matko milin faculty of science, university of zagreb, croatia reactions induced by low energy 6 he...

Matko MilinFaculty of Science,

University of Zagreb,Croatia

Reactions induced by low energy 6He beam

S.Blagus, D.Jelavić, Ð.Miljanić, N.Soić, M.Uroić, M.Zadro

Ruđer Bošković Institute, Zagreb, Croatia

neutronhalo

neutronskin

protonhalo

10He

neutron drip

line

Introduction: light nuclei

Introduction: 6He structure Borromean structure two loosely bound neutrons

orbiting an -core large interaction radius! RRMS≈ 2.5 fm vs. RRMS()≈ 1.7 fm components: di-neutron and cigar-

like

M.V. Zhukov et al, Phys. Rep. 231 (1993) 151

6He J= 0+,

S1n=1.87 MeV, S2n=0.97 MeV, T1/2=0.807 s

Introduction: 6He induced reactions

before our campaign: elastic scattering on different targets two-neutron transfer reaction 4He(6He,) break-up reactions suppression or enhancement of 6He-

induced fusion? …

what happens when another particle is added to such an loose object? would “nuclear molecules” be formed?

Introduction: nuclear molecules

similar to atomic case: two strongly bound inert cores (e.g. -particles) weak attractive potential that becomes

repulsive at small distances weakly bound single-particle orbits of valence

particles large transfer probability of valence particlesessential difference: mass of valence

particles (electrons vs. nucleons)

equality of valence particles and parts of cores (identical nucleons Pauli principle!) W.von Oertzen

Z.Phys. A354 (1996) 37W.von Oertzen et al,

Phys. Rep. 432 (2006) 43

Nuclear molecules: experimental signatures

production reaction mechanism:

cluster transfers preferred decay reduced widths:

large for cluster decay “resonant particle decay spectroscopy”:

production of the state of interest and its sequential decay

rotational bands (deformed quantum objects can rotate!) strong gamma-transitions within members of band parity splitting

“complete” spectroscopy!

wave function overlap

two cyclotrons primary beam: protons at 30 MeV

- intensity: 0.5 mA (15 kW at target!) production reaction: 7Li(p,2p)6He

Louvain-la-Neuve RNB facility

Louvain-la-Neuve RNB facility

two cyclotrons primary beam: protons at 30 MeV

- intensity: 0.5 mA (15 kW at target!) production reaction: 7Li(p,2p)6He 6He extracted and purified with electric /

magnetic fields and chemical traps (as fast as possible)

secondary beam (6He):

- energy: 5-70 MeV

- intensity: up to 106 - 107 pps (≈ pA)

- only impurity: HeH2

Detectors

silicon strip detectors different configurations developed in

collaboration with Micron Semiconductors Ltd.

modular design allows different geometries dimensions: up to 5cm x 5cm, thickness 20-

1000 m

T. Davinson et al, Nucl.Instrum.Meth. A454 (2000) 544

Detector set-ups

small intensity of RNBs large solid angle covered

20 sectors with 16 silicon strip-detectors, grouped into 3 arrays:

- LEDA (4-12 deg) - LAMP1 (20-65 deg) - LAMP2 (115-160 deg)

6He+6,7Li,9Be,12C

LAMP

CD/PAD LEDA

FCT

small intensity of RNBs large solid angle covered

CD – 40 m thick E detector segmented into 4x16 strips

PAD – 500 m thick E detector segmented into 4 quadrants

Detector set-ups

6He+1,2H,12,14C,16O

Experimental results

elastic and inelastic scattering on 6Li, 7Li, 9Be, 12C and 19F

large cross sections for 6He induced -particle pick-up to some 10Be states

first results for the (6He,8Be) two-proton pick-up reactions on 9Be, 12C, 16O and 19F

(6He,) transfer reactions studied on 6Li, 7Li, 9Be, 12C and 19F

widths, spins and parities for several 10Be states decay mode for 9Be, 10Be, 11Be and 14C states quasi-free scattering of 6He on deuteron in 6Li and

on -particle in 9Be production of 10-12B by fusion in 6He+6Li and 6He+7Li

reactions …

Transfer reactions: (6He,8Be)

