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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. IS525 experiment - October 2014. Franck DELAUNAY, LPC Caen, France ISOLDE Workshop and Users Meeting 2014. LPC Caen : N.L. Achouri, J. Gibelin, F.M. Marqués, N. Orr, M. Pârlog, J. Pereira

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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 IS525 experiment - October 2014 Franck DELAUNAY, LPC Caen, France ISOLDE Workshop and Users Meeting 2014 LPC Caen: N.L. Achouri, J. Gibelin, F.M. Marqués, N. Orr, M. Pârlog, J. Pereira CIEMAT Madrid: D. Cano-Ott, J. Balibrea, T. Martinez, E. Mendoza, C. Santos Universidad Complutense Madrid: L.M. Fraile, V. Vedia Aarhus University: K. Riisager, M. V. Lund ISOLDE CERN: M. Madurga CSIC IEM Madrid: M.J.G. Borge, O. Tengblad, I. Marroquin VECC Kolkata: C. Bhattacharya, K. Banerjee CEA/SPhN Saclay: M. Senoville Universidade de Santiago de Compostela: B. Fernandez IPN Orsay: M. Assié IFIC Valencia: A. Algora

  2. Motivation: 11Li b-decay • b-decay of 11Li: • Qb = 20.6 MeV • Weakly bound daughter 11Be • Variety of delayed particle emissions: 1n, 2n, 3n, n+a, t,d... • Delayed 2-neutron emission: • P2n = 4.2 % • No measurement of 2-neutron kinematics • Tentative 2-neutron decay paths from 1-neutron transitions • Delayed 1-neutron emission still unclear: • Unresolved weak transitions, uncertain branching ratios

  3. Goals of the experiment • Measure directly for the 1st time 2 delayed neutrons in coincidence • Feasibility of correlation studies between delayed neutrons • Sequential or simultaneous emission? • Correlated or uncorrelated neutrons? • Array of liquid scintillator neutron detectors • Granularity  Angular resolution  nn relative angle • Neutron TOF Energy • Liquid  n-g discrimination Background suppression (g, m…) • Digital electronics  Improved discrimination  Lower En threshold • + Improved picture of single neutron emission

  4. Far array (10 det’s) 2.5 m Experimental setup Near array (29 det’s) 1.5 m LA1, 3-12 Oct 2014, 18 shifts of 11Li GPS, Ta-Re target-IS, RILIS : 1300 /s • 39 liquid scintillator modules • 20 or 15 cm in diam., 5 cm thick • 40 % intrinsic efficiency • n-g discrimination • Near array: d = 1.5 m •  = 3 % of 4p • dE = 60 keV at 1 MeV • n-n coincidences • Far array: d = 2.5 m • dE = 35 keV at 1 MeV •  = 0.3 % of 4p • Improved 1n data Digital electronics (LPC) • Al foil • Plastic scint. • b rays • TOF start 70% HPGe 11Li beam 60% HPGe

  5. 11Li b-1n: Near array  34 hours n-g discrimination L > 75 keVee (En > 530 keV)  5 times Hirayama et al’s statistics with similar En resolution* TOF resolution  750 ps FWHM PRELIMINARY * Hirayama et al., PLB 611 (2005) 239

  6. 11Li b-n-g: Near array and 60% Ge detector  34 hours n-g discrimination L > 75 keVee (En > 530 keV) 2590 10Be 3368 10Be FWHM = 2.5 keV at 1.4 MeV PRELIMINARY 2857 SE (3368) 2346 DE (3368) 2895 10Be 511 603 2811 10Be 219 10Be 2080 847 Energy (keV)

  7. 11Li b-2n: Simple cross-talk rejection 37 h (25%), near array,TET2b<120 ms, n-g discrimination, L > 0.1 MeVee PRELIMINARY 1st neutron hit: Tn1 [60, 67 ns] (En1 [2.7, 3.4 MeV]) 2 Counts / 1 ns  1st n in b-1n line  cross-talk d12 Tn1 < Tn2 1 Time-of-flight Tn1, Tn2 (ns) Counts / 50 keV 1st order cross-talk rejection: Keep nn events with d12 > 1.4 m (qnn > 50 °) Enn (MeV)

  8. 11Li b-2n PRELIMINARY 37 h (25%), near array,TET2b<120 ms, n-g discrimination, L > 0.1 MeVee d12 > 1.4 m 1169 events Counts / 1 ns 161 events Full time  600 events 1000 events expected Time-of-flight Tn1, Tn2 (ns) Counts / 50 keV Counts / 100 keV Q2n (MeV) Enn (MeV)

  9. 11Li b-2n: Without n-g discrimination 37 h (25%), near array,TET2b<120 ms, L > 0.1 MeVee d12 > 1.4 m PRELIMINARY Counts / 1 ns 5234 events 2108 events Time-of-flight Tn1, Tn2 (ns)  Dominated by random coincidences involving background

  10. Summary • 11Li b-2n and b-1n studied with an array of liquid scintillator neutron detectors • Aim: • Kinematics of 2-neutron emission • Improved picture of b-1n • Double coincidences: b-1n, b-g • Triple coincidences: b-n-g, b-2n • n-g discrimination crucial to extract 2n events • b-2n events with expected statistics after preliminary cross-talk rejection • Analysis in progress...

