Crystal growth and optical properties of new neutron detectors Ce 3+:Li6R(BO3)3 (R=Gd,Y)

An efficient new scintillator that contains lithium, gadolinium, and boron, all three of which possess large neutron capture cross-section isotopes for highly exothermic reactions, has been recently developed. The homologous yttrium material was also investigated. These compounds of composition Li₆R(BO₃ )₃ (R=Gd, Y) can be activated by Ce³⁺. The synthesis of powders was carried out by high-temperature solid-state reaction from the starting materials LiOH, H₂O, H₃BO₃, Gd₂O₃, or Y₂ O₃, and Ce(NO₃)₃, 6H₂O of purity ⩾99.99%, under a flow of argon/H₂ (5%). Under ultraviolet excitation, they show a broadband emission peaking at 390 nm. The gadolinium emission lies near the maximum of a 4f-5d Ce³⁺ absorption band, so efficient Gd³⁺-Ce³⁺ transfer occurs. Ce³⁺:Li₆R(BO₃)₃ (R=Gd, Y) crystals were grown by the Czochralski method in a resistance heating furnace using a conical vitreous carbon crucible of 150 cm³ under deoxygenated pure argon. Monocrystalline boules as large as 3 cm diameter and 6 cm length have been obtained. The interest of these new materials is the high scintillation efficiency-as much as six times that of Li-glass scintillators for the Gd material. Moreover, these scintillators offer the ability to tailor their response to the neutron spectrum by varying the isotopic composition of the key constituents [lithium, gadolinium (yttrium), boron]