8Begs= 2+93 keV: unique signature simple extraction

other advantages: 0+, Q-values, wave-function overlaps,…

clearly observed on the 12C (clearly direct!), 16O and 19F (populating many states in 10Be, 14C and 17N) M.Milin et al,

Phys.Rev. C70 (2004) 044603

6He

10Be

6He6Li

2H

Sequential decay reactions

several 10Be states seen in 6,7Li(6He, 10Be* 6He)3,2H reaction

Results for 10Be: resonant elastic scattering

EExx=10.2 MeV=10.2 MeV JJ=4=4++

with 4He gas target: 6He+4He 10Be* 6He+4He

the 10.15 MeV state again the strongest

M.Freer et al, Phys.Rev.Lett. 96 (2006) 042501

22++ state at E state at Exx= 7.54 = 7.54 MeVMeV

very strong in -transfer observed -decay large -reduced width

state at Estate at Exx= 10.15 = 10.15 MeVMeV

the strongest peak in 6He+ coincidences J=4+ assignment favoured

known 0known 0++ intruder state intruder state at Eat Exx= 6.18 MeV= 6.18 MeV

NUCLEAR MOLECULE!NUCLEAR MOLECULE!

M.Milin et al, Nucl.Phys. A753 (2005) 263

rotational bandrotational band

extreme deformation! moment of inertia >2.5 times larger than for already deformed 10Be ground state band

Results for 10Be


22++ state at E state at Exx= 7.54 = 7.54 MeVMeV

very strong in -transfer observed -decay large -reduced width

state at Estate at Exx= 10.15 = 10.15 MeVMeV

the strongest peak in 6He+ coincidences J=4+ assignment favoured

known 0known 0++ intruder state intruder state at Eat Exx= 6.18 MeV= 6.18 MeV


Results for 10Be


Theory: 10Be

Y

.Kan

ad

a-E

n'y

o e

t al,

P

hys.

Rev.

C 6

0 (

1999)

064304

Catania/Edinburgh/LLN/Zagreb collaboration: 6He+64Zn in LLN

fusion cross section NOT enhanced!

reaction cross section

enhanced

Fusion of halo nuclei around barrier

... 7Li+7Li (Zagreb ‘94) 7Li+9Be, 7Li+11B (Catania, ‘96) 6He+6Li (Louvain-la-Neuve, ‘98) 6He+6Li, 6He+7Li, 6He+12C (Louvain-la-Neuve, ‘99) 7Li+7Li (Zagreb ‘99) 18O+9Be (Catania, ‘00) 13C+9Be (Catania, ‘02) 6He+14C, 6He+9Be (Louvain-la-Neuve, ‘05) …

+ in collaboration with Berlin group: 14N+10Be, 7Li+9Be, 18O+13C, 12C+12C, 12C+13C, 12C+14C, 7Li+12-

14C, ...+ in collaboration with Birmingham group: 9Be+7Li, 7Li+7Li, 10Be+12C, 18O+12C, 13C+14C, 18O+9Be, 12Be+12C, 6He+4He, ...

Nuclear molecules: list of experiments

IRB-experiments: 10.15 MeV state in 10Be

Zagreb: 7Li(7Li,6He)4He at 8 MeV

decay mode: alpha-particle emission

10.6 MeV state: decays by neutron emission

N. Soić et al, Europhys. Lett. 34 (1996) 7

DSSSD

DSSSD

T FC

Conclusions and outlook

different reactions measured with 6He radioactive

beam: 6He+1,2H,4He,6,7Li,9Be,12,14C,16O clustering in 8Li, 9Be, 10Be, 11Be, 14C studied (partial) angular distributions obtained for different transfer reactions, some data still under analysis (part of) future work of Zagreb group: 7Be induced reactions!

