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Phase stability and lithium loading capacity in a liquid scintillation cocktail Denis E. Bergeron, H. Pieter Mumm, Mark Tyra Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA LSC 2017, Copenhagen, 1 May 2017 Neutrino detection by LSC β’ Inverse beta decay (threshold 1.8 MeV) + ππππ + ππ β ππ + ππ β’ Proton-rich target for good detection efficiency and energy resolution β’ Loading cocktail with a neutron capture agent (Gd or 6Li) further improves performance ππ + 6Li β Ξ± + π‘π‘ + 4.78 MeV β’ Timing and pulse shape discrimination to reduce backgrounds from gammarays and neutrons High-background applications β’ Many large-scale liquid scintillation detectors are intended for detection of solar or cosmic neutrinos, requiring ultra-low backgrounds* β’ Recent interest in the reactor flux and spectrum anomalies** has prompted the design of experiments intended to operate with much higher neutrino flux β’ With volumes measured in thousands of liters, price is a concern *Benziger and Calaprice (2016), Large-scale liquid scintillation detectors for solar neutrinos, Eur. Phys. J. A 52, 81. **Ashenfelter, et al. (2016), The PROSPECT physics program, J. Phys. G, 43, 113001; An et al. (2016), Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay, Phys. Rev. Lett. 116, 061801. Picking a LS cocktail to load β’ Earlier work at NIST* developed a formula based on Quickszint, loaded with up to 0.40 % 6Li by mass β’ H/C: 1.5 β’ Quickszint no longer available. β’ Options? *Fisher, et al. (2011), NIMA 646, 126-134 Bass, et al. (2013), ARI Picking a LS cocktail to load β’ Earlier work at NIST* developed a formula based on Quickszint, loaded with up to 0.40 % 6Li by mass β’ H/C: 1.5 β’ Quickszint no longer available. β’ Options? *Fisher, et al. (2011), NIMA 646, 126-134 Bass, et al. (2013), ARI Scintillant Ultima Gold HiSafe 2 Ultima Gold AB HiSafe 3 HionicFluor H/C 1.46 1.03 1.51 1.47 1.73 **Certain commercial materials are identified to foster understanding. Such identification does not imply recommendation by the National Institute of Standards and Technology, nor does it imply that they are necessarily the best available for the purpose. Picking a LS cocktail to load β’ Earlier work at NIST* developed a formula based on Quickszint, loaded with up to 0.40 % 6Li by mass β’ H/C: 1.5 β’ Quickszint no longer available. β’ Options? *Fisher, et al. (2011), NIMA 646, 126-134 Bass, et al. (2013), ARI Scintillant Ultima Gold HiSafe 2 Ultima Gold AB HiSafe 3 HionicFluor H/C 1.46 1.03 1.51 1.47 1.73 **Certain commercial materials are identified to foster understanding. Such identification does not imply recommendation by the National Institute of Standards and Technology, nor does it imply that they are necessarily the best available for the purpose. Ultima Gold AB and HiSafe 3 show the best Li loading capacity Ultima Gold AB 600 550 1M 2M 4M 8M 450 turbid 400 turbid 350 300 Observed phase separation 0 1 2 f (% Li by mass) 1M 2M 4M 8M 450 350 250 Observed phase separation 500 tSIE tSIE 500 400 HiSafe 3 550 3 turbid 300 250 0 0.5 1 1.5 f (% Li by mass) 2 In a long term experimentβ¦ β’ Phase separation: separation into aqueous and organic domains β’ Turbidity: cloudiness due to presence of many large particles A true microemulsion is thermodynamically stable, optically isotropic, and has relatively low viscosity. Aqueous domains (reverse micelles) are of nanometer dimension. The eye can be deceived β’ Sometimes, an agitated emulsion looks like a microemulsion β’ Over time, thermodynamic instability drives agglomeration of aqueous domains ο phase separation β’ In a multi-year experiment, phase stability is absolutely essential Aging samples 140 UGAB with 2.5 % Li by mass 120 80 60 UGAB 40 20 0 UGAB with 1.5 % Li by mass 104 102 0 0.05 0.1 0.15 days β’ Centrifugation can drive phase separation control 100 H# H# 100 β’ Quench indicating parameters based on the Compton spectrum of a scintillant are sensitive to phase dynamics 98 96 8 h centrifugation 94 92 0 10 days 20 Aging samples 0.5 % Li 0.75 % Li H# control 8 h centrifugation 80 H# 75 60 1.0 % Li 40 80 1.5 % Li 95 35 120 100 65 75 8 h centrifuge 20 2.5 % Li No added Li 25 0 5 10 15 days 20 25 0 1 2 Mass fraction of Li / % 3 β’ Loading up to 1.0 % Li by mass (with 8 mol/L LiCl) produced stable microemulsions Dynamic light scattering 2.5 % Li water 10 H.D. / nm 15 1.5 % Li 5 0 Polydispersity Index 8 mol/L LiCl 0 0.2 0.4 0.4 0.3 0.2 0.1 0 0.2 faq 0.4 0.6 2.5 % Li 18 16 14 0.6 0.5 0 20 Polydispersity Index H.D. / nm 20 0 0.5 10 20 30 40 20 30 40 2.5 % Li 0.4 0.3 0.2 0.1 0 0 10 telapsed / min Conclusions: it works β’ Very high loading β’ Using 8 mol/L aqueous LiCl, we achieved stable loading of up to 1 % Li by mass in Ultima Gold AB β’ Cheap β’ Commercially available scintillant and a simple loading procedure β’Our formulation is being deployed in experiments at NIST β’We have investigated light yield, optical transmission, and material compatibilities for the loaded UGAB (to be reported) Tak
