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Study of multi-neutron emission in the b -decay of 11 Li

Study of multi-neutron emission in the b -decay of 11 Li. Towards 2-neutron correlation studies. 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

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Study of multi-neutron emission in the b -decay of 11 Li

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  1. Study of multi-neutron emission in the b-decay of 11Li Towards 2-neutron correlation studies 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 CERN INTC-P-307

  2. Motivation • b-decay of 11Li: • Qb = 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… CERN INTC-P-307

  3. Previous studies: b-1n Latest study: Hirayama et al., PLB 611 (2005) 239 20 40 60 80 100 120 140 TOF (ns) CERN INTC-P-307

  4. Previous studies: b-2n Detection of 2 neutrons in coincidence  energies and angles F.M. Marqués et al., TONNERRE plastic array, GANIL/LISE3 b-m-m b-n-m No particle discrimination  Data dominated by random coincidences involving b-rays, ambient g-rays, cosmic rays (80-90 %...) CERN INTC-P-307

  5. Goals 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-g discrimination  suppression of background (g, m…) • 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 CERN INTC-P-307

  6. Near array (30 det’s) Experimental setup • 40 liquid modules: • 20 cm in diameter, 5 cm thick • ~40 % intrinsic efficiency • n-g discrimination • Near array: d = 1.5 m • solid angle : 3.3 % of 4p • dE=70 keV at 1 MeV • n-n coincidences • Far array: d = 3 m • dE=35 keV at 1 MeV • solid angle : 0.3 % of 4p • Precise tagging of 1 of the 2 n • Improved 1n data Modules characterised with monoenergetic neutrons HPGe 11Li beam • Plastic • b • TOF start Far array (10 det’s) + Digital electronics & DAQ CERN INTC-P-307

  7. Count-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 b-n-g coincidences(b-1n to excited states of 10Be): Assuming 2 % photopeak efficiency, 1 % 1n-line, 1 g-ray in 10Be • 8 events/h in near array • 0.7 event/h in far array CERN INTC-P-307

  8. Beamtime 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 • b-n-g coincidences: • 1 % 1n transition, 2 % g-efficiency, 1 g-ray in 10Be • 900 events involving near array • 80 events involving far array CERN INTC-P-307

  9. Summary of beamtime request • 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 CERN INTC-P-307

  10. Collaboration LPCCaen : 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 CERN INTC-P-307

  11. CERN INTC-P-307

  12. 11Li decay scheme Hirayama et al., PLB 611 (2005) 239 CERN INTC-P-307

  13. 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 CERN INTC-P-307

  14. bnm + bmm + b2n Previous studies: 11Li b-2n with TONNERRE F.M. Marqués CERN INTC-P-307

  15. TOF response to monoenergetic neutrons Tests at CEA Bruyères-le-Châtel Liquid cell (CIEMAT) 20 cm diameter, 5 cm thick En=1.2 MeV, Threshold ~500 keV TONNERRE plastic bar 160 x 20 x 4 cm3 En=1 MeV, Threshold ~750 keV Preliminary S. Pietri, LPC, PhD thesis, 2003 23-28 Oct. 2011 CERN INTC-P-307

  16. A Cross-talk probability measurement Target 51° 86 cm CEA Bruyères-le-Châtel 23-28 Oct. 2011 Shield B 1.5 MeV neutrons Cross-talk Threshold ~ 500 keV NAB/NA ~ 10-4 Simulations: NAB/NA ~ 1.5 x 10-4 Preliminary M. Sénoville N.L. Achouri CERN INTC-P-307

  17. Neutron-g discrimination d + d →3He + n(4.3 MeV) Qslow / Qtot Neutrons g Threshold = 100 keVee  En~500 keV CERN INTC-P-307

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