectroscopic factors from TISM. But there is a poor agreement at large angles at E=18 и 36 МэВ and in the region of θ=130о(E=50 and 59 MeV)

• Taking into account two-step deuteron

transfer improves the condition. The role of this process decreases with the increase the energy and at E>60 MeV two-step mechanism can be neglected.

α

α

-particles scattering

_{-particles scattering}

Optical potentials

Optical potentials

E_α, МэВ V, МэВ I_V, МэВ фм3 V, МэВ I_W, МэВ фм3 18.54 142.9 545 10.0 74 36.6 120.0 458 19.7 146 45.0 115.0 438 11.0 81 50.5 110.0 420 12.0 89 59 105.0 401 14.0 104 104 90.0 343 19.0 140 166 85.0 324 21.0 155

• r

V

=1.15 fm, a

V

=0.78 fm

r

W

=1.7 fm, a

W

=0.65 fm

CONCLUSIONS

CONCLUSIONS

• An unified description of elastic scattering of d,

3

He

and α-particles on

6

Li has been obtained in the

broad energy range with taking into account the

coupled channels effects and the clusters exchange

mechanisms.

• It was shown that the experimental angular

distributions can be described only if the exchange

mechanism of the elastic transfer of d, t, α-clusters

was taken into account.

• In case of α scattering there is an evidence of

visible contribution of two-step deuteron transfer.

• Two-step contribution decreased with the energy

increase and at E >60 MeV this process can be

neglected.

• It was shown that the global optical potential

obtained for nuclei with A >12 can be applied for