Neutron detector developments at LPC Caen

1. Neutron detector developments at LPC Caen • b-delayed neutron detectors •  current limitations • future issues • Search for new solid scintillators (Neutromania) • Simulations for future neutron arrays • Developments of digital electronics

2. TONNERRE EXOGAM b-delayed n detectors : current state of the art TONNERRE array 32 bars, 160 x 20 x 4 cm3 BC400 plastic Up to 45% of 4p Intrinsic en ~ 45% at 1 MeV En from TOF (d=1.2 m) dEn/En ~ 10% Threshold : En ~ 300 keV A. Buta et al., NIM A455 (2000) 412

3. number of counts 50 100 150 200 250 300 time-of-flight (ns) bn detectors : current limitations 46Cl29 No n-g discrimination : g background dEn/En limited by thickness & dflight • Tails : • slow scintillation component? • light transmission? S. Grévy and the TONNERRE collaboration

4. bnm + mm + b2n b2n with current detectors Test on 11Li(b)9Be+2n with TONNERRE (F.M. Marqués et al.) • background dominant • n-g discrimination needed

5. Issues for future b-delayed neutron detectors • n-g discrimination : background reduction, multiple neutrons (eg b2n) •  liquid scintillators or new solid scintillators • improve En resolution • increase distance of flight, thin detectors • cross-talk rejection : multiple neutrons (eg b2n) • modular, high granularity • lower threshold : • thin, small volume detectors, digital electronics, good discrimination From b-n Meeting, LPC, Feb. 2007 & Neutron Detector Workshop, Madrid, July 2006

6. bxn detectors : plans • Possible test experiment in 2008 : • feasibility of b2n with n-g discrimination • learn about issues • EDEN (NE213, 5 cm thick) and standard electronics • test of digital electronics (LPC or other)

7. Neutromania at Caen • Sample synthesis at LCMT-ENSICAEN (chemistry lab) : • PMMA- or polystyrene-based polymers • various fluors tested • secondary solvents and/or solutes (naphthalene, POPOP…) Scintillation and discrimination properties tested at LPC with sources • Results : • no major difficulties to obtain scintillation • some samples show high light output (~BC400) • discrimination is challenging • no sample shows discrimination T. Dalet et al., in preparation • Understand discrimination mechanisms : • test of current solid & liquid scintillators

8. Discriminating plastic « plastic 77 », Brooks et al, IRE Trans. Nucl. Sci., NS-7, 35 (1960) • No exotic compounds (similarities with NE213) • Light output ~ BC400 • Clean synthesis process (CEA Saclay) Test at LPC with digital ADC : 2 GHz, 12 bits, 2500 samples (1.25 ms), low rate Qtotal Qslow neutrons g neutrons g

9. Geant4 simulations • Design future neutron detectors for • fast neutrons from breakup reactions (Eurisol) • b-delayed neutron spectroscopy (Spiral2, Eurisol) •  2 year postdoc (Eurisol DS, task 10), Brian Roeder • Why Geant4 ? • handles complex geometries • tracking built-in • lots of available physics models for particle interactions But need to validate

10. Geant4 issues } built-in elastic & inelastic models } inelastic cross-sections from Menate No satisfying models B. Roeder

11. Geant4 simulations with home-made model • Develop our own models • Start with low energy elastic scattering on H & C • Data-based model Good at low energy Add inelastic scattering… B. Roeder

12. Geant4 simulations with home-made model Home made Looks good Add inelastic scattering… B. Roeder

13. Digital electronics developments • Current developments : • Fast DAQ, « FASTER » • Digital Spectroscopy Amplifier • Planned developments : • Digital CFD • Digital trigger • Neutron-detector dedicated electronics • Issues for n-detector electronics : • What ADC sampling rate do we need for timing ~500 ps? • What resolution for Qslow/Qfast? • Improve n-g discrimination? TOF Qslow Qfast Detector ADC FPGA CFD, gates... PhD starting Nov. 2007 D. Etasse et al

14. Conclusions & Outlook • New materials : • solids can discriminate n & g • why? how? • Feasibility of b2n : • test experiment with thin detectors & discrimination (~2008) •  issues, improvements • Design of future n-detectors : • simulations being tested & improved • special emphasis on cross-talk performances (multiple neutrons) •  first designs in 2008/2009 • Digital electronics : • developments in the next 3 years (PhD) • test experiment ~ 2008 • improve n-g discrimination?

15. The DEMON array Neutrons from break up reactions @ tens of AMeV 96 modules, 16 x 20 cm2 (4 liters) NE213 liquid scintillator n-g discrimination En from TOF (d~3 m) Modular : position, solid angle, cross-talk rejection En threshold ~ 2 MeV Intrinsic en > 30 % for 3 < En < 60 MeV Angular acceptance ~ 30%

16. DEMON & digital electronics Test at LPC with digital ADC : 2 GHz, 12 bits, 2500 samples (1.25 ms), low rate Qslow vs Qfast 137Cs source Qslow vs Qfast AmBe source

17. DEMON efficiency with Menate DEMON intrinsic efficiency Efficiency MENATE simulation • Reactions : • H(n,n) • 12C(n,n) • 12C(n,n’g) • 12C(n,2n) • 12C(n,a) • 12C(n,n’3a) • 12C(n,p) • 12C(n,np) 500 keVee threshold H(n,n) All processes C(n,n’3a) C(n,np) C(n,p) C(n,a) Neutron energy (MeV) Simple Reasonably accurate Only cylindrical detectors with NE213 scintillator P. Désesquelles et al, NIM A 307, 366 (1991)

18. n-g discrimination with digital electronics • With digitized n & g signals (eg from DEMON) : • discrimination with Qslow/Qfast comparison : • optimal gates • event by event baseline correction • no signal splitting • discrimination threshold? • En threshold? • better separation? • develop & test new discrimination algorithms