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Study of multi-neutron emission in the Study of multi-neutron emission in the -decay of -decay of 1111LiLi

Spokespersons

F. Delaunay (LPC Caen), D. Cano-Ott (CIEMAT Madrid)

Collaboration

LPC Caen

CIEMAT Madrid

IEM, CSIC, Madrid

Chalmers University, Göteborg

IFIC, Valencia

UPC, Barcelona

University of Aarhus

IPN Orsay

CEA/DAM/DIF, Bruyères-le-Châtel

Towards 2-neutron correlation studies

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MotivationMotivation

-decay of 11Li:

• Q = 20.6 MeV• Weakly bound daughter 11Be Variety of delayed particle emissions

Delayed 2-neutron emission:

• P2n = 4.2 %• No measurement of 2-neutron kinematics (correlations?)• Tentative 2-neutron decay paths from 1-neutron transitions

Delayed 1-neutron emission still unclear:

• Unresolved weak transitions, uncertain branching ratios…

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Latest study: Hirayama et al., PLB 611 (2005) 239

Previous studies: Previous studies: -1n-1n

TOF (ns)20 40 60 80 100 120 140

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Detection of 2 neutrons in coincidence energies and angles

F.M. Marqués et al., TONNERRE plastic array, GANIL/LISE3

No particle discrimination Data dominated by random coincidences involving -rays, ambient -rays, cosmic rays (80-90 %...)

-n-

--

Previous studies: Previous studies: -2n-2n

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Goals of the experimentGoals of the experiment

Measure directly for the 1st time 2 delayed neutrons in coincidence

Use an array of liquid scintillator modules• Granularity Angular resolution• Neutron TOF Energy• Liquid n- discrimination suppression of background (, …)

Digital signal processing improved discrimination lower En threshold

Feasibility of correlation studies between delayed neutrons Sequential or simultaneous emission? Correlated or uncorrelated neutrons? Possible insight into configuration of neutrons in the decaying state

+ Improved picture of single neutron emission

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Experimental setupExperimental setup

Far array(10 det’s)

Near array (30 det’s)

HPGe

+ Digital electronics & DAQ

11Li beam

Plastic TOF start

40 liquid modules:• 20 cm in diameter, 5 cm thick• ~40 % intrinsic efficiency• n- discrimination

Near array: d = 1.5 m• solid angle : 3.3 % of 4• E=70 keV at 1 MeV n-n coincidences

Far array: d = 3 m• E=35 keV at 1 MeV • solid angle : 0.3 % of 4 Precise tagging of 1 of the 2 n Improved 1n data

Modules characterised with monoenergetic neutrons

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Count-rate estimatesCount-rate estimates

11Li rate: ~1000 ions/s(Ta foil target + W surface ionisation source)

2-neutron coincidences:Assuming 50 % of the 2-neutron intensity detectable (threshold En~500 keV)

10 events/h in near array 1 event/h between near and far array

1-neutron emission: for a transition with 1 % intensity 380 events/h in near array 30 events/h in far array

-n- coincidences (-1n to excited states of 10Be):Assuming 2 % photopeak efficiency, 1 % 1n-line, 1 -ray in 10Be

8 events/h in near array 0.7 event/h in far array

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Beamtime requestBeamtime request

For ~1000 2n events in near array: 15 shifts

15 shifts will also give:

• For a 1 % 1n transition: 46000 events in near array ~10 times Hirayama’s statistics 3800 events in far array with E resolution twice as good as Hirayama’s

• -n- coincidences:

1 % 1n transition, 2 % -efficiency, 1 -ray in 10Be 900 events involving near array 80 events involving far array

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• 11Li, ~1000 ions/s: 15 shifts

• Test & calibration beam: 49K (P1n = 86 %), ~500 ions/s 2 shifts

• Electronics & DAQ tuning: 1 shift

• 49K-11Li beam changeover: 1 shift

Total beamtime request: 19 shifts

Summary of beamtime requestSummary of beamtime request

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CollaborationCollaboration

LPC Caen : N.L. Achouri, F. Delaunay, J. Gibelin, F.M. Marqués, N.A. Orr,M. Parlog, M. Sénoville

CIEMAT, Madrid : D. Cano-Ott, A. Garcia Rios, T. Martinez, M. Mendoza,C. Santos

IEM, CSIC, Madrid : M.J.G. Borge, E. Nacher, A. Perea, O. Tengblad

Chalmers University, Göteborg : A. Heinz, B. Jonson, T. Nilsson, G. Nyman

IFIC, Valencia : A. Algora, C. Domingo, B. Rubio, J.L. Tain

UPC, Barcelona : R. Baeturia, F. Calvino, B. Gomez

University of Aarhus : H.O.U. Fynbo, K. Riisager

IPN Orsay : M. Assié, N. de Séréville

CEA/DAM/DIF, Bruyères-le-Châtel : B. Laurent, X. Ledoux

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11Li decay scheme Hirayama et al., PLB 611 (2005) 239

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Simulated TOF spectra

Near array

46000 counts for a 1% 1-n line

Far array

3800 counts for a 1% 1-n line

M. Sénoville

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n + + 2n

Previous studies: Previous studies: 11Li -2n with TONNERRE

F.M. Marqués

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TOF response to monoenergetic neutrons

Liquid cell (CIEMAT)20 cm diameter, 5 cm thickEn=1.2 MeV, Threshold ~500 keV

TONNERRE plastic bar160 x 20 x 4 cm3

En=1 MeV, Threshold ~750 keV

Preliminary

S. Pietri, LPC, PhD thesis, 2003

Tests at CEA Bruyères-le-Châtel

23-28 Oct. 2011

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Cross-talk probability measurement

86 cm51°

A

BShield

Target

1.5 MeV neutrons

Cross-talk

Preliminary

NAB/NA ~ 10-4

Threshold ~ 500 keV

M. SénovilleN.L. Achouri

CEA Bruyères-le-Châtel23-28 Oct. 2011

Simulations:NAB/NA ~ 1.5 x 10-4

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Neutron- discrimination

d + d → 3He + n(4.3 MeV) Q

slow

/ Q

tot

Threshold = 100 keVee En~500 keV

Neutrons