Fabrication of Liquid Scintillators Loaded with 6-Phenylhexanoic Acid-Modified ZrO2 Nanoparticles for Observation of Neutrinoless Double Beta Decay

Abstract

The observation of neutrinoless double beta decay is an important issue in nuclear and particle physics. The development of organic liquid scintillators with high transparency and a high concentration of the target isotope would be very useful for neutrinoless double beta decay experiments. Therefore, we propose a liquid scintillator loaded with metal oxide nanoparticles containing the target isotope. In this work, 6-phenylhexanoic acid-modified ZrO2 nanoparticles, which contain 96Zr as the target isotope, were synthesized under sub/supercritical hydrothermal conditions. The effects of the synthesis temperature on the formation and surface modification of the nanoparticles were investigated. Performing the synthesis at 250 and 300 °C resulted in the formation of nanoparticles with smaller particle sizes and higher surface modification densities than those prepared at 350 and 400 °C. The highest modification density (3.1 ± 0.2 molecules/nm2) and Zr concentration of (0.33 ± 0.04 wt.%) were obtained at 300 °C. The surface-modified ZrO2 nanoparticles were dispersed in a toluene-based liquid scintillator. The liquid scintillator was transparent to the scintillation wavelength, and a clear scintillation peak was confirmed by X-ray-induced radioluminescence spectroscopy. In conclusion, 6-phenylhexanoic acid-modified ZrO2 nanoparticles synthesized at 300 °C are suitable for loading in liquid scintillators.

Recent progress of organic scintillators

“…86) The third case is for exploration of neutrinoless double beta decay events. From this viewpoint, we have developed liquid scintillators loaded with ZrO 2 87,88) or alkaline earth molybdate nanoparticles. 89) In these cases, the nanoparticles were fabricated in a sub/supercritical hydrothermal synthesis, which is advantageous in the fabrication of small nanoparticles with their surface modified with organic molecules and also suitable for mass production.…”

“…11. 88) The transparent dispersion of the nanoparticles was obtained with scattered light by the nanoparticles (Tyndall effect) for green laser. Stable dispersion of Zr up to 0.33 wt% has been achieved.…”

Development of Ce-doped Gd3Al5−yGayO12 Nanoparticle Scintillators

“…The usage of nanoparticles in scintillators is divided into two categories: in one category, nanoparticles are included in scintillators (mainly in organic liquid or plastic scintillators) to enhance the interaction probability of the scintillators with high-energy photons (3,(19)(20)(21)(22)(23)(24) or to include the sample nuclei for neutron experiments. (25)(26)(27) The other category is the use of scintillators in the form of nanoparticles. As examples of this usage, X-ray-induced photodynamic therapy has been performed (28) using Pr-doped Y 3 Al 5 O 12 (29) or CsI(Na)@MgO (30) nanoparticles.…”

Photoluminescence and Scintillation Properties of Ce-, Pr-, and Tb-doped (Gd,Lu)2Hf2O7 Crystals

“…Therefore, there has been continuous R&D to develop more desirable materials in single crystal, (4)(5)(6)(7)(8)(9)(10)(11)(12) ceramic, (13)(14)(15) glass, (16)(17)(18)(19) and liquid forms. (20)(21)(22) A high density and a large effective atomic number are important for obtaining large cross sections against X-and γ-rays; (23) thus, pyrochlore rare-earth hafnates (RE 2 Hf 2 O 7 , RE: rare earth) are potential scintillators with high density (9.0 and 9.7 g/cm 3 for Gd 2 Hf 2 O 7 and Lu 2 Hf 2 O 7 , respectively (24) ) and large effective atomic numbers (66-69). (25) To date, there have been a few reports on pyrochlore RE 2 Hf 2 O 7 but only in a polycrystalline form.…”