7Be+6,7Li approved in LLN, to be

measured in automn 2008

ISOLDE, CERN 11/06

property of theHuelva group

Collaborators Ð.Miljanić, S. Blagus, D.Jelavić, N.Soić, M.Uroić,

M.Zadro, Ruđer Bošković Institute, Zagreb, Croatia;

M.Majer, University of Zagreb, Zagreb, Croatia;

C.Angulo, E.Casarejos, N.de Sereville, A.M.Sánchez-Benitez, Institut de Physique Nucléaire, Université Catholique de Louvain, Louvain-la-Neuve, Belgium;

S.Cherubini, A.Di Pietro, P.Figuera, M.Lattuada, A.Maggio, A.Musumarra, M.G.Pellegriti, C.Spitaleri,

LNS, INFN, Catania, Italy;

T.Davinson, A.N.Ostrowski, A.C.Shotter, University of Edinburgh, Edinburgh,

Great Britain;

N.Ashwood, N.Curtis, M.Freer, D.Price, V.Ziman,University of Birmingham, Birmingham,

United Kingdom;

L.Acosta, M.A.G.Alvarez, I.Martel. Universidad de Huelva, Huelva, Spain

Introduction

6He+1H elastic scattering, two neutron transfer

Quasi-free scattering 6He quasi-free scattering off d- and -clusters in 6Li observed, and not observed for the case of 7Li (L=0 for -d in 6Li and L=1 for -t in 7Li)

Ð.M

ilja

nić

et

al,

to b

e

pu

blish

ed

d3dEd1d2

~ k.f. |(q)|2 d212

d

Fusion strong contribution from the xLi+ coincidences observed (in both 6He+6Li and 6He+7Li)

peaks corresponding to the 10-12B states identified…

the influence of halo structure on reaction mechanism around the Coulomb barrier

theory:

1) fusion probability enhanced because weakly bound neutrons effectively reduces the barrier

Fusion of halo-nuclei around the barrier

animation taken from: http://fys.kuleuven.be/iks/lisol/research/fusion/6hefusion_g

eneralpub.htm



eneralpub.htm

the influence of halo structure on reaction mechanism around the Coulomb barrier

theory:

2) fusion suppressed due to projectile break-up

Fusion of halo-nuclei around the barrier the influence of halo structure on reaction

mechanism around the Coulomb barrier

theory:

3) fusion probability enhanced because weakly bound projectiles tunnels


eneralpub.htm

First results:6He+209Bi - J.J.Kolata et al., Phys.Rev.Lett. 81 (1998) 4580

6He+238U – M.Trotta et al., Phys.Rev.Lett. 84 (2000) 2342

...

reaction cross section enhanced

fusion cross section enhanced

transfer cross sections large

break-up cross sections large




A.Di Pietro et al., Europhys.Lett. 64 (2003) 309

A.Di Pietro et al., Phys. Rev. C 69 (2004) 044613





reaction cross section

enhanced

The same results for 6He+238U R.Raabe et al.,

Nature 431 (2004) 823

M.Milin et al, Nucl. Phys. A746 (2004) 183

M.Milin et al, Nucl. Phys. A730 (2004) 285

Elastic and inelastic scattering

fair agreement with optical model predictions, using the 6Li –potentials

half of 15% enhancement for the 12C target due to the Borromean structure of 6He (Matsumoto et al., PRC 70, 061601)

inelastic scattering observed only for the first excited state of 12C and 9Be

Elastic and inelastic scattering

6He+9Be 17 MeV

analysis by Marija Majer

elasticinelastic

6He+9Be @ 17 MeV

only inelastic peak corresponds to the 2.45 MeV state

different states seen in the 9Be(6He,)11Be reaction, still under analysis

Transfer reactions

large solid angle

large efficiency for detecting coincidences

partial angular distributions:

