Crystal growth and optical properties of new neutron detectors Ce/sup 3+/:Li/sub 6/R(BO/sub 3/)/sub 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 Li/sub 6/R(BO/sub 3/)/sub 3/ (R=Gd, Y) can be activated by Ce/sup 3+/. The synthesis of powders was carried out by high-temperature solid-state reaction from the starting materials LiOH, H/sub 2/O, H/sub 3/BO/sub 3/, Gd/sub 2/O/sub 3/, or Y/sub 2/O/sub 3/, and Ce(NO/sub 3/)/sub 3/, 6H/sub 2/O of purity /spl ges/99.99%, under a flow of argon/H/sub 2/ (5%). Under ultraviolet excitation, they show a broadband emission peaking at 390 nm. The gadolinium emission lies near the maximum of a 4f-5d Ce/sup 3+/ absorption band, so efficient Gd/sup 3+/-Ce/sup 3+/ transfer occurs. Ce/sup 3+/:Li/sub 6/R(BO/sub 3/)/sub 3/ (R=Gd, Y) crystals were grown by the Czochralski method in a resistance heating furnace using a conical vitreous carbon crucible of 150 cm/sup 3/ 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].