  11. Many thanks to: • ISOLDE Team • RILIS team • PhD students: V. Vedia, I. Marroquin, M. Lund • O. Tengblad • B. Laurent (CEA), N. de Séréville (IPN Orsay) Thank you for your attention

  12. 20 40 60 80 100 120 140 TOF (ns) Previous b-1n study Hirayama et al., PLB 611 (2005) 239

  13. Hirayama et al., PLB 611 (2005) 239

  14. Neutron lines

  15. Experimental setup (LA1 line)

  16. Digital Electronics and DAQ • FASTER project, LPC Caen, D. Etasse et al. (faster.in2p3.fr) • CFD + QDC: 500 MHz, 12 bits, 2.3 V, 100 MHz BW • b plastic scintillator, neutron modules, ET2 (impact + 1ms) • Time and charges • Spec amp + ADC: 125 MHz, 14 bits, 1-10 V, 25 MHz BW •  Ge detectors: Energy and time Baseline restoration No common dead-time Time stamping Triggerless 50 channel capability (MicroTCA standard)

  17. 9Li b-n: Near array 1.5 m - 24 detectors ~ 2 hours / 1.5 shift (15 %) Rough neutron cut L > 75 keVee (En > 530 keV) 682 keV neutron line

  18. 11Li b-1n: Far array 2.5 m - 10 detectors ~ 34 hours - 4.3 shifts  25 % of total statistics Rough neutron cut L > 100 keVee (En > 630 keV) ~ 40 % of Hirayama’s statistics with better En resolution g-ray peak FWHM ~800 ps

  19. 11Li b-g - 60% Ge detector (tb - tET2 < 100 ms & tg - tb < 250 ns, 7 h) 320 11Be 3368 10Be 2590 10Be 2857 SE 2346 DE 603 847 E (keV) Eg resolution: 2.5 keV FWHM at 1.4 MeV

  20. 11Li b-g-X: Ge 60% Counts / 3 keV 3368 10Be 320 11Be 2856 SE (3368) 2590 10Be 2345 DE (3368) 511 603 2812 10Be 2895 10Be 574 220 10Be 845 1216 2082 2124 1045 1015 1709 ? 1565 1124 E (keV)

  21. 11Li b-g-X: Ge 70% Counts / 3 keV 320 11Be 3368 10Be 2856 SE (3368) 511 2590 10Be 2345 DE (3368) 220 10Be 603 845 2812 10Be 2895 10Be 574 1045 1015 2082 1216 1565 E (keV)

  22. 11Li - Half-life 20 ms beam gate 1 h tb - tET2

  23. 11Li b-n-g: Near array - Ge 70% 2590 10Be 3368 10Be 511 2857 SE (3368) 219 10Be 2346 DE (3368) 603 2895 10Be 2811 10Be 847 E (keV)

  24. 11Li b-2n : Preliminary selection • 37 hours, near array (1.5m, 28 detectors) • 25% of full statistics • TET2-b [8, 120 ms] • Neutron selection: • n-g discrimination • Light  [0.1, 5.5 MeVee]  En [0.63, 9.6 MeV] • Tn [35, 150 ns]  En [0.54, 10 MeV]

  25. Cross-talk j Ti, di vi Ei Ei,loss = f(particle, Li) Ei,out = Ei - Ei,loss Ej,loss = f(particle, Lj) Tj, Lj dj dij,min Ti < Tj di Ti, Li i Strong cross-talk filter: Ei > Ei,loss = f(e, Li) Ei,out > Eij,min Ei,out > Ej,loss = f(e, Lj) F. M. Marqués et al., NIM A 450 (2000) 109

  26. 11Li b-2n : Strong Cross-Talk Filter 1169 events Counts / 1 ns Counts / 2 deg. 208 events Time-of-flight Tn1, Tn2 (ns) qnn (deg.) Counts / 50 keV Counts / 100 keV Q2n (MeV) Enn (MeV)

  27. Previous studies: b-2n Detection of 2 neutrons in coincidence  energies and angles F.M. Marqués et al., TONNERRE plastic scintillator 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 %...)

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