Experimental research programme of Zagreb group on

structure of light nuclei

Neven Soić Ruđer Bošković Institute Zagreb, Croatia

Workshop “Ab initio understanding of light nuclei” Birmingham, 12. Dec 2012.

Ruđer Bošković Institute + Physics Department, Faculty of Science, University of Zagreb, Zagreb, Croatia

A. Di Pietro, P. Figuera, M. Lattuada, LNS INFN, Catania, Italy

M. Freer, N. Ashwood, N. Curtis, Tz. Kokalova Wheldon, C. Wheldon, V. Ziman, University of Birmingham, United Kingdom

W. von Oertzen, H. G. Bohlen, Hahn-Meitner-Institut, Berlin, Germany

I. Martel, L. Acosta, A. M. Sánchez-Benitez, Universidad de Huelva, Spain

T. Davinson, M. Aliotta, A. Shotter, University of Edinburgh, United Kingdom

N. Orr, F. Delaunay, J. Gibelin, F. M. Marqués, Laboratoire de Physique Corpusculaire, Caen, France

Collaborators

Local motivation Zagreb group (Šlaus, Cindro, Miljanić, Zadro, …):

- tradition in neutron induced reactions

- one of the world’s first 14 MeV neutron generator was locally built at Ruđer Bošković Institute

clustering in neutron rich nuclei

end of ’80 installed 6MV EN Tandem van de Graaff accelerator

Clustering in light nuclei with extra neutrons

4<A<20, situation in middle 90’s:

- spectroscopy very incomplete

- almost no information on alpha-decay of excited states

- other interesting decays (6He, 8Be, …) unexplored

Cluster states in light nuclei: 10Be

2+ state at Ex= 7.54 MeV

very strong in a-transfer

observed a-decay large a-reduced width

state at Ex= 10.15 MeV

does not decay through the 9Be+n channel!

the strongest peak in 6He+a coincidences

Jp=4+ assignment favoured

known 0+ intruder state at Ex= 6.18 MeV

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

NUCLEAR MOLECULE!

rotational band

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

extreme deformation!

Cluster states in light nuclei: 10Be

N.Soić et al, Europhys.Lett. (1995)

Đ.Miljanić et al, Fizika (2001)

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

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

M.Freer et al,

Phys.Rev.Lett. (2006)

American Institute of Physics Physics News Update 762,

“Nuclear Molecule: Nature’s smallest dumbbell”

Nuclear molecules

similar to atomic case:

two strongly bound inert cores (e.g. a-particles)

weak attractive potential that becomes repulsive at small distances

weakly bound single-particle orbits of valence particles

large transfer probability of valence particles

essential 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) 37

W.von Oertzen, M.Freer, Y.Kanada-En’yo , Phys. Rep. 432 (2006) 43

M.Freer, Rep. Prog. Phys. 70 (2007) 2149

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

10Be: selectivity in decay

tVDG @ IRB Zagreb:

7Li(7Li,6Hea)4He and

7Li(7Li,9Bea)n at 8 MeV

new 10.15 MeV state: decays by alpha-particle emission

10.6 MeV state: decays by neutron emission

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

10Be: state at 10.15 MeV not seen in inclusive spectra?

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

10Be: state at 10.15 MeV not seen in inclusive spectra?

Catania ‘02, M.Milin et al, unpublished

plus many 9Be(d,p) experiments…

10Be: state at 10.15 MeV

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

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

a + 6He(0+)

Decay:

a + 6He(2+)

a + 6He(0+)

10Be: state at 10.15 MeV

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

Jp= 3- !

same experiment:

- first observation of the a-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

6He+6,7Li experiment

development of RNB: 6He

idea: pick-up of alpha-particle by 6He-beam

6He: alpha-particle + 2 halo-neutrons

6,7Li – well-clusterised targets

single-events: spectroscopic factors for 10Be=6He+a

highly-segmented set-up covering large (4 sr) solid angle multiple (4!) coincidences

detailed reconstruction of sequential decay reactions

results also for cluster states in 9Be and 14C

6He Jp= 0+, S1n=1.87

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

RRMS≈ 2.5 fm, (RRMS(a)≈ 1.7 fm)

6He+6,7Li experiment at Louvain-la-Neuve

energy: 18 MeV, intensity: up to 107 pps (≈ pA)

only impurity: HeH2

targets, 6,7LiF, 12C

set-up: 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 – results for 10Be

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

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

(curves: DWBA with S=1)

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

(spectroscopic factor 4 times larger than for the ground state)

6He+6,7Li – results for 10Be

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

large reduced width for a-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+a coincidences

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

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 Jp= 0+)

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

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

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

Results for 10Be: resonant elastic scattering

Ex=10.2 MeV Jp=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

M.Ito, N.Itagaki: 10Be, 12Be - more states to look for!

