Crystal growth and optical properties of new neutron detectors [Ce.sup.3+]:[Li.sub.6]R[(B[O.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[(B[O.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]B[O.sub.3], [Gd.sub.2][O.sub.3], or [Y.sub.2][O.sub.3], and Ce[(N[O.sub.3]).sub.3], 6[H.sub.2]O of purity [is greater than or equal to] 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[(B[O.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]. Index Terms--Crystal growth, neutron detectors, scintillation detectors.