Ion beam induced amorphization of monazite

Monazite, monoclinic CePO ₄, is an often used phase in geologic age dating 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 critical temperature for amorphization is 428 K. A single stage annealing process is attributed to epitaxial recrystallization due to radiation-enhanced defect mobility (activation energy = 0.064 eV). The response of monazite to irradiation is compared to that of structurally and chemically related minerals: zircon (ZrSiO ₄), fluorapatite [Ca ₅(PO ₄) ₃F], and berlinite (AlPO ₄), having critical temperatures of amorphization of 1101, 475, and 650 K, respectively.