“ionic” states

“molecular” states

“atomic” states

10Be, 10B, 10C

10B

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

- 10B state at Ex= 11.3 MeV decays via 6Li**+a

M.Uroić et al., AIP Conf. Proc. 1165 (2009) 31

10B

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

- 10B state at Ex= 11.3 MeV decays via 6Li**+a

M.Uroić et al., AIP Conf. Proc. 1165 (2009) 31

10Be:

0+- 6.18, 2+- 7.54, 4+- 10.15 MeV

10B:

0+- 7.56, 2+- 8.89, 4+- 11.3 MeV

- spin assignment needed for the state at 11.3 MeV!

moment-of-inertia for 10B slightly (5-10%) larger

DSSSD

DSSSD

T FC

10B and 10C: 7Be+6,7Li experiment at LLN

LLN ’08

7Be at 45 MeV, I≈ 107 pps (7 days of beam on target)

targets: 6LiF, 7LiF, 12C

10B and 10C: 7Be+6,7Li experiment at LLN

idea: 6Li (g.s.) dominantly a+d, but also 3He+t

(see e.g. Werby et al., Phys.Rev.C 8, 106)

direct comparison between two mirror channels!

also to be compared to the 7Li+6Li measurement already performed in Catania at the same energy

also:

and many other channels

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

7Be+6Li

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

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

A=10 – data analysis in progress

7Be+6Li

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

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

7Li+6Li

t+10B* (T=1) t+a+6Li (T=1)

3He+10Be* 3He+a+6He

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

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

10B+10B 10B+10B* 10B+10B 10Be+10C

LLN exp analysis M.Milin

Catania exp analysis M.Uroić

2nd Catania exp analysis

D. Jelavić Malenica

11B, 11C

• bands of alpha- cluster states?

N.Soić et al., Nucl.Phys.A 742(2004) 271

Nuclear molecules with three centres: 13C?

Nuclear molecules with three centres: 13C?

M.Milin and W.von Oertzen, EPJA 14 (2002) 295

13C from 9Be+a resonant elastic scattering

M.Freer et al., PRC 84 (2011) 034317

Experiment performed @ tVdG RBI Zagreb

Neutron rich light nuclei - search for three-centre structures in 14C and 16C

N. Soić et al, Phys. Rev. C 68 (2003) 014321

Future: Search for 6He decay of 14C states

GANIL experiment E580S: Spectroscopy of neutron rich light nuclei: decays of 16C and 5H unbound states RBI, Uni of Zagreb, Uni of Birmingham, INFN-LNS, Uni of Huelva, LPC Caen, GANIL, iThemba Labs

Measurement of the 6He+18O reaction: 16C objectives: characterization of the He-decaying excited states identification of the members of the rotational bands. - rotational bands with triangular structure - oblate (band head 0+ and 3-) and linear chain structure – prolate (band head 0+) - the 18O(6He,8Be)16C*, 18O(6He,8Be6He)10Be and 18O(6He,8Be4He)12Be reactions - 2 proton pick-up reaction (6He,8Be)

Measurement of the 6He+7Li reaction: 5H objectives: search for di-neutron decay of the resonances, identification of the ground state resonance - measurements of the 7Li(6He,8Be)5H and 7Li(6He,8Be3H)2n reactions - proton stripping from 6He beam and 2 proton pick-up from 7Li target

17O from 13C+a resonant elastic scattering

Experiment performed @ tVdG RBI Zagreb analysis Lovro Prepolec

18O

“shell-model” states

“ionic” states

“molecular” states

Experiment at IPN Orsay (Oct/Nov 2012)

13C + 9Be → α + 18O* 18O*→ α + 14C, Q = 6.604 MeV 18O*→ 6He + 12C, Q = -5.549 MeV 18O*→ 8Be + 10Be, Q = -5.500 MeV

Kinematically complete measurement

coincidences α + α/6He/ 8Be

Ethr(α + 14C) = 6.228 MeV

Ethr(6He + 12C) = 18.380 MeV

Ethr(8Be + 10Be) = 18.332 MeV

Goal: characterization of the 18O resonances in excitation energy range 7 - 25 MeV: excitation energy, width, partial widths

13C 9Be

α

18O*

Setup

T1,T2: 10o-30o

T3,T4: 50o-80o ; T5,T6: 80o-115o

Identification of all helium nuclei

Kinematically complete measurements:total reaction energy, relative energy between any pair of nuclei in the exit channel

Resolution: 4,6He:energy 200 keV, Q-value < 500 keV, exc. en. 100 keV

DEMON chamber (LPC – GANIL)

E (MeV)

ΔE

(MeV

)

6He

4He

analysis Lovro Prepolec

Carbon – carbon burning

• Objective: search for 12C+12C resonances at 24Mg excitations 15 -20 MeV and full characterization of the resonances (excitation energy, width, spin, parity, partial decay widths)

• Two-fold reason: nuclear structure & astrophysical motivation

D. A. Bromley, J. A. Kuehner, E. Almquist, Phys. Rev Lett 4 (1960) 385

Elastic scattering data Resonant phenomena in heavy ion reaction

E. Almquist, D. A. Bromley, J. A. Kuehner, Phys Rev Lett 4 (1960) 515

Reaction data Formation of quasi-molecular states in 24Mg

50 years later: - number of resonances decaying into various channels - kind of unique nuclear system, very complex structure - governed by cluster structure of 12C – oblate deformation in gs - not fully understand yet

B. R. Fulton et al, Phys Lett B 267 (1991) 325

M. Freer et al, Phys Rev C 57 (1998) 1277 C. Metelko et al, Phys Rev C 68 (2003) 054321

M. Freer et al, Phys Rev C 57 (1998) 1277

But main focus of these studies has been on higher excitations in 24Mg No data below 20 MeV !