1H(6He,)3H

6Li(6He,)8Li

6Li(6He,t)9Be

6Li(6He,d)10Be

7Li(6He,)9Li

7Li(6He,t)10Be

12C(6He,)14C

… M.Milin et al,

Nucl. Phys. A746 (2004) 183

Transfer reactions: 6He+6Li +8Li

direct transfers of 2n and d allow comparison of the +2n configuration in 6He with the +d configuration in 6Li

spectroscopic factors equal within 10%

more complete angular distributions needed! M.Milin et al,

Phys.Atom.Nucl. 69 (2006) 1360

2-mode DWBA

M.Milin et al, Europhys.Lett. 48 (1999) 616

and to be published

Results for 10Be: transfer reactions 6Li and 7Li: -cluster

structure ideal targets for -pickup

large cross sections for -transfer to some high-excited 10Be states observed

at least one of the states of the doublet at ≈7.5 MeV shows strong -clustering

M.Milin et al, Nucl.Phys. A730 (2004) 285and Eur.Phys.J. A, accepted


triple coincidences 6He+12C 10Be+2 strong peaks corresponding to 10Be g.s., 2+ and groups of states at ≈ 6.0 and ≈ 7.5 MeV seen

cluster states in 14C reconstructed – no strong selectivity

problems with the 14C target 16C spectrum not clean

16C

10.15 MeV state in 10Be

The data has never been published!

“weak resonances for En= 3.73 and 4.27 MeV (Ex=10.15 and 10.65 MeV in 10Be)”

9Be(n,)6He reaction (3.3 – 6.1 MeV):


A.A. Ogloblin et al., Heidelberg conference '69

Dubna: 7Li(7Li,)10Be reaction at 30 MeV


S.Hamada et al, Phys. Rev. C 49 (1994) 3192

Tokyo: 7Li(p)10Be reaction at 65 MeV


FSU: 7Li(7Li,6He)4He and 6Li(7Li,6He)3He at 34 MeV

same experiment:

- first observation of the -decay of the 2+ state at Ex= 7.54 MeV;

- decay energy only 129 keV very large reduced width!

N. Curtis et al, Phys. Rev. C 64 (2001)044604


Catania: 7Li+7Li and 7Li+9Be at 30 MeV

Đ. Miljanić et al, Fizika B 10 (2001) 235

+ 6He(0+)

Decay:

+ 6He(2+)

+ 6He(0+)

Other A=10 nuclei: 10B and 10C

10Be: rotational band of very deformed states established!

analogue states in 10B and 10C?

10B

Zagreb: p+9Be excitation functions from 5.5-9.5 MeV

diploma thesis D.Jelavić

10B

Zagreb: 11B(3He,)6Li at 15 MeV

analysis by M.Uroić

10B

Zagreb: 11B(3He,)6Li at 15 MeV

preliminary

analysis by M.Uroić

10B and 10C6Li+7Li 3He+10Be* 3He++6He

6Li+7Be

3He+10B* (T=1) 3He++6Li (T=1)

t+10C* t++6Be t+++2p

7Li+7Be +10B* (T=1) +6Li (T=1)

7Li+7Li +10Be* ++6He

N.Curtis et al, Phys.Rev.C 64 (2001) 044604

appr

oved

in

LLN new results on 10C, talk by

N.Curtis, Tuesday 17:00


triple coincidences observed: 6He+6Li 6He++d 6He+7Li 6He++t 6He+6Li 2+t+n 6He+12C 10Be+2 decay and structure of some 9Be and 14C states studied

peak in 8Be excitation spectrum at ≈0.5 MeV: decay of the 2.45 MeV state in 9Be through the 8Be*(2+)+n channel (or 5He+?)

(double coincidencesnot enough!)


6He+6Li 2+t+n

Results for 10Be: sequential decay reactions

several 10Be states seen in 6,7Li(6He, 10Be* 6He)3,2H reaction

large reduced width for -decay found for the 2+ state at Ex= 7.54 MeV; agrees with the results of Liendo et al, Phys. Rev. C 2001.

the 10.15 MeV state is always the strongest peak in the 6He+ coincidences


6He+6Li 10Be*+d 6He+6Li+d

angular correlations between the decay products can be used to assign spin and parity of the state that decays (if the decay products have J= 0+)

Monte Carlo simulations compared with the exp. results strongly favour J=4+

10Be, Ex= 10.15 MeV, J = 4+


matko milin faculty of science, university of zagreb, croatia reactions induced by low energy 6 he...

Documents

c slide

mev state

s slide

o slide

croatia slide

mev intensity

li reactions

h reaction slide