ION-BEAM-INDUCED AMORPHIZATION OF MONAZITE

Monazite, monoclinic CePO4, is an often used phase in geologic age dat ing because of its high U content and has more recently been proposed to be host phase for the immobilization of nuclear waste. A naturally occurring monazite from Petaca, New Mexico, was irradiated by 1.5 MeV Kr+ ions over temperatures ranging from 30 to 480 K. The calculated cr itical temperature for amorphization is 428 K. A single stage annealin g process is attributed to epitaxial recrystallization due to radiatio n-enhanced defect mobility (activation energy = 0.064 eV). The respons e of monazite to irradiation is compared to that of structurally and c hemically related minerals: zircon (ZrSiO4), fluorapatite [Ca-5(PO4)(3 )F], and berlinite (AlPO4), having critical temperatures of amorphizat ion of 1101, 475, and 650 K, respectively.