• Low energy data for 12C+12C fusion reaction crucial for many astrophysical phenomena: quiescent burning of massive starts, super-AGB stars, super-bursts and supernovae type Ia

• The most relevant quantity: total reaction fusion rate 12C + 12C → 24Mg +

12C + 12C → 20Ne + α

12C + 12C → 23Na + p 12C + 12C → 23Mg + n

Existing data show large discrepancies Low energy resonance ?

E. F. Aguilera et al, Phys. Rev. C 73 (2006) 064601 T. Spillane et al, Phys. Rev. Lett. 98 (2007) 122501

12C+16O measurement at LNS Catania Apr 2010

Coincident detection of 2 reaction products 12C + 16O → 4He + 12C + 12C Q=-7.16 MeV Ethr(

24Mg)=13.93 MeV

→ 4He + 16O + 8Be Q=-7.37 MeV Ethr(24Mg)= 14.14 MeV

→ 4He + 20Ne + 4He Q=-2.54 MeV Ethr(24Mg)= 9.31 MeV

→ 4He + 23Na + 1H Q=-4.92 MeV Ethr(24Mg)= 11.69 MeV

16O a

12C

24Mg

Excitation energy range: 1 – 6 MeV above the 12C + 12C threshold, 15 – 20 MeV in 24Mg excitation Resonance parameters: excitation energy, width, spin, parity and partial decay widths of the resonances

Main goal: identify low spin states with significant 12C+12C partial width

16O beam energy: 90 MeV, target: 60 μm/cm2 carbon target

RBI, Uni of Zagreb INFN-LNS Catania, Uni of Birmingham, Uni of Huelva

6 detector telescopes: 20 μm SSSD & 500 or 1000 μm DSSD or PSSD

24,26Mg - Resonant scattering measurements

- heavy ion beam: 20Ne / 23Na for 24Mg studies, 22Ne for 26Mg - light gas target: 4He / 1H – all chamber volume filled up at low pressure (astrophysical), 4He high pressure (structure studies) - resonant scattering and resonant reactions -proposal submitted to LNL INFN PAC

beam slows down through gas, at resonance energy enhanced scattering and production of 12C+12C

Clustering phenomena in nuclear physics: strengthening of

the Zagreb–Catania–Birmingham partnership

FP7 REGPOT, Start May 2008, End: July 2011

http://lnr.irb.hr/cluna

Partners • Ruđer Bošković Institute – coordinator • University of Zagreb • University of Birmingham, UK • INFN – Laboratori Nazionali del Sud Catania, Italy

Funding: 370,000 € Equipment ~ 35 % total Upgrade of experimental beam line at the RBI Tandem New PhD student position Travelling – exchange of knowledge and experience, practical trainings

Equipment Si detectors: SSSD thin 20 μm, DSSSD and PSD Neutron detectors- EJ-309 Electronics, VME DAQ units

Upgraded Facility for Development of Silicon and

Diamond Particle Detector Systems

FP7 REGPOT, Start August 2010

http://lnr.irb.hr/pd

• 3 largest laboratories of the Division of Experimental Physics

•Laboratory for ion beam interactions •Laboratory for nuclear physics •Laboratory for high energy physics

~33 employees, 15 directly included

All three laboratories participate in WP2 Development of novel detector arrays LIBI – strip, PSD LNP- strip, PSD, pixel LHEP – strip, pixel

Funding: 1,319,538 € silicon part: 405,156 €

Equipment ~ 35 % total New postdoc position Travelling – exchange of knowledge and experience, practical trainings

Partners

University of Birmingham (Department of Physics), UK

University of Huelva, Spain

University of Bristol (Department of Physics), UK

University of Manchester, (Department of Physics), UK

University of Torino, (Department of Experimental Physics), Italy

University of Frankfurt/NA61/CERN

GSI (Detectorlabor group), Germany.

SILICON DETECTORS

DAQ/System control /FPGA

DIAMOND DETECTORS

VACUUM CHAMBER LASER TESTING

Detector telescopes: 50 x 50 mm2

20 μm SSSD + 1000/500 μm PSD and DSSSD (+ CsI) Particle identification from p to cca 12C

• Croatia enters EU next summer • EU structural funding 2014. – 2020. • Political decision: ~ 10% allocated for research • RBI proposal for structural funding project: large project for all

institute units at value of 50 M€; two specific smaller projects in collaboration with Uni of Zagreb and other research institutions at the RBI campus, in total 85 – 90 M€

• Our department propose upgrade of the Tandem Van de Graaff accelerator, detector & electronics R&D & testing facilities, new beam line with large scattering chamber for nuclear physics research, new laboratory areas of cca 1000 m2

• Letters of support from European (research) institutions are required and very much appreciated !