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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